CEREBRAL PIAL ARTERIAL INNERVATION WITH SPECIAL REFERENCE TO GABAERGIC INNERVATION

Glutamic acid decarboxylase (GAD)-immunoreactive (I) nerve fibers were observed to run parallel to other autonomic nerve fibers, especially vasoactive intestinal polypeptide (VIP)- and calcitonin gene-related p eptide (CGRP)-I nerve fibers at the light microscopic level. At the ul trastructual level, GAD-immunoreactivities co-localized with CGRP immu noreactivities in nerve terminals, but not with choline acetyltransfer ase, VIP, tyrosine hydroxylase and neuropeptide Y immunoreactivities. GAD immunoreactivities were observed in the trigeminal ganglion, some of which were co-localized with CGRP-immunoreactivities. In the proxim al portion of the internal carotid artery, GAD-I adventitial ganglion cells were observed and some were also immunoreactive for CGRP. These results strongly suggest that the origin of GABAergic innervation of t he major cerebral pial arteries of the cat is mainly in the trigeminal ganglion, and partly in the adventitial ganglia of the internal carot id artery.