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The neuropeptide corticotropin-releasing factor (CRF) acts in the nucleus accumbens of mice to increase dopamine release through coactivation of CRF receptor 1 (CRFR1) and CRFR2, but exposure to severe stress results in loss of this regulation and a switch in the reaction to CRF from appetitive to aversive. How stress deepens depression Severe stress can exacerbate major depression, characterized by a shift from engagement with the environment to withdrawal. Paul Phillips and colleagues now identify a cellular mechanism involved in this shift. Using a mouse model, they find that corticotrophin-releasing factor (CRF), a stress-response-related neuropeptide, increases dopamine release in the nucleus accumbens, but that this regulation is lost after exposure to acute stress. Animals also show opposing responses to CRF application before and after stress. The authors suggest that severe stress switches the emotional response to stressful stimuli, and that this may be central to stress-induced depressive disorders. Stressors motivate an array of adaptive responses ranging from ‘fight or flight’ to an internal urgency signal facilitating long-term goals 1 . However, traumatic or chronic uncontrollable stress promotes the onset of major depressive disorder, in which acute stressors lose their motivational properties and are perceived as insurmountable impediments 2 . Consequently, stress-induced depression is a debilitating human condition characterized by an affective shift from engagement of the environment to withdrawal 3 . An emerging neurobiological substrate of depression and associated pathology is the nucleus accumbens, a region with the capacity to mediate a diverse range of stress responses by interfacing limbic, cognitive and motor circuitry 4 . Here we report that corticotropin-releasing factor (CRF), a neuropeptide released in response to acute stressors 5 and other arousing environmental stimuli 6 , acts in the nucleus accumbens of naive mice to increase dopamine release through coactivation of the receptors CRFR1 and CRFR2. Remarkably, severe-stress exposure completely abolished this effect without recovery for at least 90 days. This loss of CRF’s capacity to regulate dopamine release in the nucleus accumbens is accompanied by a switch in the reaction to CRF from appetitive to aversive, indicating a diametric change in the emotional response to acute stressors. Thus, the current findings offer a biological substrate for the switch in affect which is central to stress-induced depressive disorders.

A long-standing paradigm posits that hypothalamic corticotropin-releasing hormone (CRH) regulates neuroendocrine functions such as adrenal glucocorticoid release, whereas extra-hypothalamic CRH has a key role in stressor-triggered behaviors. Here we report that hypothalamus-specific Crh knockout mice ( Sim1CrhKO mice, created by crossing Crh flox with Sim1 Cre mice) have absent Crh mRNA and peptide mainly in the paraventricular nucleus of the hypothalamus (PVH) but preserved Crh expression in other brain regions including amygdala and cerebral cortex. As expected, Sim1Crh KO mice exhibit adrenal atrophy as well as decreased basal, diurnal and stressor-stimulated plasma corticosterone secretion and basal plasma adrenocorticotropic hormone, but surprisingly, have a profound anxiolytic phenotype when evaluated using multiple stressors including open-field, elevated plus maze, holeboard, light–dark box and novel object recognition task. Restoring plasma corticosterone did not reverse the anxiolytic phenotype of Sim1CrhKO mice. Crh -Cre driver mice revealed that PVHCrh fibers project abundantly to cingulate cortex and the nucleus accumbens shell, and moderately to medial amygdala, locus coeruleus and solitary tract, consistent with the existence of PVHCrh-dependent behavioral pathways. Although previous, nonselective attenuation of CRH production or action, genetically in mice and pharmacologically in humans, respectively, has not produced the anticipated anxiolytic effects, our data show that targeted interference specifically with hypothalamic Crh expression results in anxiolysis. Our data identify neurons that express both Sim1 and Crh as a cellular entry point into the study of CRH-mediated, anxiety-like behaviors and their therapeutic attenuation.

Structural analysis of class B G-protein-coupled receptors (GPCRs), cell-surface proteins that respond to peptide hormones, has been restricted to the amino-terminal extracellular domain, thus providing little understanding of the membrane-spanning signal transduction domain. The corticotropin-releasing factor receptor type 1 is a class B receptor which mediates the response to stress and has been considered a drug target for depression and anxiety. Here we report the crystal structure of the transmembrane domain of the human corticotropin-releasing factor receptor type 1 in complex with the small-molecule antagonist CP-376395. The structure provides detailed insight into the architecture of class B receptors. Atomic details of the interactions of the receptor with the non-peptide ligand that binds deep within the receptor are described. This structure provides a model for all class B GPCRs and may aid in the design of new small-molecule drugs for diseases of brain and metabolism. Approximately 30% of known drugs target G protein-coupled receptors (GPCRs), but all the published structures of GPCRs to date are from the class A family of GPCRs; here the first X-ray crystal structure of a member of the class B family of GPCRs, the human corticotropin-releasing factor receptor 1, is determined. Two class B human GPCR receptors G-protein-coupled receptors (GPCRs) are membrane proteins that act as sensors for a broad range of extracellular signals, including photons, ions, small organic molecules and even entire proteins. Approximately a third of known drugs target GPCRs. Until now all the published structures of GPCRs have been from class A GPCRs. In this issue of Nature two groups independently report the crystal structures of two receptors of the B family, the second largest of four family divisions based on primary sequence and pharmacology. Hollenstein et al . solved the structure of human corticotropin-releasing factor receptor 1. This GPCR binds to corticotropin-releasing hormone, a potent mediator of endocrine, autonomic, behavioral and immune responses to stress. In all known class A GPCRs, the ligand-binding sites are close to the extracellular boundaries of the receptors; in this GPCR, the antagonist (CP-376395) binds in a hydrophobic pocket located in the cytoplasmic half of the V-shaped receptor. Siu et al . solved the X-ray crystal structure of the human glucagon receptor. This GPCR binds to the glucagon peptide, which triggers the release of glucose from the liver, making it a potential drug target for type 2 diabetes. The structure reveals a larger ligand-binding pocket than that seen in class A GPCRs.

RationaleCorticotropin-releasing factor (CRF), the apical stress-inducing hormone, exacerbates stress and addictive behaviors. TCAP-1 is a peptide that directly inhibits both CRF-mediated stress and addiction-related behaviors; however, the direct action of TCAP-1 on morphine withdrawal-associated behaviors has not previously been examined.ObjectiveTo determine whether TCAP-1 administration attenuates behavioral and physiological consequences of morphine withdrawal in mice.MethodsMice were administered via subcutaneous route TCAP-1 either before or after initial morphine exposure, after which jumping behavior was quantified to assess the effects of TCAP-1 on naloxone-precipitated morphine withdrawal. As a comparison, mice were treated with nonpeptide CRF1 receptor antagonist CP-154,526. In one experiment, plasma corticosterone (CORT) was also measured as a physiological stress indicator.ResultsPretreatment with TCAP-1 (10–250 nmol/kg) before morphine treatment significantly inhibited the development of naloxone-precipitated withdrawal. TCAP-1 (250–500 nmol/kg) treatment administered after morphine treatment attenuated the behavioral expression of naloxone-precipitated withdrawal. TCAP-1 (250 nmol/kg) treatment during morphine treatment was more effective than the optimal dosing of CP-154,526 (20 mg/kg) at suppressing the behavioral expression of naloxone-precipitated withdrawal, despite similar reduction of withdrawal-induced plasma CORT level increases.ConclusionsThese findings establish TCAP-1 as a potential therapeutic candidate for the prevention and treatment of morphine withdrawal.

RationaleThe serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous data show that stressors can inhibit 5-HT neuronal activity and release by stimulating the release of the stress neurohormone corticotropin-releasing factor (CRF) within the serotonergic dorsal raphe nucleus (DRN). The inhibitory effects of CRF on 5-HT DRN neurons are indirect, mediated by CRF-R1 receptors located on GABAergic afferents.ObjectivesWe tested the hypothesis that DRN CRF-R1 receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP). We also examined the role of this circuitry in stress-induced negative affective state with 22-kHz distress ultrasonic vocalizations (USVs), which are naturally emitted by rats in response to environmental challenges such as pain, stress, and drug withdrawal.MethodsFirst, we tested if activation of CRF-R1 receptors in the DRN with the CRF-R1-preferring agonist ovine CRF (oCRF) would reinstate morphine CPP and then if blockade of CRF-R1 receptors in the DRN with the CRF-R1 antagonist NBI 35965 would attenuate swim stress–induced reinstatement of morphine CPP. Second, we tested if intra-DRN pretreatment with NBI 35965 would attenuate foot shock stress–induced 22-kHz USVs.ResultsIntra-DRN injection of oCRF reinstated morphine CPP, while intra-DRN injection of NBI 35965 attenuated swim stress–induced reinstatement. Moreover, intra-DRN pretreatment with NBI 35965 significantly reduced 22-kHz distress calls induced by foot shock.ConclusionsThese data provide evidence that stress-induced negative affective state is mediated by DRN CRF-R1 receptors and may contribute to reinstatement of morphine CPP.

Dysfunction of the neuroendocrine HPA axis is associated with a variety of physiological and psychological pathologies. The authors show that corticotropin-releasing factor type 1 receptors within the hypothalamic paraventricular nucleus are a key central component of HPA axis regulation that prepares the organism for chronic exposure to stressful stimuli. The hypothalamic–pituitary–adrenal axis is a pivotal component of an organism's response to stressful challenges, and dysfunction of this neuroendocrine axis is associated with a variety of physiological and psychological pathologies. We found that corticotropin-releasing factor type 1 receptor within the paraventricular nucleus of the hypothalamus is an important central component of hypothalamic–pituitary–adrenal axis regulation that prepares the organism for successive exposure to stressful stimuli.

Lower urinary tract symptoms (LUTS) significantly affect patient quality of life. Treatment options for bladder outlet obstruction (BOO) due to benign prostatic hyperplasia (BPH) (a common cause of LUTS) are insufficient to relieve discomfort. As the incidence of BPH is increasing, new pharmacological targets for LUTS treatment are required. Corticotropin-releasing hormone (CRH) is a neuropeptide that controls normal micturition in rodents. Herein, we investigated the role of spinal CRH in regulating micturition in sham and BOO rats, and evaluated CRH as a therapeutic target for bladder dysfunction in BOO model Sprague–Dawley rats. Histological analysis, cystometry with intrathecal administration of CRH agonists/antagonists, western blotting, and real-time PCR assessed the role of CRH and its receptors (CRHR1 and CRHR2) in micturition in sham and BOO rats. CRH administration shortened the voiding interval, while pretreatment with antagonists against CRHR2 (but not CRHR1) suppressed CRH-induced frequent voiding. Western blotting confirmed CRHR1 expression in the dorsal root ganglia (DRG) and bladder, but not the spinal cord, of rats. Real-time PCR showed higher CRHR2 mRNA expression in the spinal cord and DRG than in the bladder in both groups. Overall, spinal CRH facilitates the micturition reflex via CRHR2, and is a promising therapeutic target for LUTS.

The interplay between corticotropin-releasing hormone (CRH) and the dopaminergic system has predominantly been studied in addiction and reward, while CRH–dopamine interactions in anxiety are scarcely understood. We describe a new population of CRH-expressing, GABAergic, long-range-projecting neurons in the extended amygdala that innervate the ventral tegmental area and alter anxiety following chronic CRH depletion. These neurons are part of a distinct CRH circuit that acts anxiolytically by positively modulating dopamine release.

The corticotropin-releasing hormone receptor 1 (CRHR1) critically controls behavioral adaptation to stress and is causally linked to emotional disorders. Using neurochemical and genetic tools, we determined that CRHR1 is expressed in forebrain glutamatergic and γ-aminobutyric acid— containing (GABAergic) neurons as well as in midbrain dopaminergic neurons. Via specific CRHR1 deletions in glutamatergic, GABAergic, dopaminergic, and serotonergic cells, we found that the lack of CRHR1 in forebrain glutamatergic circuits reduces anxiety and impairs neurotransmission in the amygdala and hippocampus. Selective deletion of CRHR1 in midbrain dopaminergic neurons increases anxiety-like behavior and reduces dopamine release in the prefrontal cortex. These results define a bidirectional model for the role of CRHR1 in anxiety and suggest that an imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disorders.

Corticotropin-releasing hormone (CRH) is a peptide associated with stress and anxiety that acts as a potent modulator throughout the nervous system. The thalamic reticular nucleus (TRN) displays high expression of the CRH receptor 1 (CRHR1), but whether CRH modulates key TRN functions, such as sleep spindle rhythmogenesis, remained unexplored. Combining polysomnographic and photometric recordings in mice, we show that CRH release in TRN during non-rapid-eye movement sleep (NREMS) oscillates with a ~50-s periodicity, anti-correlating with sleep spindle dynamics. Optogenetic manipulations of CRH release in TRN modulated NREMS fragmentation through microarousals with corresponding changes in sigma and delta power. In ex-vivo recordings, CRHR1 activation decreased the propensity of TRN neurons to fire calcium bursts. CRHR1 knockdown in parvalbumin TRN neurons prevented the effects of CRH on NREMS and TRN bursting. Thus, CRHR1 impacts NREMS by modulating thalamic excitability, providing a potential target to stabilize sleep impairments associated with stress and anxiety. Corticotropin-releasing hormone (CRH), known for activating the HPA axis during stress, also acts centrally in the brain. Here, the authors show that CRH modulates thalamic activity involved in sleep spindle generation, disrupting sleep consolidation.