Conditioned lever-press avoidance responses in mice and effects of psychotropic drugs thereon

Abstract

Although conditioned lever-press avoidance responses in rats have been commonly used for the evaluation of the effects of psychotropic drugs, there are very few experiments in which the avoidance tests have been carried out by using mice. In this experiment, the acquisition processes of conditioned lever-press avoidance responses in mice were investigated, and effects of psychotropic drugs were also examined. Adult male mice of dd strain were trained in an operant chamber of 18x9x10 cm on either of two types of avoidance situations, namely Sidman-type (R-S=30 sec and S-S=5sec) and discriminated-type (lTI=25 sec, CS=5 sec and escape=3 sec). After 15 sessions of the training for 1 hr each, about 60 and 80 % of the mice subjected acheved critical levels of the avoidance response, i.e., shock rate being less than 0.5/min (Sidman-type) and avoidance rate being higher than 75 % (discriminated-type). The avoidance responses established were stable for a long period. When 0.13-1 mg/kg methamphetamine, 0.5-4 mg/kg chlorpromazine, 0.025-0.2 mg/kg haloperidol, 1-4 mg/kg pilocarpine and 0.05 -0.4 mg/kg physostigmine were administered s.c, the changes in the avoidance responses of the mice were qualitatively the same as those of the rats. However, the mice had a lower sensitivity to chlorpromazine and haloperidol, while they had a higher sensitivity to pilocarpine and physostigmine than the rats. Scopolamine, O.O3I-O.5 mg/kg s.c, suppressed the avoidance responses of the mice in spite of the fact that the drug facilitated those of the rats. The present results suggest that the conditioned lever-press avoidance responses in mice are applicable for the evaluation of the effects of psychotropic drugs.