Central Noradrenergic Regulation of Brain Microcirculation
Earlier studies, as well as anatomical findings of others, led to the development of a working hypothesis that the central noradrenergic system is analogous to the peripheral sympathetic system except that it is specialized, in part, for performing specific functions related to brain microvasculature. This hypothesis has been tested in adult rhesus monkeys with chronic bilateral superior cervical ganglionectomies in whom stereotaxically placed cannulae were permanently located in the locus coeruleus for electrical stimulation using concentric bipolar electrodes passed through the cannulae. Cerebral blood flow and brain permeability for water (H2 15O) were simultaneously measured as previously described. The results demonstrated that electrical stimulation of the locus coeruleus produced a prompt increase in brain water permeability and a reduction of cerebral blood flow. Transient increase in water permeability and a decrease in cerebral blood flow was also induced by intracarotid infusion of hypertonic urea. Neurally mediated mechanism for regulation of brain water permeability is proposed which would account for changes in permeability induced by electrical stimulation and by mechanical distortion.
KeywordsCerebral Blood Flow Tight Junction Locus Coeruleus Superior Cervical Ganglion Diffusible Tracer
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