Histochemical study of the distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive neurons in the chicken caecum.

The distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive neurones was investigated in the chicken caecum. Double staining combined NADPHd histochemistry with immunohistochemistry for neural nitric oxide synthase (nNOS) indicated that NADPHd-positive neurones also showed immunoreactivity for nNOS. NADPHd-positive nerve cell bodies were observed in both the myenteric and the submucous plexuses. Nerve fibres showing enzyme activity were mainly distributed in the circular muscle layer, but only a few fibres in the mucosal layer. Fine nerve fibres showing NADPHd activity were found running between germinal centres in the caecal tonsil. Quantitative analysis showed no significant differences in the number of enzyme-positive nerve cell bodies per ganglion of the myenteric and the submucous plexuses among three different caecal regions; proximal, middle and distal regions. Larger numbers of ganglia were detected in the submucous plexus than the myenteric plexus at all three regions. These data indicate that nitrergic neurones in the submucous plexus mainly project to the circular muscle layer in the chicken caecum. It is possible that nitrergic nerves regulate the motility of the chicken caecum.