CRF2 alpha and CRF2 beta receptor mRNAs are differentially distributed between the rat central nervous system and peripheral tissues

The diverse role of corticotropin-releasing factor (CRF) and its CRF1 and CRF2 receptors under pathophysiological conditions: Insights into stress/anxiety, depression, and brain injury processes

Corticotropin-releasing factor (CRF, corticoliberin) is a neuromodulatory peptide activating the hypothalamic-pituitary-adrenal (HPA) axis, widely distributed in the central nervous system (CNS) in mammals. In addition to its neuroendocrine effects, CRF is essential in regulating many functions under physiological and pathophysiological conditions through CRF1 and CRF2 receptors (CRF1R, CRF2R). This review aims to present selected examples of the diverse and sometimes opposite effects of CRF and its receptor ligands in various pathophysiological states, including stress/anxiety, depression, and processes associated with brain injury. It seems interesting to draw particular attention to the fact that CRF and its receptor ligands exert different effects depending on the brain structures or subregions, likely stemming from the varied distribution of CRFRs in these regions and interactions with other neurotransmitters. CRFR-mediated region-specific effects might also be related to brain site-specific ligand binding and the associated activated signaling pathways. Intriguingly, different types of CRF molecules can also influence the diverse actions of CRF in the CNS.

Chronic oxytocin-driven alternative splicing of Crfr2α induces anxiety

The neuropeptide oxytocin (OXT) has generated considerable interest as potential treatment for psychiatric disorders, including anxiety and autism spectrum disorders. However, the behavioral and molecular consequences associated with chronic OXT treatment and chronic receptor (OXTR) activation have scarcely been studied, despite the potential therapeutic long-term use of intranasal OXT. Here, we reveal that chronic OXT treatment over two weeks increased anxiety-like behavior in rats, with higher sensitivity in females, contrasting the well-known anxiolytic effect of acute OXT. The increase in anxiety was transient and waned 5 days after the infusion has ended. The behavioral effects of chronic OXT were paralleled by activation of an intracellular signaling pathway, which ultimately led to alternative splicing of hypothalamic corticotropin-releasing factor receptor 2α (Crfr2α), an important modulator of anxiety. In detail, chronic OXT shifted the splicing ratio from the anxiolytic membrane-bound (mCRFR2α) form of CRFR2α towards the soluble CRFR2α (sCRFR2α) form. Experimental induction of alternative splicing mimicked the anxiogenic effects of chronic OXT, while sCRFR2α-knock down reduced anxiety-related behavior of male rats. Furthermore, chronic OXT treatment triggered the release of sCRFR2α into the cerebrospinal fluid with sCRFR2α levels positively correlating with anxiety-like behavior. In summary, we revealed that the shifted splicing ratio towards expression of the anxiogenic sCRFR2α underlies the adverse effects of chronic OXT treatment on anxiety.

Distinct populations of corticotropin-releasing factor (CRF) neurons mediate divergent yet complementary defensive behaviors in response to a threat

Defensive behaviors in response to a threat are shared across the animal kingdom. Active (fleeing, sheltering) or passive (freezing, avoiding) defensive responses are adaptive and facilitate survival. Selecting appropriate defensive strategy depends on intensity, proximity, temporal threat threshold, and past experiences. Hypothalamic corticotropin-releasing factor (CRF) is a major driver of an acute stress response, whereas extrahypothalamic CRF mediates stress-related affective behaviors. In this review, we shift the focus from a monolithic role of CRF as an anxiogenic peptide to comprehensively dissecting contributions of distinct populations of CRF neurons in mediating defensive behaviors. Direct interrogation of CRF neurons of the central amygdala (CeA) or the bed nucleus of the stria terminalis (BNST) show they drive unconditioned defensive responses, such as vigilance and avoidance of open spaces. Although both populations also contribute to learned fear responses in familiar, threatening contexts, CeA-CRF neurons are particularly attuned to the ever-changing environment. Depending on threat intensities, they facilitate discrimination of salient stimuli predicting manageable threats, and prevent their generalization. Finally, hypothalamic CRF neurons mediate initial threat assessment and active defense such as escape to shelter. Overall, these three major populations of CRF neurons demonstrate divergent, yet complementary contributions to the versatile defense system: heightened vigilance, discriminating salient threats, and active escape, representing three legs of the defense tripod. Despite the 'CRF exhaustion' in the field of affective neuroscience, understanding contributions of specific CRF neurons during adaptive defensive behaviors is needed in order to understand the implications of their dysregulation in fear- and anxiety-related psychiatric disorders. This article is part of the Special Issue on "Fear, Anxiety and PTSD".

Activation of Mast Cells by Neuropeptides: The Role of Pro-Inflammatory and Anti-Inflammatory Cytokines

Mast cells (MCs) are tissue cells that are derived from bone marrow stem cells that contribute to allergic reactions, inflammatory diseases, innate and adaptive immunity, autoimmunity, and mental disorders. MCs located near the meninges communicate with microglia through the production of mediators such as histamine and tryptase, but also through the secretion of IL-1, IL-6 and TNF, which can create pathological effects in the brain. Preformed chemical mediators of inflammation and tumor necrosis factor (TNF) are rapidly released from the granules of MCs, the only immune cells capable of storing the cytokine TNF, although it can also be produced later through mRNA. The role of MCs in nervous system diseases has been extensively studied and reported in the scientific literature; it is of great clinical interest. However, many of the published articles concern studies on animals (mainly rats or mice) and not on humans. MCs are known to interact with neuropeptides that mediate endothelial cell activation, resulting in central nervous system (CNS) inflammatory disorders. In the brain, MCs interact with neurons causing neuronal excitation with the production of neuropeptides and the release of inflammatory mediators such as cytokines and chemokines. This article explores the current understanding of MC activation by neuropeptide substance P (SP), corticotropin-releasing hormone (CRH), and neurotensin, and the role of pro-inflammatory cytokines, suggesting a therapeutic effect of the anti-inflammatory cytokines IL-37 and IL-38.

Corticotropin-Releasing Hormone: Biology and Therapeutic Opportunities

In 1981, Wylie Vale, Joachim Spiess, Catherine Rivier, and Jean Rivier reported on the characterization of a 41-amino-acid peptide from ovine hypothalamic extracts with high potency and intrinsic activity stimulating the secretion of adrenocorticotropic hormone and β-endorphin by cultured anterior pituitary cells. With its sequence known, this neuropeptide was determined to be a hormone and consequently named corticotropin-releasing hormone (CRH), although the term corticotropin-releasing factor (CRF) is still used and preferred in some circumstances. Several decades have passed since this seminal contribution that opened a new research era, expanding the understanding of the coding of stress-related processes. The characterization of CRH receptors, the availability of CRH agonists and antagonists, and advanced immunocytochemical staining techniques have provided evidence that CRH plays a role in the regulation of several biological systems. The purpose of this review is to summarize the present knowledge of this 41-amino-acid peptide.

Urocortins as biomarkers in cardiovascular disease

The urocortins (Ucns) belong to the corticotropin-releasing factor (CRF) family of peptides and have multiple effects within the central nervous and the cardiovascular systems. With growing evidence indicating significant cardioprotective properties and cardiovascular actions of these peptides, the question arises as to whether the plasma profiles of the Ucns are altered in pathologic settings. While reports have shown conflicting results and findings have not been corroborated in multiple independent cohorts, it seems likely that plasma Ucn concentrations are elevated in multiple cardiovascular conditions. The degree of increase and accurate determination of circulating values of the Ucns requires further validation.

Hypothalamic Regulation of Corticotropin-Releasing Factor under Stress and Stress Resilience

This review addresses the molecular mechanisms of corticotropin-releasing factor (CRF) regulation in the hypothalamus under stress and stress resilience. CRF in the hypothalamus plays a central role in regulating the stress response. CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary. ACTH stimulates glucocorticoid secretion from the adrenal glands. Glucocorticoids are essential for stress coping, stress resilience, and homeostasis. The activated hypothalamic-pituitary-adrenal axis is suppressed by the negative feedback from glucocorticoids. Glucocorticoid-dependent repression of cAMP-stimulated Crf promoter activity is mediated by both the negative glucocorticoid response element and the serum response element. Conversely, the inducible cAMP-early repressor can suppress the stress response via inhibition of the cAMP-dependent Crf gene, as can the suppressor of cytokine signaling-3 in the hypothalamus. CRF receptor type 1 is mainly involved in a stress response, depression, anorexia, and seizure, while CRF receptor type 2 mediates “stress coping” mechanisms such as anxiolysis in the brain. Differential effects of FK506-binding immunophilins, FKBP4 and FKBP5, contribute to the efficiency of glucocorticoids under stress resilience. Together, a variety of factors contribute to stress resilience. All these factors would have the differential roles under stress resilience.

Modified UCN2 peptide treatment improves skeletal muscle mass and function in mouse models of obesity-induced insulin resistance

BACKGROUND

Type 2 diabetes and obesity are often seen concurrently with skeletal muscle wasting, leading to further derangements in function and metabolism. Muscle wasting remains an unmet need for metabolic disease, and new approaches are warranted. The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin releasing factor receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance, glucose metabolism, and muscle mass. The aim of this study was to investigate the effects of modified UCN2 peptides as a pharmaceutical therapy to counteract the loss of skeletal muscle mass associated with obesity and casting immobilization.

METHODS

High-fat-fed mice (C57Bl/6J; 26 weeks old) and ob/ob mice (11 weeks old) were injected daily with a PEGylated (Compound A) and non-PEGylated (Compound B) modified human UCN2 at 0.3 mg/kg subcutaneously for 14 days. A separate group of chow-fed C57Bl/6J mice (12 weeks old) was subjected to hindlimb cast immobilization and, after 1 week, received daily injections with Compound A. In vivo functional tests were performed to measure protein synthesis rates and skeletal muscle function. Ex vivo functional and molecular tests were performed to measure contractile force and signal transduction of catabolic and anabolic pathways in skeletal muscle.

RESULTS

Skeletal muscles (extensor digitorum longus, soleus, and tibialis anterior) from high-fat-fed mice treated with Compound A were ~14% heavier than muscles from vehicle-treated mice. Chronic treatment with modified UCN2 peptides altered the expression of structural genes and transcription factors in skeletal muscle in high-fat diet-induced obesity including down-regulation of Trim63 and up-regulation of Nr4a2 and Igf1 (P < 0.05 vs. vehicle). Signal transduction via both catabolic and anabolic pathways was increased in tibialis anterior muscle, with increased phosphorylation of ribosomal protein S6 at Ser^235/236 , FOXO1 at Ser²⁵⁶ , and ULK1 at Ser³¹⁷ , suggesting that UCN2 treatment modulates protein synthesis and degradation pathways (P < 0.05 vs. vehicle). Acutely, a single injection of Compound A in drug-naïve mice had no effect on the rate of protein synthesis in skeletal muscle, as measured via the surface sensing of translation method, while the expression of Nr4a3 and Ppargc1a4 was increased (P < 0.05 vs. vehicle). Compound A treatment prevented the loss of force production from disuse due to casting. Compound B treatment increased time to fatigue during ex vivo contractions of fast-twitch extensor digitorum longus muscle. Compound A and B treatment increased lean mass and rates of skeletal muscle protein synthesis in ob/ob mice.

CONCLUSIONS

Modified human UCN2 is a pharmacological candidate for the prevention of the loss of skeletal muscle mass associated with obesity and immobilization.

Neuroendocrine interactions of the stress and reproductive axes

Reproduction is controlled by a sequential regulation of the hypothalamo-pituitary-gonadal (HPG) axis. The HPG axis integrates multiple inputs to maintain proper reproductive functions. It has long been demonstrated that stress alters fertility. Nonetheless, the central mechanisms of how stress interacts with the reproductive system are not fully understood. One of the major pathways that is activated during the stress response is the hypothalamo-pituitary-adrenal (HPA) axis. In this review, we discuss several aspects of the interactions between these two neuroendocrine systems to offer insights to mechanisms of how the HPA and HPG axes interact. We have also included discussions of other systems, for example GABA-producing neurons, where they are informative to the overall picture of stress effects on reproduction.

Corticotropin-Releasing Factor Family: A Stress Hormone-Receptor System's Emerging Role in Mediating Sex-Specific Signaling

No organ in the body is impervious to the effects of stress, and a coordinated response from all organs is essential to deal with stressors. A dysregulated stress response that fails to bring systems back to homeostasis leads to compromised function and ultimately a diseased state. The components of the corticotropin-releasing factor (CRF) family, an ancient and evolutionarily conserved stress hormone-receptor system, helps both initiate stress responses and bring systems back to homeostasis once the stressors are removed. The mammalian CRF family comprises of four known agonists, CRF and urocortins (UCN1–3), and two known G protein-coupled receptors (GPCRs), CRF₁ and CRF₂. Evolutionarily, precursors of CRF- and urocortin-like peptides and their receptors were involved in osmoregulation/diuretic functions, in addition to nutrient sensing. Both CRF and UCN1 peptide hormones as well as their receptors appeared after a duplication event nearly 400 million years ago. All four agonists and both CRF receptors show sex-specific changes in expression and/or function, and single nucleotide polymorphisms are associated with a plethora of human diseases. CRF receptors harbor N-terminal cleavable peptide sequences, conferring biased ligand properties. CRF receptors have the ability to heteromerize with each other as well as with other GPCRs. Taken together, CRF receptors and their agonists due to their versatile functional adaptability mediate nuanced responses and are uniquely positioned to orchestrate sex-specific signaling and function in several tissues.

Type 2β Corticotrophin Releasing Factor Receptor Forms a Heteromeric Complex With Dopamine D1 Receptor in Living Cells

Corticotrophin releasing factor (CRF) and its related peptides differentially bind to CRF receptors to modulate stress-related behaviors. CRF receptors comprise two G-protein coupled receptors (GPCR), type-1 CRF receptors (CRF1), and type-2 CRF receptors (CRF2). CRF2 encompasses three spliced variants in humans, alpha (CRF2α), beta (CRF2β), and gamma (CRF2γ), which differ in their N-terminal extracellular domains and expression patterns. Previously, we showed that CRF2α form a heteromeric protein complex with dopamine D1 receptors (D1R), leading to changes in the signaling of D1R. Based on the high sequence identity between CRF2α and CRF2β, we hypothesized that CRF2β also heteromerize with D1R. To test the hypothesis, we compared the expression and localization of both CRF2 isoforms and whether CRF2β form stable protein complexes with D1R in HEK293 and ATR75 cell lines. We observed that the immunoreactivity for CRF2β was similar to that of CRF2α in the endoplasmic compartment but significantly higher in the Golgi compartment. Immunoprecipitation analysis showed that CRF2β forms a heteromeric protein complex with D1R. Furthermore, the protein complex formed by CRF2β and D1R was stable enough to change the sub-cellular localization of CRF2β when it was co-expressed with a construct of D1R bearing a nuclear localization signal. Immunofluorescence in A7R5 cells, which endogenously express CRF2β and D1R, shows significant colocalization of CRF2β with D1R. In conclusion, our results show that CRF2β forms a stable heteromeric protein complex with D1R, a potential new therapeutic target in tissues where both receptors are co-expressed, such as the septum in the brain, and heart, kidney, and skeletal muscle in the periphery.

Modified UCN2 Peptide Acts as an Insulin Sensitizer in Skeletal Muscle of Obese Mice

The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin-releasing hormone receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance and glucose metabolism. We investigated a modified UCN2 peptide as a potential therapeutic agent for the treatment of obesity and insulin resistance, with a specific focus on skeletal muscle. High-fat-fed mice (C57BL/6J) were injected daily with a PEGylated UCN2 peptide (compound A) at 0.3 mg/kg subcutaneously for 14 days. Compound A reduced body weight, food intake, whole-body fat mass, and intramuscular triglycerides compared with vehicle-treated controls. Furthermore, whole-body glucose tolerance was improved by compound A treatment, with increased insulin-stimulated Akt phosphorylation at Ser⁴⁷³ and Thr³⁰⁸ in skeletal muscle, concomitant with increased glucose transport into extensor digitorum longus and gastrocnemius muscle. Mechanistically, this is linked to a direct effect on skeletal muscle because ex vivo exposure of soleus muscle from chow-fed lean mice to compound A increased glucose transport and insulin signaling. Moreover, exposure of GLUT4-Myc-labeled L6 myoblasts to compound A increased GLUT4 trafficking. Our results demonstrate that modified UCN2 peptides may be efficacious in the treatment of type 2 diabetes by acting as an insulin sensitizer in skeletal muscle.

Mom doesn't care: When increased brain CRF system activity leads to maternal neglect in rodents

Mothers are the primary caregivers in mammals, ensuring their offspring's survival. This strongly depends on the adequate expression of maternal behavior, which is the result of a concerted action of "pro-maternal" versus "anti-maternal" neuromodulators such as the oxytocin and corticotropin-releasing factor (CRF) systems, respectively. When essential peripartum adaptations fail, the CRF system has negative physiological, emotional and behavioral consequences for both mother and offspring often resulting in maternal neglect. Here, we provide an elaborate and unprecedented review on the implications of the CRF system in the maternal brain. Studies in rodents have advanced our understanding of the specific roles of brain regions such as the limbic bed nucleus of the stria terminalis, medial preoptic area and lateral septum even in a CRF receptor subtype-specific manner. Furthermore, we discuss potential interactions of the CRF system with other neurotransmitters like oxytocin and noradrenaline, and present valuable translational aspects of the recent research.

Hypermethylation of Proopiomelanocortin and Period 2 Genes in Blood Are Associated with Greater Subjective and Behavioral Motivation for Alcohol in Humans

BACKGROUND

Epigenetic modifications of a gene have been shown to play a role in maintaining a long-lasting change in gene expression. We hypothesize that alcohol's modulating effect on DNA methylation on certain genes in blood is evident in binge and heavy alcohol drinkers and is associated with alcohol motivation.

METHODS

Methylation-specific polymerase chain reaction (PCR) assays were used to measure changes in gene methylation of period 2 (PER2) and proopiomelanocortin (POMC) genes in peripheral blood samples collected from nonsmoking moderate, nonbinging, binge, and heavy social drinkers who participated in a 3-day behavioral alcohol motivation experiment of imagery exposure to either stress, neutral, or alcohol-related cues, 1 per day, presented on consecutive days in counterbalanced order. Following imagery exposure on each day, subjects were exposed to discrete alcoholic beer cues followed by an alcohol taste test (ATT) to assess behavioral motivation. Quantitative real-time PCR was used to measure gene expression of PER2 and POMC gene levels in blood samples across samples.

RESULTS

In the sample of moderate, binge, and heavy drinkers, we found increased methylation of the PER2 and POMC DNA, reduced expression of these genes in the blood samples of the binge and heavy drinkers relative to the moderate, nonbinge drinkers. Increased PER2 and POMC DNA methylation was also significantly predictive of both increased levels of subjective alcohol craving immediately following imagery (p < 0.0001), and with presentation of the alcohol (2 beers) (p < 0.0001) prior to the ATT, as well as with alcohol amount consumed during the ATT (p < 0.003).

CONCLUSIONS

These data establish significant association between binge or heavy levels of alcohol drinking and elevated levels of methylation and reduced levels of expression of POMC and PER2 genes. Furthermore, elevated methylation of POMC and PER2 genes is associated with greater subjective and behavioral motivation for alcohol.

Corticotropin-Releasing Hormone Family and Their Receptors in the Cardiovascular System

The identification of corticotropin-releasing hormone (CRH) has led to the discovery of a growing family of ligands and receptors. CRH receptor 1 (CRHR1) and CRHR2 are mammalian G-protein coupled receptors (GPCRs) with high affinity for CRH and the CRH family of peptides. CRHR1 is predominantly expressed in the brain and plays a vital role in the hypothalamic-pituitary-adrenal (HPA) axis stress responses by secreting adrenal corticotropic hormone (ACTH). CRHR2 is predominantly expressed in the heart, and a CRHR2-specific ligand, urocortin 2 (UCN2), shows positive cardiac chronotropic and inotropic effects through 3´,5´-cyclic adenosine monophosphate (cAMP) signaling in response to CRHR2-mediated Gαs activation in mice and humans. Central administration of the CRH family of peptides increases mean arterial pressure through CRHR1 activation, whereas peripheral administration of the peptides decreases mean arterial pressure through CRHR2 activation. These observations have led to further investigations of CRHR2 as an important and unique GPCR in the physiological and pathological functioning of the cardiovascular (CV) system. Moreover, recent clinical trials demonstrate CRHR2 as a potentially therapeutic target in the treatment of heart failure. We present recent reviews of the role of CRHRs in basic CV physiology and in the pathophysiology of CV diseases.

The CRF Family of Neuropeptides and their Receptors - Mediators of the Central Stress Response

Background:

Dysregulated stress neurocircuits, caused by genetic and/or environmental changes, underlie the development of many neuropsychiatric disorders. Corticotropin-releasing factor (CRF) is the major physiological activator of the hypothalamic-pituitary-adrenal (HPA) axis and conse-quently a primary regulator of the mammalian stress response. Together with its three family members, urocortins (UCNs) 1, 2, and 3, CRF integrates the neuroendocrine, autonomic, metabolic and behavioral responses to stress by activating its cognate receptors CRFR1 and CRFR2.

Objective:

Here we review the past and current state of the CRF/CRFR field, ranging from pharmacologi-cal studies to genetic mouse models and virus-mediated manipulations.

Results:

Although it is well established that CRF/CRFR1 signaling mediates aversive responses, includ-ing anxiety and depression-like behaviors, a number of recent studies have challenged this viewpoint by revealing anxiolytic and appetitive properties of specific CRF/CRFR1 circuits. In contrast, the UCN/CRFR2 system is less well understood and may possibly also exert divergent functions on physiol-ogy and behavior depending on the brain region, underlying circuit, and/or experienced stress conditions.

Conclusion:

A plethora of available genetic tools, including conventional and conditional mouse mutants targeting CRF system components, has greatly advanced our understanding about the endogenous mecha-nisms underlying HPA system regulation and CRF/UCN-related neuronal circuits involved in stress-related behaviors. Yet, the detailed pathways and molecular mechanisms by which the CRF/UCN-system translates negative or positive stimuli into the final, integrated biological response are not completely un-derstood. The utilization of future complementary methodologies, such as cell-type specific Cre-driver lines, viral and optogenetic tools will help to further dissect the function of genetically defined CRF/UCN neurocircuits in the context of adaptive and maladaptive stress responses.

Urocortins and their unfolding role in mammalian social behavior

The corticotropin-releasing factor (CRF) system is well known for its major role in coordinating the endocrine, autonomic and behavioral responses to stress. These functions have been shown to be mediated mainly by the binding of the CRF neuropeptide to its specific receptor CRFR1. Yet, the CRF system comprises several more neuropeptides, including the three urocortins, UCN1, UCN2 and UCN3, of which the latter two bind specifically to a distinct receptor-CRFR2. Unlike the brain-wide abundant expression of CRF and CRFR1, the brain expression of the urocortins and CRFR2 is rather restricted and seems to be focused in limbic areas associated with social behavior. Here, we will review accumulating evidence from recent studies that unfold the role of UCN2 and UCN3 in regulating mammalian social behavior, via activation of CRFR2.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Anatomical Organization of Urocortin 3-Synthesizing Neurons and Immunoreactive Terminals in the Central Nervous System of Non-Human Primates [Sapajus spp.]

Urocortin 3 (UCN3) is a neuropeptide member of the corticotropin-releasing factor (CRF) peptide family that acts as a selective endogenous ligand for the CRF, subtype 2 (CRF₂) receptor. Immunohistochemistry and in situ hybridization data from rodents revealed UCN3-containing neurons in discrete regions of the central nervous system (CNS), such as the medial preoptic nucleus, the rostral perifornical area (PFA), the medial nucleus of the amygdala and the superior paraolivary nucleus. UCN3-immunoreactive (UCN3-ir) terminals are distributed throughout regions that mostly overlap with regions of CRF₂ messenger RNA (mRNA) expression. Currently, no similar mapping exists for non-human primates. To better understand the role of this neuropeptide, we aimed to study the UCN3 distribution in the brains of New World monkeys of the Sapajus genus. To this end, we analyzed the gene and peptide sequences in these animals and performed immunohistochemistry and in situ hybridization to identify UCN3 synthesis sites and to determine the distribution of UCN3-ir terminals. The sequencing of the Sapajus spp. UCN3-coding gene revealed 88% and 65% identity to the human and rat counterparts, respectively. Additionally, using a probe generated from monkey cDNA and an antiserum raised against human UCN3, we found that labeled cells are mainly located in the hypothalamic and limbic regions. UCN3-ir axons and terminals are primarily distributed in the ventromedial hypothalamic nucleus (VMH) and the lateral septal nucleus (LS). Our results demonstrate that UCN3-producing neurons in the CNS of monkeys are phylogenetically conserved compared to those of the rodent brain, that the distribution of fibers agrees with the distribution of CRF₂ in other primates and that there is anatomical evidence for the participation of UCN3 in neuroendocrine control in primates.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Urocortins and CRF receptor type 2 variants in the male rat colon: gene expression and regulation by endotoxin and anti-inflammatory effect

Urocortins (Ucns) 1, 2, and 3 and corticotropin-releasing factor receptor 2 (CRF2) mRNA are prominently expressed in various layers of the upper gut. We tested whether Ucns and CRF2 variants are also expressed in the different layers of the rat colon, regulated by LPS (100 μg/kg ip) and play a modulatory role in the colonic immune response to LPS. Transcripts of Ucns and CRF2b, the most common isoform in the periphery, were detected in all laser microdissected layers, including myenteric neurons. LPS increased the mRNA level of Ucn 1, Ucn 2, and Ucn 3 and decreased that of CRF2b in both the colonic mucosa and submucosa + muscle (S+M) layers at 2, 6, and 9 h after injection with a return to basal at 24 h. In addition, CRF2a, another variant more prominent in the brain, and a novel truncated splice variant CRF2a-3 mRNA were detected in all segments of the large intestine. LPS reciprocally regulated the colonic expression of these CRF2 variants by decreasing both CRF2a and CRF2b, while increasing CRF2a-3 in the mucosa and S+M. The CRF2 antagonist astressin2-B further enhanced LPS-induced increase of mRNA level of interleukin (IL)-1β, TNF-α, and inducible nitric oxide synthase in S+M layers and IL-1β in the mucosa and evoked TNF-α expression in the mucosa. These data indicate that Ucns/CRF2 variants are widely expressed in all colonic layers and reciprocally regulated by LPS. CRF2 signaling dampens the CD14/TLR4-mediated acute inflammatory response to Gram-negative bacteria in the colon.

Corticotropin-Releasing Hormone Receptor 2 Gene Variants in Irritable Bowel Syndrome

Background

Corticotropin-releasing hormone (CRH) plays an important role in the pathophysiology of irritable bowel syndrome (IBS) and regulates the stress response through two CRH receptors (R1 and R2). Previously, we reported that a CRHR1 gene polymorphism (rs110402, rs242924, and rs7209436) and haplotypes were associated with IBS. However, the association between the CRHR2 gene and IBS was not investigated. We tested the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are associated with IBS pathophysiology and negative emotion in IBS patients.

Methods

A total of 142 IBS patients and 142 healthy controls participated in this study. Seven single nucleotide polymorphisms (SNPs) of the CRHR2 gene (rs4722999, rs3779250, rs2240403, rs2267710, rs2190242, rs2284217, and rs2284220) were genotyped. Subjects' psychological states were evaluated using the Perceived-Stress Scale, the State-Trait Anxiety Inventory, and the Self-Rating Depression Scale.

Results

We found that rs4722999 and rs3779250, located in intronic region, were associated with IBS in terms of genotype frequency (rs4722999: P = 0.037; rs3779250: P = 0.017) and that the distribution of the major allele was significantly different between patients and controls. There was a significant group effect (controls vs. IBS), and a CRHR2 genotype effect was observed for three psychological scores, but the interaction was not significant. We found a haplotype of four SNPs (rs4722999, rs3779250, rs2240403, and rs2267710) and two SNPs (rs2284217 and rs2284220) in strong linkage disequilibrium (D′ > 0.90). We also found that haplotypes of the CRHR2 gene were significantly different between IBS patients and controls and that they were associated with negative emotion.

Conclusion

Our findings support the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are related to IBS. In addition, we found associations between CRHR2 genotypes and haplotypes and negative emotion in IBS patients and controls. Further studies on IBS and the CRH system are warranted.

Functional Impact of Corticotropin-Releasing Factor Exposure on Tau Phosphorylation and Axon Transport

Stress exposure or increased levels of corticotropin-releasing factor (CRF) induce hippocampal tau phosphorylation (tau-P) in rodent models, a process that is dependent on the type-1 CRF receptor (CRFR1). Although these preclinical studies on stress-induced tau-P provide mechanistic insight for epidemiological work that identifies stress as a risk factor for Alzheimer’s disease (AD), the actual impact of stress-induced tau-P on neuronal function remains unclear. To determine the functional consequences of stress-induced tau-P, we developed a novel mouse neuronal cell culture system to explore the impact of acute (0.5hr) and chronic (2hr) CRF treatment on tau-P and integral cell processes such as axon transport. Consistent with in vivo reports, we found that chronic CRF treatment increased tau-P levels and caused globular accumulations of phosphorylated tau in dendritic and axonal processes. Furthermore, while both acute and chronic CRF treatment led to significant reduction in CREB activation and axon transport of brain-derived neurotrophic factor (BDNF), this was not the case with mitochondrial transport. Acute CRF treatment caused increased mitochondrial velocity and distance traveled in neurons, while chronic CRF treatment modestly decreased mitochondrial velocity and greatly increased distance traveled. These results suggest that transport of cellular energetics may take priority over growth factors during stress. Tau-P was required for these changes, as co-treatment of CRF with a GSK kinase inhibitor prevented CRF-induced tau-P and all axon transport changes. Collectively, our results provide mechanistic insight into the consequences of stress peptide-induced tau-P and provide an explanation for how chronic stress via CRF may lead to neuronal vulnerability in AD.

Evidence for the role of corticotropin-releasing factor in major depressive disorder

Major depressive disorder (MDD) is a devastating disease affecting over 300 million people worldwide, and costing an estimated 380 billion Euros in lost productivity and health care in the European Union alone. Although a wealth of research has been directed toward understanding and treating MDD, still no therapy has proved to be consistently and reliably effective in interrupting the symptoms of this disease. Recent clinical and preclinical studies, using genetic screening and transgenic rodents, respectively, suggest a major role of the CRF1 gene, and the central expression of CRF1 receptor protein in determining an individual's risk of developing MDD. This gene is widely expressed in brain tissue, and regulates an organism's immediate and long-term responses to social and environmental stressors, which are primary contributors to MDD. This review presents the current state of knowledge on CRF physiology, and how it may influence the occurrence of symptoms associated with MDD. Additionally, this review presents findings from multiple laboratories that were presented as part of a symposium on this topic at the annual 2014 meeting of the International Behavioral Neuroscience Society (IBNS). The ideas and data presented in this review demonstrate the great progress that has been made over the past few decades in our understanding of MDD, and provide a pathway forward toward developing novel treatments and detection methods for this disorder.

The centrally projecting Edinger-Westphal nucleus--I: Efferents in the rat brain

The oculomotor accessory nucleus, often referred to as the Edinger-Westphal nucleus [EW], was first identified in the 17th century. Although its most well known function is the control of pupil diameter, some controversy has arisen regarding the exact location of these preganglionic neurons. Currently, the EW is thought to consist of two different parts. The first part [termed the preganglionic EW-EWpg], which controls lens accommodation, choroidal blood flow and pupillary constriction, primarily consists of cholinergic cells that project to the ciliary ganglion. The second part [termed the centrally projecting EW-EWcp], which is involved in non-ocular functions such as feeding behavior, stress responses, addiction and pain, consists of peptidergic neurons that project to the brainstem, the spinal cord and prosencephalic regions. However, in the literature, we found few reports related to either ascending or descending projections from the EWcp that are compatible with its currently described functions. Therefore, the objective of the present study was to systematically investigate the ascending and descending projections of the EW in the rat brain. We injected the anterograde tracer biotinylated dextran amine into the EW or the retrograde tracer cholera toxin subunit B into multiple EW targets as controls. Additionally, we investigated the potential EW-mediated innervation of neuronal populations with known neurochemical signatures, such as melanin-concentrating hormone in the lateral hypothalamic area [LHA] and corticotropin-releasing factor in the central nucleus of the amygdala [CeM]. We observed anterogradely labeled fibers in the LHA, the reuniens thalamic nucleus, the oval part of the bed nucleus of the stria terminalis, the medial part of the central nucleus of the amygdala, and the zona incerta. We confirmed our EW-LHA and EW-CeM connections using retrograde tracers. We also observed moderate EW-mediated innervation of the paraventricular nucleus of the hypothalamus and the posterior hypothalamus. Our findings provide anatomical bases for previously unrecognized roles of the EW in the modulation of several physiologic systems.

Dopamine D1 and corticotrophin-releasing hormone type-2α receptors assemble into functionally interacting complexes in living cells

BACKGROUND AND PURPOSE

Dopamine and corticotrophin-releasing hormone (CRH; also known as corticotrophin-releasing factor) are key neurotransmitters in the interaction between stress and addiction. Repeated treatment with cocaine potentiates glutamatergic transmission in the rat basolateral amygdala/cortex pathway through a synergistic action of D1 -like dopamine receptors and CRH type-2α receptors (CRF2 α receptors). We hypothesized that this observed synergism could be instrumented by heteromers containing the dopamine D1 receptor and CRF2 α receptor.

EXPERIMENTAL APPROACH

D1 /CRF2 α receptor heteromerization was demonstrated in HEK293T cells using co-immunoprecipitation, BRET and FRET assays, and by using the heteromer mobilization strategy. The ability of D1 receptors to signal through calcium, when singly expressed or co-expressed with CRF2 α receptors, was evaluated by the calcium mobilization assay.

KEY RESULTS

D1 /CRF2 α receptor heteromers were observed in HEK293T cells. When singly expressed, D1 receptors were mostly located at the cell surface whereas CRF2 α receptors accumulated intracellularly. Interestingly, co-expression of both receptors promoted D1 receptor intracellular and CRF2 α receptor cell surface targeting. The heteromerization of D1 /CRF2 α receptors maintained the signalling through cAMP of both receptors but switched D1 receptor signalling properties, as the heteromeric D1 receptor was able to mobilize intracellular calcium upon stimulation with a D1 receptor agonist.

CONCLUSIONS AND IMPLICATIONS

D1 and CRF2 α receptors are capable of heterodimerization in living cells. D1 /CRF2 α receptor heteromerization might account, at least in part, for the complex physiological interactions established between dopamine and CRH in normal and pathological conditions such as addiction, representing a new potential pharmacological target.

Differential stress response in rats subjected to chronic mild stress is accompanied by changes in CRH-family gene expression at the pituitary level

The purpose of this study was to examine molecular markers of the stress response at the pituitary and peripheral levels in animals that responded differently to chronic mild stress (CMS). Rats were subjected to 2-weeks CMS and symptoms of anhedonia was measured by the consumption of 1% sucrose solution. mRNA levels of CRH-family neuropeptides (Crh-corticotropin-releasing hormone, Ucn1-urocortin 1, Ucn2-urocortin 2, Ucn3-urocortin 3), CRH receptors (Crhr1-corticotropin-releasing hormone receptor 1, Crhr2-corticotropin-releasing hormone receptor 2) and Crhbp (corticotropin-releasing factor binding protein) in the pituitaries of rats were determined with real-time PCR. Plasma levels of ACTH (adrenocorticotropin), CRH and urocortins were measured with ELISA assays. CMS procedure led to the development of anhedonia manifested by the decreased sucrose consumption (stress-reactive, SR, stress-susceptible group). Additionally, the group of animals not exhibiting any signs of anhedonia (stress non-reactive, SNR, stress-resilient group) and the group characterized by the increased sucrose consumption (stress invert-reactive group SIR) were selected. The significant increases in ACTH plasma level accompanied by the decreases in the pituitary gene expression of the Crh, Ucn2 and Ucn3 in both stress non-reactive and stress invert-reactive groups were observed. The only molecular change observed in stress-reactive group was the increase in UCN2 plasma level. The differentiated behavioral stress responses were reflected by gene expression changes in the pituitary. Alterations in the mRNA levels of Crh, Ucn2 and Ucn3 in the pituitary might confirm the paracrine and/or autocrine effects of these peptides in stress response. The opposite behavioral effect between SNR vs. SIR groups and the surprising similarity at gene expression and plasma ACTH levels in these two groups may suggest the discrepancy between molecular and behavioral stress responses; however, there results might indicate to similarity underlying different ways to cope with stress conditions.

Local corticotropin releasing hormone (CRH) signals to its receptor CRHR1 during postnatal development of the mouse olfactory bulb

Neuropeptides play important physiological functions during distinct behaviors such as arousal, learning, memory, and reproduction. However, the role of local, extrahypothalamic neuropeptide signaling in shaping synapse formation and neuronal plasticity in the brain is not well understood. Here, we characterize the spatiotemporal expression profile of the neuropeptide corticotropin-releasing hormone (CRH) and its receptor CRHR1 in the mouse OB throughout development. We found that CRH-expressing interneurons are present in the external plexiform layer, that its cognate receptor is expressed by granule cells, and show that both CRH and CRHR1 expression enriches in the postnatal period when olfaction becomes important towards olfactory-related behaviors. Further, we provide electrophysiological evidence that CRHR1-expressing granule cells functionally respond to CRH ligand, and that the physiological circuitry of CRHR1 knockout mice is abnormal, leading to impaired olfactory behaviors. Together, these data suggest a physiologically relevant role for local CRH signaling towards shaping the neuronal circuitry within the mouse OB.

Alcohol-preferring rats show decreased corticotropin-releasing hormone-2 receptor expression and differences in HPA activation compared to alcohol-nonpreferring rats

BACKGROUND

Corticotropin-releasing hormone (CRH) and urocortins (UCNs) bind to corticotropin-releasing hormone type 2 receptor (CRF2 receptor ), a Gs protein-coupled receptor that plays an important role in modulation of anxiety and stress responses. The Crhr2 gene maps to a quantitative trait locus (QTL) for alcohol preference on chromosome 4 previously identified in inbred alcohol-preferring (iP) and-nonpreferring (iNP) F2 rats.

METHODS

Real-time polymerase chain reaction was utilized to screen for differences in Crhr2 mRNA expression in the central nervous system (CNS) of male iP and iNP rats. DNA sequence analysis was then performed to screen for polymorphism in Crhr2 in order to identify genetic variation, and luciferase reporter assays were then applied to test their functional significance. Next, binding assays were used to determine whether this polymorphism affected CRF2 receptor binding affinity as well as CRF2 receptor density in the CNS. Finally, social interaction and corticosterone levels were measured in the P and NP rats before and after 30-minute restraint stress.

RESULTS

Crhr2 mRNA expression studies found lower levels of Crhr2 mRNA in iP rats compared to iNP rats. In addition, DNA sequencing identified polymorphisms in the promoter region, coding region, and 3'-untranslated region between the iP and iNP rats. A 7 bp insertion in the Crhr2 promoter of iP rats altered expression in vitro as measured by reporter assays, and we found that CRF2 receptor density was lower in the amygdala of iP as compared to iNP rats. Male P rats displayed decreased social interaction and significantly higher corticosterone levels directly following 30-minute restraint when compared to male NP rats.

CONCLUSIONS

This study identified Crhr2 as a candidate gene of interest underlying the chromosome 4 QTL for alcohol consumption that was previously identified in the P and NP model. Crhr2 promoter polymorphism is associated with reduced mRNA expression in certain brain regions, particularly the amygdala, and lowered the density of CRF2 receptor in the amygdala of iP compared to iNP rats. Together, these differences between the animals may contribute to the drinking disparity as well as the anxiety differences of the P and NP rats.

Corticotropin-releasing factor facilitates epileptiform activity in the entorhinal cortex: roles of CRF2 receptors and PKA pathway

Whereas corticotropin-releasing factor (CRF) has been considered as the most potent epileptogenic neuropeptide in the brain, its action site and underlying mechanisms in epilepsy have not been determined. Here, we found that the entorhinal cortex (EC) expresses high level of CRF and CRF2 receptors without expression of CRF1 receptors. Bath application of CRF concentration-dependently increased the frequency of picrotoxin (PTX)-induced epileptiform activity recorded from layer III of the EC in entorhinal slices although CRF alone did not elicit epileptiform activity. CRF facilitated the induction of epileptiform activity in the presence of subthreshold concentration of PTX which normally would not elicit epileptiform activity. Bath application of the inhibitor for CRF-binding proteins, CRF6-33, also increased the frequency of PTX-induced epileptiform activity suggesting that endogenously released CRF is involved in epileptogenesis. CRF-induced facilitation of epileptiform activity was mediated via CRF2 receptors because pharmacological antagonism and knockout of CRF2 receptors blocked the facilitatory effects of CRF on epileptiform activity. Application of the adenylyl cyclase (AC) inhibitors blocked CRF-induced facilitation of epileptiform activity and elevation of intracellular cyclic AMP (cAMP) level by application of the AC activators or phosphodiesterase inhibitor increased the frequency of PTX-induced epileptiform activity, demonstrating that CRF-induced increases in epileptiform activity are mediated by an increase in intracellular cAMP. However, application of selective protein kinase A (PKA) inhibitors reduced, not completely blocked CRF-induced enhancement of epileptiform activity suggesting that PKA is only partially required. Our results provide a novel cellular and molecular mechanism whereby CRF modulates epilepsy.

Control of stress-induced persistent anxiety by an extra-amygdala septohypothalamic circuit

The extended amygdala has dominated research on the neural circuitry of fear and anxiety, but the septohippocampal axis also plays an important role. The lateral septum (LS) is thought to suppress fear and anxiety through its outputs to the hypothalamus. However, this structure has not yet been dissected using modern tools. The type 2 CRF receptor (Crfr2) marks a subset of LS neurons whose functional connectivity we have investigated using optogenetics. Crfr2(+) cells include GABAergic projection neurons that connect with the anterior hypothalamus. Surprisingly, we find that these LS outputs enhance stress-induced behavioral measures of anxiety. Furthermore, transient activation of Crfr2(+) neurons promotes, while inhibition suppresses, persistent anxious behaviors. LS Crfr2(+) outputs also positively regulate circulating corticosteroid levels. These data identify a subset of LS projection neurons that promote, rather than suppress, stress-induced behavioral and endocrinological dimensions of persistent anxiety states and provide a cellular point of entry to LS circuitry.

Hypothalamic neurohormones and immune responses

The aim of this review is to provide a comprehensive examination of the current literature describing the neural-immune interactions, with emphasis on the most recent findings of the effects of neurohormones on immune system. Particularly, the role of hypothalamic hormones such as Thyrotropin-releasing hormone (TRH), Corticotropin-releasing hormone (CRH) and Gonadotropin-releasing hormone (GnRH). In the past few years, interest has been raised in extrapituitary actions of these neurohormones due to their receptors have been found in many non-pituitary tissues. Also, the receptors are present in immune cells, suggesting an autocrine or paracrine role within the immune system. In general, these neurohormones have been reported to exert immunomodulatory effects on cell proliferation, immune mediators release and cell function. The implications of these findings in understanding the network of hypothalamic neuropeptides and immune system are discussed.

Intracerebroventricular injection of stresscopin-related peptide enhances cardiovascular function in conscious rats

Stresscopin-related peptide (SRP), which is a member of the corticotropin-releasing factor (CRF) family, is a high-affinity ligand for the type 2 corticotropin-releasing factor receptor (CRF-R2) and is involved in stress-coping responses. Central treatment with SRP suppresses food intake, delays gastric emptying and decreases heat-induced edema, but the effects of central administration of SRP on the cardiovascular system are unclear. Here we examined the effects of intracerebroventricular (i.c.v.) administration of SRP on cardiovascular function, and compared the cardiovascular effects of SRP and stresscopin (SCP). Our results showed that i.c.v. administration of SRP (0.5nmol) increased mean arterial blood pressure (MABP) and heart rate (HR), but failed to increase plasma norepinephrine and epinephrine levels. Compared with an equivalent dose of SCP, the area under the curve (AUC) values for the changes in MABP and HR were significantly smaller with SRP, indicating that the cardiovascular effects of SRP were weaker than those mediated by SCP. Pre-treatment with a selective CRF-R2 antagonist, antisauvagine-30 (4nmol, i.c.v.) abolished the SRP and SCP induced changes in MABP and HR. These results indicate that central administration of SRP induces a weaker enhancement of cardiovascular function through CRF-R2 than that induced by SCP and that these effects are mediated without increasing plasma norepinephrine and epinephrine levels.

Cellular adaptations of dorsal raphe serotonin neurons associated with the development of active coping in response to social stress

BACKGROUND

Social stress is a risk factor for affective disorders for certain vulnerable individuals. Stress and depression are linked in part through regulation of the dorsal raphe (DR)-serotonin (5-HT) system by the stress-related neuropeptide, corticotropin-releasing factor (CRF). We used a rat social stress model that shows individual differences in coping strategies to determine whether differences in CRF-5-HT interactions underlie individual differences in the vulnerability to social stress.

METHODS

Rats were exposed to the resident-intruder model of social stress for 5 days. In vivo single-unit recordings assessed DR-5-HT neuronal responses to CRF and immunoelectron microscopy assessed CRF1 and CRF2 cellular localization 24 hours after the last stress.

RESULTS

Rats responded to social stress passively, assuming defeat with short latencies (48%), or actively, with proactive behaviors and longer defeat latencies (LL, 52%). Whereas CRF (30 ng, intra-DR) inhibited 5-HT neuronal activity of control and SL rats, it activated 5-HT neurons of LL rats, an effect that was CRF2-mediated. Consistent with this, social stress promoted CRF1 internalization together with CRF2 recruitment to the plasma membrane of DR neurons selectively in LL rats.

CONCLUSIONS

These data suggest that a proactive coping strategy toward social stress is associated with a redistribution of CRF1 and CRF2 in DR-5-HT neurons that primes the system to be activated by subsequent stress. The lack of this adaptation in passive coping rats may contribute to their depressive-like phenotype. These studies provide a cellular mechanism for individual differences in stress responses and consequences.

Food-intake regulation during stress by the hypothalamo-pituitary-adrenal axis

The prevalence of obesity is increasing worldwide with serious consequences such as diabetes mellitus type 2 and cardiovascular diseases. Emotional stress is considered to be one of the main reasons of obesity development in humans. However, there are some contradictory results, which should be addressed. First of all stress induces anorexia, but not overeating in laboratory animals. Glucocorticoids, the effector molecules of the hypothalamo-pituitary-adrenocortical (HPA) axis stimulate and stress inhibits food intake. It is also not clear if stress is diabetogenic or an antidiabetogenic factor. The review will discusses these issues and the involvement of the whole HPA axis and its separate molecules (glucocorticoids, adrenocorticotropin, corticotropin-releasing hormone) in food intake regulation under stress.

Is it really a matter of simple dualism? Corticotropin-releasing factor receptors in body and mental health

Physiological responses to stress coordinated by the hypothalamo-pituitary-adrenal axis are concerned with maintaining homeostasis in the presence of real or perceived challenges. Regulators of this axis are corticotrophin releasing factor (CRF) and CRF related neuropeptides, including urocortins 1, 2, and 3. They mediate their actions by binding to CRF receptors (CRFR) 1 and 2, which are located in several stress-related brain regions. The prevailing theory has been that the initiation of and the recovery from an elicited stress response is coordinated by two elements, viz. the (mainly) opposing, but well balanced actions of CRFR1 and CRFR2. Such a dualistic view suggests that CRF/CRFR1 controls the initiation of, and urocortins/CRFR2 mediate the recovery from stress to maintain body and mental health. Consequently, failed adaptation to stress can lead to neuropathology, including anxiety and depression. Recent literature, however, challenges such dualistic and complementary actions of CRFR1 and CRFR2, and suggests that stress recruits CRF system components in a brain area and neuron specific manner to promote adaptation as conditions dictate.

Melanocortin-4 receptor in the medial amygdala regulates emotional stress-induced anxiety-like behaviour, anorexia and corticosterone secretion

The central melanocortin system has been implicated in emotional stress-induced anxiety, anorexia and activation of the hypothalamo-pituitary-adrenal (HPA) axis. However, the underlying neural substrates have not been identified. The medial amygdala (MeA) is highly sensitive to emotional stress and expresses high levels of the melanocortin-4 receptor (MC4R). This study investigated the effects of activation and blockade of MC4R in the MeA on anxiety-like behaviour, food intake and corticosterone secretion. We demonstrate that MC4R-expressing neurons in the MeA were activated by acute restraint stress, as indicated by induction of c-fos mRNA expression. Infusion of a selective MC4R agonist into the MeA elicited anxiogenic-like effects in the elevated plus-maze test and decreased food intake. In contrast, local MeA infusion of SHU 9119, a MC4R antagonist, blocked restraint stress-induced anxiogenic and anorectic effects. Moreover, plasma corticosterone levels were increased by intra-MeA infusion of the MC4R agonist under non-stressed conditions and restraint stress-induced elevation of plasma corticosterone levels was attenuated by pretreatment with SHU 9119 in the MeA. Thus, stimulating MC4R in the MeA induces stress-like anxiogenic and anorectic effects as well as activation of the HPA axis, whereas antagonizing MC4R in this region blocks such effects induced by restraint stress. Together, our results implicate MC4R signalling in the MeA in behavioural and endocrine responses to stress.

Effects of stresscopin on rat hypothalamic paraventricular nucleus neurons in vitro

The effects of stresscopin (SCP) on rat paraventricular nucleus (PVN) neurons were examined using whole-cell patch-clamp recordings and single-cell reverse-transcription multiplex polymerase chain reaction (SC-RT-mPCR) techniques. Under current-clamp conditions, bath application of SCP (100 nM) induced inhibition in 35.2% (37/105) of putative magnocellular neurons and 24.7% (20/81) of putative parvocellular neurons, and excitation in 5.7% (6/105) of putative magnocellular neurons and 18.5% (15/81) of putative parvocellular neurons. SCP-induced inhibition persisted in the presence of a mixture of TTX, a voltage-gated Na+ channel blocker, CNQX, an AMPA/kainate receptor antagonist and bicuculline, a GABA_A receptor antagonist, whereas SCP-induced excitation of PVN neurons was reversed by the mixture. The SCP-induced inhibition of PVN neurons was abolished by bath application of antisauvagine-30, a selective CRF receptor 2 (CRF-R2) antagonist. Under voltage-clamp conditions, SCP evoked outward currents at the holding potential (−60 mV), which reversed near the potassium equilibrium potential. The SCP-evoked membrane currents were completely blocked by bath application of tertiapin-Q, a selective blocker of G protein-activated inwardly rectifying potassium (GIRK) channels. SC-RT-mPCR analysis indicated that all the SCP-sensitive PVN neurons (57 SCP-inhibited neurons, 21 SCP-excited neurons) expressed CRF-R1 and CRF-R2 mRNAs. Among SCP-hyperpolarized PVN neurons, oxytocin (OT) mRNA was detected in 91.8% of putative magnocellular neurons and 45.0% of putative parvocellular neurons. OT mRNA was also detected in 26.6% of SCP-depolarized parvocellular neurons, but not in SCP-depolarized magnocellular neurons. These results indicate that SCP inhibits a subpopulation of PVN neurons, especially OTergic magnocellular neurons, by enhancing the activity of GIRK channels via CRF-R2.

Regulation of gonadotropins by corticotropin-releasing factor and urocortin

While stress activates the hypothalamic-pituitary-adrenal (HPA) axis, it suppresses the hypothalamic-pituitary-gonadal (HPG) axis. Corticotropin-releasing factor (CRF) is a major regulatory peptide in the HPA axis during stress. Urocortin 1 (Ucn1), a member of the CRF family of peptides, has a variety of physiological functions and both CRF and Ucn1 contribute to the stress response via G protein-coupled seven transmembrane receptors. Ucn2 and Ucn3, which belong to a separate paralogous lineage from CRF, are highly selective for the CRF type 2 receptor (CRF(2) receptor). The HPA and HPG axes interact with each other, and gonadal function and reproduction are suppressed in response to various stressors. In this review, we focus on the regulation of gonadotropins by CRF and Ucn2 in pituitary gonadotrophs and of gonadotropin-releasing hormone (GnRH) via CRF receptors in the hypothalamus. In corticotrophs, stress-induced increases in CRF stimulate Ucn2 production, which leads to the inhibition of gonadotropin secretion via the CRF(2) receptor in the pituitary. GnRH in the hypothalamus is regulated by a variety of stress conditions. CRF is also involved in the suppression of the HPG axis, especially the GnRH pulse generator, via CRF receptors in the hypothalamus. Thus, complicated regulation of GnRH in the hypothalamus and gonadotropins in the pituitary via CRF receptors contributes to stress responses and adaptation of gonadal functions.

Antiinflammatory treatment ameliorates HPA stress axis dysfunction in a mouse model of stress sensitivity

Dysregulated stress responsivity is a hallmark of neuropsychiatric disease. The regulation of stress activation and recovery involves tight coordination between neuronal and glial networks. At a certain threshold of sensitivity, stress exposure can evoke a neuroimmune response. Astrocytes are potential mediators of these effects because they are able to respond to neuroimmune effector molecules and regulate neuronal activity. Mice deficient in corticotropin-releasing factor receptor-2 display increased stress sensitivity and are therefore a useful model in which to examine the intersection of neuroimmune activation and stress pathway dysregulation. We hypothesized that a component of elevated stress reactivity may involve an engagement of neuroimmune effectors, including astrocytes. Therefore, we hypothesized that this phenotype may be rescued by concomitant nonsteroidal antiinflammatory drug (NSAID) treatment. To examine this, mice exposed to chronic stress were treated with NSAID in their drinking water, and changes in hypothalamic-pituitary-adrenal stress axis function were examined. As a correlate of altered astrocyte function, levels of glial fibrillary acidic protein were measured. Supportive of our hypothesis, NSAID treatment rescued the hypothalamic-pituitary-adrenal stress axis dysfunction in stress-sensitive corticotropin-releasing factor receptor-2(-/-) mice and also reversed the stress-induced increase in glial fibrillary acidic protein in stress-regulating brain regions including the paraventricular nucleus of the hypothalamus, ventral hippocampus, and prefrontal cortex. These findings support the local involvement of astrocytes in the exacerbation of stress pathway dysregulation. The specificity of these effects in a stress-sensitive genotype highlights the importance of utilizing a model of stress dysregulation in the examination of factors that may translate to neuropsychiatric disease.

Regulation of corticotropin releasing hormone receptor type 1 messenger RNA level in Y-79 retinoblastoma cells: potential implications for human stress response and immune/inflammatory reaction

We report the regulation of type 1 receptor mRNA in Y-79 human retinoblastoma cells, grown in the absence or presence of pharmacological levels of phorbol esters, forskolin, glucocorticoids and their combinations. To control for inducibility and for assessing the sensitivity of the Y-79 system to glucocorticoids, corticotropin releasing hormone mRNA levels were measured in parallel. All treatments stimulated corticotropin releasing hormone receptor type 1 gene expression relative to baseline. A weak suppression of corticotropin releasing hormone mRNA level was observed during dexamethasone treatment. The cell line expressed ten-fold excess of receptor to ligand mRNA under basal conditions. The findings predict the presence of functional phorbol ester, cyclic AMP and glucocorticoid response elements in the promoter region of corticotropin releasing hormone receptor type 1 gene and support a potential role for its product during chronic stress and immune/inflammatory reaction.

On the role of corticotropin-releasing hormone receptors in anxiety and depression

On the basis of extensive basic and clinical studies, corticotropin-releasing hormone (CRH) and its related family members are considered to play a pivotal role in stress-related disorders, such as anxiety and depression. CRH is regarded as the principal mediator in the brain of the stress response, as it mediates neuroendocrine, autonomic, and behavioral responses to stressful challenges. Recently, this neuropeptide family has expanded due to the discovery of two new members, urocortin II (also termed stresscopin-related peptide) and urocortin III (also termed stresscopin), which are selective agonists for the CRH receptor type 2. They show a discrete neuroanatomical localization and are involved in stress-coping responses, such as anxiolysis. Here, on the basis of recent developments, we suggest that CRH, the urocortins, and their receptors form a complex system in the brain, which is recruited during both the acute and the recovery phases of the stress response.

Stress and addiction: contribution of the corticotropin releasing factor (CRF) system in neuroplasticity

Corticotropin releasing factor (CRF) has been shown to induce various behavioral changes related to adaptation to stress. Dysregulation of the CRF system at any point can lead to a variety of psychiatric disorders, including substance use disorders (SUDs). CRF has been associated with stress-induced drug reinforcement. Extensive literature has identified CRF to play an important role in the molecular mechanisms that lead to an increase in susceptibility that precipitates relapse to SUDs. The CRF system has a heterogeneous role in SUDs. It enhances the acute effects of drugs of abuse and is also responsible for the potentiation of drug-induced neuroplasticity evoked during the withdrawal period. We present in this review the brain regions and circuitries where CRF is expressed and may participate in stress-induced drug abuse. Finally, we attempt to evaluate the role of modulating the CRF system as a possible therapeutic strategy for treating the dysregulation of emotional behaviors that result from the acute positive reinforcement of substances of abuse as well as the negative reinforcement produced by withdrawal.

Urocortin 3 elevates cytosolic calcium in nucleus ambiguus neurons

Urocortin 3 (also known as stresscopin) is an endogenous ligand for the corticotropin-releasing factor receptor 2 (CRF(2)). Despite predominant G(s) coupling of CRF(2), promiscuous coupling with other G proteins has been also associated with the activation of this receptor. As urocortin 3 has been involved in central cardiovascular regulation at hypothalamic and medullary sites, we examined its cellular effects on cardiac vagal neurons of nucleus ambiguus, a key area for the autonomic control of heart rate. Urocortin 3 (1 nM-1000 nM) induced a concentration-dependent increase in cytosolic Ca(2+) concentration that was blocked by the CRF(2) antagonist K41498. In the case of two consecutive treatments with urocortin 3, the second urocortin 3-induced Ca(2+) response was reduced, indicating receptor desensitization. The effect of urocortin 3 was abolished by pre-treatment with pertussis toxin and by inhibition of phospolipase C with U-73122. Urocortin 3 activated Ca(2+) influx via voltage-gated P/Q-type channels as well as Ca(2+) release from endoplasmic reticulum. Urocortin 3 promoted Ca(2+) release via inositol 1,4,5 trisphosphate receptors, but not ryanodine receptors. Our results indicate a novel Ca(2+) -mobilizing effect of urocortin 3 in vagal pre-ganglionic neurons of nucleus ambiguus, providing a cellular mechanism for a previously reported role for this peptide in parasympathetic cardiac regulation.