MicroRNA-mediated GABAAα-1 receptor subunit down-regulation in adult spinal cord following neonatal cystitis-induced chronic visceral pain in rats

The nociceptive transmission under pathological chronic pain conditions involves transcriptional and/or translational alteration in spinal neurotransmitters, receptor expressions, and modification of neuronal functions. Studies indicate the involvement of microRNA (miRNA) - mediated transcriptional deregulation in the pathophysiology of acute and chronic pain. In the present study, we tested the hypothesis that long-term cross-organ colonic hypersensitivity in neonatal zymosan-induced cystitis is due to miRNA-mediated posttranscriptional suppression of the developing spinal GABAergic system. Cystitis was produced by intravesicular injection of zymosan (1% in saline) into the bladder during postnatal (P) days P14 through P16 and spinal dorsal horns (L6-S1) were collected either on P60 (unchallenged groups) or on P30 after a zymosan re-challenge on P29 (re-challenged groups). miRNA arrays and real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed significant, but differential, up-regulation of mature miR-181a in the L6-S1 spinal dorsal horns from zymosan-treated rats compared with saline-treated controls in both the unchallenged and re-challenged groups. The target gene analysis demonstrated multiple complementary binding sites in miR-181a for GABA(A) receptor subunit GABA(Aα-1) gene with a miRSVR score of -1.83. An increase in miR-181a concomitantly resulted in significant down-regulation of GABA(Aα-1) receptor subunit gene and protein expression in adult spinal cords from rats with neonatal cystitis. Intrathecal administration of the GABA(A) receptor agonist muscimol failed to attenuate the viscero-motor response (VMR) to colon distension in rats with neonatal cystitis, whereas in adult zymosan-treated rats the drug produced significant decrease in VMR. These results support an integral role for miRNA-mediated transcriptional deregulation of the GABAergic system in neonatal cystitis-induced chronic pelvic pain.