POSTNATAL MATURATION OF THE GABAERGIC SYSTEM IN RAT NEOCORTEX
POSTNATAL MATURATION OF THE GABAERGIC SYSTEM IN RAT NEOCORTEX
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DOI：
10.1152/jn.1991.65.2.247
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发表时间：
1991-02-01
影响因子：
2.5
通讯作者：
PRINCE, DA
中科院分区：
文献类型：
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作者：
LUHMANN, HJ;PRINCE, DA
1. 本研究在体外培养的大鼠初级体感皮层和初级视皮层第II层和第III层锥体和非锥体神经元中，研究了皮质内抑制回路的生后成熟和对GABA和巴氯芬反应的发育. 当加载硝酸盐时，大约70%的幼年（出生后第4-10天; P4-10）、幼年（P11-16）和成年（P28-41）细胞分别记录到去极化自发抑制性突触后电位（IPSP）。 应用GABA（A）受体拮抗剂bicuculline methiodide（BMI）可阻断所有年龄组的自发性事件，表明它们是通过激活GABA（A）受体介导的. 在122的130个成年细胞测试，标准化的电刺激的白色物质或VI层引起了短暂的兴奋性突触后电位（EPSP），其次是快速（f-）和长潜伏期（l-）IPSP。 类似的刺激引起的双相IPSP中只有51的98青少年和只有1的56个年轻的神经元研究。 f-IPSP和1-IPSP的平均峰值电导分别从幼年细胞的50.2和7.5 nS显著增加到成年细胞的84.2和18.0 nS. 应用N-甲基-D-天冬氨酸（NMDA）受体拮抗剂D-氨基-膦酰基戊酸（D-APV）的青少年细胞诱导的f-IPSP和l-IPSP的逆转电位显着负移。 这种效果是伴随着减少在这些事件的峰值电导分别为31%和48%，表明一个突出的持久的NMDA受体介导的EPSP同时发生与早期和晚期IPSP在未成熟的神经元。 在成年神经元中，D-APV对f-和l-IPSP的逆转电位没有显著影响，尽管峰值电导分别降低了20%和5%，表明在这个年龄组中存在较小的NMDA受体的同时激活。 GABA（A）和GABA（B）受体的功能成熟通过将GABA局部应用于索马和顶端树突来研究。 将体细胞GABA应用于保持在去极化膜电位的成年神经元引起三相反应，包括1）GABA（A）介导的超极化快速成分（GABA（hf）;逆转电位，-76 mV），2）GABA（A）介导的去极化相（GABA（d）; -54 mV）和3）超极化晚期反应（GABA（hl）; -80 mV）。 GABA（d）反应在所有年龄段的神经元中均有表达。 具有体细胞GABA（hf）和GABA（hl）反应的细胞的百分比随着年龄的增长而增加，从年轻动物的17%分别增加到成年大鼠的96%和74%。 当GABA作用于顶树突时，三个年龄组的每个细胞都能获得GABA（d）反应。 树突GABA（HF）的反应可以证明在14%的年轻的神经元，并在50%和35%的青少年和成年细胞，分别。 树突状GABA（HL）细胞的百分比从年轻动物的7%分别增加到幼年和成年大鼠的38%和44%。 巴氯芬诱发一个持久的，小幅度超极化的膜电位在60%的青少年（逆转电位，-94 mV）和88%的成年神经元（-90 mV），当应用于附近的顶端树突。 体细胞巴氯芬反应可在75%的幼年细胞（-86 mV）和75%的成年细胞（-90 mV）中得到证实。 在年轻动物的切片中，只有23%的细胞显示出体细胞巴氯芬反应，而树突反应从未出现。 通过用Cl-加载细胞并使用正向f-IPSP振幅的变化作为细胞内Cl-浓度（[Cl-]i）变化的指数，研究了Cl-挤出机制效率的依赖性改变。 而Cl-挤出的时间常数为6.8秒的成年神经元，5 7 Cl-加载的青少年细胞响应于顺向刺激与延长的去极化和突出的爆发性放电，持续整个刺穿，并推测与[Cl-]i的增加。 这些发现表明，在未成熟的神经元中，向外的Cl-转运是相对无效的。 我们的数据表明，GABA能抑制在大鼠新皮层逐渐成熟，在出生后的第一个月。 GABA（A）受体早在P4时就已存在，而GABA（B）受体在出生后第二周中期开始功能性活跃，此时抑制性神经支配开始，顺向诱发的IPSP可首先得到证实。 在幼年皮层中GABA能抑制的相对无效性促进了NMDA受体介导的活性在该年龄的表达，这反过来可能在发育可塑性和未成熟皮层的癫痫易感性增加中发挥作用。
1. The postnatal maturation of intracortical inhibitory circuitry and the development of responses to applied gamma-aminobutyric acid (GABA) and baclofen were studied in pyramidal and nonpyramidal neurons from layers II and III of the rat primary somatosensory and primary visual cortex, in vitro.2. Depolarizing spontaneous inhibitory postsynaptic potentials (IPSPs) could be recorded in approximately 70% of the young (postnatal day 4-10; P4-10), juvenile (P11-16), and adult cells (P28-41), respectively, when they were loaded with nitrate. At all ages these spontaneous events could be blocked by application of the GABA(A) receptor antagonist bicuculline methiodide (BMI), indicating that they were mediated by activation of GABA(A) receptors.3. In 122 of the 130 adult cells tested, standardized electrical stimulation of the white matter or layer VI evoked a brief excitatory postsynaptic potential (EPSP), followed by both a fast (f-) and a long-latency (l-)IPSP. Similar stimuli evoked a biphasic IPSP in only 51 of the 98 juvenile and in only 1 of the 56 young neurons studied. The mean peak conductance of the f-IPSP and the 1-IPSP increased significantly from 50.2 and 7.5 nS, respectively, in juvenile cells to 84.2 and 18.0 nS, respectively, in adult neurons.4. Application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-amino-phosphonovaleric acid (D-APV) to juvenile cells induced a significant negative shift in the reversal potential of both the f-IPSP and l-IPSP. This effect was accompanied by a reduction in the peak conductance during these events by 31 and 48%, respectively, indicating that a prominent long-lasting NMDA receptor-mediated EPSP occurs concurrent with the early and late IPSP in immature neurons. In adult neurons, D-APV had no significant effect on the reversal potential of the f- and l-IPSP, although the peak conductance decreased by 20 and 5%, respectively, suggesting that there was a smaller concurrent activation of NMDA receptors in this age group.5. The functional maturation of GABA(A) and GABA(B) receptors was studied using focal applications of GABA to the soma and the apical dendrite. Somatic GABA applications to adult neurons held at depolarized membrane potentials evoked a triphasic response, consisting of 1) a GABA(A)-mediated hyperpolarizing fast component (GABA(hf); reversal potential, -76 mV), 2) a GABA(A)-mediated depolarizing phase (GABA(d); -54 mV), and 3) a hyperpolarizing late response (GABA(hl); -80 mV). The GABA(d) response could be demonstrated at all ages in almost every neuron. The percentage of cells with a somatic GABA(hf) and GABA(hl) response increased with age from 17% each in young animals to 96 and 74%, respectively, in adult rats.6. GABA(d) response could be obtained from every cell studied in all three age groups when GABA was applied to the apical dendrite. A dendrite GABA(hf) response could be demonstrated in 14% of the young neurons, and in 50 and 35% of the juvenile and adult cells, respectively. The percentage of cells with a dendritic GABA(hl) increased from 7% in young animals to 38 and 44% in juvenile and adult rats, respectively.7. Baclofen evoked a long-lasting, small-amplitude hyperpolarization of the membrane potential in 60% of the juvenile (reversal potential, -94 mV) and in 88% of the adult neurons (-90 mV), when applied near the apical dendrite. A somatic baclofen response could be demonstrated in 75% of the juvenile (-86 mV) and 75% of the adult cells (-90 mV). In slices from young animals, only 23% of the cells showed a somatic baclofen response, and a dendritic response was never observed.8. Age-dependent alterations in the efficiency of Cl- -extruding mechanisms were investigated by loading cells with Cl- and using changes in the amplitude of the positive-going f-IPSP as an index of changes in intracellular Cl- concentration ([Cl-]i). Whereas Cl- was extruded with a time constant of 6.8 s in adult neurons, 5 of 7 Cl- -loaded juvenile cells responded to orthodromic stimulation with prolonged depolarizations and prominent burst discharges that persisted for the entire impalement and were presumably related to increases in [Cl-]i. These findings suggest that outward Cl- transport is relatively ineffective in immature neurons.9. Our data indicate that GABAergic inhibition in rat neocortex matures gradually during the first postnatal month. Whereas GABA(A) receptors are already present as early as P4, GABA(B) receptors become functionally active in the middle of the second postnatal week, at a time when inhibitory innervation begins and orthodromically evoked IPSPs can first be demonstrated. The relative inefficacy of GABAergic inhibition in juvenile cortex promotes the expression of NMDA receptor-mediated activity at this age, which in turn may play a role in developmental plasticity and increased seizure susceptibility of immature cortex.