Adcy3 null mice exhibit absence of chronic intermittent hypoxia (CIH)–induced augmented carotid body (CB) sensory response to hypoxia. (A) Examples of carotid body sensory nerve (CSN) response to hypoxia (medium PO₂ ∼40 mmHg) in Adcy3^+/+ and Adcy3^−/− mice treated with either room air (control = CON) or CIH. PO₂ (mmHg) in the medium irrigating CBs was measured with an O₂ electrode placed close to the CB. Action potential frequencies are integrated and presented as impulses per second (imp/s). The duration of hypoxic challenge (Hx) is denoted by black bars. (B) Average data (mean ± SEM) of CSN responses to graded hypoxia presented as stimulus-evoked minus baseline sensory nerve activity (delta impulse/s) in Adcy3^+/+ and Adcy3^−/− treated with either room air (CON) or CIH. Numbers in parentheses represent the number of CBs from n = 5-7 mice in each group. ** and *** denote P < .01 and < .001, respectively, and n.s. denotes P > .05 analyzed by 2-way ANOVA with repeated measures followed by the Holm-Sidak test. (B) Main factor effect of treatment (CON vs. CIH), P < .001; main factor effect of hypoxic levels, P < .001; interaction effect (treatment × hypoxic levels), P = .388. (C) Main factor effect of treatment (CON vs. CIH), P = .562; main factor effect of hypoxic levels, P < .001; interaction effect (treatment × hypoxic levels), P = .374.