Molecular and cellular control of dendrite maturation during brain development.

Neuronal dendrites are generated during development by a series of processes involving extension and retraction of dendritic branches in a first step, and subsequently stabilisation of existing dendrites through building of synaptic connections. These processes are tightly controlled at any of these time points and control of dendritic development follows individual differentiation stages. This review describes aspects of the maturation process in cerebellar Purkinje cells and spinal motoneurons. Although motoneurons are glutamatergic whereas Purkinje cells are GABAergic and thereby functionally very different, dendritic maturation processes appear to share common mechanisms and processes in both neuronal cell types. Genetically-regulated cell-intrinsic processes control dendritic outgrowth at an early stage, being thereafter supported by local growth factors. In contrast, increasing synaptic input promotes dendritic maturation by limiting overgrowth at a later stage, with Ca2+-dependent signalling involving PKC or CaMKII as the common mode of action. This series of events apparently is common for other neuronal cell types suggesting a generalised concept for intercellular control of neuronal connectivity.