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Ionic and pharmacological properties of reciprocal inhibition in Xenopus embryo motoneurones.
Author(s) -
Soffe S R
Publication year - 1987
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1987.sp016378
Subject(s) - strychnine , bicuculline , picrotoxin , xenopus , depolarization , gaba receptor antagonist , inhibitory postsynaptic potential , reversal potential , chemistry , hyperpolarization (physics) , biophysics , intracellular , glycine , electrophysiology , medicine , gabaa receptor , endocrinology , biology , biochemistry , neuroscience , patch clamp , stereochemistry , amino acid , receptor , nuclear magnetic resonance spectroscopy , gene
1. Properties of rhythmic, compound mid‐cycle inhibitory post‐synaptic potentials (i.p.s.p.s), which constitute one of the three main synaptic drives to motoneurones during fictive swimming in Xenopus embryos, have been examined using ionic and pharmacological manipulation. 2. Mid‐cycle i.p.s.p.s are Cl‐ dependent. They are reversed by intracellular Cl‐ injection and attenuated by lowered extracellular Cl‐ concentration. 3. In response to bath application of 100 microM‐glycine or 100 microM‐gamma‐aminobutyric acid (GABA), motoneurones show a decrease in cell input resistance of 24 +/‐ 2.9 M omega (mean +/‐ S.E. of mean) or 16 +/‐ 3.7% and 26 +/‐ 6.0 M omega or 14 +/‐ 2.0% respectively. This is associated with a weak hyperpolarization or depolarization of 0 +/‐ 1.5 mV and ‐3 +/‐ 1.4 mV respectively. Both responses can be made strongly depolarizing by intracellular Cl‐ injection. 4. The response to glycine is blocked by 1 microM‐strychnine but is largely unaffected by bicuculline below 50 microM. The response to GABA is largely blocked by 10 microM‐bicuculline but is unaffected by 1 microM‐strychnine. Both strychnine and bicuculline are therefore specific antagonists in the amphibian embryo preparation. Glycine and GABA are both partially antagonized by 10 microM‐picrotoxin. 5. Mid‐cycle i.p.s.p.s recorded in motoneurones during fictive swimming are reduced in amplitude by 0.5‐1 microM‐strychnine but are largely unaffected by 40 microM‐bicuculline. In embryos immobilized by ventral root transection, 100 microM‐tubocurarine, a likely GABA antagonist in the embryo, has no effect on mid‐cycle inhibition. Glycine is suggested to be the probable transmitter released by commissural interneurones and mediating mid‐cycle inhibition during fictive swimming, acting to increase conductance of Cl‐.