Parasympathetic innervation of cephalic arteries in rabbits: comparison with sympathetic and sensory innervation

We investigated the distribution of parasympathetic, sympathetic, and sensory perivascular nerve fibers in rabbit cephalic arteries supplying the brain, exocrine glands, nasal mucosa, masseter muscles, tongue, and skin in the face and also examined cranial autonomic and sensory ganglia. NADPH diaphorase (NADPHd)-positive and vasoactive intestinal peptide-like immunoreactive (VIP-LI) neurons were located in the cranial parasympathetic ganglia. Neuropeptide Y (NPY)-LI neurons occurred mainly, and dopamine beta-hydroxylase (DBH)-LI neurons occurred exclusively, in the superior cervical (sympathetic) ganglion. Substance P (SP)-LI and calcitonin gene-related peptide (CGRP)-LI neurons occurred only in the trigeminal (sensory) ganglion. Therefore, it was assumed that NADPHd-positive and VIP-LI perivascular nerve fibers in cephalic arteries were parasympathetic, all DBH-LI and most NPY-LI fibers were sympathetic, and SP-LI and CGRP-LI fibers were sensory in nature. In the cerebral arteries, NADPHd-positive and VIP-LI varicose fibers were more numerous in the rostral than in the caudal half of the Circle of Willis. In the extracranial arteries, NADPHd-positive and VIP-LI fibers were most abundant in the lingual, lacrimal, and supraorbital arteries; sparse in the parotid and submandibular arteries; and absent in the ear artery. There was an obvious proximal-to-distal density gradient along individual cephalic arterial trees. In contrast, DBH-LI, NPY-LI, SP-LI, and CGRP-LI varicose nerve fibers were similar in density in all cephalic arteries and their branches. These neuroanatomical findings suggest that differential parasympathetic innervation in cephalic arteries may play a role in the partitioning of blood flow between different cephalic tissues.