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Anesth Analg 1999;89:721
© 1999 International Anesthesia Research Society

REGIONAL ANESTHESIA AND PAIN MANAGEMENT

The Effect of Spinal Analgesia on Visceral Nociceptive Neurons in Caudal Medulla of the Rat

T. J. Ness, MD, PhD*, J. G. Piper, MD{dagger}, and K. A. Follett, MD, PhD{dagger}

*Department of Anesthesiology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama; and {dagger}Division Neurosurgery, University of Iowa College of Medicine, Iowa City, Iowa

Address correspondence and reprint requests to Dr. Timothy J. Ness, Department of Anesthesiology, University of Alabama at Birmingham, 619 19th St., South, ZRB 940, Birmingham, AL 35233. Address e-mail to Tim.Ness{at}ccc.uab.edu

A population of neurons resident in the caudal ventrolateral medulla are excited by noxious cutaneous and visceral stimuli from large portions of the body. These neurons act as monitors of ascending nociceptive information, and we hypothesized that they would be inhibited by spinally administered analgesics in a clinically relevant fashion. Rats were anesthetized with oxygen/halothane. The caudal medulla was surgically exposed, and a catheter placed into the intrathecal space overlying the lower thoracic spinal cord via the surgical site. Single medullary neurons were characterized for responses to cutaneous and visceral (colorectal distension) stimuli. The effects of IV and intrathecally administered morphine and lidocaine were determined. The intrathecal infusion of morphine for 6 days before testing was also used as a pretreatment. Colorectal distension-evoked responses of medullary nociceptive neurons were inhibited in a dose-dependent, naloxone-reversible fashion by intrathecal and IV morphine (50% effective dose values: 3.5 and 440 µg/kg, respectively). Intrathecal lidocaine abolished responses to colorectal distension and produced a spinal level at doses producing minimal effects when administered systemically. Prior treatment with an infusion of morphine produced tolerance to the effects of subsequent intrathecal morphine administration. These findings support the use of this preparation as a neurophysiologic model of spinal analgesia.

Implications: Neurons in the brainstem, isolated electrophysiologically, were used as whole body monitors of pain-related activity in the rat. As a neurophysiologic model of nociception, this preparation may prove useful for the study of regionally administered analgesics and local anesthetics.






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 1999 by the International Anesthesia Research Society.