Effects of an antitussive mixture and its constituents in rats discriminating methamphetamine from saline.
The discriminative effects of over-the-counter antitussive syrup containing dihydrocodeine (DHC), methylephedrine (MEP), caffeine (CAF), and chlorpheniramine (CPA) were compared with those of methamphetamine (MA) in a drug discrimination experiment using rats. Rats were trained to discriminate the effects of MA at 0.5 mg/kg SC and saline for food reinforcement under the fixed-ratio 10 schedule in a two-lever operant chamber situation. In substitution testing using a cumulative dose procedure by the subcutaneous route, DHC (4 and 8 mg/kg, expressed hereafter as referred to cumulative dose) or CPA (16-64 mg/kg) individually did not produce MA lever selection. On the other hand, MEP (128 mg/kg) and CAF (64 mg/kg) produced MA lever selection 41.5 and 57.2% of the time, respectively. The complete mixture (16 mg/kg DHC + 32 mg/kg MEP + 33.2 mg/kg CAF + 6.4 mg/kg CPA) produced MA level selection 65.8% of the time. The partial mixture containing only MEP + CAF at the above doses produced MA lever selection 95.6% of the time. Thus, the complete mixture only partially substituted for MA in rats while the partial mixture containing MEP and CAF completely substituted for MA.
Ando
K
K
Preclinical Research Laboratories, Central Institute for Experimental Animals, Kawasaki, Japan.
Yanagita
T
T
D000818:Animals; D000996:Antitussive Agents / Q000494:pharmacology*; D004193:Discrimination Learning / Q000187:drug effects*; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D008297:Male; D008694:Methamphetamine; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride
D000996:Antitussive Agents; D008694:Methamphetamine; D012965:Sodium Chloride