Introduction: Neurohormones like testosterone and estradiol have an important role in learning and memory. The hippocampus is essentially involved in learning and memory, and is known to be a target for estradiol actions. Estrogen receptors (ERs) are highly expressed in CA1 of rat hippocampus, and mediate the effects of estrogen on learning and memory. Estradiol receptor belong to a family of transcription factors, the nuclear receptor superfamily, and has two subtypes ER
and ER. The current research has been conducted to assess the effect of ER selective agonist, diarylpropionitrile (DPN), on passive avoidance of adult male rats, by using passive avoidance task.

Methods: Male adult rats were bilaterally cannulated into the CA1 area of hippocampus, and then received vehicle (dimethyl sulfoxide, DMSO) or DPN (0.2, 0.5, 1 micro-g/0.5 micro-l/side), 30 min before training on passive avoidance task.

Results: The results showed that pre-training intra-CA1 injections of DPN (0.5, 1 micro-g/0.5 micro-l/side), significantly decreased step-through latencies and increased time spent in dark on passive avoidance learning (P<0.01).

Conclusion: Our data suggest that intra-CA1 administration of DPN could impair learning and memory acquisition on passive avoidance task.