Expression of peptidergic and nitrergic structures in dorsal root ganglia of the rabbit

In this study we have demonstrated the presence of neuropeptide substance P (SP)and nonpeptide neurotransmiter NO (nitric oxide) in the dorsal root ganglia (DRG) of rabbits. NADPH-diaphorase histochemical staining was used for detection of NO and an immunohistochemical method for detection of substance P. A number of DRG cells were stained by SP- and NADPH-d reactions. The presence of SP and NADPH-diaphorase positive cells varied depending upon the spinal level of the DRG. Positively stained neurons were only small and intermediate in size. Cells of large diameter profiles showed no staining. Substance P immunoreactive cells were of brown and dark brown colour, the intensity of NADPH-d staining varied from light to very dark blue. In some DRG cells, there was very significant neuronal co-localization of immunoreactivity for SP and reactivity for NADPH-d. In summary, DRG cells appear to express diaphorase and substance P activity, and some of them show the presence of both neurotransmitters. Recent studies on the participation of NO in the regulation of SP release in the spinal cord suggest, that also in the DRG neurons there may be a close interaction between NO and SP.