BEHAVIOR-DEPENDENT ACTIVITIES OF A CENTRAL PATTERN GENERATOR IN FREELY BEHAVING LYMNAEA-STAGNALIS

Cyclic or repeated movements are thought to be driven by networks of n eurons (central pattern generators) that are dynamic in their connecti vity. During two unrelated behaviors (feeding and egg laying), we inve stigated the behavioral output of the buccal pattern generator as well as the electrical activity of a pair of identified interneurons that have been shown to be involved in setting the level of activity of thi s pattern generator (PG). Analysis of the quantile plots of the parame ters that describe the behavior (movements of the buccal mass) reveals that during egg laying, the behavioral output of the PG is different compared with that during feeding. Comparison of the average durations of the different parts of the buccal movements showed that during egg laying, the duration of one specific part of buccal movement is incre ased. Correlated with these changes in the behavioral output of the PG were changes in the firing rate of the cerebral giant neurons (CGC), a pair of interneurons that have been shown to modulate the activity o f the PG by means of multiple synaptic contacts with neurons in the bu ccal ganglion. Interval-and autocorrelation histograms of the behavior al output and CGC spiking show that both the PG output and the spiking properties of the CGCs are different when comparing egg-laying animal s with feeding animals. Analysis of the timing relations between the C GCs and the behavioral output of the PG showed that both during feedin g and egg laying, the electrical activity of the CGCs is largely in ph ase with the PG output, although small changes occur. We discuss how t hese results lead to specific predictions about the kinds of changes t hat are likely to occur when the animal switches the PG from feeding t o egg laying and how the hormones that cause egg laying are Likely to be involved.