The Roles Of Inhibitory Amino Acid Receptors In Long-term Potentiation Of Spinal Cord Motoneurons

To investigate the effect of inhibitory amino acid receptors on long-term potentiation(LTP)of excitatory postsynaptic potentials from ipsilateral pericentral canal(iPCC)to motoneuron(MN),intracellular recording techniques were performed in MNs of spinal cord slices isolated from neonatal rats(8-14 days old).Mainly excitatory postsynaptic potentials(EPSPs)were induced by electrical stimulation of iPCC in MNs.During the i PCC-LTP induced by tetanic stimulation of iPCC,the apparent receptor kinetic parameters K1,K2,KT of i PCC-EPSPs were analysed to observe the changes of apparent receptor kinetics.Moreover,during combined perfusion of glycine receptor antagonist strychnine and GABAA receptor antagonist bicuculline,iPCC-LTP was induced by tetanic stimulation of iPCC.The results were reported as follows:1.Apparent receptors kinetics analyses of iPCC-EPSPs in 7 MNs indicated that K2 and KT showed some degree of reduction,and were negatively correlated with the intensity of stimulation,with the values of correlation coefficient(r)were-0.8753 and-0.8426(P<0.05),respectively.2.Among 9 MNs with iPCC-EPSPs,the tetanic electrical stimulation(100 Hz,50 pulses/train,duration 0.4-1.0 ms,6 trains,main interval 10 s,10-100 V)on i PCC,enhanced the amplitude of iPCC-EPSPs more than 120% of the baseline values,andthe enlargement lasted longer than 30 min in 2 MNs,which can be referred to as LTP(i PCC-LTP).3.In the process of iPCC-LTP,the area under curve and the maximum left slope of iPCC-EPSPs were increased significantly,which was consistent with the increasing trend of EPSP amplitude.The maximum right slope of iPCC-EPSPs exhibited some tendency to decrease.4.Receptor kinetics analyses of iPCC-EPSPs in 2 MNs with iPCC-LTP indicated that K1 was increased and then decreased after tetanic stimulation,while K2 and KT values were slightly decreased and then increased gradually,but did not change significantly.5.Bicuculline and strychnine were perfused in the MN,in which iPCC-LTP was not induced after tetanic stimulation,and then iPCC-LTP was induced by tetanic stimulation.6.Strychnine(1?mol/L,3?mol/L)successive perfusion for 30 min in 1 MN with induced i PCC-LTP after the tetanic electrical stimulation,the amplitude,area under curve and the maximum left slope of iPCC-EPSPs were increased significantly.The apparent receptor kinetics analyses of iPCC-EPSPs suggest that there are perhaps more high-affinity receptors activated in the postsynaptic mermbrane;the results of parameter analyses of iPCC-EPSPs after perfusion of glycine receptor and GABAA receptor antagonists,indicated activation of glycine receptors and GABAA receptors may have inhibitory effects on iPCC-EPSPs.During iPCC-LTP,K2 and KT are decreased,suggesting an enhancement of postsynaptic high-affinity receptors,but their late increase probably suggests an activation of postsynaptic inhibitory receptors with low-affinity.The iPCC-LTP induced after perfusion of inhibitory amino acid receptor antagonists suggests inhibitory amino acid receptor antagonist may facilitate induction of iPCC-LTP.