Abstract
Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) and related drugs have been studied extensively in rodents, although the generality of those findings across species is not known. The goals of this study were to see whether monkeys could discriminate DOM and to characterize the DOM discriminative stimulus by studying a variety of drugs, including those with hallucinogenic activity in humans. Four rhesus monkeys discriminated between 0.32 mg/kg s.c. DOM and vehicle after an average of 116 (range = 85–166) sessions while responding under a fixed ratio 5 schedule of stimulus shock termination. Increasing doses of DOM occasioned increased responding on the drug lever with the training dose occasioning DOM-lever responding for up to 2 h. The serotonin (5-HT)2A/2C receptor antagonists ritanserin and ketanserin, the 5-HT2A receptor antagonist (+)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol] (MDL100907), and its (-)stereoisomer MDL100009 [(-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol], but not haloperidol, completely blocked the discriminative stimulus effects of DOM. Quipazine as well as several drugs with hallucinogenic activity in humans, including (+)lysergic acid diethylamide, (-)DOM, and 2,5-dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7), occasioned DOM-lever responding. The κ-opioid receptor agonists U-50488 and salvinorin A (a hallucinogen) did not exert DOM-like effects and neither did ketamine, phencyclidine, amphetamine, methamphetamine, cocaine, morphine, yohimbine, fenfluramine, 8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT), or (±)-2-(N-phenethyl-N-1′-propyl)amino-5-hydroxytetralin hydrochloride (N-0434). These data confirm in nonhuman primates a prominent role for 5-HT2A receptors in the discriminative stimulus effects of some drugs with hallucinogenic activity in humans. The failure of another drug with hallucinogenic activity (salvinorin A) to substitute for DOM indicates that different classes of hallucinogens exert qualitatively different discriminative stimulus effects in nonhumans.
Footnotes
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This work was supported in part by Alcon Research, Ltd. C.P.F. is the recipient of a Senior Scientist Award (DA17918) from the National Institute on Drug Abuse, NIH. A portion of this work was supported by the intramural programs of the National Institute on Drug Abuse and the National Institute on Alcohol Abuse and Alcoholism.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.130625.
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ABBREVIATIONS: DOM, 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane; 8-OH-DPAT, 8-hydroxy-2-(dipropylamino)tetralin hydrobromide; FR, fixed ratio; 5-HT, serotonin; DOI, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane; LSD, (+)lysergic acid diethylamide; 2C-T-7, 2,5-dimethoxy-4-(n)-propylthiophenethylamine; N-0434, (±)-2-(N-phenethyl-N-1′-propyl)amino-5-hydroxytetralin hydrochloride; MDL100907, (+)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol]; MDL100009, (-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol]; U50488, trans-(1R,2R)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamine hydrochloride; LY-53857, 6-methyl-1-(1-methylethyl)-ergoline-8-carboxylic acid 2-hydroxy-1-methylpropyl ester maleate; CP-52215, 8-fluoro-5-(4-fluorophenyl)-2-(4-(4-fluorophenyl)-4-hydroxybutyl)-1a,2,3,4,4a,5-hexahydro-1H-pyrido[4,3-b]indole hydrochloride; U69,593, (5α,7α,8β)-(-)-N-methyl-N-7-(1-pyrrolidinyl)-1-oxaspiro(4,5) dec-8-yl) benzeneacetamide.
- Received August 21, 2007.
- Accepted November 8, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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