The effect of injection of estradiol benzoate into hippocampal CA1 area on spatial learning and memory in intact and castrated adult male rats

Estrogen has a widespread and complex influence on brain capabilities such as learning and memory. On the other hand, hippocampus as one of the main brain structures has an important role in spatial information processing. There is some evidence on the existence of estrogen receptors in the hippocampal CA1 area. So, in this study the effect of intrahippocampal injection of estradiol benzoate on spatial learning and memory were investigated in intact and castrated adult male NMRI rats The animals were randomly divided into eight groups and bilaterally cannulated (n=7). The intact and castrated control groups (no injection) were trained in Y-maze. The castrated and intact rats received sesame oil vehicle, sham physiological saline and estradiol. Test groups received bilaterally 0.5 µl of sesame oil, 0.5 µl of physiological saline, and 1 µg/0.5 µl of estradiol benzoate respectively into the CA1 region of hippocampus immediately before training. Then, each rat was trained in 30 trials every day for a total of 5 days with Y-maze. After one month, all of the groups were again tested for memory performance. Statistical analysis of data showed that estradiol increases spatial learning in castrated and intact groups. There was also no significant difference between castrated and intact groups regarding memory performance. In conclusion, it seems that estradiol increases spatial learning task through an interaction with cholinergic system an enhancement of synaptic plasticity in CA1 region.