[NADPH-diaphorase activity in autonomic preganglionic neurons in the rabbit]

In order to provide a morphological basis for the understanding of the role of nitric oxide (NO) in autonomic preganglionic neurons, the present study was designed to clarify the localization and distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity, a marker of NO synthase, in the rabbit spinal cord.

11 Chinchilla rabbits of both sexes were used in this study. Animals were kept under conditions of controlled light and heat regimens. NADPH-d activity was examined by histochemical methods.

The presence of NADPH-d activity in the spinal cord was detected in the dorsal horn, around the central canal (lamina X) and in autonomic preganglionic neurons. Focused on the latter, there was a prominent NADPH-d activity between T1 and L5 segments in the intermediate zone and less intensive NADPH-d staining between S1 and S3 segments. Differences between the two parts of the autonomic system were seen in the arrangement (periodical in sympathetic, and continuous in parasympathetic), in the length of neuronal processes length (shorter in sacral preganglionic neurons) and in their localization (both are seen in the intermediolateral nucleus, but neurons of the sympathetic autonomic system can be found also medially towards the central canal, whilst those of the parasympathetic system were not).

The present results suggest that NO can be used as a transmitter in preganglionic neurons and can be involved in autonomic and sensory processes. (Fig. 10, Ref. 37.)