Distribution of neuropeptides in rat pterygopalatine ganglion: light and electron microscopic immunohistochemical studies.

The distribution and quantity of neuropeptides in the rat pterygopalatine ganglion were studied by using complete serial paraffin sections of the ganglion immunostained with antiserum against several neuropeptides. The pterygopalatine ganglion, composed of 4932 +/- 291 (mean +/- SD) neurons, was triangular in shape with a tapering caudal tail. The most commonly found peptide in neurons was vasoactive intestinal polypeptide (VIP) (99.0%), followed by neuropeptide Y (NPY) (54.1%) and enkephalin (10.5%). The rostro-ventromedial and caudal parts of the ganglion where intensely VIP-immunoreactive neurons predominate project to the nasal mucosa, while the rostro-dorsolateral part of the ganglion where NPY-immunoreactive neurons predominate projects to the Harderian gland. The coexistence of VIP/NPY (47.4%), VIP/NPY/enkephalin (6.6%) or VIP/enkephalin (3.9%) in the ganglionic neurons was recognized. Calcitonin gene-related peptide (CGRP)- and substance P-immunoreactive varicosities formed synaptic contacts with the somatic spine or soma, which confirmed that the reflex arch, composed of axon collaterals of trigeminal ganglionic neurons and parasympathetic ganglionic neurons, operates through direct synapses. Enkephalin-immunoreactive varicosities, which were probably derived from parasympathetic preganglionic neurons, also made synaptic contact with the somatic spine.