Histogenesis of the cerebellar climbing fiber in the rat.

Abstract

AbstractEarly climbing fiber metamorphosis has been studied in 250 Golgi preparations of 5–12 day postnatal rat cerebellum, and in less numerous 12–18 day ones. EM controls were provided for the early phase covering maturation of Purkinje cytoplasm, status of axonal neuropil, and synapses between the evanescent nid structure and Purkinje soma membrane.Ramon y Cajal (1890, '11), Athias (1897) and others have contributed extensively to climbing fiber histogenesis. Our results are confirmatory but support more varied developmental detail including that of axonal collateralization within the granular layer, all of which may not persist to maturity. Distinguishing characteristics of climbing fibers are recognized early in histogenesis, including varicosities, redundancies in course, and a manner of branching called cross‐over. The curvaceous path a climbing fiber pursues across the granular layer can be corrected at the ganglionic level by a horizontal segment having length equivalent to the offset. These and other redundancies may straighten out with areal expansion of cortical surface as compared to the restricted white matter base.While supporting multiple innervation of nids by local collateralizations proceeding from stem axons in white matter, the study does not preclude a one to one relationship between adult climbing fiber and Purkinje cell as basic design. Unknown factors are the relative amounts of local collateralization proceeding from several versus a single axon stem, and the extent to which branches are issued from a single fiber to different folia.