Differential behavioural effects of chronic infusion of CRH 1 and CRH 2 receptor antisense oligonucleotides into the rat brain

The CRF1 receptor antagonist R121919 attenuates the neuroendocrine and behavioral effects of precipitated lorazepam withdrawal

RATIONALE

Corticotropin-releasing factor (CRF) is the primary physiologic regulator of the hypothalamic-pituitary-adrenal (HPA) axis and serves to globally coordinate the mammalian stress response. Hyperactivity of central nervous system CRF neurotransmission, acting primarily via the CRF(1) receptor, has been strongly implicated in the pathophysiology of depression and anxiety. Furthermore, there is evidence of enhanced CRF transcription, release, and neuronal activity after the administration of and withdrawal from several drugs of abuse, including cannabis, cocaine, ethanol, and morphine. Treatment with CRF antagonists has been demonstrated to reduce the severity of certain drug withdrawal symptoms, implicating a specific role for activation of CRF neurons in mediating the anxiogenic and stress-like reactions observed after abrupt drug discontinuation.

OBJECTIVES/METHODS

To extend these findings, we investigated whether pretreatment with the selective CRF(1) receptor antagonist R121919 decreases the behavioral and neuroendocrine activation observed after the precipitation of benzodiazepine (BZ) withdrawal in BZ-dependent rats.

RESULTS

Pretreatment with R121919 attenuated the subsequent HPA axis activation, behavioral measures of anxiety, and expression of the CRF gene in the paraventricular nucleus of the hypothalamus, as measured by CRF heteronuclear RNA, which occurs after flumazenil-precipitation of withdrawal from the BZ, lorazepam.

CONCLUSIONS

These results indicate that the activation of CRF neuronal systems may be a common neurobiological mechanism in withdrawal from drugs of abuse and moreover, that the CRF(1) receptor subtype plays a major role in mediating the effects of CRF on neuroendocrine and behavioral responses during BZ withdrawal. Therefore, CRF(1) receptor antagonists may be of therapeutic utility in the treatment of drug withdrawal syndromes.

A CRF(2) agonist administered into the central nucleus of the amygdala decreases ethanol self-administration in ethanol-dependent rats

Alcohol dependence is characterized by excessive consumption, loss of control over intake and the presence of a withdrawal syndrome, including both motivational and physical symptoms. Previous studies have implicated the brain corticotropin-releasing factor (CRF) stress systems in mediating the negative emotional state associated with ethanol withdrawal. CRF(1) receptor-specific antagonists, administered systemically, and CRF receptor subtype nonspecific antagonists, administered into the central nucleus of the amygdala (CeA), selectively decrease the anxiety-like behaviors and increased ethanol self-administration associated with ethanol withdrawal. In the present study, we investigated the role of CRF(2) receptors within the CeA in mediating ethanol self-administration in ethanol-dependent and nondependent animals. Male Wistar rats were made dependent on ethanol using an intermittent ethanol vapor exposure paradigm. Nondependent animals received similar conditions but were exposed to air only. Following 2 h of withdrawal from ethanol vapors, ethanol and water self-administration were measured following administration of urocortin 3, a highly selective CRF(2) agonist, in the CeA. In dependent rats, urocortin 3 (0.1 microg/microl and 0.5 microg/microl) decreased ethanol self-administration, with no effect on water self-administration. In nondependent rats, urocortin 3 (0.5 microg/microl) increased ethanol self-administration, with no effect on water self-administration. These data demonstrate an opposing role of the CRF(2) receptor subtype within the CeA in mediating ethanol self-administration in withdrawn, dependent and nondependent rats.

Neuroendocrinological mechanisms of actions of antidepressant drugs

Noradrenaline or serotonin (5-HT) reuptake-inhibiting antidepressants such as reboxetine or citalopram acutely stimulate cortisol and adrenocorticotrophic hormone (ACTH) secretion in healthy volunteers, whereas mirtazapine acutely inhibits the ACTH and cortisol release, probably due to its antagonism at central 5-HT(2) and/or H(1) receptors. These differential effects of antidepressants on cortisol and ACTH secretion in healthy subjects after single administration are also reflected by their different time course in the down-regulation of hypothalamic-pituitary-adrenocortical (HPA) axis hyperactivity in depressed patients as assessed by serial dexamethasone (DEX)/corticotrophin-releasing hormone (CRH) tests: Reuptake-inhibiting antidepressants such as reboxetine gradually normalise HPA axis hyperactivity in depressed patients during several weeks of treatment via up-regulation of mineralocorticoid and glucocorticoid receptor function and by step-by-step restoration of the disturbed feedback control. By contrast, mirtazapine markedly reduces HPA axis activity in depressed patients within 1 week, but there is a partial re-enhancement of HPA hormone secretion after several weeks of therapy. In all studies performed to date, the short-term effects of daily treatment with antidepressants on the DEX/CRH test results are comparable in responders and nonresponders. Moreover, a reduction in HPA axis activity is not necessarily followed by a favourable clinical response and some depressed patients keep on showing nonsuppression in the DEX/CRH test despite clinical improvement. Therefore, the importance of HPA axis dysregulation for the short-term efficacy of antidepressants continues to be a matter of debate. However, there are convincing data suggesting that persisting nonsuppression in the DEX/CRH test despite clinical remission predicts an enhanced risk for relapse of depressive symptomatology with respect to the medium- and long-term outcome.

Corticotropin-releasing factor (CRF) receptor type 1-dependent modulation of synaptic plasticity

CRF receptor type (CRHR) 1 exerts neuroregulatory control on associative learning processes such as fear and anxiety like behaviour. Using hippocampal slices, we investigated the neuronal excitability in mice lacking CRHR1 (Crhr1(-/-)). Compared to wild-type mice, long-term potentiation (LTP) elicited by 100 pulses at 100Hz was not different. Unexpectedly, at lower frequencies (1, 5 or 10Hz), the resulting synaptic changes in CA1 neurons of Crhr1(-/-) were systematically shifted towards long-term depression (LTD). Furthermore, testing paired-pulse paradigm revealed a GABA receptor-dependent decrease of paired-pulse ratio in Crhr1(-/-). It might be assumed that a lack of CRHR1 induce developmental changes which resulted in altered GABAergic activity, producing attenuated synaptic potentiation after repetitive stimulation and thus favouring LTD in principal neurons. Since CRHR1 are located in GABAergic somata, axons and boutons the activity of these receptor types rather might contribute to the development of the neuronal ability for plasticity like processes on the level of NMDAR subunit composition and GABAergic activity.

Development of CRF1 receptor antagonists as antidepressants and anxiolytics: progress to date

Depression and anxiety disorders are highly prevalent forms of mental illness that are considered to be stress-related disorders because some form of stressful life event often triggers their symptoms. Corticotropin-releasing factor (CRF) is a 41-amino-acid neuropeptide involved in mediating neuroendocrine, autonomic and behavioural responses to stress, and clinical studies provide evidence for the role of CRF in the development of depression and anxiety disorders. Two CRF receptor subtypes have been identified to date - the CRF(1) receptor and the CRF(2) receptor. Preclinical models provide evidence of a role for CRF(1) receptors in the activation of the stress response. Data from these experiments suggest that antagonism of CRF(1) receptor activity may provide an effective pharmacological treatment for stress-related psychiatric disorders. This review highlights progress to date with the development of CRF(1) receptor antagonists as potential pharmacotherapies for depression and anxiety disorders. Although additional research is needed to fully investigate the efficacy and safety profiles of CRF(1) receptor antagonists as candidate medications for these disorders, the results of preclinical experiments and clinical trials are encouraging. Further development of these compounds is warranted.

Corticotropin-releasing factor 1 antagonists selectively reduce ethanol self-administration in ethanol-dependent rats

BACKGROUND

Alcohol dependence is characterized by excessive alcohol consumption, loss of control over intake, and the presence of a withdrawal syndrome, which includes both motivational and physical symptoms. Similar to human alcoholics, ethanol-dependent animals display enhanced anxiety-like behaviors and enhanced ethanol self-administration during withdrawal, effects hypothesized to result from a dysregulation of corticotropin-releasing factor (CRF) stress systems. Here, we used an animal model of ethanol dependence to test the effects of CRF(1) receptor antagonists on excessive ethanol self-administration in dependent rats.

METHODS

Wistar rats, trained to orally self-administer ethanol, were exposed intermittently to ethanol vapors to induce ethanol dependence. Nondependent animals were exposed to control air. Following a 2-hour period of withdrawal, dependent and nondependent animals were systemically administered antalarmin, MJL-1-109-2, or R121919 (CRF(1) antagonists) and ethanol self-administration was measured.

RESULTS

The nonpeptide, small molecule CRF(1) antagonists selectively reduced excessive self-administration of ethanol in dependent animals during acute withdrawal. The antagonists had no effect on ethanol self-administration in nondependent rats.

CONCLUSIONS

These data demonstrate that CRF(1) receptors play an important role in mediating excessive ethanol self-administration in dependent rats, with no effect in nondependent rats. CRF(1) antagonists may be exciting new pharmacotherapeutic targets for the treatment of alcoholism in humans.

Conditional CRF receptor 1 knockout mice show altered neuronal activation pattern to mild anxiogenic challenge

RATIONALE

Regional-specific corticotropin-releasing factor receptor 1 (CRF-R1) knockout mice have been generated recently as a tool to dissociate CNS functions modulated by this receptor. In these mice, CRF-R1 function is postnatally inactivated in the anterior forebrain including limbic brain structures but not in the pituitary leading to normal activity of the hypothalamic-pituitary-adrenocortical (HPA) axis under basal conditions and reduced anxiety-related behavior in the light-dark box and the elevated plus maze (EPM) as compared to wild-type (WT) mice (Müller et al., Nat Neurosci 6:1100-1107, 2003).

OBJECTIVE

To identify neurobiological correlates underlying this reduced anxiety-like behavior, the expression of c-Fos, an established marker for neuronal activation, which was examined in response to a mild anxiogenic challenge.

MATERIALS AND METHODS

Mice were placed for 10 min on the open arm (OA) of the EPM, and regional c-Fos expression was investigated by immunohistochemistry.

RESULTS

OA exposure enhanced c-Fos expression in both conditional CRF-R1 knockout and WT mice in a number of brain areas (39 of 55 quantified), including cortical, limbic, thalamic, hypothalamic, and hindbrain regions. The c-Fos response in conditional CRF-R1 knockout animals was reduced in a restricted subset of activated neurons (4 out of 39 regions) located in the medial amygdala, ventral lateral septum, prelimbic cortex, and dorsomedial hypothalamus.

CONCLUSIONS

These results underline the importance of limbic CRF-R1 in modulating anxiety-related behavior and suggest that reduced neuronal activation in the identified limbic and hypothalamic key structures of the anxiety circuitry may mediate or contribute to the anxiolytic-like phenotype observed in mice with region-specific deletion of forebrain CRF-R1.

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

Prenatal stress affects the developmental trajectory of the rat amygdala

The amygdala plays a critical role in generating the emotion of fear, and alterations in amygdala fear processing are thought to underlie the acquisition and maintenance of anxiety disorders. The prenatally stressed (PS) rat displays hormonal, behavioral and brain anatomical similarities to anxious humans and is useful to study the neurobiological underpinnings of pathological anxiety. We studied PS and control male rats at postnatal days 7 (P7), P25, P45 and P60. Using unbiased stereological analyses we examined the volumes, anterior-posterior lengths and total numbers of neurons and glia of the basolateral (BL), central (Ce) and lateral (La) amygdalar nuclei. We found prenatal stress-associated differences in the developmental trajectories of each nucleus. These were apparent in some measures as early as P7, most extensive at P25 and resolved by P45, at least as seen by Nissl staining. These changes were not a result of differential brain growth. This early divergence in developmental trajectories seen here may be the harbinger of PS rat amygdalas that ultimately function very differently in adulthood.

Corticotropin-releasing factor, vasopressin and receptor systems in depression and anxiety

Affective disorders tend to be chronic and life-threatening diseases: suicide is estimated to be the cause of death in 10-15% of individuals with major depressive disorders. Major depression is one of the most prevalent and costly brain diseases with up to 20% of the worldwide population suffering from moderate to severe forms of the disease. Only 50% of individuals with depression show full remission in response to currently available antidepressant drug therapies which are based on serendipitous discoveries made in the 1950s. Previously underestimated, other severe depression-associated deleterious health-related effects have increasingly been recognized. Epidemiological studies have provided substantial evidence that patients with depression have a 2-4-fold increased risk both of developing cardiovascular disease and of mortality after experiencing a myocardial infarction. The majority of patients suffering from affective disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have increasingly been translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) and vasopressin (AVP) system elements. The cumulative evidence makes a strong case implicating dysfunction of these systems in the etiology and pathogenesis of depression and pathological anxiety. Translation of these advances into novel therapeutic strategies has already been started.

Corticotropin-releasing factor receptor type 2-deficient mice display impaired coping behaviors during stress

Two cognate receptors (CRF(1) and CRF(2)) mediate the actions of the stress-regulatory corticotropin-releasing factor (CRF) family of peptides. Defining the respective roles of these receptors in the central nervous system is critical in understanding stress neural circuitry and the development of psychiatric disorders. Here, we examined the role of CRF(2) in several paradigms that assess coping responses to stress. We report that CRF(2) knockout mice responded to a novel setting with increased aggressive behavior toward a bulbectomized conspecific male and show increased immobility during acute swim stress compared with wild-type mice. In addition, CRF(2)-deficient mice exhibited impaired adaptation to isolation stress as evinced by prolonged hypophagia and associated weight loss. Collectively, these results point toward a role for CRF(2) pathways in neural circuits that subserve stress-coping behaviors.

Vital functions of corticotropin-releasing factor (CRF) pathways in maintenance and regulation of energy homeostasis

Regulation of energy homeostasis is a vital function of the CNS requiring adaptive responses to maintain and support life after stress perturbations. The mechanisms whereby these processes occur are, however, only partially understood. A major determinate of these responses is corticotropin-releasing factor (CRF). Receptors for CRF, CRFR1 and CRFR2, have been hypothesized to play distinct roles in the alterations necessary for homeostatic maintenance. The function of CRFR2, in particular, has remained elusive despite its presence in both the CNS and periphery. In this work, we have used complimentary gene deletion and pharmacological approaches to elucidate the crucial role CRFR2 plays in the regulation of regional tissue thermogenesis and adaptive physiology. Analyses of interscapular brown adipose tissue (IBAT) thermogenesis by thermal signature analysis and the concordant biochemical changes in key sympathetic components in mice deficient for CRFR2 revealed significantly elevated basal IBAT thermogenesis and prolonged adrenergic responsivity of IBAT in older mice. Measurement of metabolic rates by indirect calorimetry after chronic high-fat diet challenge and treatment with the CRFR1 antagonist NBI-27914 revealed a decreased respiratory exchange ratio of these mice that was normalized with NBI-27914. Further, as a definitive measure for physiological pathology, mice examined in a behavioral model of differential temperature selection showed a predilection for warmer external temperatures, supporting a loss of body heat in these mice. These studies provide physiological, biochemical, and behavioral evidence for the critical participation of CRF pathways in the maintenance and adaptive responses necessary for regulation of energy homeostasis.

Prenatal stress: opposite effects on anxiety and hypothalamic expression of vasopressin and corticotropin-releasing hormone in rats selectively bred for high and low anxiety

We studied the mechanisms of genetic-early environmental interactions to modulate adult stress-coping and tested the hypothesis that prenatal stress (PS) can differentially alter the consequences of a genetic predisposition to either hyper- or hypo-anxiety. Exposure of male Wistar rats, bred for high (HAB) or low (LAB) anxiety-related behaviour, to PS between pregnancy days 4 and 18 resulted in opposite effects on anxiety in adulthood, i.e. HAB rats became less and LAB rats became more anxious compared with their unstressed controls (plus-maze and holeboard). The high anxiety of HAB controls was accompanied by elevated expression of vasopressin and corticotropin-releasing hormone (CRH) mRNA within the hypothalamic paraventricular nucleus compared with LAB rats. PS reduced CRH mRNA expression in HAB rats but increased vasopressin mRNA expression in LAB rats, which may explain the opposite effects of PS on adult emotionality. Differential effects of PS were also found with respect to hypothalamo-pituitary-adrenal axis reactivity; the hypothalamo-pituitary-adrenal hyper-response in virgin female HAB controls became attenuated after PS, without affecting plasma corticosterone concentrations in LAB rats. Differences in maternal plasma corticosterone measured between pregnancy days 6 and 14 of HAB and LAB dams or differential effects of PS on maternal behaviour can be excluded. In conclusion, exposure of rats with genetically determined high or low emotionality to PS mitigates the extremes in behavioural and neuroendocrine stress-coping, thus allowing adequate and similar behavioural responses to potentially dangerous stimuli in adulthood. Differential effects of PS on the activity of the brain vasopressin and CRH systems might represent possible underlying molecular mechanisms.

Corticotropin-releasing factor type-1 receptor antagonists: the next class of antidepressants?

Corticotropin-releasing factor (CRF) is a neuropeptide that plays a primary role in the neuroendocrine, autonomic, and behavioral responses to stressors. Numerous reports suggest that alterations in CRF function contribute to the pathogenesis of depression. Recently, selective nonpeptide CRF type 1 (CRF1) receptor antagonists have been discovered and several of these CRF1 receptor antagonists have demonstrated antidepressant-like efficacy in animals. The CRF1 receptor antagonists appear to be unique, as they exhibit antidepressant-like activity principally in animal models that are hyperresponsive to stress or under experimental conditions that alter endogenous stress-hormone activity. A nonpeptide CRF1 receptor antagonist has also been shown to reduce symptoms of major depression in an open-label clinical trial. Accumulating evidence supports a role for nonpeptide CRF1 receptor antagonists among the future pharmacotherapies for the treatment of depression.

Urocortin 1, urocortin 3/stresscopin, and corticotropin-releasing factor receptors in human adrenal and its disorders

CONTEXT

Urocortin 1 (Ucn1) and urocortin 3 (Ucn3)/stresscopin are new members of the corticotropin-releasing factor (CRF) neuropeptide family. Ucn1 binds to both CRF type 1 (CRF1) and type 2 receptors (CRF2), whereas Ucn3 is a specific agonist for CRF2. Recently, direct involvement of the locally synthesized CRF family in adrenocortical function has been proposed.

OBJECTIVE, DESIGN, AND SETTING

We examined in situ expression of Ucn and CRF receptors in nonpathological human adrenal gland and its disorders using immunohistochemistry and mRNA in situ hybridization.

RESULTS

Ucn immunoreactivity was localized in the cortex and medulla of nonpathological adrenal glands. Ucn1 immunoreactivity was marked in the medulla, whereas Ucn3 was immunostained mostly in the cortex. Both CRF type 1 and CRF2 were expressed in the cortex, particularly in the zonae fasciculata and reticularis but very weakly or undetectably in the medulla. Immunohistochemistry in serial tissue sections with mirror images revealed that both Ucn3 and CRF2 were colocalized in more than 85% of the adrenocortical cells. mRNA in situ hybridization confirmed these findings above. In fetal adrenals, Ucn and CRF receptors were expressed in both fetal and definitive zones of the cortex. Ucn and CRF receptors were all expressed in the tumor cells of pheochromocytomas, adrenocortical adenomas, and carcinomas, but its positivity was less than that in nonpathological adrenal glands, suggesting that Ucn1, Ucn3, and CRF receptors were down-regulated in these adrenal neoplasms.

CONCLUSIONS

Ucn1, Ucn3, and CRF receptors are all expressed in human adrenal cortex and medulla and may play important roles in physiological adrenal functions.

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

The effects of CRF antagonists, antalarmin, CP154,526, LWH234, and R121919, in the forced swim test and on swim-induced increases in adrenocorticotropin in rats

RATIONALE

Exposure to extreme stress has been suggested to produce long-term, detrimental alterations in the hypothalamic-pituitary-adrenal (HPA) axis leading to the development of mental disorders such as depression. Therefore, compounds that block the effects of stress hormones were investigated as potential therapeutics for depression.

OBJECTIVES

In the present study, we compared the potential antidepressant-like effects of four CRF antagonists, antalarmin, CP154,526, R121919, and LWH234 (at 3, 10, and 30 mg/kg i.p., 60 min prior to the forced swim test) and the corresponding effect on swim-induced HPA activation to better elucidate the relation between HPA activity and antidepressant activity.

METHODS

The antidepressant-like effects of the CRF antagonists and known antidepressants were determined in the rat forced swim test, and blood samples were obtained before and after swimming for the evaluation of adrenocorticotropin-releasing hormone (ACTH) levels.

RESULTS

Antalarmin, CP154,526, and R121919 did not produce antidepressant-like effects in the forced swim test although these compounds decreased swim-induced increases in ACTH to various extents. In contrast, LWH234 reduced immobility in the forced swim test, without altering the swim-stress-induced ACTH response. However, this compound antagonized restraint-induced ACTH release.

CONCLUSIONS

These data suggest that reducing stress-induced increases in HPA activity alone may not be sufficient to produce antidepressant-like activity; however, reductions in HPA activity may contribute to antidepressant actions of some treatments. In addition, it is proposed that CRF antagonists may alter differentially the HPA axis depending on the type of stressor used or behavioral measure evaluated.

Corticotropin-releasing hormone and urocortin: redundant or distinctive functions?

Neuropeptides play important roles in synaptic transmission. Among them, the peptides of the corticotropin-releasing hormone (CRH) family present interesting features. The two main mammalian peptides of this family, CRH and urocortin (UCN), signal through the same receptors, CRH-R1 and CRH-R2. The question arises as to whether these peptides have redundant or distinctive functions. The fact that CRH and UCN have high affinity for both receptors has hampered the possibility to define the functional contribution of each peptide. Recent studies conducted on mice deficient in CRH, CRH-R1, CRH-R2 and CRH-R1/CRH-R2, as well as in two different UCN-deficient mice, have added relevant information towards the understanding of the role of this peptide family in the CNS. Our new anatomical evidence of UCN expression in the septum will be discussed in this context.

The role of corticotropin-releasing factor-like peptides in cannabis, nicotine, and alcohol dependence

The corticotropin-releasing factor (CRF)-like peptides, which include the mammalian peptides CRF, urocortin 1, urocortin 2, and urocortin 3, play an important role in orchestrating behavioral and physiological responses that may increase an organism's chance of survival when confronted with internal or external stressors. There is, however, evidence that a chronic overactivity of brain CRF systems under basal conditions may play a role in the etiology and maintenance of psychiatric disorders such as depression and anxiety disorders. In addition, there is evidence of a role for CRF-like peptides in acute and protracted drug abstinence syndromes and relapse to drug-taking behavior. This review focuses on the role of CRF-like peptides in the negative affective state associated with acute and protracted withdrawal from three widely abused drugs, cannabis, nicotine, and alcohol. In addition, we discuss the high comorbidity between stress-associated psychiatric disorders and drug dependence. A better understanding of the brain stress systems that may underlie psychiatric disorders, acute and protracted drug withdrawal, and relapse to drug-taking behavior may help in the development of new and improved pharmacotherapies for these widespread psychiatric disorders.

Mutagenesis and knockout models: hypothalamic-pituitary-adrenocortical system

Hyperactivity of central neuropeptidergic circuits such as the corticotropin-releasing hormone (CRH) and vasopressin (AVP) neuronal systems is thought to play a causal role in the etiology and symptomatology of anxiety disorders. Indeed, there is increasing evidence from basic science that chronic stress-induced perturbation of CRH and AVP neurocircuitries may contribute to abnormal neuronal communication in conditions of pathological anxiety. Anxiety disorders aggregate in families, and accumulating evidence supports the notion that the major source of familial risk is genetic. In this context, refined molecular technologies and the creation of genetically engineered mice have allowed us to specifically target individual genes involved in the regulation of the elements of the CRH (e.g., CRH peptides, CRH-related peptides, their receptors, binding protein). During the past few years, studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of CRH-related systems in the pathogenesis of anxiety disorders and depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies.

New pharmacological treatment approaches for anxiety disorders

New developments in the pharmacological treatment of anxiety disorders will have distinct backgrounds: characterization of pathophysiological processes including evolving techniques of genomics and proteomics will generate new drug targets. Drug development design will generate new pharmacological substances with specific action at specific neurotransmitter and neuropeptide receptors or affecting their reuptake and metabolism. New anxiolytic drugs may target receptor systems that only recently have been linked to anxiety-related behavior. This includes the N-methyl-D-aspartate (NMDA), S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and the cannabinoid receptors. In addition, signal transduction pathways, neurotrophic factors, and gases such as nitric oxide or carbon monoxide may be new drug targets. Combining psychopharmacological and psychotherapeutical interventions is a further field where benefits for the treatment of anxiety disorders could be achieved. Although the road of drug development is arduous, improvements in the pharmacological treatment of anxiety disorders are expected for the near future.

Listening to mutant mice: a spotlight on the role of CRF/CRF receptor systems in affective disorders

Genetically engineered mice were originally generated to delineate the role of a specific gene product in behavioral or neuroendocrine phenotypes, rather than to produce classic animal models of depression. To learn more about the neurobiological mechanisms underlying a clinical condition such as depression, it has proven worthwhile to investigate changes in behaviors characteristic of depressed humans, such as anxiety, regardless of whether or not these alterations may also occur in other disorders besides depression. The majority of patients with mood and anxiety disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have been increasingly translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) system elements (e.g. CRF and CRF-related peptides, their receptors, binding protein). Studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of these systems in the pathogenesis of depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies for depression.

Neuropeptides in anxiety modulation

This review is focused on the involvement of neuropeptides in the modulation of physiological and pathological anxiety. Neuropeptides play a major role as endogenous modulators of complex behaviours, including anxiety-related behaviour and psychopathology, particularly due to their high number and diversity, the dynamics of release patterns in distinct brain areas and the multiple and variable modes of interneuronal communication they are involved in. Manipulations of central neuropeptidergic systems to reveal their role in anxiety (and often comorbid depression-like behaviour) include a broad spectrum of loss-of-function and gain-of-function approaches. This article concentrates on those neuropeptides for which an involvement as endogenous anxiolytic or anxiogenic modulators is well established by such complementary approaches. Particular attention is paid to corticotropin-releasing hormone (CRH) and vasopressin (AVP) which, closely linked to stress, neuroendocrine regulation, social behaviour and learning/memory, play critical roles in the regulation of anxiety-related behaviour of rodents. Provided that their neurobiology, neuroendocrinology and molecular-genetic background are well characterized, these and other neuropeptidergic systems may be promising targets for future anxiolytic strategies.

Endocrine disturbances in depression

Depression is one of the most common psychiatric disorders. For a long time, clinicians suspected a causal link between depression and the endocrine system. The most frequently occurring endocrine abnormality in depressed subjects is hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. CRH and AVP are likely to play a substantial role in the pathophysiology of this disorder, and their receptors appear to be a specific target for future antidepressant drugs. Depression also affects the hypothalamic-pituitary-GH (HPGH) and -thyroid (HPT) axes. Alterations in the reproductive system may also play a role in the pathology of depression. In addition, there is increasing evidence that leptin and neurosteroids, such as DHEA, are implicated in mood disorders.

Corticotropin-releasing factor type II (CRF₂) receptors in the bed nucleus of the stria terminalis modulate conditioned defeat in Syrian hamsters (Mesocricetus auratus)

In Syrian hamsters (Mesocricetus auratus), social defeat produces a subsequent increase in submissive and defensive behavior and a loss of normal territorial aggression, which the authors have called conditioned defeat. In this study, the authors investigated the effect of blocking corticotropin-releasing factor (CRF) Type I and Type II receptors on conditioned defeat. Intracerebroventricular infusion of the CRF-sub-2 receptor antagonist antisauvagine-30 prior to testing significantly reduced conditioned defeat compared with vehicle controls, whereas the CRF-sub-1 receptor antagonist CP-154,526 had no effect. Also, infusion of antisauvagine-30 into the bed nucleus of the stria terminalis (BNST) 15 min, but not immediately, prior to testing reduced conditioned defeat in a dose-dependent manner. The authors' results provide evidence that CRF-sub-2 receptors in the BNST, but not CRF-sub-1 receptors, are an important component in the neural circuitry regulating conditioned defeat.

Urocortins and corticotropin releasing factor type 2 receptors in the hypothalamus and the cardiovascular system

In addition to urocortin (Ucn I), Ucn II and Ucn III were identified as endogenous ligands for corticotropin-releasing factor type 2 receptor (CRF2 receptor). CRF2 receptor is abundantly located in central hypothalamic ventromedial nucleus (VMH) and in peripheral cardiovascular system. In this mini-review, we focused on the roles of these urocortins and CRF2 receptor in the hypothalamus and the cardiovascular system. Ucn II mRNA was increased in the parvocellular part or the magnocellular part of the hypothalamic paraventricular nucleus (PVN) following immobilization stress or 3 days of water deprivation, respectively. Therefore, it is thought that Ucn II may modulate CRF and vasopressin synthesis in the PVN in a paracrine or autocrine fashion through PVN CRF2 receptor. The early and later phases of Ucn I-mediated feeding suppression may be CRF1 and CRF2 receptor-mediated events, respectively. Ucn II decreases food intake at a later phase, beyond 4 h post injection. A large dose of corticosterone increased plasma leptin and insulin levels as well as the levels of CRF2 receptor mRNA. Adrenalectomy, starvation, and immobilization each lowered plasma leptin and insulin levels and were associated with decrements in CRF2 receptor mRNA levels in the VMH. Peripheral injection of leptin increased VMH CRF2 receptor mRNA, as can induce reductions of food intake and body weight, indicating that circulating leptin is involved in the regulation of VMH CRF2 receptor mRNA expression. Therefore, it is also plausible that VMH CRF2 receptor transduces the anorexogenic effects of leptin as well as those of urocortins. The systemic administration of Ucn II decreases mean arterial pressure (arterial vascular tone) and causes tachycardia via vascular CRF2 receptor in rats, similar to the effects of Ucn I. Thus, CRF2 receptor seems to mediate cardioprotective effects of urocortins.

Antidepressant-like activity of corticotropin-releasing factor type-1 receptor antagonists in mice

The development of selective corticotropin-releasing factor type-1 (CRF1) receptor antagonists represents a potential novel treatment for depression. These studies evaluated CRF1 receptor antagonists for antidepressant-like activity in mice. Subchronic dosing of both R 121919 (3-[6-(dimethylamino)-4-methyl-pyrid-3-yl]-2,5-dimethyl-N,N-dipropyl-pyrazolo[2,3-a]pyrimidin-7-amine) and DMP 696 (4-(1,3-dimethoxyprop-2-ylamino)-2,7-dimethyl-8-(2,4-dichlorophenyl)-pyrazolo[1,5-a]-1,3,5-triazine) significantly decreased immobility time in the tail suspension test (at 30 and at 3 and 10 mg/kg, i.p., respectively). These antidepressant-like effects were observed at doses that did not impair general locomotor activity. Neither antalarmin (N-butyl-N-ethyl-[2,5,6-trimethyl-7-(2,4,6)trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amine) nor DMP 904 (4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1,5-a]-pyrimidine) had an effect indicative of antidepressant-like activity. These results suggest that the tail suspension assay may have utility to identify CRF1 receptor antagonists with antidepressant-like activity. Moreover, the results lend support to the theory that some nonpeptidic CRF1 receptor antagonists may possess antidepressant-like activity and therefore represent a promising novel pharmacotherapeutic strategy in the treatment of depression.

Corticotropin-releasing factor and Urocortin I modulate excitatory glutamatergic synaptic transmission

Corticotropin-releasing factor (CRF)-related peptides serve as hormones and neuromodulators of the stress response and play a role in affective disorders. These peptides are known to alter complex behaviors and neuronal properties, but their receptor-mediated effects at CNS synapses are not well described. Here we show that excitatory glutamatergic transmission is modulated by two endogenous CRF-related peptide ligands, corticotropin-releasing factor [CRF rat/human (r/h)] and Urocortin I (Ucn I), within the central nucleus of the amygdala (CeA) and the lateral septum mediolateral nucleus (LSMLN). These limbic nuclei are reciprocally innervated, are involved in stress and affective disorders, and have high densities of the CRF receptors CRF1 and CRF2. Activation of these receptors exerts diametrically opposed actions on glutamatergic transmission in these nuclei. In the CeA, CRF(r/h) depressed excitatory glutamatergic transmission through a CRF1-mediated postsynaptic action, whereas Ucn I facilitated synaptic responses through presynaptic and postsynaptic CRF2-mediated mechanisms. Conversely, in the LSMLN, CRF caused a CRF1-mediated facilitation of glutamatergic transmission via postsynaptic mechanisms, whereas Ucn I depressed EPSCs by postsynaptic and presynaptic CRF2-mediated actions. Furthermore, antagonists of these receptors also affected glutamatergic neurotransmission, indicating that endogenous ligands tonically modulated synoptic activity at these synapses. These data show that CRF receptors in CeA and LSMLN synapses exert and maintain a significant synaptic tone and thereby regulate excitatory glutamatergic transmission. The results also suggest that CRF receptors may provide novel targets in affective disorders and stress.

CRF and CRF receptors: role in stress responsivity and other behaviors

Since corticotropin-releasing factor (CRF) was first characterized, a growing family of ligands and receptors has evolved. The mammalian family members include CRF, urocortinI (UcnI), UcnII, and UcnIII, along with two receptors, CRFR1 and CRFR2, and a CRF binding protein. These family members differ in their tissue distribution and pharmacology. Studies have provided evidence supporting an important role of this family in regulation of the endocrine and behavioral responses to stress. Although CRF appears to play a stimulatory role in stress responsivity through activation of CRFR1, specific actions of UcnII and UcnIII on CRFR2 may be important for dampening stress sensitivity. As the only ligand with high affinity for both receptors, UcnI's role may be promiscuous. Regulation of the relative contribution of the two CRF receptors to brain CRF pathways may be essential in coordinating physiological responses to stress. The development of disorders related to heightened stress sensitivity and dysregulation of stress-coping mechanisms appears to involve regulatory mechanisms of CRF family members.

High-quality antidepressant discovery by understanding stress hormone physiology

Compensating the consequences of impaired corticosteroid receptor signaling is a novel strategy to discover better antidepressants. The prevailing drugs gradually improve stress hormone regulation along with ameliorating psychopathology. The current understanding of how neuropeptides, such as corticotropin-releasing hormone (CRH) and vasopressin (AVP), drive cortisol secretion via corticotrophin has paved the way for CRH- and AVP-receptor antagonists. As alternative strategies, the blockade of corticosteroid receptors or inhibition of cortisol synthesis has emerged. All these strategies are not yet fully clinically developed, but preliminary data from basic and clinical research strongly underscore that such strategies may lead to innovative treatment modalities.

Treatment with the CRH1-receptor-antagonist R121919 improves sleep-EEG in patients with depression

Well documented changes of sleep electroencephalogram (EEG) in patients with depression include rapid eye movement (REM) sleep disinhibition, decreases of slow-wave-sleep (SWS) and increase in wakefulness. Twenty-seven inpatients with major depression were admitted subsequently to a clinical trial with the CRH(1)-receptor-antagonist R121919 administered in two different dose escalation panels. A random subgroup of 10 patients underwent three sleep-EEG recordings (baseline before treatment, at the end of the first week and at the end of the fourth week of active treatment). SWS time increased significantly compared with baseline after 1 week and after 4 weeks. The number of awakenings and REM density showed a trend toward a decrease during the same time period. Separate evaluation of these changes for both panels showed no significant effect at lower doses, whereas in the higher doses after R121919 REM density decreased and SWS increased significantly between baseline and week 4. Furthermore positive associations between HAMD scores and SWS at the end of active treatment were found. Although these data might indicate that R121919 has a normalizing influence on the sleep EEG, the design of the study does not allow to differentiate genuine drug effects from those of clinical improvement and habituation to the clinical setting.

Alterations in central neuropeptide expression, release, and receptor binding in rats bred for high anxiety: critical role of vasopressin

To model aspects of trait anxiety/depression, Wistar rats were bred for extremes in either hyper (HAB)- or hypo(LAB)-anxiety as measured on the elevated plus-maze and in a variety of additional behavioral tests. Similar to psychiatric patients, HAB rats prefer passive stress-coping strategies, indicative of depression-like behavior, show hyper-reactivity of the hypothalamo-pituitary-adrenal axis, and a pathological response to the dexamethasone/corticotropin-releasing hormone (CRH) challenge test. Here we tested central mRNA expression, release patterns, and receptor binding of neuropeptides critically involved in the regulation of both anxiety-related behavior and the HPA axis. Thus, CRH, arginine-8-vasopressin (AVP), and oxytocin (OXT) were studied in brains of HAB and LAB males both under basal conditions and after exposure to a mild emotional stressor. In HAB rats, CRH mRNA was decreased in the bed nucleus of the stria terminalis only. While no significant difference in CRH1-receptor binding was found in any brain area, CRH2-receptor binding was elevated in the hypothalamic paraventricular nucleus (PVN), the ventromedial hypothalamus, and the central amygdala of HABs compared to LABs. AVP, but not OXT, mRNA expression as well as release of the neuropeptide, were higher in the PVN of HABs, whereas AVP V1a-receptor binding failed to show significant differences in any brain region studied. Remarkably, intra-PVN treatment of HABs with the AVP V1-receptor antagonist d (CH(2))(5) Tyr (Me) AVP resulted in a decrease in anxiety/depression-related behavior. The elevated expression and release of AVP within the PVN of HAB rats together with the behavioral effects of the AVP V1-receptor antagonist suggest a critical involvement of this neuropeptide in neuroendocrine and behavioral phenomena associated with trait anxiety/depression.

Anxiogenic-like effect of corticotropin-releasing factor receptor 2 antisense oligonucleotides infused into rat brain

Corticotropin-releasing factor (CRF) is widely distributed in the brain and coordinates behavioural responses to stress. Its receptor subtypes, CRF-R1 and CRF-R2, are expressed in the brain. For this study, we tested the effect of a continuous infusion of CRF-R2 antisense oligonucleotides into the lateral ventricle on anxiety-related behaviours in rats. Our results indicate that CRF-R2 antisense oligonucleotides produced an anxiogenic-like effect in elevated plus maze, black and white box and conditioned fear stress in rats. No significant effect on general locomotor activity was seen. These results indicate that inhibition of CRF-R2 induces an increase in anxiety-related behaviours suggesting an anxiogenic-like effect.

Corticosteroid Receptor Transgenic Mice

Dysregulations and dysfunctions of corticosteroids and their receptors have been implicated in the pathogenesis of stress-related disorders, in particular in depression. It is currently under debate, however, whether corticosteroid imbalances are a cause or rather a consequence of affective disorders. Corticosteroids exert their effects mainly by two receptors: glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs). We present here analyses made on several strains of mice with targeted mutations of corticosteroid receptors. The results help to understand how corticosteroid receptors regulate the hypothalamic-pituitary-adrenal (HPA) system. Furthermore, first behavioral analyses have indicated that corticosteroid receptor mutant mice show alterations in their emotional behavior. Certain mouse strains with specific alterations of GR or MR expression may represent genetic models of depression or at least have a predisposition to develop a depressive or a depression-resistant state upon exposure to stress. The corticosteroid receptor-regulated target genes to be identified in these models may code for proteins that could represent new drug-targets for the treatment of affective disorders.

Treatment of depression with the CRH-1-receptor antagonist R121919: endocrine changes and side effects

A dysregulation of the hypothalamus-pituitary-adrenocortical (HPA) system has been hypothesized to account for a myriad of cardinal symptoms of affective disorders. Specifically, increased CRH signalling via CRH type 1 receptors is thought to be an important factor in the pathogenesis of major depression and anxiety disorders. Consequently, a number of drugs have been developed in order to target the postulated increase in CRH/CRH 1 receptor signalling. One of these compounds, R121919, binds with high affinity to CRH1 receptors antagonising the action of CRH. R121919 was recently tested in an open-label study conceptualized as a safety and tolerability study. As part of this study, a thorough endocrine evaluation and detailed clinical laboratory analysis were assessed several times during 30 days of treatment with two different dose regimens of R121919 (5-40 mg vs. 40-80 mg) in 24 patients with a major depressive episode. During treatment with the experimental drug no serious side effects were noted. In particular, there were no adverse effects or impairment of the hypothalamic-pituitary-gonadal system, the hypothalamic-pituitary-thyroid axis, the renin-angiotensin system, prolactin or vasopressin secretion. Furthermore, no changes in the serum corticotropin and cortisol concentrations and in the responsivity of corticotropin and cortisol following a CRH stimulation test were noted. No effects of R121919 on clinical laboratory parameters including liver enzymes, EEG and ECG were observed. These results encourage the development of other CRH-1-R antagonists as a novel class of antidepressive drugs.

Limbic corticotropin-releasing hormone receptor 1 mediates anxiety-related behavior and hormonal adaptation to stress

Corticotropin-releasing hormone (CRH) is centrally involved in coordinating responses to a variety of stress-associated stimuli. Recent clinical data implicate CRH in the pathophysiology of human affective disorders. To differentiate the CNS pathways involving CRH and CRH receptor 1 (Crhr1) that modulate behavior from those that regulate neuroendocrine function, we generated a conditional knockout mouse line (Crhr1(loxP/loxP)Camk2a-cre) in which Crhr1 function is inactivated postnatally in anterior forebrain and limbic brain structures, but not in the pituitary. This leaves the hypothalamic-pituitary-adrenocortical (HPA) system intact. Crhr1(loxP/loxP)Camk2a-cre mutants showed reduced anxiety, and the basal activity of their HPA system was normal. In contrast to Crhr1 null mutants, conditional mutants were hypersensitive to stress corticotropin and corticosterone levels remained significantly elevated after stress. Our data clearly show that limbic Crhr1 modulates anxiety-related behavior and that this effect is independent of HPA system function. Furthermore, we provide evidence for a new role of limbic Crhr1 in neuroendocrine adaptation to stress.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The effects of chronic treatment with the mood stabilizers valproic acid and lithium on corticotropin-releasing factor neuronal systems

Corticotropin-releasing factor (CRF) plays a preeminent role in coordinating the endocrine, autonomic, and behavioral responses to stress. Dysregulation of both hypothalamic and extrahypothalamic CRF systems have been reported in patients with major depression and post-traumatic stress disorder. Moreover, effective treatment of these conditions leads to normalization of these CRF systems. Although there is virtually no data concerning alterations of CRF systems in bipolar disorder (manic depressive illness), previous work indicates that valproic acid, an anticonvulsant also effective in the treatment of acute mania, alters central CRF neuronal systems. In the current studies, we chronically administered valproic acid and lithium, two clinically effective mood stabilizers, in nonstressed rats to extend our previous findings. Chronic valproic acid administration decreased CRF mRNA expression in the paraventricular nucleus of the hypothalamus; lithium administration increased CRF mRNA expression in the central nucleus of the amygdala. Although valproic acid increased CRF(1) receptor mRNA expression in the cortex, CRF(1) receptor binding was decreased in both the basolateral amygdala and cortex, suggesting that chronic valproate treatment may in fact dampen the overall tone in this central stress pathway. Valproate treatment decreased CRF(2A) mRNA expression in both the lateral septum and hypothalamus, although CRF(2A) receptor binding was unchanged. Lithium administration decreased CRF(1) mRNA expression in both the amygdala and frontal cortex, but CRF(1) receptor binding also remained unchanged. These results suggest that the therapeutic actions of these mood stabilizers may, in part, result from their actions on central CRF neuronal systems. The distinct actions of each drug on CRF systems may underlie their synergistic clinical effects.

Depressive-like behavior and stress reactivity are independent traits in a Wistar Kyoto x Fisher 344 cross

Depression is a heritable disorder that is often precipitated by stress. Abnormalities of the stress-reactive hypothalamic-pituitary-adrenal (HPA) axis are also common in depressed patients. In animal models, the forced swim test (FST) is the most frequently used test of depressive-like behavior. We have used a proposed animal model of depression, the Wistar Kyoto (WKY) rat, to investigate the relationship as well as the mode of inheritance of FST behaviors and HPA measures. Through reciprocal breeding of WKY and F344 parent strains and brother-sister breeding of the F1 generation, we obtained 486 F2 animals. Parent, F1 and F2 animals were tested in the FST. Blood samples were collected for determination of basal and stress (10-min restraint) plasma corticosterone (CORT) levels, and adrenal weights were measured. We found that all measures were heritable to some extent and that this heritability was highly sex dependent. Both correlation and factor analyses of the F2 generation data demonstrate that FST behavior and HPA axis measures are not directly related. Thus, the underlying genetic components of depressive-like behavior and HPA axis abnormalities are likely to be disparate in the segregating F2 generation of a WKY x F344 cross.

Dopamine-dependent responses to cocaine depend on corticotropin-releasing factor receptor subtypes

The effects on locomotor response to cocaine challenge, acquisition of cocaine conditioned place preference and cocaine-induced dopamine (DA) release in nucleus accumbens and ventral tegmental area by the non-specific corticotropin-releasing factor (CRF) receptors antagonist alpha-helical CRF, the selective CRF receptor subtype 1 antagonist CP-154,526 and the selective CRF receptor subtype 2 antagonist anti-sauvagine-30 (AS-30) were investigated in rats. Both alpha-helical CRF (10 microg, i.c.v.) and CP-154,526 (3 microg, i.c.v.) decreased the cocaine-induced distance travelled, whereas AS-30 (3 microg, i.c.v.) did not show such an effect. The CRF receptor antagonists also have significant effects on stereotype counts induced by cocaine injection, in which the alpha-helical CRF or CP-154,526 but not AS-30 did significantly reduce the stereotype counts. alpha-Helical CRF (10 microg) prior to each injection of cocaine blocked cocaine conditioned place preference with no significant difference observed in the time spent in the drug-paired side between post- and pre-training and both 1 and 3 microg CP-154,526 also had significant inhibitory effects on cocaine-induced place preference. However, pre-treatment with an i.c.v. infusion of AS-30 (1 or 3 microg) prior to each injection of cocaine did not affect the acquisition of conditioned place preference. The alpha-helical CRF and CP-154,526 reduced extracellular DA levels of nucleus accumbens and ventral tegmental area in response to the injection of cocaine. However, both alpha-helical CRF and CP-154,526 did not modify extracellular DA levels under basal conditions. In contrast, the i.c.v. infusion of AS-30 had no effects on either the basal DA or the cocaine-induced increase in DA release in nucleus accumbens and ventral tegmental area. These findings demonstrate that activation of the CRF receptor is involved in behavioral and neurochemical effects of cocaine challenge and cocaine reward and that the role of CRF receptor subtypes 1 and 2 in cocaine-induced locomotion, reward and DA release is not identical. The CRF receptor subtype 1 is largely responsible for the action of the CRF system on cocaine locomotion and reward. These results suggest that the CRF receptor antagonist, particularly the CRF receptor subtype 1 antagonist, might be of some value in the treatment of cocaine addiction and cocaine-related behavioral disorders.

A robust animal model of state anxiety: fear-potentiated behaviour in the elevated plus-maze

Fear (i.e., decreased percentage time spent on open-arm exploration) in the elevated plus-maze can be potentiated by prior inescapable stressor exposure, but not by escapable stress. The use of fear-potentiated plus-maze behaviour has several advantages as compared to more traditional animal models of anxiety. (a) In contrast to the traditional (spontaneous) elevated plus-maze, which measures innate fear of open spaces, fear-potentiated plus-maze behaviour reflects an enhanced anxiety state (allostatic state). This "state anxiety" can be defined as an unpleasant emotional arousal in face of threatening demands or dangers. A cognitive appraisal of threat is a prerequisite for the experience of this type of emotion. (b) Depending on the stressor used (e.g., fear of shock, predator odour, swim stress, restraint, social defeat, predator stress (cat)), this enhanced anxiety state can last from 90 min to 3 weeks. Stress effects are more severe when rats are isolated in comparison to group housing. (c) Drugs can be administered in the absence of the original stressor and after stressor exposure. As a consequence, retrieval mechanisms are not affected by drug treatment. (d) Fear-potentiated plus-maze behaviour is sensitive to proven/putative anxiolytics and anxiogenics which act via mechanisms related to the benzodiazepine-gamma-aminobutyric acid receptor, but it is also sensitive to corticotropin-releasing receptor antagonists and glucocorticoid receptor antagonists and serotonin receptor agonists/antagonists complex (high predictive validity). (e) Fear-potentiated plus-maze behaviour is very robust, and experiments can easily be replicated in other labs. (f) Fear-potentiated plus-maze behaviour can be measured both in males and females. (g) Neural mechanisms involved in contextual fear conditioning, fear potentiation and state anxiety can be studied.Thus, fear-potentiated plus-maze behaviour may be a valuable measure in the understanding of neural mechanisms involved in the development of anxiety disorders and in the search for novel anxiolytics. Finally, the involvement of corticotropin-releasing factor and corticosteroid-corticotropin-releasing factor interactions in the production of fear-potentiated plus-maze behaviour are discussed.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Effect of chronic administration of a CRF(1) receptor antagonist, CRA1000, on locomotor activity and endocrine responses to stress

Corticotropin-releasing factor (CRF) is involved in the regulation of stress responses. The actions of CRF in the brain are mediated through two distinct CRF receptor subtypes, CRF(1) and CRF(2) receptors. In the present study, we examined the effects in rat of chronic administration of a nonpeptidic CRF(1) receptor-selective antagonist, CRA1000, 2-[N-(2-methylthio-4-isopropylphenyl)-N-ethylamino]-4-[4-(3-fluorophenyl)-1,2,3,6-tetrahydropyridin-1-yl]-6-methylpyrimidine), on locomotor activity, feeding behavior and the hypothalamic-pituitary-adrenal axis. Chronic CRA1000 treatment significantly decreased locomotor activity in the dark phase of the diurnal cycle. However, chronic CRA1000 treatment showed no effect on food and water intake, or on body weight. After a 10-day period of CRA1000 treatment, plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone in basal conditions and under immobilization stress were no different from those in rats treated with vehicle. However, CRA1000 administered 2 h before immobilization stress significantly reduced ACTH and corticosterone responses to stress with no effect on basal ACTH and corticosterone concentrations. These results suggest that CRF(1) receptors are involved in the regulation of locomotor activity during the dark period, but are not involved in the regulation of feeding behavior under non-stressful conditions. Furthermore, the results suggest that a 10-day treatment with CRA1000 does not affect hypothalamic-pituitary-adrenal axis activity either under basal conditions or after acute stress.

Effects of antalarmin, a CRF type 1 receptor antagonist, on anxiety-like behavior and motor activation in the rat

Molecular studies point to a role for the type 1 corticotropin-releasing factor receptor (CRF(1)) in anxiogenic-like and activating effects of CRF and stress. However, CP-154,526, a selective CRF(1) antagonist, has yielded mixed results in such tests. Few studies have examined the behavioral effects of other CRF(1) antagonists. Therefore, we examined the effects of antalarmin, a structurally related analog of CP-154,526, on anxiety-like behavior and motor activation. Antalarmin blocked the anxiogenic-like effect of CRF in the elevated plus maze, without affecting anxiety-like behavior in vehicle-treated animals. Antalarmin decreased spontaneous defensive withdrawal behavior in a novel, brightly illuminated open field. Finally, antalarmin blocked the activating effects of CRF, but not D-amphetamine, without producing motor sedation. These findings indicate that the CRF(1) receptor mediates anxiogenic-like effects of novelty stress and the anxiogenic-like and activating effects of CRF and support the hypothesis that CRF(1) antagonists may be useful for the pharmacotherapy of pathological anxiety.

Human urocortin II: mild locomotor suppressive and delayed anxiolytic-like effects of a novel corticotropin-releasing factor related peptide

Recently, human urocortin II (hUcn II), a member of the corticotropin-releasing factor (CRF) peptide family, was identified. The following experiments sought to compare the effects of this novel CRF-related peptide versus those of ovine CRF (oCRF) on locomotor activation and anxiety-related behavior, using the locomotor activity test and the elevated plus maze, respectively. To examine locomotor activity during the active (dark) and inactive (light) phases, rats were intracerebroventricularly (i.c.v.) injected with 0, 0.1, 1.0 or 10 microg of hUcn II (n=8/group active; n=6-9/group inactive) or oCRF (n=8/group active; n=8/group inactive) 2 h after the onset of their respective testing phase and monitored for 3 (inactive) or 5 (active) h. To compare the effects of CRF-related peptides on exploration of the elevated plus maze, rats were pretreated (i.c.v. 0, 0.1, 1.0 or 10 microg) with hUcn II (n=7-11/group) or oCRF (n=7-10/group), 10 min prior to testing. Delayed effects in the elevated plus maze were examined in rats injected with 1.0 microg of hUcn II (n=8/group) or oCRF (n=6-8/group), or vehicle (n=8/group) 1, 4 or 6 h before testing. In contrast to the activational effects of oCRF, hUcn II mildly suppressed locomotor activity during the inactive phase. hUcn II did not acutely affect open arm exploration in the elevated plus maze, whereas oCRF decreased this measure. However, hUcn II increased open arm exploration 4 h after injection. Thus, hUcn II exhibits mild motor suppressive effects and delayed anxiolytic-like effects, suggesting a time-dependent role for hUcn II in the regulation of stress-related behavior.

The CRH1 receptor antagonist R121919 attenuates stress-elicited sleep disturbances in rats, particularly in those with high innate anxiety

Excessive corticotropin-releasing hormone (CRH) secretion in limbic and prefrontal brain areas has been postulated to underly stress-related clinical conditions. Studies in mice with deleted or pharmacologically compromised CRH type 1 receptors (CRH-R1) point to a key role of the CRH/CRH-R1 signaling cascade as a potential drug target. Therefore, we compared the effect of a selective high affinity CRH-R1 antagonist (R121919) on sleep-wake behavior in two rat lines selectively bred for either high or low innate anxiety. We found that the subcutaneous injection of the solvent of R121919, a citrate buffer solution, transiently increased circulating levels of the stress hormones ACTH and corticosterone and reduced sleep, especially in high-anxiety animals. When R121919 was added to the solvent, hormone levels and sleep patterns returned to baseline and were indistinguishable between the rat lines. This finding is in accord with previous observations from a clinical trial in depressed patients and studies in rats with high innate anxiety that suggested major effects of CRH-R1 antagonism in the presence of a pathological (i.e. CRH hypersecretion) condition only.