The development of radial glia and radial dendrites during barrel formation in mouse somatosensory cortex

The development of the mouse barrel field (the mystacial whisker representation in SI cortex) was examined using immunocytochemical probes for radial glia and neuronal dendrites. The maturing dendrites were revealed using antibodies against microtubule-associated protein 2 (MAP2) and the radial glia were demonstrated with a recently described monoclonal antibody, RC2. By postnatal day 7 both antibodies clearly demonstrated a non-uniform distribution of dendrites and glia that was unique to layer IV of the barrel field. Both MAP2-immunoreactive dendrites and RC2-immunoreactive radial glial fibers were dense near the walls (sides and septae) of barrels than near the hollows (centers) of barrels. In contrast, in other cortical regions, radial glia and dendrites did not appear obviously patterned. Not until postnatal day 4 did the pattern of both radial glial fibers and apical dendrites begin to emerge in a barrel-like distribution. We conclude that the non-uniform distribution of radially oriented dendrites and radial glial fibers appears with a similar developmental time course to that described for the appearance of the cellular barrels themselves.