Figure 6. Blockade of the cation–chloride co-transporter NKCC1 increases the phase-coupling between the two sigh burst components at E18.5 but not at E16.5.

A, left, recording of preBötC activity in an E16.5 slice preparation that spontaneously generated independent small- (eupnoeic) and large-amplitude (sigh, grey dots) bursts. The arrowheads indicate the eupnoeic burst immediately preceding each large-amplitude sigh burst. Middle, superimposed large-amplitude bursts (n = 14) and averaged trace in red showing their mono-phasic waveform. Right, histograms showing the wide distribution of associated T values (from 72 bursts). B, left, in the presence of the NKCC1 blocker bumetanide (20 μm), the same preparation continued to generate large-amplitude sigh bursts that occurred independently of eupnoeic bursts. Middle, superimposed bursts (n = 15) and averaged trace (red trace, as in A) showing the still mono-phasic waveform of large-amplitude bursts (n = 74). C and D, same figure layout and description as in A and B, respectively, for an E18.5 slice preparation. At this developmental stage, bumetanide's presence facilitated the expression of bi-phasic large-amplitude bursts (green arrow indicates the initial eupnoeic-like component in the averaged red trace at middle, n = 20 bursts) that resembled typical biphasic sigh activity. The tighter phase-coupling between the large- and preceding small-amplitude components resulted in a narrower range of T value distributions (right).