The core-shell dichotomy of nucleus accumbens in the rhesus monkey as revealed by double-immunofluorescence and morphology of cholinergic interneurons

Double-immunolabelling experiments for the combinations, calretinin (CR)-ca lbindin, CR-tyrosine hydroxylase (TH) and calbindin-TH, were performed in r hesus monkeys to compare the chemical organization of the nucleus accumbens (ACC) in primates and rodents. Additionally, the soma sizes and numbers of primary dendrites of cholinergic neurons in the subregions of ACC were com pared with those of caudate-putamen. Our findings subserve the shell-core c oncept also in the primate ACC, as like in the rat, CR immunoreactivity (-i r) due to intense neuropil labelling is very strong in the shell of rhesus monkey, but poor in the core. The staining intensity of this marker decreas es in dorsoventral direction. An almost complementary pattern was noted in sections of the monkey ACC immunostained for both calbindin and TH. The cho linergic interneurons of the nucleus caudatus-putamen are clearly distingui shed from those of the ACC and insula Calleja magna by their much bigger so ma sizes and higher numbers of primary dendrites. Cholinergic neurons of th e shell were found to be slightly, but significantly, larger than those of the core that also subserves subdivision of the primate ACC into shell and core. A low proportion of tyrosine-hydroxylase-immunostained cells, already previously described below the rostral ACC, co-expressed CR but not calbin din. A CR-immunoreactive neuronal population, intermingled with these cells , extends as a stripe medially to the ACC along the septal part of corpus c allosum into the lateral septal area. The presumed origin of CR-immunoreact ive fibres in the shell of ACC is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.