Effects of psychotropic drugs on impairment of acquisition of shuttle avoidance produced by pretreatment with pairs of tone signal and shock in mice.

The acquisition of discrete shuttle avoidance of mouse was significantly impaired by presentation of 120 pairs of a tone signal and an unavoidable/unescapable shock at 30 sec intervals for 3 consecutive days prior to the training session. Caffeine (3 and 10 mg/kg s.c.) reduced such an impairment of the avoidance acquisition, whereas diazepam (0.5-2 mg/kg s.c.), imipramine (30 mg/kg i.p.) and chlorpromazine (2 mg/kg s.c.) enhanced it, when these drugs were administered 10 min before each shock-presenting session. Ethanol (0.8-2.4 g/kg p.o.), nicotine (0.1-1 mg/kg s.c.), methamphetamine (0.1-1 mg/kg s.c.) and morphine (1-10 mg/kg s.c.) did not modify the avoidance acquisition. These results indicate that the nature of impairment of the avoidance acquisition caused by this condition is different from learned helplessness, and elicits different responses to psychotropics.