Brain age of rhesus macaques over the lifespan

Through the application of machine learning algorithms to neuroimaging data the brain age methodology was shown to provide a useful individual-level biological age prediction and identify key brain regions responsible for the prediction. In this study, we present the methodology of constructing a rhesus macaque brain age model using a machine learning algorithm and discuss the key predictive brain regions in comparison to the human brain, to shed light on cross-species primate similarities and differences. Structural information of the brain (e.g., parcellated volumes) from brain magnetic resonance imaging of 43 rhesus macaques were used to develop brain atlas-based features to build a brain age model that predicts biological age. The best-performing model used 22 selected features and achieved an R2 of 0.72. We also identified interpretable predictive brain features including Right Fronto-orbital Cortex, Right Frontal Pole, Right Inferior Lateral Parietal Cortex, and Bilateral Posterior Central Operculum. Our findings provide converging evidence of the parallel and comparable brain regions responsible for both non-human primates and human biological age prediction.

Immune proteins C1q and CD47 may contribute to aberrant microglia-mediated synapse loss in the aging monkey brain that is associated with cognitive impairment

Cognitive impairment in learning, memory, and executive function occurs in normal aging even in the absence of Alzheimer's disease (AD). While neurons do not degenerate in humans or monkeys free of AD, there are structural changes including synapse loss and dendritic atrophy, especially in the dorsolateral prefrontal cortex (dlPFC), and these correlate with cognitive age-related impairment. Developmental studies revealed activity-dependent neuronal properties that lead to synapse remodeling by microglia. Microglia-mediated phagocytosis that may eliminate synapses is regulated by immune "eat me" and "don't eat me" signaling proteins in an activity-dependent manner, so that less active synapses are eliminated. Whether this process contributes to age-related synapse loss remains unknown. The present study used a rhesus monkey model of normal aging to investigate the balance between the "eat me" signal, complement component C1q, and the "don't eat me" signal, transmembrane glycoprotein CD47, relative to age-related synapse loss in dlPFC Area 46. Results showed an age-related elevation of C1q and reduction of CD47 at PSD95+ synapses that is associated with cognitive impairment. Additionally, reduced neuronal CD47 RNA expression was found, indicating that aged neurons were less able to produce the protective signal CD47. Interestingly, microglia do not show the hypertrophic morphology indicative of phagocytic activity. These findings suggest that in the aging brain, changes in the balance of immunologic proteins give microglia instructions favoring synapse elimination of less active synapses, but this may occur by a process other than classic phagocytosis such as trogocytosis.

Enhanced Multiscale Human Brain Imaging by Semi-supervised Digital Staining and Serial Sectioning Optical Coherence Tomography

A major challenge in neuroscience is to visualize the structure of the human brain at different scales. Traditional histology reveals micro- and meso-scale brain features, but suffers from staining variability, tissue damage and distortion that impedes accurate 3D reconstructions. Here, we present a new 3D imaging framework that combines serial sectioning optical coherence tomography (S-OCT) with a deep-learning digital staining (DS) model. We develop a novel semi-supervised learning technique to facilitate DS model training on weakly paired images. The DS model performs translation from S-OCT to Gallyas silver staining. We demonstrate DS on various human cerebral cortex samples with consistent staining quality. Additionally, we show that DS enhances contrast across cortical layer boundaries. Furthermore, we showcase geometry-preserving 3D DS on cubic-centimeter tissue blocks and visualization of meso-scale vessel networks in the white matter. We believe that our technique offers the potential for high-throughput, multiscale imaging of brain tissues and may facilitate studies of brain structures.

Comparison of monkey and human retrosplenial neurocytology

Retrosplenial cortex (RSC) has unique problems for human neuroimaging studies as its divisions are small, at the lower end of functional scanner spatial resolution, and it is buried in the callosal sulcus. The present study sought to define the cytoarchitecture of RSC in human and monkey brains along its entire anteroposterior extent. The results show anterior extensions, a newly defined dichotomy of area 30, a new area p30, and an area p29v in monkey that differentiates into three divisions in human. Accordingly, anterior (a), intermediate (i), and posterior (p) divisions of areas 29l, 29m, 30l, and 30m were identified. Posterior area 29 has higher neuron packing in the granular layer than anterior and intermediate divisions of area 29. A newly detected dysgranular area p30 has larger neurons in layers II-IIIab than a30 and i30 and with substantially higher NFP expression  in layer IIIab of posterior areas than areas a30 and i30. Medial area 30 has larger pyramids and higher NFP expression in all layers than area 30l. The new area p30 was seen between areas p29m and p30I in both species. Finally, a ventral area p29v is present in monkeys. This latter area appears to differentiate into three divisions in human with the most extensive granular layer adjacent to layer I in p29vm and p29vl. Functional imaging has identified pRSC as part of a cognitive map which is engaged in spatial navigation and localization of personally relevant objects.

Pattern of ventral temporal lobe interconnections in rhesus macaques

The entorhinal cortex (EC, A28) is linked through reciprocal pathways with nearby perirhinal and visual, auditory, and multimodal association cortices in the temporal lobe, in pathways associated with the flow of information for memory processing. The density and laminar organization of these pathways is not well understood in primates. We studied interconnections within the ventral temporal lobe in young adult rhesus monkeys of both sexes with the aid of neural tracers injected in temporal areas (Ts1, Ts2, TE1, area 36, temporal polar area TPro, and area 28) to determine the density and laminar distribution of projection neurons within the temporal lobe. These temporal areas can be categorized into three different cortical types based on their laminar architecture: the sensory association areas Ts1, Ts2, and TE1 have six layers (eulaminate); the perirhinal limbic areas TPro and area 36 have an incipient layer IV (dysgranular); and area 28 lacks layer IV (agranular). We found that (1) temporal areas that are similar in laminar architecture by cortical type are strongly interconnected, and (2) the laminar pattern of connections is dependent on the difference in cortical laminar structure between linked areas. Thus, agranular A28 is more strongly connected with other agranular/dysgranular areas than with eulaminate cortices. Further, A28 predominantly projected via feedback-like pathways that originated in the deep layers, and received feedforward-like projections from areas of greater laminar differentiation, which emanated from the upper layers. Our results are consistent with the Structural Model, which relates the density and laminar distribution of connections to the relationship of the laminar structure between the linked areas. These connections were viewed in the context of the inhibitory microenvironment of A28, which is the key recipient of pathways from the cortex and of the output of hippocampus. Our findings revealed a higher population of calretinin (CR)-expressing neurons in EC, with a significantly higher density in its lateral division. Medial EC had a higher density of CR neurons in the deep layers, particularly in layer Va. In contrast, parvalbumin (PV) neurons were more densely distributed in the deep layers of the lateral subdivisions of rostral EC, especially in layer Va, whereas the densities of calbindin (CB) neurons in the medial and lateral EC were comparable in all layers, except for layer IIIa, in which medial EC had a higher CB population than the lateral. The pattern of connections in the inhibitory microenvironment of EC, which sends and receives input from the hippocampus, may shed light on signal propagation in this network associated with diverse aspects of memory, and disruptions in neurologic and psychiatric diseases that affect this region.

Human-to-monkey transfer learning identifies the frontal white matter as a key determinant for predicting monkey brain age

The application of artificial intelligence (AI) to summarize a whole-brain magnetic resonance image (MRI) into an effective "brain age" metric can provide a holistic, individualized, and objective view of how the brain interacts with various factors (e.g., genetics and lifestyle) during aging. Brain age predictions using deep learning (DL) have been widely used to quantify the developmental status of human brains, but their wider application to serve biomedical purposes is under criticism for requiring large samples and complicated interpretability. Animal models, i.e., rhesus monkeys, have offered a unique lens to understand the human brain - being a species in which aging patterns are similar, for which environmental and lifestyle factors are more readily controlled. However, applying DL methods in animal models suffers from data insufficiency as the availability of animal brain MRIs is limited compared to many thousands of human MRIs. We showed that transfer learning can mitigate the sample size problem, where transferring the pre-trained AI models from 8,859 human brain MRIs improved monkey brain age estimation accuracy and stability. The highest accuracy and stability occurred when transferring the 3D ResNet [mean absolute error (MAE) = 1.83 years] and the 2D global-local transformer (MAE = 1.92 years) models. Our models identified the frontal white matter as the most important feature for monkey brain age predictions, which is consistent with previous histological findings. This first DL-based, anatomically interpretable, and adaptive brain age estimator could broaden the application of AI techniques to various animal or disease samples and widen opportunities for research in non-human primate brains across the lifespan.

Mesenchymal-derived extracellular vesicles enhance microglia-mediated synapse remodeling after cortical injury in aging Rhesus monkeys

Understanding the microglial neuro-immune interactions in the primate brain is vital to developing therapeutics for cortical injury, such as stroke or traumatic brain injury. Our previous work showed that mesenchymal-derived extracellular vesicles (MSC-EVs) enhanced motor recovery in aged rhesus monkeys following injury of primary motor cortex (M1), by promoting homeostatic ramified microglia, reducing injury-related neuronal hyperexcitability, and enhancing synaptic plasticity in perilesional cortices. A focal lesion was induced via surgical ablation of pial blood vessels over lying the cortical hand representation of M1 of aged female rhesus monkeys, that received intravenous infusions of either vehicle (veh) or EVs 24 h and again 14 days post-injury. The current study used this same cohort to address how these injury- and recovery-associated changes relate to structural and molecular interactions between microglia and neuronal synapses. Using multi-labeling immunohistochemistry, high-resolution microscopy, and gene expression analysis, we quantified co-expression of synaptic markers (VGLUTs, GLURs, VGAT, GABARs), microglia markers (Iba1, P2RY12), and C1q, a complement pathway protein for microglia-mediated synapse phagocytosis, in perilesional M1 and premotor cortices (PMC). We compared this lesion cohort to age-matched non-lesion controls (ctr). Our findings revealed a lesion-related loss of excitatory synapses in perilesional areas, which was ameliorated by EV treatment. Further, we found region-dependent effects of EVs on microglia and C1q expression. In perilesional M1, EV treatment and enhanced functional recovery were associated with increased expression of C1q + hypertrophic microglia, which are thought to have a role in debris-clearance and anti-inflammatory functions. In PMC, EV treatment was associated with decreased C1q + synaptic tagging and microglia-spine contacts. Our results suggest that EV treatment may enhance synaptic plasticity via clearance of acute damage in perilesional M1, and thereby preventing chronic inflammation and excessive synaptic loss in PMC. These mechanisms may act to preserve synaptic cortical motor networks and a balanced normative M1/PMC synaptic function to support functional recovery after injury.

Mesenchymal-Derived Extracellular Vesicles Enhance Microglia-mediated Synapse Remodeling after Cortical Injury in Rhesus Monkeys

Understanding the microglial neuro-immune interactions in the primate brain is vital to developing therapeutics for cortical injury, such as stroke. Our previous work showed that mesenchymal-derived extracellular vesicles (MSC-EVs) enhanced motor recovery in aged rhesus monkeys post-injury of primary motor cortex (M1), by promoting homeostatic ramified microglia, reducing injury-related neuronal hyperexcitability, and enhancing synaptic plasticity in perilesional cortices. The current study addresses how these injury- and recovery-associated changes relate to structural and molecular interactions between microglia and neuronal synapses. Using multi-labeling immunohistochemistry, high resolution microscopy, and gene expression analysis, we quantified co-expression of synaptic markers (VGLUTs, GLURs, VGAT, GABARs), microglia markers (Iba-1, P2RY12), and C1q, a complement pathway protein for microglia-mediated synapse phagocytosis, in perilesional M1 and premotor cortices (PMC) of monkeys with intravenous infusions of either vehicle (veh) or EVs post-injury. We compared this lesion cohort to aged-matched non-lesion controls. Our findings revealed a lesion-related loss of excitatory synapses in perilesional areas, which was ameliorated by EV treatment. Further, we found region-dependent effects of EV on microglia and C1q expression. In perilesional M1, EV treatment and enhanced functional recovery were associated with increased expression of C1q + hypertrophic microglia, which are thought to have a role in debris-clearance and anti-inflammatory functions. In PMC, EV treatment was associated with decreased C1q + synaptic tagging and microglial-spine contacts. Our results provided evidence that EV treatment facilitated synaptic plasticity by enhancing clearance of acute damage in perilesional M1, and thereby preventing chronic inflammation and excessive synaptic loss in PMC. These mechanisms may act to preserve synaptic cortical motor networks and a balanced normative M1/PMC synaptic connectivity to support functional recovery after injury.

Neuronal properties of pyramidal cells in lateral prefrontal cortex of the aging rhesus monkey brain are associated with performance deficits on spatial working memory but not executive function

Age-related declines in cognitive abilities occur as early as middle-age in humans and rhesus monkeys. Specifically, performance by aged individuals on tasks of executive function (EF) and working memory (WM) is characterized by greater frequency of errors, shorter memory spans, increased frequency of perseverative responses, impaired use of feedback and reduced speed of processing. However, how aging precisely differentially impacts specific aspects of these cognitive functions and the distinct brain areas mediating cognition are not well understood. The prefrontal cortex (PFC) is known to mediate EF and WM and is an area that shows a vulnerability to age-related alterations in neuronal morphology. In the current study, we show that performance on EF and WM tasks exhibited significant changes with age, and these impairments correlate with changes in biophysical properties of layer 3 (L3) pyramidal neurons in lateral LPFC (LPFC). Specifically, there was a significant age-related increase in excitability of L3 LPFC pyramidal neurons, consistent with previous studies. Further, this age-related hyperexcitability of LPFC neurons was significantly correlated with age-related decline on a task of WM, but not an EF task. The current study characterizes age-related performance on tasks of WM and EF and provides insight into the neural substrates that may underlie changes in both WM and EF with age.

Prefrontal and medial temporal interactions in memory functions in the rhesus monkey

Both the medial temporal lobe and the dorsolateral prefrontal cortex have been implicated in learning and memory. However, it has been difficult to ascertain the degree to which the two structures are dependent on each other or interact in subserving these cognitive functions. To investigate this question directly, we prepared two group of monkeys. First, the contralateral frontal-hippocampal split group (CFHS) received a unilateral lesion of the hippocampus and surrounding posterior parahippocampal cortices (H +), combined with a contralateral lesion of the dorsolateral prefrontal cortex (DLPFC) plus transection of the corpus callosum and anterior commissure. This preparation functionally "disconnects" the remaining intact H + from the sole intact DLPFC in the opposite hemisphere. As a surgical control group, a second set of animals, the ipsilateral frontal-hippocampal split group, was prepared with a unilateral lesion of the DLPFC and an ipsilateral H + lesion together plus transection of the corpus callosum and anterior commissure. This preparation matches the locus and extent of damage in the cross-lesion group but allows the intact H + and intact DLPFC to interact ipsilaterally. Following recovery from surgery, all animals were then tested on the delayed nonmatching to sample task (DNMS), a test of recognition memory. The crossed-lesion split-brain group (CFHS) was markedly impaired on DNMS in both acquisition (rule learning) and performance over delays (recognition memory). The results provide evidence of a functionally dependent interaction between the medial temporal lobe and the dorsolateral prefrontal cortex in learning and memory. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Neuronal properties of pyramidal cells in lateral prefrontal cortex of the aging rhesus monkey brain are associated with performance deficits on spatial working memory but not executive function

Age-related declines in cognitive abilities occur as early as middle-age in humans and rhesus monkeys. Specifically, performance by aged individuals on tasks of executive function (EF) and working memory (WM) is characterized by greater frequency of errors, shorter memory spans, increased frequency of perseverative responses, impaired use of feedback and reduced speed of processing. However, how aging precisely differentially impacts specific aspects of these cognitive functions and the distinct brain areas mediating cognition are not well understood. The prefrontal cortex (PFC) is known to mediate EF and WM and is an area that shows a vulnerability to age-related alterations in neuronal morphology. In the current study, we show that performance on EF and WM tasks exhibited significant changes with age and these impairments correlate with changes in biophysical properties of L3 pyramidal neurons in lateral LPFC (LPFC). Specifically, there was a significant age-related increase in excitability of Layer 3 LPFC pyramidal neurons, consistent with previous studies. Further, this age-related hyperexcitability of LPFC neurons was significantly correlated with age-related decline on a task of WM, but not an EF task. The current study characterizes age-related performance on tasks of WM and EF and provides insight into the neural substrates that may underlie changes in both WM and EF with age.

Aging compromises oligodendrocyte precursor cell maturation and efficient remyelination in the monkey brain

Age-associated cognitive decline is common among otherwise healthy elderly people, even in the absence of Alzheimer's disease and neuron loss. Instead, white matter loss and myelin damage are strongly associated with cognitive decline. Myelin is subject to lifelong oxidative stress that damages the myelin sheath, which is repaired by cells of the oligodendrocyte lineage. This process is mediated by oligodendrocyte precursor cells (OPCs) that sense the damage and respond by proliferating locally and migrating to the region, where they differentiate into mature myelinating oligodendrocytes. In aging, extensive myelin damage, in combination with inefficient remyelination, leads to chronically damaged myelin and loss of efficient neuronal conduction. This study used the rhesus monkey model of normal aging to examine how myelin regeneration capacity is affected by age. Results show that older subjects have reduced numbers of new BCAS1 + myelinating oligodendrocytes, which are newly formed cells, and that this reduction is associated with poorer cognitive performance. Interestingly, this does not result from limited proliferation of progenitor OPCs. Instead, the transcription factor NKX2.2, which regulates OPCs differentiation, is significantly decreased in aged OPCs. This suggests that these OPCs have a diminished potential for differentiation into mature oligodendrocytes. In addition, mature oligodendrocytes have reduced RNA expression of two essential myelin protein markers, MBP and PLP. These data collectively suggest that in the normal aging brain, there is a reduction in regenerative OPCs as well as myelin production that impairs the capacity for remyelination.

Vascular Collagen Type-IV in Hypertension and Cerebral Small Vessel Disease

BACKGROUND

Cerebral small vessel disease (SVD) is common in older people and causes lacunar stroke and vascular cognitive impairment. Risk factors include old age, hypertension and variants in the genes COL4A1/COL4A2 encoding collagen alpha-1(IV) and alpha-2(IV), here termed collagen-IV, which are core components of the basement membrane. We tested the hypothesis that increased vascular collagen-IV associates with clinical hypertension and with SVD in older persons and with chronic hypertension in young and aged primates and genetically hypertensive rats.

METHODS

We quantified vascular collagen-IV immunolabeling in small arteries in a cohort of older persons with minimal Alzheimer pathology (N=52; 21F/31M, age 82.8±6.95 years). We also studied archive tissue from young (age range 6.2-8.3 years) and older (17.0-22.7 years) primates (M mulatta) and compared chronically hypertensive animals (18 months aortic stenosis) with normotensives. We also compared genetically hypertensive and normotensive rats (aged 10-12 months).

RESULTS

Collagen-IV immunolabeling in cerebral small arteries of older persons was negatively associated with radiological SVD severity (ρ: -0.427, P=0.005) but was not related to history of hypertension. General linear models confirmed the negative association of lower collagen-IV with radiological SVD (P<0.017), including age as a covariate and either clinical hypertension (P<0.030) or neuropathological SVD diagnosis (P<0.022) as fixed factors. Reduced vascular collagen-IV was accompanied by accumulation of fibrillar collagens (types I and III) as indicated by immunogold electron microscopy. In young and aged primates, brain collagen-IV was elevated in older normotensive relative to young normotensive animals (P=0.029) but was not associated with hypertension. Genetically hypertensive rats did not differ from normotensive rats in terms of arterial collagen-IV.

CONCLUSIONS

Our cross-species data provide novel insight into sporadic SVD pathogenesis, supporting insufficient (rather than excessive) arterial collagen-IV in SVD, accompanied by matrix remodeling with elevated fibrillar collagen deposition. They also indicate that hypertension, a major risk factor for SVD, does not act by causing accumulation of brain vascular collagen-IV.

Investigating the contribution of cytoarchitecture to diffusion MRI measures in gray matter using histology

Postmortem studies are currently considered a gold standard for investigating brain structure at the cellular level. To investigate cellular changes in the context of human development, aging, or disease treatment, non-invasive in-vivo imaging methods such as diffusion MRI (dMRI) are needed. However, dMRI measures are only indirect measures and require validation in gray matter (GM) in the context of their sensitivity to the underlying cytoarchitecture, which has been lacking. Therefore, in this study we conducted direct comparisons between in-vivo dMRI measures and histology acquired from the same four rhesus monkeys. Average and heterogeneity of fractional anisotropy and trace from diffusion tensor imaging and mean squared displacement (MSD) and return-to-origin-probability from biexponential model were calculated in nine cytoarchitectonically different GM regions using dMRI data. DMRI measures were compared with corresponding histology measures of regional average and heterogeneity in cell area density. Results show that both average and heterogeneity in trace and MSD measures are sensitive to the underlying cytoarchitecture (cell area density) and capture different aspects of cell composition and organization. Trace and MSD thus would prove valuable as non-invasive imaging biomarkers in future studies investigating GM cytoarchitectural changes related to development and aging as well as abnormal cellular pathologies in clinical studies.

Neural recovery after cortical injury: Effects of MSC derived extracellular vesicles on motor circuit remodeling in rhesus monkeys

Reorganization of motor circuits in the cortex and corticospinal tract are thought to underlie functional recovery after cortical injury, but the mechanisms of neural plasticity that could be therapeutic targets remain unclear. Recent work from our group have shown that systemic treatment with mesenchymal stem cell derived (MSCd) extracellular vesicles (EVs) administered after cortical damage to the primary motor cortex (M1) of rhesus monkeys resulted in a robust recovery of fine motor function and reduced chronic inflammation. Here, we used immunohistochemistry for cfos, an activity-dependent intermediate early gene, to label task-related neurons in the surviving primary motor and premotor cortices, and markers of axonal and synaptic plasticity in the spinal cord. Compared to vehicle, EV treatment was associated with a greater density of cfos⁺ pyramidal neurons in the deep layers of M1, greater density of cfos⁺ inhibitory interneurons in premotor areas, and lower density of synapses on MAP2+ lower motor neurons in the cervical spinal cord. These data suggest that the anti-inflammatory effects of EVs may reduce injury-related upper motor neuron damage and hyperexcitability, as well as aberrant compensatory re-organization in the cervical spinal cord to improve motor function.

Curcumin improves reversal learning in middle-aged rhesus monkeys

Age-related impairments in cognitive function occur in multiple animal species including humans and nonhuman primates. Humans and rhesus monkeys exhibit a similar pattern of cognitive decline beginning in middle age, particularly within the domain of executive function. The prefrontal cortex is the brain region most closely associated with mediating executive function. Previous studies in rhesus monkeys have demonstrated that normal aging leads to an increase in myelin degradation in the prefrontal regions that correlates with cognitive decline. This myelin deterioration is thought to result, at least in part, from the age-related emergence of chronic low levels of inflammation. One therapeutic that may arrest the deleterious effects of neuroinflammation is curcumin (CUR), the primary component of the spice turmeric. CUR has been shown to be a potent anti-inflammatory and antioxidant and improves performance on tasks for working memory and motor function. In the present study, middle-aged monkeys (12-21 years old) were given daily dietary supplementation of 500 mg of curcumin or vehicle over a period of 3-4 years. Here, we present data from a series of both object and spatial reversal tasks. Compared to vehicle, the CUR group showed enhanced performance on object, but not spatial reversal learning. These findings suggest that curcumin may improve specific aspects of executive function. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Specializations of somatosensory innervation in the skin of humpback whales (Megaptera novaeangliae)

Cetacean behavior and life history imply a role for somatosensory detection of critical signals unique to their marine environment. As the sensory anatomy of cetacean glabrous skin has not been fully explored, skin biopsy samples of the flank skin of humpback whales were prepared for general histological and immunohistochemical (IHC) analyses of innervation in this study. Histology revealed an exceptionally thick epidermis interdigitated by numerous, closely spaced long, thin diameter penicillate dermal papillae (PDP). The dermis had a stratified organization including a deep neural plexus (DNP) stratum intermingled with small arteries that was the source of intermingled nerves and arterioles forming a more superficial subepidermal neural plexus (SNP) stratum. The patterns of nerves branching through the DNP and SNP that distribute extensive innervation to arteries and arterioles and to the upper dermis and PDP provide a dense innervation associated through the whole epidermis. Some NF-H+ fibers terminated at the base of the epidermis and as encapsulated endings in dermal papillae similar to Merkel innervation and encapsulated endings seen in terrestrial mammals. However, unlike in all mammalian species assessed to date, an unusual acellular gap was present between the perineural sheaths and the central core of axons in all the cutaneous nerves perhaps as mechanism to prevent high hydrostatic pressure from compressing and interfering with axonal conductance. Altogether the whale skin has an exceptionally dense low-threshold mechanosensory system innervation most likely adapted for sensing hydrodynamic stimuli, as well as nerves that can likely withstand high pressure experienced during deep dives.

Exosomes derived from bone marrow mesenchymal stromal cells promote remyelination and reduce neuroinflammation in the demyelinating central nervous system

Injury of oligodendrocytes (OLs) induces demyelination, and patients with neurodegenerative diseases exhibit demyelination concomitantly with neurological deficit and cognitive impairment. Oligodendrocyte progenitor cells (OPCs) are present in the adult central nervous system (CNS), and they can proliferate, differentiate, and remyelinate axons after damage. However, remyelination therapies are not in clinical use. Multiple sclerosis (MS) is a major demyelinating disease in the CNS. Mesenchymal stromal cells (MSCs) have demonstrated therapeutic promise in animal models and in clinical trials of MS. Exosomes are nanoparticles generated by nearly all cells and they mediate cell-cell communication by transferring cargo biomaterials. Here, we hypothesize that exosomes harvested from MSCs have a similar therapeutic effect on enhancement of remyelination as that of MSCs. In the present study we employed exosomes derived from rhesus monkey MSCs (MSC-Exo). Two mouse models of demyelination were employed: 1) experimental autoimmune encephalomyelitis (EAE), an animal model of MS; and 2) cuprizone (CPZ) diet model, a toxic demyelination model. MSC-Exo or PBS were intravenously injected twice a week for 4 weeks, starting on day 10 post immunization in EAE mice, or once a week for 2 weeks starting on the day of CPZ diet withdrawal. Neurological and cognitive function were tested, OPC differentiation and remyelination, neuroinflammation and the potential underlying mechanisms were investigated using immunofluorescent staining, transmission electron microscopy and Western blot. Data generated from the EAE model revealed that MSC-Exo cross the blood brain barrier (BBB) and target neural cells. Compared with the controls (p < 0.05), treatment with MSC-Exo: 1) significantly improved neurological outcome; 2) significantly increased the numbers of newly generated OLs (BrdU+/APC+) and mature OLs (APC+), and the level of myelin basic protein (MBP); 3) decreased amyloid-β precursor protein (APP)+ density; 4) decreased neuroinflammation by increasing the M2 phenotype and decreasing the M1 phenotype of microglia, as well as their related cytokines; 5) inhibited the TLR2/IRAK1/NFκB pathway. Furthermore, we confirmed that the MSC-Exo treatment significantly improved cognitive function, promoted remyelination, increased polarization of M2 phenotype and blocked TLR2 signaling in the CPZ model. Collectively, MSC-Exo treatment promotes remyelination by both directly acting on OPCs and indirectly by acting on microglia in the demyelinating CNS. This study provides the cellular and molecular basis for this cell-free exosome therapy on remyelination and modulation of neuroinflammation in the CNS, with great potential for treatment of demyelinating and neurodegenerative disorders.

Sex differences in recovery of motor function in a rhesus monkey model of cortical injury

BACKGROUND

Stroke disproportionately affects men and women, with women over 65 years experiencing increased severity of impairment and higher mortality rates than men. Human studies have explored risk factors that contribute to these differences, but additional research is needed to investigate how sex differences affect functional recovery and hence the severity of impairment. In the present study, we used our rhesus monkey model of cortical injury and fine motor impairment to compare sex differences in the rate and degree of motor recovery following this injury.

METHODS

Aged male and female rhesus monkeys were trained on a task of fine motor function of the hand before undergoing surgery to produce a cortical lesion limited to the hand area representation of the primary motor cortex. Post-operative testing began two weeks after the surgery and continued for 12 weeks. All trials were video recorded and latency to retrieve a reward was quantitatively measured to assess the trajectory of post-operative response latency and grasp pattern compared to pre-operative levels.

RESULTS

Postmortem analysis showed no differences in lesion volume between male and female monkeys. However, female monkeys returned to their pre-operative latency and grasp patterns significantly faster than males.

CONCLUSIONS

These findings demonstrate the need for additional studies to further investigate the role of estrogens and other sex hormones that may differentially affect recovery outcomes in the primate brain.

Layer-specific pyramidal neuron properties underlie diverse anterior cingulate cortical motor and limbic networks

The laminar cellular and circuit mechanisms by which the anterior cingulate cortex (ACC) exerts flexible control of motor and affective information for goal-directed behavior have not been elucidated. Using multimodal tract-tracing, in vitro patch-clamp recording and computational approaches in rhesus monkeys (M. mulatta), we provide evidence that specialized motor and affective network dynamics can be conferred by layer-specific biophysical and structural properties of ACC pyramidal neurons targeting two key downstream structures -the dorsal premotor cortex (PMd) and the amygdala (AMY). AMY-targeting neurons exhibited significant laminar differences, with L5 more excitable (higher input resistance and action potential firing rates) than L3 neurons. Between-pathway differences were found within L5, with AMY-targeting neurons exhibiting greater excitability, apical dendritic complexity, spine densities, and diversity of inhibitory inputs than PMd-targeting neurons. Simulations using a pyramidal-interneuron network model predict that these layer- and pathway-specific single-cell differences contribute to distinct network oscillatory dynamics. L5 AMY-targeting networks are more tuned to slow oscillations well-suited for affective and contextual processing timescales, while PMd-targeting networks showed strong beta/gamma synchrony implicated in rapid sensorimotor processing. These findings are fundamental to our broad understanding of how layer-specific cellular and circuit properties can drive diverse laminar activity found in flexible behavior.

In vivo microdialysis shows differential effects of prenatal protein malnutrition and stress on norepinephrine, dopamine, and serotonin levels in rat orbital frontal cortex

Prenatal protein malnutrition (PPM) alters the developing brain including changes in monoaminergic systems and attention. In the present study, we used in vivo microdialysis to examine the relationship between PPM, acute stress, and extracellular serotonin (5HT), dopamine (DA) and norepinephrine (NE) in both hemispheres of lateral orbital frontal cortices (lOFC) in the adult rat. We hypothesized that prenatal protein malnutrition would alter extracellular concentrations of cortical monoamines. The effects of an acute restraint stress were also assessed because PPM alters the brain's response to stress. We used adult male, Long-Evans rats [10 prenatally malnourished (6% casein) and 10 prenatally well-nourished (25% casein)]. Samples were collected from the left and right hemispheres of the lOFC every 20 min for 6 hr total and quantified using high-performance liquid chromatography (HPLC). After 2 hr of sampling, animals were exposed to a 40-min restraint stress. Extracellular levels of NE were significantly higher in PPM animals than in well-nourished controls across both hemispheres at all time-points. In contrast, baseline levels of 5HT and DA levels did not differ between nutritional groups. 5HT levels, but not NE or DA levels, were elevated compared to baseline levels in both nutritional groups and in both hemispheres during the first 20 min of stress exposure. These data highlight the impact of PPM on neuromodulatory systems and the profile of changes in response to acute stress. Additional studies are needed to determine how these basal and stress-related responses impact cognitive performance and whether these differences persist during cognitive testing. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The relationship of age and hypertension with cognition and gray matter cerebral blood volume in a rhesus monkey model of human aging

The goal of this study was to investigate whether alterations in cerebral microvasculature, as measured by cerebral blood volume (CBV), contribute to age- and hypertension-related impairments in cognitive function with a focus on executive function and memory. Data were collected on 19 male rhesus monkeys ranging from 6.4 to 21.6 years of age. Hypertension was induced through surgical coarctation of the thoracic aorta. We assessed whether performance on tasks of memory and executive function corresponded to CBV in either the hippocampus or prefrontal cortex. We found a relationship between duration of hypertension and CBV in the gray matter of the prefrontal cortex, but not the hippocampus. No relationships were found with the degree of hypertension or age. Increased prefrontal CBV was related to greater impairment in executive function while hippocampal CBV was not related to memory performance. These findings suggest that duration, but not severity, of hypertension or age are important factors underlying alterations in brain microvasculature and that executive function is more vulnerable than memory function. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

MRI-based Parcellation and Morphometry of the Individual Rhesus Monkey Brain: the macaque Harvard-Oxford Atlas (mHOA), a translational system referencing a standardized ontology

Investigations of the rhesus monkey (Macaca mulatta) brain have shed light on the function and organization of the primate brain at a scale and resolution not yet possible in humans. A cornerstone of the linkage between non-human primate and human studies of the brain is magnetic resonance imaging, which allows for an association to be made between the detailed structural and physiological analysis of the non-human primate and that of the human brain. To further this end, we present a novel parcellation method and system for the rhesus monkey brain, referred to as the macaque Harvard-Oxford Atlas (mHOA), which is based on the human Harvard-Oxford Atlas (HOA) and grounded in an ontological and taxonomic framework. Consistent anatomical features were used to delimit and parcellate brain regions in the macaque, which were then categorized according to functional systems. This system of parcellation will be expanded with advances in technology and, like the HOA, will provide a framework upon which the results from other experimental studies (e.g., functional magnetic resonance imaging (fMRI), physiology, connectivity, graph theory) can be interpreted.

Barcoded viral tracing of single-cell interactions in central nervous system inflammation

Cell-cell interactions control the physiology and pathology of the central nervous system (CNS). To study astrocyte cell interactions in vivo, we developed rabies barcode interaction detection followed by sequencing (RABID-seq), which combines barcoded viral tracing and single-cell RNA sequencing (scRNA-seq). Using RABID-seq, we identified axon guidance molecules as candidate mediators of microglia-astrocyte interactions that promote CNS pathology in experimental autoimmune encephalomyelitis (EAE) and, potentially, multiple sclerosis (MS). In vivo cell-specific genetic perturbation EAE studies, in vitro systems, and the analysis of MS scRNA-seq datasets and CNS tissue established that Sema4D and Ephrin-B3 expressed in microglia control astrocyte responses via PlexinB2 and EphB3, respectively. Furthermore, a CNS-penetrant EphB3 inhibitor suppressed astrocyte and microglia proinflammatory responses and ameliorated EAE. In summary, RABID-seq identified microglia-astrocyte interactions and candidate therapeutic targets.

Distribution and overlap of entorhinal, premotor, and amygdalar connections in the monkey anterior cingulate cortex

The anterior cingulate cortex (ACC) is important for decision-making as it integrates motor plans with affective and contextual limbic information. Disruptions in these networks have been observed in depression, bipolar disorder, and post-traumatic stress disorder. Yet, overlap of limbic and motor connections within subdivisions of the ACC is not well understood. Hence, we administered a combination of retrograde and anterograde tracers into structures important for contextual memories (entorhinal cortex), affective processing (amygdala), and motor planning (dorsal premotor cortex) to assess overlap of labeled projection neurons from (outputs) and axon terminals to (inputs) the ACC of adult rhesus monkeys (Macaca mulatta). Our data show that entorhinal and dorsal premotor cortical (dPMC) connections are segregated across ventral (A25, A24a) and dorsal (A24b,c) subregions of the ACC, while amygdalar connections are more evenly distributed across subregions. Among all areas, the rostral ACC (A32) had the lowest relative density of connections with all three regions. In the ventral ACC, entorhinal and amygdalar connections strongly overlap across all layers, especially in A25. In the dorsal ACC, outputs to dPMC and the amygdala strongly overlap in deep layers. However, dPMC input to the dorsal ACC was densest in deep layers, while amygdalar inputs predominantly localized in upper layers. These connection patterns are consistent with diverse roles of the dorsal ACC in motor evaluation and the ventral ACC in affective and contextual memory. Further, distinct laminar circuits suggest unique interactions within specific ACC compartments that are likely important for the temporal integration of motor and limbic information during flexible goal-directed behavior.

Extracellular vesicles derived from bone marrow mesenchymal stem cells enhance myelin maintenance after cortical injury in aged rhesus monkeys

Cortical injury, such as stroke, causes neurotoxic cascades that lead to rapid death and/or damage to neurons and glia. Axonal and myelin damage in particular, are critical factors that lead to neuronal dysfunction and impair recovery of function after injury. These factors can be exacerbated in the aged brain where white matter damage is prevalent. Therapies that can ameliorate myelin damage and promote repair by targeting oligodendroglia, the cells that produce and maintain myelin, may facilitate recovery after injury, especially in the aged brain where these processes are already compromised. We previously reported that a novel therapeutic, Mesenchymal Stem Cell derived extracellular vesicles (MSC-EVs), administered intravenously at both 24 h and 14 days after cortical injury, reduced microgliosis (Go et al. 2019), reduced neuronal pathology (Medalla et al. 2020), and improved motor recovery (Moore et al. 2019) in aged female rhesus monkeys. Here, we evaluated the effect of MSC-EV treatment on changes in oligodendrocyte maturation and associated myelin markers in the sublesional white matter using immunohistochemistry, confocal microscopy, stereology, qRT-PCR, and ELISA. Compared to vehicle control monkeys, EV-treated monkeys showed a reduction in the density of damaged oligodendrocytes. Further, EV-treatment was associated with enhanced myelin maintenance, evidenced by upregulation of myelin-related genes and increases in actively myelinating oligodendrocytes in sublesional white matter. These changes in myelination correlate with the rate of motor recovery, suggesting that improved myelin maintenance facilitates this recovery. Overall, our results suggest that EVs act on oligodendrocytes to support myelination and improves functional recovery after injury in the aged brain. SIGNIFICANCE: We previously reported that EVs facilitate recovery of function after cortical injury in the aged monkey brain, while also reducing neuronal pathology (Medalla et al. 2020) and microgliosis (Go et al. 2019). However, the effect of injury and EVs on oligodendrocytes and myelination has not been characterized in the primate brain (Dewar et al. 1999; Sozmen et al. 2012; Zhang et al. 2013). In the present study, we assessed changes in myelination after cortical injury in aged monkeys. Our results show, for the first time, that MSC-EVs support recovery of function after cortical injury by enhancing myelin maintenance in the aged primate brain.

Abstract P811: Oral Curcumin Treatment Facilitates Recovery of Function in a Rhesus Monkey Model of Cortical Injury

Curcumin is a primary component of the spice turmeric, and is a potent anti-inflammatory and anti-oxidant compound. In rodent models of brain damage from stroke or trauma, curcumin acts primarily on microglia and astrocytes to inhibit pro-inflammatory signaling pathways and to reduce inflammation and levels of reactive oxygen species (ROS). Further, rats with cortical injury treated with curcumin have smaller lesions and fewer neurological impairments than those treated with vehicle. However, it is not clear whether curcumin exerts the same biological effect in primate brains as in rodent brains, and the effects of curcumin have not yet been extensively tested in monkey models of brain injury. Data from our laboratory has demonstrated that curcumin enhances spatial working memory and motor function in normal aging rhesus monkeys given daily doses of dietary curcumin over two years. The question remains as to whether chronic dietary curcumin can enhance neuroprotection and dampen or ameliorate functional motor deficits after cortical injury. Thus, we administered curcumin to adult, male rhesus monkeys daily for two weeks prior to and 12 weeks following induced cortical injury to the hand-representation of primary motor cortex (M1). Monkeys given daily treatment with oral doses of curcumin, but not those given vehicle, demonstrated significantly enhanced recovery of function in terms of time to retrieve a food reward on our hand dexterity task (HDT). In addition, treated monkeys returned to pre-injury finger-thumb grasp patterns on the HDT, while monkeys that received vehicle developed a compensatory whole hand grasp pattern and never returned to pre-injury grasp. These findings provide evidence that the anti-inflammatory compound, curcumin, is an effective treatment for facilitating recovery of function following cortical injury. Studies investigating the effect of curcumin on the microglia and astrocytes in the brains from these monkeys will provide evidence of the role of curcumin in reducing inflammation and ROS following injury.

Diffusion interactions between crossing fibers of the brain

PURPOSE

Recent observations of several preferred orientations of diffusion in deep white matter may indicate either (a) that axons in different directions are independently bundled in thick sheets and function noninteractively, or more interestingly, (b) that the axons are closely interwoven and would exhibit branching and sharp turns. This study aims to investigate whether the dependence of dMRI Q-ball signal on the interpulse time Δ can decode the smaller-than-voxel-size brain structure, in particular, to distinguish scenarios (a) and (b).

METHODS

High-resolution Q-ball images of a healthy brain taken with b = 8000  s/mm² for 3 different values of Δ were analyzed. The exchange of water molecules between crossing fibers was characterized by the fourth Fourier coefficient f 4 ( Δ ) of the signal profile in the plane of crossing. To interpret the empirical results, a model consisting of differently oriented parallel sheets of cylinders was developed. Diffusion of water molecules inside and outside cylinders was simulated by the Monte Carlo method.

RESULTS

Simulations predict that f 4 ( Δ ) , agreeing with the empirical results, must increase with Δ for large b-values, but may peak at a typical Δ that depends on the thickness of the cylinder sheets for intermediate b-values. Thus, the thickness of axon layers in voxels with 2 predominant orientations can be detected from empirical f 4 ( Δ ) taken at smaller b-values.

CONCLUSION

Based on the simulation results, recommendations are made on how to design a dMRI experiment with optimal b-value and range of Δ in order to measure the thickness of axon sheets in the white matter, hence to distinguish (a) and (b).

T Cells Actively Infiltrate the White Matter of the Aging Monkey Brain in Relation to Increased Microglial Reactivity and Cognitive Decline

Normal aging is characterized by declines in processing speed, learning, memory, and executive function even in the absence of neurodegenerative diseases such as Alzheimer's Disease (AD). In normal aging monkeys and humans, neuronal loss does not account for cognitive impairment. Instead, loss of white matter volume and an accumulation of myelin sheath pathology begins in middle age and is associated with cognitive decline. It is unknown what causes this myelin pathology, but it likely involves increased neuroinflammation in white matter and failures in oligodendrocyte function (maturation and repair). In frontal white matter tracts vulnerable to myelin damage, microglia become chronically reactive and secrete harmful pro-inflammatory cytokines. Despite being in a phagocytic state, these microglia are ineffective at phagocytosing accruing myelin debris, which directly inhibits myelin sheath repair. Here, we asked whether reported age-related increases in pro-inflammatory markers were accompanied by an adaptive immune response involving T cells. We quantified T cells with immunohistochemistry in the brains of 34 cognitively characterized monkeys and found an age-related increase in perivascular T cells that surround CNS vasculature. We found a surprising age-related increase in T cells that infiltrate the white matter parenchyma. In the cingulum bundle the percentage of these parenchymal T cells increased with age relative to those in the perivascular space. In contrast, infiltrating T cells were rarely found in surrounding gray matter regions. We assessed whether T cell infiltration correlated with fibrinogen extravasation from the vasculature as a measure of BBB leakiness and found no correlation, suggesting that T cell infiltration is not a result of passive extravasation. Importantly, the density of T cells in the cingulum bundle correlated with microglial reactivity and with cognitive impairment. This is the first demonstration that T cell infiltration of white matter is associated with cognitive decline in the normal aging monkey.

Gut-licensed IFNγ+ NK cells drive LAMP1+TRAIL+ anti-inflammatory astrocytes

Astrocytes are glial cells that are abundant in the central nervous system (CNS) and that have important homeostatic and disease-promoting functions1. However, little is known about the homeostatic anti-inflammatory activities of astrocytes and their regulation. Here, using high-throughput flow cytometry screening, single-cell RNA sequencing and CRISPR-Cas9-based cell-specific in vivo genetic perturbations in mice, we identify a subset of astrocytes that expresses the lysosomal protein LAMP12 and the death receptor ligand TRAIL3. LAMP1+TRAIL+ astrocytes limit inflammation in the CNS by inducing T cell apoptosis through TRAIL-DR5 signalling. In homeostatic conditions, the expression of TRAIL in astrocytes is driven by interferon-γ (IFNγ) produced by meningeal natural killer (NK) cells, in which IFNγ expression is modulated by the gut microbiome. TRAIL expression in astrocytes is repressed by molecules produced by T cells and microglia in the context of inflammation. Altogether, we show that LAMP1+TRAIL+ astrocytes limit CNS inflammation by inducing T cell apoptosis, and that this astrocyte subset is maintained by meningeal IFNγ+ NK cells that are licensed by the microbiome.

Quantitative birefringence microscopy for imaging the structural integrity of CNS myelin following circumscribed cortical injury in the rhesus monkey

Significance: Myelin breakdown is likely a key factor in the loss of cognitive and motor function associated with many neurodegenerative diseases. Aim: New methods for imaging myelin structure are needed to characterize and quantify the degradation of myelin in standard whole-brain sections of nonhuman primates and in human brain. Approach: Quantitative birefringence microscopy (qBRM) is a label-free technique for rapid histopathological assessment of myelin structural breakdown following cortical injury in rhesus monkeys. Results: We validate birefringence microscopy for structural imaging of myelin in rhesus monkey brain sections, and we demonstrate the power of qBRM by characterizing the breakdown of myelin following cortical injury, as a model of stroke, in the motor cortex. Conclusions: Birefringence microscopy is a valuable tool for histopathology of myelin and for quantitative assessment of myelin structure. Compared to conventional methods, this label-free technique is sensitive to subtle changes in myelin structure, is fast, and enables more quantitative assessment, without the variability inherent in labeling procedures such as immunohistochemistry.

The use of hydrogel-delivered extracellular vesicles in recovery of motor function in stroke: a testable experimental hypothesis for clinical translation including behavioral and neuroimaging assessment approaches

Neural tissue engineering, nanotechnology and neuroregeneration are diverse biomedical disciplines that have been working together in recent decades to solve the complex problems linked to central nervous system (CNS) repair. It is known that the CNS demonstrates a very limited regenerative capacity because of a microenvironment that impedes effective regenerative processes, making development of CNS therapeutics challenging. Given the high prevalence of CNS conditions such as stroke that damage the brain and place a severe burden on afflicted individuals and on society, it is of utmost significance to explore the optimum methodologies for finding treatments that could be applied to humans for restoration of function to pre-injury levels. Extracellular vesicles (EVs), also known as exosomes, when derived from mesenchymal stem cells, are one of the most promising approaches that have been attempted thus far, as EVs deliver factors that stimulate recovery by acting at the nanoscale level on intercellular communication while avoiding the risks linked to stem cell transplantation. At the same time, advances in tissue engineering and regenerative medicine have offered the potential of using hydrogels as bio-scaffolds in order to provide the stroma required for neural repair to occur, as well as the release of biomolecules facilitating or inducing the reparative processes. This review introduces a novel experimental hypothesis regarding the benefits that could be offered if EVs were to be combined with biocompatible injectable hydrogels. The rationale behind this hypothesis is presented, analyzing how a hydrogel might prolong the retention of EVs and maximize the localized benefit to the brain. This sustained delivery of EVs would be coupled with essential guidance cues and structural support from the hydrogel until neural tissue remodeling and regeneration occur. Finally, the importance of including non-human primate models in the clinical translation pipeline, as well as the added benefit of multi-modal neuroimaging analysis to establish non-invasive, in vivo, quantifiable imaging-based biomarkers for CNS repair are discussed, aiming for more effective and safe clinical translation of such regenerative therapies to humans.

The neural basis of attentional alterations in prenatally protein malnourished rats

Protein malnutrition during gestation alters brain development and produces specific behavioral and cognitive changes that persist into adulthood and increase the risks of neuropsychiatric disorders. Given evidence for the role of the prefrontal cortex in such diseases, it is significant that studies in humans and animal models have shown that prenatal protein malnutrition specifically affects functions associated with prefrontal cortex. However, the neural basis underlying these changes is unclear. In the current study, prenatally malnourished and control rats performed a sustained attention task with an unpredictable distractor, a task that depends on intact prefrontal cortical function. Radiolabeled 2-deoxyglucose was used to measure neural and brain network activity during the task. Results confirmed that adult prenatally malnourished rats were more distractible than controls and exhibited lower functional activity in prefrontal cortices. Thus, prefrontal activity was a predictor of task performance in controls but not prenatally malnourished animals. Instead, prenatally malnourished animals relied on different brain networks involving limbic structures such as the hippocampus. These results provide evidence that protein reduction during brain development has more wide-reaching effects on brain networks than previously appreciated, resulting in the formation of brain networks that may reflect compensatory responses in prenatally malnourished brains.

The enduring effect of prenatal protein malnutrition on brain anatomy, physiology and behavior

There is increasing evidence that the maternal environment exerts enduring influences on the fetal brain. In response to certain environmental stimuli such as reduced protein content, the fetus changes the course of its brain development, which leads to specific and programed changes in brain anatomy and physiology. These alterations produce a brain with a fundamentally altered organization, which then translates to alterations in adult cognitive function. The effects on brain and behavior may be linked, such that a prenatal stimulus relays a signal to alter brain development and encourage the selection and development of brain circuits and behaviors that would be beneficial for the environment in which the animal was anticipated to emerge. At the same time, the signal would deselect behaviors unlikely to be adaptive. We draw on evidence from rodent models to suggest that the brain that develops after a reduction in protein during the prenatal phase is not uniformly dysfunctional, but simply different. This perspective has implications for the role of prenatal factors in the production and expression of behavior, and may account for the elevation of risk factors for neurological and psychiatric illnesses.

Amyloidosis increase is not attenuated by long-term calorie restriction or related to neuron density in the prefrontal cortex of extremely aged rhesus macaques

As human lifespan increases and the population ages, diseases of aging such as Alzheimer's disease (AD) are a major cause for concern. Although calorie restriction (CR) as an intervention has been shown to increase healthspan in many species, few studies have examined the effects of CR on brain aging in primates. Using postmortem tissue from a cohort of extremely aged rhesus monkeys (22-44 years old, average age 31.8 years) from a longitudinal CR study, we measured immunohistochemically labeled amyloid beta plaques in Brodmann areas 32 and 46 of the prefrontal cortex, areas that play key roles in cognitive processing, are sensitive to aging and, in humans, are also susceptible to AD pathogenesis. We also evaluated these areas for cortical neuron loss, which has not been observed in younger cohorts of aged monkeys. We found a significant increase in plaque density with age, but this was unaffected by diet. Moreover, there was no change in neuron density with age or treatment. These data suggest that even in the oldest-old rhesus macaques, amyloid beta plaques do not lead to overt neuron loss. Hence, the rhesus macaque serves as a pragmatic animal model for normative human aging but is not a complete model of the neurodegeneration of AD. This model of aging may instead prove most useful for determining how even the oldest monkeys are protected from AD, and this information may therefore yield valuable information for clinical AD treatments.

Copy number variants and fixed duplications among 198 rhesus macaques (Macaca mulatta)

The rhesus macaque is an abundant species of Old World monkeys and a valuable model organism for biomedical research due to its close phylogenetic relationship to humans. Copy number variation is one of the main sources of genomic diversity within and between species and a widely recognized cause of inter-individual differences in disease risk. However, copy number differences among rhesus macaques and between the human and macaque genomes, as well as the relevance of this diversity to research involving this nonhuman primate, remain understudied. Here we present a high-resolution map of sequence copy number for the rhesus macaque genome constructed from a dataset of 198 individuals. Our results show that about one-eighth of the rhesus macaque reference genome is composed of recently duplicated regions, either copy number variable regions or fixed duplications. Comparison with human genomic copy number maps based on previously published data shows that, despite overall similarities in the genome-wide distribution of these regions, there are specific differences at the chromosome level. Some of these create differences in the copy number profile between human disease genes and their rhesus macaque orthologs. Our results highlight the importance of addressing the number of copies of target genes in the design of experiments and cautions against human-centered assumptions in research conducted with model organisms. Overall, we present a genome-wide copy number map from a large sample of rhesus macaque individuals representing an important novel contribution concerning the evolution of copy number in primate genomes.

A method for assessing recovery of fine motor function of the hand in a rhesus monkey model of cortical injury: an adaptation of the Fugl-Meyer Scale and Eshkol-Wachman Movement Notation

Motor dysfunction of the upper extremity can result from stroke, cortical injury and neurological diseases and causes significant disruption of activities of daily living. While some spontaneous recovery in terms of compensatory movements does occur after injury to cortical motor areas, full recovery is rare. The distinction between complete recovery and compensatory recovery is important as the development of compensatory movements in the upper extremity may not translate into full functional use in human patients. However, current animal models of stroke do not distinguish full recovery from compensatory recovery. We have developed a Non-Human Primate Grasp Assessment Scale (GRAS) to quantify the precise recovery of composite movement, individual digit action, and finger-thumb pinch in our rhesus monkey model of cortical injury. To date, we have applied this GRAS scale to assess the recovery of fine motor function of the hand in young control and cell-therapy treated monkeys with cortical injury confined to the hand representation in the dominant primary motor cortex. We have demonstrated that with this scale we can detect and quantify significant impairments in fine motor function of the hand, the development of compensatory function during recovery and finally a return to full fine motor function of the hand in monkeys treated with a cell therapy.

Mesenchymal derived exosomes enhance recovery of motor function in a monkey model of cortical injury

BACKGROUND

Exosomes from mesenchymal stromal cells (MSCs) are endosome-derived vesicles that have been shown to enhance functional recovery in rodent models of stroke.

OBJECTIVE

Building on these findings, we tested exosomes as a treatment in monkeys with cortical injury.

METHODS

After being trained on a task of fine motor function of the hand, monkeys received a cortical injury to the hand representation in primary motor cortex. Twenty-four hours later and again 14 days after injury, monkeys received exosomes or vehicle control. Recovery of motor function was followed for 12 weeks.

RESULTS

Compared to monkeys that received vehicle, exosome treated monkeys returned to pre-operative grasp patterns and latency to retrieve a food reward in the first three-five weeks of recovery.

CONCLUSIONS

These results provide evidence that in monkeys exosomes delivered after cortical injury enhance recovery of motor function.

Hypothalamic Paraventricular Nucleus Gαi2 (Guanine Nucleotide-Binding Protein Alpha Inhibiting Activity Polypeptide 2) Protein-Mediated Neural Control of the Kidney and the Salt Sensitivity of Blood Pressure

We have previously reported that in salt-resistant rat phenotypes brain, Gαi2 (guanine nucleotide-binding protein alpha inhibiting activity polypeptide 2) proteins are required to maintain blood pressure and sodium balance. However, the impact of hypothalamic paraventricular nucleus (PVN) Gαi2 proteins on the salt sensitivity of blood pressure is unknown. Here, by the bilateral PVN administration of a targeted Gαi2 oligodeoxynucleotide, we show that PVN-specific Gαi2 proteins are required to facilitate the full natriuretic response to an acute volume expansion (peak natriuresis [μeq/min] scrambled (SCR) oligodeoxynucleotide 41±3 versus Gαi2 oligodeoxynucleotide 18±4; P<0.05) via a renal nerve-dependent mechanism. Furthermore, in response to chronically elevated dietary sodium intake, PVN-specific Gαi2 proteins are essential to counter renal nerve-dependent salt-sensitive hypertension (mean arterial pressure [mm Hg] 8% NaCl; SCR oligodeoxynucleotide 128±2 versus Gαi2 oligodeoxynucleotide 147±3; P<0.05). This protective pathway involves activation of PVN Gαi2 signaling pathways, which mediate sympathoinhibition to the blood vessels and kidneys (renal norepinephrine [pg/mg] 8% NaCl; SCR oligodeoxynucleotide 375±39 versus Gαi2 oligodeoxynucleotide 850±27; P<0.05) and suppression of the activity of the sodium chloride cotransporter assessed as peak natriuresis to hydrochlorothiazide. Additionally, central oligodeoxynucleotide-mediated Gαi2 protein downregulation prevented PVN parvocellular neuron activation, assessed by FosB immunohistochemistry, in response to increased dietary salt intake. In our analysis of the UK BioBank data set, it was observed that 2 GNAI2 single nucleotide polymorphism (SNP) (rs2298952, P=0.041; rs4547694, P=0.017) significantly correlate with essential hypertension. Collectively, our data suggest that selective targeting and activation of PVN Gαi2 proteins is a novel therapeutic approach for the treatment of salt-sensitive hypertension.

Extracellular vesicles from mesenchymal stem cells reduce microglial-mediated neuroinflammation after cortical injury in aged Rhesus monkeys

Cortical injury, such as injuries after stroke or age-related ischemic events, triggers a cascade of degeneration accompanied by inflammatory responses that mediate neurological deficits. Therapeutics that modulate such neuroinflammatory responses in the aging brain have the potential to reduce neurological dysfunction and promote recovery. Extracellular vesicles (EVs) from mesenchymal stem cells (MSCs) are lipid-bound, nanoscale vesicles that can modulate inflammation and enhance recovery in rodent stroke models. We recently assessed the efficacy of intravenous infusions of MSC-EVs (24-h and 14-days post-injury) as a treatment in aged rhesus monkeys (Macaca mulatta) with cortical injury that induced impairment of fine motor function of the hand. Aged monkeys treated with EVs after injury recovered motor function more rapidly and more fully than aged monkeys given a vehicle control. Here, we describe EV-mediated inflammatory changes using histological assays to quantify differences in markers of neuroinflammation in brain tissue between EV and vehicle-treated aged monkeys. The activation status of microglia, the innate macrophages of the brain, is critical to cell fate after injury. Our findings demonstrate that EV treatment after injury is associated with greater densities of ramified, homeostatic microglia, along with reduced pro-inflammatory microglial markers. These findings are consistent with a phenotypic switch of inflammatory hypertrophic microglia towards anti-inflammatory, homeostatic functions, which was correlated with enhanced functional recovery. Overall, our data suggest that EVs reduce neuroinflammation and shift microglia towards restorative functions. These findings demonstrate the therapeutic potential of MSC-derived EVs for reducing neuroinflammation after cortical injury in the aged brain.

Cell based therapy reduces secondary damage and increases extent of microglial activation following cortical injury

Cortical injury elicits long-term cytotoxic and cytoprotective mechanisms within the brain and the balance of these pathways can determine the functional outcome for the individual. Cytotoxicity is exacerbated by production of reactive oxygen species, accumulation of iron, and peroxidation of cell membranes and myelin. There are currently no neurorestorative treatments to aid in balancing the cytotoxic and cytoprotective mechanisms following cortical injury. Cell based therapies are an emerging treatment that may function in immunomodulation, reduction of secondary damage, and reorganization of surviving structures. We previously evaluated human umbilical tissue-derived cells (hUTC) in our non-human primate model of cortical injury restricted to the hand area of primary motor cortex. Systemic hUTC treatment resulted in significantly greater recovery of fine motor function compared to vehicle controls. Here we investigate the hypothesis that hUTC treatment reduces oxidative damage and iron accumulation and increases the extent of the microglial response to cortical injury. To test this, brain sections from these monkeys were processed using immunohistochemistry to quantify oxidative damage (4-HNE) and activated microglia (LN3), and Prussian Blue to quantify iron. hUTC treated subjects exhibited significantly reduced oxidative damage in the sublesional white matter and iron accumulation in the perilesional area as well as a significant increase in the extent of activated microglia along white matter pathways. Increased perilesional iron accumulation was associated with greater perilesional oxidative damage and larger reconstructed lesion volume. These findings support the hypothesis that systemic hUTC administered 24 h after cortical damage decreases the cytotoxic response while increasing the extent of microglial activation.

Neurophysiological Characterization of a Non-Human Primate Model of Traumatic Spinal Cord Injury Utilizing Fine-Wire EMG Electrodes

This study aims to characterize traumatic spinal cord injury (TSCI) neurophysiologically using an intramuscular fine-wire electromyography (EMG) electrode pair. EMG data were collected from an agonist-antagonist pair of tail muscles of Macaca fasicularis, pre- and post-lesion, and for a treatment and control group. The EMG signals were decomposed into multi-resolution subsets using wavelet transforms (WT), then the relative power (RP) was calculated for each individual reconstructed EMG sub-band. Linear mixed models were developed to test three hypotheses: (i) asymmetrical volitional activity of left and right side tail muscles (ii) the effect of the experimental TSCI on the frequency content of the EMG signal, (iii) and the effect of an experimental treatment. The results from the electrode pair data suggested that there is asymmetry in the EMG response of the left and right side muscles (p-value < 0.001). This is consistent with the construct of limb dominance. The results also suggest that the lesion resulted in clear changes in the EMG frequency distribution in the post-lesion period with a significant increment in the low-frequency sub-bands (D4, D6, and A6) of the left and right side, also a significant reduction in the high-frequency sub-bands (D1 and D2) of the right side (p-value < 0.001). The preliminary results suggest that using the RP of the EMG data, the fine-wire intramuscular EMG electrode pair are a suitable method of monitoring and measuring treatment effects of experimental treatments for spinal cord injury (SCI).

White matter hyperintensities in vascular contributions to cognitive impairment and dementia (VCID): Knowledge gaps and opportunities

White matter hyperintensities (WMHs) are frequently seen on brain magnetic resonance imaging scans of older people. Usually interpreted clinically as a surrogate for cerebral small vessel disease, WMHs are associated with increased likelihood of cognitive impairment and dementia (including Alzheimer's disease [AD]). WMHs are also seen in cognitively healthy people. In this collaboration of academic, clinical, and pharmaceutical industry perspectives, we identify outstanding questions about WMHs and their relation to cognition, dementia, and AD. What molecular and cellular changes underlie WMHs? What are the neuropathological correlates of WMHs? To what extent are demyelination and inflammation present? Is it helpful to subdivide into periventricular and subcortical WMHs? What do WMHs signify in people diagnosed with AD? What are the risk factors for developing WMHs? What preventive and therapeutic strategies target WMHs? Answering these questions will improve prevention and treatment of WMHs and dementia.

Lifespan Trajectories of White Matter Changes in Rhesus Monkeys

Progress in neurodevelopmental brain research has been achieved through the use of animal models. Such models not only help understanding biological changes that govern brain development, maturation and aging, but are also essential for identifying possible mechanisms of neurodevelopmental and age-related chronic disorders, and to evaluate possible interventions with potential relevance to human disease. Genetic relationship of rhesus monkeys to humans makes those animals a great candidate for such models. With the typical lifespan of 25 years, they undergo cognitive maturation and aging that is similar to this observed in humans. Quantitative structural neuroimaging has been proposed as one of the candidate in vivo biomarkers for tracking white matter brain maturation and aging. While lifespan trajectories of white matter changes have been mapped in humans, such knowledge is not available for nonhuman primates. Here, we analyze and model lifespan trajectories of white matter microstructure using in vivo diffusion imaging in a sample of 44 rhesus monkeys. We report quantitative parameters (including slopes and peaks) of lifespan trajectories for 8 individual white matter tracts. We show different trajectories for cellular and extracellular microstructural imaging components that are associated with white matter maturation and aging, and discuss similarities and differences between those in humans and rhesus monkeys, the importance of our findings, and future directions for the field. Significance Statement: Quantitative structural neuroimaging has been proposed as one of the candidate in vivo biomarkers for tracking brain maturation and aging. While lifespan trajectories of structural white matter changes have been mapped in humans, such knowledge is not available for rhesus monkeys. We present here results of the analysis and modeling of the lifespan trajectories of white matter microstructure using in vivo diffusion imaging in a sample of 44 rhesus monkeys (age 4-27). We report and anatomically map lifespan changes related to cellular and extracellular microstructural components that are associated with white matter maturation and aging.

Prenatal Protein Malnutrition Leads to Hemispheric Differences in the Extracellular Concentrations of Norepinephrine, Dopamine and Serotonin in the Medial Prefrontal Cortex of Adult Rats

Exposure to prenatal protein malnutrition (PPM) leads to a reprogramming of the brain, altering executive functions involving the prefrontal cortex (PFC). In this study we used in vivo microdialysis to assess the effects of PPM on extracellular concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) bilaterally in the ventral portion of the medial prefrontal cortex (vmPFC; ventral prelimbic and infralimbic cortices) of adult Long-Evans rats. Female Long-Evans rats were fed either a low protein (6%) or adequate protein diet (25%) prior to mating and throughout pregnancy. At birth, all litters were culled and fostered to dams fed a 25% (adequate) protein diet. At 120 days of age, 2 mm microdialysis probes were placed into left and right vmPFC. Basal extracellular concentrations of NE, DA, and 5-HT were determined over a 1-h period using HPLC. In rats exposed to PPM there was a decrease in extracellular concentrations of NE and DA in the right vmPFC and an increase in the extracellular concentration of 5-HT in the left vmPFC compared to controls (prenatally malnourished: N = 10, well-nourished: N = 20). Assessment of the cerebral laterality of extracellular neurotransmitters in the vmPFC showed that prenatally malnourished animals had a significant shift in laterality from the right to the left hemisphere for NE and DA but not for serotonin. In a related study, these animals showed cognitive inflexibility in an attentional task. In animals in the current study, NE levels in the right vmPFC of well-nourished animals correlated positively with performance in an attention task, while 5-HT in the left vmPFC of well-nourished rats correlated negatively with performance. These data, in addition to previously published studies, suggest a long-term reprogramming of the vmPFC in rats exposed to PPM which may contribute to attention deficits observed in adult animals exposed to PPM.

WP1-23 Vascular collagen 4A1 in subcortical white matter of older people and primates

Objectives

To test whether collagen 4A1 in cerebral small arteries associated with age, hypertension or small vessel disease (SVD).

Design

Neuropathology cohort study.

Subjects

Older people age >65 years with minimal Alzheimer’s Disease.

Methods

We examined subcortical white matter in archived brain tissue from older people (n=34, 15F/19M, median age 84, range 65–99 y) and from experimental non-human primates (NHP, Macaca mulatta) that were young adults (n=9, age 6.2–8.3 y) or older adults (n=8, age 17.0–22.7 y). Some of the primates (5 young, 3 older) were chronically hypertensive. Vascular collagen 4A1 immunohistochemical labelling was examined qualitatively and quantified as percent area fraction.

Results

Collagen 4A1 labelling was common in arterial myocytes and in the adventitial layer in human and primate brain arteries, as well as in basement membrane, which frequently exhibited replication. Among older people, collagen 4A1 associated with neuropathological SVD severity (sclerotic index; r=−0.461, p=0.0409, least squares) and with radiological SVD severity (leukoaraiosis; p=0.0455, 1-way ANOVA) but not with age or clinical history of hypertension. In NHP, age but not hypertension was significantly associated with collagen-4A1 labelling (p=0.0396, 0.232 respectively, 2-way ANOVA).

Conclusions

In this small cohort, vascular collagen 4A1 was related to SVD severity in older humans, in accord with genetic associations of COL4A1 with SVD phenotypes.