Brain injury induces trophic effects within adjacent tissue through an unknown molecular mechanism. One model of this lesion effect involves the enhanced outgrowth of neuronal processes from transplanted substantia nigra in animals with cerebral cortex lesions. Since cell recognition molecules are involved in the molecular mechanisms of contact between cells and surrounding extracellular matrix components, and are important in plasticity of the nervous system, we investigated changes in L1, N-CAM, and tenascin, as well as synapse-associated proteins and gliosis, in the striatum of mice with cortical lesions. The removal of somato-sensory and motor cortex would be expected to produce changes predominantly in the dorsal striatum. Lesioned mice, however, showed a significant enhancement of both L1 and N-CAM immunostaining intensity only within the most medial-periventricular and dorsomedial parts of the striatum, as compared to the nonlesioned side. Tenascin expression was significantly decreased, but only in the most medial part of the striatum. The changes in intensity of immunostaining with L1, N-CAM, and tenascin did not diminish with time after lesioning. These changes in cell recognition molecule expression indicate a possible molecular basis of lesion-induced plasticity in neuronal circuits within the dorsomedial striatum. These changes were accompanied by decreased synapsin and synaptophysin expression, but without any significant change in neurofilament expression. In contrast, glial fibrillary acidic protein and vimentin immunoreactivities were increased in almost the entire striatum on the lesioned side. Therefore, the areas of changes in cell recognition molecule expression did not simply correlate to the increased astrogliosis or neuronal fiber damage. We postulate that the periventricular dorsomedial striatum is relatively sensitive to disturbances of corticostriatonigral circuits and, simultaneously, this striatal area has a unique ability to support and promote neurite growth.