The nociceptive transmission under pathological chronic pain conditions involves transcriptional and/or translational alteration in spinal neurotransmitters and receptors expression, and modification of neuronal function. Studies indicate the involvement of MicroRNA (miRNA)-mediated transcriptional deregulation in pathophysiology of acute and chronic pain. In the present study, we tested the hypothesis that long-term cross-organ colonic hypersensitivity in neonatally 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 (unchallenge groups) or on P30 following a zymosan re-challenge on P29 (re-challenge groups). miRNA arrays and Real-time reverse transcription polymerase chain reaction revealed significant, but differential, upregulation of mature miR-181a in the L6-S1 spinal dorsal horns from zymosan-treated rats compared with saline controls in both unchallenge and re-challenge groups. The target gene analysis demonstrated multiple complementary binding sites in miR-181a for GABAA receptor subunit GABAAα−1 gene with a miRSVR score of −1.83. Increase in miR-181a concomitantly resulted in significant downregulation of GABAAα−1 receptor subunit gene and protein expression in adult spinal cords from neonatal cystitis rats. Intrathecal administration of GABAA receptor agonist muscimol failed to attenuate viscero-motor response (VMR) to colon distension in neonatal cystitis rats, 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 GABAergic system in neonatal cystitis-induced chronic pelvic pain.
Irritable bowel syndrome (IBS) is a common health issue that is characterized by abdominal pain, abnormal bowel movements and altered visceral perception. The complexity and variability in symptoms pose serious challenges in treating IBS. Current therapy for IBS is primarily focused on reducing the abdominal pain, thereby improving the quality of life to a significant extent. Although the use of fiber rich diet is widely recommended in treating IBS, some studies have questioned its use. Intracolonic butyrate, a short chain fatty acid, is primarily produced by the fermentation of dietary fibers in the colon. In the existing literature there are conflicting reports about the function of butyrate. In rats it is known to induce visceral hypersensitivity without altered pathology, whereas in humans it has been reported to reduce visceral pain. Understanding the molecular mechanisms responsible for this contrasting effect of butyrate is important before recommending fiber rich diet to IBS patients.
Results document that in rats LGG can attenuate neonatally induced chronic visceral pain measured in adulthood. Prolonged intake of LGG alters some key brain neurotransmitters and biogenic amines that could be involved in pain modulation.
The present study investigates the analgesic effect of minocycline, a semi-synthetic tetracycline antibiotic, in a rat model of inflammation-induced visceral pain. Inflammation was induced in male rats by intracolonic administration of tri-nitrobenzenesulphonic acid (TNBS). Visceral hyperalgesia was assessed by comparing the viscero-motor response (VMR) to graded colorectal distension (CRD) prior and post 7 days after TNBS treatment. Electrophysiology recordings from CRD-sensitive pelvic nerve afferents (PNA) and lumbo-sacral (LS) spinal neurons were performed in naïve and inflamed rats. Colonic inflammation produced visceral hyperalgesia characterized by increase in the VMRs to CRD accompanied with simultaneous activation of microglia in the spinal cord and satellite glial cells (SGCs) in the dorsal root ganglions (DRGs). Selectively inhibiting the glial activation following inflammation by araC (Arabinofuranosyl Cytidine) prevented the development of visceral hyperalgesia. Intrathecal minocycline significantly attenuated the VMR to CRD in inflamed rats, whereas systemic minocycline produced a delayed effect. In electrophysiology experiments, minocycline significantly attenuated the mechanotransduction of CRD-sensitive PNAs and the responses of CRD-sensitive LS spinal neurons in TNBS-treated rats. While the spinal effect of minocycline was observed within 5 min of administration, systemic injection of the drug produced a delayed effect (60 min) in inflamed rats. Interestingly, minocycline did not exhibit analgesic effect in naïve, non-inflamed rats. The results demonstrate that intrathecal injection of minocycline can effectively attenuate inflammation-induced visceral hyperalgesia. Minocycline might as well act on neuronal targets in the spinal cord of inflamed rats, in addition to the widely reported glial inhibitory action to produce analgesia.
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