Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath, United Kingdom.
School of Biomedical & Healthcare Sciences, Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, United Kingdom.
PLoS One. 2014 Jan 15;9(1):e85125. doi: 10.1371/journal.pone.0085125. eCollection 2014.
The entorhinal cortex (EC) controls hippocampal input and output, playing major roles in memory and spatial navigation. Different layers of the EC subserve different functions and a number of studies have compared properties of neurones across layers. We have studied synaptic inhibition and excitation in EC neurones, and we have previously compared spontaneous synaptic release of glutamate and GABA using patch clamp recordings of synaptic currents in principal neurones of layers II (L2) and V (L5). Here, we add comparative studies in layer III (L3). Such studies essentially look at neuronal activity from a presynaptic viewpoint. To correlate this with the postsynaptic consequences of spontaneous transmitter release, we have determined global postsynaptic conductances mediated by the two transmitters, using a method to estimate conductances from membrane potential fluctuations. We have previously presented some of this data for L3 and now extend to L2 and L5. Inhibition dominates excitation in all layers but the ratio follows a clear rank order (highest to lowest) of L2>L3>L5. The variance of the background conductances was markedly higher for excitation and inhibition in L2 compared to L3 or L5. We also show that induction of synchronized network epileptiform activity by blockade of GABA inhibition reveals a relative reluctance of L2 to participate in such activity. This was associated with maintenance of a dominant background inhibition in L2, whereas in L3 and L5 the absolute level of inhibition fell below that of excitation, coincident with the appearance of synchronized discharges. Further experiments identified potential roles for competition for bicuculline by ambient GABA at the GABAA receptor, and strychnine-sensitive glycine receptors in residual inhibition in L2. We discuss our results in terms of control of excitability in neuronal subpopulations of EC neurones and what these may suggest for their functional roles.
内嗅皮层（entorhinal cortex，EC）控制海马的输入和输出，在记忆和空间导航中发挥主要作用。EC 的不同层具有不同的功能，许多研究比较了不同层的神经元特性。我们研究了 EC 神经元的突触抑制和兴奋，我们之前使用 II 层（L2）和 V 层（L5）主神经元的突触电流的膜片钳记录比较了谷氨酸和 GABA 自发突触释放的特性。在这里，我们增加了 L3 层的比较研究。这种研究从突触前的角度来看基本上是神经元活动。为了将其与自发递质释放的突触后后果相关联，我们使用一种从膜电位波动估计电导的方法确定了两种递质介导的全局突触后电导。我们之前已经为 L3 呈现了部分此类数据，现在扩展到 L2 和 L5。在所有层中，抑制都占主导地位，但兴奋的比例遵循明显的等级顺序（从高到低）：L2>L3>L5。与 L3 或 L5 相比，L2 中的背景电导的方差对于兴奋和抑制明显更高。我们还表明，通过 GABA 抑制阻断诱导同步网络癫痫样活动揭示了 L2 相对不愿意参与这种活动。这与 L2 中背景抑制的主导地位保持相关，而在 L3 和 L5 中，抑制的绝对水平下降到兴奋以下，与同步放电的出现一致。进一步的实验确定了环境 GABA 在 GABAA 受体上对双氯苯氧丁酸的竞争以及 L2 中残留抑制中的斯特里克斯敏感甘氨酸受体的潜在作用。我们根据 EC 神经元的兴奋性神经元亚群的控制及其对功能角色的可能暗示来讨论我们的结果。
