Dual effect of GABA on descending monosynaptic excitatory postsynaptic potential in frog lumbar motoneurons

• Published in: Neuroscience 2004, Vol.129 (3), p.639-646
• Main Authors: Ovsepian, S.V., Vesselkin, N.P.
• Format: Article
• Language: English
• Subjects: Animals; Baclofen - analogs & derivatives; Baclofen - pharmacology; Drug Interactions; Electric Stimulation - methods; Evoked Potentials - drug effects; Evoked Potentials - radiation effects; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - radiation effects; frog; GABA Agonists; GABA Antagonists - pharmacology; gamma-Aminobutyric Acid - pharmacology; In Vitro Techniques; Lumbosacral Region; Motor Neurons - drug effects; Motor Neurons - radiation effects; presynaptic inhibition; Rana ridibunda; spinal cord; Spinal Cord - cytology; Synapses - drug effects; Synapses - radiation effects; synaptic transmission; Synaptic Transmission - drug effects
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2004.07.050

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 GABA B 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.