Electrical Stimulation of Afferent Lumbar Sympathetic Nerve Impacts Cardio‐Respiratory Functions in Anesthetized Rats

Abstract

The lumbar sympathetic chains (LSC) contain post-ganglionic vasodilator and vasoconstrictor fibers that control hindlimb vascular tone. The LSC also contain dorsal root ganglion afferent fibers whose roles in cardiorespiratory status remain poorly understood. The objective of the present study was to characterize the cardiorespiratory responses elicited by electrical stimulation (ES) of a LSC in urethane-anaesthetized male Sprague-Dawley rats (n=6) instrumented to measure/calculate mean arterial blood pressure (MAP), femoral artery blood flow (FBF) and femoral vascular resistance (FVR), brachial artery blood flow (BBF), and brachial vascular resistances (BVR), upper airway pressure (UAP), diaphragmatic EMG, respiratory frequency, inspiratory (iTV) and expiratory (eTV) tidal volumes. The right LSC was identified at the level of L4-L6 and a bipolar electrode was placed for ES (5 Hz, 0.5 msec duration, 0.5 mA amplitude for 10 sec). LSC stimulation caused a distinct pattern of cardiorespiratory responses including (a) a 12% decrease in MAP, (b) 15% decrease in ipsilateral FVR, (c) a 10% decrease in BVR (all measured at the peak decrease in MAP), (d) a 15% increase in iVT, (e) a 10% increase in eVT, (f) a15% increase in respiratory frequency, and (g) a 9% increase in diaphragmatic EMG activity. The result of this study demonstrates that ES of afferent fibers within the LSC elicits an array of cardiorespiratory changes in anesthetized rats that would be consistent with preparing the rats for exercise and for flight.