Psychoactive compounds and audiogenic seizure susceptibility.
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Prominent among the class of hallucinogenic phenylisopropylamines is the 2,5-dimethoxy substitution pattern; this pattern has long been recognized as being an important feature of the more potent agents within this class. The purpose of this present study was to explore the behavioral properties of a series of methoxylated phenylisopropylamines in order to determine the effect of other substitution patterns and the relative importance of individual methoxy groups. Rats, trained to discriminate the hallucinogenic agent 2,5-dimethoxy-4-methyl-phenylisopropylamine (DOM) from saline in a two-lever drug discrimination task, were challenged with a series of di- and trimethoxyphenylisopropylamines (i.e., DMA and TMA derivatives). DOM-stimulus generalization was found to occur with 2,4-DMA but not with 2,3-DMA, 2.6-DMA, or 3,5-DMA; generalization also occurred with 2,3,4-TMA, 2,3,5-TMA, 2,4,6-TMA and 3,4,5-TMA. The 2,4-dimethoxy pattern also emerges as an important feature among the more active agents.
A group of six rats was trained to discriminate the effects of para-methoxyamphetamine (PMA; 3 mg/kg, 15 min pretreatment time) and saline in a two-lever choice task using a fixed ratio 10 schedule of water reinforcement. Stimulus control was assumed to be present when 80% or more of the first ten responses were appropriate for the treatment condition on each of five consecutive days. PMA established stimulus control in each of the subjects. The mean number of sessions prior to the onset of criterion performance was 19 (SE = 2, range = 14-24). A second group of ten rats was similarly trained with lysergic acid diethylamide (LSD; 0.1 mg/kg, 15 min pretreatment time) and saline. In rats trained with PMA, LSD yielded intermediate results, i.e., significantly different from both training conditions. Likewise, the response distribution was intermediate in nature when LSD-trained subjects were tested with PMA. Pizotyline did not antagonize PMA-induced stimulus control in rats trained with PMA and saline but did antagonize the intermediate responding produced by PMA in LSD-trained subjects. It is concluded that PMA-induced stimulus control does not depend upon activation of serotonergic receptors but that PMA does possess some LSD-like effects which are mediated serotonergically.
The nature of the stereochemistry and aromatic ring substituents and their importance to biological activity for phenethylamine-type hallucinogens is presented. The possibility of a hydrophobic site to bind to the 4-substituent and its likely geometry is described. A brief discussion of the structure-activity relationships for tryptamines such as psilocin and DMT is also given, with comments about the stereochemistry of alpha-methyltryptamines. Evaluation of a series of N(6)-alkyl-nor-LSD derivatives indicated that selected members such as N(6)-ethyl, allyl and propyl were as potent as, if not more potent than LSD, both in a two-lever drug discrimination assay in rats, and in man. N(6)-alkyl groups longer than n-propyl, such as n-butyl or 2-phenethyl, gave compounds that were greatly reduced in activity.
Studies indicate that hallucinogens markedly suppress the discharge of serotonin containing neurons in the dorsal raphe nucleus. Forebrain neurons receiving a major serotonergic input are relatively insensitive to hallucinogens. These actions of hallucinogens are not sufficient to explain the psychoactive effects of these drugs. Evidence is presented to indicate that hallucinogens sensitize serotonin and norepinephrine receptors in the facial nucleus. This receptor sensitizing effect is common to all, and specific for, hallucinogens. It is suggested that a mechanism of receptor sensitization might account for the altered perceptual reactivity produced by hallucinogens.
An animal model for studying the actions of hallucinogenic drugs using primate social colonies is presented. Although hallucinogens induce a number of behavioral changes in this paradigm, one emergent behavior, limb jerks, appears to be selectively induced by three classes of hallucinogens in doses which correlate with those reported to be hallucinogenic in humans. Several non-hallucinogenic congeners of hallucinogens failed to significantly elicit this response. Other behavioral changes induced by hallucinogens in monkeys such as ptosis and social withdrawal may be useful in studying aspects of hallucinogen intoxication other than hallucinations, or psychosis in general. Upon daily administration, tolerance developed to all hallucinogens tested except two, as is seen in humans. Moreover, cross-tolerance between hallucinogens could be demonstrated. Further experiments with the hallucinogen 5-methoxy N,N-dimethyltryptamine revealed that although certain individual behaviors could be antagonized by serotonin antagonists, dopamine antagonists, and physostigmine, no drug completely reversed the behavioral abnormalities induced by this hallucinogen. It is suggested that this paradigm, which offers an hallucinogen-induced behavior which correlates well with the human hallucinogen response and permits observation of a wide variety of other potentially relevant behaviors in primates, may be useful in developing and testing theories of hallucinogenic drug action. It may be especially valuable in view of the present difficulties of conducting hallucinogen research in humans.
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BACKGROUND: Hallucinogens are widely used, both by drug abusers and by peoples of traditional cultures who ingest these substances for religious or healing purposes. However, the long-term residual psychological and cognitive effects of hallucinogens remain poorly understood. METHODS: We recruited three groups of Navajo Native Americans, age 18-45: 1) 61 Native American Church members who regularly ingested peyote, a hallucinogen-containing cactus; 2) 36 individuals with past alcohol dependence, but currently sober at least 2 months; and 3) 79 individuals reporting minimal use of peyote, alcohol, or other substances. We administered a screening interview, the Rand Mental Health Inventory (RMHI), and ten standard neuropsychological tests of memory and attentional/executive functions. RESULTS: Compared to Navajos with minimal substance use, the peyote group showed no significant deficits on the RMHI or any neuropsychological measures, whereas the former alcoholic group showed significant deficits (p < .05) on every scale of the RMHI and on two neuropsychological measures. Within the peyote group, total lifetime peyote use was not significantly associated with neuropsychological performance. CONCLUSIONS: We found no evidence of psychological or cognitive deficits among Native Americans using peyote regularly in a religious setting. It should be recognized, however, that these findings may not generalize to illicit hallucinogen users.