Effects of psychotropic drugs on avoidance response in rats: Role of baseline performances

Abstract

Effects of d-amphetamine, chlorpromazine and diazepam on the discriminated avoidance response (intertrial interval = 25 sec; warning duration = 5 sec) in rats were studied with reference to levels of the behavioral baseline. After the administration of d-amphetamine 0.25–2.0 mg/kg SC, the avoidance and response rates increased in all cases dose-dependently. The individual changes of avoidance rates were more marked in the poor performers (initial avoidance rate: 0–33%) with higher baseline response rates than in those with lower response rates. Chlorpromazine 0.5–2.0 mg/kg SC suppressed the avoidance performances in all cases in proportion ith the doses. More marked changes were observed in the good performers (68–100%) than in the poor performers regardless of the baseline response rates. After administration of diazepam 0.5–4.0 mg/kg SC, the response rates decreased in almost all cases, while the avoidance rates varied depending on their baseline levels. Diazepam increased the avoidance rates of the poor performers, but conversely decreased the rates in the good performers in proportion with the doses. Moreover, the improvement of the avoidance rates was more marked in the poor performers with higher baseline response rates than in those with lower rates. The present results suggest that the behavioral effects of psychotropic drugs are a function of the avoidance baseline levels.