Effect of chlorpromazine on conditioned avoidance as a function of CS-US interval length.

Abstract

Three groups of four rats learned to avoid electric shock (US) by turning a wheel in response to a buzzer stimulus (CS). The CS-US intervals for each group were 5, 10, and 20 sec, respectively. After each animal had learned the avoidance procedure and had achieved a stable level of performance, the effect of several doses of chlorpromazine on percent avoidance, on latency time from CS onset to termination by a response, and on response rate was determined as a function of CS-US interval length. No consistent relationship between increasing interval length and response rate was observed. Neither lengthening the CS-US interval nor the interaction of this lengthening with chlorpromazine dose was found to exert a statistically significant effect on percent avoidance. Furthermore, although a statistically significant increase in response latency was found to be associated with increasing CS-US interval length, the increases in latency noted were not of sufficient magnitude to corroborate the hypothesis that lengthening the CS-US interval contributes importantly to increased avoidance responding in animals tested with chlorpromazine. Further, the results of this study do not support induction of a locomotor deficit as the mechanism by which chlorpromazine suppresses the avoidance response.