Adult Male Rhesus Macaques Research Articles

Dissociating cholinergic influence on alertness and temporal attention in primates in a simple reaction time paradigm.

The ability to promptly respond to behaviourally relevant events depends on both general alertness and phasic changes in attentional state driven by temporal expectations. Using a variable foreperiod simple reaction time (RT) task in four adult male rhesus macaques, we investigated the role of the cholinergic system in alertness and temporal expectation. Foreperiod effects on RT reflect temporal expectation, while alertness is quantified as overall response speed. We measured these RT parameters under vehicle treatment and systemic administration of the muscarinic receptor antagonist scopolamine. We also investigated whether and to what extent the effects of scopolamine were reversed by donepezil, a cholinesterase inhibitor widely used for the treatment of dementia. In the control condition, RT showed a continuous decrease as the foreperiod duration increased, which clearly indicated the effect of temporal expectation on RT. This foreperiod effect was mainly detectable on the faster tail of the RT distribution and was eliminated by scopolamine. Furthermore, scopolamine treatment slowed down the average RT. Donepezil treatment was efficient on the slower tail of the RT distribution and improved scopolamine-induced impairments only on the average RT reflecting a general beneficial effect on alertness without any improvement in temporal expectation. The present results highlight the role of the cholinergic system in temporal expectation and alertness in primates and help delineate the efficacy and scope of donepezil and other cholinomimetic agents as cognitive enhancers in present and future clinical practice.

Daily Ethanol Drinking Followed by an Abstinence Period Impairs Bone Marrow Niche and Mitochondrial Function of Hematopoietic Stem/Progenitor Cells in Rhesus Macaques.

Unhealthy consumption of alcohol is a major public health crisis with strong associations between immunological dysfunctions, high vulnerability to infectious disease, anemia, and an increase in the risk of hematological malignancies. However, there is a lack of studies addressing alcohol-induced changes in bone marrow (BM) and hematopoiesis as fundamental aspects of immune system function. To address the effect of chronic alcohol consumption on hematopoietic stem and progenitor cells (HSPCs) and the BM niche, we used an established rhesus macaque model of voluntary alcohol drinking. A cohort of young adult male rhesus macaques underwent a standard ethanol self-administration protocol that allowed a choice of drinking alcohol or water 22hours/day with periods of forced abstinence that elevated subsequent intakes when alcohol availability resumed. Following the last month of forced abstinence, the monkeys were euthanized. HSPCs and bone samples were collected and analyzed in functional assays and by confocal microscopy. HSPCs from alcohol animals exhibited reduced ability to formgranulocyte-monocyte and erythroidcolonies in vitro. HSPCs also displayed a decrease in mitochondrial oxygen consumption linked to ATP production and basal respiratory capacity. Chronic alcohol use led to vascular remodeling of the BM niche, a reduction in the number of primitive HSPCs, and a shift in localization of HSPCs from an adipose to a perivascular niche. Our study demonstrates, for the first time, that chronic voluntary alcohol drinking in rhesus macaque monkeys leads to the long-term impairment of HSPC function, a reduction in mitochondrial respiratory activity, and alterations in the BM microenvironment. Further studies are needed to determine whether these changes in hematopoiesis are persistent or adaptive during the abstinent period and whether an initial imprinting to alcohol primes BM to become more vulnerable to future exposure to alcohol.

Trio housing of adult male rhesus macaques (Macaca mulatta): Methodology and outcome predictors.

This study evaluated the feasibility of trio housing caged adult male rhesus macaques and attempted to identify outcome predictors for trio housing formation and its intermediary introduction steps. Subjects were familiarized consecutively to each potential group member via protected contact prior to introduction into the trio. Seven trios were attempted, involving 18 males, with three males attempted in two different trios. One group was deemed successful, with a tenure of 51days. Five were disbanded within minutes, and one was deemed unsuccessful the following morning. Two males sustained wounds requiring veterinary care over the course of the study. Outcome of the protected contact phase was predicted by age and temperament disparities as well as initial behavior. While outcomes were poor, it suggests that attempts can be made relatively safely, and alternative introduction strategies should be explored to increase the feasibility of trio housing for adult males.

Post mortem evaluation of inflammation, oxidative stress, and PPARγ activation in a nonhuman primate model of cardiac sympathetic neurodegeneration.

Cardiac dysautonomia is a common nonmotor symptom of Parkinson's disease (PD) associated with loss of sympathetic innervation to the heart and decreased plasma catecholamines. Disease-modifying strategies for PD cardiac neurodegeneration are not available, and biomarkers of target engagement are lacking. Systemic administration of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA) recapitulates PD cardiac dysautonomia pathology. We recently used positron emission tomography (PET) to visualize and quantify cardiac sympathetic innervation, oxidative stress, and inflammation in adult male rhesus macaques (Macaca mulatta; n = 10) challenged with 6-OHDA (50mg/kg; i.v.). Twenty-four hours post-intoxication, the animals were blindly and randomly assigned to receive daily doses of the peroxisome proliferator-activated receptor gamma (PPARγ) agonist pioglitazone (n = 5; 5mg/kg p.o.) or placebo (n = 5). Quantification of PET radioligand uptake showed increased oxidative stress and inflammation one week after 6-OHDA which resolved to baseline levels by twelve weeks, at which time pioglitazone-treated animals showed regionally preserved sympathetic innervation. Here we report post mortem characterization of heart and adrenal tissue in these animals compared to age and sex matched normal controls (n = 5). In the heart, 6-OHDA-treated animals showed a significant loss of sympathetic nerve fibers density (tyrosine hydroxylase (TH)-positive fibers). The anatomical distribution of markers of sympathetic innervation (TH) and inflammation (HLA-DR) significantly correlated with respective in vivo PET findings across left ventricle levels and regions. No changes were found in alpha-synuclein immunoreactivity. Additionally, CD36 protein expression was increased at the cardiomyocyte intercalated discs following PPARγ-activation compared to placebo and control groups. Systemic 6-OHDA decreased adrenal medulla expression of catecholamine producing enzymes (TH and aromatic L-amino acid decarboxylase) and circulating levels of norepinephrine, which were attenuated by PPARγ-activation. Overall, these results validate in vivo PET findings of cardiac sympathetic innervation, oxidative stress, and inflammation and illustrate cardiomyocyte CD36 upregulation as a marker of PPARγ target engagement.

3D printed porous titanium cages filled with simvastatin hydrogel promotes bone ingrowth and spinal fusion in rhesus macaques.

Three-dimensional (3D) printing technology can be used to manufacture implants with individualized external shapes, internal porous structures and elastic moduli similar to those of natural bone, although such implants lack biological activity. Here, we developed a porous titanium cage by electron beam melting that was filled with simvastatin/poloxamer 407 hydrogel and evaluated bone ingrowth and spinal fusion. Six adult male rhesus macaques underwent interbody fusion of the L3/4 (cage without simvastatin or hydrogel), L4/5 (cage with 0.5 mg simvastatin in hydrogel) and L5/6 (cage with 0 mg simvastatin in hydrogel) segments. 18F-NaF PET/CT imaging confirmed that simvastatin/poloxamer 407 hydrogel increased bone blood flow, osteoblastic activity and bone ingrowth; histological analysis demonstrated that simvastatin/poloxamer 407 hydrogel promoted bone ingrowth in and osseointegration around the L4/5 cages; and biomechanical analysis verified that simvastatin/poloxamer 407 hydrogel enhanced spinal fusion. We conclude that 3D-printed porous cages containing simvastatin hydrogel promote bone ingrowth and spinal fusion, which could be a convenient and promising method for clinical translation. Using PET/CT to monitor the osteoblast activity may provide a new method for assessing the intervertebral fusion effect in preclinical study or clinical postoperative evaluation.

Discriminative Stimulus Effects and Metabolism of Ethanol in Rhesus Monkeys.

Animal models are an essential feature of drug and pharmacotherapy development for treating alcohol use disorders (AUDs). The rhesus macaque is a robust animal model for many aspects of AUDs particularly in exploiting individual differences in oral self-administration of ethanol (EtOH), endocrine orchestration of stress response, and menstrual cycle characteristics. However, the clearance rates of EtOH have not been reported in this species, and the GABAA and N-methyl-D-aspartate (NMDA) receptor involvement in EtOH's discriminative stimulus effects has not been fully characterized. EtOH clearance rates following 2 doses of EtOH on separate days (0.5 and 1.0g/kg, i.g.) were determined in 8 young adult male rhesus macaques. The EtOH was given by nasogastric gavage, and repeated blood samples were taken over 5hours without sedation. Next, all subjects were trained on a 2-choice 1.0g/kg EtOH (i.g.) versus water discrimination with a 60-minutes pretreatment period to capture peak blood EtOH concentration (BEC). Substitution testing was conducted with GABAA ligands pentobarbital (i.g. and i.m.) and midazolam (i.g.), as well as NMDA antagonist MK-801 (i.m.). Peak BECs were 34 and 87mg/dl for 0.5 and 1.0g/kg doses, respectively, and occurred at 66 and 87minutes following gavage. All GABAA and NMDA ligands tested resulted in responding on the EtOH-appropriate lever with the potency ranking of MK-801 (ED50 : 0.017mg/kg)>midazolam (ED50 : 1.6mg/kg)>pentobarbital (ED50 : 3.7mg/kg)>EtOH (ED50 : 700mg/kg, or 0.7g/kg) in these subjects. These results suggest that the compound discriminative stimulus effects of EtOH are highly consistent across species, providing further support for the rhesus macaque as strong model for pharmacotherapy development for AUD.

A Practical Method for Creating Targeted Focal Ischemic Stroke in the Cortex of Nonhuman Primates.

Ischemic stroke is a major cause of disability among adults worldwide. Despite its prevalence, few effective treatment options exist to alleviate sensory and motor dysfunctions that result from stroke. In the past, rodent models of stroke have been the primary experimental models used to develop stroke therapies. However, positive results in these studies have failed to replicate in human clinical trials, highlighting the importance of nonhuman primate (NHP) models as a preclinical step. Although there are a few NHP models of stroke, the extent of tissue damage is highly variable and dependent on surgical skill. In this study, we employed the photothrombotic stroke model in NHPs to generate controlled, reproducible ischemic lesions. Originally developed in rodents, the photothrombotic technique consists of intravenous injection of a photosensitive dye such as Rose Bengal followed by illumination of an area of interest to induce endothelial damage resulting in the formation of thrombi in the illuminated vasculature. We developed a quantitative model to predict the extent of tissue damage based on the light scattering profile of light in the cortex of NHPs. We then employed this technique in the sensorimotor cortex of two adult male Rhesus Macaques. In vivo optical coherence tomography imaging of the cortical microvasculature and subsequent histology confirmed the formation of focal cortical infarcts and demonstrated its reproducibility and ability to control the sizes and locations of light-induced ischemic lesions in the cortex of NHPs. This model has the potential to enhance our understanding of perilesional neural dynamics and can be used to develop reliable neurorehabilitative therapeutic strategies to treat stroke.

Determining overweight and underweight with a new weight-for-height index in captive group-housed macaques.

Housing primates in naturalistic groups provides social benefits relative to solitary housing. However, food intake may vary across individuals, possibly resulting in overweight and underweight individuals. Information on relative adiposity (the amount of fat tissue relative to body weight) is needed to monitor overweight and underweight of group‐housed individuals. However, the upper and lower relative adiposity boundaries are currently only known for macaques living solitarily in small cages. We determined the best measure of relative adiposity and explored the boundaries of overweight and underweight to investigate their incidence in group‐housed adult male and female rhesus macaques and long‐tailed macaques living in spacious enclosures at the Biomedical Primate Research Centre (BPRC), the Netherlands. During yearly health checks different relative adiposity measures were obtained. For long‐tailed macaques, comparable data on founder and wild animals were also available. Weight‐for‐height indices (WHI) with height to the power of 3.0 (WHI3.0) for rhesus macaques and 2.7 (WHI2.7) for long‐tailed macaques were optimally independent of height and were highly correlated with other relative adiposity measures. The boundary for overweight was similar in group‐housed and solitary‐housed macaques. A lower boundary for underweight, based on 2% body fat similar to wild primates, gave a better estimate for underweight in group‐housed macaques. We propose that for captive group‐housed rhesus macaques relative adiposity should range between 42 and 67 (WHI3.0) and for long‐tailed macaques between 39 and 62 (WHI2.7). The majority of group‐housed macaques in this facility have a normal relative adiposity, a considerable proportion (17–23%) is overweight, and a few (0–3%) are underweight.

Monocyte Polarization is Altered by Total-Body Irradiation in Male Rhesus Macaques: Implications for Delayed Effects of Acute Radiation Exposure.

Radiation-induced fibrosis (RIF) is a common delayed effect of acute ionizing radiation exposure (DEARE) affecting diverse tissues including the heart, lungs, liver and skin, leading to reduced tissue function and increased morbidity. Monocytes, which may be classified into classical (CD14++, CD16-), intermediate (CD14++, CD16+) and non-classical (CD14+/low, CD16++) subtypes in humans and non-human primates (NHPs), and monocyte-derived macrophages may play an integral role in the pathogenesis of RIF. We tested the hypothesis that moderate to high levels of total-body exposure to radiation would alter monocyte polarization and produce phenotypes that could promote multi-organ fibrosis in a wellestablished NHP model of DEARE. Subjects were 16 young adult male rhesus macaques, ten of which were exposed to high-energy, 4 Gy X-ray total-body irradiation (TBI) and six that received sham irradiation (control). Total monocytes assessed by complete blood counts were 89% depleted in TBI animals by day 9 postirradiation (P < 0.05), but recovered by day 30 postirradiation and did not differ from control levels thereafter. Monocytes were isolated from peripheral blood mononuclear cells (PBMCs) and sorted into classical, intermediate and non-classical subsets using fluorescence-activated cell sorting (FACS) prior to and at 6 months post-TBI. At 6 months postirradiation, monocyte polarization shifted towards lower classical (92% → 86%) and higher intermediate (7% → 12%) and non-classical monocyte subsets (0.6% → 2%) (all P < 0.05) in TBI animals compared to baseline. No change in monocyte subsets was observed in control animals. Transcriptional profiles in classical and intermediate monocyte subsets were assessed using RNAseq. Classical monocyte gene expression did not change significantly over time or differ cross-sectionally between TBI and control groups. In contrast, significant numbers of differentially expressed genes (DEGs) were detected in intermediate monocyte comparisons between the TBI animals and all animals at baseline (304 DEGs), and in the TBI versus control animals at 6 months postirradiation (67 DEGs). Intermediate monocytes also differed between baseline and 6 months in control animals (147 DEGs). Pathway analysis was used to identify genes within significant canonical pathways, yielding 52 DEGs that were specific to irradiated intermediate monocytes. These DEGs and significant canonical pathways were associated with pro-fibrotic and anti-inflammatory signaling pathways that have been noted to induce M2 macrophage polarization. These findings support the hypothesis that TBI may alter monocyte programming and polarization towards a profibrotic phenotype, providing a novel target opportunity for therapies to inhibit or prevent RIF.

Low plasma adropin concentrations increase risks of weight gain and metabolic dysregulation in response to a high-sugar diet in male nonhuman primates

Mouse studies linking adropin, a peptide hormone encoded by the energy homeostasis-associated (ENHO) gene, to biological clocks and to glucose and lipid metabolism suggest a potential therapeutic target for managing diseases of metabolism. However, adropin's roles in human metabolism are unclear. In silico expression profiling in a nonhuman primate diurnal transcriptome atlas (GSE98965) revealed a dynamic and diurnal pattern of ENHO expression. ENHO expression is abundant in brain, including ventromedial and lateral hypothalamic nuclei regulating appetite and autonomic function. Lower ENHO expression is present in liver, lung, kidney, ileum, and some endocrine glands. Hepatic ENHO expression associates with genes involved in glucose and lipid metabolism. Unsupervised hierarchical clustering identified 426 genes co-regulated with ENHO in liver, ileum, kidney medulla, and lung. Gene Ontology analysis of this cluster revealed enrichment for epigenetic silencing by histone H3K27 trimethylation and biological processes related to neural function. Dietary intervention experiments with 59 adult male rhesus macaques indicated low plasma adropin concentrations were positively correlated with fasting glucose, plasma leptin, and apolipoprotein C3 (APOC3) concentrations. During consumption of a high-sugar (fructose) diet, which induced 10% weight gain, animals with low adropin had larger increases of plasma leptin and more severe hyperglycemia. Declining adropin concentrations were correlated with increases of plasma APOC3 and triglycerides. In summary, peripheral ENHO expression associates with pathways related to epigenetic and neural functions, and carbohydrate and lipid metabolism, suggesting co-regulation in nonhuman primates. Low circulating adropin predicts increased weight gain and metabolic dysregulation during consumption of a high-sugar diet.

1856-P: A High Sugar (Fructose) Diet Increases C-Reactive Protein (CRP) in Rhesus Macaques: Relationships with Changes of Apolipoproteins and Adiponectin

CRP is produced by the liver in response to factors released from macrophages and adipocytes. High circulating CRP concentrations are therefore an indicator of inflammation and/or injury. We examined the effects of dietary fructose on plasma CRP concentrations in a nonhuman primate model of diet-induced metabolic syndrome. Adult male rhesus macaques 12±3 years of age, weighing 16.2±1.9 kg (n=29) maintained on chow (LabDiet 5047) ad libitum were provided with flavored fructose beverages containing 75g of fructose (300 kcal/day). Fasting plasma samples were collected at baseline and after 1 and 3 months. Indices of glucose homeostasis (insulin, glucose, HOMA-IR), adiposity/metabolic homeostasis (leptin, adiponectin) and lipid metabolism (TG, cholesterol, LDL-C, HDL-C, VLDL-C, ApoA1, ApoB, ApoC3 and ApoE) were analyzed. Fructose consumption induced weight gain +1.5±0.2 kg, and insulin resistance, accompanied by increases of plasma leptin, decreased adiponectin, hypertriglyceridemia and increases of ApoC3 and ApoE. Plasma CRP increased from 1.9±0.2 mg/l to 2.9±0.3 mg/l (%∆ = 81±13%) and 2.9±0.3 mg/l (%∆ = +91±14%; both p&amp;lt;0.001) at 1 and 3 months respectively. Bivariate correlation analysis of log-transformed data compared fructose-induced changes (Δ) of CRP with Δ’s of body weight and metabolic indices. After 1 month of fructose consumption, strong positive associations were identified between ΔCRP and ΔApoE (r=0.62, p&amp;lt;0.001), ΔApoC3 (r=0.56, p=0.002), and negatively with Δadiponectin (r=-0.49, p=0.007). After 3 months of fructose exposure, the strong associations between ΔCRP and ΔApoE (r=0.49, p=0.007) and significant relationships with ΔApoC3 (r=0.45, p=0.015) and Δadiponectin (r=-0.39, p=0.038) remained. These results support an important link between fructose diet-induced inflammation with changes of the anti-inflammatory adipocyte hormone (adiponectin) and dysregulated hepatic lipoprotein metabolism. Disclosure P.J. Havel: Research Support; Self; Arrowhead Research, Bristol-Myers Squibb Company, Magnamosis Inc. J.L. Graham: Research Support; Self; Arrowhead Research, Bristol-Myers Squibb Company, Magnamosis Inc. K.L. Stanhope: None. A. Butler: None. Funding National Institutes of Health

Toward a Standardized Test of Fearful Temperament in Primates: A Sensitive Alternative to the Human Intruder Task for Laboratory-Housed Rhesus Macaques (Macaca mulatta).

Standardized and sensitive tests to assess differences in temperament among primates housed in captivity are essential for monitoring welfare and improving science outcomes through reduced noise in data. Fearful temperament in primates has traditionally been assessed using the Human Intruder Test (HIT) in which duration of bodily freeze in response to approach by an unknown human is measured. The HIT is susceptible to variation between facilities in execution, interpretation of data and could be stressful for animals with more fearful temperaments. We tested the applicability of a touch-screen task with putatively negative stimuli as a more standardizable and sensitive tool for measuring fearful temperament in laboratory primates. Seventeen adult male rhesus macaques were assessed for fearfulness using the HIT. They were then tested on a touch-screen task designed to measure two behavioral indices of fearfulness: behavioral inhibition and response-slowing. We predicted monkeys assessed as having more fearful temperament in the HIT, would show the greatest degree of behavioral inhibition and response-slowing to negative pictures in the touch-screen task. In Study 1, monkeys were rewarded with juice for touching gray squares on the screen (control trials). On test trials a picture of an unknown male conspecific face with direct-gaze (signaling threat) was shown. Monkeys were less likely to touch direct-gaze faces than control trials, indicating behavioral inhibition to threat. Behavioral inhibition was greatest amongst monkeys scored with most fearful temperament in the HIT. This primary result indicates the touch-screen task may be sensitive to a more subtle form of the bodily freeze behavior measured using the HIT. In Study 2, we tested whether these findings generalized to other classes of putatively negative stimuli; monkeys were shown pictures of the human intruder and objects associated with veterinary and husbandry procedures, interspersed with control trials (gray squares). There was no evidence of behavioral inhibition in Study 2. There was some evidence for response-slowing, which was greater for pictures of objects than pictures of the human intruder, and occurred independently of fearfulness in the HIT. We propose touch-screen tasks provide a more standardized and sensitive approach for assessing fearful temperament in laboratory primates.

Enhanced wound healing promotion by immune response-free monkey autologous iPSCs and exosomes vs. their allogeneic counterparts.

BackgroundComparing non-inbred autologous and allogeneic induced pluripotent stem cells (iPSCs) and their secreted subcellular products among non-human primates is critical for choosing optimal iPSC products for human clinical trials.MethodsiPSCs were induced from skin fibroblastic cells of adult male rhesus macaques belonging to four unrelated consanguineous families. Teratoma generativity, host immune response, and skin wound healing promotion were evaluated subsequently.FindingsAll autologous, but no allogeneic, iPSCs formed teratomas, whereas all allogeneic, but no autologous, iPSCs caused lymphocyte infiltration. Macrophages were not detectable in any wound. iPSCs expressed significantly more MAMU A and E of the major histocompatibility complex (MHC) class I but not more other MHC genetic alleles than parental fibroblastic cells. All topically disseminated autologous and allogeneic iPSCs, and their exosomes accelerated skin wound healing, as demonstrated by wound closure, epithelial coverage, collagen deposition, and angiogenesis. Allogeneic iPSCs and their exosomes were less effective and viable than their autologous counterparts. Some iPSCs differentiated into new endothelial cells and all iPSCs lost their pluripotency in 14 days. Exosomes increased cell viability of injured epidermal, endothelial, and fibroblastic cells in vitro. Although exosomes contained some mRNAs of pluripotent factors, they did not impart pluripotency to host cells.InterpretationAlthough all of the autologous and allogeneic iPSCs and exosomes accelerated wound healing, allogeneic iPSC exosomes were the preferred choice for “off-the shelf” iPSC products, owing to their mass-production, with no concern of teratoma formation.FundNational Natural Science Foundation of China and National Key R&D Program of China.

Low-ranking individuals present high and unstable fecal cortisol levels in provisioned free-ranging adult male rhesus macaques (Macaca mulatta) during the birth season in a mountain area of northern China.

Social hierarchy commonly exists in animal societies, affecting both the endocrine functioning and the behavior of animals. In nonhuman primates, the relationship between social rank and cortisol levels varies across species and even within species. Here, we assessed the relationships between social rank and fecal cortisol levels in adult male Taihangshan macaques (rhesus macaques, Macaca mulatta tcheliensis) from the provisioned, free-ranging Wulongkou-2 (WLK-2) group inhabiting Wulongkou Scenic Area, Jiyuan, China. From March to May 2014, we recorded 195 agonistic behaviors and collected 54 fresh fecal samples from eight adult male Taihangshan macaques. Males were assigned a social rank according to an agonistic behavior matrix, and enzyme-linked immunosorbent assay was then used to measure the cortisol concentration in the fecal samples. We found that social rank among the eight male Taihangshan macaques in WLK-2 group followed a strict linear hierarchy, and that fecal cortisol levels were significantly higher and more variable in low-ranking males than in more dominant individuals. Age was not significantly associated with social rank or fecal cortisol levels. Our results suggest that social rank and maintenance of the social hierarchy within the WLK-2 group is a chronic stressor, with low-ranking males maintaining heightened stress levels and enlarged reactive scope relative to dominant males. This provides new support for the theory that social environment can influence endocrine functioning.

Lorcaserin decreases the reinforcing effects of heroin, but not food, in rhesus monkeys

Preclinical studies indicate that lorcaserin (Belviq®), an FDA-approved serotonin 2 C receptor agonist, may be a promising medication for the treatment of stimulant addiction. However, few studies have investigated its effects on self-administration of drugs of abuse from other pharmacological classes, including opioids. Here, adult male rhesus macaques (N = 3) responded under a fixed ratio 30 schedule of food (1-g banana-flavored pellets) and IV heroin delivery. Following stable self-administration of a range of heroin doses (0.32–32 μg/kg/inj, IV), the effects of acute pretreatment with lorcaserin (0.32–1.0 mg/kg, IM) on heroin- and food-maintained responding was determined. The ability of repeated treatment with lorcaserin (1.0 mg/kg) to produce sustained decreases in heroin and/or food intake and reinforcing strength were then analyzed using behavioral economic demand procedures. Results show that self-administration of intravenous heroin was dose-dependent, with peak responding maintained, on average, by the unit dose of 3.2 μg/kg/inj. Lorcaserin pretreatment produced a dose-dependent flattening of the dose-response function for heroin self-administration in each subject. On the other hand, lorcaserin did not decrease food-maintained responding. Repeated lorcaserin treatment reduced heroin intake by selectively decreasing its reinforcing strength, as evidenced by a leftward shift in the demand curves for heroin and the absence of comparable changes in the reinforcing strength of food. These results indicate that serotonin 2 C receptor agonists, such as lorcaserin, have behaviorally selective effects on IV self-administration behavior, and deserve further consideration as candidates for the management of opioid use disorder.

The Magnitude of Intraocular Pressure Elevation Associated with Eye Rubbing

ABSTRACT Purpose To determine the magnitude of IOP elevation associated with eye rubbing Study Design Experimental Study Subjects Three nonhuman primates (NHPs) Methods Three young adult male rhesus macaques were briefly anesthetized with ketamine and dexmedetomidine, and antibiotic ointment was placed in both eyes. The anesthetic was immediately reversed with atipamezole, and the animals quickly recovered. IOP was continuously recorded at 500 measurements per second during the experiment using a validated implantable wireless telemetry system; high-definition video was recorded while the NHP rubbed its eyes to remove the ointment, and rubbing events were marked in the IOP data. The experiment was repeated four times in each NHP, with numerous eye rubs recorded for each session, and these data were marked and the IOP elevation magnitudes were analyzed using NOTOCORD-hem software. Main Outcome Measures IOP elevation above baseline IOP due to eye rubbing Results IOP increased as much as 310 mmHg due to eye rubbing. The largest IOP elevations were associated with rubbing the eye and orbit with the back of the hand or wrist, rather than the fingers or knuckle. Eye rubs elicited mean IOP elevations of ∼80-150 mmHg above baseline for 3-4 seconds, with peak IOP elevations reaching 205-310 mmHg depending on the individual NHP and eye. Conclusions Rubbing the eyes causes momentary IOP elevations that average 109 mmHg above baseline IOP and can exceed 300 mmHg above baseline IOP in NHP eyes.

Female social behaviour during three male introductions in captive groups of rhesus macaques

Introductions of new males into captive primate groups are often necessary to prevent inbreeding, but also bear high social risks. To minimize these risks, it is crucial to understand the social behaviour accompanying male introductions. While the behaviour of new males is generally understood, information on resident female behaviour during introductions is lacking. We studied female behaviour towards the new male during introductions of three adult male rhesus macaques (Macaca mulatta)—each into a different captive group. All three males were successfully introduced; respectively 100%, 92%, and 83% of the females tolerated the male as a group-member at the end of the introductions. Older females started tolerating the male significantly faster than younger females, while no additional effect of female dominance rank, fertility, or the number of female coalitionary partners on timing of tolerance was found. During the course of the integration, female aggression and submission towards the male, and male mating access decreased, while female affiliation towards the male increased. The increase of female tolerance and the changes in social behaviour were similar between the introductions, indicating a general pattern in female behaviour, although some variation in effect size and significance level was observed. Based on these results, we suggest that low female submission levels towards an introduced male may constitute a criterion to assess the risk of leaving the male in the group full-time. Moreover, low female aggression levels at the end of the introduction may signal long-term group stability. Overall, we conclude that female behaviour can provide valuable information about the male introduction process and should not be overlooked.

Assessment of stress responses in rhesus macaques (Macaca mulatta) to daily routine procedures in system neuroscience based on salivary cortisol concentrations.

Non-human primates participating in neurophysiological research are exposed to potentially stressful experimental procedures, such as dietary control protocols, surgical implants and their maintenance, or social separation during training and experimental session. Here, we investigated the effect of controlled access to fluid, surgical implants, implant-related cleaning of skin margins, and behavioral training sessions on salivary cortisol levels of adult male rhesus macaques participating in neurophysiological research. The animals were trained to chew flavored cotton swabs to non-invasively collect saliva samples. Our data show no differences in cortisol levels between animals with and without implants, but both, controlled access to fluid and cleaning of implants individually increased salivary cortisol concentrations, while both together did not further increase the concentration. Specifically, before cleaning, individuals with controlled access to fluid had 55% higher cortisol concentrations than individuals with free access to fluid. Under free access to fluid, cortisol concentrations were 27% higher after cleaning while no effect of cleaning was found for individuals under controlled fluid access. Training sessions under controlled access to fluid also did not affect salivary cortisol concentrations. The observed changes in cortisol concentrations represent mild stress responses, as they are only a fraction of the range of the regular circadian changes in cortisol levels in rhesus monkeys. They also indicate that combinations of procedures do not necessarily lead to cumulative stress responses. Our results indicate that salivary cortisol levels of rhesus monkeys respond to neurophysiological experimental procedures and, hence, may be used to assess further refinements of such experimental methods.

Effect of repeated abstinence on chronic ethanol self-administration in the rhesus monkey.

Abstinence-based approaches to treating alcohol use disorder (AUD) are highly prevalent, but abstinence from chronic drinking may exacerbate subsequent levels of alcohol intake in relapse. Use a non-human primate model that encompasses a range of chronic voluntary ethanol drinking to isolate biological responses to repeated cycles of imposed abstinence as a function of baseline voluntary alcohol drinking levels. Over a 26-month protocol, young adult male rhesus macaques were first induced to drink alcohol and then given continuous access to 4% (w/v) ethanol (n=8) or water (n=4) for approximately 14months, followed by three 28- to 35-day abstinence phases, with 3months of ethanol access in between. Ethanol intake and blood ethanol concentration (BEC) were the primary dependent variables. Observational signs of physical dependence and circulating ACTH and cortisol were monitored. Prior to abstinence, stable, categorical, individual differences in voluntary ethanol intake under chronic access conditions were found. Following abstinence, categorical "non-heavy" drinking subjects increased drinking transiently (increased between 0.7 and 1.4g/kg/day in first month after abstinence) but returned to baseline after 3months. Categorical "heavy" drinkers, however, maintained drinking 1.0-2.6g/kg above baseline for over 3months following abstinence. Signs of physical dependence were rare, although huddling and social withdrawal increased in ethanol and control subjects. The most prominent effect on hormonal measures was heightened cortisol during abstinence that increased to a greater extent in ethanol subjects. Involuntary abstinence increases drinking in the absence of overt physical withdrawal symptoms, and heavy drinkers are more robustly affected compared to non-heavy drinkers.

Preference for Averageness in Faces Does Not Generalize to Non-Human Primates.

Facial attractiveness is a long-standing topic of active study in both neuroscience and social science, motivated by its positive social consequences. Over the past few decades, it has been established that averageness is a major factor influencing judgments of facial attractiveness in humans. Non-human primates share similar social behaviors as well as neural mechanisms related to face processing with humans. However, it is unknown whether monkeys, like humans, also find particular faces attractive and, if so, which kind of facial traits they prefer. To address these questions, we investigated the effect of averageness on preferences for faces in monkeys. We tested three adult male rhesus macaques using a visual paired comparison (VPC) task, in which they viewed pairs of faces (both individual faces, or one individual face and one average face); viewing time was used as a measure of preference. We did find that monkeys looked longer at certain individual faces than others. However, unlike humans, monkeys did not prefer the average face over individual faces. In fact, the more the individual face differed from the average face, the longer the monkeys looked at it, indicating that the average face likely plays a role in face recognition rather than in judgments of facial attractiveness: in models of face recognition, the average face operates as the norm against which individual faces are compared and recognized. Taken together, our study suggests that the preference for averageness in faces does not generalize to non-human primates.