Effects of intrahippocampal injection of 17-β estradiol on memory consolidation in the female ovariectomized rats

Sexual hormones affect most of the cerebral functions as well as learning and memory. More investigations are required to clarify the effects of local administration of estradiol in the central nervous system. In this research we aimed at the effects of different doses of estradiol on memory consolidation in female gonadectomized rats.

Female Wistar rats (weighing 200-250 g, aged 3-4 months) were divided into 6 groups randomly (n=9). Five groups of animals were ovariectomized and implanted by cannulae in the CA1 region of hippocampus. Except sham group the other groups treated respectively with saline, sesame oil 0.5 μL and estradiol at the doses of 0.5, 1 and 2 μg / 0.5 μL sesame oil bilaterally in the CA1 region immediately after the passive avoidance training session. They were tested 10 min and 2 h after training.

Our results demonstrated that 0.5 μg estradiol had no significant effect on retention latency compared to sham group,1 μg estradiol treated group showed a significant increase (p<0.001) in retention latency compared to sham group while it decreased in the group treated with 2 μg dose of estradiol (p<0.05).

According to our findings, it seems that effects of estradiol in local administration are dose dependent and high doses of estradiol caused impairment of passive avoidance learning.