Cholinergic and nitrergic interneurones in the myenteric plexus of the human colon

Background: Myenteric interneurones are involved in the reflexes that control the motility of the human colon. Aims: The distribution of choline acetyltransferase (ChAT) and nitric oxide synthase (NOS) immunoreactivity in myenteric interneurones was investigated in this study. Methods: Dil (1,1'-diclodecyl 3,3,3',3'-indocarbocyanine perchlorate) was applied to the myenteric plexus of the human colon followed by organotypic culture. Retrogradely labelled neurones, with projections longer than motor neurones (>10 mm), were studied to exclude motor neurone populations. ChAT and NOS immunoreactivity was then determined in the interneurones. Results: We found that 90% of interneurones projecting orally contained ChAT and none contained NOS. Ninety five per cent of descending interneurones were labelled with ChAT and/or NOS antisera; 46% contained NOS immunoreactivity alone, 20% contained ChAT immunoreactivity alone, and 29% contained both ChAT and NOS. Anally directed interneurones had significantly longer projections than orally projecting interneurones. Conclusions: Nearly all interneurones contain either NOS or ChAT immunoreactivity. Orally projecting interneurones are of two types: 90% contain ChAT alone and the remainder contain immunoreactivity for neither ChAT nor NOS. There are three main types of anally projecting interneurones: the largest, which contains NOS but not ChAT, and the two smaller classes which contain ChAT and NOS, and CHAT alone.