Potentiation of the hypoxic ventilatory response by one day of hyperoxia in neonatal rats

The O 2 sensitivity of the neonatal rat carotid body is increased after one day in moderate hyperoxia (60% O 2 ) (Donnelly et al., Respir. Physiol. Neurobiol. 168: 189–197, 2009). We investigated whether this enhanced peripheral chemosensitivity increases the hypoxic ventilatory response (HVR) and tested the hypothesis that this plasticity is mediated by the superoxide anion. Neonatal rats (7 d old) were injected with saline or MnTMPyP, a superoxide scavenger, and placed into 60% O 2 for 23–28 h. Baseline ventilation was reduced and the acute HVR (12% O 2 ) was enhanced in hyperoxia-treated rats relative to age-matched controls; MnTMPyP did not block these effects. An additional group of rats was studied after only 30 min in 60% O 2 . This shorter exposure had no effect on normoxic ventilation or the HVR. We conclude that 1 d, but not 30 min, of 60% O 2 augments the HVR of neonatal rats and that production of the superoxide anion does not contribute to this plasticity.