THE PRESSOR REFLEX EVOKED BY STATIC CONTRACTION - NEUROCHEMISTRY AT THE SITE OF THE FIRST SYNAPSE

Stimulation of somatic sensory neurons activates the sympathetic nervo us system, in turn enhancing cardiovascular function. This has been re peatedly demonstrated when afferent fibers arising from skeletal muscl e serve as the sensory neurons. Over the past several years, studies h ave been performed examining the central nervous system (CNS) mechanis ms that cause the reflex increases in arterial blood pressure and hear t rate when skeletal muscle contracts. These studies have provided ins ights into how the CNS alters cardiovascular function, and have helped to enhance our understanding of central sensory transduction processe s. Using a variety of techniques, several sites have been identified w ithin the brain and spinal cord that are responsible for producing the reflex presser response to static contraction. However, the purpose o f this manuscript is to review the recent developments concerning only one CNS site: the dorsal horn of the spinal cord. This region serves as the first synapse for afferent fibers from skeletal muscle. The rel ease of neurotransmitters, and possibly neuromodulators, into this reg ion initiates the CNS component of this reflex. In addition, the magni tude of the reflex cardiovascular changes can be modulated at this sit e. The studies described in this review suggest that the dorsal horn o f the spinal cord serves as an important site of integration for senso ry signals that influence the cardiovascular system.