The somatosensory cortex of reeler mutant mice shows absent layering but intact formation and behavioral activation of columnar somatotopic maps.

Sensory information acquired via the large facial whiskers is processed and relayed in the whisker-to-barrel pathway, which shows multiple somatotopic maps of the receptor periphery. These maps consist of individual structural modules, the development of which may require intact cortical lamination. In the present study we examined the whisker-to-barrel pathway in the reeler mouse and thus used a model with disturbed cortical organization. A combination of histological (fluorescent Nissl and cytochrome oxidase staining) as well as molecular methods (c-Fos and laminar markers Rgs8, RORB, and ER81 expression) revealed wild type-equivalent modules in reeler. At the neocortical level, however, we found extensive alterations in the layout of the individual modules of the map. Nevertheless, they showed a columnar organization that included compartments equivalent to those of their wild-type counterparts. Moreover, all examined modules showed distinct activation as a consequence of behavioral whisker stimulation. Analysis of the magnitude of the cortical lamination defect surprisingly revealed an extensive disorganization, rather than an inversion, as assumed previously. Striking developmental plasticity of thalamic innervation, as suggested by vGluT2 immunohistochemistry, seems to ensure the proper formation of columnar modules and topological maps even under highly disorganized conditions.