Department of Cellular and Network Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Hippocampus. 2012 Jun;22(6):1379-91. doi: 10.1002/hipo.20974. Epub 2011 Sep 28.
The two main glutamatergic pathways to the CA1 area, the Schaffer collateral/commissural input and the entorhinal fibers, as well as the local axons of CA1 pyramidal cells innervate both pyramidal cells and interneurons. To determine whether these inputs differ in their weights of activating GABAergic circuits, we have studied the relative proportion of pyramidal cells and interneurons among their postsynaptic targets in serial electron microscopic sections. Local axons of CA1 pyramidal cells, intracellularly labeled in vitro or in vivo, innervated a relatively high proportion of interneuronal postsynaptic targets (65.9 and 53.8%, in vitro and in vivo, respectively) in stratum (str.) oriens and alveus. In contrast, axons of in vitro labeled CA3 pyramidal cells in str. oriens and str. radiatum of the CA1 area made synaptic junctions predominantly with pyramidal cell spines (92.9%). The postsynaptic targets of anterogradely labeled medial entorhinal cortical boutons in CA1 str. lacunosum-moleculare were primarily pyramidal neuron dendritic spines and shafts (90.8%). The alvear group of the entorhinal afferents, traversing str. oriens, str. pyramidale, and str. radiatum showed a higher preference for innervating GABAergic cells (21.3%), particularly in str. oriens/alveus. These data demonstrate that different glutamatergic pathways innervate CA1 GABAergic cells to different extents. The results suggest that the numerically smaller CA1 local axonal inputs together with the alvear part of the entorhinal input preferentially act on GABAergic interneurons in contrast to the CA3, or the entorhinal input in str. lacunosum-moleculare. The results highlight differences in the postsynaptic target selection of the feed-forward versus recurrent glutamatergic inputs to the CA1 and CA3 areas.
向 CA1 区投射的两个主要谷氨酸能通路，即 Schaffer 侧支/联合传入和内嗅纤维，以及 CA1 锥体神经元的局部轴突，既支配锥体神经元也支配中间神经元。为了确定这些传入在激活 GABA 能回路方面的权重是否不同，我们研究了在连续电镜切片中它们的突触后靶标中锥体神经元和中间神经元的相对比例。在体外或体内进行细胞内标记的 CA1 锥体细胞的局部轴突，在层（str.）或门区（alveus）中支配相对较高比例的中间神经元突触后靶标（分别为 65.9%和 53.8%，在体外和体内）。相比之下，CA1 区的体外标记 CA3 锥体细胞的轴突在层（str.）或门区（str. radiatum）和层（str. radiatum）中主要与锥体细胞的棘突形成突触连接（92.9%）。顺行标记的内侧嗅皮质传入在 CA1 层（str. lacunosum-moleculare）中的终末的突触后靶标主要是锥体神经元树突棘和轴突（90.8%）。穿过层（str. oriens）、层（str. pyramidale）和层（str. radiatum）的内嗅传入的肺泡群对支配 GABA 能细胞（21.3%）表现出更高的偏好，特别是在层（str. oriens/alveus）中。这些数据表明，不同的谷氨酸能通路以不同的程度支配 CA1 GABA 能细胞。结果表明，与 CA3 或内嗅传入的 lacunosum-moleculare 层相比，数量较少的 CA1 局部轴突输入以及内嗅传入的肺泡部分优先作用于 GABA 能中间神经元。结果强调了前馈与反馈谷氨酸能输入到 CA1 和 CA3 区的突触后靶标选择的差异。
