Chapter 11 - Electrical Coupling in the Generation of Vertebrate Motor Rhythms

Abstract

Many forms of vertebrate motor activity like chewing, breathing, and locomotion are rhythmic. This requires synchronized discharges of motoneurons controlling different muscle groups in an orchestrated manner. We provide a brief review of the presence and role of electrical coupling in a few well-studied systems: the pacemaker nucleus in weakly electric fish; mesencephalic trigeminal nucleus involved in chewing rhythms; mammalian spinal motoneurons and excitatory interneurons in the Xenopus tadpole swimming circuit, brainstem circuits underlying breathing rhythm, and central respiratory chemosensitivity. Gap junctions in these systems can improve activity synchronization among coupled neurons. However, they do not appear to be essential in the intrinsic pacemaker properties. At the network level, coupling can influence rhythmogenesis by redistributing chemical synaptic potentials. Generally, the role of electrical coupling in vertebrate motor rhythms appears to be critically dependent on developmental age, with more crucial functions in the early postnatal period than in the adult.