Central urocortin 3 administration decreases limited-access ethanol intake in nondependent mice

The urocortin peptides: biological relevance and laboratory aspects of UCN3 and its receptor

The urocortins are polypeptides belonging to the corticotropin-releasing hormone family, known to modulate stress responses in mammals. Stress, whether induced physically or psychologically, is an underlying cause or consequence of numerous clinical syndromes. Identifying biological markers associated with the homeostatic regulation of stress could provide a clinical laboratory approach for the management of stress-related disorders. The neuropeptide, urocortin 3 (UCN3), and the corticotropin-releasing hormone receptor 2 (CRHR2) constitute a regulatory axis known to mediate stress homeostasis. Dysregulation of this peptide/receptor axis is believed to play a role in several clinical conditions including post-traumatic stress, sleep apnea, cardiovascular disease, and other health problems related to stress. Understanding the physiology and measurement of the UCN3/CRHR2 axis is important for establishing a viable clinical laboratory diagnostic. In this article, we focus on evidence supporting the role of UCN3 and its receptor in stress-related clinical syndromes. We also provide insight into the measurements of UCN3 in blood and urine. These potential biomarkers provide new opportunities for clinical research and applications of laboratory medicine diagnostics in stress management.

Expression Patterns of the Neuropeptide Urocortin 3 and Its Receptor CRFR2 in the Mouse Central Auditory System

Sensory systems have to be malleable to context-dependent modulations occurring over different time scales, in order to serve their evolutionary function of informing about the external world while also eliciting survival-promoting behaviors. Stress is a major context-dependent signal that can have fast and delayed effects on sensory systems, especially on the auditory system. Urocortin 3 (UCN3) is a member of the corticotropin-releasing factor family. As a neuropeptide, UCN3 regulates synaptic activity much faster than the classic steroid hormones of the hypothalamic-pituitary-adrenal axis. Moreover, due to the lack of synaptic re-uptake mechanisms, UCN3 can have more long-lasting and far-reaching effects. To date, a modest number of studies have reported the presence of UCN3 or its receptor CRFR2 in the auditory system, particularly in the cochlea and the superior olivary complex, and have highlighted the importance of this stress neuropeptide for protecting auditory function. However, a comprehensive map of all neurons synthesizing UCN3 or CRFR2 within the auditory pathway is lacking. Here, we utilize two reporter mouse lines to elucidate the expression patterns of UCN3 and CRFR2 in the auditory system. Additional immunolabelling enables further characterization of the neurons that synthesize UCN3 or CRFR2. Surprisingly, our results indicate that within the auditory system, UCN3 is expressed predominantly in principal cells, whereas CRFR2 expression is strongest in non-principal, presumably multisensory, cell types. Based on the presence or absence of overlap between UCN3 and CRFR2 labeling, our data suggest unusual modes of neuromodulation by UCN3, involving volume transmission and autocrine signaling.

Role of corticotropin-releasing factor in alcohol and nicotine addiction

The two most prevalent substance use disorders involve alcohol and nicotine, which are often co-abused. Robust preclinical and translational evidence indicates that individuals initiate drug use for the acute rewarding effects of the substance. The development of negative emotional states is key for the transition from recreational use to substance use disorders as subjects seek the substance to obtain relief from the negative emotional states of acute withdrawal and protracted abstinence. The neuropeptide corticotropin-releasing factor (CRF) is a major regulator of the brain stress system and key in the development of negative affective states. The present review examines the role of CRF in preclinical models of alcohol and nicotine abuse and explores links between CRF and anxiety-like, dysphoria-like, and other negative affective states. Finally, the present review discusses preclinical models of nicotine and alcohol use with regard to the CRF system, advances in molecular and genetic manipulations of CRF, and the importance of examining both males and females in this field of research.

The Corticotropin Releasing Factor Receptor 1 in Alcohol Use Disorder: Still a Valid Drug Target?

Corticotropin releasing factor (CRF) is a neuropeptide that plays a key role in behavioral and physiological responses to stress. A large body of animal literature implicates CRF acting at type 1 CRF receptors (CRFR1) in consumption by alcohol-dependent subjects, stress-induced reinstatement of alcohol seeking, and possibly binge alcohol consumption. These studies have encouraged recent pilot studies of CRFR1 antagonists in humans with alcohol use disorder (AUD). It was a great disappointment to many in the field that these studies failed to show an effect of these compounds on stress-induced alcohol craving. Here, we examine these studies to explore potential limitations and discuss preclinical and human literature to ask whether CRFR1 is still a valid drug target to pursue for the treatment of AUD.

Corticotropin-Releasing Factor (CRF) and Addictive Behaviors

Drug addiction is a complex disorder that is characterized by compulsivity to seek and take the drug, loss of control in limiting intake of the drug, and emergence of a withdrawal syndrome in the absence of the drug. The transition from casual drug use to dependence is mediated by changes in reward and brain stress functions and has been linked to a shift from positive reinforcement to negative reinforcement. The recruitment of brain stress systems mediates the negative emotional state produced by dependence that drives drug seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. In this chapter we focus on behavioral and cellular neuropharmacological studies that have implicated brain stress systems (i.e., corticotropin-releasing factor [CRF]) in the transition to addiction and the predominant brain regions involved. We also discuss the implication of CRF recruitment in compulsive eating disorders.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Glutamatergic and HPA-axis pathway genes in bipolar disorder comorbid with alcohol- and substance use disorders

Glutamatergic neurotransmission has been shown to be dysregulated in bipolar disorder (BD), alcohol use disorder (AUD) and substance use disorder (SUD). Similarly, disruption in the hypothalamic-pituitary-adrenal (HPA)-axis has also been observed in these conditions. BD is often comorbid with AUD and SUD. The effects of the glutamatergic and HPA systems have not been extensively examined in individuals with BD-AUD and BD-SUD comorbidity. The aim of this investigation was to determine whether variants in the glutamatergic pathway and HPA-axis are associated with BD-AUD and BD-SUD comorbidity. The research cohort consisted of 498 individuals with BD type I from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD). A subset of the cohort had comorbid current AUD and current SUD. A total of 1935 SNPs from both the glutamatergic and HPA pathways were selected from the STEP-BD genome-wide dataset. To identify population stratification, IBS clustering was performed using the program Plink 1.07. Single SNP association and gene-based association testing were conducted using logistic regression. A pathway analysis of glutamatergic and HPA genes was performed, after imputation using IMPUTE2. No single SNP was associated with BD-AUD or BD-SUD comorbidity after correction for multiple testing. However, from the gene-based analysis, the gene PRKCI was significantly associated with BD-AUD. The pathway analysis provided overall negative findings, although several genes including GRIN2B showed high percentage of associated SNPs for BD-AUD. Even though the glutamatergic and HPA pathways may not be involved in BD-AUD and BD-SUD comorbidity, PRKCI deserves further investigation in BD-AUD.

Ethanol produces corticotropin-releasing factor receptor-dependent enhancement of spontaneous glutamatergic transmission in the mouse central amygdala

BACKGROUND

Ethanol (EtOH) modulation of central amygdala (CeA) neurocircuitry plays a key role in the development of alcoholism via activation of the corticotropin-releasing factor (CRF) receptor (CRFR) system. Previous work has predominantly focused on EtOH × CRF interactions on the CeA GABA circuitry; however, our laboratory recently showed that CRF enhances CeA glutamatergic transmission. Therefore, this study sought to determine whether EtOH modulates CeA glutamate transmission via activation of CRF signaling.

METHODS

The effects of EtOH on spontaneous excitatory postsynaptic currents (sEPSCs) and basal resting membrane potentials were examined via standard electrophysiology methods in adult male C57BL/6J mice. Local ablation of CeA CRF neurons (CRF(CeAhDTR) ) was achieved by targeting the human diphtheria toxin receptor (hDTR) to CeA CRF neurons with an adeno-associated virus. Ablation was quantified post hoc with confocal microscopy. Genetic targeting of the diphtheria toxin active subunit to CRF neurons (CRF(DTA) mice) ablated CRF neurons throughout the central nervous system, as assessed by quantitative reverse transcriptase polymerase chain reaction quantification of CRF mRNA.

RESULTS

Acute bath application of EtOH significantly increased sEPSC frequency in a concentration-dependent manner in CeA neurons, and this effect was blocked by pretreatment of co-applied CRFR1 and CRFR2 antagonists. In experiments utilizing a CRF-tomato reporter mouse, EtOH did not significantly alter the basal membrane potential of CeA CRF neurons. The ability of EtOH to enhance CeA sEPSC frequency was not altered in CRF(CeAhDTR) mice despite a ~78% reduction in CeA CRF cell counts. The ability of EtOH to enhance CeA sEPSC frequency was also not altered in the CRF(DTA) mice despite a 3-fold reduction in CRF mRNA levels.

CONCLUSIONS

These findings demonstrate that EtOH enhances spontaneous glutamatergic transmission in the CeA via a CRFR-dependent mechanism. Surprisingly, our data suggest that this action may not require endogenous CRF.

Preclinical evidence implicating corticotropin-releasing factor signaling in ethanol consumption and neuroadaptation

The results of many studies support the influence of the corticotropin-releasing factor (CRF) system on ethanol (EtOH) consumption and EtOH-induced neuroadaptations that are critical in the addiction process. This review summarizes the preclinical data in this area after first providing an overview of the components of the CRF system. This complex system involves hypothalamic and extra-hypothalamic mechanisms that play a role in the central and peripheral consequences of stressors, including EtOH and other drugs of abuse. In addition, several endogenous ligands and targets make up this system and show differences in their involvement in EtOH drinking and in the effects of chronic or repeated EtOH treatment. In general, genetic and pharmacological approaches paint a consistent picture of the importance of CRF signaling via type 1 CRF receptors (CRF(1)) in EtOH-induced neuroadaptations that result in higher levels of intake, encourage alcohol seeking during abstinence and alter EtOH sensitivity. Furthermore, genetic findings in rodents, non-human primates and humans have provided some evidence of associations of genetic polymorphisms in CRF-related genes with EtOH drinking, although additional data are needed. These results suggest that CRF(1) antagonists have potential as pharmacotherapeutics for alcohol use disorders. However, given the broad and important role of these receptors in adaptation to environmental and other challenges, full antagonist effects may be too profound and consideration should be given to treatments with modulatory effects.

Increased alcohol consumption in urocortin 3 knockout mice is unaffected by chronic inflammatory pain

AIMS

Stress neurocircuitry may modulate the relationship between alcohol drinking and chronic pain. The corticotropin-releasing factor (CRF) system is crucial for regulation of stress responses. The current study aimed to elucidate the role of the endogenous CRF ligand Urocortin 3 (Ucn3) in the relationship between alcohol drinking behavior and chronic pain using a genetic approach.

METHODS

Ucn3 (KO) and wildtype (WT) littermates were subjected to a 24-h access drinking procedure prior to and following induction of chronic inflammatory pain.

RESULTS

Ucn3 KO mice displayed significantly increased ethanol intake and preference compared with WT across the time course. There were no long-term effects of chronic pain on alcohol drinking behavior, regardless of genotype, nor any evidence for alcohol-induced analgesia.

CONCLUSION

The increased drinking in Ucn3 KO supports a role for this peptide in alcohol-related behavior. These data suggest the necessity for more research exploring the relationship between alcohol drinking, chronic pain and the CRF system in rodent models.

Methamphetamine drinking microstructure in mice bred to drink high or low amounts of methamphetamine

Genetic factors likely influence individual sensitivity to positive and negative effects of methamphetamine (MA) and risk for MA dependence. Genetic influence on MA consumption has been confirmed by selectively breeding mouse lines to consume high (MAHDR) or low (MALDR) amounts of MA, using a two-bottle choice MA drinking (MADR) procedure. Here, we employed a lickometer system to characterize the microstructure of MA (20, 40, and 80mg/l) and water intake in MAHDR and MALDR mice in 4-h limited access sessions, during the initial 4hours of the dark phase of their 12:12h light:dark cycle. Licks at one-minute intervals and total volume consumed were recorded, and bout analysis was performed. MAHDR and MALDR mice consumed similar amounts of MA in mg/kg on the first day of access, but MAHDR mice consumed significantly more MA than MALDR mice during all subsequent sessions. The higher MA intake of MAHDR mice was associated with a larger number of MA bouts, longer bout duration, shorter interbout interval, and shorter latency to the first bout. In a separate 4-h limited access MA drinking study, MALDR and MAHDR mice had similar blood MA levels on the first day MA was offered, but MAHDR mice had higher blood MA levels on all subsequent days, which corresponded with MA intake. These data provide insight into the microstructure of MA intake in an animal model of differential genetic risk for MA consumption, which may be pertinent to MA use patterns relevant to genetic risk for MA dependence.

Urocortin 3 expression at baseline and during inflammation in the colon: corticotropin releasing factor receptors cross-talk

Urocortins (Ucn1-3), members of the corticotropin-releasing factor (CRF) family of neuropeptides, are emerging as potent immunomodulators. Localized, cellular expression of Ucn1 and Ucn2, but not Ucn3, has been demonstrated during inflammation. Here, we investigated the role of Ucn3 in a rat model of Crohn's colitis and the relative contribution of CRF receptors (CRF1 and CRF2) in regulating Ucn3 expression at baseline and during inflammation. Ucn3 mRNA and peptide were ubiquitously expressed throughout the GI tract in naïve rats. Ucn3 immunoreactivity was seen in epithelial cells and myenteric neurons. On day 1 of colitis, Ucn3 mRNA levels decreased by 80% and did not recover to baseline even by day 9. Next, we ascertained pro- or anti-inflammatory actions of Ucn3 during colitis. Surprisingly, unlike observed anti-inflammatory actions of Ucn1, exogenous Ucn3 did not alter histopathological outcomes during colitis and neither did it alter levels of pro-inflammatory cytokines IL-6 and TNF-α. At baseline, colon-specific knockdown of CRF1, but not CRF2 decreased Ucn3 mRNA by 78%, whereas during colitis, Ucn3 mRNA levels increased after CRF1 knockdown. In cultured cells, co-expression of CRF1+CRF2 attenuated Ucn3-stimulated intracellular Ca(2+) peak by 48% as compared to cells expressing CRF2 alone. Phosphorylation of p38 kinase increased by 250% during colitis and was significantly attenuated after Ucn3 administration. Thus, our results suggest that a balanced and coordinated expression of CRF receptors is required for proper regulation of Ucn3 at baseline and during inflammation.

Corticotropin releasing factor: a key role in the neurobiology of addiction

Drug addiction is a chronically relapsing disorder characterized by loss of control over intake and dysregulation of stress-related brain emotional systems. Since the discovery by Wylie Vale and his colleagues of corticotropin-releasing factor (CRF) and the structurally-related urocortins, CRF systems have emerged as mediators of the body's response to stress. Relatedly, CRF systems have a prominent role in driving addiction via actions in the central extended amygdala, producing anxiety-like behavior, reward deficits, excessive, compulsive-like drug self-administration and stress-induced reinstatement of drug seeking. CRF neuron activation in the medial prefrontal cortex may also contribute to the loss of control. Polymorphisms in CRF system molecules are associated with drug use phenotypes in humans, often in interaction with stress history. Drug discovery efforts have yielded brain-penetrant CRF1 antagonists with activity in preclinical models of addiction. The results support the hypothesis that brain CRF-CRF1 systems contribute to the etiology and maintenance of addiction.

Binge ethanol-drinking potentiates corticotropin releasing factor R1 receptor activity in the ventral tegmental area

BACKGROUND

Corticotropin releasing factor (CRF) and urocortin play an important role in many stress responses and also can regulate ethanol (EtOH) intake. Adaptations in CRF signaling in the central amygdala promote EtOH consumption after long-term EtOH intake in dependent animals and also after brief periods of binge EtOH intake. Thus, even brief episodes of EtOH consumption can alter the function of the CRF system, allowing CRF to regulate EtOH intake. Here, we examined whether brief binge EtOH consumption leads to CRF receptor adaptations within the ventral tegmental area (VTA), a structure involved in signaling rewarding and aversive events and important in the development and expression of drug and alcohol addiction.

METHODS

We utilized a mouse model of binge drinking known as drinking in the dark (DID), where C57BL/6J mice drink approximately 6 g/kg in 4 hours and achieve blood EtOH concentrations of approximately 100 mg/dl, which is equivalent to binge drinking in humans. We used ex vivo whole-cell recordings from putative VTA dopamine (DA) neurons to examine CRF regulation of NMDA receptor (NMDAR) currents. We also examined the impact of CRF receptor antagonist injection in the VTA on binge EtOH intake.

RESULTS

Ex vivo whole-cell recordings from putative VTA DA neurons showed enhanced CRF-mediated potentiation of NMDAR currents in juvenile mice that consumed EtOH in the DID procedure. CRF-induced potentiation of NMDAR currents in EtOH-drinking mice was blocked by administration of CP-154,526 (3 μM), a selective CRF1 receptor antagonist. Furthermore, intra-VTA infusion of CP-154,526 (1 μg) significantly reduced binge EtOH consumption in adult mice. These results were not due to alterations of VTA NMDAR number or function, suggesting that binge drinking may enhance signaling through VTA CRF1 receptors onto NMDARs.

CONCLUSIONS

Altered CRF1 receptor-mediated signaling in the VTA promotes binge-like EtOH consumption in mice, which supports the idea that CRF1 receptors may therefore be a promising pharmacological target for reducing binge drinking in humans.

Alcohol in excess: CRF₁ receptors in the rat and mouse VTA and DRN

RATIONALE

Manipulation of the stress neuropeptide corticotropin-releasing factor (CRF), specifically central antagonism of the type 1 receptors (CRF-R1), effectively reduces alcoholic-like ethanol drinking in rodents. Escalated consumption is largely controlled by neurocircuitry that is important for reward and affect, such as the ventral tegmental area (VTA) and the dorsal raphé nucleus (DRN).

OBJECTIVE

The current studies investigated the role of CRF-R1 within the VTA and DRN and their relation to escalated ethanol drinking in two species. An additional goal was to explore whether high alcohol-drinking individuals would be more affected by CRF-R1 antagonism than low alcohol-drinking individuals.

METHODS

With a two-bottle choice drinking procedure, adult male C57BL/6J mice and Long-Evans rats were given 24-h access to 20 % ethanol and water on an intermittent schedule. Rats and mice were implanted with cannulae targeting the VTA or DRN. Doses of the CRF-R1 antagonist CP-154,526 (butyl-[2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]ethylamine)) were microinfused to modulate drinking of ethanol and water over the course of 24 h.

RESULTS

In both mice and rats, intra-VTA CP-154,526 selectively decreased ethanol intake, while identical doses (0.3 and 0.6 μg) infused intra-DRN reduced both ethanol and water drinking. Long-Evans rats displayed a range of individual differences for ethanol preference, and CP-154,526 suppressed ethanol drinking in the high-preferring animals regardless of brain site manipulation.

CONCLUSIONS

The current findings confirm previous studies that blockade of CRF-R1 efficaciously reduces escalated drinking while also suggesting that the effects of intermittent access on alcohol consumption may require CRF interaction with dopamine in the VTA.

Stress-related neuropeptides and addictive behaviors: beyond the usual suspects

Addictive disorders are chronic, relapsing conditions that cause extensive disease burden. Genetic factors partly account for susceptibility to addiction, but environmental factors such as stressful experiences and prolonged exposure of the brain to addictive drugs promote its development. Progression to addiction involves neuroadaptations within neurocircuitry that mediates stress responses and is influenced by several peptidergic neuromodulators. While corticotrophin releasing factor is the prototypic member of this class, recent work has identified several additional stress-related neuropeptides that play an important role in regulation of drug intake and relapse, including the urocortins, nociceptin, substance P, and neuropeptide S. Here, we review this emerging literature, discussing to what extent the properties of these neuromodulators are shared or distinct and considering their potential as drug targets.

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

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

Urocortin-1 within the centrally-projecting Edinger-Westphal nucleus is critical for ethanol preference

Converging lines of evidence point to the involvement of neurons of the centrally projecting Edinger-Westphal nucleus (EWcp) containing the neuropeptide Urocortin-1 (Ucn1) in excessive ethanol (EtOH) intake and EtOH sensitivity. Here, we expanded these previous findings by using a continuous-access, two-bottle choice drinking paradigm (3%, 6%, and 10% EtOH vs. tap water) to compare EtOH intake and EtOH preference in Ucn1 genetic knockout (KO) and wild-type (WT) mice. Based on previous studies demonstrating that electrolytic lesion of the EWcp attenuated EtOH intake and preference in high-drinking C57BL/6J mice, we also set out to determine whether EWcp lesion would differentially alter EtOH consumption in Ucn1 KO and WT mice. Finally, we implemented well-established place conditioning procedures in KO and WT mice to determine whether Ucn1 and the corticotropin-releasing factor type-2 receptor (CRF-R2) were involved in the rewarding and aversive effects of EtOH (2 g/kg, i.p.). Results from these studies revealed that (1) genetic deletion of Ucn1 dampened EtOH preference only in mice with an intact EWcp, but not in mice that received lesion of the EWcp, (2) lesion of the EWcp dampened EtOH intake in Ucn1 KO and WT mice, but dampened EtOH preference only in WT mice expressing Ucn1, and (3) genetic deletion of Ucn1 or CRF-R2 abolished the conditioned rewarding effects of EtOH, but deletion of Ucn1 had no effect on the conditioned aversive effects of EtOH. The current findings provide strong support for the hypothesis that EWcp-Ucn1 neurons play an important role in EtOH intake, preference, and reward.

Role of corticotropin-releasing factor in drug addiction: potential for pharmacological intervention

Drug dependence is a chronically relapsing disorder that places an enormous strain on healthcare systems. For treatments to have long-term clinical value, they must address the causes of relapse. Corticotropin-releasing factor (CRF), a neuropeptide central to the stress response, may be one key to solving the relapse cycle. CRF is hypothesized to mediate the elevated anxiety and negative emotional states experienced during the development of dependence. This review summarizes existing data on changes in the CRF system produced by drugs of abuse and the function of CRF receptors in regulating behavioural responses to drugs of abuse, with an emphasis on drug dependence. Drug-induced changes in neuronal excitability throughout the limbic system, as well as the reversal of these neuroadaptations by CRF receptor antagonists, are also addressed. CRF receptor antagonists, by reducing the motivational effects of drug withdrawal and protracted abstinence, are proposed to be novel therapeutic targets for drug abuse and addiction.

Centrally administered urocortin 3 inhibits food intake and gastric emptying in mice

Urocortin 3 (Ucn3) is recognized as a member of the corticotropin-releasing factor (CRF) family, which plays an important role in regulating food intake. We investigated the effects of centrally administered Ucn3 on food intake and gastric emptying in mice. Intracerebroventricular (ICV)administration of Ucn3 (0.1–1 nmol per mouse) decreased food intake in a dose-dependent manner. The inhibitory effect of Ucn3 on food intake was less potent than that of centrally administered CRF and Urocortin 1. ICV administration of Ucn3 (0.1–1 nmol per mouse) decreased the gastric emptying rate in a dose-dependent manner. Ucn3 decreased food intake in high-fat diet-fed obese mice as well as in lean mice. These results indicated that Ucn3 influences feeding behavior and gut motility, and may be a promising therapeutic target in the treatment of eating and functional gastrointestinal disorders.

The role of CRF and CRF-related peptides in the dark side of addiction

Drug addiction is a chronically relapsing disorder characterized by a compulsion to seek and take drugs, the development of dependence, and the manifestation of a negative emotional state when the drug is removed. Activation of brain stress systems is hypothesized to be a key element of the negative emotional state produced by dependence that drives drug-seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. The focus of the present review is on the role of corticotropin-releasing factor (CRF) and CRF-related peptides in the dark side of addiction. CRF is a key mediator of the hormonal, autonomic, and behavior responses to stressors. Emphasis is placed on the role of CRF in extrahypothalamic systems in the extended amygdala, including the central nucleus of the amygdala, bed nucleus of the stria terminalis, and a transition area in the shell of the nucleus accumbens, in the dark side of addiction. The urocortin/CRF(2) systems have been less explored, but results suggest their role in the neuroadaptation associated with chronic drug use, sometimes in opposition to the effects produced by the CRF(1) receptor. Compelling evidence argues that the CRF stress system, including its activation of the hypothalamic-pituitary-adrenal axis, plays a key role in engaging the transition to dependence and maintaining dependence once it is initiated. Understanding the role of the CRF systems in addiction not only provides insight into the neurobiology of the dark side of addiction, but also provides novel targets for identifying vulnerability to addiction and the treatment of addiction.