Effect of CIH on carotid body responses to graded hypoxia in neonates and adults. A, top: average data of the carotid body response to graded hypoxia from rat pups conditioned with 720 episodes of CIH (closed box) and age-matched control pups (open box). A, bottom: similar data in adult rats conditioned with 720 episodes of CIH (closed box) and normoxic controls (open box). Medium PCO2 was kept at 35–36 mmHg in both groups. B: average data of hypoxic sensory response (medium PO2 = 35 ± 3 mmHg) presented as percentage of age-matched controls in neonatal rat pups and adult rats exposed to 720 episodes of CIH. Data presented are means ± SE from 7 carotid bodies from 7 rats in each group, respectively. *P < 0.05, **P < 0.005, CIH vs. control.