The Effects Of Histamine On Synaptic Transmission Of Spinal Motoneurons

Objective:Histamine?HA?is a small molecule synthesized by amino acid histidine and plays an important physiological role in animals.The central histamine system is involved in many basic homeostasis and high brain functions,such as sleep-arousal regulation,circadian rhythm and feeding rhythm,vestibular function,synaptic plasticity and learning and memory.The effects of histamine and its receptors on spinal motoneurons?motoneuron,MN?have not been thoroughly studied.Therefore,the purpose of this study was to investigate the effect of histamine on synaptic transmission in spinal motoneurons.Methods:The synaptic responses evoked by the stimulation of ipsilateral dorsal root?iDR?and ventrolateral funiculus?iVLF?of the spinal cord can be recorded in MNs in our laboratory.Therefore,the spinal cord of newborn SD rats?7-12 days old?was sliced to prepare the segment of lumbosacral enlargement?about 400⁵00?m?.The synaptic responses of the iDR and the iVLF inputs to MNs evoked by electric stimulation?monopulse,0.1 ms,total 10 pulses,pulse interval 1 s,15-24 V?were recorded by using intracellular recording technique of motoneurons.A certain concentration of histamine was perfused to observe the effects of histamine on the action potential and synaptic transmission of spinal motoneurons.Results:1.Basic electrophysiological parameters of spinal motoneuronsThe electrophysiological parameters of spinal MNs were measured in 11 cells with stable recording for more than 15 min.The electrophysiological parameters were as follows:resting potential-70.92±8.14 mV,membrane resistance 87.64±44.90 M?,time constant 11.67±14.02 ms,the amplitude of action potential 77.32±7.61 mV,the threshold potential-58.69±6.84 mV,and the overshoot value 9.02±7.99 mV.2.IDR-EPSP-IPSP and iVLF-EPSP induced by electrical stimulation of ipsilateral dorsal root and ipsilateral ventrolateral chordaeThe postsynaptic responses of 13 MNs were recorded by electrical stimulation,of which 10 responses were excitatory postsynaptic potentials?EPSP?induced by electrical stimulation of the ipsilateral ventrolateral cord.The EPSP parameters were as follows:the amplitude 3.57±1.00 mV,the area under the curve 81.67±54.24 mV·ms,the latency 4.17±2.22 ms,the duration is 75.45±22.42 ms,the half amplitude duration14.21±6.53 ms,the maximum rise slope 3.72±1.23 mV/ms,and the maximum decay slope-2.64±3.52 mV/ms.of which 2 responses were excitatory postsynaptic potentials?EPSP?induced by electrical stimulation of the ipsilateral dorsal root and the other is compound postsynaptic potential?EPSP-IPSP?evoked by the ipsilateral dorsal root.3.Effects of histamine on spinal cord MNThe changes of membrane potential,action potential and different synaptic potentials were observed by perfusion with histamine at a certain concentration on three recorded MNs.The reversible depolarization of MN₁ was induced by 5 min perfusion of1 mmol/L histamine,which also increased the frequency of action potential,and enhanced the EPSP-IPSP compound postsynaptic potential induced by iDR electric stimulation,resulting in the discharge of action potentials.In MN₂,5 min perfusion with100?mol/L histamine not only causes depolarization,but also increases the EPSP induced by electric stimulation of iVLF.In MN₃,The enhancement effect of histamine on iVLF-EPSP and iDR-EPSP could be observed at the same time after perfusion with100?mol/L histamine for 5 minutes in the ipsilateral ventrolateral cord and ipsilateral dorsal root of the same cell.Conclusion:These preliminary results suggest that histamine may produce excitatory effects on spinal cord MNs by generating depolarization,increasing action potential dischargerelease and enhancing synaptic transmission,but further studies are needed to confirm that histamines may play an excitatory role in the development of spinal MNese results yet.