Regional differences in glial-derived factors that promote dendritic outgrowth from mouse cortical neurons in vitro

To determine whether glia from different CNS regions differ in their ability to support axons or dendrites, embryonic (E18) mouse cortical neurons were cocultured with early postnatal (P4) rat astroglial derived from cortex, retina, olfactory bulb, mesencephalon, striatum, and spinal cord. After 5 d in vitro, axon and dendrite outgrowth from isolated neurons was quantified with double-labeling immunohistochemical techniques. Whereas axonal growth was similar on the various monolayers, total primary dendritic outgrowth was nearly threefold greater on glia derived from the cortex, retina, and olfactory bulb than on glia derived from mesencephalon, striatum, or spinal cord. This effect was principally on the number of primary dendrites rather than the elongation of individual dendrites. Similar morphological differences were observed when cortical neurons were grown on polylysine in a noncontact coculture system with glia continuously conditioning the media. This selective promotion of dendrite growth was independent of neuron survival. These results indicate that there are regional differences in the ability of CNS glia to support dendritic growth and that this effect is due, in part, to release of a diffusable factor.