Anxiolytic- and antidepressant-like profile of a new CRF1 receptor antagonist, R278995/CRA0450

Melanin-concentrating hormone receptor: A therapeutic target for novel anxiolytics

Anxiety disorders are chronic, disabling psychiatric disorders, and there is a growing medical need for the development of novel pharmacotherapeutic agents showing improved efficacy and an improved side effect profile as compared with the currently prescribed anxiolytic drugs. In the course of the search for next-generation anxiolytics, neuropeptide receptors have garnered interest as potential therapeutic targets, underscored by pivotal roles in modulating stress responses and findings from animal studies using pharmacological tools. Among these neuropeptide receptors, the type 1 receptor for melanin-concentrating hormone (MCH1), which has been demonstrated to be involved in an array of physiological processes, including the regulation of stress responses and affective states, has gained attraction as a therapeutic target for drugs used in the treatment of psychiatric disorders, including anxiety disorders. To date, a plethora of MCH1 antagonists have been synthesized, and studies using MCH1 antagonists and genetically manipulated mice lacking MCH1 have revealed that the blockade of MCH1 produces anxiolytic-like effects across diverse rodent paradigms. In addition, MCH1 antagonists have been demonstrated to show a rapid onset of antidepressant-like effects; therefore, they may be effective for conditions commonly encountered in patients with anxiety disorders, which is an advantage for anxiolytic drugs. Notably, MCH1 antagonists have not manifested the undesirable side effects observed with the currently prescribed anxiolytics. All these preclinical findings testify to the potential of MCH1 antagonists as novel anxiolytics. Although there are still issues that need to be resolved prior to the initiation of clinical trials, such as elucidating the precise neuronal mechanisms underlying their anxiolytic effects and exploring pertinent biomarkers that can be used in clinical trials, MCH1 blockade appears to be an attractive way to tackle anxiety disorders.

Sex Differences in Stress Response: Classical Mechanisms and Beyond

Neuropsychiatric disorders, which are associated with stress hormone dysregulation, occur at different rates in men and women. Moreover, nowadays, preclinical and clinical evidence demonstrates that sex and gender can lead to differences in stress responses that predispose males and females to different expressions of similar pathologies. In this curated review, we focus on what is known about sex differences in classic mechanisms of stress response, such as glucocorticoid hormones and corticotrophin-releasing factor (CRF), which are components of the hypothalamicpituitary- adrenal (HPA) axis. Then, we present sex differences in neurotransmitter levels, such as serotonin, dopamine, glutamate and GABA, as well as indices of neurodegeneration, such as amyloid β and Tau. Gonadal hormone effects, such as estrogens and testosterone, are also discussed throughout the review. We also review in detail preclinical data investigating sex differences caused by recentlyrecognized regulators of stress and disease, such as the immune system, genetic and epigenetic mechanisms, as well neurosteroids. Finally, we discuss how understanding sex differences in stress responses, as well as in pharmacology, can be leveraged into novel, more efficacious therapeutics for all. Based on the supporting evidence, it is obvious that incorporating sex as a biological variable into preclinical research is imperative for the understanding and treatment of stress-related neuropsychiatric disorders, such as depression, anxiety and Alzheimer's disease.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Sigma-1 Receptor Is Critical for Mitochondrial Activity and Unfolded Protein Response in Larval Zebrafish

The sigma-1 receptor (S1R) is a highly conserved transmembrane protein highly enriched in mitochondria-associated endoplasmic reticulum (ER) membranes, where it interacts with several partners involved in ER-mitochondria Ca2+ transfer, activation of the ER stress pathways, and mitochondria function. We characterized a new S1R deficient zebrafish line and analyzed the impact of S1R deficiency on visual, auditory and locomotor functions. The s1r+25/+25 mutant line showed impairments in visual and locomotor functions compared to s1rWT. The locomotion of the s1r+25/+25 larvae, at 5 days post fertilization, was increased in the light and dark phases of the visual motor response. No deficit was observed in acoustic startle response. A critical role of S1R was shown in ER stress pathways and mitochondrial activity. Using qPCR to analyze the unfolded protein response genes, we observed that loss of S1R led to decreased levels of IRE1 and PERK-related effectors and increased over-expression of most of the effectors after a tunicamycin challenge. Finally, S1R deficiency led to alterations in mitochondria bioenergetics with decreased in basal, ATP-linked and non-mitochondrial respiration and following tunicamycin challenge. In conclusion, this new zebrafish model confirmed the importance of S1R activity on ER-mitochondria communication. It will be a useful tool to further analyze the physiopathological roles of S1R.

Considering Sex as a Biological Variable in Basic and Clinical Studies: An Endocrine Society Scientific Statement

In May 2014, the National Institutes of Health (NIH) stated its intent to "require applicants to consider sex as a biological variable (SABV) in the design and analysis of NIH-funded research involving animals and cells." Since then, proposed research plans that include animals routinely state that both sexes/genders will be used; however, in many instances, researchers and reviewers are at a loss about the issue of sex differences. Moreover, the terms sex and gender are used interchangeably by many researchers, further complicating the issue. In addition, the sex or gender of the researcher might influence study outcomes, especially those concerning behavioral studies, in both animals and humans. The act of observation may change the outcome (the "observer effect") and any experimental manipulation, no matter how well-controlled, is subject to it. This is nowhere more applicable than in physiology and behavior. The sex of established cultured cell lines is another issue, in addition to aneuploidy; chromosomal numbers can change as cells are passaged. Additionally, culture medium contains steroids, growth hormone, and insulin that might influence expression of various genes. These issues often are not taken into account, determined, or even considered. Issues pertaining to the "sex" of cultured cells are beyond the scope of this Statement. However, we will discuss the factors that influence sex and gender in both basic research (that using animal models) and clinical research (that involving human subjects), as well as in some areas of science where sex differences are routinely studied. Sex differences in baseline physiology and associated mechanisms form the foundation for understanding sex differences in diseases pathology, treatments, and outcomes. The purpose of this Statement is to highlight lessons learned, caveats, and what to consider when evaluating data pertaining to sex differences, using 3 areas of research as examples; it is not intended to serve as a guideline for research design.

Advances in novel molecular targets for antidepressants

Depression is the most common psychiatric illness affecting numerous people world-wide. The currently available antidepressant treatment presents low response and remission rates. Thus, new effective antidepressants need to be developed or discovered. Aiming to give an overview of novel possible antidepressant drug targets, we summarized the molecular targets of antidepressants and the underlying neurobiology of depression. We have also addressed the multidimensional perspectives on the progress in the psychopharmacological treatment of depression and on the new potential approaches with effective drug discovery.

The sigma receptor ligand N-phenylpropyl-N'-(4-methoxyphenethyl)3piperazine (YZ-067) enhances the cocaine conditioned-rewarding properties while inhibiting the development of sensitization of cocaine in mice

RATIONALE

The N-phenylpropyl-N'-substituted piperazines SA-4503 (N-phenylpropyl-N'-(3,4-dimethoxyphenethyl)piperazine) and YZ-185 (N-phenylpropyl-N'-(3-methoxyphenethyl)piperazine) bind to sigma (σ) receptors and block the development of cocaine-induced conditioned place preference at concentrations that inhibit cocaine-induced hyperactivity. YZ-067 (N-phenylpropyl-N'-(4-methoxyphenethyl)piperazine) also binds to sigma receptors and attenuates cocaine-induced hyperactivity in mice.

OBJECTIVES

The present study determined the effect of YZ-067 on the development and expression of cocaine (66 μmol/kg or 33 μmol/kg) conditioned place preference (CPP) and locomotor sensitization in mice.

RESULTS

YZ-067 (10 or 31.6 μmol/kg) did not have intrinsic effects on place preference or place aversion. Interestingly, the 31.6 μmol/kg YZ-067 dose enhanced the development of cocaine place preference, while 10 μmol/kg YZ-067 attenuated the development of cocaine-induced locomotor sensitization. However, YZ-067 did not alter the expression of cocaine place preference nor cocaine-induced locomotor sensitization. In follow-up studies, YZ-067 did not affect performance in the zero maze or rotarod, indicating that sigma receptors probed by this ligand do not regulate anxiety-like or coordinated motor skill behaviors, respectively.

CONCLUSION

Overall, these results are consistent with previous studies demonstrating a role for sigma receptors in the behavioral effects of cocaine. However, the present findings also indicate that N-phenylpropyl-N'-substituted piperazines do not strictly block cocaine's behavioral effects and that sigma receptor may differentially mediate cocaine-induced hyperactivity and place conditioning.

Corticotropin releasing factor-binding protein (CRF-BP) as a potential new therapeutic target in Alzheimer's disease and stress disorders

Alzheimer's disease is the most common cause of dementia and one of the most complex human neurodegenerative diseases. Numerous studies have demonstrated a critical role of the environment in the pathogenesis and pathophysiology of the disease, where daily life stress plays an important role. A lot of epigenetic studies have led to the conclusion that chronic stress and stress-related disorders play an important part in the onset of neurodegenerative disorders, and an enormous amount of research yielded valuable discoveries but has so far not led to the development of effective treatment strategies for Alzheimer's disease. Corticotropin-releasing factor (CRF) is one of the major hormones and at the same time a neuropeptide acting in stress response. Deregulation of protein levels of CRF is involved in the pathogenesis of Alzheimer's disease, but little is known about the precise roles of CRF and its binding protein, CRF-BP, in neurodegenerative diseases. In this review, we summarize the key evidence for and against the involvement of stress-associated modulation of the CRF system in the pathogenesis of Alzheimer's disease and discuss how recent findings could lead to new potential treatment possibilities in Alzheimer's disease by using CRF-BP as a therapeutic target.

Sex differences in the hypothalamic-pituitary-adrenal axis: An obstacle to antidepressant drug development?

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has long been implicated in the pathophysiology of depression, and HPA axis-based compounds have served as potential new therapeutic targets, but with no success. This review details sex differences from animal and human studies in the function of HPA axis elements (glucocorticoids, corticotropin releasing factor, and vasopressin) and related compounds tested as candidate antidepressants. We propose that sex differences contribute to the failure of novel HPA axis-based drugs in clinical trials. Compounds studied preclinically in males were tested in clinical trials that recruited more, if not exclusively, women, and did not control, but rather adjusted, for potential sex differences. Indeed, clinical trials of antidepressants are usually not stratified by sex or other important factors, although preclinical and epidemiological data support such stratification. In conclusion, we suggest that clinical testing of HPA axis-related compounds creates an opportunity for targeted, personalized antidepressant treatments based on sex. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Sex differences in corticotropin releasing factor regulation of medial septum-mediated memory formation

Stress can disrupt memory and contribute to cognitive impairments in psychiatric disorders, including schizophrenia and attention deficit hyperactivity disorder. These diseases are more common in men than in women, with men showing greater cognitive impairments. Mnemonic deficits induced by stress are mediated, in part, by corticotropin releasing factor (CRF). However, where CRF is acting to regulate memory, and sex differences therein, is understudied. Here we assessed whether CRF in the medial septum (MS), which projects to the hippocampus, affected memory formation in male and female rats. CRF in the MS did not alter hippocampal-independent object recognition memory, but impaired hippocampal-dependent object location memory in both sexes. Interestingly, males were more sensitive than females to the disruptive effect of a low dose of CRF in the MS. Female resistance was not due to circulating ovarian hormones. However, compared to males, females had higher MS expression of CRF binding protein, which reduces CRF bioavailability and thus may mitigate the effect of the low dose of CRF in females. In contrast, there was no sex difference in CRF₁ expression in the MS. Consistent with this finding, CRF₁ antagonism blocked the memory impairment caused by the high dose of CRF in the MS in both sexes. Collectively, these results suggest that males are more vulnerable than females to the memory impairments caused by CRF in the MS. In both sexes, CRF₁ antagonists prevented MS-mediated memory deficits caused by high levels of CRF, and such levels can result from very stressful events. Thus, CRF₁ antagonists may be a viable option for treating cognitive deficits in stressed individuals with psychiatric disorders.

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

Characterization of CRF1 receptor antagonists with differential peripheral vs central actions in CRF challenge in rats

The aim of this study was to investigate peripheral and central roles of corticotropin-releasing factor (CRF) in endocrinological and behavioral changes. Plasma adrenocorticotropin (ACTH) concentration was measured as an activity of hypothalamic-pituitary-adrenal (HPA) axis. As behavioral changes, locomotion and anxiety behavior were measured after CRF challenge intravenously (i.v.) for the peripheral administration or intracerebroventricularly (i.c.v.) for the central administration. Plasma ACTH concentration was significantly increased by both administration routes of CRF; however, hyperlocomotion and anxiety behavior were induced only by the i.c.v. administration. In the drug discovery of CRF₁ receptor antagonists, we identified two types of compounds, Compound A and Compound B, which antagonized peripheral CRF-induced HPA axis activation to the same extent, but showed different effects on the central CRF signal. These had similar in vitro CRF₁ receptor binding affinities (15 and 10nM) and functional activities in reporter gene assay (15 and 9.5nM). In the ex vivo binding assays using tissues of the pituitary, oral treatment with Compound A and Compound B at 10mg/kg inhibited [¹²⁵I]-CRF binding, whereas in the assay using tissues of the frontal cortex, treatment of Compound A but not Compound B inhibited [¹²⁵I]-CRF binding, indicating that only Compound A inhibited central [¹²⁵I]-CRF binding. In the peripheral CRF challenge, increase in plasma ACTH concentration was significantly suppressed by both Compound A and Compound B. In contrast, Compound A inhibited the increase in locomotion induced by the central CRF challenge while Compound B did not. Compound A also reduced central CRF challenge-induced anxiety behavior and c-fos immunoreactivity in the cortex and the hypothalamic paraventricular nucleus. These results indicate that the central CRF signal, rather than the peripheral CRF signal would be related to anxiety and other behavioral changes, and CRF₁ receptor antagonism in the central nervous system may be critical for identifying drug candidates for anxiety and mood disorders.

Inhibition of the CRF1 receptor influences the activity of antidepressant drugs in the forced swim test in rats

Hyperactivity of the hypothalamic-pituitary-adrenal axis (HPA) and impairment of the central corticotropin-releasing factor (CRF) system are factors in the pathogenesis of depression. Though several antagonists of the CRF₁ receptor were effective in the recognized behavioral tests for antidepressant activity, there is still little information on the potential interactions between CRF₁ receptor inhibitors and conventional antidepressant therapy. The aim of our study was to assess the influence of SN003, a CRF₁ receptor blocker, on the activity of imipramine and fluoxetine in the forced swim test (FST) in rats which presented some signs of depression. The experiments were carried out on female Wistar rats subjected to 14-day subcutaneous corticosterone (CORT) administration (20 mg/kg/day). The antidepressant-like effect was determined by the FST and the CRF levels in the hypothalamus, amygdala, and peripheral blood were measured by a high-sensitivity immunoenzymatic test. SN003 (0.5 mg/kg) potentiated the antidepressant-like effect of imipramine (15 mg/kg) and fluoxetine (7.5 mg/kg). Moreover, the co-administration of the tested agents abolished CORT-induced increase in CRF levels in the examined biological material more profoundly than monotherapy. Our present findings give further evidence that the blockage of CRF action may be useful in the treatment of mood disorders. The concurrent use of well-known antidepressants with CRF₁ receptor antagonists could be beneficial in terms of safety, since it requires lower doses of the applied agents.

Selective corticotropin-releasing factor 1 receptor antagonist E2508 reduces restraint stress-induced defecation and visceral pain in rat models

N-Cyclopropylmethyl-7-(2,6-dimethoxy-4-methoxymethylphenyl)-2-ethyl-N-(tetrahydro-2H-pyran-4-ylmethyl)pyrazolo[1,5-a]pyridin-3-amine tosylate (E2508) is a newly discovered selective corticotropin-releasing factor 1 receptor antagonist. Here, we investigated the effects of E2508 on wrap restraint stress-induced defecation and visceral pain in rats. Oral pretreatment with E2508 dose-dependently decreased stool weights after 20min wrap restraint stress and significant effects were observed at doses of 30 and 100mg/kg. However, E2508 did not affect basal defecation at doses up to 100mg/kg. In contrast, alosetron, a 5-HT₃ receptor antagonist, decreased both wrap restraint stress-induced and basal stool output at a dose of 0.1mg/kg. In a rat visceral pain model, subcutaneous injections of both E2508 (0.01 and 0.1mg/kg) and alosetron (0.001 and 0.01mg/kg) significantly decreased the number of abdominal muscle contractions induced by colonic distention, suggesting these drugs reduced visceral pain. Together, these results demonstrate E2508 has the potential to be an effective therapy for the treatment of irritable bowel syndrome with a lower risk of adverse events such as constipation compared with the current clinically used 5-HT₃ receptor antagonist.

Selective corticotropin-releasing factor 1 receptor antagonist E2508 has potent antidepressant-like and anxiolytic-like properties in rodent models

Corticotropin-releasing factor (CRF) is a hormone secreted by the hypothalamus in response to stress, and CRF antagonists may be effective for the treatment of stress-related disorders including major depressive and anxiety disorders. Here, we investigated the in vivo pharmacological profile of N-cyclopropylmethyl-7-(2,6-dimethoxy-4-methoxymethylphenyl)-2-ethyl-N-(tetrahydro-2H-pyran-4-ylmethyl)pyrazolo[1,5-a]pyridin-3-amine tosylate (E2508), a recently synthesized, orally active CRF1 receptor antagonist. Oral administration of a single dose of E2508 (3 or 10mg/kg), but not fluoxetine (30mg/kg), a selective serotonin reuptake inhibitor (SSRI), significantly shortened immobility time in rats in the forced swim test. E2508 (10, 30, or 100mg/kg) also showed an antidepressant-like effect in the forced swim test in mice, with no sedative or muscle relaxant effects for doses up to 100mg/kg. Moreover, E2508 (5 or 20mg/kg) significantly reduced anxiety-like behavior in the rat defensive burying test. Diazepam, a benzodiazepine anxiolytic agent, also showed an anxiolytic effect in the defensive burying test at the same dose that induced a muscle relaxant effect in mice. Administration of E2508 (30mg/kg) for 14 consecutive days did not affect sexual behavior. By contrast, fluoxetine (30mg/kg) administration for ≥7 consecutive days decreased sexual behavior. These results indicate that E2508 has both potent antidepressant-like and anxiolytic-like effects in rodent models, and is well tolerated compared with a commonly prescribed therapeutic SSRI or benzodiazepine.

Reduced vasopressin receptors activation mediates the anti-depressant effects of fluoxetine and venlafaxine in bulbectomy model of depression

RATIONALE

In response to stress, corticotropin releasing hormone (CRH) and vasopressin (AVP) are released from the hypothalamus, activate their receptors (CRHR1, CRHR2 or AVPr1b), and synergistically act to induce adrenocorticotropic hormone (ACTH) release from the anterior pituitary. Overstimulation of this system has been frequently associated with major depression states.

OBJECTIVE

The objective of the study is to assess the role of AVP and CRH receptors in fluoxetine and venlafaxine effects on the expression of depression-related behavior.

METHODS

In an animal model of depression (olfactory bulbectomy in mice, OB), we evaluated the effects of fluoxetine or venlafaxine (both 10 mg/kg/day) chronic administration on depression-related behavior in the tail suspension test. Plasma levels of AVP, CRH, and ACTH were determined as well as participation of their receptors in the expression of depression related-behavior and gene expression of AVP and CRH receptors (AVPr1b, CRHR1, and CRHR2) in the pituitary gland.

RESULTS

The expression of depressive-like behavior in OB animals was reversed by treatment with both antidepressants. Surprisingly, OB-saline mice exhibited increased AVP and ACTH plasma levels, with no alterations in CRH levels when compared to sham mice. Chronic fluoxetine or venlafaxine reversed these effects. In addition, a significant increase only in AVPr1b gene expression was found in OB-saline.

CONCLUSION

The antidepressant therapy used seems to be more likely related to a reduced activation of AVP rather than CRH receptors, since a positive correlation between AVP levels and depressive-like behavior was observed in OB animals. Furthermore, a full restoration of depressive behavior was observed in OB-fluoxetine- or venlafaxine-treated mice only when AVP was centrally administered but not CRH.

PSD-95 regulates CRFR1 localization, trafficking and β-arrestin2 recruitment

Corticotropin-releasing factor (CRF) is a neuropeptide commonly associated with the hypothalamic-pituitary adrenal axis stress response. Upon release, CRF activates two G protein-coupled receptors (GPCRs): CRF receptor 1 (CRFR1) and CRF receptor 2 (CRFR2). Although both receptors contribute to mood regulation, CRFR1 antagonists have demonstrated anxiolytic and antidepressant-like properties that may be exploited in the generation of new pharmacological interventions for mental illnesses. Previous studies have demonstrated CRFR1 capable of heterologously sensitizing serotonin 2A receptor (5-HT2AR) signaling: another GPCR implicated in psychiatric disease. Interestingly, this phenomenon was dependent on Postsynaptic density 95 (PSD-95)/Disc Large/Zona Occludens (PDZ) interactions on the distal carboxyl termini of both receptors. In the current study, we demonstrate that endogenous PSD-95 can be co-immunoprecipitated with CRFR1 from cortical brain homogenate, and this interaction appears to be primarily via the PDZ-binding motif. Additionally, PSD-95 colocalizes with CRFR1 within the dendritic projections of cultured mouse neurons in a PDZ-binding motif-dependent manner. In HEK 293 cells, PSD-95 overexpression inhibited CRFR1 endocytosis, whereas PSD-95 shRNA knockdown enhanced CRFR1 endocytosis. Although PSD-95 does not appear to play a significant role in CRF-mediated cAMP or ERK1/2 signaling, PSD-95 was demonstrated to suppress β-arrestin2 recruitment: providing a potential mechanism for PSD-95's inhibition of endocytosis. In revisiting previously documented heterologous sensitization, PSD-95 shRNA knockdown did not prevent CRFR1-mediated enhancement of 5-HT2AR signaling. In conclusion, we have identified and characterized a novel functional relationship between CRFR1 and PSD-95 that may have implications in the design of new treatment strategies for mental illness.

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

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

Antidepressant/anxiolytic potential and adverse effect liabilities of melanin-concentrating hormone receptor 1 antagonists in animal models

Melanin-concentrating hormone receptor 1 (MCH1 receptor) is known to be involved in the control of mood and stress, in addition to the regulation of feeding. Here, we report further evidence that the blockade of the MCH1 receptor exhibits antidepressant and anxiolytic-like effects in a variety of animal models using TASP0382650 and TASP0489838, newly synthesized MCH1 receptor antagonists, with different scaffolds. Both TASP0382650 and TASP0489838 exhibited high affinities for human MCH1 receptor with IC50 values of 7.13 and 3.80nM, respectively. Both compounds showed potent antagonist activities at the MCH1 receptor, as assessed using MCH-increased [(35)S]GTPγS binding to human MCH1 receptor and an MCH-induced [Ca(2+)]i assay in rat MCH1 receptor expressing cells. In contrast, neither TASP0382650 nor TASP0489838 showed an affinity for the MCH2 receptor, another MCH receptor subtype. The oral administration of TASP0382650 or TASP0489838 significantly reduced the immobility time during the forced swimming test in rats, and reduced hyperemotionality induced by an olfactory bulbectomy, both of which are indicative of an antidepressant-like potential. In the olfactory bulbectomy model, the antidepressant effect of TASP0382650 appeared following a single administration, suggesting a faster onset of action, compared with current medications. Moreover, both TASP0382650 and TASP0489838 exhibited anxiolytic effects in several animal models of anxiety. In contrast, both TASP0382650 and TASP0489838 did not affect spontaneous locomotor activity, motor function, spatial memory during the Morris water maze task, or the convulsion threshold to pentylenetetrazole. These findings provide additional evidence that the blockade of the MCH1 receptor exhibits antidepressant- and anxiolytic activities with no adverse effects in experimental animal models.

Antidepressant and anxiolytic profiles of newly synthesized arginine vasopressin V1B receptor antagonists: TASP0233278 and TASP0390325

BACKGROUND AND PURPOSE

Vasopressin V1B receptor antagonists may be effective for the treatment of depression and anxiety and the objective of this study was to characterize the pharmacological profiles of two newly synthesized arginine vasopressin receptor 1B (V1B receptor) antagonists, TASP0233278 and TASP0390325.

EXPERIMENTAL APPROACH

We investigated the in vitro profiles of TASP0233278 and TASP0390325. In addition, the effect of TASP0390325 on the increase in plasma adrenocorticotropic hormone (ACTH) levels induced by corticotropin-releasing factor (CRF)/desmopressin (dDAVP) was investigated. We also investigated the antidepressant and anxiolytic profiles of TASP0233278 and TASP0390325 in animal models.

KEY RESULTS

Both TASP0233278 and TASP0390325 showed a high affinity and potent antagonist activity for V1B receptors. Oral administration of TASP0390325 antagonized the increase in plasma ACTH levels induced by CRF/dDAVP in rats, indicating that TASP0390325 blocks the anterior pituitary V1B receptor in vivo. Oral administration of TASP0233278 or TASP0390325 also exerted antidepressant effects in two models of depression (a forced swimming test and an olfactory bulbectomy model). Moreover, TASP0233278 improved depressive-like behaviour induced by repeated treatment with corticosterone, a model that has been shown to be resistant to treatment with currently prescribed antidepressants. In addition to depression models, TASP0233278 or TASP0390325 exerted anxiolytic effects in several anxiety models (social interaction, elevated plus-maze, stress-induced hyperthermia, separation-induced ultrasonic vocalization and sodium lactate-induced panic-like responses in panic-prone rats).

CONCLUSION

TASP0233278 and TASP0390325 are potent and orally active V1B receptor antagonists with antidepressant and anxiolytic activities in rodents.

PDZK1/NHERF3 differentially regulates corticotropin-releasing factor receptor 1 and serotonin 2A receptor signaling and endocytosis

The corticotropin-releasing factor receptor 1 (CRFR1) and serotonin 2A receptor (5-HT2AR) are linked to cellular mechanisms underlying stress anxiety and depression. Both receptors are members of the G protein-coupled receptor (GPCR) superfamily and encode class I PSD-95/DiscsLarge/Zona Occludens 1 (PDZ) binding motifs (-S/T-x-V/I/L) at the end of their carboxyl-terminal tails. We have identified PDZK1, also referred to as Na(+)/H(+) exchange regulatory cofactor 3 (NHERF3) as both a CRFR1- and 5-HT2AR-interacting protein. We have examined whether PDZK1 plays a role in regulating both CRFR1 and 5-HT2AR activity. We find that while PDZK1 interactions with CRFR1 are PDZ binding motif-dependent, PDZK1 associates with 5-HT2AR in a PDZ binding motif-independent manner and CRFR1 expression, but not 5-HT2AR expression, redistributes PDZK1 to the plasma membrane in PDZ binding motif-dependent manner. PDZK1, negatively regulates 5-HT2AR endocytosis and has no effect upon 5-HT2AR-mediated ERK1/2 phosphorylation. In contrast, PDZK1 overexpression does not affect CRFR1 endocytosis, but selectively increases CRFR1-stimulated ERK1/2 phosphorylation. Similar to what has been previously reported for PSD-95 and SAP97, PDZK1 positively influences 5-HT2AR-stimulated inositol phosphate formation, but does not contribute to the regulation of CRFR1-mediated cAMP signaling. Taken together, these results indicate that PDZK1 differentially regulates the signaling and trafficking of CRFR1 and 5-HT2AR via PDZ-dependent and -independent mechanisms, respectively.

Influence of genetic polymorphisms involved in the hypothalamic-pituitary-adrenal axis and their interactions with environmental factors on antidepressant response

AIMS

To investigate the role of genetic polymorphisms in candidate genes associated with the HPA axis and their interactions with environmental stressors in antidepressant response.

METHODS

The remission of depressive symptoms after 8 weeks of antidepressant treatment was tested against 21 single nucleotide polymorphisms (SNPs) in five candidate genes associated with the HPA axis in a Chinese Han sample suffering from unipolar depression (n = 273). Any history of childhood trauma and recent negative life events were measured using the Childhood Trauma Questionnaire-Short Form (CTQ-SF) (n = 206) and the Life Event Scale (48 item, LES) (n = 207), respectively. Reporter gene assays were used to evaluate the possible effects of the most significant SNP on gene expression.

RESULTS

A functional polymorphism at 3'UTR of the corticotropin-releasing hormone receptor 1 (CRHR1) gene (rs28364032) and three haplotypes containing it showed significant relationships with antidepressant remission. Further laboratory-based genomic studies showed that the G-to-A change of rs28364032 resulted in a 10-12% decrease in the intensity of luciferase activity. However, we failed to find association of environments and their interaction with HPA system-related genes with antidepressant remission.

CONCLUSIONS

Our results support a definite role for CRHR1 in the pharmacogenetics of antidepressant drugs. This may contribute to interpatient differences in their responses to antidepressant drugs.

N-Phenylpropyl-N'-(3-methoxyphenethyl)piperazine (YZ-185) Attenuates the Conditioned-Rewarding Properties of Cocaine in Mice

Sigma receptor antagonists diminish the effects of cocaine in behavioral assays, including conditioned place preference. Previous locomotor activity experiments in mice determined that the sigma receptor ligand YZ-185 (N-phenylpropyl-N′-(3-methoxyphenethyl)piperazine) enhanced cocaine-induced hyperactivity at a lower (0.1 μmol/kg) dose and dose-dependently attenuated cocaine-induced hyperactivity at higher (3.16–31.6 μmol/kg) doses. The present study investigated the effect of YZ-185 on cocaine's conditioned-rewarding properties in mice. YZ-185 (0.1, 0.316, 3.16, and 31.6 μmol/kg) did not have intrinsic activity to produce conditioned place preference or aversion. A higher (31.6 μmol/kg) YZ-185 dose, but not lower (0.1–3.16 μmol/kg) YZ-185 doses, prevented the development of place preference to cocaine (66 μmol/kg). YZ-185 did not alter the expression of cocaine place preference. To further characterize YZ-185's behavioral profile, its effects in the elevated zero maze and rotarod procedures were also determined; YZ-185 produced no significant change from baseline in either assay, indicating that the sigma receptors probed by YZ-185 do not regulate anxiety-like or coordinated motor skill behaviors. Overall, these results suggest that YZ-185 is a sigma receptor antagonist at the 31.6 μmol/kg dose and demonstrate that sigma receptors can mediate the development of the conditioned-rewarding properties of cocaine.

Behavioural and neurochemical changes induced by stress-related conditions are counteracted by the neurokinin-2 receptor antagonist saredutant

These experiments were undertaken to assess the mechanisms underlying the antidepressant-like effects of the neurokinin-2 (NK(2)) receptor antagonist saredutant (SR48968) in rats tested in the forced swim test (FST), by analysing hippocampal brain-derived neurotrophic factor (BDNF) and plasma corticosterone [as index of hypothalamic-pituitary-adrenal (HPA) axis activity]. Male Wistar rats received three intraperitoneal injections over 24 h of vehicle, saredutant (5 mg/kg), citalopram (15 mg/kg), clomipramine (50 mg/kg). Rats were subjected to restraint stress (4 h) 24 h prior to the FST procedure. This stress procedure increased immobility and decreased swimming behaviour in the FST; furthermore, it lowered hippocampal BDNF protein expression and increased plasma corticosterone levels. Saredutant and clomipramine or citalopram, used here as positive controls, reduced the immobility time in the FST both under basal conditions and after stress exposure. This effect was not attributable to changes in locomotion, because locomotor activity was unchanged when assessed in the open field test. Pretreatment with para-cholorophenylalanine (150 mg/kg, 72 h and 48 h prior to FST) abolished the effect of citalopram and saredutant on immobility time. At neurochemical level, saredutant attenuated activation of HPA axis in stressed animals more than clomipramine or citalopram. The behavioural effects of saredutant support the hypothesis that NK(2) receptor activity is involved in stress-related disorders. These effects of saredutant may be related to normalization of the HPA axis. Moreover, saredutant increases BDNF expression in the hippocampus, confirming the role of NK(2) receptor blockade in BDNF activation following stressor application.

Role of SAP97 protein in the regulation of corticotropin-releasing factor receptor 1 endocytosis and extracellular signal-regulated kinase 1/2 signaling

The corticotropin-releasing factor (CRF) receptor 1 (CRFR1) is a target for the treatment of psychiatric diseases such as depression, schizophrenia, anxiety disorder, and bipolar disorder. The carboxyl-terminal tail of the CRFR1 terminates in a PDZ-binding motif that provides a potential site for the interaction of PSD-95/Discs Large/Zona Occludens 1 (PDZ) domain-containing proteins. In this study, we found that CRFR1 interacts with synapse-associated protein 97 (SAP97; also known as DLG1) by co-immunoprecipitation in human embryonic 293 (HEK 293) cells and cortical brain lysates and that this interaction is dependent upon an intact PDZ-binding motif at the end of the CRFR1 carboxyl-terminal tail. Similarly, we demonstrated that SAP97 is recruited to the plasma membrane in HEK 293 cells expressing CRFR1 and that mutation of the CRFR1 PDZ-binding motif results in the redistribution of SAP97 into the cytoplasm. Overexpression of SAP97 antagonized agonist-stimulated CRFR1 internalization, whereas single hairpin (shRNA) knockdown of endogenous SAP97 in HEK 293 cells resulted in increased agonist-stimulated CRFR1 endocytosis. CRFR1 was internalized as a complex with SAP97 resulting in the redistribution of SAP97 to endocytic vesicles. Overexpression or shRNA knockdown of SAP97 did not significantly affect CRFR1-mediated cAMP formation, but SAP97 knockdown did significantly attenuate CRFR1-stimulated ERK1/2 phosphorylation in a PDZ interaction-independent manner. Taken together, our studies show that SAP97 interactions with CRFR1 attenuate CRFR1 endocytosis and that SAP97 is involved in coupling G protein-coupled receptors to the activation of the ERK1/2 signaling pathway.

Behavioral, biological, and chemical perspectives on targeting CRF(1) receptor antagonists to treat alcoholism

BACKGROUND

Alcohol use disorders are chronic disabling conditions for which existing pharmacotherapies have only modest efficacy. In the present review, derived from the 2012 Behavior, Biology and Chemistry "Translational Research in Addiction" symposium, we summarize the anti-relapse potential of corticotropin-releasing factor type 1 (CRF(1)) receptor antagonists to reduce negative emotional symptoms of acute and protracted alcohol withdrawal and stress-induced relapse to alcohol seeking.

METHODS

We review the biology of CRF(1) systems, the activity of CRF(1) receptor antagonists in animal models of anxiolytic and antidepressant activity, and experimental findings in alcohol addiction models. We also update the clinical trial status of CRF(1) receptor antagonists, including pexacerfont (BMS-562086), emicerfont (GW876008), verucerfont (GSK561679), CP316311, SSR125543A, R121919/NBI30775, R317573/19567470/CRA5626, and ONO-2333Ms. Finally, we discuss the potential heterogeneity and pharmacogenomics of CRF(1) receptor pharmacotherapy for alcohol dependence.

RESULTS

The evidence suggests that brain penetrant-CRF(1) receptor antagonists have therapeutic potential for alcohol dependence. Lead compounds with clinically desirable pharmacokinetic properties now exist, and longer receptor residence rates (i.e., slow dissociation) may predict greater CRF(1) receptor antagonist efficacy. Functional variants in genes that encode CRF system molecules, including polymorphisms in Crhr1 (rs110402, rs1876831, rs242938) and Crhbp genes (rs10055255, rs3811939) may promote alcohol seeking and consumption by altering basal or stress-induced CRF system activation.

CONCLUSIONS

Ongoing clinical trials with pexacerfont and verucerfont in moderately to highly severe dependent anxious alcoholics may yield insight as to the role of CRF(1) receptor antagonists in a personalized medicine approach to treat drug or alcohol dependence.

Anxiolytic effects of yokukansan, a traditional Japanese medicine, via serotonin 5-HT1A receptors on anxiety-related behaviors in rats experienced aversive stress

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan, a traditional Japanese medicine (Kampo), has been reported in the treatment of behavioral and psychological symptoms of dementia (BPSD) such as aggression, anxiety and depression in patients with Alzheimer's disease and other forms of senile dementia.

AIMS OF THE STUDY

In the present study, we investigated the anxiolytic effects of yokukansan on anxiety-related behaviors in rats that have experienced aversive stress.

MATERIALS AND METHODS

We used male Wistar/ST rats which received an electrical footshock as aversive stress. Yokukansan at a dose of 1.0 g/kg was administered orally once a day for 14 or 16 day before behavioral tests. To evaluate the anxiolytic effects, we used the contextual fear conditioning (CFC) test and elevated plus-maze (EPM) test. And we also investigated effects of yokukansan on locomotor activity in the Open-field (OF) test and on the change in plasma corticosterone after CFC stress, in rats that had experienced footshock stress.

RESULTS

In the CFC test, rats that had experienced footshock showed significant freezing behavior on re-exposure to the box 14 day after footshock stress. Yokukansan significantly suppressed freezing behavior in the CFC test. In the EPM test on the 16th day after the CFC test, yokukansan significantly increased the time spent in open arms after footshock stress compared to control rats. However, repeated administration of yokukansan on the 14th day did not affect the decrease in locomotor activity and the increase in plasma corticosterone by re-exposure to the box 14 day after footshock stress in the OF test and determination of serum corticosterone, respectively. These anxiolytic effects by yokukansan were antagonized by WAY-100635, a selective 5-HT(1A) receptor antagonist, in the CFC test, but not the EPM test. Furthermore, 5-HT(1A) receptor agonist buspirone significantly suppressed freezing behavior in the CFC test; however, buspirone induced no change in the time spent in open arms in the EPM test.

CONCLUSION

These findings suggested that yokukansan has anxiolytic effects on anxiety-like behaviors induced by both innate fear and memory-dependent fear. In particular, yokukansan produced anxiolytic effects via 5-HT(1A) receptors in memory-dependent fear induced by aversive stress. Furthermore, yokukansan could be useful as one of the therapeutic drugs for the treatment of anxiety disorders and various mental disorders that have comorbid anxiety.

Severe stress switches CRF action in the nucleus accumbens from appetitive to aversive

Stressors motivate an array of adaptive responses ranging from “fight or flight” to an internal urgency signal facilitating long-term goals¹. However, traumatic or chronic uncontrollable stress promotes the onset of Major Depressive Disorder where acute stressors lose their motivational properties and are perceived as insurmountable impediments². Consequently, stress-induced depression is a debilitating human condition characterized by an affective shift from engagement of the environment to withdrawal³. An emerging neurobiological substrate of depression and associated pathology is the nucleus accumbens, a region with the capacity to mediate a diverse range of stress responses by interfacing limbic, cognitive and motor circuitry⁴. Here we report that corticotropin releasing factor (CRF), a neuropeptide released in response to acute stressors⁵ and other arousing environmental stimuli⁶, acts in the nucleus accumbens of naïve mice to increase dopamine release through co-activation of CRF R1 and R2 receptors. Remarkably, severe stress exposure completely abolished this effect without recovery for at least 90 days. This loss of CRF’s capacity to regulate dopamine release in the nucleus accumbens is accompanied by a switch in the reaction to CRF from appetitive to aversive, indicating a diametric change in the emotional response to acute stressors. Thus, the current findings offer a biological substrate for the switch in affect which is central to stress-induced depressive disorders.

Blockade of CRF1 receptors in the central nucleus of the amygdala attenuates the dysphoria associated with nicotine withdrawal in rats

The majority of smokers relapse during the acute withdrawal phase when withdrawal symptoms are most severe. The goal of the present studies was to investigate the role of corticotropin-releasing factor (CRF) and noradrenergic transmission in the central nucleus of the amygdala (CeA) in the dysphoria associated with smoking cessation. It was investigated if blockade of CRF1 receptors, blockade of α1-adrenergic receptors, or stimulation of α2-adrenergic receptors in the CeA diminishes the deficit in brain reward function associated with nicotine withdrawal in rats. Nicotine dependence was induced by implanting minipumps that delivered a nicotine solution. Withdrawal was precipitated with the nicotinic acetylcholine receptor antagonist mecamylamine. A discrete-trial intracranial self-stimulation procedure was used to assess the negative affective aspects of nicotine withdrawal. Elevations in brain reward thresholds are indicative of a deficit in brain reward function. In all the experiments, mecamylamine elevated the brain reward thresholds of the rats chronically treated with nicotine and did not affect the brain reward thresholds of the saline-treated control rats. Intra-CeA administration of the CRF1 receptor antagonist R278995/CRA0450 completely prevented the mecamylamine-induced elevations in brain reward thresholds in the nicotine-treated rats and did not affect the brain reward thresholds of the saline-treated control rats. R278995/CRA0450 has also been shown to block sigma-1 receptors but there is no evidence that this could affect negative mood states. Intra-CeA administration of the α1-adrenergic receptor antagonist prazosin or the α2-adrenergic receptor agonist clonidine did not affect the brain reward thresholds of the nicotine or saline-treated rats. These studies suggest that CRF1 receptor antagonists may diminish the dysphoria associated with smoking cessation by blocking CRF1 receptors in the CeA.

R278995/CRA0450, a corticotropin-releasing factor (CRF(1)) receptor antagonist modulates REM sleep measures in rats: Implication for therapeutic indication

Abnormalities in the regulation of the hypothalamic stress hormone corticotropin-releasing factor (CRF) are thought to play a critical role in mood disorders. Consequently, CRF receptor antagonists have been proposed as potential novel therapeutic agents of these conditions. Sleep disturbance is common in depressed patients and changed sleep-wake architecture is considered as potential predictor or surrogate marker of response to treatment. The aim of our study was to characterise the effects of oral administration of the corticotropin-releasing factor CRF(1) receptor antagonist R278995/CRA0450 (3 and 10mg/kg) on sleep-wake organization and electroencephalographic (EEG) components in Sprague-Dawley rats, and to determine whether the changes observed in the sleep-EEG pattern resemble those seen with antidepressants. At 3mg/kg, R278995/CRA0450 produced minor changes in sleep behaviour, while an overall reduction in power spectra was observed during deep slow wave sleep. At 10mg/kg, R278995/CRA0450 consistently reduced rapid eye movement (REM) sleep (-75.4%) and increased the REM sleep onset latency (+67%, 92.1±4.9min for vehicle vs. 153.8±24min for R278995/CRA0450), in the absence of systematic changes in spectral EEG pattern, which are characteristic anti-depressant-like effects. These findings in rats indicate that the corticotropin-releasing factor CRF(1) receptor antagonist R278995/CRA0450 is centrally active under standard conditions as it inhibits REM sleep and promotes wakefulness. The characteristic changes found in the sleep EEG model further support the hypothesis that R278995/CRA0450 could exert a non-sedative, antidepressant-like action.

Corticotropin releasing factor receptor antagonists for major depressive disorder

INTRODUCTION

Major depressive disorder is a serious and common psychiatric illness, and many of the depressive patients benefit from pharmacological treatment. Available antidepressants produce remission in only about 30 -- 40% of the patients. Therefore, new concepts are being explored for the development of innovative antidepressants with higher efficacy.

AREAS COVERED

The use of corticotropin releasing factor type 1 (CRF1) receptor antagonists for depression is supported by abundant evidence of target validation, the availability of in vitro and in vivo assays and specific small ligands. Some of these compounds have advanced to clinical studies, with discouraging results so far in depression. This review covers the development of CRF1 receptor antagonists at different stages of the development pipeline of the pharmaceutical industry and its bottlenecks. Most of the available CRF1 receptor antagonists known so far share a common chemical scaffold. We present possible strategies to overcome obstacles in the discovery and development process at the levels of library screenings and clinical studies to find more diverse compounds.

EXPERT OPINION

CRF1 receptor antagonists are expected to be beneficial only for those patients with CRF overexpression and the need for tests to identify these individuals is discussed. New technical developments and diagnostic tools might eventually lead to a more successful treatment of major depression with CRF1 receptor antagonists.

The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology

Anxiety disorders are highly comorbid with each other and with major depressive disorder. As syndromes, anxiety and mood disorders share many symptoms, and several treatments are effective for both. Despite this overlap, there exist many distinguishing features that support the continued classification of individual anxiety disorders that are distinct from each other and from major depression. The goal of this article is to describe the key biological similarities and differences between anxiety disorders.

A role for delta opioid receptors in the central nucleus of the amygdala in anxiety-like behaviors

RATIONALE

Compounds acting on delta opioid receptors (DOR) modulate anxiety-like behaviors, yet the site of action underlying this effect is unknown. DOR mRNA and protein are expressed in the central nucleus of the amygdala, a region that plays an important role in processing fear, stress, and anxiety. We hypothesized that this brain region may contribute to the modulation of anxiety by DOR drugs.

OBJECTIVE

The present study investigated the role of DOR in the central amygdala in anxiety-like behaviors.

METHODS

The selective DOR agonist [D-Pen 2,5]-enkephalin (DPDPE) or antagonist naltrindole was bilaterally microinjected into the central nucleus of the amygdala of adult male Sprague Dawley rats and anxiety-like behaviors were assessed using the elevated plus maze. The effects of DOR agonists on heightened anxiety produced by stress were also investigated.

RESULTS

Rats injected with DPDPE into the central nucleus of the amygdala demonstrated less anxiety-like behavior, as evidenced by significantly greater number of open-arm entries and time spent in the open arms than controls. Naltrindole administered alone did not affect the duration or number of entries onto the open arms; however, naltrindole pre-treatment blocked the anxiolytic effects produced by DPDPE. Systemic administration of the selective DOR agonist, SNC80, or microinjection of DPDPE into the central amygdala prior to a swim stress blocked the anxiogenic effect produced by the swim stress.

CONCLUSIONS

These findings provide direct evidence that activation of DOR in the central amygdala reduces anxiety-like behavior and suggest that DOR in this area are important for regulating anxious states.

The beta3 adrenoceptor agonist, amibegron (SR58611A) counteracts stress-induced behavioral and neurochemical changes

These experiments were made to study the mechanisms underlying the antidepressant-like effects of the beta(3) adrenoceptor agonist amibegron (SR58611A). To this purpose, the expression levels of the hippocampal cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl-2) and Bax proteins were assessed, by using western blot analysis, in rats tested in the forced swim test (FST). Under basal conditions (no previous exposure to stressors), different groups of male Wistar rats received acutely or repeatedly (once/day for 7days) intraperitoneal (i.p.) injections of amibegron (1, 5 and 10mg/kg), the tricyclic antidepressant (TCA) clomipramine (50mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (15mg/kg) or their vehicles. The influence of stress-related conditions was studied in rats subjected to acute (4h) or repeated (4h/day for 7days) restraint stress, applied prior to the FST procedure. Compared to the control groups, both stressor procedures increased the immobility time in the FST and reduced hippocampal BDNF and Bcl-2/Bax ratio proteins expression, which were counteracted by amibegron (5 and 10mg/kg) treatment. Opposite effects were found in the CREB expression, since it was lower after acute and higher after repeated stress procedure, respectively. Again, these effects were reversed by amibegron treatment. Different results were obtained in animals treated with clomipramine or citalopram. Hence, it is likely that the observed behavioral effects of amibegron could be due, at least in part, to its action on hippocampal expression of neurotrophic and/or anti-apoptotic factors, supporting the hypothesis that beta(3) adrenoceptors may be a therapeutic target for the treatment of stress-related disorders.

Therapeutic utility of non-peptidic CRF1 receptor antagonists in anxiety, depression, and stress-related disorders: evidence from animal models

Adaptive responding to threatening stressors is of fundamental importance for survival. Dysfunctional hyperactivation of corticotropin releasing factor type-1 (CRF(1)) receptors in stress response system pathways is linked to stress-related psychopathology and CRF(1) receptor antagonists (CRAs) have been proposed as novel therapeutic agents. CRA effects in diverse animal models of stress that detect anxiolytics and/or antidepressants are reviewed, with the goal of evaluating their potential therapeutic utility in depression, anxiety, and other stress-related disorders. CRAs have a distinct phenotype in animals that has similarities to, and differences from, those of classic antidepressants and anxiolytics. CRAs are generally behaviorally silent, indicating that CRF(1) receptors are normally in a state of low basal activation. CRAs reduce stressor-induced HPA axis activation by blocking pituitary and possibly brain CRF(1) receptors which may ameliorate chronic stress-induced pathology. In animal models sensitive to anxiolytics and/or antidepressants, CRAs are generally more active in those with high stress levels, conditions which may maximize CRF(1) receptor hyperactivation. Clinically, CRAs have demonstrated good tolerability and safety, but have thus far lacked compelling efficacy in major depressive disorder, generalized anxiety disorder, or irritable bowel syndrome. CRAs may be best suited for disorders in which stressors clearly contribute to the underlying pathology (e.g. posttraumatic stress disorder, early life trauma, withdrawal/abstinence from addictive substances), though much work is needed to explore these possibilities. An evolving literature exploring the genetic, developmental and environmental factors linking CRF(1) receptor dysfunction to stress-related psychopathology is discussed in the context of improving the translational value of current animal models.

Effects of prolonged ethanol vapor exposure on forced swim behavior, and neuropeptide Y and corticotropin-releasing factor levels in rat brains

Depressive symptoms in alcohol-dependent individuals are well-recognized and clinically relevant phenomena. The etiology has not been elucidated although it is clear that the depressive symptoms may be alcohol independent or alcohol induced. To contribute to the understanding of the neurobiology of chronic ethanol use, we investigated the effects of chronic intermittent ethanol vapor exposure on behaviors in the forced swim test (FST) and neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) levels in specific brain regions. Adult male Wistar rats were subjected to intermittent ethanol vapor (14 h on/10 h off) or air exposure for 2 weeks and were then tested at three time points corresponding to acute withdrawal (8-12 h into withdrawal) and protracted withdrawal (30 and 60 days of withdrawal) in the FST. The behaviors that were measured in the five-min FST consisted of latency to immobility, swim time, immobility time, and climbing time. The FST results showed that the vapor-exposed animals displayed depressive-like behaviors; for instance, decreased latency to immobility in acute withdrawal and decreased latency to immobility, decreased swim time and increased immobility time in protracted withdrawal, with differences between air- and vapor-exposed animals becoming more pronounced over the 60-day withdrawal period. NPY levels in the frontal cortex of the vapor-exposed animals were decreased compared with the control animals, and CRF levels in the amygdala were correlated with increased immobility time. Thus, extended ethanol vapor exposure produced long-lasting changes in FST behavior and NPY levels in the brain.

Riluzole rapidly attenuates hyperemotional responses in olfactory bulbectomized rats, an animal model of depression

Growing evidence indicates that the glutamatergic neurotransmitter system is central to the neurobiology and treatment of depression. Riluzole, a drug currently used to slow the progression of amyotrophic lateral sclerosis (ALS), directly affects the glutamatergic system. In this study, we investigated the effects of riluzole in olfactory bulbectomy (OBX) rats, an animal model of depression. The olfactory bulbs in rats were removed by suction. The emotionality of rats was measured by scoring their responses to given stimuli, i.e., attack, startle, struggle, and fight responses. The OBX rats chronically treated with vehicle for 7 days at 14 days following surgery showed significant increases in emotionality responses. Single (1st day administration) and subchronic (7th day administration) riluzole treatment (1-10 mg/kg, po) significantly and dose-dependently reduced hyperemotional responses in OBX rats. Both single and subchronic riluzole treatment (10 mg/kg, po) had no significant effects on the emotional responses in sham operated rats. In addition, we demonstrated that single riluzole treatment (10 mg/kg, po) significantly decreased extracellular glutamate levels in medial prefrontal cortex of OBX rats by in vivo microdialysis. We provide the first experimental evidence that riluzole rapidly attenuated hyperemotional responses in OBX rats, an animal model of depression.

CRF receptor blockade prevents initiation and consolidation of stress effects on affect in the predator stress model of PTSD

Post traumatic stress disorder (PTSD) is a chronic anxiety disorder initiated by an intensely threatening, traumatic event. There is a great need for more efficacious pharmacotherapy and preventive treatments for PTSD. In animals, corticotropin-releasing factor (CRF) and the CRF1 receptor play a critical role in behavioural and neuroendocrine responses to stress. We tested the hypothesis that CRF1 activation is required for initiation and consolidation of long-term effects of trauma on anxiety-like behaviour in the predator exposure (predator stress) model of PTSD. Male C57BL6 mice were treated with the selective CRF1 antagonist CRA0450 (2, 20 mg/kg) 30 min before or just after predator stress. Long-term effects of stress on rodent anxiety were measured 7 d later using acoustic startle, elevated plus maze (EPM), light/dark box, and hole-board tests. Predator stress increased startle amplitude and delayed startle habituation, increased time in and decreased exits from the dark chamber in the light/dark box test, and decreased risk assessment in the EPM. CRF1 antagonism had limited effects on these behaviours in non-stressed controls, with the high dose decreasing risk assessment in the EPM. However, in stressed animals CRF1 antagonism blocked initiation and consolidation of stressor effects on startle, and returned risk assessment to baseline levels in predator-stressed mice. These findings implicate CRF1 activation in initiation and post-trauma consolidation of predator stress effects on anxiety-like behaviour, specifically on increased arousal as measured by exaggerated startle behaviours. These data support further research of CRF1 antagonists as potential prophylactic treatments for PTSD.

Corticotropin-Releasing Hormone, Glutamate, and γ-Aminobutyric Acid in Depression

Stress response and depression have a significant impact on modern society. Although the symptoms are well characterized, the molecular mechanisms underlying depression are largely unknown. The monoamine hypothesis, which postulates dysfunctional noradrenergic and serotonergic systems as the underlying primary cause of depression, has been valuable for the development of conventional antidepressants, which can reverse these dysfunctional states to some degree. However, recent data from various neuroscience disciplines have questioned the major role of amines in the pathogenesis of depression. A considerable amount of evidence has accumulated that suggests that normalization of the hypothalamo—pituitary—adrenal (HPA) system might be the final step necessary for a remission of depression. In addition, an increasing body of clinical and postmortem evidence is pointing to a role played by γ-aminobutyric acid (GABA) and glutamate in the etiology of depression. This review examines the evidence, mainly obtained from clinical studies or from postmortem brain material, for a major role of the HPA axis, glutamatergic, and GABAergic systems in the pathogenesis of major and bipolar depression. The authors hope that these insights will stimulate further studies with the final aim of developing new types of antidepressants that combine increased efficacy with a shorter delay of the onset of action and reduced side-effect profiles.

Progress in corticotropin-releasing factor-1 antagonist development

Corticotropin releasing factor (CRF) receptor antagonists have been sought since the stress-secreted peptide was isolated in 1981. Although evidence is mixed concerning the efficacy of CRF(1) antagonists as antidepressants, CRF(1) antagonists might be novel pharmacotherapies for anxiety and addiction. Progress in understanding the two-domain model of ligand-receptor interactions for CRF family receptors might yield chemically novel CRF(1) receptor antagonists, including peptide CRF(1) antagonists, antagonists with signal transduction selectivity and nonpeptide CRF(1) antagonists that act via the extracellular (rather than transmembrane) domains. Novel ligands that conform to the prevalent pharmacophore and exhibit drug-like pharmacokinetic properties have been identified. The therapeutic utility of CRF(1) antagonists should soon be clearer: several small molecules are currently in Phase II/III clinical trials for depression, anxiety and irritable bowel syndrome.

Disrupted startle modulation in animal models for affective disorders

Affective startle modulation is used to study emotional reactivity in humans, and blunted affective startle modulation has been reported in depressed patients. To determine whether blunted affective startle modulation is also a common feature in animal models for affective disorders, light-enhanced startle was studied in three models: inescapable foot shock (IFS), repeated restraint stress (RRS) and olfactory bulbectomy (OBX). In addition, prepulse inhibition was studied in these models. Light-enhanced startle was blunted following IFS and OBX and RRS decreased overall startle responding. Prepulse inhibition, however, was unaffected. These findings indicate that induction models for affective disorders may be associated with long term effects on affective startle modulation. The lack of changes in sensory motor gating suggests that these changes can be ascribed to alterations in emotional reactivity. In conclusion, our results indicate that the blunted affective startle modulation seen in animal models for affective disorders may be used to examine the mechanisms underlying altered emotional reactivity.