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Roles of Glycinergic Inhibition and N‐Methyl‐D‐Aspartate Receptor Mediated Excitation in the Locomotor Rhythmicity of One Half of the Xenopus Embryo Central Nervous System
Author(s) -
Soffe S. R.
Publication year - 1989
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1989.tb00363.x
Subject(s) - hindbrain , strychnine , neuroscience , xenopus , glycine receptor , bicuculline , nmda receptor , spinal cord , reciprocal inhibition , biology , central pattern generator , extracellular , inhibitory postsynaptic potential , central nervous system , rhythm , anatomy , receptor , medicine , microbiology and biotechnology , gabaa receptor , glycine , biochemistry , amino acid , gene
Recent investigations into the neural basis for swimming in Xenopus embryos have pointed to central roles played by N‐methyl‐D‐aspartate (NMDA) receptor‐mediated excitation acting within and glycinergic reciprocal inhibition acting between motor systems for the muscular antagonists on the two sides of the CNS. A ‘reduced’ preparation consisting of only one half of the CNS divided sagittally along its midline is used here to examine the basis for rhythmicity within each side in the absence of reciprocal connections. Divided preparations transected rostrally at levels between the otic capsule and the obex can all generate a rhythmic pattern of motor discharge similar to that which underlies swimming. All rhythm generation is blocked by the NMDA antagonist (+/ ‐)‐2‐amino‐5‐phosphonovaleric acid (APS) at 20 μM. However, neither glycinergic nor GABAergic inhibition is required for a basic rhythmicity since some rhythm persists in the presence of 10 μM strychnine and 50 μM bicuculline, though it is no longer sustained. In the divided spinal cord alone, rhythm generation requires extracellular Mg 2+ . If the most caudal segment of the divided hindbrain is left attached, extracellular Mg 2+ is required only if strychnine is present. If more of the hindbrain is included, extracellular Mg 2+ is no longer necessary for rhythm generation even in the presence of strychnine. It seems that rhythm generation by a single side of the spinal cord requires NMDA receptor‐mediated excitation together with the voltage dependency conferred on it by extracellular Mg 2+ , but not inhibition in order to occur. As more of the hindbrain is left attached, the requirement for extracellular Mg 2+ becomes progressively less strong. For sustained rhythm generation, one side of the CMS requires both excitation and glycinergic inhibition.