PROTECTION OF CEREBRAL VESSELS BY SYMPATHETIC NERVES*

In the midst of continuing controversy fl-leistad and Marcus, 1978; Purves, 19781, it is difficult for the physiologist to place in perspective the role of neural mechanisms in regulation of cerebral blood flow (CBF). This tutorial will focus primarily on the role of sympathetic nerves and will attempt to support 3 major conclusions: First, cerebral vessels are extremely responsive to changes in metabolism, blood gases, and arterial pressure, but the role of sympathetic nerves is smaller and circumscribed. Se-cond, although sympathetic nerves probably have little effect on CBF under normal conditions, there is wide agreement that sym-pathetrc nerves protect cerebral vessels during acute, severe hypertension. Third, several factors appear to have contributed to different results obtained by different investigators: species dif-ferences, temporal factors, anesthesia, mode of stimulation (reflex or electrical), metabolic state, and most importantly th