CHARACTERIZATION AND DEVELOPMENTAL ASPECTS OF ANOXIA-INDUCED GASPING IN THE RAT

With increasing postnatal age, mammals display diminished tolerances f or prolonged exposures to severe oxygen deprivation. Similarly, durati on and efficiency of gasping, a unique mechanism for enhancing surviva l after anoxia-induced apnea, are also affected by postnatal age. We h ypothesized that maturational patterns of anoxia-induced gasping may e ncompass more than a single monophasic phenomenon. Each of the putativ e phases of the gasping response may underlie unique characteristics w hich could be of relevance to survival capability. To study these issu es, adult rats and rat pups at 2-3, 5, 10, 15, and 25 days of age unde rwent anoxic exposures with 100% N-2 in a barometric chamber. In pups aged <25 days but not thereafter, following an age-dependent period of central apnea, an initial gasping phase characterized by vigorous and frequent periodic bursts of a large inspiratory effort preceded and f ollowed by expiration excursions emerged (phase I). This phase was fol lowed by a period of relative respiratory silence of variable duration with occasional, interspersed phase I-like gasps (phase II). Finally, a third phase easily recognized by the onset of frequent inspiratory- only gasping efforts developed (phase III). The amplitude of phase III inspiratory gasps progressively diminished until their complete cessa tion. Although overlap between gasping phases was present, a marked ag e dependency in both duration and gasping frequency within each phase occurred. We conclude that anoxia-induced gasping responses in rat pup s <25 days old are triphasic in nature, exhibit defined phase-locked p eriodicities and respiratory effort patterns, and undergo significant maturation.