Mechanisms of striatal pattern formation: conservation of mammalian compartmentalization.

The striatum is composed of two neuroanatomically and neurochemically defined compartments, termed the patches and matrix. We compared this compartmentalization of the striatum in sections from the rat, rhesus monkey and human, in terms of (1) total striatal area, (2) the ratio of patch to matrix areas, (3) the number of patches and (4) the cross-sectional area of individual patches. Dense mu-opiate receptor binding and immunohistochemical staining for enkephalin were used as histochemical markers for the patch compartment and heavy immunostaining for calcium binding protein was used as a matrix marker. Analysis of coronal sections revealed that a relatively constant ratio of 15% patch to 85% matrix area is maintained in each species. The numbers of patches also remain relatively constant across species, despite a 19-fold increase in total striatal area from rat to human. The constant ratio of patch to matrix areas is maintained by an increase in the size of the individual patches. We hypothesize that the maintenance of a 15% patch to 85% matrix ratio in the striata of different mammalian species occurs through proportionate changes in the length of striatal neurogenesis and the numbers of striatal precursors in the ventricular zone, whereas the maintenance of average patch number is proposed to be a function of reciprocal connections with the substantia nigra and adhesive factors that are specific to patch cells.