Transgenerational effects of variable foraging demand stress in female bonnet macaques.

Stress coping is an important part of mammalian life, influencing somatic and mental health, social integration, and reproductive success. The experience of early psychological stress helps shape lifelong stress coping strategies. Recent studies have shown that the effects of early stress may not be restricted to the affected generation, but may also be transmitted to offspring. Understanding whether early stress influences development in subsequent generations may help us understand somewhat why many stress-related traits and diseases, for which little genetic basis has been discovered, run in families. Experimental early life "variable foraging demand" (VFD) stress has been associated with behavioral hypo-responsiveness to stress in infant and adolescent bonnet macaques. The present study examined the behavioral effects of experimental early VFD stress in adult bonnet macaques, and further investigated whether non-exposed adolescent offspring of VFD macaques were also affected. Thirty female bonnet macaques from four rearing histories were observed for behavioral response during stress: adults which had been VFD reared as infants (n = 11), adults which had been Control reared as infants (n = 9), and foraging demand naïve adolescents whose mothers were VFD (n = 4) or Control reared (n = 6). Subjects were observed for behavioral response during two experimental stressor conditions, including: (1) relocation to a novel environment; and (2) relocation with exposure to a "human intruder" making eye contact. Factor analysis yielded five factors that described categories of behavior across stress conditions. While adult VFD and Control reared females unexpectedly did not differ significantly, non-exposed adolescent offspring of VFD reared mothers displayed significant hypo-responsiveness in all behavioral categories compared with non-exposed adolescent offspring of Control females. We suggest that stress hypo-responsiveness previously observed in adolescent VFD reared animals may abate with age, but is nonetheless observed in the next generation. We conclude that VFD stress affects behavioral development of subsequent generations in non-human primates.

DNA methylation as a risk factor in the effects of early life stress.

Epigenetic marks (e.g., DNA 5-methylcytosine [5mC] content or CpG methylation) within specific gene regulatory regions have been demonstrated to play diverse roles in stress adaptation and resulting health trajectories following early adversity. Yet the developmental programming of the vast majority of the epigenome has not yet been characterized, and its role in the impact of early stress largely unknown. In the present study, we investigated the relationships among early life stress, whole-epigenome and candidate stress pathway gene (serotonin transporter, 5-HTT) methylation patterns, and adult behavioral stress adaptation in a non-human primate model. Early in life, experimental variable foraging demand (VFD) stress or control conditions were administered to two groups each of 10 female bonnet macaques (Macaca radiata) and their mothers. As adults (3-13 years of age), these females were assessed for behavioral adaptation to stress across four conditions of increasing intensity. Blood DNA 5-HTT 5mC status was determined using sodium bisulfite pyrosequencing and total 5mC content was determined using ELISA. Neither stress reactivity nor DNA methylation differed based on early life stress. However, we found that both greater 5-HTT and whole-genome 5mC was associated with enhanced behavioral stress reactivity following early life stress, but not control conditions. Therefore, regardless of developmental origin, greater DNA methylation conferred a genomic background of "risk" in the context of early stress. We suggest that this may arise from constrained plasticity in gene expression needed for stress adaptation early in development. This risk may have wider implications for psychological and physical stress adaptation and health.