title: Drug trace discrimination with nicotine and morphine in rats.
abstract: In typical drug discrimination experiments, subjects are exposed to psychoactive substances both prior to and during training sessions. The present experiments aimed to determine whether pre-session effects of drugs could serve as discriminative stimuli. Rats were trained in a two-lever discrimination procedure with food reinforcers presented on a tandem variable interval-fixed ratio (VI-FR) schedule. Injections of nicotine (0.6mg/kg 20 min pre-session) or saline were followed by administration of the nicotine antagonist mecamylamine (1.0 mg/kg 10 min pre-session) to block effects of nicotine during training sessions. Similarly, the action of morphine (10 mg/kg 30 min pre-session) was terminated by administering naloxone (0.1 mg/kg 10 min pre-session). These drug discriminations were acquired slowly to an accuracy of only 70-75% (n=10-12). Extinction tests confirmed stimulus control by nicotine in the presence of mecamylamine and by morphine in the presence of naloxone. The antagonists attenuated the response-rate reducing effects of the training doses of their respective agonists. The results are interpreted in terms of stimulus control by pre-session effects of the training drugs, but other explanations are considered. Stimulus control by pre-session drug states may be weak due to the time elapsed between termination of drug effects and training (trace conditioning).
authors: Section of Behavioural Pharmacology, Institute of Psychiatry, King's College London, UK. i.stolerman@iop.kcl.ac.uk
authors: I P
authors: IP
authors: Stolerman
authors: E
authors: E
authors: Childs
authors: B
authors: B
authors: Hahn
authors: A
authors: A
authors: Morley
mesh_terms: D000818:Animals; D004193:Discrimination Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005108:Extinction, Psychological / Q000187:drug effects; D008297:Male; D008464:Mecamylamine / Q000493:pharmacokinetics; D011939:Mental Recall / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000493:pharmacokinetics; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats
chemical_list: D009270:Naloxone; D008464:Mecamylamine; D009538:Nicotine; D009020:Morphine