Expression of GABA and its receptor in the rat spinal pain conduction path

【Objective】To study the mRNA expression of GABA and GABAAβ3 receptor in spinal dorsal horn of painful rats induced by formalin.【Methods】Thirty-two male Sprague Dawley rats were made into formalin pain models.They were randomly divided into four groups:control group(n =8);pain control group(n =8);catheter group(n =8);muscimol group(n =8).Rats were killed after 24 h respectively.The number of persistent flinching of rats was counted and immunocytochemistry method was used to observe the changes of the number of GABA immunoreactive cells,the expression of the GABAAβ3 receptor mRNA in the spinal dorsal horn were determinded by in situ hybridization.【Results】All of the rats of peripheral formalin injected could be observed persistent flinching.Intrathecally administrated muscimol could decrease the flinch response during phase 2 of the formalin test,the number of flinch response in muscimol group was lower than in pain control group and catheter group(P 0.05).Twenty-four hours after formalin injection,GABA immunoreactive cells were observed at superficial laminae Ⅰ～Ⅲ of formalin foot side lumbar spinal dorsal horn in pain control group and catheter group rats,more than in bilateral spinal dorsal horn of control group and non-formalin foot side spinal dorsal horn of pain control group and catheter group(P 0.05),there were no difference among muscimol group and control group in bilateral spinal dorsal horn,pain control group and catheter group in non-formalin foot side spinal dorsal horn on expression of GABA immunoreactive cells(P 0.05),but the GABA immunoreactive cells were lower in bilateral spinal dorsal horn of muscimol group than in formalin foot side spinal dorsal horn of pain control group and catheter group(P 0.05).A significant increase of the expression of GABAAβ3 receptor mRNA reactive cells was observed at superficial laminae Ⅱ～Ⅲ of bilateral lumbar spinal dorsal horn in pain control group and catheter group than in control group and muscimol group(P 0.05),there were no difference between control group and muscimol group on their expression(P 0.05).【Conclusion】 GABA and GABAAβ3 receptor may play an important role in regulating nociceptive modulation in spinal cord.