Effects of cyanide on the neural mechanisms controlling breathing in the neonatal rat in vitro.

The effects of hydrogen cyanide (HCN) on the neural mechanisms controlling breathing were studied. Two in vitro experimental models were utilized; the brain stem-spinal cord and the medullary slice preparations isolated from neonatal rats. Cyanide, at concentrations deemed lethal in vivo (50 microM), caused a modest (< 15%) depression of the frequency and amplitude of inspiratory rhythmic discharge when added to the bathing media. Moreover, the neuronal network underlying respiratory rhythmogenesis continued to function for hours in the presence of very high concentrations of cyanide (600 microM). We hypothesize that the rapid suppression of breathing caused by cyanide in vivo is due to changes in neuronal excitability in respiratory modulating populations in the CNS rather than due to perturbations of cellular oxidative metabolism or neurons within respiratory rhythm generating centres.