Enhancement of freezing behaviour by metoclopramide: implications for neuroleptic-induced avoidance deficits

Administration of the neuroleptic drug metoclopramide (5.0 mg/kg) potentiated freezing responses of rats following 1.0 mA footshock, but did not produce any freezing prior to shock onset. To determine if inappropriate freezing responses to shock could contribute to deficits in active avoidance produced by metoclopramide, drugged and undrugged rats received unavoidable footshock prior to each of ten one-way avoidance trials, or in a separate apparatus prior to the avoidance session (Experiment 2). In neither case was the performance of control rats affected adversely, but in each case the performance of metoclopramide-treated rats was significantly disrupted. Experiment 3 demonstrated that the avoidance performance of metoclopramide-treated rats was disrupted by presentation of an additional conditional stimulus previously paired with shock, whereas the performance of saline-treated rats was enhanced by this procedure. It was concluded that the enhancement of freezing by neuroleptic drugs contributes to the deficit in avoidance responding produced by dopamine receptor antagonists.