: The fundamental hypothesis guiding this proposal is that plasticity in adult respiratory control can be used to enhance respiratory function in rats that had been impaired during development. Environmental conditions during development may permanently alter the structure and/or function of neural systems. Indeed, one week or one month of hyperoxia during postnatal development causes life-long attenuation of hypoxic ventilator responses in rats, an. effect unique to development. Mature animals still retain considerable capacity for different forms of respiratory plasticity. For example, chronic intermittent (CIH) and sustained (CSH) hypoxia elicits respiratory plasticity, increasing subsequent hypoxic ventilatory responses. We propose to study the capacity for ClH-induced recovery of the hypoxic ventilatory response in adult rats exposed to prenatal hyperoxIa (one week) and the mechanisms underlying this plasticity. These experiments will enhance our understanding of developmental plasticity and the expression of respiratory plasticity in functionally impaired and unimpaired animals, and may ultimately suggest new therapies for augmenting blunted chemoreflexes.