Barrels in somatosensory cortex of normal and reeler mutant mice

The pattern of projection of the ventrobasal thalamic complex (VB) upon the neocortical barrel field of normal and reeler mutant mice was determined by orthograde degeneration experiments and by Timm's histochemical method. In both reeler and normal mice the thalamic terminals are concentrated at the midcortical zone dominated by granule cells and the adjacent zone dominated by medium-sized pyramidal cells. The medium-sized pyramids are principally supragranular in normal cortex but infragranular in the reeler. Throughout the barrel fields of reeler and normal mice thalamic terminals are organized as a mosaic of radially oriented columns coextensive in the tangential plane with barrels whose cross-sectional areas and shapes are similar in both genotypes. The radial extent of the columns in reeler is 2-3 times that in normal cortex. These observations suggest that the tangential organization of the thalamocortical projection is normal in reeler and that thalamic terminals are distributed among the same neuronal classes in normal and reeler mice despite cell malposition in the mutant.