Stereoselective behavioral effects of the isomers of pentobarbital and secobarbital in the pigeon
Wenger, G.R.; Donald, J.M.; Cunny, H.C.
Journal of Pharmacology and Experimental Therapeutics 237(2): 445-449
1986
ISSN/ISBN: 0022-3565 PMID: 3701640 Document Number: 275707
Little information is available on the contribution of the isomers of pentobarbital and secobarbital to the behavioral effects of the racemic mixtures. To determine the contribution of each isomer on food-maintained behavior, pigeons were trained to respond under either a multiple fixed-ratio 30, fixed-interval 600 (mult FR30 FI600) schedule, or a multiple fixed-ratio 30, variable interval 60-sec (mult FR30 VI60) schedule under which every response under both the FR and VI components also produced a brief electrical shock (punishment). Dose-response curves were determined separately for each isomer of pentobarbital (1-17.5 mg/kg i.m.) and secobarbital (1-17.5 mg/kg i.m.). Under the mult FR30 FI600 schedule, the S-(-)-isomers of pentobarbital and secobarbital were slightly less than 2-fold more potent than the R-(+)-isomers, but both isomers produced qualitatively similar effects on responding. The S-(-)-isomers of both barbiturates produced increases in punished responding under the mult FR30 VI60 at lower doses than the R-(+)-isomers. At high doses (> 10 mg/kg), the S-(-)-isomers suppressed responding early in the session resulting in a lower average rate of punished responding for the session than the R-(+)-isomers. The peak increase in punished responding was observed after 10 mg/kg of the R-(+)-isomers of pentobarbital and secobarbital. These results indicate that the effect of the isomers of pentobarbital and secobarbital on mult FR30 FI600 responding and on suppressed responding are qualitatively similar. They do, however, show different magnitudes of potency differences depending upon the behavior being studied, but in all cases the S-(-)-isomers are either more potent or equipotent with the R-(+)-isomers.