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

Enkephalin-like immunoreactive nerve fibers in the celiac ganglion of guinea pigs were characterized by a high population of large granular vesicles mixed with small clear vesicles. The immunoreactive material is confined to the large granular vesicles. The immunoreactive nerve fibers formed many axo-dendritic as well as axo-somatic synapses and also formed a few synapses with presumed preganglionic axons containing numerous vesicles. The immunoreactive fibers were regarded as presynaptic at these synapses. These findings suggest that enkephalin might play a role as a neurotransmitter or neuromodulator in the ganglionic transmission of this prevertebral ganglion.