Synaptology and sources of vasoactive intestinal polypeptide and substance P containing axons of the cat celiac ganglion. An experimental electron microscopic immunohistochemical study.

We have examined the possible origin of vasoactive intestinal polypeptide (VIP) and substance P-containing axons and the synapses formed by these axons in the celiac ganglion of the cat, by means of ultrastructural immunohistochemistry combined with various surgical lesions. Axons containing VIP as well as those immunopositive for substance P, formed axo-dendritic and axosomatic synapses with principal ganglion cells. After transection of the superior mesenteric nerve numerous degenerated axonal profiles could be found in the celiac ganglion. Some of these contained VIP immunoreactivity. By contrast in alternate sections stained with substance P antibody only intact axons were labelled. Bilateral vagotomy resulted in the appearance of degenerating axonal profiles in the celiac ganglion, some of which could be stained with substance P antiserum but not with VIP antiserum. Following removal of dorsal root ganglia (Th6-Th12) from both sides, a large number of degenerated axons were found, many of which were immunopositive for substance P but not for VIP. We conclude that the peripheral input to the celiac ganglion contains VIP fibers which form synapses with principal ganglion cells. Substance P-containing fibers reach the celiac ganglion via the vagal nerve as well as from the dorsal root ganglia, and they form synapses with the principal ganglion cells. It is proposed that the VIP and the substance P-containing axons are involved in two different peripheral reflex loops.