EN
To understand the organization of inhibitory circuitries in the striatum of the opossum, the distribution of parvalbumin (PV), calretinin (CR) and calbindin (CB) was investigated within the nucleus accumbens (Acc), caudate nucleus (Cd) and putamen (Pu). Brains from six adult opossum (both sexes) were stained for PV, CR and CB and analyzed using fl uorescent or confocal microscopy. Within neurons immunostained for each calcium-binding protein four major types of neurons were distinguished. Type 1 – small ovoid or roundish somata with three to fi ve thin dendrites of approximately equal thickness; type 2 – medium-to-large-sized multipolar neurons with dendrites of variable thickness; type 3 – fusiform neurons of variable size emanating dendrites from the opposite poles of the somata; type 4 – pyramidal neurons. Moderate-to-high density of CB immunoreactive (-ir) neurons was observed in the Cd and Pu, but staining in the Acc was lighter. Light density of PV-ir neurons was present in the Cd, Pu and Acc, but PV-immunoreactivity of neuropil was high. Only single CR-ir neurons were scattered through the all studied structures, but the immunostaning of neuropil was much higher. Our data provide baseline information for comparisons of distribution of calcium binding proteins in different species, including rat, monkey and human.