Prenatal programming of stress responsiveness and behaviours: Progress and perspectives

Parental exposure to stress or glucocorticoids either before or during pregnancy can have profound influences on neurodevelopment, neuroendocrine function and behaviours in offspring. Specific outcomes are dependent on the nature, intensity and timing of the exposure, as well as species, sex and age of the subject. Most recently, it has become evident that outcomes are not confined to first‐generation offspring and that there may be intergenerational and transgenerational transmission of effects. There has been intense focus on the mechanisms by which such early exposure leads to long‐term and potential transgenerational outcomes, and there is strong emerging evidence that epigenetic processes (histone modifications, DNA methylation, and small non‐coding RNAs) are involved. New knowledge in this area may allow the development of interventions that can prevent, ameliorate or reverse the long‐term negative outcomes associated with exposure to early adversity. This review will focus on the latest research, bridging human and pre‐clinical studies, and will highlight some of the limitations, challenges and gaps that exist in the field.     

Potential neurotoxicity of prenatal exposure to sevoflurane on offspring: Metabolomics investigation on neurodevelopment and underlying mechanism

Repeated or prolonged anesthesia to pregnant women disturbs neurodevelopment of developing infants, but its mechanism has not been elaborated absolutely. This study was conducted to investigate the mechanism of potential neurotoxicity on their offspring generation after sevoflurane anesthesia in adult animals during pregnancy based on metabolomics. 16 pregnant rats were equally assigned to sevoflurane group and control group, and serum samples were collected from their 7-day-old offspring for metabolomics analysis using ultra performance liquid chromatography coupled to time-of-flight mass spectrometry. Principal component analysis and partial least squares-discriminate analysis were used for pattern recognition, and pathway analysis was performed by MetaboAnalyst platform. 29 metabolites were discovered as neurotoxicity related-biomarkers, among which S-Adenosylmethioninamine was inhibited dramatically after sevoflurane exposure. Prenatal exposure to sevoflurane led to a significant reduction in S-Adenosylmethionine level, as shown by enzyme-linked immunosorbent assay. Pathway analysis highlighted that prenatal exposure to sevoflurane induced alteration in arginine/proline metabolism, cysteine/methionine metabolism, and so on. The most important altered metabolic pathway was arginine/proline metabolism. This study suggests that abnormal methylation and disturbed arginine/proline metabolism may crucially contribute to the mechanism with neurotoxicity on offspring generation after sevoflurane anesthesia in adult animals during pregnancy, and dietary supplement of S-Adenosylmethionine and modulating arginine/proline metabolism may be the potential therapeutic targets for protecting neurodevelopment from detrimental effects of prenatal exposure to inhalational anesthetics.     

Seizure length with sevoflurane and thiopental for induction of general anesthesia in electroconvulsive therapy: a randomized double-blind trial

In general, seizure length does not correlate with clinical outcome with electroconvulsive therapy (ECT), but whether markedly short seizures are still therapeutic is unknown. Furthermore, seizure length effects on clinical outcome in ECT may be different among the various anesthetic agents available. Several studies have investigated the use of inhalational anesthesia in ECT with sevoflurane. In general, seizure length when reported has been in the range of typical values encountered in practice. We recently completed a randomized double blind trial with sevoflurane induction compared with thiopental. Seizure duration with sevoflurane anesthesia was 8 seconds shorter than with thiopental for electroencephalogram and 6.4 seconds shorter for motor, the latter just barely missing statistical significance. Absolute values for seizure duration with both sevoflurane and thiopental are well within typical ranges for those seen with the more commonly used methohexital as anesthetic.     

Epigenetic mechanisms and the transgenerational effects of maternal care

The transmission of traits across generations has typically been attributed to the inheritance by offspring of genomic information from parental generations. However, recent evidence suggests that epigenetic mechanisms are capable of mediating this type of transmission. In the case of maternal care, there is evidence for the behavioral transmission of postpartum behavior from mothers to female offspring. The neuroendocrine and molecular mediators of this transmission have been explored in rats and implicate estrogen-oxytocin interactions and the differential methylation of hypothalamic estrogen receptors. These maternal effects can influence multiple aspects of neurobiology and behavior of offspring and this particular mode of inheritance is dynamic in response to environmental variation. In this review, evidence for the generational transmission of maternal care and the mechanisms underlying this transmission will be discussed as will the implications of this inheritance system for offspring development and for the transmission of environmental information from parents to offspring.     

Multiple sevoflurane exposures during mid-trimester induce neurotoxicity in the developing brain initiated by 15LO2-Mediated ferroptosis

Aims

Mid-gestational sevoflurane exposure may induce notable long-term neurocognitive impairment in offspring. This study was designed to investigate the role and potential mechanism of ferroptosis in developmental neurotoxicity induced by sevoflurane in the second trimester.

Methods

Pregnant rats on day 13 of gestation (G13) were treated with or without 3.0% sevoflurane, Ferrostatin-1 (Fer-1), PD146176, or Ku55933 on three consecutive days. Mitochondrial morphology, ferroptosis-relative proteins, malondialdehyde (MDA) levels, total iron content, and glutathione peroxidase 4 (GPX4) activities were measured. Hippocampal neuronal development in offspring was also examined. Subsequently, 15-lipoxygenase 2 (15LO2)-phosphatidylethanolamine binding protein 1 (PEBP1) interaction and expression of Ataxia telangiectasia mutated (ATM) and its downstream proteins were also detected. Furthermore, Morris water maze (MWM) and Nissl's staining were applied to estimate the long-term neurotoxic effects of sevoflurane.

Results

Ferroptosis mitochondria were observed after maternal sevoflurane exposures. Sevoflurane elevated MDA and iron levels while inhibiting GPX4 activity, and resultant long-term learning and memory dysfunction, which were alleviated by Fer-1, PD146176, and Ku55933. Sevoflurane could enhance 15LO2-PEBP1 interaction and activate ATM and its downstream P53/SAT1 pathway, which might be attributed to excessive p-ATM nuclear translocation.

Conclusion

This study proposes that 15LO2-mediated ferroptosis might contribute to neurotoxicity induced by maternal sevoflurane anesthesia during the mid-trimester in the offspring and its mechanism may be ascribed to hyperactivation of ATM and enhancement of 15LO2-PEBP1 interaction, indicating a potential therapeutic target for ameliorating sevoflurane-induced neurotoxicity.     

Parental Advisory: Maternal and Paternal Stress Can Impact Offspring Neurodevelopment

Parental stress exposures are implicated in the risk for offspring neurodevelopmental and neuropsychiatric disorders, prompting critical examination of preconception and prenatal periods as vulnerable to environmental insults such as stress. Evidence from human studies and animal models demonstrates the influence that both maternal and paternal stress exposures have in changing the course of offspring brain development. Mechanistic examination of modes of intergenerational transmission of exposure during pregnancy has pointed to alterations in placental signaling, including changes in inflammatory, nutrient-sensing, and epigenetic pathways. Transmission of preconception paternal stress exposure is associated with changes in epigenetic marks in sperm, with a primary focus on the reprogramming of DNA methylation, histone posttranslational modifications, and small noncoding RNAs. In this review, we discuss evidence supporting the important contribution of intergenerational parental stress in offspring neurodevelopment and disease risk, and the currently known epigenetic mechanisms underlying this transmission.     

General anesthesia activates the mitochondrial unfolded protein response and induces age-dependent,long-lasting changes in mitochondrial function in the developing brain

General anesthesia induces changes in dendritic spine number and synaptic transmission in developing mice. These changes are rather disturbing, as similar changes are seen in animal models of neurodevelopmental disorders. We previously suggested that mTor-dependent upregulation of mitochondrial function may be involved in such changes. To further understand the significance of mitochondrial changes after general anesthesia during neurodevelopment, we exposed young mice to 2.5 % sevoflurane for 2 h followed by injection of rotenone, a mitochondrial complex I inhibitor. In postnatal day 17 (PND17) mice, intraperitoneal injection of rotenone not only blocked sevoflurane-induced increases in mitochondrial function, it also prevented sevoflurane-induced changes in excitatory synaptic transmission. Interestingly, similar changes were not observed in younger, neonatal mice (PND7). We next assessed whether the mitochondrial unfolded protein response (UPR^mt) acted as a link between anesthetic exposure and mitochondrial function. Expression of UPR^mt proteins, which help maintain protein-folding homeostasis and increase mitochondrial function, was increased 6 h after sevoflurane exposure. Our results show that a single, brief sevoflurane exposure induces age-dependent changes in mitochondrial function that constitute an important mechanism for the increase in excitatory synaptic transmission in late postnatal mice, and also suggest mitochondria and UPR^mt as potential targets for preventing anesthesia toxicity.     

The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity

Early exposure to general anesthesia (GA) causes developmental neuroapoptosis in the mammalian brain and long-term cognitive impairment. Recent evidence suggests that GA also causes functional and morphological impairment of the immature neuronal mitochondria. Injured mitochondria could be a significant source of reactive oxygen species (ROS), which, if not scavenged in timely fashion, may cause excessive lipid peroxidation and damage of cellular membranes. We examined whether early exposure to GA results in ROS upregulation and whether mitochondrial protection and ROS scavenging prevent GA-induced pathomorphological and behavioral impairments. We exposed 7-day-old rats to GA with or without either EUK-134, a synthetic ROS scavenger, or R(+) pramipexole (PPX), a synthetic aminobenzothiazol derivative that restores mitochondrial integrity. We found that GA causes extensive ROS upregulation and lipid peroxidation, as well as mitochondrial injury and neuronal loss in the subiculum. As compared to rats given only GA, those also given PPX or EUK-134 had significantly downregulated lipid peroxidation, preserved mitochondrial integrity, and significantly less neuronal loss. The subiculum is highly intertwined with the hippocampal CA1 region, anterior thalamic nuclei, and both entorhinal and cingulate cortices; hence, it is important in cognitive development. We found that PPX or EUK-134 co-treatment completely prevented GA-induced cognitive impairment. Because mitochondria are vulnerable to GA-induced developmental neurotoxicity, they could be an important therapeutic target for adjuvant therapy aimed at improving the safety of commonly used GAs.     

Dopamine D1-receptor-expressing pathway from the nucleus accumbens to ventral pallidum-mediated sevoflurane anesthesia in mice

Background

General anesthesia has long been used in clinical practice, but its precise pharmacological effects on neural circuits are not fully understood. Recent investigations suggest that the sleep–wake system may play a role in the reversible loss of consciousness induced by general anesthetics. Studies in mice have shown that microinjection of dopamine receptor 1 (D1R) agonists into the nucleus accumbens (NAc) promotes recovery from isoflurane anesthesia, while microinjection of D1R antagonists has the opposite effect. Furthermore, during the induction and maintenance of sevoflurane anesthesia, there is a significant decrease in extracellular dopamine levels in the NAc, which subsequently increases during the recovery period. These findings suggest the involvement of the NAc in the regulation of general anesthesia. However, the specific role of D1R-expressing neurons in the NAc during general anesthesia and the downstream effect pathways are still not well understood.

Methods

In order to analyze the impact of sevoflurane anesthesia on NAc^D1R neurons and the NAc^D1R-VP pathway, this study employed calcium fiber photometry to investigate alterations in the fluorescence intensity of calcium signals in dopamine D1-receptor-expressing neurons located in the nucleus accumbens (NAc^D1R neurons) and the NAc^D1R-VP pathway during sevoflurane anesthesia. Subsequently, optogenetic techniques were utilized to activate or inhibit NAc^D1R neurons and their synaptic terminals in the ventral pallidum (VP), aiming to elucidate the role of NAc^D1R neurons and the NAc^D1R-VP pathway in sevoflurane anesthesia. These experiments were supplemented with electroencephalogram (EEG) recordings and behavioral tests. Lastly, a genetically-encoded fluorescent sensor was employed to observe changes in extracellular GABA neurotransmitters in the VP during sevoflurane anesthesia.

Results

Our findings revealed that sevoflurane administration led to the inhibition of NAc^D1R neuron population activity, as well as their connections within the ventral pallidum (VP). We also observed a reversible reduction in extracellular GABA levels in the VP during both the induction and emergence phases of sevoflurane anesthesia. Additionally, the optogenetic activation of NAc^D1R neurons and their synaptic terminals in the VP resulted in a promotion of wakefulness during sevoflurane anesthesia, accompanied by a decrease in EEG slow wave activity and burst suppression rate. Conversely, the optogenetic inhibition of the NAc^D1R-VP pathway exerted opposite effects.

Conclusion

The NAc^D1R-VP pathway serves as a crucial downstream pathway of NAc^D1R neurons, playing a significant role in regulating arousal during sevoflurane anesthesia. Importantly, this pathway appears to be associated with the release of GABA neurotransmitters from VP cells.     

Lifetime stress experience: transgenerational epigenetics and germ cell programming

The transgenerational epigenetic programming involved in the passage of environmental exposures to stressful periods from one generation to the next has been examined in human populations, and mechanistically in animal models. Epidemiological studies suggest that gestational exposures to environmental factors including stress are strongly associated with an increased risk of neurodevelopmental disorders, including attention deficit-hyperactivity disorder, schizophrenia, and autism spectrum disorders. Both maternal and paternal life experiences with stress can be passed on to offspring directly during pregnancy or through epigenetic marks in the germ cell. Animal models of parental stress have examined relevant offspring phenotypes and transgenerational outcomes, and provided unique insight into the germ cell epigenetic changes associated with disruptions in neurodevelopment. Understanding germline susceptibility to exogenous signals during stress exposure and the identification of the types of epigenetic marks is critical for defining mechanisms underlying disease risk.     

High-concentration sevoflurane exposure in mid-gestation induces apoptosis of neural stem cells in rat offspring

Sevoflurane is the most commonly used volatile anesthetic during pregnancy.The viability of neural stem cells directly affects the development of the brain.However,it is unknown whether the use of sevoflurane during the second trimester affects the survival of fetal neural stem cells.Therefore,in this study,we investigated whether exposure to sevoflurane in mid-gestation induces apoptosis of neural stem cells and behavioral abnormalities.On gestational day 14,pregnant rats were anesthetized with 2% or 3.5% sevoflurane for 2 hours.The offspring were weaned at 28 days and subjected to the Morris water maze test.The brains were harvested to examine neural stem cell apoptosis by immunofluorescence and to measure Nestin and SOX-2 levels by western blot assay at 6,24 and 48 hours after anesthesia as well as on postnatal day(P) 0,14 and 28.Vascular endothelial growth factor(VEGF) and phosphoinositide 3-kinase(PI3 K)/AKT pathway protein levels in fetal brain at 6 hours after anesthesia were assessed by western blot assay.Exposure to high-concentration(3.5%) sevoflurane during mid-gestation increased escape latency and path length to the platform,and it reduced the average duration spent in the target quadrant and platform crossing times.At 6,24 and 48 hours after anesthesia and at P0,P14 and P28,the percentage of Nestin/terminal deoxynucleotidyl transferase d UTP nick end labeling(TUNEL)-positive cells was increased,but Nestin and SOX-2 protein levels were decreased in the hippocampus of the offspring.At 6 hours after anesthesia,VEGF,PI3 K and phospho-AKT(p-AKT) levels were decreased in the fetal brain.These changes were not observed in animals given low-concentration(2%) sevoflurane exposure.Together,our findings indicate that exposure to a high concentration of sevoflurane(3.5%) in mid-gestation decreases VEGF,PI3 K and p-AKT protein levels and induces neural stem cell apoptosis,thereby causing learning and memory dysfunction in the offspring.     

Chronic exposure of gestation rat to sevoflurane impairs offspring brain development

Recently it was demonstrated that the exposure of the developing brain during the period of synaptogenesis to drugs that block NMDA glutamate receptors can trigger widespread apoptotic neurodegeneration. Sevoflurane is a new inhalation anesthetic agent commonly used in the clinic. Here we address whether sevoflurane could induce neurotoxicity in the developing brain. Sevoflurane was administered to rats before pregnancy and pregnant rats on embryonic days E6, E10, E14, and E18 1MAC for 6 h, and we employed histopathological, immunochemistry, semiquantitative RT-PCR, and Western blot to investigate the effect of the exposure of pregestation and gestation rats to sevoflurane on the offspring brain development. The results showed that the exposure of gestation but not pregestation rats to sevoflurane-induced extensive apoptotic neurodegeneration in the hippocampus of offspring at P0, P7, and P14, accompanied by altered expression of casepase-3, GAP-43, nNOS, NMDAR1, NMDAR2A, and NMDAR2B. Furthermore, upregulation of PKCα and p-JNK and downregulation of p-ERK and FOS protein levels were observed in the hippocampus of offspring at P0, P7, and P14 from rats exposed to sevoflurane at gestation, but not pregestation. In summary, our data suggest that sevoflurane induces developmental neurotoxicity in rats and this may be attributed to the upregulation of PKCα and p-JNK and downregulation of p-ERK and FOS protein in the hippocampus.     

The histamine H1 receptor antagonist hydroxyzine enhances sevoflurane and propofol anesthesia: A quantitative EEG study

ObjectiveThe aim of this study was to determine the anesthesia-promoting effects of hydroxyzine on electroencephalograms during sevoflurane anesthesia and during propofol anesthesia.MethodsWe analyzed 40 patients scheduled for elective surgery under sevoflurane anesthesia (n = 20) or propofol anesthesia (n = 20). Anesthesia was adjusted at a bispectral index value of 50–60, and then 0.5 mg/kg of hydroxyzine was administered intravenously. We analyzed frontal electroencephalograms before and after hydroxyzine injection with power spectral and bicoherence analyses, which are suitable for assessing the anesthetic depth induced by γ-aminobutyric acid (GABA)ergic anesthetics.ResultsHydroxyzine increased the α bicoherence peaks in both sevoflurane anesthesia (mean difference, 11.2%; 95% confidence interval (CI), 7.6 to 14.8; P < 0.001) and propofol anesthesia (mean difference, 5.6%; 95% CI, 1.7 to 9.4; P = 0.008). Hydroxyzine increased the averaged δ bicoherence values in both sevoflurane anesthesia (mean difference, 5.5%; 95% CI, 2.1 to 8.8; P = 0.003) and propofol anesthesia (mean difference, 3.9%; 95% CI, 1.0 to 6.8; P = 0.011).ConclusionsHydroxyzine enhances both sevoflurane anesthesia and propofol anesthesia probably by facilitation of GABAergic neural circuit mechanisms.SignificanceThe findings provide a new insight into the role of histaminergic neurons during general anesthesia in humans.     

Aberrant epigenetic regulation could explain the relationship of paternal age to schizophrenia

The causal mechanism underlying the well-established relation between advancing paternal age and schizophrenia is hypothesized to involve mutational errors during spermatogenesis that occur with increasing frequency as males age. Point mutations are well known to increase with advancing paternal age while other errors such as altered copy number in repeat DNA and chromosome breakage have in some cases also been associated with advancing paternal age. Dysregulation of epigenetic processes may also be an important mechanism underlying the association between paternal age and schizophrenia. Evidence suggests that advancing age as well as environmental exposures alter epigenetic regulation. Errors in epigenetic processes, such as parental imprinting can have serious effects on the offspring both pre- and postnatally and into adulthood. This article will discuss parental imprinting on the autosomal and X chromosomes and the alterations in epigenetic regulation that may lead to such errors.     

Epigenetic mechanisms mediating the long-term effects of maternal care on development

The long-term consequences of early environmental experiences for development have been explored extensively in animal models to better understand the mechanisms mediating risk of psychopathology in individuals exposed to childhood adversity. One common feature of these models is disruption of the mother-infant relationship which is associated with impairments in stress responsivity and maternal behavior in adult offspring. These behavioral and physiological characteristics are associated with stable changes in gene expression which emerge in infancy and are sustained into adulthood. Recent evidence suggests that these long-term effects may be mediated by epigenetic modification to the promoter regions of steroid receptor genes. In particular, DNA methylation may be critical to maternal effects on gene expression and thus generate phenotypic differentiation of offspring and, through effects on maternal behavior of offspring, mediate the transmission of these effects across generations. In this review we explore evidence for the influence of mother-infant interactions on the epigenome and consider evidence for and the implications of such epigenetic effects for human mental health.     

Driving the Next Generation: Paternal Lifetime Experiences Transmitted via Extracellular Vesicles and Their Small RNA Cargo

Epidemiological studies provide strong evidence for the impact of diverse paternal life experiences on offspring neurodevelopmental disease risk. While these associations are well established, the molecular mechanisms underlying these intergenerational transmissions remain elusive, though recent studies focusing on the influence of paternal experience before conception have implicated germ cell epigenetic programming. Any model accounting for the germline transfer of nongenetic information from sire to offspring must include certain components, such as 1) a vector to carry any signal from the paternal compartment to the maternal reproductive tract and future embryo; 2) a molecular signal, encoded by a paternal experience, to carry this memory and enact downstream responses; and 3) a target cell or tissue to receive the signal and convert it into an effect on embryonic development. We explore the current understanding of the potential processes and candidate factors that may serve as these components. We specifically discuss the growing appreciation for the importance of extracellular vesicles in these processes, beginning with their known role in delivering potential signals, including small RNAs, to sperm, the prototypical vector, during their posttesticular maturation. Finally, we explore the possibility that paternal extracellular vesicles could themselves serve as vectors, delivering signals not only to gametes or the zygote but also to tissues of the maternal reproductive tract to influence fetal development.     

Developmental consequences and biological significance of mother-infant bonding

Mother-infant bonding is universal to all mammalian species. Here, we review how mutual communication between the mother and infant leads to mother-infant bonding in non-primate species. In rodents, mother-infant bond formation is reinforced by various pup stimuli, such as tactile stimuli and ultrasonic vocalizations. Evidence suggests that the oxytocin neural system plays a pivotal role in each aspect of the mother-infant bonding, although the mechanisms underlying bond formation in the brain of infants has not yet been clarified. Impairment of mother-infant bonding strongly influences offspring sociality. We describe the negative effects of mother-infant bonding deprivation on the neurobehavioral development in rodent offspring, even if weaning occurs in the later lactating period. We also discuss similar effects observed in pigs and dogs, which are usually weaned earlier than under natural conditions. The comparative understanding of the developmental consequences of mother-infant bonding and the underlying mechanisms provide insight into the biological significance of this bonding in mammals, and may help us to understand psychiatric disorders related to child abuse or childhood neglect.     

Sevoflurane exposure in 7-day-old rats affects neurogenesis, neurodegeneration and neurocognitive function

Objective Sevoflurane is widely used in pediatric anesthesia and former studies showed that it causes neurodegeneration in the developing brain. The present study was carried out to investigate the effects of sevoflurane on neurogenesis, neurodegeneration and behavior. Methods We administered 5-bromodeoxyuridine, an S-phase marker, before, during, and after 4 h of sevoflurane given to rats on postnatal day 7 to assess dentate gyrus progenitor proliferation and Fluoro-Jade staining for degeneration. Spatial reference memory was tested 2 and 6 weeks after anesthesia. Results Sevoflurane decreased progenitor proliferation and increased cell death until at least 4 days after anesthesia. Spatial reference memory was not affected at 2 weeks but was affected at 6 weeks after sevoflurane administration. Conclusion Sevoflurane reduces neurogenesis and increases the death of progenitor cells in developing brain. This might mediate the lateonset neurocognitive outcome after sevoflurane application.     

Mechanism of action of glatiramer acetate in treatment of multiple sclerosis

Glatiramer acetate (GA) (Copolymer-1, Copaxone, Teva, Israel, YEAK) is a polypeptide-based therapy approved for the treatment of relapsing-remitting multiple sclerosis. Most investigations have attributed the immunomodulatory effect of GAs to its capability to alter T-cell differentiation. Specifically, GA treatment is believed to promote development of Th2-polarized GA-reactive CD4⁺ T-cells, which may dampen neighboring inflammation within the central nervous system. Recent reports indicate that the deficiency in CD4⁺CD25⁺FoxP3⁺ regulatory T-cells in multiple sclerosis is restored by GA treatment. GA also exerts immunomodulatory activity on antigen presenting cells, which participate in innate immune responses. These new findings represent a plausible explanation for GA-mediated T-cell immune modulation and may provide useful insight for the development of new and more effective treatment options for multiple sclerosis.