The Role Of PKC Signaling Pathways In Long-term Potentiation Of Spinal Cord Motoneurons

To explore the types and electrophysiological characteristics of synaptic transmission type of synaptic transmission evoked by ipsilateral pericentral(iPCC),the possible molecular mechanisms underlying long-term potentiation(LTP) in motoneurons(MNs), intracellular recording techniques were performed in MNs of spinal cord slices isolated from neonatal rats(8-14 days old).Mainly excitatory postsynaptic potential(EPSPs) were induced by electrical stimulation of iPCC in MNs. During the iPCC-LTP induced by tetanic stimulation of iPCC, the apparent receptor kinetic parameters K1, K2, KT of iPCC-EPSPs were analysed to observe the changes of apparent receptor kinetics. Moreover, PMA, a activator of PKC, was applied after induction of iPCC-LTP induced by iPCC tetanic electrical stimulation to estimate the PKC action in LTP. The results were reported as follows:1. Apparent receptors kinetics analyses of iPCC-EPSPs in 12 MNs showed that K1 of iPCC-EPSPs presented no significant change from 1T to 1.2T(P>0.05),K2 presented dramatic decrease with stimulation intensity from 1T to 1.2T,and were nagatively correlated with the intensity of stimulation,the values of correlation coefficient(r3) were-0.9062(P>0.05). KT also showed some degree of reduction, and were nagatively correlated with the intensity of stimulation,the values of correlation coefficient(r3) were-0.8067(P>0.05).While during 1.3T to 1.5T, K1 and KT all decreased significantly, K2 also presented some degree of reduction, the values of correlation coefficient(r) were-0.8823 ?-0.7857 ?-0.4334( P1? P4?P4>0.05),respectively2. Apparent receptors kinetics analyses of iPCC-IPSP in an MN showed that K1 of iPCC-IPSP increased with stimulation intensity from 1.3T to 1.5T and was positivly correlated with the intensity of stimulation(r2=0.9936, P2>0.05). Moreover, K2 of iPCC-EPSPs decreased with stimulation intensity from 1.3T-1.5T,and were nagatively correlated with the intensity of stimulationin.,the values of correlation coefficient(r2) were-0.9348(P2<0.05). KT of iPCC-EPSPs decreased with stimulation intensity from 1.3T-1.5T,and were nagatively correlated with the intensity of stimulationin.,the values of correlation coefficient(r3) were-0.9920(P3>0.05).3. Among 8 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 iPCC, enhanced the amplitude of iPCC-EPSPs to or above 120% of the baseline and the enlargement lasted longer than 30 min in 3 MNs, which could be referred to as LTP(iPCC-LTP).4. During iPCC-LTP, the area under curve and the maximun left slope of iPCC-EPSPs were increased significantly, which was consistent with the increasing trend of EPSP amplitude. The maximun right slope of iPCC-EPSPs may exhibit some tendency to increase.5. Before and after tetanus stimulation, the stimulus intensity-dependent properties of iPCC were compared. It was observed that under the same stimulus intensity, tetanic stimulation increased amplitude of iPCC. May be tetanic stimulation activated more excitory receptors,or there may be some other neurotransmitter-receptor mechanisms involved.6. During iPCC-LTP induced by 3 MNs, receptor kinetics analyses of iPCC-EPSPs indicated that K1 was increased significantly to 220%, and gradually returned to baseline levels after 35 min. After tetanic stimulation, K2 and KT were reduced significantly to 50% and 40% of the baseline.7. During iPCC-LTP, PMA perfusion(1 ?mol/L, 3 ?mol/L) for 30 min at least in an MN, the amplitude and area under curve of iPCC-EPSP showed tendency of decrease after 1 ?mol/L PMA perfusion, and showed some degree of recovery after 3 ?mol/L PMA perfusion. After washed by ACSF, the amplitude and area under curve of iPCC-EPSP reduced. The latency of iPCC-EPSP had no significant change after 1 ?mol/L PMA perfusion, and showed some degree of extend after 3 ?mol/L PMA perfusion. Duration, maximun left slope, maximun right slope of iPCC-EPSP had no significant change.The results showed that the apparent receptors kinetics analyses is applicable to analyzing the role of neurotransmitters and receptor kinetics of synaptic responses. Parametric analysis showed there may be some other neurotransmitter- receptor mechanisms involved, in addition to glutamate, in iPCC-EPSPs, while complex apparent receptors kinetics in iPCC-IPSP. During LTP, K2 and KT significantly reduce within 10 min after tetanus stimulation, which suggests postsynaptic receptor affinity may be increased and a large number of high-affinity NMDA receptors may be activated. PKC might participate in the maintenance of iPCC-LTP in spinal cord.