RESUMO
Objective To study the effects of subsrachnoid implantation of APA microcapsules-filled with bovine chromaffin cells (BCCs) on expression of mRNA for ?2 and ?2 subunits of GABAA receptor in spinal cord in rats with chronic constrictive injury (CCI) of sciatic nerve and to determine if GABAA receptor is involved in the mechanisms of analgesia produced by subarachnoid implantation of micro-capsulized BCCs. Methods Twenty SD rats weighing 200-250 g were randomly divided into 4 groups with 5 animals in each group : (Ⅰ) control group (group C); (Ⅱ) CCI group in which right sciatic nerve was loosely ligated; (Ⅲ) APA group in which 500-600 empty APA micro-capsules were implanted in subarachnoid space and (Ⅳ) APA-BCC group in which 5?106 APA micro-capsules filled with BCCs were implanted in subarachnoid space. In group Ⅲ and Ⅳ subarachnoid implantation was performed at L1-3 level 7 days after CCI operation. Pain threshold to mechanical stimulation with Von-Frey filament and thermal stimulation with CO2 laser was measured before and 7 days after implantation. Expression of mRNA for GABAA receptor ?2 and ?2 subunit in spinal cord was measured by RT-PCR.Results The expression of mRNA for GABAA receptor ?2 and ?2 subunit in spinal cord was significantly lower in CCI and APA groups (group Ⅱ and Ⅲ) than that in control group (group Ⅰ). In APA-BCC group (group Ⅳ) pain threshold of surgical side to mechanical and thermal stimuli and the expression of mRNA for GABAA receptor ?2 and ?2 subunit in spinal cord were significantly higher than those in group Ⅱ and Ⅲ . Conclusion The expression of mRNA for GABAA receptor?2 and ?2 subunit in spinal cord is down-regulated by CCI and subarachnoid implantation of micro-capsulized BCCs can reverse the down-regulation. Recovery of GABAA-nergic neuron activity contributes to the analgesic effect of aubarachnoid implantation of micro-capsalized BCCs.