CHOLINERGIC INNERVATION IN THE HUMAN STRIATUM - A 3-COMPARTMENT MODEL

The mammalian striatum is divided into compartments that are anatomica lly and neurochemically distinct. The dorsal striatum has been describ ed as containing two compartments, striosomes and matrix, while the ve ntral striatum is thought to have a more complex, multi-compartmental organization. In this study, we sought to characterize the compartment alization of the dorsal and ventral portions of the human striatum usi ng choline acetyltransferase as a marker. Image analysis was used to a ssess relative densities of immunostaining, and three distinct, cholin e acetyltransferase-immunostained compartments were demonstrated: inte nsely immunostained, moderately immunostained and weakly immunostained areas. The dorsomedial portion of the striatum was made up of moderat ely immunostained regions embedded within a densely immunostained back ground, thus manifesting the characteristic striosome/matrix organizat ion of the dorsal striatum. However, the ventral and lateral two-third s of the striatum were made up of a mixture of densely immunostained, moderately immunostained and weakly immunostained areas, with the mode rately immunostained region forming the bulk of the background tissue, and smaller, densely immunostained and weakly immunostained regions e mbedded within it. These compartments were compared to regions defined by distinct levels of acetylcholinesterase immunostaining in adjacent sections; the staining patterns produced by the two cholinergic marke rs were found to be identical except in some portions of the nucleus a ccumbens, where acetylcholinesterase immunostaining was found to be mo re intense than choline acetyltransferase immunostaining. The immunore active somata were mapped within sections stained for choline acetyltr ansferase taken from different rostrocaudal levels of the striatum, an d the distributions and densities of immunoreactive somata within thes e three cholinergic compartments were determined. In general, the dens ities of cholinergic somata roughly correlated with immunostaining int ensity of regions, e.g. the most intensely immunostained compartment a lso had the highest densities of cholinergic somata. However, in the r ostroventral striatum, the densities of cholinergic somata in the weak ly immunostained compartment roughly equalled the densities of choline rgic somata in the moderately immunostained compartment, suggesting th at local axonal arborizations of cholinergic cells may differ in densi ty or orientation between the two compartments, or, alternatively, tha t some of the cholinergic cells in the weakly immunostained compartmen t may project outside of the striatum. The large proportion of striatu m displaying ventral striatal characteristics (a complex, multi-compar tmental organization) in humans relative to that observed in other mam mals suggests that the role of the ventral striatum may be expanded an d more highly differentiated in the human brain. Copyright (C) 1996 IB RO.