Cholinergic mechanisms in pial vessels. Histochemistry, electron microscopy and pharmacology.

Abstract

Plexuses of cholinergic nerve terminals were demonstrated (acetylcholinesterase staining) in pial arteries (down to a diameter of about 15μ) at the base of the brain and on the brain convexities of mice, rats, rabbits, hamsters, guinea-pigs, and cats. The pial veins were less well supplied than the arteries. Consecutive formaldehyde gas treatment (to visualize adrenergic nerves) and acetylcholinesterase staining revealed that the adrenergic and cholinergic plexuses followed each other closely, the axon terminals running together in the same Schwann cell strands. This was confirmed by electron microscopy after KMnO4 fixation or 5-hydroxydopamine treatment. The varicosities of cholinergic and adrenergic axons were sometimes seen as close as 250 A. In the neuro-effector area, the terminals of both nerve types (naked or surrounded by an incomplete Schwann cell covering) approached the smooth muscle cells as close as 800–1100 A, and they were separated from the latter only by the fused neuronal and muscular basement membranes. In this area axo-axonal contacts were observed. The adrenergic, but not the cholinergic, nerves disappeared after bilateral removal of the superior cervical sympathetic ganglia. Isolated cat middle cerebral artery contracted strongly with acetylcholine, and the effect was inhibited by atropine.