ABSTRACT
The distribution of NADPH-diaphorase (NADPH-d) activity was studied in the central nervous system of an infrared sensitive snake. An inhibitor of nitric oxide synthase, dichloroindophenol (DPIP), was used to distinguish the characteristics of NADPH-d activity. Intensely and weakly NADPH-d-stained neurons and fibers were found in discrete regions throughout the snake brain and cervical spinal cord, such as the olfactory bulb, subcommissural organ, stratum griseum periventriculare, locus coeruleus, dorsal root, dorsal horn, and area X. It was particularly noticed that the trigeminal descending nuclei and reticular formation of the medulla oblongata contained many positive neurons and fibers, but the lateral descending nucleus and nucleus reticularis calons (infrared sensory nuclei) certainly did not. The positive neurons and fibers were also observed in supraspinal sensory ganglia. DPIP inhibited NADPH-d activity in all regions except for the olfactory/vomeronasal nerve and glomeruli. The results prove for the first time the presence of NADPH-d activity in the ophidian brain and suggest that nitric oxide may be involved in many neural functions, but not in infrared sensory processing.
