CALRETININ-IMMUNOREACTIVE NEURONS IN THE HUMAN STRIATUM

The human striatum contains two types of neurons displaying immunoreac tivity for the calcium-binding protein calretinin (CR): (1) large (22- 44 mu m), multipolar neurons with 5-7 long, aspiny and highly branched dendrites, and (2) medium-sized (9-18 mu m), round-to-oval neurons wi th 2-3 long, varicose and poorly branched dendrites. These CR neurons represent only a small proportion of the total neuronal population and they are heterogeneously distributed in the striatum. The large CR ne urons are more numerous in the putamen than in the caudate nucleus, wh ereas the inverse is true for the medium-sized CR neurons. The ratio o f large- to medium-sized CR neurons is 1:4 in the putamen compared to 1:16 in the caudate nucleus. The existence of these two distinct subse ts of chemospecific striatal neurons suggest that CR may play an impor tant role in the intrinsic organization of the human striatum.