COMPARTMENTAL ORGANIZATION OF CALRETININ IN THE RAT STRIATUM

The present study examined the compartmental distribution of a calcium -binding protein, calretinin, in the rat striatum. Calretinin-immunore active cells were homogeneously scattered throughout the striatum, but calretinin-immunoreactive fibers were clustered as patches in the med ial, central and ventral caudoputamen and in the lateral nucleus accum bens. These patches corresponded to striosomes, identified by immunost aining for calbindin-D-28K in adjacent sections. In the medial nucleus accumbens, calretinin-immunoreactive fibers showed diffuse distributi on with occasional islands of calretinin-poor zones. These islands con tained tightly packed, Nissl-stained cells, which have been previously shown to correspond to mu-opiate receptor-rich patches. Calretinin-po sitive fibers fill striosomes/patches in the caudoputamen and in the l ateral nucleus accumbens and avoid them in the medial nucleus accumben s.