Fig. 1.

Activity of the phrenic nerve in eupnea (trace A) and gasping (trace B) in the mouse. Top: integrated phrenic (Phr) activity, with perfusate equilibrated with a hyperoxic gas mixture (trace A). Bottom: in expanded trace A, note incrementing pattern of discharge. Small oscillations in baseline activity represent artifacts of electrocardiogram. During the period designated by the solid horizontal bar, perfusion was terminated, and the pattern of phrenic discharge was altered to gasping. Note decrementing pattern of integrated phrenic discharge in B. On a recommencement of perfusion (top traces), phrenic discharge returned within 5 s.