Fig. 1.

Quantal acceleration of late-expiratory (late-E) abdominal activity with the development of hypercapnia (increase in the CO₂ concentration in the perfusate). A, 1–4: simultaneously recoded activity of (bottom-up) phrenic (PN, red), abdominal (AbN, black), cervical vagus (cVN, green), and hypoglossal (HN, blue) nerves. Activity of each nerve is represented by 2 traces: raw recording (bottom) and integrated activity (top). A1: normocapnia (5% CO₂): late-E activity is absent in the AbN. A, 2–4: quantal acceleration of AbN activity: with the development of hypercapnia, the ratio between the AbN and PN frequencies goes through step-wise changes from 1:3 and 1:2 (A, 2 and 3, 7% CO₂) to 1:1 (A4, 10% CO₂). B: time-series representation of the entire experimental epoch with the oscillation periods in the PN (red squares) and AbN (black circles) plotted continuously versus time. The AbN late-E bursts were synchronized with the PN bursts with a ratio increasing quantally from 1:5 to 1:1. The content of CO₂ in the perfusate of this preparation was changed at times indicated by short arrows and vertical dashed lines. Large arrows indicate times corresponding to the episodes shown in A, 1–4.