Cannabinoid-induced upregulation of serotonin 2A receptors in the hypothalamic paraventricular nucleus and anxiety-like behaviors in rats

Recent behavioral reports suggest that repeated exposure to cannabis and synthetic cannabinoid agonists is linked with mental disorders associated with dysfunction of serotonin 2A (5-HT_2A) receptor neurotransmission such as anxiety and depression. Here, we studied the effect of a nonselective cannabinoid agonist, CP55940, on the activity of 5-HT_2A receptors in hypothalamic paraventricular nucleus (PVN). We detected that repeated exposure to CP55940 enhanced the prolactin and corticosterone neuroendocrine responses mediated by 5-HT_2A receptors and increased the membrane-associated levels of 5-HT_2A receptors in PVN. Importantly, we also detected increased anxiety-like behaviors in CP55940 treated rats compared to controls. The data presented here suggest that the mechanisms mediating the cannabinoid-induced upregulation of 5-HT_2A receptors would be brain-region specific, as we were unable to detect a CP55940-induced upregulation of 5-HT_2A mRNA. Our results might provide insight into the molecular mechanism by which repeated exposure to cannabinoids could be associated with the pathophysiology of neuropsychiatric disorders.