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1 Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
* To whom correspondence should be addressed. E-mail: lling{at}partners.org.
Respiratory long-term facilitation (LTF) declines in middle-aged versus adult male rats. Chronic intermittent hypoxia (CIH, 5-min 11-12% O2/5-min air, 12h/night, 7 nights) enhances LTF in adult rats. However, LTF in immature rats and the effect of early CIH are unevaluated. The present study compared LTF in 1-month- and 2-month-old rats, and examined the effect of neonatal CIH (initiated at 2 days after birth) on the LTF. Ventilatory LTF, elicited by 5 (Protocol 1) or 10 (Protocol 2) episodes of poikilocapnic hypoxia (5-min 12% O2/5-min air), was measured twice by plethysmography on the same male conscious rat when they were 1-month and 2-month old. In untreated (without CIH) rats, both resting ventilation (54.7 ± 0.6 vs. 43.0 ± 0.2 ml.100g-1.min-1) and hypoxic ventilatory response (HVR: 131 ± 4% vs. 66 ± 3% above baseline) were greater in 1-month- versus 2-month-old rats. Protocol 1 elicited LTF in 1-month- (12.5 ± 1.0% above baseline) but not 2-month-old rats. Protocol 2 elicited a greater LTF in 1-month- (24.3 ± 0.8%) versus 2-month-old rats (18.2 ± 0.5%). In CIH-treated rats, Protocol 1 also elicited LTF in 1-month- (13.1 ± 1.5%) but not 2-month-old rats. Protocol 2 elicited LTF in both age groups, but LTF was enhanced by the CIH only in 1-month-old rats (28.8 ± 0.9%). These results suggest that ventilatory LTF and HVR are greater in male rats shortly before their sexual maturity and that the neonatal CIH somewhat enhances ventilatory LTF ~3 weeks after CIH, but this enhancement does not last to adulthood.
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