Cholinergic and electrical synapses between synergistic spinal motoneurones in the Xenopus laevis embryo.
- 15 May 1995
- journal article
- Published by Wiley in The Journal of Physiology
- Vol. 485 (1), 135-144
- https://doi.org/10.1113/jphysiol.1995.sp020718
Abstract
1. To investigate central motoneurone synapses within the spinal cord of a simple vertebrate, the Xenopus embryo, simultaneous intracellular recordings were made from fifty-five pairs of spinal motoneurones. 2. Chemical synapses were found between seventeen out of thirty-five pairs on the same side of the spinal cord. Current-evoked spikes in the presynaptic neurone led to fast depolarizing postsynaptic potentials (PSPs) in the postsynaptic neurone at latencies of 0.5-1.5 ms. The PSPs had an average amplitude of 7 mV, a rise time of 8 ms and a half-fall time of 18 ms. 3. The presynaptic motoneurone was always the more rostral of the pair. No excitatory connections were found which crossed the cord. The fast PSPs were blocked by 10 microM mecamylamine but not by 1 mM kynurenic acid, so were mediated by nicotinic acetylcholine receptors (nAChRs). These are the first unitary excitatory postsynaptic potentials (EPSPs) mediated by nAChRs recorded intracellularly within the vertebrate central nervous system. 4. Bidirectional electrical synapses were found between five pairs of motoneurones. All these pairs were on the same side of the spinal cord and less than 70 microns apart. Each neurone responded in a graded manner to either hyperpolarizing or depolarizing current injected into the other. 5. Since motoneurones are rhythmically active during swimming, both chemical and electrical synapses will add to the fast on-cycle excitation underlying spiking activity in other motoneurones. This may increase the reliability and local synchrony of synergistic motoneurone firing during locomotion.Keywords
This publication has 36 references indexed in Scilit:
- Nicotinic and muscarinic ACh receptors in rhythmically active spinal neurones in the Xenopus laevis embryo.The Journal of Physiology, 1994
- Structure of recurrent axon collaterals of frog lumbar motoneurons as revealed by intracellular HRP labellingBrain Research, 1993
- The Isolation and Identification of Spinal Neurons That Control Movement in the Xenopus EmbryoEuropean Journal of Neuroscience, 1991
- Short-lasting nicotinic and long-lasting muscarinic depolarizing responses of thalamocortical neurons to stimulation of mesopontine cholinergic nucleiJournal of Neurophysiology, 1991
- The role of Renshaw cells in locomotion: antagonism of their excitation from motor axon collaterals with intravenous mecamylamineExperimental Brain Research, 1987
- The time course of synaptic potentials evoked in cat spinal motoneurones at identified group Ia synapses.The Journal of Physiology, 1983
- 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
- Neural Control of Swimming in a VertebrateScience, 1981
- CHOHLINERGIC TRANSMISSION IN THE RECURRENT FACILITATORY PATHWAY OF THE SPINAL MOTONEURON OF THE TOADThe Japanese Journal of Physiology, 1971