CONICET | Buscador de Institutos y Recursos Humanos

Coupling among leech motoneurons The leech has four types of muscles implicated in the movement: the longitudinal, the circular, the dorsoventral and the oblique muscles (lm, cm, dvm & om). Contractions of each of these muscles produce characteristic movements. All these muscles are innervated by a set of excitatory and inhibitory motoneurons. These motoneurons innervate one type of muscles and region (dorsal, lateral or ventral) of one side (left-right). The lm of one side are innervated by seven motoneurons. Among the excitatory ones the dorsal excitor 3 (MNDE-3) innervates the dorsal lm, the L motoneuron (MNL) innervates all the lm, and the ventral excitor 4 (MNVE-4) innervates the ventral lm. Recently we have shown that the MNL and the MNDE-3 were coupled by a rectifying gap junction: the depolarizations passed from one to the other while the hyperpolarizations passed from MNDE-3 to L and almost nothing from MNL to MNDE-3. We have tried to reveal the electrophysiological coupling among the MNDE-3 and the MNL using the Neurobiotin tracer (Vector Labs) that pass through the gap junctions, and a fluorophore conjugated to a dextran that cannot pass through it. The experiments unfulfilled the original purpose. We have also studied the coupling among MNVE-4 and MNDE-3 by intracellular recordings. The experiments of coupling among MNVE-4 and MNDE-3 have shown that there is coupling among them although there is a low one. This low coupling, however, can change the firing of the postsynaptic cell while injecting current in the presynaptic one. This coupling among ventral and dorsal motoneurons is consistent with the previous results from the lab: there is an extensive low coupling between motoneurons that is unmasked when the polysynaptic effect is abolished.