Patches in the striatum of squirrel monkeys are enriched with calretinin fibers but devoid of calretinin cell bodies.

In squirrel monkeys, the calcium-binding protein calretinin (CR) was found to be distributed according to strikingly different patterns in striatal patch/matrix compartments, as visualized on adjacent sections immunostained for another calcium-binding protein, calbindin D-28k. Striatal patches were characterized by a dense CR-immunoreactive neuropil, whereas the matrix contained a moderate number of medium-sized and a small number of large-sized CR perikarya uniformly scattered among a few immunoreactive fibers. Matriceal CR perikarya often closely surrounded striatal patches, but none of them invaded the patches themselves. The CR-neuropil-dense patches were particularly conspicuous in ventromedial sectors of the striatum, including the limbic territory, but much less obvious in the dorsolateral sensorimotor territory. These findings indicate that CR neurons may be involved in patch/matrix intercommunication.