Effects of optical isomers of pentobarbital on behavior in rats maintained on either the D or the L optical isomer of methadone.
The effects of the d and l optical isomers of methadone and (S)-(-)- and (R)-(+)- optical isomers of pentobarbital were studied on responding maintained under a multiple fixed-ratio 30-response fixed-interval 5-min schedule of food presentation in rats before, during, and after chronic administration of d- or l- methadone. Acute administration of both isomers of pentobarbital decreased responding more during the fixed-ratio component of the schedule than during the fixed-interval component. S-(-)-pentobarbital was slightly more potent than R-(+)-pentobarbital in decreasing the rate of fixed-ratio responding and the fixed-interval quarter life. Daily administration of d-methadone for four weeks shifted the dose-effect curves for (S)-(-)-pentobarbital to the right for both schedule components; however, (R)-(+)-pentobarbital showed less tendency to shift. Daily administration of l-methadone showed little tendency to shift the dose-effect curve for either pentobarbital isomer. Before chronic treatment, acute administration of l-methadone, decreased rates of both FR and FI responding at much lower doses than d-methadone. Unlike d-methadone, chronic daily l-methadone shifted the l-methadone dose-effect curves to the right during both components of the schedule.
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003216:Conditioning, Operant / Q000187:drug effects; D008297:Male; D008691:Methadone / Q000494:pharmacology*; D010424:Pentobarbital / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012055:Reinforcement Schedule; D013237:Stereoisomerism
D010424:Pentobarbital; D008691:Methadone