Active and Passive Membrane Properties of Spinal Cord Neurons that Are Rhythmically Active during Swimming in Xenopus Embryos
- 1 January 1990
- journal article
- research article
- Published by Wiley in European Journal of Neuroscience
- Vol. 2 (1), 1-10
- https://doi.org/10.1111/j.1460-9568.1990.tb00376.x
Abstract
Cellular properties have been examined in ventrally located Xenopus spinal cord neurons that are rhythmically active during fictive swimming and presumed to be motoneurons. Resting potentials and input resistances of such neurons are -75 .+-. 2 mV (mean .+-. standard error) and 118 .+-. 17 M.OMEGA. respectively. Most cells fire a single impulse, 0.5 to 2.0 ms in duration and 48.5 .+-. 1.8 mV in amplitude, in response to a depolarizing current step. A minority fire several spikes of diminishing amplitude to more strongly depolarizing current. Cells held above spike, threshold fire on rebound from brief hyperpolarizing pulses. Spikes are blocked by 0.1 to 1.0 .mu.M tetrodotoxin (TTX) and are therefore Na+-dependent. Current/voltage (I/V) plots to injected current are approximately linear near the resting potential but become non-linear at more depolarized levels. Cells recorded in TTX with CsCl-filled microelectrodes show a linearized I/V plot at depolarized membrane potentials suggesting the normal presence of a voltage-dependent K+ conductance activated at relatively depolarized levels. Most cells recorded in this way but without TTX fire long trains of spikes of near constant amplitude, pointing to a role of the K+ conductance in limiting firing in normal cells. Spike blockage with TTX reveals, in some cells, a transient depolarizing Cd2+-sensitive and therefore presumably Ca2+-dependent potential that increases in amplitude with depolarization. Cells in TTX, Cd2+, and strychnine, and recorded with CsCl-filled microelectrodes to block active conductances respond to hyperpolarizing current steps with a two component exponential response. The cell time constant (.tau.0) obtained from the longer of these exponential peeling is relatively long (mean 15.7 ms). These findings contribute to an increased understanding of the cellular properties involved in spinal rhythm generation in this simple vertebrate.Keywords
This publication has 37 references indexed in Scilit:
- Mutual Re‐excitation with Post‐Inhibitory Rebound: A Simulation Study on the Mechanisms for Locomotor Rhythm Generation in the Spinal Cord of Xenopus EmbryosEuropean Journal of Neuroscience, 1990
- Response properties of motoneurones in a slice preparation of the turtle spinal cord.The Journal of Physiology, 1988
- The neuroanatomy of an amphibian embryo spinal cordPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1982
- Intracellular recordings from spinal neurons during ‘swimming’ in paralysed amphibian embryosPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1982
- Firing Behaviour of a Neurone Model Based on the Afterhyperpolarization Conductance Time Course and Algebraical Summation. Adaptation and Steady State FiringActa Physiologica Scandinavica, 1974
- Firing Behaviour of a Neurone Model Based on the Afterhyperpolarization Conductance Time Course. First Interval FiringActa Physiologica Scandinavica, 1974
- Repetitive Impulse Firing: Comparisons between Neurone Models Based on ‘Voltage Clamp Equations' and Spinal MotoneuronesActa Physiologica Scandinavica, 1973
- Some Electrical Measurements of Motoneuron ParametersBiophysical Journal, 1970
- Time Constants and Electrotonic Length of Membrane Cylinders and NeuronsBiophysical Journal, 1969
- ANODAL BREAK RESPONSE OF SINGLE MOTONEURON IN TOAD'S SPINAL CORDThe Japanese Journal of Physiology, 1962