Congenital and early-life Zika virus (ZIKV) infection can result in neurologic deficits. Precise mechanisms of injury, especially in the more subtle presentation of postnatal infection, are not fully elucidated. Here, we defined the effects of ZIKV on the developing brain using single cell transcriptomics, histopathology and design-based stereology, diffusion MRI, and neurobehavioral assessments in infant rhesus macaques. ZIKV upregulated interferon-stimulated genes in activated microglia and cell death pathways in neurons and downregulated metabolism and differentiation genes in mature oligodendrocytes. Abnormal micro-organization of the corpus collosum and limbic white matter tracts was seen on diffusion weighted imaging. A curated gene set associated with autism spectrum disorder risk was negatively enriched in inhibitory and excitatory neurons from ZIKV-infected infants, with increased emotional reactivity already evident two weeks following infection. From single cells to organism-level behaviors, these results define the pathways and processes disrupted by early-life ZIKV infection.

Low social status leads to chronic social stress that predicts risk for physical and mental illness, especially when it starts early in life. To examine the longitudinal effects of low social status on the immune system, this study assessed the effects of low social status on developmental secretory patterns of pro- and anti-inflammatory markers under baseline conditions, as well as in response to an immune challenge (lipopolysaccharide (LPS)-induced activation of pro- and anti-inflammatory cytokines) in a translational rhesus monkey model of lifelong social subordination stress. Baseline blood samples were collected in 27 socially housed female rhesus monkeys (13 dominants, DOM, and 14 subordinates, SUB) during infancy (6 months), the juvenile pre-pubertal period (16 months), and adulthood (9–10 years) to examine the longitudinal effects of social status on inflammatory markers in unstimulated versus LPS-stimulated conditions mimicking exposure to bacterial infection. Basal levels of the stress hormone cortisol in blood were measured to examine associations between inflammation and activity of the hypothalamic–pituitary–adrenal (HPA) axis throughout the life span. Basal peripheral levels of inflammatory markers (e.g., IL-6) increased across development in both SUB and DOM animals with no significant differences. Basal cortisol levels were significantly higher in infancy as compared to adulthood, but no significant effects of social rank were detected. However, in adulthood, SUB animals showed a cytokine-specific immune response to ex vivo LPS stimulation with significantly higher secretions of IL-1β, IL-2, and IL-10 compared to DOM animals, whereas IL-8 response to LPS was lower in SUB animals than in DOMs. This cytokine-specific response to an immune challenge that mimics bacterial infection could reflect dysregulated immune cells that may have short-term adaptation, but at the cost of longer-term risks for low-grade chronic inflammation and accelerated immune aging for socially subordinate female macaques.

Although congenital Zika virus (ZIKV) syndrome is well-characterized, the neurodevelopmental consequences of postnatal infection are less understood. Here we used a rhesus macaque model to investigate the developmental consequences of ZIKV infection during infancy on the brain and behavior, building on our prior research. Male and female infant rhesus macaques infected with ZIKV at 1 month of age were compared to sex-, age-, and rearing-matched uninfected controls and infants treated with the TLR3 agonist PolyIC as a control for activation of the innate immune system. Longitudinal behavioral assessments revealed alterations in emotional regulation following ZIKV exposure, including poor state control scores obtained from the Infant Neurobehavioral Assessment Scale early after ZIKV infection and longer-term displays of increased hostility during an acute stressor. While attachment bonds to caregivers were preserved, ZIKV-infected infants showed sex-specific alterations in behavioral regulation during caregiver separation compared to controls. At 3 months of age, MRI scans revealed larger total cerebrospinal fluid (CSF) volume and reduced volumes in visual processing regions in ZIKV-infected infants compared to controls. Postnatal ZIKV exposure also resulted in sex-specific brain structural alterations with males exhibiting amygdala hypertrophy, whereas ZIKV-infected females had volumetric reductions in temporal-limbic and temporal-auditory cortices. These findings demonstrate that postnatal ZIKV infection disrupts the development of sensory, social and emotion-regulatory systems and CSF function, highlighting the critical need for long-term monitoring of exposed children.

Animal models and human studies suggest that general anesthesia exposure during infancy results in long-lasting neurocognitive impairments. Because millions of children each year undergo procedures that require anesthesia, it is important to investigate the mechanism of anesthesia induced neurotoxicity to ultimately develop ways to protect the vulnerable developing brain. Animal models have played a key role in this investigation and have shown that neonatal general anesthesia exposure results in neuronal apoptosis, long-term mitochondrial dysfunction, and astrogliosis. The current study involved a rhesus macaque model of repeated sevoflurane exposure that has been shown to produce cognitive deficits, behavioral changes, and mitochondrial damage. This study sought to investigate whether prolonged sevoflurane exposure induced inflammation as measured in peripheral blood samples. Results found that sevoflurane exposure resulted in changing levels of inflammatory markers in the periphery. Specifically, interleukin 6 (IL-6) was increased immediately following sevoflurane exposure, but not at 24-h post-exposure. Plasma samples collected 24-h after exposure revealed increased granulocyte macrophage colony-stimulating factor (GM-CSF), but decreased monocyte chemoattractant protein-4 (MCP-4) and interferon gamma-induced protein 10 (IP-10) levels. Changes in these markers have been linked to cognitive impairment, and together these data suggest that plasma levels of cytokines and chemokines are a good potential medium to investigate anesthesia-induced inflammation in clinical populations.

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Although most SARS-CoV-2 infections result in mild or moderate symptoms not requiring hospitalization, many patients experience persistent symptoms after their initial recovery, a condition termed Post-Acute Sequelae of SARS-CoV-2 infection (PASC). The underlying pathogenesis behind infection associated chronic illnesses, such as PASC, are poorly understood, thus critically limiting the development of therapeutics to prevent or alleviate symptoms. The current study examined the neurocognitive impact of SARS-CoV-2 induced inflammation in a nonhuman primate model. Ten adult rhesus macaques (5 female, 5 male) were monitored before, during, and after recovery from a mild COVID-19 illness (SARS-CoV-2 strain 2019-noCoV/USA-WA1/2020). Macaques exhibited persistent alterations in taste and smell, as well as decreased cognitive flexibility up to 3 months post-infection. Female macaques experienced sleep disturbances, greater stress and poorer autonomic function months after SARS-CoV-2 infection. Importantly, the development of these neurocognitive changes were associated with acute cytokine response to infection and increased microglia activation in brain tissue at 4 months post-infection. These findings suggest a causative link between the inflammatory response to mild COVID-19 symptoms and persistent neurocognitive changes associated with PASC and provide rationale for therapeutic strategies aimed at reducing acute inflammatory responses to the virus.

Because DNA methylation changes reliably with age, machine learning models called epigenetic clocks can estimate an individual's age based on their DNA methylation profile. This epigenetic measure of age can deviate from one's true age, and the difference between the epigenetic age and true age, known as epigenetic age acceleration (EAA), has been found to directly correlate with morbidity and mortality in adults. Emerging evidence suggests that EAA is also associated with aberrant health outcomes in children, making epigenetic clocks useful tools for studying aging and development. We developed two highly accurate epigenetic clocks for the rhesus macaque, utilizing 1,008 blood samples from 690 macaques between 2 days and 23.4 years of age with diverse genetic backgrounds and exposure to environmental conditions. The first clock, which is trained on all samples, achieves a Pearson correlation between true age and predicted age of 0.983 and median absolute error of 0.210 years. To study phenotypes during development, the second clock is optimized for macaques younger than 6 years and achieves a Pearson correlation of 0.974 and a median absolute error of 0.148 years. Using the latter clock, we investigated whether epigenetic aging is affected by early life adversity in the form of infant maltreatment. Our data suggests that maltreatment and increased hair cortisol levels are associated with epigenetic age acceleration right after the period of maltreatment.

This study examined the role of male pubertal maturation on physical growth and development of neurocircuits that regulate stress, emotional and cognitive control using a translational nonhuman primate model. We collected longitudinal data from male macaques between pre- and peri-puberty, including measures of physical growth, pubertal maturation (testicular volume, blood testosterone -T- concentrations) and brain structural and resting-state functional MRI scans to examine developmental changes in amygdala (AMY), hippocampus (HIPPO), prefrontal cortex (PFC), as well as functional connectivity (FC) between those regions.Physical growth and pubertal measures increased from pre- to peri-puberty. The indexes of pubertal maturation -testicular size and T- were correlated at peri-puberty, but not at pre-puberty (23 months). Our findings also showed ICV, AMY, HIPPO and total PFC volumetric growth, but with region-specific changes in PFC. Surprisingly, FC in these neural circuits only showed developmental changes from pre- to peri-puberty for HIPPO-orbitofrontal FC. Finally, testicular size was a better predictor of brain structural maturation than T levels -suggesting gonadal hormones-independent mechanisms-, whereas T was a strong predictor of functional connectivity development. We expect that these neural circuits will show more drastic pubertal-dependent maturation, including stronger associations with pubertal measures later, during and after male puberty.

Because of their close relationship with humans, non-human apes (chimpanzees, bonobos, gorillas, orangutans, and gibbons, including siamangs) are of great scientific interest. The goal of understanding their complex behavior would be greatly advanced by the ability to perform video-based pose tracking. Tracking, however, requires high-quality annotated datasets of ape photographs. Here we present OpenApePose, a new public dataset of 71,868 photographs, annotated with 16 body landmarks, of six ape species in naturalistic contexts. We show that a standard deep net (HRNet-W48) trained on ape photos can reliably track out-of-sample ape photos better than networks trained on monkeys (specifically, the OpenMonkeyPose dataset) and on humans (COCO) can. This trained network can track apes almost as well as the other networks can track their respective taxa, and models trained without one of the six ape species can track the held out species better than the monkey and human models can. Ultimately, the results of our analyses highlight the importance of large specialized databases for animal tracking systems and confirm the utility of our new ape database.

Zika virus (ZIKV) infection during infancy in a rhesus macaque (RM) model negatively impacts brain development resulting in long-term behavioral alterations. The current study investigated whether postexposure prophylaxis could alleviate these negative neurodevelopmental consequences. Three RM infants received a 14-day course of sofosbuvir (SOF; 15 mg/kg p.o.) treatment starting at 3 days post-infection with a Puerto Rican strain of ZIKV (PRVABC59) and were then monitored longitudinally for one year. In contrast to ZIKV-infected infant RMs who did not receive SOF, postexposure SOF treatment mitigated the neurodevelopmental, behavioral and cognitive changes seen after postnatal ZIKV infection even while not accelerating viral clearance from the blood. These data suggest that antiviral treatment may help ameliorate some, but not all, of the neurodevelopmental abnormalities associated with early postnatal ZIKV infection.

Narrowing down the histopathological changes in the brain after early-life exposure to general anaesthesia has presented a consistent challenge for preclinical models of anaesthetic neurotoxicity. Using resting-state functional magnetic resonance imaging, in this issue of the journal Neudecker and colleagues demonstrated in vivo connectivity changes in the brain following a seed-based analysis that was derived from previously reported histopathology in the same animals. The combination of neurohistology and neuroimaging should help focus future preclinical studies investigating the developmental consequences of early exposure to general anaesthesia.

The ability to automatically estimate the pose of non-human primates as they move through the world is important for several subfields in biology and biomedicine. Inspired by the recent success of computer vision models enabled by benchmark challenges (e.g., object detection), we propose a new benchmark challenge called OpenMonkeyChallenge that facilitates collective community efforts through an annual competition to build generalizable non-human primate pose estimation models. To host the benchmark challenge, we provide a new public dataset consisting of 111,529 annotated (17 body landmarks) photographs of non-human primates in naturalistic contexts obtained from various sources including the Internet, three National Primate Research Centers, and the Minnesota Zoo. Such annotated datasets will be used for the training and testing datasets to develop generalizable models with standardized evaluation metrics. We demonstrate the effectiveness of our dataset quantitatively by comparing it with existing datasets based on seven state-of-the-art pose estimation models.

Nonhuman primates and especially rhesus macaques (Macaca mulatta) have been indispensable animal models for studies of various aspects of neurobiology, developmental psychology, and other aspects of neuroscience. While remarkable progress has been made in our understanding of influences on atypical human social behavior, such as that observed in autism spectrum disorders (ASD), many significant questions remain. Improved understanding of the relationships among variation in specific genes and variation in expressed social behavior in a nonhuman primate would benefit efforts to investigate risk factors, developmental mechanisms, and potential therapies for behavioral disorders including ASD. To study genetic influences on key aspects of social behavior and interactions-individual competence and/or motivation for specific aspects of social behavior-we quantified individual variation in social interactions among juvenile rhesus macaques using both a standard macaque ethogram and a macaque-relevant modification of the human Social Responsiveness Scale. Our analyses demonstrate that various aspects of juvenile social behavior exhibit significant genetic heritability, with estimated quantitative genetic effects similar to that described for ASD in human children. We also performed exome sequencing and analyzed variants in 143 genes previously suggested to influence risk for human ASD. We find preliminary evidence for genetic association between specific variants and both individual behaviors and multi-behavioral factor scores. To our knowledge, this is the first demonstration that spontaneous social behaviors performed by free-ranging juvenile rhesus macaques display significant genetic heritability and then to use exome sequencing data to examine potential macaque genetic associations in genes associated with human ASD.

The hippocampus is important for long-term memory storage, but also plays a role in regulating the hypothalamic-pituitary-adrenal (HPA) axis and emotional behaviors. We previously reported that early hippocampal damage in monkeys result in increased anxious expression and blunted HPA responses to an acute stressor. Here, we further probe their responses toward aversive stimuli (conditioned and unconditioned) and evaluate HPA axis dysfunction. Responses toward social, innate, and learned aversive stimuli, fear potentiated acoustic startle, and pituitary-adrenal function were investigated in 13 adult rhesus monkeys with neonatal hippocampal lesions (Neo-Hibo=6) and controls (Neo-C=7). Neo-Hibo monkeys' responses depend on the type of unconditioned stimulus, with increased anxiety behaviors toward social and learned, but decreased reactivity toward innate stimuli. Neo-C and Neo-Hibo monkeys exhibited similar performance learning conditioned cues and safety signals. Neo-Hibo monkeys were less sensitive to HPA axis stimulation, potentially suggesting adrenal fatigue. Current findings suggest that the hippocampus plays a large role in regulating not only anxiety behaviors, but also the HPA-axis, a neural system crucial to regulate how we respond to the world around us. These data have important clinical significance considering that many developmental neuropsychiatric disorders exhibit altered hippocampal structure and function, emotional and HPA axis dysregulation.

With the ultimate goal of developing a more representative animal model of Alzheimer's disease (AD), two female amyloid-β-(Aβ) precursor protein-transgenic (APPtg) rhesus monkeys were generated by lentiviral transduction of the APP gene into rhesus oocytes, followed by in vitro fertilization and embryo transfer. The APP-transgene included the AD-associated Swedish K670N/M671L and Indiana V717F mutations (APPSWE/IND) regulated by the human polyubiquitin-C promoter. Overexpression of APP was confirmed in lymphocytes and brain tissue. Upon sacrifice at 10 years of age, one of the monkeys had developed Aβ plaques and cerebral Aβ-amyloid angiopathy in the occipital, parietal, and caudal temporal neocortices. The induction of Aβ deposition more than a decade prior to its usual emergence in the rhesus monkey supports the feasibility of creating a transgenic nonhuman primate model for mechanistic analyses and preclinical testing of treatments for Alzheimer's disease and cerebrovascular amyloidosis.

Chemogenetics is a technique for obtaining selective pharmacological control over a cell population by expressing an engineered receptor that is selectively activated by an exogenously administered ligand. A promising approach for neuronal modulation involves the use of "Pharmacologically Selective Actuator Modules" (PSAMs); these chemogenetic receptors are selectively activated by ultrapotent "Pharmacologically Selective Effector Molecules" (uPSEMs). To extend the use of PSAM/PSEMs to studies in nonhuman primates, it is necessary to thoroughly characterize the efficacy and safety of these tools. We describe the time course and brain penetrance in rhesus monkeys of two compounds with promising binding specificity and efficacy profiles in in vitro studies, uPSEM792 and uPSEM817, after systemic administration. Rhesus monkeys received subcutaneous (s.c.) or intravenous (i.v.) administration of uPSEM817 (0.064 mg/kg) or uPSEM792 (0.87 mg/kg), and plasma and cerebrospinal fluid samples were collected over 48 h. Both compounds exhibited good brain penetrance, relatively slow washout, and negligible conversion to potential metabolites─varenicline or hydroxyvarenicline. In addition, we found that neither of these uPSEMs significantly altered the heart rate or sleep. Our results indicate that both compounds are suitable candidates for neuroscience studies using PSAMs in nonhuman primates.

Due to its low invasiveness and controllability, chemogenetic approaches offer a highly attractive option to modulate neuronal activity in basic research and future clinical applications. Chemogenetics have revolutionized neuroscience research by facilitating manipulations of selective brain circuits. To date, however, the large majority of these studies have been conducted in rodent models, while the wide application of chemogenetics in nonhuman primates (NHPs) is yet to occur. Still, important progress has been achieved in the use of chemogenetics in NHP studies in the last few years. Here we review the studies that have been published using chemogenetics in NHPs and discuss the current limitations of the technique to its more widespread use in NHPs and possible ways to overcome them.