Figure 1.

Experimental paradigm. A, Schematic representation of four hypothetical patterns of excitatory (red) and inhibitory (blue) synaptic input for motoneurons (gray) during rhythmic motor activity. Premotor excitatory and inhibitory interneurons may be active in-phase (reciprocal) or out-of-phase (balanced). Alternatively, only excitatory or inhibitory interneurons could provide oscillatory synaptic input to motoneurons. B, Left, Alternative activation patterns were examined with whole-cell recordings from motoneurons in an ex vivo spinal cord–carapace preparation from the adult turtle. Right, In the ex vivo preparation, mechanical stimulation of the carapace (loudspeaker) was used to induce rhythmic scratch network activity. C, A subset of the presumed motoneurons recorded from was filled with biocytin for histological verification. These neurons, recorded in the lateral part of the ventral horn, turned out to be ChAT-positive cells, i.e., motoneurons. ChAT, Choline acetyl transferase.