Cell size-dependent Nogo-A expression in layer V pyramidal neurons of the rat primary somatosensory cortex.

Nogo-A mRNA and protein are present in the perikarya of neurons in both the intact and injured CNS. The present study focused primarily on Nogo-A protein expression in the primary somatosensory cortex of the adult rat. Coronal brain sections were probed with double-immunofluorescent labeling against Nogo-A together with NeuN, RBPC, or MAP-2 for confocal imaging. The sizes of the cell somata in pyramidal neurons and the thicknesses of neurites were measured on the captured confocal images. Nogo-A was expressed in larger pyramidal neurons and thicker neurites in layer V, but not in smaller pyramidal neurons and thinner neurites. Considering the morphological properties and the cell soma size reported in previous studies together with the present data, Nogo-A-positive neurons of layer V appear to be intrinsically bursting neurons that project axons to the subcortical regions. This suggests that intraneuronal Nogo-A may play roles in neurite growth and axonal regeneration of the corticofugal neurons, but not of columnar intrinsic neurons, in layer V of the S1 barrel cortex. Additionally, this study demonstrates a novel result, which is that layer V pyramidal neurons of the S1 barrel cortex exhibit a pattern of cell size-dependent intraneuronal Nogo-A expression.