Figure 7.

Slowed-down respiratory-like rhythm unresponsive to a low pH challenge in Phox2b E16.5 mutant embryos. A, Integrated phrenic nerve discharges (C4 int) at pH 7.4 (upper trace) and pH 7.2 (lower trace) for a Phox2b^lox/+ control embryo. B–D, Same as A for a Phox2b^27Ala/+ (B), a Phox2b^lox/lox;Lbx1^cre/+ (C), and a Phox2b^lox/lox;Egr2^cre/+ (D) mutant embryo. E, Quantification of the burst frequencies for control and mutant embryos as indicated. p values are 3 × 10⁻⁸ for the effect of lowering the pH in the controls, and 2 × 10⁻⁴ to 5 × 10⁻⁵ for the differences between burst frequencies in control and mutant preparations measured at pH 7.4. ns, p > 0.1; n, number of hindbrain preparations analyzed. The motor output of the respiratory network recorded from C4 nerve roots was substantially lower in the mutants. In contrast to the marked acceleration seen in control embryos, the frequencies of the rhythmic bursts were not changed by low pH in the mutants.