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1 Department of Pediatrics, Laval University, Quebec, QC, Canada
* To whom correspondence should be addressed. E-mail: Richard.Kinkead{at}crsfa.ulaval.ca.
In awake animals, we recently showed that the hypoxic ventilatory response of adult male (but not female) rats previously subjected to neonatal maternal separation (NMS) is 25% greater than controls (Genest et al. J. Physiol. 2004). To begin mechanistic investigations of the effects of this neonatal stress on respiratory control development, we tested the hypothesis that in male rats, NMS enhances central integration of carotid body chemoafferent signals. Experiments were performed on two groups of adult male rats. Pups subjected to NMS were placed in a temperature controlled incubator 3h/day from P3 to P12. Control pups were undisturbed. At adulthood (8 to 10 weeks), rats were anesthetised (urethane; 1.6g/kg), paralysed, and ventilated with a hyperoxic gas mixture (FIO2 = 0.5), and phrenic nerve activity was recorded. The first series of experiments aimed to demonstrate that NMS-related enhancement of the inspiratory motor output (phrenic) response to hypoxia occurs inanesthetised animals also. In this series, rats were exposed to moderate, followed by severe isocapnic hypoxia (FIO2's = 0.12 and 0.08, respectively, 5-min each). NMS enhanced both the frequency and amplitude components of the phrenic response to hypoxia relative to controls thereby validating the use of this approach. In a second series of experiments, NMS increased the amplitude (but not the frequency) response to unilateral carotid sinus nerve stimulation (stimulation frequency range: 0.5-33 Hz). We conclude that enhancement of central integration of carotid body afferent signal contributes to the larger hypoxic ventilatory response observed in NMS rats.
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