5-ht2a serotonin receptor density in adult male rats’ hippocampus after morphine-based conditioned place preference

Introduction: a close interaction exists between the brain opioid and serotonin (5-ht) neurotransmitter systems. brain neurotransmitter 5-ht plays an important role in the regulation of reward-related processing. however, a few studies have investigated the potential role of 5-ht2a receptors in this behavior. therefore, the aim of the present study was to assess theinfluence of morphine and conditioned place preference (cpp) on the density of 5-ht2a receptor in neurons of rat hippocampal formation.methods: morphine (10 mg/kg, ip) was injected in male wistar rats for 7 consecutive days (intervention group), but control rats received just normal saline (1 ml/kg, ip). we used a hotplate test of analgesia to assess induction of tolerance to analgesic effects of morphine on days 1 and 8 of injections. later, two groups of rats were sacrificed one day after 7 days of injections, their whole brains removed, and the striatum and pfc immediately dissected. then, the nr1 gene expression was examined with a semi-quantitative rt-pcr method.results: our data showed that the maximum response was obtained with 2.5 mg/kg of morphine. the density of 5-ht2a receptor in different areas of the hippocampus increased significantly at sham-morphine and cpp groups (p<0.05). on the other hand, the cpp groups had more 5-ht2a receptors than sham-morphine groups and also the sham-morphine groups had more 5-ht2a receptors than the control groups.conclusion: we concluded that the phenomenon of conditioned place preference induced by morphine can cause a significant increase in the number of serotonin 5-ht2a receptors in neurons of all areas of hippocampus.