[Variability in the effects of psychotic drugs on conditioned avoidance reactions in rats due to warning stimuli]

Different effects of methamphetamine (0.25-1 mg/kg, sc), chlorpromazine (0.5-2 mg/kg, sc), haloperidol (0.25-0.1 mg/kg, sc), diazepam (1-4 mg/kg, sc) and pentobarbital (5-20 mg/kg, sc) on Sidman avoidance response were investigated according to absence or presence of stimulus control. Thirteen adult male rats of Wistar strain were divided into two groups of 6 and 7 each, and trained under Sidman avoidance schedule (WS-group) and the same schedule associated with a 5 sec warning stimulus presentation (buzzer and light) (WS+group). There was no difference in the effect of methamphetamine between the two groups. The avoidance response was inhibited in dose-dependent manner regardless of the stimulus control after chlorpromazine and haloperidol. However, more marked inhibition was always observed in WS-group than in WS+group. Diazepam and pentobarbital also inhibited the avoidance response in WS-group when ataxia-producing doses were given, while no significant inhibition was observed after the same doses of the drugs in WS+group. Thus, the avoidance response without stimulus control was more susceptible to the drugs than that with stimulus control. The present results suggest that Sidman avoidance response is reliable to evaluate psychotropic drugs in screening test.