Somatosympathetic reflex in a working heart-brainstem preparation of the rat

• Published in: Brain research bulletin Vol. 53; no. 1; pp. 59 - 67
• Main Authors: Potts, J.T, Spyer, K.M, Paton, J.F.R
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2000
• Subjects: Afferent Pathways - cytology; Afferent Pathways - physiology; Animals; Arrhythmia, Sinus - etiology; Arrhythmia, Sinus - physiopathology; brachial nerve; Brain Stem - cytology; Brain Stem - drug effects; Brain Stem - physiology; Cardiovascular Physiological Phenomena; Cardiovascular/respiratory regulation; Efferent Pathways - cytology; Efferent Pathways - drug effects; Efferent Pathways - physiology; Electric Stimulation; Female; Forelimb - innervation; Forelimb - physiology; Heart - innervation; Male; Mechanoreceptors - cytology; Mechanoreceptors - physiology; Muscle contraction; Muscle Contraction - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Nucleus of the solitary tract; Phrenic Nerve - physiology; Physical Conditioning, Animal - physiology; Rats; Reflex - drug effects; Reflex - physiology; Respiratory Physiological Phenomena; Somatosensory afferents; Spinal/supraspinal sensory pathways; Sympathetic Nervous System - cytology; Sympathetic Nervous System - drug effects; Sympathetic Nervous System - physiology; Cardiovascular/respiratory regulation; Nucleus of the solitary tract; Somatosensory afferents; Spinal/supraspinal sensory pathways; Muscle contraction
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/S0361-9230(00)00309-9

The purpose of the present study was to examine the cardiorespiratory responses (CR) evoked by a somatosympathetic reflex (SSR) in the working heart-brainstem preparation (WHBP). Sprague–Dawley rats (75–100 g) were anesthetized with halothane, bisected sub-diaphramatically and decerebrated pre-collicularly ( n = 15). The preparation was transferred to a recording chamber and perfused via the thoracic aorta with Ringer’s solution containing an oncotic agent (Ficoll, 1.25%). SSR was activated by electrical stimulation (5 s) of the brachial nerve (0.5–40 Hz, 1–20 V, 0.1 ms) or the forelimb (0.5–40 Hz, 5–60 V, 2 ms). Stimulation at 40 Hz significantly increased heart rate (HR, 366 ± 10 to 374 ± 9 beats/min), systemic perfusion pressure (PP, 83 ± 5 to 89 ± 6 mmHg) and phrenic nerve discharge (PND, 0.4 ± 0.1 to 1.4 ± 0.3 Hz). Ganglionic blockade with hexamethonium (300 μM) eliminated the tachycardia and pressor response but did not alter the tachypnea to forelimb stimulation ( n = 3). Transection of the brachial nerve plexus abolished the increase in PP and PND ( n = 4). This indicates that a neural reflex mediated these responses. Spinal transection (C1–C2) completely abolished all responses indicating that they were mediated via a supraspinal pathway ( n = 2). Based upon these findings, we conclude that activation of somatosensory afferent fibers in the WHBP evokes a programmed pattern of autonomic responses altering the activity-state of both the cardiovascular and respiratory systems. The WHBP provides a unique opportunity to investigate the medullary circuits and neuronal mechanisms that may be involved in coupling cardiorespiratory and somatomotor activity during locomotion/exercise.