Nitric oxide (NO) is an important neuronal signalling molecule (Bult et al. 1990) which mediates smooth muscle relaxation in the gastrointestinal tract and has been implicated in gastrointestinal motility disorders (Vanderwinden et al. 1992). The motility abnormalities in inflammatory bowel disease (IBD) may also, in part, be due to alterations in nitrergic innervation of the inflamed colon. In this study we examined the distribution and density of neuronal nitric oxide synthase (nNOS) in the colon of healthy (normal) controls and in IBD.
Archival, formalin-fixed, colonic specimens from normal controls (non-stenotic carcinoma, n = 6), Crohn’s disease (CD, n = 6) and ulcerative colitis (UC, n = 6) were sectioned at 6 mm. ABC-Immunoperoxidase staining was performed with a polyclonal antibody directed against nNOS (Chemicon, UK). North Glasgow Universities NHS Trust granted ethical permission for this study. Immunoreactivity was assessed in the circular and longitudinal muscle, and in the myenteric plexus using an arbitrary grading system of 0Ð4, representing absent, sparse, moderate, abundant and very abundant nNOS immunoreactivity.
nNOS-like immunoreactivity (IR) occurred in both normal and diseased bowel. The most striking area of immunoreactivity was in the myenteric plexus where strong staining of ganglion cells occurred. The proportion of specimens assigned a grade of abundant in the myenteric plexus was decreased in UC (3/6) and in CD (2/6) compared with controls (6/6). In the submucosal plexus, IR was dense in the cytoplasm of ganglion cells and connecting fibres. In the muscularis externa, the grading of abundant nNOS-like immunoreactive nerve fibres was greater in the circular than longitudinal muscle in all specimens. In both the circular (controls (5/6), UC (2/6), CD (1/6)) and longitudinal (controls (2/6), UC (0/6), CD (0/6)) muscle, the proportion of specimens graded as abundant were decreased in IBD. A small number of epithelial cells displayed nNOS IR; these cells (at most two per crypt) were located at the lower half of the crypt and were identified in all normal colon specimens. The proportion of specimens in which these nNOS immunoreactive cells were identified decreased in IBD where 4/6 UC specimens and 0/6 CD specimens displayed immunoreactivity.
The alterations of nNOS-like immunoreactivity observed in this study may represent cellular changes which contribute to defects in the control of colonic motility in IBD.
R.A.D. is supported by a Glasgow Caledonian University Research Studentship.
All procedures accord with current local guidelines.