Stepanyants Armen, Hirsch Judith A, Martinez Luis M, Kisvárday Zoltán F, Ferecskó Alex S, Chklovskii Dmitri B
Physics Department and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, MA 02115, USA.
Cereb Cortex. 2008 Jan;18(1):13-28. doi: 10.1093/cercor/bhm027. Epub 2007 Apr 9.
Time invariant description of synaptic connectivity in cortical circuits may be precluded by the ongoing growth and retraction of dendritic spines accompanied by the formation and elimination of synapses. On the other hand, the spatial arrangement of axonal and dendritic branches appears stable. This suggests that an invariant description of connectivity can be cast in terms of potential synapses, which are locations in the neuropil where an axon branch of one neuron is proximal to a dendritic branch of another neuron. In this paper, we attempt to reconstruct the potential connectivity in local cortical circuits of the cat primary visual cortex (V1). Based on multiple single-neuron reconstructions of axonal and dendritic arbors in 3 dimensions, we evaluate the expected number of potential synapses and the probability of potential connectivity among excitatory (pyramidal and spiny stellate) neurons and inhibitory basket cells. The results provide a quantitative description of structural organization of local cortical circuits. For excitatory neurons from different cortical layers, we compute local domains, which contain their potentially pre- and postsynaptic excitatory partners. These domains have columnar shapes with laminar specific radii and are roughly of the size of the ocular dominance column. Therefore, connections between most excitatory neurons in the ocular dominance column can be implemented by local synaptogenesis. Structural connectivity involving inhibitory basket cells is generally weaker than excitatory connectivity. Here, only nearby neurons are capable of establishing more than one potential synapse, implying that within the ocular dominance column these connections have more limited potential for circuit remodeling.
树突棘持续的生长和回缩以及伴随而来的突触形成与消除，可能会使皮质回路中突触连接的时不变描述难以实现。另一方面，轴突和树突分支的空间排列似乎是稳定的。这表明，可以根据潜在突触来构建连接性的不变描述，潜在突触是指一个神经元的轴突分支与另一个神经元的树突分支在神经毡中相邻的位置。在本文中，我们试图重建猫初级视觉皮层（V1）局部皮质回路中的潜在连接性。基于对轴突和树突分支的多个三维单神经元重建，我们评估了兴奋性（锥体神经元和棘状星形神经元）神经元与抑制性篮状细胞之间潜在突触的预期数量以及潜在连接的概率。结果提供了局部皮质回路结构组织的定量描述。对于来自不同皮质层的兴奋性神经元，我们计算了局部区域，其中包含它们潜在的突触前和突触后兴奋性伙伴。这些区域呈柱状，具有层特异性半径，大小大致与眼优势柱相同。因此，眼优势柱中大多数兴奋性神经元之间的连接可以通过局部突触形成来实现。涉及抑制性篮状细胞的结构连接通常比兴奋性连接弱。在这里，只有附近的神经元能够建立不止一个潜在突触，这意味着在眼优势柱内，这些连接在回路重塑方面的潜力更有限。
