Calretinin labels a specific neuronal subpopulation in primate globus pallidus

All pallidal neurones are believed to share the same chemical and morphological phenotype in primates. At variance with this idea is the present finding that calretinin (CR), a calcium binding protein, occurs only in a subset of pallidal neurones in squirrel monkeys. This chemospecific subpopulation comprises both large and small bipolar and multipolar neurones distributed according to a rostrocaudal decreasing gradient. The large neurones outnumber small neurones throughout the pallidum; they abound principally in the external pallidal segment, whereas the small neurones prevail in the internal segment. Some pallidal CR-positive neurones display dorsoventrally elongated dendrites, while others show dendrites radiating in all directions. These findings reveal that pallidal neurones form a chemically and morphologically heterogeneous population in primates.