Mechanism of acute visceral pain mediated by CB1R in hypothalamic paraventricular nucleus

Objective To investigate the effects of cannabinoid receptor 1 (CB1R) on hypothalamic paraventricular nucleus (PVN) in a model of acute acetic acid visceral pain, and provide theoretical evidence for rational drug use. Methods A total of 40 male C57 mice were selected. They were randomly divided into five groups (n=8). First, micro-injection into PVN was performed, and then a mouse model of acute acetic acid visceral pain was established. The number of writhing reaction caused by acetic acid and the peak period of writhing reaction were observed. The levels of c-Fos in PVN of each group were detected by immunofluorescence. Results ①The number of writhing reactions in the acetic acid modeling group was significantly higher than that in the normal control group, indicating that the model of acute acetic acid visceral pain was successfully established. ②Compared with micro-injection of normal saline and CB1R agonist AM-251 into PVN, micro-injection of CB1R agonist WIN55212-2 into PVN resulted in a significantly reduced number of writhing reaction in the acetic acid model group within 60 min, and reached the peak within 15~30 min. The expression of c-Fos in PVN remarkably decreased. ③Compared with micro-injection of normal saline into PVN, micro-injection of CB1R antagonist AM-251 into PVN resulted in no significant difference in the number of writhing reaction and the expression of c-Fos in PVN in the acetic acid model group within 60 min, but writhing reaction reached the peak in 0~15 min. Conclusions Micro-injection of CB1R agonist WIN55212-2 into PVN can reduce acute acetic acid visceral pain in mice by inhibiting neuronal activity in PVN.