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. Noxious stimuli do not determine reflexcardiorespiratory effects in anesthetized rabbits. J. Appl. Physiol. 81(6): 2421-2427, 1996.Themain purpose of this study is to examine whether the stimulation of anexclusively pain-sensing receptive field (dental pulp) could determinecardiorespiratory effects in animals in which the cortical integrationof the peripheral information is abolished by deep anesthesia. In 15 anesthetized (-chloralose and urethan) rabbits, low (3-Hz)- andhigh-frequency (100-Hz) electrical dental pulp stimulation wasperformed. Because this stimulation caused dynamic and static reflexcontractions of the digastric muscles leading to jaw opening[jaw-opening reflex (JOR); an indirect sign of algoceptive fiberactivation], experimentally induced direct dynamic and staticcontractions of the digastric muscle were also performed. The low- andhigh-frequency stimulation of the dental pulp determined cardiovascular[systolic arterial pressure (SAP): 21.7 ± 4.6 and 10.8 ± 4.7 mmHg, respectively] andrespiratory [pulmonary ventilation(E): 145.1 ± 44.9 and 109.3 ± 28.4 ml /min, respectively] reflexresponses similar to those observed during experimentally induceddynamic (SAP: 17.5 ± 4.2 mmHg;E: 228.0 ± 58.5 ml /min) and static (SAP: 5.8 ± 1.5 mmHg;E: 148.0 ± 75.3 ml /min) muscular contractions. The elimination ofdigastric muscular contraction (JOR) obtained by muscular paralysis didaway with the cardiovascular changes induced by dental pulpstimulation, the effectiveness of which in stimulating dental pulpreceptors has been shown by recording trigeminal-evoked potentials insix additional rabbits. The main conclusion was that, indeeply anesthetized animals, an algesic stimulus is unable to determinecardiorespiratory effects, which appear to be exclusively linked to thestimulation of ergoreceptors induced by muscular contraction.