Differential distribution of nitric oxide synthase in neural pathways to the urogenital organs (urethra, penis, urinary bladder) of the rat.

Axonal tracing techniques were used in combination with histochemical methods (NADPH-diaphorase activity and nitric oxide synthase immunoreactivity) to examine the distribution of nitric oxide synthase (NOS) in the neural pathways to the urogenital organs of the male rat. The major goal of this study was to compare the histochemical properties of the efferent and afferent neurons innervating the urethra with the properties of neurons innervating the penis and bladder. In the major pelvic ganglion (MPG) large percentages of postganglionic neurons innervating the urethra (44%) and the penis (97%) exhibited NADPH-diaphorase (NADPH-d) staining whereas only a small percentage (3.5%) of neurons innervating the bladder were N-d positive. Urethral neurons stained for N-d were on average smaller (33.3 microns diameter) than unstained neurons (54.5 microns diameter). The histochemical difference between the three types of neurons was also reflected in NOS-immunoreactivity (IR); however, the absolute percentage of neurons exhibiting NOS-IR was low: penis (21%), urethra (11%) and bladder (0%). Axonal varicosities staining for N-d or NOS-IR were noted in the MPG in close proximity to unidentified neurons and neurons innervating the urogenital organs. A considerable number of afferent neurons in the lumbosacral dorsal root ganglia (DRG) stained for N-d (64 cells/L6, 35 cells/S1 section); however, only small numbers of neurons (average 1 cell/section) exhibited NOS-IR. N-d activity was detected in a large percentage of urethral (55%) and bladder (80%) afferent neurons in the L6-S1 dorsal root ganglia (DRG) but in relatively few (12%) penile afferent neurons in the L6 ganglia. These results suggest that the contribution of nitric oxide (NO) to neurotransmission varies considerably in different urogenital organs. NO could have a significant role in postganglionic efferent pathways to the urethra and penis but very likely has no role in the efferent pathways to the bladder. Similarly, the prominence of N-d staining in some DRG neurons (e.g. urethra and bladder) but not others (penile) also raises the possibility of a varying role of NO in afferent pathways. However, in these neurons N-d staining was not paralleled by NOS-IR, which was present in only a small percentage of neurons. Thus, N-d staining may not reflect the presence of NO in afferent pathways to the pelvic viscera.