Exploitation of puddles for breakthroughs in claustrum research

High-resolution dataset of manual claustrum segmentation

The claustrum has a unique thin sheet-like structure that makes it hard to identify in typical anatomical MRI scans. Attempts have been made to identify the claustrum in anatomical images with either automatic segmentation techniques or using atlas-based approaches. However, the resulting labels fail to include the ventral claustrum portion, which consists of fragmented grey matter referred to as "puddles". The current dataset is a high-resolution label of the whole claustrum manually defined using an ultra-high resolution postmortem MRI image of one individual. Manual labelling was performed by four independent research trainees. Two trainees labelled the left claustrum and another two trainees labelled the right claustrum. For every hemisphere we created a union of the two labels and assessed the label correspondence using dice coefficients. We provide size measurements of the labels in MNI space by calculating the oriented bounding box size. These data are the first manual claustrum segmentation labels that include both the dorsal and ventral claustrum regions at such a high resolution in standard space. The label can be used to approximate the claustrum location in typical in vivo MRI scans of healthy individuals.

Proteomic Profiling Reveals Specific Molecular Hallmarks of the Pig Claustrum

The present study, employing a comparative proteomic approach, analyzes the protein profile of pig claustrum (CLA), putamen (PU), and insula (IN). Pig brain is an interesting model whose key translational features are its similarities with cortical and subcortical structures of human brain. A greater difference in protein spot expression was observed in CLA vs PU as compared to CLA vs IN. The deregulated proteins identified in CLA resulted to be deeply implicated in neurodegenerative (i.e., sirtuin 2, protein disulfide-isomerase 3, transketolase) and psychiatric (i.e., copine 3 and myelin basic protein) disorders in humans. Metascape analysis of differentially expressed proteins in CLA vs PU comparison suggested activation of the α-synuclein pathway and L1 recycling pathway corroborating the involvement of these anatomical structures in neurodegenerative diseases. The expression of calcium/calmodulin-dependent protein kinase and dihydropyrimidinase like 2, which are linked to these pathways, was validated using western blot analysis. Moreover, the protein data set of CLA vs PU comparison was analyzed by Ingenuity Pathways Analysis to obtain a prediction of most significant canonical pathways, upstream regulators, human diseases, and biological functions. Interestingly, inhibition of presenilin 1 (PSEN1) upstream regulator and activation of endocannabinoid neuronal synapse pathway were observed. In conclusion, this is the first study presenting an extensive proteomic analysis of pig CLA in comparison with adjacent areas, IN and PUT. These results reinforce the common origin of CLA and IN and suggest an interesting involvement of CLA in endocannabinoid circuitry, neurodegenerative, and psychiatric disorders in humans.

Origin and development of the claustrum in rhesus macaque

Understanding the claustrum's functions has recently progressed thanks to new anatomical and behavioral studies in rodents, which suggest that it plays an important role in attention, salience detection, slow-wave generation, and neocortical network synchronization. Nevertheless, knowledge about the origin and development of the claustrum, especially in primates, is still limited. Here, we show that neurons of rhesus macaque claustrum primordium are generated between embryonic day E48 and E55 and express some neocortical molecular markers, such as NR4A2, SATB2, and SOX5. However, in the early stages, it lacks TBR1 expression, which separates it from other surrounding telencephalic structures. We also found that two waves of neurogenesis (E48 and E55) in the claustrum, corresponding to the birthdates of layers 6 and 5 of the insular cortex, establish a "core" and "shell" cytoarchitecture, which is potentially a basis for differential circuit formation and could influence information processing underlying higher cognitive functions of the claustrum. In addition, parvalbumin-positive interneurons are the dominant interneuron type in the claustrum in fetal macaque, and their maturation is independent of that in the overlaying neocortex. Finally, our study reveals that the claustrum is likely not a continuance of subplate neurons of the insular cortex, but an independent pallial region, suggesting its potentially unique role in cognitive control.

Preferential arborization of dendrites and axons of parvalbumin- and somatostatin-positive GABAergic neurons within subregions of the mouse claustrum

The claustrum coordinates the activities of individual cortical areas through abundant reciprocal connections with the cerebral cortex. Although these excitatory connections have been extensively investigated in three subregions of the claustrum-core region and dorsal and ventral shell regions-the contribution of GABAergic neurons to the circuitry in each subregion remains unclear. Here, we examined the distribution of GABAergic neurons and their dendritic and axonal arborizations in each subregion. Combining in situ hybridization with immunofluorescence histochemistry showed that approximately 10% of neuronal nuclei-positive cells expressed glutamic acid decarboxylase 67 mRNA across the claustral subregions. Approximately 20%, 30%, and 10% of GABAergic neurons were immunoreactive for parvalbumin (PV), somatostatin (SOM), and vasoactive intestinal polypeptide, respectively, in each subregion, and these neurochemical markers showed little overlap with each other. We then reconstructed PV and SOM neurons labeled with adeno-associated virus vectors. The dendrites and axons of PV and SOM neurons were preferentially localized to their respective subregions where their cell bodies were located. Furthermore, the axons were preferentially extended in a rostrocaudal direction, whereas the dendrites were relatively isotropic. The present findings suggest that claustral PV and SOM neurons might execute information processing separately within the core and shell regions.

Developmental Patterning and Neurogenetic Gradients of Nurr1 Positive Neurons in the Rat Claustrum and Lateral Cortex

The claustrum is an enigmatic brain structure thought to be important for conscious sensations. Recent studies have focused on gene expression patterns, connectivity, and function of the claustrum, but relatively little is known about its development. Interestingly, claustrum-enriched genes, including the previously identified marker Nurr1, are not only expressed in the classical claustrum complex, but also embedded within lateral neocortical regions in rodents. Recent studies suggest that Nurr1 positive neurons in the lateral cortex share a highly conserved genetic expression pattern with claustrum neurons. Thus, we focus on the developmental progression and birth dating pattern of the claustrum and Nurr1 positive neurons in the lateral cortex. We comprehensively investigate the expression of Nurr1 at various stages of development in the rat and find that Nurr1 expression first appears as an elongated line along the anterior-posterior axis on embryonic day 13.5 (E13.5) and then gradually differentiates into multiple sub-regions during prenatal development. Previous birth dating studies of the claustrum have led to conflicting results, therefore, we combine 5-ethynyl-2'-deoxyuridine (EdU) labeling with in situ hybridization for Nurr1 to study birth dating patterns. We find that most dorsal endopiriform (DEn) neurons are born on E13.5 to E14.5. Ventral claustrum (vCL) and dorsal claustrum (dCL) are mainly born on E14.5 to E15.5. Nurr1 positive cortical deep layer neurons (dLn) and superficial layer neurons (sLn) are mainly born on E14.5 to E15.5 and E15.5 to E17.5, respectively. Finally, we identify ventral to dorsal and posterior to anterior neurogenetic gradients within vCL and DEn. Thus, our findings suggest that claustrum and Nurr1 positive neurons in the lateral cortex are born sequentially over several days of embryonic development and contribute toward charting the complex developmental pattern of the claustrum in rodents.

The claustrum of the sheep and its connections to the visual cortex

The present study analyses the organization and selected neurochemical features of the claustrum and visual cortex of the sheep, based on the patterns of calcium-binding proteins expression. Connections of the claustrum with the visual cortex have been studied by tractography. Parvalbumin-immunoreactive (PV-ir) and Calbindin-immunoreactive (CB-ir) cell bodies increased along the rostro-caudal axis of the nucleus. Calretinin (CR)-labeled somata were few and evenly distributed along the rostro-caudal axis. PV and CB distribution in the visual cortex was characterized by larger round and multipolar cells for PV, and more bitufted neurons for CB. The staining pattern for PV was the opposite of that of CR, which showed densely stained but rare cell bodies. Tractography shows the existence of connections with the caudal visual cortex. However, we detected no contralateral projection in the visuo-claustral interconnections. Since sheep and goats have laterally placed eyes and a limited binocular vision, the absence of contralateral projections could be of prime importance if confirmed by other studies, to rule out the role of the claustrum in stereopsis.

Automatic Segmentation of the Dorsal Claustrum in Humans Using in vivo High-Resolution MRI

The claustrum is a thin sheet of neurons enclosed by white matter and situated between the insula and the putamen. It is highly interconnected with sensory, frontal, and subcortical regions. The deep location of the claustrum, with its fine structure, has limited the degree to which it could be studied in vivo. Particularly in humans, identifying the claustrum using magnetic resonance imaging (MRI) is extremely challenging, even manually. Therefore, automatic segmentation of the claustrum is an invaluable step toward enabling extensive and reproducible research of the anatomy and function of the human claustrum. In this study, we developed an automatic algorithm for segmenting the human dorsal claustrum in vivo using high-resolution MRI. Using this algorithm, we segmented the dorsal claustrum bilaterally in 1068 subjects of the Human Connectome Project Young Adult dataset, a publicly available high-resolution MRI dataset. We found good agreement between the automatic and manual segmentations performed by 2 observers in 10 subjects. We demonstrate the use of the segmentation in analyzing the covariation of the dorsal claustrum with other brain regions, in terms of macro- and microstructure. We identified several covariance networks associated with the dorsal claustrum. We provide an online repository of 1068 bilateral dorsal claustrum segmentations.

A Re-evaluation of the Anatomy of the Claustrum in Rodents and Primates-Analyzing the Effect of Pallial Expansion

The components of the claustrum have been identified by gene expression in mice, but there is still uncertainty about the location of homologous components in primates. To aid interpretation of homologous elements between rodents and primates, we used a current understanding of pallial topology, species-specific telencephalic deformation, and gene expression data. In both rodents and primates, pallial areas maintain conserved topological relationships regardless of relative differences in pallial expansion. The components of the claustrum in primates can, therefore, be identified on the basis of their conserved topological relationships and patterns of gene expression. In rodents, a fairly straight telencephalic long axis runs between the early septopreoptic and amygdalar poles of the pallium. In primates, however, the remarkable dorsal pallial expansion causes this axis to be distorted to form a C shape. This has resulted in a number of errors in the interpretation of the location of claustral components. These errors are likely to have resulted from the unexpected topographical positioning of claustral components due to the bent telencephalic axis. We argue that, once the telencephalic distortion has been accounted for, both rodents and primates have homologous claustral components, and that the topological relationships of these components are conserved regardless of differences in the relative expansion of pallial areas.

The catecholaminergic innervation of the claustrum of the pig

Over the past decades, the number of studies employing the pig brain as a model for neurochemical studies has dramatically increased. The key translational features of the pig brain are the similarities with the cortical and subcortical structures of the human brain. In addition, the caudalmost part of the pig claustrum (CL) is characterized by a wide enlargement called posterior puddle, an ideal structure for physiological recordings. Several hypotheses have been proposed for CL function, the key factor being its reciprocal connectivity with most areas of the cerebral cortex and selected subcortical structures. However, afferents from the brainstem could also be involved. The brainstem is the main source of catecholaminergic axons that play an important neuromodulatory action in different brain functions. To study a possible role of the CL in catecholaminergic pathways, we analyzed the presence and the distribution of afferents immunostained with antibodies against tyrosine hydroxylase (TH) and dopamine betahydroxylase (DBH) in the pig CL. Here we show that the CL contains significant TH immunoreactive axons contacting perikarya, whereas projections staining for DBH are very scarce. Our findings hint at the possibility that brainstem catecholaminergic afferents project to the CL, suggesting (i) a possible role of this nucleus in functions controlled by brainstem structures; and, consequently, (ii) its potential involvement in the pathophysiology of neurodegenerative pathologies, including Parkinson's disease (PD).

Cortical hierarchy governs rat claustrocortical circuit organization

The claustrum is a telencephalic gray matter structure with various proposed functions, including sensory integration and attentional allocation. Underlying these concepts is the reciprocal connectivity of the claustrum with most, if not all, areas of the cortex. What remains to be elucidated to inform functional hypotheses further is whether a pattern exists in the strength of connectivity between a given cortical area and the claustrum. To this end, we performed a series of retrograde neuronal tract tracer injections into rat cortical areas along the cortical processing hierarchy, from primary sensory and motor to frontal cortices. We observed that the number of claustrocortical projections increased as a function of processing hierarchy; claustrum neurons projecting to primary sensory cortices were scant and restricted in distribution across the claustrum, whereas neurons projecting to the cingulate cortex were densely packed and more evenly distributed throughout the claustrum. This connectivity pattern suggests that the claustrum may preferentially subserve executive functions orchestrated by the cingulate cortex. J. Comp. Neurol. 525:1347-1362, 2017. © 2016 Wiley Periodicals, Inc.

Interhemispheric connections between the infralimbic and entorhinal cortices: The endopiriform nucleus has limbic connections that parallel the sensory and motor connections of the claustrum

We have previously shown that the claustrum is part of an interhemispheric circuit that interconnects somesthetic-motor and visual-motor cortical regions. The role of the claustrum in processing limbic information, however, is poorly understood. Some evidence suggests that the dorsal endopiriform nucleus (DEn), which lies immediately ventral to the claustrum, has connections with limbic cortical areas and should be considered part of a claustrum-DEn complex. To determine whether DEn has similar patterns of cortical connections as the claustrum, we used anterograde and retrograde tracing techniques to elucidate the connectivity of DEn. Following injections of retrograde tracers into DEn, labeled neurons appeared bilaterally in the infralimbic (IL) cortex and ipsilaterally in the entorhinal and piriform cortices. Anterograde tracer injections in DEn revealed labeled terminals in the same cortical regions, but only in the ipsilateral hemisphere. These tracer injections also revealed extensive longitudinal projections throughout the rostrocaudal extent of the nucleus. Dual retrograde tracer injections into IL and lateral entorhinal cortex (LEnt) revealed intermingling of labeled neurons in ipsilateral DEn, including many double-labeled neurons. In other experiments, anterograde and retrograde tracers were separately injected into IL of each hemisphere of the same animal. This revealed an interhemispheric circuit in which IL projects bilaterally to DEn, with the densest terminal labeling appearing in the contralateral hemisphere around retrogradely labeled neurons that project to IL in that hemisphere. By showing that DEn and claustrum have parallel sets of connections, these results suggest that DEn and claustrum perform similar functions in processing limbic and sensorimotor information, respectively. J. Comp. Neurol. 525:1363-1380, 2017. © 2016 Wiley Periodicals, Inc.