Keller A, Asanuma H
Department of Anatomy and Cell Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814.
J Comp Neurol. 1993 Oct 8;336(2):229-42. doi: 10.1002/cne.903360206.
The intracortical synaptic relationships of pyramidal neurons in the cat motor cortex were studied by intracellular recording and labeling techniques. Neurons that responded with monosynaptic excitatory postsynaptic potentials (EPSPs) to microstimulation in the somatosensory cortex were identified by intracellular recordings. Long-term potentiation (LTP) was evoked in all of these neurons (n = 15), following tetanic stimulation (50 Hz, 5 s) of their afferents from the somatosensory cortex. Three of these cells (cells A-C) were identified as pyramidal neurons, following intracellular injections of Neurobiotin. The intracortical axon collaterals of these labeled cells arborized extensively, forming terminal clusters both in close proximity to the parent soma and along their long, horizontal branches. Terminal clusters in both the proximal and in the distal termination zones of each of the cells were studied by electron microscopy. In their proximal arborization zones, the axon collaterals of the labeled pyramidal neurons synapsed preferentially with dendritic spines belonging to other pyramidal cells. In contrast, in their distal terminal clusters, the axon collaterals of each of the cells formed synapses in different proportions with different postsynaptic targets. The distal axon collaterals of cell A formed 86% of their synapses with pyramidal neurons; those of cell B formed 64% of their synapses with pyramidal cells, the remaining synapses with the dendritic shafts and somata of nonpyramidal neurons, and those of cell C provided most of their output (68%) to nonpyramidal, presumably inhibitory neurons. These findings suggest a high selectivity of intrinsic axon collaterals to form specific patterns of synapses. The patterns of synaptic interactions formed by these intrinsic axon collaterals may be a substrate for shaping and modulating representation maps in the motor cortex.
通过细胞内记录和标记技术，对猫运动皮层中锥体神经元的皮质内突触关系进行了研究。通过细胞内记录，识别出对体感皮层微刺激产生单突触兴奋性突触后电位（EPSP）反应的神经元。在对来自体感皮层的传入纤维进行强直刺激（50 Hz，5 s）后，所有这些神经元（n = 15）均诱发了长时程增强（LTP）。在细胞内注射Neurobiotin后，其中三个细胞（A - C细胞）被鉴定为锥体神经元。这些标记细胞的皮质内轴突侧支广泛分支，在靠近母细胞体处及其长的水平分支上均形成终末簇。通过电子显微镜研究了每个细胞近端和远端终末区的终末簇。在其近端分支区，标记的锥体神经元的轴突侧支优先与属于其他锥体细胞的树突棘形成突触。相比之下，在其远端终末簇中，每个细胞的轴突侧支与不同的突触后靶点形成不同比例的突触。细胞A的远端轴突侧支86%的突触与锥体神经元形成；细胞B的远端轴突侧支64%的突触与锥体细胞形成，其余突触与非锥体神经元的树突干和细胞体形成，而细胞C的远端轴突侧支大部分输出（68%）提供给非锥体神经元，推测为抑制性神经元。这些发现表明内在轴突侧支形成特定突触模式具有高度选择性。这些内在轴突侧支形成的突触相互作用模式可能是塑造和调节运动皮层表征图谱的基础。
