Is delay of reward mediated by shock-avoidance behavior a critical target for anti-punishment effects of diazepam in rats?

The present study investigated in rats whether variables which may affect the animals' tolerance for delay of reward could be critical for the benzodiazepine-induced release of punished behavior. Rats were subjected to conflict situations during which signalled FR4 non-punished periods (lights-off) alternated with punished periods of different durations signalled by lights-on stimuli. Lever presses during punished periods resulted in the delivery of both one food-pellet and one electric foot-shock (0.45 mA). The antipunishment effect of diazepam (2 mg/kg IP) clearly depended on the duration of the punished periods, release of punished behavior being observed only when punished periods exceeded 1 min. The duration of punished periods required for diazepam-induced release of responding was affected by factors which modified the contrast between rewards received in punished and non-punished periods. One of these factors was the FR schedule imposed during non-punished periods, since the anti-punishment effect of diazepam was observed during short-lasting (30-s and 1-min) punished periods separated by FR24 non-punished periods. A second factor was the ratio of the durations of punished and non-punished periods: diazepam released behavior during 2-min punished periods when the duration of the intercurrent non-punished periods was 1 min, but not when it was 4 min. The predictability of the duration of the punished periods also modulated the effect of diazepam since: with 1 min punished periods, diazepam released punished responding during the first exposures of the rats to the experimental session, but lost part or all its efficacy in animals extensively trained to the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)