The Role of Ventral Hippocampal (CA3) 5-HT4 Receptor in Rats Emotional Memory in Elevated Plus-Maze Task

Many studies have demonstrated the important role of hippocampal serotonergic receptors in the emotional memory formation. Therefore, it is necessary to investigate the possible role of hippocampal serotonergic receptors in emotional memory formation in several animal model tasks. The aim of this study was to investigate the possible role of ventral hippocampal (CA3) 5-HT4 receptors in emotional memory formation of rats in elevated plus-maze task. 102 male Wistar rats were divided to 16 groups (n=7), randomly. Two guide cannulae were implanted bilaterally, into the left and right hippocampi, using stereotaxic apparatus. At the test time and following the injections of saline, 5-HT4 receptor’s agonist and/or antagonist, the elevated plus-maze was used for evaluation of the emotional memory. A pre-test intra-CA3 injection of competitive agonist (RS67333; 1.2 µg/rat) and competitive antagonist (RS23597-190; 1.2 µg/rat) of 5-HT4 receptor, increased OAT% and OAE% by themselves while only the RS23597-190 decreased the closed arm entries, indicating that these drugs impaired the memory formation. Also, a pre-retest intra-CA3 injection of RS67333 and RS23597-190 (1.2 µg/rat) increased OAT% and OAE% by themselves, indicating that these drugs prevented the recall of the memories that formed on first day. The results revealed that the hippocampal 5-HT4 serotonergic receptor have an important role in memory formation and memory recall, at the time of emotional arousal and stressful situations.