Behavioral inhibition in rhesus monkeys (Macaca mulatta) is related to the airways response, but not immune measures, commonly associated with asthma

Behavioral inhibition in a translational nonhuman primate model: A pilot study of Kagan's behavioral inhibition paradigm modified for use in infant rhesus macaques (Macaca mulatta)

Behavioral inhibition (BI), a temperamental trait first described by Jerome Kagan, is characterized by wariness to unfamiliar persons and novel situations. BI is a moderately stable trait, with biological and genetic underpinnings. Kagan's methodology for assessing BI is widely used in humans. Although this paradigm could be readily translated for use in nonhuman primates, thereby increasing generalizability from nonhuman primates to humans and fortifying evidence that BI is evolutionarily conserved, researchers have not done so. To address this, this study utilized a modified version of Kagan's paradigm to assess behaviors and biological markers of BI in nonhuman primates. Over the first 5 weeks of life, nursery-reared rhesus monkeys (Macaca mulatta; N = 12) were rated using the standardized Infant Behavior Assessment Scale for nonhuman primates on measures related to BI (consolability, irritability, struggle, and predominant state). Three months later, behavioral assessments were made in relation to a novel playroom, an unfamiliar peer, and a variety of attention-grabbing, unfamiliar stimuli, followed by the introduction of a human stranger. Behaviors from Kagan's studies of BI in toddlers (freezing, exploration, and latency to approach) and physiological measures related to BI (heart rate) were assessed. Random effects models showed that subjects rated high in temperamental BI spent less time exploring the environment and socializing with peers and more time freezing (an indication of anxiety in rhesus monkeys). These findings suggest that Kagan's paradigm is readily adapted for use in nonhuman primates and support the utility of rhesus monkeys as translational models for assessing the causes and consequences of human BI. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Variation in infant rhesus monkeys' (Macaca mulatta) neutrophil-to-lymphocyte ratio is associated with environmental conditions, emotionality, and cortisol concentrations, and predicts disease-related outcomes

The neutrophil-to-lymphocyte ratio (NLR) is a predictor of morbidity for a variety of medical conditions, but little is known about how variation in NLR arises. We examined variation in this measure in a sample of 4577 infant rhesus monkeys (54.8 % female), who participated in the BioBehavioral Assessment program at the California National Primate Research Center at 3-4 months of age. Lower values for NLR were seen for animals reared indoors, for animals that were raised to be free of specific pathogens, and for males. In addition lower NLR was associated with higher stress values of cortisol and with greater emotionality in response to an acute stressor. Finally, lower NLR in infancy was associated with greater risk for developing airways hyperresponsiveness (a hallmark of asthma); with display of diarrhea up to 3.97 years later; and with greater viral load when infected with the simian immunodeficiency virus at a mean of 6.1 years of age. Infant NLR was a better predictor of viral load than was a contemporaneously obtained measure of NLR. Infant and adult values of NLR were only modestly correlated; one reason may be that the infant measure was obtained during stressful conditions and the adult measure was obtained under baseline conditions. We propose that NLR is an integrated outcome measure reflecting organization and interaction of stress-response and immune systems. As such, assessment of NLR under conditions of stress may be a particularly useful marker of individual differences in morbidity, especially for conditions in which stress plays an important role, as in asthma, diarrhea/colitis, and AIDS.

The relationship of maternal rank, 5-HTTLPR genotype, and MAOA-LPR genotype to temperament in infant rhesus monkeys (Macaca mulatta)

Temperament is a construct whose manifestations are quantifiable from an early age, and whose origins have been proposed as "biological." Our goal was to determine whether maternal rank and infant genotype are associated with five measures of temperament in 3- to 4-month old rhesus monkeys (Macaca mulatta), all of whom were born and reared by their mothers in large, outdoor, half-acre cages. Maternal rank was defined as the proportion of animals outranked by each female, and the two genes of interest to us were monoamine oxidase and serotonin transporter, both of which are polymorphic in their promoter regions (MAOA-LPR and 5-HTTLPR, respectively), with one allele of each gene considered a "plasticity" allele, conferring increased sensitivity to environmental events. Our large sample size (n = 2014-3140) enabled us to examine the effects of individual genotypes rather than combining genotypes as is often done. Rank was positively associated with Confident temperament, but only for animals with the 5-repeat allele for MAOA-LPR. Rank had no other effect on temperament. In contrast, genotype had many different effects, with 5-HTTLPR associated with behavioral inhibition, and MAOA-LPR associated with ratings-based measures of temperament. We also examined the joint effect of the two genotypes and found some evidence for a dose-response: animals with the plasticity alleles for both genes were more likely to be behaviorally inhibited. Our results suggest phenotypic differences between animals possessing alleles for MAOA-LPR that show functional equivalence based on in vitro tests, and our data for 5-HTTLPR revealed differences between short/short homozygotes and long/short heterozygotes, strongly suggesting that combining genotypes for statistical analysis should be avoided if possible. Our analysis also provides evidence of sex differences in temperament, and, to our knowledge, the only evidence of differences in temperament based on specific pathogen-free status. We suggest several directions for future research.

A Novel Nonhuman Primate Model of Nonatopic Asthma

Nonhuman primate models have an essential role in understanding progressive respiratory disease pathogenesis. Immune and physiologic parameters in the nonhuman primate closely reflect the complexity of human systems and provide an exceptional translational impact for the investigation of the mucosal immune changes in response to environmental exposures. This potential warrants the development of novel models that will clarify the interaction of respiratory disease and the inhalable environment and the potential of novel therapies to alleviate the untoward results of these interactions. Nonhuman primate models of asthma can be spontaneous, induced, or experimentally manipulated by various exposures. Here we describe a model of exacerbation of airway hyperreactivity induced by exposure to an air pollutant, ozone, in a cohort of young adult asthmatic rhesus macaques.

Knowledge of Biobehavioral Organization Can Facilitate Better Science: A Review of the BioBehavioral Assessment Program at the California National Primate Research Center

Animals vary on intrinsic characteristics such as temperament and stress responsiveness, and this information can be useful to experimentalists for identifying more homogeneous subsets of animals that show consistency in risk for a particular research outcome. Such information can also be useful for balancing experimental groups, ensuring animals within an experiment have similar characteristics. In this review, we describe the BioBehavioral Assessment Program at the California National Primate Research Center, which, since its inception in 2001, has been providing quantitative information on intrinsic characteristics to scientists for subject selection and balancing, and to colony management staff for management purposes. We describe the program and review studies relating to asthma, autism, behavioral inhibition, etc., where the BBA Program was used to select animals. We also review our work, showing that factors such as rearing, ketamine exposure, and prenatal experience can affect biobehavioral organization in ways that some investigators might want to control for in their studies. Attention to intrinsic characteristics of subject populations is consistent with the growing interest in precision medicine and can lead to a reduction in animal numbers, savings in time and money for investigators, and reduced distress for the animals.

Lipid metabolism is associated with temperament, corticosteroid, and hematological measures in infant rhesus monkeys ( Macaca mulatta)

Individuals can differ in how their behavioral and physiological systems are organized. The fact that these individual differences persist across life suggests they are supported by physical structures that may co-vary. Here, we explored three datasets associated with health and behavioral outcomes, which were obtained from infant rhesus monkeys during standardized assessment of biobehavioral organization. Variation in biobehavioral measures was related to variation in molecular pathways, as assessed by metabolomics. Plasma from infant male rhesus monkeys ( Macaca mulatta) ( n=52) was subjected to metabolite profiling. Principal component analyses identified multiple factors that explained 60%-80% of the variance in the metabolite measures. Correlational and regression analyses of corticosteroid, hematological, and temperament measures revealed significant relationships with indicators of lipid metabolism. Significant relationships were found for cortisol responses to stress and adrenocorticotropin (ACTH) stimulation, indicators of innate immunity (monocytes and natural killer (NK) cells), hemoglobin/hematocrit, and three measures of temperament. It will be important to replicate this first-of-a-kind study to determine whether the relationship between measures of biobehavioral organization and lipid metabolism are a general result, or one that is specific to early development.

Ozone-induced enhancement of airway hyperreactivity in rhesus macaques: Effects of antioxidant treatment

BACKGROUND

Ozone (O3) inhalation elicits airway inflammation and impairs treatment responsiveness in asthmatic patients. The underlying immune mechanisms have been difficult to study because of the lack of relevant experimental models. Rhesus macaques spontaneously have asthma and have a similar immune system to human subjects.

OBJECTIVES

We sought to investigate mucosal immune changes after O3 inhalation in a clinically relevant nonhuman primate asthma model and to study the effects of an antioxidant synthetic lignan (synthetic secoisolariciresinol diglucoside [LGM2605]).

METHODS

A cohort of macaques (n = 17) previously characterized with airway hyperreactivity (AHR) to methacholine was assessed (day 1). Macaques were treated (orally) with LGM2605 (25 mg/kg) or placebo twice per day for 7 days, exposed to 0.3 ppm O3 or air for 6 hours (on day 7), and studied 12 hours later (day 8). Lung function, blood and bronchoalveolar lavage (BAL) fluid immune cell profile, and bronchial brushing and blood cell mRNA expression were assessed.

RESULTS

O3 induced significant BAL fluid neutrophilia and eosinophilia and increased AHR and expression of IL6 and IL25 mRNA in the airway epithelium together with increased BAL fluid group 2 innate lymphoid cell (ILC2s), CD1c+ myeloid dendritic cell, and CD4+ T-cell counts and diminished surfactant protein D expression. Although LGM2605 attenuated some of the immune and inflammatory changes, it completely abolished O3-induced AHR.

CONCLUSION

ILC2s, CD1c+ myeloid dendritic cells, and CD4+ T cells are selectively involved in O3-induced asthma exacerbation. The inflammatory changes were partially prevented by antioxidant pretreatment with LGM2605, which had an unexpectedly disproportionate protective effect on AHR.

Naturally Occurring Nonhuman Primate Models of Psychosocial Processes

Human research into psychological processes such as anxiety, depression, or loneliness typically involves accruing cases in which the phenomenon of interest is naturally occurring, and then comparing such a sample with control cases. In contrast, animal research designed to model similar processes to test mechanistic hypotheses typically involves inducing the phenomenon of interest via some exogenously (i.e., human) administered procedure. In the present review, the author proposes that naturally occurring animal models can complement induced models in understanding complex psychological phenomena. Advantages and disadvantages of naturally occurring versus induced models are described, and detailed examples of three naturally occurring models-for loneliness and health, behavioral inhibition and asthma, and social functioning and autism-are described, along with a formal program (the BioBehavioral Assessment program) at the California National Primate Research Center, that is designed to quantify variation in biobehavioral processes in infant rhesus macaques to facilitate development of naturally occurring models. It is argued that, because of the similarity in complex behavioral and psychological processes between macaques and humans, naturally occurring primate models provide a bridge between human studies and induced primate models and have the potential to identify new models for translational research.

Nonhuman Primate Models of Respiratory Disease: Past, Present, and Future

The respiratory system consists of an integrated network of organs and structures that primarily function for gas exchange. In mammals, oxygen and carbon dioxide are transmitted through a complex respiratory tract, consisting of the nasal passages, pharynx, larynx, and lung. Exposure to ambient air throughout the lifespan imposes vulnerability of the respiratory system to environmental challenges that can contribute toward development of disease. The importance of the respiratory system to human health is supported by statistics from the Centers for Disease Control and Prevention; in 2015, chronic lower respiratory diseases were the third leading cause of death in the United States. In light of the significant mortality associated with respiratory conditions that afflict all ages of the human population, this review will focus on basic and preclinical research conducted in nonhuman primate models of respiratory disease. In comparison with other laboratory animals, the nonhuman primate lung most closely resembles the human lung in structure, physiology, and mucosal immune mechanisms. Studies defining the influence of inhaled microbes, pollutants, or allergens on the nonhuman primate lung have provided insight on disease pathogenesis, with the potential for elucidation of molecular targets leading to new treatment modalities. Vaccine trials in nonhuman primates have been crucial for confirmation of safety and protective efficacy against infectious diseases of the lung in a laboratory animal model that recapitulates pathology observed in humans. In looking to the future, nonhuman primate models of respiratory diseases will continue to be instrumental for translating biomedical research for improvement of human health.

Developmental consequences of behavioral inhibition: a model in rhesus monkeys (Macaca mulatta)

In children, behavioral inhibition is characterized by a disposition to withdraw in the presence of strangers and novel situations. Later in life, behavioral inhibition can result in an increased risk for anxiety and depression and a decrease in social behavior. We selected rhesus monkeys that, during infancy, showed evidence of behavioral inhibition in response to separation, and contrasted them with non-inhibited peers. To understand the development of behavioral inhibition at juvenile age, we collected behavioral data in response to relocation; in response to a human intruder challenge; and in naturalistic outdoor field corrals. At 4 years of age (young adulthood), we again collected behavioral data in the outdoor field corrals to understand the adult social consequences of behavioral inhibition. We also included sex, dominance rank, and number of available kin in our analyses. Finally, to understand the consistency in behavior in behaviorally inhibited animals, we conducted exploratory analyses contrasting behaviorally inhibited animals that showed high vs. low durations of non-social behaviors as adults. At juvenile age, behaviorally inhibited animals continued to show behavioral differences in the novel testing room and during the human intruder challenge, generally showing evidence of greater anxiety and emotionality compared to non-inhibited controls. In their outdoor corrals, behaviorally inhibited juveniles spent more time alone and less time in proximity and grooming with mother and other adult females. In young adulthood, we found that behavioral inhibition was not related to time spent alone. We did find that duration of time alone in adulthood was related to time alone exhibited as juveniles; sex, dominance rank, or the number of kin were not influential in adult non-social duration, either as main effects or as moderators. Finally, exploratory analyses revealed that behaviorally inhibited females that were more sociable (less time spent alone) as adults had spent more time grooming as juveniles, suggesting that high-quality social interaction at a young age might mitigate the social consequences of behavioral inhibition. Overall, we believe that the many similarities with the human data that we found suggest that this monkey model of naturally occurring behavioral inhibition can be valuable for understanding social development.

Paternal early experiences influence infant development through non-social mechanisms in Rhesus Macaques

BACKGROUND

Early experiences influence the developing organism, with lifelong and potentially adaptive consequences. It has recently become clear that the effects of early experiences are not limited to the exposed generation, but can influence physiological and behavioral traits in the next generation. Mechanisms of transgenerational effects of parental early experiences on offspring development are often attributed to prenatal or postnatal parental influence, but recent data suggest that germ-line plasticity may also play a role in the transgenerational effects of early experiences. These non-genetic transgenerational effects are a potentially important developmental and evolutionary force, but the effects of parental experiences on behavior and physiology are not well understood in socially complex primates. In the non-human primate, the rhesus macaque, nursery rearing (NR) is an early life manipulation used for colony management purposes, and involves separating infants from parents early in life. We examined the effects of maternal and paternal early NR on infant rhesus macaque immunity, physiology, and behavior.

RESULTS

We theorized that differences in behavior or physiology in the absence of parent-offspring social contact would point to biological and perhaps germ-line, rather than social, mechanisms of effect. Thus, all subjects were themselves NR. Male and female infant rhesus macaques (N= 206) were separated from parents and social groups in the first four days of life to undergo NR. These infants differed only in their degree of NR ancestry - whether their dams or sires were themselves NR. At 3-4 months of age, infants underwent a standardized biobehavioral assessment. Factors describing immunity, plasma cortisol, and emotion regulation were generated from these data using factor analysis. Paternal, but not maternal, NR was associated with greater emotionality and higher plasma cortisol, compared with infants born to CONTROL reared fathers.

CONCLUSIONS

These data suggest that macaque biobehavioral makeup is strongly influenced by paternal experiences, and via non-social mechanisms.