Poncer J C, Miles R
Laboratoire de Neurobiologie Cellulaire, Institut Pasteur, Paris, France.
J Neurobiol. 1995 Mar;26(3):386-95. doi: 10.1002/neu.480260310.
Pyramidal cells form excitatory synaptic connections with local inhibitory neurons in the hippocampus. This recurrent synapse plays a crucial stabilizing role in the control of hippocampal activity, since it transforms pyramidal cell activity into inhibition of the same pyramidal cell population. Using a combination of dual recording from presynaptic and postsynaptic cells and anatomical techniques, we show that these synaptic connections often comprise a single site for liberation of excitatory transmitter. The resulting excitatory postsynaptic potentials (EPSCs) have a fast time course and a similar amplitude to miniature EPSCs recorded in tetrodotoxin and cobalt. In contrast, activation of metabotropic glutamate receptors (mGluRs) by transmitter liberated during repetitive activation of these synapses produces an excitation with a much slower time course. In addition to somatodendritic mGluRs, which excite inhibitory cells, a different species of mGluR is present on inhibitory cell terminals. This mGluR is activated by higher concentrations of the agonist t-1-amino-cyclopentyl-1,3-decarboxylate and acts to reduce gamma-aminobutyric acid release. mGluRs, thus, have a dual action to enhance and to depress synaptic inhibition in the hippocampus.
锥体细胞与海马体中的局部抑制性神经元形成兴奋性突触连接。这种反馈性突触在海马体活动控制中发挥着关键的稳定作用，因为它将锥体细胞的活动转化为对同一锥体细胞群体的抑制。通过结合对突触前和突触后细胞的双记录以及解剖学技术，我们发现这些突触连接通常包含一个释放兴奋性递质的单一部位。由此产生的兴奋性突触后电位（EPSCs）具有快速的时间进程，其幅度与在河豚毒素和钴中记录的微小EPSCs相似。相比之下，在这些突触的重复激活过程中释放的递质对代谢型谷氨酸受体（mGluRs）的激活产生的兴奋具有慢得多的时间进程。除了兴奋抑制性细胞的树突体mGluRs外，抑制性细胞终末还存在一种不同类型的mGluR。这种mGluR被更高浓度的激动剂t-1-氨基环戊基-1,3-二羧酸激活，并起到减少γ-氨基丁酸释放的作用。因此，mGluRs在增强和抑制海马体突触抑制方面具有双重作用。
