CP-154,526, a selective, non-peptide antagonist of the corticotropin-releasing factor1 receptor attenuates stress-induced relapse to drug seeking in cocaine- and heroin-trained rats

Paradoxical effects of chronic morphine treatment on the temperature and pituitary-adrenal responses to acute restraint stress: a chronic stress paradigm

Body temperature and pituitary-adrenal responses to restraint (15 min or 4 h) stress were evaluated in nondependent and morphine-dependent rats. Male Sprague-Dawley rats were treated twice daily with increasing doses of morphine (10-100 mg/kg, s.c.) for 16 days. Transmitters were implanted in the peritoneal cavity to monitor body temperature and blood was collected for hormone assays. Acute withdrawal from chronic morphine treatment was associated with reduced body weight, increased adrenal weight and decreased thymus weight. Sixteen days after termination of chronic morphine treatment, rats had recovered normal adrenal size, but still displayed marked thymus involution and reduced body weight. Restraint-induced hyperthermia was attenuated in morphine-dependent rats that had undergone 12-h withdrawal. Sixteen days after withdrawal, rats still had not fully recovered the hyperthermic response to restraint. Chronic morphine treatment resulted in a marked elevation of basal corticosterone concentrations. Despite the negative-feedback effects of elevated basal corticosterone concentrations, morphine-dependent rats that had undergone 12-h withdrawal displayed a potentiated and prolonged corticosterone response to restraint stress. In contrast, rats that had undergone 8-day and 16-day morphine withdrawal had recovered normal basal pituitary-adrenal activity, but displayed significantly reduced and shorter adrenocorticotropic hormone and corticosterone responses to restraint. These results suggest that chronic morphine dependence is a chronic stressor, resulting in profound and long-lasting changes in the temperature and pituitary-adrenal responses to acute restraint stress in a time-dependent manner. This morphine-dependence model may be useful in understanding the role that hormonal stress responses play in the maintenance and relapse to opioid use in humans.

The role of CRH in behavioral responses to stress

Corticotropin-releasing hormone (CRH) and urocortin in the central nervous system affect behavior and can enhance behavioral responses to stressors. The action of CRH-related peptides is mediated through multiple receptors that differ markedly in their pharmacological profiles and anatomical distribution. Comparative pharmacology of CRH receptor agonists suggests that CRH, urocortin, sauvagine and urotensin consistently mimic, and CRH receptor antagonists consistently lessen, functional consequences of stressor exposure. Recently, important advances have been made in understanding the CRH system and its role in behavioral responses to stress by the development of specific CRH receptor antagonists, application of antisense oligonucleotides and development of transgenic mice lacking peptides and functional receptors. This review summarizes recent findings with respect to components of the CRH system and their role in stress-induced behavioral responses.

Reduction of opioid dependence by the CB(1) antagonist SR141716A in mice: evaluation of the interest in pharmacotherapy of opioid addiction

Several compounds, mainly opioid agonists such as methadone, are currently used for long term medication of heroin addicts. Nevertheless, these maintenance treatments have the disadvantage to induce a dependence to another opiate. As interactions between opioid and cannabinoid systems have been demonstrated, the ability of the CB(1) antagonist, SR141716A to reduce morphine-induced addiction was investigated. The effects of SR141716A on the rewarding responses of morphine were evaluated in the place conditioning paradigm. No significant conditioned preference or aversion were observed after repeated treatment with the CB(1) antagonist alone. However, SR141716A was able to antagonize the acquisition of morphine-induced conditioned place preference. SR141716A was co-administered with morphine for 5 days, and the withdrawal syndrome was precipitated by naloxone administration. A reduction in the incidence of two main signs of abstinence: wet dog shakes and jumping was observed while the other were not significantly modified. In contrast, an acute injection of the CB(1) antagonist just before naloxone administration was unable to modify the incidence of the behavioural manifestations of the withdrawal, suggesting that only chronic blockade of CB(1) receptors is able to reduce morphine-induced physical dependence. Several biochemical mechanisms could explain the reduction of opioid dependence by CB(1) antagonists. Whatever the hypotheses, this study supports the reported interaction between the endogenous cannabinoid and opioid systems, and suggests that SR 141716A warrants further investigations for a possible use in opioid addiction.

Therapeutic potential of CRF receptor antagonists: a gut-brain perspective

Activation of the corticotropin-releasing factor (CRF) family of neuropeptide receptors in the brain and periphery appears to mediate stress-related changes in a variety of physiological and functional domains. Comparative pharmacology of CRF receptor agonists suggests that CRF, urocortin, sauvagine and urotensin consistently mimic, and conversely peptide CRF receptor antagonists lessen, the functional consequences of stressor exposure. Together with the development of novel non-peptide CRF receptor antagonists, a growing number of CRF receptor selective ligands are available to elucidate the neurobiology and physiological role of CRF systems. The present review considers available preclinical evidence as well as results from one Phase II clinical trial which address the hypothesis that CRF receptor antagonists may represent a new option for pharmacotherapy of stress-related disorders.

Corticotropin-releasing factor receptor type 1 mediates stress-induced relapse to cocaine-conditioned place preference in rats

Corticotropin-releasing factor (CRF) has been suggested to play an important role in the development of drug dependence and withdrawal. Based on the recent finding that CRF receptor antagonists inhibit the stress-induced relapse to opiate dependence and attenuate anxiety-like responses related to cocaine withdrawal, the present experiment was performed to examine the possible effect of different CRF receptor antagonists on reactivation of cocaine-conditioned place preference induced by cocaine and stress in rats. The results show that a single injection of cocaine (10 mg/kg, i.p.) could reactivate cocaine-conditioned place preference following a 28-day extinction, and pretreatment with i.c.v. 10 microg alpha-helical CRF, a nonspecific CRF receptor antagonist, significantly attenuated this reactivation of conditioned place preference. However, pretreatment with i.p. 1 or 10 mg/kg CP-154,526 (butyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]-ethylamine), a specific CRF receptor subtype 1 antagonist, and i.c.v. 1 or 10 microg AS-30 ([D-Phe(11),His(12)]Svg-(11-40)), a specific CRF receptor subtype 2 antagonist, failed to show the same effects. In addition, a single footshock stress also elicited the reactivation of cocaine-conditioned place preference following a 28-day extinction and pretreatment with alpha-helical CRF (10 microg, i.c.v.) and CP-154,526 (1 or 10 mg/kg, i.p.) significantly blocked this effect. In contrast, pretreatment with AS-30 at a dose of 1 or 10 microg (i.c.v.) did not affect the stress-induced reactivation of cocaine-conditioned place preference. The present study demonstrated that CRF receptor type 1, but not CRF receptor type 2, mediates the stress-induced reactivation of cocaine-conditioned place preference. These findings suggest that CRF receptor subtype 1 antagonists might be of some value in the treatment and prevention of stress-induced relapse to drug dependence long after detoxification.

Are CRF receptor antagonists potential antidepressants?

Corticotropin-releasing factor (CRF) is the major regulator of the hypothalamic-pituitary-adrenal (HPA) axis, and plays a key role in coordinating the endocrine, as well as autonomic and behavioral responses of an organism to stress. Direct CNS administration of CRF to laboratory animals produces an aggregate of effects that mimic the mammalian stress response. Impeding CRF function with CNS administration of a peptidergic CRF antagonist can block these manifestations of the stress response whether produced by exogenous CRF or occurring naturally in response to a stressor. A role for hypersecretion of CRF in the pathophysiology of depression is suggested by the finding that CNS administration of CRF mirrors many of the signs and symptoms utilized as diagnostic criteria for major depression. In addition, a large body of clinical evidence points to excess hypothalamic secretion of CRF and an accompanying HPA axis hyperactivity in patients with major depression. The recent development of selective, small molecule CRF(1) receptor antagonists, which block the effects of CRF both in vitro and in vivo, suggest that these compounds may be effective in the treatment of affective and anxiety disorders. Early evidence indicates that these agents possess anxiolytic and antidepressant activity in animal behavioral models. Copyright 2001 John Wiley & Sons, Ltd.

Stress-induced relapse to heroin and cocaine seeking in rats: a review

Studies in humans suggest that exposure to stress increases the probability of relapse to drug use, but until recently there has been no animal model to study the mechanisms that mediate this effect. We have developed a reinstatement procedure that allows us to study the effect of stress on relapse to drug seeking in rats. Using this procedure, we have shown that exposure to intermittent footshock stress reliably reinstates heroin and cocaine seeking after prolonged drug-free periods. In the present paper, we summarize results from several studies on stress-induced reinstatement of heroin and cocaine seeking in rats. We first assess the degree to which the phenomenon of stress-induced relapse generalizes to other stressors, to behaviors controlled by other drugs of abuse, and to behaviors controlled by non-drug reinforcers. We then review evidence from studies concerned with the neurotransmitters, the brain sites, and the neural systems involved in stress-induced reinstatement of drug seeking. Finally, we consider the mechanisms that might underlie stress-induced relapse to drug seeking and the possible implications of the findings for the treatment of relapse to drug use in humans.

Design, synthesis and structure-affinity relationships of 4-methylidenepiperidine and 4-aryl-1,2,3,6-tetrahydropyridine derivatives as corticotropin-releasing factor1 receptor antagonists

Recently, various non-peptide corticotropin-releasing factor1 (CRF1) receptor antagonists have been reported. Structure-affinity relationships (SARs) of non-peptide CRF antagonists suggest that such antagonists can be constructed of three units: a hydrophobic unit (Up-Area), a proton accepting unit (Central-Area), and an aromatic unit (Down-Area). Our interest focused on the Up-Area in deriving the novel methylidenepiperidine derivatives 8-10 and 4-aryl-1,2,3,6-tetrahydropyridine derivatives 11-13 as non-peptide CRF1 receptor antagonists. Compounds 8a and 11a had moderate affinity for CRF1 receptor, but compounds 9, 10, 12 and 13 did not exhibit CRF1 receptor affinity. Modification of derivatives 11 afforded compounds 11i (CRA1001) and 11x (CRA1000), which had high affinity and selectivity for CRF1 receptors with potent anxiolytic-like and antidepressant-like properties in some experimental animal models. These findings suggest that the hydrophonic unit (Up-Area) may be useful for design of CRF1 antagonists. We report here the design, synthesis and SARs of the derivatives 8 and 11 and isosteres 9, 10, 12 and 13.

Effects of the high-affinity corticotropin-releasing hormone receptor 1 antagonist R121919 in major depression: the first 20 patients treated

Clinical and preclinical data suggest that unrestrained secretion of corticoctropin-releasing hormone (CRH) in the CNS produces several signs and symptoms of depression and anxiety disorders through continuous activation of CRH(1) receptors. This led to the development of drugs that selectively antagonize CRH(1) receptors suppressing anxiety-like behavior in rats and also in monkey models of anxiety. These findings led to a clinical development program exploring the antidepressive potential of R121919, a water-soluble pyrrolopyrimidine that binds with high affinity to human CRH(1) receptors and is well absorbed in humans. This compound was administered to 24 patients with a major depressive episode primarily in order to investigate whether its endocrine mode of action compromises the stress-hormone system or whether other safety and tolerability issues exist. The patients were enrolled in two dose-escalation panels: one group (n=10) where the dose range increased from 5-40 mg and another group (n=10) where the dose escalated from 40 to 80 mg within 30 days each. Four patients dropped out because of withdrawal of consent to participate (three cases) or worsening of depressive symptomatoloy in one case. We found that R121919 was safe and well tolerated by the patients during the observation period. Moreover, the data suggested that CRH(1)-receptor blockade does not impair the corticotropin and cortisol secretory activity either at baseline or following an exogenous CRH challenge. We also observed significant reductions in depression and anxiety scores using both, patient and clinician ratings. These findings, along with the observed worsening of affective symptomatology after drug discontinuation, suggests that the pharmacological principle of CRH(1)-receptor antagonism has considerable therapeutic potential in the treatment and the prevention of diseases where exaggerated central CRH activity is present at baseline or following stress exposure.

Role of corticotropin-releasing factor receptor-1 in opiate withdrawal

Previous studies indicate that corticotropin-releasing factor (CRF) contributes to the anxiety-like and aversive states associated with drug-induced withdrawal. The present study extends this work by analyzing the CRF receptor subtype involved in withdrawal responses. First, the influence of a selective CRF receptor-1 (CRF-R1) antagonist, CP-154,526, on opiate withdrawal behavior was examined. Pretreatment with the CRF-R1 antagonist significantly attenuated several behavioral signs of naltrexone-induced morphine withdrawal, including writhing, chewing, weight loss, lacrimation, salivation, and irritability, measured during the first hour of withdrawal. Next the expression of CRF-R1 was determined as a second measure of the involvement of this receptor in opiate withdrawal. Naltrexone-induced morphine withdrawal resulted in down-regulation of CRF-R1 mRNA in several brain regions, including the frontal cortex, parietal cortex, striatum, nucleus accumbens, and amygdala, but not in the hypothalamus or periaqueductal gray. Expression of CRF-R2, the other major CRF receptor subtype, was not down-regulated significantly by withdrawal in any of the regions examined, although morphine alone significantly increased levels of this receptor subtype. Taken together, the behavioral and receptor regulation findings indicate that CRF-R1 is the primary mediator of the actions of the CRF system on opiate withdrawal, although it is possible that CRF-R2 contributes to the response.

Clonidine blocks stress-induced reinstatement of heroin seeking in rats: an effect independent of locus coeruleus noradrenergic neurons

Using a reinstatement procedure, it has been shown that intermittent footshock stress reliably reinstates extinguished drug-taking behaviour in rats. Here we studied the role of noradrenaline (NE), one of the main brain neurotransmitters involved in responses to stress, in reinstatement of heroin seeking. We first determined the effect of clonidine, an alpha-2 adrenergic receptor agonist that decreases NE cell firing and release, on stress-induced reinstatement of heroin seeking. Rats were trained to self-administer heroin (0.1 mg/kg per infusion, IV, three 3-h sessions per day) for 9-10 days. Extinction sessions were given for up to 11 days during which saline was substituted for the drug. Tests for reinstatement were then conducted after exposure to intermittent footshock (5, 15 and 30 min, 0.5 mA). During testing, clonidine was injected systemically (10-40 microgram/kg, i.p.) or directly into the lateral or fourth ventricles (1-3 microram). Clonidine (1-2 microgram per site) or its charged analogue, 2-[2, 6-diethylphenylamino]-2-imidazole (ST-91, 0.5-1 microgram per site), was also injected bilaterally into the locus coeruleus (LC), the main noradrenergic cell group in the brain. Clonidine blocked stress-induced reinstatement of drug seeking when injected systemically or into the cerebral ventricles. In contrast, neither clonidine nor ST-91 consistently altered stress-induced reinstatement when injected into the locus coeruleus. We therefore studied the effect of lesions of the lateral tegmental NE neurons on stress-induced reinstatement. 6-Hydroxydopamine (6-OHDA) lesions performed after training for heroin self-administration had no effect on extinction of heroin-taking behaviour, but significantly attenuated reinstatement induced by intermittent footshock. These data suggest that: (i) clonidine prevents stress-induced relapse to heroin seeking by its action on neurons other than those of the locus coeruleus; and (ii) activation of the lateral tegmental NE neurons contributes to stress-induced reinstatement of heroin seeking.

Corticotropin-releasing hormone receptor subtypes and emotion

Preclinical data indicate that corticotropin-releasing hormone (CRH) has anxiogenic properties and a dysregulation in CRH systems has been suggested to play a role in a variety of stress-related psychiatric disorders, such as anxiety, depression, and eating disorders. Two CRH receptor subtypes have been identified, termed CRH1 receptor (CRH1) and CRH2 receptor (CRH2), with its splice variants CRH2 alpha and CRH2 beta. These receptor subtypes differ in their pharmacology and expression pattern in the brain. Mouse mutants in which the CRH1 receptor subtype has been deleted show an impaired stress response, reduced anxiety-related behavior, and cognitive deficits. Studies using antisense oligodeoxynucleotides directed against CRH1 or CRH2 alpha identified the CRH1 receptor as the main target for CRH in mediating anxiogenesis, although recent data also suggest a possible role for CRH2 alpha. More clearly, CRH2 alpha is involved in the CRH effects on food intake. Moreover, local injection of CRH into areas rich in CRH2 alpha also result in altered sexual female behavior. Therefore, it is suggested that the CRH2 alpha may primarily influence a system concerned with implicit processes necessary for survival, i.e., with motivational types of behavior including feeding, reproduction, and possibly defense, whereas the CRH1 may be more concerned with explicit processes, including attention, executive functions, the conscious experience of emotions, and possibly learning and memory related to these emotions. This also suggests that patients suffering from anxiety and depression may benefit from treatment with CRH1 antagonistic drugs, while drugs targeting CRH2 alpha may be of particular benefit for patients with eating disorders.

Corticotropin-releasing factor antagonists in affective disorders

Following a search lasting nearly three decades, corticotropin-releasing factor (CRF), a 41 amino acid-containing peptide, was isolated and characterised in 1981. In the preceding 18 years, a concatenation was developed that appears to show that CRF integrates not only the endocrine, but also the autonomic, immunologic and behavioural responses of mammalian organisms to stress. Direct CNS administration of CRF to laboratory animals produces actions similar to those observed after exposure to stress. Moreover, CNS administration of peptidergic CRF antagonists blocks many of the behavioural responses to stress. Since both early untoward life events as well as recently experienced stress have been implicated in the pathophysiology of affective disorders, and because there is substantial evidence for CRF neuronal hyperactivity in patients with affective disorders, small molecule, lipophilic CRF antagonists have been hypothesised to possess antidepressant and/or anxiolytic activity. Within the last few years, a number of pharmaceutical companies have developed selective, small molecule CRF(1) receptor antagonists. These compounds block the effects of CRF both in vitro and in vivo. There is also evidence that these agents possess anxiolytic and antidepressant activity in animal behavioural models. Compounds that act upon the CRF system have been hypothesised to be of value not only for certain psychiatric disorders, but also in neurodegenerative and inflammatory disorders. Some of these CRF(1) receptor antagonists are currently undergoing clinical trials to determine their efficacy and tolerability in patients with mood and anxiety disorders.

The role of corticotropin-releasing factor and urocortin in the modulation of ingestive behavior

Participation of the hypothalamo-pituitary-adrenocortical axis, and its primary brain trigger, corticotropin-releasing factor (CRF) in the control of ingestive behavior can be inferred from data suggesting that CRF and its homologue urocortin act in brain to limit appetite following administration in rodents. Moreover, levels of endogenous CRF, CRF(1)and CRF(2)receptors and CRF-binding protein, which sequesters CRF and urocortin, are altered by changes in nutritional status brought about by food restriction/repletion. Mediation of the anorexic effects of CRF and urocortin appear not to privilege CRF(1)receptors, unlike the anxiogenic effects of CRF which are primarily a consequence of CRF(1)receptor activation. Such fear-like consequences of CRF system activation constitute a non-specific mechanism whereby the emergence of behaviors incompatible with food intake may appear to suppress appetite without affecting hunger per se. However, enhanced appetite following administration of CRF receptor antagonists and the involvement of CRF systems in sexual appetite and drug-seeking behavior all suggest a role for CRF in ingestive behavior. In particular, available evidence suggests that physiologically relevant suppression of appetite may accompany CRF system activation occurring as a consequence of stressor exposure induced by nutrient imbalance, for example, or under conditions of excessive intake or consumption of unfamiliar foodstuffs.

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.

The role of corticotropin-releasing factor and corticosterone in stress- and cocaine-induced relapse to cocaine seeking in rats

We have shown previously that footshock stress and priming injections of cocaine reinstate cocaine seeking in rats after prolonged drug-free periods (Erb et al., 1996). Here we examined the role of brain corticotropin-releasing factor (CRF) and the adrenal hormone corticosterone in stress- and cocaine-induced reinstatement of cocaine seeking in rats. The ability of footshock stress and priming injections of cocaine to induce relapse to cocaine seeking was studied after intracerebroventricular infusions of the CRF receptor antagonist D-Phe CRF12-41, after adrenalectomy, and after adrenalectomy with corticosterone replacement. Rats were allowed to self-administer cocaine (1.0 mg/kg/infusion, i.v) for 3 hr daily for 10-14 d and were then placed on an extinction schedule during which saline was substituted for cocaine. Tests for reinstatement were given after intermittent footshock (10 min; 0.5 mA) and after priming injections of saline and cocaine (20 mg/kg, i.p.). Footshock reinstated cocaine seeking in both intact animals and animals with corticosterone replacement but not in adrenalectomized animals. The CRF receptor antagonist D-Phe CRF12-41 blocked footshock-induced reinstatement at all doses tested in both intact animals and animals with corticosterone replacement. Reinstatement by priming injections of cocaine was only minimally attenuated by adrenalectomy and by pretreatment with D-Phe CRF12-41. These data suggest that brain CRF plays a critical role in stress-induced, but only a modulatory role in cocaine-induced, reinstatement of cocaine seeking. Furthermore, the data show that although reinstatement of cocaine seeking by footshock stress requires minimal, basal, levels of corticosterone, stress-induced increases in corticosterone do not play a role in this effect.