Maribeth Champoux

Serotonin transporter gene polymorphism, differential early rearing, and behavior in rhesus monkey neonates

A polymorphism in the serotonin (5-HT) transporter gene regulatory region (5-HTTLPR) is associated with measures of 5-HT transporter (5-HTT) expression and 5-HT-mediated behaviors in humans. An analogous length variation of the 5-HTTLPR has been reported in rhesus monkeys (rh5-HTTLPR). A retrospective association study was conducted on 115 rhesus macaque infants either homozygous for the long 5HTTLPR variant (l/l) or heterozygous for the short and long form (l/s). To assess contributions of genotype and early rearing environment, 36 mother-reared monkeys (l/l = 26, l/s = 10) and 79 nursery-reared monkeys (l/l = 54, l/s = 25) were assessed on days 7, 14, 21, and 30 of life on a standardized primate neurobehavioral test designed to measure orienting, motor maturity, reflex functioning, and temperament. Both mother-reared and nursery-reared heterozygote animals demonstrated increased affective responding relative to l/l homozygotes. Nursery-reared, but not mother-reared, l/s infants exhibited lower orientation scores than their l/l counterparts. These results demonstrate the contributions of rearing environment and genetic background, and their interaction, in a nonhuman primate model of behavioral development.

Rearing condition and rh5-HTTLPR interact to influence limbic-hypothalamic-pituitary-adrenal axis response to stress in infant macaques

BACKGROUND In humans and macaques, a promoter polymorphism that decreases transcription of the serotonin transporter gene is associated with anxiety. Serotonin transporter gene disruption in rodents produces anxious animals with exaggerated limbic-hypothalamic-pituitary-adrenal (LHPA) responses to stress. We wanted to determine whether serotonin transporter gene promoter variation (rh-5HTTLPR) and rearing condition would interact to influence endocrine responses to stress in infant rhesus macaques. METHODS Animals were reared with their mothers (MR, n = 141) or in peer-only groups (PR, n = 67). At 6 months of age, adrenocorticotropic hormone (ACTH) and cortisol levels were determined at baseline and during separation stress. Serotonin transporter genotype (l/l and l/s) was determined with polymerase chain reaction followed by gel electrophoresis. RESULTS Cortisol levels increased during separation, and there was a main effect of rearing condition, with decreased cortisol levels among PR macaques. Animals with l/s rh5-HTTLPR genotypes had higher ACTH levels than did l/l animals. Adrenocorticotropic hormone levels increased during separation, and there was a separation x rearing x rh5-HTTLPR interaction, such that PR-l/s animals had higher ACTH levels during separation than did other animals studied. CONCLUSIONS These data demonstrate that serotonin transporter gene variation affects LHPA axis activity and that the influence of rh5-HTTLPR on hormonal responses during stress is modulated by early experience.

The utility of the non-human primate model for studying gene by environment interactions in behavioral research

Variation in the serotonin transporter gene‐linked polymorphic region (5‐HTTLPR) has been associated with anxiety and harm avoidance and is weakly associated with a number of neuropsychiatric disorders, including Type II alcoholism, which has a high rate of comorbidity with antisocial personality disorder. Studies have also demonstrated interactions between 5‐HTTLPR variation and environmental stress on the incidence of depression. As in humans, there is a serotonin transporter gene promoter length polymorphism in rhesus macaques that produces similar decreases in transcriptional efficiency. Macaques with histories of early‐life stress have been shown to exhibit impulsive aggression, incompetent social behavior and increased behavioral and endocrine responsivity to stress. In this paper, we review studies performed previously in our lab and present preliminary data examininng interactions between early rearing and serotonin transporter gene promoter variation on the incidences of play behavior and aggression in infant rhesus macaques. The data presented here highlight the importance of considering gene‐environment interactions when studying childhood risk factors for aggression, anxiety and related neuropsychiatric disorders and support the use of the nonhuman primate for studing gene by environment interactions in behavioral research.

Stability of Interindividual Differences in Serotonin Function and Its Relationship to Severe Aggression and Competent Social Behavior in Rhesus Macaque Females

Few studies have investigated longitudinally interindividual stability of cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) concentrations in adult nonhuman primates across time and between baseline and stressful conditions. Furthermore, whereas studies with male macaques consistently have reported a significant, negative correlation between CSG 5-HIAA and rates of spontaneous aggression, wounding, and severe aggression, very few studies have examined this relationship in adult female nonhuman primates. Even fewer studies have investigated correlations between CSF 5-HIAA and competent social behavior, such as social dominance, in female monkeys. In the present study, two social groups of adult rhesus monkeys (Macaca Mulatta) were formed by placing 16 females (aged 42 to 180 months, mean age: 68 months) in one of two indoor-outdoor enclosures with one or two adult males. CSF norepinephrine (NE), monoamine metabolites, and behavioral data were collected systematically over a 24-week period. In weed 5 of the study, one additional female, not familiar to any of the other subjects, was added to each social group Thereafter the groups were left undisturbed, and data characterizing spontaneous aggressive wounding and severe wound injuries in the females were collect for and additional year. The results showed that both group introduction and the addition of a new subject into each group resulted in increased monoamine turnover in the animals within social groups. INterinvidividual differences in CSF concentrations of each of the monoamine metabolites and NE were highly stable from the baseline period to the stress samplings, and between stress samplings. Females with low CSF 5-HIAA exhibited higher rates for spontaneous aggressive wounding, and they were more likely to be removed from their social groups for aggressive wounding and/or treatment of injuries. CSF 5-HIAA or NE. Females with above average CSF 5-HIAA prior to and following group formation were more likely to attain and maintain a high social dominance ranking within their social group than females with below average CSF 5-HIAA. The present findings indicate that CNS monoamine functioning in adult female rhesus macaques is traitlike, showing a high degree of interindividual stability across time and setting. These findings also suggest a role for serotonin in controlling impulses that regulate aggression and that competent social behavior among nonhuman primates may require average or above average serotonin functioning.

Monoamine oxidase A gene promoter variation and rearing experience influences aggressive behavior in rhesus monkeys

BACKGROUND Allelic variation of the monoamine oxidase A (MAOA) gene has been implicated in conduct disorder and antisocial, aggressive behavior in humans when associated with early adverse experiences. We tested the hypothesis that a repeat polymorphism in the rhesus macaque MAOA gene promoter region influences aggressive behavior in male subjects. METHODS Forty-five unrelated male monkeys raised with or without their mothers were tested for competitive and social group aggression. Functional activity of the MAOA gene promoter polymorphism was determined and genotypes scored for assessing genetic and environmental influences on aggression. RESULTS Transcription of the MAOA gene in rhesus monkeys is modulated by an orthologous polymorphism (rhMAOA-LPR) in its upstream regulatory region. High- and low-activity alleles of the rhMAOA-LPR show a genotype x environment interaction effect on aggressive behavior, such that mother-reared male monkeys with the low-activity-associated allele had higher aggression scores. CONCLUSIONS These results suggest that the behavioral expression of allelic variation in MAOA activity is sensitive to social experiences early in development and that its functional outcome might depend on social context.

Serotonin Transporter Gene Variation is Associated with Alcohol Sensitivity in Rhesus Macaques Exposed to Early-Life Stress

BACKGROUND Decreased sensitivity to alcohol has been demonstrated to be a predictor of alcoholism in humans, and variation in the gene-linked polymorphic region of the serotonin transporter (5-HTTLPR) is associated with the response to the motor-impairing effects of alcohol. In a nonhuman primate model of excessive alcohol intake, we have shown that decreased serotonin turnover is associated with both lower initial sensitivity to alcohol and higher prospective alcohol consumption using rhesus macaques. In addition, we have demonstrated that macaques separated from their mothers and reared in peer-only groups are more likely to consume alcohol as adults. METHOD To examine the relationship between serotonin transporter genotype, early rearing experience, and initial sensitivity to alcohol, peer- and mother-reared, adolescent, alcohol-naive rhesus macaques (n = 123) were rated for intoxication after intravenous administration of ethanol (2.2 g/kg and 2.0 g/kg for males and females, respectively) during two testing periods. Serotonin transporter (rh5-HTTLPR) genotype was determined using polymerase chain reaction followed by gel electrophoresis, and data were analyzed using ANOVA and the Mann-Whitney U test. RESULTS Our analyses demonstrate an effect of serotonin transporter gene variation on ethanol sensitivity, such that animals homozygous for the l allele exhibited decreased sensitivity to the ataxic and sedating effects of alcohol. This effect remained after correction for blood ethanol concentrations and birth cohort. When animals were segregated according to rearing condition, serotonin transporter gene variation predicted intoxication scores among peer-reared animals. CONCLUSIONS As in some human reports, this study demonstrates a diminution in the response to alcohol in animals homozygous for the l rh5-HTTLPR allele. The phenotypic expression of this genotype in l/s animals, however, is environmentally dependent.

Rearing condition and plasma cortisol in rhesus monkey infants

Previous studies comparing plasma cortisol levels in mother‐reared and nursery‐reared rhesus monkey infants under baseline and stress conditions have reported conflicting findings. Differences in subject age, procedures, and specific rearing history may account for many of the discrepant findings. In the present study, mother‐reared infants from large social groups, peer‐only reared animals, and infants reared with surrogates and limited peer contact were studied in different test conditions across the first 6 months of life. Infants were sampled under three conditions: following a neonatal assessment at Days 14 and 30, immediately upon capture on Day 60, and after 30‐min isolation periods on Days 90, 120, and 150. Mother‐reared infants exhibited higher cortisol levels on Days 14 and 30 than did both types of nursery‐reared infants. In addition, Day 60 basal values of mother‐reared infants were higher than those of both peer‐reared and surrogate/peer‐reared infants. However, on Days 90, 120, and 150, both mother‐reared and peer‐reared infants exhibited higher cortisol levels in response to separation and 30‐min isolation than did the surrogate/peer‐reared infants. These differences may reflect group‐specific variations in physical environment, capture time, feeding regimen, or diurnal HPA axis rhythms. Am. J. Primatol. 46:311–321, 1998.

Behavioral and physiological characteristics of Indian and Chinese-Indian hybrid rhesus macaque infants

Strain differences in temperament and physiology have been reported for several animal species, but nonhuman primates have not been well studied in this regard. We assessed behavioral and physiology in Chinese-Indian hybrid (n = 13) and Indian-origin (n = 29) nursery-reared rhesus monkey infants. Previous data indicate that Chinese-origin and Chinese-Indian hybrid rhesus exhibit more aggression directed toward humans and conspecifics and are more irritable in response to neonatal assessment procedures than are Indian-derived rhesus. In addition, in rhesus adults, low levels of cerebrospinal fluid 5-HIAA have been correlated with impulsivity, aggressive behavior, and diminished social competence. We therefore hypothesized that hybrid infants would exhibit more behavioral and adrenocortical reactivity in the home cage and during social separations, would be less sociable in their peer groups, and would exhibit lower CSF 5-HIAA levels than Indian-derived monkeys. Blood and cerebrospinal fluid samples were obtained on Days, 14, 30, 60, 90, 120, and 150 of life, and prior to and during social separations at 6 months of age. Behavioral observations were conducted in the home cage and during the separation condition. No differences in behavior were observed between hybrid and Indian-derived animals in the home cage. Indian-derived and hybrid infants exhibited diverging patterns of behavioral reactivity across the 4 weeks of the repetitive social-separation procedure, and during reunion periods. Although plasma cortisol levels were sensitive to the testing conditions, no group differences were observed. CSF 5-HIAA declined over time for all monkeys, and hybrid animals exhibited significantly lower 5-HIAA levels than Indian monkeys beginning at 6 months of age. These findings are consistent with the known behavioral and physiological characteristics of Chinese-origin adult rhesus.

Fatty acid formula supplementation and neuromotor development in rhesus monkey neonates.

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is highly concentrated in CNS tissues. Although breast milk contains the fatty acids DHA and arachidonic acid, infant formulas marketed in North America do not contain these nutrients. The potential deleterious effects of rearing infants with formulas devoid of these nutrients was assessed by comparing nursery-reared rhesus macaque infants (Macaca mulatta) fed standard formula with infants fed standard formula supplemented with physiologically relevant concentrations of DHA (1.0%) and arachidonic acid (1.0%). Neurobehavioral assessments were conducted on d 7, 14, 21, and 30 of life using blinded raters. The 30-min assessment consisted of 45 test items measuring orienting, temperament, reflex capabilities, and motor skills. Plasma concentrations of DHA in standard formula-fed infants were significantly lower than those fed supplemented formula or mother-raised (breast-fed) infants; however, infants fed the supplemented formula exhibited higher arachidonic acid levels than either mother-reared infants or infants fed standard formula. Infant monkeys fed the supplemented formula exhibited stronger orienting and motor skills than infants fed the standard formula, with the differences most pronounced during d 7 and 14. This pattern suggests an earlier maturation of specific visual and motor abilities in the supplemented infants. Supplementation did not affect measures of activity or state control, indicating no effect on temperament. These data support the assertion that preformed DHA and arachidonic acid in infant formulas are required for optimal development.

Early Experience and Sex Interact to Influence Limbic‐Hypothalamic‐Pituitary‐Adrenal‐Axis Function After Acute Alcohol Administration in Rhesus Macaques (Macaca mulatta)

BACKGROUND Studies in rodents demonstrate sex differences in neuroendocrine stress axis activity after treatment with alcohol. In abstinent alcoholics, atypical depressives, and individuals with posttraumatic stress disorder, limbic-hypothalamic-pituitary-adrenal (LHPA)-axis activity is often blunted; among females in these patient populations, however, resistance to glucocorticoid feedback and increased pituitary reactivity is observed. Early parental loss is a major life stressor and is a risk factor for both affective disturbances and LHPA-axis abnormalities later in life. We wanted to determine whether sex and early life parental absence would interact to influence alcohol-induced alterations in LHPA-axis activity after exposure to ethanol in macaques. METHODS Animals were reared with their mothers in social groups (MR, n = 94) or without adults in peer-only groups (PR, n = 79). At 5 years of age, they received an intravenous infusion of alcohol (2-2.2 g/kg), and the effects of alcohol, sex, and rearing condition on ACTH and cortisol levels were analyzed by ANOVA. RESULTS Peer-reared females had higher ACTH levels than did PR males, MR females, and MR males after alcohol infusion. Alcohol-induced cortisol levels were not affected by sex and rearing condition. CONCLUSIONS These findings suggest that there are sex differences in glucocorticoid negative feedback, pituitary responsivity, or release of ACTH secretagogues among individuals exposed to early life stress and emphasize the importance of considering sex effects when studying LHPA-axis dysregulation in alcoholism and other stress-related neuropsychiatric disorders.