Casanovas-Aguilar C, Miró-Bernié N, Pérez-Clausell J
Departament de Biologia Cel small middle dotlular, Universitat de Barcelona, Diagonal 645, ES-08071, Barcelona, Spain.
Neuroscience. 2002;110(3):445-58. doi: 10.1016/s0306-4522(01)00482-1.
Zinc-rich synaptic boutons in the neocortex arise from the neocortex itself. However, the precise organisation of these circuits is not known. Therefore, the laminar and areal pattern of zinc-rich cortico-cortical connections between visual areas was studied by retrograde tracing using intracerebral injections of sodium selenite. This tracer was injected in supragranular and infragranular layers in various cortical visual areas in order to precipitate zinc in the synaptic boutons, which was retrogradely transported to neuronal somata. Supragranular injections led to retrogradely labelled neurones in layer II-III, ipsilaterally and contralaterally. Neurones often appeared in groups or clusters. Infragranular injections labelled neurones in layers II-III, VI and, to a lesser extent, in layer V, both ipsilaterally and contralaterally. Neurones in layer VI formed a wide continuous band. Concerning the connections between visual (=occipital) areas, injections in occipital area 2, lateral part (Oc2L), rendered the largest number of retrogradely labelled neurones, which were located in occipital area 1 (Oc1), occipital area 2, medial part (Oc2M) and outside the visual cortex. Callosal zinc-rich projections were dense in the homotopic area but sparse in Oc1 and temporal cortex. Injections in Oc1 rendered moderate numbers of labelled neurones in occipital areas, in both hemispheres. Injections in Oc2M labelled moderate numbers of neurones in occipital areas in both hemispheres and in the frontal and cingulate cortices. These results indicate that zinc-rich cortico-cortical connections are organised into two segregated systems arising from either supragranular or infragranular neurones. In addition, in the visual cortex, zinc-rich systems appear to converge on Oc2L. Zinc-rich connections appear as an extensive, highly organised association system.
新皮层中富含锌的突触小体源自新皮层本身。然而，这些回路的确切组织方式尚不清楚。因此，通过向脑内注射亚硒酸钠进行逆行追踪，研究了视觉区域之间富含锌的皮质-皮质连接的分层和区域模式。将这种示踪剂注射到各个皮质视觉区域的颗粒上层和颗粒下层，以便在突触小体中沉淀锌，锌会被逆行运输到神经元胞体。颗粒上层注射导致同侧和对侧第II - III层出现逆行标记的神经元。神经元常常成群或成簇出现。颗粒下层注射标记了同侧和对侧第II - III层、第VI层以及程度较轻的第V层中的神经元。第VI层中的神经元形成了一条宽阔的连续带。关于视觉（枕叶）区域之间的连接，在枕叶2区外侧部（Oc2L）注射后，逆行标记的神经元数量最多，这些神经元位于枕叶1区（Oc1）、枕叶2区内侧面（Oc2M）以及视觉皮层之外。胼胝体富含锌的投射在同位区域密集，但在Oc1和颞叶皮层稀疏。在Oc1注射后，两个半球的枕叶区域都有适量数量的标记神经元。在Oc2M注射后，两个半球的枕叶区域以及额叶和扣带回皮层都有适量数量的神经元被标记。这些结果表明，富含锌的皮质-皮质连接被组织成两个分离的系统，分别源自颗粒上层或颗粒下层的神经元。此外，在视觉皮层中，富含锌的系统似乎汇聚于Oc2L。富含锌的连接呈现为一个广泛的、高度有组织的联合系统。
