Capsaicin-induced depletion of substance P-like immunoreactivity in guinea pig sympathetic ganglia.

The distribution of substance P immunoreactive nerve fibers in guinea pig sympathetic ganglia was studied in normal and capsaicin-treated animals. A marked depletion of substance P-like immunoreactivity was observed in both pre- and paravertebral ganglia after capsaicin treatment. In the inferior mesenteric and pelvic ganglia, however, intensely fluorescent fibers surrounding some of the principal ganglion cells remain after capsaicin treatment. Ligation experiments on the inferior mesenteric ganglion indicate that the capsaicin-insensitive substance P immunoreactive fibers in this ganglion are of lumbar splanchnic origin. Whether or not they represent capsaicin-resistant primary afferent neurons is not known. The enkephalin, vasoactive intestinal polypeptide, cholecystokinin and bombesin immunoreactive fiber networks in the inferior mesenteric ganglion were also studied, and no differences were observed between normal and capsaicin-treated animals.