A delayed onset of haloperidol effects on learned escape and avoidance behavior

Abstract

The effects of 0.3 mg/kg haloperidol (H) on the acquisition and maintenance of footshock escape behavior of rats in a one meter runway was investigated. In the acquisition phase, a group (N=6) given H before testing (HB) showed severely retarded acquisition and performance of the escape response, as compared with a group (N=6) given H after testing (HA). When the HB and HA treatments were reversed for the groups behavioral performance was initially unaffected. At first, the HA group switched to the HB condition continued to exhibit rapid escape behavior and the HB group switched to the HA treatment continued to have slow escape behavior. Over the course of 8 days of testing, however, the performances of the two groups gradually reversed. After completion of this testing the HB and HA treatments again were switched and the animals were tested for both avoidance and escape behavior. Again, the performance of the animals initially did not change after the treatment switch, but with repeated testing and treatments, the avoidance and escape behavior of the HB group slowed substantially and that of the HA group accelerated markedly. These findings support previous observations that over learned behaviors are much less sensitive to disruption by haloperidol treatment than behaviors which are undergoing learning. The important contribution of the present study was in demonstrating that this insensitivity is a transitional, transient phenomenon and that with chronic treatment and testing, over learned behaviors can be strongly affected by haloperidol. This observation indicates that the study of the effects of haloperidol on over learned behavior may provide a useful animal behavior model to investigate the important clinical issue of delayed onset of efficacy with neuroleptic drugs.