Evidence that Astroglia Influence Dendrite Morphogenesis and Synaptogenesis Independently in the Vertebrate Central Nervous System

In the absence of external spatial cues, dendritic arbors of neurons grown in vitro approximate those observed in situ. Absent, however, from these culture models is patterned orientation of dendritic trunks, and variation of branch geometry that provide identifiable characteristics of the cytoarchitecture of the intact brain. Although astroglia are present during key stages of dendritic development in vivo, little is known about whether local interactions with glia shape dendritic growth. Astroglial cells are good candidates for this kind of regulation because they can exert control over the formation of synapses, an event correlated with the maturational state of the dendrite. The present review highlights some key findings from vertebrate model systems offering evidence that astroglia can contribute to the shape, and growth, of the dendritic arbor. Drawing from our recent work using a co-culture system composed of neurons growing in differential contact with astroglia, we discuss findings that suggest: 1) growth of dendrites, and addition of synapses, can be independent; further, while astroglia promote synapse formation, they inhibit dendritic growth; 2) astroglia mediate dendrite growth through both paracrine, and contact-dependent mechanisms; and 3) astroglia appear to impose pattern by constraining the growth of dendrites within their zones of influence