the role of hippocampal 5ht3 receptors in harmaline-induced memory deficit

introduction: the plethora of studies indicated that there is a cross talk relationship between harmaline and serotonergic (5-ht) system on cognitive and non-cognitive behaviors. thus, the purpose of this study is to assess the effects of hippocampal 5-ht4 receptor on memory acquisition deficit induced by harmaline.  methods: harmaline was injected peritoneally, while 5-ht4 receptor agonist (rs67333) and antagonist (rs23597-190) were injected intra-hippocampal. a single-trial step-down passive avoidance, open field and tail flick tasks were used for measurement of memory, locomotor activity and pain responses, respectively.  results: the data revealed that pre-training injection of higher dose of harmaline (1 mg/kg), rs67333 (0.5 ng/mouse) and rs23597-190 (0.5 ng/mouse) decreased memory acquisition process in the adult mice. moreover, concurrent pre-training administration of subthreshold dose of rs67333 (0.005 ng/mouse) or rs23597-190 (0.005 ng/mouse) with subthreshold dose of harmaline (0.5 mg/kg, i.p.) intensify impairment of memory acquisition. all above interventions did not change locomotion and tail flick behaviors.  discussion: the results demonstrated that the synergistic effect between both hippocampal 5-ht4 receptor agonist and antagonist with impairment of memory acquisition induced by harmaline, indicating a modulatory effect for hippocampal 5ht4 receptor on harmaline induced amnesia.