An Electrophysiological Experimental Study on the Spontaneous Sympathetic Nerve Activity in the Rostral Ventrolateral Medulla Oblongata

Abstract

The sympathetic postganglionic nerve fibers, which are controlled by preganglionic fibers originating from  specific nuclei in the medulla oblongata, and the thoracic and upper lumbar segments of the spinal cord,  together with the local autoregulatory mechanisms and circulating hormones, directly influence the cardiovascular  function. Recently, the studies on the sympathetic preganglionic fibers have remarkably progressed,  and the anatomical (Strack et al., 1988), functional (Janig, 1985), and chemical (Krukoff, 1985)  characteristics of the synaptic input have been clarified. However, the peripheral sympathetic nerve activities  vary depending on the organs concerned (including the skin, muscle, or internal organs) as they have  their own physiological characteristics (Janig and McLachlan, 1986) including the response pattern to the  peripheral receptor stimulation. Many areas, including the histological and functional roles of the peripheral  part, nerve centers, and central pathway of the circulatory system, are still unknown. 

The peripheral sympathetic nerve activities in humans consist of the skin sympathetic activity (SSA) that  controls the sweat glands / skin vasomotion, and the muscle sympathetic activity (MSA) that controls the  vascular smooth muscles in the skeletal muscles, and each activity has different characteristics. SSA  involving regulation of the body temperature and MSA involving regulation of the blood pressure can be  separately recorded (Burke et al., 1977; Hagbarth et al., 1975; Vallbo et al., 1979; Wallin and Eckberg,  1982; Yatomi et al., 1989) from the sympathetic postganglionic efferent fibers by microneurography  (Hagbarth et al., 1972). 

By recording and comparing the action patterns and responses to stimulations of the premotor nuclei, along  with other vital rhythms, we hoped to clarify the complex mechanism of the sympathetic nerve activities  and to contribute in the treatment of disorders resulting from sympathetic dysfunction. We also report our  findings on the premotor nuclei that produce sympathetic preganglionic fiber activities by using topographic  mapping analysis of the changes in the central action potentials in the rostral ventrolateral medulla  oblongata (RVLM) region to visually capture the complicated action patterns to compare the cross correlations  with MSA and SSA using microneurography and ECG.