An electron microscopic study on VIP-like immunoreactive nerve fibers in the celiac ganglion of guinea pigs.

An immuno-electron microscopic study revealed that VIP-like immunoreactive nerve fibers in the celiac ganglion of guinea pigs were characterized by a conspicuously numerous large granular vesicles mixed with small clear vesicles. The immunoreactive materials were localized in the core of the large granular vesicles and a distinct halo was recognized between the core and the limiting membrane of the vesicles. These fibers made numerous axo-dendritic and a few axo-somatic synapses with the post-ganglionic principal neurons and also formed some synapses with vesicle-containing neuronal profiles which are presumably preganglionic axons. The immunoreactive fibers were presynaptic at all these synaptic sites. In addition, some synaptic contacts were found between two adjacent immunoreactive nerve fibers. These findings strongly suggests that VIP might be involved in the ganglionic transmission of the prevertebral ganglia.