Chemical anatomy of the human ventral striatum and adjacent basal forebrain structures

Calbindin D-28k (CB), calretinin (CR), substance P (SP), limbic system-associated membrane protein (LAMP), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE) were used as chemical markers to investigate the organization of the ventral striatum (VST) and adjacent structures in healthy human individuals. No clear boundary could be established between the dorsal striatum and the VST, and the core/shell subdivisions of nucleus accumbens (Acb) could be distinguished only at the midrostrocaudal level of the VST. The CB-poor shell displayed intense immunostaining for SP and CR but only weak staining for LAMP. By contrast, the core was weakly stained for SP and CR and moderately stained for LAMP and CB. There was no difference between shell and core with regard to the cholinergic markers. The Acb harbored numerous ChAT- and CR-immunoreactive cell bodies, the latter being distributed according to a marked, mediolaterally increasing gradient. The size of the ChAT- and CR-immunoreactive perikarya in the Acb varied according to their location in the core and shell. The VST was surrounded by a chemically heterogeneous group of cell clusters referred to as interface islands. The CR-rich caudal portion of the VST merged with the bed nucleus of the stria terminalis dorsally and the diagonal band of Broca ventromedially, the latter two structures displaying complex immunostaining patterns. The claustrum was markedly enriched in LAMP and harbored different types of CR- and CB-immunopositive neurons. These results demonstrate that the neurochemical organization of the human VST is strikingly complex and exhibits a greater heterogeneity than the dorsal striatum.