Distribution and termination of trigeminal nerves to the cerebral arteries in monkeys.

Wallerian degeneration was used to study the contributions of the first and second divisions of the trigeminal nerve to cerebral arterial innervation in the cynomolgus monkey. Animals were killed by intracardiac perfusion of fixative three to seven days after left ophthalmic or maxillary neurotomy or a combination of both, using three animals for each procedure. Cerebral arteries were dissected, removed and prepared for light and electron microscopy. The anterior vessels of the circle of Willis received nerve fibres, distributed via the internal carotid artery, from the ipsilateral ophthalmic branch of the trigeminal nerve and a small maxillary contribution was also observed in some animals. The posterior vessels were supplied from the same trigeminal source but by a different route, the nerves moving onto the basilar artery bilaterally or unilaterally via the recurrent nerve of the cavernous plexus using the abducent nerve for access. From the basilar, fibres distributed to both posterior cerebral arteries. Augmentation of the vascular nerve supply apparently from branches of the vagus and/or hypoglossal nerves was noted but otherwise unexamined. Trigeminal terminals were found on all vessels of the circle of Willis and their distal branches throughout the thickness of the adventitia, often lying close to the media but never contacting smooth muscle cells. These observations are consistent with results from other studies employing neurohistochemical and tracer techniques in subprimates. Comparison of operated and control material failed to reveal any distinctive features of terminals attributable to a trigeminal source.