Figure 2.

Boundaries and burst properties in 3 mm K⁺ of thin m-preBötC slices. A, Plot of the rostrocaudal boundaries of eight m-preBötC[250/−0.65]W-P0/1 slices, six m-preBötC[200/−0.63]W-P0 slices, and seven m-preBötC[175/−0.63]W-P0 slices versus the longevity of inspiratory-related bursting. The mean (±SEM) of the longevities of rhythms in the 250- and 200-μm-thin slices are indicated by the squares. The gray box represents the region common to the rhythmic slices. Note that five of seven m-preBötC[175] slices with boundaries similar to those of the two rhythmic slices did not show rhythm. In contrast, the boundaries of six nonrhythmic m-preBötC[250] slices deviated notably from those of the rhythmic slices of this type. B, A m-preBötC[250/−0.65]W-P1 slice showed bilaterally synchronous robust bursts with a pattern resembling the eupnea–sigh pattern (although with very-small-amplitude eupneic bursts) in thicker slices (compare supplemental Fig. S1, available at www.jneurosci.org as supplemental material). This rhythm was stable for >90 min, before it stopped spontaneously (in vitro apnea) shortly after 120 min. Sighs and smaller-amplitude eupneic bursts were activated by 6 mm K⁺, whereas SP, after return to 3 mm K⁺ solution, evoked primarily sighs. C, A m-preBötC[250/−0.65]W-P1 slice generated bilaterally synchronous bursts resembling the eupnea–sigh pattern in thicker slices (supplemental Figs. S1,S3, available at www.jneurosci.org as supplemental material). The burst pattern became more irregular after >60 min, partly because of disappearance of the eupneic bursts, but rhythm persisted for an additional 106 min, before rhythm stopped. A 6 mm K⁺ solution reactivated both sighs and eupneic bursts, whereas SP elicited sighs and intermittent very-small-amplitude eupneic bursts. D, After in vitro apnea after 113 min in a m-preBötC[250/−0.68]W-P1 slice, TRH evoked a regular pattern of eupneic bursts, whereas subsequent application after washout of TRH of the NK1 receptor agonist GR73632 evoked sighs at rather low-rate and intermittent very-small-amplitude eupneic bursts. E, Twenty minutes after the start of the recording, bilaterally synchronous bursting in the m-preBötC[200/−0.60]W-P0 slice of Figure 1B reached a maximal amplitude. Burst amplitude decreased, and rate slowed after 63 min to 2 bursts/min and remained at that level for an additional 80 min before rhythm stopped. Synchronous bursting of sighs and unilateral eupneic bursts were reactivated by 6 mm K⁺, whereas the addition of 2.5 mm theophylline to 6 mm K⁺ solution resulted in a faster rhythm with a eupnea pattern.