Evolutionary and developmental specialization of foveal cell types in the marmoset.

In primates, high-acuity vision is mediated by the fovea, a small specialized central region of the retina. The fovea, unique to the anthropoid lineage among mammals, undergoes notable neuronal morphological changes during postnatal maturation. However, the extent of cellular similarity across anthropoid foveas and the molecular underpinnings of foveal maturation remain unclear. Here, we used high-throughput single-cell RNA sequencing to profile retinal cells of the common marmoset (Callithrix jacchus), an early divergent in anthropoid evolution from humans, apes, and macaques. We generated atlases of the marmoset fovea and peripheral retina for both neonates and adults. Our comparative analysis revealed that marmosets share almost all their foveal types with both humans and macaques, highlighting a conserved cellular structure among primate foveas. Furthermore, by tracing the developmental trajectory of cell types in the foveal and peripheral retina, we found distinct maturation paths for each. In-depth analysis of gene expression differences demonstrated that cone photoreceptors and Müller glia (MG), among others, show the greatest molecular divergence between these two regions. Utilizing single-cell ATAC-seq and gene-regulatory network inference, we uncovered distinct transcriptional regulations differentiating foveal cones from their peripheral counterparts. Further analysis of predicted ligand-receptor interactions suggested a potential role for MG in supporting the maturation of foveal cones. Together, these results provide valuable insights into foveal development, structure, and evolution.

The Subcortical Atlas of the Marmoset ("SAM") monkey based on high-resolution MRI and histology.

A comprehensive three-dimensional digital brain atlas of cortical and subcortical regions based on MRI and histology has a broad array of applications in anatomical, functional, and clinical studies. We first generated a Subcortical Atlas of the Marmoset, called the "SAM," from 251 delineated subcortical regions (e.g. thalamic subregions, etc.) derived from high-resolution Mean Apparent Propagator-MRI, T2W, and magnetization transfer ratio images ex vivo. We then confirmed the location and borders of these segmented regions in the MRI data using matched histological sections with multiple stains obtained from the same specimen. Finally, we estimated and confirmed the atlas-based areal boundaries of subcortical regions by registering this ex vivo atlas template to in vivo T1- or T2W MRI datasets of different age groups (single vs. multisubject population-based marmoset control adults) using a novel pipeline developed within Analysis of Functional NeuroImages software. Tracing and validating these important deep brain structures in 3D will improve neurosurgical planning, anatomical tract tracer injections, navigation of deep brain stimulation probes, functional MRI and brain connectivity studies, and our understanding of brain structure-function relationships. This new ex vivo template and atlas are available as volumes in standard NIFTI and GIFTI file formats and are intended for use as a reference standard for marmoset brain research.

Anatomical variability, multi-modal coordinate systems, and precision targeting in the marmoset brain.

Localising accurate brain regions needs careful evaluation in each experimental species due to their individual variability. However, the function and connectivity of brain areas is commonly studied using a single-subject cranial landmark-based stereotactic atlas in animal neuroscience. Here, we address this issue in a small primate, the common marmoset, which is increasingly widely used in systems neuroscience. We developed a non-invasive multi-modal neuroimaging-based targeting pipeline, which accounts for intersubject anatomical variability in cranial and cortical landmarks in marmosets. This methodology allowed creation of multi-modal templates (MarmosetRIKEN20) including head CT and brain MR images, embedded in coordinate systems of anterior and posterior commissures (AC-PC) and CIFTI grayordinates. We found that the horizontal plane of the stereotactic coordinate was significantly rotated in pitch relative to the AC-PC coordinate system (10 degrees, frontal downwards), and had a significant bias and uncertainty due to positioning procedures. We also found that many common cranial and brain landmarks (e.g., bregma, intraparietal sulcus) vary in location across subjects and are substantial relative to average marmoset cortical area dimensions. Combining the neuroimaging-based targeting pipeline with robot-guided surgery enabled proof-of-concept targeting of deep brain structures with an accuracy of 0.2 mm. Altogether, our findings demonstrate substantial intersubject variability in marmoset brain and cranial landmarks, implying that subject-specific neuroimaging-based localization is needed for precision targeting in marmosets. The population-based templates and atlases in grayordinates, created for the first time in marmoset monkeys, should help bridging between macroscale and microscale analyses.

Neural network of social interaction observation in marmosets.

A crucial component of social cognition is to observe and understand the social interactions of other individuals. A promising nonhuman primate model for investigating the neural basis of social interaction observation is the common marmoset (Callithrix jacchus), a small New World primate that shares a rich social repertoire with humans. Here, we used functional magnetic resonance imaging acquired at 9.4 T to map the brain areas activated by social interaction observation in awake marmosets. We discovered a network of subcortical and cortical areas, predominately in the anterior lateral frontal and medial frontal cortex, that was specifically activated by social interaction observation. This network resembled that recently identified in Old World macaque monkeys. Our findings suggest that this network is largely conserved between New and Old World primates and support the use of marmosets for studying the neural basis of social cognition.

Multimodal cross-registration and quantification of metric distortions in marmoset whole brain histology using diffeomorphic mappings.

Whole brain neuroanatomy using tera-voxel light-microscopic data sets is of much current interest. A fundamental problem in this field is the mapping of individual brain data sets to a reference space. Previous work has not rigorously quantified in-vivo to ex-vivo distortions in brain geometry from tissue processing. Further, existing approaches focus on registering unimodal volumetric data; however, given the increasing interest in the marmoset model for neuroscience research and the importance of addressing individual brain architecture variations, new algorithms are necessary to cross-register multimodal data sets including MRIs and multiple histological series. Here we present a computational approach for same-subject multimodal MRI-guided reconstruction of a series of consecutive histological sections, jointly with diffeomorphic mapping to a reference atlas. We quantify the scale change during different stages of brain histological processing using the Jacobian determinant of the diffeomorphic transformations involved. By mapping the final image stacks to the ex-vivo post-fixation MRI, we show that (a) tape-transfer assisted histological sections can be reassembled accurately into 3D volumes with a local scale change of 2.0 ± 0.4% per axis dimension; in contrast, (b) tissue perfusion/fixation as assessed by mapping the in-vivo MRIs to the ex-vivo post fixation MRIs shows a larger median absolute scale change of 6.9 ± 2.1% per axis dimension. This is the first systematic quantification of local metric distortions associated with whole-brain histological processing, and we expect that the results will generalize to other species. These local scale changes will be important for computing local properties to create reference brain maps.

Histology-Based Average Template of the Marmoset Cortex With Probabilistic Localization of Cytoarchitectural Areas.

The rapid adoption of marmosets in neuroscience has created a demand for three dimensional (3D) atlases of the brain of this species to facilitate data integration in a common reference space. We report on a new open access template of the marmoset cortex (the Nencki-Monash, or NM template), representing a morphological average of 20 brains of young adult individuals, obtained by 3D reconstructions generated from Nissl-stained serial sections. The method used to generate the template takes into account morphological features of the individual brains, as well as the borders of clearly defined cytoarchitectural areas. This has resulted in a resource which allows direct estimates of the most likely coordinates of each cortical area, as well as quantification of the margins of error involved in assigning voxels to areas, and preserves quantitative information about the laminar structure of the cortex. We provide spatial transformations between the NM and other available marmoset brain templates, thus enabling integration with magnetic resonance imaging (MRI) and tracer-based connectivity data. The NM template combines some of the main advantages of histology-based atlases (e.g. information about the cytoarchitectural structure) with features more commonly associated with MRI-based templates (isotropic nature of the dataset, and probabilistic analyses). The underlying workflow may be found useful in the future development of 3D brain atlases that incorporate information about the variability of areas in species for which it may be impractical to ensure homogeneity of the sample in terms of age, sex and genetic background.

Marmoset Brain Mapping V3: Population multi-modal standard volumetric and surface-based templates.

The standard anatomical brain template provides a common space and coordinate system for visualizing and analyzing neuroimaging data from large cohorts of subjects. Previous templates and atlases for the common marmoset brain were either based on data from a single individual or lacked essential functionalities for neuroimaging analysis. Here, we present new population-based in-vivo standard templates and tools derived from multi-modal data of 27 marmosets, including multiple types of T1w and T2w contrast images, DTI contrasts, and large field-of-view MRI and CT images. We performed multi-atlas labeling of anatomical structures on the new templates and constructed highly accurate tissue-type segmentation maps to facilitate volumetric studies. We built fully featured brain surfaces and cortical flat maps to facilitate 3D visualization and surface-based analyses, which are compatible with most surface analyzing tools, including FreeSurfer, AFNI/SUMA, and the Connectome Workbench. Analysis of the MRI and CT datasets revealed significant variations in brain shapes, sizes, and regional volumes of brain structures, highlighting substantial individual variabilities in the marmoset population. Thus, our population-based template and associated tools provide a versatile analysis platform and standard coordinate system for a wide range of MRI and connectome studies of common marmosets. These new template tools comprise version 3 of our Marmoset Brain Mapping Project and are publicly available via marmosetbrainmapping.org/v3.html.

Marmoset Brain ISH Data Revealed Molecular Difference Between Cortical Folding Patterns.

Literature studies have demonstrated the structural, connectional, and functional differences between cortical folding patterns in mammalian brains, such as convex and concave patterns. However, the molecular underpinning of such convex/concave differences remains largely unknown. Thanks to public access to a recently released set of marmoset whole-brain in situ hybridization data by RIKEN, Japan; this data's accessibility empowers us to improve our understanding of the organization, regulation, and function of genes and their relation to macroscale metrics of brains. In this work, magnetic resonance imaging and diffusion tensor imaging macroscale neuroimaging data in this dataset were used to delineate convex/concave patterns in marmoset and to examine their structural features. Machine learning and visualization tools were employed to investigate the possible transcriptome difference between cortical convex and concave patterns. Experimental results demonstrated that a collection of genes is differentially expressed in convex and concave patterns, and their expression profiles can robustly characterize and differentiate the two folding patterns. More importantly, neuroscientific interpretations of these differentially expressed genes, as well as axonal guidance pathway analysis and gene enrichment analysis, offer novel understanding of structural and functional differences between cortical folding patterns in different regions from a molecular perspective.

Anatomy of the paranasal sinuses of the common marmoset (Callithrix jacchus Linnaeus, 1758) and radiographic positioning for diagnosis of these structures.

BACKGROUND: Callithrix jacchus, it is a species highly targeted by wild animal traffickers and, when apprehended, they need veterinary care. For safe therapeutic procedures, knowledge of anatomy is essential, as well as for diagnostic by imaging, good radiographic positioning is essential. METHODS: The anatomy of the paranasal sinuses and the radiographic projections was described using 10 carcasses of common marmosets. Radiographs were taken in two panoramic views of their head: profile and frontal-naso. For the anatomical study, paramedian and transverse macroscopic sections and microscopic transverse sections were performed. RESULTS: On the radiographs, it was possible to identify the frontal recess and maxillary sinuses in profile and frontal-naso incidences. In the anatomical study, the frontal recess and maxillary, sphenoid and ethmoid paranasal sinuses were identified. CONCLUSIONS: The ethmoidal sinus could be observed only microscopically and the sphenoidal sinus difficult to see on the radiography due to the overlapping adjoining structures.

Divergence of rodent and primate medial frontal cortex functional connectivity.

With the medial frontal cortex (MFC) centrally implicated in several major neuropsychiatric disorders, it is critical to understand the extent to which MFC organization is comparable between humans and animals commonly used in preclinical research (namely rodents and nonhuman primates). Although the cytoarchitectonic structure of the rodent MFC has mostly been conserved in humans, it is a long-standing question whether the structural analogies translate to functional analogies. Here, we probed this question using ultra high field fMRI data to compare rat, marmoset, and human MFC functional connectivity. First, we applied hierarchical clustering to intrinsically define the functional boundaries of the MFC in all three species, independent of cytoarchitectonic definitions. Then, we mapped the functional connectivity "fingerprints" of these regions with a number of different brain areas. Because rats do not share cytoarchitectonically defined regions of the lateral frontal cortex (LFC) with primates, the fingerprinting method also afforded the unique ability to compare the rat MFC and marmoset LFC, which have often been suggested to be functional analogs. The results demonstrated remarkably similar intrinsic functional organization of the MFC across the species, but clear differences between rodent and primate MFC whole-brain connectivity. Rat MFC patterns of connectivity showed greatest similarity with premotor regions in the marmoset, rather than dorsolateral prefrontal regions, which are often suggested to be functionally comparable. These results corroborate the viability of the marmoset as a preclinical model of human MFC dysfunction, and suggest divergence of functional connectivity between rats and primates in both the MFC and LFC.

Not all fine-branch locomotion is equal: Grasping morphology determines locomotor performance on narrow supports.

Fine-branch models have long played a central role in primate evolutionary research. Nevertheless, recent studies of positional behavior in nonprimate arboreal mammals have challenged the idea that synapomorphic primate features, such as grasping extremities, uniquely facilitated access to the fine-branch zone. We test the alternative hypothesis that grasping extremities specifically improve locomotor performance in a fine-branch environment by examining how support diameter influences locomotor mechanics in one sciurid rodent (Sciurus carolinensis) and two platyrrhine primates (Callithrix jacchus and Saimiri boliviensis). These species were chosen to broadly model different stages in the evolution of primate grasping morphology. The results showed that transitioning from broad to narrower supports required the greatest kinematic adjustment in squirrels and the least adjustment in squirrel monkeys, with marmosets displaying an intermediate level of adjustment. Moreover, on any given support, squirrels' locomotor mechanics differed from marmosets' in a manner consistent with a greater need for stability, despite superficial ecomorphological similarities between sciurid rodents and callitrichine primates. Morphological analyses of autopodial size and proportions suggest that variation in locomotor performance more closely tracked variation in overall hand and foot size rather than digit length per se. Indeed, a broad comparative analysis revealed that for their body mass, primates have longer hands than similarly sized arboreal rodents and marsupials (although only the primate-rodent comparison was significant after incorporating phylogenetic relatedness). Inclusion of fossil stem primates (plesiadapiforms) and euprimates (adapiforms) in these analyses suggests that this primate-wide grade shift in relative autopodial size must have occurred early in the evolutionary history of the group. Overall, our findings show that basal primate morphological adaptations may have specifically facilitated improved locomotor performance in a fine-branch niche, rather than merely permitting access to the environment. As such, future adaptive hypotheses of primate origins should incorporate the import of primate-like morphology on locomotor performance as well.

Open access resource for cellular-resolution analyses of corticocortical connectivity in the marmoset monkey.

Understanding the principles of neuronal connectivity requires tools for efficient quantification and visualization of large datasets. The primate cortex is particularly challenging due to its complex mosaic of areas, which in many cases lack clear boundaries. Here, we introduce a resource that allows exploration of results of 143 retrograde tracer injections in the marmoset neocortex. Data obtained in different animals are registered to a common stereotaxic space using an algorithm guided by expert delineation of histological borders, allowing accurate assignment of connections to areas despite interindividual variability. The resource incorporates tools for analyses relative to cytoarchitectural areas, including statistical properties such as the fraction of labeled neurons and the percentage of supragranular neurons. It also provides purely spatial (parcellation-free) data, based on the stereotaxic coordinates of 2 million labeled neurons. This resource helps bridge the gap between high-density cellular connectivity studies in rodents and imaging-based analyses of human brains.

Anatomical parameters of the body and the digestive tract of Callithrix sp. marmosets under the influence of seasonality.

Due to the ecological importance and given the scarcity of studies on the digestive morphology of primates, anatomical aspects of the body and digestive tract, as well as food content were analysed for marmosets Callithrix sp. (hybrids of exotic species) captured in forest fragments in Minas Gerais - Brazil, during the dry and rainy seasons, considering that seasonal variations affect the availability of food and quality of diet. Data such as body weight and length, and thoracic and abdominal perimeters were analysed, and no significant difference was found between dry and rainy seasons. In relation to the digestive tract, length, weight and diameter of the oesophagus, stomach, small intestine and large intestine were measured, in addition to the isolated caecum. There was a significant difference in the diameter of the ascending colon, which was larger in the animals in the dry season than in the rainy season. The difference found may be related to diet, and through analysis of the gastric and caecal contents, it was observed that gum was the main food item for the dry season marmosets, while in the rainy season the animals consumed mainly arthropods. Thus, the characteristic observed in the digestive tract of dry season marmosets is a reflection of an adaptive response to gum intake, since this food item is of low digestibility, necessitating that the food content be retained for a long time in this segment of the large intestine, helping the process of microbial fermentation and better energy utilization for these animals.

Presence of the annular ridge and location of the coronary sinus ostium as morphological features ofthe right atrium and interatrial septum in healthy common marmosets (Callithrix jacchus).

To effectively use a common marmoset (Callithrix jacchus) as an experimental animal species, it is critical to establish a normal characteristics and morphology of the organs of the common marmoset. Although gross morphology of the common marmoset heart is reportedly the same as that of humans, little information is available regarding detailed morphology of the right atrium and the interatrial septum. Heart specimens were collected from three male and 10 female marmosets aged 9 to 65 months to determine the morphological features of the right atrium and the interatrial septum. Ten specimens were evaluated morphologically with a stereoscopic microscope in accordance with preparation and investigation methods designed to facilitate evaluation. Three specimens were histologically evaluated after being stained with hematoxylin-eosin, Elastica van Gieson and periodic acid Schiff. An annular ridge that is not present in the human heart was present in the right atrium and the interatrial septum of the common marmoset hearts. Tissue structure of the annular ridge was similar to atrial myocardial fibers. Furthermore, location of the coronary sinus ostium was different to that in humans. Present findings were used to create a schematic view of the annular ridge in the common marmoset heart. In the common marmoset heart, the annular ridge may function as a valve of the superior vena cava ostium, inferior vena cava ostium, and coronary sinus ostium. Present study provides morphological evidence that common marmosets have a valve-like structure in the right atrium.

Heart anatomy and topography of the common marmoset (Callithrix jacchus Linnaeus, 1758).

INTRODUCTION: The morphological study of wild animals serves as a base for more advanced studies in clinical medicine, surgery, and pathology. Due to an urgent need and demand for professionals specialized in this area, studies of this nature have become indispensable and so the objective of the present study was to describe the heart morphology of Callithrix jacchus. METHODS: Ten anatomic pieces of common marmoset were used. The hearts were removed and dissected for better visualization and thus to makes a detailed description of the structures of the organ of the C jacchus species. RESULTS: The C jacchus heart is similar to that of other mammals, with small anatomical modifications such as division of the apex by the interventricular grooves, shallow fossa ovalis, and less salient intervenous tubercle. CONCLUSIONS: This study may serve as taxonomic base for research and also as a basis for clinical and surgical procedures with the C jacchus.

Anomalous Pigmentation in Invasive and Native Marmosets, Callithrix jacchus, Callithrix penicillata (Primates, Callitrichidae), and Their Hybrids in Brazil.

Leucism is the lack or reduction in pigmentation in the most or parts of the body, but not in the eyes and body extremities. It is extremely rare in primates and has never been reported for Callithrix, a genus endemic to Brazil. We searched for individuals of Callithrix jacchus and C. penicillata with pigmentation anomalies in a systematic survey of three protected areas in the Atlantic Forest, within museum collections in Brazil, and opportunistically during field studies. Since 2008, we have recorded 8 individuals with leucism in small urban and periurban forest patches. Four were from native populations of C. penicillata in Cerrado savannahs and of C. jacchus in the Caatinga xeric scrubland, and 4 were from populations of hybrids between C. jacchus and C. penicillata in invaded areas in the coastal Atlantic Forest. We found no pigmentation abnormalities in museum specimens. We hypothesize that the observed leucism may be linked to inbreeding within the native range, but to hybridization within the invaded range, and discuss the likely ecological consequences to leucistic individuals.

A Novel Method for Assessing Enamel Thickness Distribution in the Anterior Dentition as a Signal for Gouging and Other Extractive Foraging Behaviors in Gummivorous Mammals.

Gummivory poses unique challenges to the dentition as gum acquisition may often require that the anterior teeth be adapted to retain a sharp edge and to resist loading because they sometimes must penetrate a highly obdurate substrate during gum extraction by means of gouging or scraping. It has been observed previously that the enamel on the labial surface of the teeth used for extraction is thicker relative to that on the lingual surface in taxa that extract gums, while enamel is more evenly distributed in the anterior teeth of taxa that do not regularly engage in extractive behaviors. This study presents a quantitative methodology for measuring the distribution of labial versus lingual enamel thickness among primate and marsupial taxa in the context of gummivory. Computed microtomography scans of 15 specimens representing 14 taxa were analyzed. Ten measurements were taken at 20% intervals starting from the base of the crown of the extractive tooth to the tip of the cutting edge across the lingual and labial enamel. A method for including worn or broken teeth is also presented. Mann-Whitney U tests, canonical variates analysis, and between-group principal components analysis were used to examine variation in enamel thickness across taxa. Our results suggest that the differential distribution of enamel thickness in the anterior dentition can serve as a signal for gouging behavior; this methodology distinguishes between gougers, scrapers, and nonextractive gummivores. Gouging taxa are characterized by significantly thicker labial enamel relative to the lingual enamel, particularly towards the crown tip. Examination of enamel thickness patterning in these taxa permits a better understanding of the adaptations for the extraction of gums in extant taxa and offers the potential to test hypotheses concerning the dietary adaptations of fossil taxa.

Radiographic evaluation of the forelimbs and hind limbs of marmosets (Callithrix spp.).

BACKGROUND: The maintenance of marmosets in captivity may trigger various disorders. The objective of this study was to provide a radiographic evaluation of the forelimbs and hind limbs of marmosets rescued from illegal wildlife trade and maintained in captivity. METHODS: Fourteen marmosets were studied. RESULTS AND CONCLUSIONS: Three marmosets were apparently normal. Of the eleven marmosets with radiographic changes in the hind limbs, five had pelvic narrowing and bilateral varus deviation of the femur, with one suggestive of rickets and another of osteomalacia. The other marmosets showed changes such as malunion of acetabular fracture, transtibial amputation, tibial antecurvatum, and knee osteoarthritis. Six marmosets showed alterations in the forelimbs such as radius fracture, scapulohumeral subluxation, and elbow joint incongruence. In conclusion, 78.57% of the marmosets had bone and/or joint changes detected by plain radiography, which were found predominantly in the hind limbs and without impediment to locomotion in captivity.

Rapid modulations of the vocal structure in marmoset monkeys.

Humans and some animal species show flexibility in vocal production either voluntarily or in response to environmental cues. Studies have shown rapid spectrotemporal changes in speech or vocalizations during altered auditory feedback in humans, songbirds and bats. Non-human primates, however, have long been considered lacking the ability to modify spectrotemporal structures of their vocalizations. Here we tested the ability of the common marmoset (Callithrix jacchus), a highly vocal New World primate species to alter spectral and temporal structures of their species-specific vocalizations in the presence of perturbation signals. By presenting perturbation noises while marmosets were vocalizing phee calls, we showed that they were able to change in real-time the duration or spectral trajectory of an ongoing phee phrase by either terminating it before its completion, making rapid shifts in fundamental frequency or in some cases prolonging the duration beyond the natural range of phee calls. In some animals, we observed fragmented phee calls which were not produced by marmosets in their natural environment. Interestingly, some perturbation-induced changes persisted even in the absence of the perturbation noises. These observations provide further evidence that marmoset monkeys are capable of rapidly modulating their vocal structure and suggested potential voluntary vocal control by this non-human primate species.

Critique of Pure Marmoset.

The common marmoset, a New World (platyrrhine) monkey, is currently being fast-tracked as a non-human primate model species, especially for genetic modification but also as a general-purpose model for research on the brain and behavior bearing on the human condition. Compared to the currently dominant primate model, the catarrhine macaque monkey, marmosets are notable for certain evolutionary specializations, including their propensity for twin births, their very small size (a result of phyletic dwarfism), and features related to their small size (rapid development and relatively short lifespan), which result in these animals yielding experimental results more rapidly and at lower cost. Macaques, however, have their own advantages. Importantly, macaques are more closely related to humans (which are also catarrhine primates) than are marmosets, sharing approximately 20 million more years of common descent, and are demonstrably more similar to humans in a variety of genomic, molecular, and neurobiological characteristics. Furthermore, the very specializations of marmosets that make them attractive as experimental subjects, such as their rapid development and short lifespan, are ways in which marmosets differ from humans and in which macaques more closely resemble humans. These facts warrant careful consideration of the trade-offs between convenience and cost, on the one hand, and biological realism, on the other, in choosing between non-human primate models of human biology. Notwithstanding the advantages marmosets offer as models, prudence requires continued commitment to research on macaques and other primate species.