Involvement of Group II Metabotropic Glutamate Receptors in Modulation of Evoked Activity in Frog Spinal Motoneurons

Abstract

The effect of the agonist of group II mGluRs, including mGluR2 and mGluR3 (mGluR 2/3) receptor subtypes, on evoked activity and electric membrane properties of frog spinal (lumbar) motoneurons was studied electrophysiologically on sections of the isolated spinal cord. Extracellular recordings revealed a decrease in the amplitude of short-latency components of spinal reflexes and in the overall response area under the effect of DCG-IV [2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine], a mGluR 2/3 agonist, within its concentration range of 0.05-5 μM. The half-maximal effective concentration (EC₅₀) of the agonist for the suppression of short-latency response components was about 0.5 μM. Intracellular recordings of postsynaptic potentials from motoneurons upon DCG-IV application demonstrated a decrease in the number of spikes and the overall area of responses evoked by dorsal root stimulation. Most of motoneurons studied responded with hyperpolarization, increased amplitude of antidromic action potentials, altered afterpotential amplitude and increased excitability, indicative of the agonist effect on postsynaptic group II mGluRs in frog spinal motoneurons.