Effect of corticotropin-releasing factor antagonist on behavioral and neuroendocrine responses during exposure to defensive burying paradigm in rats

Sex differences in corticotropin releasing factor-evoked behavior and activated networks

Hypersecretion of corticotropin releasing factor (CRF) is linked to the pathophysiology of major depression and post-traumatic stress disorder, disorders that are more common in women than men. Notably, preclinical studies have identified sex differences in CRF receptors that can increase neuronal sensitivity to CRF in female compared to male rodents. These cellular sex differences suggest that CRF may regulate brain circuits and behavior differently in males and females. To test this idea, we first evaluated whether there were sex differences in anxiety-related behaviors induced by the central infusion of CRF. High doses of CRF increased self-grooming more in female than in male rats, and the magnitude of this effect in females was greater when they were in the proestrous phase of their estrous cycle (higher ovarian hormones) compared to the diestrous phase (lower ovarian hormones), which suggests that ovarian hormones potentiate this anxiogenic effect of CRF. Brain regions associated with CRF-evoked self-grooming were identified by correlating a marker of neuronal activation, cFOS, with time spent grooming. In the infralimbic region, which is implicated in regulating anxiety, the correlation for CRF-induced neuronal activation and grooming was positive in proestrous females, but negative for males and diestrous females, indicating that ovarian hormones altered this relationship between neuronal activation and behavior. Because CRF regulates a number of regions that work together to coordinate different aspects of responding to stress, we then examined more broadly whether CRF-activated functional connectivity networks differed between males and cycling females. Interestingly, hormonal status altered correlations for CRF-induced neuronal activation between a variety of brain regions, but the most striking differences were found when comparing proestrous females to males, particularly when comparing neuronal activation between prefrontal cortical and other forebrain regions. These results suggest that ovarian hormones alter the way brain regions work together in response to CRF, which could drive different strategies for coping with stress in males versus females. These sex differences in stress responses could also help explain female vulnerability to psychiatric disorders characterized by CRF hypersecretion.

Endogenous opioids: opposing stress with a cost

The stress response is characterized by the coordinated engagement of central and peripheral neural systems in response to life-threatening challenges. It has been conserved through evolution and is essential for survival. However, the frequent or continual elicitation of the stress response by repeated or chronic stress, respectively, results in the dysfunction of stress response circuits, ultimately leading to stress-related pathology. In an effort to best respond to stressors, yet at the same time maintain homeostasis and avoid dysfunction, stress response systems are finely balanced and co-regulated by neuromodulators that exert opposing effects. These opposing systems serve to restrain certain stress response systems and promote recovery. However, the engagement of opposing systems comes with the cost of alternate dysfunctions. This review describes, as an example of this dynamic, how endogenous opioids function to oppose the effects of the major stress neuromediator, corticotropin-releasing hormone, and promote recovery from a stress response and how these actions can both protect and be hazardous to health.

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.

Endogenous Opioids: The Downside of Opposing Stress

Our dynamic environment regularly exposes us to potentially life-threatening challenges or stressors. To answer these challenges and maintain homeostasis, the stress response, an innate coordinated engagement of central and peripheral neural systems is initiated. Although essential for survival, the inappropriate initiation of the stress response or its continuation after the stressor is terminated has pathological consequences that have been linked to diverse neuropsychiatric and medical diseases. Substantial individual variability exists in the pathological consequences of stressors. A theme of this Special Issue is that elucidating the basis of individual differences in resilience or its flipside, vulnerability, will greatly advance our ability to prevent and treat stress-related diseases. This can be approached by studying individual differences in "pro-stress" mediators such as corticosteroids or the hypothalamic orchestrator of the stress response, corticotropin-releasing factor. More recently, the recognition of endogenous neuromodulators with "anti-stress" activity that have opposing actions or that restrain stress-response systems suggests additional bases for individual differences in stress pathology. These "anti-stress" neuromodulators offer alternative strategies for manipulating the stress response and its pathological consequences. This review uses the major brain norepinephrine system as a model stress-response system to demonstrate how co-regulation by opposing pro-stress (corticotropin-releasing factor) and anti-stress (enkephalin) neuromodulators must be fine-tuned to produce an adaptive response to stress. The clinical consequences of tipping this fine-tuned balance in the direction of either the pro- or anti-stress systems are emphasized. Finally, that each system provides multiple points at which individual differences could confer stress vulnerability or resilience is discussed.

Experimental psychiatric illness and drug abuse models: from human to animal, an overview

Preclinical animal models have supported much of the recent rapid expansion of neuroscience research and have facilitated critical discoveries that undoubtedly benefit patients suffering from psychiatric disorders. This overview serves as an introduction for the following chapters describing both in vivo and in vitro preclinical models of psychiatric disease components and briefly describes models related to drug dependence and affective disorders. Although there are no perfect animal models of any psychiatric disorder, models do exist for many elements of each disease state or stage. In many cases, the development of certain models is essentially restricted to the human clinical laboratory domain for the purpose of maximizing validity, whereas the use of in vitro models may best represent an adjunctive, well-controlled means to model specific signaling mechanisms associated with psychiatric disease states. The data generated by preclinical models are only as valid as the model itself, and the development and refinement of animal models for human psychiatric disorders continues to be an important challenge. Collaborative relationships between basic neuroscience and clinical modeling could greatly benefit the development of new and better models, in addition to facilitating medications development.

Early adolescence as a critical window during which social stress distinctly alters behavior and brain norepinephrine activity

Many neural programs that shape behavior become established during adolescence. Adverse events at this age can have enduring consequences for both adolescent and adult mental health. Here we show that repeated social stress at different stages of adolescent development differentially affects rat behavior and neuronal activity. Early-adolescent (PND 28, EA), mid-adolescent (PND 42, MA), and adult (PND 63) rats were subjected to resident-intruder social stress (7 days) and behavior was examined 24-72 h later. In EA rats selectively, resident-intruder stress increased proactive responses in the defensive burying and forced swim tests. In adult rats, resident-intruder stress decreased burying behavior regardless of whether the animal was stressed as an adult or during early adolescence. As the locus coeruleus (LC)-norepinephrine system has been implicated in proactive defense behaviors, LC neuronal activity was quantified in separate cohorts. Stressed EA rats had elevated spontaneous LC discharge rates and diminished responses to sensory stimuli compared with controls. Microinjection of a CRF antagonist into the LC selectively inhibited neurons of stressed EA rats, suggesting that EA social stress induces tonic CRF release onto LC neurons, shifting the mode of discharge to an activated state that promotes active defensive behaviors. In all adult groups, resident-intruder stress resulted in an increased phasic response to sensory stimuli with no change in spontaneous rates. MA was a transition period during which social stress did not affect behavior or LC activity. The results suggest that social stress interacts with the brain norepinephrine system to regulate defensive strategies in an age-dependent manner.

Central CRH administration changes formalin pain responses in male and female rats

Corticotropin-releasing hormone (CRH) is suggested to be involved in the regulation of pain. To better evaluate the CRH-mediated behavioral alterations in the formalin inflammatory pain test, we administered CRH or the CRH receptor antagonist α-helical CRH(9-41) (ahCRH) intracerebroventricularly to male and female rats and compared the effects with those of saline control. Nociceptive stimulation was carried out through a subcutaneous injection of dilute formalin (50μL, 10%) in the plantar surface of the hind paw. In both sexes, formalin-induced responses, recorded for 60min, were affected by CRH but not by ahCRH treatment. Paw flexing duration was decreased in both sexes during the formalin interphase period in the CRH-treated group compared to saline control groups; however, licking of the injected paw was markedly increased by the same treatment at other time periods. Treatments induced only a few changes in spontaneous non-pain behaviors, which do not account for the effects on pain response. In conclusion, these data demonstrate the ability of CRH to affect the behavioral responses to an inflammatory nociceptive stimulus, and that the effects can be in opposite directions depending on the behavioral response considered.

Modulation of Sleep Homeostasis by Corticotropin Releasing Hormone in REM Sleep-Deprived Rats

Studies have shown that sleep recovery following different protocols of forced waking varies according to the level of stress inherent to each method. Sleep deprivation activates the hypothalamic-pituitary-adrenal axis and increased corticotropin-releasing hormone (CRH) impairs sleep. The purpose of the present study was to evaluate how manipulations of the CRH system during the sleep deprivation period interferes with subsequent sleep rebound. Throughout 96 hours of sleep deprivation, separate groups of rats were treated i.c.v. with vehicle, CRH or with alphahelical CRH(9-41), a CRH receptor blocker, twice/day, at 07:00 h and 19:00 h. Both treatments impaired sleep homeostasis, especially in regards to length of rapid eye movement sleep (REM) and theta/delta ratio and induced a later decrease in NREM and REM sleep and increased waking bouts. These changes suggest that activation of the CRH system impact negatively on the homeostatic sleep response to prolonged forced waking. These results indicate that indeed, activation of the HPA axis-at least at the hypothalamic level-is capable to reduce the sleep rebound induced by sleep deprivation.

Effects of AVP V1a and CRH receptor antagonist on psychological stress responses to frustrating condition in sheep

Arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are released in the brain to regulate behavioral and physiological stress responses. To elucidate the respective roles of these peptides under certain stressors, we examined the effects of intracerebroventricular infusions of either AVP V1a receptor antagonist, [Pmp(1), Tyr (Me)(2)]- Arg(8)-Vasopressin (Pmp, Tyr-AVP) or CRH receptor antagonist, alpha-helical CRF 9-41 (alphahCRF) on stress responses induced by frustrating condition in sheep. Four ovariectomized Corriedale ewes were assigned to the experiment. In a "frustrating" condition (FC), food was withheld for 60 minutes from only the experimental ewe while this ewe was in the presence of the other ewes that were given food. As "non-frustrating" control condition (C), food was withheld for 60 minutes from all ewes, thereby controlling for the nonspecific effects of lack of food. FC induced a significant rise in the plasma cortisol concentration (p < 0.05) and increased the pawing number and rectal temperature compared with that in C (p < 0.1). The effects of either Pmp, Tyr-AVP or alphahCRF on these stress responses were analyzed. The rise in cortisol restored nearly to the control level by infusion of Pmp, Tyr-AVP or alphahCRF. The pawing number restored nearly to the control level by alphahCRF. The hyperthermia restored nearly to the control level by Pmp, Tyr-AVP. These data suggest that both endogenous CRH and AVP might be concerned with inducing physiological and behavioral stress responses to frustrating condition in sheep.

Differential blockade of CRF-evoked behaviors by depletion of norepinephrine and serotonin in rats

RATIONALE

Central administration of corticotropin-releasing factor (CRF) elicits a specific pattern of behavioral responses resembling a stress-like state and is anxiogenic in rodent models of anxiety.

OBJECTIVES

Specific behaviors evoked by the administration of CRF were measured. The roles of CRF receptor subtypes and that of serotonergic and noradrenergic systems in mediating these responses were studied.

MATERIALS AND METHODS

Burying, grooming, and head shakes were quantified in rats following intracerebroventricular administration of CRF and urocortin II and after pretreatment with antagonists. The role of forebrain norepinephrine in the behavioral responses to CRF (0.3 microg) was examined following pretreatment with the neurotoxin DSP-4 and that of serotonin after depletion using systemic administration of para-chlorophenylalanine (p-CPA).

RESULTS

CRF at 0.3 and 3.0 microg caused robust increases in burying, grooming, and head shakes, but urocortin II was ineffective. Pretreatment with either antalarmin or propranolol significantly attenuated the CRF-evoked behaviors. Destruction of forebrain norepinephrine pathways blocked spontaneous burying behavior elicited by CRF and conditioned burying directed towards an electrified shock probe. In contrast, depletion of 5-HT selectively attenuated CRF-evoked grooming.

CONCLUSIONS

Overt behavioral responses produced by CRF, burying, grooming, and head shakes appeared to be mediated through the CRF(1) receptor. Spontaneous burying behavior evoked by CRF or conditioned burying directed towards a shock probe was disrupted by lesion of the dorsal noradrenergic bundle and may represent anxiety-like behavior caused by CRF activation of the locus ceruleus. In contrast, CRF-evoked increases in grooming were dependent on serotonin.

Acoustic startle amplitude predicts vulnerability to develop post-traumatic stress hyper-responsivity and associated plasma corticosterone changes in rats

Following exposure to trauma, a vulnerable sub-population of individuals develops post-traumatic stress disorder (PTSD) with characteristic persistent autonomic hyper-responsivity, associated increased startle response, and commonly altered hypothalamo-pituitary-adrenal regulation. A goal of this investigation was to identify a predictive marker for this vulnerability. Previous investigators have developed a model for PTSD in which male mice were exposed to a single brief episode of inescapable footshock followed by 1-min contextual reminders of this trauma at weekly intervals for 6 weeks. Exposure to these reminders induced a progressive and persistent increase in the amplitude of acoustic startle consistent with the persistently increased acoustic startle of individuals exhibiting PTSD. We adapted this model to adult male Wistar rats, with added characterization of initial (pre-trauma) startle response. After one episode of inescapable footshock (10 s, 2 mA) or control treatment followed by six weekly 1-min contextual reminders, acoustic startle was re-tested. Data were analyzed after dividing rats within each treatment into LOW vs MID vs HIGH (33% in each group) pre-treatment startle responders. Rats which exhibited pre-treatment LOW- and MID-range acoustic startle responses did not develop increased acoustic startle responses following subsequent traumatic stress+reminders ([TS+R]) treatment. However, rats which exhibited HIGH pre-treatment startle responses exhibited further significant (p<0.01) [TS+R]-induced persistent enhancement of this already elevated startle response. Furthermore, rats exhibiting HIGH pre-treatment startle responses were also the only subgroup which exhibited increased basal plasma corticosterone levels following [TS+R] treatment. These results suggest that initial pre-stress acoustic startle response can identify subgroups of rats which are predisposed to, or resistant to, developing a PTSD-like syndrome following subsequent trauma.

MPZP: a novel small molecule corticotropin-releasing factor type 1 receptor (CRF1) antagonist

The extrahypothalamic stress peptide corticotropin-releasing factor (CRF) system is an important regulator of behavioral responses to stress. Dysregulation of CRF and the CRF type 1 receptor (CRF(1)) system is hypothesized to underlie many stress-related disorders. Modulation of the CRF(1) system by non-peptide antagonists currently is being explored as a therapeutic approach for anxiety disorders and alcohol dependence. Here, we describe a new, less hydrophilic (cLogP approximately 2.95), small molecule, non-peptide CRF(1) antagonist with high affinity (K(i)=4.9 nM) and specificity for CRF(1) receptors: N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5-a] pyrimidin-7-amine (MPZP). The compound was systemically administered to adult male rats in two behavioral models dependent on the CRF(1) system: defensive burying (0, 5, 20 mg/kg, n=6-11 for each dose) and alcohol dependence (0, 5, 10, 20 mg/kg, n=8 for each self-administration group). Acute administration of MPZP reduced burying behavior in the defensive burying model of active anxiety-like behavior. MPZP also attenuated withdrawal-induced excessive drinking in the self-administration model of alcohol dependence without affecting nondependent alcohol drinking or water consumption. The present findings support the proposed significance of the CRF(1) system in anxiety and alcohol dependence and introduce a promising new compound for further development in the treatment of alcohol dependence and stress-related disorders.

Identifying early behavioral and molecular markers of future stress sensitivity

Puberty is a plastic period of neurological development when critical maturation of stress pathways occurs. Abnormal maturation may be predictive of future stress sensitivity and affective disorder risk. To identify potential early markers of stress-related disease predisposition, we examined physiological and behavioral stress responses in male pubertal mice compared with adults, using a genetic model of elevated stress sensitivity, CRF receptor-2 (CRFR2)-deficient mice. Juvenile mice of both genotypes exhibited greater basal and stress-induced corticosterone levels than adult mice, indicating that overall hypothalamic-pituitary-adrenal axis sensitivity diminishes in adulthood. However, juvenile CRFR2-deficient mice displayed a delayed stress recovery typical of adults of this genotype, suggesting an early marker of stress sensitivity. The adult phenotype of reduced hippocampal glucocorticoid receptor expression in these sensitive mice was also detected during puberty. This reduction may account for an impaired hypothalamic-pituitary-adrenal axis negative feedback and as such be an early indicator of a stress-sensitive phenotype. Examination of behavioral responses to stress revealed that CRFR2-deficient mice show exaggerated postpubertal maturation. Although wild-type mice did not alter their burying response to stress-provoking marbles after puberty, CRFR2-deficient mice showed a dramatic increase in burying behavior. We conclude that identification of abnormal pubertal stress pathway maturation may be predictive of adult heightened stress sensitivity and future susceptibility to stress-related affective disorders.

Intracerebroventricular administration of corticotrophin-releasing hormone receptor antagonists produces different effects on hypothalamic pituitary adrenal responses to novel restraint depending on the stress history of the animal

Corticotrophin-releasing hormone (CRH) regulates acute stress-induced changes in neuroendocrine function and behaviour. However, little is known about CRH functions in animals that have prior experience with repeated stress. Repeatedly-stressed rats exhibit a habituated hypothalamic-pituitary-adrenal (HPA) response to a familiar, homotypic stressor but exhibit maintained or enhanced HPA responses to a novel, heterotypic stressor. We examined the effects of intracerebroventricular (i.c.v.) administration of two different nonselective CRH receptor antagonists, alpha-helical CRH(9-41) (ahCRH) or D-Phe CRH(12-41) (D-PheCRH), on HPA responses to acute restraint in rats previously exposed to repeated cold stress (i.e. facilitated responses). Antagonists were administered as single i.c.v. injections prior to restraint to provide a general index of CRH function in control versus repeatedly-stressed rats. CRH receptor blockade with either ahCRH or D-PheCRH produced different effects on HPA responses to novel restraint depending on whether the animal had been previously cold stressed or not. Interestingly, some agonist-type effects were observed but only in repeatedly-stressed rats. In summary, these results indicate that manipulations of the CRH receptor have different effects on HPA activity depending on the stress history of the animal.

Glucocorticoids, chronic stress, and obesity

Glucocorticoids either inhibit or sensitize stress-induced activity in the hypothalamo-pituitary-adrenal (HPA) axis, depending on time after their administration, the concentration of the steroids, and whether there is a concurrent stressor input. When there are high glucocorticoids together with a chronic stressor, the steroids act in brain in a feed-forward fashion to recruit a stress-response network that biases ongoing autonomic, neuroendocrine, and behavioral outflow as well as responses to novel stressors. We review evidence for the role of glucocorticoids in activating the central stress-response network, and for mediation of this network by corticotropin-releasing factor (CRF). We briefly review the effects of CRF and its receptor antagonists on motor outflows in rodents, and examine the effects of glucocorticoids and CRF on monoaminergic neurons in brain. Corticosteroids stimulate behaviors that are mediated by dopaminergic mesolimbic "reward" pathways, and increase palatable feeding in rats. Moreover, in the absence of corticosteroids, the typical deficits in adrenalectomized rats are normalized by providing sucrose solutions to drink, suggesting that there is, in addition to the feed-forward action of glucocorticoids on brain, also a feedback action that is based on metabolic well being. Finally, we briefly discuss the problems with this network that normally serves to aid in responses to chronic stress, in our current overindulged, and underexercised society.

Retrograde amnesia following hippocampal lesions in the shock-probe conditioning test

The present experiment examined the role of the hippocampal formation (HPC) in long-term memory of an association between an object and a fear-eliciting event. Rats either received sham or neurotoxic lesions of the HPC 1 or 14 days after learning that contacting a wire-wrapped probe (i.e., object) elicits a shock. After recovery from the surgery, rats were re-exposed to the wire-wrapped probe and burying and avoidance of the probe were assessed and used as memory and fear indices. Regardless of the learning-to-surgery interval, the rats with hippocampal lesions buried and avoided the probe significantly less than sham rats and no more than rats that never experienced shock from the probe. These findings suggest that the lesions caused severe retrograde amnesia and that the HPC has a long-lasting role in memory of a discrete stimulus associated with a fear-eliciting event.

Nociceptin/orphanin FQ-induced delay in gastric emptying: role of central corticotropin-releasing factor and glucocorticoid receptors

When injected intracerebroventricularly (i.c.v.) in rats, nociceptin/orphanin FQ (N/OFQ) delays gastric emptying and increases plasma corticosterone levels. Our aim in this study was to investigate changes in gastric emptying of a phenol red meal, and the plasma corticosterone response to N/OFQ in adrenalectomized (ADX) rats, in ADX rats injected with corticosterone at 1, 24 and 72 h before the gastric emptying assay, and in intact rats i.c.v. pretreated with a glucocorticoid antagonist (RU486) and with a corticotropin-releasing factor receptor antagonist (alpha-helical CRF9-41). In adrenal intact rats, i.c.v. injection of N/OFQ (2.5 nmol rat-1) significantly delayed gastric emptying (by 70%) and increased plasma corticosterone concentrations. Conversely, in ADX rats, N/OFQ left gastric emptying unchanged. In ADX rats, corticosterone injected at 1, 24 and 72 h before the gastric emptying assay almost restored the N/OFQ-induced delay in gastric emptying. Finally, pretreatment with RU486- and alpha-helical CRF9-41 abolished the N/OFQ-induced inhibition of gastric emptying. These findings suggest that central N/OFQ inhibits gastric emptying through an integrated orphaninergic system-CRF interaction in which corticosterone plays a permissive role.

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.

Involvement of central amygdalar and bed nucleus of the stria terminalis corticotropin-releasing factor in behavioral responses to social defeat

The authors investigated whether corticotropin-releasing factor (CRF) within the central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST) is a critical component of the neural circuitry mediating conditioned defeat. In this model, hamsters that have experienced social defeat subsequently display only submissive-defensive agonistic behavior instead of territorial aggression. Conditioned defeat was significantly reduced following infusion of the CRF receptor antagonist D-Phe CRF((12-41)) into the BNST but not into the CeA. In another experiment, hamsters given unilateral lesions of the CeA and infusions of D-Phe CRF((12-41)) into the contralateral BNST displayed significantly less submissive behavior than did controls. These data suggest that CRF acts within a neural circuit that includes the amygdala and the BNST to modulate agonistic behavior following social defeat.

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.

Differential regulation of behavioral, genomic, and neuroendocrine responses by CRF infusions in rats

Studies suggest that behavioral, genomic, and endocrine functions mediated by central corticotropin-releasing factor (CRF)-containing circuits may be differentially regulated. However, this hypothesis has never been tested directly by simultaneous assessment of distinct CRF-mediated responses within the same animal. The present study addressed this issue by concurrently examining the effects of central CRF infusions on anxiety responses, plasma corticosterone release, and c-fos mRNA induction within limbic brain circuits. Bilateral intracerebroventricular (icv) infusions of CRF (0.1-10 microg total) dose-dependently reduced exploratory behavior in a novel open field, increased circulating corticosterone (CORT) levels and augmented c-fos mRNA expression in the central nucleus of the amygdala (CeA) and the hypothalamic paraventricular nucleus (PVN). Plasma CORT levels increased significantly after 0.1 microg CRF, whereas behavioral and genomic responses required at least 1 microg CRF, suggesting that the distinct responses mediated by CRF are differentially regulated. Further characterization of intracerebroventricular CRF at 1 microg also demonstrated a disruption of social interaction behavior. The majority of behavioral effects and the elevated c-fos mRNA expression were attenuated by 10 mg/kg DMP696, a CRF(1) antagonist. However, plasma CORT elevation required 30 mg/kg DMP696 for attenuation. Thus, our studies demonstrate a greater sensitivity of the hypothalamic-pituitary-adrenal axis to intracerebroventricular CRF compared with the induction of innate fear-like responses and associated genomic changes.

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.

Chronic stress alters behavior in the conditioned defensive burying test: role of the posterior paraventricular thalamus

In the present studies, we examined the effects of chronic restraint on behavior in the conditioned defensive burying paradigm, a well-validated test of anxiety. This test is based on the findings that rodents tend to cover or bury the source of a noxious or aversive stimulus. However, little is known about whether prior chronic stress exposure can alter this anxiety-related behavior. In the present study, we examined whether chronic restraint affects indices of behavior in the conditioned defensive burying paradigm. Furthermore, since the posterior division of the paraventricular thalamus (pPVTh) regulates neuroendocrine activity specifically in chronically stressed but not control rats, we hypothesized that the pPVTh may also regulate any chronic stress-induced changes in behavior observed in the defensive burying test. Chronically stressed rats (30-min restraint per day for seven consecutive days) exhibited decreased latency to bury compared to control rats regardless of the presence of lesions suggesting increased reactivity to the shock in these animals. Importantly, pPVTh-lesioned chronically stressed rats exhibited increased duration and height of burying compared to control rats with pPVTh lesions, whereas no differences existed between sham-lesioned control and chronically stressed rats. Since both burying height and duration of burying are considered indices of anxiety in the defensive burying test, the present results suggest that the intact pPVTh may be important in dampening behaviors related to anxiety in chronically stressed rats.

Light-enhanced and fear-potentiated startle: temporal characteristics and effects of alpha-helical corticotropin-releasing hormone

BACKGROUND

It has been suggested that the light-enhanced startle paradigm (LES) is an animal model for anxiety, because of the unconditioned and nonspecific cue and the long-term effect. In contrast, the fear-potentiated startle (FPS) is suggested to model fear. In the present study, we assessed in detail the time course of LES and FPS and investigated whether corticotropin-releasing hormone (CRH) is differentially involved in these two models.

METHODS

In experiment 1, the amplitude of the startle response was tracked in the presence of the light and after light offset, in both models. In experiment 2, the effects of intracerebroventricular administration of the CRH-receptor antagonist alpha-helical CRH (0, 1, 5, and 25 microg) on LES and FPS were studied.

RESULTS

In LES, light onset resulted in a long-lasting potentiation of the startle response and a slow return to baseline after light offset. In FPS, the potentiation of the startle response returned to baseline almost immediately after light offset. Alpha-helical CRH reduced the potentiation in LES at the 5-microg dose but not at 25 microg. In FPS, alpha-helical CRH had no effect.

CONCLUSIONS

The results show that the time course of LES is markedly different from that of FPS, which together with the differences in eliciting stimuli suggest that they model anxiety and fear, respectively. Moreover, the results suggest that CRH is involved in LES and not in FPS.

Chronic corticotropin-releasing hormone and vasopressin regulate corticosteroid receptors in rat hippocampus and anterior pituitary

Corticotropin-releasing hormone (CRH) and vasopressin (AVP) participate in the endocrine, autonomic, immunological and behavioral response to stress. CRH and AVP receptors are found in hippocampus and anterior pituitary, where mineralocorticoid (MR) and glucocorticoid (GR) receptors are abundant. We investigated the possible influence of CRH and AVP on the regulation of MR and GR in both tissues. CRH, AVP, or their antagonists were administered to adrenalectomized rats substituted with corticosterone, to avoid interference with adrenal secretion. Repeated i.c.v. oCRH injections (10 microgram) for 5 days significantly decreased MR and GR mRNA in hippocampus and MR mRNA in anterior pituitary. AVP significantly increased both corticosteroid receptor mRNAs, as repeated i.c.v. injections (5 microgram) for 5 days in hippocampus, and as continuous i.c.v. infusion (10 ng/h/5 days) in anterior pituitary. The i.c.v. infusion of 5 or 10 microgram/day of the alpha-helical CRH antagonist during intermittent restraint stress (5 days), induced a significant decrease in hippocampal MR binding. In anterior pituitary, 5 microgram/day significantly decreased MR binding, while 10 microgram/day significantly increased GR binding. Under the same conditions of stress, the infusion of 15 microgram/day of the vasopressin V1a/1b receptor antagonist [dP Tyr (Me)(2)AVP] significantly increased MR and GR binding in hippocampus and anterior pituitary; 5 microgram/day significantly decreased pituitary MR binding. Our results show that CRH and AVP regulate MR and GR in hippocampus and anterior pituitary. This reveals another important function of CRH and AVP, which could be relevant to understand stress adaptation and the pathophysiology of stress-related disorders like major depression.

Receptor occupancy of nonpeptide corticotropin-releasing factor 1 antagonist DMP696: correlation with drug exposure and anxiolytic efficacy

4-(1,3-Dimethoxyprop-2-ylamine)-2,7-dimethyl-8-(2,4-dichlorophenyl)-pyrazolo[1,5-a]-1,3,5-triazine (DMP696) is a highly selective and potent, nonpeptide corticotropin-releasing factor 1 (CRF(1)) antagonist. In this study, we measured in vivo CRF(1) receptor occupancy of DMP696 by using ex vivo ligand binding and quantitative autoradiography and explored the relationship of receptor occupancy with plasma and brain exposure and behavioral efficacy. In vitro affinity (IC(50)) of DMP696 to brain CRF(1) receptors measured using the brain section binding autoradiography in this study is similar to that assessed using homogenized cell membrane assays previously. The ex vivo binding assay was validated by demonstrating that potential underestimation of receptor occupancy with this procedure could be minimized by identifying an appropriate in vitro incubation time (40 min) based upon the dissociation kinetics of DMP696. Orally administrated DMP696 dose dependently occupied CRF(1) receptors in the brain, with ~60% occupancy at 3 mg/kg. In the defensive withdrawal test of anxiety, this dose of DMP696 produced approximately 50% reduction in the exit latency. The time course of plasma and brain drug levels paralleled that of receptor occupancy, with peak exposure at 90 min after dosing. The plasma-free concentration of DMP696 corresponding to 50% CRF(1) receptor occupancy (in vivo IC(50), 1.22 nM) was similar to the in vitro IC(50) (~1.0 nM). Brain concentrations of DMP696 were over 150-fold higher than the plasma-free levels. In conclusion, doses of DMP696 occupying over 50% brain CRF(1) receptors are consistent with doses producing anxiolytic efficacy in the defense withdrawal test of anxiety, and the IC(50) value estimated in vivo based on plasma-free drug concentrations is consistent with the in vitro IC(50) value.

Defensive burying in rodents: ethology, neurobiology and psychopharmacology

Defensive burying refers to the typical rodent behavior of displacing bedding material with vigorous treading-like movements of their forepaws and shoveling movements of their heads directed towards a variety of noxious stimuli that pose a near and immediate threat, such as a wall-mounted electrified shock-prod. Since its introduction 25 years ago by Pinel and Treit [J. Comp. Physiol. Psychol. 92 (1978) 708], defensive (shock-prod) burying has been the focus of a considerable amount of research effort delineating the methodology/ethology, psychopharmacology and neurobiology of this robust and species-specific active avoidance or coping response. The present review gives a summary of this research with special reference to the behavioral (face and construct) and pharmacological (predictive) validity of the shock-prod burying test as an animal model for human anxiety. Emphasis is also placed on some recent modifications of the paradigm that may increase its utility and reliability as to individual differences in expressed emotional coping responses and sensitivity to pharmacological treatments. Overall, the behavioral and physiological responses displayed in the shock-prod paradigm are expressions of normal and functionally adaptive coping patterns and the extremes of either active (i.e., burying) or passive (i.e., freezing) forms of responding in this test cannot simply be regarded as inappropriate, maladaptive or pathological. For this reason, the shock-prod paradigm is not an animal model for anxiety disorder or for any other psychiatric disease, but instead possesses a high degree of face and construct validity for normal and functionally adaptive human fear and anxious apprehension. However, the apparent good pharmacological validation (predictive validity) of this test reinforces the view that normal and pathological anxiety involves, at least partly, common neurobiological substrates. Therefore, this paradigm is not only suitable for screening potential anxiolytic properties of new drugs, but seems to be especially valuable for unraveling the neural circuitry and neurochemical mechanisms underlying the generation of active and passive coping responses as different expressions of anxiety.

Differential release of corticotropin-releasing hormone (CRH) in the amygdala during different types of stressors

The purpose of this study was to determine if differences exist between the effects of acute treadmill running and restraint stress on corticotropin-releasing hormone (CRH) release within the amygdala of rats. Extracellular CRH immunoreactivity (CRH-IR) was measured in microdialysate collected from the central nucleus of the amygdala (CeA) during exposure to an inactivated treadmill (TC), during 1 h treadmill running to exhaustion (RUN), and 1 h restraint (RES). Extracellular CRH-IR increased from control levels during the first 20-min period for TC, RUN, and RES, with the largest increase during RES. During the second 20-min period, only RES maintained levels higher than control values. CRH release was higher than control during the third 20-min period of RES and RUN. A second experiment consisted of four groups of either cage controls (CC), TC, RUN, or RES. Immediately following the 60-min treatment, brains were removed and trunk blood collected for analysis of tissue CRH-IR and plasma corticosterone. While amygdala tissue CRH-IR was not different in the CC, TC and RUN rats, these groups had significantly lower levels than the RES animals. Hypothalamic tissue CRH-IR was not different between the CC and TC rats, but the levels were significantly higher in the RES and RUN rats than in the two control groups. Plasma corticosterone levels were elevated only in RES and RUN rats. Results from tissue analysis indicate that increased tissue CRH-IR in the amygdala and hypothalamus can be elicited by RES, while only the hypothalamus shows an increase following RUN. Further, extracellular CRH release in the CeA is increased throughout the period of RES, when rats are placed on the treadmill, and when the animals are approaching physical exhaustion. No increase is observed during the running period between placement on the treadmill and intense exertion. Overall, the data suggest that amygdala CRH release is regulated differently during treadmill running and restraint.

Anxiolytic effect of a CRH receptor antagonist in the dorsal periaqueductal gray

Corticotropin-releasing hormone (CRH) is anxiogenic when microinjected into the dorsal periaqueductal gray (DPAG). Microinjection of alpha-helical-CRH9-41 (0.5 microgram), a CRH receptor antagonist, however, failed to change anxiety levels. The objective of this study was to verify if this compound has any effect in the anxiogenic behavior of rats submitted to 4 hr of restraint stress 24 hr before the test in an elevated plus maze. Results showed that stressed rats had a decreased exploration of open arms without changing the number of enclosed arm entries. The stress effect was reversed by intra-DPAG injection of alpha-helical-CRH9-41 (0.5 microgram). These results suggest that the anxiogenic behavior of rats previously stressed by forced immobilization might involve facilitation of CRH-mediated neurotransmission in the DPAG.

Differential effect of low doses of intracerebroventricular corticotropin-releasing factor in forced swimming test

In this work, we studied the effect of low doses of intracerebroventricular corticotropin-releasing factor (CRF) in six sessions of forced swimming test (FST). When CRF (0.01 and 0.1 microg) was administered pre-test, results showed that the 0.1-microg dose significantly increased swimming in SESSION2, SESSION3 and SESSION4, while the 0.01-microg dose proved ineffective. When CRF (0.1 and 0.03 microg) was administered post-test to evaluate retention of swimming response, the dose of 0.1 microg impaired retention, while the dose of 0.03 microg improved it, although these effects only reached significance in SESSION2. In an additional session (SESSION6), testing long-term retention of this swimming response, the 0.1-microg dose significantly impaired retention, whereas the 0.03-microg dose proved ineffective. A high dose of CRF (1 microg) was also included as a control of previous results [García-Lecumberri C, Ambrosio E. Role of corticotropin-releasing factor in forced swimming test. Eur J Pharmacol 1998;343:17-26]. In all the FST sessions, this high dose increased swimming when administered pre-test, while impairing retention when administered post-test. Preliminary data obtained with low doses of CRF suggest that a differential effect on retention of swimming response seems to exist depending on the dose, whereas a high dose of CRF clearly impairs retention. The role of CRF in learning and memory processes in FST is discussed.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Stress, corticotropin-releasing factor, and drug addiction

The neuropeptide corticotropin-releasing factor (CRE) and related neuropeptides not only mediate hormonal responses to stressors but also have a neurotropic role in the central nervous system to mediate behavioral responses to stressors. CRF antagonists effectively block CRF responses and have effects opposite those of CRF in many stress-related situations. Recent advances suggest that in addition to CRF itself there is another CRF-related neuropeptide, urocortin, that may be involved in stress-related responses, particularly those involving appetite. At least two CRF receptors have been discovered to date, CRF-1 and CRF-2. CRF may be involved in various aspects of the addiction cycle associated with drugs of abuse. CRF appears to be activated during stress-induced reinstatement of drug taking as well as acute withdrawal from all major drugs of abuse. CRF is hypothesized to be part of an allostatic change leading to vulnerability to relapse during prolonged abstinence from drugs of abuse.

A role for corticotropin releasing factor and urocortin in behavioral responses to stressors

Corticotropin-releasing factor (CRF) and CRF-related neuropeptides have an important role in the central nervous system to mediate behavioral responses to stressors. CRF receptor antagonists are very effective in reversing stress-induced suppression and activation in behavior. An additional CRF-like neuropeptide, urocortin, has been identified in the brain and has a high affinity for the CRF-2 receptor in addition to the CRF-1 receptor. Urocortin has many of the effects of CRF but also is significantly more potent than CRF in decreasing feeding in both meal-deprived and free-feeding rats. In mouse genetic models, mice over-expressing CRF show anxiogenic-like responses compared to wild-type mice, and mice lacking the CRF-1 receptor showed an anxiolytic-like behavioral profile compared to wild-type mice. Results to date have led to the hypothesis that CRF-1 receptors may mediate CRF-like neuropeptide effects on behavioral responses to stressors, but CRF-2 receptors may mediate the suppression of feeding produced by CRF-like neuropeptides. Brain sites for the behavioral effects of CRF include the locus coeruleus (LC), paraventricular nucleus (PVN) of the hypothalamus, the bed nucleus of the stria terminalis (BNST), and the central nucleus of the amygdala. CRF may also be activated during acute withdrawal from all major drugs of abuse, and recent data suggest that CRF may contribute to the dependence and vulnerability to relapse associated with chronic administration of drugs of abuse. These data suggest that CRF systems in the brain have a unique role in mediating behavioral responses to diverse stressors. These systems may be particularly important in situations were an organism must mobilize not only the pituitary adrenal system, but also the central nervous system in response to environmental challenge. Clearly, dysfunction in such a fundamental brain-activating system may be the key to a variety of pathophysiological conditions involving abnormal responses to stressors such as anxiety disorders, affective disorders, and anorexia nervosa.

Structure-activity studies on 4-substituted-2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists

Structure-activity studies around the 4-position of 2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists suggest that there is a large lipophilic cavity in the rat CRF receptor, which can accommodate a wide variety of substituents at this position in contrast to the steric constraints observed for other positions on the 2-anilinopyrimidine core. The chemical syntheses and biological activities of 2-anilinopyrimidine CRF antagonists with carbon-linked substituents at the 4-position are reported. Significant improvements in rat pharmacokinetic parameters were achieved relative to those for the lead structure. While the lead compound 1 (rCRF Ki = 44 nM) afforded no detectable rat plasma levels after intraperitoneal (i.p.) or oral (p.o.) dosing, compounds 3-3 (rCRF Ki = 16 nM) and 3-4 (rCRF Ki 59 nM) gave high rat plasma levels at 30 mg/kg (i.p., p.o.) (Cmax = 1389 nM and 8581 nM (i.p.) respectively; Cmax = 113 nM and 988 nM (p.o.), respectively). Furthermore 3-3 and 3-4 had superior bioavailabilities at these doses (59 and 46% (i.p.), respectively; 2 and 10%, (p.o.), respectively).

Corticotropin-releasing factor, norepinephrine, and stress

Corticotropin-releasing factor (CRF) and related peptides in the central nervous system appears to have activating properties on behavior and to enhance behavioral responses to stressors. CRF and urocortin injected into the brain produces increases in arousal as measured by locomotor activation and increased responsiveness to stressful stimuli. These effects of CRF appear to be independent of the pituitary adrenal axis and can be reversed by specific and selective CRF antagonists alpha-helical CRF9-41 and D-Phe CRF12-41. Perhaps more importantly, CRF antagonists can reverse behavioral responses to many stressors. These results suggest that endogenous CRF systems in the brain may have a role in mediating behavioral responses to stressors. Norepinephrine systems emanating from the nucleus locus coeruleus also long have been hypothesized to be involved in mediating behavioral constructs associated with alertness, arousal, and stress. Pharmacologic, physiologic, and neuroanatomic evidence supports an important role for a CRF-norepinephrine interaction in the region of the locus coeruleus in response to stressors that may be modality-specific where CRF neurons activate the locus coeruleus. One may hypothesize that another norepinephrine-CRF interaction may occur in the terminal projections of the forebrain norepinephrine systems in the paraventricular nucleus of the hypothalamus, the bed nucleus of the stria terminalis, and the central nucleus of the amygdala where norepinephrine stimulates CRF release. Such a feed-forward system may be particularly important in situations where an organism must mobilize not only the pituitary adrenal system but also the central nervous system, in response to environmental challenge. However, such a feed-forward mechanism in a fundamental brain-activating system may be particularly vulnerable to dysfunction and thus, may be the key to a variety of pathophysiologic conditions involving abnormal responses to stressors such as anorexia nervosa, anxiety, and affective disorders.

Differential effects of two corticotropin-releasing factor antagonists on conditioned defeat in male Syrian hamsters (Mesocricetus auratus)

The purpose of the present study was to determine whether corticotropin-releasing factor (CRF) is involved in mediating the expression of conditioned defeat in male Syrian hamsters. The present study examined the effects of two different competitive CRF receptor antagonists on the expression of conditioned defeat. Specifically, Experiment 1 examined whether peripheral administration of CP-154,526, a specific non-peptide CRF1 receptor antagonist, would reduce the expression of conditioned defeat. Experiment 2 examined whether D-Phe CRF(12-41), a nonspecific CRF1/CRF2 receptor antagonist, infused directly into the brain, would reduce the expression of conditioned defeat. The results revealed that i.p. injections of CP-154,526 did not reduce the expression of conditioned defeat, whereas i.c.v. injections of D-Phe CRF(12-41) successfully reduced the expression of conditioned defeat. The duration of submissive/defensive behaviors in hamsters that received the high dose of D-Phe CRF(12-41) was significantly less than that exhibited by animals that received a vehicle control. The present data suggest that central CRF may be involved in mediating the expression of conditioned defeat and other behavioral responses to stressful stimuli.

Neuroendocrine and behavioral effects of CRH blockade and stress in male rats

Our previous data have shown that restraint (RT), a mild nonpainful stressor, acutely impairs nonsocial and social behavior in male rats. Corticotropin-releasing hormone (CRH) is a regulator of these behavioral responses. To evaluate whether CRH mediates the neuroendocrine and behavioral alterations present 24 h after restraint stress, we administered the CRH antagonist alpha-helical CRH(9-41) (alpha-hCRH) intracerebroventricularly to male rats and we compared its effects with those of saline. Twenty-four hours after treatment, nonsocial behaviors were significantly decreased by alpha-hCRH, this effect being independent of RT. Among social behaviors, only introductory activity showed significant differences as a result of both RT and alpha-hCRH. The concentrations of ACTH in the plasma and those of beta-endorphin in the anterior and neurointermediate lobes of the pituitary were affected by alpha-hCRH treatment. The effect on ACTH was simply related to the administration of the alpha-hCRH, while for beta-endorphin, significant interactions between alpha-hCRH and RT were found. On the whole, these results point to the role played by CRH in the control of neuronal mechanisms involved in the stress-induced effects.

The rationale for corticotropin-releasing hormone receptor (CRH-R) antagonists to treat depression and anxiety

Neuroendocrine studies strongly suggest that dysregulation of the hypothalamic pituitary-adrenocortical (HPA) system plays a causal role in the development and course of depression. Whereas the initial mechanism resulting in HPA hyperdrive remains to be elucidated, evidence has emerged that corticosteroid receptor function is impaired in many patients with depression and in many healthy individuals at increased genetic risk for an depressive disorder. Assuming such impaired receptor function, then central secretion of CRH would be enhanced in many brain areas, which would account for a variety of depressive symptoms. As shown in rats and also in transgenic mice with impaired glucocorticoid receptor function, antidepressants enhance the signaling through corticosteroid receptors. This mechanism of action can be amplified through blocking central mechanisms that drive the HPA system. Animal experiments using antisense oligodeoxynucleotides directed against the mRNA of both CRH receptor subtypes identified the CRH1 receptor as the mediator of the anxiogenic effects of CRH. Studies in mouse mutants in which this receptor subtype had been deleted extended these findings as the animals were less anxious than wild-type mice when experimentally stressed. Thus, patients with clinical conditions that are causally related to HPA hyperactivity may profit from treatment with a CRH1 receptor antagonist.

Is there a future for neuropeptide receptor ligands in the treatment of anxiety disorders?

This review provides an overview of preclinical and clinical evidence of a role for the neuroactive peptides cholecystokinin (CCK), corticotropin-releasing factor (CRF), neuropeptide Y (NPY), tachykinins (i.e., substance P, neurokinin [NK] A and B), and natriuretic peptides in anxiety and/or stress-related disorders. Results obtained with CCK receptor antagonists in animal studies have been highly variable, and clinical trials with several of these compounds in anxiety disorders have been unsuccessful so far. However, future investigations using CCK receptor antagonists with better pharmacokinetic characteristics and animal models other than those validated with the classical anxiolytics benzodiazepines may permit a more precise evaluation of the potential of these compounds as anti-anxiety agents. Results obtained with peptide CRF receptor antagonists in animal models of anxiety convincingly demonstrated that the blockade of central CRF receptors may yield anxiolytic-like activity. However, the discovery of nonpeptide and more lipophilic CRF receptor antagonists is essential for the development of these agents as anxiolytics. Similarly, there is clear preclinical evidence that the central infusion of NPY and NPY fragments selective for the Y1 receptor display anxiolytic-like effects in a variety of tests. However, synthetic nonpeptide NPY receptor agonists are still lacking, thereby hampering the development of NPY anxiolytics. Unlike selective NK1 receptor antagonists, which have variable effects in anxiety models, peripheral administration of selective NK2 receptor antagonists and central infusion of natriuretic peptides produce clear anxiolytic-like activity. Taken as a whole, these findings suggest that compounds targeting specific neuropeptide receptors may become an alternative to benzodiazepines for the treatment of anxiety disorders.

Non-peptide corticotropin-releasing hormone antagonists: syntheses and structure-activity relationships of 2-anilinopyrimidines and -triazines

Screening of our chemical library using a rat corticotropin-releasing hormone (CRH) receptor assay led to the discovery that 2-anilinopyrimidine 15-1 weakly displaced [125I]-0-Tyr-oCRH from rat frontal cortex homogenates when compared to the known peptide antagonist alpha-helical CRH(9-41) (Ki = 5700 nM vs 1 nM). Furthermore, 15-1 weakly inhibited CRH-stimulated adenylate cyclase activity in the same tissue, but it was less potent than alpha-helical CRH(9-41) (IC50 = 20 000 nM vs 250 nM). Systematic structure-activity relationship studies, using the cloned human CRH1 receptor assay, defined the pharmacophore for optimal binding to hCRH1 receptors. Several high-affinity 2-anilinopyrimidines and -triazines were discovered, some of which had superior pharmacokinetic profiles in the rat. This paper describes the structure-activity studies which improved hCRH1 receptor binding affinity and pharmacokinetic parameters in the rat. Compound 28-17 (mean hCRH1 Ki = 32 nM) had a significantly improved pharmacokinetic profile in the rat (19% oral bioavailability at 30 mg/kg) as well as in the dog (20% oral bioavailability at 5 mg/kg) relative to the early lead structures.

The impact of the nonpeptide corticotropin-releasing hormone antagonist antalarmin on behavioral and endocrine responses to stress

The nonpeptide CRH antagonist antalarmin has been shown to block both behavioral and endocrine responses to CRH. However, it's potential activity in blunting behavioral and endocrine sequelae of stressor exposure has not been assessed. Because antagonism of central CRH by alpha-helical CRH attenuates conditioned fear responses, we sought to test antalarmin in this regard. In addition, it remains unclear as to whether this is a result of receptor blockade during conditioning or during testing. Thus, we explored whether CRH mediates the induction or expression of conditioned fear (freezing in a context previously associated with 2 footshocks; 1.0 mA, 5 sec each). Furthermore, because rats previously exposed to inescapable shock (IS; 100 shocks, 1.6 mA, 5 sec each), demonstrate enhanced fear conditioning, we investigated whether this effect would be blocked by antalarmin. Antalarmin (20 mg/kg x 2 ml i.p.) impaired both the induction and expression of conditioned fear. In addition, antalarmin blocked the enhancement of fear conditioning produced by prior exposure to IS. Despite the marked behavioral effects observed in antalarmin-treated rats, antalarmin had no effect on IS-induced rises in ACTH or corticosterone. However, antalarmin did block the ACTH response produced by exposure to 2 footshocks.

Differential effects of CRH infusion into the central nucleus of the amygdala in the Roman high-avoidance and low-avoidance rats

Roman-high (RHA/Verh) and low (RLA/Verh) avoidance rats are selected and bred for rapid learning versus non-acquisition of two-way, active avoidance behavior in a shuttle box. RHA/Verh rats generally show a more active coping style than do their RLA/Verh counterparts when exposed to various environmental challenges. The central nucleus of the amygdala (CeA) is known to be involved in the regulation of autonomic, neuroendocrine and behavioural responses to stress and stress-free conditions, and it is considered in relation to coping strategies. Corticotropin-releasing hormone (CRH) seems to be a key factor in the control of the CeA output. Neuroanatomical studies have revealed that the majority of CRH fibers from the CeA have direct connections with autonomic regulatory nuclei in the brainstem, e.g. lateral parabrachial nucleus (lPB), ventrolateral periaquaductal gray (vlPAG). The modulating effects of CRH (30 ng) on CeA activity were studied by infusion of CRH into the CeA in freely moving male RHA/Verh and RLA/Verh rats under stress-free conditions. Heart-rate and behavioural activities were repeatedly measured before, during and after local administration of CRH or vehicle, after which early gene product FOS immunocytochemistry and CRH-mRNA in situ hybridisation were carried out in selected brain areas. CRH infusion into the CeA caused a long lasting increase in heart-rate and behavioural activation in the RHA/Verh rats, leaving the RLA/Verh rats unaffected. As a result of CRH infusion, the number of FOS positive cells in the CeA and lPB of RLA/Verh rats was increased whereas an opposite response was found in the RHA/Verh rats. However, CRH into the CeA of the Roman rat lines induced no pronounced effects on FOS staining in the vlPAG and CRH mRNA levels in the CeA. These results indicate that the CRH system of the CeA, connected with the output brainstem areas, is differentially involved in cardiovascular and behavioural responses.

The role of CRF in behavioral aspects of stress

CRF in the central nervous system appears to hve activating properties on behavior and to coordinate behavioral responses to stressors. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by CRF antagonists. CRF antagonist administration reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF 9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stressors that can be modified by suppression of endogenous CRF activity therein. These actions of CRF in coordinating coping responses to stress at several bodily levels are consistent with a role for CRF similar to the dual role of other hypothalamic releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters. Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.