Effect of Intrahippocampal CA3 Injection of Spexin on Passive Avoidance Learning and Memory in Normal and Castrated Rats

[Background and Objectives:]Spexin is a neuropeptide involved in learning and memory. The aim of the present study was to investigate the effect of intrahippocampal CA3 injection of spexin on passive avoidance learning and memory in normal and castrated rats.[Methods]A total of 42 adult male rats were divided into 6 groups. Sham 1 (received 0.5 µL ACSF); sham 2 (sham castrated rats that received 0.5 µL ACSF); experimental 1 and 2 (healthy rats that received 0.5 µL spexin 10 or 30 nmol/rat); experimental 3 and 4 (castrated rats that received 0.5 µL spexin 10 or 30 nmol/rat). In all groups, injection was done in the CA3 region of hippocampus. CA3 region of hippocampus was cannulated unilaterally by the stereotaxic procedure.[Results]Present data showed that castrated significantly (P < 0.05) increased lighting time in comparison to sham 2 group in memory sessions. In normal rats intrahippocampal CA3 injection of spexin in 2 doses significantly (P < 0.05) increased lighting time in comparison to the sham group in learning and memory sessions. In castrated rats, intrahippocampal CA3 injection of spexin 30 nmole/rat significantly (P < 0.05) induced even further increase in lighting time as compared to the sham group in memory sessions. In memory consolidation and memory retention sessions lighting time was significantly (P < 0.05) higher in castrated rats than normal animals. [Conclusions]According to the present results, castration and spexin at 2 doses in normal rats improve learning and memory; while in castrated rats spexin, in 30 nM/rat, produced more improvement in memory. Memory improvement in castrated rats was higher than that in normal rats.