Effect of dezocine on c-fos expression in neurons in midbrain periaqueductal gray in a rat model of incisional pain

Abstract

Objective To evaluate the effect of dezocine on the c-fos expression in neurons in the midbrain periaqueductal gray in a rat model of incisional pain. Methods Thirty-six pathogen-free healthy adult male Wistar rats, weighing 250-300 g, were divided into 3 groups (n=12 each) using a random number table: control group (group C), incisional pain group (group I) and dezocine group (group D). A 1 cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the right hind paw in sevoflurane-anesthetized rats.In group C, the rats were only anesthetized and underwent no operation.In group I, 0.9% sodium chloride solution 2 ml was injected via the caudal vein at 15 min before the model was established.In group D, dezocine 1 mg/kg (diluted to 2 ml in 0.9% sodium chloride solution) was injected via the caudal vein at 15 min before the model was established.At 24 h before operation (T0) and 2, 6 and 24 h after operation (T1-3), the mechanical paw withdrawal threshold (MWT) and cumulative pain score were measured.After measurement of the pain threshold at T3, the whole brain was removed for determination of the c-fos expression in neurons in the midbrain periaqueductal gray by immunohistochemistry. Results Compared with group C, the MWT was significantly decreased, cumulative pain scores were increased, and the expression of c-fos in neurons in the midbrain periaqueductal gray was up-regulated at T1-3 in I and D groups (P<0.05). Compared with group I, the MWT was significantly increased, the cumulative pain score was decreased, and the expression of c-fos protein in neurons in the midbrain periaqueductal gray was down-regulated at T1-3 in group D (P<0.05). Conclusion Dezocine mitigates incisional pain through inhibiting the expression of c-fos in neurons in the midbrain periaqueductal gray of rats. Key words: Analgesics, opioid; Pain, postoperative; Periaqueductal gray; Proto-oncogene proteins c-fos