Abstract: Objective To investigate the expression of γ-aminobutyric acid A receptor α1 subunit ( GABAAα1 ) in the ventrolateral periaqueductal gray ( vLPAG ) in rats with formalin-induced acute pain. Methods The rats were randomly divided into two groups: control group ( group C ) and formalin-induced pain group (group F)，12 rats in each group: 0.9% sodium chloride solution or 2% formaldehyde 50 μL was injected into the ventral surface of right hind paw respectively. The pain scores were recorded for every 5 minutes and the mechanical pain threshold were recorded for every 10 minutes until 1 h. The expression levels of GABAAα1 in vLPAG were determined by Western blotting analysis in each group. Results The rats in formalin group showed significant nociceptive behaviors immediately, such as paw withdrawal and/or paw licking. Results demonstrated that the rats exhibited a biphasic response to pain. The pain behavior scores in group F were significantly higher than that in group C ( P <0.05 ), and the mechanical pain threshold in group F was decreased after injection compared with group C ( P <0.05 ). The expression of GABAAα1 protein in group F was significantly higher than that in group C ( P <0.05 ). Conclusion The up-regulation of GABAAα1 expression in ventrolateral periaqueductal gray is associated with the decrease of pain threshold in rats with acute pain.

Key words: Keywords：Acute pain, Ventrolateral periaqueductal gray, vLPAG, GABAAα1