The Roles Of 5-HT_1A Receptor In Synaptic Plasticity Of Spinal Cord Motoneurons In Vitro

To study the roles of 5-HT1 A receptor in synaptic plasticity of spinal cord motoneurons,the intracellular recordings were carried out in the ventral horn MNs of spinal cord slices isolated from neonatal rats(7 to 14 days of age)and excitatory postsynaptic potentials(EPSPs)were evoked by electrical stimulation on ipsilateral postsynaptic canal(iPCC),i.e.iPCC-EPSPs.Before tetanic stimulation on iPCC,8-OH-DPAT,bicuculline and strychnine(inhibitory amino acid receptor antagonists),PMA were perfused to observe whether the induction of LTP of iPCC-EPSP(iPCC-LTP)was facilitated by pretreatment of these reagents,And APV(NMDA receptor antagonist)was used to analyze the maintenance mechanisms underlying iPCC-LTP.Electrophysiological parameters and the apparent receptor kinetics parameters were analyzed.The results are as follows: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 2 MNs,which could be referred to as LTP(iPCC-LTP).Apparent receptor kinetics analyses of iPCC-EPSPs during iPCC-LTP in 2 MNs showed that after tetanic stimulation,K1 was decreased a little,K2 and KT were slightly increased in MN1,and K1 was moderately increased,K2 and KT were increased lightly after transient decrease in MN2.8-OH-DPAT(1?mol/L)was perfused in 3 MNs before tetanic electrical stimulation,as a result,LTP was induced in 2 MNs.Bicuculline(GABAA receptor antagonist,30 ?mol/L)and strychnine(glycine receptor antagonist,30 ?mol/L)were perfused in 6 MNs before tetanic electrical stimulations,and LTP was induced in only one MN.And then APV was given,the amplitude and area under curve was depressed largely.PMA(1 ?mol/L,3 ?mol/L)was perfused to 5 MNs,the changes of iPCC-EPSP parameters were not obvious,and then tetanic electrical stimulation was applied to three of them,however,no LTP was induced.Frome these results we can conclude that LTP of the EPSPs from iPCC to MNs can be induced,however,the induction rate of iPCC-LTP is relatively low.8-OH-DPAT may facilitate the induction of iPCC-LTP.Inhibitory amino acid receptor antagonists may not play a facilitation role in the induction of LTP from iPCC to spinal MNs.No significant effect of PMA on the iPCC-EPSPs or on the induction of iPCC-LTP is found here.