Central neural organization and control of sympathetic nervous system in mammals.

The past decade has witnessed rapid progress in defining neural circuits and mechanisms in the brain, responsible for regulation of the sympathetic nerve activity and cardiovascular functions. Several groups of cardiovascular neurons in the brainstem form the fundamental neural circuits, through which reflexly and centrally initiated sympathetic responses are processed. Their interplay determines the levels of sympathetic nerve activity and vascular tone. Substantial evidence indicates that a small population of reticulospinal vasomotor neurons in the rostroventrolateral reticular nucleus of the medulla oblongata play critical and integrative roles by: 1) providing, largely by their intrinsic pacemaker activity, tonic sympathoexcitation, thus maintaining normal blood pressure and organ blood flows, 2) mediating a variety of circulatory reflexes and centrally initiated sympathetic responses thereby helping to match organ blood flow to metabolic demands, and 3) acting as intrinsic oxygen detectors which orchestrate appropriate autonomic response programs to protect the integrity of brain in response to acute hypoxia-ischemia. Elaboration of the neural mechanisms and cellular and molecular properties of these vasomotor neurons related to dynamic regulation of the cardiovascular system in normal and disease states will be of relevance to a full appreciation of their role in adaptation of the organism to its internal and external environments and to the development of strategies to fight against neurogenic cardiovascular diseases and to restore normal functions.