On the occurrence of substance P-containing fibers in sympathetic ganglia: immunohistochemical evidence.

Several sympathetic ganglia of the guinea pig, cat and rat were studied with indirect immunofluorescence technique using antibodies to substance P (SP) and dopamine-beta-hydroxylase (DBH), the latter of which represents a marker for noradrenaline containing neurons. In all ganglia studied SP-like immunoreactivity could be observed in certain nerve fibers (SP-positive fibers). Their number, localization fluorescence intensity and 'fluorescence morphology' varied considerably between the different ganglia as well as between species. In the inferior mesenteric ganglion and the coeliac-superior mesenteric ganglion complex of all species, and in particular of the guinea pig, a dense plexus of varicose SP-positive fibers was observed around the mostly DBH-positive, principal ganglion cells. In contrast no such fibers were seen in relation to the DBH-positive SIF cells of the ganglia. No SP-positive ganglion cells were observed in any of the ganglia studied. Previous biochemical and immunohistochemical studies have indicated that peripheral SP-positive fibers may represent the branches of primary sensory neurons. The rich supply of varicose, SP-positive nerve terminals, often surrounding the noradrenergic ganglion cells in a basket-like manner, may indicate that these fibers may play a functional role within the ganglia. Instead of merely passing through the ganglion they may be involved in special types of reflex arches.