Funahashi M, Stewart M
Department of Physiology, State University of New York Health Science Center at Brooklyn, Box 31, 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
Brain Res. 1998 Mar 16;787(1):19-33. doi: 10.1016/s0006-8993(97)01384-x.
Inhibitory post-synaptic potentials (IPSPs) were studied in neurons of presubiculum, parasubiculum and medial entorhinal cortex in horizontal slices from rat brains. Isolated IPSPs were evoked by extracellular electrical stimuli in the presence of glutamate receptor antagonists. Cellular morphology was identified using Neurobiotin labeling. IPSPs were compared: (a) across morphological cell types, (b) across laminae within regions, and (c) across regions. IPSPs were visible in stellate and pyramidal cells from layers II, III, and V of all retrohippocampal areas during bath application of glutamate antagonists. Qualitative and quantitative differences in IPSPs were only found when comparing responses by superficial layer II, III cells to responses by deep layer V cells. Responses by stellate and pyramidal cells within the same or adjacent layers did not differ, nor did responses differ from region to region. All cell types exhibited an early hyperpolarizing response. The majority (85%) of superficial layer cells in all regions, regardless of cell shape, exhibited a second hyperpolarizing component. Fewer (50%) deep layer cells exhibited the late peak with similar long latencies. IPSPs were typically larger in superficial layer cells. IPSPs were comprised of GABAA and GABAB (gamma-aminobutyric acid) receptor-mediated components. With repetitive stimulation, the peak amplitude of the GABAA receptor-mediated component decreased with successive stimuli, but stabilized during the first five or fewer stimuli to a level that did not vary with stimulation frequency. The GABAB receptor-mediated component also stabilized, but the final amplitude appeared to decrease as the stimulation frequency increased. With high-frequency repetitive stimulation, both components of the IPSP showed summation. We conclude that the most meaningful distinction for IPSPs among retrohippocampal neurons is a laminar distinction, between superficial and deep layer neurons, and not one across cell shape or retrohippocampal subregion. These laminar differences can contribute to synchronous activity by deep layer neurons and restrict the activity of superficial layer neurons.
在大鼠脑水平切片的前下托、下托旁区和内嗅皮质内侧的神经元中研究了抑制性突触后电位（IPSPs）。在存在谷氨酸受体拮抗剂的情况下，通过细胞外电刺激诱发孤立的IPSPs。使用Neurobiotin标记来识别细胞形态。对IPSPs进行了比较：（a）跨形态细胞类型，（b）跨区域内的层，以及（c）跨区域。在浴用谷氨酸拮抗剂期间，所有海马后区域的II、III和V层的星状细胞和锥体细胞中都可见到IPSPs。仅在比较浅层II、III层细胞的反应与深层V层细胞的反应时，才发现IPSPs存在定性和定量差异。同一层或相邻层内的星状细胞和锥体细胞的反应没有差异，不同区域之间的反应也没有差异。所有细胞类型均表现出早期超极化反应。所有区域中，无论细胞形状如何，大多数（85%）浅层细胞都表现出第二个超极化成分。较少比例（50%）的深层细胞表现出具有相似长潜伏期的晚期峰值。IPSPs通常在浅层细胞中更大。IPSPs由GABAA和GABAB（γ-氨基丁酸）受体介导的成分组成。重复刺激时，GABAA受体介导成分的峰值幅度随连续刺激而降低，但在前五次或更少次刺激期间稳定在一个不随刺激频率变化的水平。GABAB受体介导的成分也稳定下来，但最终幅度似乎随着刺激频率的增加而降低。高频重复刺激时，IPSPs的两个成分均表现出总和。我们得出结论，海马后神经元中IPSPs最有意义的区别在于浅层和深层神经元之间的层间区别，而不是细胞形状或海马后亚区域之间的区别。这些层间差异可促进深层神经元的同步活动，并限制浅层神经元的活动。
