When explants or reaggregates of small neurons from early postnatal mouse cerebella are plated on a mixture of laminin and poly-d-lysine, one observes small cells with an orientation of processes largely perpendicular to the direction of granule cell neurites after several days. These cells first have a bipolar morphology and then elaborate a rich dendritic arbor-like structure opposite a long, thin axon-like process. Several lines of evidence suggest that these cells are the small inhibitory interneurons of the cerebellar cortex: They take up GABA, express high levels of the embryonic form of N-CAM, do not express L1, the oligodendrocyte marker O4, or the glial marker vimentin, and display ultrastructural features reminiscent of stellate and/or basket cells in vivo. These observations suggest that the elaboration of directional positioning of small inhibitory interneurons can be studied in culture, thus offering the possibility to elucidate the cellular and molecular mechanisms underlying the orientation of particular neural cells with regard to others.
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