Drug sensitivity of individual rats determines degree of drug discrimination.
Rats were observed to learn to discriminate between the stimulus properties of intraperitoneal 0.16 mg/kg apomorphine and saline, in a two-lever operant task, at different rates. Half of the 12 rats reached criterion performance in a mean of 22.5 session, whereas the other half reached criterion in a mean of 44.2 sessions. These two groups, i.e., the early and later learners, were tested with a range of apomorphine doses and the former group had an ED50 of 0.01 mg/kg, whereas the later group generated an ED50 of 0.07 mg/kg apomorphine. These results suggest that the early learners were significantly more sensitive to apomorphine than the later learners and this may explain the discrepancies in the drug-discrimination literature regarding different ED50's generated at the same drug training dose.
D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D004193:Discrimination Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D007274:Injections, Intraperitoneal; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012653:Self Stimulation
D001058:Apomorphine