ABSTRACT
Objective To evaluate the role of microglia in paraventricular nucleus (PVN) in sus-ceptibility to depression in rats with chronic visceral pain. Methods Ninety-six pathogen-free healthy male Sprague-Dawley rats, aged 8 days, were divided into 6 groups (n= 16 each) using a random number table: sham operation group (S group), chronic visceral pain group (CHVP group), sham operation plus colorectal distension group (S+C group), chronic visceral pain plus colorectal distension group (CHVP+C group), chronic visceral pain plus phosphate buffer solution plus colorectal distension group (CHVP+P+C group) and chronic visceral pain plus minocycline plus colorectal distension group (CHVP+M+C group). Colorectal distension was not performed in S group. In CHVP group, chronic visceral pain was induced by performing colorectal distension twice daily on postnatal days 8, 10, and 12. Phosphate buffer solution 0. 5μl was injected into PVN by stereotaxic method at 8th week after birth in CHVP+P+C group, and 2％ mi-nocycline 0. 5 μl was injected into PVN at 8th week after birth in CHVP+M+C group. Eight rats in each group were selected 2 h later for measurement of visceral pain threshold. In S+C, CHVP+C, CHVP+P+C and CHVP+M+C groups, colorectal distension was performed for 2 times, open field test and sucrose preference test were then performed, the rats were sacrificed and PVN was removed for determination of micro-glial activation by immunofluorescence. Results The pain threshold was significantly decreased in CHVP, CHVP+C, CHVP+P+C and CHVP+M+C groups as compared with S and S+C groups (P<0. 05). The pain threshold was significantly increased in CHVP+M+C group when compared with CHVP +P +C group (P<0. 05). Compared with S, CHVP and S+C groups, the total locomotor distance, the number of rea-ring and sucrose consumption were significantly reduced, and the proportion of activated microglia in PVN was increased in CHVP+C, CHVP+P+C and CHVP+M+C groups (P<0. 05). Compared with CHVP+P+C group, the total locomotor distance, the number of rearing and sucrose consumption were significantly in-creased, and the proportion of activated microglia in PVN was decreased in CHVP+M+C group (P<0. 05). Conclusion Microglia in PVN is involved in regulation of susceptibility to depression in rats with chronic visceral pain.