Disturbances of colonic motility in mouse models of Hirschsprung's disease

Mutations in genes encoding members of the GDNF and endothelin-3 (Et-3) signaling pathways can cause Hirschsprung's disease, a congenital condition associated with an absence of enteric neurons in the distal gut. GDNF signals through Ret, a receptor tyrosine kinase, and Et-3 signals through endothelin receptor B (Ednrb). The effects of Gdnf, Ret, and ET-3 haploinsufficiency and a null mutation in ET-3 on spontaneous motility patterns in adult and developing mice were investigated. Video recordings were used to construct spatiotemporal maps of spontaneous contractile patterns in colon from postnatal and adult mice in vitro. In Ret(+/-) and ET-3(+/-) mice, which have normal numbers of enteric neurons, colonic migrating motor complexes (CMMCs) displayed similar properties under control conditions and following inhibition of nitric oxide synthase (NOS) activity to wild-type mice. In the colon of Gdnf(+/-) mice and in the ganglionic region of ET-3(-/-) mice, there was a 50-60% reduction in myenteric neuron number. In Gdnf(+/-) mice, CMMCs were present, but abnormal, and the proportion of myenteric neurons containing NOS was not different from that of wild-type mice. In the ganglionic region of postnatal ET-3(-/-) mice, CMMCs were absent, and the proportion of myenteric neurons containing NOS was over 100% higher than in wild-type mice. Thus impairments in spontaneous motility patterns in the colon of Gdnf(+/-) mice and in the ganglionic region of ET-3(-/-) mice are correlated with a reduction in myenteric neuron density.     

Gastrointestinal neuropeptides suppress human colonic lamina propria lymphocyte DNA synthesis.

Gastrointestinal neuropeptides have been shown to modulate the circulatory immune system, but their effect on the mucosal immune system is not well defined. We studied the effect of VIP, SOM, S-P and Bomb on thymidine incorporation into human colonic lamina propria lymphocyte (LPL) DNA. Physiologic concentrations of VIP, SOM, S-P and Bomb significantly suppressed thymidine incorporation into Con A-stimulated human LPL. These neuropeptides did not affect DNA synthesis when LPL were induced with phorbol ester (PDB) and calcium ionophore (ionomycin). Our data suggest that a) VIP, SOM, S-P, and Bomb may have a regulatory role in the human mucosal immune system, and b) Bomb should be added to the list of neuropeptides which affect the gut immune system.     

Molecular heterogeneity of RET loss of function in Hirschsprung's disease.

The RET proto-oncogene encodes a receptor with tyrosine kinase activity (RET) that is involved in several neoplastic and non-neoplastic diseases. Oncogenic activation of RET, achieved by different mechanisms, is detected in a sizeable fraction of human thyroid tumors, as well as in multiple endocrine neoplasia types 2A and 2B (MEN2A and MEN2B) and familial medullary thyroid carcinoma tumoral syndromes. Germline mutations of RET have also been associated with a non-neoplastic disease, the congenital colonic aganglionosis, i.e. Hirschsprung's disease (HSCR). To analyse the impact of HSCR mutations on RET function, we have introduced into wild-type RET and activated RET(MEN2A) and RET(MEN2B) alleles three missense mutations associated with HSCR. Here we show that the three mutations caused a loss of function of RET when assayed in two model cell systems, NIH 3T3 and PC12 cells. The effect of different HSCR mutations was due to different molecular mechanisms. The HSCR972 (Arg972-->Gly) mutation, mapping in the intracytoplasmic region of RET, impaired its tyrosine kinase activity, while two extracellular mutations, HSCR32 (Ser32-->Leu) and HSCR393 (Phe393-->Leu), inhibited the biological activity of RET by impairing the correct maturation of the RET protein and its transport to the cell surface.     

Hirschsprung's disease and congenital deafness

Summary A family is described showing deafness in three consecutive generations. Hirschsprung's disease was present in at least two of the affected patients and a history of bowel dysfunction was present in the third. The association of the two disorders in this family may be due to a single autosomal dominant gene and in this regard differs from previously reported isolated patients with Hirschsprung's disease and deafness.     

Pharmacological characteristics of the ganglionic and aganglionic colon in Hirschsprung's disease.

The pharmacological characteristics of circular and longitudinal muscle strips from normal and aganglionic colon were investigated in vitro in 13 patients with Hirschsprung's disease. The sensitivity for acetylcholine, noradrenaline and isoprenaline is normal in aganglionic tissue. Betanechol, carbacholine, metacholine and pilocarpine induce stronger contractions in aganglionic strips than in normal strips. Serotonine has an inhibitory effect in strips from both the proximal and distal segment. Nicotine, lobeline and DMPP do not induce a relaxation in aganglionic muscle strips. All strips contract after histamine, but the contractions are stronger in aganglionic strips. It is concluded that there are no pharmacological arguments and no explanations for spasticity of the distal aganglionic colon and that the type of denervation is certainly different from the type described by Cannon.     

Flexible sigmoidoscopy in outpatients with suspected colonic disease.

One hundred and fifteen patients attending a gastroenterology clinic were investigated by flexible sigmoidoscopy as outpatients. There were asked to fast before the examination and give a high-volume enema and sedated before the examination. A standard long colonoscope was used rather than the 60-cm sigmoidoscope, which limits the distance that can be examined and forces the operator to work very close to the patient. Preparation was considered good in 95 patients and 49 were examined as far as the hepatic flexure or beyond. Sixty-one patients were found to have lesions of the colon, 25 of them ulcerative colitis, 16 a poly, and nine carcinoma. Despite the fact that these patients were selected (some of them had already had ulcerative colitis diagnosed), flexible sigmoidoscopy proved to be a valuable initial outpatient investigation. The proximal colon was well visualised in 46 patients and a subsequent barium enema was considered unnecessary. There were no complications and the procedure seemed to be well tolerated.