title: Dual effect of GABA on descending monosynaptic excitatory postsynaptic potential in frog lumbar motoneurons.
abstract: Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulating ipsilateral ventrolateral column (VLC) in the thoracic section were recorded in lumbar motoneurons within the isolated spinal cord of the frog Rana ridibunda. Bath application of the selective GABAB receptor agonist (-)-baclofen (0.05 mM) caused a reduction in the peak amplitude of VLC EPSP. Baclofen did not cause any consistent change in the membrane potential or in the EPSP waveform within frog motoneurones. The selective GABA(B) receptor antagonist saclofen (0.1 mM) completely blocked the effect of (-)-baclofen on VLC EPSP. A decrease in VLC EPSP peak amplitude was also observed during GABA (0.5 mM) application. Unlike (-)-baclofen, inhibition of VLC EPSP induced by GABA was accompanied by a shortening of the EPSP time course and a reduction in membrane input resistance within lumbar motoneurons. The decrease in VLC EPSP peak amplitude induced by (-)-baclofen and GABA was accompanied by an increase in the paired-pulse facilitation. These data provide evidence for a dual pre- and postsynaptic GABAergic inhibition of the VLC monosynaptic EPSP in lumbar motoneurons within the frog spinal cord.
authors.affiliation: Department of Pharmacology and Therapeutics, Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: S V
authors.initials: SV
authors.lastname: Ovsepian
authors.forename: N P
authors.initials: NP
authors.lastname: Vesselkin
mesh_terms: D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives* / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects / Q000528:radiation effects; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects* / Q000528:radiation effects; D018755:GABA Agonists; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008161:Lumbosacral Region; D009046:Motor Neurons / Q000187:drug effects* / Q000528:radiation effects; D011895:Rana ridibunda; D013116:Spinal Cord / Q000166:cytology*; D013569:Synapses / Q000187:drug effects* / Q000528:radiation effects; D009435:Synaptic Transmission / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D018755:GABA Agonists; D018756:GABA Antagonists; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; C080629:saclofen