![]() ![]() Collectively, these findings point toward mechanisms whereby astroglia could influence the competence, or developmental state, of the dendrite. ![]() Moreover, a number of growth factors have been identified that selectively alter dendritic, but not axonal growth, of forebrain neurons, e.g., and these factors may be produced, or regulated by astroglia. In addition, astroglia produce factors that modulate synaptic efficacy and regulate synapse pruning. Because immature dendrites are not receptive to innervation, these synaptogenic effects could imply an astroglial contribution to dendrite maturation. Astroglia secrete factors that facilitate synapse formation, both in terms of the onset and of rate. Mounting evidence, however, demonstrated that interactions between neurons and astroglia were crucial to other aspects of dendritic development. In 2010, Procko and Shaham proposed that glial cells might play such a role, although, at that time, direct evidence in vertebrate systems was lacking. The hypothesis that astrocytes might also shape dendrites has received less attention. It is hard to envision how these homotypic mechanisms contribute to the cases where branching pattern and density vary stereotypically along a single primary stalk of the arbor, however. Such an arrangement optimizes dendritic capture of incoming afferents and is now understood at a mechanistic level. Similarly, segregation of branch territories has also been recognized as important in understanding how the dendritic arbors of a single type, or class, of neuron within a brain region are arranged in a territorial configuration. The mechanism of “self-avoidance” between dendrites within a given arbor can help establish appropriate spacing of branches (for review, see ). For example, interactions within, and between, neurons are one important source of cues involved in ontogenesis of the dendritic arbor. ![]() Based on the shape of the soma, and orientation of the primary dendrites, the major dendrite that points toward the upper left of the frame might be a candidate “apical” dendrite.īut while fundamental questions remain, new tools are being brought to bear in this area of active investigation, and a series of insights have unfolded over the last decade. (D) An individual cultured neuron, labeled by transfection with eGFP, from within a similarly dense field of neurons (unstained) as in (C). (C) Dissociated hippocampal neurons growing in primary culture, immunostained with MAP2 to reveal the dendritic arbors of the neurons present in the field of view. (B) A hippocampal neuron labeled by biolistic transfection of eGFP in an organotypic slice culture from rat. The dendritic arbor has pronounced apical and basilar domains that are physically segregated and oriented in opposite directions. (A) Camera lucida drawing of the dendritic arbors of pyramidal neurons of the CA fields of the hippocampus and granule cells of the dentate gyrus, based on Golgi-Cox impregnation of an adult rat (modified from ). 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.Ĭomparing hippocampal pyramidal neurons grown under different conditions can help distinguish intrinsically determined features of the dendritic arbor from those under extracellular control. 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. 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. Although astroglia are present during key stages of dendritic development in vivo, little is known about whether local interactions with glia shape dendritic growth. 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. In the absence of external spatial cues, dendritic arbors of neurons grown in vitro approximate those observed in situ. ![]()
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