Maternal care influences hippocampal N-methyl-D-aspartate receptor function and dynamic regulation by corticosterone in adulthood

Cage effects on synaptic plasticity and its modulation in a mouse model of fragile X syndrome

Fragile X syndrome (FXS) is characterized by impairments in executive function including different types of learning and memory. Long-term potentiation (LTP), thought to underlie the formation of memories, has been studied in the Fmr1 mouse model of FXS. However, there have been many discrepancies in the literature with inconsistent use of littermate and non-littermate Fmr1 knockout (KO) and wild-type (WT) control mice. Here, the influence of the breeding strategy (cage effect) on short-term potentiation (STP), LTP, contextual fear conditioning (CFC), expression of N-methyl-d-aspartate receptor (NMDAR) subunits and the modulation of NMDARs, were examined. The largest deficits in STP, LTP and CFC were found in KO mice compared with non-littermate WT. However, the expression of NMDAR subunits was unchanged in this comparison. Rather, NMDAR subunit (GluN1, 2A, 2B) expression was sensitive to the cage effect, with decreased expression in both WT and KO littermates compared with non-littermates. Interestingly, an NMDAR-positive allosteric modulator, UBP714, was only effective in potentiating the induction of LTP in non-littermate KO mice and not the littermate KO mice. These results suggest that commonly studied phenotypes in Fmr1 KOs are sensitive to the cage effect and therefore the breeding strategy may contribute to discrepancies in the literature.This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Guidelines for in vivo models of developmental programming of cardiovascular disease risk

Research using animals depends on the generation of offspring for use in experiments or for the maintenance of animal colonies. Although not considered by all, several different factors preceding and during pregnancy, as well as during lactation, can program various characteristics in the offspring. Here, we present the most common models of developmental programming of cardiovascular outcomes, important considerations for study design, and provide guidelines for producing and reporting rigorous and reproducible cardiovascular studies in offspring exposed to normal conditions or developmental insult. These guidelines provide considerations for the selection of the appropriate animal model and factors that should be reported to increase rigor and reproducibility while ensuring transparent reporting of methods and results.

Epigenetic regulation in major depression and other stress-related disorders: molecular mechanisms, clinical relevance and therapeutic potential

Major depressive disorder (MDD) is a chronic, generally episodic and debilitating disease that affects an estimated 300 million people worldwide, but its pathogenesis is poorly understood. The heritability estimate of MDD is 30-40%, suggesting that genetics alone do not account for most of the risk of major depression. Another factor known to associate with MDD involves environmental stressors such as childhood adversity and recent life stress. Recent studies have emerged to show that the biological impact of environmental factors in MDD and other stress-related disorders is mediated by a variety of epigenetic modifications. These epigenetic modification alterations contribute to abnormal neuroendocrine responses, neuroplasticity impairment, neurotransmission and neuroglia dysfunction, which are involved in the pathophysiology of MDD. Furthermore, epigenetic marks have been associated with the diagnosis and treatment of MDD. The evaluation of epigenetic modifications holds promise for further understanding of the heterogeneous etiology and complex phenotypes of MDD, and may identify new therapeutic targets. Here, we review preclinical and clinical epigenetic findings, including DNA methylation, histone modification, noncoding RNA, RNA modification, and chromatin remodeling factor in MDD. In addition, we elaborate on the contribution of these epigenetic mechanisms to the pathological trait variability in depression and discuss how such mechanisms can be exploited for therapeutic purposes.

Synergistic, long-term effects of glutamate dehydrogenase 1 deficiency and mild stress on cognitive function and mPFC gene and miRNA expression

Glutamate abnormalities in the medial prefrontal cortex (mPFC) are associated with cognitive deficits. We previously showed that homozygous deletion of CNS glutamate dehydrogenase 1 (Glud1), a metabolic enzyme critical for glutamate metabolism, leads to schizophrenia-like behavioral abnormalities and increased mPFC glutamate; mice heterozygous for CNS Glud1 deletion (C-Glud1^+/- mice) showed no cognitive or molecular abnormalities. Here, we examined the protracted behavioral and molecular effects of mild injection stress on C-Glud1^+/- mice. We found spatial and reversal learning deficits, as well as large-scale mPFC transcriptional changes in pathways associated with glutamate and GABA signaling, in stress-exposed C-Glud1^+/- mice, but not in their stress-naïve or C-Glud1^+/+ littermates. These effects were observed several weeks following stress exposure, and the expression levels of specific glutamatergic and GABAergic genes differentiated between high and low reversal learning performance. An increase in miR203-5p expression immediately following stress may provide a translational regulatory mechanism to account for the delayed effect of stress exposure on cognitive function. Our findings show that chronic glutamate abnormalities interact with acute stress to induce cognitive deficits, and resonate with gene x environment theories of schizophrenia. Stress-exposed C-Glud1^+/- mice may model a schizophrenia high-risk population, which is uniquely sensitive to stress-related 'trigger' events.

Delayed Formation of Neonatal Reflexes and of Locomotor Skills Is Associated with Poor Maternal Behavior in OXYS Rats Prone to Alzheimer's Disease-like Pathology

Postnatal brain development is characterized by high plasticity with critical windows of opportunity where any intervention may positively or adversely influence postnatal growth and lead to long-lasting consequences later in life. Poor maternal care is among these interventions. Here, we found that senescence-accelerated OXYS rats prone to an Alzheimer's disease-like pathology are characterized by more passive maternal behavior and insufficient care for pups as compared to control (Wistar) rats. OXYS pups demonstrated a delay in physical development (of auricle detachment, of emergence of pelage and incisors, of eye opening, and of vaginal opening in females) and late manifestation of reflexes and locomotor skills. All observed behavioral abnormalities are connected either with poor coordination of limbs' movements or with a decrease in motivation and development of depression-like behavior. It is possible that their manifestations can be promoted by the features of maternal behavior of OXYS rats. Overall, these early-life events may have long-lasting consequences and contribute to neurodegeneration and development of the Alzheimer's disease-like pathology later in life.

Early life adversity shapes neural circuit function during sensitive postnatal developmental periods

Early life adversity (ELA) is a major risk factor for mental illness, but the neurobiological mechanisms by which ELA increases the risk for future psychopathology are still poorly understood. Brain development is particularly malleable during prenatal and early postnatal life, when complex neural circuits are being formed and refined through an interplay of excitatory and inhibitory neural input, synaptogenesis, synaptic pruning, myelination, and neurogenesis. Adversity that influences these processes during sensitive periods of development can thus have long-lasting and pervasive effects on neural circuit maturation. In this review, we will discuss clinical and preclinical evidence for the impact of ELA on neural circuit formation with a focus on the early postnatal period, and how long-lasting impairments in these circuits can affect future behavior. We provide converging evidence from human and animal studies on how ELA alters the functional development of brain regions, neural circuits, and neurotransmitter systems that are crucial for cognition and affective behavior, including the hippocampus, the hypothalamus-pituitary-adrenal (HPA) axis, neural networks of fear responses and cognition, and the serotonin (5-HT) system. We also discuss how gene-by-environment (GxE) interactions can determine individual differences in susceptibility and resilience to ELA, as well as molecular pathways by which ELA regulates neural circuit development, for which we emphasize epigenetic mechanisms. Understanding the molecular and neurobiological mechanisms underlying ELA effects on brain function and psychopathology during early postnatal sensitive periods may have great potential to advance strategies to better treat or prevent psychiatric disorders that have their origin early in life.

Molecular impacts of childhood abuse on the human brain

Childhood abuse (CA) is a prevalent global health concern, increasing the risk of negative mental health outcomes later in life. In the literature, CA is commonly defined as physical, sexual, and emotional abuse, as well as neglect. Several mental disorders have been associated with CA, including depression, bipolar disorder, schizophrenia, and post-traumatic stress disorder, along with an increased risk of suicide. It is thought that traumatic life events occurring during childhood and adolescence may have a significant impact on essential brain functions, which may persist throughout adulthood. The interaction between the brain and the external environment can be mediated by epigenetic alterations in gene expression, and there is a growing body of evidence to show that such changes occur as a function of CA. Disruptions in the HPA axis, myelination, plasticity, and signaling have been identified in individuals with a history of CA. Understanding the molecular impact of CA on the brain is essential for the development of treatment and prevention measures. In this review, we will summarize studies that highlight the molecular changes associated with CA in the human brain, along with supporting evidence from peripheral studies and animal models. We will also discuss some of the limitations surrounding the study of CA and propose extracellular vesicles as a promising future approach in the field.

Age-dependent shift in spontaneous excitation-inhibition balance of infralimbic prefrontal layer II/III neurons is accelerated by early life stress, independent of forebrain mineralocorticoid receptor expression

In this study we tested the hypothesis i) that age-dependent shifts in the excitation-inhibition balance of prefrontal neurons are accelerated by early life stress, a risk factor for the etiology of many psychiatric disorders; and if so, ii) that this process is exacerbated by genetic forebrain-specific downregulation of the mineralocorticoid receptor, a receptor that was earlier found to be a protective factor for negative effects of early life stress in both rodents and humans. In agreement with the literature, an age-dependent downregulation of the excitation-inhibition balance was found both with regard to spontaneous and evoked synaptic currents. The age-dependent shift in spontaneous excitatory relative to inhibitory currents was significantly accelerated by early life stress, but this was not exacerbated by reduction in mineralocorticoid receptor expression. The age-dependent changes in the excitation-inhibition balance were mirrored by similar changes in receptor subunit expression and morphological alterations, particularly in spine density, which could thus potentially contribute to the functional changes. However, none of these parameters displayed acceleration by early life stress, nor depended on mineralocorticoid receptor expression. We conclude that, in agreement with the hypothesis, early life stress accelerates the developmental shift of the excitation-inhibition balance but, contrary to expectation, there is no evidence for a putative protective role of the mineralocorticoid receptor in this system. In view of the modest effect of early life stress on the excitation-inhibition balance, alternative mechanisms potentially underlying the development of psychiatric disorders should be further explored.

Ventral Hippocampal Afferents to Nucleus Accumbens Encode Both Latent Vulnerability and Stress-Induced Susceptibility

BACKGROUND

Stress is a major risk factor for depression, but not everyone responds to stress in the same way. Identifying why certain individuals are more susceptible is essential for targeted treatment and prevention. In rodents, nucleus accumbens (NAc) afferents from the ventral hippocampus (vHIP) are implicated in stress-induced susceptibility, but little is known about how this pathway might encode future vulnerability or specific behavioral phenotypes.

METHODS

We used fiber photometry to record in vivo activity in vHIP-NAc afferents during tests of depressive- and anxiety-like behavior in male and female mice, both before and after a sex-specific chronic variable stress protocol, to probe relationships between prestress neural activity and behavior and potential predictors of poststress behavioral adaptation. Furthermore, we examined chronic variable stress-induced alterations in vHIP-NAc activity in vivo and used ex vivo slice electrophysiology to identify the mechanism of this change.

RESULTS

We identified behavioral specificity of the vHIP-NAc pathway to anxiety-like and social interaction behavior. We also showed that this activity is broadly predictive of stress-induced susceptibility in both sexes, while prestress behavior is predictive only of anxiety-like behavior. We observed a stress-induced increase in in vivo vHIP-NAc activity coincident with an increase in spontaneous excitatory postsynaptic current frequency.

CONCLUSIONS

We implicate vHIP-NAc in social interaction and anxiety-like behavior and identify markers of vulnerability in this neural signal, with elevated prestress vHIP-NAc activity predicting increased susceptibility across behavioral domains. Our findings indicate that individual differences in neural activity and behavior play a role in predetermining susceptibility to later stress, providing insight into mechanisms of vulnerability.

It Is All in the Right Amygdala: Increased Synaptic Plasticity and Perineuronal Nets in Male, But Not Female, Juvenile Rat Pups after Exposure to Early-Life Stress

Early-life stress (ELS) is associated with increased vulnerability to mental disorders. The basolateral amygdala (BLA) plays a critical role in fear conditioning and is extremely sensitive to ELS. Using a naturalistic rodent model of ELS, the limited bedding paradigm (LB) between postnatal days 1-10, we previously documented that LB male, but not female preweaning rat pups display increased BLA neuron spine density paralleled with enhanced evoked synaptic responses and altered BLA functional connectivity. Since ELS effects are often sexually dimorphic and amygdala processes exhibit hemispheric asymmetry, we investigated changes in synaptic plasticity and neuronal excitability of BLA neurons in vitro in the left and right amygdala of postnatal days 22-28 male and female offspring from normal bedding or LB mothers. We report that LB conditions enhanced synaptic plasticity in the right, but not the left BLA of males exclusively. LB males also showed increased perineuronal net density, particularly around parvalbumin (PV) cells, and impaired fear-induced activity of PV interneurons only in the right BLA. Action potentials fired from right BLA neurons of LB females displayed slower maximal depolarization rates and decreased amplitudes compared with normal bedding females, concomitant with reduced NMDAR GluN1 subunit expression in the right BLA. In LB males, reduced GluA2 expression in the right BLA might contribute to the enhanced LTP. These findings suggest that LB differentially programs synaptic plasticity and PV/perineuronal net development in the left and right BLA. Furthermore, our study demonstrates that the effects of ELS exposure on BLA synaptic function are sexually dimorphic and possibly recruiting different mechanisms.SIGNIFICANCE STATEMENT Early-life stress (ELS) induces long-lasting consequences on stress responses and emotional regulation in humans, increasing vulnerability to the development of psychopathologies. The effects of ELS in a number of brain regions, including the amygdala, are often sexually dimorphic, and have been reproduced using the rodent limited bedding paradigm of early adversity. The present study examines sex differences in synaptic plasticity and cellular activation occurring in the developing left and right amygdala after limited bedding exposure, a phenomenon that could shape long-term emotional behavioral outcomes. Studying how ELS selectively produces effects in one amygdala hemisphere during a critical period of brain development could guide further investigation into sex-dependent mechanisms and allow for more targeted and improved treatment of stress-and emotionality-related disorders.

Transgenerational deep sequencing revealed hypermethylation of hippocampal mGluR1 gene with altered mRNA expression of mGluR5 and mGluR3 associated with behavioral changes in Sprague Dawley rats with history of prolonged febrile seizure

The impact of febrile seizure has been shown to transcend immediate generation with the alteration of glutamatergic pathway being implicated. However, transgenerational effects of this neurological disorder particularly prolonged febrile seizure (PFS) on neurobehavioral study and methylation profile is unknown. We therefore hypothesized that transgenerational impact of prolonged febrile seizure is dependent on methylation of hippocampal mGluR1 gene. Prolonged febrile seizure was induced on post-natal day (PND) 14, by injecting lipopolysaccharide (LPS; 217μg/kg ip) and kainic acid (KA; 1.83 mg/kg ip). Sucrose preference test (SPT) and Forced swim test (FST) were carried out in the first generation (F0) of animals at PND37 and PND60. The F0 rats were decapitated at PND 14, 37 and 60 which corresponded to childhood, adolescent and adulthood respectively and their hippocampal tissue collected. The second generation (F1) rats were obtained by mating F0 generation at PND 60 across different groups, F1 rats were subjected to SPT and FST test on PND 37 only. Decapitation of F1rats and collection of hippocampal tissues were done on PND 14 and 37. Assessment of mGluR5 and mGluR3 mRNA was done with PCR while mGluR1 methylation profile was assessed with the Quantitative MassARRAY analysis. Results showed that PFS significantly leads to decreased sucrose consumption in the SPT and increased immobility time in the FST in both generations of rats. It also leads to significant decrease in mGluR5 mRNA expression with a resultant increased expression of mGluR3 mRNA expression and hypermethylation of mGluR1 gene across both generations of rats. This study suggested that PFS led to behavioral changes which could be transmitted on to the next generation in rats.

Early life stress impairs fear memory and synaptic plasticity; a potential role for GluN2B

Programming of the brain by early life stress has been associated with alterations in structure and function of the dorsal hippocampus. Yet, the underlying molecular mechanisms remain largely elusive. In this study, we examined the effects of early life stress (ELS) - by housing mouse dams with limited nesting and bedding material from postnatal days 2-9 and examined in 6 month old offspring; 1) auditory fear conditioning, 2) expression of the hippocampal N-methyl-d-aspartate receptor (NMDA-R) subunits 2A and 2B (GluN2A, GluN2B), and expression of PSD-95 and synaptophysin, and 3) short- and long-term (LTP) synaptic plasticity. Given its critical role in NMDA receptor function and synaptic plasticity, we further examined the role of GluN2B in effects of ELS on synaptic plasticity and fear memory formation. We demonstrate that ELS impaired fear memory in 6 month old mice and decreased hippocampal LTP as well as the paired-pulse ratio (PPR). ELS also reduced hippocampal GluN2B expression. Interestingly, pharmacological blockade of GluN2B with the selective antagonist Ro25 6981 was less effective to reduce synaptic plasticity in ELS mice, and was also ineffective to impair memory retrieval in ELS mice. These studies suggest that ELS reduces hippocampal synaptic plasticity and fear memory formation and hampers GluN2B receptor function. As such, GluN2B may provide an important target for future strategies to prevent lasting ELS effects on cognition.

Neuroplasticity-related correlates of environmental enrichment combined with physical activity differ between the sexes

Environmental enrichment (EE), comprising positive physical (exercise) and cognitive stimuli, influences neuronal structure and usually improves brain function. The promise of EE as a preventative strategy against neuropsychiatric disease is especially high during early postnatal development when the brain is still amenable to reorganization. Despite the fact that male and female brains differ in terms of connectivity and function that may reflect early life experiences, knowledge of the neural substrates and mechanisms by which such changes arise remains limited. This study compared the impact of EE combined with physical activity on neuroplasticity and its functional consequences in adult male and female rats; EE was provided during the first 3 months of life and our analysis focused on the hippocampus, an area implicated in cognitive behavior as well as the neuroendocrine response to stress. Both male and female rats reared in EE displayed better object recognition memory than their control counterparts. Interestingly, sex differences were revealed in the effects of EE on time spent exploring the objects during this test. Independently of sex, EE increased hippocampal turnover rates of dopamine and serotonin and reduced expression of 5-HT_1A receptors; in addition, EE upregulated expression of synaptophysin, a presynaptic protein, in the hippocampus. As compared to their respective controls, EE-exposed males exhibited parallel increases in phosphorylated Tau and the GluN2B receptor, whereas females responded to EE with reduced hippocampal levels of glutamate and GluN2B. Together, these observations provide further evidence on the differential effects of EE on markers of hippocampal neuroplasticity in males and females.

Vulnerability and resilience to Alzheimer's disease: early life conditions modulate neuropathology and determine cognitive reserve

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a high prevalence among the elderly and a huge personal and societal impact. Recent epidemiological studies have indicated that the incidence and age of onset of sporadic AD can be modified by lifestyle factors such as education, exercise, and (early) stress exposure. Early life adversity is known to promote cognitive decline at a later age and to accelerate aging, which are both primary risk factors for AD. In rodent models, exposure to 'negative' or 'positive' early life experiences was recently found to modulate various measures of AD neuropathology, such as amyloid-beta levels and cognition at later ages. Although there is emerging interest in understanding whether experiences during early postnatal life also modulate AD risk in humans, the mechanisms and possible substrates underlying these long-lasting effects remain elusive.

METHODS

We review literature and discuss the role of early life experiences in determining later age and AD-related processes from a brain and cognitive 'reserve' perspective. We focus on rodent studies and the identification of possible early determinants of later AD vulnerability or resilience in relation to early life adversity/enrichment.

RESULTS

Potential substrates and mediators of early life experiences that may influence the development of AD pathology and cognitive decline are: programming of the hypothalamic-pituitary-adrenal axis, priming of the neuroinflammatory response, dendritic and synaptic complexity and function, overall brain plasticity, and proteins such as early growth response protein 1 (EGR1), activity regulated cytoskeleton-associated protein (Arc), and repressor element-1 silencing transcription factor (REST).

CONCLUSIONS

We conclude from these rodent studies that the early postnatal period is an important and sensitive phase that influences the vulnerability to develop AD pathology. Yet translational studies are required to investigate whether early life experiences also modify AD development in human studies, and whether similar molecular mediators can be identified in the sensitivity to develop AD in humans.

Generalization of Conditioned Auditory Fear is Regulated by Maternal Effects on Ventral Hippocampal Synaptic Plasticity

Maternal care shapes individual differences in fear-associated neural circuitry. In rats, maternal licking and grooming (LG) in early life regulates ventral hippocampal (VH) function and plasticity in adulthood, but its consequent effect on the regulation of fear memories remains unknown. We report an effect of maternal care on generalization of learned fear, such that offspring of high LG mothers express generalized fear responses when confronted with neutral stimuli following auditory fear conditioning. These animals simultaneously display a reduction in the magnitude of VH long-term potentiation (LTP) expressed and reduced input-output transformation in Schaffer collateral synapses. Inhibition of VH-LTP during learning specifically increases fear generalization in offspring of low LG mothers during recall, suggesting a role for VH synaptic plasticity in the specification of fear memories. These findings suggest that rearing by low LG dams enhances the efficacy of fear-related neural systems to support accurate encoding of fear memories through effects on the VH.

Daily maternal separations during stress hyporesponsive period decrease the thresholds of panic-like behaviors to electrical stimulation of the dorsal periaqueductal gray of the adult rat

The present study examined whether early life maternal separation (MS), a model of childhood separation anxiety, predisposes to panic at adulthood. For this purpose, male pups were submitted to 3-h daily maternal separations along postnatal (PN) days of either the 'stress hyporesponsive period' (SHRP) from PN4 to PN14 (MS11) or throughout lactation from PN2 to PN21 (MS20). Pups were further reunited to conscious (CM) or anesthetized (AM) mothers to assess the effect of mother-pup interaction upon reunion. Controls were subjected to brief handling (15 s) once a day throughout lactation (BH20). As adults (PN60), rats were tested for the thresholds to evoke panic-like behaviors upon electrical stimulation of dorsal periaqueductal gray matter and exposed to an elevated plus-maze, an open-field, a forced swim and a sucrose preference test. A factor analysis was also performed to gain insight into the meaning of behavioral tests. MS11-CM rather than MS20-CM rats showed enhanced panic responses and reductions in both swimming and sucrose preference. Panic facilitations were less intense in mother-neglected rats. Although MS did not affect anxiety, MS11-AM showed robust reductions of defecation in an open-field. Factor analysis singled out anxiety, hedonia, exploration, coping and gut activity. Although sucrose preference and coping loaded on separate factors, appetite (adult weight) correlated with active coping in both forced swim and open-field (central area exploration). Concluding, whereas 3h-daily maternal separations during SHRP increased rat's susceptibility to experimental panic attacks, separations throughout lactation had no effects on panic and enhanced active coping.

Early life stress determines the effects of glucocorticoids and stress on hippocampal function: Electrophysiological and behavioral evidence respectively

Exposure to early-life adversity may program brain function to prepare individuals for adaptation to matching environmental contexts. In this study we tested this hypothesis in more detail by examining the effects of early-life stress - induced by raising offspring with limited nesting and bedding material from postnatal days 2-9 - in various behavioral tasks and on synaptic function in adult mice. Early-life stress impaired adult performance in the hippocampal dependent low-arousing object-in-context recognition memory task. This effect was absent when animals were exposed to a single stressor before training. Early-life stress did not alter high-arousing context and auditory fear conditioning. Early-life stress-induced behavioral modifications were not associated with alterations in the dendritic architecture of hippocampal CA1 pyramidal neurons or principal neurons of the basolateral amygdala. However, early-life stress reduced the ratio of NMDA to AMPA receptor-mediated excitatory postsynaptic currents and glutamate release probability specifically in hippocampal CA1 neurons, but not in the basolateral amygdala. These ex vivo effects in the hippocampus were abolished by acute glucocorticoid treatment. Our findings support that early-life stress can hamper object-in-context learning via pre- and postsynaptic mechanisms that affect hippocampal function but these effects are counteracted by acute stress or elevated glucocorticoid levels.

Transient Prepubertal Mifepristone Treatment Normalizes Deficits in Contextual Memory and Neuronal Activity of Adult Male Rats Exposed to Maternal Deprivation

Early life adversity is a well-known risk factor for behavioral dysfunction later in life, including the formation of contextual memory; it is also (transiently) accompanied by hyperactivity of the stress system. We tested whether mifepristone (MIF) treatment, which among other things blocks glucocorticoid receptors (GRs), during the prepubertal period [postnatal days (PND)26-PND28] normalizes memory deficits in adult male rats exposed to 24-h maternal deprivation (MD) at PND3. MD reduced body weight gain and increased basal corticosterone (CORT) levels during the PND26, but not in adulthood. In adulthood, contextual memory formation of MD compared to noMD (i.e., control) male rats was significantly impaired. This impairment was fully prevented by MIF treatment at PND26-PND28, whereas MIF by itself did not affect behavior. A second behavioral test, a rodent version of the Iowa Gambling Task (rIGT), revealed that flexible spatial learning rather than reward-based aspects of performance was impaired by MD; the deficit was prevented by MIF. Neuronal activity as tested by c-Fos staining in the latter task revealed changes in the right hippocampal-dorsomedial striatal pathway, but not in prefrontal areas involved in reward learning. Follow-up electrophysiological recordings measuring spontaneous glutamate transmission showed reduced frequency of miniature postsynaptic excitatory currents in adult CA1 dorsal hippocampal and enhanced frequency in dorsomedial striatal neurons from MD versus noMD rats, which was not seen in MIF-treated rats. We conclude that transient prepubertal MIF treatment normalizes hippocampus-striatal-dependent contextual memory/spatial learning deficits in male rats exposed to early life adversity, possibly by normalizing glutamatergic transmission.

Stress hormone rapidly tunes synaptic NMDA receptor through membrane dynamics and mineralocorticoid signalling

Stress hormones, such as corticosteroids, modulate the transmission of hippocampal glutamatergic synapses and NMDA receptor (NMDAR)-dependent synaptic plasticity, favouring salient behavioural responses to the environment. The corticosterone-induced synaptic adaptations partly rely on changes in NMDAR signalling, although the cellular pathway underlying this effect remains elusive. Here, we demonstrate, using single molecule imaging and electrophysiological approaches in hippocampal neurons, that corticosterone specifically controls GluN2B-NMDAR surface dynamics and synaptic content through mineralocorticoid signalling. Strikingly, extracellular corticosterone was sufficient to increase the trapping of GluN2B-NMDAR within synapses. Functionally, corticosterone-induced potentiation of AMPA receptor content in synapses required the changes in NMDAR surface dynamics. These high-resolution imaging data unveiled that, in hippocampal networks, corticosterone is a natural, potent, fast and specific regulator of GluN2B-NMDAR membrane trafficking, tuning NMDAR-dependent synaptic adaptations.

Overexpression of Mineralocorticoid Receptors in the Mouse Forebrain Partly Alleviates the Effects of Chronic Early Life Stress on Spatial Memory, Neurogenesis and Synaptic Function in the Dentate Gyrus

Evidence from human studies suggests that high expression of brain mineralocorticoid receptors (MR) may promote resilience against negative consequences of stress exposure, including childhood trauma. We examined, in mice, whether brain MR overexpression can alleviate the effects of chronic early life stress (ELS) on contextual memory formation under low and high stress conditions, and neurogenesis and synaptic function of dentate gyrus granular cells. Male mice were exposed to ELS by housing the dam with limited nesting and bedding material from postnatal day (PND) 2 to 9. We investigated the moderating role of MRs by using forebrain-specific transgenic MR overexpression (MR-tg) mice. Low-stress contextual (i.e., object relocation) memory formation was hampered by ELS in wildtype but not MR-tg mice. Anxiety like behavior and high-stress contextual (i.e., fear) memory formation were unaffected by ELS and/or MR expression level. At the cellular level, an interaction effect was observed between ELS and MR overexpression on the number of doublecortin-positive cells, with a significant difference between the wildtype ELS and MR-tg ELS groups. No interaction was found regarding Ki-67 and BrdU staining. A significant interaction between ELS and MR expression was further observed with regard to mEPSCs and mIPSC frequency. The ratio of evoked EPSC/IPSC or NMDA/AMPA responses was unaffected. Overall, these results suggest that ELS affects contextual memory formation under low stress conditions as well as neurogenesis and synaptic transmission in dentate granule cells, an effect that can be alleviated by MR-overexpression.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

Exposure to stress during critical periods in development can have severe long-term consequences, increasing overall risk on psychopathology. One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis; a cascade of central and peripheral events resulting in the release of corticosteroids from the adrenal glands. Activation of the HPA-axis affects brain functioning to ensure a proper behavioral response to the stressor, but stress-induced (mal)adaptation of the HPA-axis' functional maturation may provide a mechanistic basis for the altered stress susceptibility later in life. Development of the HPA-axis and the brain regions involved in its regulation starts prenatally and continues after birth, and is protected by several mechanisms preventing corticosteroid over-exposure to the maturing brain. Nevertheless, early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood, affecting both its basal and stress-induced activity. According to the match/mismatch theory, encountering ELS prepares an organism for similar ("matching") adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context. Here, we review studies investigating the mechanistic underpinnings of the ELS-induced alterations in the structural and functional development of the HPA-axis and its key external regulators (amygdala, hippocampus, and prefrontal cortex). The effects of ELS appear highly dependent on the developmental time window affected, the sex of the offspring, and the developmental stage at which effects are assessed. Albeit by distinct mechanisms, ELS induced by prenatal stressors, maternal separation, or the limited nesting model inducing fragmented maternal care, typically results in HPA-axis hyper-reactivity in adulthood, as also found in major depression. This hyper-activity is related to increased corticotrophin-releasing hormone signaling and impaired glucocorticoid receptor-mediated negative feedback. In contrast, initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder, and future studies should investigate its neural/neuroendocrine foundation in further detail. Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.

Early life adversity: Lasting consequences for emotional learning

The early postnatal period is a highly sensitive time period for the developing brain, both in humans and rodents. During this time window, exposure to adverse experiences can lastingly impact cognitive and emotional development. In this review, we briefly discuss human and rodent studies investigating how exposure to adverse early life conditions - mainly related to quality of parental care - affects brain activity, brain structure, cognition and emotional responses later in life. We discuss the evidence that early life adversity hampers later hippocampal and prefrontal cortex functions, while increasing amygdala activity, and the sensitivity to stressors and emotional behavior later in life. Exposure to early life stress may thus on the one hand promote behavioral adaptation to potentially threatening conditions later in life -at the cost of contextual memory formation in less threatening situations- but may on the other hand also increase the sensitivity to develop stress-related and anxiety disorders in vulnerable individuals.

Role of calcium, glutamate and NMDA in major depression and therapeutic application

Major depression is a common, recurrent mental illness that affects millions of people worldwide. Recently, a unique fast neuroprotective and antidepressant treatment effect has been observed by ketamine, which acts via the glutamatergic system. Hence, a steady accumulation of evidence supporting a role for the excitatory amino acid neurotransmitter (EAA) glutamate in the treatment of depression has been observed in the last years. Emerging evidence indicates that N-methyl-D-aspartate (NMDA), group 1 metabotropic glutamate receptor antagonists and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) agonists have antidepressant properties. Indeed, treatment with NMDA receptor antagonists has shown the ability to sprout new synaptic connections and reverse stress-induced neuronal changes. Based on glutamatergic signaling, a number of therapeutic drugs might gain interest in the future. Several compounds such as ketamine, memantine, amantadine, tianeptine, pioglitazone, riluzole, lamotrigine, AZD6765, magnesium, zinc, guanosine, adenosine aniracetam, traxoprodil (CP-101,606), MK-0657, GLYX-13, NRX-1047, Ro25-6981, LY392098, LY341495, D-cycloserine, D-serine, dextromethorphan, sarcosine, scopolamine, pomaglumetad methionil, LY2140023, LY404039, MGS0039, MPEP, 1-aminocyclopropanecarboxylic acid, all of which target this system, have already been brought up, some of them recently. Drugs targeting the glutamatergic system might open up a promising new territory for the development of drugs to meet the needs of patients with major depression.

Influence of maternal care on the developing brain: Mechanisms, temporal dynamics and sensitive periods

Variation in maternal care can lead to divergent developmental trajectories in offspring with implications for neuroendocrine function and behavioral phenotypes. Study of the long-term outcomes associated with mother-infant interactions suggests complex mechanisms linking the experience of variation in maternal care and these neurobiological consequences. Through integration of genetic, molecular, cellular, neuroanatomical, and neuroendocrine approaches, significant advances in our understanding of these complex pathways have been achieved. In this review, we will consider the impact of maternal care on male and female offspring development with a particular focus on the issues of timing and mechanism. Identifying the period of sensitivity to maternal care and the temporal dynamics of the molecular and neuroendocrine changes that are a consequence of maternal care represents a critical step in the study of mechanism.

Epigenetics/Programming in the HPA Axis

The hypothalamic-pituitary-adrenal axis provides physiological adaptations to various environmental stimuli in mammals. These stimuli including maternal care, diet, immune challenge, stress, and others have the potential to stably modify or program the functioning of the HPA axis when experienced early in life or at later critical stages of development. Epigenetic mechanisms mediate the biological embedding of environmental stimuli or conditions. These changes are influenced by the genotype and both, environment and genotype contribute to the development of a specific phenotype with regard to the stress response that might be more susceptible or resilient to the development of mental conditions. The effects of stress might be a result of cumulative stress or a mismatch between the environments experienced early in life versus the conditions much later. These effects including the associated epigenetic modifications are potentially reversible.

Transgenerational Transmission of Stress Pathology

Abstract. The impact of the environment early in life on long-term outcomes is well known. Stressful experiences during pre- and postnatal development can modulate the genetic programming of specific brain circuits underlying emotional and cognitive aspects of behavioral adaptation to stressful experiences later in life. Furthermore, there is documented evidence for gene-environment interactions in the context of early-life stress. Identical gene variants can be associated with different phenotypes depending on environmental factors. DNA methylation, an enzymatically-catalyzed modification of the DNA, is the mechanism through which phenotypes are regulated. The dynamics and plasticity of epigenetic mechanisms can have short-term, long-term, or transgenerational consequences. In epigenetic research, rodent models have targeted several behavioral and emotional phenotypes. These models have contributed significantly to our understanding of the environmental regulation of the developmental brain in early life. This review will highlight studies with rats and mice on epigenetic processes in fetal programming of stress-related mental disorders.

Early life adversity and the epigenetic programming of hypothalamic-pituitary-adrenal function

We review studies with human and nonhuman species that examine the hypothesis that epigenetic mechanisms, particularly those affecting the expression of genes implicated in stress responses, mediate the association between early childhood adversity and later risk of depression. The resulting studies provide evidence consistent with the idea that social adversity, particularly that involving parent-offspring interactions, alters the epigenetic state and expression of a wide range of genes, the products of which regulate hypothalamic-pituitary-adrenal function. We also address the challenges for future studies, including that of the translation of epigenetic studies towards improvements in treatments.

Maternal care differentially affects neuronal excitability and synaptic plasticity in the dorsal and ventral hippocampus

Variations in early life maternal care modulate hippocampal development to program distinct emotional-cognitive phenotypes that persist into adulthood. Adult rat offspring that received low compared with high levels of maternal licking and grooming (low LG offspring) in early postnatal life show reduced long term potentiation (LTP) and impaired hippocampal-dependent memory, suggesting a 'detrimental' maternal effect on neural development. However, these studies focused uniquely on the dorsal hippocampus. Emerging evidence suggests a distinct role of the ventral hippocampus in mediating aggression, anxiety, and fear-memory formation, which are enhanced in low LG offspring. We report that variations in maternal care in the rat associate with opposing effects on hippocampal function in the dorsal and ventral hippocampus. Reduced pup licking associated with suppressed LTP formation in the dorsal hippocampus, but enhanced ventral hippocampal LTP. Ventral hippocampal neurons in low LG offspring fired action potentials at lower threshold voltages that were of larger amplitude and faster rise rate in comparison with those in high LG offspring. Furthermore, recordings of excitatory postsynaptic potential-to-spike coupling (E-S coupling) revealed an increase in excitability of ventral hippocampal CA1 neurons in low LG offspring. These effects do not associate with changes in miniature excitatory postsynaptic currents or paired-pulse facilitation, suggesting a specific effect of maternal care on intrinsic excitability. These findings suggest region-specific influences of maternal care in shaping neural development and synaptic plasticity.

Pathogenesis of depression: Insights from human and rodent studies

Major depressive disorder (MDD) will affect one out of every five people in their lifetime and is the leading cause of disability worldwide. Nevertheless, mechanisms associated with the pathogenesis of MDD have yet to be completely understood and current treatments remain ineffective in a large subset of patients. In this review, we summarize the most recent discoveries and insights for which parallel findings have been obtained in human depressed subjects and rodent models of mood disorders in order to examine the potential etiology of depression. These mechanisms range from synaptic plasticity mechanisms to epigenetics and the immune system where there is strong evidence to support a functional role in the development of specific depression symptomology. Ultimately we conclude by discussing how novel therapeutic strategies targeting central and peripheral processes might ultimately aid in the development of effective new treatments for MDD and related stress disorders.

Tuning hippocampal synapses by stress-hormones: Relevance for emotional memory formation

While stress is often associated with an increased risk to develop (psycho) pathology, the initial response after exposure to stressors is often highly beneficial and allows individuals to optimally cope with challenging situations. Various neurotransmitters and neuromodulators - such as catecholamines and glucocorticoids - are released upon exposure to stressors and regulate behavioural adaptation to stress and enhance the storage of salient information. Studies over the past years have revealed that catecholamines and glucocorticoids regulate synaptic function and synaptic plasticity - which underlie memory formation - in a highly dynamic manner. In this brief review we will summarise how catecholamines and glucocorticoids regulate synaptic function and discuss how these effects may contribute to acquisition and storage of emotional information. This article is part of a Special Issue entitled SI: Brain and Memory.

Loss of dysbindin-1, a risk gene for schizophrenia, leads to impaired group 1 metabotropic glutamate receptor function in mice

The expression of dysbindin-1, a protein coded by the risk gene dtnbp1, is reduced in the brains of schizophrenia patients. Evidence indicates a role of dysbindin-1 in dopaminergic and glutamatergic transmission. Glutamatergic transmission and plasticity at excitatory synapses is critically regulated by G-protein coupled metabotropic glutamate receptor (mGluR) family members, that have been implicated in schizophrenia. Here, we report a role of dysbindin-1 in hippocampal group 1 mGluR (mGluRI) function in mice. In hippocampal synaptoneurosomal preparations from sandy (sdy) mice, that have a loss of function mutation in dysbindin-1 gene, we observed a striking reduction in mGluRI agonist [(S)-3, 5-dihydroxyphenylglycine] (DHPG)-induced phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2). This mGluR-ERK1/2 deficit occurred in the absence of significant changes in protein levels of the two members of the mGluRI family (i.e., mGluR1 and mGluR5) or in another mGluRI signaling pathway, i.e., protein kinase C (PKC). Aberrant mGluRI-ERK1/2 signaling affected hippocampal synaptic plasticity in the sdy mutants as DHPG-induced long-term depression (LTD) at CA1 excitatory synapses was significantly reduced. Behavioral data suggest that the mGluRI hypofunction may underlie some of the cognitive abnormalities described in sdy mice as the administration of CDPPB (3-cyano-N-(1, 3-diphenyl-1H-pyrazol-5-yl benzamide), a positive allosteric modulator of mGluR5, rescued short-term object recognition and spatial learning and memory deficits in these mice. Taken together, our data suggest a novel role of dysbindin-1 in regulating mGluRI functions.

GABAA receptor-acting neurosteroids: a role in the development and regulation of the stress response

Regulation of hypothalamic-pituitary-adrenocortical (HPA) axis activity by stress is a fundamental survival mechanism and HPA-dysfunction is implicated in psychiatric disorders. Adverse early life experiences, e.g. poor maternal care, negatively influence brain development and programs an abnormal stress response by encoding long-lasting molecular changes, which may extend to the next generation. How HPA-dysfunction leads to the development of affective disorders is complex, but may involve GABAA receptors (GABAARs), as they curtail stress-induced HPA axis activation. Of particular interest are endogenous neurosteroids that potently modulate the function of GABAARs and exhibit stress-protective properties. Importantly, neurosteroid levels rise rapidly during acute stress, are perturbed in chronic stress and are implicated in the behavioural changes associated with early-life adversity. We will appraise how GABAAR-active neurosteroids may impact on HPA axis development and the orchestration of the stress-evoked response. The significance of these actions will be discussed in the context of stress-associated mood disorders.

Impaired adrenergic-mediated plasticity of prefrontal cortical glutamate synapses in rats with developmental disruption of the ventral hippocampus

Neonatal ventral hippocampus (nVH) lesion in rats is a useful model to study developmental origins of adult cognitive deficits and certain features of schizophrenia. nVH lesion-induced reorganization of excitatory and inhibitory neurotransmissions within prefrontal cortical (PFC) circuits is widely believed to be responsible for many of the behavioral abnormalities in these animals. Here we provide evidence that development of an aberrant medial PFC (mPFC) α-1 adrenergic receptor (α-1AR) function following neonatal lesion markedly affects glutamatergic synaptic plasticity within PFC microcircuits and contributes to PFC-related behavior abnormalities. Using whole-cell patch-clamp recording, we report that norepinephrine-induced α-1AR-dependent long-term depression (LTD) in a subset of cortico-cortical glutamatergic inputs is strikingly diminished in mPFC slices from nVH-lesioned rats. The LTD impairment occurs in conjunction with completely blunted α-1AR signaling through extracellular signal-regulated kinase 1/2. These α-1AR abnormalities have functional significance in a mPFC-related function, that is, extinction of conditioned fear memory. Post-pubertal animals with nVH lesion show significant resistance to extinction of fear by repeated presentations of the conditioned tone stimulus. mPFC infusion of an α-1AR antagonist (benoxathian) or LTD blocking peptide (Tat-GluR23Y) impaired fear extinction in sham controls, but had no significant effect in the lesioned animals. The data suggest that impaired α-1 adrenergic regulation of cortical glutamatergic synaptic plasticity may be an important mechanism in cognitive dysfunctions reported in neurodevelopmental psychiatric disorders.

The consequences of early-life adversity: neurobiological, behavioural and epigenetic adaptations

During the perinatal period, the brain is particularly sensitive to remodelling by environmental factors. Adverse early-life experiences, such as stress exposure or suboptimal maternal care, can have long-lasting detrimental consequences for an individual. This phenomenon is often referred to as 'early-life programming' and is associated with an increased risk of disease. Typically, rodents exposed to prenatal stress or postnatal maternal deprivation display enhanced neuroendocrine responses to stress, increased levels of anxiety and depressive-like behaviours, and cognitive impairments. Some of the phenotypes observed in these models of early-life adversity are likely to share common neurobiological mechanisms. For example, there is evidence for impaired glucocorticoid negative-feedback control of the hypothalamic-pituitary-adrenal axis, altered glutamate neurotransmission and reduced hippocampal neurogenesis in both prenatally stressed rats and rats that experienced deficient maternal care. The possible mechanisms through which maternal stress during pregnancy may be transmitted to the offspring are reviewed, with special consideration given to altered maternal behaviour postpartum. We also discuss what is known about the neurobiological and epigenetic mechanisms that underpin early-life programming of the neonatal brain in the first generation and subsequent generations, with a view to abrogating programming effects and potentially identifying new therapeutic targets for the treatment of stress-related disorders and cognitive impairment.

Age-dependent sensitivity to glucocorticoids in the developing mouse basolateral nucleus of the amygdala

Experiences of severe trauma during childhood are thought to be risk factors for developing mental disorders, such as anxiety and mood disorders, later in life. Correspondingly, exposure of rodents to early-life stress has been shown to affect neuronal circuitry and emotional behavior in adulthood, indicating a significant impact of stress on brain development. One current hypothesis proposes that the developing central nervous system is more sensitive to environmental influences, such as stress, than the adult. To test this hypothesis, we compared long-lasting effects of systemic corticosterone (CORT) administrations in two distinct early developmental periods. Mice exposed to early-neonatal CORT treatment on postnatal days (PD) 2-4 exhibited strongly enhanced excitability of neurons of the basolateral nucleus of the amygdala (BLA) in early adolescence and displayed impaired extinction of contextually conditioned fear memory, a type of behavior in which the BLA plays an important role. Furthermore, gene-expression of NMDA receptor subunits as well as calcium-activated K(+)-channels was reduced in the amygdala. In contrast, exposure to the same CORT concentrations in a late-neonatal period (PD17-19) did not significantly affect BLA electrophysiology or extinction learning in adolescence. These results suggest age-dependent consequences of neonatal CORT exposure in amygdala neurons and provide evidence for a detrimental influence of early-neonatal stress on adolescent fear-memory processing.

DNA methylation and childhood maltreatment: from animal models to human studies

Childhood maltreatment (CM) has estimated prevalence among Western societies between 10% and 15%. As CM associates with increased risk of several psychiatric disorders, early age of illness onset, increased comorbidity and negative clinical outcome, it imposes a major public health, social and economic impact. Although the clinical consequences of CM are well characterized, a major challenge remains to understand how negative early-life events can affect brain function over extended periods of time. We review here both animal and human studies indicating that the epigenetic mechanism of DNA methylation is a crucial mediator of early-life experiences, thereby maintaining life-long neurobiological sequelae of CM, and strongly determining psychopathological risk.

Hydroxymethylation and DNA methylation profiles in the prefrontal cortex of the non-human primate rhesus macaque and the impact of maternal deprivation on hydroxymethylation

5-Hydroxymethylcytosine (5hmC) is abundant in the brain, suggesting an important role in epigenetic control of neuronal functions. In this paper, we show that 5hmC and 5-methylcytosine (5mC) levels are coordinately distributed in gene promoters of the rhesus macaque prefrontal cortex. Although promoter hydroxymethylation and methylation are overall negatively correlated with expression, a subset of highly expressed genes involved in specific cerebral functions is associated with high levels of 5mC and 5hmC. These relationships were also observed in the mouse cortex. Furthermore, we found that early-life maternal deprivation is associated, in the adult monkey cortex, with DNA hydroxymethylation changes of promoters of genes related to neurological functions and psychological disorders. These results reveal that early social adversity triggers variations in brain DNA hydroxymethylation that could be detected in adulthood.

Age- and sex-dependent effects of early life stress on hippocampal neurogenesis

Early life stress is a well-documented risk factor for the development of psychopathology in genetically predisposed individuals. As it is hard to study how early life stress impacts human brain structure and function, various animal models have been developed to address this issue. The models discussed here reveal that perinatal stress in rodents exerts lasting effects on the stress system as well as on the structure and function of the brain. One of the structural parameters strongly affected by perinatal stress is adult hippocampal neurogenesis. Based on compiled literature data, we report that postnatal stress slightly enhances neurogenesis until the onset of puberty in male rats; when animals reach adulthood, neurogenesis is reduced as a consequence of perinatal stress. By contrast, female rats show a prominent reduction in neurogenesis prior to the onset of puberty, but this effect subsides when animals reach young adulthood. We further present preliminary data that transient treatment with a glucocorticoid receptor antagonist can normalize cell proliferation in maternally deprived female rats, while the compound had no effect in non-deprived rats. Taken together, the data show that neurogenesis is affected by early life stress in an age- and sex-dependent manner and that normalization may be possible during critical stages of brain development.

Context modulates outcome of perinatal glucocorticoid action in the brain

Prematurely born infants may be at risk, because of inadequate maturation of tissues. If there are signs of preterm birth, it has become common practice therefore to treat either antenatally the mother or postnatally the infant with glucocorticoids to accelerate tissue development, particularly of the lung. However, this life-saving early glucocorticoid treatment was found to increase the risk of adverse outcome in later life. In one animal study, the authors reported a 25% shorter lifespan of rats treated as newborns with the synthetic glucocorticoid dexamethasone, but so far this finding has not been replicated. After a brief clinical introduction, we discuss studies in rodents designed to examine how perinatal glucocorticoid action affects the developing brain. It appears that the perinatal action of the glucocorticoid depends on the context and the timing as well as the type of administered steroid. The type of steroid is important because the endogenous glucocorticoids cortisol and corticosterone bind to two distinct receptor populations, i.e., mineralocorticoid and glucocorticoid receptors (GR), while synthetic glucocorticoids predominantly bind to the GR. In addition, if given antenatally hydrocortisone is inactivated in the placenta by 11β-HSD type 2, and dexamethasone is not. With respect to timing, the outcome of glucocorticoid effects is different in early vs. late phases of brain development. The context refers to the environmental input that can affect the susceptibility to glucocorticoid action in the newborn rodent brain; early handling of pups and maternal care obliterate effects of post-natal dexamethasone treatment. Context also refers to coping with environmental conditions in later life, for which the individual may have been programed epigenetically by early-life experience. This knowledge of determinants affecting the outcome of perinatal glucocorticoid exposure may have clinical implications for the treatment of prematurely born infants.

Long-lasting Consequences of Early Life Stress on Brain Structure, Emotion and Cognition

During the perinatal period, the brain undergoes substantial structural changes, synaptic rearrangements, and development of neuronal circuits which ultimately determine brain function and behavior. Environmental factors-such as exposure to adverse experiences-have major impact on brain function and structure during this sensitive period. These alterations can be long-lasting, and have been implicated in psychopathology such as cognitive decline and emotional dysfunction. Here we briefly review how early postnatal adversity determines structure and function of the hippocampus, amygdala, and prefrontal cortex (PFC) areas, which are crucial for proper cognitive and emotional function.

Interactions between parents and parents and pups in the monogamous California mouse (Peromyscus californicus)

The California mouse (Peromyscuscalifornicus) may be a valuable animal model to study parenting as it is one of the few monogamous and biparental rodent species. By using automated infra-red imaging and video documentation of established pairs spanning two days prior to birth of the litter until d 5 of post natal development (PND), it was possible to follow interactions between parents and between parents and pups. The paired males were attentive to their partners in the form of grooming and sniffing throughout the time period studied. Both these and other activities of the partners, such as eating and drinking, peaked during late light/ mid-dark period. Beginning the day before birth, and most significantly on PND 0, the female made aggressive attempts to exclude the male from nest-attending, acts that were not reciprocated by the male, although he made repeated attempts to mate his partner during that period. By PND 1, males were permitted to return to the nest, where they initiated grooming, licking, and huddling over the litter, although time spent by the male on parental care was still less than that of the female. Male and female pups were of similar size and grew at the same rate. Pups, which are believed to be exothermic for at least the first two weeks post-natally, maintained a body temperature higher than that of their parents until PND 16. Data are consistent with the inference that the male California mouse parent is important in helping retain pup body heat and permit dams increased time to procure food to accommodate her increased energy needs for lactation. These assessments provide indices that may be used to assess the effects of extrinsic factors, such as endocrine disrupting chemicals, on biparental behaviors and offspring development.

The three-hit concept of vulnerability and resilience: toward understanding adaptation to early-life adversity outcome

Stressful experiences during early-life can modulate the genetic programming of specific brain circuits underlying emotional and cognitive aspects of behavioral adaptation to stressful experiences later in life. Although this programming effect exerted by experience-related factors is an important determinant of mental health, its outcome depends on cognitive inputs and hence the valence an individual assigns to a given environmental context. From this perspective we will highlight, with studies in rodents, non-human primates and humans, the three-hit concept of vulnerability and resilience to stress-related mental disorders, which is based on gene-environment interactions during critical phases of perinatal and juvenile brain development. The three-hit (i.e., hit-1: genetic predisposition, hit-2: early-life environment, and hit-3: later-life environment) concept accommodates the cumulative stress hypothesis stating that in a given context vulnerability is enhanced when failure to cope with adversity accumulates. Alternatively, the concept also points to the individual's predictive adaptive capacity, which underlies the stress inoculation and match/mismatch hypotheses. The latter hypotheses propose that the experience of relatively mild early-life adversity prepares for the future and promotes resilience to similar challenges in later-life; when a mismatch occurs between early and later-life experience, coping is compromised and vulnerability is enhanced. The three-hit concept is fundamental for understanding how individuals can either be prepared for coping with life to come and remain resilient or are unable to do so and succumb to a stress-related mental disorder, under seemingly identical circumstances.

Stress and excitatory synapses: from health to disease

Individuals are exposed to stressful events in their daily life. The effects of stress on brain function ranges from highly adaptive to increasing the risk to develop psychopathology. For example, stressful experiences are remembered well which can be seen as a highly appropriate behavioral adaptation. On the other hand, stress is an important risk factor, in susceptible individuals, for depression and anxiety. An important question that remains to be addressed is how stress regulates brain function and what determines the threshold between adaptive and maladaptive responses. Excitatory synapses play a crucial role in synaptic transmission, synaptic plasticity and behavioral adaptation. In this review we discuss how brief and prolonged exposure to stress, in adulthood and early life, regulate the function of these synapses, and how these effects may contribute to behavioral adaptation and psychopathology.

A rapid facilitation of acid-sensing ion channels current by corticosterone in cultured hippocampal neurons

Acid-sensing ion channels (ASIC) play an important role in the central neuronal system and excessive activation of ASICs induces neuronal damage. Recent studies show that ASIC1a, a subunit of ASIC, is involved in stress processes but the mechanisms by which ASIC1a is regulated by corticosterone (CORT), a stress-induced hormone, are as yet unelucidated. In the present study, to explore the effects of CORT on ASIC1a in cultured hippocampal neurons, the whole-cell patch clamp technique was used. We present data showing that extracellular application of 1 and 10 μM CORT increase the inward current when solution of pH 6.0 is applied to the exterior of the cell. Moreover, extracellular application of membrane-impermeable CORT-BSA (1 μM) maintains current elevation induced by the action of ASIC1a. However, intracellular application of CORT (1 μM) did not increase ASIC1a current. Subsequent extracellular application of CORT enhanced the amplitude of ASIC1a current. Also, RU38486 (10 μM), an antagonist of nuclear glucocorticoids receptor, did not block an increase of ASIC1a current induced by CORT. In addition, CORT application further resulted in a significant enhancement of ASIC1a current in the presence of phorbol 12-myristate 13-acetate (0.5 μM) or bryostatin1 (1 μM), which are both protein kinase C (PKC) agonists. On the contrary, after pretreatment with GF109203X (3 μM), an antagonist of PKC, CORT did not elevate ASIC1a current. These data indicate that the rapid increase of ASIC1a current induced by CORT may be caused by the activation of corticosteroid receptors found on the cell membranes of hippocampal neurons and it may involve a PKC-dependent mechanism.