Cerebral microcirculation: heterogeneity of pial arterial network controlling microcirculation of cerebral cortex

Analysis of the functional behaviour of pial arterial ramifications feeding small areas of the cerebral cortex of rabbits uncovered well-defined heterogeneity of vascular responses during development of functional hyperemia. In the network of the smaller pial arteries, under 100 microns in diameter, the most active segments, the sphincters of offshoots of smaller arterial branches from larger trunks and the precortical arteries just before their penetration as the radial arteries into the cerebral cortex, have been discovered. The frequency of their dilatation was found to be higher, the latent periods of the vascular responses significantly shorter, and the degree of vasodilatation greater than of the adjacent arterial segments. An abundant amount of cholinergic nerve plexuses (containing the cholinesterase) was found in the walls of these active vascular segments, and microapplication of atropine resulted in a considerable decrease of their dilatation. These experimental results indicate the involvement of the cholinergic neurogenic mechanism in the functional vasodilatation, as distinct from the largely accepted effect of the humoral mechanism accomplished by diffusion of active vasodilatory substances from tissue elements to the walls of the feeding arterial branches.