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Objective To evaluate the modulatory action of group Ⅰ metabotropic glutamate receptors (mGluRs) on descending activation ofmotoneurons (MNs) in neonatal rat spinal cord slices.Methods The intracellular recordings were made in MNs of spinal cord slices isolated from neonatal rats (7-14 days old), and excitatory postsynaptic potential (EPSP) was evoked by ipsilateral ventrolateral funiculus (iVLF) stimulation, i.e.iVLF-EPSP.By superfusion of group Ⅰ mGluRs agonist (S)-3,5-dihydroxyphenylglycine hydrate (DHPG), the modulatory action was observed on the MN membrane electrical properties, action potential (AP), as well as on the iVLF-EPSP.Results Application of DHPG (5 μmol/L) significantly depolarized the motoneuron membrane (n=7, P<0.01), with reduced time constant (n=7, P<0.05), and extended the half-width of the spike potential (n=5, P<0.05).The amplitude of iVLF-EPSPs in 7 tested MNs was reversibly and concentration-dependently suppressed by superfusion of DHPG (5-10 μmol/L, 15 min, P<0.01).Pretreatment of picrotoxin (30 μmol/L), an antagonist of γ-aminobutyric acid A (GABAA) receptors, partially prevented the inhibitory action of DHPG at 5 μmol/L on iVLF-EPSPs.Conclusion The preliminary results suggest that DHPG inhibits the descending activation of MNs by activation of group Ⅰ mGluRs, in which at least the potentiation of GABAA receptor and inhibition of sodium channels may be involved.