α-Ethyltryptamine (α-ET) as a discriminative stimulus in rats☆

Abstract

Abstractα-Ethyltryptamine (etryptamine, α-ET) is a drug of abuse that first appeared on the clandestine market in the mid 1980s. Its pharmacological actions are poorly understood. In this investigation, it is reported for the first time that α-ET serves as a training drug in drug discrimination studies. Male Sprague-Dawley rats were trained to discriminate (30-min pretreatment time) 2.5 mg/kg of α-ET (ED 50 = 1.3 mg/kg) from saline vehicle using a standard two-lever operant paradigm and a VI-15s schedule of reinforcement for appetitive reward. Once established, the α-ET stimulus was shown to have an onset to action of 30 min and a duration of effect of at least 4 hours. In tests of stimulus generalization (substitution), the α-ET stimulus generalized to S(−)α-ET (ED 50 = 1.6 mg/kg) and R (+)α-ET (ED 50 = 1.3 mg/kg). Tests of stimulus generalization were also conducted with prototypical phenylisopropylamines: (+)amphetamine, 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), and N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA). The α-ET stimulus generalized to DOM (ED 50 = 0.4 mg/kg) and PMMA (ED 50 = 0.7 mg/kg), but only partially generalized (ca. 40% maximal drug-appropriate responding) to (+)amphetamine. The results suggest that α-ET produces a complex stimulus. Keywordsα-Ethyltryptamine; α-ET; (+)α-ET; (−)α-ET; DOM; PMMA; Amphetamine; Drug discrimination α-Ethyltryptamine, also known as etryptamine, α-ET, or AET, was first synthesized in 1947 as a potential synthetic precursor to the β-carbolines, and other syntheses have since been reported (e.g. Heinzelman et al., 1960;Hester et al., 1964;Snyder and Katz, 1947). Within about a decade of its first synthesis, α-ET was shown to interact with serotonin receptors of various isolated tissue preparations Khan, 1959a, 1959b;Gaddum et al., 1955;Vane, 1959) and to act as an inhibitor of monoamine oxidase (MAO) (Govier et al., 1953; Greig et al., 1953). The latter action, due to the growing interest at that time in the relationship between inhibition of MAO and depression, led to clinical trials of α-ET as an antidepressant. α-ET was soon thereafter (1961) introduced as an antidepressant ("Monase"); but, despite its apparent effectiveness (e.g. Robie, 1961), it was withdrawn from the market within a year of its introduction due to problems with agranulocytosis and other side effects. This led to the subsequent synthesis (Hester et al., 1964) and patenting (Anthony, 1970) of the individual optical isomers of α-ET-presumably in an attempt to divorce its therapeutic action from its † Presented at the College Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errorsmaybe discovered which could affect the content, and all legal disclaimers th...

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