Stability of parental care across siblings from undisturbed and challenged pregnancies: intrinsic maternal dispositions of female rhesus monkeys

Proteobacteria abundance during nursing predicts physical growth and brain volume at one year of age in young rhesus monkeys

Over the last decade, multiple studies have highlighted the essential role of gut microbiota in normal infant development. However, the sensitive periods during which gut bacteria are established and become associated with physical growth and maturation of the brain are still poorly defined. This study tracked the assembly of the intestinal microbiota during the initial nursing period, and changes in community structure after transitioning to solid food in infant rhesus monkeys (Macaca mulatta). Anthropometric measures and rectal swabs were obtained at 2-month intervals across the first year of life and bacterial taxa identified by 16S rRNA gene sequencing. At 12 months of age, total brain and cortical regions volumes were quantified through structural magnetic resonance imaging. The bacterial community structure was dynamic and characterized by discrete maturational phases, reflecting an early influence of breast milk and the later transition to solid foods. Commensal microbial taxa varied with diet similar to findings in other animals and human infants; however, monkeys differ in the relative abundances of Lactobacilli and Bifidobacteria, two taxa predominant in breastfed human infants. Higher abundances of taxa in the phylum Proteobacteria during nursing were predictive of slower growth trajectories and smaller brain volumes at one year of age. Our findings define discrete phases of microbial succession in infant monkeys and suggest there may be a critical period during nursing when endogenous differences in certain taxa can shift the community structure and influence the pace of physical growth and the maturational trajectory of the brain.

Hormone levels in neonatal hair reflect prior maternal stress exposure during pregnancy

Hormones present in hair provide summative information about endocrine activity while the hair was growing. Therefore, it can be collected from an infant after birth and still provide retrospective information about hormone exposure during prenatal development. We employed this approach to determine whether a delimited period of maternal stress during pregnancy affected the concentrations of glucocorticoids and gonadal hormones in the hair of neonatal rhesus monkeys. Hair from 22 infant monkeys exposed to 5 weeks of gestational disturbance was compared to specimens from 13 infants from undisturbed control pregnancies. Using an LC/MS/MS based technique, which permitted seven steroid hormones to be quantified simultaneously, we found 2 hormones were significantly different in infants from disturbed pregnancies. Cortisol and testosterone levels were lower in the hair of both male and female neonates. Maternal hair hormone levels collected on the same day after delivery no longer showed effects of the disturbance earlier during pregnancy. This study documents that a period of acute stress, lasting for 20% of gestation, has sustained effects on the hormones to which a developing fetus is exposed.