Corticotropin-releasing Factor Receptor Research Articles

Abandoned prairie vole mothers show normal maternal care but altered emotionality: Potential influence of the brain corticotropin-releasing factor system

When fathers leave the family, mothers are at increased risk of developing depression and anxiety disorders. In biparental, socially monogamous prairie voles (Microtus ochrogaster), sudden bond disruption increases passive stress-coping, indicative of depressive-like behavior, and acts as chronic stressor in both males and females. However, the consequences of separation in lactating prairie vole mothers are unknown. In the present study, following 18 days of cohousing, half of the prairie vole pairs were separated by removing the male. In early lactation, maternal care was unaffected by separation, whereas anxiety-related behavior and passive stress-coping were significantly elevated in separated mothers. Separation significantly increased corticotropin-releasing factor (CRF) mRNA expression in the paraventricular nucleus of the hypothalamus under basal conditions, similar to levels of paired females after acute exposure to forced swim stress. A second cohort of lactating prairie voles was infused intracerebroventricularly with either vehicle or the CRF receptor antagonist D-Phe just prior to behavioral testing. The brief restraining during acute infusion significantly decreased arched back nursing in vehicle-treated paired and separated groups, whereas in the D-Phe-treated separated group the behavior was not impaired. Furthermore, in the latter, anxiety-related behavior and passive stress-coping were normalized to levels similar to vehicle-treated paired mothers. In conclusion, maternal investment is robust enough to withstand loss of the partner, whereas the mother’s emotionality is affected, which may be - at least partly - mediated by a CRF-dependent mechanism. This animal model has potential for mechanistic studies of behavioral and physiological consequences of partner loss in single mothers.

The effect of Nesfatin-1 on food intake in neonatal chicks: role of CRF1 /CRF2 and H1/ H3 receptors.

The present study was designed to determine the effect of central injection of Nesfatin-1 and corticotropin and histaminergic systems on food intake in neonatal meat-type chicks. In this study, 7 experiments were designed, each with 4 treatment groups. In experiment 1, four groups of chicks received the ICV injection of (A) phosphate-buffered saline (PBS), (B) Nesfatin-1 (10ng), (C) Nesfatin-1 (20ng) and (D) Nesfatin-1 (40ng). In experiment 2, (A) PBS, (B) Astressin-B (CRF1/CRF2 receptors antagonist; 30µg), (C) Nesfatin-1 (40ng) and (D) Nesfatin-1 + Astressin-B were injected. In experiments 3-6, chicken received ICV injection of the Astressin2-B (CRF2 receptor antagonist; 30µg), α-FMH (alpha fluoromethyl histidine; as inhibitor of histidine decarboxylase, 250nmol), Chlorpheniramine (histamine H1 receptors antagonist, 300nmol), Famotidine (histamine H2 receptors antagonist, 82nmol) and Thioperamide (histamine H3 receptors antagonist, 300nmol) instead of the Astressin-B. Then the cumulative food intake measured until 120min post-injection. According to the results, ICV injection of Nesfatin-1 dose dependently decreased food intake in neonatal chicks (P < 0.05). Co-injection of the Nesfatin-1 and Astressin-B (CRF1/CRF2) inhibited Nesfatin-1 induced hypophagia (P < 0.05). ICV inejction of the Nesfatin-1 + Astressin-B significantly inhibited the effect of Nesfatin-1 on food intake (P < 0.05). In addition, α-FMH and chlorpheniramine attenuated Nesfatin-1-induced hypophagia in chicks (P < 0.05); while thioperamide significantly amplified the effect of Nesfatin-1 on food intake in chicks (P < 0.05). These results suggested Nesfatin-1 has an anorectic effect in 3-hour food deprived neonatal meat-type chicks and this effect was mediated by corticotropin CRF1/CRF2 as well as histamine H1 and H3 receptors.

Similar effect of CRF1 and CRF2 receptor in the basolateral or central nuclei of the amygdala on tonic immobility behavior

Studies have used paradigms based on animal models to understand human emotional behavior because they appear to be correlated with fear- and anxiety-related defensive patterns in non-human mammals. In this context, tonic immobility (TI) behavior is an innate response associated with extreme threat situations, such as predator attack. Some reports have demonstrated the involvement of corticotropin-releasing factor (CRF) in regulation of the endocrine system, defensive behaviors and behavioral responses to stress. Particularly, a previous study showed that the activation of CRF receptors in the basolateral (BLA) or central (CeA) nuclei of the amygdala increased TI responses, whereas treatment with a non-selective CRF antagonist, alpha-helical-CRF9-41, decreased this innate fear response. However, while CRF1 receptors have pronounced effects in stress-induced anxiety, CRF2 receptors appear be involved in the expression of both stress-induced anxiety and spontaneous anxiety behavior. In this study, we investigated the effects of specific CRF receptors, CRF1 and CRF2, in the BLA and CeA on the duration of TI in guinea pigs. The results show that blockade of CRF1 and CRF2 receptors in the BLA and CeA produces a decrease in fear and/or anxiety, as suggested by a decrease in TI duration in the guinea pigs. Additionally, the specific antagonists for CRF1 and CRF2 receptors were able to prevent the increase in TI duration induced by CRF administration at the same sites. These results suggest that the modulation of fear and anxiety by the CRF system in the BLA and CeA occurs through concomitant effects on CRF1 and CRF2 receptors.

Effects on Hedonic Feeding, Energy Expenditure and Balance of the Non-opioid Peptide DYN-A2-17

The dynorphin (DYN) peptide family includes opioid and non-opioid peptides, yet the physiological role of the non-opioid DYN peptides remains poorly understood. Recent evidence shows that administering the non-opioid peptide DYN-A2-17 into the paraventricular hypothalamic nucleus (PVN) simultaneously increased short-term intake of standard rodent chow and spontaneous physical activity (SPA). The present studies aimed to expand upon the mechanisms and role of DYN-A2-17 on food intake and energy expenditure. Injection of DYN-A2-17 in PVN increased SPA, energy expenditure and wheel running in the absence of food. Repeated DYN-A2-17 injection in PVN increased short-term chow intake, but this effect habituated over time and failed to alter cumulative food intake, body weight or adiposity. Pre-treatment with a CRF receptor antagonist into PVN blocked the effects of DYN-A2-17 on food intake while injection of DYN-A2-17 in PVN increased plasma ACTH. Finally, as DYN peptides are co-released with orexin peptides, we compared the effects of DYN-A2-17 to orexin-A and the opioid peptide DYN-A1-13 on food choice and intake in PVN when palatable snacks and chow were available. DYN-A1-13 selectively increased intake of palatable snacks. DYN-A2-17 and orexin-A decreased palatable snack intake while orexin-A also increased chow intake. These findings demonstrate that the non-opioid peptide DYN-A2-17 acutely regulates physical activity, energy expenditure and food intake without long-term effects on energy balance. These data also propose different roles of opioid, non-opioid DYN and orexin peptides on food choice and intake when palatable and non-palatable food options are available.

Stress-induced suppression of neuropeptide Y-induced hunger in anorexic chicks involves corticotrophin-releasing factor signalling and the paraventricular nucleus of the hypothalamus.

The Virginia lines of chickens have been selected for low (LWS) or high (HWS) juvenile body weight and have different severities of anorexia and obesity, respectively. The LWS that are exposed to stressors at hatch are refractory to neuropeptide Y (NPY)-induced food intake and the objective of the present study was to determine the underlying mechanisms. Chicks were exposed to a stressor (-20°C for 6minutes and 22°C and delayed access to food for 24hours) after hatching and the hypothalamic nuclei, including the lateral hypothalamus (LH), paraventricular nucleus (PVN), ventromedial hypothalamus (VMH) and arcuate nucleus (ARC), were collected 5days later. In LWS but not HWS, stress exposure up-regulated corticotrophin-releasing factor (CRF), CRF receptor subtypes 1 and 2 (CRFR1 and CRFR2, respectively), melanocortin receptor 4 and urocortin 3 in the PVN, as well as CRFR2 mRNA in the VMH and ARC. In LWS, stress exposure was also associated with greater NPY and NPY receptor subtype 5 mRNA in the ARC and PVN, respectively, as well as decreased agouti-related peptide mRNA in the ARC. In HWS, stress exposure was associated with increased CRFR1 and decreased cocaine- and amphetamine-regulated transcript in the ARC and PVN, respectively. Refractoriness of the food intake response to NPY in LWS may thus result from the over-riding anorexigenic tone in the PVN associated with CRF signalling. Indeed, the orexigenic effect of NPY was restored when LWS were injected with a CRF receptor antagonist, astressin, before stress exposure. The results of the present study provide insights into the molecular basis of eating disorders and suggest that CRF signalling in the PVN may exacerbate the anorexic phenotype in the presence of environmental stressors.

Effects of adolescent alcohol exposure on stress-induced reward deficits, brain CRF, monoamines and glutamate in adult rats.

Adolescent alcohol exposure may increase depression vulnerability in adulthood by increasing the anhedonic response to stress. Male Wistar rats (postnatal days 28-53) were exposed to binge-like adolescent intermittent ethanol (AIE) or water. In adulthood, rats were exposed to social defeat, consisting of daily confrontations with an aggressive conspecific, followed by testing of brain reward function in a discrete-trial current-intensity intracranial self-stimulation procedure for 10 consecutive days. Neurochemistry and corticotropin-releasing factor (CRF) and CRF receptor 1 (CRFR1) mRNA levels were assessed in corticolimbic brain areas on day 11 of social defeat stress. Social defeat elevated reward thresholds in both AIE- and water-exposed rats indicating stress-induced anhedonia. However, AIE-exposed rats were more likely to show threshold elevations after repeated stress compared to water-exposed rats. AIE exposure decreased CRF mRNA levels in the nucleus accumbens and increased CRFR1 mRNA levels in the prefrontal cortex, while stress increased CRF mRNA levels in the central amygdala. In the caudate putamen, AIE exposure decreased dopamine turnover, while stress increased glutamate and serotonin metabolism and turnover. These results demonstrate increased risk of repeated stress-induced anhedonia after AIE exposure, an effect that may be due to alterations in brain CRF and dopamine systems. These results suggest that the increased rates of depression reported in people with a history of adolescent alcohol exposure may be related to alterations in brain reward and stress systems that may contribute to increased stress-induced anhedonia.

Repeated water avoidance stress induces visceral hypersensitivity: Role of interleukin-1, interleukin-6, and peripheral corticotropin-releasing factor.

Repeated water avoidance stress (WAS) induces visceral hypersensitivity. Additionally, it is also known to activate corticotropin-releasing factor (CRF), mast cells, and pro-inflammatory cytokines systems, but their precise roles on visceral sensation have not been determined definitely. The aim of the study was to explore this issue. Abdominal muscle contractions induced by colonic balloon distention, that is, visceromotor response (VMR) was detected electrophysiologically in conscious rats. WAS or sham stress as control for 1h daily was loaded, and the threshold of VMR was determined before and at 24h after the stress. Repeated WAS for three consecutive days reduced the threshold of VMR, but sham stress did not induce any change. Astressin, a CRF receptor antagonist (50μg/kg) intraperitoneally (ip) at 10min before each WAS session, prevented the visceral allodynia, but the antagonist (200μg/kg) ip at 30min and 15h before measurement of the threshold after completing 3-day stress session did not modify the response. Ketotifen, a mast cell stabilizer (3mg/kg), anakinra, an interleukin (IL)-1 receptor antagonist (20mg/kg) or IL-6 antibody (16.6μg/kg) ip for two times before the measurement abolished the response. Repeated WAS for three consecutive days induced visceral allodynia, which was mediated through mast cells, IL-1, and IL-6 pathways. Inhibition of peripheral CRF signaling prevented but did not reverse this response, suggesting that peripheral CRF may be an essential trigger but may not contribute to the maintenance of repeated WAS-induced visceral allodynia.

Activation of CRF/CRFR1 signaling in the basolateral nucleus of the amygdala contributes to chronic forced swim-induced depressive-like behaviors in rats

The basolateral nucleus of the amygdala (BLA) plays a key role in processing stressful events and affective disorders. Previously we have documented that exposure of chronic forced swim (FS) to rats produces a depressive-like behavior and that sensitization of BLA neurons is involved in this process. In the present study, we demonstrated that chronic FS stress (CFSS) could activate corticotropin-releasing factor (CRF)/CRF receptor type 1 (CRFR1) signaling in the BLA, and blockade of CRF/CRFR1 signaling by intra-BLA injection of NBI27914 (NBI), a selective CRFR1 antagonist, could prevent the CFSS-induced depressive-like behaviors in rats, indicating that activation of CRF/CRFR1 signaling in the BLA is required for CFSS-induced depression. Furthermore, we discovered that exposure of chronic FS to rats could reinforce long-term potentiation (LTP) at the external capsule (EC)-BLA synapse and increase BLA neuronal excitability, and that all these alterations were inhibited by CRFR1 antagonist NBI. Moreover, we found that application of exogenous CRF also may facilitate LTP at the EC-BLA synapse and sensitize BLA neuronal excitability in normal rats via the activation of CRFR1. We conclude that activation of CRF/CRFR1 signaling in the BLA contributes to chronic FS-induced depressive-like behaviors in rats through potentiating synaptic efficiency at the EC-BLA pathway and sensitizing BLA neuronal excitability.

Oxytocin induces penile erection and yawning when injected into the bed nucleus of the stria terminalis: Involvement of glutamic acid, dopamine, and nitric oxide

Oxytocin (5–100ng), but not Arg8-vasopressin (100ng), injected unilaterally into the bed nucleus of the stria terminalis (BNST) induces penile erection and yawning in a dose-dependent manner in male rats. The minimal effective dose was 20ng for penile erection and 5ng for yawning. Oxytocin responses were abolished not only by the oxytocin receptor antagonist d(CH2)5Tyr(Me)2-Orn8-vasotocin (1μg), but also by (+) MK-801 (1μg), an excitatory amino acid receptor antagonist of the N-methyl-d-aspartic acid (NMDA) subtype, SCH 23390 (1μg), a D1 receptor antagonist, but not haloperidol (1μg), a D2 receptor antagonist, and SMTC (40μg), an inhibitor of neuronal nitric oxide synthase, injected into the BNST 15min before oxytocin. Oxytocin-induced penile erection, but not yawning, was also abolished by CNQX (1μg), an excitatory amino acid receptor antagonist of the AMPA subtype. In contrast, oxytocin responses were not reduced by bicuculline (20ng), a GABAA receptor antagonist, phaclofen (5μg), a GABAB receptor antagonist, CP 376395, a CRF receptor-1 antagonist (5μg), or astressin 2B, a CRF receptor-2 antagonist (150ng). Considering the ability of NMDA (100ng) to induce penile erection and yawning when injected into the BNST and the available evidence showing possible interaction among oxytocin, glutamic acid, and dopamine in the BNST, oxytocin possibly activates glutamatergic neurotransmission in the BNST. This in turn leads to the activation of neural pathways projecting back to the paraventricular nucleus, medial preoptic area, ventral tegmental area, and/or ventral subiculum/amygdala, thereby inducing penile erection and yawning.

ANTIDEPRESSANT ACTIVITY OF THYMOQUINONE POSSIBLY THROUGH INVOLVEMENT OF CORTICOTROPIN RELEASING FACTOR

Objective: Present study aimed to evaluate the antidepressant-like activity of thymoquinone (TQ) in unstressed and stressed condition and to explore the possible underlying mechanism for this activity.Methods: TQ (5, 10, and 20 mg/kg) and fluoxetine per se were administered to the unstressed and stressed mice; immobility periods were observed using forced swim test (FST) and tail suspension test (TST). Effect of corticotropin-releasing factor (CRF)-1 antagonist on antidepressant-like activity was also evaluated. The mechanism of action was also explored by measuring plasma corticosterone levels.Results: TQ (20 mg/kg) and fluoxetine per se significantly decreased immobility periods in stressed mice indicating significant antidepressant-like activity under stress. There was no significant effect on locomotor activity of the mice on treatment with TQ and fluoxetine per se. It significantly decreased plasma corticosterone level. Antalarmin (a CRF-1 receptor antagonist) significantly attenuated TQ induced the antidepressant-like effect in both FST and TST.Conclusion: TQ significantly produced antidepressant-like activity in mice possi‑bly through inhibiting CRF activity and decreasing plasma corticosterone levels.

Peripheral Corticotropin Releasing Factor Signaling Inhibits Gastric Emptying: Mechanisms of Action and Role in Stress-related Gastric Alterations of Motor Function.

The activation of Corticotrophin Releasing-Factor (CRF) receptors in the brain is well established to coordinate the endocrine, behavioral, autonomic and visceral responses to stress. In addition, CRF receptors are also expressed within the gut where they exert biological actions and play a role in modulating stress-related gastrointestinal function. In particular, peripheral injection of CRF and related peptides, urocortin 1, 2 or 3 inhibit Gastric Emptying (GE) and alters fasted and fed pattern of gastroduodenal motility in several experimental species. Urocortin 1 interacts synergistically with cholecystokin-8 to inhibit gastric emptying in lean mice which is no longer observed in diet-induced obese rats. In in vitro circular or longitudinal muscle preparation of rat antrum, CRF and urocortin 1 and 2 suppressed spontaneous contractile activity. CRF and urocortins interact with the CRF receptor 2 (CRF-R2) to inhibit gastric motor function monitored both in vivo and in vitro. The CRF-R2 mediated inhibition of antral and corpus contractility involves a direct action on gastric myenteric neurons where CRF-R2 is expressed and may also involve the activation of serotonin acting on 5-HT3 receptor. The involvement of peripheral CRF receptors in gastric motor alterations occurring under stress conditions are stressors specific with CRF-R2 mediating the early phase of gastric ileus induced by abdominal surgery and the delayed emptying elicited by acute restraint stress. However gastric stasis elicited by endotoxin is not mediated by CRF-R2 and CRF receptors are not involved in the basal regulation of fed or fasted pattern of gastric motility.

Activation of corticotropin-releasing factor receptor 1 aggravates dextran sodium sulphate-induced colitis in mice by promoting M1 macrophage polarization

The corticotropin-releasing factor (CRF) family is involved in modulating gastrointestinal motility, sensitivity and inflammation. CRF signalling exerts an important role in inflammatory bowel disease (IBD), predominantly by activating CRF receptors. The aim of the present study was to investigate the function of CRF receptor 1 (CRF-R1) in the development of mucosal inflammation induced by dextran sulphate sodium (DSS) and the underlying mechanism. Consecutive administration of CRF or CP154526 was used to activate or block the CRF-R1 in DSS-treated mice. Colonic inflammation was evaluated by determining the Disease Activity Index (DAI) and histology score. CRF-R1 expression was proportional to the DAI, the histology score and the number of macrophages. Activation of CRF-R1 aggravated mucosal inflammation by activating nuclear factor (NF)-κB and subsequently increasing the expression levels of tumour necrosis factor (TNF)-α and interleukin (IL)-6. Inhibition of CRF-R1 decreased the expression level of CRF-R1, macrophage infiltration, NF-κB activation, and TNF-α and IL-6 expression levels, ultimately alleviating the mucosal inflammation. Thus, CRF-R1 expression was proportional to the severity of DSS-induced colitis. Activation of CRF-R1 increased the DAI and histological scores of the colons from DSS-treated mice by promoting M1 macrophage polarization, demonstrated as increased NF-κB activation, and TNF-α and IL-6 release. These results provide evidence of the pro-inflammatory role of CRF-R1 in a DSS-induced ulcerative colitis (UC) model and a possible underlying mechanism, which may facilitate the elucidation of potential treatment approaches for UC.

The Corticotropin Releasing Factor Receptor 1 in Alcohol Use Disorder: Still a Valid Drug Target?

Corticotropin releasing factor (CRF) is a neuropeptide that plays a key role in behavioral and physiological responses to stress. A large body of animal literature implicates CRF acting at type 1 CRF receptors (CRFR1) in consumption by alcohol-dependent subjects, stress-induced reinstatement of alcohol seeking, and possibly binge alcohol consumption. These studies have encouraged recent pilot studies of CRFR1 antagonists in humans with alcohol use disorder (AUD). It was a great disappointment to many in the field that these studies failed to show an effect of these compounds on stress-induced alcohol craving. Here, we examine these studies to explore potential limitations and discuss preclinical and human literature to ask whether CRFR1 is still a valid drug target to pursue for the treatment of AUD.

Functional Significance of the Signal Peptides of Corticotropin-Releasing Factor Receptors.

The corticotropin releasing factor (CRF) receptors belong to the large family of G proteincoupled receptors (GPCRs) and must be transported to the plasma membrane to function properly. The first step of the intracellular transport of GPCRs is their insertion into the membrane of the endoplasmic reticulum (ER). This process is mediated by the translocon complex of the ER membrane and the signal sequences of the receptors. Most GPCRs possess signal sequences which form part of the mature proteins, the so called signal anchor sequences (usually transmembrane domain 1). The CRF receptors possess instead signal sequences at their extreme N tails which were thought to be cleaved off following integration of the receptors into the ER membrane (signal peptides, SPs, also called cleaved signal sequences). Recent work, however, showed that not all subtypes of CRF receptors stick to this rule. Whereas the corticotropin-releasing factor receptor type 1 (CRF1R) and the corticotropin-releasing factor receptor type 2b (CRF2(b)R) possess conventional SPs which are indeed cleaved off following ER insertion, the SP of the cortictropin-releasing factor receptor type 2a (CRF2(a)R) remains uncleaved. It forms a unique N-terminal domain (pseudo signal peptide, PSP) which has surprising functions beyond the ER level. Its presence not only influences expression levels at the plasma membrane but also receptor homodimerisation and, as a consequence, G protein selectivity. In this mini-review, we summarize the progress in understanding the functions of SPs of CRF receptors. Recent data also allow deriving hypotheses for a physiological significance of these sequences.

Understanding Corticotropin Releasing Factor Receptor (CRFR) Activation Using Structural Models.

The corticotropin-releasing factor type 1 and 2 receptors (CRF1R and CRF2R) belong to the secretin-like family, also known as class B1, of G protein-coupled receptors (GPCRs). Several endogenous hormones mediate their responses through the CRF receptors, such as CRF and the urocortins. The structures for the N-terminus extracellular domain of both CRF1R and CRF2R in complex with peptidic ligands were released a few years ago and permitted the study of hormone binding to the orthosteric binding site. Until the crystal structure of the transmembrane domain of human CRF1R in its inactive state bound to an allosteric antagonist became available. Together with the crystal structures of the transmembrane domain of the glucagon receptor (GCGR), they have enabled the structural alignment between the rhodopsin and secretin-like families, which permits the direct comparison of the functional domains in both classes. In this report, we review the current structural landscape, in addition to the knowledge regarding activation of both CRF receptors and the generalization to secretin-like GPCRs in general. Thus, significant effort was put in trying to identify possible analogous microswitches in the class B1, with the hypothesis that both families could maintain a similar arrangement of their functional domain.

Structures of the First Extracellular Domain of CRF Receptors.

Corticotropin releasing factor (CRF) receptors belong to the secretin family of G proteincoupled receptors (GPCRs) and are responsible for initiating endocrine stress responses and mediating anxiety related behaviors upon activation via stressors. The main binding site for the CRF ligands is the first extracellular domain (ECD) of the receptors. Several structures of ligand-free and ligand-bound ECDs were recently determined either by nuclear magnetic resonance (NMR) spectroscopy or X-ray crystallography. They reveal how the ligands bind through both hydrophobic and hydrophilic interactions to the ECDs, which is highly dynamic in the absence of ligands. It is the purpose of this review to discuss these structures with a particular focus on ligand-receptor interaction.

Decoding Corticotropin-Releasing Factor Receptor Type 1 Crystal Structures.

The structural analysis of class B G protein-coupled receptors (GPCR), cell surface proteins responding to peptide hormones, has until recently been restricted to the extracellular domain (ECD). Cor-ticotropin-releasing factor receptor type 1 (CRF1R) is a class B receptor mediating stress response and also considered a drug target for depression and anxiety. Here we report the crystal structure of the trans-membrane domain of human CRF1R in complex with the small-molecule antagonist CP-376395 in a hex-agonal setting with translational non-crystallographic symmetry. Molecular dynamics and metadynamics simulations on this novel structure and the existing TMD structure for CRF1R provides insight as to how the small molecule ligand gains access to the induced-fit allosteric binding site with implications for the observed selectivity against CRF2R. Furthermore, molecular dynamics simulations performed using a full-length receptor model point to key interactions between the ECD and extracellular loop 3 of the TMD providing insight into the full inactive state of multidomain class B GPCRs.

Non-peptide CRF-Receptor Antagonists: Allosterism, Kinetics and Translation to Efficacy in Human Disease.

G-Protein coupled receptors (GPCRs) have been, and remain a key target of drug discovery programs for human disease. While many drugs have been developed that interact with these proteins in the simple classic manner - that is - physically blocking the cognate ligand from simply binding to its target receptor, drug discovery approaches have elucidated alternative more complex methods by which small molecules can interact with these receptors and block their function. This is most evident in the Class B GPCRs where the cognate ligands are relatively large peptides with multiple points of contact on the GPCR spanning both hydrophilic and hydrophobic domains on the same protein to elicit function. It has therefore been difficult to precisely determine not only the mechanism by which a small molecule can inhibit the function of a large peptide but also the nature of that mechanism that drives the differences in efficacy. This review will examine in detail the nature of small molecule inhibition of corticotropin-releasing factor receptors and illustrate the role that allosteric binding and kinetics play in the functional inhibition of this Class B GPCR.

Structure and Function of Small Non-Peptide CRF Antagonists and their Potential Clinical Use.

Corticotropin-releasing factor (CRF) can be considered a very important hormone or a chemical mediator. It works closely with other systems to regulate the manner through which the body may respond to stress. Thus it affects many biological processes associated with stress. Dysfunction of this system has also been correlated with various diseases such as major depression, anxiety, drug addiction and eating disorders. Rationally, this means that interfering with binding of CRF to its intended receptors can be an attractive target for drug design aiming at developing new medications for many ailments that are associated with stress such as depression, anxiety and stress-induced relapse in drug addiction. Hundreds of accounts of small molecule antagonists have appeared in the literature and the preclinical and clinical pharmacology have been reported for many of these agents. Several classes of small molecule CRF receptor antagonists which belong to the non-peptide class have been developed with many being widely used for research purposes. Currently several major pharmaceutical companies are pursuing development of small non-peptide CRF1 receptor antagonists. In this review article we explain the importance of development of non-peptide CRF antagonists and their clinical relevance with emphasis on those members that showed great promise or those that were advanced to clinical trials.

CRF1 Receptor-Dependent Increases in Irritability-Like Behavior During Abstinence from Chronic Intermittent Ethanol Vapor Exposure.

In humans, emotional and physical signs of withdrawal from ethanol are commonly seen. Many of these symptoms, including anxiety-like and depression-like behavior, have been characterized in animal models of ethanol dependence. One issue with several current behavioral tests that measure withdrawal in animal models is that they are often not repeatable within subjects over time. Additionally, irritability, one of the most common symptoms of ethanol withdrawal in humans, has not been well characterized in animal models. The corticotropin-releasing factor (CRF)-CRF1 receptor system has been suggested to be critical for the emergence of anxiety-like behavior in ethanol dependence, but the role of this system in irritability-like behavior has not been characterized. The present study compared the effects of chronic intermittent ethanol (CIE) vapor exposure-induced ethanol dependence on irritability-like behavior in rats using the bottle-brush test during acute withdrawal and protracted abstinence. Rats were trained to self-administer ethanol in operant chambers and then either left in a nondependent state or made dependent via CIE. Naïve, nondependent, and dependent rats were tested for irritability-like behavior in the bottle-brush test 8hours and 2weeks into abstinence from ethanol. Separate cohorts of dependent and nondependent rats were used to examine the effect of the specific CRF1 receptor antagonist R121919 on irritability-like behavior. Dependent rats exhibited escalated ethanol intake compared with their own pre-CIE baseline and nondependent rats. At both time points of abstinence, ethanol-dependent rats exhibited increased aggressive-like responses compared with naïve and nondependent rats. R121919 reduced irritability-like behavior in both dependent and nondependent rats, but dependent rats were more sensitive to R121919. Irritability-like behavior is a clinically relevant and reliable measure of negative emotional states that is partially mediated by activation of the CRF-CRF1 system and remains elevated during protracted abstinence in ethanol-dependent rats.