Tetteh Hannnah, Lee Jihwan, Lee Jinho, Kim Jae Geun, Yang Sunggu
Department of Biomedical Sciences, City University of Hong Kong;
Department of Biomedical Sciences, City University of Hong Kong.
J Vis Exp. 2019 Aug 11(150). doi: 10.3791/59879.
The study of synaptic plasticity in the hippocampus has focused on the use of the CA3-CA1 lamellar network. Less attention has been given to the longitudinal interlamellar CA1-CA1 network. Recently however, an associational connection between CA1-CA1 pyramidal neurons has been shown. Therefore, there is the need to investigate whether the longitudinal interlamellar CA1-CA1 network of the hippocampus supports synaptic plasticity. We designed a protocol to investigate the presence or absence of long-term synaptic plasticity in the interlamellar hippocampal CA1 network using electrophysiological field recordings both in vivo and in vitro. For in vivo extracellular field recordings, the recording and stimulation electrodes were placed in a septal-temporal axis of the dorsal hippocampus at a longitudinal angle, to evoke field excitatory postsynaptic potentials. For in vitro extracellular field recordings, hippocampal longitudinal slices were cut parallel to the septal-temporal plane. Recording and stimulation electrodes were placed in the stratum oriens (S.O) and the stratum radiatum (S.R) of the hippocampus along the longitudinal axis. This enabled us to investigate the directional and layer specificity of evoked excitatory postsynaptic potentials. Already established protocols were used to induce long-term potentiation (LTP) and long-term depression (LTD) both in vivo and in vitro. Our results demonstrated that the longitudinal interlamellar CA1 network supports N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) with no directional or layer specificity. The interlamellar network, however, in contrast to the transverse lamellar network, did not present with any significant long-term depression (LTD).
海马体中突触可塑性的研究主要集中在CA3-CA1层状网络的应用上。而对纵向层间CA1-CA1网络的关注较少。然而，最近研究表明CA1-CA1锥体神经元之间存在一种联合连接。因此，有必要研究海马体的纵向层间CA1-CA1网络是否支持突触可塑性。我们设计了一个实验方案，利用体内和体外的电生理场记录来研究海马体层间CA1网络中是否存在长期突触可塑性。对于体内细胞外场记录，将记录电极和刺激电极以纵向角度放置在背侧海马体的隔颞轴上，以诱发场兴奋性突触后电位。对于体外细胞外场记录，将海马体纵向切片平行于隔颞平面切割。记录电极和刺激电极沿纵轴放置在海马体的原层（S.O）和辐射层（S.R）中。这使我们能够研究诱发的兴奋性突触后电位的方向和层特异性。我们使用已建立的实验方案在体内和体外诱导长时程增强（LTP）和长时程抑制（LTD）。我们的结果表明，纵向层间CA1网络支持N-甲基-D-天冬氨酸（NMDA）受体依赖性长时程增强（LTP），且没有方向或层特异性。然而，与横向层状网络相比，层间网络未出现任何显著的长时程抑制（LTD）。
