Effects of sevoflurane on respiratory rhythm oscillators in the medulla oblongata

Using in vitro newborn rat brainstem-spinal cord preparations with and without the parafacial respiratory group (pFRG), we examined the effects of the volatile anaesthetic sevoflurane on the respiratory rhythm oscillators of the pFRG and the preBötzinger complex (preBötC). Our study indicated that sevoflurane depressed pre-inspiratory neurons (Pre-Is) in the pFRG via gamma-aminobutyric acid-A (GABA(A))ergic and glycinergic inhibition and that it depressed preBötC inspiratory neurons via GABA(A)ergic but not via glycinergic inhibition. We also found that sevoflurane had stimulant effects on the respiratory rhythm oscillators. Our results shed light on respiratory rhythm generation. In all preparations (n=16) in which Pre-Is activity was recorded, inspiratory-related cervical motor output remained after application of 0.47 mM sevoflurane, despite the disappearance of the burst activity of Pre-Is. This finding shows that Pre-Is are not essential for respiratory rhythm generation and suggests that sevoflurane, when applied at a proper concentration, might offer a pharmacological means to eliminate pFRG function while preserving preBötC activity.