The use of extinction to investigate the nature of neuroleptic-induced avoidance deficits.

Abstract

Four groups (N=8) of rats received five 15-trial sessions of one-way avoidance training. Each trial was signaled by a ten-second tone stimulus and shock followed on a random 67% of the trials. Prior to each session two groups were injected with 1.0 mg/kg of the neuroleptic pimozide and the other two groups received vehicle injections. The pimozide groups failed to acquire the avoidance response although they escaped readily when shock was presented, and the vehicle groups acquired the avoidance response. Three 15-trial nondrug test sessions followed. For one group that had been trained under pimozide and one vehicle group, shock continued to follow the tone on 67% of the test trials. The remaining two groups were tested in extinction, i.e., shocks were no longer presented. Both groups that were trained under pimozide showed gradual acquisition of the avoidance response in the first nondrug test session. The group that received vehicle during training and shock during testing continued to avoid whereas the other vehicle group showed extinction of the avoidance response across test sessions. The acquisition of responding in the extinction group trained under pimozide indicated that the association of environmental stimuli with shock had been learned during training in spite of the failure to avoid. The gradual acquisition of the response indicated that this group had failed to learn the appropriate motor response during training. These results support previous observations of associative learning in animals treated with neuroleptics but further suggest that dopamine plays a role in mechanisms of response learning.