Regulation of pituitary corticotropin releasing hormone receptors

The role of rs242941, rs1876828, rs242939 and rs110402 polymorphisms of CRHR1 gene and the depression: systematic review and meta-analysis

BACKGROUND

Several studies have evaluated the possible association between polymorphisms or variants in Corticotropin-releasing hormone 1 receptor gene (CRHR1) with depression; however, results remain contradictory and heterogeneous.

OBJECTIVE

To our knowledge, we conducted the first comprehensive systematic review and meta-analysis evaluating the association of the CRHR1 gene and the risk of depression.

METHODS

A search online was conducted in databases for any CRHR1 genetic association studies in depression. Data were extracted for evaluation of pooled estimates using meta-analytic techniques. Statistical analyses were performed using the Comprehensive Meta-analysis, v2.0 software.

RESULT

A total of 1403 cases and 2353 mentally healthy controls were included in this study. We found a significant association of rs242941, rs1876828 and rs242939 variants of the CRHR1 gene with depression. No association of CRHR1 rs110402 and depression was observed.

CONCLUSION

Our meta-analysis shows that some variants of the CRHR1 gene (rs242941, rs1876828 and rs242939) might confer susceptibility to depression. Further studies with larger sample sizes need to be conducted.

New effects of caffeine on corticotropin-releasing hormone (CRH)-induced stress along the intrafollicular classical hypothalamic-pituitary-adrenal (HPA) axis (CRH-R1/2, IP3 -R, ACTH, MC-R2) and the neurogenic non-HPA axis (substance P, p75NTR and TrkA) in ex vivo human male androgenetic scalp hair follicles

BACKGROUND

Human hair is highly responsive to stress, and human scalp hair follicles (HFs) contain a peripheral neuroendocrine equivalent of the systemic hypothalamic-pituitary-adrenal (HPA) stress axis. Androgenetic alopecia (AGA) is supposed to be aggravated by stress. We used corticotropin-releasing hormone (CRH), which triggers the HPA axis, to induce a stress response in human ex vivo male AGA HFs. Caffeine is known to reverse testosterone-mediated hair growth inhibition in the same hair organ culture model.

OBJECTIVES

To investigate whether caffeine would antagonize CRH-mediated stress in these HFs.

METHODS

HFs from balding vertex area scalp biopsies of men affected by AGA were incubated with CRH (10-7 mol L-1 ) with or without caffeine (0·001% or 0·005%).

RESULTS

Compared to controls, CRH significantly enhanced the expression of catagen-inducing transforming growth factor-β2 (TGF-β2) (P < 0·001), CRH receptors 1 and 2 (CRH-R1/2) (P < 0·01), adrenocorticotropic hormone (ACTH) (P < 0·001) and melanocortin receptor 2 (MC-R2) (P < 0·001), and additional stress-associated parameters, substance P and p75 neurotrophin receptor (p75NTR ). CRH inhibited matrix keratinocyte proliferation and expression of anagen-promoting insulin-like growth factor-1 (IGF-1) and the pro-proliferative nerve growth factor receptor NGF-tyrosine kinase receptor A (TrkA). Caffeine significantly counteracted all described stress effects and additionally enhanced inositol trisphosphate receptor (IP3 -R), for the first time detected in human HFs.

CONCLUSIONS

These findings provide the first evidence in ex vivo human AGA HFs that the stress mediator CRH induces not only a complex intrafollicular HPA response, but also a non-HPA-related stress response. Moreover, we show that these effects can be effectively antagonized by caffeine. Thus, these data strongly support the hypothesis that stress can impair human hair physiology and induce hair loss, and that caffeine may effectively counteract stress-induced hair damage and possibly prevent stress-induced hair loss.

The vasotocinergic system and its role in the regulation of stress in birds

The regulation of stress in birds includes a complex interaction of neural systems affecting the hypothalamic-pituitary-adrenal (HPA) axis. In addition to the hypothalamic paraventricular nucleus, a structure called the nucleus of the hippocampal commissure likewise affects the output of pituitary stress hormones and appears to be unique to avian species. Within the anterior pituitary, the avian V1a and V1b receptors were found in corticotropes. Based on our studies with central administration of hormones in the chicken, corticotropic releasing hormone (CRH) is a more potent ACTH secretagogue than arginine vasotocin (AVT). In contrast, when applied peripherally, AVT is more efficacious. Co-administration of AVT and CRH peripherally, resulted in a synergistic stimulation of corticosterone release. Data suggest receptor oligomerization as one possible mechanism. In birds, vasotocin receptors associated with stress responses include the V1a and V1b receptors. Three-dimensional, homology-based structural models of the avian V1aR were built to test agonists and antagonists for each receptor that were screened by molecular docking to map their binding sites on each receptor. Additionally, binding affinity values for each available peptide antagonist to the V1aR and V1bR were determined. An anterior pituitary primary culture system was developed to determine how effective each antagonist blocked the function of each receptor in culture when stimulated by a combination of AVT/CRH administration. Use of an antagonist in subsequent in vivo studies identified the V1aR in regulating food intake in birds. The V1aR was likewise found in circumventricular organs of the brain, suggesting a possible function in stress.

Acyloxyacyl hydrolase modulates depressive-like behaviors through aryl hydrocarbon receptor

Corticotropin-releasing factor (CRF) regulates stress responses, and aberrant CRF signals are associated with depressive disorders. Crf expression is responsive to arachidonic acid (AA), where CRF is released from the hypothalamic paraventricular nucleus (PVN) to initiate the hypothalamic-pituitary-adrenal axis, culminating in glucocorticoid stress hormone release. Despite this biological and clinical significance, Crf regulation is unclear. Here, we report that acyloxyacyl hydrolase, encoded by Aoah, is expressed in the PVN, and Aoah regulates Crf through the aryl hydrocarbon receptor (AhR). We previously showed that AOAH-deficient mice mimicked interstitial cystitis/bladder pain syndrome, a condition frequently associated with comorbid anxiety and depression. With the use of novelty-suppressed feeding and sucrose preference assays to quantify rodent correlates of anxiety/depression, AOAH-deficient mice exhibited depressive behaviors. AOAH-deficient mice also had increased CNS AA, increased Crf expression in the PVN, and elevated serum corticosterone, consistent with dysfunction of the hypothalamic-pituitary-adrenal axis. The human Crf promoter has putative binding sites for AhR and peroxisome proliferator-activated receptor (PPARγ). PPARγ did not affect AA-dependent Crf expression in vitro, and conditional Pparγ knockout did not alter the AOAH-deficient depressive phenotype, despite previous studies implicating PPARγ as a therapeutic target for depression. In contrast, Crf induction was mediated by AhR binding sites in vitro and increased by AhR overexpression. Furthermore, conditional Ahr knockout rescued the depressive phenotype of AOAH-deficient mice. Finally, an AhR antagonist rescued the AOAH-deficient depressive phenotype. Together, our results demonstrate that Aoah is a novel genetic regulator of Crf mediated through AhR, and AhR is a therapeutic target for depression.

Behavioural tactic predicts preoptic-hypothalamic gene expression more strongly than developmental morph in fish with alternative reproductive tactics

Reproductive success relies on the coordination of social behaviours, such as territory defence, courtship and mating. Species with extreme variation in reproductive tactics are useful models for identifying the neural mechanisms underlying social behaviour plasticity. The plainfin midshipman (Porichthys notatus) is a teleost fish with two male reproductive morphs that follow widely divergent developmental trajectories and display alternative reproductive tactics (ARTs). Type I males defend territories, court females and provide paternal care, but will resort to cuckoldry if they cannot maintain a territory. Type II males reproduce only through cuckoldry. We sought to disentangle gene expression patterns underlying behavioural tactic, in this case ARTs, from those solely reflective of developmental morph. Using RNA-sequencing, we investigated differential transcript expression in the preoptic area-anterior hypothalamus (POA-AH) of courting type I males, cuckolding type I males and cuckolding type II males. Unexpectedly, POA-AH differential expression was more strongly coupled to behavioural tactic than morph. This included a suite of transcripts implicated in hormonal regulation of vertebrate social behaviour. Our results reveal that divergent expression patterns in a conserved neuroendocrine centre known to regulate social-reproductive behaviours across vertebrate lineages may be uncoupled from developmental history to enable plasticity in the performance of reproductive tactics.

Differential dendritic remodeling in prelimbic cortex of male and female rats during recovery from chronic stress

Chronic stress produces differential dendritic remodeling of pyramidal neurons in medial prefrontal cortex of male and female rats. In males, this dendritic remodeling is reversible. However, the timeline of recovery, as well as the potential for reversibility in females, is unknown. Here, we examined dendritic recovery of pyramidal neurons in layer II-II of prelimbic cortex in male and female rats following chronic restraint stress (3h/day for 10days). Dendritic morphology and spine density were analyzed immediately following the cessation of stress, or following a 7- or 10-day recovery period. Chronic stress produced apical dendritic retraction in males, which was coupled with a decrease in the density of stubby spine on apical dendrites. Further, following a 10-day recovery period, the morphology of neurons from stressed rats resembled that of unstressed rats. Male rats given a 7-day recovery period had apical dendritic outgrowth compared to unstressed rats. Immediately after cessation of stress, females showed only minimal dendritic remodeling. The morphology of neurons in stressed females resembled those of unstressed rats following only 7days of recovery, at which time there was also a significant increase in stubby spine density. Males and females also showed different changes in baseline corticosterone concentrations during recovery. These findings not only indicate that dendritic remodeling in prelimbic cortex following chronic stress is different between males and females, but also suggest chronic stress induces differential hypothalamic-pituitary-adrenal axis dysregulation in males and females. These differences may have important implications for responses to subsequent stressors.

Polymorphism in CRHR1 gene affects the IL-1β levels in suicidal attempters

Approximately one million people commit suicide every year, being suicide attempts and ideation even more common. Changes in stress response and activation of the immune system have been associated with suicide risk. Here we investigated the interaction between immune system and HPA axis alterations in the suicide risk, looking for the influence of rs110402 CRHR1 SNP in the IL-1β levels according to suicide ideation and attempt. This study evaluated 171 subjects of which 15 had suicidal ideation, 20 had suicide attempt and 136 were controls. Genotyping was performed by real-time PCR and IL-1β levels were measured by ELISA. Our data showed that for each point increase in IL-1β levels the risk of suicide attempt increased 5% [relative risk = 1.05 (95% CI: 1.0-1.10)]. After sample stratification by rs110402 SNP genotypes, we observed that in subjects carrying the A allele the risk raised to 15% [relative risk = 1.15 (95% CI: 1.03-1.28)], suggesting an apparent effect modification. Thus, this study showed that alterations in CRHR1 gene were associated with higher levels of IL-1β, and increased risk for suicide, reinforcing the importance of multifactorial interactions of biological markers for psychiatric disorders.

CRH peptide evolution occurred in three phases: Evidence from characterizing sea lamprey CRH system members

The corticotropin releasing hormone (CRH) system, which includes the CRH family of peptides, their receptors (CRHRs) and a binding protein (CRHBP), has been strongly conserved throughout vertebrate evolution. The identification of invertebrate homologues suggests this system evolved over 500 million years ago. However, the early vertebrate evolution of the CRH system is not understood. Current theory indicates that agnathans (hagfishes and lampreys) are monophyletic with a conservative evolution over the past 500million years and occupy a position at the root of vertebrate phylogeny. We isolated the cDNAs for three CRH family members, two CRHRs and a CRHBP from the sea lamprey, Petromyzon marinus. Two of the CRH peptides are related to the CRH/urotensin-1 (UI) lineage, whereas the other is a urocortin (Ucn) 3 orthologue. The predicted amino acid identity of CRH and UI is 61% but they possess distinct motifs indicative of each peptide, suggesting an early divergence of the two genes. Based on our findings we propose the CRH peptides evolved in at least 3 distinct phases. The first occurring prior to the agnathans gave rise to the CRH/UI-like and Ucn2/3-like paralogous lineages. The second was a partial sub-genomic duplication of the ancestral CRH/UI-like gene, but not the Ucn2/3-like gene, giving rise to the CRH and UI (Ucn) lineages. The third event which resulted in the appearance of Ucn2 and Ucn3 must have occurred after the evolution of the cartilaginous fishes. Interestingly, unlike other vertebrate CRHRs, we were unable to classify our two P. marinus receptors (designated CRHRα and CRHRβ) as either type 1 or type 2, indicating that this split evolved later in vertebrate evolution. A single CRHBP gene was found suggesting that either this gene has not been affected by the vertebrate genome duplications or there have been a series of paralogous gene deletions. This study suggests that P. marinus possess a functional CRH system that differs from that of the gnathostomes and may represent a model for the earliest functioning CRH system in vertebrates.

Regulation of gene expression of vasotocin and corticotropin-releasing hormone receptors in the avian anterior pituitary by corticosterone

The effect of chronic stress (CS) on gene expression of the chicken arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) receptors [VT2R, VT4R, CRH-R1, and CRH-R2] was examined by measuring receptor mRNA levels in the anterior pituitary gland of the chicken after chronic immobilization stress compared to acute stress (AS). Radioimmunoassay results showed that blood circulating corticosterone (CORT) levels in the CS group were significantly decreased compared to that of birds in the AS group (P<0.05). The VT2R and CRH-R2 mRNA in CS birds were significantly decreased to that of controls. The VT4R mRNA was significantly decreased compared to controls in AC birds and was further decreased in the CS group compared to controls (P<0.05). The CRH-R1 mRNA was significantly decreased in the AS birds compared to controls. However, there was no significant difference of CRH-R1 mRNA between acute stress and chronic stress birds. Using primary anterior pituitary cell cultures, the effect of exogenous CORT on VT/CRH receptor gene expression was examined. Receptor mRNA levels were measured after treatment of CORT followed by AVT/CRH administration. The CORT pretreatment resulted in a dose-dependent decrease of proopiomelanocortin heteronuclear RNA, a molecular marker of a stress-induced anterior pituitary. Without CORT pretreatment of anterior pituitary cell cultures, the VT2R, VT4R and CRH-R1mRNA levels were significantly increased within 15 min and then decreased at 1 h and 6 h by AVT/CRH administration (P<0.05). Pretreatment of CORT in anterior pituitary cells induced a dose-dependent increase of VT2R, VT4R and CRH-R2 mRNA levels, and a significant decrease of CRH-R1 mRNA levels at only the high dose (10 ng/ml) of CORT (P<0.05).Taken together, results suggest a modulatory role of CORT on the regulation of VT/CRH receptor gene expression in the avian anterior pituitary gland dependent upon CORT levels.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Effects of social isolation on mRNA expression for corticotrophin-releasing hormone receptors in prairie voles

Previous studies have demonstrated that various type of stressors modulate messenger ribonucleic acid (mRNA) for type 1 corticotropin-releasing hormone (CRH) receptor (CRH-R1 mRNA) and type 2 CRH receptor (CRH-R2 mRNA). The purpose of this study was to explore the effect of social isolation stress of varying durations on the CRH, CRH-R1 and CRH-R2 mRNAs expression in the hypothalamus, hippocampus and pituitary of socially monogamous female and male prairie voles (Microtus ochrogaster). Isolation for 1h (single isolation) or 1h of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma corticosterone levels. Single or repeated isolation increased hypothalamic CRH mRNA expression, but no changes in CRH-R1 mRNA in the hypothalamus were observed. Continuous isolation for 4 weeks (chronic isolation) showed no effect on hypothalamic CRH or CRH-R1 mRNAs in female or male animals. However, hypothalamic CRH-R2 mRNA was significantly reduced in voles exposed to chronic isolation. Single or repeated isolation, but not chronic isolation, significantly increased CRH-R1 mRNA and decreased CRH-R2 mRNA in the pituitary. Despite elevated CRH mRNA expression, CRH-R1 and CRH-R2 mRNAs were not modulated in the hippocampus following single or repeated isolation. Although, chronic isolation did not affect hippocampal CRH or CRH-R1 mRNAs, it did increase CRH-R2 mRNA expression in females and males. The results of the present study in prairie voles suggest that social isolation has receptor subtype and species-specific consequences for the modulation of gene expression for CRH and its receptors in brain and pituitary. Previous studies have revealed a female-biased increase in oxytocin in response to chronic isolation; however, we did not find a sex difference in CRH or its receptors following single, repeated or chronic social isolation, suggesting that sexually dimorphic processes beyond the CRH system, possibly involving vasopressin, might explain this difference.

Long-term survival effect of corticosterone manipulation in Black-legged kittiwakes

The secretion of corticosterone in response to stress is thought to be an adaptive mechanism, which promotes immediate survival at the expense of current reproduction. However, at the individual level, the hypothesis of a corticosterone-related survival appears to be complex. In this study, we tested this hypothesis by combining for the first time an experimental manipulation of corticosterone levels and capture-mark-recapture (CMR) models. To do so, we increased corticosterone levels of chick-rearing Black-legged kittiwakes (Rissa tridactyla) via subcutaneous implants. Then, we monitored the long-term survival of kittiwakes over the 2 consecutive years. Corticosterone-implanted birds showed a significantly lower apparent annual survival than sham-implanted ones (46.9% vs 77.8%). This result is supported by the well-known deleterious effects of elevated corticosterone levels on cognitive and immune functions. Alternately and in the light of recent studies, our experimental manipulation may have down-regulated the endogenous secretion of corticosterone through a prolonged negative feedback. If so, the corticosterone-implanted kittiwakes may have failed to trigger an appropriate stress response during subsequent life-threatening perturbations, hence being unable to adjust their behavior and physiology toward immediate survival. This study highlights the complex long-term consequences of corticosterone manipulation on fitness in free-living vertebrates.

A novel chronic social stress paradigm in female mice

Major depression is one of the most prevalent stress-related psychiatric diseases. Next to environmental influences such as chronic social stress, gender is among the strongest risk factors for major depression, with women having a twice as high risk to develop the disease compared to men. While there is abundant literature on the effects of chronic social stress in male rodents, there is a serious lack of information on gender-specific effects. Especially in mice, which due to the wide availability of transgenic lines offer a unique opportunity to study gene x environment interactions, there is no existing model of chronic social stress that is applicable to both sexes. We here describe the effects of chronic social stress based on the disruption of the social network in a group-housed situation in female mice, a model that was recently described and validated for male mice. In this model, the group composition of the mice is changed twice per week for a period of 7 weeks, covering the adolescent and early adulthood period. We observed that housing in an unpredictable social environment resulted in chronic stress in female mice. The observed effects, which included increased adrenal weight, decreased thymus weight, increased corticosterone levels, and increased anxiety-like behavior, were very similar to the described effects of this paradigm in male mice. In addition, we observed a distinct expression of stress system-related genes in female mice following chronic stress exposure. Our results validate this model as a suitable approach to study chronic social stress in female mice and open up the opportunity to use this model with transgenic or knockout mouse lines.

Minireview: Nuclear receptor-controlled steroid hormone synthesis and metabolism

Steroid hormones are essential in normal physiology whereas disruptions in hormonal homeostasis represent an important etiological factor for many human diseases. Steroid hormones exert most of their functions through the binding and activation of nuclear hormone receptors (NRs or NHRs), a superfamily of DNA-binding and often ligand-dependent transcription factors. In recent years, accumulating evidence has suggested that NRs can also regulate the biosynthesis and metabolism of steroid hormones. This review will focus on the recent progress in our understanding of the regulatory role of NRs in hormonal homeostasis and the implications of this regulation in physiology and diseases.

Endocrine, behavioral and autonomic effects of neuropeptide AF

The actions of neuropeptide AF (NPAF), on the hypothalamic-pituitary-adrenal (HPA) axis, behavior and autonomic functions were investigated. NPAF (0.25, 0.5, 1, 2 nmol) was administered intracerebroventricularly to rats, the behavior of which was monitored by means of telemetry, open-field (OF) observations and elevated plus-maze (EPM) tests. The temperature and heart rate were recorded by telemetry, and the plasma ACTH and corticosterone levels were used as indices of the HPA activation. The dopamine release from striatal and amygdala slices after peptide treatment (100 nM and 1 microM) was measured with a superfusion apparatus. To establish the transmission of the HPA response, animals were pretreated with the corticotrophin-releasing hormone (CRH) receptor antagonist antalarmin or astressin 2B (0.5 nmol). In the OF test, the animals were pretreated with antalarmin or haloperidol (10 microg/kg), while in the EPM test they were pretreated with antalarmin or diazepam (1 mg/kg). NPAF stimulated ACTH and corticosterone release, which was inhibited by antalarmin. It activated exploratory locomotion (square crossings and rearings) and grooming in OF observations, and decreased the entries to and the time spent in the open arms during the EPM tests. The antagonists inhibited the locomotor responses, and also attenuated grooming and the EPM responses. NPAF also increased spontaneous locomotion, and tended to decrease the core temperature and the heart rate in telemetry, while it augmented the dopamine release from striatal and amygdala slices. These results demonstrate, that acute administration of exogenous NPAF stimulates the HPA axis and behavioral paradigms through CRH and dopamine release.

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

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

Stress differentially modulates mRNA expression for corticotrophin-releasing hormone receptors in hypothalamus, hippocampus and pituitary of prairie voles

This study compares the effect of an acute stressor (restraint for 1h) versus a chronic stressor (social isolation for 4 weeks) on the expression of mRNAs for corticotropin-releasing hormone (CRH), CRH receptor type 1 (CRH-R1) and type 2 (CRH-R2) in the hypothalamus, hippocampus and pituitary of socially monogamous female prairie voles (Microtus ochrogaster). Animals were studied immediately following a stressor or as a function of repairing with a familiar sibling. Despite elevated expression of CRH mRNA, no alteration of CRH-R1 mRNA in the hypothalamus was observed following restraint stress or 4 weeks of social isolation. Hypothalamic CRH-R2 mRNA was significantly lower in voles exposed to restraint or isolation. CRH-R2 mRNA also remained down-regulated in isolated animals when these animals were re-paired with their sibling for one day following 28 days of isolation. Restraint, but not isolation, significantly increased CRH-R1 mRNA and decreased CRH-R2 mRNA in the pituitary. However, these differences were no longer observed when these animals were re-paired with their sibling for one day. Despite elevated CRH mRNA expression, CRH-R1 mRNA did not increase in the hippocampus following restraint or social isolation. Social isolation, but not restraint stress, increased CRH-R2 mRNA in the hippocampus, when these animals were re-paired with their sibling for one day the modulation of CRH mRNA remained up-regulated. Plasma corticosterone was elevated only following restraint, and not in animals that were handled, isolated or re-paired. The results of the present study reveal that acute restraint as well as social isolation can have significant consequences for the modulation of gene expression for the CRH receptors in brain and pituitary of prairie voles.

Impaired hypothalamic-pituitary-adrenal axis and its feedback regulation in serotonin transporter knockout mice

Our previous studies have demonstrated that mice with reduced or absent serotonin transporter (SERT+/- and SERT-/- mice, respectively) are more sensitive to stress relative to their SERT normal littermates (SERT+/+ mice). The aim of the present study was to test the hypothesis that the hypothalamic-pituitary-adrenal (HPA) axis and its feedback regulation are impaired in these mice. The function and gene expression of several components in the HPA axis and its feedback regulation in SERT+/+, +/( and -/- mice were studied under basal (non-stressed) and stressed conditions. The results showed that (1) under basal conditions, corticotrophin-releasing factor (CRF) mRNA levels in the paraventricular nucleus (PVN) of the hypothalamus was lower in both SERT+/( and (/( mice relative to SERT+/+ mice; (2) an increased response to CRF challenge was found in SERT(/( mice, suggesting that the function of CRF type 1 receptors (CRF R1) in the pituitary is increased. Consistent with these findings, (125)I-sauvagine (a CRF receptor antagonist) binding revealed an increased density of CRF R1 in the pituitary of SERT(/( under basal conditions. These data suggest that CRF R1 in the pituitary of SERT(/( mice is up-regulated. However, in the pituitary of SERT+/( mice, the function of CRF R1 was not changed and the density of CRF R1 was reduced relative to SERT+/+ mice; and (3) the expression of the glucocorticoid receptor (GR) in the hypothalamus, pituitary and adrenal cortex was significantly reduced in SERT+/( and (/( mice in comparison with SERT+/+ mice under basal conditions. Consistent with these findings, the corticosterone response to dexamethasone was blunted in SERT(/( mice relative to SERT+/+ and +/( mice. Furthermore, stress induces a rapid increase of the GR expression in the hypothalamus of SERT+/( and (/( mice relative to their basal levels. Together, the present results demonstrated that the HPA axis and its feedback regulation are altered in SERT knockout mice, which could account for the increased sensitivity to stress in these mice.

Chronic stress and individual vulnerability

Over the last decades the burden of disease in Western countries has shifted from comparably easily treated infectious diseases to more complex diseases, such as the metabolic syndrome, cardiovascular disease, and psychiatric disorders. A common characteristic of these illnesses is the interplay of multiple genetic and nongenetic factors, which eventually results in the manifestation of disease symptoms. Large-scale epidemiological studies in humans have resulted in the identification of various environmental and genetic risk factors, which contribute to the onset, duration, and severity of disease. While tremendous progress has been made, it is still impossible to predict which combination of risk factors will result in the manifestation of a specific illness. This lack of knowledge is also frequently reflected in inadequate treatment strategies, which mainly focus on symptom reversal rather than targeting the cause of the diseases. One of the most prominent environmental risk factors described for numerous diseases is chronic exposure to stressful situations. In this paper we address clinical and preclinical evidence of chronic stress as a risk factor for disease and introduce a novel, high-throughput mouse model for chronic social stress. We can show that this model has a high degree of construct, face, and predictive validity in terms of physiological, behavioral, and gene expression changes. We further illustrate how novel animal models of chronic social stress can help to unravel the complex interaction of individual genetic vulnerability and environmental risk factors.

Endocrine and behavioral effects of neuromedin S

The present experiments focused on the effects of neuromedin S on hypothalamic-pituitary-adrenal (HPA) activation and behavior. The peptide (0.25-1 nmol) was administered intracerebroventricularly to rats, the behavior of which was monitored by means of telemetry, open field observations and an elevated plus-maze (EPM) test. Autonomic functions such as the temperature and the heart rate were recorded by telemetry. The action on the HPA axis was assessed via measurements of the plasma corticosterone and ACTH levels. To reveal the transmission of the endocrine responses, animals were pretreated with corticotrophin releasing hormone receptor (CRHR) antagonists (1 nmol). In the open field test, the animals were pretreated with either a CRHR(1) antagonist (antalarmin) or haloperidol (10 microg/kg), while in the EPM test they were pretreated with antalarmin or diazepam (1 mg/kg). The dopamine release from striatal and amygdala slices after peptide treatment was measured with a superfusion apparatus. Neuromedin S exerted dose-dependent effects on the HPA system, which were inhibited by antalarmin. It also activated grooming and decreased the entries to and time spent in the open arms during the EPM test. The grooming response was abolished by haloperidol and antalarmin pretreatment, while diazepam and antalarmin showed a tendency to attenuate the response evoked in the EPM test. In the superfusion studies, neuromedin S enhanced the dopamine release from the amygdala slices. These results demonstrate that neuromedin S stimulates the HPA axis through the CRHR(1) pathway and evokes stereotyped behavior and anxiety through mesolimbic dopamine and corticotrophin releasing hormone release.

Impaired adaptation to repeated restraint and decreased response to cold in urocortin 1 knockout mice

Urocortin 1 (UCN1) is a corticotropin-releasing factor (CRF)-like peptide whose role in stress is not well characterized. To study the physiological role of UCN1 in the response of the hypothalamic-pituitary-adrenal (HPA) axis to stress, we generated UCN1-knockout (KO) mice and examined their adaptation to repeated restraint and to cold environment. Wild-type (WT) and UCN1-KO animals were restrained hourly for 15 min from 9 AM to 2 PM, and blood samples were obtained for corticosterone measurement. WT animals adapted to repeated restraint with a decreased corticosterone response; the restraint-stimulated corticosterone levels fell from 215 +/- 31 ng/ml in naïve animals to 142 +/- 50 ng/ml in mice subjected to repeated restraint (P < 0.01) and from 552 +/- 98 to 314 +/- 58 ng/ml (P < 0.001) in males and females, respectively. Male UCN1-KO mice did not show any adaptation to repeated restraint; instead, restraint-stimulated corticosterone levels were increased from 274 +/- 80 ng/ml in naïve animals to 480 +/- 75 ng/ml in mice subjected to repeated restraint (P < 0.001). Female UCN1-KO mice showed only a partial adaptation to repeated restraint, with a decrease in the restraint-stimulated corticosterone response from 631 +/- 102 ng/ml in naïve animals to 467 +/- 78 ng/ml in mice subjected to repeated restraint (P < 0.01). In addition, UCN1-KO mice showed no corticosterone response to 2-h cold environment. These data demonstrate an important role for UCN1 in the HPA axis adaptation to repeated restraint and in the corticosterone response to a cold environment.

Persistent neuroendocrine and behavioral effects of a novel, etiologically relevant mouse paradigm for chronic social stress during adolescence

Chronic stress is widely regarded as a key risk factor for a variety of diseases. A large number of paradigms have been used to induce chronic stress in rodents. However, many of these paradigms do not consider the etiology of human stress-associated disorders, where the stressors involved are mostly of social nature and the effects of the stress exposure persist even if the stressor is discontinued. In addition, many chronic stress paradigms are problematic with regard to stress adaptation, continuity, duration and applicability. Here we describe and validate a novel chronic social stress paradigm in male mice during adolescence. We demonstrate persistent effects of chronic social stress after 1 week of rest, including altered adrenal sensitivity, decreased expression of corticosteroid receptors in the hippocampus and increased anxiety. In addition, pharmacological treatments with the antidepressant paroxetine (SSRI) or with the corticotropin-releasing hormone receptor 1 antagonist DMP696 were able to prevent aversive long-term consequences of chronic social stress. In conclusion, this novel chronic stress paradigm results in persistent alterations of hypothalamus-pituitary-adrenal axis function and behavior, which are reversible by pharmacological treatment. Moreover, this paradigm allows to investigate the interaction of genetic susceptibility and environmental risk factors.

Temazepam triggers the release of vasopressin into the rat hypothalamic paraventricular nucleus: novel insight into benzodiazepine action on hypothalamic-pituitary-adrenocortical system activity during stress

We investigated the influence of a representative classical benzodiazepine on the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis activity both under basal conditions and stress. Adult male Wistar rats were intravenously administered with temazepam (0.5, 1, and 3 mg/kg body weight) and plasma concentrations of corticotropin (ACTH) and vasopressin (AVP) were measured in blood samples collected via chronically implanted jugular venous catheters. Simultaneously, the release of AVP within the hypothalamic paraventricular nucleus (PVN) was monitored via microdialysis. Plasma AVP levels remained unaffected by the different treatment conditions. Temazepam blunted the stressor exposure-induced secretion of ACTH in a dose-dependent manner. Concurrently, and also in a dose-dependent manner temazepam enhanced the intra-PVN release of AVP, known to originate from magnocellular neurons of the hypothalamic neurohypophyseal system. Furthermore, temazepam did not affect the in vitro secretion of ACTH from the adenohypophyseal cells. Taken together, the results of this study suggest that temazepam modulates the central nervous regulation of the HPA axis by altering intra-PVN AVP release. An increasingly released AVP of magnocellular origin seems to provide a negative tonus on ACTH secretion most probably via inhibiting the release of ACTH secretagogues from the median eminence into hypophyseal portal blood.

Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF-2 deficient mice

The transcription-intermediary-factor-2 (TIF-2) is a coactivator of the glucocorticoid receptor (GR), and its disruption would be expected to influence glucocorticoid-mediated control of the hypothalamo-pituitary-adrenal (HPA) axis. Here, we show that its targeted deletion in mice is associated with altered expression of several glucocorticoid-dependent components of HPA regulation (e.g., corticotropin-releasing hormone, vasopressin, ACTH, glucocorticoid receptors), suggestive of hyperactivity under basal conditions. At the same time, TIF-2(-/-) mice display significantly lower basal corticosterone levels and a sluggish and blunted initial secretory response to brief emotional and prolonged physical stress. Subsequent analysis revealed this discrepancy to result from pronounced aberrations in the structure and function of the adrenal gland, including the cytoarchitectural organization of the zona fasciculata and basal and stress-induced expression of key elements of steroid hormone synthesis, such as the steroidogenic acute regulatory (StAR) protein and 3beta-hydroxysteroid dehydrogenase (3beta-HSD). In addition, altered expression levels of two nuclear receptors, DAX-1 and steroidogenic factor 1 (SF-1), in the adrenal cortex strengthen the view that TIF-2 deletion disrupts adrenocortical development and steroid biosynthesis. Thus, hyperactivity of the hypothalamo-pituitary unit is ascribed to insidious adrenal insufficiency and impaired glucocorticoid feedback.

Regulation of the hypothalamic-pituitary-adrenocortical system in patients with panic disorder

Anxiety and depressive disorders are among the most common psychiatric disorders with a high number of hospital admissions and a lifetime prevalence of up to 25%. So far, the pathophysiological mechanisms for anxiety disorders remain to be found. Preclinical studies suggest that changes in hypothalamic-pituitary-adrenocortical (HPA) system function are causally related to the expression of anxiety-related behavior. The findings on HPA system function in patients with anxiety disorders are, however, heterogeneous. Both hypo- and hyperresponsiveness of HPA response in various anxiety disorders under different experimental conditions were found. In order to characterize putative case/control differences in HPA system function, we performed a Dex-CRH test, a widely used test to pick up changes in HPA system regulation with high sensitivity, in 30 patients with panic disorder, 35 patients with major depressive episode and in 30 controls individually matched for ethnicity, age and gender. The results indicate a similar dysregulation of the HPA system response in the Dex-CRH test in both patient groups. This finding further underlines the hypothesis that both, depression and panic disorder, share impaired HPA system regulation, supporting the notion that the impairment is involved in the pathophysiology of these clinical conditions. However, differences in the suppression effects and psychopathological correlation patterns between depressed and panic patients suggest different biological mechanisms of HPA system dysregulation in both disorders.

Corticotropin releasing hormone and the skin

Cotricotropin-releasing hormone (CRH) and related peptides are produced in skin that is dependent on species and anatomical location. Local peptide production is regulated by ultraviolet radiation (UVR), glucocorticoids and phase of the hair cycle. The skin also expresses the corresponding receptors (CRH-R1 and CRH-R2), with CRH-R1 being the major receptor in humans. CRH-R1 is expressed in epidermal and dermal compartments, and CRH-R2 predominantly in dermal structures. The gene coding for CRH-R1 generates multiple isoforms through a process modulated by UVR, cyclic adenosine monophosphate (cAMP) and phorbol 12-myristate 13-acetate. The phenotypic effects of CRH in human skin cells are largely mediated by CRH-R1alpha through increases in concentrations of cAMP, inositol triphosphate (IP3), or Ca2+ with subsequent activation of protein kinases A (PKA) and C (PKC) dependent pathways. CRH also modulates the activity of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kappaB), activator protein 1 (AP-1) and cAMP responsive element binding protein (CREB). The cellular functions affected by CRH depend on cell type and nutritional status and include modulation of differentiation program(s), proliferation, viability and immune activity. The accumulated evidence indicates that cutaneous CRH is also a component of a local structure organized similarly to the hypothalamo-pituitary-adrenal axis.

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.

Modulation of the human hair follicle pigmentary unit by corticotropin-releasing hormone and urocortin peptides

Human skin is a local source of corticotropin-releasing hormone (CRH) and expresses CRH and CRH receptors (CRH-R) at mRNA and protein levels. Epidermal melanocytes respond to CRH by induction of cAMP with up-regulation of pro-opiomelanocortin gene expression and subsequent production of adrenocorticotropin hormone. However, the role of CRH/CRH-R in melanocyte biology is complicated by the significant heterogeneity of cutaneous melanocyte subpopulations, from continuously active and UV-responsive melanocytes in epidermis to UV nonresponsive, hair growth cycle-coupled melanogenesis in hair follicles. In the present study we report that normal human scalp hair follicle melanocytes express CRH at the mRNA level. Furthermore, CRH, urocortin and CRH-R 1 and 2 were differentially expressed in follicular melanocytes, fibroblasts, and keratinocytes depending on anatomic location and differentiation status in situ and in vitro. Stimulation of follicular melanocytes with CRH and CRH peptides, modified for selectivity for CRH-R1 and/or CRH-R2, variably induced cell melanogenesis, dendricity, and proliferation. CRH-peptides also stimulated the expression and activity of Tyrosinase, and expression of Tyrosinase-related protein-1 and-2. However, a modified urocortin peptide highly selective for CRH-R2 down-regulated melanocyte differentiation phenotype. This study indicates that CRH peptides can differentially influence hair follicle melanocyte behavior not only via CRH-R1 signaling but also by complex cross-talk between CRH-R1 and CRH-R2.

Corticotropin-releasing hormone-receptor 1 (CRH-R1) and CRH-binding protein (CRH-BP) are expressed in the gills and skin of common carp Cyprinus carpio L. and respond to acute stress and infection

We established that corticotropin-releasing hormone (CRH), CRH-binding protein (CRH-BP) and CRH-receptor 1 (CRH-R1) are expressed in the gills and skin of common carp Cyprinus carpio, an early vertebrate. Immunoreactive CRH was detected in macrophage-like cells in gills and skin, in fibroblasts in the skin and in endothelial cells in the gills. The involvement of the CRH system in gills and skin was investigated in response to infection and in an acute restraint stress paradigm. Carp were infected with the protozoan leech-transmitted blood flagellate Trypanoplasma borreliand subjected to acute restraint stress by netting for 24 h. The expression of CRH-BP and CRH-R1 genes in the gills and in the skin is downregulated after both infection and restraint. Thus the peripheral CRH system reacts to infection and stress. The gills and skin separate the internal from the external environment and are permanently exposed to stress and pathogens. Because of their pivotal role in maintaining the homeostatic equilibrium,these organs must act locally to respond to diverse stresses. Clearly, the CRH system is involved in the response of the integument to diverse stresses at the vulnerable interface of the internal and external milieu.

The pathogenesis of clinical depression: stressor- and cytokine-induced alterations of neuroplasticity

Stressful events promote neurochemical changes that may be involved in the provocation of depressive disorder. In addition to neuroendocrine substrates (e.g. corticotropin releasing hormone, and corticoids) and central neurotransmitters (serotonin and GABA), alterations of neuronal plasticity or even neuronal survival may play a role in depression. Indeed, depression and chronic stressor exposure typically reduce levels of growth factors, including brain-derived neurotrophic factor and anti-apoptotic factors (e.g. bcl-2), as well as impair processes of neuronal branching and neurogenesis. Although such effects may result from elevated corticoids, they may also stem from activation of the inflammatory immune system, particularly the immune signaling cytokines. In fact, several proinflammatory cytokines, such as interleukin-1, tumor necrosis factor-alpha and interferon-gamma, influence neuronal functioning through processes involving apoptosis, excitotoxicity, oxidative stress and metabolic derangement. Support for the involvement of cytokines in depression comes from studies showing their elevation in severe depressive illness and following stressor exposure, and that cytokine immunotherapy (e.g. interferon-alpha) elicited depressive symptoms that were amenable to antidepressant treatment. It is suggested that stressors and cytokines share a common ability to impair neuronal plasticity and at the same time altering neurotransmission, ultimately contributing to depression. Thus, depressive illness may be considered a disorder of neuroplasticity as well as one of neurochemical imbalances, and cytokines may act as mediators of both aspects of this illness.

Gene expression profiles highlight adaptive brain mechanisms in corticotropin releasing factor overexpressing mice

Corticotropin-releasing factor (CRF) plays an important role in mediating central and peripheral responses to stress. Alterations in CRF system activity have been linked to a number of psychiatric disorders, including anxiety and depression. Aim of this study was to elucidate homeostatic mechanisms induced by lifelong elevated CRF levels in the brain. We therefore profiled gene expression in several brain areas of transgenic mice overexpressing CRF (CRF-OE), a model for chronic stress. Several genes showed altered expression levels in CRF-OE mice when compared to their wild type littermates and were confirmed by quantitative PCR. Differences in gene expression profiles revealed the presence of previously unrecognized homeostatic mechanisms in CRF-OE animals. These included changes in glucocorticoid signaling, as exemplified by changes in 11beta-hydroxysteroid dehydrogenase type 1, FK506 binding protein 5 and serum/glucocorticoid kinase. Alterations in expression of genes involved in myelination (myelin, myelin-associated glycoprotein), cell proliferation and extracellular matrix formation (Edg2, Fgfr2, decorin, brevican) suggest changes in the dynamics of neurogenesis in CRF-OE. Pronounced changes in neurotensin (NT) receptors 1 and 2 mRNA were identified. Overall downregulation of NT receptors in CRF-OE animal was substantiated by receptor binding studies. Pronounced neurotensin receptor downregulation was observed for NT type 1 receptors in limbic brain areas, suggesting that NT could be implicated in some of the effects attributed to CRF overexpression. These data show that lifelong exposure to excessive CRF leads to adaptive changes in the brain which could play a role in some of the behavioral and physiological alterations seen in these animals.

Stress-related gene expression in brain and adrenal gland of porcine fetuses and neonates

This study was conducted to examine stress-induced effects on gene expression of specific markers for HPA axis and neuronal activity in fetuses and neonatal pigs. Brain, pituitary gland, and adrenal gland were obtained to determine the mRNA levels for corticotropin-releasing hormone (CRH), CRH receptor 1 (CRHR1), pro-opiomelanocortin (POMC), ACTH receptor (MC2R), c-jun and c-fos. The suitability of these molecular markers was determined in neonatal pigs which were maternally deprived for two hours. It was found that maternal deprivation caused significantly higher transcript levels of c-fos and CRH in brain accompanied by a down-regulation of CRHR1 mRNA and an up-regulation of c-jun in the pituitary gland. To determine the effect of elevated maternal cortisol levels on gene expression of these molecular markers in fetuses, pregnant sows were treated with 100 IU ACTH (Synacthen Depot) s.c. every two days between Day 49 and Day 75 of gestation (normal gestation length 114 days). Animals were killed 48 hours after the last ACTH administration and fetuses of each sow were isolated. The ACTH treatment of sows significantly increased mRNA expression of c-fos but not of CRH in the fetal brain, and significantly decreased MC2R mRNA expression in the adrenal gland. However, HPA axis seems not to be fully developed in Day 77-fetuses because fetal pituitary CRHR1 and POMC mRNA expression was low in most of the fetuses. Although the expression of endocrine regulatory factors was partially incomplete in fetuses at the beginning of the third-trimester, ACTH dependent activation of c-fos mRNA in brain indicates a stress-related increase of neuronal activity. Based on these results it is assumed that prenatal stress in pigs may also have effects on the activity of the HPA axis in the offspring.

Reduced hypothalamic vasopressin secretion underlies attenuated adrenocorticotropin stress responses in pregnant rats

We sought to explain decreased ACTH secretory responses to stress in pregnant rats by investigating hypothalamic CRH and vasopressin secretion and actions on anterior pituitary corticotrophs. In late pregnancy median eminence, CRH content was reduced (by 12%). Anterior pituitary proopiomelanocortin mRNA expression, measured by in situ hybridization but not radioimmunoassayed ACTH content, was also reduced (by 45% on d 21); CRH receptor (CRHR)1 mRNA expression was unaltered in pregnancy, but V1b receptor mRNA expression was reduced (by 19%). ACTH secretory responses, measured in jugular blood, to CRH (200 ng/kg iv) or vasopressin (1.7 microg/kg, iv) were reduced on d 21 vs. virgins (49% and 44%), but the response to combined CRH and vasopressin injection was intact. Either antalarmin (CRHR1 antagonist; 20 mg/kg ip) or dP(Tyr(Me)2),Arg-NH2(9))AVP (V1a/b antagonist; 10 microg/kg, iv) pretreatment reduced the ACTH secretory response to forced swimming (90 sec) in virgin rats (by 57% and 40%), but only antalarmin was effective in pregnant rats (53% decrease). In vitro, measuring ACTH secretion from acutely dispersed anterior pituitary cells showed increased corticotroph sensitivity in pregnancy to CRH and to CRH augmentation by vasopressin, attributable to increased intracellular cAMP action. Hence, in late pregnancy, reduced anterior pituitary CRHR1 or V1b receptor expression did not impair corticotroph responses to CRH or vasopressin. Rather, diminished secretagogue secretion in vivo accounts for reduced action of stress levels of exogenous CRH or vasopressin alone; the late pregnancy attenuated ACTH secretory response to swim stress is deduced to be due to reduced vasopressin release by parvocellular paraventricular nuclei neurones.

A fully functional proopiomelanocortin/melanocortin-1 receptor system regulates the differentiation of human scalp hair follicle melanocytes

The proopiomelanocortin (POMC)-derived peptides, ACTH and alpha-MSH, are the principal mediators of human skin pigmentation via their action at the melanocortin-1 receptor (MC-1R). Recent data have demonstrated the existence of a functionally active beta-endorphin/mu-opiate receptor system in both epidermal and hair follicle melanocytes, whereby beta-endorphin can regulate melanogenesis, dendricity, and proliferation in these cells. However, a role for ACTH and alpha-MSH in the regulation of the human follicular pigmentary unit has not been determined. This study was designed to examine the involvement of ACTH and the alpha-MSH/MC-1R system in human follicular melanocyte biology. To address this question we employed RT-PCR and immunohisto/cytochemistry, and a functional role for these POMC peptides was assessed in follicular melanocyte cultures. Human scalp hair follicle melanocytes synthesized and processed POMC. ACTH and alpha-MSH in association with their processing enzymes and MC-1R are expressed in human follicular melanocytes at the message level in vitro and at the protein level both in situ and in vitro. The expression of the POMC/MC-1R receptor system was confined only to subpopulations of poorly and moderately differentiated melanocytes. In addition, functional studies revealed that ACTH and alpha-MSH are able to promote follicular melanocyte differentiation by up-regulating melanogenesis, dendricity, and proliferation in less differentiated melanocyte subpopulations. Thus, these findings suggest a role for these POMC peptides in regulating human hair follicle melanocyte differentiation.

Chronic cortisol suppresses pituitary and hypothalamic peptide message expression in pigtailed macaques

The effects of chronic elevations in circulating glucocorticoids on the expression of peptides and peptide receptors of the hypothalamic-pituitary-adrenal (HPA) axis have been studied extensively in rodents, but they have not been examined in primates. To determine the responses of the HPA axis in primates to elevated cortisol, hypothalamic and pituitary tissue from normal older pigtailed macaques (Macaca nemestrina) that had received daily oral administration of cortisol or placebo for 1 year were studied. Pro-opiomelanocortin in the anterior pituitary and corticotropin-releasing factor (CRF) mRNA expression in the hypothalamic paraventricular nucleus (PVN) were significantly reduced in cortisol-treated monkeys in comparison with controls. CRF receptor 1 (CRF-R1) expression in the anterior pituitary and arginine vasopressin mRNA expression in the PVN were unchanged by chronic cortisol administration. Sustained elevation of circulating glucocorticoids results in suppression of HPA peptide and peptide receptor expression in the PVN and anterior pituitary similar to those found in rodents. Chronic therapeutic administration of glucocorticoids in humans may have unintended consequences for hypothalamic and pituitary function.

Dysregulation in the suicide brain: mRNA expression of corticotropin-releasing hormone receptors and GABA(A) receptor subunits in frontal cortical brain region

Corticotropin-releasing hormone (CRH) and GABA have been implicated in depression, and there is reason to believe that GABA may influence CRH functioning. The levels of CRH, and mRNA for CRH-binding protein, CRH1, and CRH2 receptors, as well as various GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha4, alpha5, delta, and gamma2), were determined in several frontal cortical brain regions of depressed suicide victims and nondepressed individuals who had not died by suicide. Relative to the comparison group, CRH levels were elevated in frontopolar and dorsomedial prefrontal cortex, but not in the ventrolateral prefrontal cortex of suicide victims. Conversely, using quantitative PCR analyses, it was observed that, in frontopolar cortex, mRNA for CRH1, but not CRH2, receptors were reduced in suicide brains, possibly secondary to the high levels of CRH activity. In addition, mRNA of the alpha1, alpha3, alpha4, and delta receptor subunits was reduced in the frontopolar region of suicide victims. Interestingly, a partial analysis of the GABA(A) receptor functional genome revealed high cross-correlations between subunit expression in cortical regions of nondepressed individuals, suggesting a high degree of coordinated gene regulation. However, in suicide brains, this regulation was perturbed, independent of overall subunit abundance. These findings raise the possibility that the CRH and GABA(A) receptor subunit changes, or the disturbed coordination between these GABA(A) receptor subunits, contribute to depression and/or suicidality or are secondary to the illness/distress associated with it.

Galanin in pituitary adenomas

Tumor galanin content was measured in extracts from human pituitary adenomas using a specific RIA method for monitoring human galanin. Twenty-two out of twenty-four tumors contained galanin with notably high levels in corticotroph adenomas, varying levels in clinically inactive tumors, and low levels in GH secreting adenomas. Tumor galanin and ACTH contents were closely correlated in all tumors. In four young patients with microadenomas and highly active Mb Cushing tumor galanin was inversely related to tumor volume. The molecular form of tumor galanin, studied with reverse-phase HPLC, was homogeneous with the majority of tumor galanin coeluting with standard human galanin. In the tumors analysed with in situ hybridization there was a good correlation between galanin peptide levels and galanin mRNA expression. In some tumors galanin mRNA and POMC levels coexisted, in others they were essentially in different cell populations. Levels of plasma galanin-LI were not related to tumor galanin concentration, and galanin levels were in the same range in sinus petrosus close to the pituitary venous drainage as in peripheral blood. Corticotrophin releasing hormone injections in two patients caused ACTH, but no detectable galanin release into sinus petrosus. Our results demonstrate that corticotroph, but not GH adenomas, express high levels of galanin, in addition to ACTH, and that in some tumors both polypeptides are synthesised in the same cell population. However, galanin levels in plasma were not influenced by the tumor galanin content.

Corticotropin-releasing factor receptor type 1 and 2 mRNA expression in the rat anterior pituitary is modulated by intermittent hypoxia, cold and restraint

We had previously demonstrated that continual-hypoxia stimulated corticotropin-releasing factor (CRF)mRNA in hypothalamus, and release of CRF, as well as enhancing plasma adrenocorticotropic-hormone and corticosterone of rats. The present study demonstrates using in situ autoradiography that CRF receptor 1 (CRFR1) and CRF receptor 2 (CRFR2) mRNA in the rat anterior pituitary is changed by intermittent hypoxia, cold, restraint, alone and in combination. Rats were exposed to intermittent hypoxia for 4 h/day during various periods in a hypobaric chamber. Hypoxia equivalent to an altitude of around 2 km (16.0% O2) or 5 km (10.8% O2) caused a biphasic change in both CRFR1 and R2 mRNA, there being an initial significant decline on day 1 and then an enhancement by day 2. The increase of both receptor subtypes mRNA was relatively well maintained up to 15 days in rats exposed to 2 km intermittently. CRFR2 mRNA in rats exposed to 5 km, after peaking at day 2 therefore declined and was not different to controls at 15 days. Five kilometer hypoxia markedly reduced body weight gain. The increased CRFR1 mRNA was also induced by restraint alone, hypoxia+restraint and hypoxia+cold but not by cold alone. The CRFR2 mRNA was significantly increased by all the stresses except for hypoxia+restraint. These results show that the acute response to intermittent hypoxia is a decrease in the CRF receptor mRNA whereas longer exposure to the three environmental stressors hypoxia, cold and restraint is needed to provoke an increase. This may have important consequences for adaptation to high altitude. The significant differences between the expression of CRFR1 mRNA and CRFR2 mRNA in response to the different stimuli might suggest that the two receptors in the pituitary play different roles in behavior.

Altered serotonergic neurotransmission but normal hypothalamic-pituitary-adrenocortical axis activity in mice chronically treated with the corticotropin-releasing hormone receptor type 1 antagonist NBI 30775

Antagonists of the corticotropin-releasing hormone receptor type 1 (CRH-R1) are regarded as promising tools for the treatment of stress-related psychiatric disorders. Owing to the intricate relationship between CRH and serotonin (5-HT), we studied the effects of chronic oral treatment of C57Bl6/N mice with the CRH-R1 antagonist NBI 30775 (formerly known as R121919) on hippocampal serotonergic neurotransmission during basal (on 15th day of treatment) and stress (forced swimming; on 16th day of treatment) conditions by in vivo microdialysis. Given the important role of CRH in the regulation of hypothalamic-pituitary-adrenocortical (HPA) axis activity and behavior, the effects of NBI 30775 on dialysate-free corticosterone levels, and on home cage and forced swimming-related behavior were also assessed. Chronic administration of NBI 30775 (18.4+/-0.9 mg/kg/day) did not result in alterations in food consumption and body weight. NBI 30775 caused complex changes in hippocampal serotonergic neurotransmission. Whereas no effects on the diurnal rhythms of 5-HT and its metabolite 5-hydroxyindoleacetic acid were found, the responses of the neurotransmitter and its metabolite to 10 min of forced swim stress were reduced and prolonged, respectively. NBI 30775 did not change free corticosterone levels over the diurnal rhythm. Moreover, NBI 30775-treated mice showed a similar forced swim stress-induced increase in corticosterone as observed in the control group. No effects of NBI 30775 on home cage, and swim stress-related active behaviors (climbing, swimming) and immobility were found. Thus, whereas chronic antagonism of CRH-R1 did not compromise HPA axis performance and behavior, distinct changes in serotonergic neurotransmission developed. Owing to the important role of 5-HT in the pathophysiology of mood and anxiety disorders, the latter observation may contribute to the therapeutical efficacy of CRH-R1 antagonists in these illnesses.

Tamoxifen is an estrogen antagonist on gonadotropin secretion and responsiveness of the hypothalamic-pituitary- adrenal axis in female monkeys

The selective estrogen receptor modulator, tamoxifen, effectively slows the progression of estrogen-positive breast cancer and reduces the possibility of this cancer developing in women at high risk. Despite the widespread acceptance of tamoxifen as a therapeutic agent for this disease, its effects on other estrogen-dependent pathways, particularly on neural circuits regulating brain function and peripheral hormone secretion, are poorly understood. The present study, using previously ovariectomized rhesus monkeys, examined the effects of tamoxifen, in both the presence and absence of estradiol replacement, on the reproductive and hypo-thalamic-pituitary-adrenal (HPA) axes. In Experiment 1, monkeys randomly assigned to three groups (n = 8 each) were treated with placebo and either two doses of estradiol, two doses of tamoxifen alone, or two doses of tamoxifen plus high-dose estradiol to assess the effects on negative feedback suppression of luteinizing hormone (LH). Both doses of tamoxifen effectively antagonized the negative feedback efficacy of estradiol on LH secretion. In contrast, neither the low- or high-dose tamoxifen alone had any effect on LH secretion, as concentrations during tamoxifen treatments were indistinguishable from those during placebo. In Experiment 2, females were randomly assigned to one of four treatment groups (placebo, n = 6; estradiol, n = 5; tamoxifen only, n = 5; or tamoxifen plus estradiol, n = 6) to assess the effects on glucocorticoid negative feedback and pituitary and adrenal responsiveness to exogenous corticotropin- releasing hormone (CRH). Tamoxifen also antagonized the facilitating effects of estradiol on basal and CRH-induced ACTH and cortisol secretion. However, this antagonism produced basal and CRH-stimulated cortisol and ACTH concentrations that were lower than placebo-treated females. Interestingly, tamoxifen in the absence of estradiol produced a similar diminution in ACTH and cortisol response. These data suggest that, in the presence of estradiol, tamoxifen not only antagonized estrogenic facilitation of HPA responsivity but also actually attenuated the response compared with the placebo-treatment condition. Taken together, these data indicate that tamoxifen acts as an estrogen antagonist on the neural circuits controlling the neuroendocrine regulation of the hypothalamic-pituitary-ovarian and adrenal axes in ovariectomized macaque females.

Neuropeptide systems as novel therapeutic targets for depression and anxiety disorders

The health burden of stress-related diseases, including depression and anxiety disorders, is rapidly increasing, whereas the range of available pharmacotherapies to treat these disorders is limited and suboptimal with regard to efficacy and tolerability. Recent findings support a major role for neuropeptides in mediating the response to stress and thereby identify neuropeptide systems as potential novel therapeutic targets for the treatment of depression and anxiety disorders. In preclinical models, pharmacological and/or genetic manipulation of substance P, corticotropin-releasing factor (CRF), vasopressin, neuropeptide Y and galanin function alters anxiety- and depression-related responses. Recently, specific and highly potent small-molecule neuropeptide receptor agonists and antagonists have been developed that can readily cross the blood-brain barrier. Clinical assessment of several compounds is currently underway, with antidepressant efficacy confirmed in double-blind, placebo-controlled trials of tachykinin NK(1) (substance P) receptor antagonists, and preliminary evidence of antidepressant activity in an open-label trial of a CRF(1) receptor antagonist.

Endocrine and cardiovascular responses to corticotropin-releasing hormone in patients with posttraumatic stress disorder: a role for atrial natriuretic peptide?

Hypothalamic-pituitary-adrenocortical (HPA) axis data, such as low plasma cortisol concentrations in spite of increased corticotropin-releasing hormone (CRH) levels in patients with posttraumatic stress disorder (PTSD), are difficult to interpret. Atrial natriuretic peptide (ANP) may be an explanatory link in the neuroendocrine pathophysiology of the disorder, since it is a neuromodulator with antianxiety effects that inhibits HPA activity at multiple levels. Seventeen patients with chronic PTSD and 17 healthy control subjects were given 100 microg of human CRH at 3 p.m. ANP, adrenocorticotropic hormone (ACTH), and cortisol levels in plasma as well as blood pressure and heart rate were measured during basal conditions and after CRH stimulation. Basal ANP levels were significantly lower in PTSD patients in comparison with normal controls, but the response to CRH was undistinguishable. In contrast to our expectation, no significant differences in basal or CRH-stimulated ACTH or cortisol parameters could be observed. Systolic and diastolic blood pressures at baseline and after CRH were significantly elevated in PTSD patients. All group differences remained significant after controlling for basal blood pressure and/or body mass index. Our data do not support a role of ANP in abnormal HPA axis regulation in PTSD. However, the persistently low ANP plasma levels in PTSD patients despite elevated blood pressure may serve to facilitate anxiety behavior and have adverse long-term cardiovascular consequences. Further studies to assess ANP secretion in PTSD patients and to clarify its pathophysiological impact are needed.

Corticotropin-releasing hormone (CRH) expression and protein kinase A mediated CRH receptor signalling in an immortalized hypothalamic cell line

Corticotropin-releasing hormone (CRH) is a 41 amino acid neuropeptide which plays an important role in the stress response in the hypothalamus. We describe the development of an immortalized hypothalamic cell line which expresses CRH. We hypothesized that this cell line would possess the relevant characteristics of parvocellular CRH-expressing neurones such as glucocorticoid receptor (GR) expression and vasopressin (VP) coexpression. For production of hypothalamic cells, embryonic day 19 rat pup hypothalami were dissected and dissociated into tissue culture dishes. They were immortalized by retrovirus-mediated transfer of the SV40 large T antigen gene at 3 days of culture and then screened for expression of CRH following dilution cloning. One cell line was chosen (IVB) which exhibited CRH-like immunoreactivity (CRH-LI) and expressed CRH, VP and CRH1 receptor RNA via the reverse transcriptase-polymerase chain reaction. In addition, the cell line expressed the neuronal marker, microtubule-associated protein-2. We verified that the CRH-LI from IVB cell lysates coeluted with CRH standard via reversed-phase high-performance liquid chromatography (HPLC). Furthermore, oxidation of the lysate converted its HPLC profile to that identical with oxidized CRH standard. In addition, IVB cells exhibited high affinity binding to CRH. Incubation of IVB cells with CRH lead to increases in cAMP levels and protein kinase A activity in a concentration-dependent manner. Incubation of IVB cells with CRH also resulted in increases in phospho-cyclic-AMP response element binding protein (CREB) immunostaining as detected by immunocytochemical analysis. Finally, CRH treatment of IVB cell lines has been linked to CREB-mediated gene expression as determined via the PathDetect CREB trans-reporting system. The characteristics of IVB cells, such as CRH and VP coexpression, GR expression and a biologically active CRH-R1-mediated signalling pathway, suggest that this neuronal cell line may serve as model of parvocellular CRH neurones.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Hypothalamic pituitary adrenal axis and immune responses to endotoxin in rats with chronic adjuvant-induced arthritis

We investigated the effect of immune challenge with LPS in both control rats and rats with adjuvant-induced arthritis (AA). Fourteen day-AA rats showed the expected activation of the hypothalamic-pituitary adrenal axis associated with increases in vasopressin mRNA and paradoxical decreases in corticotropin-releasing hormone (CRH) mRNA in parvocellular neurons of the hypothalamic paraventricular nucleus (PVN). However, following LPS there was an increase in both CRH and vasopressin mRNA in the PVN. Neither control rats nor rats with AA had measurable plasma levels of IL-6, but plasma levels of IL-1beta were 2.7-fold higher in AA animals. Following LPS injection both IL-1beta and IL-6 increased more markedly in AA than in control rats. Neither controls nor AA rats expressed IL-1beta or IL-6 mRNA in the brain. However, following LPS these were induced in the subfornical organ, choroid plexus, and median eminence of both groups of animals. The areas expressing IL-1b mRNA were larger in the AA animals and exhibited a punctate pattern throughout the brain parenchyma and PVN. These data reveal an increased peripheral and central immunological response to LPS during the chronic inflammatory process of AA, providing a mechanism through which inflammatory disease can influence the response to a novel immunological challenge.

Increased sensitivity to the locomotor-activating effects of corticotropin-releasing hormone in cholestatic rats

BACKGROUND & AIMS

Fatigue is a common complaint of patients with cholestatic liver disease. Defective central corticotropin-releasing hormone (CRH) release has been postulated as playing a role in the genesis of fatigue and decreased hypothalamic CRH expression has been identified in an animal model of cholestatic liver injury. Therefore, we hypothesized that reduced central CRH release contributes to fatigue associated with cholestatic liver disease and tested this hypothesis in cholestatic rats.

METHODS

Locomotor activity during prolonged observation, measured by using an infrared beam activity monitor, was used as a surrogate marker of fatigue or fatigability. Rats with cholestasis secondary to bile duct resection (BDR) had significantly lower basal locomotor activity compared with sham controls.

RESULTS

Intracerebroventricular injections of CRH (0.05, 0.1, 1.0 microg/rat) caused significantly greater locomotor activation in BDR animals than controls. In BDR rats, this locomotor activation was blocked by the coadministration of the nonspecific CRH-receptor antagonist astressin (25 microg/rat) and the specific CRH type 1-receptor antagonist NBI-27941 (10 microg/rat). Immunoblotting showed a dramatic increase in hypothalamic CRH type 1-receptor expression in BDR rats compared with controls, which was paralleled by a striking reduction in hypothalamic CRH levels.

CONCLUSIONS

These findings are consistent with defective central CRH neurotransmission contributing to decreased locomotor activity in cholestatic rats and have direct implications for cholestasis-associated fatigue.

The CRF peptide family and their receptors: yet more partners discovered

Abnormal signaling at corticotropin-releasing factor CRF1 and CRF2 receptors might contribute to the pathophysiology of stress-related disorders such as anxiety, depression and eating disorders, in addition to cardiac and inflammatory disorders. Recently, molecular characterization of CRF1 and CRF2 receptors and the cloning of novel ligands--urocortin, stresscopin-related peptide/urocortin II, and stresscopin/urocortin III--have revealed a far-reaching physiological importance for the family of CRF peptides. Although the physiological roles of the CRF2 receptor remain to be defined, the preclinical and clinical development of specific small-molecule antagonists of the CRF1 receptor opens new avenues for the treatment of psychiatric and neurological disorders.