CORTICOSTRIATAL INNERVATION OF THE PATCH AND MATRIX IN THE RAT NEOSTRIATUM

The distribution of rat corticostrial axons in the patch (striosome) a nd matrix compartments of the neostriatum was studied by using axonal labeling with biotinylated dextran amine (BDA) and identifying patch a nd matrix in the same section with calbindin immunocytochemistry. Smal l injections of BDA were made in the anterior cingulate, medial agranu lar, lateral agranular, or somatosensory cortex. Each area projected t o both the patch and matrix compartments, except for the somatosensory cortex, which had only matrix projections. Within the remaining corti cal areas, injections in layers Vb and VI preferentially labeled axons in patches whereas injections in layers III-Va preferentially labeled matrix axons. Axons from these injections formed varicosities prefere ntially, but not exclusively, in one compartment. There was a populati on of axons that crossed compartmental boundaries and arborized in bot h patch and matrix. Two distinct patterns of corticostriatal axonal ar borizations were observed. Small, discrete foci of innervation were se en in the patch compartment and in some regions of the matrix. The foc al arborizations in the matrix were observed through the rostrocaudal extent of the neostriatum but were most obvious in the caudal one-thir d. They resembled the matrisomes observed in cat and primate corticost riatal projections. The second pattern of innervation consisted of ext ended axonal arborizations that covered large regions of the rostral n eostriatal matrix. These results support the concept of multiple class es of corticostriatal neurons having different targets within the neos triatum, following different topographical rules, and having different but overlapping distributions across cortical areas. (C) 1996 Wiley-L is, Inc.