Flumazenil antagonizes the effect of diazepam on negative contrast in one-way avoidance learning.

The main aim of the present work was to study whether the effect of diazepam upon successive negative contrast in one-way avoidance learning-induced by shifting rats from a large reward (30s spent in the safe compartment) to a small reward (1s)-is mediated by the action of this drug on the benzodiazepine (BZ) receptor. Therefore, we studied the influence of flumazenil (FL), a BZ antagonist, on the effect of diazepam (DZ) on negative contrast. The i.p. administration of 5 and 12mg/kg, but not of 2mg/kg of FL, reliably antagonized the abolition by DZ (1mg/kg) on successive negative contrast. Moreover, FL (12mg/kg) did not affect either the avoidance response or the contrast effect. These results suggest that the GABA system is involved in the successive negative contrast effect in one-way avoidance learning, and that this experimental procedure may be useful in studies of anti-anxiety agents.

Effect of diazepam on successive negative contrast in one-way avoidance learning.

The effect of administration of diazepam on successive negative contrast in one-way avoidance learning was examined in rats. Contrast was induced by shifting rats from a large reward, 30 s spent in the safe compartment, to a small reward, 1 s spent in the safe compartment. IP administration of 2 mg/kg diazepam eliminated this negative contrast. Moreover, this effect is dose dependent, with doses of 2 and 2.5 mg/kg, but not 0.5 mg/kg, effective in reliably reducing contrast. These results suggest the existence of similar or common underlying mechanisms in both aversive and appetitive contrast effects; they are discussed in light of the current theories of frustrative nonreward and as a mean of studying the behavioral and biological mechanisms of anxiety.

Successive negative contrast in one-way avoidance learning in rats.

In three experiments, successive negative contrast was examined in one-way avoidance learning. Reward magnitude in first (pre-shift) and second (post-shift) phases was manipulated by time spent in the safe compartment. Experiment 1 demonstrated that when time in the danger compartment was held constant, a group shifted from a large reward--30 sec spent in the safe compartment--to a small reward--1 sec--showed poor performance and longer response latency than a group conditioned with the small reward in both phases. Experiment 2 replicated this effect with a less intense shock and also demonstrated that a group shifted from large to small reward performed more poorly than a group exposed to large reward--30 sec--in both phases. Finally, Experiment 3 showed that changes in intertrial interval, defined as total time spent in the safe compartment and the danger compartment before the onset of the warning signal, were not responsible for this contrast effect. These results suggest that time spent in a safe place can act as appetitive incentive during one-way avoidance learning.