Modified sensitivity to pentobarbital in a continuous avoidance situation

Summary Rats were trained on a continuous avoidance schedule where the response was running from one end of a box to the other. In this situation hypers sensitivity to 15 mg/kg of sodium pentobarbital was found, when this dose wainjected before a previous dose was completly metabolized but after the behavior had returned to baseline. Acute tolerance was observed after injections of 40 mg/kg of pentobarbital intraperitoneally and 500 g intraventricularly. The latter finding suggested a CNS component tolerance. The nonsignificant difference in the half life indices of the drug suggested the same recovery rate for tolerance and nontolerance animals, which was not consistent with the hypothesis of increased hepatic metabolism as the mechanism of tolerance after single preinjections.This research was supported by USPHS Grant No. MH-06997-03 to Indiana University.