Intra hippocampal injection of testosterone impaired acquisition, consolidation and retrieval of inhibitory avoidance learning and memory in adult male rats

The hippocampus is essentially involved in learning and memory, and is known to be a target for androgen actions. Androgen receptors are densely expressed in CA1 of rat hippocampus, and mediate the effects of testosterone (T) on learning and memory. T depletion or administration can modulate neural function and cognitive performance. We conducted series of experiments to further investigate the effect of castration or intra hippocampal injection of T on acquisition, consolidation and retrieval of inhibitory avoidance learning and memory. Male adult rats were bilaterally cannulated into CA1 of hippocampus, and then received T (1, 10, 20, 40 and 80 μg/0.5 μl/side) or vehicle (DMSO), 30 min before training, immediately after training and 30 min before retrieval in inhibitory avoidance task. Castration was made by gonadectomy of male rats and behavioral tests performed 4 weeks later. Our results showed that gonadectomy of male rats did not influence performance on inhibitory avoidance task, as compared to sham-operated rats. We have also found that pre-training, post-training and pre-retrieval intra CA1 injections of T significantly decreased step-through latencies in inhibitory avoidance learning at doses 1 and 80, 20, and 20 and 40 μg/0.5 μl/side, respectively. The data suggest that intra CA1 administration of T could impair learning and memory acquisition, consolidation and retrieval, while systemic androgen's depletion have no effect on memory, in inhibitory avoidance task.