Corticotropin-releasing factor CRF1, but not CRF2, receptors mediate anxiogenic-like behavior

Novel Pharmacological Targets of Post-Traumatic Stress Disorders

Post-traumatic stress disorder (PTSD) is a psychopathological condition with a heterogeneous clinical picture that is complex and challenging to treat. Its multifaceted pathophysiology still remains an unresolved question and certainly contributes to this issue. The pharmacological treatment of PTSD is mainly empirical and centered on the serotonergic system. Since the therapeutic response to prescribed drugs targeting single symptoms is generally inconsistent, there is an urgent need for novel pathogenetic hypotheses, including different mediators and pathways. This paper was conceived as a narrative review with the aim of debating the current pharmacological treatment of PTSD and further highlighting prospective targets for future drugs. The authors accessed some of the main databases of scientific literature available and selected all the papers that fulfilled the purpose of the present work. The results showed that most of the current pharmacological treatments for PTSD are symptom-based and show only partial benefits; this largely reflects the limited knowledge of its neurobiology. Growing, albeit limited, data suggests that the hypothalamic-pituitary-adrenal axis, opioids, glutamate, cannabinoids, oxytocin, neuropeptide Y, and microRNA may play a role in the development of PTSD and could be targeted for novel treatments. Indeed, recent research indicates that examining different pathways might result in the development of novel and more efficient drugs.

Ouabain Reverts CUS-Induced Disruption of the HPA Axis and Avoids Long-Term Spatial Memory Deficits

Ouabain (OUA) is a cardiotonic steroid that modulates Na+, K+ -ATPase activity. OUA has been identified as an endogenous substance that is present in human plasma, and it has been shown to be associated with the response to acute stress in both animals and humans. Chronic stress is a major aggravating factor in psychiatric disorders, including depression and anxiety. The present work investigates the effects of the intermittent administration of OUA (1.8 μg/kg) during the chronic unpredictable stress (CUS) protocol in a rat's central nervous system (CNS). The results suggest that the intermittent OUA treatment reversed CUS-induced HPA axis hyperactivity through a reduction in (i) glucocorticoids levels, (ii) CRH-CRHR1 expression, and by decreasing neuroinflammation with a reduction in iNOS activity, without interfering with the expression of antioxidant enzymes. These changes in both the hypothalamus and hippocampus may reflect in the rapid extinction of aversive memory. The present data demonstrate the ability of OUA to modulate the HPA axis, as well as to revert CUS-induced long-term spatial memory deficits.

Type 1 Corticotropin-Releasing Factor Receptor Differentially Modulates Neurotransmitter Levels in the Nucleus Accumbens of Juvenile versus Adult Rats

Adversity is particularly pernicious in early life, increasing the likelihood of developing psychiatric disorders in adulthood. Juvenile and adult rats exposed to social isolation show differences in anxiety-like behaviors and significant changes in dopamine (DA) neurotransmission in the nucleus accumbens (NAc). Brain response to stress is partly mediated by the corticotropin-releasing factor (CRF) system, composed of CRF and its two main receptors, CRF-R1 and CRF-R2. In the NAc shell of adult rats, CRF induces anxiety-like behavior and changes local DA balance. However, the role of CRF receptors in the control of neurotransmission in the NAc is not fully understood, nor is it known whether there are differences between life stages. Our previous data showed that infusion of a CRF-R1 antagonist into the NAc of juvenile rats increased DA levels in response to a depolarizing stimulus and decreased basal glutamate levels. To extend this analysis, we now evaluated the effect of a CRF-R1 antagonist infusion in the NAc of adult rats. Here, we describe that the opposite occurred in the NAc of adult compared to juvenile rats. Infusion of a CRF-R1 antagonist decreased DA and increased glutamate levels in response to a depolarizing stimulus. Furthermore, basal levels of DA, glutamate, and γ-Aminobutyric acid (GABA) were similar in juvenile animals compared to adults. CRF-R1 protein levels and localization were not different in juvenile compared to adult rats. Interestingly, we observed differences in the signaling pathways of CRF-R1 in the NAc of juveniles compared to adult rats. We propose that the function of CRF-R1 receptors is differentially modulated in the NAc according to life stage.

(3α,5α)3-Hydroxypregnan-20-one (3α,5α-THP) Regulation of the HPA Axis in the Context of Different Stressors and Sex

Corticotropin-releasing factor (CRF) regulates the stress response in the hypothalamus and modulates neurotransmission across the brain through CRF receptors. Acute stress increases hypothalamic CRF and the GABAergic neurosteroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP). We previously showed that 3α,5α-THP regulation of CRF is sex and brain region dependent. In this study, we investigated 3α,5α-THP regulation of stress-induced hypothalamic CRF, CRF receptor type 1 (CRFR1), CRF binding protein (CRFBP), pro-opiomelanocortin (POMC), and glucocorticoid receptor (GR) by western blot and circulating corticosterone (CORT) by enzyme-linked immunosorbent assay (ELISA) in male and female Sprague Dawley rats. Tissue was collected after rats were injected with 3α,5α-THP (15 mg/kg, IP) or vehicle 15 min prior to 30 min of restraint stress (RS), or 10 min of forced swim stress (FSS) and 20 min recovery. The initial exposure to a stress stimulus increased circulating CORT levels in both males and females, but 3α,5α-THP attenuated the CORT response only in females after RS. 3α,5α-THP reduced GR levels in male and females, but differently between stressors. 3α,5α-THP decreased the CRF stress response after FSS in males and females, but after RS, only in female rats. 3α,5α-THP reduced the CRFR1, CRFBP, and POMC increases after RS and FSS in males, but in females only after FSS. Our results showed different stress responses following different types of stressors: 3α,5α-THP regulated the HPA axis at different levels, depending on sex.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Role of Basolateral Amygdalar Somatostatin 2 Receptors in a Rat Model of Chronic Anxiety

Repeated exposure to stress has been implicated in inducing chronic anxiety states. Stress related increases in anxiety responses are likely mediated by activation of corticotropin-releasing factor receptors (CRFR) in the amygdala, particularly the basolateral amygdala (BLA). Within the BLA, acute injections of the CRFR agonist urocortin 1 (Ucn1) leads to acute anxiety, whereas repeated daily injections of subthreshold-doses of Ucn1 produces a long-lasting, persistent anxiety-like phenotype, a phenomenon referred to as Ucn1-priming. Relative gene expressions from the BLA of vehicle and Ucn1-primed rats were analyzed with quantitative RT-PCR using a predesigned panel of 82 neuroscience-related genes. Compared to vehicle-primed rats, only expression of the somatostatin receptor 2 gene (Sstr2) was significantly reduced in the BLA of Ucn1-primed rats. The contribution of Sstr2 on an anxiety phenotype was tested by injecting a Sstr2 antagonist into the BLA in un-primed rats. The Sstr2 antagonist increased anxiety-like behavior. Notably, pretreatment with Sstr2 agonist injected into the BLA blocked anxiety-inducing effects of acute Ucn1 BLA-injections and delayed anxiety expression during Ucn1-priming. However, concomitant Sstr2 agonist pretreatment during Ucn-1 priming did not prevent either the development of a chronic anxiety state or a reduction of BLA Sstr2 expression induced by priming. The data demonstrate that the persistent anxiety-like phenotype observed with Ucn1-priming in the BLA is associated with a selective reduction of Sstr2 gene expression. Although Sstr2 activation in the BLA blocks acute anxiogenic effects of stress and down-regulation of BLA Sstr2, it does not suppress the long-term consequences of prolonged exposure to stress-related challenges.

Synthesis, in vitro biological investigation, and molecular dynamics simulations of thiazolopyrimidine based compounds as corticotrophin releasing factor receptor-1 antagonists

Corticotrophin releasing factor receptor-1 (CRFR1) is a potential target for treatment of depression and anxiety through modifying stress response. A series of new thiazolo[4,5-d]pyrimidine derivatives were designed, prepared and biologically evaluated as potential CRFR1 antagonists. Four compounds produced more than fifty percent inhibition in the [125I]-Tyr0-sauvagine specific binding assay. Assessment of binding affinities revealed that compound (3-(2,4-dimethoxyphenyl)-7-(dipropylamino)-5-methylthiazolo[4,5-d]pyrimidin-2(3H)-one) 8c was the best candidate with highest binding affinity (Ki = 32.1 nM). Further evaluation showed the ability of compound 8c to inhibit CRF induced cAMP accumulation in a dose response manner. Docking and molecular dynamics simulations were used to investigate potential binding modes of synthesized compounds as well as the stability of 8c-CRFR1 complex. These studies suggest similar allosteric binding of 8c compared to that of the co-crystalized ligand CP-376395 in 4K5Y pdb file.

Negative consequences of early-life adversity on substance use as mediated by corticotropin-releasing factor modulation of serotonin activity

Early-life adversity is associated with increased risk for substance abuse in later life, with women more likely to report past and current stress as a mediating factor in their substance use and relapse as compared to men. Preclinical models of neonatal and peri-adolescent (early through late adolescence) stress all support a direct relationship between experiences of early-life adversity and adult substance-related behaviors, and provide valuable information regarding the underlying neurobiology. This review will provide an overview of these animal models and how these paradigms alter drug and alcohol consumption and/or seeking in male and female adults. An introduction to the corticotropin-releasing factor (CRF) and serotonin systems, their development and their interactions at the level of the dorsal raphe will be provided, illustrating how this particular stress system is sexually dimorphic, and is well positioned to be affected by stressors early in development and throughout maturation. A model for CRF-serotonin interactions in the dorsal raphe and how these influence dopaminergic activity within the nucleus accumbens and subsequent reward-associated behaviors will be provided, and alterations to the activity of this system following early-life adversity will be identified. Overall, converging findings suggest that early-life adversity has long-term effects on the functioning of the CRF-serotonin system, highlighting a potentially important and targetable mediator linking stress to addiction. Future work should focus on identifying the exact mechanisms that promote long-term changes to the expression and activity of CRF receptors in the dorsal raphe. Moreover, it is important to clarify whether similar neurobiological mechanisms exist for males and females, given the sexual dimorphism both in CRF receptors and serotonin indices in the dorsal raphe and in the behavioral outcomes of early-life adversity.

•

Early life stress increases risk for substance abuse in adulthood.

•

Stress and drugs increase CRF which alters serotonin release in the brain.

•

CRF₂ receptor expression in the dorsal raphe is altered by early life stress.

•

Resultant changes to serotonin output facilitates dopamine in the accumbens.

•

CRF₂-sertotonin-dopamine interactions may link early life stress with substance abuse.

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.

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

Studies have used paradigms based on animal models to understand human emotional behavior because they appear to be correlated with fear- and anxiety-related defensive patterns in non-human mammals. In this context, tonic immobility (TI) behavior is an innate response associated with extreme threat situations, such as predator attack. Some reports have demonstrated the involvement of corticotropin-releasing factor (CRF) in regulation of the endocrine system, defensive behaviors and behavioral responses to stress. Particularly, a previous study showed that the activation of CRF receptors in the basolateral (BLA) or central (CeA) nuclei of the amygdala increased TI responses, whereas treatment with a non-selective CRF antagonist, alpha-helical-CRF_9-41, decreased this innate fear response. However, while CRF₁ receptors have pronounced effects in stress-induced anxiety, CRF₂ receptors appear be involved in the expression of both stress-induced anxiety and spontaneous anxiety behavior. In this study, we investigated the effects of specific CRF receptors, CRF₁ and CRF₂, in the BLA and CeA on the duration of TI in guinea pigs. The results show that blockade of CRF₁ and CRF₂ receptors in the BLA and CeA produces a decrease in fear and/or anxiety, as suggested by a decrease in TI duration in the guinea pigs. Additionally, the specific antagonists for CRF₁ and CRF₂ receptors were able to prevent the increase in TI duration induced by CRF administration at the same sites. These results suggest that the modulation of fear and anxiety by the CRF system in the BLA and CeA occurs through concomitant effects on CRF₁ and CRF₂ receptors.

The Place of Stress and Emotions in the Irritable Bowel Syndrome

Our emotional state can have many consequences on our somatic health and well-being. Negative emotions such as anxiety play a major role in gut functioning due to the bidirectional communications between gut and brain, namely, the brain-gut axis. The irritable bowel syndrome (IBS), characterized by an unusual visceral hypersensitivity, is the most common disorder encountered by gastroenterologists. Among the main symptoms, the presence of current or recurrent abdominal pain or discomfort associated with bloating and altered bowel habits characterizes this syndrome that could strongly alter the quality of life. This chapter will present the physiopathology of IBS and explain how stress influences gastrointestinal functions (permeability, motility, microbiota, sensitivity, secretion) and how it could be predominantly involved in IBS. This chapter will also describe the role of the autonomic nervous system and the hypothalamic-pituitary axis through vagal tone and cortisol homeostasis. An analysis is made about how emotions and feelings are involved in the disruption of homeostasis, and we will see to what extent the balance between vagal tone and cortisol may reflect dysfunctions of the brain-gut homeostasis. Finally, the interest of therapeutic treatments focused on stress reduction and vagal tone enforcement is discussed.

Region-specific roles of the corticotropin-releasing factor-urocortin system in stress

Dysregulation of the corticotropin-releasing factor (CRF)-urocortin (UCN) system has been implicated in stress-related psychopathologies such as depression and anxiety. It has been proposed that CRF-CRF receptor type 1 (CRFR1) signalling promotes the stress response and anxiety-like behaviour, whereas UCNs and CRFR2 activation mediate stress recovery and the restoration of homeostasis. Recent findings, however, provide clear evidence that this view is overly simplistic. Instead, a more complex picture has emerged that suggests that there are brain region- and cell type-specific effects of CRFR signalling that are influenced by the individual's prior experience and that shape molecular, cellular and ultimately behavioural responses to stressful challenges.

Cognitive disruptions in stress-related psychiatric disorders: A role for corticotropin releasing factor (CRF)

This article is part of a Special Issue "SBN 2014". Stress is a potential etiology contributor to both post-traumatic stress disorders (PTSD) and major depression. One stress-related neuropeptide that is hypersecreted in these disorders is corticotropin releasing factor (CRF). Dysregulation of CRF has long been linked to the emotion and mood symptoms that characterize PTSD and depression. However, the idea that CRF also mediates the cognitive disruptions observed in patients with these disorders has received less attention. Here we review literature indicating that CRF can alter cognitive functions. Detailed are anatomical studies revealing that CRF is poised to modulate regions required for learning and memory. We also describe preclinical behavioral studies that demonstrate CRF's ability to alter fear conditioning, impair memory consolidation, and alter a number of executive functions, including attention and cognitive flexibility. The implications of these findings for the etiology and treatment of the cognitive impairments observed in stress-related psychiatric disorders are described.

Polymorphism in the corticotropin-releasing factor receptor 1 (CRF1-R) gene plays a role in shaping the high anxious phenotype of Marchigian Sardinian alcohol-preferring (msP) rats

INTRODUCTION

Marchigian Sardinian alcohol-preferring (msP) rats exhibit innate preference for alcohol along with anxious phenotype. In these animals, two single-nucleotide polymorphisms in position -1,836 and -2,097 from the first start codon of the CRF1-R transcript have been found.

MATERIALS AND METHODS

Here, we examined whether these point mutations account for the heightened anxiety-like behavior and stress responsiveness of msP rats. We rederived the msP rats to obtain two distinct lines carrying the wild-type (GG) and point mutations (AA), respectively.

RESULTS

CRF1-R gene expression analysis revealed significant dysregulation of the system in the extended amygdala of AA rats. At the behavioral level, using the elevated plus maze, we found that both AA and GG lines had higher basal anxiety compared to Wistar rats. In the defensive burying test, AA rats showed decreased burying behavior compared to the GG and the unselected Wistar lines. Freezing/immobility did not differ among AA and GG but was higher than that of Wistars. The selective CRF1-R antagonist antalarmin (0, 10, and 20 mg/kg) reduced burying behavior in Wistar animals. However, antalarmin (10 mg/kg) tended to increase rather than reducing this behavior when tested in the msP lines, an effect that appeared more marked in the GG as compared to the AA line.

CONCLUSION

The present data suggest that rats with msP genetic background are more anxious and show different sensitivity to stress and CRF1-R blockade than Wistars. The point mutations occurring in the CRF1-R gene do not seem to influence basal anxiety while they appear to affect active responses to stress.

Sex differences in stress-related psychiatric disorders: neurobiological perspectives

Stress is associated with the onset and severity of several psychiatric disorders that occur more frequently in women than men, including posttraumatic stress disorder (PTSD) and depression. Patients with these disorders present with dysregulation of several stress response systems, including the neuroendocrine response to stress, corticolimbic responses to negatively valenced stimuli, and hyperarousal. Thus, sex differences within their underlying circuitry may explain sex biases in disease prevalence. This review describes clinical studies that identify sex differences within the activity of these circuits, as well as preclinical studies that demonstrate cellular and molecular sex differences in stress responses systems. These studies reveal sex differences from the molecular to the systems level that increase endocrine, emotional, and arousal responses to stress in females. Exploring these sex differences is critical because this research can reveal the neurobiological underpinnings of vulnerability to stress-related psychiatric disorders and guide the development of novel pharmacotherapies.

Genetic variants in the genes of the stress hormone signalling pathway and depressive symptoms during and after pregnancy

Purpose. The aim of this study was to investigate whether single nucleotide polymorphisms (SNPs) in genes of the stress hormone signaling pathway, specifically FKBP5, NR3C1, and CRHR1, are associated with depressive symptoms during and after pregnancy. Methods. The Franconian Maternal Health Evaluation Study (FRAMES) recruited healthy pregnant women prospectively for the assessment of maternal and fetal health including the assessment of depressiveness. The German version of the 10-item Edinburgh Postnatal Depression Scale (EPDS) was completed at three time points in this prospective cohort study. Visit 1 was at study entry in the third trimester of the pregnancy, visit 2 was shortly after birth, and visit 3 was 6–8 months after birth. Germline DNA was collected from 361 pregnant women. Nine SNPs in the above mentioned genes were genotyped. After construction of haplotypes for each gene, a multifactorial linear mixed model was performed to analyse the depression values over time. Results. EPDS values were within expected ranges and comparable to previously published studies. Neither did the depression scores differ for comparisons among haplotypes at fixed time points nor did the change over time differ among haplotypes for the examined genes. No haplotype showed significant associations with depressive symptoms severity during pregnancy or the postpartum period. Conclusion. The analysed candidate haplotypes in FKBP5, NR3C1, and CRHR1 did not show an association with depression scores as assessed by EPDS in this cohort of healthy unselected pregnant women.

Neurochemical mechanisms and pharmacologic strategies in managing nausea and vomiting related to cyclic vomiting syndrome and other gastrointestinal disorders

Nausea and vomiting are common gastrointestinal complaints which could be triggered by stimuli in both the peripheral and central nervous systems. They may be considered as defense mechanisms when threatening toxins/agents enter the gastrointestinal tract or there is excessive retention of gastrointestinal contents due to obstruction. The pathophysiology of nausea and vomiting is complex and much still remains unknown. Therefore, treatments are restricted or ineffective in many cases. Nausea and vomiting with functional etiologies including cyclic vomiting syndrome are challenging in gastroenterology. In this article, we review potential pathways, neurochemical transmitters, and their receptors which are possibly involved in the pathophysiology of nausea and vomiting including the entity cyclic vomiting syndrome.

Fenproporex increases locomotor activity and alters energy metabolism, and mood stabilizers reverse these changes: a proposal for a new animal model of mania

Fenproporex (Fen) is converted in vivo into amphetamine, which is used to induce mania-like behaviors in animals. In the present study, we intend to present a new animal model of mania. In order to prove through face, construct, and predictive validities, we evaluated behavioral parameters (locomotor activity, stereotypy activity, and fecal boli amount) and brain energy metabolism (enzymes citrate synthase; malate dehydrogenase; succinate dehydrogenase; complexes I, II, II-III, and IV of the mitochondrial respiratory chain; and creatine kinase) in rats submitted to acute and chronic administration of fenproporex, treated with lithium (Li) and valproate (VPA). The administration of Fen increased locomotor activity and decreased the activity of Krebs cycle enzymes, mitochondrial respiratory chain complexes, and creatine kinase, in most brain structures evaluated. In addition, treatment with mood stabilizers prevented and reversed this effect. Our results are consistent with the literature that demonstrates behavioral changes and mitochondrial dysfunction caused by psychostimulants. These findings suggest that chronic administration of Fen may be a potential animal model of mania.

Cortagine infused into the medial prefrontal cortex attenuates predator-induced defensive behaviors and Fos protein production in selective nuclei of the amygdala in male CD1 mice

Corticotropin-releasing factor (CRF) plays an essential role in coordinating the autonomic, endocrine and behavioral responses to stressors. In this study, we investigated the role of CRF within the medial prefrontal cortex (mPFC) in modulating unconditioned defensive behaviors, by examining the effects of microinfusing cortagine a selective type-1 CRF receptor (CRF1) agonist, or acidic-astressin a preferential CRF1 antagonist, into the mPFC in male CD-1 mice exposed to a live predator (rat exposure test--RET). Cortagine microinfusions significantly reduced several indices of defense, including avoidance and freezing, suggesting a specific role for CRF1 within the infralimbic and prelimbic regions of the mPFC in modulating unconditioned behavioral responsivity to a predator. In contrast, microinfusions of acidic-astressin failed to alter defensive behaviors during predator exposure in the RET. Cortagine microinfusions also reduced Fos protein production in the medial, central and basomedial, but not basolateral subnuclei of the amygdala in mice exposed to the rat predatory threat stimulus. These results suggest that CRF1 activation within the mPFC attenuates predator-induced unconditioned anxiety-like defensive behaviors, likely via inhibition of specific amygdalar nuclei. Furthermore, the present findings suggest that the mPFC represents a unique neural region whereby activation of CRF1 produces behavioral effects that contrast with those elicited following systemic administration of CRF1 agonists.

Differential activation of neuronal cell types in the basolateral amygdala by corticotropin releasing factor

Enhanced corticotropin releasing factor (CRF) release in the basolateral amygdala (BLA) is strongly associated with the generation of behavioral stress responses through activation of the CRF-R1 receptor subtype. Stress and anxiety-like behavior are modulated in part by the balance of peptide actions such as excitatory CRF and inhibitory neuropeptide Y (NPY) receptor activation in the BLA. While the actions of CRF are clear, little is known about the cell type influenced by CRF receptor stimulation. These studies were designed to identify the cell types within the BLA activated by intra-BLA administration of CRF using multi-label immunohistochemistry for cFos and markers for pyramidal (CaMKII-immunopositive) and interneuronal [glutamic acid decarboxylase (GAD65)] cell populations. Administration of CRF into the BLA produced a dose-dependent increase in the expression of cFos-ir. Intra-BLA injection of CRF induced significant increases in cFos-ir in the CaMKII-ir population. Although increases in cFos-ir in GAD65-ir cells were observed, this did not reach statistical significance perhaps in part due to the decreased numbers of GAD65-ir cells within the BLA after CRF treatment. These findings demonstrate that CRF, when released into the BLA, activates projection neurons and that the activity of GABAergic interneurons is also altered by CRF treatment. Decreases in the number of GAD65-ir neurons could reflect either increased or decreased activity of these cells and future studies will more directly address these possibilities. The expression of cFos is associated with longer term regulation of gene expression which may be involved in the profound long term effects of neuropeptides, such as CRF, on the activity and plasticity of BLA pyramidal neurons.

Central corticotropin releasing factor and social stress

Social interactions are a main source of stress in vertebrates. Social stressors, as well as other stressors, activate the hypothalamic–pituitary–adrenal (HPA) axis resulting in glucocorticoid release. One of the main components of the HPA axis is corticotropin releasing factor (CRF). The neuropeptide CRF is part of a peptide family including CRF, urocortin 1–3, urotensin 1–3, and sauvagine. The actions of the CRF family are mediated by at least two different receptors with different anatomical distribution and affinities for the peptides. The CRF peptides affect several behavioral and physiological responses to stress including aggression, feeding, and locomotor activity. This review will summarize recent research in vertebrates concerning how social stress interacts with components of the CRF system. Consideration will be taken to the different models used for social stress ranging from social isolation, dyadic interactions, to group dominance hierarchies. Further, the temporal effect of social stressor from acute, intermittent, to chronic will be considered. Finally, strains selected for specific behavior or physiology linked to social stress will also be discussed.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Sex differences in stress-related receptors: ″micro″ differences with ″macro″ implications for mood and anxiety disorders

Stress-related psychiatric disorders, such as unipolar depression and post-traumatic stress disorder (PTSD), occur more frequently in women than in men. Emerging research suggests that sex differences in receptors for the stress hormones, corticotropin releasing factor (CRF) and glucocorticoids, contribute to this disparity. For example, sex differences in CRF receptor binding in the amygdala of rats may predispose females to greater anxiety following stressful events. Additionally, sex differences in CRF receptor signaling and trafficking in the locus coeruleus arousal center combine to make females more sensitive to low levels of CRF, and less adaptable to high levels. These receptor differences in females could lead to hyperarousal, a dysregulated state associated with symptoms of depression and PTSD. Similar to the sex differences observed in CRF receptors, sex differences in glucocorticoid receptor (GR) function also appear to make females more susceptible to dysregulation after a stressful event. Following hypothalamic pituitary adrenal axis activation, GRs are critical to the negative feedback process that inhibits additional glucocorticoid release. Compared to males, female rats have fewer GRs and impaired GR translocation following chronic adolescent stress, effects linked to slower glucocorticoid negative feedback. Thus, under conditions of chronic stress, attenuated negative feedback in females would result in hypercortisolemia, an endocrine state thought to cause depression. Together, these studies suggest that sex differences in stress-related receptors shift females more easily into a dysregulated state of stress reactivity, linked to the development of mood and anxiety disorders. The implications of these receptor sex differences for the development of novel pharmacotherapies are also discussed.

Exercise offers anxiolytic potential: a role for stress and brain noradrenergic-galaninergic mechanisms

Although physical activity reduces anxiety in humans, the neural basis for this response is unclear. Rodent models are essential to understand the mechanisms that underlie the benefits of exercise. However, it is controversial whether exercise exerts anxiolytic-like potential in rodents. Evidence is reviewed to evaluate the effects of wheel running, an experimental mode of exercise in rodents, on behavior in tests of anxiety and on norepinephrine and galanin systems in neural circuits that regulate stress. Stress is proposed to account for mixed behavioral findings in this literature. Indeed, running promotes an adaptive response to stress and alters anxiety-like behaviors in a manner dependent on stress. Running amplifies galanin expression in noradrenergic locus coeruleus (LC) and suppresses stress-induced activity of the LC and norepinephrine output in LC-target regions. Thus, enhanced galanin-mediated suppression of brain norepinephrine in runners is supported by current literature as a mechanism that may contribute to the stress-protective effects of exercise. These data support the use of rodents to study the emotional and neurobiological consequences of exercise.

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

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

Behavioral Studies and Genetic Alterations in Corticotropin-Releasing Hormone (CRH) Neurocircuitry: Insights into Human Psychiatric Disorders

To maintain well-being, all organisms require the ability to re-establish homeostasis in the presence of adverse physiological or psychological experiences. The regulation of the hypothalamic-pituitary adrenal (HPA) axis during stress is important in preventing maladaptive responses that may increase susceptibility to affective disorders. Corticotropin-releasing hormone (CRH) is a central stress hormone in the HPA axis pathway and has been implicated in stress-induced psychiatric disorders, reproductive and cardiac function, as well as energy metabolism. In the context of psychiatric disorders, CRH dysfunction is associated with the occurrence of post-traumatic stress disorder, major depression, anorexia nervosa, and anxiety disorders. Here, we review the synthesis, molecular signaling and regulation, as well as synaptic activity of CRH. We go on to summarize studies of altered CRH signaling in mutant animal models. This assembled data demonstrate an important role for CRH in neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation. Next, we present findings regarding human genetic polymorphisms in CRH pathway genes that are associated with stress and psychiatric disorders. Finally, we discuss a role for regulators of CRH activity as potential sites for therapeutic intervention aimed at treating maladaptive behaviors associated with stress.

Urocortins: CRF's siblings and their potential role in anxiety, depression and alcohol drinking behavior

It is widely accepted that stress, anxiety, depression and alcohol abuse-related disorders are in large part controlled by corticotropin-releasing factor (CRF) receptors. However, evidence is accumulating that some of the actions on these receptors are mediated not by CRF, but by a family of related Urocortin (Ucn) peptides Ucn1, Ucn2 and Ucn3. The initial narrow focus on CRF as the potential main player acting on CRF receptors appears outdated. Instead it is suggested that CRF and the individual Ucns act in a complementary and brain region-specific fashion to regulate anxiety-related behaviors and alcohol consumption. This review, based on a symposium held in 2011 at the research meeting on "Alcoholism and Stress" in Volterra, Italy, highlights recent evidence for regulation of these behaviors by Ucns. In studies on stress and anxiety, the roles of Ucns, and in particular Ucn1, appear more visible in experiments analyzing adaptation to stressors rather than testing basal anxiety states. Based on these studies, we propose that the contribution of Ucn1 to regulating mood follows a U-like pattern with both high and low activity of Ucn1 contributing to high anxiety states. In studies on alcohol use disorders, the CRF system appears to regulate not only dependence-induced drinking, but also binge drinking and even basal consumption of alcohol. While dependence-induced and binge drinking rely on the actions of CRF on CRFR1 receptors, alcohol consumption in models of these behaviors is inhibited by actions of Ucns on CRFR2. In contrast, alcohol preference is positively influenced by actions of Ucn1, which is capable of acting on both CRFR1 and CRFR2. Because of complex distribution of Ucns in the nervous system, advances in this field will critically depend on development of new tools allowing site-specific analyses of the roles of Ucns and CRF.

Site-specific genetic manipulation of amygdala corticotropin-releasing factor reveals its imperative role in mediating behavioral response to challenge

BACKGROUND

Faulty regulation of the central extrahypothalamic corticotropin-releasing factor (CRF) expression is associated with stress-related psychopathologies including anxiety disorders and depression. Extensive pharmacological literature describes the effects of CRF agonists or antagonists' administration on anxiety-like behavior. However, the relevance of the endogenous agonist, presumed to be CRF, has never been explicitly demonstrated. Several genetic models have been used to study the role of CRF in the physiological response to stress and in stress-related disorders. Nevertheless, developmental compensatory mechanisms and lack of spatial and temporal specificity limited the interpretations of these studies.

METHODS

Two lentiviral-based systems were designed, generated, and used to knockdown (KD) or conditionally overexpress (OE) CRF in the central amygdala (CeA) of adult mice. Behavioral responses associated with the CeA, such as anxiety, depression and fear memory, and the plasma corticosterone levels were evaluated under both basal and stressful conditions.

RESULTS

Changing the CeA-CRF levels mildly affected anxiety-like behaviors under basal conditions. However, following exposure to an acute stressor, CeA-CRF-KD strongly attenuated stress-induced anxiety-like behaviors, whereas a short-term CeA-CRF-overexpression enhanced the stress-induced effects on these behaviors. Interestingly, a significant increase in basal corticosterone levels in the CeA-CRF-KD mice was observed, demonstrating the importance of endogenous CeA-CRF levels for basal, but not stress-induced, corticosterone levels.

CONCLUSIONS

These results highlight the pivotal role of CeA CRF expression regulation in mediating adequate behavioral responses to stress and introduce these novel viral tools as a useful approach for dissecting the role of central CRF in mediating behavioral and neuroendocrine responses to stress.

Nicotine stimulates secretion of corticosterone via both CRH and AVP receptors

Corticosterone-releasing hormone (CRH) and arginine vasopressin (AVP) are crucial components of the hypothalamic-pituitary-adrenal axis that stimulates the release of adrenocorticotropic hormone from the pituitary and mediate the stress response. CRH binds to two subtypes of CRH receptors (CRH-R1 and CRH-R2) that are present in both central and peripheral tissues. We used the CRH-R1-specific antagonist, antalarmin (ANT), the CRH-R1 and CRH-R2 peptide antagonist, astressin (AST), and the CRH-R2-specific peptide antagonist, astressin2b (AST2b), to determine which CRH receptor is involved in the nicotine-stimulated secretion of corticosterone. Male C57BL/6 mice were administered ANT (20 mg/kg, i.p.), AST (0.3 mg/kg, i.p.), AST2b (0.3 mg/kg, i.p.) or vehicle prior to administration of nicotine (1.0 mg/kg, s.c.), CRH (10 μg/kg, s.c.), AVP (10 μg/kg, s.c.) or saline (s.c.), killed 15 min later and trunk blood collected and assayed for corticosterone plasma levels. We found that CRH enhanced corticosterone release, and this response was blocked by both AST and ANT. Nicotine also increased corticosterone secretion, but this effect persisted in the presence of either CRH antagonist. Furthermore, AST but not ANT or AST2b decreased corticosterone levels associated with stress of handling and injection. We also assessed the role of AVP V(1b) -specific receptor antagonist, SSR149415 alone and in combination with AST and AST2b. Although the AVP antagonist did not alter basal or nicotine-stimulated corticosterone secretion, it attenuated the AVP-induced stimulation of corticosterone and its combination with AST but not AST2b completely abolished nicotine-mediated stimulation of corticosterone secretion. Our results demonstrate that the nicotine-induced stimulation of the hypothalamic-pituitary-adrenal axis is mediated by both the CRH-R and the AVP V(1b) receptor and when the CRH receptor is blocked, nicotine may utilize the AVP V(1b) receptor to mediate secretion of corticosterone. These results argue in favor of the development of specific antagonists that block both AVP and CRH receptors to decrease the pleasurable component of nicotine, which may be mediated by corticosterone.

Lifelong CRF overproduction is associated with altered gene expression and sensitivity of discrete GABA(A) and mGlu receptor subtypes

RATIONALE

Repeated activation of corticotropin-releasing factor (CRF) receptors is associated with increased anxiety and enhanced stress responsivity, which may be mediated via limbic GABAergic and glutamatergic transmission.

OBJECTIVE

The present study investigated molecular and functional alterations in GABA(A) receptor (GABA(A)R) and metabotropic glutamate receptor (mGluR) responsivity in transgenic mice that chronically overexpress CRF.

METHODS

CRF(1) receptor, GABA(A)R, and mGluR sensitivity were determined in CRF-overexpressing mice using the stress-induced hyperthermia (SIH) test. In addition, we measured mRNA expression levels of GABA(A)R α subunits and mGluRs in the amygdala and hypothalamus.

RESULTS

CRF-overexpressing mice were less sensitive to the anxiolytic effects of the CRF(1) receptor antagonists CP154,526 and DMP695, the GABA(A)R α(3)-selective agonist TP003 (0-3 mg/kg) and the mGluR(2/3) agonist LY379268 (0-10 mg/kg) in the SIH test. The hypothermic effect of the non-selective GABA(A)R agonist diazepam (0-4 mg/kg) and the α(1)-subunit-selective GABA(A)R agonist zolpidem (0-10 mg/kg) was reduced in CRF-overexpressing mice. No genotype differences were found using the GABA(A)R α(5)-subunit preferential compound SH-053-2'F-R-CH(3) and mGluR(5) antagonists MPEP and MTEP. CRF-overexpressing mice showed decreased expression levels of GABA(A)R α(2) subunit and mGluR(3) mRNA levels in the amygdala, whereas these expression levels were increased in the hypothalamus. CRF-overexpressing mice also showed increased hypothalamic mRNA levels of α(1) and α(5) GABA(A)R subunits.

CONCLUSIONS

We found that lifelong CRF overproduction is associated with altered gene expression and reduced functional sensitivity of discrete GABA(A) and mGluR receptor subtypes. These findings suggest that sustained over-activation of cerebral CRF receptors may contribute to the development of altered stress-related behavior via modulation of GABAergic and glutamatergic transmission.

Prolonged and site-specific over-expression of corticotropin-releasing factor reveals differential roles for extended amygdala nuclei in emotional regulation

Corticotropin-releasing factor (CRF) has a key role in the central stress response, and altered levels of this neuropeptide are linked to stress-related psychopathologies such as anxiety and depression. These disorders are associated with the inability to properly regulate stress response, specifically following exposure to prolonged stressful stimuli. Therefore, the current study assessed the effects of prolonged and site-specific over-expression of CRF, which mimics the state of chronic production, in extended amygdala nuclei that are known to be involved in mediating anxiety-like states. We first constructed and generated lentiviruses that overexpress (OE) CRF in a robust and stable manner, and then generated two male mouse models continuously over-expressing CRF, either at the central nucleus of the amygdala (CeA), or at the dorsolateral subdivision of the bed nucleus of the stria terminalis (BNSTdl). After 4 months, behavioral assessments were conducted for anxiety and depressive indices on these mice. Surprisingly, prolonged CRF OE at the CeA attenuated stress-induced anxiety-like behaviors, whereas prolonged CRF OE in the BNSTdl increased depressive-like behaviors, without affecting anxiety levels. These results show possible differential roles for CRF expressed by distinct loci of the extended amygdala, in mediating stress-induced emotional behaviors.

Activation of corticotropin-releasing factor receptors from the basolateral or central amygdala increases the tonic immobility response in guinea pigs: an innate fear behavior

The tonic immobility (TI) behavior is an innate response associated with extreme threat situations such as a predator attack. Several studies have provided evidence suggesting an important role for corticotropin-releasing factor (CRF) in the regulation of the endocrine system, defensive behaviors and behavioral responses to stress. TI has been shown to be positively correlated with the basal plasma levels of corticosterone. CRF receptors and neurons that are immunoreactive to CRF are found in many cerebral regions, especially in the amygdaloid complex. Previous reports have demonstrated the involvement of the basolateral amygdaloid (BLA) and central amygdaloid (CeA) nuclei in the TI response. In this study, we evaluated the CRF system of the BLA and the CeA in the modulation of the TI response in guinea pigs. The activation of CRF receptors in the BLA and in the CeA promoted an increase in the TI response. In contrast, the inhibition of these receptors via alpha-helical-CRF(9-41) decreased the duration of the TI response. Moreover, neither the activation nor inhibition of CRF receptors in the BLA or the CeA altered spontaneous motor activity in the open-field test. These data suggest that the activation of the CRF receptors in the BLA or the CeA probably potentiates fear and anxiety, which may be one of the factors that promote an increase in the TI behavior. Therefore, these data support the role of the CRF system in the control of emotional responses, particularly in the modulation of innate fear.

CRF and urotensin I effects on aggression and anxiety-like behavior in rainbow trout

Corticotropin-releasing factor (CRF) is central in the stress response but also modulates several behaviors including anxiety-related behaviors and aggression. In this study, juvenile rainbow trout (Oncorhynchus mykiss) were tested for competitive ability, determined during dyadic fights for dominance, after intracerebroventricular (i.c.v.) administration of CRF, urotensin I (UI), the non-specific CRF antagonist α-helical RF(9-41) (ahCRF) or the CRF receptor subtype 1-specific antagonist antalarmin, when paired with a mass-matched con-specific injected with saline. In addition, isolated fish received the same substances. Plasma cortisol and brain monoamines were monitored in all fish. Most fish receiving CRF showed a conspicuous behavior consisting of flaring the opercula, opening the mouth and violent shaking of the head from side to side. When this occurred, the fish immediately forfeited the fight. Similar behavior was observed in most fish receiving UI but no effect on outcome of dyadic fights was noted. This behavior seems similar to non-ambulatory motor activity seen in rats and could be anxiety related. Furthermore, fish receiving CRF at a dose of 1000 ng became subordinate, whereas all other treatments had no effects on the outcome of dyadic fights. In addition, isolated fish receiving ahCRF had lower brain stem concentrations of 5-hydroxyindoleacetic acid, serotonin, 3,4-dihydroxyphenylacetic acid and dopamine. In conclusion, CRF seems to attenuate competitive ability, and both CRF and UI seem to induce anxiety-like behavior.

Differential effect of prenatal stress on the expression of corticotrophin-releasing hormone and its receptors in the hypothalamus and amygdala in male and female rats

The present study examined the effect of prenatal stress in rats from days 13-20 of gestation on anxiogenic behaviour in the elevated plus maze (EPM) together with changes in the gene expression of corticotrophin-releasing hormone (CRH), its receptors, CRHR1 and CRHR2, as well as CRH binding protein (CRH-BP) in the paraventricular nucleus (PVN) and amygdala of their male and female offspring. Both prenatally-stressed (PS) males and females showed heightened anxiety in the EPM. Prenatal stress did not alter the gene expression of CRH or its receptors in the male PVN, although it decreased CRH-BP mRNA, which could augment the activity of free CRH. In the PVN of PS females, there was an increase in the expression of CRH, coupled with a decrease in that of CRHR2 and CRH-BP. These changes are compatible with the greater activation of the hypothalamic pituitary adrenal axis to stress in females. Anxiogenic behaviour of PS rats was associated with a reduction of CRHR2 mRNA and of CRH-BP mRNA in the amygdala of males and an increase in CRH mRNA and decrease in CRHR2 mRNA in females. Two hours after acute stress of exposure to the elevated plus maze in which heightened anxiety was manifested, increases were seen only in the amygdala of females in CRH and CRHR1 signalling, whereas CRHR2 mRNA was reduced in both sexes. The data show that both prenatal stress and acute stress in adulthood have a differential sex-dependent effect on the expression of CRH its receptors and binding protein in the PVN and amygdala of rats.

Anorexia nervosa: a unified neurological perspective

The roles of corticotrophin-releasing factor (CRF), opioid peptides, leptin and ghrelin in anorexia nervosa (AN) were discussed in this paper. CRF is the key mediator of the hypothalamo-pituitary-adrenal (HPA) axis and also acts at various other parts of the brain, such as the limbic system and the peripheral nervous system. CRF action is mediated through the CRF1 and CRF2 receptors, with both HPA axis-dependent and HPA axis-independent actions, where the latter shows nil involvement of the autonomic nervous system. CRF1 receptors mediate both the HPA axis-dependent and independent pathways through CRF, while the CRF2 receptors exclusively mediate the HPA axis-independent pathways through urocortin. Opioid peptides are involved in the adaptation and regulation of energy intake and utilization through reward-related behavior. Opioids play a role in the addictive component of AN, as described by the "auto-addiction opioids theory". Their interactions have demonstrated the psychological aspect of AN and have shown to prevent the functioning of the physiological homeostasis. Important opioids involved are β-lipotropin, β-endorphin and dynorphin, which interact with both µ and κ opioids receptors to regulate reward-mediated behavior and describe the higher incidence of AN seen in females. Moreover, ghrelin is known as the "hunger" hormone and helps stimulate growth hormone (GH) and hepatic insulin-like-growth-factor-1(IGF-1), maintaining anabolism and preserving a lean body mass. In AN, high levels of GH due to GH resistance along with low levels of IGF-1 are observed. Leptin plays a role in suppressing appetite through the inhibition of neuropeptide Y gene. Moreover, the CRF, opioid, leptin and ghrelin mechanisms operate collectively at the HPA axis and express the physiological and psychological components of AN. Fear conditioning is an intricate learning process occurring at the level of the hippocampus, amygdala, lateral septum and the dorsal raphe by involving three distinct pathways, the HPA axis-independent pathway, hypercortisolemia and ghrelin. Opioids mediate CRF through noradrenergic stimulation in association with the locus coeruleus. Furthermore, CRF's inhibitory effect on gonadotropin releasing hormone can be further explained by the direct relationship seen between CRF and opioids. Low levels of gonadotropin have been demonstrated in AN where only estrogen has shown to mediate energy intake. In addition, estrogen is involved in regulating µ receptor concentrations, but in turn both CRF and opioids regulate estrogen. Moreover, opioids and leptin are both an effect of AN, while many studies have demonstrated a causal relationship between CRF and anorexic behavior. Moreover, leptin, estrogen and ghrelin play a role as predictors of survival in starvation. Since both leptin and estrogen are associated with higher levels of bone marrow fat they represent a longer survival than those who favor the ghrelin pathway. Future studies should consider cohort studies involving prepubertal males and females with high CRF. This would help prevent the extrapolation of results from studies on mice and draw more meaningful conclusions in humans. Studies should also consider these mechanisms in post-AN patients, as well as look into what predisposes certain individuals to develop AN. Finally, due to its complex pathogenesis the treatment of AN should focus on both the pharmacological and behavioral perspectives.

The CRF system, stress, depression and anxiety-insights from human genetic studies

A concatenation of findings from preclinical and clinical studies support a preeminent function for the corticotropin-releasing factor (CRF) system in mediating the physiological response to external stressors and in the pathophysiology of anxiety and depression. Recently, human genetic studies have provided considerable support to several long-standing hypotheses of mood and anxiety disorders, including the CRF hypothesis. These data, reviewed in this report, are congruent with the hypothesis that this system is of paramount importance in mediating stress-related psychopathology. More specifically, variants in the gene encoding the CRF(1) receptor interact with adverse environmental factors to predict risk for stress-related psychiatric disorders. In-depth characterization of these variants will likely be important in furthering our understanding of the long-term consequences of adverse experience.

Comparative biotransformation of pyrazinone-containing corticotropin-releasing factor receptor-1 antagonists: minimizing the reactive metabolite formation

(S)-5-Chloro-1-(1-cyclopropylethyl)-3-(2,6-dichloro-4-(trifluoromethyl)phenylamino)pyrazin-2(1H)-one (BMS-665053), a pyrazinone-containing compound, is a potent and selective antagonist of corticotropin-releasing factor receptor-1 (CRF-R1) that showed efficacy in the defensive withdrawal model for anxiety in rats, suggesting its use as a potential treatment for anxiety and depression. In vitro metabolism studies of BMS-665053 in rat and human liver microsomes revealed cytochrome P450-mediated oxidation of the pyrazinone moiety, followed by ring opening, as the primary metabolic pathway. Detection of a series of GSH adducts in trapping experiments suggested the formation of a reactive intermediate, probably as a result of epoxidation of the pyrazinone moiety. In addition, BMS-665053 (20 mg/kg i.v.) underwent extensive metabolism in bile duct-cannulated (BDC) rats. The major drug-related materials in rat plasma were the pyrazinone oxidation products. In rat bile and urine (0-7 h), only a trace amount of the parent drug was recovered, whereas significant levels of the pyrazinone epoxide-derived metabolites and GSH-related conjugates were detected. Further evidence suggested that GSH-related conjugates also formed at the dichloroarylamine moiety possibly via an epoxide or a quinone imine intermediate. Other major metabolites in BDC rat bile and urine included glucuronide conjugates. To reduce potential liability due to metabolic activation of BMS-665053, a number of pyrazinone analogs with different substituents were synthesized and investigated for reactive metabolite formation, leading to the discovery of a CRF-R1 antagonist with diminished in vitro metabolic activation.

Icariin attenuates chronic mild stress-induced dysregulation of the LHPA stress circuit in rats

Chronic mild stress (CMS) is suggested to develop dysregulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) stress circuit. Icariin, a major constituent of flavonoids isolated from Epimedium brevicornum, has been previously confirmed to rescue the HPA axis abnormalities in animal models of depression. However, antidepressant treatment of icariin on corticotropin-releasing factor (CRF) system within the LHPA stress circuit and its interaction with serotonergic receptor are still seldom studied in CMS model of animals. The present study further investigated the effects of CMS procedure and subsequent icariin treatment on mRNA and protein levels of CRF, CRF receptor 1 (CRFR1) and CRF binding protein (CRFBP), as well as sucrose intake in rats. Moreover, the levels of cyclic adenosine 3',5'-monophosphate (cAMP) response element binding protein (CREB), glucocorticoid receptor (GR) and 5-hydroxytryptamine 1A receptor (5-HTR1A) in hypothalamus, hippocampus and frontal cortex were simultaneously evaluated for their participations in CRF system in this model. We found that CMS procedure significantly increased CRF expression levels in the brain regions, and decreased GR and 5-HTR1A in hippocampus and frontal cortex, with sucrose intake reduction representing the hedonic deficit in rats. Icariin restored these alterations in CMS rats. These results confirmed the hypothesis that icariin exerted antidepressant-like effect via its regulation of central CRF system. And hippocampus was suggested as an important neural area controlling the LHPA stress circuit in icariin-treated CMS rats. These findings for the first time proved that the potential molecular mechanism of antidepressant action of icariin was targeted on the interaction of the LHPA stress circuit and serotonergic function in CMS rats.

Consequences of post-weaning social isolation on anxiety behavior and related neural circuits in rodents

Exposure to adverse experiences in early-life is implicated in the later vulnerability to development of psychiatric disorders, including anxiety and affective disorders in humans. Adverse early-life experiences likely impart their long-term consequences on mental health by disrupting the normal development of neural systems involved in stress responses, emotional behavior and emotional states. Neural systems utilizing the neurotransmitters serotonin, dopamine and the neuropeptide corticotropin-releasing factor (CRF) are implicated in mediating emotive behaviors, and dysfunction of these neurochemical systems is associated with mood/anxiety disorders. These neural systems continue maturing until early or mid-adolescence in humans, thus alterations to their development are likely to contribute to the long-term consequences of adverse early-life experiences. A large body of literature suggests that post-weaning isolation rearing of rodents models the behavioral consequences of adverse early-life experiences in humans. Overall, the majority findings suggest that post-weaning social isolation that encompasses pre-adolescence produces long-lasting alterations to anxiety behavior, while measures of monoaminergic activity in various limbic regions during social isolation suggest alterations to dopamine and serotonin systems. The goal of this review is to evaluate and integrate findings from post-weaning social isolation studies specifically related to altered fear and anxiety behaviors and associated changes in neuroendocrine function and the activity of monoaminergic systems.

Decline in serotonergic firing activity and desensitization of 5-HT1A autoreceptors after chronic unpredictable stress

Chronic stressful life events are risk factors for contracting depression, the pathophysiology of which is strongly associated with impairments in serotonergic (5-HT) neurotransmission. Indeed, in rodents, exposure to chronic unpredictable stress (CUS) produces depressive-like behaviours such as behavioural despair and anhedonia. To date, there have not been many studies that especially explore in vivo changes in 5-HT neurotransmission associated with CUS in the rat. Therefore, using in vivo electrophysiology, we evaluated whether CUS that induces anhedonia-like behaviours concurrently impairs midbrain raphe 5-HT neuronal activity. Unlike unstressed and acutely stressed rats, CUS produced progressive reductions in sucrose intake and preference (anhedonia-like). These were associated with a decrease in the spontaneous firing activity (35.4%) as well as in the number of spontaneously active 5-HT neurons, and a desensitization of somatodendritic 5-HT1A autoreceptors in the dorsal raphe. These results suggest that CUS dramatically decreases 5-HT neural activity and 5-HT1A autoreceptor sensitivity, and may represent endophenotypic features of depressive-like states.

Electron microscopic localization of corticotropin-releasing factor (CRF) and CRF receptor in rat and mouse central nucleus of the amygdala

Corticotrophin-releasing factor (CRF) is expressed in the central nucleus of the amygdala (CeA), where the CRF receptor (CRFr) plays an important role in anxiety- and stress-related behaviors. To determine the subcellular sites of CRFr activation in this region, we examined the electron microscopic immunolabeling of antisera recognizing CRF or CRFr. The ultrastructural analysis was principally conducted in the lateral subdivision of the rat CeA, with comparisons being made in mice so as to optimally utilize mutant mice in control experiments. The CRFr labeling was seen in many small dendrites and dendritic spines as well as in a few somata, large dendrites, axons, and axon terminals or more rarely in glial processes. Approximately 35% of the CRFr-labeled dendrites contained CRF immunoreactivity, which was distributed diffusely throughout the cytoplasm, or specifically affiliated with either endomembranes or large dense-core vesicles. The CRF-immunoreactive vesicles also were present in somata and axon terminals with or without CRFr labeling. The CRF immunoreactivity was usually absent from both terminals and dendrites joined by asymmetric, excitatory-type synapses, where a postsynaptic location of the CRFr was commonly observed. Numerous terminals containing both CRF and CRFr were seen, however, within the neuropil and sometimes apposing the excitatory synapses. These results provide ultrastructural evidence for a primary involvement of CRF receptors in modulation of the postsynaptic excitability of CeA neurons, an effect that may be limited by the availability of CRF. The findings have important implications for understanding CRF mediation of rapid responses to stress.