Rumberger A, Tyler C J, Lund J S
Department of Visual Science, Institute of Ophthalmology, UCL, 11-43 Bath Street, EC1 V9EL, London, UK.
Neuroscience. 2001;102(1):35-52. doi: 10.1016/s0306-4522(00)00475-9.
We have qualitatively and quantitatively analysed the anatomical connections within and between rat primary visual cortex (V1) and the rim region surrounding area V1, using both ortho- and retrograde anatomical tracers (biotinylated dextran amine, biocytin, cholera toxin b subunit). From the analysis of the projection patterns, and with the assumption that single points in the rat visual cortex, as in other species, have projection fields made up of multiple patches of terminals, we have concluded that just two V1 recipient areas occupy the entire rim region: an anterolateral area, probably homologous with V2 in other mammals, previously named Oc2L, and a medial area, corresponding to Oc2M. A non-reciprocal projection from the anterolateral area to the medial area was identified. Small injections (300-600microm uptake zone diameter) of the anatomical tracers in area V1, or in the rim region, label orthograde intra-areal connections from each injection site to offset small patches. This is found in all regions of the rim and within at least the relatively expanded central dorsal field representation of V1. From the extent of these projections in V1 and the two rim regions, we have estimated that the neurons at the injection site send diverging laterally spreading projections to other neurons whose receptive fields share any part of the area included in the pooled receptive fields of the neurons at the injection site. Orthogradely labelled inter-areal feedforward projections from V1 to either rim region are estimated to diverge in their projections to neurons that share any part of the area of the pooled receptive fields of the V1 intra-areal connectional field of the same injection. The orthogradely labelled feedback projections to V1, from injection sites in either rim region, reach V1 neurons whose pooled receptive fields match those of the neurons in the rim injection site, i.e. with no divergence. Despite patchy anatomical connectional fields, our estimates indicate that visual space is represented continuously in the receptive fields of neurons postsynaptic to each intra- or inter-areal field of orthograde label. We suggest that, despite the absence of regularly mapped functions in rat V1 (e.g. regularly arranged orientation specificity), which in other species (e.g. primates and cats) relate to the patchy connectional patterns, the rat visual cortex intra- and inter-areal anatomical connections follow similar patterns and scaling factors to those in other species.
我们使用正向和逆向解剖示踪剂（生物素化葡聚糖胺、生物胞素、霍乱毒素b亚基），对大鼠初级视觉皮层（V1）内部以及V1与V1周围边缘区域之间的解剖连接进行了定性和定量分析。通过对投射模式的分析，并假设与其他物种一样，大鼠视觉皮层中的单个点具有由多个终末斑块组成的投射场，我们得出结论，整个边缘区域仅由两个V1接受区占据：一个前外侧区域，可能与其他哺乳动物的V2同源，之前称为Oc2L，以及一个内侧区域，对应于Oc2M。我们确定了从前外侧区域到内侧区域的非互惠投射。在V1区域或边缘区域小剂量注射（摄取区直径300 - 600微米）解剖示踪剂，会标记从每个注射部位到偏移小斑块的正向区域内连接。在边缘的所有区域以及至少在V1相对扩展的中央背侧视野表征内都发现了这种情况。根据这些在V1和两个边缘区域的投射范围，我们估计注射部位的神经元向其他神经元发出横向扩散的发散投射，这些神经元的感受野共享注射部位神经元合并感受野中包含区域的任何部分。从V1到任一边缘区域的正向标记的区域间前馈投射估计在其投射到共享同一注射的V1区域内连接场合并感受野区域任何部分的神经元时会发散。从任一边缘区域的注射部位到V1的正向标记的反馈投射到达其合并感受野与边缘注射部位神经元的合并感受野匹配的V1神经元，即没有发散。尽管存在斑块状的解剖连接场，但我们的估计表明，在正向标记的每个区域内或区域间场的突触后神经元的感受野中，视觉空间是连续表征的。我们认为，尽管大鼠V1中不存在像其他物种（如灵长类动物和猫）那样规则映射的功能（例如规则排列的方向特异性），而这些功能与斑块状连接模式相关，但大鼠视觉皮层区域内和区域间的解剖连接遵循与其他物种相似的模式和缩放因子。
