The morphological changes of colonic submucusal plexus in rats of irritable bowel syndrome with diarrhea

Objective To investigate the morphological responses of enteric nervous system (ENS) neurons of submucosal plexus (SMP) in distal colon of rat models with irritable bowel syndrome with diarrhea (IBS-D). Methods Rat models with IBS-D were established with chronic unpredictable mild stress and acute wrap restrain stress (CAS). Double staining with immunohistofluorescence for colonic whole mount preparations was used to evaluate the distribution and proportion of SMP neurons expressing specific neurochemical markers [choline acetyltransferase (CHAT), vasoactive intestinal polypeptide (VIP), and nitric oxide synthase (NOS)] and their colocalization with anti-Hu antibody, which is the hallmark for whole enteric neurons. Results There was no obvious difference in the total numbers of anti-Hu positive neurons and ganglia between IBS-D and control group. The proportions of both VIP-immunoreactive (VIP-IR) and NOS-IR neurons in colonic SMP were higher in IBS-D rats compared with controls (62.2%±6.2% vs 55.4% ±5.4%;15.0%±4.0%vs 10.5%±2.9%, P<0.05). There was no difference in the proportion of ChAT-IR neurons between two groups. Conclusions VIP is the most specific neurotransmitter for excitatory secretomotor neurons in rat SMP, the increase of VIP-IR neurons can promote intestinal mucosal secretion, which might play an important role in the pathophysiological mechanisms of IBS with diarrhea. Key words: Irritable bowel syndrome; Submucosal plexus; Neurons