Neurobehavioral Toxicology of Substances of Abuse

History

Ethanol is surely the oldest known substance of abuse. The details of the original discovery of fermented beverages have been lost to time because of the unavailability of the written word. Thus no one really knows exactly when humans started drinking fermented beverages. Animals such as birds, insects, and elephants have shown signs of drunkenness by purposefully eating ripened fruit in which yeast produced ethanol. It is known that intentionally fermented beverages existed as early as 10,000 BCE. Aristotle, the founding father of the scientific method, showed in the 3rd century BCE that boiled wine lost its intoxicating character, but he never took the next step of condensing the ethanol. The distillation of ethanol from wine was discovered by a Muslim chemist in the 8th century. There are a myriad of accounts of the incorporation of alcoholic beverages into the daily life of every society. As with all substances of abuse, ethanol was probably not used abusively at first. For example, early versions of beer were used as food. Alcoholic beverages such as beer and wine were used in ritualistic religious exercises, and evidence of the use of beer and wine as medicinal remedies exist from at least 2000 BCE.

A recently published book describes in detail the cultural history of alcohol. The use of alcoholic beverages in most societies is certainly evident. It has produced social and health benefits as well as significant detrimental forensic and health problems. For example, light to moderate alcohol intake may be associated with lower risk of cardiovascular mortality in hypertensive men. On the other hand, excessive ethanol consumption is closely associated with abnormal elevation of blood pressure in normotensive and hypertensive individuals. Despite its social and possible health benefits, excessive ethanol consumption is a major medical health problem. In 1995, it was reported that about 10 million Americans were considered to be alcoholic.

Chemical Properties

Ethanol is a relatively simple molecule (C ₂ H ₆ O) with a molecular weight of 46 and density of 0.789 g/cm ³ . At ambient temperatures, it is a clear, colorless liquid that is highly volatile, flammable, and miscible with water and many other organic solvents. Its lipid-to-water partition coefficient is 0.096, so the distribution of ethanol favors an aqueous versus a lipid phase. In humans, this solubility ratio explains the distribution of ethanol in total body water.

Ethanol concentration is expressed in a variety of ways depending on the area of application. For example, a blood alcohol concentration of 0.1% (w/v) is the upper limit of the legal range while driving a car in many states. This concentration can also be expressed as 100 mg%, 100 mg/dL, 1 g/L, and 21.7 mM. The concentration of ethanol in commercially available forms of consumable, distilled alcoholic beverages is expressed in terms of proof, which is a number that is approximately double the percentage of ethanol (200 proof = 100% ethanol). Of interest, the term “proof” was used in the 19th century by English sailors who developed a test for the minimal concentration of ethanol in rum. If the sailor could successfully ignite gun powder soaked in the rum, it was proof that the rum was acceptably potent and had not been diluted with water. At least 50% (v/v) of ethanol is necessary to ignite gun powder. This simple test was important because the sailors were given rum as part of their pay.

Pharmacokinetics

Pharmacodynamics

The small size and simplicity of ethanol’s structure ( Fig. 17.1 ) is in contrast to its significant and complicated pharmacodynamic effects. When compared with most other drugs, very high concentrations of ethanol, in the millimolar range, are required to produce biological effects. Because of its simple chemical structure and the concentrations required for physiological effects, ethanol binding sites with high affinity (μM or nM range) most likely do not exist. It has been proposed that an ethanol binding site exists on γ-aminobutyric acid A (GABA _A ) receptors that contain a combination of α4 (or α6), β3, and δ subunits, making them sensitive to concentrations of ethanol as low as 3 mM. Furthermore, relatively recent reports indicate that a certain domain of the enzyme adenylyl cyclase is responsible for sensitivity to ethanol. Amino acid mutations of target proteins designed to modify ethanol’s effects have suggested that specific groups of amino acid residues in transmembrane regions of proteins may be binding sites for ethanol. The results of these relatively recent studies suggest that ethanol situates itself into tiny pockets in protein structures to produce significant changes in biochemical, physiological, and behavioral functions (see Fig. 17.1 )

Toxicology

Whether ethanol produces an acute, satisfying, possibly beneficial effect versus an acute or chronic, unhealthy toxic effect is related to the concentration of ethanol, the dose of ethanol, and the length of exposure to ethanol. From a medical perspective, ethanol consumption of less than two standard drinks per day (≤ ∼30 g) by humans appears to decrease mortality and the mechanism is probably related to a reduction of coronary heart disease. Thus low or moderate levels of ethanol consumption are thought to be healthful. On the other hand, chronic heavy ethanol consumption of five standard drinks per day (∼75 g) or more for men and four standard drinks per day (∼60 g) or more for women, or frequent binging, can cause severe, detrimental health problems. These health problems result from direct toxic effects of ethanol on the liver, heart, brain, kidneys, and stomach. Indirectly, the replacement of calories from food by calories from ethanol (malnutrition) can cause additional negative effects on these organ systems. These serious effects of ethanol abuse can eventually result in alcoholism, a pathology that includes very serious medical and behavioral difficulties.

History

Cocaine is a derivative of the coca plant Erythroxylon coca , which is native to the mountains of South America. Traditionally, South American natives have chewed coca leaves as a stimulant to fend off fatigue, especially at relatively hypoxic elevations of the Andes Mountains. In 1574, the Spanish physician Nicolas Bautista Alfaro (1493–1588) published a description of the plant, its use, and its effects. In 1862, the German chemist Albert Neiman (Gottingen, Germany, 1834–1861) isolated the active component of the coca plant and called it cocaine. He was also the first to report the local anesthetic properties of cocaine, noting its numbing effects on his own tongue. In 1880, pharmacologist Basil Von Anrep of the University of Leipzig proposed use of cocaine as a surgical anesthetic in humans. Canadian surgeon William S. Halsted became the first physician to use cocaine for a nerve block during surgery and subsequently became the first known physician to develop a cocaine addiction. In 1884, psychiatrist Sigmund Freud published a cocaine monograph entitled Uber Coca in which he advocated for the use of cocaine to treat a variety of conditions including asthma, wasting diseases, and syphilis. Freud also eventually became addicted to cocaine. In the late 1800s, cocaine was added to a number of beverages including the “medicinal” wine Vin Mariani in France. In 1895, The Lancet published a report of six cocaine-associated deaths, underscoring the significant potential toxicity of this drug. Cocaine was an ingredient in the original version of John Pemberton’s Coca Cola; cocaine was removed from the popular soft drink in 1906. With passage of the Harrison Narcotics Tax Act in 1914, nonprescription use of cocaine was made illegal. In 1970 cocaine was classified as a Schedule II drug (Comprehensive Drug Abuse Prevention and Control Act).

Pharmacodynamics

Cocaine is a tropane (aminoester) alkaloid with a p K _a of 8.6. Crack cocaine (free-base) is produced by combining cocaine HCl with an alkali. Crack cocaine is more heat-stable than is cocaine HCl and therefore can be smoked.

Cocaine interacts primarily with these central nervous system biogenic amine systems. Cocaine blocks the in vitro reuptake of norepinephrine, dopamine, and serotonin. Saturable, high-affinity Na ⁺ -independent and Na ⁺ -dependent [ ³ H]-cocaine binding has been associated with sites for serotonin and for dopamine reuptake, respectively, in the central nervous system. With acute or low-dose administration of cocaine, this reuptake inhibition leads to increased aminergic concentrations within aminergic synapses and increased binding both to pre- and postsynaptic aminergic receptors. Chronic cocaine administration is generally believed to result in aminergic depletion for the duration of drug exposure. However, unlike high doses of methamphetamine, chronic cocaine does not produce dopamine nerve terminal degeneration, at least in the prefrontal and frontal cortex or dorsal raphe.

Various addictive drugs such as cocaine that act as positive reinforcers increase synaptic dopaminergic concentrations in selected areas such as the nucleus accumbens. Homologous recombination targeting the dopamine transporter results in an absence of cocaine- or amphetamine-induced behavioral activation. The ventral tegmental area, nucleus accumbens, and caudate nucleus, areas rich in the neurotransmitter dopamine, are collectively considered the reward pathway. Cocaine antagonism of presynaptic dopamine transport results in elevated dopamine levels in mesolimbic synapses with resultant drug reinforcement. Maintenance of higher dopamine levels in reward pathway synapses leads to feelings of euphoria and a cocaine high. The increased availability of synaptic dopamine is thought to act on D1-like (D1 and D5) and D2-like (D2, D3, and D4) receptors in the mesocorticolimbic synapses. The effects of cocaine acting on the D1 receptor in the nucleus accumbens and ventral tegmental area are thought to be responsible, at least in part, for the reinforcing properties associated with long-term exposure to this drug.

Long-term cocaine use is associated with a selective decrease in D1 receptors in striatal reward areas both in rodents and in nonhuman primates. Dopamine depletion using the neurotoxin 6-hydroxydopamine infused into either the nucleus accumbens or the ventral tegmental area results in an attenuation of the reinforcing effects of cocaine self-administration. Similarly, dopamine D1 receptor knockout mice have demonstrated a lack of reinforcing effect of cocaine in contrast to wild-type controls. D1 and D2 receptors have opposing intracellular and behavioral effects and thus may differentially affect drug-reinforcing behaviors. David Self and colleagues demonstrated that cocaine self-administration behavior was mediated by dopamine D1 and not by dopamine D2 receptors and that this behavior progressively diminished in rats when cocaine was replaced with saline (extinction behavior).

Cocaine also blocks voltage-gated sodium channels and thus reversibly attenuates conduction of nerve impulses, which accounts for the local anesthetic properties of the drug. Depending on the relative distribution of the drug, a relatively selective depression of inhibitory neurons can produce cerebral excitation at lower concentrations of the drug, and this in turn can lead to generalized convulsions. At high concentrations, cocaine could produce more profound depression of brain function and ultimately coma, cardiorespiratory arrest, and death.

Pharmacokinetics

Metabolism/Elimination

Cocaine metabolism is catalyzed by esterase activity, principally within plasma and liver. Liver esterase activity accounts for 30%–50% of the metabolism of cocaine to ecgonine methyl ester. Another 30%–40% of cocaine is nonenzymatically hydrolyzed into benzoylecgonine ( Fig. 17.2 ). The elimination half-lives of these major metabolites of cocaine are 6 and 4 hours, respectively. These metabolites can be detected in urine samples up to 60 hours after cocaine administration. A small amount (1%–5%) of cocaine is excreted unchanged in urine within 8 hours of administration. Individuals with liver dysfunction or malnutrition, or who are being treated with plasmapheresis, who are pregnant, or who have taken anticholinesterase medication (e.g., echothiophate eye drops, neostigmine) are relatively esterase-deficient, resulting in reduced capacity to degrade cocaine and thus elevated circulating levels of the drug with the potential for increased toxicity (see Fig. 17.2 ).

Cocaine metabolism demonstrates first-order kinetics over a wide range of doses. Within 4–5 hours, almost all of a dose of cocaine has been metabolized, with metabolites present in urine for 4–8 hours following intranasal dosing. . Measurable levels of the metabolite benzoylecgonine may be detected in urine as long up to 60 hours after a single dose of cocaine and for up to 3 weeks after heavy use of cocaine.

Less than 10% of cocaine is N -methylated into the active metabolite norcocaine. Liver N -methylation activity is increased by progesterone. N -methylation of cocaine into norcocaine is thus enhanced under conditions of elevated progesterone, for example, during pregnancy. This may account for the reported increased cocaine-associated cardiotoxicity during pregnancy.

Concurrent use of cocaine and alcohol results in the production of the active metabolite cocaethylene (ethylbenzoylecgonine) ( Fig. 17.3 ). Cocaethylene has a significantly longer elimination half-life than cocaine and may be more cardiotoxic than cocaine (see Fig. 17.3 ).

Toxicology

Cocaine-induced antagonism of nigrostriatal dopamine activity may result in extrapyramidal motor dysfunction including bradykinesia, akinesia, akathisia, catalepsy and dystonic reactions. In a study conducted between 1979 and 1990 by the medical examiner’s office for Dade County, Florida, excited delirium was associated with approximately one in every six cocaine-related deaths. These victims were described as having experienced an immediate onset of bizarre and sometimes violent behavior, including extreme paranoia, ending in cardiorespiratory collapse and death.

In addition, cocaine abuse is associated with both acute and long-term cardiotoxicity. Acutely, cocaine acts as a vasoconstrictor, reducing blood flow to myocardium with an increased risk for cardiac ischemia and infarction. Cocaine-inhibited reuptake of norepinephrine also leads to increased intracellular concentrations of calcium within cardiocytes, which through membrane depolarization can trigger sustained action potentials, extrasystolic contractions, and tachycardia. Long-term effects of cocaine on cardiac function can include a depression in contractility, in part related to the activity of cocaine as a local anesthetic. Cardiomyopathy associated with long-term cocaine abuse may be a result of oxidative stress to the myocardium. Systemic effects include peripheral vascular constriction with resultant ischemic compromise of various organs.

Long-term use of cocaine is also associated with elevated circulating levels of muscle enzymes such as creatine kinase, suggesting muscle degradation or rhabdomyolysis. Thirty-three percent of the participants in a study of cocaine-induced rhabdomyolysis experienced acute renal failure, severe liver dysfunction, and disseminated intravascular coagulation; six of them died.

Cocaine has been shown repeatedly to adversely affect reproductive function in female rats, male and female nonhuman primates, and male and female humans. In the rat, cocaine administration produces loss of estrous cyclicity, which at higher doses of cocaine may become permanent. Maternal cocaine use during gestation has also been associated with numerous adverse effects on the developing fetus, including growth retardation, dysmorphic features, seizures and strokes, and numerous postnatal behavioral abnormalities. Because such fetuses are typically exposed to various confounding variables, such as a lack of prenatal care, poor maternal nutrition, and polydrug exposures, the idea of a specific cocaine teratophilia (or “cocaine baby”) syndrome has been called into question.

History

The Chinese plant ma hung ( Ephedra vulgaris ) has been used traditionally to treat asthma. In the 1920s the active ingredient in extracts of this plant was identified as ephedrine. In 1887, the Romanian chemist Lazar Edeleanu (1861–1941) first synthesized alpha-methylphenethylamine, now more commonly known as amphetamine ( a lpha- m ethyl ph en et hyl amine ). Originally named phenylisopropylamine, amphetamine was largely forgotten for the next four decades. In the late 1930s, amphetamine was prescribed for narcolepsy as well as hyperactivity syndromes. In 1932, the pharmaceutical company Smith, Kline & French marketed the racemic amphetamine ( dl -amphetamine) mixture Benzedrine as an over-the-counter medication for treating congestion by inhalation of the drug. Benzedrine was typically administered via inhalers. From its introduction in the 1930s until 1954, ephedrine was available without prescription (i.e., over-the-counter). By the 1940s and 1950s, reported abuse of these inhalers began to emerge. Benzedrine inhalers as well as other preparations of the drug could be used to produce a stimulant effect and were sometimes abused as “bennies.” With passage of the Comprehensive Drug Abuse Prevention and Control Act in 1970, methamphetamine and amphetamine became classified as Schedule II and III drugs, respectively. The following year, the classification of amphetamine was changed to Schedule II.

The term “amphetamines” also refers to a class of drugs derived from amphetamine, the substituted amphetamines. In recent years, the easily synthesized N -methylated form of amphetamine, methamphetamine (METH), has become readily available and one of the most commonly abused stimulants in the United States. But METH is not a recent addition to the list of amphetamine-related drugs. In 1885, the Japanese physician-chemist Nagayoshi Nagai (1844–1929) isolated ephedrine from the plant E. vulgaris and, in 1893, synthesized METH by reduction of ephedrine using red phosphorus and iodine. In 1929, he was the first to synthesize and elucidate the structure of ephedrine. In 1919, the Japanese chemist Akira Ogata (1887–1978) synthesized crystallized METH. In the 1980s, METH became increasingly more popular as a street drug. In 1996, the Methamphetamine Control Act was enacted, to regulate the key ingredients (e.g., ephedrine, pseudoephedrine, phenylpropanolamine), in manufacturing METH and increasing criminal penalties for possession, distribution, and manufacturing of the drug. The price of methamphetamine is largely determined by the availability of ephedrine, a key ingredient. Regulation of ephedrine, and its resulting unavailability, has increased its wholesale price. As a result, drug traffickers have switched to a less regulated and more economical substitute, pseudoephedrine. However, the Combat Methamphetamine Epidemic Act of 2005, a part of HR 3199, was enacted regulating over-the-counter sales of cold medicines containing pseudoephedrine. Methamphetamine can be smoked, snorted, or injected and has significantly longer-lasting stimulant effects than cocaine and is generally much less expensive to purchase than cocaine. Methamphetamine is considered highly addictive. Methamphetamine users typically develop tolerance to the drug that leads to higher and more frequent use.

Amphetamine is a homologue of phenethylamine and a weak base with a chemical structure very similar to that of dopamine and norepinephrine. Amphetamine is the parent compound for a class of similar psychoactive drugs including the N -methylated form of amphetamine, methamphetamine, and the methylenedioxy analog of methamphetamine, 3,4-methylenedioxy- N -methylamphetamine (MDMA; Ecstasy). Typically formulated as a racemic mixture ( d - and l -amphetamine), d -amphetamine is thought to act primarily on the dopaminergic systems, whereas l -amphetamine is comparatively norepinephrinergic (noradrenergic). Amphetamine and related drugs are lipid-soluble in nonionized form and as such are readily absorbed across the gastrointestinal tract lining as well as across the blood-brain barrier. Amphetamines can thus be taken effectively either by oral or parenteral routes of administration ( Fig. 17.4 ).

Pharmacologist David E. Nichols formulated the term “enactogen” to describe a class of synthetic drugs similar in structure to the stimulant MDMA (Ecstasy) but which exhibit hallucinogenic properties. The term “entactogen” is a combination of the roots “en” (Greek: within ), “tactus” (Latin: touch ), and “gen” (Greek: produce ). Enactogens are characterized by a substituted amphetamine core thus belonging to the phenethylamine class of psychoactive drugs. Enactogens include 3,4-methylenedioxyamphetamine (MDA or tenamfetamine), 4-methylenedioxy- N -ethylamphetamine, (MDEA), 3,4-methylenedioxy-alpha-ethyl- N -methylphenethylamine (MBDB; EDEN or Methyl-J), α-ethyltryptamine (etryptamine, α-ethyltryptamine, α-ET, or AET), and 4-bromo-2,5-dimethyphenethylamine (2C-B). MDMA is also often considered a member of the entactogen family.

4-Bromo-2,5-dimethyphenethylamine, or 2C-B, was first synthesized from 2,5-dimethoxybenzaldehyde by the Russian-American pharmacologist Alexander Shulgin in 1974. In the late 1970s, the German pharmaceutical company Drittewelle began manufacturing and marketing the drug as an aphrodisiac called Eros. Shortly after its introduction to clinical psychiatry, 2C-B made its way into the recreational drug scene. 2C-B remains popular within the rave subculture but is often confused with MDMA (Ecstasy). 2C-B and related entactogens are now classified as Schedule I drugs in the United States.

Based on the known mechanisms of action of MDMA, entactogens are thought to act by increasing synaptic levels of dopamine (DA), norepinephrine (NE), and serotonin (5-HT). However, there have been very few research studies to examine the pharmacology of entactogens in humans or experimental animal models.

Mechanism of Action

Amphetamines are CNS and sympathetic nervous system stimulants, acting on biogenic amine pathways. Physical effects include reduced appetite, hyperactivity, restlessness and insomnia, tachycardia, and increased blood pressure and constipation. Behavioral effects include anxiety and generalized excitability, a perception of increased energy, repetitive actions, increased alertness, emotional lability and, with higher or long-term dosing, occasional psychosis. These effects are similar to those of other stimulates such as cocaine. The amount of releasable as well as previously released DA at dopaminergic nerve terminals is closely regulated by two selective membrane-bound transporters. DA is moved via vesicular monoamine transporter-2 (VMAT-2) into synaptic vesicles for storage and eventual release. Without vesicular transport, DA remains within the cytoplasm where it is subject to degradation including oxidation and presynapse via the DA transporter (DAT). DAT inhibition or blockade results in increased levels of extracellular DA. Amphetamines induce presynaptic DA release, block DA reuptake, inhibit DA storage within presynaptic vesicles, and block enzyme-catalyzed DA metabolism. Shortly after amphetamine administration, reversal of the DAT results in nonvesicular DA efflux. In addition, the movement of DA into synaptic vesicles is blocked by amphetamine, resulting in increased DA release into the synapse and the potential for DA oxidation and damaging free radical formation within the presynapse. Although also acting through similar mechanisms on NE and, to a lesser extent, 5HT terminals, amphetamine’s reinforcing and behavioral-stimulant effects are associated with enhanced dopaminergic activity, primarily within the mesolimbic DA system. The targeted effects of amphetamine on dopaminergic activity in caudate nucleus, nucleus accumbens, and ventral striatum correlate well with stereotypic onset of euphoria associated with this drug. Amphetamine also acts to increase glutamate release in selected brain areas such as the nucleus accumbens, striatum, and prefrontal cortex. These areas are implicated in reward pathways.

In similar fashion to the DA transporter (DAT), amphetamine can also induce reverse the direction of serotonin movement via the serotonin transporter (SERT). Amphetamine interacts with the serotoninergic system in selected brain regions such as the mesocorticolimbic pathway. Similar to amphetamine, methamphetamine induces release of 5HT, DA, and NE as well as blockade of 5HT, DA, and NE transporters within the CNS, leading to increased synaptic activities of these biogenic amines.

Formation of free radicals including oxygen and nitrogen species (ROS and RNS, respectively) is particularly characteristic of methamphetamine administration. An amphetamine analog, methamphetamine, induces selective degeneration of DA neuron terminals without cell body loss. Methamphetamine-induced terminal degeneration may be mediated in part by excitatory amino acid (e.g., glutamate) activity. Methamphetamine also induces rapid and reversible decreases in the rate-limiting enzyme for serotonin (5-hydroxytrypamine, 5-HT) synthesis, leading to reduced levels of this biogenic amine within various CNS areas.

Amphetamine, MDMA, and other psychotropic agents may also interact with a relatively new class of receptors called the trace amine-associated receptors (TAARs). TAARs represent a class of G protein–coupled binding sites for endogenous trace amines, metabolic products of the better-known biogenic amines such as NE, DA, 5HT, and histamine. Trace amines are normally present in very low (nanomolar) concentrations and include tyramine, octopamine, tryptamine and β-phenylethylamine. Trace amines such as β-phenylethylamine may function to modulate biogenic amine synaptic activities in select brain areas related to affective states and thus in maintaining levels of excitement and alertness. Branchek and Blackburn have hypothesized a role for trace amines in substance abuse, depression, attention-deficit/hyperactivity disorder, eating disorders, schizophrenia, and other neuropsychiatric diseases.

Pharmacokinetics

Toxicology

The toxic effects of amphetamine and related drugs can be dangerous and potentially fatal. Short-term effects of amphetamine include increased heart rate and blood pressure, decreased appetite, feelings of elation and self-assuredness, and reduced fatigue. Long-term, repetitive amphetamine use has been associated with insomnia and restlessness, significant weight loss, hallucinations, and paranoid psychosis. Amphetamine use can also include psychic dependence and tolerance as well as psychotic episodes in some individuals. Continuous high-dose amphetamine use has been associated with a state of paranoid (amphetamine) psychosis closely resembling the symptoms of paranoid schizophrenia. Symptoms include hyperactivity, anxiety, paranoid delusions, and auditory-tactile hallucinations in a setting of clear consciousness with little if any disorientation.

Use of amphetamines and related stimulants is particularly dangerous in patients with a history of heart disease or underlying hypertension as well as patients with glaucoma. Amphetamines and stimulants should also be avoided by anorexic individuals because of the appetite- suppressing properties of these drugs. In addition, amphetamines can cause life-threatening hypertensive crisis and possibly neurotoxic reactions when taken with monoamine oxidase (MAO) inhibitors for clinical depression. Amphetamine-associated death is considered to be a direct consequence of excessive sympathomimetic activity. Amphetamine toxicity includes hypertension, hyperpyrexia, delirium, convulsions, and severe tachycardia leading to cardiovascular collapse. Amphetamine also increases sympathetic tone, regulating smooth muscle contraction and thus can affect adversely the functions of the gastrointestinal tract, uterus, urinary bladder, and other organs dependent on smooth muscle activity.

MDMA has been associated with serotoninergic depletion and neuronal degeneration in rodent and nonhuman primate models. These neurotoxic effects were more pronounced in nonhuman primates than in rodents. Within 3 weeks of MDMA administration, profound serotoninergic neurodegeneration was seen in nonhuman primates in most brain areas. Some CNS areas showed evidence of partial recovery, that is, hippocampus, caudate nucleus, and frontal cortex. However, the partial recoveries appeared to be short-term, with a return to the dramatic patterns of serotoninergic losses seen 2 weeks after drug exposure.

Colado and colleagues reported that MDMA administration to pregnant rats does not produce damage to 5-HT nerve terminals in the brains of the fetuses, in contrast to the serotoninergic neurodegeneration seen in the CNS of the mothers. They hypothesized that this contrast in maternal versus fetal effects may be due to MDMA converted into free radical–associated metabolites in the adult brain but not in the immature brain. Alternatively, the developing CNS may have more effective or more active free radical scavenging mechanisms than the mature adult CNS.

Therapeutic administration of amphetamines is usually by the oral route. When used recreationally/illicitly, amphetamines are taken orally, snorted, smoked, or by intravenous injection. Methamphetamine’s methyl group is lipid soluble and easily transported across the blood-brain barrier as well as relatively resistant to enzymatic degradation catalyzed by MAO activity. After an oral administration (4 x 10 mg), methamphetamine is initially detected in plasma samples within 15 minutes to 2 hours. Maximal plasma concentrations (14.5–33.8 μg/L) are achieved within 2–12 hours and the drug remains measurable for 36–72 hours after administration. Methamphetamine has an elimination half-life of 9–15 hours primarily via urinary excretion. Methamphetamine elimination half-life varies with differences in urinary pH. One of the metabolites of methamphetamine is amphetamine.

Amphetamine and amphetamine-like derivatives are potent CNS stimulants affecting regulatory centers for heart rate, body temperature, blood pressure, appetite, attention, mood, and responses associated with alertness or alarm responses. Physiological and psychological responses to amphetamines closely resemble the sympathetic nervous system–induced fight-or-flight responses, including increased heart rate and blood pressure, vasoconstriction, bronchodilation, and hyperglycemia. Users report increased ability to focus on tasks, an overall increase in mental alertness, avoidance of fatigue, and decrease in appetite.

Drug tolerance develops rapidly in amphetamine abuse. Tolerance to the drug’s effects results in increasing amounts of the drug needed to obtain similar rewarding effects. However, chronic amphetamine use can produce so-called reverse tolerance, or sensitization to some of the psychological effects of the drug. Amphetamine users will often take more of the drug during withdrawal periods and may use other drugs such as benzodiazepines, or less commonly, barbiturates to lessen the effects of withdrawal.

Methamphetamine administration is associated with both dopaminergic and serotoninergic neurodegeneration. The generation of free radicals as a byproduct of increased DA and 5HT metabolism is postulated to play a key role in this neurodegeneration. Blocking increases in METH-induced release of DA or 5HT reduce the neurodegeneration seen with administration of this drug. In addition, pretreating with multiple injections of escalating doses of methamphetamine produces tolerance to the long-term neurotoxic effects of methamphetamine on striatal DA neurons. Although not yet well defined, the mechanism for this tolerance may be related to aberrant monoamine transporter-2 (VMAT-2) and dopamine transporter function in these neurons.

History

The leaves of the Catha edulis (khat) plant, which is native to the Horn of Africa and Arabian Peninsula, have been chewed for thousands of years, purportedly for their stimulant-like effects. In 1930, Wolfes identified the primary active constituent of khat to be cathine [(+) pseudonorephedrine]; cathinone [β-keto-amphetamine] was later identified to be a more potent contributor to the stimulant effects of khat and for which cathine is a primary metabolite.

Recent estimates suggest that khat is used daily by approximately 20 million people ⁸⁸ ; however, because its use is concentrated in the Arabian Peninsula and portions of Eastern Africa, it is not considered to a represent a major public health problem worldwide. Nevertheless, khat has received significant attention from international regulators, with its potential for abuse/dependence first discussed by the League of Nations in 1935, and again by the United Nations and World Health Organization at the Single Convention on Narcotic Drugs in 1961. However, it was not until the Convention on Psychoactive Substances in 1971 that cathinone was placed on the international list of Schedule I drugs. Subsequently, the US Drug Enforcement Administration (DEA) added cathinone to its list of Schedule I drugs in 1993.

Because of its use as a precursor to the chemical synthesis of ephedrine and norephedrine, cathinone was first synthesized in 1915 by Eberhard. With slight modifications to Eberhard’s synthesis, Adams and colleagues (Hyde et al., 1928) developed a method for synthesizing cathinone and several derivatives of cathinone that are still in use today. Driven in large part by chemical and pharmacological similarities among cathinone, ephedrine, and the amphetamines, numerous cathinone derivatives have been synthetized and patented by drug companies for their putative antidepressant and/or antiparkinsonian effects. For instance, methcathinone (α-methylamino-propiophenone) was first patented in Germany in 1936 (German Patent 639,126) as a chemical precursor for the synthesis of ephedrine (and ephedrine derivatives), later used in the Soviet Union for its antidepressant properties (1930s to 1940s), and subsequently patented by Parke Davis in 1957 (US Patent 2802865). Because of concern for abuse, methcathinone was listed as a Schedule I drug in 1994 by the International Convention on Psychotropic Substances, as well as the DEA.

Although recreational use of methcathinone in the 1970s provided early indications that synthetic cathinones possess high abuse potential, it was not until mephedrone (4-methylmethcathinone) and methylone (3,4-methylenedioxy- N -methylcathinone) emerged on the European club scene in around 2000 that these cathinone derivatives gained widespread popularity among drug abusers. Since that time, the recreational use of synthetic cathinones has increased dramatically around the world. They are widely available, marketed as “bath salts,” “research chemicals,” or “plant food,” and can be easily purchased on the Internet and in local shops as “safe” and “legal highs.” Indeed, anecdotal and survey data suggest that their effects are similar to those produced by cocaine and methamphetamine. Coincident with the increasing popularity of these agents as recreational drugs, poison control centers and emergency departments around the world have seen dramatic increases in the number of patients presenting with cardiovascular and/or neuropsychiatric toxicities as well as overdose fatalities related to the use of synthetic cannabinoids and/or cathinones. Because of the rapid increase in abuse and toxicity associated with the recreational use of these synthetic cathinone derivatives, in 2011 the DEA used its emergency scheduling authority to temporarily list three synthetic cathinones (mephedrone, methylone, and MDPV) as Schedule I. Although these regulations temporarily reduced the production/sale/use of these particular compounds, new derivatives with similar pharmacologic properties, and presumably high potential for abuse, quickly took their place in the market. In 2014, the list of synthetic cathinones placed under Schedule I was expanded to include 10 additional derivatives (4-MEC [4-methylethcathinone], 4-MePPP [4’-methyl-α-pyrrolidinopropiophenone], α-PVP [α-(pyrrolidin-1-yl)valerophenone], butylone [β-keto- N -methylbenzodioxolylbutanamine], pentedrone [α-methylamino-valerophenone], pentylone [β-keto-methylbenzodioxolylpentanamine], 4-FMC [flephedrone; 4-fluoromethcathinone], 3-FMC [3-fluoromethcathinone], naphyrone [naphthylpyrovalerone], and α-PBP [α-(pyrrolidinobuterophenone]), bringing the total number of synthetic cathinones listed as Schedule I drugs to 13 as of 2016.

Chemical Properties

Similar to amphetamine, cathinone is a chemical derivative of phenethylamine; however, in addition to the alkyl group on the alpha carbon, cathinone also contains a ketone group on the beta carbon (i.e., β-keto-amphetamine). This core cathinone structure (phenethylamine with an alkyl group on the alpha carbon and a ketone group on the beta carbon) contains four locations for chemical modification (see Fig. 17.1 ), and is conserved across the more than 200 chemical derivatives of cathinone that have been described. Despite similarities among the chemical structures of the synthetic cathinones, the cathinone superfamily has a relatively heterogeneous pharmacology, with two main subfamilies of compounds defined by their capacity to inhibit the uptake monoamines by their transporters (i.e., inhibitors), or to both inhibit the uptake and stimulate the release of monoamines (i.e., substrates) ( Fig. 17.5 ).

Pharmacokinetics

Cathinone and its derivatives are readily absorbed and have high blood-brain barrier permeability, with behavioral effects apparent within minutes after systemic administration in rodents. ^a Although the pharmacokinetic profiles of cathinone and several of the abused cathinone derivatives (e.g., MDPV, α-PVP, mephedrone, and methylone) have been examined, little is known about the pharmacokinetic properties of the majority of the synthetic cathinones. As with most amphetamine-like compounds, cathinone and its derivatives are metabolized primarily by liver enzymes. Although it is well known that cathinone is metabolized to pharmacologically active compounds (i.e., cathine and norephedrine), less is known about the pharmacologic activities of the metabolites of other cathinone derivatives. Of interest, whereas some of the synthetic cathinones (e.g., MDPV) exhibit linear pharmacokinetics, other cathinone derivatives exhibit nonlinear pharmacokinetics. For example, whereas methylone is metabolized primarily by CYP2D6, it is also known to function as a mechanism-based inactivator of CYP2D6 function, effectively inhibiting its own metabolism in a time- and dose-dependent manner.

a References .

Pharmacodynamics

Similar to other CNS and sympathetic nervous system stimulant drugs, cathinone and its synthetic derivatives increase extracellular levels of monoamines through their interactions with transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT). As mentioned earlier in this chapter text, chemical diversity within the cathinone superfamily has resulted in subfamilies of compounds with slight, but important, differences in their primary mechanism of action. Similar to amphetamine, cathinone and some of its derivatives (e.g., substrates such as mephedrone, methylone, and 3-FMC) are known to both inhibit the uptake and stimulate the release of dopamine, norepinephrine, and serotonin, whereas other cathinone derivatives (e.g., inhibitors such as MDPV, α-PVP, naphyrone) are capable of inhibiting monoamine uptake without stimulating their release, a mechanism of action more similar to that of cocaine than amphetamine. In addition to differences in their effects at monoamine transporters (i.e., release and/or inhibition), a great deal of diversity exists among the synthetic cathinones with respect to the selectivity with which they act at dopamine, norepinephrine, and serotonin transporters, as well as other nontransporter sites. For example, among inhibitors, some compounds (e.g., naphyrone, pentylone) inhibit the uptake of dopamine, norepinephrine, and serotonin at comparable doses, whereas other compounds, including MDPV, and α-PVP, are potent inhibitors of dopamine and norepinephrine uptake with low affinity for the serotonin transporter. Similar differences are also apparent among substrates, with compounds such as cathinone being more potent at releasing dopamine than serotonin, whereas other cathinone derivatives, such as mephedrone, are equipotent at releasing dopamine and serotonin.

Although relatively little is known about the effects of synthetic cathinones at sites other than the monoamine transporters, affinity for serotonin (1A, 2A, and/or 2C) and/or adrenergic (α1, α2a) receptors has been reported for some cathinones. Similar binding profiles have been reported for other amphetamine-like compounds (e.g., amphetamine, methamphetamine, MDMA); however, it is worth noting that unlike many amphetamine-like compounds, beta-keto containing cathinones appear to be devoid of activity at TAARs.

To date, the majority of preclinical studies on the behavioral effects of cathinones have focused on characterizing their acute locomotor effects. ^b Although the discriminative stimulus and reinforcing effects of cathinones have been described in much less detail, preliminary evidence is generally consistent with human reports as well as early studies of behavioral effects of cathinone and methcathinone in laboratory animals. ^c For instance, studies in rats and mice suggest that the common bath salts constituents MDPV, mephedrone, methylone, α-PVP, α-PBP, methcathinone, pentedrone, pentylone, naphyrone, flephedrone, 3-FMC4-MEC, and 4-MePPP all produce cocaine- and/or methamphetamine-like discriminative stimulus effects, ^d and that MDPV, mephedrone, and methylone, function as reinforcers when delivered intravenously. ^e Although MDPV, mephedrone, methylone, and α-PVP are all capable of maintaining responding in standard self-administration assays, there is still much we do not know about the factors that contribute to the purported high abuse potential of bath salts, including whether their abuse-related effects are altered when administered in combination with other bath salt constituents.

b References .

c References .

d References .

e References .

Toxicology

Although national drug use surveys (e.g., Substance Abuse and Mental Health Services Administration [SAMSHA] National Survey on Drug Use and Health) have yet to be updated to include data on synthetic cathinone (i.e., bath salts) overdoses, the Drug Abuse Warning Network recorded over 20,000 emergency department visits involving bath salts in 2011 alone. ⁷⁴ As with other stimulants, the most common symptoms associated with bath salts overdose are cardiovascular (e.g., tachycardia, hypertension, and chest pain) and/or neuropsychiatric complications (e.g., agitation, paranoia, and hallucination (see references 19, 199, and 237). Whereas acute myocardial infarction can seriously compromise the health of the user, case reports suggest that the paranoia and hallucinations produced by bath salts can precipitate self-destructive or violent behavior that can put users, their families, and medical staff at risk. (Stimulants such as cocaine, methamphetamine, and MDMA have well-characterized cardiovascular effects in rats and preliminary evidence suggests that mephedrone and MDPV produce similar, if not greater, increases in heart rate and mean arterial pressure. ) Given the overlap between the toxic effects of cathinones and other stimulants (e.g., cocaine, methamphetamine, MDMA), it is not surprising that current treatments for cathinone overdose parallel those used for cocaine, including the use of benzodiazepines to decrease cardiovascular effects and agitation. In some cases, haloperidol has been used to decrease the central stimulant effects of cathinones; however, as with cocaine, beta-blockers are contraindicated for the treatment of hypertension because they have been shown to result in further increases in blood pressure.

However, it should be noted that because bath salts preparations often contain multiple psychoactive compounds, with mixtures of two cathinones, and mixtures of a cathinone and caffeine being the most common, ^f it is difficult to say whether the toxicities observed in bath salts can be attributed to a single cathinone, or whether they result from interactions among the various bath salts constituents.

f References .

History

Crude opium is a component of the opaque, milky-white sap obtained from the seedpods of the poppy plant ( Papaver somniferum ). This plant and its product opium were likely cultivated in the Mediterranean region as early as 5000 BCE by ancient Egyptians and Greeks and later by the ancient Romans. Opium was introduced into China around BC 800 and, with the arrival of European explorers to China, to Europe by the early 18th century. In 1680, a famous English physician named Thomas Syndenham introduced opium to the medical field. In the 17th century, many people in Europe were treated for a variety of health problems with opium. In 1729, opium smoking was made illegal in China and soon the importation of opium was banned. This ban upset the British who were in charge of trading this valuable product. Opium was still smuggled into China and is considered the underlying cause of the so-called Opium Wars (1839–1842 and 1856–1860) between the British and the Chinese. In the United States, opium was used to treat soldiers during the Civil War (1861–1865). During the late 1800s, doctors prescribed “tonics” containing opiates for many conditions. Typically, these medicines failed to list opiates as one of the ingredients.

Opium represents a complex of sugars, proteins, fats, water, meconic acid, plant wax, latex, gums, ammonia, sulfuric and lactic acids, and numerous alkaloids. Alkaloids present in opium include morphine (10%–15%), codeine (1%–3%), papaverine (1%–3%), and thebaine (1%–2%). Noscapine, narceine, and approximately 25 other alkaloids are also present, but have essentially little to no effect on the CNS and are not usually considered to be opiates. Thebaine is considered highly toxic and thus not used therapeutically ; it acts as a potent stimulant rather than as a depressant, at higher concentrations, causing strychnine-like convulsions. Thebaine can be used to produce the semisynthetic morphine analogues oxycodone, dihydromorphinone, hydrocodone, and etorphine.

In 1805 the German pharmacist Frederick Serturner isolated morphine from opium. He named this newfound compound after Morpheus, the Greek god of dreams. Morphine-related analogues include the diphenylpropylamines (e.g., methadone), the 4-phenylpiperidines (e.g., meperidine), the morphinans (e.g., levorphanol), and 6,7-benzomorphans (e.g., metazocine), each of which has in common a piperidine ring or a key component of that ring structure. Heroin was first synthesized in 1874 by the British chemist C. Adler Wright. Heroin is synthesized from morphine. Heroin is the 3, 6-diacetyl ester of morphine, that is, diacetylmorphine (see Fig. 17.5 ). Heroin became widely accepted within the medical community in the early 1900s. The high risk for addiction was not initially recognized by physicians at that time. With a better understanding of its abuse potential, heroin was later regulated with passage of the Harrison Narcotics Tax Act of 1914. The drug is now classified as a Schedule I substance with significant abuse potential but no accepted medical use.

The term “opiate” refers to morphine-like alkaloids (e.g., morphine itself, heroin, codeine, thebaine, and papaverine) derived from opium as well as a number of semisynthetic and synthetic opiates. Opioid refers to endogenous substances with morphine-like activity. Endogenous opioids include dynorphins, enkephalins, endorphins, endomorphins, and nociceptin/orphanin FQ. The term “endorphin” was first used in the mid-1970s to describe any endogenous morphine-like substance, now classified as endogenous opioidergic peptides. We now recognize several classes of endogenous opioidergic peptides including enkephalins, endorphins, dynorphins, and endomorphins. Opiates such as morphine and heroin bind to and activate the same receptors used by endogenous opioidergic peptides, namely mu (μ), kappa (κ) and delta (δ) receptors. Opioidergic receptors are expressed only in the CNS, gastrointestinal tract, and vas deferens. Most opioid receptors are linked to an inhibitory G protein (G _i ). Thus endogenous opioidergic peptide receptor binding is associated with inhibition of adenylate/cAMP second-messenger systems and inhibition of the target neuron.

Endogenous opioidergic peptides are generally involved with homeostasis or regulation of basic physiological functions including respiration, endocrine functions, and nociception (pain). Endogenous opioidergic peptides may also play important roles in mood and affect. The greatest density of opioidergic receptors is found in the limbic system (emotions and affect) and in the dorsal horn of the spinal cord (nociception). Thus it should not be surprising that endogenous opioidergic peptides are thought to integrate euphoric and emotional components of pain relief ( Fig. 17.6 ).

Mechanism of Action

Opiate agonists and antagonists bind to stereospecific, saturable receptors in the brain and other tissues. CNS opioidergic receptors are widely but unevenly distributed. These receptors were originally classified according to their affinity for binding agonists: mu (μ) receptors preferentially bind to morphine, kappa (κ) receptors to ketocyclazocine, and delta (δ) receptors to deltorphin II. Morphine also binds to both kappa and delta receptors, although with less affinity than to mu receptors. In 2000, these receptors were reclassified as OP ₁ (delta), OP ₂ (kappa), and OP ₃ (μ) by a subcommittee of the International Union of Basic and Clinical Pharmacology. Mu receptors are located widely throughout the CNS, especially in the limbic system (frontal and temporal cortex, amygdala, and hippocampus); thalamus; striatum; hypothalamus; and midbrain. Kappa receptors are located primarily in the spinal cord, periaqueductal gray area, and cerebral cortex. Delta receptors are located primarily in pontine nuclei, amygdala, olfactory bulbs, and deep cerebral cortex. Opiate receptors are G-protein-coupled and function as modulators, both positive and negative, of synaptic transmission. Most known opiates exhibit no ceiling effect for analgesia with the exception of codeine for which a ceiling effect is estimated as 7mg/kg. Mu receptor activation results in analgesia, euphoria, respiratory depression, miosis, decreased gastrointestinal motility, and physical dependence. Kappa-receptor stimulation also produces analgesia, miosis, respiratory depression, as well as dysphoria and some psychomimetic effects (i.e., disorientation and/or depersonalization). Delta receptor activation produces dysphoria, is hallucinogenic, and produces respiratory depression at high doses and cardiac stimulation. Opiates working primarily through mu receptors also suppress cough reflex. The antitussive effects of codeine are mediated through direct action on receptors in the cough center of the medulla.

Heroin is transported rapidly across the blood-brain barrier and metabolized into morphine and related compounds. It is generally assumed that heroin itself has only minor pharmacological effects. Most of the pharmacological effects associated with heroin are actually caused by morphine as well to some degree, the other two major metabolites 6-acetylmorphine (6-AM) and metabolites 6-acetylmorphine (M6G). M6G possesses analgesic properties, although M3G does not seem to have any agonistic effect either in vivo or in cell cultures.

Most opiates such as heroin and morphine produce a profound sense of euphoria in most users, although this effect diminishes with development of tolerance to the drug. Heroin and morphine share in common the ability to induce euphoria, relaxation, as well as, with time, drowsiness and sleepiness. Short-term studies among users suggested that heroin tolerance develops no more rapidly than tolerance to morphine. This is perhaps not surprising given the physicochemical properties of heroin and morphine and the metabolism of heroin metabolism to morphine.

Pharmacokinetics

Toxicology

The psychological dependence associated with opioidergic addiction is both protracted and complex. Well beyond the recovery from the physical need for the drug, the opiate addict may obsess about use of the drug and feel an inability to deal with daily activities without use of the drug. These individuals are at high risk for relapse assuming neither the physical environment.

Opiate withdrawal symptoms in opiate users can be seen as early as 2–3 hours after the last dose of drug. Major withdrawal signs peak between 48 to 72 hours after last dose and subside within 9 to 12 days. Initial signs of withdrawal include dilated pupils, profuse sweating, and anxiety. These individuals also experience progressively stronger drug craving, severe abdominal distress, diarrhea, nausea and vomiting, restlessness, muscle and bone pain, insomnia, cold flashes with goose bumps (“cold turkey”) alternating with high temperature spiking (“hot flashes”), and kicking movements (“kicking the habit”). Severe depression is a common manifestation. Opiate withdrawal is rarely fatal, although sudden withdrawal by heavily dependent users in poor health may be fatal. Opiate withdrawal is considered less risky than alcohol, benzodiazepine, or barbiturate withdrawal.

Following intravenous infusion of heroin, the user experiences a surge of euphoria (“rush”) along with dry mouth, a warm flushing of the skin, and a heaviness of the extremities. The user then becomes alternately somnolent and alert (“on the nod”), shifting between wakeful and drowsy states. Mental functioning declines. Tolerance to the effects of the drug develop over time and regular use. In effect, the user must use more heroin to achieve the same intensity of effect. Eventually, drug-induced neural plasticity within reward pathways of the brain results in addiction to the drug.

It is very difficult to establish a lethal dose50 (LD ₅₀ ) for heroin among regular users. Individuals have overdosed on as little as 1 mg/kg of heroin. An LD ₅₀ for nonaddicts has been suggested as 1–5 mg/kg. However, there may be no easily identifiable upper limit to the amount of heroin a heavily addicted individual can take. Research studies conducted in the 1920s in opiate addicts described administering heroin in doses of 1600 to 1800 mg with no obvious adverse side effects. These results are supported by studies in rats showing that 14 days of pretreatment with morphine or heroin reduced mortality associated with subsequent morphine administration. Thus long-term opiate abuse is typically associated with development of highly significant drug tolerance.

Neurological complications associated with heroin use include peripheral neuropathies, nerve pressure palsies, hypoxic encephalopathy, seizures, rhabdomyolysis, and transverse myelopathies. Spongiform leukoencephalopathy is a relatively rare complication of heroin use, with only 70 reported cases from the first reported case in 1984 through 2004. This complication is typically seen among users who inhale fumes generated by heating heroin, a practice called “chasing the dragon.” The typical lesions include abnormal white matter with patchy spongiform change and prominent reactive fibrous gliosis consisting of glial fibrillary acidic protein- (GFAP-)positive fibrous astrocytes. Symptoms vary according the brain regions involved but often include cognitive dysfunction, cerebellar ataxia, dysarthria, and motor restlessness with an estimated mortality rate of approximately 25%.

Heroin-related death has been associated with the phenomenon of place tolerance and overdose as a result of using the drug in an unaccustomed environment. The mechanism for fatal overdosing in this situation was described as an overriding of conditioned or place tolerance. Because heroin use is such a highly ritualized behavior, long-time users exhibit increased tolerance to the drug in locations in which they have repeatedly administered heroin. When they used in a different location, this environment-conditioned tolerance does not occur, which produces enhanced effects of the drug. In response to this decrease in tolerance, the user increases the typical dose of the drug. If extreme in self-dosing, the result can be a fatal overdose.

Morphine also affects immune system function via interactions with dendritic cells. Dendritic cells, a type of antigen-presenting cell, express opiate receptors. Dendritic cells exposed to morphine during their maturation produce increased levels of interleukin-12, a cytokine responsible for promoting the proliferation, growth, and differentiation of T lymphocytes, which are active in adaptive immune responses and less so, interleukin-10, a cytokine responsible for promoting B-lymphocyte responsiveness.

History

Hallucinogens comprise a class of drugs defined by their ability to induce changes in the user’s perception of reality. Users describe seemingly real images, sounds, and sensations that do not in fact exist. Traditionally, these drugs were derived from plant sources but are now synthetic with resultant greater purity of product (Drug Enforcement Administration, Drug Descriptions: Hallucinogens). Commonly used hallucinogens include lysergic acid diethylamide (LSD) and psilocybin ( Fig. 17.7 ).

Lysergic acid is a component of ergot alkaloids found in the ergot fungus ( Claviceps purpurea ), which infects cereal grains including rye. Ergot alkaloids are very potent compounds responsible for ergotism (also known as ergotoxicosis, ergot poisoning, and St. Anthony’s Fire) characterized by convulsive and vasoconstrictive symptoms including gangrene and hallucinations, mania and psychoses.

Lysergic acid diethylamide (or LSD) was first synthesized in 1938 by Swiss chemist Albert Hofmann (1905–2008). The hallucinogenic effects of LSD were not immediately recognized and the drug was ignored over the next several years. But in 1943, Hofmann accidentally absorbed a very small amount of LSD and experienced first-hand the psychogenic effects of the drug. He then followed up with an additional self-administration of LSD, later reporting the intensely psychedelic effects associated with the drug. The abbreviation LSD is derived from its early codename LSD-25 (German “lysergsäure-diethylamid” followed by a sequential development number). LSD was initially marketed by Sandoz Laboratories as a therapeutic drug with numerous potentially useful psychiatric applications. However, the drug’s entry into the illicit, recreational environment with ensuing political repercussions eventually precluded further interest in the drug among pharmaceutical companies and physicians. The substance was eventually banned for any use other than research as a DEA Schedule I substance.

For a time during the 1950s and early 1960s, intelligence agencies in the United States and other countries had an interest in use of LSD to facilitate interrogations and mind control. The Central Intelligence Agency (CIA) conducted such studies through the Office of Scientific Intelligence largely in response to similar studies employed by the Soviet Union and China in the early 1950s. One such study involved the use of US soldiers dosed with LSD to study the effects of panic. By the late 1960s the CIA had ended these LSD studies, the results of which were considered too unpredictable.

The principal psychoactive component of so-called magic mushrooms is an indole related to tryptamine, psilocybin. Use of hallucinogenic mushrooms (Psilocybe cubensis and P. semilanceata ) may go back as far as prehistoric humans, although conclusive evidence for this is lacking. Their early use was probably associated with religious communing, divination, and healing just as they are among some present-day Native Americans. Bernardino de Sahagún (1499–1590), a Franciscan missionary, described the ritualistic use of teonanácatl or “flesh of the gods” among the Central American Aztecs. In the 1960s, recreational use of hallucinogenic mushrooms was promoted by R. Gordon and Valentina Wasson, Timothy Leary, and others, which led to the popularization of a number of psychoactive Psilocybe species found in North America, Europe, and Asia.

In 1958, Hofmann had identified psilocin and psilocybin as the active compounds in psychoactive mushrooms. By the early 1970s, a number of psychoactive Psilocybe species were described, these variants being found in North America, Europe, and Asia. These mushrooms may also contain small amounts of other psychoactive tryptamines. Psilocybin and psilocin are listed as Schedule I drugs in the United States and many other countries ( Fig. 17.8 ).

Mushroom concentrations of psilocybin and psilocin vary significantly among varieties of psychoactive mushrooms but averages 0.5%–2.0% of the dry weight of the average mushroom. The more common species P. cubensis contains approximately 10–25 mg psilocybin and psilocin. When psilocybin is ingested, it is broken down to produce psilocin, which is responsible for the hallucinogenic effects. Twenty-five milligrams to 50 mg of psilocybin and/or psilocin is generally thought to be a heavy psychoactive dose of these drugs.

Pharmacodynamics

Mechanisms of Action

The hallucinogenic effects of LSD and phenethylamine hallucinogens are thought to be mediated by the binding of these drugs to the 5HT _2A receptor. LSD administered in so-called recreational doses has been shown to interact with 5-HT _1A , 5-HT _2A , 5-HT _2C , 5-HT _5A , 5-HT _5B , and 5-HT ₆ receptors. More specifically, the hallucinogenic effects of LSD have been attributed to the drug’s strong partial agonist effects at 5-HT _2A receptors ; selective 5-HT _2A specific antagonists block the psychotropic activity of LSD. With the exception of the ligand-gated ion channel 5-HT ₃ receptor, all other 5-HT receptors are G-protein-coupled seven transmembrane receptors that activate intracellular second messenger pathways. The exact sites and mechanisms of action and are not yet known. In addition to the drug’s effects on 5HT _2A receptors, LSD has been shown to affect glutaminergic systems within the CNS. Systemic LSD (0.1 mg/kg, i.p.) or direct LSD infusion (10 μM) into prefrontal cortex has been associated with elevated levels of glutamate release in this brain region, an effect blocked by administration of the 5HT _2A antagonist M100907 (0.05 mg/kg, i.p.). Chronically, LSD may activate dopamine- and cyclic AMP-regulated phosphoprotein with molecular weight 32 kDa (DARPP-32)–related pathways, a mechanism of action shared by numerous other psychoactive drugs including cocaine, amphetamine, methamphetamine, nicotine, caffeine, LSD, PCP, ethanol, and morphine.

Typical doses of LSD are measured in microgram amounts rather than the more typical milligram amounts associated with other drugs of abuse. Hofmann determined that an active dose of mescaline, roughly 0.2 to 0.5 g, has effects comparable to 100 μg or less of LSD. A single dose of LSD is typically 100 to 500 μg; threshold psychotropic effects of the drug experienced with as little as 25 μg. . The LD ₅₀ for LSD has been estimated to range from 200 μg/kg to more than 1 mg/kg, although there are no known deaths attributed directly to the use of LSD. LSD users do not exhibit the typical features of drug addiction and dependence; however, tolerance to the drug can develop rapidly. Users demonstrate cross-tolerance between LSD and psilocybin. Attenuation of tolerance to LSD is thought to be related to drug-induced downregulation of 5HT _2A receptors in as yet undefined CNS areas.

Adverse reactions to LSD have been treated using fast-acting benzodiazepines such as diazepam or triazolam. These serve as anxiolytics, calming the patient but without directly blocking LSD binding at 5HT _2A sites. Theoretically, specific 5-HT _2A receptor antagonists, for example, the atypical antipsychotic quetiapine fumarate, would act to block LSD binding at these receptors, thus attenuating the psychoactive effects of LSD.

Mescaline (3,4,5-trimethoxyphenethylamine) is a naturally occurring hallucinogenic phenethylamine. Mescaline is one of several psychoactive alkaloids produced by several species of cactus including the peyote cactus ( Lophophora williamsii ), the San Pedro cactus ( Echinopsis pachanoi ), and the Peruvian Torch cactus ( Echinopsis peruviana ). The peyote cacti are primarily subterranean, with underground roots and a relatively small above-ground crown consisting of several disk-shaped “buttons.” These buttons are cut from the cactus and dried. Peyote includes a number of alkaloids including mescaline. Peyote has been used as a part of religious rites by Native American Indians of the arid northern Mexico and southwest United States for thousands of years. Peyote buttons with measurable levels of mescaline were found within prehistoric native Indian ruins and traced back to 3780–3660 BCE by radiocarbon dating. Mescaline was first isolated and identified in 1897 by German chemist Arthur Heffter and first synthesized in 1919 by Ernst Späth ( Fig. 17.9 ).

Mescaline is rapidly absorbed after oral ingestion by rats. In human, the effective dose range is 300–500 mg of pure mescaline. The hallucinogenic effects of associated with ingestion of mescaline are seen in doses of 300–600 mg, the equivalent of 9–20 small peyote cactus tops. Mescaline is 1000–3000 times less potent than LSD, and 30 times less potent than psilocybin. The LD ₅₀ has been estimated as 212 mg/kg, i.p., for mice; 132 mg/kg, i.p., for rats; and 328 mg/kg, i.p., for guinea pigs. About half the initial dosage is excreted after 6 hours, but some studies suggest that it is not metabolized at all before excretion. The effects of mescaline can last up to 12 hours. Tolerance to mescaline increases with repeated administration. Mescaline may exhibit cross-tolerance with either LSD or psilocin. Equipotent doses of mescaline and LSD have been described as all but indistinguishable in psychoactivity. A significant amount (20%–50%) of an ingested dose of mescaline is excreted in the urine unchanged in canine experimental models. Lesser amounts (7%) are excreted in urine by humans.

In contrast to LSD-induced hallucinations, those associated with mescaline use are described as being consistent with actual experiences but are typically intensified through visual and auditory inputs. Mescaline elicits a pattern of sympathetic arousal, with the peripheral nervous system being a major target for this drug. Similar to LSD, mescaline binds to and activates brain serotonin 5-HT _2A receptors with a high nanomolar affinity.