Cossart R, Hirsch J C, Cannon R C, Dinoncourt C, Wheal H V, Ben-Ari Y, Esclapez M, Bernard C
INSERM U29-INMED, Parc Scientifique de Luminy, BP 13, 13273 Cedex 09, Marseille, France.
Neuroscience. 2000;99(4):593-603. doi: 10.1016/s0306-4522(00)00231-1.
Excitatory and inhibitory pathways have specific patterns of innervation along the somato-dendritic axis of neurons. We have investigated whether this morphological diversity was associated with variations in the frequencies of spontaneous and miniature GABAergic and glutamatergic synaptic currents along the somato-dendritic axis of rat hippocampal CA1 pyramidal neurons. Using in vitro whole cell recordings from somata, apical dendrites and basal dendrites (for which we provide the first recordings) of CA1 pyramidal neurons, we report that over 90% of the spontaneous currents were GABAergic, <10% being glutamatergic. The frequency of spontaneous GABAergic currents was comparable in the soma and in the dendrites. In both somata and dendrites, the Na(+) channel blocker tetrodotoxin abolished more than 80% of the spontaneous glutamatergic currents. In contrast, tetrodotoxin abolished most dendritic (>90%) but not somatic (<40%) spontaneous GABAergic currents. Computer simulations suggest that in our experimental conditions, events below 40pA are electrotonically filtered to such a degree that they are lost in the recording noise. We conclude that, in vitro, inhibition is massively predominant over excitation and quantitatively evenly distributed throughout the cell. However, inhibition appears to be mainly activity-dependent in the dendrites whereas it can occur in the absence of interneuron firing in the soma. These results can be used as a benchmark to compare values obtained in pathological tissue, such as epilepsies, where changes in the balance between excitation and inhibition would dramatically alter cell behaviour.
兴奋性和抑制性通路在神经元的胞体 - 树突轴上具有特定的神经支配模式。我们研究了这种形态学上的多样性是否与大鼠海马CA1锥体神经元胞体 - 树突轴上自发的以及微小的GABA能和谷氨酸能突触电流频率的变化相关。通过对CA1锥体神经元的胞体、顶端树突和基底树突（我们首次对其进行记录）进行体外全细胞记录，我们发现超过90%的自发电流是GABA能的，谷氨酸能的不到10%。自发GABA能电流的频率在胞体和树突中相当。在胞体和树突中，钠通道阻滞剂河豚毒素消除了超过80%的自发谷氨酸能电流。相比之下，河豚毒素消除了大部分树突（>90%）但不是胞体（<40%）的自发GABA能电流。计算机模拟表明，在我们的实验条件下，低于40pA的事件在电紧张性上被过滤到如此程度，以至于它们在记录噪声中丢失。我们得出结论，在体外，抑制作用在数量上大大超过兴奋作用，并且在整个细胞中定量均匀分布。然而，抑制作用在树突中似乎主要依赖于活动，而在胞体中，即使在中间神经元不放电的情况下也可能发生。这些结果可作为一个基准，用于比较在病理组织（如癫痫）中获得的值，在这些病理组织中，兴奋与抑制之间平衡的变化会显著改变细胞行为。
