The development and neuromodulation of motor control systems in pro-metamorphic Xenopus laevis frog tadpoles
Year: 2014
Type: dissertation
Abstract: My thesis has accomplished 3 significant contributions to neuroscience. Firstly, I \nhave discovered a novel example of vertebrate deep-brain photoreception. \nSpontaneously generated fictive locomotion from the isolated nervous system of \npro-metamorphic Xenopus tadpoles is sensitive to the ambient light conditions, \ndespite input from the classical photoreceptive tissues of the retina and pineal \ncomplex being absent. The photosensitivity is found to be tuned to short \nwavelength UV light and is localised to a small region of the caudal diencephalon. \nWithin this region, I have discovered a population of neurons immuno-positive for \na UV-specific opsin protein, suggesting they are the means of phototransduction. \nThis may be a hitherto overlooked mechanism linking environmental luminance to \nmotor behaviour. Secondly, I have advanced the collective knowledge of how both \nnitric oxide and dopamine contribute to neuromodulation within motor control \nsystems. Nitric oxide is shown to have an excitatory effect on the occurrence of \nspontaneous locomotor activity, representing a switch in its role from earlier in \nXenopus development. Moreover, this excitatory effect is found to be mediated in \nthe brainstem despite nitric oxide being shown to depolarise spinal neurons. \nThirdly, I have developed a new preparation for patch-clamp recording in pro-metamorphic Xenopus tadpoles. My data suggest there are several changes to the \ncellular properties of neurons in the older animals compared with the embryonic \ntadpole; there appears to be an addition of Ih and K[sub](Ca) channels and the presence \nof tonically active and intrinsically rhythmogenic neurons. In addition, I have \nshown that at low doses dopamine acts via D2-like to hyperpolarise the membrane \npotential of spinal neurons, while at higher doses dopamine depolarises spinal \nneurons. These initial data corroborate previously reported evidence that \ndopamine has opposing effects on motor output via differential activation of \ndopamine receptor subtypes in Xenopus tadpoles.
Author: Stephen P. Currie
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2585388499