Neural regulation of cerebral blood flow

Abstract

The brain is encased in a rigid container, the skull, and thus the total volume of cerebral blood flow (CBF) per se is maintained at a stable level within very narrow ranges. The change in regional CBF (rCBF) has been considered to be broadly attributable to the rate of glucose metabolism by regional neurons. Although autonomic nerves have been proposed to contribute to maintenance of autoregulation of the CBF, the regulation of rCBF by metabolites produced in the regional cerebral tissues has received more attention. However, the fact that most blood vessels in the brain are innervated by fibers containing noradrenaline, acetylcholine, serotonin and some peptides, indicates a functional role for these neurons in the regulation of rCBF. Recently, Alzheimer's disease has become an important research target at both the clinical and neuroscientific levels. In this disease, degeneration of cells in the basal forebrain, e.g., cholinergic neurons originating in the nucleus basalis of Meynert (NBM) and projecting to the cerebral cortex, is quite striking. However, the function of these cholinergic neurons in the cerebral cortex has remained unclear until recently. Over the last few years, new evidence concerning the role of cortical and hippocampal cholinergic fibers has accumulated and revealed a physiological vasodilative function for these cholinergic fibers. I would like to introduce recent studies on vasodilative regulation of the cerebral cortex and hippocampus by these central cholinergic nerves originating in the NBM and septal complex. I shall also briefly introduce the related subjects of vasomotor regulation in the brain by other central noradrenergic, serotonergic, and dopaminergic fibers, and also by peripheral sympathetic and parasympathetic nerves.