In order to explore the modulaory effects of metabotropic glutamate receptors (mGluRs) on descending activation of spinal motoneurons (MNs), the intracellular recording techniques were conducted in MNs of spinal cord slices isolated from neonatal rats (7~14 days old).Trans-(1S, 3R)-l-amino-1, 3-cyclopentanedicarboxylic acid (ACPD, an agonist of Group Ⅰ and Group Ⅱ mGluRs), (S)-3,5-dihydroxyphenylglycine hydrate (DHPG, a specific agonist of group Ⅰ mGluRs), were used to activate mGluRs, and-methyl-4-carboxyphenylglycine (MCPG, an antagonist of Group Ⅰ and Group Ⅱ mGluRs) was applied to block mGluRs, respectively.During successive perfusion of ACPD at 5 and 25 μmol/L, DHPG at 5 and 10 mol/L, or MCPG at 400 mol/L, the excitatory postsynaptic potentials (EPSPs) evoked by ipsilateral ventrolateral funiculus (iVLF) stimulation (i.e.iVLF-EPSPs) were recorded from MNs.It was observed that the ACPD superfusion reversibly and concentration-dependently suppressed iVLF-EPSPs (n=11, P<0.05), while MCPG at 400 mol/L did not potentiated the iVLF-EPSPs in other MNs (n=10, P<0.05).In presence of picrotoxin (30 μmol/L), a GABAA receptor antagonist, and strychnine (1.0 μmol/L), a glycine receptor antagonist, iVLF-EPSPs in 14 cells were inhibited by ACPD at 10 μmol/L (P<0.05).Moreover, the amplitude of iVLF-EPSPs in 7 tested MNs was reversibly and concentration-dependently suppressed by superfusion of DHPG (P<0.01), but pretreatment of picrotoxin (30 mol/L) partially prevented the action of DHPG at 5 mol/L.At the same time of above tests, a medium intervention of membrane properties and action potentials of MNs was present either, including increase of membrane resistance and firing frequency of action potentials by ACPD, depolarization by DHPG, but decrease of amplitude of action potentials by ACPD and DHPG.These results suggest that modulatory actions of mGluRs, specifically Group I mGluRs, are involved in the descending activation pathways to MNs, possibly by pre-and post-synaptic mechanisms.