Dissociable roles for cortical and subcortical structures in memory encoding and retrieval

The spatial pattern of the dendritic arborization is a critical determinant of neuronal connectivity and integration. The cerebellar Purkinje cell elaborates a highly branched dendritic tree in a single parasagittal plane. We previously reported that Purkinje cell dendrites extended in multiple sagittal planes and became rapidly confined to a single plane in the third postnatal week. Using confocal and electron microscopy, we observed that multiplanar dendrites in the third week were often associated with ectopic climbing fibers (CFs) extending from adjacent Purkinje cells in distinct sagittal planes. These CFs form VGluT2-positive presynaptic terminals, while many dendritic spines juxtaposing to the CF terminals were immature and did not form obvious postsynaptic membrane thickening. The ectopic CFs with abnormal synapses were not seen in monoplanar Purkinje cells in the fourth postnatal week. The dendrite remodeling was impaired by pharmacological disruption of normal CF activity during remodeling period. Thus, dendritic remodeling is coupled to the selection of proper afferents during the specification of Purkinje cell connectivity.