Journal of Applied Physiology, Vol 78, Issue 2 433-440, Copyright © 1995 by American Physiological Society
Sulfide-induced perturbations of the neuronal mechanisms controlling breathing in rats
J. J. Greer, R. J. Reiffenstein, A. F. Almeida and J. E. Carter
Department of Physiology, University of Alberta, Edmonton, Canada.
The effects of sulfide on neonatal rat respiration were studied. Two in
vitro experimental models were utilized: the isolated brain stem-spinal
cord preparation and the medullary slice preparation containing respiratory
rhythm-generating regions from neonatal rats. Plethysmographic measurements
of the effects of sulfide on the breathing patterns of unanesthetized
neonatal rats were also made to compare the sensitivities of neonatal and
adult rats to sulfide toxicity. In vitro, sulfide acted at sites within the
ventrolateral medulla to depress the frequency of respiratory rhythmic
discharge by approximately 50-60%. However, the neuronal network underlying
respiratory rhythmogenesis continued to function in the presence of
concentrations of sulfide far beyond those deemed to be lethal in vivo.
Intraperitoneal administration of sulfide caused a dose-dependent decrease
in the frequency and amplitude of breathing of neonatal rats of all ages
(0-19 days postnatal), although the sensitivity to sulfide increased with
age. We hypothesize that the rapid suppression of breathing caused by
sulfide is due to changes in neuronal excitability within respiratory
rhythm-generating centers rather than, as previously hypothesized, to
perturbations of cellular oxidative metabolism.
