Distribution and origin of vasoactive intestinal polypeptide (VIP)-immunoreactive, acetylcholinesterase-positive and adrenergic nerves of the cerebral arteries in the bent-winged bat (Mammalia: Chiroptera)

Abstract

The overall distribution and origins of vasoactive intestinal polypeptide (VIP)-immunoreactive (IR), acetylcholinesterase (AChE)-positive and adrenergic nerves in the walls of the cerebral arteries were investigated in the bent-winged bat. VIP-IR and AChE-positive nerves innervating the bat cerebral vasculature appear to arise mainly from VIP-IR and AChE-positive cell bodies within microganglia found in the nerve bundle accompanying the sympathetic nerve bundle within the tympanic cavity. These microganglia, as well as the nerve bundle containing them, do not emit catecholamine fluorescence, suggesting that they are of the cranial parasympathetic outflow, probably the facial or glossopharyngeal one. The axons from VIP-IR and AChE-positive microganglia run intermingled with sympathetic adrenergic nerves in the same thick fiber bundles, and reach the cranial cavity through the carotid canal. In addition, some of the VIP-IR fibers innervating the vertebro-basilar system, at least the basilar artery, originate from VIP-IR nerve cells located in the wall of this artery. The supply of VIP-IR fibers to the bat major cerebral arteries is the richest among mammals in that it is much greater in the vertebro-basilar system than in the internal carotid system: plexuses of VIP-IR nerves are particularly dense along the walls from the posterior ramus to posterior cerebral and basilar arteries. Small pial and intracerebral arteries of the vertebro-basilar system, especially those of the posterior cerebral artery which supply most parts of the diencephalon and cerebrum, are also richly innervated by peripheral VIP-IR fibers. This pattern corresponds well with the innervation pattern of adrenergic and AChE-positive nerves.