Maternal immune activation increases the corticosterone response to acute stress without affecting the hypothalamic monoamine content and sleep patterns in male mice offspring

Genes Participating in the Ensheathment of Neurons Are Affected by Postnatal Stress and Maternal Immune Activation in the Pituitary Gland

Immune challenges during gestation are associated with neurodevelopmental disorders and can interact with stress later in life. The pituitary gland participates in endocrine- and immune-related processes that influence development, growth, and reproduction and can modulate physiological and behavioral responses to challenges. The objective of this study was to investigate the effect of stressors at different time points on the molecular mechanisms of the pituitary gland and detect sex differences. RNA sequencing was used to profile the pituitary glands of female and male pigs exposed to weaning stress and virally induced maternal immune activation (MIA), relative to unchallenged groups. Significant effects (FDR-adjusted p-value < 0.05) of MIA and weaning stress were detected in 1829 and 1014 genes, respectively. Of these, 1090 genes presented significant interactions between stressors and sex. The gene ontology biological process of the ensheathment of neurons (GO:0007272), substance abuse, and immuno-related pathways, including the measles disease (ssc05162), encompasses many genes with profiles impacted by MIA and weaning stress. A gene network analysis highlighted the under-expression of myelin protein zero (Mpz) and inhibitors of DNA binding 4 (Id4) among the non-stressed males exposed to MIA, relative to the control and non-MIA males exposed to weaning stress, relative to non-stressed pigs. The detection of changes in the molecular mechanisms of the pituitary gland could advance our understanding of disruptions in the formation of the myelin sheath and the transmission of neuron-to-neuron signals in behavioral disorders associated with maternal immune activation and stress.

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.

Maternal immune activation in rats attenuates the excitability of monoamine-secreting neurons in adult offspring in a sex-specific way

Higher risk of depression and schizophrenia in descendants of mothers experienced acute infection during the pregnancy has been reported. Since monoamines are fundamental in mentioned psychopathologies, it is possible that maternal immune activation leads to impaired functioning of serotonin (5-HT), noradrenaline, and dopamine neurons in offspring. To test this hypothesis, we examined the effect of maternal immune activation by lipopolysaccharide (LPS) in rats on the excitability of monoamine-secreting neurons in the offspring. LPS was administered during days 15-19 of the gestation in the rising doses of 20-80 µg/kg; control dams received vehicle. During days 53-63 postpartum, rats were anesthetized and electrodes were inserted into the dorsal raphe nucleus, locus coeruleus, and ventral tegmental area for in vivo excitability assessment of 5-HT, noradrenaline, and dopamine neurons. Maternal immune activation suppressed the firing rate of 5-HT neurons in both sexes and stimulated the firing rate of dopamine neurons in males. Decrease in the firing rate of 5-HT neurons was accompanied with an increase, and increase in the firing rate of dopamine neurons with a decrease, in the density of spontaneously active cells. Maternal immune activation also decreased the variability of interspike intervals in 5-HT and dopamine neurons. It is possible that the alteration of excitability of 5-HT and dopamine neurons by maternal immune activation is involved in the psychopathologies induced by infectious disease during the pregnancy. Stimulation of dopamine excitability in males might be a compensatory mechanism secondary to the maternal immune challenge-induced suppression of 5-HT neurons.

Therapeutic efficacy of environmental enrichment on behavioral, endocrine, and synaptic alterations in an animal model of maternal immune activation

Maternal immune activation (MIA) has been identified as a significant risk factor for several neurodevelopmental disorders. We have previously demonstrated that postpubertal environmental enrichment (EE) rescues and promotes resiliency against MIA in male rats. Importantly, EE protocols have demonstrated clinical relevancy in human rehabilitation settings. Applying some of the elements of these EE protocols (e.g. social, physical, cognitive stimulation) to animal models of health and disease allows for the exploration of the mechanisms that underlie their success. Here, using a MIA model, we further investigate the rehabilitative potential of complex environments with a focus on female animals. Additionally, we expand upon some of our previous work by exploring genetic markers of synaptic plasticity and stress throughout several brain regions of both sexes. In the current study, standard housed female Sprague-Dawley rats were challenged with either the inflammatory endotoxin lipopolysaccharide (LPS; 100 μg/kg) or saline (equivolume) on gestational day 15. On postnatal day 50, male and female offspring were randomized into one of three conditions that differed in terms of cage size, number of cage mates (social stimulation) and enrichment materials. Spatial discrimination ability and social behavior were assessed six weeks later. Similar to our previously published work in males, our results revealed that a single LPS injection during mid gestation disrupted spatial discrimination ability in female rats. Postpubertal EE rescued this disruption. On the endocrine level, EE dampened elevations in plasma corticosterone that followed MIA, which may mediate EE's rehabilitative effects in female offspring. Within the prefrontal cortex, hippocampus, amygdala, and hypothalamus, MIA and EE altered the mRNA expression of several genes associated with resiliency and synaptic plasticity in both sexes. Overall, our findings provide further evidence that EE may serve as a therapeutic intervention for MIA-induced behavioral and cognitive deficits. Moreover, we identify some sexually dimorphic molecular mechanisms that may underlie these impairments and their rescue.

Sleep as a translationally-relevant endpoint in studies of autism spectrum disorder (ASD)

Sleep has numerous advantages for aligning clinical and preclinical (basic neuroscience) studies of neuropsychiatric illness. Sleep has high translational relevance, because the same endpoints can be studied in humans and laboratory animals. In addition, sleep experiments are conducive to continuous data collection over long periods (hours/days/weeks) and can be based on highly objective neurophysiological measures. Here, we provide a translationally-oriented review on what is currently known about sleep in the context of autism spectrum disorder (ASD), including ASD-related conditions, thought to have genetic, environmental, or mixed etiologies. In humans, ASD is frequently associated with comorbid medical conditions including sleep disorders. Animal models used in the study of ASD frequently recapitulate dysregulation of sleep and biological (diurnal, circadian) rhythms, suggesting common pathophysiologies across species. As our understanding of the neurobiology of ASD and sleep each become more refined, it is conceivable that sleep-derived metrics may offer more powerful biomarkers of altered neurophysiology in ASD than the behavioral tests currently used in humans or lab animals. As such, the study of sleep in animal models for ASD may enable fundamentally new insights on the condition and represent a basis for strategies that enable the development of more effective therapeutics.

Chronic Gestational Inflammation: Transfer of Maternal Adaptation over Two Generations of Progeny

Changes in the in utero environment result in generational transfer of maladapted physiology in the context of conditions such as stress, obesity, and anxiety. Given the significant contribution of noncommunicable diseases-which are characterised by chronic inflammation-to population mortality, the potential for chronic maternal inflammation mediating foetal programming is a growing concern. The extent of generational transfer in terms of immune functionality and leukocyte glucocorticoid sensitivity was investigated over two generations of offspring (F1 and F2) in a model of chronic LPS-induced maternal inflammation in C57/BL/6 mice. Maternal inflammation resulted in glucocorticoid hypersensitivity (increased glucocorticoid receptor expression levels) in the majority of leukocyte subpopulations in both F1 and F2 offspring. Furthermore, splenocytes stimulated with LPS in vitro exhibited exacerbated inflammatory cytokine responses, which were even more prominent in F2 than F1; this effect could be ascribed to NLRP3 inflammasome hyperactivity in F1 but not F2. Current data illustrates that parental chronic inflammation may mediate the inflammatory profile in offspring, potentially propagating a maladapted proinflammatory phenotype in subsequent generations.

d-Limonene protects PC12 cells against corticosterone-induced neurotoxicity by activating the AMPK pathway

The stress-induced hormone corticosterone initiates oxidative stress and inflammatory responses, culminating in cell apoptosis and neurological changes. We assessed the effects of d-Limonene on a PC12 cellular model of corticosterone-induced neurotoxicity, and whether these effects involved the AMP-activated protein kinase (AMPKα) pathway. PC12 cells were treated with corticosterone with or without d-limonene for 24 h. Western blots were performed to measure activation of AMPK pathway members [Silent mating type information regulation 2 homolog-1 (SIRT1), AMPKα, and nuclear factor (NFκB)], reactive oxygen species, inflammatory cytokines, and markers of apoptosis. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) was used to measure cell death after treatment. d-Limonene reversed the effects of corticosterone on PC12 cells: it decreased the levels of malondialdehyde (MDA) and nitric oxide (NO), activities of NADPH oxidase (p67-phox and p47-phox), expression of pro-inflammatory markers [inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin 6 (IL-6), interleukin 1β (IL-1β), and tumor necrosis factor α (TNF-α)], and expression of pro-apoptotic proteins [Bcl2 associated with X protein (Bax) and cleaved caspase-3)]. d-Limonene also increased levels of the antioxidant enzymes superoxide dismutase 1 (SOD1) and heme oxygenase 1 (HO-1) and the anti-apoptotic protein Bcl-2 while decreasing the number of TUNEL-positive cells. d-limonene significantly activated AMPKα and suppressed NF-κB nuclear translocation through up-regulation of SIRT1. Addition of compound C, an AMPK inhibitor, severely weakened these neuroprotective effects of d-limonene. d-Limonene has a neuroprotective effect on corticosterone-induced PC12 cell injury induced by activating the AMPKα signaling pathway, and thereby inhibiting reactive oxygen species and inflammatory factors. These data suggest that d-limonene might protect against neuronal death to improve depressive symptoms.

Immunity and ultrasonic vocalization in rodents

Ultrasonic vocalizations (USVs) serve important communicative functions in rodents. Different types of USVs can be triggered in the sender, for example, by maternal separation, social interactions, or exposure to predators, and they evoke affiliative or alarming behaviors in recipients. This review focusses on studies evaluating possible links between immunity and USVs. Most studies have been performed in a murine model of maternal immune activation and subsequent evaluation of effects in the offspring. This model has received large attention in recent years because it mimics behavioral abnormalities observed in certain human neuropsychiatric disorders, including autism spectrum disorder. Although there is still some controversy, the results indicate that stimulation of the immune system of mice and rats during pregnancy affects ultrasonic calling in pups. Few studies are available on immunization during adulthood and USVs. In most cases, immune stimulation led to disease, complicating conclusions about a possible direct link between vocalization and immunity. Although much work is still needed, this is certainly a rather new and promising aspect of interactions between the immune system and behavior.

Prenatal Activation of Toll-Like Receptor-4 Dampens Adult Hippocampal Neurogenesis in An IL-6 Dependent Manner

Prenatal immune challenge has been associated with alteration in brain development and plasticity that last into adulthood. We have previously shown that prenatal activation of toll-like receptor 4 by lipopolysaccharide (LPS) induces IL-6-dependent STAT-3 signaling pathway in the fetal brain. Whether this IL-6-dependent activation of fetal brain results in long lasting impact in brain plasticity is still unknown. Furthermore, it has been shown that prenatal LPS heightens the hypothalamic-pituitary-adrenal (HPA) response in adulthood. In the present study we tested whether LPS administration during pregnancy affects neurogenesis in adult male offspring. Because corticosterone, the end-product of HPA axis activity in rats, alters neurogenesis we tested whether this enhanced HPA axis responsiveness in adult male offspring played a role in the long lasting impact of LPS on neurogenesis during adulthood. Pregnant rats were given either LPS, or LPS and an IL-6 neutralizing antibody (IL-6Ab). The newly born neurons were monitored in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus of adult male offspring by monitoring doublecortin and T-box brain protein-2 expression: two well-established markers of newly born neurons. Prenatal LPS decreased the number of newly born neurons in the DG, but not in the SVZ of adult offspring. This decreased number of newly born neurons in the DG was absent when IL-6Ab was co-injected with LPS during pregnancy. Furthermore, administration of a corticosterone receptor blocker, RU-486, to adult offspring blunted the prenatal LPS induced decrease in newly born neurons in the DG. These data suggest that maternally triggered IL-6 plays a crucial role in the long lasting impact of LPS on adult neurogenesis.

Long-term pathological consequences of prenatal infection: beyond brain disorders

Prenatal immunological adversities such as maternal infection have been widely acknowledged to contribute to an increased risk of neurodevelopmental brain disorders. In recent years, epidemiological and experimental evidence has accumulated to suggest that prenatal exposure to immune challenges can also negatively affect various physiological and metabolic functions beyond those typically associated with primary defects in CNS development. These peripheral changes include excessive accumulation of adipose tissue and increased body weight, impaired glycemic regulation and insulin resistance, altered myeloid lineage development, increased gut permeability, hyperpurinergia, and changes in microbiota composition. Experimental work in animal models further suggests that at least some of these peripheral abnormalities could directly contribute to CNS dysfunctions, so that normalization of peripheral pathologies could lead to an amelioration of behavioral deficits. Hence, seemingly unrelated central and peripheral effects of prenatal infection could represent interrelated pathological entities that emerge in response to a common developmental stressor. Targeting peripheral abnormalities may thus represent a valuable strategy to improve the wide spectrum of behavioral abnormalities that can emerge in subjects with prenatal infection histories.

Maternal immune activation in late gestation increases neuroinflammation and aggravates experimental autoimmune encephalomyelitis in the offspring

Multiple sclerosis (MS) is characterized by an autoimmune response against myelin antigens driven by autoreactive T cells. Several lines of evidence indicate that environmental factors, such as previous infection, can influence and trigger autoimmune responses. However, the importance of the gestational period, particularly under inflammatory conditions, on the modulation of MS and related neuroinflammation by the offspring is unknown. This study aimed to evaluate the impact of prenatal exposure to lipopolysaccharide (LPS) during late gestation on the neuroinflammatory response in primary mixed glial cultures and on the progression of experimental autoimmune encephalomyelitis (EAE, an animal model of MS) in the offspring. LPS (Escherichia coli 0127:B8, 120μg/kg) was administered intraperitoneally to pregnant C57BL/6J mice on gestational day 17, and the offspring were assigned to two experiments: (1) mixed glial cultures generated using the brain of neonates, stimulated in vitro with LPS, and (2) adult offspring immunized with MOG35-55. The EAE clinical symptoms were followed for 30days. Different sets of animals were sacrificed either during the onset (7days post-immunization [p.i.]), when spleen and lymph nodes were collected, or the peak of disease (20days p.i.), when CNS were collected for flow cytometry, cytokine production, and protein/mRNA-expression analysis. The primary CNS cultures from the LPS-treated group produced exaggerated amounts of IL-6, IL-1β and nitrites after in vitro stimulus, while IL-10 production was lowered compared to the data of the control group. Prenatal exposure to LPS worsened EAE disease severity in adult offspring, and this worsening was linked to increased CNS-infiltrating macrophages, Th1 cells and Th17 cells at the peak of EAE severity; additionally, exacerbated gliosis was evidenced in microglia (MHC II) and astrocytes (GFAP protein level and immunoreactivity). The IL-2, IL-6 and IL-17 levels in the spleen and lymph nodes were increased in the offspring of the LPS-exposed dams. Our results indicate that maternal immune activation during late gestation predispose the offspring to increased neuroinflammation and potentiate the autoimmune response and clinical manifestation of EAE.