To elucidate the detailed organization of corticostriatal projections from rodent somatosensory cortex, the anterograde tracers biotinylated dextran amine (BDA) and fluoro-ruby (FR) were injected into separate parts of the whisker "barrel" representation. In one group of rats, the two tracers were injected into different barrel columns residing in the same row; in the other group of rats, the tracers were deposited into barrel columns residing in different rows. Reconstructions of labeled axonal varicosities in the neostriatum and ventrobasal thalamus were analyzed quantitatively to compare the extent of overlapping projections to these subcortical structures. For both groups of animals, corticostriatal projections terminated in densely packed clusters that occupied curved lamellar-shaped regions along the dorsolateral edge of the neostriatum. When the tracers were injected into different whisker barrel rows, the distribution of BDA- and FR-labeled terminals in the neostriatum followed a crude somatotopic organization in which the amount of overlap was approximately the same as in the ventrobasal thalamus. When both tracers were injected into the same whisker barrel row, however, the amount of corticostriatal overlap was significantly higher than the amount of overlap observed in the ventrobasal thalamus. These results indicate that corticostriatal projections from whisker barrel cortex have an anisotropic organization that correlates with the pattern of vibrissal movements during whisking behavior.

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