Corticotropin-releasing hormone (CRH) downregulates the function of its receptor (CRF1) and induces CRF1 expression in hippocampal and cortical regions of the immature rat brain

Child labour in cocoa growing regions of Ghana and Côte d'Ivoire: an analysis of academic attainment in children engaged in hazardous labour

This paper examines the relationship between child labour and educational attainment and explores the distinction between harmful and non-harmful agricultural cocoa work. We conduct a secondary analysis of data on 3,338 children who reported attending school in 2018 across cocoa growing regions of Ghana and Côte d'Ivoire. To address differences between harmful and non-harmful child labour, we differentiated work completed by a child by hazardous activity engagement. These groups of child labour were then modelled against educational attainment, defined by a whether or not the child needed to repeat a class. We then conducted mediation analysis to assess whether injury mediates this relationship. Our results show that hazardous child labour increases the odds of repeating a class and work-related injury compared to non-hazardous labour. The effect of hazardous child labour on academic attainment was also found to be mediated by work-related injuries by 14%. Educational attainment is associated with hazardous labour activities and the odds of injury and not the act of participation in agricultural labour alone. Programmes based on strong measures of harmful work will foster better protection for children who are most at risk and may inform global debates around the benefits versus the risks of child labour.

Genetic Tagging Uncovers a Robust, Selective Activation of the Thalamic Paraventricular Nucleus by Adverse Experiences Early in Life

Background

Early-life adversity (ELA) is associated with increased risk for mood disorders, including depression and substance use disorders. These disorders are characterized by impaired reward-related behaviors, suggesting compromised operations of reward-related brain circuits. However, the brain regions engaged by ELA that mediate these enduring consequences of ELA remain largely unknown. In an animal model of ELA, we identified aberrant reward-seeking behaviors, a discovery that provides a framework for assessing the underlying circuits.

Methods

Employing TRAP2 (targeted recombination in active populations) male and female mice, in which neurons activated within a defined time frame are permanently tagged, we compared ELA- and control-reared mice, assessing the quantity and distribution of ELA-related neuronal activation. After validating the TRAP2 results using native c-Fos labeling, we defined the molecular identity of this population of activated neurons.

Results

We uniquely demonstrated that the TRAP2 system is feasible and efficacious in neonatal mice. Surprisingly, the paraventricular nucleus of the thalamus was robustly and almost exclusively activated by ELA and was the only region distinguishing ELA from typical rearing. Remarkably, a large proportion of ELA-activated paraventricular nucleus of the thalamus neurons expressed CRF1, the receptor for the stress-related peptide, corticotropin-releasing hormone, but these neurons did not express corticotropin-releasing hormone itself.

Conclusions

The paraventricular nucleus of the thalamus, an important component of reward circuits that is known to encode remote, emotionally salient experiences to influence future motivated behaviors, encodes adverse experiences as remote as those occurring during the early postnatal period and is thus poised to contribute to the enduring deficits in reward-related behaviors consequent to ELA.

The CRHR1/CREB/REST signaling cascade regulates mammalian embryonic neural stem cell properties

Growing evidence suggests that the corticotropin-releasing hormone (CRH) signaling pathway, mainly known as a critical initiator of humoral stress responses, has a role in normal neuronal physiology. However, despite the evidence of CRH receptor (CRHR) expression in the embryonic ventricular zone, the exact functions of CRH signaling in embryonic brain development have not yet been fully determined. In this study, we show that CRHR1 is required for the maintenance of neural stem cell properties, as assessed by in vitro neurosphere assays and cell distribution in the embryonic cortical layers following in utero electroporation. Identifying the underlying molecular mechanisms of CRHR1 action, we find that CRHR1 functions are accomplished through the increasing expression of the master transcription factor REST. Furthermore, luciferase reporter and chromatin immunoprecipitation assays reveal that CRHR1-induced CREB activity is responsible for increased REST expression at the transcriptional level. Taken together, these findings indicate that the CRHR1/CREB/REST signaling cascade plays an important role downstream of CRH in the regulation of neural stem cells during embryonic brain development.

Role of CRF and the hypothalamic-pituitary-adrenal axis in stroke: revisiting temporal considerations and targeting a new generation of therapeutics

Ischaemic neurovascular stroke represents a leading cause of death in the developed world. Preclinical and human epidemiological evidence implicates the corticotropin-releasing factor (CRF) family of neuropeptides as mediators of acute neurovascular injury pathology. Preclinical investigations of the role of CRF, CRF receptors and CRF-dependent activation of the hypothalamic-pituitary-adrenal (HPA) axis have pointed toward a tissue-specific and temporal relationship between activation of these pathways and physiological outcomes. Based on the literature, the major phases of ischaemic stroke aetiology may be separated into an acute phase in which CRF and anti-inflammatory stress signalling are beneficial and a chronic phase in which these contribute to neural degeneration, toxicity and apoptotic signalling. Significant gaps in knowledge remain regarding the pathway, temporality and systemic impact of CRF signalling and stress biology in neurovascular injury progression. Heterogeneity among experimental designs poses a challenge to defining the apparent reciprocal relationship between neurological injury and stress metabolism. Despite these challenges, it is our opinion that the elucidated temporality may be best matched with an antibody against CRF with a half-life of days to weeks as opposed to minutes to hours as with small-molecule CRF receptor antagonists. This state-of-the-art review will take a multipronged approach to explore the expected potential benefit of a CRF antibody by modulating CRF and corticotropin-releasing factor receptor 1 signalling, glucocorticoids and autonomic nervous system activity. Additionally, this review compares the modulation of CRF and HPA axis activity in neuropsychiatric diseases and their counterpart outcomes post-stroke and assess lessons learned from antibody therapies in neurodegenerative diseases.

Glucocorticoid production in the thymus and brain: Immunosteroids and neurosteroids

Glucocorticoids (GCs) regulate a myriad of physiological systems, such as the immune and nervous systems. Systemic GC levels in blood are often measured as an indicator of local GC levels in target organs. However, several extra-adrenal organs can produce and metabolize GCs locally. More sensitive and specific methods for GC analysis (i.e., mass spectrometry) allow measurement of local GC levels in small tissue samples with low GC concentrations. Consequently, is it now apparent that systemic GC levels often do not reflect local GC levels. Here, we review the use of systemic GC measurements in clinical and research settings, discuss instances where systemic GC levels do not reflect local GC levels, and present evidence that local GC levels provide useful insights, with a focus on local GC production in the thymus (immunosteroids) and brain (neurosteroids). Lastly, we suggest key areas for further research, such as the roles of immunosteroids and neurosteroids in neonatal programming and the potential clinical relevance of local GC modulators.

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.

Peripheral Corticotropin-Releasing Factor Triggers Jejunal Mast Cell Activation and Abdominal Pain in Patients With Diarrhea-Predominant Irritable Bowel Syndrome

INTRODUCTION

To determine the effect of peripheral CRF on intestinal barrier function in diarrhea-predominant IBS (IBS-D). Irritable bowel syndrome (IBS) pathophysiology has been linked to life stress, epithelial barrier dysfunction, and mast cell activation. Corticotropin-releasing factor (CRF) is a major mediator of stress responses in the gastrointestinal tract, yet its role on IBS mucosal function remains largely unknown.

METHODS

Intestinal response to sequential i.v. 5-mL saline solution (placebo) and CRF (100 μg) was evaluated in 21 IBS-D and 17 healthy subjects (HSs). A 20-cm jejunal segment was perfused with an isosmotic solution and effluents collected at baseline, 30 minutes after placebo, and 60 minutes after CRF. We measured water flux, albumin output, tryptase release, stress hormones, cardiovascular and psychological responses, and abdominal pain. A jejunal biopsy was obtained for CRF receptor expression assessment.

RESULTS

Water flux did not change after placebo in IBS-D and HS but significantly increased after CRF in IBS-D (P = 0.007). Basal luminal output of albumin was higher in IBS-D and increased further after CRF in IBS-D (P = 0.042). Basal jejunal tryptase release was higher in IBS-D, and CRF significantly increased it in both groups (P = 0.004), the response being higher in IBS-D than in HS (P = 0.0023). Abdominal pain worsened only in IBS-D after CRF and correlated with jejunal tryptase release, water flux, and albumin output. IBS-D displayed jejunal up-regulation of CRF2 and down-regulation of CRF1 compared with HS.

DISCUSSION

Stress via CRF-driven mast cell activation seems to be relevant in the pathophysiology of IBS-D.

Long-range inputome of cortical neurons containing corticotropin-releasing hormone

Dissection of the neural circuits of the cerebral cortex is essential for studying mechanisms underlying brain function. Herein, combining a retrograde rabies tracing system with fluorescent micro-optical sectional tomography, we investigated long-range input neurons of corticotropin-releasing hormone containing neurons in the six main cortical areas, including the prefrontal, somatosensory, motor, auditory, and visual cortices. The whole brain distribution of input neurons showed similar patterns to input neurons distributed mainly in the adjacent cortical areas, thalamus, and basal forebrain. Reconstruction of continuous three-dimensional datasets showed the anterior and middle thalamus projected mainly to the rostral cortex whereas the posterior and lateral projected to the caudal cortex. In the basal forebrain, immunohistochemical staining showed these cortical areas received afferent information from cholinergic neurons in the substantia innominata and lateral globus pallidus, whereas cholinergic neurons in the diagonal band nucleus projected strongly to the prefrontal and visual cortex. Additionally, dense neurons in the zona incerta and ventral hippocampus were found to project to the prefrontal cortex. These results showed general patterns of cortical input circuits and unique connection patterns of each individual area, allowing for valuable comparisons among the organisation of different cortical areas and new insight into cortical functions.

Corticotropin-releasing factor receptor signaling and modulation: implications for stress response and resilience

Introduction In addition to their role in regulation of the hypothalamic-pituitary-adrenal-axis, corticotropin-releasing factor (CRF) and its related peptides, the urocortins, are important mediators of physiological and pathophysiological processes of the central nervous, cardiovascular, gastrointestinal, immune, endocrine, reproductive, and skin systems. Altered regulation of CRF-mediated adaptive responses to various stressful stimuli disrupts healthy function and might confer vulnerability to several disorders, including depression and anxiety. Methodology This narrative review was conducted through search and analysis of studies retrieved from online databases using a snowball method. Results This review covers aspects beginning with the discovery of CRF, CRF binding protein and their actions via interaction with CRF receptors type 1 and type 2. These are surface plasma membrane receptors, activation of which is associated with conformational changes and interaction with a variety of G-proteins and signaling pathways. We also reviewed the pharmacology and mechanisms of the receptor signaling modulatory activity of these receptors. Conclusion This review compiles and presents knowledge regarding the CRFergic system, including CRF related peptides, CRF binding protein, and CRF receptors, as well as some evidence that is potentially indicative of the biological roles of these entities in several physiological and pathophysiological processes.

Blocking CRH receptors in adults mitigates age-related memory impairments provoked by early-life adversity

In humans, early-life adversity is associated with impairments in learning and memory that may emerge later in life. In rodent models, early-life adversity directly impacts hippocampal neuron structure and connectivity with progressive deficits in long-term potentiation and spatial memory function. Previous work has demonstrated that augmented release and actions of the stress-activated neuropeptide, CRH, contribute to the deleterious effects of early-life adversity on hippocampal dendritic arborization, synapse number and memory-function. Early-life adversity increases hippocampal CRH expression, and blocking hippocampal CRH receptor type-1 (CRHR1) immediately following early-life adversity prevented the consequent memory and LTP defects. Here, we tested if blocking CRHR1 in young adults ameliorates early-life adversity-provoked memory deficits later in life. A weeklong course of a CRHR1 antagonist in 2-month-old male rats prevented early-life adversity-induced deficits in object recognition memory that emerged by 12 months of age. Surprisingly, whereas the intervention did not mitigate early-life adversity-induced spatial memory losses at 4 and 8 months, it restored hippocampus-dependent location memory in 12-month-old rats that experienced early-life adversity. Neither early-life adversity nor CRHR1 blockade in the adult influenced anxiety- or depression-related behaviors. Altogether, these findings suggest that cognitive deficits attributable to adversity during early-life-sensitive periods are at least partially amenable to interventions later in 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.

Enhancing the Utility of Preclinical Research in Neuropsychiatry Drug Development

Most large pharmaceutical companies have downscaled or closed their clinical neuroscience research programs in response to the low clinical success rate for drugs that showed tremendous promise in animal experiments intended to model psychiatric pathophysiology. These failures have raised serious concerns about the role of preclinical research in the identification and evaluation of new pharmacotherapies for psychiatry. In the absence of a comprehensive understanding of the neurobiology of psychiatric disorders, the task of developing "animal models" seems elusive. The purpose of this review is to highlight emerging strategies to enhance the utility of preclinical research in the drug development process. We address this issue by reviewing how advances in neuroscience, coupled with new conceptual approaches, have recently revolutionized the way we can diagnose and treat common psychiatric conditions. We discuss the implications of these new tools for modeling psychiatric conditions in animals and advocate for the use of systematic reviews of preclinical work as a prerequisite for conducting psychiatric clinical trials. We believe that work in animals is essential for elucidating human psychopathology and that improving the predictive validity of animal models is necessary for developing more effective interventions for mental illness.

Prenatal stress disrupts social behavior, cortical neurobiology and commensal microbes in adult male offspring

In utero and early neonatal exposure to maternal stress is linked with psychiatric disorders, and the underlying mechanisms are currently being elucidated. We used a prenatal stressor in pregnant mice to examine novel relationships between prenatal stress exposure, changes in the gut microbiome, and social behavior. Here, we show that males exposed to prenatal stress had a significant reduction in social behavior in adulthood, with increased corticosterone release following social interaction. Male offspring exposed to prenatal stress also had neuroinflammation, decreased oxytocin receptor, and decreased serotonin metabolism in their cortex in adulthood, which are linked to decreased social behavior. Finally, we found a significant difference in commensal microbes, including decreases in Bacteroides and Parabacteroides, in adult male offspring exposed to prenatal stress when compared to non-stressed controls. Our findings indicate that gestation is a critical window where maternal stress contributes to the development of aberrant social behaviors and alterations in cortical neurobiology, and that prenatal stress is sufficient to disrupt the male gut-brain axis into adulthood.

Regulation of anxiety-like behavior and Crhr1 expression in the basolateral amygdala by LMO3

The LIM domain only protein LMO3 is a transcriptional regulator that has been shown to regulate several behavioral responses to alcohol. Specifically, Lmo3 null (Lmo3^Z) mice consume more ethanol in a binge-drinking test and show enhanced ethanol-induced sedation. Due to the high comorbidity of alcohol use and anxiety, we investigated anxiety-like behavior in Lmo3^Z mice. Lmo3^Z mice spent more time in the open arms of the elevated plus maze compared with their wild-type littermates, but the effect was confounded by reduced locomotor activity. To verify the anxiety phenotype in the Lmo3^Z mice, we tested them for novelty-induced hypophagia and found that they also showed reduced anxiety in this test. We next explored the mechanism by which LMO3 might regulate anxiety by measuring mRNA and protein levels of corticotropin releasing factor (encoded by the Crh gene) and its receptor type 1 (Crhr1) in Lmo3^Z mice. Reduced Crhr1 mRNA and protein was evident in the basolateral amygdala (BLA) of Lmo3^Z mice. To examine whether Lmo3 in the amygdala is important for anxiety-like behavior, we locally reduced Lmo3 expression in the BLA of wild type mice using a lentiviral vector expressing a short hairpin RNA targeting the Lmo3 transcript. Mice with Lmo3 knockdown in the BLA exhibited decreased anxiety-like behavior relative to control mice. These results suggest that Lmo3 promotes anxiety-like behavior specifically in the BLA, possibly by altering Crhr1 expression. This study is the first to support a role for Lmo3 in anxiety-like behavior.

Social rank-associated stress vulnerability predisposes individuals to cocaine attraction

Studies of personality have suggested that dissimilarities in ability to cope with stressful situations results in differing tendency to develop addictive behaviors. The present study used selectively bred stress-resilient, socially-dominant (Dom) and stress-vulnerable, socially-submissive (Sub) mice to investigate the interaction between environmental stress and inbred predisposition to develop addictive behavior to cocaine. In a Conditioned Place Preference (CPP) paradigm using cocaine, Sub mice displayed an aversion to drug, whereas Dom mice displayed drug attraction. Following a 4-week regimen of Chronic Mild Stress (CMS), Sub mice in CPP displayed a marked increase (>400%) in cocaine attraction, whereas Dom mice did not differ in attraction from their non-stressed state. Examination of hippocampal gene expression revealed in Sub mice, exposure to external stimuli, stress or cocaine, increased CRH expression (>100%), which was evoked in Dom mice only by cocaine exposure. Further, stress-induced decreases in DRD1 (>60%) and DRD2 (>50%) expression in Sub mice differed markedly from a complete lack of change in Dom mice. From our findings, we propose that social stratification dictates vulnerability to stress-induced attraction that may lead to addiction via differential regulation of hippocampal response to dopaminergic input, which in turn may influence differing tendency to develop addictive behaviors.

Upregulations of CRH and CRHR1 in the Epileptogenic Tissues of Patients with Intractable Infantile Spasms

AIM

Infantile spasms (IS) are an age-specific epileptic syndrome with specific clinical symptom and electroencephalogram (EEG) features, lacking treatment options, and a poor prognosis. Excessive endogenous corticotropin-releasing hormone (CRH) in infant brain might result in IS. However, the data from human IS are limited. In our study, we investigated the expressions of CRH and its receptor type 1 (CRHR1) in surgical tissues from patients with IS and autopsy controls.

METHODS

Specimens surgically removed from 17 patients with IS, and six autopsy controls were included in the study. Real-time PCR, Western blotting, and immunostaining were used to detect the expressions of mRNA, protein expression, and distribution. The correlation between variates was analyzed by Spearman rank correlation.

RESULTS

The expressions of CRH and CRHR1 were significantly upregulated in the epileptogenic tissues of IS patients compared with the control group. CRH was distributed mainly in neurons, while CRHR1 was distributed in neurons, astrocytes, and microglia. The expression levels of CRH and CRHR1 were positively correlated with the frequency of epileptic spasms. Moreover, the expression of protein kinase C (PKC), which was an important downstream factor of CRHR1, was significantly upregulated in the epileptogenic tissues of patients with IS and was positively correlated with the CRHR1 expression levels and the frequency of epileptic spasms.

CONCLUSION

These results suggest that the CRH signal transduction pathway might participate in the epileptogenesis of IS, supporting the hypothesis that CRH is related to the pathogenesis of IS.

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.

Noise stress changes mRNA expressions of corticotropin-releasing hormone, its receptors in amygdala, and anxiety-related behaviors

Noise is a psychological, environmental stressor that activates limbic sites in the brain. Limbic sites such as the amygdala and the amygdaloid corticotropin-releasing hormone (CRH) system play an important role in integrating stress response. We investigated the association between noise exposures, CRH-related molecules in the amygdala, and behavioral alterations. In total 54 Sprague-Dawley rats were divided into the following three groups: Control (CON), acute noise exposure (ANE), and chronic noise exposure (CNE). The ANE group was exposed to 100 dB white noise only once in 4 h and the CNE group was exposed to the same for 4 h per day for 30 days. Expression profiles of CRH and its receptors CRH-R1 and CRH-R2 were analyzed by quantitative real-time polymerase chain reaction (qPCR). The same stress procedure was applied to the ANE and CNE groups for behavior testing. The anxiety responses of the animals after acute and chronic stress exposure were measured in the defensive withdrawal test. CNE upregulated CRH and CRH-R1 mRNA levels but downregulated CRH-R2 mRNA levels. ANE led to a decrease in both CRH-R1 and CRH-R2 expression. In the defensive withdrawal test, while the ANE increased, CNE reduced anxiety-like behaviors. The present study shows that the exposure of rats to white noise (100 dB) leads to behavioral alterations and molecule-specific changes in the CRH system. Behavioral alterations can be related to these molecular changes in the amygdala.

Long-term effects of early adolescent stress: dysregulation of hypothalamic-pituitary-adrenal axis and central corticotropin releasing factor receptor 1 expression in adult male rats

Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experiences. Studies have found that exposure to early stressful events is a risk factor for developing PTSD. However, a limited number of studies have explored the effects of traumatic stress in early adolescence on behavior, hypothalamic-pituitary-adrenal (HPA) axis function, central corticotropin releasing factor receptor 1 (CRFR1) expression and the relative vulnerability of PTSD in adulthood. The current study aims to explore these issues using inescapable electric foot shock to induce a PTSD model in early adolescent rats. Meanwhile, running on a treadmill for six weeks and administration of the antagonist with 3.2mg/kg/day of CP-154, 526 for 14 consecutive days were used as therapeutic measures. Presently, the stress (S) group showed more anxiety and depression in the open field (OF) test and elevated plus maze (EPM) test, memory damage in the Y maze test, decreased basal CORT level, increased DEX negative feedback inhibition and exacerbated and longer-lasting reaction to CRH challenge in the DEX/CRH test compared with the control group. Central CRFR1 expression was also changed in the S group, as evidenced by the increased CRFR1 expression in the hypothalamus, amygdala and the prefrontal cortex (PFC). However, treadmill exercise alleviated early adolescent stress-induced behavior abnormalities and improved the functional state of the HPA axis, performing a more powerful effect than the CRFR1 antagonist CP-154, 526. Additionally, this study revealed that the alteration of central CRFR1 expression might play an important role in etiology of PTSD in adulthood.

Effects of electroconvulsive seizures on depression-related behavior, memory and neurochemical changes in Wistar and Wistar-Kyoto rats

BACKGROUND

Investigations in healthy outbred rat strains have shown a potential role for brain-derived neurotrophic factor (BDNF) and the hypothalamic-pituitary-adrenal (HPA) axis in the antidepressant and memory side effects of electroconvulsive therapy (ECT, or ECS in animals). The Wistar-Kyoto (WKY) rat strain is used as a genetic model of depression yet no studies to date have directly compared the impact of ECS on the WKY strain to its healthy outbred control (Wistar).

OBJECTIVE

The objective of this study is to examine behavioral (antidepressant and retrograde memory) and neurochemical (BDNF and HPA axis) changes immediately (1day) and at a longer delay (7days) after repeated ECS (5 daily administrations) in WKY and Wistar rats.

METHODS

Male Wistar and WKY rats received 5days of repeated ECS or sham treatment and were assessed 1 and 7days later for 1) depression-like behavior and mobility; 2) retrograde memory; and 3) brain BDNF protein, brain corticotropin-releasing factor (CRF) and plasma corticosterone levels.

RESULTS

Both strains showed the expected antidepressant response and retrograde memory impairments at 1day following ECS, which were sustained at 7days. In addition, at 1day after ECS, Wistar and WKY rats showed similar elevations in brain BDNF and extra-hypothalamic CRF and no change in plasma corticosterone. At 7days after ECS, Wistar rats showed sustained elevations of brain BDNF and CRF, whereas WKY rats showed a normalization of brain BDNF, despite sustained elevations of brain CRF.

CONCLUSIONS

The model of 5 daily ECS was effective at eliciting behavioral and neurochemical changes in both strains. A temporal association was observed between brain CRF levels, but not BDNF, and measures of antidepressant effectiveness of ECS and retrograde memory impairments suggesting that extra-hypothalamic CRF may be a potential important contributor to these behavioral effects after repeated ECS/ECT.

Increased anxiety in corticotropin-releasing factor type 2 receptor-null mice requires recent acute stress exposure and is associated with dysregulated serotonergic activity in limbic brain areas

Background

Corticotropin-releasing factor type 2 receptors (CRFR2) are suggested to facilitate successful recovery from stress to maintain mental health. They are abundant in the midbrain raphe nuclei, where they regulate serotonergic neuronal activity and have been demonstrated to mediate behavioural consequences of stress. Here, we describe behavioural and serotonergic responses consistent with maladaptive recovery from stressful challenge in CRFR2-null mice.

Results

CRFR2-null mice showed similar anxiety levels to control mice before and immediately after acute restraint stress, and also after cessation of chronic stress. However, they showed increased anxiety by 24 hours after restraint, whether or not they had been chronically stressed.

Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) contents were quantified and the level of 5-HIAA in the caudal dorsal raphe nucleus (DRN) was increased under basal conditions in CRFR2-null mice, indicating increased 5-HT turnover. Twenty-four hours following restraint, 5-HIAA was decreased only in CRFR2-null mice, suggesting that they had not fully recovered from the challenge. In efferent limbic structures, CRFR2-null mice showed lower levels of basal 5-HT in the lateral septum and subiculum, and again showed a differential response to restraint stress from controls.

Local cerebral glucose utilization (LCMRglu) revealed decreased neuronal activity in the DRN of CRFR2-null mice under basal conditions. Following 5-HT receptor agonist challenge, LCMRglu responses indicated that 5-HT_1A receptor responses in the DRN were attenuated in CRFR2-null mice. However, postsynaptic 5-HT receptor responses in forebrain regions were intact.

Conclusions

These results suggest that CRFR2 are required for proper functionality of 5-HT_1A receptors in the raphe nuclei, and are key to successful recovery from stress. This disrupted serotonergic function in CRFR2-null mice likely contributes to their stress-sensitive phenotype. The 5-HT content in lateral septum and subiculum was notably altered. These areas are important for anxiety, and are also implicated in reward and the pathophysiology of addiction. The role of CRFR2 in stress-related psychopathologies deserves further consideration.

Prereproductive stress to female rats alters corticotropin releasing factor type 1 expression in ova and behavior and brain corticotropin releasing factor type 1 expression in offspring

BACKGROUND

Human and animal studies indicate that vulnerability to stress may be heritable and that changes in germline may mediate some transgenerational effects. Corticotropin releasing factor type 1 (CRF1) is a key component in the stress response. We investigated changes in CRF1 expression in brain and ova of stressed female rats and in the brain of their neonate and adult offspring. Behavioral changes in adulthood were also assessed.

METHODS

Adult female rats underwent chronic unpredictable stress. We extracted mature oocytes and brain regions from a subset of rats and mated the rest 2 weeks following the stress procedure. CRF1 expression was assessed using quantitative reverse-transcription polymerase chain reaction. Tests of anxiety and aversive learning were used to examine behavior of offspring in adulthood.

RESULTS

We show that chronic unpredictable stress leads to an increase in CRF1 messenger RNA expression in frontal cortex and mature oocytes. Neonatal offspring of stressed female rats show an increase in brain CRF1 expression. In adulthood, offspring of stressed female rats show sex differences in both CRF1 messenger RNA expression and behavior. Moreover, CRF1 expression patterns in frontal cortex of female offspring depend upon both maternal and individual adverse experience.

CONCLUSIONS

Our findings demonstrate that stress affects CRF1 expression in brain but also in ova, pointing to a possible mechanism of transgenerational transmission. In offspring, stress-induced changes are evident at birth and are thus unlikely to result from altered maternal nurturance. Finally, brain CRF1 expression in offspring depends upon gender and upon maternal and individual exposure to adverse environment.

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.

Sex differences in prenatally programmed anxiety behaviour in rats: differential corticotropin-releasing hormone receptor mRNA expression in the amygdaloid complex

We recently reported that male, but not female, offspring born to mothers exposed to social stress during late gestation show heightened anxiety-type behaviour in adulthood. The amygdala organises anxious behaviour, which involves actions of corticotropin-releasing hormone (CRH). CRH gene expression and/or its release are increased in the amygdala in prenatally stressed (PNS) rats. CRH type 1 receptor (CRH-R1) mediates actions of CRH and urocortin I to promote anxiety-like behaviour, whereas the CRH type 2 receptor (CRH-R2) may mediate anxiolytic actions, through actions of urocortins 2 and 3. Here, using quantitative in situ hybridisation, we investigated whether altered CRH receptor mRNA expression in the amygdaloid nuclei may explain the sex differences in anxiety behaviour in adult male and female PNS rats. CRH-R1 mRNA expression was significantly greater in the central amygdala and basolateral amygdala (BLA) in male PNS rats compared with controls, with no change in the basomedial amygdala (BMA) or medial amygdala (MeA). In PNS females, CRH-R1 mRNA expression was greater than controls only in the MeA. Conversely, CRH-R2 mRNA expression was significantly lower in the BMA of male PNS rats compared with controls, but greater in female PNS rats, with no change in the BLA or MeA in either sex. The ratio of CRH-R1:CRH-R2 mRNA in the amygdaloid nuclei was generally increased in PNS males, but not in the PNS females. In conclusion, sex differences in anxiety-type behaviour in PNS rats may be explained by differential mRNA expression for CRH-R1 (pro-anxiogenic) and CRH-R2 (pro-anxiolytic) in the amygdaloid complex.

Prolonged and site-specific over-expression of corticotropin-releasing factor reveals differential roles for extended amygdala nuclei in emotional regulation

Corticotropin-releasing factor (CRF) has a key role in the central stress response, and altered levels of this neuropeptide are linked to stress-related psychopathologies such as anxiety and depression. These disorders are associated with the inability to properly regulate stress response, specifically following exposure to prolonged stressful stimuli. Therefore, the current study assessed the effects of prolonged and site-specific over-expression of CRF, which mimics the state of chronic production, in extended amygdala nuclei that are known to be involved in mediating anxiety-like states. We first constructed and generated lentiviruses that overexpress (OE) CRF in a robust and stable manner, and then generated two male mouse models continuously over-expressing CRF, either at the central nucleus of the amygdala (CeA), or at the dorsolateral subdivision of the bed nucleus of the stria terminalis (BNSTdl). After 4 months, behavioral assessments were conducted for anxiety and depressive indices on these mice. Surprisingly, prolonged CRF OE at the CeA attenuated stress-induced anxiety-like behaviors, whereas prolonged CRF OE in the BNSTdl increased depressive-like behaviors, without affecting anxiety levels. These results show possible differential roles for CRF expressed by distinct loci of the extended amygdala, in mediating stress-induced emotional behaviors.

The hypothalamic-pituitary-adrenal axis and serotonin abnormalities: a selective overview for the implications of suicide prevention

Suicidal behavior and mood disorders are one of the world's largest public health problems. The biological vulnerability for these problems includes genetic factors involved in the regulation of the serotonergic system and stress system. The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system that regulates the body's response to stress and has complex interactions with brain serotonergic, noradrenergic and dopaminergic systems. Corticotropin-releasing hormone and vasopressin act synergistically to stimulate the secretion of ACTH that stimulates the biosynthesis of corticosteroids such as cortisol from cholesterol. Cortisol is a major stress hormone and has effects on many tissues, including on mineralocorticoid receptors and glucocorticoid receptors in the brain. Glucocorticoids produce behavioral changes, and one important target of glucocorticoids is the hypothalamus, which is a major controlling center of the HPA axis. Stress plays a major role in the various pathophysiological processes associated with mood disorders and suicidal behavior. Serotonergic dysfunction is a well-established substrate for mood disorders and suicidal behavior. Corticosteroids may play an important role in the relationship between stress, mood changes and perhaps suicidal behavior by interacting with 5-HT1A receptors. Abnormalities in the HPA axis in response to increased levels of stress are found to be associated with a dysregulation in the serotonergic system, both in subjects with mood disorders and those who engage in suicidal behavior. HPA over-activity may be a good predictor of mood disorders and perhaps suicidal behavior via abnormalities in the serotonergic system.

Hippocampal dysfunction and cognitive impairments provoked by chronic early-life stress involve excessive activation of CRH receptors

Chronic stress impairs learning and memory in humans and rodents and disrupts long-term potentiation (LTP) in animal models. These effects are associated with structural changes in hippocampal neurons, including reduced dendritic arborization. Unlike the generally reversible effects of chronic stress on adult rat hippocampus, we have previously found that the effects of early-life stress endure and worsen during adulthood, yet the mechanisms for these clinically important sequelae are poorly understood. Stress promotes secretion of the neuropeptide corticotropin-releasing hormone (CRH) from hippocampal interneurons, activating receptors (CRF(1)) located on pyramidal cell dendrites. Additionally, chronic CRF(1) occupancy negatively affects dendritic arborization in mouse organotypic slice cultures, similar to the pattern observed in middle-aged, early-stressed (CES) rats. Here we found that CRH expression is augmented in hippocampus of middle-aged CES rats, and then tested whether the morphological defects and poor memory performance in these animals involve excessive activation of CRF(1) receptors. Central or peripheral administration of a CRF(1) blocker following the stress period improved memory performance of CES rats in novel-object recognition tests and in the Morris water maze. Consonant with these effects, the antagonist also prevented dendritic atrophy and LTP attenuation in CA1 Schaffer collateral synapses. Together, these data suggest that persistently elevated hippocampal CRH-CRF(1) interaction contributes importantly to the structural and cognitive impairments associated with early-life stress. Reducing CRF(1) occupancy post hoc normalized hippocampal function during middle age, thus offering potential mechanism-based therapeutic interventions for children affected by chronic stress.

Maternal separation modulates short-term behavioral and physiological indices of the stress response

Early-life stress produces an anxiogenic profile in adulthood, presumably by activating the otherwise quiescent hypothalamic-pituitary-adrenal (HPA) axis during the vulnerable 'stress hyporesponsive period'. While the long-term effects of such early-life manipulations have been extensively characterized, little is known of the short-term effects. Here, we compared the short-term effects of two durations of maternal separation stress and one unseparated group (US) on behavioral and physiological indices of the stress response in rat pups. Separations included 3h on each of 12days, from postnatal day (PND) 2 to 13 (MS2-13) and 3days of daily, 6-h separation from PND11-13 (MS11-13). On PND14 (Experiment 1), both MS2-13 and MS11-13 produced marked reductions in freezing toward an adult male conspecific along with reduced levels of glucocorticoid type 2 (GR) and CRF type-1 (CRF(1)) receptor mRNA in the hippocampus. Group MS2-13 but not MS11-13 produced deficits in stressor-induced corticosterone secretion, accompanied by reductions in body weight. Our results suggest that GR and/or CRF(1) levels, not solely the magnitude of corticosterone secretion, may be involved in the modulation of freezing. In a second experiment, we aimed to extend these findings by testing male and female separated and unseparated pups' unconditioned defensive behaviors to cat odor on PND26, and subsequent cue+context conditioning and extinction throughout postnatal days 27-32. Our results show that maternal separation produced reductions in unconditioned freezing on PND26, with MS2-13 showing stronger deficits than MS11-13. However, separation did not affect any other defensive behaviors. Furthermore, separated rats failed to show conditioned freezing, although they did avoid the no-odor block conditioned cue. There were no sex differences other than weight. We suggest that maternal separation may have produced these changes by disrupting normal development of hippocampal regions involved in olfactory-mediated freezing, not in mechanisms of learning and memory per se. These findings may have direct relevance for understanding the mechanisms by which early-life adverse experiences produce short-term and lasting psychopathologies.

Electron microscopic localization of corticotropin-releasing factor (CRF) and CRF receptor in rat and mouse central nucleus of the amygdala

Corticotrophin-releasing factor (CRF) is expressed in the central nucleus of the amygdala (CeA), where the CRF receptor (CRFr) plays an important role in anxiety- and stress-related behaviors. To determine the subcellular sites of CRFr activation in this region, we examined the electron microscopic immunolabeling of antisera recognizing CRF or CRFr. The ultrastructural analysis was principally conducted in the lateral subdivision of the rat CeA, with comparisons being made in mice so as to optimally utilize mutant mice in control experiments. The CRFr labeling was seen in many small dendrites and dendritic spines as well as in a few somata, large dendrites, axons, and axon terminals or more rarely in glial processes. Approximately 35% of the CRFr-labeled dendrites contained CRF immunoreactivity, which was distributed diffusely throughout the cytoplasm, or specifically affiliated with either endomembranes or large dense-core vesicles. The CRF-immunoreactive vesicles also were present in somata and axon terminals with or without CRFr labeling. The CRF immunoreactivity was usually absent from both terminals and dendrites joined by asymmetric, excitatory-type synapses, where a postsynaptic location of the CRFr was commonly observed. Numerous terminals containing both CRF and CRFr were seen, however, within the neuropil and sometimes apposing the excitatory synapses. These results provide ultrastructural evidence for a primary involvement of CRF receptors in modulation of the postsynaptic excitability of CeA neurons, an effect that may be limited by the availability of CRF. The findings have important implications for understanding CRF mediation of rapid responses to stress.

Peripherally administered angiotensin II AT1 receptor antagonists are anti-stress compounds in vivo

Angiotensin II AT(1) receptor blockers (ARBs) are commonly used in the clinical treatment of hypertension. Subcutaneous or oral administration of the ARB candesartan inhibits brain as well as peripheral AT(1) receptors, indicating transport across the blood-brain barrier. Pretreatment with candesartan profoundly modifies the response to stress. The ARB prevents the peripheral and central sympathetic activation characteristic of isolation stress and abolishes the activation of the hypothalamic-pituitary-adrenal axis during isolation. In addition, candesartan prevents the isolation-induced decrease in cortical corticotropin-releasing factor 1 and benzodiazepine receptors induced by isolation. When administered before cold-restraint stress, candesartan totally prevents the production of gastric ulcerations. This preventive effect of candesartan is the consequence of profound anti-inflammatory effects, reduction of sympathetic stimulation, and preservation of blood flow to the gastric mucosa. The ARB does not reduce the hypothalamic-pituitary-adrenal axis stimulation during cold restraint. Preservation of the effects of endogenous glucocorticoids is essential for protection of the gastric mucosa during cold restraint. Administration of the ARB to nonstressed rats decreases anxiety in the elevated plus-maze. Our results demonstrate that Angiotensin II, through AT(1) receptor stimulation, is a major stress hormone, and that ARBs, in addition to their antihypertensive effects, may be considered for the treatment of stress-related disorders.

Sex differences in plasma corticosterone release in undisturbed chickens (Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

In birds, two neuropeptides, corticotropin releasing hormone (CRH) and arginine vasotocin (AVT), are major regulators of the hypothalamo-pituitary-adrenal axis (HPA) during the stress response. In birds, however, the relative efficacy of CRH and AVT to stimulate the HPA axis in males and females remains unknown. The purpose of this study was to determine the time course of CORT release following central CRH and AVT administration to male and female chickens. Chickens were fitted with a stainless steel cannula surgically implanted in the lateral ventricle and a catheter chronically inserted in the jugular vein. Birds were housed individually in cages behind a one-way glass partition and unnecessary noise was avoided during the sampling period. Each bird received a single 5.0microtracerebroventricular (ICV) injection of either saline (SAL), AVT (10 and 100pmol), or CRH (10 and 100pmol). Blood was sampled remotely every 15min for 2h and plasma CORT was determined by radioimmunoassay. There was a significant increase in plasma CORT concentration in males injected with 100pmol AVT beginning at 15min post-injection through 2h compared with SAL injected birds. In males, injection of 100pmol CRH was significantly more effective in releasing CORT compared to an equal molar concentration of AVT or SAL. In females, ICV injection of 100pmol AVT induced moderate increase in CORT levels. In contrast, 100pmol CRH significantly increased plasma CORT compared to SAL injected controls but the CORT response was nearly 50% less than that obtained in males.

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.

Cellular localization of the full-length isoform of the type 2 corticotropin releasing factor receptor in the postnatal mouse cerebellar cortex

Corticotropin releasing factor (CRF) and its cognate receptors, defined as Type 1 and Type 2 have been localized within the cerebellum. The Type 2 CRF receptor (CRF-R2) is known to have both a full length (CRF-R2alpha) and a truncated (CRF-R2alpha-tr) isoform. A recent study documented CRF-R2alpha primarily in Bergann glia and astrocytes, as well as in populations of Purkinje cells in the adult cerebellum. The goal of the present study is to determine if CRF-R2alpha is present in the postnatal cerebellum, and if so to describe its cellular distribution. RT-PCR data showed that CRF-R2alpha is expressed in the mouse cerebellum from birth through postnatal day 21. Between birth and P14, CRF-R2alpha-immunoreactivity was localized within the somata of Purkinje cells, and migrating GABAergic interneurons. GFAP-immunoreactive astrocytes, including Bergmann glia, also expressed CRF-R2alpha-immunoreactivity from P3-P14. There is a change, however, in CRF-R2alpha immunolabeling within neurons as the cerebellum matures. Compared to its expression in the adult cerebellum, Purkinje cells, and GABAergic interneurons showed more extensive CRF-R2alpha immunolabeling during early postnatal development. We postulate that CRF-R2alpha could be involved in developmental events related to the survival and differentiation of Purkinje cells and GABAergic neurons, whereas in the adult, this isoform of the CRF receptor family is likely involved in modulating Bergmann glia that have been shown to play a role in regulating the synaptic environment around Purkinje neurons.

Brain and peripheral angiotensin II play a major role in stress

Angiotensin II (Ang II), the active principle of the renin-angiotensin system (RAS), was discovered as a vasoconstrictive, fluid retentive circulating hormone. It was revealed later that there are local RAS in many organs, including the brain. The physiological receptor for Ang II, the AT(1) receptor type, was found to be highly expressed in many tissues and brain areas involved in the hypothalamic-pituitary-adrenal axis response to stress and in the sympathoadrenal system. The production of circulating and local Ang II, and the expression of AT(1) receptors increase during stress. Blockade of peripheral and brain AT(1) receptors with receptor antagonists administered peripherally prevented the hormonal and sympathoadrenal response to isolation stress, the stress-related alterations in cortical CRF(1) and benzodiazepine receptors, part of the GABA(A) complex, and reduced anxiety in rodents. AT(1) receptor blockade prevented the ulcerations of the gastric mucosa produced by cold-restraint stress, by preservation of the gastric blood flow, prevention of the stress-induced inflammatory response of the gastric mucosa, and partial blockade of the sympathoadrenal response to the stress. Our observations demonstrate that Ang II is an important stress hormone, and that blockade of AT(1) receptors could be proposed as a potentially useful therapy for stress-induced disorders.

Posttraumatic stress disorder: memory and learning performance in children and adolescents

BACKGROUND

Despite the wealth of information in adult posttraumatic stress disorder (PTSD) literature, few studies have explored the memory and learning performance of trauma-exposed youth. This study examined if memory deficits are associated with PTSD or with trauma exposure in the absence of PTSD.

METHODS

Youth exposed to traumatic incidents underwent clinical interviews to diagnose PTSD and exclude major comorbid disorders. Youth with conditions that could impede performance on a memory scale (e.g., limited intellectual functioning, current substance abuse, psychopharmacological treatment) were excluded. Three groups of participants were identified (PTSD positives [n = 29], traumatized PTSD negatives [n = 62], and nontraumatized control subjects [n = 40]). Participants completed the Wide Range Assessment of Memory and Learning (WRAML).

RESULTS

Youth with PTSD evidenced significantly lower scores on the WRAML General Memory, Verbal Memory, and Learning indices compared with nontraumatized control subjects. With the exception of Verbal Memory, youth with and without PTSD performed comparably on all other indices. Nonsignificant differences were noted on the Visual Memory Index.

CONCLUSIONS

General memory and verbal memory impairments as evidenced in adult populations were observed among this sample of youth. Given the developmental trajectory of memory capabilities, the implications of such early trauma exposure and memory deficits are considered.

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.

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

Hippocampal neuroplasticity induced by early-life stress: functional and molecular aspects

Whereas genetic factors contribute crucially to brain function, early-life events, including stress, exert long-lasting influence on neuronal function. Here, we focus on the hippocampus as the target of these early-life events because of its crucial role in learning and memory. Using a novel immature-rodent model, we describe the deleterious consequences of chronic early-life 'psychological' stress on hippocampus-dependent cognitive tasks. We review the cellular mechanisms involved and discuss the roles of stress-mediating molecules, including corticotropin releasing hormone, in the process by which stress impacts the structure and function of hippocampal neurons.

A centrally acting, anxiolytic angiotensin II AT1 receptor antagonist prevents the isolation stress-induced decrease in cortical CRF1 receptor and benzodiazepine binding

Long-term pretreatment with an angiotensin II AT1 antagonist blocks angiotensin II effects in brain and peripheral organs and abolishes the sympathoadrenal and hypothalamic-pituitary-adrenal responses to isolation stress. We determined whether AT1 receptors were also important for the stress response of higher regulatory centers. We studied angiotensin II and corticotropin-releasing factor (CRF) receptors and benzodiazepine binding sites in brains of Wistar Hannover rats. Animals were pretreated for 13 days with vehicle or a central and peripheral AT1 antagonist (candesartan, 0.5 mg/kg/day) via osmotic minipumps followed by 24 h of isolation in metabolic cages, or kept grouped throughout the study (grouped controls). In another study, we determined the influence of a similar treatment with candesartan on performance in an elevated plus-maze. AT1 receptor blockade prevented the isolation-induced increase in brain AT1 receptors and decrease in AT2 binding in the locus coeruleus. AT1 receptor antagonism also prevented the increase in tyrosine hydroxylase mRNA in the locus coeruleus. Pretreatment with the AT1 receptor antagonist completely prevented the decrease in cortical CRF1 receptor and benzodiazepine binding produced by isolation stress. In addition, pretreatment with candesartan increased the time spent in and the number of entries to open arms of the elevated plus-maze, measure of decreased anxiety. Our results implicate a modulation of upstream neurotransmission processes regulating cortical CRF1 receptors and the GABA(A) complex as molecular mechanisms responsible for the anti-anxiety effect of centrally acting AT1 receptor antagonists. We propose that AT1 receptor antagonists can be considered as compounds with possible therapeutic anti-stress and anti-anxiety properties.

The molecular mechanisms underlying the regulation of the biological activity of corticotropin-releasing hormone receptors: implications for physiology and pathophysiology

The CRH receptor (CRH-R) is a member of the secretin family of G protein-coupled receptors. Wide expression of CRH-Rs in the central nervous system and periphery ensures that their cognate agonists, the family of CRH-like peptides, are capable of exerting a wide spectrum of actions that underpin their critical role in integrating the stress response and coordinating the activity of fundamental physiological functions, such as the regulation of the cardiovascular system, energy balance, and homeostasis. Two types of mammal CRH-R exist, CRH-R1 and CRH-R2, each with unique splicing patterns and remarkably distinct pharmacological properties, but similar signaling properties, probably reflecting their distinct and sometimes contrasting biological functions. The regulation of CRH-R expression and activity is not fully elucidated, and we only now begin to fully understand the impact on mammalian pathophysiology. The focus of this review is the current and evolving understanding of the molecular mechanisms controlling CRH-R biological activity and functional flexibility. This shows notable tissue-specific characteristics, highlighted by their ability to couple to distinct G proteins and activate tissue-specific signaling cascades. The type of activating agonist, receptor, and target cell appears to play a major role in determining the overall signaling and biological responses in health and disease.

Distribution and expression of CRF receptor 1 and 2 mRNAs in the CRF over-expressing mouse brain

Corticotropin-releasing factor (CRF) acts through CRF 1 and CRF 2 receptors (CRF1, CRF2). To test the hypothesis that CRF controls the expression of these receptors in a brain site- and receptor-type specific manner, we studied CRF1 mRNA and CRF2 mRNA expressions in mice with central CRF over-expression (CRF-OE) and using in situ hybridization. CRF1 and CRF2 mRNAs appear to be differentially distributed across the brain. The brain structures expressing the receptors are the same in wild-type (WT) and in CRF-OE mice. We therefore conclude that chronically elevated CRF does not induce or inhibit expression of these receptors in structures that normally do not or do, respectively, show these receptors. However, from counting cell body profiles positive for CRF1 and CRF2 mRNAs, clear differences appear in receptor expression between CRF-OE and WT mice, in a brain-structure-specific fashion. Whereas some structures do not differ, CRF-OE mice exhibit remarkably lower numbers of CRF1 mRNA-positive profiles in the subthalamic nucleus (-38.6%), globus pallidus (-31.5%), dorsal part of the lateral septum (-23.5%), substantia nigra (-22,8%), primary somatosensory cortex (-18.9%) and principal sensory nucleus V (-18.4%). Furthermore, a higher number of CRF2 mRNA-positive profiles are observed in the dorsal raphe nucleus (+32.2%). These data strongly indicate that central CRF over-expression in the mouse brain is associated with down-regulation of CRF1 mRNA and up-regulation of CRF2 mRNA in a brain-structure-specific way. On the basis of these results and the fact that CRF-OE mice reveal a number of physiological and autonomic symptoms that may be related to chronic stress, we suggest that CRF1 in the basal nuclei may be involved in disturbed information processing and that CRF2 in the dorsal raphe nucleus may play a role in mediating stress-induced release of serotonin by CRF.

Single exposure to social defeat increases corticotropin-releasing factor and glucocorticoid receptor mRNA expression in rat hippocampus

Stressful life events are able to induce long-term modifications in physiological and neuroendocrine parameters that are related to the onset of several psychiatric disorders. To gain information on molecular modifications involved in long-term changes triggered by stress, we evaluated gene expression in the hippocampus of rats exposed to a single social defeat session. In the social defeat model, the experimental animal is defeated by a dominant male. The defeat induced an increase in body temperature, in distress vocalisations, in serum corticosterone levels and in anxiety-related behaviour measured with an open field test applied 6 h after the exposure to the dominant rat. In the open field test, anxiety-related behaviours were not detectable anymore 30 h after the exposure to the dominant rat and mRNA levels were evaluated at this time-point. The mRNA levels of genes modulated by stress (corticotropin-releasing factor; corticotropin-releasing factor receptor 1; corticotropin-releasing factor binding protein; mineralocorticoid and glucocorticoid receptors; Ca2+/calmodulin-dependent protein kinase-like kinase; Krox20; Bcl-2) and control genes (glyceraldehyde-3-phosphate dehydrogenase; beta-actin and cyclophilin A) were measured with real-time reverse transcription polymerase chain reaction. Corticotropin-releasing factor and glucocorticoid receptor mRNA levels were significantly modulated by the stress procedure, both genes showing an increase in rats exposed to a social defeat. No expression level differences were detected for the other genes. In conclusion, we report that 30 h after an acute social stress, a modification in mRNA levels can be detected in rat hippocampus, thus suggesting potential candidate genes involved in mediating long-term responses.

Brain angiotensin II: new developments, unanswered questions and therapeutic opportunities

1. There are two Angiotensin II systems in the brain. The discovery of brain Angiotensin II receptors located in neurons inside the blood brain barrier confirmed the existence of an endogenous brain Angiotensin II system, responding to Angiotensin II generated in and/or transported into the brain. In addition, Angiotensin II receptors in circumventricular organs and in cerebrovascular endothelial cells respond to circulating Angiotensin II of peripheral origin. Thus, the brain responds to both circulating and tissue Angiotensin II, and the two systems are integrated. 2. The neuroanatomical location of Angiotensin II receptors and the regulation of the receptor number are most important to determine the level of activation of the brain Angiotensin II systems. 3. Classical, well-defined actions of Angiotensin II in the brain include the regulation of hormone formation and release, the control of the central and peripheral sympathoadrenal systems, and the regulation of water and sodium intake. As a consequence of changes in the hormone, sympathetic and electrolyte systems, feed back mechanisms in turn modulate the activity of the brain Angiotensin II systems. It is reasonable to hypothesize that brain Angiotensin II is involved in the regulation of multiple additional functions in the brain, including brain development, neuronal migration, process of sensory information, cognition, regulation of emotional responses, and cerebral blood flow. 4. Many of the classical and of the hypothetical functions of brain Angiotensin II are mediated by stimulation of Angiotensin II AT1 receptors. 5. Brain AT2 receptors are highly expressed during development. In the adult, AT2 receptors are restricted to areas predominantly involved in the process of sensory information. However, the role of AT2 receptors remains to be clarified. 6. Subcutaneous or oral administration of a selective and potent non-peptidic AT1 receptor antagonist with very low affinity for AT2 receptors and good bioavailability blocked AT1 receptors not only outside but also inside the blood brain barrier. The blockade of the complete brain Angiotensin II AT1 system allowed us to further clarify some of the central actions of the peptide and suggested some new potential therapeutic avenues for this class of compounds. 7. Pretreatment with peripherally administered AT1 antagonists completely prevented the hormonal and sympathoadrenal response to isolation stress. A similar pretreatment prevented the development of stress-induced gastric ulcers. These findings strongly suggest that blockade of brain AT1 receptors could be considered as a novel therapeutic approach in the treatment of stress-related disorders. 8. Peripheral administration of AT1 receptor antagonists strongly affected brain circulation and normalized some of the profound alterations in cerebrovascular structure and function characteristic of chronic genetic hypertension. AT1 receptor antagonists were capable of reversing the pathological cerebrovascular remodeling in hypertension and the shift to the right in the cerebral autoregulation, normalizing cerebrovascular compliance. In addition, AT1 receptor antagonists normalized the expression of cerebrovascular nitric oxide synthase isoenzymes and reversed the inflammatory reaction characteristic of cerebral vessels in hypertension. As a consequence of the normalization of cerebrovascular compliance and the prevention of inflammation, there was, in genetically hypertensive rats a decreased vulnerability to brain ischemia. After pretreatment with AT1 antagonists, there was a protection of cerebrovascular flow during experimental stroke, decreased neuronal death, and a substantial reduction in the size of infarct after occlusion of the middle cerebral artery. At least part of the protective effect of AT1 receptor antagonists was related to the inhibition of the Angiotensin II system, and not to the normalization of blood pressure. These results indicate that treatment with AT1 receptor antagonists appears to be a major therapeutic avenue for the prevention of ischemia and inflammatory diseases of the brain. 9. Thus, orally administered AT1 receptor antagonists may be considered as novel therapeutic compounds for the treatment of diseases of the central nervous system when stress, inflammation and ischemia play major roles. 10. Many questions remain. How is brain Angiotensin II formed, metabolized, and distributed? What is the role of brain AT2 receptors? What are the molecular mechanisms involved in the cerebrovascular remodeling and inflammation which are promoted by AT1 receptor stimulation? How does Angiotensin II regulate the stress response at higher brain centers? Does the degree of activity of the brain Angiotensin II system predict vulnerability to stress and brain ischemia? We look forward to further studies in this exiting and expanding field.

Anti-stress and anti-anxiety effects of centrally acting angiotensin II AT1 receptor antagonists

The brain and the peripheral (hormonal) angiotensin II systems are stimulated during stress. Activation of brain angiotensin II AT(1) receptors is required for the stress-induced hormone secretion, including CRH, ACTH, corticoids and vasopressin, and for stimulation of the central sympathetic activity. Long-term peripheral administration of the angiotensin II AT(1) antagonist candesartan blocks not only peripheral but also brain AT(1) receptors, prevents the hormonal and sympathoadrenal response to isolation stress and prevents the formation of stress-induced gastric ulcers. The mechanisms responsible for the prevention of stress-induced ulcers by the AT(1) receptor antagonist include protection from the stress-induced ischemia and inflammation (neutrophil infiltration and increase in ICAM-1 and TNF-alpha) in the gastric mucosa and a partial blockade of the stress-induced sympathoadrenal stimulation, while the protective effect of the glucocorticoid release during stress is maintained. AT(1) receptor antagonism prevents the stress-induced decrease in cortical CRH(1) and benzodiazepine binding and is anxiolytic. Blockade of brain angiotensin II AT(1) receptors offers a novel therapeutic opportunity for the treatment of anxiety and other stress-related disorders.

Enduring, handling-evoked enhancement of hippocampal memory function and glucocorticoid receptor expression involves activation of the corticotropin-releasing factor type 1 receptor

Early-life experience, including maternal care, influences hippocampus-dependent learning and memory throughout life. Handling of pups during postnatal d 2-9 (P2-9) stimulates maternal care and leads to improved memory function and stress-coping. The underlying molecular mechanisms may involve early (by P9) and enduring reduction of hypothalamic corticotropin-releasing factor (CRF) expression and subsequent (by P45) increase in hippocampal glucocorticoid receptor (GR) expression. However, whether hypothalamic CRF levels influence changes in hippocampal GR expression (and memory function), via reduced CRF receptor activation and consequent lower plasma glucocorticoid levels, is unclear. In this study we administered selective antagonist for the type 1 CRF receptor, NBI 30775, to nonhandled rats post hoc from P10-17 and examined hippocampus-dependent learning and memory later (on P50-70), using two independent paradigms, compared with naive and vehicle-treated nonhandled, and naive and antagonist-treated handled rats. Hippocampal GR and hypothalamic CRF mRNA levels and stress-induced plasma corticosterone levels were also examined. Transient, partial selective blockade of CRF1 in nonhandled rats improved memory functions on both the Morris watermaze and object recognition tests to levels significantly better than in naive and vehicle-treated controls and were indistinguishable from those in handled (naive, vehicle-treated, and antagonist-treated) rats. GR mRNA expression was increased in hippocampal CA1 and the dentate gyrus of CRF1-antagonist treated nonhandled rats to levels commensurate with those in handled cohorts. Thus, the extent of CRF1 activation, probably involving changes in hypothalamic CRF levels and release, contributes to the changes in hippocampal GR expression and learning and memory functions.

Synchronized maternal-infant elevations of primate CSF CRF concentrations in response to variable foraging demand

BACKGROUND

The study of environment-gene interactions during neurodevelopment may facilitate our understanding of the origins of psychiatric disorders. Environmental contribution to the neurobiology of psychopathology is perhaps most relevant during infancy, where vulnerability to early-life stressors is particularly evident.

OBJECTIVES

In the current study, we wished to examine if central corticotropin-releasing factor (CRF) would provide a plausible biological vehicle for synchronized increases in mothers and their infant.

METHODS

Twenty-four mother-infant bonnet macaques (Macaca radiata) dyads, of known age and weight served as subjects. The subjects were group-housed in four pens of 5-7 dyads each, stabilized for several weeks prior to the study period. Although adequate food was always available, mothers faced uncertainty of food availability for 16 weeks within the first year of infant life, through a procedure dubbed "variable foraging demand" (VFD). Pre- and post-VFD cerebrospinal fluid (CSF) samples were obtained simultaneously on mothers and infants.

RESULTS

Maternal CSF CRF concentrations exhibited a significant mean elevation of 26% from pre-VFD to post-VFD; there was no effect of number of days postpartum on maternal pre-VFD CSF CRF levels. There was a significant mean increase (45%) in infant CSF CRF concentrations over the 16-week period of the VFD paradigm. No infant sex differences were evident. Post-VFD minus pre-VFD differences in infant CSF CRF concentrations were positively correlated (r = .52; N = 16; P = .0384) with the magnitude of maternal CRF response to VFD, providing evidence of synchronized CSF CRF expression by the dyad.

CONCLUSION

This parallel response within the dyad suggests, as one testable hypothesis, that maternal responsivity to the stress of the VFD condition is "communicated" between mother and infant via a CRF-mediated mechanism. The VFD stressor produces a parallel activation of the central CRF system in both mothers and their infants.