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NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

Organic solvent inhalation is the cause of several neuropathological
changes that are associated with decreased cognitive functioning. Workers
chronically exposed to mixtures of organic solvents in the environment at
concentrations within or slightly exceeding the acceptable values, present
with subtle cognitive deficits, detected through visual evoked potentials
(Indulski et al., 1996). Chronic inhalation of primarily toluene-based solvents
can produce a persistent paranoid psychosis, temporal lobe epilepsy and a
decrease in IQ. These psychiatric and neurological sequelae of chronic solvent
use are serious and potentially irreversible (Byrne et al., 1991). The degree to
which these chronic neuropsychiatric effects modulate the persistent use of
solvents or other substances needs clarification.

Hallucinogens
Introduction
The hallucinogens are a chemically diverse class, but are characterized by
their ability to produce distortions in sensations, and to markedly alter mood
and thought processes. They include substances from a wide variety of natural
and synthetic sources, and are structurally dissimilar (Jacobs & Fehr, 1987).
The name hallucinogen refers to hallucination-producing properties of these
drugs. However, hallucinations are not the only effects caused by these drugs,
and often occur only at very high doses. The hallucinations are most often
visual, but can affect any of the senses, as well as the individual’s perception
of time, the world, and the self. The subjective effects vary greatly between
individuals, and from one use to the next within the same person.
The hallucinogens are divided into classes based on structural similarity of
the drugs. One class is related to lysergic acid diethylamide (LSD). These are
the indolealkylamines, which are structurally similar to the neurotransmitter
serotonin. This group includes LSA (d-lysergic acid amine, found in the seeds
of several varieties of morning glory), psilocybin, and dimethyltryptamine
(DMT). These latter three compounds are all naturally occurring.
The next group of hallucinogens consists of phenylethylamine drugs, of
which mescaline, methylenedioxyamphetamine (MDA), and methylenedioxy-
methamphetamine (MDMA) are the most popular members. MDMA, or
ecstasy, is considered separately in this chapter due to its widespread use and
current popularity. Paramethoxyamphetamine (PMA), dimethoxy-4-
methylamphetamine (DOM) and trimethoxyamphetamine (TMA) are other
members of this group. These drugs bear a close structural relationship with
amphetamine.
Phencyclidine (PCP) and ketamine are dissociative anaesthetics that
belong to the arylcycloalkylamine family of drugs, and act on glutamate
receptors.
Finally, there is the atropinic family, which includes atropine, scopolamine
and hyoscyamine. They are found naturally in many species of potato plants.

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