Localization of choline acetyltransferase and NADPH diaphorase activities in the submucous ganglia of the guinea-pig colon

A combined immunohistochemical and histochemical demonstration of choline acetyltransferase (ChAT) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was carried out, respectively, to determine the localization of the neurotransmitters, acetylcholine and nitric oxide (NO) in the submucous neurons of guinea-pig colon. Almost half of the submucous neurons in the guinea-pig colon exhibited ChAT-immunoreactivity. Some of the ChAT-immunoreactive neurons were also stained for NADPH-d, although most of them showed only weak to moderate diaphorase activity. Many of the submucous neurons displayed exclusively either ChAT or NADPH-d activity. A close spatial relationship was observed between the cholinergic and nitrergic submucous neurons. Thus, in light microscopy, some ChAT-immunoreactive fibres were closely associated with the NADPH-d-positive nerve cell bodies. Ultrastructural study extended the fact that many of the ChAT-immunoreactive terminals made synaptic contacts with the soma of the NADPH-d-positive submucous neurons. A remarkable feature was the demonstration of ChAT and NADPH-d in some of the neurons and their presynaptic axon terminals, suggesting the co-localization of acetylcholine and NO as neurotransmitters in the submucous neurons and their presynaptic axon terminals. It is suggested that the submucous neurons with their specific neurochemical codings would subserve different functions.