Abstract: Objective Overlapping syndrome is a common condition for functional gastrointestinal disorders(FGIDs), the underlying pathophysiological mechanisms are not clear. The aim of this study is to evaluate gastric emptying rates and changes of gastric myenteric neurons in rat models with irritable bowel syndrome with constipation(IBS-C). Methods Rat models with IBS-C were established by stomach irritation with ice-water daily for 14-days. The gastric emptying rate was detected with phenol red. Double staining with immunohistofluorescence with anti-Hu antibody and choline acetyltransferase (ChAT) or nitric oxide synthases (NOS) was applied with gastric transverse section preparations to evaluate the proportion of specific neurons in myenteric plexus of the distal stomach. Results The gastric emptying rate at 15min after gastric gavage increased significantly in IBS-C rats comparing to control(P＜0.05). The proportion of ChAT immunoreactive(ChAT-IR) neurons in myenteric plexus of distal stomach was higher in IBS-C rats than control group(79.0% ± 2.4% vs 68.3% ± 1.0%, P＜0.05), while the proportion of NOS-IR neurons decreased significantly in IBS-C rats (18.9% ± 5.0% vs 33.1% ± 4.5%, P＜0.001). Conclusions Considering with the changes of myenteric neurons as well as the gastric emptying rate in IBS-C rat model, enteric nervous system might play an important role in the pathogenesis of IBS-C and functional dyspepsia. This study provides a new insight on understanding the underlying mechanisms for FGIDs overlap syndrome.

Key words: functional gastrointestinal disorders, overlapping syndrome, irritable bowel syndrome with constipation, functional dyspepsia, enteric nervous system