The role of climbing fibers in the formation of Purkinje cell dendrites

Abstract

Abstract The relationship of the climbing fibers to developing Purkinje cells in the cerebellums of fetal macaques at 75‐, 100‐, 125‐, and 150‐days after conception was studied using Golgi stains and electron microscopic techniques. Between 125 and 150 days of fetal life the somatic processes of the Purkinje cells were most prominent and the apical dendrites were in the initial stages of their development. Serial sections of Purkinje cells, in the cerebellums of 125‐day fetuses, were made and photographed in the electron microscope. Montages of individual Purkinje cells were prepared to permit tracing of the somatic processes and the climbing fibers. It was observed that Purkinje cells developed processes only after becoming associated with climbing fibers and that the climbing fiber terminals capped the growing ends of the processes at this critical stage. In several cases, growing tips of these processes penetrated the terminal boutons. The fine structure of the synaptic junction between the climbing fiber terminal and the Purkinje cell was analyzed using stereo‐electron micrographs (× 125,000). From these observations and those of other authors it was concluded that the climbing fiber induces the formation of somatic processes which then develop into the elaborate dendritic tree. Furthermore, it is proposed that synaptic connections have contractile properties, and that it is this contractility which induces dendrite elaboration.