Genome-wide DNA methylation data from adult brain following prenatal immune activation and dietary intervention

Fructooligosaccharides and Aspergillus enzymes increase brain GABA and homocarnosine by modulating microbiota in adolescent mice

Recent research suggests that dietary prebiotics, probiotics, or healthy fecal-microbiota transplantation attenuate gut microbiota dysbiosis and ameliorate neurological disorders, in which gut-microbiota-derived γ-aminobutyric acid (GABA) has gained much attention as one of key mediators in the gut-brain axis. Although it is widely accepted that prebiotics and probiotics induce gut and brain GABA production via modulating gut microbiota, only evidence of probiotics has been solidly demonstrated while this evidence of prebiotics is scarce. Here, we demonstrated that prebiotic fructo-oligosaccharides and Aspergillus-derived enzymes elevated gut and brain GABA concentrations by modulating gut microbiota. Interestingly, we found that the prebiotic and enzymes increased a brain-specific dipeptide, homocarnosine. Gut GABA levels were found correlated with brain GABA/homocarnosine levels. Parabateroides, Akkermansia, Muribaculum, Hungatella, Marvinbryantia, Flavonifractor, and Incertae_sedis exhibited a positive correlation with gut GABA and brain GABA/homocarnosine levels, while Blautia, Unclassified_Lachnospiraceae, Colidextribacter, Acetatifactor, Roseburia, Unclassified_Oscillospiraceae, Romboutsia, and Eubacterium_coprostanoligenes exhibited a negative correlation with those levels.

Chronic corticosterone exposure in rats induces sex-specific alterations in hypothalamic reelin fragments, MeCP2, and DNMT3a protein levels

Women are disproportionately affected by stress-related disorders like depression. In our prior research, we discovered that females exhibit lower basal hypothalamic reelin levels, and these levels are differentially influenced by chronic stress induced through repeated corticosterone (CORT) injections. Although epigenetic mechanisms involving DNA methylation and the formation of repressor complexes by DNA methyl-transferases (DNMTs) and Methyl-CpG binding protein 2 (MeCP2) have been recognized as regulators of reelin expression in vitro, there is limited understanding of the impact of stress on the epigenetic regulation of reelin in vivo and whether sex differences exist in these mechanisms. To address these questions, we conducted various biochemical analyses on hypothalamic brain samples obtained from male and female rats previously treated with either 21 days of CORT (40 mg/kg) or vehicle (0.9 % saline) subcutaneous injections. Upon chronic CORT treatment, a reduction in reelin fragment NR2 was noted in males, while the full-length molecule remained unaffected. This decrease paralleled with an elevation in MeCP2 and a reduction in DNMT3a protein levels only in males. Importantly, sex differences in baseline and CORT-induced reelin protein levels were not associated with changes in the methylation status of the Reln promoter. These findings suggest that CORT-induced reelin decreases in the hypothalamus may be a combination of alterations in downstream processes beyond gene transcription. This research brings novel insights into the sexually distinct consequences of chronic stress, an essential aspect to understand, particularly concerning its role in the development of depression.

Preclinical animal models of mental illnesses to translate findings from the bench to the bedside: Molecular brain mechanisms and peripheral biomarkers associated to early life stress or immune challenges

Animal models are useful preclinical tools for studying the pathogenesis of mental disorders and the effectiveness of their treatment. While it is not possible to mimic all symptoms occurring in humans, it is however possible to investigate the behavioral, physiological and neuroanatomical alterations relevant for these complex disorders in controlled conditions and in genetically homogeneous populations. Stressful and infection-related exposures represent the most employed environmental risk factors able to trigger or to unmask a psychopathological phenotype in animals. Indeed, when occurring during sensitive periods of brain maturation, including pre, postnatal life and adolescence, they can affect the offspring's neurodevelopmental trajectories, increasing the risk for mental disorders. Not all stressed or immune challenged animals, however, develop behavioral alterations and preclinical animal models can explain differences between vulnerable or resilient phenotypes. Our review focuses on different paradigms of stress (prenatal stress, maternal separation, social isolation and social defeat stress) and immune challenges (immune activation in pregnancy) and investigates the subsequent alterations in several biological and behavioral domains at different time points of animals' life. It also discusses the "double-hit" hypothesis where an initial early adverse event can prime the response to a second negative challenge. Interestingly, stress and infections early in life induce the activation of the hypothalamic-pituitary-adrenal (HPA) axis, alter the levels of neurotransmitters, neurotrophins and pro-inflammatory cytokines and affect the functions of microglia and oxidative stress. In conclusion, animal models allow shedding light on the pathophysiology of human mental illnesses and discovering novel molecular drug targets for personalized treatments.