Recurrent inhibition in motor systems, a comparative analysis

Excitatory Motor Neurons are Local Central Pattern Generators in an Anatomically Compressed Motor Circuit for Reverse Locomotion

“…In the lobster stomatogastric ganglion, MNs, with one interneuron, constitute an oscillatory network that underlies digestive behaviors (Marder and Bucher, 2001;Selverston and Moulins, 1985). In all described locomotor CPG circuits, however, MNs are thought to provide feedbacks to the rhythm generating premotor INs (Heitler, 1978;Song et al, 2016;Szczupak, 2014). This study provides the first example of a single neuron type performing both motor and rhythm-generating roles in a circuit that underlies locomotor behaviors.…”

“…Mixed electric coupling and inhibitory chemical synapses between AB and VD allows the electrically coupled VD and PD MNs to fire out-of-phase (Marder, 1984). In the leech swimming circuit, mixed electric coupling and hyperpolarizing chemical synapses between the descending INs and MNs facilitate recurrent inhibition on the MN activity (Szczupak, 2014). In the crayfish, snail, and zebrafish ventral and spinal nerve cords (Heitler, 1978;Song et al, 2016;Staras et al, 1998), gap junctions allow MNs to retrogradely regulate the activity of premotor INs.…”

“…In vertebrates, multiple pools of spinal premotor INs instruct and coordinate the output of different MN groups (Grillner, 2006;Kiehn, 2006Kiehn, , 2016. MNs may retrogradely regulate the activity of CPG circuits, as in the crayfish and leech swimmerets 5 (Heitler, 1978;Rela and Szczupak, 2003;Szczupak, 2014), or of premotor INs, as in the C. elegans motor circuit (Liu et al, 2017) and the zebrafish spinal cord (Song et al, 2016). In all cases, manipulation of MN activity affects the activity of their input premotor INs through a mixed electric and chemical synaptic configuration (More in Discussion).…”

Graded boosting of synaptic signals by low-threshold voltage-activated calcium conductance

“…These premotor cells are linked to motoneurons by chemical and electrical synapses that form a recurrent inhibitory network (Rela and Szczupak 2003;Rodriguez et al 2009;Szczupak 2014). The NS neurons receive inhibitory inputs from motoneurons by chemical connections and, in addition, exchange information with the motoneurons via electrical connections.…”

“…NS neurons do not fire Na ϩ -dependent spikes but express an LT-VACC that is activated at around Ϫ55 mV (Rela et al 2009). These neurons are at the center of a recurrent inhibitory circuit that modulates motor output in this annelid (Szczupak 2014). There is one pair of NS neurons per leech midbody ganglion that extend broad neuritic trees in the ganglionic neuropil (see Fig.…”