A Study of the Barium‐sensitive and ‐insensitive Components of the Action of Thyrotropin‐releasing Hormone on Lumbar Motoneurons of the Rat Isolated Spinal Cord
- 1 October 1993
- journal article
- Published by Wiley in European Journal of Neuroscience
- Vol. 5 (10), 1360-1369
- https://doi.org/10.1111/j.1460-9568.1993.tb00922.x
Abstract
The electrophysiological action of thyrotropin-releasing hormone (TRH) on rat spinal motoneurons was studied in vitro using single-electrode voltage- and current-clamp techniques. In current-clamp conditions TRH elicited a slowly developing depolarization, associated with a large input resistance increase and sustained neuronal firing; the primary metabolites of TRH were ineffective. Under voltage-clamp conditions in the presence of tetrodotoxin, TRH evoked a large inward current (ITRH; peaking at approximately –40 mV) associated with a large input conductance fall. Only 44% of cells displayed ITRH reversal; when the chord conductance values of these cells were plotted against membrane potential, a bell-shaped relation occurred, indicating voltage-dependent block by TRH of a persistent conductance active over a wide range of membrane potentials. ITRH reversal values were shifted to more positive levels in high K+ solution in Nernstian fashion; hence a large proportion of the TRH response is suggested to be mediated by the block of a K+ conductance (IK(T)). IK(T) (and its voltage-dependent block by TRH) was resistant to certain K+ channel antagonists (tetraethylammonium, Cs+, 4-aminopyridine or apamin), but was depressed by Ba2+. The Ba2+-resistant fraction of ITRH was attenuated by Cd2+, Mn2+ or Co2+, indicating that it probably involved a Ca2+-sensitive inward current. Concomitant application of Ba2+ and Cd2+ induced a near-total block of the response to TRH. It is suggested that suppression of IK(T), associated with the onset of a Ca2+-sensitive current, can explain the excitatory effect of TRH on rat spinal motoneurons.Keywords
This publication has 46 references indexed in Scilit:
- Neuromodulation of vertebrate motor neuron membrane propertiesCurrent Opinion in Neurobiology, 1992
- Activation of three types of membrane currents by various divalent cations in identified molluscan pacemaker neurons.The Journal of general physiology, 1989
- Electrical properties of facial motoneurons in brainstem slices from guinea pigBrain Research, 1989
- On the resting potential of isolated frog sympathetic neuronsNeuron, 1989
- Temporal integration by a slowly inactivating K+ current in hippocampal neuronsNature, 1988
- Multiple types of neuronal calcium channels and their selective modulationTrends in Neurosciences, 1988
- Serotonin and co-localized peptides: Effects on spinal motoneuron excitabilityPeptides, 1985
- Thyrotropin-releasing hormone mimics descending slow synaptic potentials in rat spinal motoneuronsProceedings of the Royal Society of London. B. Biological Sciences, 1985
- Inward current channels activated by intracellular Ca in cultured cardiac cellsNature, 1981
- Electrophysiology of mammalian spinal cord in vitroNature, 1974