Psychostimulants

Neurologic Complications of Psychomotor Stimulant Abuse

Psychomotor stimulants are drugs that act on the central nervous system (CNS) to increase alertness, elevate mood, and produce a sense of well-being. These drugs also decrease appetite and the need for sleep. Stimulants can enhance stamina and improve performance in tasks that have been impaired by fatigue or boredom. Approved therapeutic applications of stimulants include attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. These agents also possess potent reinforcing properties that can result in excessive self-administration and abuse. Chronic use is associated with adverse effects including psychosis, seizures, and cerebrovascular accidents, though these complications usually occur in individuals with preexisting risk factors. This chapter reviews the adverse neurologic consequences of chronic psychomotor stimulant use and abuse, with a focus on two prototypical stimulants methamphetamine and cocaine.

(±)3,4-Methylenedioxyamphetamine elicits action potential bursts in a central snail neuron

The effects of (+/-)3,4-methylenedioxyamphetamine (MDA) were studied in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. The RP4 neuron generated spontaneous action potentials. Extracellular or intracellular application of MDA elicited action potential bursts of the central RP4 neuron. The action potential bursts elicited by MDA were not blocked when neurons were immersed in high-Mg2+ solution, Ca2+-free solution, nor after continuous perfusion with atropine, d-tubocurarine, propranolol, prazosin, haloperidol, sulpiride or methiothepin. Notably, the induction of action potential bursts was blocked by pretreatment with protein kinase C (PKC) inhibitors, chelerythrine and Ro 31-8220, but not by protein kinase A (PKA) inhibitors, KT-5720 and H89, nor by the phospholipase C (PLC) inhibitor, U73122. PKC activators, i.e., phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acety-sn-glycerol (OAG; a membrane-permeant DAG analog), facilitate the induction of action potential bursts elicited by MDA. Voltage-clamp studies revealed that MDA decreased the delayed rectifying K+ current (I(KD)) of the RP4 neuron. Further, although Ro 31-8220 did not affect the I(KD), Ro 31-8220 decreased the inhibitory effect of MDA on the I(KD). These results suggest that the generation of action potential bursts elicited by MDA was not due to (1) the synaptic effects of neurotransmitters, (2) the cholinergic, adrenergic, dopaminergic or serotoninergic receptors of the excitable membrane. Instead, the MDA-elicited action potential bursts are closely related to PKC activity and the inhibitory effects on the I(KD).

Psychostimulants and epilepsy

PURPOSE

The aim of this article is to review the literature on the effects of psychostimulants in epileptic subjects in order to reach a consensus statement regarding the use or abuse of these substances.

METHODS

Psychostimulant substances have been considered the drugs that share the ability to produce excitation of the CNS leading to convulsions. The stimulation may be at cortical, brainstem, or spinal levels. In this article, the following cortical stimulants are analyzed and discussed: cocaine, amphetamine and related agents, caffeine, cannabinoids, and psychedelic drugs. This review is based on research done using pharmacological textbooks and Medline.

RESULTS

The use of cocaine is associated with the occurrence of seizures. The reported frequency varies from 1% to 40% of addicted subjects, based on the typology of the considered study. Amphetamines and related drugs rarely induce epileptic seizures at therapeutic doses, but seizures may occur after the first dosing. Caffeine at high doses may induce epileptic seizures because of its adenosine receptor-antagonizing properties. Marijuana, at variance with other psychostimulants, owing to its serotonin-mediated anticonvulsant action, could have a medical use for the treatment of epilepsy. Psychedelic compounds rarely induce epileptic seizures, but the most common clinical CNS complication after ingestion of ecstasy is the occurrence of seizures.

CONCLUSIONS

The use of psychostimulants, except for marijuana, can induce single or multiple seizures in healthy subjects.

Distinct features of seizures induced by cocaine and amphetamine analogs

Seizure-related emergencies caused by stimulants of abuse have been increasing. To better understand the nature of these drug-induced convulsions, we characterized the seizure patterns associated with high doses of cocaine, and the amphetamine analogs, methamphetamine, methylenedioxymethamphetamine (MDMA) and 4-methylaminorex. The features of the stimulant-induced seizures were distinct and included the following: (1) the duration of convulsive activity was shortest for cocaine and longest for methamphetamine, (2) only MDMA produced a secondary clonic phase after the initial ictal event, and (3) 4-methylaminorex manifested a very steep dose-response curve. Differential preventive profiles of anticonvulsant agents on the stimulant-induced seizures also were observed. For example, cocaine-related seizures were most effectively prevented by, while methamphetamine-induced seizures were completely refractory to, phenytoin pretreatment. The only anticonvulsants which appeared to influence methamphetamine-related convulsions were diazepam and valproate. A unique feature of 4-methylaminorex was that related seizures were almost completely blocked by the calcium channel blocker, flunarizine.

Cocaine babies: a result of multiple teratogenic influences

The history of cocaine use is reviewed. Cocaine teratogenesis has only recently been studied, and initial human studies had serious methodological flaws. These flaws included ascertainment bias, publication bias (studies finding cocaine effects have been more likely to be presented or published), and overemphasis on the perinatal period. Comparison with alcohol teratogenesis shows that alcohol is a more potent teratogen, which, however, produces major and specific effects (fetal alcohol syndrome) in less than 10% of offspring with heavy alcohol exposure during pregnancy. Nonspecific minor congenital anomalies or fetal alcohol effects are seen in a larger number. Personal experience with two groups of children exposed to cocaine in utero is reviewed. Insurance patients gained weight, took vitamins, and generally, their children did well in spite of cocaine use. Indigent patients were usually unmarried and often "street people," probably used more cocaine, generally used other drugs as well, often did not gain weight during pregnancy, and were much more likely to have children with problems. Surveys show that most cocaine users also use alcohol, often simultaneously. Those who use both agents are more likely to have troubled backgrounds and antisocial behavior and to drop out of treatment programs than those who use only alcohol. Cocaethylene or ethylbenzoylecgonine is formed in the liver when cocaine and alcohol are simultaneously ingested. It is a potent stimulant and dopamine uptake blocker that is more toxic to myocardial cells than is cocaine. Good nutrition is now known to be very important in preventing congenital anomalies and fetal death. A multihit model of neurologic handicap, which stresses the importance of a good postnatal environment, is briefly outlined.(ABSTRACT TRUNCATED AT 250 WORDS)