Biology subjects

Baxter, M. G.

Publications and source records attributed to Baxter, M. G..

At least 19 recordsLinked to original sources

bioRxiv2023

Hippocampal timestamp for goals

Our brain must manage multiple goals that differ in their temporal proximity. Some goals require immediate attention, while others have already been accomplished, or will be relevant later in time. Here, we examined how the hippocampus represents the temporal distance to different goals using a novel space-themed paradigm during 7T functional MRI (n=31). The hippocampus has an established role in mental time travel and a system in place to stratify information along its longitudinal axis on the basis of representational granularity. Previous work has documented a functional transformation from fine-grained, detail rich representations in the posterior hippocampus to coarse, gist-like representations in the anterior hippocampus. We tested whether the hippocampus uses this long axis system to dissociate goals based upon their temporal distance from the present. We hypothesized that the hippocampus would distinguish goals relevant for ones current needs from those that are removed in time along the long axis, with temporally removed past and future goals eliciting increasingly anterior activation. We sent participants on a mission to Mars where they had to track goals that differed in when they needed to be accomplished. We observed a long-axis dissociation, where temporally removed past and future goals activated the left anterior hippocampus and current goals activated the left posterior hippocampus. Altogether, this study demonstrates that the timestamp attached to a goal is a key driver in where the goal is represented in the hippocampus. This work extends the scope of the hippocampus long axis system to the goal-mapping domain.

neuroscience↗

bioRxiv2023

Neuropsychology of cognitive aging in rhesus monkeys

Aged rhesus monkeys, like aged humans, show declines in cognitive function. We present cognitive test data from a large sample of male and female rhesus monkeys, 34 young (3.5-13.6 years) and 71 aged (19.9-32.5 years of age at the start of cognitive testing). Monkeys were tested on spatiotemporal working memory (delayed response), visual recognition memory (delayed nonmatching-to-sample), and stimulus-reward association learning (object discrimination), tasks with an extensive evidence base in nonhuman primate neuropsychology. On average, aged monkeys performed worse than young on all three tasks. Acquisition of delayed response and delayed nonmatching-to-sample was more variable in aged monkeys than in young. Performance scores on delayed nonmatching-to-sample and object discrimination were associated with each other, but neither was associated with performance on delayed response. Sex and chronological age were not reliable predictors of individual differences in cognitive outcome among the aged monkeys. These data establish population norms for cognitive tests in young and aged rhesus monkeys in the largest sample reported to date. They also illustrate independence of cognitive aging in task domains dependent on the prefrontal cortex and medial temporal lobe. (181 words)

neuroscience↗

bioRxiv2023

Development of prefrontal corticostriatal connectivity in mice

Rational decision making is grounded in learning to associate actions with outcomes, a process that depends on projections from prefrontal cortex to dorsomedial striatum. Symptoms associated with a variety of human pathological conditions ranging from schizophrenia and autism to Huntingtons and Parkinsons disease point toward functional deficits in this projection, but its development is not well understood, making it difficult to investigate how perturbations in development of this circuitry could contribute to pathophysiology. We applied a novel strategy based on Hotspot Analysis to assess the developmental progression of anatomical positioning of prefrontal cortex to striatal projections. Corticostriatal axonal territories established at P7 expand in concert with striatal growth but remain largely unchanged in positioning through adulthood, indicating they are generated by directed, targeted growth and not modified extensively by postnatal experience. Consistent with these findings, corticostriatal synaptogenesis increased steadily from P7 to P56, with no evidence for widescale pruning. As corticostriatal synapse density increased over late postnatal ages, the strength of evoked PFC input onto dorsomedial striatal projection neurons also increased, but spontaneous glutamatergic synaptic activity was stable. Based on its pattern of expression, we asked whether the adhesion protein, Cdh8, influenced this progression. In mice lacking Cdh8 in PFC corticostriatal projection neurons, axon terminal fields in dorsal striatum shifted ventrally. Corticostriatal synaptogenesis was unimpeded, but spontaneous EPSC frequency declined and mice failed to learn to associate an action with an outcome. Collectively these findings show that corticostriatal axons grow to their target zone and are restrained from an early age, do not undergo postnatal synapse pruning as the most dominant models predict, and that a relatively modest shift in terminal arbor positioning and synapse function has an outsized, negative impact on corticostriatal-dependent behavior.

neuroscience↗

bioRxiv2022

Ensemble remodeling supports memory-updating

Memory-updating is critical in dynamic environments because updating memories with new information promotes versatility. However, little is known about how memories are updated with new information. To study how neuronal ensembles might support memory-updating, we used a hippocampus-dependent spatial reversal task to measure hippocampal ensemble dynamics when mice switched navigational goals. Using Miniscope calcium imaging, we identified neuronal ensembles (co-active neurons) in dorsal CA1 that were spatially tuned and stable across training sessions. When reward locations were moved during a reversal session, a subset of these ensembles decreased their activation strength, correlating with memory-updating. These "remodeling" ensembles were a result of weakly-connected neurons becoming less co-active with their peers. Middle-aged mice were impaired in reversal learning, and the prevalence of their remodeling ensembles correlated with their memory-updating performance. Therefore, we have identified a mechanism where the hippocampus breaks down ensembles to support memory-updating.

neuroscience↗

bioRxiv2022

Neonatal exposures to sevoflurane in rhesus monkeys alter synaptic ultrastructure in later life

Early-life exposure to anesthesia in infant humans and monkeys increases the risk for cognitive and socioemotional impairments. However, the long-term effects of neonatal anesthesia on synaptic ultrastructure have not been thoroughly investigated in primates. We used electron microscopy with unbiased stereological sampling to assess synaptic ultrastructure in the CA1 of the hippocampus and the dorsolateral prefrontal cortex (dlPFC) of female and male rhesus macaques four years after three 4-hour exposures to sevoflurane during the first five postnatal weeks. We counted synapses and measured synapse areas for all synapses and those classified as perforated or nonperforated with spine or dendritic shaft targets. We measured numbers and shapes of mitochondria within presynaptic boutons and calculated vesicle docking rates. In monkeys exposed to anesthesia as infants, synapse areas were reduced in the largest 20% of synapses in CA1 and the largest 5% of synapses in dlPFC, with differential sex effects for the largest 10% of synapses in CA1. Synapse areas were reduced by 7.6% for perforated spinous synapses in CA1, and by 10.4% for nonperforated spinous synapses in dlPFC. Perforated and nonperforated dendritic synapse numbers in CA1 increased by 180% and 63% respectively. Curved mitochondria decreased 25% in CA1 after anesthesia exposure, and dlPFC boutons with 0 mitochondria showed an interaction of anesthesia and sex. These results demonstrate that exposure to anesthesia in infancy can cause long-term structural deficits in primates. These structural changes may be substrates for long-term alterations in the strength and efficiency of synaptic transmission in hippocampus and prefrontal cortex. Key pointsO_LIExposure to anesthesia in early life causes lasting cognitive and socioemotional impairments in human and nonhuman primates, but the extent to which early-life exposure to anesthesia alters synaptic ultrastructure in later life has not been known. C_LIO_LIFour years after rhesus monkeys were given multiple exposures to anesthesia in infancy, the area of spinous synapses was reduced in CA1 and dlPFC, dendritic synapse numbers were elevated in CA1, there were fewer curved presynaptic mitochondria in CA1, and numbers of presynaptic boutons without mitochondria were altered in dlPFC. C_LIO_LIThe long-term ultrastructural changes to synapses and presynaptic mitochondria of rhesus monkeys that were exposed to anesthesia as infants could help explain their behavioral deficits later in life. C_LI

neuroscience↗

bioRxiv2022

Cognitive Deficits and Altered Cholinergic Innervation in Young Adult Mice Carrying a Parkinson's Disease LRRK2-G2019S Knockin Mutation

Impaired executive function is a common and debilitating non-motor symptom of idiopathic and hereditary Parkinsons disease (PD), but there is little understanding of the underlying pathophysiological mechanisms and circuits. The G2019S mutation in the kinase domain of leucine-rich repeat kinase 2 (LRRK2) greatly increases risk for late-onset PD, and non-manifesting LRRK2-G2019S carriers also exhibit early and significant cognitive impairment. Here, we subjected young adult mice carrying a Lrrk2-G2019S knockin mutation to touchscreen-based operant tasks that measure attention, goal-directed learning and cognitive flexibility, all of which rely on prefrontal-striatal connectivity and are strongly modulated by cholinergic innervation. In a visuospatial attention task, mutant mice exhibited significantly more omissions and longer response latencies than controls that could not be attributed to deficits in motivation, visual sensory perception per se or locomotion, thereby suggesting impairment in divided attention and slower information processing speed. Pretreating mice with the acetylcholinesterase inhibitor donepezil normalized both higher omission rates and longer reward latencies in the mutants, but did not affect any performance metric in controls. Strikingly, cholinergic fiber density in mPFC and dorsomedial striatum was significantly sparser in mutants than in controls, while further behavioral interrogation of the mutants revealed significant impairments in action-outcome associations but preserved cognitive flexibility. These data suggest that the G2019S mutation impacts cholinergic innervation and impairs corticostriatal network function in young adulthood that may contribute to early PD-associated cognitive deficits. STATEMENT OF SIGNIFICANCEThe LRRK2-G2019S mutation causes hereditary Parkinsons disease and is found in some idiopathic cases. Early cognitive impairment is a common symptom of hereditary and idiopathic PD, yet there is little mechanistic understanding of such impairment. Here, we tested young adult Lrrk2-G2019S knockin mice in a series of touchscreen-based visuospatial tasks. We found that mutants exhibited significant deficits in attention and goal-directed learning, and had significantly slower information processing speed. Treatment with an acetylcholinesterase inhibitor reversed some of these behavioral deficits, while anatomical analyses showed significantly sparser cholinergic innervation of brain structures important for executive function. These findings suggest the G2019S mutation alters cholinergic signaling in young adulthood, and thus may contribute to early PD-associated impairment in several cognitive domains.

neuroscience↗

bioRxiv2020

A pragmatic reevaluation of the efficacy of nonhuman primate optogenetics

Translational neuroscience is committed to generating discoveries in the laboratory that ultimately can improve human lives. Optogenetics has received considerable attention because of its demonstrated promise in rodent brains to manipulate cells and circuits. In a recent report, Tremblay and colleagues (2020) introduce an open resource detailing optogenetic studies of the nonhuman primate (NHP) brain and make robust claims about the translatability of the technology. We propose that their quantitative (e.g., a 91% success rate) and theoretical claims are questionable because the data were analyzed at a level relevant to the rodent but not NHP brain, injections were clustered within a few monkeys in a few studies in a few brain regions, and their definitions of success was not clearly relevant to human neuropsychiatric disease. A reanalysis of the data with a modified definition of success that included a behavioral and biological effect revealed an 62.5% success rate that was lower when considering only strong outcomes (53.1%). This calls into question the current efficacy of optogenetic techniques in the NHP brain and suggests that we are a long way from being able to leverage them in "the service of patients with neurological or psychiatric conditions" as the Tremblay report claims.

neuroscience↗

bioRxiv2020

Temporal emergence of age-associated changes in cognitive and physical function in vervets (Chlorocebus aethiops sabaeus)

Dual declines in gait speed and cognitive performance are associated with increased risk of developing dementia. Characterizing the patterns of such impairments therefore is paramount to distinguishing healthy from pathological aging. Nonhuman primates such as vervet/African green monkeys (Chlorocebus aethiops sabaeus) are important models of human neurocognitive aging, yet the trajectory of dual decline has not been characterized. We therefore 1) assessed whether cognitive and physical performance (i.e., gait speed) are lower in older aged animals; 2) explored the relationship between performance in a novel task of executive function (Wake Forest Maze Task - WFMT) and a well-established assessment of working memory (Delayed Response Task - DR Task); and 3) examined the association between baseline gait speed with executive function and working memory at one-year follow-up. We found 1) physical and cognitive declines with age; 2) strong agreement between performance in the novel WFMT and DR task; and 3) that slow gait predicted poor cognitive performance in both domains. Our results suggest that older-aged vervets exhibit a coordinated suite of traits consistent with human aging and that slow gait may be a risk factor for cognitive decline. This integrative approach provides evidence that gait speed and cognitive function differ across the lifespan in female vervet monkeys, which advances them as a model that could be used to evaluate the trajectory of dual decline over time.

animal behavior and cognition↗

bioRxiv2019

Chemogenetic actuator drugs impair prefrontal cortex-dependent working memory in rhesus monkeys

The most common chemogenetic neuromodulatory system, Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), uses a non-endogenous actuator ligand to activate a modified muscarinic acetylcholine receptor that is no longer sensitive to acetylcholine. It is crucial in studies using these systems to test the potential effects of DREADD actuators prior to any DREADD transduction, so that effects of DREADDs can be attributed to the chemogenetic system rather than the actuator drug. We investigated working memory performance after injections of three DREADD agonists, clozapine, olanzapine, and deschloroclozapine, in male rhesus monkeys tested in a spatial delayed response task. Performance at 0.1 mg/kg clozapine and 0.1 mg/kg deschloroclozapine did not differ from mean performance after vehicle in any of the four subjects. Administration of 0.2 mg/kg clozapine impaired working memory function in three of the four monkeys. Two monkeys were impaired after administration of 0.1 mg/kg olanzapine and two monkeys were impaired after the 0.3 mg/kg dose of deschloroclozapine. We speculate that the unique neuropharmacology of prefrontal cortex function makes the primate prefrontal cortex especially vulnerable to off-target effects of DREADD actuator drugs with affinity for endogenous monoaminergic receptor systems. These findings underscore the importance of within-subject controls for DREADD actuator drugs to confirm that effects following DREADD receptor transduction are not due to the actuator drug itself, as well as validating the behavioral pharmacology of DREADD actuator drugs in the specific tasks under study. Significance StatementChemogenetic technologies, such as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), allow for precise and remote manipulation of neuronal circuits. In the present study, we tested monkeys in a spatial delayed response task after injections of three actuator drugs - clozapine, olanzapine, and deschloroclozapine. We found that monkeys showed significant working memory impairments after 0.2 mg/kg clozapine, 0.1 mg/kg olanzapine, and 0.3 mg/kg deschloroclozapine compared to vehicle performance. In monkeys that showed impairments, these deficits were particularly apparent at longer delay periods. It is imperative to validate the drugs and dosages in the particular behavioral test to ensure any behavior after DREADD transduction can be attributed to activation of the receptors and not administration of the actuator drug itself.

neuroscience↗

bioRxiv2019

Resting state functional connectivity in early post-anesthesia recovery is characterized by globally reduced anticorrelations

Though a growing body of literature is addressing the possible longer-term cognitive effects of anesthetics, to date no study has delineated the normal trajectory of neural recovery due to anesthesia alone in older adults. We obtained resting state functional magnetic resonance imaging scans on 62 healthy human volunteers between ages forty and eighty before, during, and after sevoflurane (general) anesthesia, in the absence of surgery, as part of a larger study on cognitive function post-anesthesia. Resting state networks expression decreased consistently one hour after emergence from anesthesia. This corresponded to a global reduction in anticorrelated functional connectivity post-anesthesia, seen across individual regions-of-interest. Positively correlated functional connectivity remained constant across peri-anesthetic states. All measures returned to baseline 1 day later, with individual regions-of-interest essentially returning to their pre-anesthesia connectivity levels. These results define normal peri-anesthetic changes in resting state connectivity in healthy older adults.

neuroscience↗

bioRxiv2018

Disruption of the KH1 domain of Fmr1 leads to transcriptional alterations and attentional deficits in rats

Fragile X Syndrome (FXS) is a neurodevelopmental disorder caused by mutations in the FMR1 gene. FXS is a leading monogenic cause of autism spectrum disorder (ASD) and inherited intellectual disability (ID). In most cases, the mutation is an expansion of a microsatellite (CGG triplet), which leads to suppressed expression of the fragile X mental retardation protein (FMRP), an RNA-binding protein involved in multiple aspects of mRNA metabolism. Interestingly, we found that the previously published Fmr1 knockout rat model of FXS expresses a transcript with an in-frame deletion of a K-homology (KH) domain, KH1. KH domains are RNA-binding domains of FMR1 and several of the few, known point mutations associated with FXS are found within them. We observed that this deletion leads to medial prefrontal cortex (mPFC)-dependent attention deficits, similar to those observed in FXS, and to alterations in transcriptional profiles within the mPFC, which mapped to two weighted gene coexpression network analysis modules. We demonstrated that these modules are conserved in human frontal cortex, are enriched for known FMRP targets and for genes involved in neuronal and synaptic processes, and that one is enriched for genes that are implicated in ASD, ID, and schizophrenia. Hub genes in these conserved modules represent potential targets for FXS. These findings provide support for a prefrontal deficit in FXS, indicate that attentional testing might be a reliable cross-species tool for investigating the pathophysiology of FXS and a potential readout for pharmacotherapy testing, and identify dysregulated gene expression modules in a relevant brain region.\n\nSignificance StatementThe significance of the current study lies in two key domains. First, this study demonstrates that deletion of the Fmrp-KH1 domain is sufficient to cause major mPFC-dependent attention deficits in both males and females, like those observed in both individuals with FXS and in knockout mouse models for FXS. Second, the study shows that deletion of the KH1 domain leads to alterations in the transcriptional profiles within the medial prefrontal cortex (mPFC), which are of potential translational value for subjects with FXS. These findings indicate that attentional testing might be a reliable cross-species tool for investigating the pathophysiology of FXS and a potential readout for pharmacotherapy testing and also highlight hub genes for follow up.

neuroscience↗

bioRxiv2018

Behavioral effect of chemogenetic inhibition is directly related to receptor transduction levels in rhesus monkeys

We used inhibitory DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) to reversibly disrupt dorsolateral prefrontal cortex (dlPFC) function in male macaque monkeys. Monkeys were tested on a spatial delayed response task to assess working memory function after intramuscular injection of either clozapine-N-oxide (CNO) or vehicle. CNO injections given before DREADD transduction were without effect on behavior. rAAV5/hsyn-hM4Di-mCherry was injected bilaterally into the dlPFC of five male rhesus monkeys, to produce neuronal expression of the inhibitory (Gi-coupled) DREADD receptor. We quantified the percentage of DREADD- transduced cells using stereological analysis of mCherry-immunolabeled cells. We found a greater number of immunolabeled neurons in monkeys that displayed CNO-induced behavioral impairment after DREADD transduction compared to monkeys that showed no behavioral effect after CNO. Even in monkeys that showed reliable effects of CNO on behavior after DREADD transduction, the number of prefrontal neurons transduced with DREADD receptor was on the order of 3% of total prefrontal neurons counted. This level of histological analysis facilitates our understanding of behavioral effects, or lack thereof, after DREADD vector injection in monkeys. It also implies that a functional silencing of a relatively small fraction of dlPFC neurons, albeit in a widely distributed area, is sufficient to disrupt spatial working memory.\n\nSignificance StatementCognitive domains such as working memory and executive function are mediated by the dorsolateral prefrontal cortex (dlPFC). Impairments in these domains are common in neurodegenerative diseases as well as normal aging. The present study sought to measure deficits in a spatial delayed response task following activation of viral-vector transduced inhibitory DREADD (Designer Receptor Exclusively Activated by Designer Drug) receptors in rhesus macaques and compare this to the level of transduction in dlPFC using stereology. We found a significant relationship between the extent of DREADD transduction and the magnitude of behavioral deficit following administration of the DREADD actuator compound clozapine-N- oxide (CNO). These results demonstrate it will be critical to validate transduction to ensure DREADDs remain a powerful tool for neuronal disruption.

neuroscience↗

bioRxiv2018

The rhesus monkey hippocampus critically contributes to scene memory retrieval, but not new learning

Humans can recall a large number of memories years after the events that triggered them. Early studies of humans with amnesia led to the hippocampus being viewed as the critical structure for episodic memory, but human lesions are imprecise, making it difficult to identify the anatomical structures underlying memory impairments. Rodent studies enable great temporal and anatomical precision in hippocampal manipulations, but not investigation of the rich assortment of interleaved memories that occurs in humans. Thus it is not known how lesions restricted to the hippocampus affect the retrieval of multiple sequentially encoded memories. Furthermore, disagreement exists as to whether hippocampal inactivations lead to a temporally graded, or ungraded amnesia, which could be a consequence of different types hippocampal disruption observed in rodent and human studies. In the current study, four rhesus monkeys received bilateral neurotoxic lesions of the hippocampus, and were compared to thirteen unoperated controls on recognition and new learning of visual object-in-place scenes. Monkeys with hippocampal lesions were significantly impaired compared to controls at remembering scenes that were encoded before the lesion. We did not observe any temporal gradient effect of the lesion on memory recognition, with recent and remote memories being equally affected by the lesion. Monkeys with hippocampal lesions showed no deficits in learning and later recognising new scenes. Thus, the hippocampus, like other cortical regions, may be engaged in the acquisition and storage of new memories, but its role can be taken over by spared regions following a lesion. These findings illustrate the utility of experimental paradigms for studying retrograde and anterograde amnesia that make use of the capacity of nonhuman primates to rapidly acquire many distinct visual memories.

neuroscience↗

bioRxiv2018

Quantitative analysis of synaptic pathology and neuroinflammation: an initial study in a female rhesus monkey model of the “synaptic” phase of Alzheimer’s disease

BackgroundSoluble oligomers of the A{beta} peptide (A{beta}Os) are toxins that target and disrupt synapses. Generation of A{beta}Os has been recently recognized as a probable initiating event in Alzheimers disease (AD), leading to cognitive impairment. There is a translational gap in AD studies, with promising drugs developed based on work in rodent models failing in AD patients in clinical trials. Additionally, although women have a two-fold greater lifetime risk of developing AD compared to men, females have not been a focus of preclinical studies. Thus, we sought to develop a model of A{beta}O toxicity in female rhesus monkeys, to take advantage of the more highly differentiated cortical structure in this species as well as the similarities in the endocrine system between rhesus monkeys and humans.\n\nMethodsRepeated intracerebroventricular (i.c.v) injections of A{beta}Os were performed in adult female rhesus monkeys. Controls were unoperated aged matched monkeys. High-resolution confocal microscopy and morphometric analysis of Alexa 568 (A568) filled neurons were used to evaluate synaptic, neuronal, and glial markers in the dorsolateral prefrontal cortex (dlPFC) and hippocampus after A{beta}O injections. Cerebrospinal fluid (CSF) and brain tissue were also collected and analyzed for biomarkers of AD pathology, including: phosphorylated Tau protein (pTau), total Tau, A{beta}1-42, A{beta}1-40 and TNF- levels.\n\nResultsHere, we report that A{beta}O injection into the lateral ventricle of the brain induces loss of 37% of thin spines in targeted dlPFC neurons, an area highly vulnerable in AD and aging. Further, A{beta}Os associate with the synaptic marker PSD95, inducing loss of more than 60% of local excitatory synapses. A{beta}Os induce a robust neuroinflammatory response in the hippocampus, far from the injection site, with numerous activated ameboid microglia and TNF- release. Finally, A{beta}Os increased CSF levels of A{beta}1-42, pTau Ser396 and pTau Ser199, but not A{beta}1-40 or total Tau.\n\nConclusionsThese initial findings from detailed quantitative analysis of effects of A{beta}O administration on synapses in a female nonhuman primate model are a very promising step toward understanding the mechanism of early AD pathogenesis in the primate brain, and may help develop an effective disease-modifying therapy of high relevance to womens health.

neuroscience↗

bioRxiv2018

Timing of Cyclic Estradiol Treatment Differentially Affects Cognition in Aged Female Rhesus Monkeys

Some evidence suggests that there may be a limited \"window of opportunity\" for beneficial effects of hormone therapy on physiology after menopause in women. We tested, in aged, surgically menopausal (ovariectomized) rhesus monkeys, whether the timing of cyclic estradiol (E2) treatment impacted its effect on cognitive function. Monkeys were assigned to one of four treatment conditions after ovariectomy: either vehicle or E2 treatment for the duration of the protocol, vehicle for the first 2 years of the protocol followed by E2 for the remainder (delayed treatment), or E2 for the first year of the protocol followed by vehicle for the remainder (withdrawn treatment). Delayed treatment addressed the hypothesis that E2 treatment initiated more than 2 years after ovariectomy would have a reduced effect on cognitive function. Withdrawn treatment mirrors current clinical advice to women to use hormone therapy in the initial post-menopausal period then discontinue it. Two periods of cognitive testing assessed treatment effects on cognition over time. E2 treatment predominantly affected a prefrontal cortex-dependent test of spatiotemporal working memory (delayed response). Monkeys with delayed E2 treatment improved in delayed response performance over time, whereas vehicle-treated monkeys declined. Monkeys with withdrawn E2 treatment maintained their performance across assessments, as did monkeys treated with E2 across the entire protocol. These findings suggest that a \"window of opportunity\" for hormone treatment after cessation of ovarian function, if present in nonhuman primates, lasts longer than 2 years. It also supports the notion that beneficial effects of hormone therapy may persist after discontinuation of treatment.

neuroscience↗

bioRxiv2018

Estradiol treatment in a nonhuman primate model of menopause preserves affective reactivity

As humans age, their affective lives tend to become more positive and less negative. This phenomenon, known as the positivity effect (or positivity bias), occurs even as aging leads to declines in health and cognitive outcomes. Despite these well documented effects in humans, extent to which affective processes change in nonhuman animals, and in particular nonhuman primates - is unclear. As a first step towards developing a model for human affective aging in rhesus monkeys (Macaca mulatta), we tested aged, surgically menopausal aged and middle-aged gonadally intact female rhesus monkeys on a classic index of affective reactivity in monkeys, the Human Intruder task. The Human Intruder task evaluates behavioral responses to varying levels of threat. Aged, surgically menopausal monkeys received hormone replacement therapy consisting of a cyclic estradiol regimen, or vehicle injections as a control. Average responsivity to threat did not vary by condition, but middle aged monkeys and aged monkeys on estradiol were more reactive to the most potent level of threat than to a moderate level of threat, replicating previously published results in other age groups and male monkeys. In contrast, aged monkeys not on estradiol did not show such calibration to threat level. These findings suggest that estrogen may be important for maintaining more youthful affective responding. They also illustrate the utility of behavioral assays of affective reactivity in nonhuman primate models of cognitive and reproductive aging in humans.

animal behavior and cognition↗

bioRxiv2017

An open resource for nonhuman primate imaging

Non-human primate neuroimaging is a rapidly growing area of research that promises to transform and scale translational and cross-species comparative neuroscience.\n\nUnfortunately, the technological and methodological advances of the past two decades have outpaced the accrual of data, which is particularly challenging given the relatively few centers that have the necessary facilities and capabilities. The PRIMate Data Exchange (PRIME-DE) addresses this challenge by aggregating independently acquired non-human primate magnetic resonance imaging (MRI) datasets and openly sharing them via the International Neuroimaging Data-sharing Initiative (INDI). Here, we present the rationale, design and procedures for the PRIME-DE consortium, as well as the initial release, consisting of 13 independent data collections aggregated across 11 sites (total = 98 macaque monkeys). We also outline the unique pitfalls and challenges that should be considered in the analysis of the non-human primate MRI datasets, including providing automated quality assessment of the contributed datasets.

neuroscience↗

bioRxiv2017

Lack of evidence for sex differences in higher cognitive function in macaques

Here we assessed whether higher cognitive function differed between male and female rhesus monkeys using tests of episodic memory and strategy implementation. We did not find any difference between males and females on behavioral performance or on analyses of grey matter volume of key regions. Our findings suggest that, at least where higher cognitive function in healthy monkeys is concerned, the sexes may not differ.

neuroscience↗