Abdominal pain in patients with Inflammatory bowel disease (IBD) confers significant lifelong morbidity and is experienced during inflammatory flare and while in remission. Visceral hypersensitivity (VHS) is implicated as a contributing factor to the etiology and pathophysiology of this functional abdominal pain. Epidemiological studies identify early-life infections and adolescent or adult gastrointestinal infections as risk factors for the development or onset and relapse of IBD respectively. We tested the hypothesis that neonatal colonic inflammation (NCI) epigenetically modulates pro-nociceptive gene expression resulting in VHS to colorectal distention (CRD), when exposed to subsequent colonic inflammation through increase of central sympathetic activity and increased expression of spinal cord neurotrophin Brain Derived nuetrophic Factor (BDNF).Methods:
We studied 4 groups of animals: (1) saline control rats (Ctr. rats); (2) rats subjected only to NCI on post-natal day 10 by colonic administration of trinitrobenzene sulfonic acid (TNBS, 130 mg/kg) (NCI rats); (3) 8 to 12 weeks old naive rats subjected to adult colon inflammation (ACI) for the first time (ACI rats); and (4) 8 to 12 weeks old adult NCI rats subjected to adult colon inflammation by TNBS (68 mg/kg) (NCI + ACI rats). Tissues were collected 7 days following adult TNBS administration.Results:
When compared to all groups, NCI + ACI results in a significant (P < 0.05) increase in VHS to CRD. Additionally heart rate variability in this group showed increased sympathetic and decreased vagal tone. Both plasma and CSF norepinephrine were increased (2-fold, P < 0.05) in the NCI + ACI groups when compared to all groups. Tyrosine hydroxylase mRNA and protein expression were significantly increased in the locus ceruleus (P < 0.05). VHS was significantly reduced when NCI + ACI rats were treated with either systemic of intrathecal β2 adrenergic receptor (AR) antagonist propranolol. BDNF mRNA was significantly increased in the colon projecting neurons of the SI DRG in the NCI + ACI rats when compared to ACI rats (7-fold versus 3-fold). Additionally BDNF protein and mRNA expression was significantly increased in the LS- and TL-spinal cord (30% and 35%, P < 0.05). VHS in NCI + ACI rats was significantly reduced following intrathecal administration of BDNF receptor antagonist trkBFc. CHIP analysis revealed increased RNA Pol II (2.5-fold, P < 0.05) bindng at the transcription start site and increased p-CREB binding (1.5-fold, P < 0.05) at CRE1 on the BDNF promoter. Furthermore central AR blockade reversed enhanced RNA Pol II and p-CREB binding at the BDNF promoter (P < 0.05).Conclusions:
These findings validate the hypothesis that early-life colonic inflammation triggers epigenetic programming that upregulates adrenergic signaling and spinal cord neurotrophin expression which enhances VHS in a preclinical rat model of IBD.