The effects of intrahippocampus injection of progesterone on passive avoidance learning and memory in adult male rats

Progesterone as a reproductive hormone is studied in the brain structure. New studies are mainly about systemic injection and have shown that the progesterone has different effects on memory. But it is not clear if hippocampus is mediator of progesterone in reinforcement of memory and learning. So, the effects of intra-hippocampal injection of progesterone on passive avoidance memory and learning was studied in male Wistar rats. Animals were divided in eightgroups as a control, saline, almond oil (as a vehicle) and progesterone groups (0.5, 1, 1.5, 2, 3µg/Kg. body weight). All groups except the control were cannulated in left CA1 area by stereotaxic device. One week after recovery, all groups were trained by shuttle box and immediately after training different doses of progesterone in the volume of 0.5μL were injected through the cannula in CA1 of hippocampus and control groups received saline and almond oil at the same volume and condition respectively. After 48 hours passive avoidance memory and learning was evaluated. Statistical analysis showed that 0.5, 1.5, 2 µg/µl progesterone groups had significantly improved passive avoidance learning and memory compared with saline group (p <0.001), but 1 and 3 µg/µl progesterone groups did not show significant effect on passive avoidance learning and memory compared with saline group. Also almond oil increased passive avoidance learning and memory compared with saline group (p <0.001). It seems that effects of progesterone as a neurosteroid on memory and learning depend on its dose. Also almond oil contains vitamin E, omega 3 and oleic acid that has beneficial effects on learning and memory.