Gender considerations in ventilatory and metabolic development in rats: special emphasis on the critical period.

In rats, a critical period exists around postnatal day (P) 12-13, when an imbalance between heightened inhibition and suppressed excitation led to a weakened ventilatory and metabolic response to acute hypoxia. An open question was whether the two genders follow the same or different developmental trends throughout the first 3 postnatal weeks and whether the critical period exists in one or both genders. The present large-scale, in-depth ventilatory and metabolic study was undertaken to address this question. Our data indicated that: (1) the ventilatory and metabolic rates in both normoxia and acute hypoxia were comparable between the two genders from P0 to P21; thus, gender was never significant as a main effect; and (2) the age effect was highly significant in all parameters studies for both genders, and both genders exhibited a significantly weakened response to acute hypoxia during the critical period. Thus, the two genders have comparable developmental trends, and the critical period exists in both genders in rats.