Neurobiology of the stress response early in life: evolution of a concept and the role of corticotropin releasing hormone

Potential Benefits of a 'Trauma-Informed Care' Approach to Improve the Assessment and Management of Dogs Presented with Anxiety Disorders

Dog caregiver reporting on the spectrum of fearful-aggressive behaviours often describes 'unpredictable' or 'exaggerated' responses to a situation/animal/person. A possible explanation for these behavioural responses considers that the dog is reacting to triggered memories for which the dog has a negative association. For many dogs undergoing veterinary behavioural treatment or rehabilitation through a canine rescue organisation, the assessing clinician relies on "proxy" reporting of the history/background by a caregiver (dog owner, foster carer, or shelter personnel). Detailed information on the event or circumstances resulting in this negative association may be limited or absent altogether. Consideration of a trauma-informed care (TIC) approach, currently applied in a wide range of human psychology and social care fields, may be helpful in guiding the clinical approach taken. The literature relating to adverse early experience (AEE) and trauma-informed care (TIC) in puppies/dogs compared to children/adults was evaluated to identify common themes and conclusions identified across both species. In the absence of known/identifiable trauma, behavioural assessment and management should consider that a 'problem' dog may behave as it does, as the result of previous trauma. The dog can then be viewed through a lens of empathy and understanding, often lacking for dogs presenting with impulsive, reactive, or aggressive behaviours. Assessment must avoid re-traumatising the animal through exposure to triggering stimuli and, treatment options should include counselling of caregivers on the impact of adverse early experiences, consideration of the window of tolerance, and TIC behavioural modification techniques.

Improving behavioral deficits induced by perinatal ethanol and stress exposure in adolescent male rat progeny via maternal melatonin treatment

BACKGROUND AND AIM

Early-life stressful situations and binge drinking have been thus far acknowledged as two burdensome conditions that potentially give rise to negative outcomes and then synergistically affect brain development. In this context, the hippocampus, with the greatest number of glucocorticoid receptors (GCRs) in the brain, is responsible for regulating negative responses to stress. Prolonged glucocorticoid (GC) exposure can accordingly cause oxidative stress (OS), leading to cognitive and emotional dysfunction. Against this background, melatonin, as a powerful antioxidant and hypothalamus-pituitary-adrenal (HPA) axis regulator, was administered in this study to ameliorate cognitive impairments induced by perinatal ethanol and stress exposure in adolescent male rat progeny.

METHODS

Wistar rat dams were exposed to ethanol (4 g/kg) and melatonin (10 mg/kg) from gestational day (GD) 6 to postnatal day (PND) 14 and then limited nesting material (LNS) from PND0 to PND14 individually or in combination. Maternal behavior was then investigated in mothers. Afterward, the plasma corticosterone (CORT) concentration, the OS marker, the corticotropin-releasing hormone receptor type 1 (CRHR1) expression, and the GCR and brain-derived neurotrophic factor (BDNF) levels were measured in the male pups. Moreover, behavioral tasks, including the elevated plus maze (EPM), the Morris water maze (MWM), the novel object recognition (NORT), and the object-location memory (OLM) tests were completed and assessed.

RESULTS

The quantity and quality of maternal care significantly decreased in the mothers with dual exposure to ethanol and stress. The plasma CORT concentration in the progeny also dropped in the Ethanol + LNS group, but the risk-taking behavior elevated significantly. The ethanol and stress exposure further revealed a significant fall in the GCR and CRHR1 expression levels, compared with stress alone. The results of learning and memory tasks also indicated a significant reduction in spatial learning and memory among animals exposed to ethanol and stress. The BDNF mRNA levels correspondingly increased in the Ethanol + LNS group, compared with LNS alone. In the presence of ethanol and stress, the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities correspondingly declined. On the other hand, the malondialdehyde (MDA) levels augmented in the hippocampus of the animals with ethanol and LNS dual exposure, as compared with the control group. Melatonin treatment (MT) thus improved nursing behaviors in dams, prevented OS, enhanced the CRHR1 and GCR expression, and reduced the BDNF levels to the similar ones in the control group. The animals in the Ethanol + LNS + MT group ultimately showed an ameliorated performance at behavioral tasks, including the memory and risk-taking behavior.

CONCLUSION

It was concluded that MT could prevent stress response and memory impairments arising from dual exposure to ethanol and stress by inhibiting OS.

Molecular characterization of nervous system organization in the hemichordate acorn worm Saccoglossus kowalevskii

Hemichordates are an important group for investigating the evolution of bilaterian nervous systems. As the closest chordate outgroup with a bilaterally symmetric adult body plan, hemichordates are particularly informative for exploring the origins of chordates. Despite the importance of hemichordate neuroanatomy for testing hypotheses on deuterostome and chordate evolution, adult hemichordate nervous systems have not been comprehensively described using molecular techniques, and classic histological descriptions disagree on basic aspects of nervous system organization. A molecular description of hemichordate nervous system organization is important for both anatomical comparisons across phyla and for attempts to understand how conserved gene regulatory programs for ectodermal patterning relate to morphological evolution in deep time. Here, we describe the basic organization of the adult hemichordate Saccoglossus kowalevskii nervous system using immunofluorescence, in situ hybridization, and transgenic reporters to visualize neurons, neuropil, and key neuronal cell types. Consistent with previous descriptions, we found the S. kowalevskii nervous system consists of a pervasive nerve plexus concentrated in the anterior, along with nerve cords on both the dorsal and ventral side. Neuronal cell types exhibited clear anteroposterior and dorsoventral regionalization in multiple areas of the body. We observed spatially demarcated expression patterns for many genes involved in synthesis or transport of neurotransmitters and neuropeptides but did not observe clear distinctions between putatively centralized and decentralized portions of the nervous system. The plexus shows regionalized structure and is consistent with the proboscis base as a major site for information processing rather than the dorsal nerve cord. In the trunk, there is a clear division of cell types between the dorsal and ventral cords, suggesting differences in function. The absence of neural processes crossing the basement membrane into muscle and extensive axonal varicosities suggest that volume transmission may play an important role in neural function. These data now facilitate more informed neural comparisons between hemichordates and other groups, contributing to broader debates on the origins and evolution of bilaterian nervous systems.

Analysis of autonomic function during natural defecation in patients with irritable bowel syndrome using real-time recording with a wearable device

BACKGROUND

Autonomic dysfunction is a factor in irritable bowel syndrome (IBS). However, there are no reports of autonomic nervous system (ANS) activity during natural defecation in patients with IBS. We aimed to clarify the relationship between ANS activity and life events, such as defecation and abdominal symptoms, using real-time recording.

METHODS

Six patients with IBS and 14 healthy controls were enrolled in this prospective multicenter study. ANS activity was recorded for 24 h using a T-shirt wearable device, and life events were recorded simultaneously in real time using a smartphone application software. Low frequency/high frequency (LF/HF) and HF calculated by power spectrum analysis were defined as activity indicators of the sympathetic and parasympathetic nerves, respectively.

RESULTS

The means of LF/HF and HF in the period with positive symptoms were comparable between the groups; however, the sum of LF/HF, sum of ΔLF/HF, and the maximum variation in ΔLF/HF were significantly higher in the IBS group. In the IBS group, the sum of ΔLF/HF and LF/HF increased significantly from 2 min before defecation, and the sum of LF/HF remained significantly higher until 9 min after defecation. The sum of ΔLF/HF at 2 min before defecation was significantly positively correlated with the intensity of abdominal pain and diarrhea and constipation scores. In contrast, it was significantly negatively correlated with defecation satisfaction and health-related quality of life.

CONCLUSIONS

In patients with IBS, sympathetic nerve activity was activated 2 min before defecation, which was correlated with abdominal symptoms and lower QOL.

Childhood Trauma, the HPA Axis and Psychiatric Illnesses: A Targeted Literature Synthesis

Studies of early life stress (ELS) demonstrate the long-lasting effects of acute and chronic stress on developmental trajectories. Such experiences can become biologically consolidated, creating individual vulnerability to psychological and psychiatric issues later in life. The hippocampus, amygdala, and the medial prefrontal cortex are all important limbic structures involved in the processes that undermine mental health. Hyperarousal of the sympathetic nervous system with sustained allostatic load along the Hypothalamic Pituitary Adrenal (HPA) axis and its connections has been theorized as the basis for adult psychopathology following early childhood trauma. In this review we synthesize current understandings and hypotheses concerning the neurobiological link between childhood trauma, the HPA axis, and adult psychiatric illness. We examine the mechanisms at play in the brain of the developing child and discuss how adverse environmental stimuli may become biologically incorporated into the structure and function of the adult brain via a discussion of the neurosequential model of development, sensitive periods and plasticity. The HPA connections and brain areas implicated in ELS and psychopathology are also explored. In a targeted review of HPA activation in mood and psychotic disorders, cortisol is generally elevated across mood and psychotic disorders. However, in bipolar disorder and psychosis patients with previous early life stress, blunted cortisol responses are found to awakening, psychological stressors and physiological manipulation compared to patients without previous early life stress. These attenuated responses occur in bipolar and psychosis patients on a background of increased cortisol turnover. Although cortisol measures are generally raised in depression, the evidence for a different HPA activation profile in those with early life stress is inconclusive. Further research is needed to explore the stress responses commonalities between bipolar disorder and psychosis in those patients with early life stress.

Amygdalar Corticotropin-Releasing Factor Signaling Is Required for Later-Life Behavioral Dysfunction Following Neonatal Pain

Neonatal pain such as that experienced by infants in the neonatal intensive care unit is known to produce later-life dysfunction including heightened pain sensitivity and anxiety, although the mechanisms remain unclear. Both chronic pain and stress in adult organisms are known to influence the corticotropin-releasing factor (CRF) system in the Central Nucleus of the Amygdala, making this system a likely candidate for changes following neonatal trauma. To examine this, neonatal rats were subjected to daily pain, non-painful handling or left undisturbed for the first week of life. Beginning on postnatal day, 24 male and female rats were subjected to a 4-day fear conditioning and sensory testing protocol. Some subjects received intra-amygdalar administration of either Vehicle, the CRF receptor 1 (CRF₁) receptor antagonist Antalarmin, or the CRF receptor 2 (CRF₂) receptor antagonist Astressin 2B prior to fear conditioning and somatosensory testing, while others had tissue collected following fear conditioning and CRF expression in the CeA and BLA was assessed using fluorescent in situ hybridization. CRF₁ antagonism attenuated fear-induced hypersensitivity in neonatal pain and handled rats, while CRF₂ antagonism produced a general antinociception. In addition, neonatal pain and handling produced a lateralized sex-dependent decrease in CRF expression, with males showing a diminished number of CRF-expressing cells in the right CeA and females showing a similar reduction in the number of CRF-expressing cells in the left BLA compared to undisturbed controls. These data show that the amygdalar CRF system is a likely target for alleviating dysfunction produced by early life trauma and that this system continues to play a major role in the lasting effects of such trauma into the juvenile stage of development.

Evolutionary Significance of the Neuroendocrine Stress Axis on Vertebrate Immunity and the Influence of the Microbiome on Early-Life Stress Regulation and Health Outcomes

Stress is broadly defined as the non-specific biological response to changes in homeostatic demands and is mediated by the evolutionarily conserved neuroendocrine networks of the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Activation of these networks results in transient release of glucocorticoids (cortisol) and catecholamines (epinephrine) into circulation, as well as activation of sympathetic fibers innervating end organs. These interventions thus regulate numerous physiological processes, including energy metabolism, cardiovascular physiology, and immunity, thereby adapting to cope with the perceived stressors. The developmental trajectory of the stress-axis is influenced by a number of factors, including the gut microbiome, which is the community of microbes that colonizes the gastrointestinal tract immediately following birth. The gut microbiome communicates with the brain through the production of metabolites and microbially derived signals, which are essential to human stress response network development. Ecological perturbations to the gut microbiome during early life may result in the alteration of signals implicated in developmental programming during this critical window, predisposing individuals to numerous diseases later in life. The vulnerability of stress response networks to maladaptive development has been exemplified through animal models determining a causal role for gut microbial ecosystems in HPA axis activity, stress reactivity, and brain development. In this review, we explore the evolutionary significance of the stress-axis system for health maintenance and review recent findings that connect early-life microbiome disturbances to alterations in the development of stress response networks.

Early Life Stress Preceding Mild Pediatric Traumatic Brain Injury Increases Neuroinflammation but Does Not Exacerbate Impairment of Cognitive Flexibility during Adolescence

Early life stress (ELS) followed by pediatric mild traumatic brain injury (mTBI) negatively impacts spatial learning and memory and increases microglial activation in adolescent rats, but whether the same paradigm negatively affects higher order executive function is not known. Hence, we utilized the attentional set-shifting test (AST) to evaluate executive function (cognitive flexibility) and to determine its relationship with neuroinflammation and hypothalamic-pituitary-adrenal (HPA) axis activity after pediatric mTBI in male rats. ELS was induced via maternal separation for 180 min per day (MS180) during the first 21 post-natal (P) days, while controls (CONT) were undisturbed. At P21, fully anesthetized rats received a mild controlled cortical impact (2.2 mm tissue deformation at 4 m/sec) or sham injury. AST was evaluated during adolescence on P35-P40 and cytokine expression and HPA activity were analyzed on P42. The data indicate that pediatric mTBI produced a significant reversal learning deficit on the AST versus sham (p < 0.05), but that the impairment was not exacerbated further by MS180. Additionally, ELS produced an overall elevation in set-loss errors on the AST, and increased hippocampal interleukin (IL)-1β expression after TBI. A significant correlation was observed in executive dysfunction and IL-1β expression in the ipsilateral pre-frontal cortex and hippocampus. Although the combination of ELS and pediatric mTBI did not worsen executive function beyond that of mTBI alone (p > 0.05), it did result in increased hippocampal neuroinflammation relative to mTBI (p < 0.05). These findings provide important insight into the susceptibility to incur alterations in cognitive and neuroimmune functioning after stress exposure and TBI during early life.

The Effects of Acute Neonatal Pain on Expression of Corticotropin-Releasing Hormone and Juvenile Anxiety in a Rodent Model

Premature infants in the neonatal intensive care unit (NICU) may be subjected to numerous painful procedures without analgesics. One necessary, though acutely painful, procedure is the use of heel lances to monitor blood composition. The current study examined the acute effects of neonatal pain on maternal behavior as well as amygdalar and hypothalamic activation, and the long-term effects of neonatal pain on later-life anxiety-like behavior, using a rodent model. Neonatal manipulations consisted of either painful needle pricks or non-painful tactile stimulation in subjects’ left plantar paw surface which occurred four times daily during the first week of life [postnatal day (PND)1–PND7]. Additionally, maternal behaviors in manipulated litters were compared against undisturbed litters via scoring of videotaped interactions to examine the long-term effects of pain on dam-pup interactions. Select subjects underwent neonatal brain collection (PND6) and fluorescent in situ hybridization (FISH) for corticotropin-releasing hormone (CRH) and the immediate early gene c-fos. Other subjects were raised to juvenile age (PND24 and PND25) and underwent innate anxiety testing utilizing an elevated plus maze (EPM) protocol. FISH indicated that neonatal pain influenced amygdalar CRH and c-fos expression, predominately in males. No significant increase in c-fos or CRH expression was observed in the hypothalamus. Additionally, neonatal pain altered anxiety behaviors independent of sex, with neonatal pain subjects showing the highest frequency of exploratory behavior. Neonatal manipulations did not alter maternal behaviors. Overall, neonatal pain drives CRH expression and produces behavioral changes in anxiety that persist until the juvenile stage.

NRSF-dependent epigenetic mechanisms contribute to programming of stress-sensitive neurons by neonatal experience, promoting resilience

Resilience to stress-related emotional disorders is governed in part by early-life experiences. Here we demonstrate experience-dependent re-programming of stress-sensitive hypothalamic neurons, which takes place through modification of neuronal gene expression via epigenetic mechanisms. Specifically, we found that augmented maternal care reduced glutamatergic synapses onto stress-sensitive hypothalamic neurons and repressed expression of the stress-responsive gene, Crh. In hypothalamus in vitro, reduced glutamatergic neurotransmission recapitulated the repressive effects of augmented maternal care on Crh, and this required recruitment of the transcriptional repressor repressor element-1 silencing transcription factor/neuron restrictive silencing factor (NRSF). Increased NRSF binding to chromatin was accompanied by sequential repressive epigenetic changes which outlasted NRSF binding. chromatin immunoprecipitation-seq analyses of NRSF targets identified gene networks that, in addition to Crh, likely contributed to the augmented care-induced phenotype, including diminished depression-like and anxiety-like behaviors. Together, we believe these findings provide the first causal link between enriched neonatal experience, synaptic refinement and induction of epigenetic processes within specific neurons. They uncover a novel mechanistic pathway from neonatal environment to emotional resilience.

Evaluation of the Role of ABCB1gene Polymorphic Variants on Psychiatric Disorders Predisposition in Macedonian Population

The psychiatric and other CNS disorders are characterized with unregulated neuro-inflammatory processes and chronic microglia cell activation resulting with detrimental effect. ABCB1gene polymorphismsC1236T, G2677T/Aand C3435T are associated with P-glycoprotein expression and function andare linked with predisposition to psychiatric disorders such as schizophrenia and bipolar disorders. The relationship between mood disorders and glucocorticoids has been confirmed and ABCB1 SNPs influence the glucocorticoids access to the brain. The aim of the study is evaluation of the influence of the three most common ABCB1SNPs on predisposition to psychiatric disorders in Macedonian population. In the study 107 unrelated healthy Macedonians of both sexes were enrolled as a control group and patient population of 54 patients (22 to 65 years old) diagnosed with schizophrenia or bipolar disorder. ABCB1 for three polymorphisms were analyzed by Real-Time PCR in both groups. The results have confirmed the role of the ABCB1 gene in predisposition to psychiatric disorders and increased risk of developing bipolar disorder in carriers of the heterozygotes and mutant homozygotes for polymorphic variations in 1236 and 2677 in comparison to the normal genotype carriers. Three-fold higher risk was estimated for psychiatric illness in women that are 1236 and 2677 heterozygous carrier (heterozygous and mutant homozygous) compared to healthy control (men and women) population and four-fold higher risk in comparison only to healthy women population. Mutant allele carriers for 1236 and 2677 polymorphisms that are 35 years and below in patients population have almost three-fold higher risk for development of psychiatric illness.

Circuit and synaptic mechanisms of repeated stress: Perspectives from differing contexts, duration, and development

The current review is meant to synthesize research presented as part of a symposium at the 2016 Neurobiology of Stress workshop in Irvine California. The focus of the symposium was "Stress and the Synapse: New Concepts and Methods" and featured the work of several junior investigators. The presentations focused on the impact of various forms of stress (altered maternal care, binge alcohol drinking, chronic social defeat, and chronic unpredictable stress) on synaptic function, neurodevelopment, and behavioral outcomes. One of the goals of the symposium was to highlight the mechanisms accounting for how the nervous system responds to stress and their impact on outcome measures with converging effects on the development of pathological behavior. Dr. Kevin Bath's presentation focused on the impact of disruptions in early maternal care and its impact on the timing of hippocampus maturation in mice, finding that this form of stress drove accelerated synaptic and behavioral maturation, and contributed to the later emergence of risk for cognitive and emotional disturbance. Dr. Scott Russo highlighted the impact of chronic social defeat stress in adolescent mice on the development and plasticity of reward circuity, with a focus on glutamatergic development in the nucleus accumbens and mesolimbic dopamine system, and the implications of these changes for disruptions in social and hedonic response, key processes disturbed in depressive pathology. Dr. Kristen Pleil described synaptic changes in the bed nuclei of the stria terminalis that underlie the behavioral consequences of allostatic load produced by repeated cycles of alcohol binge drinking and withdrawal. Dr. Eric Wohleb and Dr. Ron Duman provided new data associating decreased mammalian target of rapamycin (mTOR) signaling and neurobiological changes in the synapses in response to chronic unpredictable stress, and highlighted the potential for the novel antidepressant ketamine to rescue synaptic and behavioral effects. In aggregate, these presentations showcased how divergent perspectives provide new insights into the ways in which stress impacts circuit development and function, with implications for understanding emergence of affective pathology.

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.

Lifetime Modulation of the Pain System via Neuroimmune and Neuroendocrine Interactions

Chronic pain is a debilitating condition that still is challenging both clinicians and researchers. Despite intense research, it is still not clear why some individuals develop chronic pain while others do not or how to heal this disease. In this review, we argue for a multisystem approach to understand chronic pain. Pain is not only to be viewed simply as a result of aberrant neuronal activity but also as a result of adverse early-life experiences that impact an individual's endocrine, immune, and nervous systems and changes which in turn program the pain system. First, we give an overview of the ontogeny of the central nervous system, endocrine, and immune systems and their windows of vulnerability. Thereafter, we summarize human and animal findings from our laboratories and others that point to an important role of the endocrine and immune systems in modulating pain sensitivity. Taking "early-life history" into account, together with the past and current immunological and endocrine status of chronic pain patients, is a necessary step to understand chronic pain pathophysiology and assist clinicians in tailoring the best therapeutic approach.

Effects of acute and chronic stress on telencephalic neurochemistry and gene expression in rainbow trout (Oncorhynchus mykiss)

By filtering relevant sensory inputs and initiating stress responses, the brain is an essential organ in stress coping and adaptation. However, exposure to chronic or repeated stress can lead to allostatic overload, where neuroendocrinal and behavioral reactions to stress become maladaptive. This work examines forebrain mechanisms involved in allostatic processes in teleost fishes. Plasma cortisol, forebrain serotonergic (5-HTergic) neurochemistry, and mRNA levels of corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), CRF receptors (CRFR1 and CRFR2), mineralocorticoid receptor (MR), glucocorticoid receptors (GR1 and GR2) and serotonin type 1A (5-HT_1A) receptors (5-HT_1Aα and 5-HT_1Aβ) were investigated at 1 h before and 0, 1 and 4 h after acute stress, in two groups of rainbow trout held in densities of 25 and 140 kg m^-3 for 28 days. Generally, being held at 140 kg m^-3 resulted in a less pronounced cortisol response. This effect was also reflected in lower forebrain 5-HTergic turnover, but not in mRNA levels in any of the investigated genes. This lends further support to reports that allostatic load causes fish to be incapable of mounting a proper cortisol response to an acute stressor, and suggests that changes in forebrain 5-HT metabolism are involved in allostatic processes in fish. Independent of rearing densities, mRNA levels of 5-HT_1Aα and MR were downregulated 4 h post-stress compared with values 1 h post-stress, suggesting that these receptors are under feedback control and take part in the downregulation of the hypothalamic-pituitary-interrenal (HPI) axis after exposure to an acute stressor.

Genetic predisposition for high stress reactivity amplifies effects of early-life adversity

A dysregulation of the hypothalamus-pituitary-adrenocortical (HPA) axis and the experience of early-life adversity are both well-established risk factors for the development of affective disorders, such as major depression. However, little is known about the interaction of these two factors in shaping endophenotypes of the disease. Here, we studied the gene-environment interaction of a genetic predisposition for HPA axis dysregulation with early-life stress (ELS), assessing the short-, as well as the long-lasting consequences on emotional behavior, neuroendocrine functions and gene expression profiles. Three mouse lines, selectively bred for either high (HR), intermediate (IR), or low (LR) HPA axis reactivity, were exposed to one week of ELS using the limited nesting and bedding material paradigm. Measurements collected during or shortly after the ELS period showed that, regardless of genetic background, ELS exposure led to impaired weight gain and altered the animals' coping behavior under stressful conditions. However, only HR mice additionally showed significant changes in neuroendocrine stress responsiveness at a young age. Accordingly, adult HR mice also showed lasting consequences of ELS, including hyperactive stress-coping, HPA axis hyperreactivity, and gene expression changes in the Crh system, as well as downregulation of Fkbp5 in relevant brain regions. We suggest that the genetic predisposition for high stress reactivity interacts with ELS exposure by disturbing the suppression of corticosterone release during a critical period of brain development, thus exerting lasting programming effects on the HPA axis, presumably via epigenetic mechanisms. In concert, these changes lead to the emergence of important endophenotypes associated with affective disorders.

Early life stress accelerates behavioral and neural maturation of the hippocampus in male mice

Early life stress (ELS) increases the risk for later cognitive and emotional dysfunction. ELS is known to truncate neural development through effects on suppressing cell birth, increasing cell death, and altering neuronal morphology, effects that have been associated with behavioral profiles indicative of precocious maturation. However, how earlier silencing of growth drives accelerated behavioral maturation has remained puzzling. Here, we test the novel hypothesis that, ELS drives a switch from growth to maturation to accelerate neural and behavioral development. To test this, we used a mouse model of ELS, fragmented maternal care, and a cross-sectional dense sampling approach focusing on hippocampus and measured effects of ELS on the ontogeny of behavioral development and biomarkers of neural maturation. Consistent with previous work, ELS was associated with an earlier developmental decline in expression of markers of cell proliferation (Ki-67) and differentiation (doublecortin). However, ELS also led to a precocious arrival of Parvalbumin-positive cells, led to an earlier switch in NMDA receptor subunit expression (marker of synaptic maturity), and was associated with an earlier rise in myelin basic protein expression (key component of the myelin sheath). In addition, in a contextual fear-conditioning task, ELS accelerated the timed developmental suppression of contextual fear. Together, these data provide support for the hypothesis that ELS serves to switch neurodevelopment from processes of growth to maturation and promotes accelerated development of some forms of emotional learning.

Early adversity, hypocortisolism, and behavior problems at school entry: A study of internationally adopted children

The hypothalamic-pituitary-adrenal (HPA) axis is influenced by early life adversity; however, less is known about the potential for recovery following marked improvements in care. The present study examined longitudinal changes in children's cortisol reactivity in the laboratory (4 assessments over 2 years) after adoption. Post-institutionalized (N=65) and post-foster care children (N=49) demonstrated blunted reactivity relative to non-adopted peers (N=53). Furthermore, post-institutionalized children exhibited no evidence of expected adaptation to repeated sessions in the 2 years following adoption. As evidenced by blunted cortisol reactivity, flatter diurnal slope, and lower home morning cortisol, we found support for hypocortisolism among children experiencing adverse early care. Hypocortisolism served as a mediator between adversity and teacher-reported attention and externalizing problems during kindergarten. Early adversity appears to contribute to the down-regulation of the HPA axis under both basal and stress conditions.

Stress and neuroinflammation: a systematic review of the effects of stress on microglia and the implications for mental illness

RATIONALE

Psychosocial stressors are a well-documented risk factor for mental illness. Neuroinflammation, in particular elevated microglial activity, has been proposed to mediate this association. A number of preclinical studies have investigated the effect of stress on microglial activity. However, these have not been systematically reviewed before.

OBJECTIVES

This study aims to systematically review the effects of stress on microglia, as indexed by the histological microglial marker ionised calcium binding adaptor molecule 1 (Iba-1), and consider the implications of these for the role of stress in the development of mental disorders.

METHODS

A systematic review was undertaken using pre-defined search criteria on PubMed and EMBASE. Inclusion and data extraction was agreed by two independent researchers after review of abstracts and full text.

RESULTS

Eighteen studies met the inclusion criteria. These used seven different psychosocial stressors, including chronic restraint, social isolation and repeated social defeat in gerbils, mice and/or rats. The hippocampus (11/18 studies) and prefrontal cortex (13/18 studies) were the most frequently studied areas. Within the hippocampus, increased Iba-1 levels of between 20 and 200 % were reported by all 11 studies; however, one study found this to be a duration-dependent effect. Of those examining the prefrontal cortex, ∼75 % found psychosocial stress resulted in elevated Iba-1 activity. Elevations were also consistently seen in the nucleus accumbens, and under some stress conditions in the amygdala and paraventricular nucleus.

CONCLUSIONS

There is consistent evidence that a range of psychosocial stressors lead to elevated microglial activity in the hippocampus and good evidence that this is also the case in other brain regions. These effects were seen with early-life/prenatal stress, as well as stressors in adulthood. We consider these findings in terms of the two-hit hypothesis, which proposes that early-life stress primes microglia, leading to a potentiated response to subsequent stress. The implications for understanding the pathoaetiology of mental disorders and the development of new treatments are also considered.

Variation in the corticotropin-releasing hormone receptor 1 (CRHR1) gene modulates age effects on working memory

Decline in working memory (WM) functions during aging has been associated with hippocampal dysfunction mediated by age-related changes to the corticotropin-releasing hormone (CRH) system. Recent reports suggest that GG-homozygous individuals of single nucleotide polymorphisms (rs110402 and rs242924) in the CRH receptor 1 (CRHR1) gene show increased stress vulnerability and decreased BOLD responses in WM relevant regions. However, until now, no study investigated the interaction effects of variation in the CRHR1 gene and age on individual differences in WM. Here, young, middle-aged and old subjects (N = 466) were genotyped for rs110402 and rs242924 within the CRHR1 gene and an n-back task was used to investigate the hypothesis that vulnerable genotypes (GG-homozygotes) would show impaired WM functions that might be magnified by increased CRH production with advancing age. Our results show an impact of genotype already in middle-age with significantly better performance in AT-carriers. Working memory performance in AT-carriers did not differ between young and middle-aged subjects, but was significantly impaired in old age. In GG-homozygotes, severe working memory dysfunction occurred already in middle age. Our data indicate that GG-homozygotes of CRHR1 rs110402 and rs242924 represent a genetically driven subtype of early WM impairments due to alterations in hippocampal CRHR1 activation. Early interventions that have proven effective in delaying cognitive decline appear to be particularly important for these subjects at risk for premature memory decline, who are in the prime of their personal and professional lives.

Synaptic rewiring of stress-sensitive neurons by early-life experience: a mechanism for resilience?

Genes and environment interact to influence cognitive and emotional functions throughout life. Early-life experiences in particular contribute to vulnerability or resilience to a number of emotional and cognitive illnesses in humans. In rodents, early-life experiences directly lead to resilience or vulnerability to stress later in life, and influence the development of cognitive and emotional deficits. The mechanisms for the enduring effects of early-life experiences on cognitive and emotional outcomes are not completely understood. Here, we present emerging information supporting experience-dependent modulation of the number and efficacy of synaptic inputs onto stress-sensitive neurons. This synaptic 'rewiring', in turn, may influence the expression of crucial neuronal genes. The persistent changes in gene expression in resilient versus vulnerable rodent models are likely maintained via epigenetic mechanisms. Thus, early-life experience may generate resilience by altering synaptic input to neurons, which informs them to modulate their epigenetic machinery.

Early-life adversity programs emotional functions and the neuroendocrine stress system: the contribution of nutrition, metabolic hormones and epigenetic mechanisms

Clinical and pre-clinical studies have shown that early-life adversities, such as abuse or neglect, can increase the vulnerability to develop psychopathologies and cognitive decline later in life. Remarkably, the lasting consequences of stress during this sensitive period on the hypothalamic-pituitary-adrenal axis and emotional function closely resemble the long-term effects of early malnutrition and suggest a possible common pathway mediating these effects. During early-life, brain development is affected by both exogenous factors, like nutrition and maternal care as well as by endogenous modulators including stress hormones. These elements, while mostly considered for their independent actions, clearly do not act alone but rather in a synergistic manner. In order to better understand how the programming by early-life stress takes place, it is important to gain further insight into the exact interplay of these key elements, the possible common pathways as well as the underlying molecular mechanisms that mediate their effects. We here review evidence that exposure to both early-life stress and early-life under-/malnutrition similarly lead to life-long alterations on the neuroendocrine stress system and modify emotional functions. We further discuss how the different key elements of the early-life environment interact and affect one another and next suggest a possible role for the early-life adversity induced alterations in metabolic hormones and nutrient availability in shaping later stress responses and emotional function throughout life, possibly via epigenetic mechanisms. Such knowledge will help to develop intervention strategies, which gives the advantage of viewing the synergistic action of a more complete set of changes induced by early-life adversity.

Hyper-excitability and epilepsy generated by chronic early-life stress

Epilepsy is more prevalent in populations with high measures of stress, but the neurobiological mechanisms are unclear. Stress is a common precipitant of seizures in individuals with epilepsy, and may provoke seizures by several mechanisms including changes in neurotransmitter and hormone levels within the brain. Importantly, stress during sensitive periods early in life contributes to ‘brain programming’, influencing neuronal function and brain networks. However, it is unclear if early-life stress influences limbic excitability and promotes epilepsy. Here we used an established, naturalistic model of chronic early-life stress (CES), and employed chronic cortical and limbic video-EEGs combined with molecular and cellular techniques to probe the contributions of stress to age-specific epilepsies and network hyperexcitability and identify the underlying mechanisms.

In control male rats, EEGs obtained throughout development were normal and no seizures were observed. EEGs demonstrated epileptic spikes and spike series in the majority of rats experiencing CES, and 57% of CES rats developed seizures: Behavioral events resembling the human age-specific epilepsy infantile spasms occurred in 11/23 (48%), accompanied by EEG spikes and/or electrodecrements, and two additional rats (9%) developed limbic seizures that involved the amygdala. Probing for stress-dependent, endogenous convulsant molecules within amygdala, we examined the expression of the pro-convulsant neuropeptide corticotropin-releasing hormone (CRH), and found a significant increase of amygdalar--but not cortical--CRH expression in adolescent CES rats.

In conclusion, CES of limited duration has long-lasting effects on brain excitability and may promote age-specific seizures and epilepsy. Whereas the mechanisms involved require further study, these findings provide important insights into environmental contributions to early-life seizures.

Stress in Neonatal Rats with Different Maternal Care Backgrounds: Monoaminergic and Hormonal Responses

The first 2 weeks of life in rats are known as the stress hyporesponsive period because stress responses in pups are diminished as compared to adult animals. However, it is considered a critical period in development in which infant rats are susceptible to environmental events, such as stressful stimuli and quality of maternal care received. These early life events have long-lasting effects, shaping a variety of outcomes, such as stress responsivity. This study investigated the effects of maternal care and sex differences on the response to an aversive stimulus in rat pups from high (HL) and low licking (LL) mothers. Plasma corticosterone, oxytocin, and central monoaminergic activity in 13-day-old rats submitted to cold stress were analyzed. Stress increased plasma corticosterone and marginally decreased hypothalamic dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratio. HL pups showed higher levels of plasma oxytocin than LL pups. The maternal effect was also detected in the hippocampus, in which 5-hydroxyindole-3-acetic acid/serotonin (5-HIAA/5-HT) ratio was increased in HL pups, independently of the sex and stress. Investigating the early life events is useful not only into understand the neurobiological and hormonal mechanisms underlying maternal and stressful influences on infant development into a healthy or psychopathological adult phenotype, but also to unveil the immediate outcomes on infancy.

Naturalistic rodent models of chronic early-life stress

A close association between early-life experience and cognitive and emotional outcomes is found in humans. In experimental models, early-life experience can directly influence a number of brain functions long-term. Specifically, and often in concert with genetic background, experience regulates structural and functional maturation of brain circuits and alters individual neuronal function via large-scale changes in gene expression. Because adverse experience during sensitive developmental periods is often associated with neuropsychiatric disease, there is an impetus to create realistic models of distinct early-life experiences. These can then be used to study causality between early-life experiential factors and cognitive and emotional outcomes, and to probe the underlying mechanisms. Although chronic early-life stress has been linked to the emergence of emotional and cognitive disorders later in life, most commonly used rodent models of involve daily maternal separation and hence intermittent early-life stress. We describe here a naturalistic and robust chronic early-life stress model that potently influences cognitive and emotional outcomes. Mice and rats undergoing this stress develop structural and functional deficits in a number of limbic-cortical circuits. Whereas overt pathological memory impairments appear during adulthood, emotional and cognitive vulnerabilities emerge already during adolescence. This naturalistic paradigm, widely adopted around the world, significantly enriches the repertoire of experimental tools available for the study of normal brain maturation and of cognitive and stress-related disorders including depression, autism, post-traumatic stress disorder, and dementia.

Corticotropin releasing factor in neuroplasticity

Stress is among the strongest signals promoting neuroplasticity: Stress signals, indicating real or perceived danger, lead to alterations of neuronal function and often structure, designed to adapt to the changed conditions and promote survival. Corticotropin releasing factor (CRF) is expressed and released in several types of neuronal populations that are involved in cognition, emotion and the regulation of autonomic and endocrine function. CRF expressing neurons undergo functional and structural plasticity during stress and, in addition, the peptide acts via specific receptors to promote plasticity of target neurons.

Differential contribution of CBP:CREB binding to corticotropin-releasing hormone expression in the infant and adult hypothalamus

Corticotropin-releasing hormone (CRH) contributes crucially to the regulation of central and peripheral responses to stress. Because of the importance of a finely tuned stress system, CRH expression is tightly regulated in an organ- and brain region-specific manner. Thus, in the hypothalamus, CRH is constitutively expressed and this expression is further enhanced by stress; however, the underlying regulatory mechanisms are not fully understood. The regulatory region of the crh gene contains several elements, including the cyclic-AMP response element (CRE), and the role of the CRE interaction with the cyclic-AMP response element binding protein (CREB) in CRH expression has been a focus of intensive research. Notably, whereas thousands of genes contain a CRE, the functional regulation of gene expression by the CRE:CREB system is limited to ∼100 genes, and likely requires additional proteins. Here, we investigated the role of a member of the CREB complex, CREB binding protein (CBP), in basal and stress-induced CRH expression during development and in the adult. Using mice with a deficient CREB-binding site on CBP, we found that CBP:CREB interaction is necessary for normal basal CRH expression at the mRNA and protein level in the nine-day-old mouse, prior to onset of functional regulation of hypothalamic CRH expression by glucocorticoids. This interaction, which functions directly on crh or indirectly via regulation of other genes, was no longer required for maintenance of basal CRH expression levels in the adult. However, CBP:CREB binding contributed to stress-induced CRH expression in the adult, enabling rapid CRH synthesis in hypothalamus. CBP:CREB binding deficiency did not disrupt basal corticosterone plasma levels or acute stress-evoked corticosterone release. Because dysregulation of CRH expression occurs in stress-related disorders including depression, a full understanding of the complex regulation of this gene is important in both health and disease.

Prenatal corticosteroids modify glutamatergic and GABAergic synapse genomic fabric: insights from a novel animal model of infantile spasms

Prenatal exposure to corticosteroids has long-term postnatal somatic and neurodevelopmental consequences. Animal studies indicate that corticosteroid exposure-associated alterations in the nervous system include hypothalamic function. Infants with infantile spasms, a devastating epileptic syndrome of infancy with characteristic spastic seizures, chaotic irregular waves on interictal electroencephalogram (hypsarhythmia) and mental deterioration, have decreased concentrations of adrenocorticotrophic hormone (ACTH) and cortisol in cerebrospinal fluid, strongly suggesting hypothalamic dysfunction. We have exploited this feature to develop a model of human infantile spasms by using repeated prenatal exposure to betamethasone and a postnatal trigger of developmentally relevant spasms with NMDA. The spasms triggered in prenatally primed rats are more severe compared to prenatally saline-injected ones and respond to ACTH, a treatment of choice for infantile spasms in humans. Using autoradiography and immunohistochemistry, we have identified a link between the spasms in our model and the hypothalamus, especially the arcuate nucleus. Transcriptomic analysis of the arcuate nucleus after prenatal priming with betamethasone but before trigger of spasms indicates that prenatal betamethasone exposure down-regulates genes encoding several important proteins participating in glutamatergic and GABAergic transmission. Interestingly, there were significant sex-specific alterations after prenatal betamethasone in synapse-related gene expression but no such sex differences were found in prenatally saline-injected controls. A pairwise relevance analysis revealed that, although the synapse gene expression in controls was independent of sex, these genes form topologically distinct gene fabrics in males and females and these fabrics are altered by betamethasone in a sex-specific manner. These findings may explain the sex differences with respect to both normal behaviour and the occurrence and severity of infantile spasms. Changes in transcript expression and their coordination may contribute to a molecular substrate of permanent neurodevelopmental changes (including infantile spasms) found after prenatal exposure to corticosteroids.

Effects of denial of reward through maternal contact in the neonatal period on adult hypothalamic-pituitary-adrenal axis function in the rat

Emotional behavioral traits associated with stress response are well documented to be affected by early life events. In the present work, we used a novel paradigm of neonatal experience, in which pups were trained in a T-maze and either received (RER rats) or were denied (DER) the reward of maternal contact, during postnatal days 10-13. We then evaluated stress coping and key factors controlling the function of the hypothalamic-pituitary-adrenal axis in adulthood. Adult male DER rats exposed to a single session of forced swim stress (FSS) showed increased immobility, while RER rats exhibited increased escape attempts. The corticosterone response following this stressor was higher although not prolonged in the DER rats. Their CRH mRNA levels in the PVN were increased up to 2h after the forced swim. However, basal levels of these hormones did not differ among groups. In addition, the DER neonatal experience induced an increase in hippocampal GR but a decrease in CRH-R1 immunopositive cells in the CA1 area of the hippocampus and the central amygdala. Overall, these data show a distinct stress response profile in the DER male rats, characterized by passive coping during the forced swim, increased hormonal response following stress, increased inhibitory control through GR and an indirect contribution of CRH-R1, the latter two factors resulting in a modified regulation of the response termination. It thus appears that DER rats have an enhanced potential for appropriate reactivity upon an incoming challenge, while maintaining in parallel an adequate control of the duration of their stress responses.

The impact of acute mental stress on vascular endothelial function: evidence, mechanisms and importance

Cardiovascular disease is a principle cause of morbidity and mortality worldwide, and it has a complex etiology that involves lifestyle factors such as psychosocial stress. Recent evidence suggests that temporary impairments in vascular endothelial cell function may contribute to the relationship between stress and cardiovascular disease. Indeed, impaired endothelial function has been observed to occur transiently (lasting up to 1.5h) following mental stress, and such periods of impairment could accumulate to become clinically relevant over the long term. The finding of acute stress induced endothelial dysfunction is not universal however, and both physiological (e.g. sympathetic nervous system and hypothalamic-pituitary-adrenal axis reactivity), and methodological factors contribute to the conflicting results. A clear understanding of the interaction between stress response activation and endothelial function is critical to elucidating the complexities of the relationship between psychosocial stress and cardiovascular disease. Therefore, the purpose of this review is: 1) to briefly describe the importance of vascular endothelial function and how it is assessed, 2) to review the literature investigating the impact of acute mental stress on endothelial function in humans, identifying factors that may explain contradictory results, and 3) to summarize our current understanding of the mechanisms that may mediate an acute mental stress-endothelial function interaction.

Homeodomain protein otp and activity-dependent splicing modulate neuronal adaptation to stress

Regulation of corticotropin-releasing hormone (CRH) activity is critical for the animal's adaptation to stressful challenges, and its dysregulation is associated with psychiatric disorders in humans. However, the molecular mechanism underlying this transcriptional response to stress is not well understood. Using various stress paradigms in mouse and zebrafish, we show that the hypothalamic transcription factor Orthopedia modulates the expression of CRH as well as the splicing factor Ataxin 2-Binding Protein-1 (A2BP1/Rbfox-1). We further show that the G protein coupled receptor PAC1, which is a known A2BP1/Rbfox-1 splicing target and an important mediator of CRH activity, is alternatively spliced in response to a stressful challenge. The generation of PAC1-hop messenger RNA isoform by alternative splicing is required for termination of CRH transcription, normal activation of the hypothalamic-pituitary-adrenal axis and adaptive anxiety-like behavior. Our study identifies an evolutionarily conserved biochemical pathway that modulates the neuronal adaptation to stress through transcriptional activation and alternative splicing.

Maternal deprivation in rats is associated with corticotrophin-releasing hormone (CRH) promoter hypomethylation and enhances CRH transcriptional responses to stress in adulthood

Exposure to stress during early development causes long-lasting alterations in behaviour and hypothalamic pituitary adrenal (HPA) axis activity, including increased expression of corticotrophin-releasing hormone (CRH). To determine whether early-life stress causes epigenetic changes in the CRH promoter leading to increased CRH transcription, 8-week old female and male rats, subjected to maternal deprivation (MD) between days 2 and 13 post-birth, were studied for HPA axis responses to stress and CRH promoter methylation in the hypothalamic paraventricular nucleus (PVN) and central nucleus of the amygdala (CeA). Plasma corticosterone and PVN CRH heteronuclear (hn)RNA responses to acute restraint stress were higher in MD rats of both sexes. DNA methylation analysis of the CRH promoter revealed a significantly lower percentage of methylation in two CpGs preceding (CpG1) and inside (CpG2) the cyclic AMP-response element (CRE) at -230 bp in the CRH promoter in the PVN but not the CeA of MD rats. Gel-shift assays, using nuclear proteins from forskolin-treated hypothalamic 4B cells and CRH promoter CRE oligonucleotides, unmethylated or methylated at CpG1, revealed a strong band that was supershifted by phospho-cAMP response element-binding antibody. This band was 50% weaker using oligonucleotides methylated at CpG2 (intra-CRE), or methylated at both CpG1 and CpG2. These findings demonstrate that HPA axis hypersensitivity caused by neonatal stress causes long-lasting enhanced CRH transcriptional activity in the PVN of both sexes. Hypomethylation of the CRH promoter CRE, a region critical for CRH transcriptional activation, could serve as a mechanism for the increased transcriptional responses to stress observed in MD rats.

Atypical febrile seizures, mesial temporal lobe epilepsy, and dual pathology

Febrile seizures occurring in the neonatal period, especially when prolonged, are thought to be involved in the later development of mesial temporal lobe epilepsy (mTLE) in children. The presence of an often undetected, underlying cortical malformation has also been reported to be implicated in the epileptogenesis process following febrile seizures. This paper highlights some of the various animal models of febrile seizures and of cortical malformation and portrays a two-hit model that efficiently mimics these two insults and leads to spontaneous recurrent seizures in adult rats. Potential mechanisms are further proposed to explain how these two insults may each, or together, contribute to network hyperexcitability and epileptogenesis. Finally the clinical relevance of the two-hit model is briefly discussed in light of a therapeutic and preventive approach to mTLE.

Maternal prolactin inhibition at the end of lactation affects learning/memory and anxiety-like behaviors but not novelty-seeking in adult rat progeny

Maternal hypoprolactinemia at the end of lactation in rats reduces milk production and is associated with offspring's malnutrition. Since malnutrition during development is also known to have long lasting effects on cognition and emotion, in the present study we tested the hypothesis that maternal hypoprolactinemia, induced by bromocriptine treatment, at the end of the lactating period affects memory/learning, novelty-seeking and anxiety-like behaviors in adult male Wistar rats using, respectively, the radial arm water maze (RAWM), the hole board (HB) arena and the elevated plus-maze (EPM). We also analyzed serum corticosterone and thyroid hormone levels at postnatal day (PN) 21. Lactating dams were treated with bromocriptine (BRO, 1mg twice a day, inhibiting prolactin) or saline from PN19 to 21 (the last 3 days of lactation). BRO offspring had hypercorticosteronemia and hypothyroidism at PN21. In the RAWM, reductions in latency observed in CON rats were initially more accentuated than in BRO ones. By the end of the testing period, latencies became similar between groups. No difference was observed between groups regarding the number of nose-pokes in the HB. In the EPM, BRO rats stayed less time in and had fewer entries into the open-arms than CON ones. This pattern of results indicates that maternal bromocriptine treatment at the end of the lactating period results in poorer memory/learning performance and in higher levels of anxiety-like behavior in the adult offspring, demonstrating that even a relatively short period of malnutrition during development can have long lasting detrimental effects regarding cognition and emotion.

Emerging roles of epigenetic mechanisms in the enduring effects of early-life stress and experience on learning and memory

Epigenetic mechanisms are involved in programming gene expression throughout development. In addition, they are key contributors to the processes by which early-life experience fine-tunes the expression levels of key neuronal genes, governing learning and memory throughout life. Here we describe the long-lasting, bi-directional effects of early-life experience on learning and memory. We discuss how enriched postnatal experience enduringly augments spatial learning, and how chronic early-life stress results in persistent and progressive deficits in the structure and function of hippocampal neurons. The existing and emerging roles of epigenetic mechanisms in these fundamental neuroplasticity phenomena are illustrated.

Plasticity of the stress response early in life: mechanisms and significance

The concept that early-life experience influences the brain long-term has been extensively studied over the past 50 years, whereas genetic factors determine the sequence and levels of expression of specific neuronal genes, this genetic program can be modified enduringly as a result of experience taking place during critical developmental periods. This programming is of major importance because it appears to govern many behavioral and physiological phenotypes and promote susceptibility or resilience to disease. An established example of the consequences of early-life experience-induced programming includes the effects of maternal care, where patterns of augmented care result in decreased neuroendocrine stress responses, improved cognition and resilience to depression in the recipients of this care. Here, we discuss the nature and mechanisms of this programming phenomenon, focusing on work from our lab that was inspired by Seymour Levine and his fundamental contributions to the field.

Correlated memory defects and hippocampal dendritic spine loss after acute stress involve corticotropin-releasing hormone signaling

Stress affects the hippocampus, a brain region crucial for memory. In rodents, acute stress may reduce density of dendritic spines, the location of postsynaptic elements of excitatory synapses, and impair long-term potentiation and memory. Steroid stress hormones and neurotransmitters have been implicated in the underlying mechanisms, but the role of corticotropin-releasing hormone (CRH), a hypothalamic hormone also released during stress within hippocampus, has not been elucidated. In addition, the causal relationship of spine loss and memory defects after acute stress is unclear. We used transgenic mice that expressed YFP in hippocampal neurons and found that a 5-h stress resulted in profound loss of learning and memory. This deficit was associated with selective disruption of long-term potentiation and of dendritic spine integrity in commissural/associational pathways of hippocampal area CA3. The degree of memory deficit in individual mice correlated significantly with the reduced density of area CA3 apical dendritic spines in the same mice. Moreover, administration of the CRH receptor type 1 (CRFR(1)) blocker NBI 30775 directly into the brain prevented the stress-induced spine loss and restored the stress-impaired cognitive functions. We conclude that acute, hours-long stress impairs learning and memory via mechanisms that disrupt the integrity of hippocampal dendritic spines. In addition, establishing the contribution of hippocampal CRH-CRFR(1) signaling to these processes highlights the complexity of the orchestrated mechanisms by which stress impacts hippocampal structure and function.

Re-examination of the Controversial Coexistence of Traumatic Brain Injury and Posttraumatic Stress Disorder: Misdiagnosis and Self-Report Measures

The coexistence of traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) remains a controversial issue in the literature. To address this controversy, we focused primarily on the civilian-related literature of TBI and PTSD. Some investigators have argued that individuals who had been rendered unconscious or suffered amnesia due to a TBI are unable to develop PTSD because they would be unable to consciously experience the symptoms of fear, helplessness, and horror associated with the development of PTSD. Other investigators have reported that individuals who sustain TBI, regardless of its severity, can develop PTSD even in the context of prolonged unconsciousness. A careful review of the methodologies employed in these studies reveals that investigators who relied on clinical interviews of TBI patients to diagnose PTSD found little or no evidence of PTSD. In contrast, investigators who relied on PTSD questionnaires to diagnose PTSD found considerable evidence of PTSD. Further analysis revealed that many of the TBI patients who were initially diagnosed with PTSD according to self-report questionnaires did not meet the diagnostic criteria for PTSD upon completion of a clinical interview. In particular, patients with severe TBI were often misdiagnosed with PTSD. A number of investigators found that many of the severe TBI patients failed to follow the questionnaire instructions and erroneously endorsed PTSD symptoms because of their cognitive difficulties. Because PTSD questionnaires are not designed to discriminate between PTSD and TBI symptoms or determine whether a patient's responses are accurate or exaggerated, studies that rely on self-report questionnaires to evaluate PTSD in TBI patients are at risk of misdiagnosing PTSD. Further research should evaluate the degree to which misdiagnosis of PTSD occurs in individuals who have sustained mild TBI.

A review of adversity, the amygdala and the hippocampus: a consideration of developmental timing

A review of the human developmental neuroimaging literature that investigates outcomes following exposure to psychosocial adversity is presented with a focus on two subcortical structures – the hippocampus and the amygdala. Throughout this review, we discuss how a consideration of developmental timing of adverse experiences and age at measurement might provide insight into the seemingly discrepant findings across studies. We use findings from animal studies to suggest some mechanisms through which timing of experiences may result in differences across time and studies. The literature suggests that early life may be a time of heightened susceptibility to environmental stressors, but that expression of these effects will vary by age at measurement.

Stress hormones mediate environment-genotype interactions during amphibian development

Environments experienced by organisms during early development shape the character and timing of developmental processes, leading to different probabilities of survival in the developmental habitat, and often profound effects on phenotypic expression later in life. Amphibian larvae have immense capacity for plasticity in behavior, morphology, growth and development rate. This creates the potential for extreme variation in the timing of, and size at metamorphosis, and subsequent phenotype in the juvenile and adult stage. Hormones of the neuroendocrine stress axis play pivotal roles in mediating environmental effects on animal development. Corticotropin-releasing factor, whose secretion by hypothalamic neurons is induced by environmental stress, influences the timing of amphibian metamorphosis by controlling the activity of the thyroid and interrenal (adrenal; corticosteroids) glands. At target tissues, corticosteroids synergize with thyroid hormone to promote metamorphosis. Thus, environmental stress acts centrally to increase the activity of the two principle endocrine axes controlling metamorphosis, and the effectors of these axes synergize at the level of target tissues to promote morphogenesis. While stress hormones can promote survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Furthermore, exposure to elevated corticosteroids early in life can cause permanent changes in the expression of genes of the neuroendocrine stress axis, leading to altered physiology and behavior in the juvenile/adult stage. Persistent effects of stress hormone actions early in life may have important fitness consequences.

Disruptions of the mother-infant relationship and stress-related behaviours: altered corticosterone secretion does not explain everything

The hypothalamic-pituitary-adrenal (HPA) axis is the main neuroendocrine system of response to stress, and an imbalance of this system's activity is believed to be at the core of numerous psychiatric pathologies. During the neonatal period, the glucocorticoid response to stress is maintained at low levels by specific maternal behaviours, which is essential for proper brain development. Effective evaluation of the impact of increased secretion of corticosterone during an essentially anabolic developmental period on adulthood behaviour involved separation of the neonate from its mother for periods ranging from 3 to 24h. It has been shown that disinhibition of the stress response is achieved by such procedures. The pioneering studies by Seymour Levine set the stage for a prolific and promising field of study that may help neuroscientists unveil the neurobiological underpinnings of stress-related disorders. Based on a series of studies, we propose that maternal separation and maternal deprivation change stress-related behaviours, but that corticosterone seem to be only partially involved in these changes in adulthood. It appears that extra-hypothalamic corticotrophin-releasing factor and neurotransmitter systems may be the primary mediators of these behavioural outcomes.

A single episode of restraint stress regulates central corticotrophin- releasing hormone receptor expression and binding in specific areas of the mouse brain

The importance of restraining stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) system within tolerable limits requires efficient mechanisms for feedback inhibition. Recently, central corticotrophin-releasing hormone (CRH) receptor type 1 (CRHR1) has been shown to mediate HPA system feedback inhibition. To date, most of the data regarding stress-associated expression changes of CRHR1 and CRHR2 mRNA and their ligand CRH have been generated in rats. Taken considerable species differences into consideration, and with the growing importance of transgenic mice, a systematic analysis of the time course of expression changes of CRH and its two receptors in the mouse brain is needed to provide more insight into the regulation of the HPA system, both under physiological and pathophysiological conditions in this species. We analysed in detail the time course of expression changes of CRH, CRHR1 and CRHR2 mRNA after of restraint stress in mice in stress-relevant brain regions (paraventricular nucleus, hippocampus, neocortex). We could show a rapid, strong and long-lasting decrease in cortical and hippocampal CRHR1 mRNA expression after stress, whereas CRHR2 mRNA increased in the same neuroanatomical areas. In situ hybridisation analyses could be further confirmed at the protein level by CRH receptor autoradiography with changes in CRH binding that persisted even 7 days after a single episode of restraint stress. Our observation that stress has opposing effects on CRHR1 and CRHR2 neuronal systems supports the idea that regulation of the relative contribution of the two CRH receptors to brain CRH pathways may be essential in coordinating physiological responses to stress. We further hypothesise that the sustained alteration of CRH receptor expression and binding after a single episode of stress could mediate the long-term effects of stress on neuroendocrine function and emotional regulation.

Hippocampal and amygdala volumes in children and adults with childhood maltreatment-related posttraumatic stress disorder: a meta-analysis

Little work has directly examined the course of hippocampal volume in children and adults with childhood maltreatment-related posttraumatic stress disorder (PTSD). Data from adults suggest that hippocampal volume deficits are associated with PTSD, whereas findings from children with PTSD generally show no hippocampal volume deficits in PTSD. Additionally, the role of the amygdala in emotional response makes it a possible region for investigation in children and adults with childhood maltreatment-related PTSD. The objectives of this study were 2-fold: (1) to meta-analytically determine whether hippocampal and amygdala volumes in children and adults with PTSD from childhood maltreatment differ from those in healthy controls, and (2) to use cross-sectional findings performed with meta-analyses as a proxy for longitudinal studies to estimate the course of hippocampal and amygdala volumes in child and adult subjects with PTSD from childhood maltreatment. Using electronic databases, we identified articles containing hippocampal and amygdala data for children with PTSD and adults with PTSD from childhood maltreatment. Data were extracted and effect sizes were calculated using Comprehensive Meta-Analysis Version 2.0. Reduced bilateral hippocampal volume was found in adults with childhood maltreatment-related PTSD compared with healthy controls, but this deficit was not seen in children with maltreatment-related PTSD, suggesting hippocampal volume deficits from childhood maltreatment may not be apparent until adulthood. Greater left than right hippocampal volume was found in the adult healthy control group but not in the PTSD group. Amygdala volume in children with maltreatment-related PTSD did not differ from that in healthy controls. Hippocampal volume is normal in children with maltreatment-related PTSD but not in adults with PTSD from childhood maltreatment, suggesting an initially volumetrically normal hippocampus with subsequent abnormal volumetric development occurring after trauma exposure. However, longitudinal studies are needed to support these preliminary findings.

Gene-environment interaction and covariation in schizophrenia: the role of obstetric complications

While genetic factors account for a significant proportion of liability to schizophrenia, a body of evidence attests to a significant environmental contribution. Understanding the mechanisms through which genetic and environmental factors coalesce in influencing schizophrenia is critical for elucidating the pathways underlying psychotic illness and for developing primary prevention strategies. Although obstetric complications (OCs) remain among the most well-documented environmental indicators of risk for schizophrenia, the pathogenic role they play in the etiology of schizophrenia continues to remain poorly understood. A question of major importance is do these factors result from a genetic diathesis to schizophrenia (as in gene-environment covariation), act additively or interactively with predisposing genes for the disorder in influencing disease risk, or independently cause disease onset? In this review, we evaluate 3 classes of OCs commonly related to schizophrenia including hypoxia-associated OCs, maternal infection during pregnancy, and maternal stress during pregnancy. In addition, we discuss several mechanisms by which OCs impact on genetically susceptible brain regions, increasing constitutional vulnerability to neuromaturational events and stressors later in life (ie, adolescence), which may in turn contribute to triggering psychosis.