Effect of bilateral cervical vagotomy on microglial activation in spinal cord in a rat model of persistent postoperative pain

Objective To investigate the effect of bilateral cervical vagotomy on microglial activation in spinal cord in a rat model of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR). Methods Thirty six male Sprague-Dawley rats were randomly divided into three groups (n= 12 each group): group sham operation, group SMIR, and group SMIR+ bilateral cervical vagotomy (SV). The rat model of persistent postoperative pain evoked by SMIR was established according to the method described by Flatter. Pain behavior was assessed by paw mechanical withdrawal threshold (MWT) to von Frey filament stimulation at 1, 3, and 5 days after operation. Four animals were sacrificed at each time point in each group to detect the expression of Iba-1 (a specific marker of microglia) in the spinal dorsal horn with immunofluorescence and the microglia was counted. Results MWT was significantly decreased at T1-5 in SMIR and SV (10.3±0.6, 9.7±0.8, 9.6±0.5; 8.0±0.7, 7.7±0.4, 7.6±0.3), while the expression of Iba-1 and microglia counts in the spinal dorsal horn were significantly increased at T1-5 in SMIR and SV (1428±134, 1245±129, and 1001±117; 8.0±0.7, 7.7±0.4, and 7.6±0.3; 187±13, 164±11, and 142±14; and 241±21, 230±21, and 202±19). In group SV as compared to group SMIR, MWT was significantly decreased at T1-5, while the expression of Iba-1 and microglia counts in the spinal dorsal horn were significantly increased at T1-5. Conclusions Vagus nerve plays an important role in microglial activation in spinal cord in a rat model of persistent postoperative pain evoked by skin/muscle incision and retraction. Key words: Vagotomy; Pain, postoperative; Microglia; Rats, Sprague-Dawley