Intrinsic versus extrinsic determinants during the development of Purkinje cell dendrites

The peculiar shape and disposition of Purkinje cell (PC) dendrites, planar and highly branched, offers an optimal model to analyze cellular and molecular regulators for the acquisition of neuronal dendritic trees. During the first 2 weeks after the end of the proliferation period, PCs undergo a 2-phase remodeling process of their dendrites. The first phase consists in the complete retraction of the primitive but extensive dendritic tree, together with the formation of multiple filopodia-like processes arising from the cell body. In the second phase, there is a progressive disappearance of the somatic processes along with rapid growth and branching of the mature dendrite. Mature Purkinje cell dendrites bear two types of spiny protrusions, named spine and thorn. The spines are numerous, elongated, located at the distal dendritic compartment and form synapses with parallel fibers, whereas the thorns are shorter, rounded, emerge from the proximal compartment and synapse with climbing fibers.