Figure 8.

Cell 257 is a dedicated interneuron. A, The morphology of cell 257, located in the posterior medial glial packet on the ventral surface. B, Dual intracellular recording of cell AE and cell 257 along with an extracellular recording from a DP nerve in a nearby segmental ganglion to determine the contraction and elongation phases of the crawling motor program. Cell 257 oscillated 180° out-of-phase with cell AE, producing high-frequency impulse bursts in the elongation phase of crawling. C, Dual intracellular recording of cell CV and cell 257, along with an extracellular recording from a DP nerve to determine the dorsal and ventral phases of the swimming motor program. Cell 257 became strongly hyperpolarized during swim episodes. C, Contraction; E, elongation; D, dorsal; V, ventral.