Circadian Rhythms in the Fetus and Newborn: Significance of Interactions with Maternal Physiology and the Environment

From gestational chronodisruption to noncommunicable diseases: Pathophysiological mechanisms of programming of adult diseases, and the potential therapeutic role of melatonin

During gestation, the developing fetus relies on precise maternal circadian signals for optimal growth and preparation for extrauterine life. These signals regulate the daily delivery of oxygen, nutrients, hormones, and other biophysical factors while synchronizing fetal rhythms with the external photoperiod. However, modern lifestyle factors such as light pollution and shift work can induce gestational chronodisruption, leading to the desynchronization of maternal and fetal circadian rhythms. Such disruptions have been associated with adverse effects on cardiovascular, neurodevelopmental, metabolic, and endocrine functions in the fetus, increasing the susceptibility to noncommunicable diseases (NCDs) in adult life. This aligns with the Developmental Origins of Health and Disease theory, suggesting that early-life exposures can significantly influence health outcomes later in life. The consequences of gestational chronodisruption also extend into adulthood. Environmental factors like diet and stress can exacerbate the adverse effects of these disruptions, underscoring the importance of maintaining a healthy circadian rhythm across the lifespan to prevent NCDs and mitigate the impact of gestational chronodisruption on aging. Research efforts are currently aimed at identifying potential interventions to prevent or mitigate the effects of gestational chronodisruption. Melatonin supplementation during pregnancy emerges as a promising intervention, although further investigation is required to fully understand the precise mechanisms involved and to develop effective strategies for promoting health and preventing NCDs in individuals affected by gestational chronodisruption.

What is resilience: an affiliative neuroscience approach

Resilience - a key topic in clinical science and practice - still lacks a clear conceptualization that integrates its evolutionary and human-specific features, refrains from exclusive focus on fear physiology, incorporates a developmental approach, and, most importantly, is not based on the negation (i.e., absence of symptoms following trauma). Building on the initial condition of mammals, whose brain matures in the context of the mother's body and caregiving behavior, we argue that systems and processes that participate in tuning the brain to the social ecology and adapting to its hardships mark the construct of resilience. These include the oxytocin system, the affiliative brain, and biobehavioral synchrony, all characterized by great flexibility across phylogenesis and ontogenesis. Three core features of resilience are outlined: plasticity, sociality and meaning. Mechanisms of sociality by which coordinated action supports diversity, endurance and adaptation are described across animal evolution. Humans' biobehavioral synchrony matures from maternal attuned behavior in the postpartum to adult-adult relationships of empathy, perspective-taking and intimacy, and extends from the mother-child relationship to other affiliative bonds throughout life, charting a fundamental trajectory in the development of resilience. Findings from three high-risk cohorts, each tapping a distinct disruption to maternal-infant bonding (prematurity, maternal depression, and early life stress/trauma), and followed from birth to adolescence/young adulthood, demonstrate how components of the neurobiology of affiliation confer resilience and uniquely shape the social brain.

Chronotype: Implications for Epidemiologic Studies on Chrono-Nutrition and Cardiometabolic Health

Chrono-nutrition is an emerging research field in nutritional epidemiology that encompasses 3 dimensions of eating behavior: timing, frequency, and regularity. To date, few studies have investigated how an individual's circadian typology, i.e., one's chronotype, affects the association between chrono-nutrition and cardiometabolic health. This review sets the directions for future research by providing a narrative overview of recent epidemiologic research on chronotype, its determinants, and its association with dietary intake and cardiometabolic health. Limited research was found on the association between chronotype and dietary intake in infants, children, and older adults. Moreover, most of the evidence in adolescents and adults was restricted to cross-sectional surveys with few longitudinal cohorts simultaneously collecting data on chronotype and dietary intake. There was a gap in the research concerning the association between chronotype and the 3 dimensions of chrono-nutrition. Whether chronotype modifies the association between diet and cardiometabolic health outcomes remains to be elucidated. In conclusion, further research is required to understand the interplay between chronotype, chrono-nutrition, and cardiometabolic health outcomes.

Gestational chronodisruption leads to persistent changes in the rat fetal and adult adrenal clock and function

KEY POINTS

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Here we explored the developmental impact of gestational chronodisruption (chronic photoperiod shift, CPS) on adult and fetal adrenal biorhythms and function. We found that gestational chronodisruption altered fetal and adult adrenal function, at the molecular, morphological and physiological levels. The differences between control and CPS offspring suggest desynchronization of the adrenal circadian clock and steroidogenic pathway, leading to abnormal stress responses and metabolic adaptation, potentially increasing the risk of developing chronic diseases.

ABSTRACT

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Indeed, an abnormal photoperiod during gestation alters fetal development, inducing long-term effects on the offspring. Accordingly, we carried out a longitudinal study in rats, exploring the impact of gestational chronodisruption on the adrenal biorhythms and function of the offspring. Adult rats (90 days old) gestated under chronic photoperiod shift (CPS) decrease the time spent in the open arm zone of an elevated plus maze to 62% and increase the rearing time to 170%. CPS adults maintained individual daily changes in corticosterone, but their acrophases were distributed from 12.00 h to 06.00 h. CPS offspring maintained clock gene expression and oscillation, nevertheless no daily rhythm was observed in genes involved in the regulation and synthesis of steroids. Consistent with adult adrenal gland being programmed during fetal life, blunted daily rhythms of corticosterone, core clock gene machinery, and steroidogenic genes were observed in CPS fetal adrenal glands. Comparisons of the global transcriptome of CPS versus control fetal adrenal gland revealed that 1078 genes were differentially expressed (641 down-regulated and 437 up-regulated). In silico analysis revealed significant changes in Lipid Metabolism, Small Molecule Biochemistry, Cellular Development and the Inflammatory Response pathway (z score: 48-20). Altogether, the present results demonstrate that gestational chronodisruption changed fetal and adult adrenal function. This could translate to long-term abnormal stress responses and metabolic adaptation, increasing the risk of developing chronic diseases.

Developmental Programming of Capuchin Monkey Adrenal Dysfunction by Gestational Chronodisruption

In the capuchin monkey (Cebus apella), a new-world nonhuman primate, maternal exposure to constant light during last third of gestation induces precocious maturation of the fetal adrenal and increased plasma cortisol in the newborn. Here, we further explored the effects of this challenge on the developmental programming of adrenal function in newborn and infant capuchin monkeys. We measured (i) plasma dehydroepiandrosterone sulphate (DHAS) and cortisol response to ACTH in infants with suppressed endogenous ACTH, (ii) plasma DHAS and cortisol response to ACTH in vitro, and (iii) adrenal weight and expression level of key factors in steroid synthesis (StAR and 3β-HSD). In one-month-old infants from mothers subjected to constant light, plasma levels of cortisol and cortisol response to ACTH were twofold higher, whereas plasma levels of DHAS and DHAS response to ACTH were markedly reduced, compared to control conditions. At 10 months of age, DHAS levels were still lower but closer to control animals, whereas cortisol response to ACTH was similar in both experimental groups. A compensatory response was detected at the adrenal level, consisting of a 30% increase in adrenal weight and about 50% reduction of both StAR and 3β-HSD mRNA and protein expression and the magnitude of DHAS and cortisol response to ACTH in vitro. Hence, at birth and at 10 months of age, there were differential effects in DHAS, cortisol production, and their response to ACTH. However, by 10 months of age, these subsided, leading to a normal cortisol response to ACTH. These compensatory mechanisms may help to overcome the adrenal alterations induced during pregnancy to restore normal cortisol concentrations in the growing infant.

Deciphering the Function of the Blunt Circadian Rhythm of Melatonin in the Newborn Lamb: Impact on Adrenal and Heart

Neonatal lambs, as with human and other neonates, have low arrhythmic endogenous levels of melatonin for several weeks until they start their own pineal rhythm of melatonin production at approximately 2 weeks of life. During pregnancy, daily rhythmic transfer of maternal melatonin to the fetus has important physiological roles in sheep, nonhuman primates, and rats. This melatonin rhythm provides a circadian signal and also participates in adjusting the physiology of several organs in preparation for extrauterine life. We propose that the ensuing absence of a melatonin rhythm plays a role in neonatal adaptation. To test this hypothesis, we studied the effects of imposing a high-amplitude melatonin rhythm in the newborn lamb on (1) clock time-related changes in cortisol and plasma variables and (2) clock time-related changes of gene expression of clock genes and selected functional genes in the adrenal gland and heart. We treated newborn lambs with a daily oral dose of melatonin (0.25 mg/kg) from birth to 5 days of age, recreating a high-amplitude melatonin rhythm. This treatment suppressed clock time-related changes of plasma adrenocorticotropic hormone, cortisol, clock gene expression, and functional genes in the newborn adrenal gland. In the heart, it decreased heart/body weight ratio, increased expression of Anp and Bnp, and resulted in different heart gene expression from control newborns. The interference of this postnatal melatonin treatment with the normal postnatal pattern of adrenocortical function and heart development support a physiological role for the window of flat postnatal melatonin levels during the neonatal transition.

Transforming Life: A Broad View of the Developmental Origins of Health and Disease Concept from an Ecological Justice Perspective

The influential scientist Rene J. Dubos (1901–1982) conducted groundbreaking studies concerning early-life environmental exposures (e.g., diet, social interactions, commensal microbiota, housing conditions) and adult disease. However, Dubos looked beyond the scientific focus on disease, arguing that “mere survival is not enough”. He defined mental health as fulfilling human potential, and expressed concerns about urbanization occurring in tandem with disappearing access to natural environments (and elements found within them); thus modernity could interfere with health via “missing exposures”. With the advantage of emerging research involving green space, the microbiome, biodiversity and positive psychology, we discuss ecological justice in the dysbiosphere and the forces—financial inequity, voids in public policy, marketing and otherwise—that interfere with the fundamental rights of children to thrive in a healthy urban ecosystem and learn respect for the natural environment. We emphasize health within the developmental origins of health and disease (DOHaD) rubric and suggest that greater focus on positive exposures might uncover mechanisms of resiliency that contribute to maximizing human potential. We will entrain our perspective to socioeconomic disadvantage in developed nations and what we have described as “grey space”; this is a mental as much as a physical environment, a space that serves to insidiously reinforce unhealthy behavior, compromise positive psychological outlook and, ultimately, trans-generational health. It is a dwelling place that cannot be fixed with encephalobiotics or the drug-class known as psychobiotics.