Cortical stimulation induces fos expression in striatal neurons.

Electrical stimulation of a broad area of the frontoparietal cortex in the rat brain induces immunocytochemically detectable Fos in striatal neurons normally devoid of the protein. The vividness of labeling within striatal neurons was maximal at 0.5 h after the cessation of a 15-min-long stimulation period and became weaker by 3 h. Although Fos-reactive neurons were widely distributed in the striata of both hemispheres in an uneven pattern, those on the stimulated side were more numerous and more darkly stained. At no time-point were labeled neurons found in the globus pallidus, entopeduncular nucleus or substantia nigra. Destruction of the nigrostriatal dopamine projection with 6-hydroxydopamine did not induce Fos production and failed to prevent the induction of Fos by cortical stimulation. That many of the Fos-positive neurons project to the substantia nigra was confirmed by retrograde labeling with Fluoro-Gold. The data suggest that corticostriatal excitatory transmission may directly influence the genomic activity of striatal neurons by way of Fos.