SULFIDE-INDUCED PERTURBATIONS OF THE NEURONAL MECHANISMS CONTROLLING BREATHING IN RATS

The effects of sulfide on neonatal rat respiration were studied. Two i n vitro experimental models were utilized: the isolated brain stem-spi nal cord preparation and the medullary slice preparation containing re spiratory rhythm-generating regions from neonatal rats. Plethysmograph ic measurements of the effects of sulfide on the breathing patterns of unanesthetized neonatal rats were also made to compare the sensitivit ies of neonatal and adult rats to sulfide toxicity. In vitro, sulfide acted at sites within the ventrolateral medulla to depress the frequen cy of respiratory rhythmic discharge by similar to 50-60%. However, th e 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 sulfid e caused a dose-dependent decrease in the frequency and amplitude of b reathing 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 ra ther than, as previously hypothesized, to perturbations of cellular ox idative metabolism.