The CRF1 receptor antagonist antalarmin reduces volitional ethanol consumption in isolation-reared fawn-hooded rats

Emerging Therapeutics in the Treatment of Substance Use Disorders: A Focus on GLP-1 Receptor Agonists, D3R Antagonists, and CRF Antagonists

The prevalence and rising use of alcohol, opioids, and stimulants have led to substance use disorders (SUDs) that are a significant public health challenge. Traditional treatments offer some benefit; however, they often limited by efficacy, side effects, and accessibility, highlighting the urgent need for novel therapeutics. This review explores the current literature surrounding three different classes of novel treatments: glucagon-like peptide-1 (GLP-1) receptor agonists, dopamine D3 receptor (D3R) antagonists, and corticotropin-releasing factor (CRF) antagonists. These therapeutics collectively target different aspects of the addiction process, such as stress and relapse prevention, reward modulation, and the reduction of drug-seeking behavior, leading to a combined multifaceted approach to treating SUDs. This review includes preclinical and clinical evidence supporting the use of these therapies, highlighting their potential to reduce substance use and prevent relapse to alcohol, opioid, and stimulant use. Despite the potentially promising findings of these treatments, further research is necessary to fully understand their mechanisms, optimize their application, and confirm their efficacy in clinical settings.

Corticotropin releasing hormone receptor 1 in the medial prefrontal cortex mediates aversion resistant alcohol intake

RATIONALE

Alcohol consumption despite negative consequences is a core symptom of Alcohol Use Disorder. In animal models, this is studied by pairing aversive stimuli with alcohol access, and continuation of drinking under these conditions is known as aversion resistance. Previously, we found that female mice are more aversion resistant than males. Corticotropin releasing hormone (Crh) and the Crh receptor 1 (Crhr1) regulate stress-induced reinstatement, alcohol dependence, and binge-like drinking. However, the role of the Crh system in aversion resistance has not been assessed.

OBJECTIVES

We aimed to identify sex differences in the Crh system during quinine-adulterated alcohol intake.

METHODS

We used two-bottle choice and adulterated the alcohol solution with quinine. Next, we measured Crh and Crhr1 levels in brain tissue using real-time polymerase chain reaction (RT-qPCR) and RNAscope in situ hybridization. We then infused a Crhr1 antagonist into the medial prefrontal cortex (mPFC) prior to quinine-alcohol intake.

RESULTS

After quinine-alcohol consumption, females exhibited increased mPFC Crhr1 mRNA levels as measured by RT-qPCR. This was confirmed with greater anatomical specificity using RNAscope, with females exhibiting an increased number of Crhr1 + cells in the dorsomedial PFC and the ventromedial PFC. mPFC Crhr1 antagonist treatment reduced quinine-alcohol consumption in females but did not impact consumption in males. Quinine-free alcohol intake was unaffected by Crhr1 antagonist treatment.

CONCLUSIONS

Our findings suggest that Crhr1 in mPFC plays a role in aversion resistant alcohol intake in females. Future experiments will examine the sources of Crh innervation to the mPFC and their distinct roles in alcohol seeking.

The CRF/Urocortin systems as therapeutic targets for alcohol use disorders

Development and maintenance of alcohol use disorders have been proposed to recruit critical mechanisms involving Corticotropin Releasing Factor and Urocortins (CRF/Ucns). The CRF/Ucns system is comprised of a family of peptides (CRF, Ucn 1, Ucn 2, Ucn 3) which act upon two receptor subtypes, CRFR1 and CRFR2, each with different affinity profiles to the endogenous peptides and differential brain distribution. Activity of CRF/Ucn system is further modulated by CRF binding protein (CRF-BP), which regulates availability of CRF and Ucns to exert their actions. Extensive evidence in preclinical models support the involvement of CRF/Ucn targets in escalated alcohol drinking, as well as point to changes in CRF/Ucn brain function as a result of chronic alcohol exposure and/or withdrawal. It highlights the role of CRF and CRFR1-mediated signaling in conditions of excessive alcohol taking and seeking, including during various stages of withdrawal and relapse to alcohol. Besides its role in the hypothalamic-pituitary-adrenal (HPA) axis, the importance of extra-hypothalamic CRF pathways, especially in the extended amygdala, in the neurobiology of alcohol abuse and dependence is emphasized. Emerging roles for other targets of the CRF/Ucn system, such as CRF2 receptors, CRF-BP and Ucns in escalated alcohol drinking is also discussed. Finally, the limited translational value of CRF/Ucn interventions in stress-related and alcohol use disorders is discussed. So far, CRFR1 antagonists have shown little or no efficacy in human clinical trials, although a range of unexplored conditions and possibilities remain to be explored.

Blockade of corticotropin-releasing factor-1 receptors in the infralimbic cortex prevents stress-induced reinstatement of alcohol seeking in male Wistar rats: Evidence of interaction between CRF1 and orexin receptor signaling

Alcohol use dysregulates responsivity to stress, which is mediated by corticotropin-releasing factor (CRF). With repeated cycles of alcohol use, the hypothalamic-pituitary-adrenal axis becomes hyporesponsive, rendering individuals vulnerable to the reinstatement of alcohol-seeking behavior during stressful episodes. Orexin (Orx; also called hypocretin) plays a well-established role in regulating diverse physiological processes, including stress, and interacts with CRF. The infralimbic cortex (IL) is a CRF-rich region. Anatomical evidence suggests that CRF and Orx interact in this area. To test the behavioral implication of CRF and Orx transmission in the IL during the stress-induced reinstatement of alcohol-seeking behavior, male Wistar rats were trained to self-administer 10% alcohol for 3 weeks. The rats then underwent two weeks of extinction training (identical to the alcohol self-administration sessions, but alcohol was withheld). The day after the last extinction session, the rats received a bilateral intra-IL injection of the CRF1 receptor antagonist CP154,526 (0.6 μg/0.5 μl/side), the dual Orx receptor antagonist TCS1102 (15 μg/0.5 μl/side), or their combination and then were tested for the footshock stress-induced reinstatement of alcohol-seeking behavior. CP154,526 significantly prevented reinstatement, but TCS1102 did not produce such an effect. Interestingly, the co-administration of TCS1102 and CP154,526 reversed the effect of CP154,526 alone, and footshock stress induced a significant increase in Crhr1 and Hcrtr2 mRNA expression in the IL. These results demonstrate a functional interaction between Orx receptor and CRF1 receptor signaling and suggest that CRF1 receptor antagonism may ameliorate stress-induced alcohol-seeking behavior.

FACTORS CONTRIBUTING TO THE ESCALATION OF ALCOHOL CONSUMPTION

Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.

Chronic Voluntary Alcohol Drinking Causes Anxiety-like Behavior, Thiamine Deficiency, and Brain Damage of Female Crossed High Alcohol Preferring Mice

The central nervous system is vulnerable to chronic alcohol abuse, and alcohol dependence is a chronically relapsing disorder which causes a variety of physical and mental disorders. Appropriate animal models are important for investigating the underlying cellular and molecular mechanisms. The crossed High Alcohol Preferring mice prefer alcohol to water when given free access. In the present study, we used female cHAP mice as a model of chronic voluntary drinking to evaluate the effects of alcohol on neurobehavioral and neuropathological changes. The female cHAP mice had free-choice access to 10% ethanol and water, while control mice had access to water alone at the age of 60-day-old. The mice were exposed to alcohol for 7 months then subjected to neurobehavioral tests including open field (OF), elevated plus maze (EPM), and Morris water maze (MWM). Results from OF and EPM tests suggested that chronic voluntary drinking caused anxiety-like behaviors. After behavior tests, mice were sacrificed, and brain tissues were processed for biochemical analyses. Alcohol altered the levels of several neurotransmitters and neurotrophic factors in the brain including gamma-Aminobutyric acid (GABA), corticotropin-releasing factor, cAMP response element-binding protein (CREB) and brain-derived neurotrophic factor. Alcohol increased the expression of neuroinflammation markers including interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and C-C chemokine receptor 2 (CCR2). Alcohol also induced cleaved caspase-3 and glial fibrillary acidic protein, indicative of neurodegeneration and gliosis. In addition, alcohol inhibited the expression of thiamine transporters in the brain and reduced thiamine levels in the blood. Alcohol also caused oxidative stress and endoplasmic reticulum (ER) stress, and stimulated neurogenesis.

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.

Biological intersection of sex, age, and environment in the corticotropin releasing factor (CRF) system and alcohol

The neuropeptide corticotropin-releasing factor (CRF) is critical in neural circuit function and behavior, particularly in the context of stress, anxiety, and addiction. Despite a wealth of preclinical evidence for the efficacy of CRF receptor 1 antagonists in reducing behavioral pathology associated with alcohol exposure, several clinical trials have had disappointing outcomes, possibly due to an underappreciation of the role of biological variables. Although he National Institutes of Health (NIH) now mandate the inclusion of sex as a biological variable in all clinical and preclinical research, the current state of knowledge in this area is based almost entirely on evidence from male subjects. Additionally, the influence of biological variables other than sex has received even less attention in the context of neuropeptide signaling. Age (particularly adolescent development) and housing conditions have been shown to affect CRF signaling and voluntary alcohol intake, and the interaction between these biological variables is particularly relevant to the role of the CRF system in the vulnerability or resilience to the development of alcohol use disorder (AUD). Going forward, it will be important to include careful consideration of biological variables in experimental design, reporting, and interpretation. As new research uncovers conditions in which sex, age, and environment play major roles in physiological and/or pathological processes, our understanding of the complex interaction between relevant biological variables and critical signaling pathways like the CRF system in the cellular and behavioral consequences of alcohol exposure will continue to expand ultimately improving the ability of preclinical research to translate to the clinic. This article is part of the special issue on Neuropeptides.

Repeated maternal separation: Alcohol consumption, anxious behavior and corticosterone were reversed by a non-pharmacological treatment

Adverse events in early life have been related to a maladaptive stress response during adulthood, which could predispose individuals to psychiatric and physiological disorders. The purpose of this work was to study the implications of repeated maternal separation (RMS) plus a physical stressor (cold stress), voluntary ethanol consumption and plasmatic levels of corticosterone (Cor) via conflict behavior tests. To this aim, pups were separated daily from their mothers for one hour and subjected to cold stress (4 °C) between postnatal days (PD) 2 and 20. Control groups were left undisturbed with their mothers. Afterwards, all groups were exposed to voluntary ethanol (6%) or dextrose (1%) intake for 7 days. After a 30-day period of environmental enrichment (EE), the animals were again exposed to the voluntary intake protocol for 7 days. At 66 days, they were subjected to different conflict tests. Thereafter, rats were sacrificed by decapitation and blood trunk was collected to determine plasma corticosterone levels. We demonstrated that early RMS increased both voluntary alcohol intake and Cor levels. Moreover, young adult animals showed excessive activity in conflict tests. Whereas in animals exposed to a non-pharmacological treatment, known as environmental enrichment (EE), the effects previously obtained were reversed and/or prevented. In summary, we can conclude that the combination of maternal separation in early life plus cold stress increase both the voluntary exposure to alcohol and disruptive behaviors. This is a risk factor for the development of chronic diseases such as alcoholism and long-term depression. However, we found that an enriched environment may have a beneficial effect with respect to alcohol intake and aggressive behaviors.

Persistent escalation of alcohol consumption by mice exposed to brief episodes of social defeat stress: suppression by CRF-R1 antagonism

RATIONALE

Episodic bouts of social stress can precede the initiation, escalation, or relapse to disordered alcohol intake. Social stress may engender neuroadaptations in the hypothalamic-pituitary-adrenal (HPA) axis and in extrahypothalamic stress circuitry to promote the escalation of alcohol intake.

OBJECTIVES

We aimed to (1) confirm a pattern of escalated drinking in socially defeated mice and to (2) test drugs that target distinct aspects of the HPA axis and extrahypothalamic neural substrates for their effectiveness in reducing murine, stress-escalated drinking.

METHODS

Male C57BL/6J (B6) mice were socially defeated by resident Swiss-derived males for ten consecutive days receiving 30 bites/day. Ten days after the final defeat, cohorts of B6 mice received continuous or intermittent access to 20% EtOH (w/v) and water. After 4 weeks of drinking, mice were injected with weekly, systemic doses of the CRF-R1 antagonist, CP376395; the glucocorticoid receptor antagonist, mifepristone; the 11-beta-hydroxylase inhibitor, metyrapone; or the 5-alpha-reductase inhibitor, finasteride.

RESULTS

Prior to drug treatments, defeated mice reliably consumed more EtOH than non-defeated controls, and mice given alcohol intermittently consumed more EtOH than those with continuous access. CP376395 (17-30 mg/kg) reduced continuous, but not intermittent EtOH intake (g/kg) in socially defeated mice. Mifepristone (100 mg/kg), however, increased drinking by defeated mice with intermittent access to alcohol while reducing drinking during continuous access. When administered finasteride (100 mg/kg) or metyrapone (50 mg/kg), all mice reduced their EtOH intake while increasing their water consumption.

CONCLUSIONS

Mice with a history of episodic social defeat stress were selectively sensitive to the effects of CRF-R1 antagonism, suggesting that CRF-R1 may be a potential target for treating alcohol use disorders in individuals who escalate their drinking after exposure to repeated bouts of psychosocial stress. Future studies will clarify how social defeat stress may alter the expression of extrahypothalamic CRF-R1 and glucocorticoid receptors.

Alcohol, psychomotor-stimulants and behaviour: methodological considerations in preclinical models of early-life stress

BACKGROUND

In order to assess the risk associated with early-life stress, there has been an increase in the amount of preclinical studies investigating early-life stress. There are many challenges associated with investigating early-life stress in animal models and ensuring that such models are appropriate and clinically relevant.

OBJECTIVES

The purpose of this review is to highlight the methodological considerations in the design of preclinical studies investigating the effects of early-life stress on alcohol and psychomotor-stimulant intake and behaviour.

METHODS

The protocols employed for exploring early-life stress were investigated and summarised. Experimental variables include animals, stress models, and endpoints employed.

RESULTS

The findings in this paper suggest that there is little consistency among these studies and so the interpretation of these results may not be as clinically relevant as previously thought.

CONCLUSION

The standardisation of these simple stress procedures means that results will be more comparable between studies and that results generated will give us a more robust understanding of what can and may be happening in the human and veterinary clinic.

Novel approaches to alcohol rehabilitation: Modification of stress-responsive brain regions through environmental enrichment

Relapse remains the most prominent hurdle to successful rehabilitation from alcoholism. The neural mechanisms underlying relapse are complex, but our understanding of the brain regions involved, the anatomical circuitry and the modulation of specific nuclei in the context of stress and cue-induced relapse have improved significantly in recent years. In particular, stress is now recognised as a significant trigger for relapse, adding to the well-established impact of chronic stress to escalate alcohol consumption. It is therefore unsurprising that the stress-responsive regions of the brain have also been implicated in alcohol relapse, such as the nucleus accumbens, amygdala and the hypothalamus. Environmental enrichment is a robust experimental paradigm which provides a non-pharmacological tool to alter stress response and, separately, alcohol-seeking behaviour and symptoms of withdrawal. In this review, we examine and consolidate the preclinical evidence that alcohol seeking behaviour and stress-induced relapse are modulated by environmental enrichment, and these are primarily mediated by modification of neural activity within the key nodes of the addiction circuitry. Finally, we discuss the limited clinical evidence that stress-reducing approaches such as mindfulness could potentially serve as adjunctive therapy in the treatment of alcoholism. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Nucleus incertus corticotrophin-releasing factor 1 receptor signalling regulates alcohol seeking in rats

Alcoholism is a chronic relapsing disorder, and stress is a key precipitant of relapse. The nucleus incertus (NI) is highly responsive to corticotrophin-releasing factor (CRF) and psychological stressors, receives a CRF innervation and expresses CRF₁ and CRF₂ receptor mRNA. Furthermore, the ascending NI relaxin-3 system is implicated in alcohol seeking in rats. Therefore, in alcohol-preferring rats, we examined the effect of bilateral injections into the NI of the CRF₁ receptor antagonist, CP376395 or the CRF₂ receptor antagonist, astressin-2B on yohimbine-induced reinstatement of alcohol seeking. Using quantitative PCR analysis of NI micropunches, we assessed the effects of chronic alcohol consumption on gene expression profiles for components of the relaxin-3 and CRF systems. Bilateral intra-NI injections of CP376395 (500 ng/0.25 µl) attenuated yohimbine-induced reinstatement of alcohol seeking. In contrast, intra-NI injections of astressin-2B (200 ng/0.25 µl) had no significant effect. In line with these data, CRF₁ , but not CRF₂ , receptor mRNA was upregulated in the NI following chronic ethanol intake. Relaxin family peptide 3 receptor mRNA was also increased in the NI following chronic ethanol. Our quantitative PCR analysis also identified CRF mRNA within the rat NI, and the existence of a newly identified population of CRF-containing neurons was subsequently confirmed by detection of CRF immunoreactivity in rat and mouse NI. These data suggest that NI neurons contribute to reinstatement of alcohol seeking, via an involvement of CRF₁ signalling. Furthermore, chronic ethanol intake leads to neuroadaptive changes in CRF and relaxin-3 systems within rat NI.

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.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

Social Isolation Blunted the Response of Mesocortical Dopaminergic Neurons to Chronic Ethanol Voluntary Intake

Previous studies have shown that stress can increase the response of mesolimbic dopaminergic neurons to acute administration of drugs of abuse included ethanol. In this study, we investigated the possible involvement of the mesocortical dopaminergic pathway in the development of ethanol abuse under stress conditions. To this aim we trained both socially isolated (SI) and group housed (GH) rats to self administer ethanol which was made available only 2 ha day (from 11:00 to 13:00 h). Rats have been trained for 3 weeks starting at postnatal day 35. After training, rats were surgically implanted with microdialysis probes under deep anesthesia, and 24 hlater extracellular dopamine concentrations were monitored in medial prefrontal cortex (mPFC) for the 2 hpreceding ethanol administration (anticipatory phase), during ethanol exposure (consummatory phase) and for 2 hafter ethanol removal. Results show that, in GH animals, dopamine extracellular concentration in the mPFC increased as early as 80 min before ethanol presentation (+50% over basal values) and remained elevated for 80 min during ethanol exposure. In SI rats, on the contrary, dopamine extracellular concentration did not show any significant change at any time point. Ethanol consumption was significantly higher in SI than in GH rats. Moreover, mesocortical dopaminergic neurons in SI animals also showed a decreased sensitivity to an acute administration of ethanol with respect to GH rats. Our results show that prolonged exposure to stress, as in social isolation, is able to induce significant changes in the response of mesocortical dopaminergic neurons to ethanol exposure and suggest that these changes might play an important role in the compulsivity observed in ethanol addiction.

Relaxin-3 receptor (RXFP3) signalling mediates stress-related alcohol preference in mice

Stressful life events are causally linked with alcohol use disorders (AUDs), providing support for a hypothesis that alcohol consumption is aimed at stress reduction. We have previously shown that expression of relaxin-3 mRNA in rat brain correlates with alcohol intake and that central antagonism of relaxin-3 receptors (RXFP3) prevents stress-induced reinstatement of alcohol-seeking. Therefore the objectives of these studies were to investigate the impact of Rxfp3 gene deletion in C57BL/6J mice on baseline and stress-related alcohol consumption. Male wild-type (WT) and Rxfp3 knockout (KO) (C57/B6J^{RXFP3TM1/DGen}) littermate mice were tested for baseline saccharin and alcohol consumption and preference over water in a continuous access two-bottle free-choice paradigm. Another cohort of mice was subjected to repeated restraint followed by swim stress to examine stress-related alcohol preference. Hepatic alcohol and aldehyde dehydrogenase activity was assessed in mice following chronic alcohol intake and in naive controls. WT and Rxfp3 KO mice had similar baseline saccharin and alcohol preference, and hepatic alcohol processing. However, Rxfp3 KO mice displayed a stress-induced reduction in alcohol preference that was not observed in WT littermates. Notably, this phenotype, once established, persisted for at least six weeks after cessation of stress exposure. These findings suggest that in mice, relaxin-3/RXFP3 signalling is involved in maintaining high alcohol preference during and after stress, but does not appear to strongly regulate the primary reinforcing effects of alcohol.

Chronic postnatal stress induces voluntary alcohol intake and modifies glutamate transporters in adolescent rats

Postnatal stress alters stress responses for life, with serious consequences on the central nervous system (CNS), involving glutamatergic neurotransmission and development of voluntary alcohol intake. Several drugs of abuse, including alcohol and cocaine, alter glutamate transport (GluT). Here, we evaluated effects of chronic postnatal stress (CPS) on alcohol intake and brain glutamate uptake and transporters in male adolescent Wistar rats. For CPS from postnatal day (PD) 7, pups were separated from their mothers and exposed to cold stress (4 °C) for 1 h daily for 20 days; controls remained with their mothers. Then they were exposed to either voluntary ethanol (6%) or dextrose (1%) intake for 7 days (5-7 rats per group), then killed. CPS: (1) increased voluntary ethanol intake, (2) did not affect body weight gain or produce signs of toxicity with alcohol exposure, (3) increased glutamate uptake by hippocampal synaptosomes in vitro and (4) reduced protein levels (Western measurements) in hippocampus and frontal cortex of glial glutamate transporter-1 (GLT-1) and excitatory amino-acid transporter-3 (EAAT-3) but increased glutamate aspartate transporter (GLAST) levels. We propose that CPS-induced decrements in GLT-1 and EAAT-3 expression levels are opposed by activation of a compensatory mechanism to prevent excitotoxicity. A greater role for GLAST in total glutamate uptake to prevent enlarged extracellular glutamate levels is inferred. Although CPS strongly increased intake of ethanol, this had little impact on effects of CPS on brain glutamate uptake or transporters. However, the impact of early life adverse events on glutamatergic neurotransmission may underlie increased alcohol consumption in adulthood.

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.

Future pharmacological treatments for substance use disorders

Substance use disorders represent a serious public health and social issue worldwide. Recent advances in our understanding of the neurobiological basis of the addictive processes have led to the development of a growing number of pharmacological agents to treat addictions. Despite this progress, there are no approved pharmacological treatments for cocaine, methamphetamine and cannabis addiction. Moving treatment development to the next stage will require novel ways of approaching substance use disorders. One such novel approach is to target individual vulnerabilities, such as cognitive function, sex differences and psychiatric comorbidities. This review provides a summary of promising pharmacotherapies for alcohol, opiate, stimulant and nicotine addictions. Many medications that target positive and negative reinforcement of drugs, as well as individual vulnerabilities to addiction, are in different phases of development. Clinical trials testing the efficacy of these medications for substance use disorder are warranted.

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.

The CRF system and social behavior: a review

The corticotropin-releasing factor (CRF) system plays a key role in a diversity of behaviors accompanying stress, anxiety and depression. There is also substantial research on relationships between social behaviors and the CRF system in a variety of taxa including fish, birds, rodents, and primates. Some of these relationships are due to the broad role of CRF and urocortins in stress and anxiety, but these peptides also modulate social behavior specifically. For example, the social interaction (SI) test is often used to measure anxiety-like behavior. Many components of the CRF system including CRF, urocortin1, and the R1 receptor have been implicated in SI, via general effects on anxiety as well as specific effects depending on the brain region. The CRF system is also highly responsive to chronic social stressors such as social defeat and isolation. Animals exposed to these stressors display a number of anxiety- and stress-related behaviors, accompanied by changes in specific components the CRF system. Although the primary focus of CRF research on social behavior has been on the deleterious effects of social stress, there are also insights on a role for CRF and urocortins in prosocial and affiliative behaviors. The CRF system has been implicated in parental care, maternal defense, sexual behavior, and pair bonding. Species differences in the ligands and CRF receptors have been observed in vole and bird species differing in social behavior. Exogenous administration of CRF facilitates partner preference formation in monogamous male prairie voles, and these effects are dependent on both the CRF R1 and R2 receptors. These findings are particularly interesting as studies have also implicated the CRF and urocortins in social memory. With the rapid progress of social neuroscience and in understanding the complex structure of the CRF system, the next challenge is in parsing the exact contribution of individual components of this system to specific social behaviors.

Behavioral, biological, and chemical perspectives on targeting CRF(1) receptor antagonists to treat alcoholism

BACKGROUND

Alcohol use disorders are chronic disabling conditions for which existing pharmacotherapies have only modest efficacy. In the present review, derived from the 2012 Behavior, Biology and Chemistry "Translational Research in Addiction" symposium, we summarize the anti-relapse potential of corticotropin-releasing factor type 1 (CRF(1)) receptor antagonists to reduce negative emotional symptoms of acute and protracted alcohol withdrawal and stress-induced relapse to alcohol seeking.

METHODS

We review the biology of CRF(1) systems, the activity of CRF(1) receptor antagonists in animal models of anxiolytic and antidepressant activity, and experimental findings in alcohol addiction models. We also update the clinical trial status of CRF(1) receptor antagonists, including pexacerfont (BMS-562086), emicerfont (GW876008), verucerfont (GSK561679), CP316311, SSR125543A, R121919/NBI30775, R317573/19567470/CRA5626, and ONO-2333Ms. Finally, we discuss the potential heterogeneity and pharmacogenomics of CRF(1) receptor pharmacotherapy for alcohol dependence.

RESULTS

The evidence suggests that brain penetrant-CRF(1) receptor antagonists have therapeutic potential for alcohol dependence. Lead compounds with clinically desirable pharmacokinetic properties now exist, and longer receptor residence rates (i.e., slow dissociation) may predict greater CRF(1) receptor antagonist efficacy. Functional variants in genes that encode CRF system molecules, including polymorphisms in Crhr1 (rs110402, rs1876831, rs242938) and Crhbp genes (rs10055255, rs3811939) may promote alcohol seeking and consumption by altering basal or stress-induced CRF system activation.

CONCLUSIONS

Ongoing clinical trials with pexacerfont and verucerfont in moderately to highly severe dependent anxious alcoholics may yield insight as to the role of CRF(1) receptor antagonists in a personalized medicine approach to treat drug or alcohol dependence.

Effects of stress on alcohol drinking: a review of animal studies

RATIONALE

While stress is often proposed to play a significant role in influencing alcohol consumption, the relationship between stress and alcohol is complex and poorly understood. Over several decades, stress effects on alcohol drinking have been studied using a variety of animal models and experimental procedures, yet this large body of literature has generally produced equivocal results.

OBJECTIVES

This paper reviews results from animal studies in which alcohol consumption is evaluated under conditions of acute/sub-chronic stress exposure or models of chronic stress exposure. Evidence also is presented indicating that chronic intermittent alcohol exposure serves as a stressor that consequently influences drinking.

RESULTS

The effects of various acute/sub-chronic stress procedures on alcohol consumption have generally been mixed, but most study outcomes suggest either no effect or decreased alcohol consumption. In contrast, most studies indicate that chronic stress, especially when administered early in development, results in elevated drinking later in adulthood. Chronic alcohol exposure constitutes a potent stressor itself, and models of chronic intermittent alcohol exposure reliably produce escalation of voluntary alcohol consumption.

CONCLUSIONS

A complex and dynamic interplay among a wide array of genetic, biological, and environmental factors govern stress responses, regulation of alcohol drinking, and the circumstances in which stress modulates alcohol consumption. Suggestions for future directions and new approaches are presented that may aid in developing more sensitive and valid animal models that not only better mimic the clinical situation, but also provide greater understanding of mechanisms that underlie the complexity of stress effects on alcohol drinking.

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.

Pharmacological blockade of corticotropin-releasing hormone receptor 1 (CRH1R) reduces voluntary consumption of high alcohol concentrations in non-dependent Wistar rats

BACKGROUND

A dysregulation of the corticotropin-releasing hormone (CRH) system has been implicated in the development of excessive alcohol consumption and dependence. The aim of the present study was to evaluate whether the CRH system is also recruited when non-dependent Wistar rats escalate to high alcohol intake in the intermittent (alternate days) model of drinking.

METHODS

We compared intermittent and continuous access to 20% (v/v) alcohol in a two-bottle free choice drinking paradigm. Following a total of twenty 24-hour exposures for every experimental group, we assessed signs of alcohol withdrawal, including anxiety-like behavior and sensitivity to stress. The selective CRH1 receptor (CRH1R) antagonist antalarmin (0, 10, 20 mg/kg, i.p.) was tested on alcohol consumption.

RESULTS

Intermittent access to 20% alcohol led non-selected Wistar rats to escalate their voluntary intake to a high and stable level, whereas continuously exposed animals maintained a lower consumption. These groups did not differ in physical withdrawal signs. In addition, no differences were found when anxiogenic-like behavior was studied, neither under basal conditions or following restraint stress. Nevertheless, sensitivity to the treatment with the CRH1R antalarmin was observed since a reduction of 20% alcohol intake was found in both groups of animals regardless of the regimen of alcohol exposure. In addition, antalarmin was effective when injected to animals exposed to intermittent 10% (v/v) alcohol whereas it failed to suppress 10% continuous alcohol intake.

CONCLUSIONS

Pharmacological blockade of CRH1R reduced alcohol drinking when sustained high levels of intake were achieved suggesting that the CRH system plays a key role when high doses of ethanol are consumed by non-dependent subjects. This supports the notion that CRH system not only maintains the dependent state but also engages the transition to dependence.

Chronic social isolation and chronic variable stress during early development induce later elevated ethanol intake in adult C57BL/6J mice

Experience with stress situations during early development can have long-lasting effects on stress- and anxiety-related behaviors. Importantly, this can also favor drug self-administration. These studies examined the effects of chronic social isolation and/or variable stress experiences during early development on subsequent voluntary ethanol intake in adult male and female C57BL/6J mice. The experiments were conducted to evaluate the effect of chronic isolation between weaning and adulthood (Experiment 1), chronic isolation during adulthood (Experiment 2), and chronic variable stress (CVS) alone or in combination with chronic social isolation between weaning and adulthood (Experiment 3) on subsequent voluntary ethanol intake. Mice were born in our facility and were separated into two housing conditions: isolate housed (one mouse/cage) or group housed (four mice/cage) according to sex. Separate groups were isolated for 40 days starting either at time of weaning postnatal day 21 (PD 21) (early isolation, Experiments 1 and 3) or at adulthood (PD 60: late isolation, Experiment 2). The effects of housing condition on subsequent ethanol intake were assessed starting at around PD 65 in Experiments 1 and 3 or PD 105 days in Experiment 2. In Experiment 3, starting at PD 32, isolate-housed and group-housed mice were either subjected to CVS or left undisturbed. CVS groups experienced random presentations of mild stressors for 14 days, including exposure to an unfamiliar open field, restraint, physical shaking, and forced swim, among others. All mice were tested for ethanol intake for 14 days using a two-bottle choice (ethanol 15% vol/vol vs. water) for a 2-h limited access procedure. Early social isolation resulted in greater ethanol intake compared with the corresponding group-housed mice (Experiment 1). In contrast, social isolation during adulthood (late isolation) did not increase subsequent ethanol intake compared with the corresponding group-housed mice (Experiment 2). For mice that did not experience CVS, early social isolation resulted in greater ethanol intake compared with group-housed mice (Experiment 3). CVS subsequently resulted in a significant increase in ethanol intake in group-housed mice, but CVS failed to further increase ethanol intake in mice that experienced chronic social isolation early in life (Experiment 3). Overall, female mice consumed more ethanol than males, whether isolated (early or late) or group housed. These results indicate that early but not late social isolation can subsequently influence ethanol consumption in C57BL/6J mice. Thus, the developmental timing of chronic social isolation appears to be an important factor in defining later effects on ethanol self-administration behavior. In addition, experience with CVS early in life results in elevated ethanol intake later in adulthood. Taken together, these results emphasize the important role of early stress experiences that modulate later voluntary ethanol intake during adulthood.

The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats

BACKGROUND/OBJECTIVE

The galanin-3 receptor (GALR3) subtype has been identified as having a role in both feeding behaviour and the regulation of emotional states including anxiety. Despite the evidence for an association between galanin and alcohol, the current study is the first to explore the direct role of GALR3 in this context. The present study investigated the potential of the novel selective GALR3 antagonist, SNAP 37889, to reduce anxiety-like behaviour and voluntary ethanol consumption in the iP (alcohol-preferring) rat. This was achieved through a number of behavioural paradigms testing for anxiety, along with the operant self-administration model.

RESULTS

Overall, male iP rats treated with SNAP 37889 at a dose of 30 mg/kg (i.p.) did not show altered locomotor activity or changes in anxiety-like behaviour in the elevated plus maze or light-dark paradigms. Treatment with SNAP 37889 (30 mg/kg, i.p.) reduced operant responding for solutions containing ethanol, sucrose and saccharin. Collectively, results from the current study showed that SNAP 37889 (30 mg/kg, i.p.) is effective in reducing operant responding for ethanol, independent of a sedative effect.

CONCLUSIONS

These findings provide evidence that GALR3 antagonism reduces alcohol consumption and further suggest that GALR3 may be implicated in the rewarding effects of natural and drug reinforcers.

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in C57BL/6J mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, alpha-helical CRF(9-41) (0, 1, 5, 10 microg/1 microl). The contribution of central CRF type 2 receptor (CRF(2)R) signaling was assessed with i.c.v. infusion of the selective CRF(2)R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 microg/1 microl). The role of the hypothalamic-pituitary-adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF(1)R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 microg dose of alpha-helical CRF(9-41) significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF(1)R and CRF(2)R signaling, such that blockade of CRF(1)R or activation of CRF(2)R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

Progress in corticotropin-releasing factor-1 antagonist development

Corticotropin releasing factor (CRF) receptor antagonists have been sought since the stress-secreted peptide was isolated in 1981. Although evidence is mixed concerning the efficacy of CRF(1) antagonists as antidepressants, CRF(1) antagonists might be novel pharmacotherapies for anxiety and addiction. Progress in understanding the two-domain model of ligand-receptor interactions for CRF family receptors might yield chemically novel CRF(1) receptor antagonists, including peptide CRF(1) antagonists, antagonists with signal transduction selectivity and nonpeptide CRF(1) antagonists that act via the extracellular (rather than transmembrane) domains. Novel ligands that conform to the prevalent pharmacophore and exhibit drug-like pharmacokinetic properties have been identified. The therapeutic utility of CRF(1) antagonists should soon be clearer: several small molecules are currently in Phase II/III clinical trials for depression, anxiety and irritable bowel syndrome.

Biological contribution to social influences on alcohol drinking: evidence from animal models

Social factors have a tremendous influence on instances of heavy drinking and in turn impact public health. However, it is extremely difficult to assess whether this influence is only a cultural phenomenon or has biological underpinnings. Research in non-human primates demonstrates that the way individuals are brought up during early development affects their future predisposition for heavy drinking, and research in rats demonstrates that social isolation, crowding or low social ranking can lead to increased alcohol intake, while social defeat can decrease drinking. Neurotransmitter mechanisms contributing to these effects (i.e., serotonin, GABA, dopamine) have begun to be elucidated. However, these studies do not exclude the possibility that social effects on drinking occur through generalized stress responses to negative social environments. Alcohol intake can also be elevated in positive social situations, for example, in rats following an interaction with an intoxicated peer. Recent studies have also begun to adapt a new rodent species, the prairie vole, to study the role of social environment in alcohol drinking. Prairie voles demonstrate a high degree of social affiliation between individuals, and many of the neurochemical mechanisms involved in regulation of these social behaviors (for example, dopamine, central vasopressin and the corticotropin releasing factor system) are also known to be involved in regulation of alcohol intake. Naltrexone, an opioid receptor antagonist approved as a pharmacotherapy for alcoholic patients, has recently been shown to decrease both partner preference and alcohol preference in voles. These findings strongly suggest that mechanisms by which social factors influence drinking have biological roots, and can be studied using rapidly developing new animal models.

Swim stress excitation of nucleus incertus and rapid induction of relaxin-3 expression via CRF1 activation

Relaxin-3 (RLX3), a newly identified member of the relaxin peptide family, is distinguished by its enriched expression in GABA projection neurons of the pontine nucleus incertus (NI), which are postulated to participate in forebrain neural circuits involved in behavioural activation and stress responses. In this regard, corticotrophin-releasing factor-1 receptor (CRF(1)) is abundantly expressed by NI neurons; central CRF administration activates c-fos expression in NI; and various stressors have been reported to increase NI neuron activity. In studies to determine whether a specific neurogenic stressor would activate RLX3 expression, we assessed the effect of a repeated forced swim (RFS) on levels of RLX3 mRNA and heteronuclear (hn) RNA in rat NI by in situ hybridization histochemistry of exon- and intron-directed oligonucleotide probes, respectively. Exposure of rats to an RFS (10 min at 23 degrees C, 24 h apart), markedly increased RLX3 mRNA levels in NI at 30-60 min after the second swim, before a gradual return to basal levels over 2-4 h, while RLX3 hnRNA levels were significantly up-regulated at 60-120 min post-RFS, following a transient decrease at 30 min. Systemic treatment of rats with a CRF(1) antagonist, antalarmin (20 mg/kg, i.p.) 30 min prior to the second swim, blunted the stress-induced effects on RLX3 transcripts. Relative levels of RLX3-immunostaining in NI neurons appeared elevated at 3 h post-swim, but not at earlier time points (30-60 min). These results suggest that acute stress-induced CRF secretion can rapidly alter RLX3 gene transcription by activation of CRF(1) present on NI neurons. More generally, these studies support a role for RLX3 neural networks in the normal neural and physiological response to neurogenic stressors in the rat.

Therapeutics for alcoholism: what's the future?

As with other addictions, human alcoholism is characterised as a chronically relapsing condition. Consequently, the therapeutic goal is the development of clinically effective, safe drugs that promote high adherence rates and prevent relapse. These products can then be used in conjunction with psychosocial approaches. In this review, preclinical studies are highlighted that indicate the mechanism of action of currently used anti-craving medications or demonstrate the potential of novel pharmacological agents for the treatment of alcohol use disorders. While current pharmacological strategies are far from ideal, there are a number of candidate molecules that may ultimately be developed into therapeutic agents. In addition, prescribing clinicians should also consider strategies such as combinations of various drugs to aid in the regulation of aberrant alcohol consumption.

Presynaptic CRF1 receptors mediate the ethanol enhancement of GABAergic transmission in the mouse central amygdala

Corticotropin-releasing factor (CRF) is a 41-amino-acid neuropeptide involved in stress responses initiated from several brain areas, including the amygdala formation. Research shows a strong relationship between stress, brain CRF, and excessive alcohol consumption. Behavioral studies suggest that the central amygdala (CeA) is significantly involved in alcohol reward and dependence. We recently reported that the ethanol augmentation of GABAergic synaptic transmission in rat CeA involves CRF1 receptors, because both CRF and ethanol significantly enhanced the amplitude of evoked GABAergic inhibitory postsynaptic currents (IPSCs) in CeA neurons from wild-type (WT) and CRF2 knockout (KO) mice, but not in neurons of CRF₁ KO mice. The present study extends these findings using selective CRF receptor ligands, gene KO models, and miniature IPSC (mIPSC) analysis to assess further a presynaptic role for the CRF receptors in mediating ethanol effects in the CeA. In whole-cell patch recordings of pharmacologically isolated GABAAergic IPSCs from slices of mouse CeA, both CRF and ethanol augmented evoked IPSCs in a concentration-dependent manner, with low EC₅₀s. A CRF₁ (but not CRF₂) KO construct and the CRF₁-selective nonpeptide antagonist NIH-3 (LWH-63) blocked the augmenting effect of both CRF and ethanol on evoked IPSCs. Furthermore, the new selective CRF₁ agonist stressin₁, but not the CRF₂ agonist urocortin 3, also increased evoked IPSC amplitudes. Both CRF and ethanol decreased paired-pulse facilitation (PPF) of evoked IPSCs and significantly enhanced the frequency, but not the amplitude, of spontaneous miniature GABAergic mIPSCs in CeA neurons of WT mice, suggesting a presynaptic site of action. The PPF effect of ethanol was abolished in CeA neurons of CRF₁ KO mice. The CRF₁ antagonist NIH-3 blocked the CRF- and ethanol-induced enhancement of mIPSC frequency in CeA neurons. These data indicate that presynaptic CRF₁ receptors play a critical role in permitting or mediating ethanol enhancement of GABAergic synaptic transmission in CeA, via increased vesicular GABA release, and thus may be a rational target for the treatment of alcohol abuse and alcoholism.

Early social isolation in male Long-Evans rats alters both appetitive and consummatory behaviors expressed during operant ethanol self-administration

BACKGROUND

Postweaning social isolation in rats produces profound and long-lasting cognitive and behavioral deficits in adult animals. Importantly, this housing manipulation alters sensitivity to a number of drugs of abuse including ethanol. However, most studies with ethanol have utilized continuous or limited home-cage access to examine interactions between juvenile social experience and drinking. More recently, social isolation was shown to increased ethanol responding in a "dipper" model of self-administration (Deehan et al., 2007). In the current study, we utilize a "sipper" operant self-administration model to distinguish the effects of isolation rearing on ethanol seeking- and drinking-related behaviors.

METHODS

Postweaning juvenile male Long-Evans rats were placed into 2 housing groups for 6 weeks: one group consisted of individually housed animals; the second group was housed 4 animals per cage. Following the isolation period, anxiety-like behavior was assessed to confirm the efficacy of the isolation procedure. In some animals, ethanol drinking in the home cage was assessed using a continuous access, 2-bottle choice paradigm. All animals were then individually housed and trained to lever-press for a sipper tube containing either an ethanol solution or a sucrose solution.

RESULTS

Postweaning social isolation increased the expression of anxiety-like behavior in the elevated plus maze but not the light-dark box. Ethanol consumption was also increased during continuous home-cage access with the 2-bottle choice paradigm. During operant self-administration, isolation housing increased the response rate and increased ethanol consumption but did not alter responding for or consumption of sucrose. The housing manipulation did not change the total number of lever responses during extinction sessions. Paired-pulse inhibition deficits that are characteristic of juvenile isolation remained intact after prolonged experience with sucrose self-administration.

DISCUSSION

The effects of postweaning social isolation on ethanol drinking in the home cage are also manifest during operant self-administration. Importantly, these alterations in adult operant self-administration are ethanol-specific.

The CRF1 receptor antagonist antalarmin attenuates yohimbine-induced increases in operant alcohol self-administration and reinstatement of alcohol seeking in rats

RATIONALE AND OBJECTIVES

Yohimbine is an alpha-2 adrenoreceptor antagonist that provokes stress- and anxiety-like responses in both humans and laboratory animals. In rats, yohimbine increases operant alcohol self-administration and reinstates alcohol seeking. In this study, we assess whether these effects of yohimbine are attenuated by systemic injections of the corticotrotropin-releasing factor 1 (CRF1) receptor antagonist antalarmin.

MATERIALS AND METHODS

In Exp. 1, we trained rats to lever press for alcohol solutions (12% w/v, 1 h/day) over several weeks; during training, the response requirement was increased from a fixed-ratio-1 (FR-1) to a fixed-ratio-3 (FR-3) reinforcement schedule. We then tested the effect of antalarmin (10 or 20 mg/kg) on yohimbine (1.25 mg/kg)-induced increases in operant alcohol self-administration (FR-3 reinforcement schedule). Subsequently, we assessed the effect of antalarmin on yohimbine-induced increases in plasma corticosterone levels in the previously self-administering rats. In Exp. 2, we trained the rats to self-administer alcohol as in Exp. 1, and after extinction of the alcohol-reinforced lever responding over 13 days, we tested antalarmin's effect on yohimbine-induced reinstatement of alcohol seeking.

RESULTS

Yohimbine increased operant alcohol self-administration and reinstated alcohol seeking after extinction. These effects of yohimbine were attenuated by antalarmin. Antalarmin injections in the absence of yohimbine had no effect on either operant alcohol self-administration or extinction responding. Antalarmin had no effect on yohimbine-induced corticosterone release in alcohol-experienced rats.

CONCLUSIONS

These results suggest that extrahypothalamic CRF1 receptors are involved in the effect of yohimbine on operant alcohol self-administration and on relapse to alcohol seeking and support the notion that CRF1 receptor antagonists should be considered in alcohol addiction treatment.

Effects of adult-onset calorie restriction on anxiety-like behavior in rats

Calorie restriction (CR) has consistently been shown to increase lifespan and ameliorate disease outcomes. Its effects on behavior are less clear, although anxiolytic-like effects have been observed. Rats were subjected to 1 of 4 dietary regimens: control, CR25%, CR50% and, an acute episode of CR and tested in 3 tests of anxiety: the open field test, the elevated plus maze, and the modified open field test. In the open field test, the CR25% and CR50% groups made more central zone entries than the control and Acute groups, which was primarily due to differences in the initial 5 min of the test. Moreover, both CR groups engaged in greater exploration of the central zone than the control group in the initial 5 min of the test. The Acute group also exhibited significantly longer latencies to leave the central zone at test onset than the control and CR50% group. In the elevated plus maze, the Acute group also displayed longer latencies to open arm entry as compared to the control and CR50% group and showed a lower ratio of open to total arm entries compared to all other groups. There were no effects of CR on any variable of the modified open field test. Possible neurochemical mechanisms underlying the anxiolytic-like effect of CR are discussed.

Drug challenges reveal differences in mediation of stress facilitation of voluntary alcohol drinking and withdrawal-induced anxiety in alcohol-preferring P rats

BACKGROUND

There is controversy over whether exposure to stress precipitates relapse and/or increases alcohol (ethanol) intake. Our laboratory has demonstrated that repeated stress prior to withdrawal from a brief forced exposure to alcohol results in withdrawal-induced anxiety-like behavior. Because anxiety is often regarded as a precipitating factor in relapsing alcoholics, we decided to examine the consequences of stressing alcohol-preferring P rats on both voluntary alcohol drinking and withdrawal-induced anxiety.

METHODS

P rats were subjected to 3 cycles of 5 days of voluntary alcohol drinking and 2 days of deprivation. Restraint stress (60 min) was applied to some animals during the first and second deprivations/withdrawals (at 4 h). Drugs (flumazenil, buspirone, SB242,084, CP154,526, CRA1000, naloxone, haloperidol, olanzapine, naloxone, and haloperidol) were given to some rats 30 min prior to restraint stress.

RESULTS

Stressed, deprived P rats exhibited both a longer duration of elevated alcohol drinking and anxiety-like behavior in the social interaction test upon withdrawal after the third cycle of voluntary alcohol drinking. When given prior to each of the restraint stresses, the benzodiazepine receptor antagonist flumazenil (5 mg/kg), the corticotrophin releasing factor receptor antagonists CRA1000 (3 mg/kg) and CP154,526 (10 mg/kg), the serotonin 5-HT(1A) receptor partial agonist buspirone (0.6 mg/kg), and the mixed 5-HT(2C)/D2 receptor antagonist olanzapine were effective in reducing the increased duration of elevated alcohol drinking and the withdrawal-induced anxiety-like behavior. In contrast, while the opiate receptor antagonist naloxone (20 mg/kg), the 5-HT(2C) receptor antagonist SB242084 (3 mg/kg), and the dopamine receptor antagonist haloperidol (0.1 mg/kg) also reduced drinking, they did not significantly alter anxiety like behavior.

CONCLUSION

These results suggest that stress-induced facilitation of alcohol drinking and withdrawal-induced anxiety-like behavior in P rats may be closely but imperfectly linked.

Dependence-induced increases in ethanol self-administration in mice are blocked by the CRF1 receptor antagonist antalarmin and by CRF1 receptor knockout

Models of dependence-induced increases in ethanol self-administration will be critical in increasing our understanding of the processes of addiction and relapse, underlying mechanisms, and potential therapeutics. One system that has received considerable attention recently is the CRF(1) system that may mediate the link between anxiety states and relapse drinking. C57BL/6J mice were trained to lever press for ethanol, were made dependent and then were allowed to self-administer ethanol following a period of abstinence. The effect of the CRF(1) antagonist, antalarmin, was examined on this abstinence-induced self-administration in a separate group of mice. Finally, dependence-induced changes in ethanol self-administration were examined in CRF(1) knockout and wild type mice. The results indicated that ethanol self-administration was increased following the induction of dependence, but only after a period of abstinence. This increase in ethanol self-administration was blocked by antalarmin. Furthermore, CRF(1) knockout mice did not display this increased ethanol self-administration following dependence and abstinence. These studies, using both a pharmacological and genetic approach, support a critical role for the CRF(1) system in ethanol self-administration following dependence. In addition, a model is presented that may be useful for studies examining underlying mechanisms of the ethanol addiction process as well as for testing potential therapeutics.

The CRF1 receptor antagonist, antalarmin, reverses isolation-induced up-regulation of dopamine D2 receptors in the amygdala and nucleus accumbens of fawn-hooded rats

We have previously shown that Fawn-Hooded (FH) rats reared in isolation display an anxiety-like phenotype and an enhanced acquisition of ethanol seeking behaviour. Furthermore, antalarmin, a selective corticotrophin-releasing factor type 1 (CRF1) receptor antagonist, reduces isolation-induced acquisition and maintenance of volitional ethanol consumption in this strain. The aim of this study was to investigate the ability of CRF1 receptor antagonism by antalarmin to impact upon brain chemistry in both isolated and group-housed FH rats. To achieve this, FH rats were reared, from weaning, in either group-housed or isolation-housed conditions and at 12 weeks of age were treated with antalarmin (20 mg/kg, i.p; n = 10 per group) or vehicle (1 mL/kg, i.p; n = 10 per group) bi-daily for ten consecutive days before being killed and their brains removed for neurochemical analyses. Autoradiography and in situ hybridization was employed to analyse changes in the dopaminergic and neurotrophin systems. Isolation rearing increased dopamine D2 receptor density in the central amygdala and nucleus accumbens, an effect reversed by antalarmin treatment. Conversely, treatment with antalarmin had no impact upon the isolation-induced alterations of the mRNA encoding brain-derived neurotrophic factor or the TrkB receptor. Collectively, these findings demonstrate that multiple signalling systems are susceptible to modulation by social isolation and that antalarmin can reverse some, but not all, isolation-induced alterations in brain chemistry.

Differential motivational properties of ethanol during early ontogeny as a function of dose and postadministration time

While appetitive reinforcement effects of ethanol are easily detected in rat neonates, such phenomena rarely have been observed in older infants. Recently, Molina et al. [Molina, J. C., Ponce L. F., Truxell, E., & Spear N. E. (2006). Infantile sensitivity to ethanol's motivational effects: ethanol reinforcement during the third postnatal week. Alcohol Clin Exp Res 30, 1506-1519] reported such effects of ethanol in 14-day-olds using a second-order conditioning procedure. Infants also appear to be sensitive to biphasic reinforcement or general motivational effects of ethanol, with appetitive effects seeming to occur early in the state of intoxication and aversive effects predominant during late stages, but tests have been inconclusive. The present study examined the possibility of biphasic motivational effects of ethanol during infancy through the use of second-order conditioning procedures. Preweanling rats (14 days old) experienced intraoral water infusions (conditioned stimulus, CS) either 5-20 or 30-45 min after administration of 0.5 or 2.0 g/kg i.g. ethanol. Pups were then exposed to the CS while over a novel texture (second-order phase). Tests of tactile preference for that texture followed. Locomotive, thermal, hormonal (corticosterone release), and pharmacokinetic patterns likely to underlie the acquisition of ethanol-mediated conditioning were also examined in subsequent experiments. Intraoral CSs paired with either early or late effects of low-dose ethanol (0.5 g/kg, blood ethanol concentration: 40 mg%) became positive second-order reinforcers. Appetitive effects were also exhibited by pups exposed to the CS during commencement of the toxic episode induced by a 2.0 g/kg ethanol dose, 5-20 min after administration of ethanol, whereas aversions emerged when CS presentation occurred 30-45 min postadministration time (blood ethanol concentrations: 157 and 200 mg%, respectively). Overall, the results indicate that infants rapidly detect differential motivational properties of ethanol as a function of dose or drug postadministration time. Relatively neutral stimuli associated with these properties are later capable of acting as either positive or aversive reinforcers. Thermal and motor responses that accompany ethanol intoxication do not seem to be directly associated with differential hedonic properties of the drug at this stage of development.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effects of stress modulation on morphine-induced conditioned place preferences and plasma corticosterone levels in Fischer, Lewis, and Sprague-Dawley rat strains

RATIONALE

There is a direct relationship between hypothalamic-pituitary-adrenal axis (HPA) reactivity and susceptibility to drug use in outbred rats. Specifically, manipulations that increase or decrease HPA activity also increase or decrease drug intake, respectively. Interestingly, this relationship has not been established in the inbred Fischer (F344) and Lewis (LEW) rat strains that are often used as animal models of susceptibility to drug use.

OBJECTIVE

The present study investigated the effects of manipulations known to affect HPA activity on morphine-induced conditioned place preference (CPP) in male LEW, F344, and Sprague-Dawley (SD) rats.

MATERIALS AND METHODS

In experiment 1, animals were exposed to an injection of methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and 2-h restraint stress prior to the conditioning of a morphine-induced place preference (1, 4, or 10 mg/kg subcutaneous). In experiment 2, animals were chronically exposed to corticotropin-releasing hormone type 1 receptor antagonist, antalarmin, prior to CPP training. The effects of DMCM/restraint and antalarmin on corticosterone levels were examined in experiments 3 and 4.

RESULTS

In outbred rats, DMCM/restraint increased both HPA activity and morphine-induced CPP, while antalarmin decreased CPP and produced a slight, but nonsignificant, decrease in corticosterone levels. In the inbred rats, however, DMCM/restraint increased plasma corticosterone yet decreased place preferences in the LEW strain, and antalarmin treatment decreased plasma corticosterone but increased place preferences in the F344 strain.

CONCLUSIONS

These data suggest that the relationship between stress and drug use may be nonmonotonic. The use of these inbred strains in genetic analysis of drug addiction may require reexamination.

Depressive-like behavior and high alcohol drinking co-occur in the FH/WJD rat but appear to be under independent genetic control

This review will consider the evidence supporting the view that a specific substrain of Fawn-Hooded rat (FH/Wjd) exhibits co-occurring depressive-like behavior and high alcohol intake independently. First, the FH/Wjd rat is compared with other Fawn-Hooded substrains (FH/Har, FHH/Eur, FHL/Eur) and it is concluded that only the FH/Wjd rat is both highly immobile in the forced swim test and drinks substantial amounts of 5-10% alcohol voluntarily. Next it is demonstrated that the FH/Wjd rat fulfils many of the criteria proposed for an animal model of alcoholism (becomes tolerant, becomes dependent and expresses withdrawal symptoms, bar-presses for alcohol). Other literature in addition to the high swim test immobility suggests that the FH/Wjd rat may also be an animal model of depression (high basal corticosterone levels, blunted hormonal responses to serotonergic agonists). To study the phenotypes more closely an inbred strain (ACI/N) of rat that drank little alcohol voluntarily and exhibited considerable swimming in the forced swim test (i.e., low immobility) was obtained. A systematic intercrossing of the parental strains and the resulting F1 progeny was carried out to generate more than 800 F2s. Swim test immobility, alcohol intake and preference and saccharin intake are four of the 7 variables assessed in each of these rats. Using classical quantitative genetics methods, it was determined that these four phenotypes exhibited modest heritability and were influenced by multiple genes. Correlation coefficients between immobility and the other measures were near zero, whereas alcohol intake and preference were highly correlated (r=0.9) and alcohol and saccharin intakes were modestly correlated (r=0.3). A final study showed that chronic fluoxetine treatment counteracted the high immobility but did not affect alcohol intake, similar to human studies. These findings suggest that although depressive-like behavior and high alcohol intake co-occur in the FH/Wjd rat, they are independently regulated.

The orexin system regulates alcohol-seeking in rats

1. Orexin-containing neurons have been implicated in feeding, sleep-wake cycles and more recently in drug-seeking behaviour. 2. Pretreatment of alcohol-preferring (iP) rats with an orexin1 receptor antagonist (SB-334867, 20 mg kg(-1), intraperitoneally) completely abolished an olfactory cue-induced reinstatement of alcohol-seeking behaviour, and also attenuated alcohol responding under an operant fixed ratio regimen without affecting water responding. 3. The mRNA encoding orexin within the hypothalamus was expressed at a similar density in iP and non-preferring (NP) rats; chronic consumption of ethanol in iP rats did not significantly regulate the density of this expression, but did increase the area of expression within the lateral, but not medial, hypothalamus. 4. These data indicate that while orexin may not be implicated in the development of an alcohol preference, re-exposure of cues previously associated with alcohol availability is sufficient and adequate to activate orexin-containing neurons and drive reinstatement of alcohol-seeking.