Nonhuman Primate Brain Research Articles

Onset Time and Durability of Huntingtin Suppression in Rhesus Putamen After Direct Infusion of Antihuntingtin siRNA.

One possible treatment for Huntington's disease involves direct infusion of a small, interfering RNA (siRNA) designed to reduce huntingtin expression into brain tissue from a chronically implanted programmable pump. Here, we studied the suppression of huntingtin mRNA achievable with short infusion times, and investigated how long suppression may persist after infusion ceases. Rhesus monkeys received 3 days of infusion of Magnevist into the putamen to confirm catheter patency and fluid distribution. After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin. After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later. Results indicate that the onset of huntingtin mRNA suppression in the rhesus putamen occurs rapidly, achieving a plateau throughout the putamen within 4 days. Conversely, loss of huntingtin suppression progresses slowly, persisting an estimated 27–39 days in the putamen and surrounding white matter. These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntington's disease and possibly other neurodegenerative diseases.

Expression and distribution of glucagon-like peptide-1 receptor mRNA, protein and binding in the male nonhuman primate (Macaca mulatta) brain.

Glucagon-like peptide-1 (GLP-1) is released from endocrine L-cells lining the gut in response to food ingestion. However, GLP-1 is also produced in the nucleus of the solitary tract, where it acts as an anorectic neurotransmitter and key regulator of many autonomic and neuroendocrine functions. The expression and projections of GLP-1-producing neurons is highly conserved between rodent and primate brain, although a few key differences have been identified. The GLP-1 receptor (GLP-1R) has been mapped in the rodent brain, but no studies have described the distribution of GLP-1Rs in the nonhuman primate central nervous system. Here, we characterized the distribution of GLP-1R mRNA and protein in the adult macaque brain using in situ hybridization, radioligand receptor autoradiography, and immunohistochemistry with a primate specific GLP-1R antibody. Immunohistochemistry demonstrated that the GLP-1R is localized to cell bodies and fiber terminals in a very selective distribution throughout the brain. Consistent with the functional role of the GLP-1R system, we find the highest concentration of GLP-1R-immunoreactivity present in select hypothalamic and brainstem regions that regulate feeding, including the paraventricular and arcuate hypothalamic nuclei, as well as the area postrema, nucleus of the solitary tract, and dorsal motor nucleus of the vagus. Together, our data demonstrate that GLP-1R distribution is highly conserved between rodent and primate, although a few key species differences were identified, including the amygdala, where GLP-1R expression is much higher in primate than in rodent.

Detection of optogenetic stimulation in somatosensory cortex by non-human primates--towards artificial tactile sensation.

Neuroprosthesis research aims to enable communication between the brain and external assistive devices while restoring lost functionality such as occurs from stroke, spinal cord injury or neurodegenerative diseases. In future closed-loop sensorimotor prostheses, one approach is to use neuromodulation as direct stimulus to the brain to compensate for a lost sensory function and help the brain to integrate relevant information for commanding external devices via, e.g. movement intention. Current neuromodulation techniques rely mainly of electrical stimulation. Here we focus specifically on the question of eliciting a biomimetically relevant sense of touch by direct stimulus of the somatosensory cortex by introducing optogenetic techniques as an alternative to electrical stimulation. We demonstrate that light activated opsins can be introduced to target neurons in the somatosensory cortex of non-human primates and be optically activated to create a reliably detected sensation which the animal learns to interpret as a tactile sensation localized within the hand. The accomplishment highlighted here shows how optical stimulation of a relatively small group of mostly excitatory somatosensory neurons in the nonhuman primate brain is sufficient for eliciting a useful sensation from data acquired by simultaneous electrophysiology and from behavioral metrics. In this first report to date on optically neuromodulated behavior in the somatosensory cortex of nonhuman primates we do not yet dissect the details of the sensation the animals exerience or contrast it to those evoked by electrical stimulation, issues of considerable future interest.

Transcallosal connectivity changes from infancy to late adulthood: an ex vivo diffusion spectrum imaging study of macaque brains.

Interhemispheric communication plays a critical role to ensure normal brain functions in cognition and behavior. Since non-human primate (NHP) brains resemble most aspects of the human brain, a thorough knowledge of interhemispheric cortical connectivity changes in NHP brains throughout the developmental and aging periods may provide valuable insights for translational and clinical research. In this study, formalin-fixed rhesus monkey brains aged from 1 to 24 years were utilized to examine transcallosal connectivity changes using diffusion spectrum imaging (DSI). It was found that the transcallosal connectivity for most frontal cortical areas, including dorso- and ventro-lateral prefrontal, premotor, and motor cortices, demonstrated pronounced age-related alterations. However, such a pattern was less obvious in temporal, posterior parietal, and visual cortices. The DSI results reveal the age-related evolution pattern of transcallosal connectivity in various cortical areas of macaque brains from infancy to late adulthood, and may have implications for assessing the functional defects or alterations in the associated cortical areas during brain development and aging in humans.

A novel analytical brain block tool to enable functional annotation of discriminatory transcript biomarkers among discrete regions of the fronto-limbic circuit in primate brain

Fronto-limbic circuits in the primate brain are responsible for executive function, learning and memory, and emotions, including fear. Consequently, changes in gene expression in cortical and subcortical brain regions housing these circuits are associated with many important psychiatric and neurological disorders. While high quality gene expression profiles can be identified in brains from model organisms, primate brains have unique features such as Brodmann Area 25, which is absent in rodents, yet profoundly important in primates, including humans. The potential insights to be gained from studying the human brain are complicated by the fact that the post-mortem interval (PMI) is variable, and most repositories keep solid tissue in the deep frozen state. Consequently, sampling the important medial and internal regions of these brains is difficult. Here we describe a novel method for obtaining discrete regions from the fronto-limbic circuits of a 4 year old and a 5 year old, male, intact, frozen non-human primate (NHP) brain, for which the PMI is exactly known. The method also preserves high quality RNA, from which we use transcriptional profiling and a new algorithm to identify region-exclusive RNA signatures for Area 25 (NFκB and dopamine receptor signaling), the anterior cingulate cortex (LXR/RXR signaling), the amygdala (semaphorin signaling), and the hippocampus (Ca++ and retinoic acid signaling). The RNA signatures not only reflect function of the different regions, but also include highly expressed RNAs for which function is either poorly understood, or which generate proteins presently lacking annotated functions. We suggest that this new approach will provide a useful strategy for identifying changes in fronto-limbic system biology underlying normal development, aging and disease in the human brain.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Therapeutic bispecific antibodies cross the blood-brain barrier in nonhuman primates

Using therapeutic antibodies that need to cross the blood-brain barrier (BBB) to treat neurological disease is a difficult challenge. We have shown that bispecific antibodies with optimized binding to the transferrin receptor (TfR) that target β-secretase (BACE1) can cross the BBB and reduce brain amyloid-β (Aβ) in mice. Can TfR enhance antibody uptake in the primate brain? We describe two humanized TfR/BACE1 bispecific antibody variants. Using a human TfR knock-in mouse, we observed that anti-TfR/BACE1 antibodies could cross the BBB and reduce brain Aβ in a TfR affinity-dependent fashion. Intravenous dosing of monkeys with anti-TfR/BACE1 antibodies also reduced Aβ both in cerebral spinal fluid and in brain tissue, and the degree of reduction correlated with the brain concentration of anti-TfR/BACE1 antibody. These results demonstrate that the TfR bispecific antibody platform can robustly and safely deliver therapeutic antibody across the BBB in the primate brain.

Identifying individual differences of fluoxetine response in juvenile rhesus monkeys by metabolite profiling.

Fluoxetine is the only psychopharmacological agent approved for depression by the US Food and Drug Administration for children and is commonly used therapeutically in a variety of neurodevelopmental disorders. Therapeutic response shows high individual variability, and severe side effects have been observed. In the current study we set out to identify biomarkers of response to fluoxetine as well as biomarkers that correlate with impulsivity, a measure of reward delay behavior and potential side effect of the drug, in juvenile male rhesus monkeys. The study group was also genotyped for polymorphisms of monoamine oxidase A (MAOA), a gene that has been associated with psychiatric disorders. We used peripheral metabolite profiling of blood and cerebrospinal fluid (CSF) from animals treated daily with fluoxetine or vehicle for one year. Fluoxetine response metabolite profiles and metabolite/reward delay behavior associations were evaluated using multivariate analysis. Our analyses identified a set of plasma and CSF metabolites that distinguish fluoxetine- from vehicle-treated animals and metabolites that correlate with impulsivity. Some metabolites displayed an interaction between fluoxetine and MAOA genotype. The identified metabolite biomarkers belong to pathways that have important functions in central nervous system physiology. Biomarkers of response to fluoxetine in the normally functioning brain of juvenile nonhuman primates may aid in finding predictors of response to treatment in young psychiatric populations and in progress toward the realization of a precision medicine approach in the area of neurodevelopmental disorders.

Alzheimer's disease-like pathology induced by amyloid-β oligomers in nonhuman primates.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder and a major medical problem. Here, we have investigated the impact of amyloid-β (Aβ) oligomers, AD-related neurotoxins, in the brains of rats and adult nonhuman primates (cynomolgus macaques). Soluble Aβ oligomers are known to accumulate in the brains of AD patients and correlate with disease-associated cognitive dysfunction. When injected into the lateral ventricle of rats and macaques, Aβ oligomers diffused into the brain and accumulated in several regions associated with memory and cognitive functions. Cardinal features of AD pathology, including synapse loss, tau hyperphosphorylation, astrocyte and microglial activation, were observed in regions of the macaque brain where Aβ oligomers were abundantly detected. Most importantly, oligomer injections induced AD-type neurofibrillary tangle formation in the macaque brain. These outcomes were specifically associated with Aβ oligomers, as fibrillar amyloid deposits were not detected in oligomer-injected brains. Human and macaque brains share significant similarities in terms of overall architecture and functional networks. Thus, generation of a macaque model of AD that links Aβ oligomers to tau and synaptic pathology has the potential to greatly advance our understanding of mechanisms centrally implicated in AD pathogenesis. Furthermore, development of disease-modifying therapeutics for AD has been hampered by the difficulty in translating therapies that work in rodents to humans. This new approach may be a highly relevant nonhuman primate model for testing therapeutic interventions for AD.

Quantification of iron in the non-human primate brain with diffusion-weighted magnetic resonance imaging

Pathological iron deposits in the brain, especially within basal ganglia, are linked to severe neurodegenerative disorders like Parkinson's disease. As iron induces local changes in magnetic susceptibility, its presence can be visualized with magnetic resonance imaging (MRI). The usual approach, based on iron induced changes in magnetic relaxation (T2/T2′), is often prone, however, to confounding artifacts and lacks specificity. Here, we propose a new method to quantify and map iron deposits using water diffusion MRI. This method is based on the differential sensitivity of two image acquisition schemes to the local magnetic field gradients induced by iron deposits and their cross-term with gradient pulses used for diffusion encoding. Iron concentration could be imaged and estimated with high accuracy in the brain cortex, the thalamus, the substantia nigra and the globus pallidus of macaques, showing iron distributions in agreement with literature. Additionally, iron maps could clearly show a dramatic increase in iron content upon injection of an UltraSmall Particle Iron Oxide (USPIO) contrast agent, notably in the cortex and the thalamus, reflecting regional differences in blood volume. The method will benefit clinical investigations on the effect of iron deposits in the brain or other organs, as iron deposits are increasingly seen as a biomarker for a wide range of diseases, notably, neurodegenerative diseases in the pre-symptomatic stage. It also has the potential for quantifying variations in blood volume induced by brain activation in fMRI studies using USPIOs.

Huntingtin-lowering strategies in Huntington's disease: antisense oligonucleotides, small RNAs, and gene editing.

The idea to lower mutant huntingtin is especially appealing in Huntington's disease (HD). It is autosomal dominant, so that expression of the mutant allele causes the disease. Advances in RNA and gene regulation provide foundations for the huntingtin gene (both normal and mutant alleles) and possibly the mutant allele only. There is much preclinical animal work to support the concept of gene and RNA silencing, but, to date, no clinical studies have been attempted in HD. Preventing expression of mutant huntingtin protein is at the cusp for a human trial. Antisense oligonucleotides delivered to patients with amyotrophic lateral sclerosis have been well tolerated; small RNAs administered to rodent and nonhuman primate brain knocked down huntingtin messenger RNA (mRNA); short-hairpin complementary DNA of microRNAs can be expressed in adeno-associated virus to provide long-term silencing of huntingtin mRNA and protein. We expect that these approaches will be ready for clinical studies in the near future, once safety has been validated. Our understanding of gene editing-changing the huntingtin gene itself-is rapidly progressing. Harnessing our knowledge of transcription and translation should push scientific creativity to new and exciting advances that overcome the lethality of the mutant gene in HD.

Dose-dependent, saturable occupancy of the metabotropic glutamate subtype 5 receptor by fenobam as measured with [11 C]ABP688 PET imaging.

Fenobam is a negative allosteric modulator of the metabotropic glutamate receptor subtype 5 (mGluR5) with inverse agonist activity and is expected to contribute to the treatment of neuropsychiatric disorders involving dysfunction of mGluR5 including Fragile X syndrome. This study examined whether [11 C]ABP688, an antagonist PET radioligand, competes with fenobam for the same binding site in the nonhuman primate brain and would allow examination of occupancy-plasma concentration relationships in the evaluation of the drug for target disorders in the human brain. Four paired PET studies with [11 C]ABP688 were performed in baboons at a baseline condition and after intravenous treatment with fenobam at different dose levels (0.3-1.33 mg/kg). Total distribution volume (VT ) and binding potential (BPND ) using the cerebellum as a reference region were obtained by the plasma reference graphical method. Then it was examined whether occupancy follows a dose-dependent, saturating pattern that was predicted by a modified first-order Hill equation in individual regions. Baseline regional VT and BPND values agreed with previously published data. Occupancy showed dose-dependent and saturating patterns in individual regions, reaching >90% occupancy at 1.33 mg/kg dose of fenobam in the majority of regions. To our knowledge, this is the first use of PET to characterize the mGluR5 therapeutic drug fenobam. This study demonstrates a proof of principle for determining the in vivo occupancy of fenobam in primates. The results indicate that [11 C]ABP688 and PET may be useful for examination of occupancy of mGluR5 by fenobam, which should prove to be useful for designing future studies and treatment of human disease states. Synapse 68:565-573, 2014. © 2014 Wiley Periodicals, Inc.

Evidence of adult neurogenesis in non-human primates and human.

Adult neurogenesis in rodents has been extensively studied. Here, we briefly summarize the studies of adult neurogenesis based on non-human primate brains and human postmortem brain samples in recent decades. The differences between rodent, primate and human neurogenesis are discussed. We conclude that these differences may contribute to distinct physiological roles and the self-repair mechanisms in the brain across species.

A simpler primate brain: the visual system of the marmoset monkey.

Humans are diurnal primates with high visual acuity at the center of gaze. Although primates share many similarities in the organization of their visual centers with other mammals, and even other species of vertebrates, their visual pathways also show unique features, particularly with respect to the organization of the cerebral cortex. Therefore, in order to understand some aspects of human visual function, we need to study non-human primate brains. Which species is the most appropriate model? Macaque monkeys, the most widely used non-human primates, are not an optimal choice in many practical respects. For example, much of the macaque cerebral cortex is buried within sulci, and is therefore inaccessible to many imaging techniques, and the postnatal development and lifespan of macaques are prohibitively long for many studies of brain maturation, plasticity, and aging. In these and several other respects the marmoset, a small New World monkey, represents a more appropriate choice. Here we review the visual pathways of the marmoset, highlighting recent work that brings these advantages into focus, and identify where additional work needs to be done to link marmoset brain organization to that of macaques and humans. We will argue that the marmoset monkey provides a good subject for studies of a complex visual system, which will likely allow an important bridge linking experiments in animal models to humans.

Diffeomorphic registration with self-adaptive spatial regularization for the segmentation of non-human primate brains.

Cerebral aging has been linked to structural and functional changes in the brain throughout life. Here, we study the marmoset, a small non-human primate, in order to get insights into the mechanisms of brain aging in normal and pathological conditions. Imaging the brain of small animals with techniques such as MRI, quickly becomes a challenging task when compared with human brain imaging. Very often, a simple pre-processing step such as brain extraction cannot be achieved with classical tools. In this paper, we propose a diffeomorphic registration algorithm, which makes use of learned constraints to propagate the manual segmentation of a marmoset brain template to other MR images of marmoset brains. The main methological contribution of our paper is to explore a new strategy to automatically tune the spatial regularization of the deformations. Results show that we obtain a robust segmentation of the brain, even for images with a low contrast.

Molecular targets of chromatin repressive mark H3K9me3 in primate progenitor cells within adult neurogenic niches

Histone 3 Lysine 9 (H3K9) methylation is known to be associated with pericentric heterochromatin and important in genomic stability. In this study, we show that trimethylation at H3K9 (H3K9me3) is enriched in an adult neural stem cell niche- the subventricular zone (SVZ) on the walls of the lateral ventricle in both rodent and non-human primate baboon brain. Previous studies have shown that there is significant correlation between baboon and human regarding genomic similarity and brain structure, suggesting that findings in baboon are relevant to human. To understand the function of H3K9me3 in this adult neurogenic niche, we performed genome-wide analyses using ChIP-Seq (chromatin immunoprecipitation and deep-sequencing) and RNA-Seq for in vivo SVZ cells purified from baboon brain. Through integrated analyses of ChIP-Seq and RNA-Seq, we found that H3K9me3-enriched genes associated with cellular maintenance, post-transcriptional and translational modifications, signaling pathways, and DNA replication are expressed, while genes involved in axon/neuron, hepatic stellate cell, or immune-response activation are not expressed. As neurogenesis progresses in the adult SVZ, cell fate restriction is essential to direct proper lineage commitment. Our findings highlight that H3K9me3 repression in undifferentiated SVZ cells is engaged in the maintenance of cell type integrity, implicating a role for H3K9me3 as an epigenetic mechanism to control cell fate transition within this adult germinal niche.

A thermostable bacterial cocaine esterase rapidly eliminates cocaine from brain in nonhuman primates.

A long-acting, thermostable bacterial cocaine esterase (CocE) has been identified that rapidly degrades cocaine with a KM of 1.33+0.085 μM. In vivo evaluation of CocE has shown protection against convulsant and lethal effects of cocaine in rodents, confirming the therapeutic potential of CocE against cocaine overdose. However, the current study is the first to evaluate the effects of CocE on cocaine brain levels. Positron emission tomogrpahy neuroimaging of [11C]cocaine was used to evaluate the time course of cocaine elimination from brain in the presence and absence of CocE in nonhuman primates. Systemic administration of CocE eliminated cocaine from the rhesus-monkey brain approximately three times faster than control conditions via peripheral actions through attenuating the input function from blood plasma. The efficiency of this process is sufficient to alleviate or prevent adverse central nervous system effects induced by cocaine. Although the present study used tracer doses of cocaine to access brain clearance, these findings further support the development of CocE for the treatment of acute cocaine toxicity.

Synthesis and imaging validation of [¹⁸F]MDL100907 enabled by Ni-mediated fluorination.

Several voids exist in reliable positron emission tomography (PET) radioligands for quantification of the serotonin (5HT) receptor system. Even in cases where 5HT radiotracers exist, challenges remain that have limited the utility of 5HT imaging in clinical research. Herein we address an unmet need in 5HT2a imaging using innovative chemistry. We report a scalable and robust synthesis of [(18)F]MDL100907, which was enabled by a Ni-mediated oxidative fluorination using [(18)F]fluoride. This first demonstration of a Ni-mediated fluorination used for PET imaging required development of a new reaction strategy that ultimately provided high specific activity [(18)F]MDL100907. Using the new synthetic strategy and optimized procedure, [(18)F]MDL100907 was evaluated against [(11)C]MDL100907 for reliability to quantify 5HT₂a in the nonhuman primate brain and was found to be superior based on a single scan analysis using the same nonhuman primate. The use of this new 5HT₂a radiotracer will afford clinical neuroscience research the ability to distinguish 5HT₂a receptor abnormalities binding between healthy subjects and patients even when group differences are small.

Amphetamine-induced release of dopamine in primate prefrontal cortex and striatum: striking differences in magnitude and timecourse.

The psychostimulant amphetamine (AMPH) is frequently used to increase catecholamine levels in attention disorders and positron emission tomography imaging studies. Despite the fact that most radiotracers for positron emission tomography studies are characterized in non-human primates (NHPs), data on regional differences of the effect of AMPH in NHPs are very limited. This study examined the impact of AMPH on extracellular dopamine (DA) levels in the medial prefrontal cortex and the caudate of NHPs using microdialysis. In addition to differences in magnitude, we observed striking differences in the temporal profile of extracellular DA levels between these regions that can likely be attributed to differences in the regulation of dopamine uptake and biosynthesis. The present data suggest that cortical DA levels may remain elevated longer than in the caudate which may contribute to the clinical profile of the actions of AMPH. Using microdialysis probes implanted in the cortex and caudate region of non-human primate brains, we observed in vivo differences in the magnitude and temporal profile of extracellular dopamine levels in response to intravenous amphetamine administration.

In vivo diffusion spectrum imaging of non-human primate brain: initial experience in transcallosal fiber examination.

In comparison with conventional diffusion tensor imaging (DTI) technique, diffusion spectrum imaging (DSI) allows for delineating crossing and touching fibers in the brain and has been explored in clinical and preclinical studies. Non-human primates (NHPs) resemble most aspects of human and are widely employed in various neuroscience researches and pharmaceutical development. In the present study, a parallel imaging-based DSI protocol was implemented for in vivo fiber tracking of macaque monkey brains on a 3.0 T clinical scanner. Transcallosal fiber tracts of adult macaque brains were examined with DSI and compared with those from a a conventional DTI protocol. The results demonstrate that DSI can reveal the transcallosal fiber bundles much more extensively than the conventional DTI. The preliminary results suggest that DSI may provide a feasible and robust approach for characterizing the fiber pathways in various disease models of NHPs.