Abstract
BackgroundThe striatum (caudate nucleus, CN, and putamen, Put) is a group of subcortical nuclei involved in planning and executing voluntary movements as well as in cognitive processes. Its neuronal composition includes projection neurons, which connect the striatum with other structures, and interneurons, whose main roles are maintaining the striatal organization and the regulation of the projection neurons. The unique electrophysiological and functional properties of the cholinergic interneurons give them a crucial modulating function on the overall striatal response.Methodology/Principle FindingsThis study was carried out using stereological methods to examine the volume and density (cells/mm3) of these interneurons, as visualized by choline acetyltransferase (ChAT) immunoreactivity, in the following territories of the CN and Put of nine normal human brains: 1) precommissural head; 2) postcommissural head; 3) body; 4) gyrus and 5) tail of the CN; 6) precommissural and 7) postcommissural Put. The distribution of ChAT interneurons was analyzed with respect to the topographical, functional and chemical territories of the dorsal striatum. The CN was more densely populated by cholinergic neurons than the Put, and their density increased along the anteroposterior axis of the striatum with the CN body having the highest neuronal density. The associative territory of the dorsal striatum was by far the most densely populated. The striosomes of the CN precommissural head and the postcommissural Put contained the greatest number of ChAT-ir interneurons. The intrastriosomal ChAT-ir neurons were abundant on the periphery of the striosomes throughout the striatum.Conclusions/SignificanceAll these data reveal that cholinergic interneurons are differentially distributed in the distinct topographical and functional territories of the human dorsal striatum, as well as in its chemical compartments. This heterogeneity may indicate that the posterior aspects of the CN require a special integration of information by interneurons. Interestingly, these striatal regions have been very much left out in functional studies.
Highlights
The striatum plays a key role in motor, cognitive and motivational processes [1,2]
Volume of perikarya We examined a total of 1,246 cholinergic neurons randomly selected with the optical dissector throughout the striatum of the nine cases included in this study (Table 1), and measured the volume of their perikarya by means of the nucleator
choline acetyltransferase (ChAT)-ir interneurons are widely scattered throughout the CN and Put (Fig. 1Aa–d)
Summary
The striatum plays a key role in motor, cognitive and motivational processes [1,2]. The projection neurons of this structure are a subset of c-aminobutyric acid (GABA)-containing medium-sized spiny cells [3] that are strongly influenced by local circuit neurons (Golgi type II cells) [3,4]. Few in number (1–2% of the total cell population of striatum) [7], the cholinergic interneurons are among the largest striatal cells and have extremely dense axonal arbors. All these data reveal that cholinergic interneurons are differentially distributed in the distinct topographical and functional territories of the human dorsal striatum, as well as in its chemical compartments. This heterogeneity may indicate that the posterior aspects of the CN require a special integration of information by interneurons. These striatal regions have been very much left out in functional studies
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