Somatosympathetic reflex in a working heart-brainstem preparation of the rat.
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.
Potts
J T
JT
Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75235-9034, USA. jpotts@mednet.swmed.edu
Spyer
K M
KM
Paton
J F
JF
D000344:Afferent Pathways / Q000166:cytology / Q000502:physiology*; D000818:Animals; D001146:Arrhythmia, Sinus / Q000209:etiology / Q000503:physiopathology; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D004525:Efferent Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D005552:Forelimb / Q000294:innervation / Q000502:physiology; D006321:Heart / Q000294:innervation; D008297:Male; D008465:Mechanoreceptors / Q000166:cytology / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology; D051381:Rats; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*