[Modulation of miniature inhibitory potentials in motoneurons of the turtle spinal cord by group II metabotropic glutamate receptors].

The role of group II metabotropic glutamate receptors (mGluRs) in modulation of inhibitory synaptic activity was studied by intracellular recording of motoneuron miniature inhibitory spontaneous postsynaptic potentials (mIPSPs) in isolated lumbar segments of the turtle spinal cord in the medium containing TTX, CNQX, AP-5. The ratio of mIPSPs with fast and slow kinetics (83% vs 17%) is in accordance with the ratio shown for glycine- and GABA-mediated IPSP or IPSCs (Jones et al., 1988; Gao et al., 2001). In the majority of investigated motoneurons, the selective group II mGluRs antagonist EGLU (100-250 microM) increased the frequency of mIPSPs by 106.6 +/- 74.4% (n = 9) without affecting average amplitude, suggesting a presynaptic site of mGluRs action providing for the transmitter release reduction. The analysis of EGLU action on mIPSPs with different time courses (selection by half-width) showed that the frequency of inhancement of miniature inhibitory activity is caused by predominantly short-duration mIPSPs (ba 84.0 +/- 18.2%; n = 9), which are probably glycineergic. However, EGLU did not influence the mIPSPs frequency under condition of GABA-receptor blockade by bicuculline (20 microM). This fact suggest that group II mGluRs could modulate glycinergic transmission to the turtle spinal motoneurons on the necessary condition that GABergic system is active.