Distribution of calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity in the trigeminal ganglion and mesencephalic trigeminal nucleus of the cat.

The distribution of calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-like immunoreactivity (LI) in the cat trigeminal ganglion (TrG) and mesencephalic trigeminal nucleus (MTN) was studied by the indirect immunofluorescent technique and unlabelled peroxidase-antiperoxidase method. A positive reaction for both CGRP and NPY was found only in the TrG primary afferent neurons. Between 40% and 50% of the perikarya displayed CGRP-LI whereas few of the trigeminal principal neurons (approximately 1%) showed NPY-LI. Most of the CGRP-immunoreactive cells were small to medium-sized (20-40 microns in diameter) and were distributed throughout the ganglion. NPY appeared specifically in medium-sized to large-sized trigeminal neurons (up to 60 microns). CGRP and NPY also occurred in varicose nerve fibres running among the cell bodies and in pericellular baskets around a small number of large unstained ganglion cells. In contrast, CGRP- and NPY-LI were present only in the nerve fibres and terminals of the cat MTN. The immunoreactive varicosities travelled towards the negative MTN neurons and formed basket-like arborizations around their cell bodies. Synaptic contact between the immunolabelled axonal profiles and perikarya of trigeminal primary afferent neurons could not be seen in the TrG and MTN of the cat. The results provide further evidence for the interrelation between sensory and autonomic systems.