Biology subjects

Schaeffer, D. J.

Publications and source records attributed to Schaeffer, D. J..

17 recordsLinked to original sources

bioRxiv2026

Noninvasive Focal Gene Delivery of Functional Neural Actuators to the Primate Spinal Cord using Focused Ultrasound

Pathologies of the spinal cord -- from degenerative diseases to chronic pain -- represent a substantial global health burden. Although surgical and pharmacological treatments for spinal cord pathologies have advanced considerably, therapies capable of addressing the cellular mechanisms underlying these conditions remain limited. Viral gene therapies present a compelling alternative, allowing for delivery of therapeutic genes that directly target the pathological processes in specific cell-types. Effective viral delivery to the spinal cord, however, remains constrained by a fundamental tradeoff between procedural invasiveness and spatial precision. As such, there remains a need for clinically tractable methods -- that are both noninvasive and focal -- to deliver gene therapeutics across the restrictive vascular boundaries of the blood-spinal cord barrier (BSCB). Here, we demonstrate noninvasive, focal disruption of the BSCB and delivery of systemically administered chemogenetic gene payloads to the cervical and thoracic spinal cord in marmoset nonhuman primates (Callithrix jacchus) using focused ultrasound (FUS). Through systematic testing of ultrasonic pressures and central frequencies, we establish a FUS parameter set optimized for robust, spatially constrained molecular delivery across the marmoset BSCB. Using these optimized parameters, we show that FUS BSCB disruption permitted focal penetrance of systemically administered viral vectors for transduction of both fluorescent transgenes and excitatory chemogenetics within targeted spinal segments. Positron emission tomography (PET) imaging following chemogenetic actuation revealed significantly increased metabolic demand within the targeted region of the spinal cord, demonstrating in vivo evidence of functional transgene expression. Behavioral and histopathological assessments demonstrated preserved neurological function and tissue integrity, supporting the safety of FUS BSCB disruption and viral delivery in nonhuman primates. To facilitate broad application of this platform for noninvasive delivery of receptor-based gene therapeutics in marmosets, we generated an ultra-high-resolution (74 m) multimodal MRI/CT spinal cord template for precise targeting and anatomical localization. We also provide open-access engineering drawings and CAD files for our M-FRAME system (Marmoset Fixation and Reorientation Apparatus for Multimodal Experiments), enabling precise and repeatable spinal targeting without surgical fixation. Together, these results establish FUS-mediated BSCB disruption as a safe and effective approach for noninvasive, focal gene delivery to the primate spinal cord.

neuroscience↗

bioRxiv2025

A common cross-species atlas of cortical gray matter

Translational neuroscience requires consistent anatomical frameworks to compare brain organization across species despite differences in size and specialization. Existing atlases are species-specific, limiting cross-species analyses. Here we developed a hierarchical common atlas delineating homologous cortical and subcortical gray matter regions across mouse, rat, marmoset, rhesus macaque, and human, built upon population-averaged minimal deformation templates and uniform tissue segmentation. The atlas was validated through cross-atlas Dice similarity against established human parcellations, cross-scale containment against species-specific atlases, cross-species geometric consistency of regional positioning, and comparison of independent mouse and marmoset invasive tracer connectivity, with a per-region homology confidence index quantifying the strength of each regional assignment. Cross-species tracer comparison revealed a structured gradient of correspondence, with sensorimotor connections showing strong conservation and association connections showing progressive divergence. This freely available atlas provides a unified coordinate system for comparative neuroscience, enabling quantitative evaluation of where cross-species correspondence holds and where species-specific divergence emerges.

neuroscience↗

bioRxiv2025

Noninvasive focal gene transfer of chemogenetic proteins in the primate brain

The development of chemogenetic neuromodulators, including Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), have enabled focally specific, long-lasting, and reversible neuromodulation in the primate brain. Although systemically delivered synthetic ligands allow for noninvasive actuation of chemogenetic receptors, direct intraparenchymal injection remains atop the available methods to precisely deliver chemogenetic payloads to a specific target of the brain. The requirement of trephination, however, is accompanied by inherent risks of infection, long recovery times, and often tissue damage with concomitant behavioral complications. When considering therapeutic injections, the requirement of transcranial surgery does not translate well to the clinic, especially when repeated administrations are required. Here, we leverage our recent development of transcranial focused ultrasound (tFUS) for noninvasive and focal delivery of adeno-associated viruses (AAVs) carrying excitatory Gq-DREADDs to frontal cortical targets (areas 6DR and 8aD) in the marmoset brain. Using [18F]-fluorodeoxyglucose (FDG) positron emission tomography, we demonstrate significant increases in glucose metabolism at the site of viral delivery after administering the DREADD-specific agonist deschloroclozapine (DCZ), as compared to vehicle control. Focal neuronal DREADD expression was confirmed by immunohistochemistry at the site of opening. Through comparison of awake resting-state functional connectivity (whole brain connectivity with the sites of delivery) and structural connectivity (directly injected viral neuronal tracing at the sites of delivery) we demonstrate that the increase in glucose metabolism occurs at both mono- and polysynaptically connected brain regions. Taken together, these results demonstrate the ability to focally deliver excitatory chemogenetics without the need for surgery, allowing for activation of long-range frontal cortex circuits of the primate brain.

neuroscience↗

bioRxiv2025

SpIC3D imaging: Spinal In-situ Contrast 3D imaging

High-definition visualization techniques are critical for understanding the neuroanatomy of the spinal cord, an essential structure for sensorimotor and autonomic functions, in both healthy and pathological conditions. Magnetic resonance imaging (MRI) is a common method for visualizing neural structures in 3D. However, techniques for spinal cord MRI have historically achieved limited visualization of rootlets and nerves, especially at lower spinal levels, due to their highly complex and compact organization. Here we developed a spinal in-situ contrast 3D imaging (SpIC3D) method that allows visualization of spinal compartments in fixed animal and human specimens with ultra-high resolution at various spinal levels. Using SpIC3D, we achieved quantification of neuronal cell density in dorsal root ganglia, multi-segment identification of individual rootlets and roots, and volumetric reconstruction of multiple spinal structures for computational modeling. SpIC3D provides a basis for accelerated spinal pathology characterization and personalized spinal cord stimulation treatments.

neuroscience↗

bioRxiv2025

Aseptic, semi-sealed cranial chamber implants for chronic multi-channel neurochemical and electrophysiological neural recording in nonhuman primates

We developed an implantable neural interface for monitoring both chemical and electrical forms of brain activity in monkeys that maintains aseptic properties for year-long periods while leveraging the modular functions (e.g., sensor moveability) provided by a chamber system. Invasive electrophysiological recordings, especially in subcortical structures from nonhuman primates usually involves implanting electrodes into the brain through a skull-mounted chamber. These electrodes may be attached temporarily for several hours of recording, or permanently. Permanent attachments are favorable to allow for sealing the chamber completely from externally originating pathogenic species that can infiltrate and compromise the health of the animal. A sealed chamber also reduces the need for frequent chamber cleaning required to minimize the accumulation of pathogenic organisms. However, neurochemical measurements require specialized electrodes with extremely fragile carbon fiber tips and are not compatible with recently developed sealed chamber systems. Here, we leveraged osseointegrating materials and hermetic sealing strategies to enable both neurochemical and electrical neural activity measurements from a sealed chamber with an aspirating port for culturing chamber fluid to ensure an aseptic environment. The system was shown to provide successful recordings of neural activity in two monkeys while maintaining negative bacteria culture results for over a year post-implant.

neuroscience↗

bioRxiv2024

An Open Access Resource for Marmoset Neuroscientific Apparatus

The use of the common marmoset (Callithrix jacchus) for neuroscientific inquiry has grown precipitously over the past two decades. Despite windfalls of grant support from funding initiatives in North America, Europe, and Asia to model human brain diseases in the marmoset, marmoset- specific apparatus are of sparse availability from commercial vendors and thus are often developed and reside within individual laboratories. Through our collective research efforts, we have designed and vetted myriad designs for awake or anesthetized magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), as well as focused ultrasound (FUS), electrophysiology, optical imaging, surgery, and behavior in marmosets across the age- span. This resource makes these designs openly available, reducing the burden of de novo development across the marmoset field. The computer-aided-design (CAD) files are publicly available through the Marmoset Brain Connectome (MBC) resource (https://www.marmosetbrainconnectome.org/apparatus/) and include dozens of downloadable CAD assemblies, software and online calculators for marmoset neuroscience. In addition, we make available a variety of vetted touchscreen and task-based fMRI code and stimuli. Here, we highlight the online interface and the development and validation of a few yet unpublished resources: Software to automatically extract the head morphology of a marmoset from a CT and produce a 3D printable helmet for awake neuroimaging, and the design and validation of 8-channel and 14- channel receive arrays for imaging deep structures during anatomical and functional MRI.

bioengineering↗

bioRxiv2023

Noninvasive focal transgene delivery with viral neuronal tracers in the marmoset monkey

Although preclinical neuroscientific modeling species permit invasive intracranial delivery of targeted neurotropic agents, direct intracranial injections are not readily translatable to clinical therapeutics. Transcranial focused ultrasound (tFUS) has been identified as a technique to circumvent surgical injections altogether by transiently opening the blood-brain barrier (BBB) with selective focus. We have recently characterized the ability to focally deliver substances across the BBB in the marmoset, a non-human primate model with similar husbandry requirements to rodents but with cortical topologies more similar to humans. Here, we establish a reliable method for selectively delivering adeno-associated viral vectors (AAVs) across the BBB in marmoset frontal cortex with tFUS and demonstrate long-range anterograde neuronal tracing. Using a single-element 1.46 MHz transducer, we focally perturbed the BBB ([~]1 x 2 mm) in area 8aD of frontal cortex in four adult marmoset monkeys using low-intensity focused ultrasound aided by microbubbles. We confirmed BBB opening via a gadolinium-enhanced MRI at 9.4 T prior to AAV delivery. Within an hour of opening the BBB, either AAV2 or AAV9 was delivered systemically via tail-vein injection. Four to six weeks later, animals were sacrificed, and microscopy was performed to confirm the presence of neurons transduced as indicated by EGFP or mCherry fluorescence. In all four marmosets, neurons were observed at the site of BBB perturbation, with AAV2 showing an exiguous distribution of transduced neurons when compared to AAV9. The results are compared to direct intracortical injections of anterograde tracers into area 8aD and similar (albeit sparser) long-range connectivity was observed. With evidence of transduced neurons specific to the region of BBB opening as well as long-distance tracing, we establish a framework for focal noninvasive transgene delivery to the marmoset brain. This technique will be of utility for the burgeoning marmoset model, with applications for noninvasive delivery of therapeutics, genetic delivery of precursors for techniques like two-photon imaging, or neuronal tracing across the lifespan.

neuroscience↗

bioRxiv2022

Non-invasive disruption of the blood-brain barrier in the marmoset monkey

The common marmoset monkey (Callithrix jacchus) is a species of rising prominence in the neurosciences due to their small size, ease of handling, fast breeding, and their shared functional and structural brain characteristics with Old World primates. With increasing attention on modeling human brain diseases in marmosets, understanding how to deliver therapeutic or neurotropic agents to the marmoset brain non-invasively is of great preclinical importance. In other species, including humans, transcranial focused ultrasound (tFUS) aided by intravenously injected microbubbles has proven to be a transient, reliable, and safe method for disrupting the blood-brain barrier (BBB), allowing for the focal passage of therapeutic agents that do not otherwise readily traverse the tight endothelial junctions of the BBB. The critical gap that we address here is to document parameters to disrupt the BBB reliably and safely in marmosets using tFUS. By integrating our marmoset brain atlases and the use of a marmoset-specific stereotactic targeting system, we conducted a series of systematic transcranial sonication experiments in nine marmosets. We demonstrate the effects of center frequency, acoustic pressure, burst period and duration, establish a minimum microbubble dose, estimate microbubble clearance time, and estimate the duration that the BBB remained open to passage. Successful BBB disruption was reported in vivo with MRI-based contrast agents, as well as Evans blue staining assessed ex vivo. Histology (Hematoxylin and Eosin staining) and immunohistochemistry indicated that the BBB can be safely and reliably opened with the parameters derived from these experiments.

neuroscience↗

bioRxiv2021

Functional organization of frontoparietal cortex in the marmoset investigated with awake resting-state fMRI

Frontoparietal networks contribute to complex cognitive functions in humans and macaques such as working memory, attention, task-switching, response suppression, grasping, reaching, and eye movement control. However, little is known about the organization of frontoparietal networks in the New World common marmoset monkey (Callithrix jacchus) which is now widely recognized as a powerful nonhuman primate experimental animal. In this study, we employed hierarchical clustering of interareal BOLD signals to investigate the hypothesis that the organization of the frontoparietal cortex in the marmoset follows the organizational principles of the macaque frontoparietal system. We found that the posterior part of the lateral frontal cortex (premotor regions) was functionally connected to the anterior parietal areas while more anterior frontal regions (frontal eye field (FEF)) were connected to more posterior parietal areas (the area around lateral intraparietal area (LIP)). These overarching patterns of inter-areal organization are consistent with a recent macaque study. These findings demonstrate parallel frontoparietal processing streams in marmosets and support the functional homologies of FEF-LIP and premotor-anterior parietal pathways between marmoset and macaque. Significant StatementFrontoparietal networks contribute to many cognitive functions in humans and macaques, but little is known about the organization of frontoparietal networks in the New World common marmoset monkey. Here, we investigated the hypothesis that the organization of the frontoparietal cortex in the marmoset follows the organizational principles of the macaque frontoparietal system. These frontoparietal connection showed overarching pattern of interareal organization consistent with Old world monkeys. These findings demonstrate parallel frontoparietal processing streams in marmosets.

neuroscience↗

bioRxiv2021

Ketamine disrupts gaze patterns during face viewing in the common marmoset

Faces are stimuli of critical importance for primates. The common marmoset (Callithrix jacchus) is a promising model for investigations of face processing, as this species possesses oculomotor and face processing networks resembling those of macaques and humans. Face processing is often disrupted in neuropsychiatric conditions such as schizophrenia (SZ) and thus it is important to recapitulate underlying circuitry dysfunction preclinically. The N-Methyl-D-aspartate (NMDA) non-competitive antagonist ketamine has been used extensively to model the cognitive symptoms of SZ. Here, we investigated the effects of a subanesthetic dose of ketamine on oculomotor behaviour in marmosets during face viewing. Four marmosets received systemic ketamine or saline injections while viewing phase-scrambled or intact videos of conspecifics faces. To evaluate effects of ketamine on scan paths during face viewing, we identified regions of interest in each face video, and classified locations of saccade onsets and landing positions within these areas. A preference for the snout over eye regions was observed following ketamine administration. In addition, regions in which saccades landed could be significantly predicted by saccade onset region in the saline but not the ketamine condition. No significant drug effects were observed for phase-scrambled videos. Effects on saccade control were limited to a reduction in saccade amplitudes during viewing of scrambled videos. Thus, ketamine induced a significant disruption of scan paths during viewing of conspecific faces but limited effects on saccade motor control. These findings support the use of ketamine in marmosets for investigating changes in neural circuits underlying social cognition in neuropsychiatric disorders.

neuroscience↗

bioRxiv2021

Interspecies activation correlations reveal functional correspondences between marmoset and human brain areas

The common marmoset has enormous promise as a nonhuman primate model of human brain functions. While resting-state functional magnetic resonance imaging (fMRI) has provided evidence for a similar organization of marmoset and human cortices, the technique cannot be used to map the functional correspondences of brain regions between species. This limitation can be overcome by movie-driven fMRI (md-fMRI), which has become a popular tool for non-invasively mapping the neural patterns generated by rich and naturalistic stimulation. Here, we used md-fMRI in marmosets and humans to identify whole-brain functional correspondences between the two primate species. In particular, we describe functional correlates for the well-known human face, body, and scene patches in marmosets. We find that these networks have a similar organization in both species, suggesting a largely conserved organization of higher-order visual areas between New World marmoset monkeys and humans. However, while face patches in humans and marmosets were activated by marmoset faces, only human face patches responded to the faces of other animals. Together, the results demonstrate that md-fMRI is a powerful tool for interspecies functional mapping and characterization of higher-order visual functions.

neuroscience↗

bioRxiv2021

Simultaneous functional MRI of socially interacting marmosets

Social cognition is a dynamic process that requires the perception and integration of a complex set of idiosyncratic features between interacting conspecifics. Here we present a method for simultaneously measuring the whole-brain activation of two socially interacting marmoset monkeys using functional magnetic resonance imaging. MRI hardware (a radiofrequency coil and peripheral devices) and image-processing pipelines were developed to assess brain responses to socialization, both on an intra-brain and inter-brain level. Notably, brain-activation maps acquired during constant interaction demonstrated neuronal synchrony between marmosets in regions of the brain responsible for processing social interaction. This method enables a wide range of possibilities for studying social function and dysfunction in a non-human primate model, including using transgenic models of neuropsychiatric disorders.

neuroscience↗

bioRxiv2020

Whole brain mapping of somatosensory responses in awake marmosets investigated with ultra-high field fMRI

The common marmoset (Callithrix jacchus) is a small-bodied New World primate that is becoming an important model to study brain functions. Despite several studies exploring the somatosensory system of marmosets, all results have come from anesthetized animals using invasive techniques and post-mortem analyses. Here we demonstrate the feasibility for getting high-quality and reproduceable sensorimotor mapping in awake marmosets with functional magnetic resonance imaging (fMRI). We acquired fMRI sequences in four animals while they received tactile stimulation (via air-puffs), delivered to the face, arm or leg. We found that the body representation progressed medially from the leg to the face in areas 3a, 3b, 1/2, and from caudal to rostral sites in areas S2 and PV. SI and SII exhibited a body representation in their functional connectivity pattern within the posterior and midcingulate and the thalamus. Interestingly, we also found a somatotopic body representation in two subcortical areas: the thalamus and, for the first time, in the putamen. These maps have similar organizations as those previously found in Old World macaque monkeys and humans, suggesting that these subcortical somatotopic organizations were already established before Old and New World primates diverged. Our results show the first whole brain mapping of somatosensory responses acquired in a non-invasive way in awake marmosets. Significant statementHere we used somatosensory stimulation combined with functional magnetic resonance imaging to map whole brain activation in awake marmosets. We used light tactile stimulation, consisting of air-puffs, delivered on the face, arm or leg. We found a topographic body representation in primary (SI) and secondary (SII) somatosensory regions, thalamus and putamen. We also revealed the existence of a body representation organization within the thalamus and the cingulate cortex by computing functional connectivity maps from seeds defined in SI/SII for face, arm and leg using resting-state fMRI data. This non-invasive approach will be essential for chronic studies by guiding invasive recording and manipulation techniques.

neuroscience↗

bioRxiv2020

Cortico-subcortical functional connectivity profiles of resting-state networks in marmosets and humans

Understanding the similarity of cortico-subcortical networks topologies between humans and nonhuman primate species is critical to study the origin of network alternations underlying human neurological and neuropsychiatric diseases. The New World common marmoset (Callithrix jacchus) has become popular as a non-human primate model for human brain function. Most marmoset connectomic research, however, has exclusively focused on cortical areas, with connectivity to subcortical networks less extensively explored. In this study, we aimed to first isolate patterns of subcortical connectivity with cortical resting-state networks (RSNs) in awake marmosets using resting-state functional magnetic resonance imaging (RS-fMRI), then to compare these networks to those in humans using connectivity fingerprinting. While we could match several marmoset and human RSNs based on their functional fingerprints, we also found a few striking differences, for example strong functional connectivity of the default mode network with the superior colliculus in marmosets that was much weaker in humans. Together, these findings demonstrate that many of the core cortico-subcortical networks in humans are also present in marmosets, but that small, potentially functionally relevant differences exist.

neuroscience↗

bioRxiv2020

Structural alterations in the macaque frontoparietal white matter network after recovery from prefrontal cortex lesions

Unilateral damage to the frontoparietal network typically impairs saccade target selection within the contralesional visual hemifield. Severity of deficits and the degree of recovery have been associated with widespread network dysfunction, yet it is not clear how these behavioural and functional changes relate with the underlying structural white matter pathways. Here, we investigated whether recovery after unilateral prefrontal cortex (PFC) lesions was associated with structural white matter remodeling in the distributed frontoparietal network. Diffusion-weighted MRI was acquired in four macaque monkeys before the lesions and at 2-4 months post-lesion, after recovery of deficits in saccade selection of contralesional targets. Probabilistic tractography was used to reconstruct inter- and intra-hemispheric frontoparietal fiber tracts: bilateral superior longitudinal fasciculus (SLF) and transcallosal fibers connecting bilateral PFC or bilateral posterior parietal cortex (PPC). After behavioural recovery, tract-specific fractional anisotropy in contralesional SLF and transcallosal PPC increased after small lesions and decreased after larger lesions compared to pre-lesion. These findings indicate that remote fiber tracts may provide optimal compensation after small PFC lesions. However, larger lesions may have induced widespread structural damage and hindered compensatory remodeling in the structural frontoparietal network.

neuroscience↗

bioRxiv2020

Face selective patches in marmoset frontal cortex

Primates have evolved the ability transmit important social information through facial expression. In humans and macaque monkeys, socially relevant face processing is accomplished via a distributed cortical and subcortical functional network that includes specialized patches in anterior cingulate cortex and lateral prefrontal cortex, regions usually associated with high-level cognition. It is unclear whether a similar network exists in New World primates, who diverged ~35 million years from Old World primates and have a less elaborated frontal cortex. The common marmoset (Callithrix jacchus) is a small New World primate that is ideally placed to address this question given the complex social repertoire inherent to this species (e.g., observational social learning; imitation; cooperative antiphonal calling). Here, we investigated the existence of a putative high-level face processing network in marmosets by employing ultra-high field (9.4 Tesla) task-based functional MRI (fMRI). We demonstrated that, like Old World primates, marmosets show differential activation in anterior cingulate cortex and lateral prefrontal cortex while they view socially relevant videos of marmoset faces. We corroborate the locations of these frontal regions by demonstrating both functional (via resting-state fMRI) and structural (via cellular-level tracing) connectivity between these regions and temporal lobe face patches. Given the evolutionary separation between macaques and marmosets, our results suggest this frontal network specialized for social face processing predates the separation between Platyrrhini and Catarrhine. These results give further credence to the marmoset as a viable preclinical modelling species for studying human social disorders.

neuroscience↗

bioRxiv2019

Visual looming and receding networks in awake marmosets investigated with fMRI

An object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. This information (motion, direction, identity, time-to-collision, size, velocity) is analyzed by the brain in order to execute the appropriate behavioral responses depending on the context: fleeing, freezing, grasping, eating, exploring. In the current study, we performed ultra-high-field functional MRI (fMRI) in awake marmosets to explore the patterns of brain activation elicited by visual stimuli looming toward or receding away from the monkey. We found that looming and receding visual stimuli both activate a large cortical network in frontal, parietal, temporal and occipital cortex in areas involved in the analysis of motion, shape, identity and features of the objects. Looming stimuli strongly activated a network composed of the pulvinar, superior colliculus, prefrontal cortex and temporal cortical areas. This may underlie the existence of an alert network that processes the visual stimuli looming toward their peripersonal space by extracting the crucial information brought by the stimulus and evaluating its potential consequences to the observer. We hypothesize that this network is involved in the planning of protective behaviors (e.g. fleeing or freezing) and in emotional reaction (e.g. anxiety, fear). These findings support the view that this network is preserved through evolution and that the marmoset is a viable model to study visual and multisensory processes by using fMRI to guide further invasive recordings and/or pharmacological manipulations.\n\nSignificant statementAn object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. Here, we identified the functional network in non-human primates that was activated by visual stimuli looming toward or away from the animals using ultra-high-field functional magnetic resonance imaging. Our findings show that large cortical activations are elicited by both looming and receding visual conditions. However, some activations were specific to the looming condition, suggesting that the integration of cues in the looming direction rely on strong connections between cortical and subcortical areas, which allows primates to react properly for protecting themselves against a potential threat.

neuroscience↗