Innervation of the spleen in the rat: evidence for absence of afferent innervation.

Catecholaminergic fibers in the spleen have been well characterized in the rat and this innervation is believed to be an important source of modulation of the immune system. The presence or role of afferent feedback from the spleen has not been systematically investigated. We have examined whether the spleen receives afferent innervation from sensory ganglia and also have assessed the sources of efferent innervation to the spleen in the rat. The fluorescent retrograde anatomical tracers fluoro-gold (FGo) or fast blue (FB) were injected into the spleens of adult female rats and dorsal root, sympathetic chain, nodose, and celiac-mesenteric plexus ganglia were collected. In additional animals, the spleen was either injected with the anatomical tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or else regular HRP was applied to the cut end of the splenic nerve. Also, we examined the effects of cutting the splenic nerve on the retrograde labeling of cell bodies in the ganglia and on the catecholamine histochemistry of the spleen. The neuroanatomical results were based primarily upon the tracer FGo and verified that the celiac-mesenteric plexus ganglia provide a major efferent input to the spleen. Furthermore, lower thoracic sympathetic chain ganglia provide an additional and substantial efferent supply to the spleen. Cutting of the splenic nerve prevented retrograde labeling of cell bodies in the celiac-mesenteric plexus ganglia and sympathetic chain ganglia of rats injected with tracers into the spleen and also eliminated catecholamine histofluorescence in the spleen. In terms of afferent labeling, the results with FGo indicated that there were no cell bodies labeled in afferent ganglia following splenic injections.(ABSTRACT TRUNCATED AT 250 WORDS)