Juliano S L, Palmer S L, Sonty R V, Noctor S, Hill G F
Department of Anatomy and Cell Biology, USUHS, Bethesda, Maryland 20814, USA.
J Comp Neurol. 1996 Oct 14;374(2):259-77. doi: 10.1002/(SICI)1096-9861(19961014)374:2<259::AID-CNE8>3.0.CO;2-1.
Ferrets have become recognized as a useful and interesting model for study of neocortical development. Because of their immaturity at birth, it is possible to study very early events in the ontogeny of the brain. We used living slices of ferret somatosensory cortex to study the formation and development of intrinsic elements within the neocortex. A small number of fixed, hemisected brains injected with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) were also used. The slices were obtained from ferret kits aged postnatal day (P)1 to P62 and maintained in a chamber; each slice received injections of fluorescent-labeled dextrans. The injections were made at different ages in several distinct sites, which included the proliferative ventricular zone, the intervening white matter (or intermediate zone), and different sites of developing cortex, including the deeper cortical plate, which incorporated the subplate in young animals, and more superficial cortical sites depending on the age of the animal. Several animals also received injections into the ventrobasal thalamus. Injections into young animals (P1-7) produced a dominant radial pattern that extended from the ventricular zone into the cortex. Injections into the ventricular zone labeled many cells that appeared morphologically like radial glia as well as presumptive neurons. Although the predominant pattern was radial, injections in the ventricular zone often produced tangentially oriented cells and horizontally arranged fibers at the outer edge of the proliferative zone. These cells and fibers may provide a substrate for tangential dispersion of neurons within the neocortex. More superficial injections within the slice labeled lines of cells that appeared to be stacked upon one another in a radial pile in the cortex; the cortical plate received very few lateral projections. Data obtained from more mature slices indicated that although the overall pattern of staining remained radial, the precise character of the pattern changed to include more lateral spread into surrounding cortex, which eventually refined and developed into distinct patches by P28, when the overall cortical architecture appeared adult like. The data involving thalamocortical connections were more limited, but they indicated that the thalamus projects precisely to the somatosensory cortex in a point-to-point fashion from the earliest date studied (P0) and that the ventrobasal nucleus terminates upon the somatosensory cortex in a patchy manner during the early postnatal days of development. This study of the development of the somatosensory cortex confirms the ubiquitous nature of column-like connections throughout the neocortex and provides a novel view of the radial nature of early neocortical maturation.
雪貂已被公认为是研究新皮质发育的一种有用且有趣的模型。由于雪貂出生时不成熟，因此有可能研究大脑个体发育过程中非常早期的事件。我们使用雪貂体感皮层的活切片来研究新皮质内固有成分的形成和发育。还使用了少量注射了高氯酸盐1,1'-二辛基-3,3,3',3'-四甲基吲哚羰花青（DiI）的固定半脑。切片取自出生后第1天（P1）至第62天的雪貂幼崽，并保存在一个腔室中；每个切片都注射了荧光标记的葡聚糖。在几个不同的部位于不同年龄进行注射，这些部位包括增殖性脑室区、中间白质（或中间区）以及发育中的皮质的不同部位，包括较深的皮质板（在幼小动物中包含亚板），以及根据动物年龄而定的更浅表的皮质部位。几只动物还接受了向腹侧基底丘脑的注射。对幼小动物（P1 - 7）的注射产生了一种占主导地位的放射状模式，从脑室区延伸到皮质。向脑室区的注射标记了许多形态上类似放射状胶质细胞以及推测的神经元的细胞。尽管主要模式是放射状的，但在脑室区的注射通常会在增殖区的外边缘产生切向排列的细胞和水平排列的纤维。这些细胞和纤维可能为新皮质内神经元的切向扩散提供了一个基质。在切片内更浅表部位的注射标记了在皮质中似乎以放射状堆积彼此堆叠的细胞线；皮质板接受的横向投射很少。从更成熟的切片获得的数据表明，尽管染色的总体模式仍然是放射状的，但模式的精确特征发生了变化，包括更多地横向扩散到周围皮质，到P28时最终细化并发展成不同的斑块，此时整体皮质结构看起来像成年个体。涉及丘脑皮质连接的数据更为有限，但它们表明，从最早研究的日期（P0）起，丘脑就以点对点的方式精确地投射到体感皮层，并且在出生后早期发育阶段，腹侧基底核以斑片状方式终止于体感皮层。这项对体感皮层发育的研究证实了柱状连接在整个新皮质中普遍存在的性质，并为早期新皮质成熟的放射状性质提供了新的视角。
