The contrasting effects of diazepam and yohimbine on conditioned defensive burying in rats

Abstract

The conditioned defensive burying (CDB) paradigm consists of placing rats in a test chamber with wood shavings on the floor, shocking them with a shock prod, and recording the time each rat spends in a burying response to the prod during a 15-min test session. This experiment revealed contrasting effects of the anxiolytic agent, diazepam (0.5 and 2 mg/kg, i.p.), and the anxiogenic agent, yohimbine (0.5 and 2 mg/kg, i.p.), on CDB of male hooded rats. During the test session, diazepam-injected rats spent significantly less time engaged in CDB than did vehicle-injected rats. On the other hand, yohimbine-injected rats spent significantly more time burying than did the vehicle-injected rats, and did so in a dose-dependent fashion. Twenty-four hours later when a retention session was conducted without any additional shocks and injections, both the facilitative effects of yohimbine and the suppressive effects of diazepam on the CDB were still observed in terms of duration, number, and latency of burying, as well as in the height of piles accumulated. These results indicate that the postshock CDB could be differentiately affected by anxiolytic and anxiogenic agents. The CDB paradigm might represent an appropriate model for studying the pharmacological analysis and neuronal mechanisms of anxiety and/or fear in animals.