Medullary Raphe Neurons in Autonomic Regulation

Abstract

The medullary raphe nuclei send both serotonergic and non-serotonergic projections to innervate spinal cord and brain stem targets, including sympathetic and parasympathetic preganglionic neurons in the spinal intermediolateral nucleus and dorsal motor nucleus, respectively. The recent discovery of retrogradely infected neurons within the medullary raphe following pseudorabies virus injections into a variety of autonomically-innervated tissues indicate s the extensive influence of the medullary raphe on visceral function and homeostasis. This review summarizes our current understanding of the role of medullary raphe neurons in the regulation of arterial pressure and heart rate and in the control of body temperature, sexual function, insulin secretion and gastric motility and acid secretion. Many of these findings suggest that medullary raphe neurons function as autonomic premotor neurons, influenc ing the discharge of preganglioni c neurons in functionally-specific reflex and central command pathways. Future research will provide insight into the integration of these medullary raphe neurons within the hierarchical control structu re of specific autonomic functions and within the raphe-spinal pathways influencing somatic motor control, respiration and pain modulation.