Introduction

Dendrites are the scaffolding onto which the majority of synapses occur. The size and shape of dendritic arbors limits the number and type of synapses that a neuron can form, and therefore, determines the complexity and function of the neuronal network to which it belongs. Since dendrite shape also influences spread and convergence of transmembrane potentials associated with synaptic input and cellular excitability, dendritic arbor morphology is integrally involved in functional properties of signal processing1,2. The diversity of patterns of dendritic arbor structures and the high conservation of these patterns within specific cell types also suggest an important link between form and function. How do developing neurons achieve elaborate dendritic arbor morphologies? The ability of neurons within a specific class to faithfully adhere to a general arbor pattern, and the recapitulation, to some degree, of this pattern when neurons are dissociated and regrown in cultures largely devoid of normal environmental cues strongly suggests a genetic basis for general arbor structure. However, the unique characteristics of individual neuronal arbors in specific dendrite characteristics such as exact positions of branch points, branch lengths, and branch number supports influence from factors extrinsic to the cell. A model involving the interplay between genetic programming of general dendritic arbor form and influence from multiple extrinsic environmental factors is supported by the recent findings of transcription factors associated with dendritic arbor shapes3,4, and a growing list of growth-modifying extracellular molecules, including neurotrophic growth factors5-9, and chemoaffinity guidance molecules10,11. Another critical component of the growing neuron's environment is neurotransmission from afferent innervation. Here we review evidence implicating neurotransmission in regulating dendrite growth and focus on the potential involvement of activity-dependent synaptogenesis in this process.

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