Neuronal density and proportion of interneurons in the associative, sensorimotor and limbic human striatum

Interneuron diversity in the human dorsal striatum

Deciphering the striatal interneuron diversity is key to understanding the basal ganglia circuit and to untangling the complex neurological and psychiatric diseases affecting this brain structure. We performed snRNA-seq and spatial transcriptomics of postmortem human caudate nucleus and putamen samples to elucidate the diversity and abundance of interneuron populations and their inherent transcriptional structure in the human dorsal striatum. We propose a comprehensive taxonomy of striatal interneurons with eight main classes and fourteen subclasses, providing their full transcriptomic identity and spatial expression profile as well as additional quantitative FISH validation for specific populations. We have also delineated the correspondence of our taxonomy with previous standardized classifications and shown the main transcriptomic and class abundance differences between caudate nucleus and putamen. Notably, based on key functional genes such as ion channels and synaptic receptors, we found matching known mouse interneuron populations for the most abundant populations, the recently described PTHLH and TAC3 interneurons. Finally, we were able to integrate other published datasets with ours, supporting the generalizability of this harmonized taxonomy.

Interneuron diversity in the human dorsal striatum

Deciphering the striatal interneuron diversity is key to understanding the basal ganglia circuit and to untangle the complex neurological and psychiatric diseases affecting this brain structure. We performed snRNA-seq of postmortem human caudate nucleus and putamen samples to elucidate the diversity and abundance of interneuron populations and their transcriptional structure in the human dorsal striatum. We propose a new taxonomy of striatal interneurons with eight main classes and fourteen subclasses and provide their specific markers and some quantitative FISH validation, particularly for a novel PTHLH-expressing population. For the most abundant populations, PTHLH and TAC3, we found matching known mouse interneuron populations based on key functional genes such as ion channels and synaptic receptors. Remarkably, human TAC3 and mouse Th populations share important similarities including the expression of the neuropeptide tachykinin 3. Finally, we were able to integrate other published datasets supporting the generalizability of this new harmonized taxonomy.

Decreased density of cholinergic interneurons in striatal territories in Williams syndrome

Williams syndrome (WS) is a rare neurodevelopmental disorder caused by the hemideletion of approximately 25-28 genes at 7q11.23. Its unusual social and cognitive phenotype is most strikingly characterized by the disinhibition of social behavior, in addition to reduced global IQ, with a relative sparing of language ability. Hypersociality and increased social approach behavior in WS may represent a unique inability to inhibit responses to specific social stimuli, which is likely associated with abnormalities of frontostriatal circuitry. The striatum is characterized by a diversity of interneuron subtypes, including inhibitory parvalbumin-positive interneurons (PV+) and excitatory cholinergic interneurons (Ch+). Animal model research has identified an important role for these specialized cells in regulating social approach behavior. Previous research in humans identified a depletion of interneuron subtypes associated with neuropsychiatric disorders. Here, we examined the density of PV+ and Ch+ interneurons in the striatum of 13 WS and neurotypical (NT) subjects. We found a significant reduction in the density of Ch+ interneurons in the medial caudate nucleus and nucleus accumbens, important regions receiving cortical afferents from the orbitofrontal and ventromedial prefrontal cortex, and circuitry involved in language and reward systems. No significant difference in the distribution of PV+ interneurons was found. The pattern of decreased Ch+ interneuron densities in WS differs from patterns of interneuron depletion found in other disorders.

Regional vesicular acetylcholine transporter distribution in human brain: A [18 F]fluoroethoxybenzovesamicol positron emission tomography study

Prior efforts to image cholinergic projections in human brain in vivo had significant technical limitations. We used the vesicular acetylcholine transporter (VAChT) ligand [¹⁸ F]fluoroethoxybenzovesamicol ([¹⁸ F]FEOBV) and positron emission tomography to determine the regional distribution of VAChT binding sites in normal human brain. We studied 29 subjects (mean age 47 [range 20-81] years; 18 men; 11 women). [¹⁸ F]FEOBV binding was highest in striatum, intermediate in the amygdala, hippocampal formation, thalamus, rostral brainstem, some cerebellar regions, and lower in other regions. Neocortical [¹⁸ F]FEOBV binding was inhomogeneous with relatively high binding in insula, BA24, BA25, BA27, BA28, BA34, BA35, pericentral cortex, and lowest in BA17-19. Thalamic [¹⁸ F]FEOBV binding was inhomogeneous with greatest binding in the lateral geniculate nuclei and relatively high binding in medial and posterior thalamus. Cerebellar cortical [¹⁸ F]FEOBV binding was high in vermis and flocculus, and lower in the lateral cortices. Brainstem [¹⁸ F]FEOBV binding was most prominent at the mesopontine junction, likely associated with the pedunculopontine-laterodorsal tegmental complex. Significant [¹⁸ F]FEOBV binding was present throughout the brainstem. Some regions, including the striatum, primary sensorimotor cortex, and anterior cingulate cortex exhibited age-related decreases in [¹⁸ F]FEOBV binding. These results are consistent with prior studies of cholinergic projections in other species and prior postmortem human studies. There is a distinctive pattern of human neocortical VChAT expression. The patterns of thalamic and cerebellar cortical cholinergic terminal distribution are likely unique to humans. Normal aging is associated with regionally specific reductions in [¹⁸ F]FEOBV binding in some cortical regions and the striatum.