Biological Sciences; Brain; Neurology; Neuroscience; 5-HT; 5-hydroxytryptamine; agonist; amphibian; antagonist; development; embryo; glutamate; glycine; interneurone; ion channel; larva; locomotion; mechanoreception; modulation; nervous system; neural network; neuropharmacology; neurotransmitter; receptor; rhythm generator; sensory neurone; serotonin; synapse

Neurobiology and development of amphibian locomotor circuitry

My research exploits the hatchling tadpole of the relatively simple model organism, Xenopus laevis. The many attractions of studying the development of locomotor activity in Xenopus tadpoles include the relative simplicity of the nervous system at early stages of development and the rapidity with which the motor pattern controlling swimming matures after hatching. Furthermore, simple electrophysiological techniques enable us to record electrical activity in immobilised animals which is analogous to that during normal swimming (termed 'fictive swimming'). Recording both motor axon discharge and from individual neurons within the cord, it becomes possible to pharmacologically investigate the individual components of the swim generating neural network.

The simplicity of the Xenopus spinal cord network provides great potential for the elucidation of more complex circuitry in higher vertebrates. Much of my work over the past decade has focused on the modulation of tadpole locomotion by the amines serotonin and noradrenaline, but more recently we have begun to investigate the likely role of nitric oxide (NO) in the nervous system. This ubiquitous gaseous signalling molecule is known to play a crucial role in the developing nervous system, but until recently, had not been directly implicated in the brain regions involved in motor control. Furthermore, NO appears to be produced by three homologous brainstem clusters in the developing motor networks of two closely related amphibian species, Xenopus laevis and Rana temporaria but, surprisingly, it plays contrasting roles in these species.

I have several years' experience working with the nervous system of crustaceans. My research focussed on the neuronal control of swimming in squat lobsters, Galathea strigosa, and walking in crayfish, Pacifastacus leniusculus. The work involved neuroanatomical, neurophysiological and neurobehavioural analyses, using the techniques of cobalt chloride staining, silver intensification, intracellular and extracellular recording, intracellular dye injection and electromyography.

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