Extracellular free water elevations are associated with brain volume and maternal cytokine response in a longitudinal nonhuman primate maternal immune activation model

Maternal infection has emerged as an important environmental risk factor for neurodevelopmental disorders, including schizophrenia and autism spectrum disorders. Animal model systems of maternal immune activation (MIA) suggest that the maternal immune response plays a significant role in the offspring's neurodevelopment and behavioral outcomes. Extracellular free water is a measure of freely diffusing water in the brain that may be associated with neuroinflammation and impacted by MIA. The present study evaluates the brain diffusion characteristics of male rhesus monkeys (Macaca mulatta) born to MIA-exposed dams (n = 14) treated with a modified form of the viral mimic polyinosinic:polycytidylic acid at the end of the first trimester. Control dams received saline injections at the end of the first trimester (n = 10) or were untreated (n = 4). Offspring underwent diffusion MRI scans at 6, 12, 24, 36, and 45 months. Offspring born to MIA-exposed dams showed significantly increased extracellular free water in cingulate cortex gray matter starting as early as 6 months of age and persisting through 45 months. In addition, offspring gray matter free water in this region was significantly correlated with the magnitude of the maternal IL-6 response in the MIA-exposed dams. Significant correlations between brain volume and extracellular free water in the MIA-exposed offspring also indicate converging, multimodal evidence of the impact of MIA on brain development. These findings provide strong evidence for the construct validity of the nonhuman primate MIA model as a system of relevance for investigating the pathophysiology of human neurodevelopmental psychiatric disorders. Elevated free water in individuals exposed to immune activation in utero could represent an early marker of a perturbed or vulnerable neurodevelopmental trajectory.

Calorie restriction and pravastatin administration during pregnancy in obese rhesus macaques modulates maternal and infant metabolism and infant brain and behavioral development

Background

Maternal obesity has been associated with a higher risk of pregnancy-related complications in mothers and offspring; however, effective interventions have not yet been developed. We tested two interventions, calorie restriction and pravastatin administration, during pregnancy in a rhesus macaque model with the hypothesis that these interventions would normalize metabolic dysregulation in pregnant mothers leading to an improvement in infant metabolic and cognitive/social development.

Methods

A total of 19 obese mothers were assigned to either one of the two intervention groups (n = 5 for calorie restriction; n = 7 for pravastatin) or an obese control group (n = 7) with no intervention, and maternal gestational samples and postnatal infant samples were compared with lean control mothers (n = 6) using metabolomics methods.

Results

Gestational calorie restriction normalized one-carbon metabolism dysregulation in obese mothers, but altered energy metabolism in her offspring. Although administration of pravastatin during pregnancy tended to normalize blood cholesterol in the mothers, it potentially impacted the gut microbiome and kidney function of their offspring. In the offspring, both calorie restriction and pravastatin administration during pregnancy tended to normalize the activity of AMPK in the brain at 6 months, and while results of the Visual Paired-Comparison test, which measures infant recognition memory, was not significantly impacted by either of the interventions, gestational pravastatin administration, but not calorie restriction, tended to normalize anxiety assessed by the Human Intruder test.

Conclusions

Although the two interventions tested in a non-human primate model led to some improvements in metabolism and/or infant brain development, negative impacts were also found in both mothers and infants. Our study emphasizes the importance of assessing gestational interventions for maternal obesity on both maternal and offspring long-term outcomes.

Increased Striatal Presynaptic Dopamine in a Nonhuman Primate Model of Maternal Immune Activation: A Longitudinal Neurodevelopmental Positron Emission Tomography Study With Implications for Schizophrenia

BACKGROUND

Epidemiological studies suggest that maternal immune activation (MIA) is a significant risk factor for future neurodevelopmental disorders, including schizophrenia (SZ), in offspring. Consistent with findings in SZ research and work in rodent systems, preliminary cross-sectional findings in nonhuman primates suggest that MIA is associated with dopaminergic hyperfunction in young adult offspring.

METHODS

In this unique prospective longitudinal study, we used [18F]fluoro-l-m-tyrosine positron emission tomography to examine the developmental time course of striatal presynaptic dopamine synthesis in male rhesus monkeys born to dams (n = 13) injected with a modified form of the inflammatory viral mimic, polyinosinic:polycytidylic acid [poly(I:C)], in the late first trimester. Striatal (caudate, putamen, and nucleus accumbens) dopamine from these animals was compared with that of control offspring born to dams that received saline (n = 10) or no injection (n = 4). Dopamine was measured at 15, 26, 38, and 48 months of age. Prior work with this cohort found decreased prefrontal gray matter volume in MIA offspring versus controls between 6 and 45 months of age. Based on theories of the etiology and development of SZ-related pathology, we hypothesized that there would be a delayed (relative to the gray matter decrease) increase in striatal fluoro-l-m-tyrosine signal in the MIA group versus controls.

RESULTS

[18F]fluoro-l-m-tyrosine signal showed developmental increases in both groups in the caudate and putamen. Group comparisons revealed significantly greater caudate dopaminergic signal in the MIA group at 26 months.

CONCLUSIONS

These findings are highly relevant to the known pathophysiology of SZ and highlight the translational relevance of the MIA model in understanding mechanisms by which MIA during pregnancy increases risk for later illness in offspring.

Multi-omic brain and behavioral correlates of cell-free fetal DNA methylation in macaque maternal obesity models

Maternal obesity during pregnancy is associated with neurodevelopmental disorder (NDD) risk. We utilized integrative multi-omics to examine maternal obesity effects on offspring neurodevelopment in rhesus macaques by comparison to lean controls and two interventions. Differentially methylated regions (DMRs) from longitudinal maternal blood-derived cell-free fetal DNA (cffDNA) significantly overlapped with DMRs from infant brain. The DMRs were enriched for neurodevelopmental functions, methylation-sensitive developmental transcription factor motifs, and human NDD DMRs identified from brain and placenta. Brain and cffDNA methylation levels from a large region overlapping mir-663 correlated with maternal obesity, metabolic and immune markers, and infant behavior. A DUX4 hippocampal co-methylation network correlated with maternal obesity, infant behavior, infant hippocampal lipidomic and metabolomic profiles, and maternal blood measurements of DUX4 cffDNA methylation, cytokines, and metabolites. We conclude that in this model, maternal obesity was associated with changes in the infant brain and behavior, and these differences were detectable in pregnancy through integrative analyses of cffDNA methylation with immune and metabolic factors.

Maternal Immune Activation during Pregnancy Alters Postnatal Brain Growth and Cognitive Development in Nonhuman Primate Offspring

Human epidemiological studies implicate exposure to infection during gestation in the etiology of neurodevelopmental disorders. Animal models of maternal immune activation (MIA) have identified the maternal immune response as the critical link between maternal infection and aberrant offspring brain and behavior development. Here we evaluate neurodevelopment of male rhesus monkeys (Macaca mulatta) born to MIA-treated dams (n = 14) injected with a modified form of the viral mimic polyinosinic:polycytidylic acid at the end of the first trimester. Control dams received saline injections at the same gestational time points (n = 10) or were untreated (n = 4). MIA-treated dams exhibited a strong immune response as indexed by transient increases in sickness behavior, temperature, and inflammatory cytokines. Although offspring born to control or MIA-treated dams did not differ on measures of physical growth and early developmental milestones, the MIA-treated animals exhibited subtle changes in cognitive development and deviated from species-typical brain growth trajectories. Longitudinal MRI revealed significant gray matter volume reductions in the prefrontal and frontal cortices of MIA-treated offspring at 6 months that persisted through the final time point at 45 months along with smaller frontal white matter volumes in MIA-treated animals at 36 and 45 months. These findings provide the first evidence of early postnatal changes in brain development in MIA-exposed nonhuman primates and establish a translationally relevant model system to explore the neurodevelopmental trajectory of risk associated with prenatal immune challenge from birth through late adolescence.SIGNIFICANCE STATEMENT Women exposed to infection during pregnancy have an increased risk of giving birth to a child who will later be diagnosed with a neurodevelopmental disorder. Preclinical maternal immune activation (MIA) models have demonstrated that the effects of maternal infection on fetal brain development are mediated by maternal immune response. Since the majority of MIA models are conducted in rodents, the nonhuman primate provides a unique system to evaluate the MIA hypothesis in a species closely related to humans. Here we report the first longitudinal study conducted in a nonhuman primate MIA model. MIA-exposed offspring demonstrate subtle changes in cognitive development paired with marked reductions in frontal gray and white matter, further supporting the association between prenatal immune challenge and alterations in offspring neurodevelopment.

New approaches to quantify social development in rhesus macaques (Macaca mulatta): Integrating eye tracking with traditional assessments of social behavior

The nonhuman primate provides a sophisticated animal model system both to explore neurobiological mechanisms underlying complex behaviors and to facilitate preclinical research for neurodevelopmental and neuropsychiatric disease. A better understanding of evolutionarily conserved behaviors and brain processes between humans and nonhuman primates will be needed to successfully apply recently released NIMH guidelines (NOT-MH-19-053) for conducting rigorous nonhuman primate neurobehavioral research. Here, we explore the relationship between two measures of social behavior that can be used in both humans and nonhuman primates-traditional observations of social interactions with conspecifics and eye gaze detection in response to social stimuli. Infant male rhesus macaques (Macaca mulatta) serving as controls (N = 14) for an ongoing study were observed in their social rearing groups and participated in a noninvasive, longitudinal eye-tracking study. We found significant positive relationships between time spent viewing eyes of faces in an eye tracker and number of initiations made for social interactions with peers that is consistent with similar observations in human populations. Although future studies are needed to determine if this relationship represents species-typical social developmental processes, these preliminary results provide a novel framework to explore the relationship between social interactions and social attention in nonhuman primate models for neurobehavioral development.

Serotonin Transporter Binding Potentials in Brain of Juvenile Monkeys 1 Year After Discontinuation of a 2-Year Treatment With Fluoxetine

BACKGROUND

The potential long-term effects of childhood fluoxetine therapy on brain serotonin systems were studied using a nonhuman primate model, the rhesus monkey.

METHODS

Juvenile male rhesus (1-4 years of age, corresponding to 4-11 years of age in children) were treated orally with fluoxetine (2 mg/kg) or vehicle daily for 2 years and removed from treatment during the third year. Each treatment group was assigned an equal number of subjects with low and high transcription polymorphisms of MAOA. One year after discontinuation of treatment, positron emission tomography scans were conducted (n = 8 treated monkeys, n = 8 control monkeys) using [¹¹C]DASB to quantify serotonin transporter in 16 cortical and subcortical regions.

RESULTS

Fluoxetine-treated monkeys with MAOA low transcription polymorphism had significantly lower [¹¹C]DASB binding potentials than control monkeys. This finding was seen throughout the brain but was strongest in prefrontal and cingulate cortices. The MAOA × fluoxetine interaction was enhanced by binding potentials that were nonsignificantly higher in monkeys with high transcription polymorphism.

CONCLUSIONS

Juvenile fluoxetine treatment has residual posttreatment effects on brain serotonin transporter that depend on MAOA genotype. MAOA genotype may be important to consider when treating children with fluoxetine.

Non-invasive Eye Tracking Methods for New World and Old World Monkeys

Eye-tracking methods measure what humans and other animals visually attend to in the environment. In nonhuman primates, eye tracking can be used to test hypotheses about how primates process social information. This information can further our understanding of primate behavior as well as offer unique translational potential to explore causes of or treatments for altered social processing as seen in people with neurodevelopmental disorders such as autism spectrum disorder and schizophrenia. However, previous methods for collecting eye-tracking data in nonhuman primates required some form of head restraint, which limits the opportunities for research with respect to the number of or kinds of primates that can undergo an eye-tracking study. We developed a novel, noninvasive method for collecting eye tracking data that can be used both in animals that are difficult to restrain without sedation as well as animals that are of different ages and sizes as the box size can be adjusted. Using a transport box modified with a viewing window, we collected eye-tracking data in both New (Callicebus cupreus) and Old World monkeys (Macaca mulatta) across multiple developmental time points. These monkeys had the option to move around the box and avert their eyes from the screen, yet, they demonstrated a natural interest in viewing species-specific imagery with no previous habituation to the eye-tracking paradigm. Provided with opportunistic data from voluntary viewing of stimuli, we found that juveniles viewed stimuli more than other age groups, videos were viewed more than static photo imagery, and that monkeys increased their viewing time when presented with multiple eye tracking sessions. This noninvasive approach opens new opportunities to integrate eye-tracking studies into nonhuman primate research.

Opportunities and challenges for intranasal oxytocin treatment studies in nonhuman primates

Nonhuman primates provide a human-relevant experimental model system to explore the mechanisms by which oxytocin (OT) regulates social processing and inform its clinical applications. Here, we highlight contributions of the nonhuman primate model to our understanding of OT treatment and address unique challenges in administering OT to awake behaving primates. Prior preclinical research utilizing macaque monkeys has demonstrated that OT can modulate perception of other individuals and their expressions, attention to others, imitation, vigilance to social threats, and prosocial decisions. We further describe ongoing efforts to develop an OT delivery system for use in experimentally naïve juvenile macaque monkeys compatible with naturalistic social behavior outcomes. Finally, we discuss future directions to further develop the rhesus monkey as a preclinical test bed to evaluate the effects of OT exposure and advance efforts to translate basic science OT research into safe and effective OT therapies.

Fluoxetine Administration in Juvenile Monkeys: Implications for Pharmacotherapy in Children

Fluoxetine therapy has been approved for children with major depressive disorder and obsessive compulsive disorder for over 14 years and has expanded to other childhood behavior disorders. As use increases, more detail on fluoxetine effects during juvenile brain development can help maintain safe and effective use of this therapy. Here, a narrative review is provided of previously published findings from a large nonhuman primate project. Fluoxetine was administered to juvenile male rhesus monkeys for an extended period (2 years) prior to puberty. Compared to controls, treated monkeys showed sleep disruption, facilitated social interaction, greater impulsivity, and impaired sustained attention during treatment. No effects on growth were seen. Metabolomics assays characterized a distinctive response to fluoxetine and demonstrated individual differences that were related to the impulsivity measure. Fluoxetine interactions with monoamine oxidase A polymorphisms that influenced behavior and metabolomics markers were an important, previously unrecognized finding of our studies. After treatment was discontinued, some behavioral effects persisted, but short-term memory and cognitive flexibility testing did not show drug effects. This detailed experimental work can contribute to clinical research and continued safe and effective fluoxetine pharmacotherapy in children.

Regulation of emotional response in juvenile monkeys treated with fluoxetine: MAOA interactions

Juvenile male rhesus macaques received therapeutic doses of fluoxetine daily from one to three years of age and were compared to vehicle-treated controls (N=16/group). Genotyping for monoamine oxidase A (MAOA) polymorphisms was used to form subgroups (N=8) with high and low expression of the gene. Behavioral responses were scored during 30-second exposures to pictures differing in affective content. As expected from its therapeutic effect, fluoxetine decreased the behavioral response to emotionally evocative pictures. A 44% reduction in number of expressive behaviors was seen, but only in subjects with low expression MAOA polymorphisms. In general, this effect occurred for pictures of varying affective content and was not due to altered occurrence of one specific behavior or type of behavior. The drug*genotype interaction was seen after one and two years of treatment and did not reverse one year after discontinuation of dosing. Two potential translational implications are suggested: (1) MAOA genetic polymorphisms may be the source of some of the variability in response to fluoxetine treatment in children; (2) extended fluoxetine treatment during juvenile brain development may result in persistent effects on emotional regulation.

Sleep disturbance as detected by actigraphy in pre-pubertal juvenile monkeys receiving therapeutic doses of fluoxetine

Sleep disturbance is a reported side effect of antidepressant drugs in children. Using a nonhuman primate model of childhood selective serotonin reuptake inhibitor (SSRI) therapy, sleep was studied quantitatively with actigraphy. Two 48-h sessions were recorded in the home cage environment of juvenile male rhesus monkeys at two and three years of age, after one and two years of treatment with a therapeutic dose of the SSRI fluoxetine, and compared to vehicle treated controls. A third session was conducted one year after discontinuation of treatment at four years of age. During treatment, the fluoxetine group demonstrated sleep fragmentation as indexed by a greater number of rest-activity transitions compared to controls. In addition fluoxetine led to more inactivity during the day as indexed by longer duration of rest periods and the reduced activity during these periods. The fluoxetine effect on sleep fragmentation, but not on daytime rest, was modified by the monkey's genotype for polymorphisms of monoamine oxidase A (MAOA), an enzyme that metabolizes serotonin. After treatment, the fluoxetine effect on nighttime rest-activity transitions persisted, but daytime activity was not affected. The demonstration in this nonhuman primate model of sleep disturbance in connection with fluoxetine treatment and specific genetic polymorphisms, and in the absence of diagnosed psychopathology, can help inform use of this drug in children.

Peer social interaction is facilitated in juvenile rhesus monkeys treated with fluoxetine

Fluoxetine improves social interactions in children with autism, social anxiety and social phobia. It is not known whether this effect is mediated directly or indirectly by correcting the underlying pathology. Genetics may also influence the drug effect. Polymorphisms of the MAOA (monoamine oxidase A) gene interact with fluoxetine to influence metabolic profiles in juvenile monkeys. Juvenile nonhuman primates provide an appropriate model for studying fluoxetine effects and drug*gene interactions in children. Male rhesus monkeys 1-3 years of age living in permanent social pairs were treated daily with a therapeutic dose of fluoxetine or vehicle (n = 16/group). Both members of each social pair were assigned to the same treatment group. They were observed for social interactions with their familiar cagemate over a 2-year dosing period. Subjects were genotyped for MAOA variable number of tandem repeats (VNTR) polymorphisms categorized for high or low transcription rates (hi-MAOA, low-MAOA). Fluoxetine-treated animals spent 30% more time in social interaction than vehicle controls. Fluoxetine significantly increased the duration of quiet interactions, the most common type of interaction, and also of immature sexual behavior typical of rhesus in this age group. Specific behaviors affected depended on MAOA genotype of the animal and its social partner. When given fluoxetine, hi-MOAO monkeys had more social invitation and initiation behaviors and low-MAOA subjects with low-MAOA partners had more grooming and an increased frequency of some facial and vocal expressive behaviors. Fluoxetine may facilitate social interaction in children independent of remediation of psychopathology. Common genetic variants may modify this effect.

Bone growth in juvenile rhesus monkeys is influenced by 5HTTLPR polymorphisms and interactions between 5HTTLPR polymorphisms and fluoxetine

Male rhesus monkeys received a therapeutic oral dose of the selective serotonin reuptake inhibitor (SSRI) fluoxetine daily from 1 to 3 years of age. Puberty is typically initiated between 2 and 3 years of age in male rhesus and reproductive maturity is reached at 4 years. The study group was genotyped for polymorphisms in the monoamine oxidase A (MAOA) and serotonin transporter (SERT) genes that affect serotonin neurotransmission. Growth was assessed with morphometrics at 4 month intervals and radiographs of long bones were taken at 12 month intervals to evaluate skeletal growth and maturation. No effects of fluoxetine, or MAOA or SERT genotype were found for growth during the first year of the study. Linear growth began to slow during the second year of the study and serotonin reuptake transporter (SERT) long polymorphic region (5HTTLPR) polymorphism effects with drug interactions emerged. Monkeys with two SERT 5HTTLPR L alleles (LL, putative greater transcription) had 25-39% less long bone growth, depending on the bone, than monkeys with one S and one L allele (SL). More advanced skeletal maturity was also seen in the LL group, suggesting earlier onset of puberty. An interaction between 5HTTLPR polymorphisms and fluoxetine was identified for femur and tibia growth; the 5HTTLPR effect was seen in controls (40% less growth for LL) but not in the fluoxetine treated group (10% less growth for LL). A role for serotonin in peripubertal skeletal growth and maturation has not previously been investigated but may be relevant to treatment of children with SSRIs.

Fetal iron deficiency and genotype influence emotionality in infant rhesus monkeys

BACKGROUND

Anemia during the third trimester of fetal development affects one-third of the pregnancies in the United States and has been associated with postnatal behavioral outcomes. This study examines how fetal iron deficiency (ID) interacts with the fetal monoamine oxidase A (MAOA) genotype. MAOA metabolizes monoamine neurotransmitters. MAOA polymorphisms in humans affect temperament and modify the influence of early adverse environments on later behavior.

OBJECTIVE

The aim of the study was to advance translation of developmental ID research in animal models by taking into account genetic factors that influence outcomes in human populations.

METHODS

Male infant rhesus monkeys 3-4 mo old born to mothers fed an ID (10 ppm iron) diet were compared with controls (100 ppm iron). Infant monkeys with high- or low-transcription rate MAOA polymorphisms were equally distributed between diet groups. Behavioral responses to a series of structured experiences were recorded during a 25-h separation of the infants from their mothers.

RESULTS

Infant monkeys with low-transcription MAOA polymorphisms more clearly demonstrated the following ID effects suggested in earlier studies: a 4% smaller head circumference, a 39% lower cortisol response to social separation, a 129% longer engagement with novel visual stimuli, and 33% lesser withdrawal in response to a human intruder. The high MAOA genotype ID monkeys demonstrated other ID effects: less withdrawal and emotionality after social separation and lower "fearful" ratings.

CONCLUSION

MAOA × ID interactions support the role of monoamine neurotransmitters in prenatal ID effects in rhesus monkeys and the potential involvement of common human polymorphisms in determining the pattern of neurobehavioral effects produced by inadequate prenatal nutrition.

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.

Developmental plasticity of red blood cell homeostasis

Most human physiologic set points like body temperature are tightly regulated and show little variation between healthy individuals. Red blood cell (RBC) characteristics such as hematocrit and mean cell volume are stable within individuals but can vary by 20% from one healthy person to the next. The mechanisms for the majority of this inter-individual variation are unknown and do not appear to involve common genetic variation. Here, we show that environmental conditions present during development, namely in utero iron availability, can exert long-term influence on a set point related to the RBC life cycle. In a controlled study of rhesus monkeys and a retrospective study of humans, we use a mathematical model of in vivo RBC population dynamics to show that in utero iron deficiency is associated with a lowered threshold for RBC clearance and turnover. This in utero effect is plastic, persisting at least 2 years after birth and after the cessation of iron deficiency. Our study reports a rare instance of developmental plasticity in the human hematologic system and also shows how mathematical modeling can be used to identify cellular mechanisms involved in the adaptive control of homeostatic set points.

Binge drinking prior to pregnancy detection in a nonhuman primate: behavioral evaluation of offspring

BACKGROUND

Minimal scientific information is available to inform public health policy on binge drinking prior to pregnancy detection. The nonhuman primate provides a valuable animal model for examining consequences to reproduction and offspring function that may result from this common pattern of alcohol abuse.

METHODS

Adult female rhesus monkeys were dosed with 1.5 g/kg per day ethanol (EtOH) by gavage 2 d/wk beginning 7 months prior to mating and continuing to pregnancy detection at 19 to 20 days gestation. Postnatal evaluation of control (n = 6) and EtOH-treated (n = 4) infants included a neonatal neurobehavioral assessment, a visual paired comparison (cognitive) test at 35 days of age, and mother-infant interaction at 100 to 112 days of age.

RESULTS

Alcohol-exposed neonates did not differ from controls in posture and reflex measures. Longer durations of visual fixation, suggesting slower visual processing, and greater novelty preference were seen in the alcohol group. At early weaning age, as infants spent more time away from their dams, more of the reunions between mother and infant were initiated by the mothers in the alcohol-exposed group, suggesting a more immature mother-infant interaction.

CONCLUSIONS

Intermittent high-dose alcohol exposure (binge drinking) discontinued at early pregnancy detection in rhesus monkey can result in altered behavioral function in the infant. Mediating effects on ovum, reproductive tract, and early embryo can be explored in this model. Studies of longer-term consequences in human populations and animal models are needed.

Predictors of hemoglobin variability in a population of weaning age (3- to 4-month old) rhesus monkeys

Sources of variability in hemoglobin concentration in blood were examined in over 600 rhesus infants at the California National Primate Research Center who had complete blood counts (CBCs) conducted at 3-4 months of age. These infants were born and raised in outdoor social housing. Hemoglobin values ranged from 8.5 to 15.3 µg/dl with a mean and standard deviation of 12.2±0.8 µg/dl. As expected, hemoglobin was strongly associated with the number of red blood cells (RBCs). Plasma protein concentration, an indicator of blood volume, was not a predictor. Associations with infant age, weight and sex, infant serum cortisol, dam's reproductive history, and birth year, month and location were evaluated in regression analyses. Cage of origin, maternal age at delivery and infant weight were associated with hemoglobin concentrations. Unexpectedly, serum cortisol, determined at the same time as CBC samples were taken, was the strongest predictor of hemoglobin concentration. The basis, as well as the functional significance, of the variation in infant hemoglobin and its association with serum cortisol in this population of rhesus fed a nutritionally optimized diet and housed under standard conditions is relevant to the development of both nonhuman and human primate infants.

Object discrimination and reversal learning in infant and juvenile non-human primates in a non-clinical laboratory

BACKGROUND

Biopharmaceutical development necessitates use of non-human primates in toxicology, leading to adoption of non-traditional methods including cognitive function assessment.

METHODS

A two-object discrimination and reversal test in cynomolgus monkeys (Macaca fascicularis) was performed using a Wisconsin General Testing Apparatus (WGTA). Non-clinical study design and regulatory considerations dictate that infants are raised by their biological mothers until weaning at 6 months. Thirty-four animals (6-21 months of age) were trained to discriminate between two randomly selected stimulus objects to retrieve a reward. Following training, days to first reversal after interchanging the reward were measured.

RESULTS

Both sexes acquired visual discrimination skills at similar rates. Trends in learning and reversals completed were uniform across age groups. Completing training early in some subjects had no impact on subsequent testing phases.

CONCLUSIONS

Weaned cynomolgus monkey infants can be successfully tested for cognitive abilities using the WGTA in a non-clinical laboratory setting.

Influence of prenatal iron deficiency and MAOA genotype on response to social challenge in rhesus monkey infants

Social and emotional behaviors are known to be sensitive to both developmental iron deficiency (ID) and monoamine oxidase A (MAOA) gene polymorphisms. In this study, male rhesus monkey infants deprived of dietary iron in utero were compared with iron sufficient (IS) controls (n = 10/group). Half of each group had low MAOA activity genotypes and half had high MAOA activity genotypes. A series of social response tests were conducted at 3-14 months of age. MAOA genotype influenced attention to a video of aggressive behavior, emotional expression (fear, grimace and sniff) in the social intruder test, social actions (displacement, grooming) in the social dyad test, and aggressive responses to a threatening picture. Interactions between MAOA and prenatal ID were seen in response to the aggressive video, in temperament ratings, in affiliative behavior in the social dyad test, in cortisol response in the social buffering test and in response to a social intruder and to pictures with social and nonsocial themes. In general, the effects of ID were dependent on MAOA genotype in terms of both direction and size of the effect. Nutrition/genotype interactions may shed new light on behavioral consequences of nutritional deprivation during brain development.

Iron deficiency anemia and affective response in rhesus monkey infants

Infant iron deficiency anemia (IDA) occurs spontaneously in monkey populations as it does in humans, providing a model for understanding effects on brain and behavior. A set of 34 monkey infants identified as IDA (hemoglobin <11 g/dl) over a 5-year period at the California National Primate Research Center (CNPRC) was compared to a set of 57 controls (hemoglobin >12 g/dl) matched for age and caging location. The infants had participated in a Biobehavioral Assessment conducted at 3-4 months of age at CNPRC that included measures of behavioral and adrenocortical response to a novel environment. IDA males differed from control males in two factors ("activity," "emotionality") derived from observational data taken on the first and second day of the exposure to the novel environment. In the male infants, IDA was associated with less restriction of activity in the novel environment on both days and less emotionality on the second day (p < .05). IDA males also displayed less response to approach by a human (human intruder test) than did control males. IDA females did not differ from controls. Adrenocortical response was not significantly affected. These findings may be relevant to functional deficits in human infants with IDA that influence later behavior.

Iron deprivation during fetal development changes the behavior of juvenile rhesus monkeys

Sensitive periods for induction of behavioral impairments by developmental iron deficiency were studied in a nonhuman primate model. Rhesus monkey infants were deprived of iron prenatally (n = 14) via the dam's diet (10 microg Fe/g) or postnatally (birth-4 mo, n = 12) via infant formula (1.5 mg Fe/L). They were compared with controls (n = 12) with adequate dietary iron throughout development in a series of cognitive tests and related assessments from 6 to 12 mo of age, a developmental stage corresponding approximately to 2-4 y of age in humans. Health, growth, and hematological status were not affected. Auditory brainstem response and white matter volumes in the cerebrum were similarly unaffected. Male infants in the prenatally deprived group had reduced spontaneous daytime activity relative to controls, as monitored by actimeter. On cognitive tests, prenatally deprived juveniles had similar level of correct responding, but showed more completed trials, and shorter latencies during early phases of the tests. Juveniles deprived of iron as infants showed a similar pattern of behavioral change, but most differences from controls were not as great. Inadequate iron nutrition during pregnancy was reflected in the juvenile period primarily as attenuated inhibitory response. This finding may be relevant to individual differences in temperament or to behavior disorders in children involving reduced inhibitory control.

Diet-induced iron deficiency anemia and pregnancy outcome in rhesus monkeys

BACKGROUND

Iron deficiency anemia (IDA) is relatively common in the third trimester of pregnancy, but causal associations with low birth weight and compromised neonatal iron status are difficult to establish in human populations.

OBJECTIVE

The objective was to determine the effects of diet-induced IDA on intrauterine growth and neonatal iron status in an appropriate animal model for third-trimester IDA in women.

DESIGN

Hematologic and iron-status measures, pregnancy outcomes, and fetal and neonatal evaluations were compared between pregnant rhesus monkeys (n = 14) fed a diet containing 10 microg Fe/g diet from the time of pregnancy detection (gestation days 28-30) and controls (n = 24) fed 100 microg Fe/g diet.

RESULTS

By the third trimester, 79% of the iron-deprived dams and 29% of the control monkeys had a hemoglobin concentration <11 g/dL. There were also significant group differences in hematocrit, mean corpuscular volume, transferrin saturation, serum ferritin, and serum iron. At birth, the newborns of monkeys iron-deprived during pregnancy had significantly lower hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin values and a lower ratio of erythroid to total colony-forming units in bone marrow than did the control newborns. Pregnancy weight gain did not differ significantly between the iron-deprived and control dams, and the fetuses and newborns of the iron-deprived dams were not growth retarded relative to the controls. Gestation length, the number of stillbirths, and neonatal neurobehavioral test scores did not differ significantly by diet group.

CONCLUSION

These data indicate that an inadequate intake of iron from the diet during pregnancy in rhesus monkeys can lead to compromised hematologic status of the neonate without indications of growth retardation or impaired neurologic function at birth.

Behavioral consequences of developmental iron deficiency in infant rhesus monkeys

Human studies have shown that iron deficiency and iron deficiency anemia in infants are associated with behavioral impairment, but the periods of brain development most susceptible to iron deficiency have not been established. In the present study, rhesus monkeys were deprived of iron by dietary iron restriction during prenatal (n=14, 10 microg Fe/g diet) or early postnatal (n=12, 1.5 mg Fe/L formula) brain development and compared to controls (n=12, 100 microg Fe/g diet, 12 mg Fe/L formula) in behavioral evaluations conducted during the first four months of life in the nonhuman primate nursery. Iron deficiency anemia was detected in the pregnant dams in the third trimester and compromised iron status was seen in the prenatally iron-deprived infants at birth, but no iron deficiency was seen in either the prenatally or postnatally iron-deprived infants during the period of behavioral evaluation. Neither prenatal nor postnatal iron deprivation led to significant delays in growth, or gross or fine motor development. Prenatally deprived infants demonstrated a 20% reduced spontaneous activity level, lower inhibitory response to novel environments, and more changes from one behavior to another in weekly observation sessions. Postnatally deprived infants demonstrated poorer performance of an object concept task, and greater emotionality relative to controls. This study indicates that different syndromes of behavioral effects are associated with prenatal and postnatal iron deprivation in rhesus monkey infants and that these effects can occur in the absence of concurrent iron deficiency as reflected in hematological measures.

Neurobehavioral evaluation of rhesus monkey infants fed cow's milk formula, soy formula, or soy formula with added manganese

The possible neurobehavioral effects of excess manganese in soy formula were studied. Male rhesus monkeys (n=8/group) were fed a commercial cow's milk based formula (Control), a commercial soy protein based formula (Soy), or the soy formula with added manganese (Soy+Mn) from birth to 4 months of age. Soy formulas naturally have higher manganese (Mn) content than cow's milk formulas. Monkeys received behavioral evaluations, growth measurements, and cerebrospinal fluid (CSF) sampling from birth to 18 months of age. Soy and Soy+Mn groups engaged in less play behavior and more affiliative clinging in social dyadic interactions. These groups also had shorter wake cycles and shorter periods of daytime inactivity than controls. An impulsivity test was sensitive to the Soy group diet. The Soy+Mn group also had a blunted response to the dopamine agonist apomorphine. Groups did not differ significantly in CSF dopamine and serotonin metabolite concentrations, but these concentrations were correlated with several tasks affected by experimental formula. This experiment suggests that components of soy formula, including Mn, may influence brain development as reflected in behavioral measures.

Endocrine disruption and cognitive function in adolescent female rhesus monkeys

Female rhesus monkeys (n=8/group) received daily oral doses of exogenous estrogen [diethylstilbestrol (DES), 0.5 mg/kg, methoxychlor (MXC), 25 or 50 mg/kg] for 6 months before and after the anticipated age of menarche. Behavior was assessed during and for 9 months after dosing. Visual discrimination performance (simultaneous nonmatch-to-sample with trial-unique stimuli) conducted during dosing demonstrated delayed improvement and poorer performance in the MXC50 group, with some similar effects in the DES group. Visual recognition memory, assessed with delays of < or = 3 s, was not apparently affected. Spatial working memory, assessed after dosing, also showed acquisition deficits and possible working memory difficulties in the MXC50 group. Spontaneous motor activity, monitored at 6-month intervals, was not affected by treatment. Late peak latencies of the auditory brainstem response (ABR) were shorter in the DES group 6 months after treatment, suggesting long-term effects on brain. The study suggests that some aspects of brain function can be modified by exposure to exogenous estrogen during pubertal development. Although DES is a more potent estrogen, the high-dose MXC group was more affected behaviorally. Differential effects of the two agents at the estrogen receptor subtypes (ER alpha and ER beta) may be relevant to the differential behavioral outcomes.

Endocrine disruption in adolescence: immunologic, hematologic, and bone effects in monkeys

Environmental contaminants with estrogenic properties have the potential to alter pubertal development. In addition to the reproductive system, other systems that mature under the influence of estrogen could be affected. This study examined the effect on immune, hematologic, and bone mass parameters of treatment with estrogenic agents (methoxychlor, MXC, 25 and 50 mg/kg/day; diethylstilbestrol, DES, 0.5 mg/kg/day) given in the peripubertal period to female rhesus monkeys. DES had striking effects on several parameters assessed measures CBC and clinical chemistry including hematocrit, hemoglobin, serum albumin, liver transaminases, and lipids. Circulating lymphocytes, particularly B cells, were depressed by DES, and a maturational shift in a memory T-cell population was altered. Bone mass and length, as measured after a 9-month recovery period, were significantly lower in the DES group and bone mass tended to be reduced in the femur of the MXC50 group relative to controls. In conclusion, the data indicate that DES had a clear effect on immunohematology and bone growth, while MXC influenced fewer parameters. Disruption in these systems during puberty could alter adolescent risk for anemia and infectious disease and subsequent adult risk for diseases such as osteoporosis, heart disease, and autoimmune disease.

Effects of exogenous estrogenic agents on pubertal growth and reproductive system maturation in female rhesus monkeys

Concern has been raised that environmental contaminants with estrogenic properties can alter normal sexual maturation. Monkeys, like humans, undergo a long and complex period of development during adolescence, which makes them important models for understanding exogenous estrogen effects during this period. This study examined the consequences of treatment with estrogenic agents (methoxychlor, MXC, 25 and 50 mg/kg/day; diethylstilbestrol, DES, 0.5 mg/kg/day) given in the peripubertal period (6 months before and after the expected age at menarche) to female rhesus monkeys. These treatments increased estrogen activity of serum as determined with an in vitro estrogen receptor alpha (ERa) transcription assay. DES completely suppressed adolescent growth (weight and height) and menses in a reversible manner; smaller effects of MXC on the timing of growth and menarche were also detected. Both DES and MXC led to premature emergence of a secondary sex characteristic, reddening and swelling of skin, but retarded growth of the nipple. As evaluated by ultrasound after an 8-month recovery period, uterine size was not affected by exogenous estrogen, but there was some indication of increased incidence of ovarian cysts/masses in MXC- and DES-treated groups. Ovarian cyclicity, as reflected in urinary hormone metabolites, demonstrated shorter follicular stages in the MXC-treated monkeys. In conclusion, the data indicate that DES had a striking effect on adolescent maturation and that the estrogenic pesticide MXC also altered development during this period. The pattern of effects across agents and doses may be based on specifics of estrogenic action, such as relative ERalpha and ERbeta binding and activation. Long-term consequences of this disruption of pubertal development are being studied in this cohort of monkeys as adults.