Corticotrophin-releasing factor receptors: from molecular biology to drug design

Molecular and cellular sex differences at the intersection of stress and arousal

Elucidating the mechanisms underlying sex biases in the prevalence and severity of diseases can advance our understanding of their pathophysiological basis and serve as a guide for developing treatments. A well-established sex difference in psychiatry is the higher incidence of mood and anxiety disorders in females. These disorders share stress as a potential etiological contributor and hyperarousal as a core symptom, suggesting that the distinction between sexes lies at the intersection of stress and arousal systems. This review focuses on the link between the stress axis and the brain norepinephrine arousal system as a key point at which sex differences occur and are translated to differences in the expression of mood disorders. Evidence for a circuit designed to relay emotion-related information via the limbic corticotropin-releasing factor (CRF) system to the locus coeruleus (LC)-norepinephrine arousal system is reviewed. This is followed by recent novel findings of sex differences in CRF receptor signaling and trafficking that would result in an enhanced arousal response and a compromised ability to adapt to chronic stress in females. Finally, we discuss the evidence for sex differences in LC dendritic structure that allow for an increased receipt and processing of limbic information in females compared to males. Together these complementary sets of data suggest that in females, the LC arousal system is poised to process more limbic information and to respond to some of this information in an enhanced manner compared to males. The clinical and therapeutic considerations arising from this perspective are discussed. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Discovery of N-(1-ethylpropyl)-[3-methoxy-5-(2-methoxy-4-trifluoromethoxyphenyl)-6-methyl-pyrazin-2-yl]amine 59 (NGD 98-2): an orally active corticotropin releasing factor-1 (CRF-1) receptor antagonist

The design, synthesis, and structure-activity relationships of a novel series of pyrazines, acting as corticotropin releasing factor-1 (CRF-1) receptor antagonists, are described. Synthetic methodologies were developed to prepare a number of substituted pyrazine cores utilizing regioselective halogenation and chemoselective derivatization. Noteworthy, an efficient 5-step synthesis was developed for the lead compound 59 (NGD 98-2), which required no chromatography. Compound 59 was characterized as an orally bioavailable, brain penetrant, and highly selective CRF-1 receptor antagonist. Occupancy of rat brain CRF-1 receptors was quantified using ex vivo receptor occupancy assays, using both brain tissue homogenates as well as brain slices receptor autoradiography. Behaviorally, oral administration of 59 significantly antagonized CRF-induced locomotor activity at doses as low as 10 mg/kg and dose-dependently reduced the restraint stress-induced ACTH increases.

Neonatal maternal separation in the rat impacts on the stress responsivity of central corticotropin-releasing factor receptors in adulthood

RATIONALE

Adverse events during early developmental stages can induce persistent changes in central stress circuits, leading to increased stress sensitivity in adulthood, as is apparent in the maternally separated (MS) rat model. It is widely accepted that the stress peptide corticotropin-releasing factor (CRF) by binding to CRF1 and 2 receptors (CRFR1 and CRFR2) is key to these phenotypic changes.

OBJECTIVES

These studies aim to investigate the effects of maternal separation on central expression of CRFR1 and CRFR2 under basal conditions and following an acute psychological stressor in adulthood.

METHODS

Western blotting techniques were employed to examine changes in receptor expression in the hypothalamus, pre-frontal and frontal cortices, amygdala and hippocampus of MS rats as compared to controls. Additionally, the effects of an acute psychological stressor (open field exposure) on these changes were assessed.

RESULTS

Under basal conditions, CRFR1 was elevated in the hypothalamus of MS rats. Exposure to an acute stress had limited effects in non-separated animals but induced significant changes in CRFR1 in the hypothalamus, pre-frontal cortex and hippocampus of MS rats. Additionally, stress-induced increases in CRFR2 were observed in the amygdala of MS rats.

CONCLUSIONS

These data demonstrate the discrete and significant alterations in how the brain CRF system responds to acute stress following maternal separation. These studies illustrate that early life perturbations induce persistent changes in central CRF receptor expression and increased sensitivity to stress, which may contribute to the stress-related behavioural changes observed in these animals.

The corticotropin-releasing factor 1 receptor antagonist, SSR125543, and the vasopressin 1b receptor antagonist, SSR149415, prevent stress-induced cognitive impairment in mice

The vasopressin 1b receptor antagonist, SSR149415, and the corticotropin-releasing factor 1 receptor antagonist, SSR125543, are orally active non-peptidic compounds with anxiolytic- and antidepressant-like activities in animals. In the present study, their effects on stress-induced deficit in cognitive performances as assessed in a modified object recognition test were investigated in mice. The object recognition task measures the ability of a mouse to remember an object it has previously explored in a learning trial. During this acquisition session, the mouse was stressed by the presence of a pair of rats under the grid floor of the apparatus. One hour later, it was placed again in the environment with the known and a novel object, but in the absence of the rats. While non-exposed mice spent more time exploring the new object, mice that had been exposed to the rats during acquisition failed to discriminate between the known and the new object during retrieval. This cognitive impairment in stressed mice was prevented by the administration of SSR149415 (10 mg/kg, ip), SSR125543 (10 mg/kg, ip) and the selective serotonin reuptake inhibitor, fluoxetine (10 mg/kg, ip). Under similar conditions, the cognitive enhancer donepezil (1 mg/kg, ip) failed to reverse object recognition deficit. These results indicate that the effects of SSR149415 and SSR125543 in the modified object recognition test, in stressed mice, involve the ability of mice to cope with stress rather than an effect on cognition per se. Together, these data suggest that SSR149415 and SSR125543 may be of interest to reduce the cognitive deficits following exposure to stress-related events, such as acute stress disorder.

Diazepam decreases leukocyte-endothelium interactions in situ

High doses of diazepam reduce the inflammatory paw edema in rats. This effect was attributed to an action of diazepam on the Translocator Protein (TSPO). We evaluated the effects of diazepam (10 mg/kg, intraperitoneally) on leukocyte rolling and migration. In carrageenan-induced acute inflammation, diazepam decreased the interaction of leukocytes with endothelial cells (rolling) and the number of leukocytes in the mesentery (migration). RU486 (antagonist of glucocorticoid receptors) reduced the effects of diazepam on leukocyte rolling and migration, suggesting a participation of endogenous corticosteroids. We also showed that the effects of diazepam on leukocyte-endothelium interactions are mediated by nitric oxide (NO), since prior treatment with l-arginine (precursor of NO) partially precludes the inhibitory effects of diazepam; conversely, pretreatment with L-NAME (false substrate of the NO synthase) somewhat potentiates the effects of diazepam. The pathways that underlie the effects of diazepam remain to be further elucidated, but we believe that both local and systemic mechanisms may overlap to explain the influence of diazepam on leukocyte-endothelium interactions.

Corticotropin-releasing factor regulates TLR4 expression in the colon and protects mice from colitis

BACKGROUND & AIMS

Defects in the colonic innate immune response have been associated with inflammatory bowel disease (IBD). Corticotropin-releasing hormone (CRH, or corticotropin-releasing factor [CRF]) is a neuropeptide that mediates the stress response in humans, is an immunomodulatory factor with proinflammatory effects, and regulates transcription of Toll-like receptors (TLR)-2 and TLR4. We investigated the role of CRF in an innate immunity-dependent mouse model of IBD.

METHODS

Crh(-/-) and wild-type (Crh(+/+)) mice, which are glucocorticoid insufficient, were given dextran sodium sulfate in their drinking water to induce colitis; in some experiments, mice were also given glucocorticoids. Phenotypes of mice were compared; tissues were analyzed by histology and for expression of immune mediators.

RESULTS

Crh(-/-) mice had more colonic inflammation than Crh(+/+) mice, characterized by reduced numbers of crypts and severe epithelial damage and ulcerations. Colonic tissue levels of the proinflammatory factors interleukin-12 and prostaglandin E(2) were increased in the Crh(-/-) mice. Colons of Crh(-/-) mice expressed lower levels of Tlr4 than wild-type mice before, but not after, colitis was induced. Administration of glucocorticoid at low levels did not prevent Crh(-/-) mice from developing severe colitis. Crh(-/-) mice were unable to recover from acute colitis, as indicated by their increased death rate.

CONCLUSIONS

Mice deficient in CRF down-regulate TLR4 and are more susceptible to dextran sodium sulfate-induced colitis. CRF has anti-inflammatory effects in innate immunity-dependent colitis and its recovery phase; these are independent of glucocorticoid administration. CRF might therefore be developed as a therapeutic target for patients with IBD.

Corticotrophin-releasing factor and urocortin inhibit system A activity in term human placental villous explants

Plasma corticotrophin-releasing factor (CRF) and urocortin are elevated in preterm labour and/or fetal growth restriction (FGR). FGR is associated with reduced placental system A amino acid transporter activity and in vitro data suggest altered endocrine status could be responsible. Here we test the hypothesis that CRF and urocortin inhibit placental system A activity. Chronic (48h) exposure of term placental villous explants to these hormones (10(-7)M) significantly reduced system A activity (Na(+)-dependent (14)C-methylaminoisobutyric acid uptake), whereas 1h exposure had no effect. We propose elevated CRF and urocortin contribute to FGR through negative regulation of placental system A activity.

Synthesis and Biological Evaluation of New CRH Analogues

A series of 7 new human/rat Corticotropin Releasing Hormone (h/r-CRH) analogues were synthesized. The induced alterations include substitution of Phe at position 12 with D-Phe, Leu at positions 14 and 15 with Aib and Met at positions 21 and 38 with Cys(Et) and Cys(Pr). The analogues were tested regarding their binding affinity to the CRH-1 receptor and their activity which is represented by means of percentage of maximum response in comparison to the native molecule. The results indicated that the introduction of Aib, or Cys derivatives although altering the secondary structure of the molecule, did not hinder receptor recognition and binding.

[Therapeutic targets]

Based on better recent knowledge of the factors involved in triggering visceral hyperalgesia, the therapeutic approach to irritable bowel syndrome (IBS) treatment is changing. The classical approach targeting first bowel movement alterations or motility disorders using spasmolytic agents has to be replaced by visceral antinociceptive drugs. Several mediators and receptors involved in gut hyperalgesia have already been identified. Serotonin (5-HT), tachykinins, CCK, NGF, and other mediators are involved in experimental models of gut hyperalgesia, and related receptor antagonists have already been introduced in clinical trials. However, IBS is associated with mucosal immune stimulation, considered a microinflammatory state associated with increased density of immunocytes and mast cells, offering new targets. Altered mucosal barrier permeability with increased entry of toxins and bacteria is considered to be responsible for the mucosal microinflammation. Endogenous but predominantly luminal factors have been identified as factors responsible for such altered permeability. These clinical data have opened the door to promising future drugs able to prevent or blunt such permeability alteration, which therefore may constitute a pathophysiological treatment for IBS.

Neurobiological mechanisms contributing to alcohol-stress-anxiety interactions

This article summarizes the proceedings of a symposium that was presented at a conference entitled "Alcoholism and Stress: A Framework for Future Treatment Strategies." The conference was held in Volterra, Italy on May 6-9, 2008 and this symposium was chaired by Jeff L. Weiner. The overall goal of this session was to review recent findings that may shed new light on the neurobiological mechanisms that underlie the complex relationships between stress, anxiety, and alcoholism. Dr. Danny Winder described a novel interaction between D1 receptor activation and the corticotrophin-releasing factor (CRF) system that leads to an increase in glutamatergic synaptic transmission in the bed nucleus of the stria terminalis. Dr. Marisa Roberto presented recent data describing how protein kinase C epsilon, ethanol, and CRF interact to alter GABAergic inhibition in the central nucleus of the amygdala. Dr. Jeff Weiner presented recent advances in our understanding of inhibitory circuitry within the basolateral amygdala (BLA) and how acute ethanol exposure enhances GABAergic inhibition in these pathways. Finally, Dr. Brian McCool discussed recent findings on complementary glutamatergic and GABAergic adaptations to chronic ethanol exposure and withdrawal in the BLA. Collectively, these investigators have identified novel mechanisms through which neurotransmitter and neuropeptide systems interact to modulate synaptic activity in stress and anxiety circuits. Their studies have also begun to describe how acute and chronic ethanol exposure influence excitatory and inhibitory synaptic communication in these pathways. These findings point toward a number of novel neurobiological targets that may prove useful for the development of more effective treatment strategies for alcohol use disorders.

The neurobiological toll of child abuse and neglect

Exposure to interpersonal violence or abuse affects the physical and emotional well-being of affected individuals. In particular, exposure to trauma during development increases the risk of psychiatric and other medical disorders beyond the risks associated with adult violence exposure. Alterations in the hypothalamic-pituitary-adrenal (HPA) axis, a major mediating pathway of the stress response, contribute to the long-standing effects of early life trauma. Although early life trauma elevates the risk of psychiatric and medical disease, not all exposed individuals demonstrate altered HPA axis physiology, suggesting that genetic variation influences the consequences of trauma exposure. In addition, the effects of abuse may extend beyond the immediate victim into subsequent generations as a consequence of epigenetic effects transmitted directly to offspring and/or behavioral changes in affected individuals. Recognition of the biological consequences and transgenerational impact of violence and abuse has critical importance for both disease research and public health policy.

Urocortin-like immunoreactivity in the primary lymphoid organs of the duck (Anas platyrhynchos)

Urocortin (UCN) is a 40 aminoacid peptide which belongs to corticotropin-releasing factor (CRF) family. This family of peptides stimulates the secretion of proopiomelanocortin (POMC)-derived peptides, adrenocorticotropic hormone (ACTH), β-endorphin and melanocyte-stimulating hormone (MSH) in the pituitary gland. In the present study, using Western blotting and immunohistochemistry, the distribution of UCN in the primary lymphoid organs of the duck was investigated at different ages. In the cloacal burse and thymus, Western blot demonstrated the presence of a peptide having a molecular weight compatible with that of the mammalian UCN. In the cloacal burse, immunoreactivity was located in the medullary epithelial cells and in the follicular associated and corticomedullary epithelium. In the thymus, immunoreactivity was located in single epithelial cells. Double labelling immunofluorescence studies showed that UCN immunoreactivity completely colocalised with cytokeratin immunoreactivity in both the thymus and cloacal burse. Statistically significant differences in the percentage of UCN immunoreactivity were observed between different age periods in the cloacal burse. The results suggest that, in birds, urocortin has an important role in regulating the function of the immune system.

Therapeutics for alcoholism: what's the future?

As with other addictions, human alcoholism is characterised as a chronically relapsing condition. Consequently, the therapeutic goal is the development of clinically effective, safe drugs that promote high adherence rates and prevent relapse. These products can then be used in conjunction with psychosocial approaches. In this review, preclinical studies are highlighted that indicate the mechanism of action of currently used anti-craving medications or demonstrate the potential of novel pharmacological agents for the treatment of alcohol use disorders. While current pharmacological strategies are far from ideal, there are a number of candidate molecules that may ultimately be developed into therapeutic agents. In addition, prescribing clinicians should also consider strategies such as combinations of various drugs to aid in the regulation of aberrant alcohol consumption.

Dihydropyrrole[2,3-d]pyridine derivatives as novel corticotropin-releasing factor-1 antagonists: mapping of the receptor binding pocket by in silico docking studies

In an effort to discover novel CRF-1 receptor antagonists exhibiting improved physicochemical properties, a dihydropirrole[2,3]pyridine scaffold was designed and explored in terms of the SAR of the substitution at the pendent phenyl ring and the nature of the heterocyclic moieties present in the upper region of the molecule. Selective and potent compounds have been discovered endowed with reduced ClogP with respect to compounds known in the literature. Of particular relevance was the finding that the in vitro affinity of the series was maintained by reducing the overall lipophilicity. The results achieved by this exploration enabled the formulation of a novel hypothesis on the nature of the receptor binding pocket of this class of CRF-1 receptor antagonists, making use of in silico docking studies of the putative nonpeptidic antagonist binding site set up in house by homology modeling techniques.

Corticotropin-releasing hormone receptor expression and functional signaling in murine gonadotrope-like cells

Corticotropin-releasing hormone (CRH) is a key regulator of the mammalian stress response, mediating a wide variety of stress-associated behaviors including stress-induced inhibition of reproductive function. To investigate the potential direct action of CRH on pituitary gonadotrope function, we examined CRH receptor expression and second messenger signaling in alpha T3-1 cells, a murine gonadotrope-like cell line. Reverse transcriptase PCR (RT-PCR) studies demonstrated that alpha T3-1 cells express mRNA for the two CRH receptor subtypes, CRHR1 and CRHR2, with CRHR2alpha as the predominant CRHR2 isoform. Stimulation of the cells with CRH or urocortin (UCN) resulted in rapid, transient increases in the intracellular levels of cAMP that were completely blocked by the addition of alpha-helical CRH 9-41 or astressin, non-selective CRH receptor antagonists. Stimulation of the cells with CRHR2-specific ligands, urocortin 2 (UCN2) or urocortin 3 (UCN3), resulted in rapid increases in intracellular cAMP levels to 50-60% of the levels observed with UCN. Treatment with a selective CRHR2 antagonist, antisauvagine, completely blocked UCN3-mediated increases in cAMP and significantly reduced, but did not completely block UCN-mediated increases in cAMP, demonstrating that both CRHR1 and CRHR2 are functionally active in these gonadotrope-like cells. Finally, UCN treatment significantly increased the transcriptional activity of the glycoprotein hormone alpha-subunit promoter as assessed by alpha-luciferase transfection assays. Together, these results demonstrate the functional signaling of CRH receptors in alpha T3-1 cells, suggesting that CRH may also modulate pituitary gonadotrope function in vivo.

From Hans Selye's discovery of biological stress to the identification of corticotropin-releasing factor signaling pathways: implication in stress-related functional bowel diseases

Selye pioneered the concept of biological stress in 1936, culminating in the identification of the corticotropin-releasing factor (CRF) signaling pathways by Vale's group in the last two decades. The characterization of the 41 amino-acid CRF and other peptide members of the mammalian CRF family, urocortin 1, urocortin 2, and urocortin 3, and the cloning of CRF(1) and CRF(2) receptors, which display distinct affinity for CRF ligands, combined with the development of selective CRF receptor antagonists enable us to unravel the importance of CRF(1) receptor in the stress-related endocrine (activation of pituitary-adrenal axis), behavioral (anxiety/depression, altered feeding), autonomic (activation of sympathetic nervous system), and immune responses. The activation of CRF(1) receptors is also one of the key mechanisms through which various stressors impact the gut to stimulate colonic propulsive motor function and to induce hypersensitivity to colorectal distension as shown by the efficacy of the CRF(1) receptor antagonists in blunting these stress-related components. The importance of CRF(1) signaling pathway in the visceral response to stress in experimental animals provided new therapeutic approaches for treatment of functional bowel disorder such as irritable bowel syndrome, a multifactor functional disorder characterized by altered bowel habits and visceral pain, for which stress has been implicated in the pathophysiology and is associated with anxiety-depression in a subset of patients.

A comparison of ligand based virtual screening methods and application to corticotropin releasing factor 1 receptor

Ligand based virtual screening approaches were applied to the CRF1 receptor. We compared ECFP6 fingerprints, FTrees, Topomers, Cresset FieldScreen, ROCS OpenEye shape Tanimoto, OpenEye combo-score and OpenEye electrostatics. The 3D methods OpenEye Shape Tanimoto, combo-score and Topomers performed the best at separating actives from inactives in retrospective experiments. By virtue of their higher enrichment the same methods identified more active scaffolds. However, amongst a given number of active compounds the Cresset and OpenEye electrostatic methods contained more scaffolds and returned ranked compounds with greater diversity. A selection of the methods were employed to recommend compounds for screening in a prospective experiment. New CRF1 actives antagonists were found. The new actives contained different underlying chemical architecture to the query molecules, results indicative of successful scaffold-hopping.

Urocortin 1 inhibits rat leydig cell function

Corticotropin-releasing factor (CRF) has previously been reported in rat testes in which it inhibits Leydig cells activity. However, recent studies in our laboratory have suggested that some of the effects originally attributed to CRF were instead due to the related peptide Urocortin 1 (Ucn 1) and that this latter hormone, not CRF, was detectable in Leydig cells. We show here that Ucn 1 [a mixed CRF receptor (CRFR) type 1 and CRFR2 agonist] and the CRFR1-selective peptide Stressin 1, but not Ucn 2 or Ucn 3 (both considered selective CRFR2 ligands), significantly blunt the testosterone response to human chorionic gonadotropin. The effect of Ucn 1 is observed regardless of whether this peptide is injected iv or directly into the testes, and it is reversed by the mixed CRFR1/R2 antagonist Astressin B. Blockade of GnRH receptors with the antagonist Azalin B does not interfere with the influence of Ucn 1, thereby demonstrating that pituitary luteinizing hormone does not appear to be involved in this model. Collectively these results suggest that Ucn 1, not CRF, is present in the rat testes and interferes with Leydig cell activity. However, whereas we previously reported that alcohol up-regulated gonadal Ucn 1 gene expression, CRF receptor antagonists were unable to reverse the inhibitory effect exerted by alcohol on human chorionic gonadotropin-induced testosterone release. The functional role played by testicular Ucn 1 in stress models characterized by blunted androgen levels therefore needs to be further investigated.

The behavioural and electrophysiological effects of CRF in rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain. The role of CRF in the behavioural activity and modulation of anxiety states in several brain structures has been well documented, but its function in the cerebral cortex still remains unknown. The aim of our study was to investigate the effect of CRF injected bilaterally into rat frontal cortex on the locomotor and exploratory activity and anxiety of rats. We also examined the effect of CRF on extracellularly recorded field potentials in rat frontal cortical slices in vitro. Behavioural experiments showed that CRF in doses of 0.05, 0.1, 0.2 microg/1 microl/site decreased locomotor and exploratory activity during a 40-min session in the open field test. In the elevated plus-maze test, CRF in a dose of 0.2 microg/1 microl/site produced a significant anxiolytic-like effect, which was prevented by CRF receptor antagonists (alpha-helicalCRF(9-41) and NBI 27914). Electrophysiological experiments showed that CRF-induced a transient depression of field potentials in slices partly disinhibited by GABA(A) and GABA(B) receptors antagonists. The blockade of NMDA receptors prevented the occurrence of that effect. The obtained results suggest that CRF may have anxiolytic-like effects in the frontal cortex. Moreover, the peptide inhibits locomotor and exploratory activity and depresses excitatory synaptic transmission in a NMDA receptor-dependent manner.

2-Arylpyrimidines: novel CRF-1 receptor antagonists

The design, synthesis and structure-activity relationship studies of a novel series of CRF-1 receptor antagonists, the 2-arylpyrimidines, are described. The effects of substitution on the aromatic ring and the pyrimidine core on CRF-1 receptor binding were investigated. A number of compounds with K(i) values below 10 nM and lipophilicity in a minimally acceptable range for a CNS drug (cLogP<5) were discovered.

Peripheral and central administration of exogenous urocortin 1 disrupts the fasted motility pattern of the small intestine in rats via the corticotrophin releasing factor receptor 2 and a cholinergic mechanism

BACKGROUND AND AIM

The action of the corticotrophin releasing factor (CRF) receptor on the small intestinal motility has been rarely investigated. The present study aimed to determine the effects of urocortin 1 on small intestinal motility in rats and the CRF receptor subtypes and autonomic pathways mediating the effects.

METHODS

Fasted or fed rats were used to investigate the effect of intravenous or intracerebroventricular urocortin 1 on duodenum and jejunum motility. NBI-27914 and astressin(2)-B (CRF receptor 1 and 2 antagonists, respectively), atropine (an M-receptor antagonist), phentolamine (an alpha-receptor antagonist), propranolol (a beta-receptor antagonist) and N(omega)-Nitro-L-arginine (a nitric oxide synthase [NOS] inhibitor) were applied to determine the involved CRF receptor subtypes and autonomic pathways.

RESULTS

In fasted rats, intravenous or intracerebroventricular injection of urocortin 1 disrupted duodenal and jejunal migrating myoelectric complex pattern, leading to an irregular spiking activity similar to the fed motility pattern. When urocortin 1 was given in the fed state, the fed motility pattern remained unchanged. In addition, urocortin 1 also inhibited small intestinal transit function. Astressin(2)-B injected intraperitoneally or intracerebroventricularly blocked urocortin 1-induced change, while NBI-27914 had no effect. The disruption of migrating myoelectric complex induced by urocortin 1 was abolished by atropine, but not affected by phentolamine, propranolol and N(omega)-Nitro-L-arginine.

CONCLUSION

Intravenous or intracerebroventricular injection of urocortin 1 acts, respectively, on peripheral and central CRF receptor 2 to disrupt the intestinal migrating myoelectric complex through an M-receptor-dependent mechanism, and such change has an inhibitory effect as proved by measuring the small intestinal transit function.

Protein kinase C epsilon mediation of CRF- and ethanol-induced GABA release in central amygdala

In the central amygdala (CeA), ethanol acts via corticotrophin-releasing factor (CRF) type 1 receptors to enhance GABA release. Amygdala CRF mediates anxiety associated with stress and drug dependence, and it regulates ethanol intake. Because mutant mice that lack PKCepsilon exhibit reduced anxiety-like behavior and alcohol consumption, we investigated whether PKCepsilon lies downstream of CRF(1) receptors in the CeA. Compared with PKCepsilon(+/+) CeA neurons, PKCepsilon(-/-) neurons showed increased GABAergic tone due to enhanced GABA release. CRF and ethanol stimulated GABA release in the PKCepsilon(+/+) CeA, but not in the PKCepsilon(-/-) CeA. A PKCepsilon-specific inhibitor blocked both CRF- and ethanol-induced GABA release in the PKCepsilon(+/+) CeA, confirming findings in the PKCepsilon(-/-) CeA. These results identify a PKCepsilon signaling pathway in the CeA that is activated by CRF(1) receptor stimulation, mediates GABA release at nerve terminals, and regulates anxiety and alcohol consumption.

Differential mechanisms of CRF1 and CRF2 receptor functions in the amygdala in pain-related synaptic facilitation and behavior

A major site of extrahypothalamic expression of corticotropin-releasing factor (CRF) and its G-protein-coupled CRF1 and CRF2 receptors is the amygdala, a key player in emotions and affective disorders. Pain-related plasticity in the laterocapsular division of the central nucleus of the amygdala (CeLC) generates emotional-affective responses and anxiety-like behavior. CRF1 receptor antagonists have anxiolytic effects. Although both CRF1 and CRF2 receptors couple positively to adenylyl cyclase, they can have opposite effects, but the underlying mechanism is unknown. This study addressed CRF1 and CRF2 receptor functions and mechanisms in the amygdala in a model of arthritic pain. Using whole-cell patch-clamp recordings of CeLC neurons, we found that a selective CRF1 receptor antagonist (NBI27914 [5-chloro-4-(N-(cyclopropyl)methyl-N-propylamino)-2-methyl-6-(2,4,6-trichlorophenyl)]) amino-pyridine inhibited synaptic facilitation in brain slices from arthritic rats through a postsynaptic mechanism. Inhibition of the NMDA receptor-mediated synaptic component was occluded by a protein kinase A (PKA) inhibitor, consistent with our previous demonstration of PKA-dependent increased NMDA receptor function in arthritis pain-related plasticity. NBI27914 also decreased neuronal excitability through inhibition of highly tetraethylammonium (TEA)-sensitive ion channels that contribute to action potential repolarization and firing rate. In contrast, a CRF2 receptor antagonist (astressin-2B [cyclo(31-34) [d-Phe11,His12,C alphaMeLeu13,39, Nle17, Glu31, Lys34] Ac-Sauvagine(8-40)]) facilitated synaptic transmission through presynaptic inhibition of GABAergic transmission (disinhibition). NBI27914 inhibited arthritis pain-related behaviors (audible and ultrasonic vocalizations and hindlimb withdrawal reflexes). Astressin-2B had no significant behavioral effect. The data suggest that endogenous CRF1 receptor activation in the amygdala contributes to pain-related synaptic facilitation, increased excitability, and pain behavior through a postsynaptic mechanism involving activation of PKA and highly TEA-sensitive K(+)-currents. Presynaptic CRF2 receptor-mediated inhibition does not reach behavioral significance.

Effects of CRF2R agonist on tumor growth and cachexia in mice implanted with Lewis lung carcinoma cells

Previous studies have demonstrated an effect of corticotropin-releasing factor 2 receptor (CRF2R) agonists in the maintenance of skeletal muscle mass. The aim of this study was to evaluate the effects of a CRF2R agonist in preserving skeletal muscle in a mouse cachexia model. Implantation of a fast-growing tumor to mice (Lewis lung carcinoma) resulted in a clear cachectic state characterized by a profound muscle wasting. We found that administration of a CRF2R agonist (PG-873637) at 100 microg/kg/day by means of osmotic minipumps to tumor-bearing mice resulted in beneficial effects on muscle weight loss. Thus, muscle loss was partially reversed by the CRF2R agonist at different stages of tumor growth (at day 14 after tumor inoculation: 12% in tibialis posterior; 9% in gastrocnemius; and 48% in soleus). Moreover, the CRF2R agonist significantly reduced both the number of metastases and their mass (at day 19 after tumor inoculation: 66% and 61%, respectively). These data suggest a potentially beneficial effect of the CRF2R agonist in preserving skeletal muscle during cancer cachexia and open a line of research for the development of new therapeutic approaches for the treatment of muscle wasting associated with cancer.

Role of brain nicotinic acetylcholine receptor in centrally administered corticotropin-releasing factor-induced elevation of plasma corticosterone in rats

The present study was undertaken to clarify the central mechanisms involved in the intracerebroventricularly administered corticotropin-releasing factor-induced elevation of plasma corticosterone in urethane- and alpha-chloralose-anesthetized rats using microdialysis and immunohistochemical techniques. When corticotropin-releasing factor was given at 0.5, 1.5, and 3.0 nmol/animal intracerebroventricularly, it dose-dependently increased noradrenaline release but not adrenaline release in the hypothalamic paraventricular nucleus. The 1.5 nmol/animal dose of corticotropin-releasing factor-induced noradrenaline release was attenuated by CP-154,526 (butyl-ethyl-{2,5-dimethyl-7-(2,4,6 trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl}amine), a selective corticotropin-releasing factor receptor 1 antagonist, at 1.3 micromol/animal, intracerebroventricularly, and was also abolished by phentolamine at 0.66 micromol/animal, intracerebroventricularly. In addition, the corticotropin-releasing factor-induced elevation of noradrenaline release in the hypothalamic paraventricular nucleus and plasma corticosterone were abolished by hexamethonium, a non-selective nicotinic acetylcholine receptor antagonist, at 1.8 micromol/animal, intracerebroventricularly, and alpha-conotoxin MII, a potent alpha(3)beta(2) nicotinic acetylcholine receptor antagonist, at 30 nmol/animal, i.c.v. Corticotropin-releasing factor at 1.5 nmol/animal, i.c.v. evoked a significant expression of Fos, an immediate-early transcription factor in neurons, on the dopamine-beta-hydroxylase-containing neurons and alpha(3) nicotinic acetylcholine receptor subunit-expressing neurons in the locus coeruleus, but not in the medullary A(1) and A(2) regions containing noradrenergic neurons. These results suggest that centrally administered corticotrophin-releasing factor elevates plasma corticosterone by the corticotropin-releasing factor 1 receptor and alpha(3) subunit-containing nicotinic acetylcholine receptor (probably alpha(3)beta(2) nicotinic acetylcholine receptor) mediated activation of the locus coeruleus noradrenergic neurons projecting to the paraventricular nucleus in rats.

Stimulation of the inferior olivary complex alters the distribution of the type 1 corticotropin releasing factor receptor in the adult rat cerebellar cortex

In a previous study, it was shown that populations of climbing fibers, derived from the inferior olivary complex (IOC) contain the peptide corticotropin releasing factor (CRF) and that the expression of this peptide in climbing fibers could be modulated by the level of activity in olivary afferents. The intent of this study was to determine if there was comparable plasticity in the distribution of the type 1 CRF receptor (CRF-R1) in the cerebellum of the rat. Our results indicate that CRF-R1 was localized primarily to Purkinje cell somata and their primary dendrites and granule cells. In addition, scattered immunolabeling was present over the somata of Golgi cells, basket cells and stellate cells, as well as Bergmann glial cells and their processes. IOC stimulation for 30 min at 1 Hz increased CRF-R1 expression in molecular layer interneurons and processes of Bergmann glial cells. Little to no effect on CRF receptor distribution was observed in Purkinje cells, granule cells, or Golgi cells. IOC stimulation at 5 Hz however, increased CRF-R1 expression in the processes of Bergmann glial cells while decreasing its expression in basket, stellate and, to some extent, in Purkinje cells. The present results suggest that there is activity-dependent plasticity in CRF-R1 expression that must be considered in defining the mechanism by which the CRF family of peptides modulates activity in cerebellar circuits. The present results also suggest that the primary targets of CRF released from climbing fibers are Bergmann glial cells and interneurons in the molecular layer. Further, interneurons responded with a decrease in receptor expression following more intense levels of stimulation suggesting the possibility of internalization of the receptor. In contrast, Bergmann glial cells showed an increased expression in receptor expression. These data suggest that CRF released from climbing fibers may modulate the physiological properties of basket and stellate cells as well as having a heretofore unidentified and potentially unique effect on Bergmann glia.

CRF1 not glucocorticoid receptors mediate prepulse inhibition deficits in mice overexpressing CRF

BACKGROUND

Both corticotropin-releasing factor (CRF) and glucocorticoid receptors (GR) are implicated in the psychotic symptoms of psychiatric disorders. Correspondingly, it is of interest to determine their respective involvement in the sensorimotor gating deficits displayed by transgenic mice overexpressing CRF. These mice reveal lifelong elevations of CRF and corticosterone levels.

METHODS

Effects of the GR antagonists ORG34517 (5-45 mg/kg by mouth [PO]) and mifepristone (5-45 mg/kg PO) and the CRF(1) receptor antagonists CP154,526 (20-80 mg/kg intraperitoneally [IP]) and DMP695 (2.5-40.0 mg/kg IP) on prepulse inhibition (PPI) of the acoustic startle response were studied in mice overexpressing CRF and in their wild-type littermates. In addition, PPI was measured in both genotypes 2 weeks after adrenalectomy with or without exogenous corticosterone administration via subcutaneous pellet implant (20 mg corticosterone).

RESULTS

ORG34517 and mifepristone did not influence perturbation of PPI in mice overexpressing CRF; reducing corticosterone levels by adrenalectomy likewise did not improve PPI. Further, elevation in corticosterone levels by pellet implantation did not disrupt PPI in wild-type mice. Conversely, both CRF(1) receptor antagonists, CP154,526 (40-80 mg/kg IP) and DMP695 (40 mg/kg IP), significantly restored PPI in CRF-overexpressing mice.

CONCLUSIONS

Sustained overactivation of CRF(1) receptors rather than excessive GR receptor stimulation underlies impaired sensorimotor gating in CRF-overexpressing mice. CRF(1) receptors thus may play a role in the expression of psychotic features in stress-related psychiatric disorders.

Convergent regulation of locus coeruleus activity as an adaptive response to stress

Although hypothalamic-pituitary-adrenal axis activation is generally considered to be the hallmark of the stress response, many of the same stimuli that initiate this response also activate the locus coeruleus-norepinephrine system. Given its functional attributes, the parallel engagement of the locus coeruleus-norepinephrine system with the hypothalamic-pituitary-adrenal axis serves to coordinate endocrine and cognitive limbs of the stress response. The elucidation of stress-related afferents to the locus coeruleus and the electrophysiological characterization of these inputs are revealing how the activity of this system is fine-tuned by stressors to facilitate adaptive cognitive responses. Emerging from these studies, is a picture of complex interactions between the stress-related neuropeptide, corticotropin-releasing factor (CRF), endogenous opioids and the excitatory amino acid neurotransmitter, glutamate. The net effect of these interactions is to adjust the activity and reactivity of the locus coeruleus-norepinephrine system such that state of arousal and processing of sensory stimuli are modified to facilitate adaptive behavioral responses to stressors. This review begins with an introduction to the basic anatomical and physiological characteristics of locus coeruleus neurons. The concept that locus coeruleus neurons operate through two activity modes, i.e., tonic vs. phasic, that determine distinct behavioral strategies is emphasized in light of its relevance to stress. Anatomical and physiological evidence are then presented suggesting that interactions between stress-related neurotransmitters that converge on locus coeruleus neurons regulate shifts between these modes of discharge in response to the challenge of a stressor. This review focuses specifically on the locus coeruleus because it is the major source of norepinephrine to the forebrain and has been implicated in behavioral and cognitive aspects of stress responses.

The design, synthesis and structure-activity relationships of 1-aryl-4-aminoalkylisoquinolines: a novel series of CRF-1 receptor antagonists

The design, synthesis and structure-activity relationships of a novel series of CRF-1 receptor antagonist, the 1-aryl-4-alkylaminoisoquinolines, is described. The effects of substitution on the aromatic ring, the amino group and the isoquinoline core on CRF-1 receptor binding were investigated.

Presence of and stress-related changes in urocortin-like molecules in neurons and immune cells from the mussel Mytilus galloprovincialis

The distribution of urocortin (UCN)-like material is investigated in the bivalve mollusc Mytilus galloprovincialis. Immunocytochemical data demonstrate that UCN-like molecules are present in ganglionic neurons, microglial cells and immunocytes. Moreover, a co-localization of UCN- and corticotrophin-releasing hormone (CRH)-like molecules is found in microglial cells and in immunocytes, but not in neurons. Following high salinity-stress experiments, immunoreactivity for UCN and CRH increased in ganglionic neurons and immunocytes. Our findings extend the number of molecules potentially used by molluscan immunocytes to confront stress situations and strengthen the idea of functional conservation of stress-related molecules during evolution.

Pain-related anxiety-like behavior requires CRF1 receptors in the amygdala

Corticotropin-releasing factor receptor CRF1 has been implicated in the neurobiological mechanisms of anxiety and depression. The amygdala plays an important role in affective states and disorders such as anxiety and depression. The amygdala is also emerging as a neural substrate of pain affect. However, the involvement of the amygdala in the interaction of pain and anxiety remains to be determined. This study tested the hypothesis that CRF1 receptors in the amygdala are critically involved in pain-related anxiety. Anxiety-like behavior was determined in adult male rats using the elevated plus maze (EPM) test. The open-arm preference (ratio of open arm entries to the total number of entries) was measured. Nocifensive behavior was assessed by measuring hindlimb withdrawal thresholds for noxious mechanical stimulation of the knee. Measurements were made in normal rats and in rats with arthritis induced in one knee by intraarticular injections of kaolin/carrageenan. A selective CRF1 receptor antagonist (NBI27914) or vehicle was administered systemically (i.p.) or into the central nucleus of the amygdala (CeA, by microdialysis). The arthritis group showed a decreased preference for the open arms in the EPM and decreased hindlimb withdrawal thresholds. Systemic or intraamygdalar (into the CeA) administration of NBI27914, but not vehicle, inhibited anxiety-like behavior and nocifensive pain responses, nearly reversing the arthritis pain-related changes. This study shows for the first time that CRF1 receptors in the amygdala contribute critically to pain-related anxiety-like behavior and nocifensive responses in a model of arthritic pain. The results are a direct demonstration that the clinically well-documented relationship between pain and anxiety involves the amygdala.

The dynamic developmental localization of the full-length corticotropin-releasing factor receptor type 2 in rat cerebellum

Corticotropin releasing factor receptor 2 (CRF-R2) is strongly expressed in the cerebellum and plays an important role in the development of the cerebellar circuitry, particularly in the development of the dendritic trees and afferent input to Purkinje cells. However, the mechanisms responsible for the distribution and stabilization of CRF-R2 in the cerebellum are not well understood. Here, we provide the first detailed analysis of the cellular localization of the full-length form of CRF-R2 in rat cerebellum during early postnatal development. We document unique and developmentally regulated subcellular distributions of CRF-R2 in cerebellar cell types, e.g. granule cells after postnatal day 15. The presence of one or both receptor isoforms in the same cell may provide a molecular basis for distinct developmental processes. The full-length form of CRF-R2 may be involved in the regulation of the first stage of dendritic growth and at later stages in the controlling of the structural arrangement of immature cerebellar circuits and in the autoregulatory pathway of the cerebellum.

Requirement of cannabinoid receptor type 1 for the basal modulation of hypothalamic-pituitary-adrenal axis function

The endocannabinoid system affects the neuroendocrine regulation of hormone secretion, including the activity of the hypothalamus-pituitary-adrenal (HPA) axis. However, the mechanisms by which endocannabinoids regulate HPA axis function have remained unclear. Here we demonstrate that mice lacking cannabinoid receptor type 1 (CB1-/-) display a significant dysregulation of the HPA axis. Although circadian HPA axis responsiveness is preserved, CB1-/- mice are characterized by an enhanced circadian drive on the HPA axis, resulting in elevated plasma corticosterone concentrations at the onset of the dark as compared with wild-type (CB1+/+) littermates. Moreover, CB1-/--derived pituitary cells respond with a significantly higher ACTH secretion to CRH and forskolin challenges as compared with pituitary cells derived from CB1+/+ mice. Both CBL-/- and CB1+/+ mice properly respond to a high-dose dexamethasone test, but response to low-dose dexamethasone is influenced by genotype. In addition, CB1-/- mice show increased CRH mRNA levels in the paraventricular nucleus of the hypothalamus but not in other extrahypothalamic areas, such as the amygdala and piriform cortex, in which CB1 and CRH mRNA have been colocalized. Finally, CB1-/- mice have selective glucocorticoid receptor mRNA down-regulation in the CA1 region of the hippocampus but not in the dentate gyrus or paraventricular nucleus. Conversely, mineralocorticoid receptor mRNA expression levels were found unchanged in these brain areas. In conclusion, our findings indicate that CB1 deficiency enhances the circadian HPA axis activity peak and leads to central impairment of glucocorticoid feedback, thus further outlining the essential role of the endocannabinoid system in the modulation of neuroendocrine functions.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

PET Imaging of CRF1 with [11C]R121920 and [11C]DMP696: is the target of sufficient density?

AIM

Overstimulation of the CRF type 1 receptor (CRF1) is implicated in anxiety and depressive disorders. The aim of this study was to investigate the in vivo binding characteristics of [11C]R121920 and [11C]DMP696 in the nonhuman primate for application in positron emission tomography (PET) studies of CRF1.

METHODS

PET imaging with the two novel CRF1 radioligands was performed in baboon. In vitro binding studies for CRF1 were performed in postmortem brain tissue of baboon and human to assess sufficiency of receptor density for PET.

RESULTS

Both [11C]R121920 and [11C]DMP696 distributed rapidly and uniformly throughout the brain. Washout was comparable across brain regions, without differences in volume of distribution between regions reported to have high and low in vitro CRF1 binding. Membrane-enriched tissue homogenate assay using [(125)I]Tyr(0)-sauvagine and specific CRF1 antagonists CP154,526 and SN003 in human occipital cortex yielded maximal binding (Bmax) of 63.3 and 147.3 fmol/mg protein, respectively, and in human cerebellar cortex yielded Bmax of 103.6 and 64.6 fmol/mg protein, respectively. Dissociation constants (K(D)) were subnanomolar. In baboon, specific binding was not detectable in the same regions; therefore, Bmax and K(D) were not measurable. Autoradiographic results were consistent except there was also detectable CRF1-specific binding in baboon cerebellum.

CONCLUSION

Neither [11C]R121920 nor [11C]DMP696 demonstrated quantifiable regional binding in vivo in baboon. In vitro results suggest CRF1 density in baboon may be insufficient for PET. Studies in man may generate more promising results due to the higher CRF1 density compared with baboon in cerebral cortex and cerebellum.

Differential effects of CRF1 and CRF2 receptor antagonists on pain-related sensitization of neurons in the central nucleus of the amygdala

As a hormone in the hypothalamic-pituitary-adrenocortical (HPA) axis corticotropin-releasing factor (CRF) mediates stress responses. CRF can also act as a neuromodulator of synaptic transmission outside the HPA axis. A major site of extrahypothalamic expression of CRF and its G-protein-coupled receptors is the amygdala, a key player in affect-related disorders such as anxiety. The laterocapsular division of the central nucleus of the amygdala (CeLC) is important for the modulation of pain affect. This study determined the effects of CRF1 and CRF2 receptor antagonists in CeLC neurons in an arthritis pain model. Extracellular single-unit recordings were made from CeLC neurons in anesthetized adult rats. All neurons responded more strongly to noxious than to innocuous mechanical stimulation (compression) of peripheral tissues, including the knee. Evoked responses and background activity were measured before and during the development of a kaolin/carrageenan-induced knee joint arthritis. Drugs were administered into the CeLC by microdialysis before and/or after arthritis induction. All CeLC neurons showed increased responses to mechanical stimuli ("sensitization") 5-6 h postinduction of arthritis. A selective CRF1 receptor antagonist (NBI27914; 1-100 microM, concentration in microdialysis probe; 15 min) inhibited evoked responses and background activity in arthritis (n = 9) but had no effect under normal conditions before arthritis (n = 9). In contrast, a selective CRF2 receptor antagonist (Astressin-2B; 1-100 microM, 15 min) had no effect in arthritis (n = 7) but increased the neurons' responses under normal conditions (n = 8). These data suggest that CRF1 receptors in the amygdala contribute to pain-related sensitization, whereas the normally inhibitory function of CRF2 receptors is lost in the arthritis pain model.

Involvement of the corticotropin-releasing factor (CRF) type 2 receptor in CRF-induced thyrotropin release by the amphibian pituitary gland

Corticotropin-releasing factor (CRF) is considered to be a main adrenocorticotropin-releasing factor in vertebrates. In non-mammalian species, CRF and related peptides cause the release of thyroid-stimulating hormone (TSH) from the anterior pituitary. The actions of CRF peptides are mediated by two G protein coupled receptors (CRF1 and CRF2) that have different ligand specificities. Using ligands that bind preferentially or selectively to the CRF2 we tested the hypothesis that TSH release by the amphibian pituitary gland is mediated by the CRF2. Injection of frog CRF, urocortin 1 or the CRF2-specific ligand urocortin 3 all produced significant, acute increases (by 2 h) in plasma thyroxine concentration in prometamorphic tadpoles. Chronic injections of CRF peptides accelerated tadpole metamorphosis, and the peptides with the highest affinity for the CRF2 (urocortin 1 and sauvagine) had the greatest potency. Ligands selective for the CRF2 (frog urocortin 3, mouse urocortins 2 and 3) all accelerated tadpole metamorphosis. We then tested frog urocortins 1 and 3, mouse urocortin 2 and sauvagine for their TSH-releasing activity using dispersed frog anterior pituitary cells in culture. All of the peptides tested markedly enhanced the release of TSH. Secretagogue-induced TSH release was completely blocked by the general CRF receptor antagonist astressin or the CRF2-specific antagonist antisauvagine-30. Conversely, the type 1 CRF receptor-specific antagonist antalarmin had no effect on TSH secretion. Our results support the hypothesis that CRF-induced TSH release by the amphibian pituitary gland is mediated by the CRF2.

The corticotropin-releasing factor receptor: a novel target for the treatment of depression and anxiety-related disorders

The treatment of mood disorders has been the subject of intense study for more than half a century and has resulted in the discovery and availability of a number of compounds that have seen tremendous success in the management of major depression and anxiety-related disorders. In spite of this success, these drugs have not provided a complete therapeutic solution for all patients and this has revitalised the need for a greater understanding of the underlying molecular mechanisms and targets involved in these disorders. Elucidation of these novel targets will enable the development of a better class of compounds which could benefit a greater majority of the patient population and be devoid of the current side effect liabilities. Towards that end, this review examines, in detail, the prospect of one such target, the corticotropin-releasing factor system, as having an enhanced therapeutic profile with the potential of a broader range of efficacy with reduced side effect liabilities.

Corticotropin-releasing factor, urocortin 1, and their receptors in the mouse spinal cord

Corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1) are involved in stress adaptation. CRF receptor 1 (CRF1) binds CRF and Ucn1 with similar high affinity, but CRF receptor 2 (CRF2) binds Ucn1 with higher affinity than CRF. We tested the hypothesis that in the spinal cord CRF and Ucn1 control peripheral components of the stress response, by assessing the distribution of CRF- and Ucn1-containing fibers, CRF1 and CRF2 mRNAs, and CRF receptor protein (CRFR) in the mouse spinal cord, by using immunofluorescence and in situ hybridization. CRF, Ucn1, and CRFR occurred throughout the spinal cord. CRF fibers predominated in laminae I, V-VII, and X of Rexed. Ucn1 fibers occurred mainly in laminae VII and X and occasionally in lamina IX. Both CRFR mRNAs occurred in all laminae except the superficial laminae of the dorsal horn, but they exhibited different distributions, CRF2 mRNA having a wider occurrence (laminae III-X) than CRF1 mRNA (laminae III-VIII). Double immunofluorescence indicated that CRF and Ucn1 fibers contacted CRFR-containing neurons, mainly in laminae VII and X. The strongest co-distribution of CRF1 and CRF2 mRNAs with CRF and Ucn1 fibers appeared in lamina VII. CRF2 mRNA predominated in lamina IX together with Ucn1, whereas CRF2 mRNA predominated in lamina X, where it had similar distributions with each ligand. In view of the lamina-specific and similar distributions of the two CRF receptor mRNAs with their ligands, we suggest that CRF1 and CRF2 are involved in peripheral stress adaptation processes, such as modulation of stress-induced analgesia and the mediation of visceral nociceptive information by CRF2.

Serotonergic and non-serotonergic targets in the pharmacotherapy of visceral hypersensitivity

Visceral hypersensitivity is considered a key mechanism in the pathogenesis of functional gastrointestinal (GI) disorders. Targeting visceral hypersensitivity seems an attractive approach to the development of drugs for functional GI disorders. This review summarizes current knowledge on targets for the treatment of visceral hypersensitivity, and the status of current and future drug and probiotic treatment development, and the role of pharmacogenomic factors.

NMR structural characterization of a minimal peptide antagonist bound to the extracellular domain of the corticotropin-releasing factor1 receptor

Natural peptide agonists of corticotrophin-releasing factor (CRF) receptors bind to the receptor by a two-site mechanism as follows: the carboxyl end of the ligand binds the N-terminal extracellular domain (ECD) of the receptor and the amino portion of the ligand binds the extracellular face of the seven transmembrane region. Recently, peptide antagonists homologous to the 12 C-terminal residues of CRF have been derived, which bind the CRF(1) receptor through an interaction with the ECD. Here we characterized the binding of a minimal 12-residue peptide antagonist while bound to the isolated ECD of the CRF(1) receptor. We have expressed and purified soluble and properly folded ECD independent from the seven-transmembrane region as a thioredoxin fusion protein in Escherichia coli. A model of the peptide antagonist, cyclic corticotrophin-releasing factor residues 30-41 (cCRF(30-41)), was calculated while bound to the recombinant ECD using transferred nuclear Overhauser effect spectroscopy. Although the peptide is unstructured in solution, it adopts an alpha-helical conformation when bound to the ECD. Residues of cCRF(30-41) comprising the binding interface with the ECD were mapped using saturation transfer difference NMR. Two hydrophobic residues (Met(38) and Ile(41)) as well as two amide groups (Asn(34) and the C-terminal amide) on one face of the helix defined the binding epitope of the antagonist. This epitope may be used as a starting point for development of non-peptide antagonists targeting the ECD of this receptor.

Role of neuropeptides in appetite regulation and obesity--a review

Obesity represents the most prevalent nutritional problem worldwide which in the long run predisposes to development of diabetes mellitus, hypertension, endometrial carcinoma, osteoarthritis, gall stones and cardiovascular diseases. Despite significant reductions in dietary fat consumption, the prevalence of obesity is on a rise and is taking on pandemic proportions. Obesity develops when energy intake exceeds energy expenditure over time. Recently, a close evolutionary relationship between the peripheral and hypothalamic neuropeptides has become apparent. The hypothalamus being the central feeding organ mediates regulation of short-term and long-term dietary intake via synthesis of various orexigenic and anorectic neuropeptides. The structure and function of many hypothalamic peptides (neuropeptide Y (NPY), melanocortins, agouti-related peptide (AGRP), cocaine and amphetamine regulated transcript (CART), melanin concentrating hormone (MCH), orexins have been characterized in rodent models The peripheral neuropeptides such as cholecystokinin (CCK), ghrelin, peptide YY (PYY3-36), amylin, bombesin regulate important gastrointestinal functions such as motility, secretion, absorption, provide feedback to the central nervous system on availability of nutrients and may play a part in regulating food intake. The pharmacological potential of several endogenous peripheral peptides released prior to, during and/or after feeding are being explored. Long-term regulation is provided by the main circulating hormones leptin and insulin. These systems implicated in hypothalamic appetite regulation provide potential targets for treatment of obesity which could potentially pass into clinical development in the next 5 years. This review summarizes various effects and interrelationship of these central and peripheral neuropeptides in metabolism, obesity and their potential role as targets for treatment of obesity.