Developmental profile of messenger RNA for the corticotropin-releasing hormone receptor in the rat limbic system

Reconsidering the nature of threat in infancy: Integrating animal and human studies on neurobiological effects of infant stress

Early life stress has been associated with elevated risk for later psychopathology. One mechanism that may contribute to such long-term risk is alterations in amygdala development, a brain region critical to stress responsivity. Yet effects of stress on the amygdala during human infancy, a period of particularly rapid brain development, remain largely unstudied. In order to model how early stressors may affect infant amygdala development, several discrepancies across the existing literatures on early life stress among rodents and early threat versus deprivation among older human children and adults need to be reconciled. We briefly review the key findings of each of these literatures. We then consider them in light of emerging findings from studies of human infants regarding relations among maternal caregiving, infant cortisol response, and infant amygdala volume. Finally, we advance a developmental salience model of how early threat may impact the rapidly developing infant brain, a model with the potential to integrate across these divergent literatures. Future work to assess the value of this model is also proposed.

The role of serum/glucocorticoid-regulated kinase 1 in brain function following cerebral ischemia

Cardiopulmonary arrest (CA) is a major cause of death/disability in the U.S. with poor prognosis and survival rates. Current therapeutic challenges are physiologically complex because they involve hypoperfusion (decreased cerebral blood flow), neuroinflammation, and mitochondrial dysfunction. We previously discovered novel serum/glucocorticoid-regulated kinase 1 (SGK1) is highly expressed in brain of neurons that are susceptible to ischemia (hippocampus and cortex). We inhibited SGK1 and utilized pharmacological (specific inhibitor, GSK650394) and neuron-specific genetic approaches (shRNA) in rodent models of CA to determine if SGK1 is responsible for hypoperfusion, neuroinflammation, mitochondrial dysfunctional, and neurological deficits after CA. Inhibition of SGK1 alleviated cortical hypoperfusion and neuroinflammation (via Iba1, GFAP, and cytokine array). Treatment with GSK650394 enhanced mitochondrial function (via Seahorse respirometry) in the hippocampus 3 and 7 days after CA. Neuronal injury (via MAP2, dMBP, and Golgi staining) in the hippocampus and cortex was observed 7 days after CA but ameliorated with SGK1-shRNA. Moreover, SGK1 mediated neuronal injury by regulating the Ndrg1-SOX10 axis. Finally, animals subjected to CA exhibited learning/memory, motor, and anxiety deficits after CA, whereas SGK1 inhibition via SGK1-shRNA improved neurocognitive function. The present study suggests the fundamental roles of SGK1 in brain circulation and neuronal survival/death in cerebral ischemia-related diseases.

Juvenile confinement exacerbates adversity burden: A neurobiological impetus for decarceration

Every year, about 700,000 youth arrests occur in the United States, creating significant neurodevelopmental strain; this is especially concerning as most of these youth have early life adversity exposures that may alter brain development. Males, Black, and Latinx youth, and individuals from low socioeconomic status households have disproportionate contact with the juvenile justice system (JJS). Youth confined in the JJS are frequently exposed to threat and abuse, in addition to separation from family and other social supports. Youths’ educational and exploratory behaviors and activities are substantially restricted, and youth are confined to sterile environments that often lack sufficient enrichment resources. In addition to their demonstrated ineffectiveness in preventing future delinquent behaviors, high recidivism rates, and costs, juvenile conditions of confinement likely exacerbate youths’ adversity burden and neurodevelopmentally harm youth during the temporally sensitive window of adolescence. Developmentally appropriate methods that capitalize on adolescents’ unique rehabilitative potential should be instated through interventions that minimize confinement. Such changes would require joint advocacy from the pediatric and behavioral health care communities. “The distinct nature of children, their initial dependent, and developmental state, their unique human potential as well as their vulnerability, all demand the need for more, rather than less, legal and other protection from all forms of violence (United Nations Committee on the Rights of the Child, 2007).”

Early life stress induces a transient increase in hippocampal corticotropin-releasing hormone in rat neonates that precedes the effects on hypothalamic neuropeptides

Early life stress (ELS) programs hypothalamus-pituitary-adrenal (HPA) axis activity and affects synaptic plasticity and cognitive performance in adults; however, the effects of ELS during the temporal window of vulnerability are poorly understood. This study aimed to thoroughly characterize the effects of ELS in the form of periodic maternal separation (MS180) during the time of exposure to stress. Hippocampal corticotropin-releasing hormone (CRH) gene expression and baseline HPA axis activity were analyzed at postnatal (P) days 6, 12, 15, and 21, and in adulthood (P75); these factors were correlated with plasticity markers and adult behavior. Our results indicate that MS180 induces an increase in hippocampal CRH expression at P9, P12, and P15, whereas an increase in hypothalamic CRH expression was observed from P12 to P21. Increased arginine-vasopressin expression and corticosterone levels were observed only at P21. Moreover, MS180 caused transient alterations in hypothalamic synaptophysin expression during early life. As adults, MS180 rats showed a passive coping strategy in the forced swimming test, cognitive impairments in the object location test, increased hypothalamic CRH expression, and decreased oxytocin (OXT) expression. Spearman's analysis indicated that cognitive impairments correlated with CRH and OXT expression. In conclusion, our data indicate that MS180 induces a transient increase in hippocampal CRH expression in neonates that precedes the effects on hypothalamic neuropeptides, confirming the role of increased CRH during the temporal window of vulnerability as a mediator of some of the detrimental effects of ELS on brain development and adult behavior.

Timing-specific associations between income-to-needs ratio and hippocampal and amygdala volumes in middle childhood: A preliminary study

It is well known that financial disadvantage is associated with alterations in brain development in regions critical to socioemotional well-being such as the hippocampus and the amygdala. Yet little is known about whether family income at different points in development is differentially associated with these structures. Furthermore, little is known about which environmental factors statistically mediate associations between income and subcortical structure. Using a longitudinal birth cohort and linear mixed-effects models, we identified associations between income-to-needs ratio (INR) at 6 timepoints throughout childhood and hippocampal and amygdala volumes at age 7-9 years (n = 41; 236 INR measurements; 41 brain measurements). Mediation analysis identified environmental sequelae of income that statistically accounted for INR-brain associations. Lower INR prior to age 4 was associated with smaller hippocampal volumes, whereas lower INR prior to age 2 was associated with smaller right amygdala volume. These associations were mediated by unmet basic needs (e.g., food, housing). These findings delineate the temporal specificity of associations between income and hippocampal and amygdala structures.

Sex differences in CRF1, CRF, and CRFBP expression in C57BL/6J mouse brain across the lifespan and in response to acute stress

Signaling pathways mediated by corticotropin-releasing factor and its receptor 1 (CRF1) play a central role in stress responses. Dysfunction of the CRF system has been associated with neuropsychiatric disorders. However, dynamic changes in the CRF system during brain development and aging are not well investigated. In this study, we characterized CRF1, CRF, and corticotropin-releasing factor binding protein (CRFBP) expression in different brain regions in both male and female C57BL/6J mice from 1 to 18 months of age under basal conditions as well as after an acute 2-hr-restraint stress. We found that CRF and CRF1 levels tended to increase in the hippocampus and hypothalamus, and to decrease in the prefrontal cortex with aging, especially at 18 months of age, whereas CRFBP expression followed an opposite direction in these brain areas. We also observed area-specific sex differences in the expression of these three proteins. For example, CRF expression was lower in females than in males in all the brain regions examined except the prefrontal cortex. After acute stress, CRF and CRF1 were up-regulated at 1, 6, and 12 months of age, and down-regulated at 18 months of age. Females showed more robust changes compared to males of the same age. CRFBP expression either decreased or remained unchanged in most of the brain areas following acute stress. Our findings suggest that brain CRF1, CRF, and CRFBP expression changes dynamically across the lifespan and under stress condition in a sex- and regional-specific manner. Sex differences in the CRF system in response to stress may contribute to the etiology of stress-related neuropsychiatric disorders.

Long term effects of early life stress on HPA circuit in rodent models

Adaptation to environmental challenges represents a critical process for survival, requiring the complex integration of information derived from both external cues and internal signals regarding current conditions and previous experiences. The Hypothalamic-pituitary-adrenal axis plays a central role in this process inducing the activation of a neuroendocrine signaling cascade that affects the delicate balance of activity and cross-talk between areas that are involved in sensorial, emotional, and cognitive processing such as the hippocampus, amygdala, Prefrontal Cortex, Ventral Tegmental Area, and dorsal raphe. Early life stress, especially early critical experiences with caregivers, influences the functional and structural organization of these areas, affects these processes in a long-lasting manner and may result in long-term maladaptive and psychopathological outcomes, depending on the complex interaction between genetic and environmental factors. This review summarizes the results of studies that have modeled this early postnatal stress in rodents during the first 2 postnatal weeks, focusing on the long-term effects on molecular and structural alteration in brain areas involved in Hypothalamic-pituitary-adrenal axis function. Moreover, a brief investigation of epigenetic mechanisms and specific genetic targets mediating the long-term effects of these early environmental manipulations and at the basis of differential neurobiological and behavioral effects during adulthood is provided.

Longitudinal changes in amygdala, hippocampus and cortisol development following early caregiving adversity

Although decades of research have shown associations between early caregiving adversity, stress physiology and limbic brain volume (e.g., amygdala, hippocampus), the developmental trajectories of these phenotypes are not well characterized. In the current study, we used an accelerated longitudinal design to assess the development of stress physiology, amygdala, and hippocampal volume following early institutional care. Previously Institutionalized (PI; N = 93) and comparison (COMP; N = 161) youth (ages 4–20 years old) completed 1–3 waves of data collection, each spaced approximately 2 years apart, for diurnal cortisol (N = 239) and structural MRI (N = 156). We observed a developmental shift in morning cortisol in the PI group, with blunted levels in childhood and heightened levels in late adolescence. PI history was associated with reduced hippocampal volume and reduced growth rate of the amygdala, resulting in smaller volumes by adolescence. Amygdala and hippocampal volumes were also prospectively associated with future morning cortisol in both groups. These results indicate that adversity-related physiological and neural phenotypes are not stationary during development but instead exhibit dynamic and interdependent changes from early childhood to early adulthood.

Premature Birth and Developmental Programming: Mechanisms of Resilience and Vulnerability

The third trimester of pregnancy represents a sensitive phase for infant brain plasticity when a series of fast-developing cellular events (synaptogenesis, neuronal migration, and myelination) regulates the development of neural circuits. Throughout this dynamic period of growth and development, the human brain is susceptible to stress. Preterm infants are born with an immature brain and are, while admitted to the neonatal intensive care unit, precociously exposed to stressful procedures. Postnatal stress may contribute to altered programming of the brain, including key systems such as the hypothalamic-pituitary-adrenal axis and the autonomic nervous system. These neurobiological systems are promising markers for the etiology of several affective and social psychopathologies. As preterm birth interferes with early development of stress-regulatory systems, early interventions might strengthen resilience factors and might help reduce the detrimental effects of chronic stress exposure. Here we will review the impact of stress following premature birth on the programming of neurobiological systems and discuss possible stress-related neural circuits and pathways involved in resilience and vulnerability. Finally, we discuss opportunities for early intervention and future studies.

Biological intersection of sex, age, and environment in the corticotropin releasing factor (CRF) system and alcohol

The neuropeptide corticotropin-releasing factor (CRF) is critical in neural circuit function and behavior, particularly in the context of stress, anxiety, and addiction. Despite a wealth of preclinical evidence for the efficacy of CRF receptor 1 antagonists in reducing behavioral pathology associated with alcohol exposure, several clinical trials have had disappointing outcomes, possibly due to an underappreciation of the role of biological variables. Although he National Institutes of Health (NIH) now mandate the inclusion of sex as a biological variable in all clinical and preclinical research, the current state of knowledge in this area is based almost entirely on evidence from male subjects. Additionally, the influence of biological variables other than sex has received even less attention in the context of neuropeptide signaling. Age (particularly adolescent development) and housing conditions have been shown to affect CRF signaling and voluntary alcohol intake, and the interaction between these biological variables is particularly relevant to the role of the CRF system in the vulnerability or resilience to the development of alcohol use disorder (AUD). Going forward, it will be important to include careful consideration of biological variables in experimental design, reporting, and interpretation. As new research uncovers conditions in which sex, age, and environment play major roles in physiological and/or pathological processes, our understanding of the complex interaction between relevant biological variables and critical signaling pathways like the CRF system in the cellular and behavioral consequences of alcohol exposure will continue to expand ultimately improving the ability of preclinical research to translate to the clinic. This article is part of the special issue on Neuropeptides.

Neurobiological Programming of Early Life Stress: Functional Development of Amygdala-Prefrontal Circuitry and Vulnerability for Stress-Related Psychopathology

Early adverse experiences are associated with heighted vulnerability for stress-related psychopathology across the lifespan. While extensive work has investigated the effects of early adversity on neurobiology in adulthood, developmental approaches can provide further insight on the neurobiological mechanisms that link early experiences and long-term mental health outcomes. In the current review, we discuss the role of emotion regulation circuitry implicated in stress-related psychopathology from a developmental and transdiagnostic perspective. We highlight converging evidence suggesting that multiple forms of early adverse experiences impact the functional development of amygdala-prefrontal circuitry. Next, we discuss how adversity-induced alterations in amygdala-prefrontal development are associated with symptoms of emotion dysregulation and psychopathology. Additionally, we discuss potential mechanisms through which protective factors may buffer the effects of early adversity on amygdala-prefrontal development to confer more adaptive long-term outcomes. Finally, we consider limitations of the existing literature and make suggestions for future longitudinal and translational research that can better elucidate the mechanisms linking early adversity, neurobiology, and emotional phenotypes. Together, these findings may provide further insight into the neuro-developmental mechanisms underlying the emergence of adversity-related emotional disorders and facilitate the development of targeted interventions that can ameliorate risk for psychopathology in youth exposed to early life stress.

Working memory moderates the association between early institutional care and separation anxiety symptoms in late childhood and adolescence

Adverse caregiving, for example, previous institutionalization (PI), is often associated with emotion dysregulation that increases anxiety risk. However, the concept of developmental multifinality predicts heterogeneity in anxiety outcomes. Despite this well-known heterogeneity, more work is needed to identify sources of this heterogeneity and how these sources interact with environmental risk to influence mental health. Here, working memory (WM) was examined during late childhood/adolescence as an intra-individual factor to mitigate the risk for separation anxiety, which is particularly susceptible to caregiving adversities. A modified "object-in-place" task was administered to 110 youths (10-17 years old), with or without a history of PI. The PI youths had elevated separation anxiety scores, which were anticorrelated with morning cortisol levels, yet there were no group differences in WM. PI youths showed significant heterogeneity in separation anxiety symptoms and morning cortisol levels, and WM moderated the link between caregiving and separation anxiety and mediated the association between separation anxiety and morning cortisol in PI youth. Findings suggest that (a) institutional care exerts divergent developmental consequences on separation anxiety versus WM, (b) WM interacts with adversity-related emotion dysregulation, and (c) WM may be a therapeutic target for separation anxiety following early caregiving adversity.

Negative consequences of early-life adversity on substance use as mediated by corticotropin-releasing factor modulation of serotonin activity

Early-life adversity is associated with increased risk for substance abuse in later life, with women more likely to report past and current stress as a mediating factor in their substance use and relapse as compared to men. Preclinical models of neonatal and peri-adolescent (early through late adolescence) stress all support a direct relationship between experiences of early-life adversity and adult substance-related behaviors, and provide valuable information regarding the underlying neurobiology. This review will provide an overview of these animal models and how these paradigms alter drug and alcohol consumption and/or seeking in male and female adults. An introduction to the corticotropin-releasing factor (CRF) and serotonin systems, their development and their interactions at the level of the dorsal raphe will be provided, illustrating how this particular stress system is sexually dimorphic, and is well positioned to be affected by stressors early in development and throughout maturation. A model for CRF-serotonin interactions in the dorsal raphe and how these influence dopaminergic activity within the nucleus accumbens and subsequent reward-associated behaviors will be provided, and alterations to the activity of this system following early-life adversity will be identified. Overall, converging findings suggest that early-life adversity has long-term effects on the functioning of the CRF-serotonin system, highlighting a potentially important and targetable mediator linking stress to addiction. Future work should focus on identifying the exact mechanisms that promote long-term changes to the expression and activity of CRF receptors in the dorsal raphe. Moreover, it is important to clarify whether similar neurobiological mechanisms exist for males and females, given the sexual dimorphism both in CRF receptors and serotonin indices in the dorsal raphe and in the behavioral outcomes of early-life adversity.

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Early life stress increases risk for substance abuse in adulthood.

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Stress and drugs increase CRF which alters serotonin release in the brain.

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CRF₂ receptor expression in the dorsal raphe is altered by early life stress.

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Resultant changes to serotonin output facilitates dopamine in the accumbens.

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CRF₂-sertotonin-dopamine interactions may link early life stress with substance abuse.

Distribution of corticotropin-releasing factor receptor 1 in the developing mouse forebrain: A novel sex difference revealed in the rostral periventricular hypothalamus

Corticotropin-releasing factor (CRF) signaling through CRF receptor 1 (CRFR1) regulates autonomic, endocrine and behavioral responses to stress and has been implicated in the pathophysiology of several disorders including anxiety, depression, and addiction. Using a validated CRFR1 reporter mouse line (bacterial artificial chromosome identified by green fluorescence protein (BAC GFP-CRFR1)), we investigated the distribution of CRFR1 in the developing mouse forebrain. Distribution of CRFR1 was investigated at postnatal days (P) 0, 4, and 21 in male and female mice. CRFR1 increased with age in several regions including the medial amygdala, arcuate nucleus, paraventricular hypothalamus, medial septum, CA1 hippocampal area, and the lateral habenula. Regions showing decreased CRFR1 expression with increased age include the intermediate portion of the periventricular hypothalamic nucleus, and CA3 hippocampal area. We report a sexually dimorphic expression of CRFR1 within the rostral portion of the anteroventral periventricular nucleus of the hypothalamus (AVPV/PeN), a region known to regulate ovulation, reproductive and maternal behaviors. Females had a greater number of CRFR1-GFP-ir cells at all time points in the AVPV/PeN and CRFR1-GFP-ir was nearly absent in males by P21. Overall, alterations in CRFR1-GFP-ir distribution based on age and sex may contribute to observed age- and sex-dependent differences in stress regulation.

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.

Consequences of early adverse rearing experience(EARE) on development: insights from non-human primate studies

Early rearing experiences are important in one's whole life, whereas early adverse rearing experience(EARE) is usually related to various physical and mental disorders in later life. Although there were many studies on human and animals, regarding the effect of EARE on brain development, neuroendocrine systems, as well as the consequential mental disorders and behavioral abnormalities, the underlying mechanisms remain unclear. Due to the close genetic relationship and similarity in social organizations with humans, non-human primate(NHP) studies were performed for over 60 years. Various EARE models were developed to disrupt the early normal interactions between infants and mothers or peers. Those studies provided important insights of EARE induced effects on the physiological and behavioral systems of NHPs across life span, such as social behaviors(including disturbance behavior, social deficiency, sexual behavior, etc), learning and memory ability, brain structural and functional developments(including influences on neurons and glia cells, neuroendocrine systems, e.g., hypothalamic-pituitary-adrenal(HPA) axis, etc). In this review, the effects of EARE and the underlying epigenetic mechanisms were comprehensively summarized and the possibility of rehabilitation was discussed.

Stress and the adolescent brain: Amygdala-prefrontal cortex circuitry and ventral striatum as developmental targets

Adolescence is a time in development when significant changes occur in affective neurobiology. These changes provide a prolonged period of plasticity to prepare the individual for independence. However, they also render the system highly vulnerable to the effects of environmental stress exposures. Here, we review the human literature on the associations between stress-exposure and developmental changes in amygdala, prefrontal cortex, and ventral striatal dopaminergic systems during the adolescent period. Despite the vast differences in types of adverse exposures presented in his review, these neurobiological systems appear consistently vulnerable to stress experienced during development, providing putative mechanisms to explain why affective processes that emerge during adolescence are particularly sensitive to environmental influences.

Discrimination of amygdala response predicts future separation anxiety in youth with early deprivation

BACKGROUND

Significant disruption in caregiving is associated with increased internalizing symptoms, most notably heightened separation anxiety symptoms during childhood. It is also associated with altered functional development of the amygdala, a neurobiological correlate of anxious behavior. However, much less is known about how functional alterations of amygdala predict individual differences in anxiety. Here, we probed amygdala function following institutional caregiving using very subtle social-affective stimuli (trustworthy and untrustworthy faces), which typically result in large differences in amygdala signal, and change in separation anxiety behaviors over a 2-year period. We hypothesized that the degree of differentiation of amygdala signal to trustworthy versus untrustworthy face stimuli would predict separation anxiety symptoms.

METHODS

Seventy-four youths mean (SD) age = 9.7 years (2.64) with and without previous institutional care, who were all living in families at the time of testing, participated in an fMRI task designed to examine differential amygdala response to trustworthy versus untrustworthy faces. Parents reported on their children's separation anxiety symptoms at the time of scan and again 2 years later.

RESULTS

Previous institutional care was associated with diminished amygdala signal differences and behavioral differences to the contrast of untrustworthy and trustworthy faces. Diminished differentiation of these stimuli types predicted more severe separation anxiety symptoms 2 years later. Older age at adoption was associated with diminished differentiation of amygdala responses.

CONCLUSIONS

A history of institutional care is associated with reduced differential amygdala responses to social-affective cues of trustworthiness that are typically exhibited by comparison samples. Individual differences in the degree of amygdala differential responding to these cues predict the severity of separation anxiety symptoms over a 2-year period. These findings provide a biological mechanism to explain the associations between early caregiving adversity and individual differences in internalizing symptomology during development, thereby contributing to individualized predictions of future clinical outcomes.

CRF type 1 receptor antagonism in ventral tegmental area of adolescent rats during social defeat: prevention of escalated cocaine self-administration in adulthood and behavioral adaptations during adolescence

BACKGROUND

Activation of corticotropin-releasing factor type 1 receptors (CRF-R1) in the ventral tegmental area (VTA) represents a critical mechanism for social defeat to escalate cocaine self-administration in adult rats.

OBJECTIVE

We determined the acute effect of a CRF-R1 antagonist (CP376395) microinfusion into the VTA prior to each episode of social defeat in adolescent rats and determined whether this drug treatment could prevent later escalation of cocaine taking in early adulthood.

METHODS

Rats were implanted with bilateral cannulae aimed at the VTA 5 days before the first social defeat. Bilateral microinfusion of CP376395 (500 ng/side) or vehicle occurred 20 min before each episode of social defeat on postnatal days (P) 35, 38, 41, and 44. Behavior was quantified on P35 and P44. On P57, rats were implanted with intra-jugular catheters, and subsequent cocaine self-administration was analyzed.

RESULTS

CP376395-treated adolescent rats walked less and were attacked more slowly but were socially investigated more than vehicle-treated adolescents. Vehicle-treated rats showed increased social and decreased non-social exploration from P35 to P44, while CP376395-treated rats did not. Socially defeated, vehicle-treated adolescents took more cocaine during a 24-h unlimited access binge during adulthood. The latency to supine posture on P44 was inversely correlated with later cocaine self-administration during fixed and progressive ratio schedules of reinforcement and during the binge.

CONCLUSIONS

CP376395 treatment in adolescence blocked escalation of cocaine taking in adulthood. Episodes of social defeat stress engender neuroadaptation in CRF-R1s in the VTA that alter coping with social stress and that persist into adulthood.

Adrenocorticotropic hormone versus prednisolone in the treatment of infantile spasms post vigabatrin failure

The Child Neurology Society/American Academy of Neurology practice parameter has recommended adrenocorticotropic hormone or vigabatrin in the short-term treatment of infantile spasms. When vigabatrin is unavailable or ineffective and adrenocorticotropic hormone is not a treatment option because of the prohibitive cost, other forms of corticosteroids have been considered in the treatment of infantile spasms. This retrospective study reviewed the Hospital for Sick Children's experience with the short-term effectiveness of prednisolone versus adrenocorticotropic hormone in patients with infantile spasms who have failed vigabatrin. The results showed that while adrenocorticotropic hormone was more likely to lead to short-term spasm freedom, there was no difference in the likelihood of longer-term spasm resolution without relapse. These findings can guide clinicians in the treatment of infantile spasms post vigabatrin failure.

The importance of early experiences for neuro-affective development

This chapter considers the functional utility of the prolonged period of immaturity in human brain development. Development of the amygdala and its connections with the prefrontal cortex is used as an example system for discussing the special role of sensitive periods in shaping neural functional architecture. The argument is made that neural immaturity during childhood may be important and confer a longer period of neuroplasticity, which can increase learning from the environment.

Molecular evolution of GPCRs: CRH/CRH receptors

Corticotrophin-releasing hormone (CRH) is the pivotal neuroendocrine peptide hormone associated with the regulation of the stress response in vertebrates. However, CRH-like peptides are also found in a number of invertebrate species. The origin of this peptide can be traced to a common ancestor of lineages leading to chordates and to arthropods, postulated to occur some 500 million years ago. Evidence indicates the presence of a single CRH-like receptor and a soluble binding protein system that acted to transduce and regulate the actions of the early CRH peptide. In vertebrates, genome duplications led to the divergence of CRH receptors into CRH1 and CRH2 forms in tandem with the development of four paralogous ligand lineages that included CRH; urotensin I/urocortin (Ucn), Ucn2 and Ucn3. In addition, taxon-specific genome duplications led to further local divergences in CRH ligands and receptors. Functionally, the CRH ligand-receptor system evolved initially as a molecular system to integrate early diuresis and nutrient acquisition. As multicellular organisms evolved into more complex forms, this ligand-receptor system became integrated with the organismal stress response to coordinate homoeostatic challenges with internal energy usage. In vertebrates, CRH and the CRH1 receptor became associated with the hypothalamo-pituitary-adrenal/interrenal axis and the initial stress response, whereas the CRH2 receptor was selected to play a greater role in diuresis, nutrient acquisition and the latter aspects of the stress response.

Forebrain-specific CRF overproduction during development is sufficient to induce enduring anxiety and startle abnormalities in adult mice

Corticotropin releasing factor (CRF) regulates physiological and behavioral responses to stress. Trauma in early life or adulthood is associated with increased CRF in the cerebrospinal fluid and heightened anxiety. Genetic variance in CRF receptors is linked to altered risk for stress disorders. Thus, both heritable differences and environmentally induced changes in CRF neurotransmission across the lifespan may modulate anxiety traits. To test the hypothesis that CRF hypersignaling is sufficient to modify anxiety-related phenotypes (avoidance, startle, and conditioned fear), we induced transient forebrain-specific overexpression of CRF (CRFOE) in mice (1) during development to model early-life stress, (2) in adulthood to model adult-onset stress, or (3) across the entire postnatal lifespan to model heritable increases in CRF signaling. The consequences of these manipulations on CRF peptide levels and behavioral responses were examined in adulthood. We found that transient CRFOE during development decreased startle habituation and prepulse inhibition, and increased avoidance (particularly in females) recapitulating the behavioral effects of lifetime CRFOE despite lower CRF peptide levels at testing. In contrast, CRFOE limited to adulthood reduced contextual fear learning in females and increased startle reactivity in males but did not change avoidance or startle plasticity. These findings suggest that forebrain CRFOE limited to development is sufficient to induce enduring alterations in startle plasticity and anxiety, while forebrain CRFOE during adulthood results in a different phenotype profile. These findings suggest that startle circuits are particularly sensitive to forebrain CRFOE, and that the impact of CRFOE may be dependent on the time of exposure.

Neuropeptides as targets for the development of anticonvulsant drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

Stress in adolescence and drugs of abuse in rodent models: role of dopamine, CRF, and HPA axis

RATIONALE

Research on adolescence and drug abuse increased substantially in the past decade. However, drug-addiction-related behaviors following stressful experiences during adolescence are less studied. We focus on rodent models of adolescent stress cross-sensitization to drugs of abuse.

OBJECTIVES

Review the ontogeny of behavior, dopamine, corticotropin-releasing factor (CRF), and the hypothalamic-pituitary-adrenal (HPA) axis in adolescent rodents. We evaluate evidence that stressful experiences during adolescence engender hypersensitivity to drugs of abuse and offer potential neural mechanisms.

RESULTS AND CONCLUSIONS

Much evidence suggests that final maturation of behavior, dopamine systems, and HPA axis occurs during adolescence. Stress during adolescence increases amphetamine- and ethanol-stimulated locomotion, preference, and self-administration under many conditions. The influence of adolescent stress on subsequent cocaine- and nicotine-stimulated locomotion and preference is less clear. The type of adolescent stress, temporal interval between stress and testing, species, sex, and the drug tested are key methodological determinants for successful cross-sensitization procedures. The sensitization of the mesolimbic dopamine system is proposed to underlie stress cross-sensitization to drugs of abuse in both adolescents and adults through modulation by CRF. Reduced levels of mesocortical dopamine appear to be a unique consequence of social stress during adolescence. Adolescent stress may reduce the final maturation of cortical dopamine through D2 dopamine receptor regulation of dopamine synthesis or glucocorticoid-facilitated pruning of cortical dopamine fibers. Certain rodent models of adolescent adversity are useful for determining neural mechanisms underlying the cross-sensitization to drugs of abuse.

New insights into the role of perinatal HPA-axis dysregulation in postpartum depression

Postpartum depression affects 10-20% of women following birth and exerts persisting adverse consequences on both mother and child. An incomplete understanding of its etiology constitutes a barrier to early identification and treatment. It is likely that prenatal hormone trajectories represent both markers of risk and also causal factors in the development of postpartum depression. During pregnancy the maternal hypothalamic-pituitary-adrenal axis undergoes dramatic alterations, due in large part, to the introduction of the placenta, a transient endocrine organ of fetal origin. We suggest that prenatal placental and hypothalamic-pituitary-adrenal axis dysregulation is predictive of risk for postpartum depression. In this model the positive feedback loop involving the systems regulating the products of the HPA axis results in higher prenatal levels of cortisol and placental corticotropin-releasing hormone. Greater elevations in placental corticotropin-releasing hormone are related to a disturbance in the sensitivity of the anterior pituitary to cortisol and also perhaps to decreased central corticotropin-releasing hormone secretion. Secondary or tertiary adrenal insufficiencies of a more extreme nature, which emerge during the prenatal period, may be predictive of an extended or more pronounced postpartum hypothalamic-pituitary-adrenal refractory period, which in turn represents a risk factor for development of postpartum depression. In addition to reviewing the relevant existing literature, new data are presented in support of this model which link elevated placental corticotropin-releasing hormone with low levels of ACTH at 3-months postpartum. Future research will further elucidate the role of hypothalamic-pituitary-adrenal axis dysregulation in postpartum depression and also whether prenatal placental and hypothalamic-pituitary-adrenal profiles might prove useful in the early identification of mothers at risk for postpartum mood dysregulation.

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.

Activation of CRH receptor type 1 expressed on glutamatergic neurons increases excitability of CA1 pyramidal neurons by the modulation of voltage-gated ion channels

Corticotropin-releasing hormone (CRH) plays an important role in a substantial number of patients with stress-related mental disorders, such as anxiety disorders and depression. CRH has been shown to increase neuronal excitability in the hippocampus, but the underlying mechanisms are poorly understood. The effects of CRH on neuronal excitability were investigated in acute hippocampal brain slices. Population spikes (PS) and field excitatory postsynaptic potentials (fEPSP) were evoked by stimulating Schaffer-collaterals and recorded simultaneously from the somatic and dendritic region of CA1 pyramidal neurons. CRH was found to increase PS amplitudes (mean ± Standard error of the mean; 231.8 ± 31.2% of control; n = 10) while neither affecting fEPSPs (104.3 ± 4.2%; n = 10) nor long-term potentiation (LTP). However, when Schaffer-collaterals were excited via action potentials (APs) generated by stimulation of CA3 pyramidal neurons, CRH increased fEPSP amplitudes (119.8 ± 3.6%; n = 8) and the magnitude of LTP in the CA1 region. Experiments in slices from transgenic mice revealed that the effect on PS amplitude is mediated exclusively by CRH receptor 1 (CRHR1) expressed on glutamatergic neurons. The effects of CRH on PS were dependent on phosphatase-2B, L- and T-type calcium channels and voltage-gated potassium channels but independent on intracellular Ca²⁺-elevation. In patch-clamp experiments, CRH increased the frequency and decay times of APs and decreased currents through A-type and delayed-rectifier potassium channels. These results suggest that CRH does not affect synaptic transmission per se, but modulates voltage-gated ion currents important for the generation of APs and hence elevates by this route overall neuronal activity.

Neurobehavioral risk is associated with gestational exposure to stress hormones

The developmental origins of disease or fetal programming model predict that early exposures to threat or adverse conditions have lifelong consequences that result in harmful outcomes for health. The maternal endocrine 'fight or flight' system is a source of programming information for the human fetus to detect threats and adjust their developmental trajectory for survival. Fetal exposures to intrauterine conditions including elevated stress hormones increase the risk for a spectrum of health outcomes depending on the timing of exposure, the timetable of organogenesis and the developmental milestones assessed. Recent prospective studies, reviewed here, have documented the neurodevelopmental consequences of fetal exposures to the trajectory of stress hormones over the course of gestation. These studies have shown that fetal exposures to biological markers of adversity have significant and largely negative consequences for fetal, infant and child emotional and cognitive regulation and reduced volume in specific brain structures.

Human amygdala development in the absence of species-expected caregiving

In altricial species, like the human, caregiver presence is necessary for typical emotional development. Children who have been raised in institutional care early in life experience caregiver deprivation and are at significantly elevated risk for emotional difficulties. The current manuscript examines the non-human and human literatures on amygdala development following caregiver deprivation and presents an argument that in the absence of the species-expected caregiver presence, human amygdala development exhibits rapid development and perhaps premature engagement that results in some of the emotional phenotypes observed following early institutional care.

Elevated amygdala response to faces following early deprivation

A functional neuroimaging study examined the long-term neural correlates of early adverse rearing conditions in humans as they relate to socio-emotional development. Previously institutionalized (PI) children and a same-aged comparison group were scanned using functional magnetic resonance imaging (fMRI) while performing an Emotional Face Go/Nogo task. PI children showed heightened activity of the amygdala, a region that supports emotional learning and reactivity to emotional stimuli, and corresponding decreases in cortical regions that support perceptual and cognitive functions. Amygdala activity was associated with decreased eye-contact as measured by eye-tracking methods and during a live dyadic interaction. The association between early rearing environment and subsequent eye-contact was mediated by amygdala activity. These data support the hypothesis that early adversity alters human brain development in a way that can persist into childhood, and they offer insight into the socio-emotional disturbances in human behavior following early adversity.

Forebrain CRF₁ modulates early-life stress-programmed cognitive deficits

Childhood traumatic events hamper the development of the hippocampus and impair declarative memory in susceptible individuals. Persistent elevations of hippocampal corticotropin-releasing factor (CRF), acting through CRF receptor 1 (CRF₁), in experimental models of early-life stress have suggested a role for this endogenous stress hormone in the resulting structural modifications and cognitive dysfunction. However, direct testing of this possibility has been difficult. In the current study, we subjected conditional forebrain CRF₁ knock-out (CRF₁-CKO) mice to an impoverished postnatal environment and examined the role of forebrain CRF₁ in the long-lasting effects of early-life stress on learning and memory. Early-life stress impaired spatial learning and memory in wild-type mice, and postnatal forebrain CRF overexpression reproduced these deleterious effects. Cognitive deficits in stressed wild-type mice were associated with disrupted long-term potentiation (LTP) and a reduced number of dendritic spines in area CA3 but not in CA1. Forebrain CRF₁ deficiency restored cognitive function, LTP and spine density in area CA3, and augmented CA1 LTP and spine density in stressed mice. In addition, early-life stress differentially regulated the amount of hippocampal excitatory and inhibitory synapses in wild-type and CRF₁-CKO mice, accompanied by alterations in the neurexin-neuroligin complex. These data suggest that the functional, structural and molecular changes evoked by early-life stress are at least partly dependent on persistent forebrain CRF₁ signaling, providing a molecular target for the prevention of cognitive deficits in adults with a history of early-life adversity.

Transitional and translational studies of risk for anxiety

Adolescence reflects a period of increased rates of anxiety, depression, and suicide. Yet most teens emerge from this period with a healthy, positive outcome. In this article, we identify biological factors that may increase risk for some individuals during this developmental period by: (1) examining changes in neural circuitry underlying core phenotypic features of anxiety as healthy individuals transition into and out of adolescence; (2) examining genetic factors that may enhance the risk for psychopathology in one individual over another using translation from mouse models to human neuroimaging and behavior; and (3) examining the effects of early experiences on core phenotypic features of anxiety using human neuroimaging and behavioral approaches. Each of these approaches alone provides only limited information on genetic and environmental influences on complex human behavior across development. Together, they reflect an emerging field of translational developmental neuroscience in forming important bridges between animal models of neurodevelopmental and neuropsychiatric disorders.

Postnatal developmental profile of urocortin 1 and cocaine- and amphetamine-regulated transcript in the perioculomotor region of C57BL/6J mice

Urocortin 1 (Ucn 1) is an endogenous corticotropin releasing factor (CRF)-related peptide. Ucn 1 is most highly expressed in the perioculomotor urocortin containing neurons (pIIIu), previously known as the non-preganglionic Edinger-Westphal nucleus (npEW). Various studies indicate that these cells are involved in stress adaptation and the regulation of ethanol (EtOH) intake. However, the developmental trajectory of these neurons remained unexamined. Expression of the cocaine- and amphetamine-regulated transcript (CART), which co-localizes with Ucn 1 in the perioculomotor area (pIII) has been examined prenatally, but not postnatally. The goal of the current study was to characterize the ontogenetic profile of Ucn 1 and CART during postnatal development in C57BL/6J (B6) mice. B6 mice were bred, and brains were collected at postnatal days (PND) 1, 4, 8, 12, 16, 24 and 45. Brightfield immunohistochemical staining for Ucn 1 and CART showed that Ucn 1-immunoreactivity (ir) was absent at PND 1, while CART-ir was already apparent in pIIIu at birth, a finding indicating that although the pIIIu neurons have already migrated to their adult position, Ucn 1 expression is triggered in them at later postnatal stages. Ucn 1-ir gradually increased with age, approaching adult levels at PND 16. This developmental profile was confirmed by double-immunofluorescence, which showed that Ucn 1 was absent in CART-positive cells of pIII at PND 4 and that Ucn 1 and CART are strongly but not completely co-localized in pIII at PND 24. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis confirmed that Ucn 1 mRNA levels are significantly lower at PND 4 and PND 12 than in adult animals. The lack of brain Ucn 1 immunoreactivity at birth and the gradual postnatal increase in Ucn 1 in pIIIu suggests that this peptide plays a greater behavioral role in adulthood than during the early postnatal development of an organism.

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.

Neonatal isolation delays the developmental decline of long-term depression in the CA1 region of rat hippocampus

Activity-dependent alterations of synaptic efficacy or connectivity are essential for the development, signal processing, and learning and memory functions of the nervous system. It was observed that, in particular in the CA1 region of the hippocampus, low-frequency stimulation (LFS) became progressively less effective at inducing long-term depression (LTD) with advancing developmental age. The physiological factors regulating this developmental plasticity change, however, have not yet been elucidated. Here we examined the hypothesis that neonatal isolation (once per day for 1 h from postnatal days 1-7) is able to alter processes underlying the developmental decline of LTD. We confirm that the magnitude of LTD induced by LFS (900 stimuli at 1 Hz) protocol correlates negatively with developmental age and illustrates that neonatal isolation delays this developmental decline via the activation of corticotrophin-releasing factor (CRF) system. Furthermore, this modulation appears to be mediated by an increased transcription of N-methyl-D-aspartate receptor NR2B subunits. We also demonstrate that intracerebroventricular injection of CRF postnatally mimicked the effect of neonatal isolation to increase the expression of NR2B subunits and delayed the developmental decline of LTD, which was specifically blocked by CRF receptor 1 antagonist NBI27914 pretreatment. These results suggest a novel role for CRF in regulating developmental events in the hippocampus and indicate that although maternal deprivation is stressful for neonate, appropriate neonatal isolation can serve to promote an endocrine state that may regulate the gradual developmental change in the induction rules for synaptic plasticity in the hippocampal CA1 region.

Corticotropin-releasing hormone stimulates SGK-1 kinase expression in cultured hippocampal neurons via CRH-R1

Corticotropin-releasing hormone (CRH) has been shown to exhibit various functions in hippocampus. In the present study, we examined the effect of CRH on the expression of serum/glucocorticoid-inducible protein kinase-1 (SGK-1), a novel protein kinase, in primary cultured hippocampal neurons. A dose-dependent increase in mRNA and protein levels of SGK-1 as well as frequency of SGK-1-positive neurons occurred upon exposure to CRH (1 pmol/l to 10 nmol/l). These effects can be reversed by the specific CRH-R1 antagonist antalarmin but not by the CRH-R2 antagonist astressin 2B. Blocking adenylate cyclase (AC) activity with SQ22536 and PKA with H89 completely prevented CRH-induced mRNA and protein expression of SGK-1. Blockage of PLC or PKC did not block CRH-induced SGK-1 expression. Our results suggest that CRH act on CRH-R1 to stimulate SGK-1 mRNA and protein expression in cultured hippocampal neurons via a mechanism that is involved in AC/PKA signaling pathways.

Corticotropin-releasing hormone (CRH) depresses n-methyl-D-aspartate receptor-mediated current in cultured rat hippocampal neurons via CRH receptor type 1

CRH, the primary regulator of the neuroendocrine responses to stress, has been shown to modulate synaptic efficacy and the process of learning and memory in hippocampus. However, effects of CRH on N-methyl-d-aspartate (NMDA) receptor, the key receptor for synaptic plasticity, remain unclear. In primary cultured hippocampal neurons, using the technique of whole-cell patch-clamp recordings, we found that CRH (1 pmol/liter to 10 nmol/liter) inhibited NMDA-induced currents in a dose-dependent manner. This effect was reversed by the CRH receptor type 1 (CRHR1) antagonist antalarmin but not by the CRHR2 antagonist astressin-2B, suggesting that CRHR1 mediated the inhibitory effect of CRH. Investigations on the signaling pathways of CRH showed that CRH dose-dependently induced phosphorylated phospholipase C (PLC)-beta3 expression and increased intracellular cAMP content in these cells. Blocking PLC activity with U73122 prevented CRH-induced depression of NMDA current, whereas blocking protein kinase A (H89) and adenylate cyclase (SQ22536) failed to affect the CRH-induced depression of NMDA current. Application of inositol-1,4,5-triphosphate receptor (IP(3)R) antagonist, Ca(2+) chelators or protein kinase C (PKC) inhibitors also mainly blocked CRH-induced depression of NMDA currents, suggesting involvement of PLC/IP(3)R/Ca(2+)and PLC/PKC signaling pathways in CRH down-regulation of NMDA receptors. Our results suggest that CRH may exert neuromodulatory actions on hippocampus through regulating NMDA receptor function.

The central corticotropin releasing factor system during development and adulthood

Corticotropin releasing factor (CRH) has been shown to contribute critically to molecular and neuroendocrine responses to stress during both adulthood and development. This peptide and its receptors are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and hippocampus. This is consistent with roles for CRH in mediating the influence of stress on emotional behavior and cognitive function. The expression of CRH and of its receptors in hypothalamus, amygdala and hippocampus is age-dependent, and is modulated by stress throughout life (including the first postnatal weeks). Uniquely during development, the cardinal influence of maternal care on the central stress response governs the levels of central CRH expression, and may alter the 'set-point' of CRH-gene sensitivity to stress in a lasting manner.

Brain corticotropin-releasing hormone (CRH) circuits in the developing rat: effect of maternal deprivation

Early in life, there is a delicate and critical balance aimed to maintain low hormone responses derived from the stress responsive hypothalamic-pituitary-adrenal axis (HPA). However, in the infant rat hypothalamic corticotrophin-releasing hormone (CRH) stress responses to environmental events are clearly seen even though other elements of the HPA axis may have limited responses. In view of the role of CRH in mediating behavior associated with stress and anxiety, we considered the ontogeny and the effects of prolonged maternal deprivation (DEP) in brain areas that express CRH-related molecules outside the hypothalamus. We hypothesized that DEP would alter the ontogeny of CRH, CRH binding protein and CRH receptor 1 in prefrontal cortex, amygdala, septum and hippocampus, areas that are part of the CRH extra hypothalamic system, and that a differential modulation would be observed in response to restraint. We compared non-deprived animals to animals subjected to 24 h of DEP at 6, 12 and 18 days of life. We found (1) developmental patterns, which were idiosyncratic to the anatomical area examined, and (2) a temporal response of mRNA levels which was also site specific. The genomic changes are not always related to maternal deprivation status, in fact DEP enhanced, suppressed or had no consequence on the underlying ontogenic progression and restraint response of these CRH-related molecules. We conclude that the extra hypothalamic CRH system is a dynamic system responding to developmental and environmental demands challenging the basic assumption of stress hypo responsiveness in the infant rat. This modulation may have important repercussions on morphological organization and events leading to neuroprotection.

The caudal migratory stream: a novel migratory stream of interneurons derived from the caudal ganglionic eminence in the developing mouse forebrain

The migratory paths of interneurons derived from the ganglionic eminence (GE), and particularly its caudal portion (CGE), remain essentially unknown. To clarify the three-dimensional migration profile of interneurons derived from each part of the GE, we developed a technique involving focal electroporation into a small, defined portion of the telencephalic hemisphere. While the medial GE cells migrated laterally and spread widely throughout the cortex, the majority of the CGE cells migrated caudally toward the caudal-most end of the telencephalon. Time-lapse imaging and an in vivo immunohistochemical study confirmed the existence of a migratory stream depicted by a population of CGE cells directed caudally that eventually reached the hippocampus. Transplantation experiments suggested that the caudal direction of migration of the CGE cells was intrinsically determined as early as embryonic day 13.5. The caudal migratory stream is a novel migratory path for a population of CGE-derived interneurons passing from the subpallium to the hippocampus.

Neonatal isolation accelerates the developmental switch in the signalling cascades for long-term potentiation induction

The molecular mechanisms underlying long-term potentiation (LTP) in the CA1 region of the hippocampus are known to vary with developmental age. The physiological factors regulating this developmental change, however, have not yet been elucidated. Here we show that mild neonatal isolation accelerates the developmental switch in the signalling cascades for hippocampal CA1 LTP induction from a cyclic AMP-dependent protein kinase (PKA)- to a Ca2(+)/calmodulin-dependent protein kinase II (CaMKII)-dependent pattern via the activation of the corticotrophin-releasing factor (CRF) system. Furthermore, this action appears to be mediated through an increased transcription of the alpha isoform of the CaMKII (CaMKIIalpha) gene. We also demonstrate that application of CRF to cultured hippocampal neurones significantly increases the expression of CaMKIIalpha, which is blocked by the non-specific CRF receptor antagonist astressin, the specific CRF receptor 1 antagonist NBI 27911, and the PKA inhibitor KT5720, but not by the CRF receptor 2 antagonist K 41498, or the protein kinase C inhibitor, bisindolylmaleimide I. CRF signalling also mediates the normal maturation of LTP. These results suggest a novel role for CRF in regulating early developmental events in the hippocampus, and indicate that, although maternal deprivation is stressful for the neonate, appropriate neonatal isolation can serve to promote an endocrine state that fosters the rate of maturation of the signalling cascades underlying the induction of LTP in the developing hippocampus.

Advances in the pathophysiology of developmental epilepsies

Pediatric epilepsies display unique characteristics that differ significantly from epilepsy in adults. The immature brain exhibits a decreased seizure threshold and an age-specific response to seizure-induced brain injury. Many idiopathic epilepsy syndromes and symptomatic epilepsies commonly present during childhood. This review highlights recent advances in the pathophysiology of developmental epilepsies. Cortical development involves maturational regulation of multiple cellular and molecular processes, such as neurogenesis, neuronal migration, synaptogenesis, and expression of neurotransmitter receptors and ion channels. These normal developmental changes of the immature brain also contribute to the increased risk for seizures and unique responses to seizure-induced brain injury in pediatric epilepsies. Recent technological advances, especially in genetics and imaging, have yielded exciting discoveries about the pathophysiology of specific pediatric epilepsy syndromes, such as the emergence of channelopathies as the cause of many idiopathic epilepsies and identification of malformations of cortical development as a major source of symptomatic epilepsies in children.

Age-specific threats induce CRF expression in the paraventricular nucleus of the hypothalamus and hippocampus of young rats

Young animals respond to threatening stimuli in an age-specific way. Their endocrine and behavioral responses reflect the potential threat of the situation at a given age. The aim of the present study was to determine whether corticotropin-releasing factor (CRF) is involved in the endocrine and behavioral responses to threat and their developmental changes in young rats. Preweaning 14-day-old and postweaning 26-day-old rats were exposed to two age-specific threats, cat odor and an adult male rat. The acute behavioral response was determined during exposure. After exposure, the time courses of the corticosterone response and of CRF expression in the paraventricular nucleus of the hypothalamus (PVN) and in extrahypothalamic areas were assessed. Preweaning rats became immobile when exposed to cat odor or the male rat, whereas postweaning rats became immobile to cat odor only. Male exposure increased serum corticosterone levels in 14-day-old rats, but cat odor failed to increase levels at either age. Exposure induced elevation of CRF mRNA levels in the PVN that paralleled changes in corticosterone levels. CRF may thus play a role in endocrine regulation and its developmental changes during early life. Neither cat odor nor the adult male altered CRF mRNA levels in the bed nucleus of the stria terminalis (BNST) or the amygdala, but both stimuli increased levels in the hippocampus. Hippocampal CRF mRNA expression levels did not parallel cat odor or male-induced immobility, indicating that CRF is not involved in this response in young rats but may be involved in aspects of learning and memory.

Basic science behind the catastrophic epilepsies

The major catastrophic epileptic syndromes of childhood include infantile spasms, Lennox-Gastaut syndrome, and the progressive myoclonus epilepsies (PMEs). Although each of these syndromes manifests in an age-specific manner and is defined by distinct electroclinical features, they are all refractory to medical therapy and are invariably associated with psychomotor deficits, and in the most severe cases, either epileptic encephalopathy or progressive neurodegeneration. While much has been written about the clinical features and natural history of the catastrophic epilepsies, very little is known about the underlying pathophysiology. Progress in our understanding and treatment of these conditions has been hampered by the lack of suitable animal models in which putative mechanisms and novel targets for intervention could be rigorously studied. Nevertheless, recent clinical and basic investigations have identified certain mechanisms that may be relevant to their pathogenesis. In this review, three major hypotheses regarding the pathophysiology of infantile spasms are highlighted: the corticotropin-releasing hormone (CRH) hypothesis, the N-methyl-D-aspartate (NMDA) hypothesis, and the serotonin-kynurenine hypothesis. One or more of these mechanisms may be relevant in part to later-onset catastrophic epilepsies since infantile spasms can persist into later childhood and, like Lennox-Gastaut syndrome, well into adulthood. There is a profound need to develop more relevant animal models of the developmental encephalopathic epilepsies to truly develop better therapeutic strategies for these catastrophic disorders.

Brain region-specific neuroprotective action and signaling of corticotropin-releasing hormone in primary neurons

CRH regulates the body's response to stressful stimuli by modulating the activity of the hypothalamic pituitary axis. In primary cultures and cell lines, CRH also acts as a potent neuroprotective factor in response to a number of toxins. Using primary neuronal cultures from the cerebellum, cerebral cortex, and hippocampus, we demonstrate that CRH exerts a brain region-specific neuroprotective effect on amyloid beta 25-35 toxicity. At low CRH concentrations (10(-8) M), neuroprotective effects can be observed only in cerebellar and hippocampal cultures, but a higher CRH concentration (10(-7) M) additionally led to the protection of cortical neurons. These neuroprotective effects were inhibited by H89, a specific protein kinase A inhibitor. Western blot analysis, carried out using phospho-specific antibodies directed against MAPK, cAMP response element-binding protein (CREB), and glycogen synthase kinase (GSK)3 beta also resulted in brain legion-specific differences regarding intracellular signaling. Correlating with cell survival, low CRH concentrations resulted in activation of the CREB pathway and inactivation of GSK3 beta in cerebellar and hippocampal cultures, but higher concentrations additionally resulted in activated CREB and inactivated GSK3 beta in cortical cultures. In contrast, MAPK activation occurred only in cortical neurons. Differences in signaling were found to be independent of receptor expression levels because RT-PCR analysis indicated no region-specific differences in CRHR1 mRNA expression.