Organization of corticostriatal projections from the vibrissal representations in the primary motor and somatosensory cortical areas of rodents

To characterize corticostriatal projections from rodent sensorimotor cortex , the anterograde tracers biotinylated dextran amine (BDA) and fluororuby ( FR) were injected into the whisker representations of the primary motor (MI ) and somatosensory (SI) cortices. Reconstructions of labeled terminals and their beaded varicosities in the neostriatum and thalamus were analyzed qu antitatively to determine the degree of labeled overlap in both of these su bcortical structures. Corticostriatal projections from the vibrissal repres entation in MI were more extensive than corresponding projections from SI. Both cortical areas sent dense projections to the dorsolateral neostriatum, but the MI vibrissal representation also projected to regions located more rostrally and medially. Despite these differences, both MI and Sl projecte d to overlapping parts of the dorsolateral neostriatum. Tracer injections i n both cortical areas also produced dense anterograde and retrograde labeli ng in the medial sector of the posterior complex of the thalamus (POm). Bec ause POm is somatotopically organized and has reciprocal. connections with both Sl and MI cortices, the amount of labeled overlap in POm was used to i ndicate whether the tracers were injected into corresponding whisker repres entations of MI and SI. We found that the proportion of labeled overlap in the neostriatum was highly correlated with the amount of labeled overlap in POm. These results indicate that the rodent neostriatum receives convergen t projections from corresponding regions in MI and SI cortex. Furthermore, the thalamocortical projections of the POm indicate that it may modulate co rticostriatal outputs from corresponding representations in MI and SI. (C) 2001 Wiley-Liss, Inc.