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

Abstract

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 microM) 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.

• Authors: J T Potts, K M Spyer, J F Paton
• Journal: Brain research bulletin (Brain Res Bull) Vol. 53 Issue 1 Pg. 59-67 (Sep 01 2000) ISSN: 0361-9230 [Print] United States
• PMID: 11033209 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Afferent Pathways (cytology, physiology)
• Animals
• Arrhythmia, Sinus (etiology, physiopathology)
• Brain Stem (cytology, drug effects, physiology)
• Cardiovascular Physiological Phenomena
• Efferent Pathways (cytology, drug effects, physiology)
• Electric Stimulation
• Female
• Forelimb (innervation, physiology)
• Heart (innervation)
• Male
• Mechanoreceptors (cytology, physiology)
• Muscle Contraction (physiology)
• Muscle, Skeletal (innervation, physiology)
• Phrenic Nerve (physiology)
• Physical Conditioning, Animal (physiology)
• Rats
• Reflex (drug effects, physiology)
• Respiratory Physiological Phenomena
• Sympathetic Nervous System (cytology, drug effects, physiology)