Cortical lesions induce an increase in cell number and PSA-NCAM expression in the subventricular zone of adult rats.

The subventricular zone (SVZ) bordering the lateral ventricle is one of the few regions of adult brain that contains dividing cells. These cells can differentiate into neurons in vivo after migration into the olfactory bulb and in vitro in the presence of appropriate growth factors. Little is known, however, about the fate of these cells in vivo after brain injury in adults. We examined cell number and expression of differentiation markers in the SVZ of adult rats after cortical lesions. Aspiration lesions of the sensorimotor cortex in adult rats induced a transient doubling of the number of cells in the SVZ at the level of the striatum without consistent increases in bromodeoxyuridine-labeled cells. Immunoreactivity to the polysialylated neural cell adhesion molecule, expressed by the majority of cells of the SVZ during development, increased dramatically after lesion. In contrast, immunolabeling for molecules found in mature neurons and glia did not increase in the SVZ after lesion, and immunoreactivity for growth factors that induce differentiation of SVZ cells in vitro decreased or remained undetectable, suggesting that lack of appropriate growth factor expression may contribute to the lack of differentiation of the newly accumulated cells in vivo. The data reveal that cells of the SVZ are capable of plasticity in the adult rat after brain injury in vivo and that the newly accumulated cells retain characteristics seen during development.