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GABA能神经元通过编码动作电位发放模式在维持大脑功能内环境的稳态中起着关键作用。研究[1]表明大脑皮层GABA能神经元的内在特性包括阈值(Vts-Vr)和绝对不应期(absolute refractory period, ARP)共同调控着神经编码模式。神经元动作电位产生过程中有着抑制成分如后超极化(AHP)通过降低电压门控钠通道介导的阈值电位和ARP来调控着动作电位的编码[2]。钾通道能以不同的方式调节神经元兴奋性和编程,例如,快速后超极化(fAHP)、慢速后超极化(sAHP)[3-6]。然而,这些AHP成分如何对大脑皮层GABA能神经元内在特性产生影响,目前尚不清楚。
大脑皮层GABA能神经元接受兴奋性突触输入与抑制性突触输入的时间和空间上的总和效应[7-8],代数和形成了膜电位的波动,正向电流促使膜电位去极化,负向电流使膜电位发生超极化。GABA能神经元整合兴奋性和抑制性突触输入后会产生的不同类型的电位波动[fAHP、sAHP、快速后去极化(fADP)、完全复极和未完全复极],它们对于内在特性和编码的影响目前还不明确。
为了解决上述问题,我们利用出生15~20 d的小鼠,使用全细胞记录来探讨不同类型电位波动对神经元内在特性和神经编码的影响,为进一步了解抑制性神经元的内在特性变化及对神经编码的影响提供实验基础和理论依据。
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大脑皮层GABA能神经元的规则发放表现为等高的峰幅度,逐渐延长的动作电位峰间距(inter-spike intervals, ISI)和较明显的频率适应性,而快发放表现为等高的峰幅度,较短的几乎相等的ISI和很小的频率适应性(见图 3)。
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通过阈强度去极化电流引导动作电位产生,在标准化超极化刺激强度下,即为阈刺激的(-0.5、-1、-1.5、-2、-2.5)倍时,量化ARP2值并进行比较。fAHP和sAHP相比,fAHP影响下的动作电位的ARP2较短(P < 0.01)(见表 1)。
分组 n -0.5 -1 -1.5 -2 -2.5 fAHP 9 4.43±0.04 4.32±0.04 4.35±0.06 4.21±0.06 4.35±0.07 sAHP 15 5.48±0.07 7.04±0.85 7.98±0.61 11.23±0.81 15.63±1.01 t — 40.94 9.51 17.64 25.73 33.16 P — < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 表 1 fAHP与sAHP对ARP2的影响
($ \overline{x}\pm s$; ms) -
通过阈强度去极化电流引导动作电位产生,在标准化超极化刺激强度下,即为阈刺激的(-0.5、-1、-1.5、-2、-2.5)倍时,量化Vts-Vr3值并进行比较。fAHP和sAHP相比,fAHP影响下的动作电位的Vts-Vr3较高(P < 0.01)(见表 2)。
分组 n -0.5 -1 -1.5 -2 -2.5 fAHP 9 38.32±0.31 39.07±0.46 37.4±0.6 37.07±0.62 35.49±0.73 sAHP 15 32.35±0.21 34.75±0.55 35.19±0.52 35.88±0.60 35.63±0.78 t — 56.41 17.94 9.52 4.65 0.44 P — < 0.01 < 0.01 < 0.01 < 0.01 >0.05 表 2 fAHP和sAHP对Vts-Vr3的影响
($ \overline{x}\pm s$; mV) -
fAHP的影响如前所述,即阈刺激的(-2.5、-2、-1.5、-1、-0.5)倍ARP2值分别为(4.43±0.04)、(4.32±0.04)、(4.35±0.06)、(4.21±0.06)、(4.35±0.07)ms(n=12)。动作电位完全复极,即为阈刺激的0倍,测得的ARP2的值为:(3.97±0.05) ms(n=12)。在动作电位产生后未复极之前立刻给予阈刺激的0.25、0.5、0.75倍的刺激,以模拟动作电位未完全复极化,量化ARP2的值,分别是:(3.72±0.04)、(3.81±0.06)和(3.82±0.05) ms(n=12)。综上,在阈刺激的(-2.5、-2、-1.5、-1、-0.5、0、0.25、0.5、0.75)倍下测得ARP2值进行比较,当为阈强度0.25倍时,ARP2最短(P < 0.05)。
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fAHP的影响如前所述,即阈刺激的(-2.5、-2、-1.5、-1、-0.5)倍ARP2值分别为(4.43±0.04)、(4.32±0.04)、(4.35±0.06)、(4.21±0.06)、(4.35±0.07) ms(n=12)。动作电位完全复极,即为阈刺激的0倍,测得的ARP2的值为:(3.97±0.05) ms(n=12)。通过阈强度去极化电流引导动作电位产生,在标准化超极化刺激强度下,在紧跟着动作电位后给予标准化去极化刺激,即为阈刺激的1.25、1.5倍,以模拟动作电位的fADP,量化ARP2的值,分别是(4.07±0.06)和(4.26±0.08) ms(n=12)。综上,在阈刺激的(-2.5、-2、-1.5、-1、-0.5、0、1.25、1.5)倍下测得ARP2值进行比较,ARP2在动作电位完全复极时最短(P < 0.05)。
膜电位的不同波动对小鼠大脑皮质GABA能神经元内在特性的影响
Effect of different fluctuations of membrane potential on the intrinsic characteristics of GABA neurons in mouse cerebral cortex
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摘要:
目的探讨膜电位的不同波动对小鼠大脑皮质γ-氨基丁酸(GABA)能神经元内在特性影响及对神经编码的调控。 方法取出生15~20 d FVB-Tg(Gad GFP)45 704 Swn/J小鼠进行麻醉,断头取脑制作切片,将脑片置于充分氧合的人工脑脊液中继续孵育2 h。采用全细胞记录方法进一步探讨快速后超极化(fAHP)、慢速后超极化(sAHP)、动作电位不同复极和快速后去极化(fADP)对神经元内在特性的影响及对神经编码的调控。 结果fAHP和sAHP相比,fAHP影响下的动作电位的绝对不应期(ARP2)较短(P < 0.01),阈值(Vts-Vr3)较高(P < 0.01);与fAHP相比,动作电位未完全复极时,ARP2较短,当为阈强度0.25倍时,ARP2最短(P < 0.05);与fAHP比较,fADP程度越低,ARP2越短,当在静息电位水平时,ARP2最短(P < 0.05)。 结论大脑皮层GABA能神经元在整合突触输入后,当膜电位波动时其内在特性发生可塑性变化,不同输入模式通过影响大脑皮层GABA能神经元动作电位的内在特性,从而调控GABA能神经元对输入信号的编程能力。 -
关键词:
- γ-氨基丁酸能神经元 /
- 后超极化 /
- 内在特性 /
- 神经编码
Abstract:ObjectiveTo explore the effects of different fluctuations of membrane potential on the intrinsic characteristics and regulation of neural coding of GABA-ergic neurons in mouse cerebral cortex. MethodsThe brain slices were prepared from FVB-Tg(Gad GFP) 4570Swn/J mice(postnatal day 15-20), and incubated in artificial cerebrospinal fluid with sufficient oxygenation for 2 h.The effects of fast post-polarization(fAHP), slow post-hyperpolarization(sAHP), different repolarization of action potential and fast post-polarization(fADP) on the intrinsic characteristics of neurons and regulation of neural coding were further studied by whole-cell recording. ResultsCompared with sAHP, the absolute refractory period(ARP2) and threshold(vts-Vr3) of the action potential under the influence of fAHP were shorter and higher, respectively(P < 0.01).Compared with fAHP, the ARP2 was shorter when the action potential was not fully repolarized, and the ARP2 was the shortest when the threshold intensity was 0.25 times(P < 0.05).Compared with fAHP, the lower the fADP level was, the shorter the ARP2 was, and the ARP2 was the shortest at the resting potential level(P < 0.05). ConclusionsAfter the integrating synaptic input, the plasticity of intrinsic characteristics of cerebral cortex GABA-ergic neurons changes when the membrane potential fluctuates.Different input modes affect the intrinsic characteristics of action potential of cerebral cortex GABA-ergic neurons, thereby regulating the programming ability of GABA-ergic neurons to input signals. -
表 1 fAHP与sAHP对ARP2的影响
( ; ms)$ \overline{x}\pm s$ 分组 n -0.5 -1 -1.5 -2 -2.5 fAHP 9 4.43±0.04 4.32±0.04 4.35±0.06 4.21±0.06 4.35±0.07 sAHP 15 5.48±0.07 7.04±0.85 7.98±0.61 11.23±0.81 15.63±1.01 t — 40.94 9.51 17.64 25.73 33.16 P — < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 表 2 fAHP和sAHP对Vts-Vr3的影响
( ; mV)$ \overline{x}\pm s$ 分组 n -0.5 -1 -1.5 -2 -2.5 fAHP 9 38.32±0.31 39.07±0.46 37.4±0.6 37.07±0.62 35.49±0.73 sAHP 15 32.35±0.21 34.75±0.55 35.19±0.52 35.88±0.60 35.63±0.78 t — 56.41 17.94 9.52 4.65 0.44 P — < 0.01 < 0.01 < 0.01 < 0.01 >0.05 -
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