APStracts 3:0380A, 1996.

Noxious stimuli do not determine reflex cardiorespiratory effects in anesthetized rabbits. Raimondi, G., J. M. Legramante, F. Iellamo, G. Frisardi, S. Cassarino, and G. Peruzzi. Dipartimento di Medicina Interna, Cattedra di Fisiopatologia Medica, Universita' di Roma "Tor Vergata", Roma 00173, ITALY

APStracts 3:0380A, 1996.

The main purpose of this study is to examine whether the stimulation of an exclusively pain sensing receptive field (dental pulp) could determine cardiorespiratory effects in animals in which the cortical integration of the peripheral information is abolished by deep anesthesia. In 15 anesthetized (chloralose and urethane) rabbits low (3 Hz) and high frequency (100 Hz) electrical dental pulp stimulation were performed. Since this stimulation caused dynamic and static reflex contractions of the digastric muscles leading to jaw opening [jaw opening reflex (JOR), an indirect sign of algoceptive fiber activation], also experimentally induced direct dynamic and static contractions of the digastric muscle were performed. The low and high frequency stimulation of the dental pulp determined cardiovascular (SAP: -21.7 +/- 4.6 and +10.8 +/- 4.7 mmHg, respectively) and respiratory (VE: +145.1 +/- 44.9 and +109.3 +/- 28.4 ml/min, respectively) reflex responses similar to those observed during experimentally induced dynamic (SAP: -17.5 +/- 4.2 mmHg; VE: +228.0 +/- 58.5 ml/min) and static (SAP: +5.8 +/- 1.5 mmHg; VE: +148.0 +/- 75.3 ml/min) muscular contractions. The elimination of digastric muscular contraction (JOR) obtained by muscular paralysis did away with the cardiovascular changes induced by dental pulp stimulation, whose effectiveness in stimulating dental pulp receptors has been shown by recording trigeminal evoked potentials in six additional rabbits. The main conclusion was that in deeply anesthetized animals an algesic stimulus is unable to determine cardiorespiratory effects which appear to be exclusively linked to the stimulation of ergoreceptors induced by muscular contraction.

Received 28 December 1995; accepted in final form 19 July 1996.
APS Manuscript Number A1359-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996