Mason C A, Christakos S, Catalano S M
Department of Pathology, Columbia University College of Physicians and Surgeons, New York, New York 10032.
J Comp Neurol. 1990 Jul 1;297(1):77-90. doi: 10.1002/cne.902970106.
The time and place of initial contacts between afferent axons and their target cells are not known for most regions of the mammalian CNS. To address this issue, we have selectively visualized afferent climbing fiber axons together with their synaptic targets, Purkinje cells, in postnatal mouse cerebellum. Climbing fibers were orthogradely labeled by injection of rhodamine isothiocyanate into their brainstem source, the inferior olivary nucleus. Purkinje cells were localized with an antibody to a calcium-binding protein, calbindin D-28k (CaBP), in the same section or in adjacent sections. A novel view of the olivocerebellar projection and the morphology of climbing fiber arbors prior to the well-known "nest" stage has emerged from this analysis. At birth, climbing fibers project into the zone of Purkinje cells, before these cells have aligned into a monolayer. During this phase, climbing fibers have simple morphologies consisting of relatively unbranched terminal arbors and small tapered growing tips. Purkinje cells are arranged 3-6 cells deep and have tufted dendrites and relatively smooth somata. By postnatal days 3-4, climbing fibers branch over several adjacent Purkinje cell perikarya, which are still organized in a band several cells thick. From postnatal days 5-7, when climbing fibers subsequently make focused nests on individual cells, Purkinje somata are smoother and form a more distinct monolayer. Up to this time, however, climbing fibers continue to associate with Purkinje perikarya, even though Purkinje cell dendrites have emerged and branched extensively. By postnatal days 8-10, climbing fiber terminals climb onto the trunk of the relatively mature Purkinje dendritic tree. At birth, mossy fibers originating from the pontine nuclei resemble immature climbing fibers in that they also have a simple unbranched morphology and growing tips, but project only so far as the internal granule cell layer. Occasional individual fibers reach into the Purkinje zone both at postnatal day 0 and postnatal day 4, confirming that the fibers formerly described as "combination fibers" (Mason and Gregory, S4. J. Neurosci, 4:1715-1735) can be mossy in origin. These data demonstrate that climbing fibers project among Purkinje cells earlier than suspected, before these afferents begin to arborize and form pericellular nests. Our observations are not in accord with the view derived from autoradiographic tracing studies that as in other cortical areas, climbing afferents wait in the vicinity of Purkinje cells in the early neonatal period, then advance onto these cells in synchrony with Purkinje cell alignment into a monolayer and dendritic maturation.(ABSTRACT TRUNCATED AT 400 WORDS)
对于哺乳动物中枢神经系统的大多数区域，传入轴突与其靶细胞最初接触的时间和地点尚不清楚。为了解决这个问题，我们在出生后的小鼠小脑中选择性地观察了传入的攀缘纤维轴突及其突触靶标浦肯野细胞。通过将异硫氰酸罗丹明注入其脑干来源——下橄榄核，对攀缘纤维进行顺行标记。在同一切片或相邻切片中，用针对钙结合蛋白钙结合蛋白D - 28k（CaBP）的抗体定位浦肯野细胞。通过该分析，出现了对橄榄小脑投射以及在著名的“巢”阶段之前攀缘纤维分支形态的全新认识。出生时，攀缘纤维投射到浦肯野细胞区域，此时这些细胞尚未排列成单层。在此阶段，攀缘纤维具有简单的形态，由相对无分支的终末分支和小的锥形生长尖端组成。浦肯野细胞排列成3 - 6层深，具有簇状树突和相对光滑的胞体。到出生后第3 - 4天，攀缘纤维在几个相邻的浦肯野细胞胞体上分支，这些胞体仍排列成几层细胞厚的带。从出生后第5 - 7天开始，当攀缘纤维随后在单个细胞上形成集中的巢时，浦肯野细胞胞体更光滑并形成更明显的单层。然而，直到此时，即使浦肯野细胞树突已经出现并广泛分支，攀缘纤维仍继续与浦肯野细胞胞体相关联。到出生后第8 - 10天左右，攀缘纤维终末爬上相对成熟的浦肯野树突的主干。出生时，源自脑桥核的苔藓纤维类似于未成熟的攀缘纤维，它们也具有简单的无分支形态和生长尖端，但仅延伸至内颗粒层。在出生后第0天和第4天，偶尔有个别纤维延伸到浦肯野细胞区域，这证实了先前描述为“联合纤维”（梅森和格雷戈里，《神经科学杂志》，4:1715 - 1735）的纤维可能起源于苔藓纤维。这些数据表明，攀缘纤维在浦肯野细胞之间的投射比预期更早，在这些传入纤维开始分支并形成细胞周巢之前。我们的观察结果与放射自显影追踪研究得出的观点不一致，即与其他皮质区域一样，攀缘传入纤维在新生儿早期在浦肯野细胞附近等待，然后与浦肯野细胞排列成单层和树突成熟同步地延伸到这些细胞上。（摘要截取自400字）
