多巴胺对脊髓运动神经元下行激活和外周传入突触传递的差异性影响

Distinct effects of dopamine on afferent and descending synaptic transmission in spinal cord motoneurons

目的:观察和比较多巴胺(DA)对新生大鼠离体脊髓运动神经元(MN)下行激活和外周传入通路的兴奋性突触后电位(EPSP)的影响。方法:选取新生SD大鼠(8~14日龄)制备脊髓横切片,对其MN进行细胞内记录,观察DA对电刺激同侧背根(iDR)、同侧腹外侧索(iVLF)在MN诱发的EPSP(iDR-EPSP、iVLF-EPSP)的影响。结果:①在17个稳定记录的MN,灌流6.25μmol/L DA 15 min,不仅增大MN膜电阻(P<0.01),还可减小动作电位(AP)幅度和超射(P<0.05)等。②在11个MN,灌流6.25μmol/L DA 15 min后同细胞iDR-EPSPs和iVLF-EPSPs的幅度、曲线下面积均减小并伴时程缩短(P<0.05)。③表观受体动力学分析显示,6.25μmol/L DA可减小iVLF-EPSPs的表观解离速率常数K 2和表观平衡解离常数K_(T)(P<0.05),但仅减小iDR-EPSPs表观结合速率常数K_(1)(P<0.05)。④给予6.25、25、100μmol/L DA累积灌流各15 min,DA可浓度依赖性(P<0.01)减小iVLF-EPSPs的幅度、曲线下面积、半幅时程和衰减时间(P<0.01),并同时减小同细胞iDR-EPSPs的幅度、时程和衰减时间(P<0.01)。且DA在同细胞对iVLF-EPSP的抑制作用比iDR-EPSP强(P<0.01)。结论:DA对MN外周传入和下行激活性兴奋性突触传递具有抑制作用,但对下行激活通路的抑制更强。

Objective:To observe the distinct effects of dopamine(DA)on afferent and descending synaptic transmission of motoneurons(MNs)in neonatal rat spinal cord slices.Methods:In spinal cord slices isolated from neonatal Sprague-Dawley rats(8-14 d),the intracellular recording technique was used to observe the effects of DA on excitatory postsynaptic potential(EPSP)of MNs evoked by electrical stimulation of ipsilateral dorsal root(iDR,iDR-EPSP)and ipsilateral ventrolateral funiculus(iVLF,iVLF-EPSP).Results:In 17 MNs,bathing DA(6.25μmol/L)for 15 min not only increased membrane resistance(P<0.01),but also reduced amplitude and overshoot of action potential(P<0.05).In 11 steadily recorded MNs,DA(6.25μmol/L)perfusion for 15 min decreased the amplitude,area under curve(AUC)and duration of iDR-EPSPs and iVLF-EPSPs in the same MNs(P<0.05).The apparent dissociation rate constant(K 2)and apparent equilibrium dissociation constant(K_(T))of iVLF-EPSPs were decreased significantly by bathing DA(6.25μmol/L)for 15 min(P<0.05),while only the apparent association rate constant(K_(1))of iDR-EPSPs reduced(P<0.05).Moreover,in 6 MNs with both iDR-EPSP and iVLF-EPSP,bath of DA(6.25,25,100μmol/L)for 15 min with each concentration not only reversibly and concentration-dependently(P<0.01)depressed the amplitude,AUC,half-width and decay time of iVLF-EPSPs(P<0.01),but also decreased the amplitude,AUC and decay time of iDR-EPSPs(P<0.01),respectively.The inhibitory effect of DA on iVLF-EPSPs was more potent than that on iDR-EPSPs(P<0.01).Conclusion:These results suggest that DA may inhibit the afferent and descending excitatory synaptic transmission in MNs,and present a more potent depression on descending activation than that on afferent pathway.