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Distinct gradients of various neurotransmitter markers in caudate nucleus and putamen of the human brain.

ABSTRACT: The caudate nucleus (CN) and the putamen (PUT) as parts of the human striatum are distinguished by a marked heterogeneity in functional, anatomical, and neurochemical patterns. Our study aimed to document in detail the regional diversity in the distribution of dopamine (DA), serotonin, γ-aminobuturic acid, and choline acetyltransferase within the CN and PUT. For this purpose we dissected the CN as well as the PUT of 12 post-mortem brains of human subjects with no evidence of neurological and psychiatric disorders (38-81 years old) into about 80 tissue parts. We then investigated rostro-caudal, dorso-ventral, and medio-lateral gradients of these neurotransmitter markers. All parameters revealed higher levels, turnover rates, or activities in the PUT than in the CN. Within the PUT, DA levels increased continuously from rostral to caudal. In contrast, the lowest molar ratio of homovanillic acid to DA, a marker of DA turnover, coincided with highest DA levels in the caudal PUT, the part of the striatum with the highest loss of DA in Parkinson's disease (N. Engl. J. Med., 318, 1988, 876). Highest DA concentrations were found in the most central areas both in the PUT and CN. We observed an age-dependent loss of DA in the PUT and CN that did not correspond to the loss described for Parkinson's disease indicating different mechanisms inducing the deficit of DA. Our data demonstrate a marked heterogeneity in the anatomical distribution of neurotransmitter markers in the human dorsal striatum indicating anatomical and functional diversity within this brain structure.

SUBMITTER: Hortnagl H

PROVIDER: S-EPMC7078952 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Neuronal networks are regulated by three-dimensional spatial and structural properties. Despite robust evidence of functional implications in the modulation of cognition, little is known about the three-dimensional internal organization of cholinergic networks in the forebrain. Cholinergic networks in the forebrain primarily occur in subcortical nuclei, specifically the septum, nucleus basalis, globus pallidus, nucleus accumbens, and the caudate-putamen. Therefore, the present investigation analyzed the three-dimensional spatial organization of 14,000 cholinergic neurons that expressed choline acetyltransferase (ChAT) in these subcortical nuclei of the mouse forebrain. Point process theory and graph signal processing techniques identified three topological principles of organization. First, cholinergic interneuronal distance is not uniform across brain regions. Specifically, in the septum, globus pallidus, nucleus accumbens, and the caudate-putamen, the cholinergic neurons were clustered compared with a uniform random distribution. In contrast, in the nucleus basalis, the cholinergic neurons had a spatial distribution of greater regularity than a uniform random distribution. Second, a quarter of the caudate-putamen is composed of axonal bundles, yet the spatial distribution of cholinergic neurons remained clustered when axonal bundles were accounted for. However, comparison with an inhomogeneous Poisson distribution showed that the nucleus basalis and caudate-putamen findings could be explained by density gradients in those structures. Third, the number of cholinergic neurons varies as a function of the volume of a specific brain region but cell body volume is constant across regions. The results of the present investigation provide topographic descriptions of cholinergic somata distribution and axonal conduits, and demonstrate spatial differences in cognitive control networks. The study provides a comprehensive digital database of the total population of ChAT-positive neurons in the reported structures, with the x,y,z coordinates of each neuron at micrometer resolution. This information is important for future digital cellular atlases and computational models of the forebrain cholinergic system enabling models based on actual spatial geometry.

Project description:BACKGROUND:The mechanisms underlying neurodegeneration in the striatum of Huntingon's Disease (HD) brain are currently unknown. While the striatum is massively degenerated in symptomatic individuals, which makes cellular characterization difficult, it is largely intact in asymptomatic HD gene positive (HD+) individuals. Unfortunately, as striatal tissue samples from HD+ individuals are exceedingly rare, recent focus has been on the Brodmann Area 9 (BA9), a relatively unaffected region, as a surrogate tissue. In this study, we analyze gene expression in caudate nucleus (CAU) from two HD+ individuals and compare the results with healthy and symptomatic HD brains. METHODS:High-throughput mRNA sequencing (mRNA-Seq) datasets were generated from post-mortem CAU of 2 asymptomatic HD+ individuals and compared with 26 HD and 56 neurologically normal controls. Datasets were analyzed using a custom bioinformatic analysis pipeline to identify and interpret differentially expressed (DE) genes. Results were compared to publicly available brain mRNA-Seq datasets from the Genotype-Tissue Expression (GTEx) project. The analysis employed current state of the art bioinformatics tools and tailored statistical and machine learning methods. RESULTS:The transcriptional profiles in HD+ CAU and HD BA9 samples are highly similar. Differentially expressed (DE) genes related to the heat shock response, particularly HSPA6 and HSPA1A, are common between regions. The most perturbed pathways show extensive agreement when comparing disease with control. A random forest classifier predicts that the two HD+ CAU samples strongly resemble HD BA9 and not control BA9. Nonetheless, when genes were prioritized by their specificity to HD+ CAU, pathways spanning many biological processes emerge. Comparison of HD+ BA9 with HD BA9 identified NPAS4 and REST1/2 as potential early responders to disease and reflect the active disease process. CONCLUSIONS:The caudate nucleus in HD brain is dramatically affected prior to symptom onset. Gene expression patterns observed in the HD BA9 are also present in the CAU, suggesting a common response to disease. Substantial caudate-specific differences implicate many different biological pathways including metabolism, protein folding, inflammation, and neurogenic processes. While these results are at best trends due to small sample sizes, these results nonetheless provide the most detailed insight to date into the primary HD disease process.

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Distinct gradients of various neurotransmitter markers in caudate nucleus and putamen of the human brain.

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