Xenopus frog metamorphosis: A model for studying locomotor network development and neuromodulation
Neural Control of Movement: Model Systems for Examining Motor Function; Ed. P. Whelan; Academic Press/Elsevier. 2020-08; : 175-203
Frog metamorphosis includes a complete switch in the animal’s locomotor strategy from larval undulatory, tail-based swimming to rhythmic hindlimb-kick propulsion in the young adult. At critical stages during this dramatic behavioral transition, both locomotor systems are present and functional, implying a progressive and dynamic remodeling of underlying spinal motor circuitry as limbs are added and the tail regresses. This process thus provides an attractive model for studying mechanisms of neural network assembly/disassembly during locomotor system development. Novel insights have been facilitated by the deployment of isolated brainstem/spinal cord preparations from the frog Xenopus, in vitro preparations that spontaneously generate the motor output rhythms driving swimming in vivo. As in vertebrates generally, the spinal locomotor circuits of Xenopus are potently modulated by biogenic amines and nitric oxide. This chapter reviews current knowledge on metamorphosis and the contrasting and changing roles of neuromodulators, both in the immediate adaptive control of axial and limb network output and in long-term circuit development.