Association between body weight of newborn rats and density of serotonin transporters in the frontal cortex at adulthood

Birth weight discordance, DNA methylation, and cortical morphology of adolescent monozygotic twins

BACKGROUND

Several studies have shown that the in utero environment, which can be indexed by birth weight (BW), is associated with cortical morphology in adolescence and adulthood. Work in monozygotic (MZ) twins suggests that this association is driven by non-shared environmental factors. This correlation could be the result of in utero impacts on DNA methylation. The aim of the present study with MZ twins is to replicate the association between discordance in BW and brain morphology and test whether discordance in DNA methylation mediates this relationship.

METHODS

One hundred and four adolescent MZ twins (52 pairs, of which 42% were male pairs) who have been followed regularly since birth underwent T1 weighted structural MRI, and epigenome-wide assessment of DNA methylation from saliva at age 15.

RESULTS

Co-twins had very similar measures of DNA methylation and cortical morphology. Higher BW members of a twin pair had increased total cortical surface area, and decreased cortical thickness compared to their lower BW sibling. BW Discordance was positively associated with both cortical surface area and cortical volume discordance. Genes involved in neurodevelopment were tentatively identified as mediators of both the BW - cortical volume, and BW- cortical surface area relationships.

CONCLUSIONS

The association between BW and cortical morphology in adolescence appears to be attributable to in utero environmental effects, and DNA methylation may play a role in mediating this relationship. Hum Brain Mapp 38:2037-2050, 2017. © 2017 Wiley Periodicals, Inc.

Evaluation of brain SERT occupancy by resveratrol against MDMA-induced neurobiological and behavioral changes in rats: A 4-[¹⁸F]-ADAM/small-animal PET study

The misuse of 3,4-methylenedioxymethamphetamine (MDMA) has drawn a growing concern worldwide for its psychophysiological impacts on humans. MDMA abusers are often accompanied by long-term serotonergic neurotoxicity, which is associated with reduced density of cerebral serotonin transporters (SERT) and depressive disorders. Resveratrol (RSV) is a natural polyphenolic phytoalexin that has been known for its antidepressant and neuroprotective effects. However, biological targets of RSV as well as its neuroprotective effects against MDMA remained largely unknown. In this study, we examined binding potency of RSV and MDMA to SERT using small-animal positron emission tomography (PET) with the SERT radioligand, N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM) and investigated the protection of RSV against the acute and long-term adverse effects of MDMA. We found that RSV exhibit binding potentials to SERT in vivo in a dose-dependent manner with variation among brain regions. When the MDMA-treated rats (10mg/kg, s.c.) were co-injected with RSV (20mg/kg, i.p.) twice daily for 4 consecutive days, MDMA-induced acute elevation in plasma corticosterone was significantly reduced. Further, 4-[(18)F]-ADAM PET imaging revealed that RSV protected against the MDMA-induced decrease in SERT availability in the midbrain and the thalamus 2 weeks following the co-treatment. The PET data were comparable to the observation from the forced swim test that RSV sufficiently ameliorated the depressive-like behaviors of the MDMA-treated rats. Together, these findings suggest that RSV is a potential antidepressant and may confer protection against neurobiological and behavioral changes induced by MDMA.

The Impact of the in utero and Early Postnatal Environments on Grey and White Matter Volume: A Study with Adolescent Monozygotic Twins

Prenatal and early postnatal adversities have been shown to be associated with brain development. However, we do not know how much of this association is confounded by genetics, nor whether the postnatal environment can moderate the impact of in utero adversity. This study used a monozygotic (MZ) twin design to assess (1) the association between birth weight (BW) and brain volume in adolescence, (2) the association between within-twin-pair BW discordance and brain volume discordance in adolescence, and (3) whether the association between BW and brain volume in adolescence is mediated or moderated by early negative maternal parenting behaviours. These associations were assessed in a sample of 108 MZ twins followed longitudinally since birth and scanned at age 15. The total grey matter (GM) and white matter (WM) volumes were obtained using the Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra (DARTEL) toolbox in the Statistical Parametric Mapping version 8 (SPM8). We found that the BW was significantly associated with the total GM and WM volumes, particularly in the superior frontal gyrus and thalamus. Within-twin-pair discordance in BW was also significantly associated with within-pair discordance in both the GM and the WM volumes, supporting the hypothesis that the specific in utero environment is associated with brain development independently of genetics. Early maternal hostile parenting behaviours and depressive symptoms were associated with total GM volume but not WM volume. Finally, greater early maternal hostility may moderate the association between the BW and GM volume in adolescence, since the positive association between the BW and total GM volume appeared stronger at higher levels of maternal hostility (trend). Together, these findings support the importance of the in utero and early environments for brain development.

Looking beyond the DNA sequence: the relevance of DNA methylation processes for the stress-diathesis model of depression

The functioning of the hypothalamic-pituitary-adrenal (HPA) axis and serotonergic (5-HT) system are known to be intertwined with mood. Alterations in these systems are often associated with depression. However, neither are sufficient to cause depression in and of themselves. It is now becoming increasingly clear that the environment plays a crucial role, particularly, the perinatal environment. In this review, we posit that early environmental stress triggers a series of epigenetic mechanisms that adapt the genome and programme the HPA axis and 5-HT system for survival in a harsh environment. We focus on DNA methylation as it is the most stable epigenetic mark. Given that DNA methylation patterns are in large part set within the perinatal period, long-term gene expression programming by DNA methylation is especially vulnerable to environmental insults during this period. We discuss specific examples of genes in the 5-HT system (serotonin transporter) and HPA axis (glucocorticoid receptor and arginine vasopressin enhancer) whose DNA methylation state is associated with early life experience and may potentially lead to depression vulnerability. We conclude with a discussion on the relevance of studying epigenetic mechanisms in peripheral tissue as a proxy for those occurring in the human brain and suggest avenues for future research.

Perinatal effects on in vivo measures of human brain serotonin synthesis in adulthood: a 27-year longitudinal study

There is an increasing evidence that prenatal and early postnatal stressors have life long impacts on physical and mental health problems. Animal studies have shown that this could include enduring changes to brain serotonin neurotransmission. In the present study, we tested whether perinatal adversity in humans has a long-term impact on brain serotonin neurotransmission in adulthood. Twenty-six healthy males, recruited from a 27-year longitudinal study, underwent a positron emission tomography scan with the tracer alpha-[¹¹C]methyl-L-tryptophan (¹¹C-AMT), as an index of serotonin synthesis capacity. The trapping constant is taken as a proxy for the regional 5-HT synthesis. Birth complications, especially a delivery where the fetus showed signs of physiological distress, predicted lower ¹¹C-AMT trapping in the hippocampus and medial orbitofrontal cortex. Lower ¹¹C-AMT trapping in the medial orbitofrontal cortex was also predicted by maternal smoking and lower birth weight. There were no effects of childhood or recent adversity. This is the first human study reporting associations between perinatal adversity and adult ¹¹C-AMT trapping in the hippocampus and medial orbitofrontal cortex. The associations suggest that limbic serotonin pathways may be particularly vulnerable to environmental challenges during the period when they undergo the most prominent neurodevelopmental changes. In combination with other risk factors, perinatal stressors may contribute to increased vulnerability for psychiatric disorders in which serotonin plays a major role.

Ontogeny and regulation of the serotonin transporter: providing insights into human disorders

Serotonin (5-hydroxytryptamine, 5-HT) was one of the first neurotransmitters for which a role in development was identified. Pharmacological and gene knockout studies have revealed a critical role for 5-HT in numerous processes, including cell division, neuronal migration, differentiation and synaptogenesis. An excess in brain 5-HT appears to be mechanistically linked to abnormal brain development, which in turn is associated with neurological disorders. Ambient levels of 5-HT are controlled by a vast orchestra of proteins, including a multiplicity of pre- and post-synaptic 5-HT receptors, heteroreceptors, enzymes and transporters. The 5-HT transporter (SERT, 5-HTT) is arguably the most powerful regulator of ambient extracellular 5-HT. SERT is the high-affinity uptake mechanism for 5-HT and exerts tight control over the strength and duration of serotonergic neurotransmission. Perturbation of its expression level or function has been implicated in many diseases, prominent among them are psychiatric disorders. This review synthesizes existing information on the ontogeny of SERT during embryonic and early postnatal development though adolescence, along with factors that influence its expression and function during these critical developmental windows. We integrate this knowledge to emphasize how inappropriate SERT expression or its dysregulation may be linked to the pathophysiology of psychiatric, cardiovascular and gastrointestinal diseases.

Body size at birth and socio-economic status in childhood: implications for Cloninger's psychobiological model of temperament at age 60

Small birth size predicts various psychiatric outcomes, including depression. While biologically based temperamental traits may constitute a vulnerability factor for depression, the extent to which birth size predicts these traits in adulthood is not known. We studied, in 1369 women and men identified from a cohort born in 1934-44 in Helsinki, Finland, whether birth size predicts the temperamental traits measured with Cloninger's Tridimensional Personality Questionnaire at an average age of 63 years. Moreover, we examined whether socio-economic status (SES) in childhood modified the associations. Data on birth size were obtained from birth records, and SES in childhood was obtained from school records. Weight and length at birth showed curvilinear, reverse J-shaped effects on harm avoidance (HA), such that the highest HA scores were most characteristic of those born small. Furthermore, high HA was confined to those belonging to a low SES group in childhood regardless of birth size, and to those belonging to the high SES group in childhood if their birth size was small. The associations were independent of several confounders. Since small birth size as well as high HA in adulthood may associate with subsequent depression, our findings might shed light on understanding the early neurodevelopmental processes that predispose to depression through vulnerability characteristics.