Wall M J, Usowicz M M
Department of Pharmacology, University of Bristol, UK.
Eur J Neurosci. 1997 Mar;9(3):533-48. doi: 10.1111/j.1460-9568.1997.tb01630.x.
The postnatal development of spontaneous GABAergic transmission between cerebellar Golgi cells and granule cells was investigated with voltage-clamp recording from rat cerebellar slices, in symmetrical Cl- conditions. Between postnatal days 7 and 14 (P7-14), bicuculline- and TTX (tetrodotoxin)-sensitive spontaneous inhibitory postsynaptic currents (sIPSCs), occurred at high frequency in 56% of granule cells. Between P10 and P14, sIPSCs were superimposed on a tonic current of -12 +/- 1.8 pA at -70 mV, that was accompanied by noise with a variance of 17 +/- 3 pA2. Both the current and noise were inhibited by bicuculline. TTX blocked the bicuculline-sensitive current and noise by approximately 60%. Between P18 and P25, sIPSCs were less frequent; all cells showed tonic, bicuculline-sensitive currents, but these were partially inhibited by TTX (approximately 35%). Between P40 and P53, sIPSCs were rare; tonic, bicuculline-sensitive currents and noise were greater in amplitude, with mean values of -17 pA and 22 pA2 at -70 mV, they were present in all cells but they were not inhibited by TTX. Glycine receptor channels that were expressed in immature, but not adult cells, did not mediate spontaneous currents. Our results indicate that spontaneous transmission onto cerebellar granule cells in immature animals consists primarily of action potential-dependent, phasic release of vesicular GABA. This generates GABAA receptor-mediated sIPSCs. The effects of GABA transporter blockers suggest that it also produces the TTX-sensitive current-noise, as GABA spills out of synapses to activate extrasynaptic receptors or receptors in neighbouring synapses. In older animals, action potential-independent release of transmitter is predominant and results in tonic activation of GABAA receptors. This does not appear to be spontaneous vesicular release of GABA. Neither does it appear to be reversed uptake of GABA, although further work is required to rule out these possibilities.
在对称氯离子条件下，通过对大鼠小脑切片进行电压钳记录，研究了小脑高尔基细胞和颗粒细胞之间自发性γ-氨基丁酸能传递的产后发育情况。在出生后第7至14天（P7 - 14），在56%的颗粒细胞中，荷包牡丹碱和河豚毒素（TTX）敏感的自发性抑制性突触后电流（sIPSCs）高频出现。在P10至P14之间，sIPSCs叠加在-70 mV时-12±1.8 pA的强直电流上，该强直电流伴有方差为17±3 pA²的噪声。电流和噪声均被荷包牡丹碱抑制。TTX使荷包牡丹碱敏感的电流和噪声阻断约60%。在P18至P25之间，sIPSCs频率降低；所有细胞均显示出强直的、荷包牡丹碱敏感的电流，但这些电流被TTX部分抑制（约35%）。在P40至P53之间，sIPSCs很少见；强直的、荷包牡丹碱敏感的电流和噪声幅度更大，在-70 mV时平均值分别为-17 pA和22 pA²，它们存在于所有细胞中，但不被TTX抑制。在未成熟而非成年细胞中表达的甘氨酸受体通道不介导自发性电流。我们的结果表明，未成熟动物中小脑颗粒细胞上的自发性传递主要由动作电位依赖性的囊泡γ-氨基丁酸阶段性释放组成。这产生了GABAA受体介导的sIPSCs。γ-氨基丁酸转运体阻滞剂的作用表明，它还产生了TTX敏感的电流噪声，因为γ-氨基丁酸从突触中溢出以激活突触外受体或相邻突触中的受体。在年龄较大的动物中，递质的非动作电位依赖性释放占主导地位，并导致GABAA受体的强直激活。这似乎不是γ-氨基丁酸的自发性囊泡释放。也似乎不是γ-氨基丁酸的反向摄取，尽管需要进一步的研究来排除这些可能性。
