Figure 5.

In whole isolated nerve cords, sucrose blockade of cephalic descending signals abolishes the posterior-directed intersegmental coordination of the DA-biased crawl oscillators. A, The number of preparations that stopped crawling (SC) and those that had altered coordination during the sucrose block. B, DP recordings of fictive crawling in two adjacent segments prior to the block (Pre-Block) and during it (Blocked). Intersegmental delays (ISDs) were altered during cephalic blockade and intersegmental phase advances (asterisks) were became evident (note: rare in controls). C, DP nerve activity from 3 segments showed robust and coordinated fictive crawling in Pre-Block (left). Shortly after blocking descending inputs (Blocked, right traces), uncoordinated DE-3 bursting emerged; this preparation exemplifies those with variable periods. D, Boxplots (black = Pre-Block; white = Blocked) summarizing changes in DE-3 intersegmental phase delays for preparations showing no significant change in cycle period (n = 9, labeled i.-ix.). Plus symbols denote outlier data points. E, Fictive crawl periods obtained from 3 segmental oscillators plotted over successive cycles in Pre-Block and again when cephalic inputs were removed (Blocked) (n = 3 whole nerve cord preparations labeled i.-iii.). Prior to the block (plots at left), the outputs from all 3 oscillators exhibited the same period. During the blockade (plots at right) periods were no longer stable and varied across all 3 segments. Data for cycle periods during the block were obtained within the following time windows: 74 s (i), 158 s (ii) and 381 s (iii); thus some cycles have only 1 or 2 symbols shown.