Early postnatal chronic intermittent hypoxia modifies hypoxic respiratory responses and long-term phrenic facilitation in adult rats

Acute isocapnic intermittent hypoxia elicits time-dependent, serotonin-dependent enhancement of phrenic motor output in anesthetized rats (phrenic long-term facilitation, pLTF). In adult rats, pLTF is enhanced by chronic intermittent hypoxia (CIH). To test the hypothesis that early postnatal CIH induces persistent modifications of ventilation and pLTF, we exposed male Sprague-Dawley rat pups on their first day of life to a CIH profile consisting of alternating room air and 10% oxygen every 90 s for 30 days during daylight hours (RAIH) or to comparable exposures consisting of room air throughout (RARA). One month after cessation of CIH, respiratory responses were recorded using whole body plethysmography, and integrated phrenic nerve activity was recorded in urethane-anesthetized, vagotomized, paralyzed, and ventilated rats at baseline and after exposures to three 5-min hypoxic episodes [inspired O2 fraction (FiO2) = 0.11] separated by 5 min of hyperoxia (FiO2 = 0.5). RAIH rats displayed greater normoxic v...