The role of substance P-containing fibers in sympathetic ganglia: effect of capsaicin.
Capsaicin was given subcutaneously to guinea pigs and the effect on substance P-immunoreactive (SP-I) fibers in the celiac/superior mesenteric and inferior mesenteric ganglia was observed at 2 day and 8-10 day intervals. Capsaicin (125 mg) treatment led to almost total disappearance of SP-I fibers from all areas examined in both short- and long-term animals. This effect applied equally to the dense network of varicose SP-I fibers and to basket-like SP-I contacts with principal ganglionic neurons. The effect of capsaicin on SP-I fibers in the mesenteric ganglia provides a strong indication that these fibers represent a homogeneous population of visceral sensory afferents. This is supported by other lines of anatomical evidence in the literature. Taken together with studies that have shown axodendritic contact of SP-I terminals on principal ganglionic neurons and neuro-modulatory effects of SP on these neurons, it may be hypothesized that SP-I fibers in the mesenteric ganglia represent collaterals of visceral sensory afferents forming a subspinal feedback arc.
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D013373:Substance P / Q000502:physiology*
D013373:Substance P; D002211:Capsaicin