Lesions of the Edinger-Westphal nucleus in C57BL/6J mice disrupt ethanol-induced hypothermia and ethanol consumption

Neuromedin U Neurons in the Edinger-Westphal Nucleus Respond to Alcohol Without Interfering with the Urocortin 1 Response

The Edinger-Westphal nucleus (EW) is a midbrain nucleus composed of a preganglionic, cholinergic subpopulation and a densely clustered peptidergic subpopulation (EWcp). The EWcp is one of the few brain regions that show consistent induction of FOS following voluntary alcohol intake. Previous results in rodents point to urocortin 1 (UCN1) as one of the peptides most involved in the control of ethanol intake and preference. Notably, the functions described for UCN1, such as reward processing, stress coping or the regulation of feeding behavior are similar to those described for the neuropeptide neuromedin U (NMU). Interestingly, NMU has been recently associated with the modulation of alcohol-related behaviors. However, little is known about the expression and functionality of NMU neurons in alcohol-responsive areas. In this study, we used the recently developed Nmu-Cre knock-in mouse model to examine the expression of NMU in the subaqueductal paramedian zone comprising the EWcp. We delved into the characterization and co-expression of NMU with other markers already described in the EWcp. Moreover, using FOS as a marker of neuronal activity, we tested whether NMU neurons were sensitive to acute alcohol administration. Overall, we provided novel insights on NMU expression and functionality in the EW region. We showed the presence of NMU within a subpopulation of UCN1 neurons in the EWcp and demonstrated that this partial co-expression does not interfere with the responsivity of UCN1-containing cells to alcohol. Moreover, we proposed that the UCN1 content in these neurons may be influenced by sex.

Functionally active TRPA1 ion channel is downregulated in peptidergic neurons of the Edinger-Westphal nucleus upon acute alcohol exposure

Introduction: The centrally projecting Edinger-Westphal nucleus (EWcp) contributes to the control of alcohol consumption by its urocortin 1 (UCN1) and cocaine- and amphetamine-regulated transcript (CART) co-expressing peptidergic neurons. Our group recently showed that the urocortinergic centrally projecting EWcp is the primary seat of central nervous system transient receptor potential ankyrin 1 (TRPA1) cation channel mRNA expression. Here, we hypothesized that alcohol and its metabolites, that pass through the blood-brain barrier, may influence the function of urocortinergic cells in centrally projecting EWcp by activating TRPA1 ion channels. We aimed to examine the functional activity of TRPA1 in centrally projecting EWcp and its possible role in a mouse model of acute alcohol exposure. Methods: Electrophysiological measurements were performed on acute brain slices of C57BL/6J male mice containing the centrally projecting EWcp to prove the functional activity of TRPA1 using a selective, potent, covalent agonist JT010. Male TRPA1 knockout (KO) and wildtype (WT) mice were compared with each other in the morphological studies upon acute alcohol treatment. In both genotypes, half of the animals was treated intraperitoneally with 1 g/kg 6% ethanol vs. physiological saline-injected controls. Transcardial perfusion was performed 2 h after the treatment. In the centrally projecting EWcp area, FOS immunohistochemistry was performed to assess neuronal activation. TRPA1, CART, and urocortin 1 mRNA expression as well as urocortin 1 and CART peptide content was semi-quantified by RNAscope in situ hybridization combined with immunofluorescence. Results: JT010 activated TRPA1 channels of the urocortinergic cells in acute brain slices. Alcohol treatment resulted in a significant FOS activation in both genotypes. Alcohol decreased the Trpa1 mRNA expression in WT mice. The assessment of urocortin 1 peptide immunoreactivity revealed lower basal urocortin 1 in KO mice compared to WTs. The urocortin 1 peptide content was affected genotype-dependently by alcohol: the peptide content decreased in WTs while it increased in KO mice. Alcohol exposure influenced neither CART and urocortin 1 mRNA expression nor the centrally projecting EWcp/CART peptide content. Conclusion: We proved the presence of functional TRPA1 receptors on urocortin 1 neurons of the centrally projecting EWcp. Decreased Trpa1 mRNA expression upon acute alcohol treatment, associated with reduced neuronal urocortin 1 peptide content suggesting that this cation channel may contribute to the regulation of the urocortin 1 release.

Oxytocin Receptors in the Mouse Centrally-projecting Edinger-Westphal Nucleus and their Potential Functional Significance for Thermoregulation

The centrally-projecting Edinger-Westphal nucleus (EWcp) has been shown to contribute to regulation of multiple functions, including responses to stress and fear, attention, food consumption, addiction, body temperature and maternal behaviors. However, receptors involved in regulation of these behaviors through EWcp remain poorly characterized. On the other hand, the oxytocin peptide (OXT) is also known to regulate a substantial number of physiological responses and behaviors. Here we show that mRNA encoding OXT receptors (Oxtr) is expressed in EWcp of male and female C57BL/6J mice. These receptors are present on urocortin 1 (Ucn) mRNA-containing neurons and, to a lesser extent, on neurons in EWcp expressing the vesicular glutamate transporter 2 (Vglut2) mRNA of EWcp. Using RNAscope in situ hybridization, we show that neurons containing Ucn and Vglut2 mRNAs are two intermingled, but independent subpopulations in EWcp and characterize their relationship with other populations of neurons in the vicinity of this nucleus. Using immunohistochemistry, we show that intraperitoneal (IP) administration of OXT can induce FOS in Oxtr-containing neurons, suggesting that these receptors on EWcp neurons are functional. A follow up study showed that injection of OXT (2.3 or 7.7 mg/kg, IP) is accompanied by a decrease in body temperature. Since EWcp is known to be involved in regulation of body temperature, we hypothesize that OXT's effects on body temperature could be mediated through the EWcp. The contribution of OXTR in EWcp to regulation of various functions of EWcp and OXT needs to be deciphered.

Vesicular glutamate transporter 2-containing neurons of the centrally-projecting Edinger-Westphal nucleus regulate alcohol drinking and body temperature

Previous studies in rodents have repeatedly demonstrated that the centrally-projecting Edinger-Westphal nucleus (EWcp) is highly sensitive to alcohol and is also involved in regulating alcohol intake and body temperature. Historically, the EWcp has been known as the main site of Urocortin 1 (Ucn1) expression, a corticotropin-releasing factor-related peptide, in the brain. However, the EWcp also contains other populations of neurons, including neurons that express the vesicular glutamate transporter 2 (Vglut2). Here we transduced the EWcp with adeno-associated viruses (AAVs) encoding Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) to test the role of the EWcp in alcohol drinking and in the regulation of body temperature. Activation of the EWcp with excitatory DREADDs inhibited alcohol intake in a 2-bottle choice procedure in male C57BL/6J mice, whereas inhibition of the EWcp with DREADDs had no effect. Surprisingly, analysis of DREADD expression indicated Ucn1-containing neurons of the EWcp did not express DREADDs. In contrast, AAVs transduced non-Ucn1-containing EWcp neurons. Subsequent experiments showed that the inhibitory effect of EWcp activation on alcohol intake was also present in male Ucn1 KO mice, suggesting that a Ucn1-devoid population of EWcp regulates alcohol intake. A final set of chemogenetic experiments showed that activation of Vglut2-expressing EWcp neurons inhibited alcohol intake and induced hypothermia in male and female mice. These studies expand on previous literature by indicating that a glutamatergic, Ucn1-devoid subpopulation of the EWcp regulates alcohol consumption and body temperature.

Gray areas: Neuropeptide circuits linking the Edinger-Westphal and Dorsal Raphe nuclei in addiction

The circuitry of addiction comprises several neural networks including the midbrain - an expansive region critically involved in the control of motivated behaviors. Midbrain nuclei like the Edinger-Westphal (EW) and dorsal raphe (DR) contain unique populations of neurons that synthesize many understudied neuroactive molecules and are encircled by the periaqueductal gray (PAG). Despite the proximity of these special neuron classes to the ventral midbrain complex and surrounding PAG, functions of the EW and DR remain substantially underinvestigated by comparison. Spanning approximately -3.0 to -5.2 mm posterior from bregma in the mouse, these various cell groups form a continuum of neurons that we refer to collectively as the subaqueductal paramedian zone. Defining how these pathways modulate affective behavioral states presents a difficult, yet conquerable challenge for today's technological advances in neuroscience. In this review, we cover the known contributions of different neuronal subtypes of the subaqueductal paramedian zone. We catalogue these cell types based on their spatial, molecular, connectivity, and functional properties and integrate this information with the existing data on the EW and DR in addiction. We next discuss evidence that links the EW and DR anatomically and functionally, highlighting the potential contributions of an EW-DR circuit to addiction-related behaviors. Overall, we aim to derive an integrated framework that emphasizes the contributions of EW and DR nuclei to addictive states and describes how these cell groups function in individuals suffering from substance use disorders. This article is part of the special Issue on 'Neurocircuitry Modulating Drug and Alcohol Abuse'.

Centrally Projecting Edinger-Westphal Nucleus in the Control of Sympathetic Outflow and Energy Homeostasis

The centrally projecting Edinger-Westphal nucleus (EWcp) is a midbrain neuronal group, adjacent but segregated from the preganglionic Edinger-Westphal nucleus that projects to the ciliary ganglion. The EWcp plays a crucial role in stress responses and in maintaining energy homeostasis under conditions that require an adjustment of energy expenditure, by virtue of modulating heart rate and blood pressure, thermogenesis, food intake, and fat and glucose metabolism. This modulation is ultimately mediated by changes in the sympathetic outflow to several effector organs, including the adrenal gland, heart, kidneys, brown and white adipose tissues and pancreas, in response to environmental conditions and the animal's energy state, providing for appropriate energy utilization. Classic neuroanatomical studies have shown that the EWcp receives inputs from forebrain regions involved in these functions and projects to presympathetic neuronal populations in the brainstem. Transneuronal tracing with pseudorabies virus has demonstrated that the EWcp is connected polysynaptically with central circuits that provide sympathetic innervation to all these effector organs that are critical for stress responses and energy homeostasis. We propose that EWcp integrates multimodal signals (stress, thermal, metabolic, endocrine, etc.) and modulates the sympathetic output simultaneously to multiple effector organs to maintain energy homeostasis under different conditions that require adjustments of energy demands.

Effects of pharmacological inhibition of the centrally-projecting Edinger-Westphal nucleus on ethanol-induced conditioned place preference and body temperature

Alcohol use disorder is a chronic disease characterized in part by repeated relapsing events. Exposure to environmental stimuli or cues that have previously been associated with the effects of alcohol can promote relapse through the triggering of craving for alcohol. Therefore, identifying and characterizing neuronal populations that may regulate these associations is of the upmost importance. Previous studies have implicated the centrally-projecting Edinger Westphal nucleus (EWcp) in this process, as the EWcp is both sensitive to, and can regulate alcohol intake. To date however, it is unclear if the EWcp is involved in the formation or expression of these alcohol-cue associations. As such, the present studies examined the involvement of the EWcp in male DBA/2J mice in the acquisition and expression of place preference for an alcohol-paired cue using the conditioned place preference (CPP) procedure. Pharmacological inhibition of the EWcp via the GABAA and GABAB receptor agonists muscimol and baclofen did not affect either the acquisition or the expression of CPP. Follow up studies did find however, that pharmacological inhibition of the EWcp increased body temperature and prevented alcohol-induced increases in c-Fos expression in the EWcp. When considered in light of previous studies, the present results indicate that the EWcp may be involved in the regulation of alcohol self-administration, and not conditioned alcohol-seeking. Additionally, the present studies provide further evidence for the involvement of the EWcp in thermoregulation and help elucidate the molecular mechanisms by which alcohol increases c-Fos in the EWcp.

Involvement of Centrally Projecting Edinger-Westphal Nucleus Neuropeptides in Actions of Addictive Drugs

The centrally-projecting Edinger-Westphal nucleus (EWcp) is a brain region distinct from the preganglionic Edinger-Westphal nucleus (EWpg). In contrast to the EWpg, the EWcp does not send projections to the ciliary ganglion and appears not to regulate oculomotor function. Instead, evidence is accumulating that the EWcp is extremely sensitive to alcohol and several other drugs of abuse. Studies using surgical, genetic knockout, and shRNA approaches further implicate the EWcp in the regulation of alcohol sensitivity and self-administration. The EWcp is also known as the site of preferential expression of urocortin 1, a peptide of the corticotropin-releasing factor family. However, neuroanatomical data indicate that the EWcp is not a monotypic brain region and consists of several distinct subpopulations of neurons. It is most likely that these subpopulations of the EWcp are differentially involved in the regulation of actions of addictive drugs. This review summarizes and analyzes the current literature of the EWcp's involvement in actions of drugs of abuse in male and female subjects in light of the accumulating evidence of complexities of this brain region.

Nonphosphorylatable Src Ser75 Mutation Increases Ethanol Preference and Consumption in Mice

Src is highly expressed in CNS neurons and contributes not only to developmental proliferation and differentiation but also to high-order brain functions, such as those contributing to alcohol consumption. Src knock-out mice exhibit no CNS abnormalities, presumably due to compensation by other Src family kinases (SFKs), but have a shortened lifespan and osteopetrosis-associated defects, impeding investigations of the role of Src on behavior in adult mice. However, the Unique domain of Src differs from those in other SFKs and is phosphorylated by cyclin-dependent kinase 1 (Cdk1) and Cdk5 at Ser75, which influences its postmitotic function in neurons. Therefore, ethanol consumption in mice harboring nonphosphorylatable (Ser75Ala) or phosphomimetic (Ser75Asp) Src mutants was investigated. Mice harboring the Ser75Ala Src mutant, but not the Ser75Asp mutant, had a higher preference for and consumption of solutions containing 5% and 10% ethanol than wild-type mice. However, plasma ethanol concentrations and sensitivities to the sedative effects of ethanol were not different among the groups. In mice harboring the Ser75Ala Src mutant, the activity of Rho-associated kinase (ROCK) in the striatum was significantly lower and Akt Ser473 phosphorylation was significantly higher than in wild-type mice. These results suggest that Src regulates voluntary ethanol drinking in a manner that depends on Ser75 phosphorylation.

Corticotropin-Releasing Factor (CRF) Neurocircuitry and Neuropharmacology in Alcohol Drinking

Alcohol use is pervasive in the United States. In the transition from nonhazardous drinking to hazardous drinking and alcohol use disorder, neuroadaptations occur within brain reward and brain stress systems. One brain signaling system that has received much attention in animal models of excessive alcohol drinking and alcohol dependence is corticotropin-releasing factor (CRF). The CRF system is composed of CRF, the urocortins, CRF-binding protein, and two receptors - CRF type 1 and CRF type 2. This review summarizes how acute, binge, and chronic alcohol dysregulates CRF signaling in hypothalamic and extra-hypothalamic brain regions and how this dysregulation may contribute to changes in alcohol reinforcement, excessive alcohol consumption, symptoms of negative affect during withdrawal, and alcohol relapse. In addition, it summarizes clinical work examining CRF type 1 receptor antagonists in humans and discusses why the brain CRF system is still relevant in alcohol research.

Contribution of Urocortin to the Development of Excessive Drinking

The corticotropin-releasing factor (CRF) system plays a role in alcohol consumption, and its dysregulation can contribute to alcohol use disorder. This system includes four peptide ligands: CRF, urocortin (Ucn)1, Ucn2, and Ucn3. Historically, attention focused on CRF, however, Ucn1 also plays a critical role in excessive alcohol use. This review covers evidence for this contribution and contrasts the role of Ucn1 with CRF. While CRF can promote binge consumption, this regulation occurs through generalized mechanisms that are not specific for alcohol. In contrast, inhibition of Ucn1 action specifically blunts escalation of alcohol drinking. Lesions, genetic knockout, and RNA interference experiments indicate that the centrally projecting Edinger-Westphal nucleus is the neuroanatomical source of Ucn1 critical for alcohol drinking. We propose that the contributions of Ucn1 to excessive drinking likely occur through enhancing rewarding properties of alcohol and symptoms of alcohol withdrawal, whereas CRF drives dependence-induced drinking at later stages of alcohol use. The transition from occasional binge drinking to dependence intricately depends on CRF system plasticity and coordination of CRF and Ucn1.

Serotonin and urocortin 1 in the dorsal raphe and Edinger-Westphal nuclei after early life stress in serotonin transporter knockout rats

The interaction of early life stress (ELS) and the serotonin transporter (5-HTT) gene-linked polymorphic region (5-HTTLPR) has been associated with increased risk to develop depression in later life. We have used the maternal separation paradigm as a model for ELS exposure in homozygous and heterozygous 5-HTT knockout rats and measured urocortin 1 (Ucn1) mRNA and/or protein levels, Ucn1 DNA methylation, as well as 5-HT innervation in the centrally projecting Edinger-Westphal (EWcp) and dorsal raphe (DR) nuclei, both implicated in the regulation of stress response. We found that ELS and 5-HTT genotype increased the number of 5-HT neurons in specific DR subdivisions, and that 5-HTT knockout rats showed decreased 5-HT innervation of EWcp-Ucn1 neurons. Furthermore, ELS was associated with increased DNA methylation of the promoter region of the Ucn1 gene and increased expression of 5-HT receptor 1A in the EWcp. In contrast, 5-HTT deficiency was associated with site-specific alterations in DNA methylation of the Ucn1 promoter, and heterozygous 5-HTT knockout rats showed decreased expression of CRF receptor 1 in the EWcp. Together, our findings extend the existing literature on the relationship between EWcp-Ucn1 and DR-5-HT neurons. These observations will further our understanding on their potential contribution to mediate affect as a function of ELS interacting with 5-HTTLPR.

Effects of isoflurane and ethanol administration on c-Fos immunoreactivity in mice

Noninvasive functional imaging holds great promise for the future of translational research, due to the ability to directly compare between preclinical and clinical models of psychiatric disorders. Despite this potential, concerns have been raised regarding the necessity to anesthetize rodent and monkey subjects during these procedures, because anesthetics may alter neuronal activity. For example, in studies on drugs of abuse and alcohol, it is not clear to what extent anesthesia can interfere with drug-induced neural activity. Therefore, the current study investigated whole-brain c-Fos activation following isoflurane anesthesia as well as ethanol-induced activation of c-Fos in anesthetized mice. In the first experiment, we examined effects of one or three sessions of gaseous isoflurane on c-Fos activation across the brain in male C57BL/6J mice. Isoflurane administration led to c-Fos activation in several areas, including the piriform cortex and lateral septum. Lower or similar levels of activation in these areas were detected after three sessions of isoflurane, suggesting that multiple exposures may eliminate some of the enhanced neuronal activation caused by acute isoflurane. In the second experiment, we investigated the ability of ethanol injection (1.5 or 2.5g/kgi.p.) to induce c-Fos activation under anesthesia. Following three sessions of isoflurane, 1.5g/kg of ethanol induced c-Fos in the central nucleus of amygdala and the centrally-projecting Edinger-Westphal nucleus (EWcp). This induction was lower after 2.5g/kg of ethanol. These results demonstrate that ethanol-induced neural activation can be detected in the presence of isoflurane anesthesia. They also suggest, that while habituation to isoflurane helps reduce neuronal activation, interaction between effects of anesthesia and alcohol can occur. Studies using fMRI imaging could benefit from using habituated animals and dose-response analyses.

Commonalities and Distinctions Among Mechanisms of Addiction to Alcohol and Other Drugs

BACKGROUND

Alcohol abuse is comorbid with abuse of many other drugs, some with similar pharmacology and others quite different. This leads to the hypothesis of an underlying, unitary dysfunctional neurobiological basis for substance abuse risk and consequences.

METHODS

In this review, we discuss commonalities and distinctions of addiction to alcohol and other drugs. We focus on recent advances in preclinical studies using rodent models of drug self-administration.

RESULTS

While there are specific behavioral and molecular manifestations common to alcohol, psychostimulant, opioid, and nicotine dependence, attempts to propose a unifying theory of the addictions inevitably face details where distinctions are found among classes of drugs.

CONCLUSIONS

For alcohol, versus other drugs of abuse, we discuss and compare advances in: (i) neurocircuitry important for the different stages of drug dependence; (ii) transcriptomics and genetical genomics; and (iii) enduring effects, noting in particular the contributions of behavioral genetics and animal models.

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.

Reduced ethanol consumption and preference in cocaine- and amphetamine-regulated transcript (CART) knockout mice

Cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide implicated in addiction to drugs of abuse. Several studies have characterized the role of CART in addiction to psychostimulants, but few have examined the role of CART in alcohol use disorders including alcoholism. The current study utilized a CART knockout (KO) mouse model to investigate the role of CART in ethanol appetitive behaviors. A two-bottle choice, unlimited-access paradigm was used to compare ethanol appetitive behaviors between CART wild type (WT) and KO mice. The mice were presented with an ethanol solution (3%-21%) and water, each concentration for 4 days, and their consumption was measured daily. Consumption of quinine (bitter) and saccharin (sweet) solutions was measured following the ethanol preference tests. In addition, ethanol metabolism rates and ethanol sensitivity were compared between genotypes. CART KO mice consumed and preferred ethanol less than their WT counterparts in both sexes. This genotype effect could not be attributed to differences in bitter or sweet taste perception or ethanol metabolism rates. There was also no difference in ethanol sensitivity in male mice; however, CART KO female mice showed a greater ethanol sensitivity than the WT females. Taken together, these data demonstrate a role for CART in ethanol appetitive behaviors and as a possible therapeutic drug target for alcoholism and abstinence enhancement.

Cannabinoid modulation of midbrain urocortin 1 neurones during acute and chronic stress

Neurones in the centrally projecting Edinger-Westphal nucleus (EWcp) are the main site of urocortin 1 (Ucn1) synthesis in the mammalian brain, and are assumed to play a role in the stress response of the animal. Because endocannabinoid signalling has also been strongly implicated in stress, we hypothesised that endocannabinoids may modulate the functioning of the urocortinergic EWcp. First, using in situ hybridisation, we demonstrated cannabinoid receptor 1 (CB1R) mRNA expression in mouse EWcp-neurones that were Ucn1-negative. Dual- and triple-label immunocytochemistry revealed the presence of CB1R in several GABA-immunopositive fibres juxtaposed to EWcp-Ucn1 neurones. To test functional aspects of such an anatomical constellation, we compared acute (1 h of restraint) and chronic (14 days of chronic mild stress) stress-induced changes in wild-type (WT) and CB1R knockout (CB1R-KO) mice. Acute and especially chronic stress resulted in an increase in Ucn1 content of the EWcp, which was attenuated in CB1R-KO mice. CB1R-KO mice had higher basal and chronic stress-induced adrenocorticotrophin and corticosterone levels and were more anxious on the elevated plus-maze versus WT. Collectively, our results show for the first time EWcp-Ucn1 neurones are putatively innervated by endocannabinoid sensitive, inhibitory, GABAergic afferents. In addition, we provide novel evidence that the absence of the CB1 receptor alters the Ucn1 mRNA and peptide levels in EWcp neurones, concomitant with an augmented stress response and increased anxiety-like behaviour.

Chronic self-administration of alcohol results in elevated ΔFosB: comparison of hybrid mice with distinct drinking patterns

Background

The inability to reduce or regulate alcohol intake is a hallmark symptom for alcohol use disorders. Research on novel behavioral and genetic models of experience-induced changes in drinking will further our knowledge on alcohol use disorders. Distinct alcohol self-administration behaviors were previously observed when comparing two F1 hybrid strains of mice: C57BL/6J x NZB/B1NJ (BxN) show reduced alcohol preference after experience with high concentrations of alcohol and periods of abstinence while C57BL/6J x FVB/NJ (BxF) show sustained alcohol preference. These phenotypes are interesting because these hybrids demonstrate the occurrence of genetic additivity (BxN) and overdominance (BxF) in ethanol intake in an experience dependent manner. Specifically, BxF exhibit sustained alcohol preference and BxN exhibit reduced alcohol preference after experience with high ethanol concentrations; however, experience with low ethanol concentrations produce sustained alcohol preference for both hybrids. In the present study, we tested the hypothesis that these phenotypes are represented by differential production of the inducible transcription factor, ΔFosB, in reward, aversion, and stress related brain regions.

Results

Changes in neuronal plasticity (as measured by ΔFosB levels) were experience dependent, as well as brain region and genotype specific, further supporting that neuronal circuitry underlies motivational aspects of ethanol consumption. BxN mice exhibiting reduced alcohol preference had lower ΔFosB levels in the Edinger-Westphal nucleus than mice exhibiting sustained alcohol preference, and increased ΔFosB levels in central medial amygdala as compared with control mice. BxN mice showing sustained alcohol preference exhibited higher ΔFosB levels in the ventral tegmental area, Edinger-Westphal nucleus, and amygdala (central and lateral divisions). Moreover, in BxN mice ΔFosB levels in the Edinger-Westphal nucleus and ventral tegmental regions significantly positively correlated with ethanol preference and intake. Additionally, hierarchical clustering analysis revealed that many ethanol-naïve mice with overall low ΔFosB levels are in a cluster, whereas many mice displaying sustained alcohol preference with overall high ΔFosB levels are in a cluster together.

Conclusions

By comparing and contrasting two alcohol phenotypes, this study demonstrates that the reward- and stress-related circuits (including the Edinger-Westphal nucleus, ventral tegmental area, amygdala) undergo significant plasticity that manifests as reduced alcohol preference.

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.

Commentary: studies on binge-like ethanol drinking may help to identify the neurobiological mechanisms underlying the transition to dependence

BACKGROUND

The goals of this commentary are to discuss the important contributions of the work by Kaur and colleagues titled "Corticotropin-releasing factor acting on corticotropin-releasing factor receptor type 1 is critical for binge alcohol drinking in mice," published in this issue of Alcoholism: Clinical and Experimental Research, and to highlight the importance of preclinical research aimed at identifying the neurobiology of binge ethanol drinking.

METHODS AND RESULTS

The work by Kaur and colleagues provides an important extension of previous pharmacological evidence implicating the corticotropin-releasing factor (CRF) type-1 receptor (CRF1R) in binge-like ethanol drinking by verifying the role of the CRF1R using genetic tools, and by establishing that CRF, but not urocortin 1 (Ucn1), is the primary neuropeptide associated with the CRF system that modulates binge-like ethanol drinking in C57BL/6J mice.

CONCLUSIONS

It is suggested that the evidence for a critical role of the CRF1R in excessive ethanol intake observed in both models of binge-like ethanol drinking and dependence-like ethanol intake indicates that overlapping mechanisms may be involved, and that studies that employ models of binge-like ethanol drinking may provide insight into the neurobiological mechanisms that underlie the transition to ethanol dependence.

Characterization of Genetic Differences within the Centrally Projecting Edinger-Westphal Nucleus of C57BL/6J and DBA/2J Mice by Expression Profiling

Detailed examination of the midbrain Edinger–Westphal (EW) nucleus revealed the existence of two distinct nuclei. One population of EW preganglionic (EWpg) neurons was found to control oculomotor functions, and a separate population of EW centrally projecting (EWcp) neurons was found to contain stress- and feeding-related neuropeptides. Although it has been shown that EWcp neurons are highly responsive to drugs of abuse and behavioral stress, a genetic characterization of the EWcp was needed. To identify genetic differences in the EWcp of inbred mouse strains that differ in behaviors relevant to EWcp function, we used publicly available tools from the Allen Brain Atlas to identify 68 transcripts that were selectively expressed in the EWcp, and examined their expression within tissue punch microdissection samples containing the EWcp of adult male C57BL/6J (B6) and DBA/2J (D2) mice. Using 96-well quantitative real-time PCR (qPCR) arrays that included the EWcp-specific genes, several other genes of interest, and five housekeeping genes, we identified strain differences in expression of 11 EWcp-specific genes (BC023892, Btg3, Bves, Cart, Cck, Ghsr, Neto1, Postn, Ptprn, Rcn1, and Ucn), two immediate early genes (Egr1 and Fos), and one dopamine-related gene (Drd5). All significant expression differences were greater in B6 vs. D2 mice, and several of these were verified either at the protein level using immunohistochemistry (IHC) or in silico using microarray data sets from whole brain and other brain areas. These results demonstrate a significant advance in our understanding of the EWcp on three levels. First, we generated a list of EWcp-specific genes (most of which had not yet been reported within the EWcp in the literature) that will be informative for future studies of EWcp function. Second, due to similarity in results from qPCR and IHC, we revealed that strain differences in basal EWcp neuropeptide content are accounted for by differential transcription and number of peptidergic neurons, rather than by differential rates of peptide release. And third, our identification of differentially expressed EWcp-specific genes between B6 and D2 mice may hold powerful insight into the neurogenetic contributions of the EWcp to stress- and addiction-related behaviors.

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.

Corticotropin-releasing factor acting on corticotropin-releasing factor receptor type 1 is critical for binge alcohol drinking in mice

BACKGROUND

The corticotropin-releasing factor (CRF) system has been implicated in the regulation of alcohol consumption. However, previous mouse knockout (KO) studies using continuous ethanol access have failed to conclusively confirm this. Recent studies have shown that CRF receptor type 1 (CRFR1) antagonists attenuate alcohol intake in the limited access "drinking in the dark" (DID) model of binge drinking. To avoid the potential nonspecific effects of antagonists, in this study, we tested alcohol drinking in CRFR1, CRFR2, CRF, and urocortin 1 (Ucn1) KO and corresponding wild-type (WT) littermates using the DID paradigm.

METHODS

On days 1 to 3, the CRFR1, CRFR2, Ucn1, and CRF KO mice and their respective WT littermates were provided with 20% ethanol or 10% sucrose for 2 hours with water available at all other times. On day 4, access to ethanol or sucrose was increased to 4 hours. At the end of each drinking session, the volume of ethanol consumed was recorded, and at the conclusion of the last session, blood was also collected for blood ethanol concentration (BEC) analysis.

RESULTS

CRFR1 KO mice had lower alcohol intakes and BECs and higher intakes of sucrose compared with WTs. In contrast, CRFR2 KO mice, while having reduced intakes initially, had similar alcohol intakes on days 2 to 4 and similar BECs as the WTs. To determine the ligand responsible, Ucn1 and CRF KO and WT mice were tested next. While Ucn1 KOs had similar alcohol intakes and BECs to their WTs, CRF KO mice showed reduced alcohol consumption and lower BECs compared with WTs.

CONCLUSIONS

Our results confirm that CRFR1 plays a key role in binge drinking and identify CRF as the ligand critically involved in excessive alcohol consumption.

The Edinger-Westphal nucleus: a historical, structural, and functional perspective on a dichotomous terminology

The eponymous term nucleus of Edinger-Westphal (EW) has come to be used to describe two juxtaposed and somewhat intermingled cell groups of the midbrain that differ dramatically in their connectivity and neurochemistry. On one hand, the classically defined EW is the part of the oculomotor complex that is the source of the parasympathetic preganglionic motoneuron input to the ciliary ganglion (CG), through which it controls pupil constriction and lens accommodation. On the other hand, EW is applied to a population of centrally projecting neurons involved in sympathetic, consumptive, and stress-related functions. This terminology problem arose because the name EW has historically been applied to the most prominent cell collection above or between the somatic oculomotor nuclei (III), an assumption based on the known location of the preganglionic motoneurons in monkeys. However, in many mammals, the nucleus designated as EW is not made up of cholinergic, preganglionic motoneurons supplying the CG and instead contains neurons using peptides, such as urocortin 1, with diverse central projections. As a result, the literature has become increasingly confusing. To resolve this problem, we suggest that the term EW be supplemented with terminology based on connectivity. Specifically, we recommend that 1) the cholinergic, preganglionic neurons supplying the CG be termed the Edinger-Westphal preganglionic (EWpg) population and 2) the centrally projecting, peptidergic neurons be termed the Edinger-Westphal centrally projecting (EWcp) population. The history of this nomenclature problem and the rationale for our solutions are discussed in this review.

Sex-specific differences in the dynamics of cocaine- and amphetamine-regulated transcript and nesfatin-1 expressions in the midbrain of depressed suicide victims vs. controls

An intriguing novel pathophysiological insight into mood disorders is the notion that one's metabolic status influences mood. In rodents, cocaine- and amphetamine-regulated transcript (CART) and nesfatin-1/NUCB2 have not only been implicated in metabolism, but in the pathobiology of anxiety and depressive-like behaviour, however they have not previously been investigated in depressed subjects. Both peptides are highly expressed in centrally projecting neurons in the Edinger-Westphal nucleus (EWcp) in the midbrain. The EWcp has been implicated in stress adaptation and stress-related mood disorders like major depressive disorder in a sex-specific manner. This is intriguing, given the fact that females have higher prevalence of mood disorders. Here, we hypothesized that the expression of CART and nesfatin-1 in EWcp would exhibit a sex-specific difference between depressed suicide victims vs. controls. We found that CART and nesfatin/NUCB2 colocalized in the human EWcp, and that CART mRNA content was much higher in both male (×3.8) and female (×5.9) drug-free suicide victims than in controls (persons who died without any diagnosed neurodegenerative or psychiatric disorder). Similarly, NUCB2 mRNA content was also higher (×1.8) in male suicides, whereas in female suicide victims, these contents were ×2.7 lower compared to controls. These observations are the first to show changes in the dynamics of CART and nesfatin/NUCB2 expressions in the midbrain of drug-free depressed suicide victims vs. controls. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Chronic binge-like moderate ethanol drinking in rats results in widespread decreases in brain serotonin, dopamine, and norepinephrine turnover rates reversed by ethanol intake

This research was initiated to assess the turnover rates (TORs) of dopamine (DA), norepinephrine (NA), serotonin (5-HT), aspartate, glutamate, and GABA in brain regions during rodent ethanol/sucrose (EtOH) and sucrose (SUC) drinking and in animals with a history of EtOH or SUC drinking to further characterize the neuronal systems that underlie compulsive consumption. Groups of five male rats were used, with two trained to drink EtOH solutions, two to drink SUC and one to serve as a non-drinking control. When stable drinking patterns were obtained, rats were pulse labeled intravenously and killed 60 or 90 min later and the TORs of DA, norepinephrine, 5-HT, aspartate, glutamate, and GABA determined in brain regions. Changes in the TOR of 5-HT, DA, and NA were detected specific to EtOH drinking, SUC drinking or a history of EtOH or SUC drinking. An acute EtOH deprivation effect was detected that was mostly reversed with EtOH drinking. These results suggest that binge-like drinking of moderate amounts of EtOH produces a deficit in neuronal function that could set the stage for the alleviation of anhedonic stimuli with further EtOH intake that strengthen EtOH seeking behaviors which may contribute to increased EtOH use in at risk individuals.

Stress-related changes in the activity of cocaine- and amphetamine-regulated transcript and nesfatin neurons in the midbrain non-preganglionic Edinger-Westphal nucleus in the rat

Cocaine- and amphetamine-regulated transcript (CART) and nesfatin-1/nucleobindin 2 (NUCB2) are assumed to play a role in feeding and adaptation to stress. Both peptides are highly expressed in the midbrain non-preganglionic Edinger-Westphal nucleus (npEW), a center implicated in the regulation of stress adaptation and in the pathogenesis of stress-induced brain disorders, in a sex-specific manner. The present study was undertaken to test whether CART and nesfatin are involved in these actions of the npEW in the rat. Acute restraint and chronic variable mild stress were used. Following stress, physiological parameters (serum corticosterone levels, body, adrenal and thymus weights) were determined, CART and nesfatin-like immunoreactivity (LI) as well as mRNA expression were analyzed in the npEW nucleus. Our results depict the following changes: (1) Acute stress resulted in an increase in serum corticosterone levels that was higher in females; (2) In males, data on corticosterone and body weight gain and in females, data on body weight gain revealed an effect of chronic stress; (3) Both acute and chronic stress activated npEW neurons expressing CART and nesfatin-LI, as shown by increased cFos immunoreactivity; (4) Chronic, but not acute stress increased the amount of CART and nesfatin-LI in both males and females; (5) Neither acute nor chronic stress had an effect on CART and NUCB2 mRNA contents of npEW neurons in either sex. Taken together, our data suggest that CART and nesfatin are involved in the response of npEW neurons to chronic stress.

Ghrelin receptor antagonism decreases alcohol consumption and activation of perioculomotor urocortin-containing neurons

BACKGROUND

The current therapies for alcohol abuse disorders are not effective in all patients, and continued development of pharmacotherapies is needed. One approach that has generated recent interest is the antagonism of ghrelin receptors. Ghrelin is a gut-derived peptide important in energy homeostasis and regulation of hunger. Recent studies have implicated ghrelin in alcoholism, showing altered plasma ghrelin levels in alcoholic patients as well as reduced intakes of alcohol in ghrelin receptor knockout mice and in mice treated with ghrelin receptor antagonists. The aim of this study was to determine the neuroanatomical locus/loci of the effect of ghrelin receptor antagonism on alcohol consumption using the ghrelin receptor antagonist, D-Lys3-GHRP-6.

METHODS

In Experiment 1, male C57BL/6J mice were injected with saline 3 hours into the dark cycle and allowed access to 15% (v/v) ethanol or water for 2 hours in a 2-bottle choice experiment. On test day, the mice were injected with either saline or 400 nmol of the ghrelin receptor antagonist, D-Lys3-GHRP-6, and allowed to drink 15% ethanol or water for 4 hours. The preference for alcohol and alcohol intake were determined. In Experiment 2, the same procedure was followed as in Experiment 1 but mice were only allowed access to a single bottle of 20% ethanol (v/v), and alcohol intake was determined. Blood ethanol levels were analyzed, and immunohistochemistry for c-Fos was carried out to investigate changes in neural activity. To further elucidate the mechanism by which D-Lys3-GHRP-6 affects alcohol intake, in Experiment 3, the effect of D-Lys3-GHRP-6 on the neural activation induced by intraperitoneal ethanol was investigated. For the c-Fos studies, brain regions containing ghrelin receptors were analyzed, i.e. the perioculomotor urocortin population of neurons (pIIIu), the ventral tegmental area (VTA), and the arcuate nucleus (Arc). In Experiment 4, to test if blood ethanol concentrations were affected by D-Lys3-GHRP-6, blood samples were taken at 2 time-points after D-Lys3-GHRP-6 pretreatment and systemic ethanol administration.

RESULTS

In Experiment 1, D-Lys3-GHRP-6 reduced preference to alcohol and in a follow-up experiment (Experiment 2) also dramatically reduced alcohol intake when compared to saline-treated mice. The resulting blood ethanol concentrations were lower in mice treated with the ghrelin receptor antagonist. Immunohistochemistry for c-Fos showed fewer immunopositive cells in the pIIIu of the antagonist-treated mice but no difference was seen in the VTA or Arc. In Experiment 3, D-Lys3-GHRP-6 reduced the induction of c-Fos by intraperitoneal ethanol in the pIIIu but had no effect in the VTA. In the Arc, there was a significant increase in the number of c-Fos immunopositive cells after D-Lys3-GHRP-6 administration, but the antagonist had no effect on ethanol-induced expression of c-Fos. D-Lys3-GHRP-6-pretreatment also did not affect the blood ethanol concentrations observed after a systemic injection of ethanol when compared to saline-pretreated mice (Experiment 4).

CONCLUSIONS

These findings indicate that the action of ghrelin on the regulation of alcohol consumption may occur via the pIIIu.

Postnatal developmental profile of urocortin 1 and cocaine- and amphetamine-regulated transcript in the perioculomotor region of C57BL/6J mice

Urocortin 1 (Ucn 1) is an endogenous corticotropin releasing factor (CRF)-related peptide. Ucn 1 is most highly expressed in the perioculomotor urocortin containing neurons (pIIIu), previously known as the non-preganglionic Edinger-Westphal nucleus (npEW). Various studies indicate that these cells are involved in stress adaptation and the regulation of ethanol (EtOH) intake. However, the developmental trajectory of these neurons remained unexamined. Expression of the cocaine- and amphetamine-regulated transcript (CART), which co-localizes with Ucn 1 in the perioculomotor area (pIII) has been examined prenatally, but not postnatally. The goal of the current study was to characterize the ontogenetic profile of Ucn 1 and CART during postnatal development in C57BL/6J (B6) mice. B6 mice were bred, and brains were collected at postnatal days (PND) 1, 4, 8, 12, 16, 24 and 45. Brightfield immunohistochemical staining for Ucn 1 and CART showed that Ucn 1-immunoreactivity (ir) was absent at PND 1, while CART-ir was already apparent in pIIIu at birth, a finding indicating that although the pIIIu neurons have already migrated to their adult position, Ucn 1 expression is triggered in them at later postnatal stages. Ucn 1-ir gradually increased with age, approaching adult levels at PND 16. This developmental profile was confirmed by double-immunofluorescence, which showed that Ucn 1 was absent in CART-positive cells of pIII at PND 4 and that Ucn 1 and CART are strongly but not completely co-localized in pIII at PND 24. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis confirmed that Ucn 1 mRNA levels are significantly lower at PND 4 and PND 12 than in adult animals. The lack of brain Ucn 1 immunoreactivity at birth and the gradual postnatal increase in Ucn 1 in pIIIu suggests that this peptide plays a greater behavioral role in adulthood than during the early postnatal development of an organism.

Increased perioculomotor urocortin 1 immunoreactivity in genetically selected alcohol preferring rats

INTRODUCTION

Urocortin 1 (Ucn 1) is an endogenous peptide related to the corticotropin-releasing factor (CRF). Ucn 1 is mainly expressed in the perioculomotor area (pIII), and its involvement in alcohol self-administration is well confirmed in mice. In other species, the relationship between the perioculomotor Ucn 1-containing population of neurons (pIIIu) and alcohol consumption needs further investigation. The pIII also has a significant subpopulation of dopaminergic neurons. Because of dopamine's (DA) role in addiction, it is important to evaluate whether this subpopulation of neurons contributes to addiction-related phenotypes. Furthermore, the effects of gender on the relationship between Ucn 1 and tyrosine hydroxylase (TH) in pIII and alcohol preference in rats have not been previously assessed.

METHODS

To address these issues, we compared 2 Sardinian alcohol-preferring sublines of rats, a population maintained at the Scripps Research Institute (Scr:sP) and a population maintained at University of Camerino-Marchigian Sardinian preferring rats (msP), to corresponding nonselectively bred Wistar rats of both sexes. Ucn 1- and TH-positive cells were detected on coronal midbrain sections from 6- to 8-week-old alcohol-naïve animals using brightfield and fluorescent immunohistochemistry. Ucn 1- and TH-positive cells in pIII were counted in the perioculomotor area, averaged across 2 to 3 sets, and binned into 3 bregma levels.

RESULTS

Results demonstrated increased average counts of Ucn 1-positive cells in the middle bregma level in preferring male rats compared to Wistar controls and no difference in TH-positive cell counts in pIII. In addition, fluorescent double labeling revealed no colocalization of Ucn 1-positive and TH-positive neurons. Ucn 1 but not TH distribution was influenced by gender with female animals expressing more Ucn 1-positive cells than male animals in the peak bregma level.

CONCLUSIONS

These findings extend previous reports of increased Ucn 1-positive cell distribution in preferring lines of animals. They indicate that Ucn1 contributes to increased alcohol consumption across different species and that this contribution could be gender specific. The results also suggest that Ucn1 regulates positive reinforcing rather than aversive properties of alcohol and that these effects could be mediated by CRF(2) receptors, independent of direct actions of DA.

Stress-related neuropeptides and alcoholism: CRH, NPY, and beyond

This article summarizes the proceedings of a symposium held at the conference on "Alcoholism and Stress: A Framework for Future Treatment Strategies" in Volterra, Italy, May 6-9, 2008. Chaired by Markus Heilig and Roberto Ciccocioppo, this symposium offered a forum for the presentation of recent data linking neuropetidergic neurotransmission to the regulation of different alcohol-related behaviors in animals and in humans. Dr. Donald Gehlert described the development of a new corticotrophin-releasing factor receptor 1 antagonist and showed its efficacy in reducing alcohol consumption and stress-induced relapse in different animal models of alcohol abuse. Dr. Andrey Ryabinin reviewed recent findings in his laboratory, indicating a role of the urocortin 1 receptor system in the regulation of alcohol intake. Dr. Annika Thorsell showed data supporting the significance of the neuropeptide Y receptor system in the modulation of behaviors associated with a history of ethanol intoxication. Dr. Roberto Ciccocioppo focused his presentation on the nociceptin/orphanin FQ (N/OFQ) receptors as treatment targets for alcoholism. Finally, Dr. Markus Heilig showed recent preclinical and clinical evidence suggesting that neurokinin 1 antagonism may represent a promising new treatment for alcoholism. Collectively, these investigators highlighted the significance of neuropeptidergic neurotransmission in the regulation of neurobiological mechanisms of alcohol addiction. Data also revealed the importance of these systems as treatment targets for the development of new medication for alcoholism.

Differential sensitivity of the perioculomotor urocortin-containing neurons to ethanol, psychostimulants and stress in mice and rats

The perioculomotor urocortin-containing population of neurons (pIIIu: otherwise known as the non-preganglionic Edinger-Westphal nucleus) is sensitive to alcohol and is involved in the regulation of alcohol intake. A recent study indicated that this brain region is also sensitive to psychostimulants. Since pIIIu has been shown to respond to stress, we investigated how psychostimulant-induced pIIIu activation compares to stress- and ethanol-induced activation, and whether it is independent from a generalized stress response. Several experiments were performed to test how the pIIIu responds to psychostimulants by quantifying the number of Fos immunoreactive nuclei after acute i.p. injections of saline, 10-30 mg/kg cocaine, 5 mg/kg methamphetamine, 5 mg/kg amphetamine, 2.5 g/kg ethanol, 2 h of restraint stress, 10 min of swim stress, or six applications of mild foot shock in male C57BL/6 J mice. We also compared Fos immunoreactivity in pIIIu after acute (20 mg/kg cocaine) and repeated cocaine exposure (7 days of 20 mg/kg cocaine) injections in male C57BL/6 J mice in order to investigate the potential habituation of this response. Finally, we quantified the number of Fos immunoreactive nuclei in pIIIu after administration of saline, 2.5 g/kg ethanol, 20 mg/kg cocaine, or 2 h of restraint stress in male Sprague-Dawley rats. We found that exposure to psychostimulants and ethanol induced significantly higher Fos levels in pIIIu compared to stress in mice. Furthermore, repeated cocaine injections did not decrease Fos immunoreactivity as would be expected if this response were due to stress. In rats, exposure to ethanol, psychostimulant and restraint stress all induced pIIIu Fos immunoreactivity compared to saline-injected controls. In both mice and rats, ethanol- and cocaine-induced Fos immunoreactivity occurred exclusively in urocortin 1-positive, but not in tyrosine hydroxylase-positive, cells. These results provide evidence that the pIIIu Fos-response to psychostimulants is independent of a generalized stress in mice, but not rats. They additionally show that the pIIIu response to stress differs significantly between species.

Urocortin 1 microinjection into the mouse lateral septum regulates the acquisition and expression of alcohol consumption

Previous studies using genetic and lesion approaches have shown that the neuropeptide urocortin 1 (Ucn1) is involved in regulating alcohol consumption. Ucn1 is a corticotropin releasing factor (CRF) -like peptide that binds CRF1 and CRF2 receptors. Perioculomotor urocortin-containing neurons (pIIIu), also known as the non-preganglionic Edinger-Westphal nucleus, are the major source of Ucn1 in the brain and are known to innervate the lateral septum. Thus, the present study tested whether Ucn1 could regulate alcohol consumption through the lateral septum. In a series of experiments Ucn1 or CRF was bilaterally injected at various doses into the lateral septum of male C57BL/6J mice. Consumption of 20% volume/volume ethanol or water was tested immediately after the injections using a modification of a 2-h limited access sweetener-free "drinking-in-the-dark" procedure. Ucn1 significantly suppressed ethanol consumption when administered prior to the third ethanol drinking session (the expression phase of ethanol drinking) at doses as low as 6 pmol. Ethanol intake was differentially sensitive to Ucn1, as equivalent doses of this peptide did not suppress water consumption. In contrast, CRF suppressed both ethanol and water intake at 40 and 60 pmol, but not at lower doses. Repeated administration of Ucn1 during the acquisition of alcohol consumption showed that 40 pmol (but not 2 or 0.1 pmol) significantly attenuated ethanol intake. Repeated administration of Ucn1 also resulted in a decrease of ethanol intake in sham-injected animals, a finding suggesting that the suppressive effect of Ucn1 on ethanol intake can be conditioned. Taken together, these studies confirm the importance of lateral septum innervation by Ucn1 in the regulation of alcohol consumption.

Differences in the urocortin 1 system between long-sleep and short-sleep mice

There is evidence that the peptide urocortin 1 (Ucn1) may be involved in mediating some of the effects of ethanol. The purpose of the present study was to characterize Ucn1 immunoreactivity in mice selectively bred for either high or low sensitivity to ethanol-induced sedation, with additional differences in their response to ethanol-induced hypothermia. The brains of naïve male mice of the inbred long sleep/short sleep (ILS/ISS) selected lines were analyzed by immunohistochemistry. Significant differences were found between lines in the number of Ucn1-containing cells in the non-preganglionic Edinger-Westphal nucleus (npEW, the main source of Ucn1 in the brain); with the ISS mice having more cells. However, significant differences in the optical density of Ucn1 immunoreactivity in individual npEW cells and differences in cell area were also found between lines, with ILS mice having a greater density of Ucn1 per cell and having larger cells in the npEW. Importantly, the ILS mice also had a significantly greater number of Ucn1-positive terminal fibers than ISS mice in the lateral septum and the dorsal raphe nucleus, projection areas of Ucn1-containing neurons. These results suggest that the greater sensitivity of ILS than ISS mice to the hypothermic effects of ethanol could be mediated by stronger innervation of the dorsal raphe by Ucn1-containing fibers. In addition, these results lend further support to previous findings implicating Ucn1-containing projections from npEW to the dorsal raphe in ethanol-induced hypothermia.

FOS expression induced by an ethanol-paired conditioned stimulus

To identify brain areas involved in ethanol-induced Pavlovian conditioning, brains of male DBA/2J mice were immunohistochemically analyzed for FOS expression after exposure to a conditioned stimulus (CS) previously paired with ethanol (2 g/kg) in two experiments. Mice were trained with a procedure that normally produces place preference (Before: ethanol before the CS) or one that normally produces place aversion (After: ethanol after the CS). Control groups received unpaired ethanol injections in the home cage (Delay) or saline only (Naïve). On the test day, mice were exposed to the 5-min CS 90 min before sacrifice. Before groups showed a conditioned increase in activity, whereas the After group showed a conditioned decrease in activity. FOS expression after a drug-free CS exposure was significantly higher in Before-group mice than in control mice in the bed nucleus of the stria terminalis (Experiment 1) and anterior ventral tegmental area (Experiments 1-2). Conditioned FOS responses were also seen in areas of the extended amygdala and hippocampus (Experiment 2). However, no conditioned FOS changes were seen in any brain area examined in After-group mice. Overall, these data suggest an important role for the mesolimbic dopamine pathway, extended amygdala and hippocampus in ethanol-induced conditioning.

Involvement of urocortinergic neurons below the midbrain central gray in the physiological response to restraint stress in pigeons

The present study was carried out to identify the diencephalic and midbrain neurons in pigeons that respond to stress (using restraint as the stressor) and determine if the urocortinergic neurons (expressing urocortin 1, Ucn1) below the midbrain central gray are among those activated. Immunolabeling for the immediate early gene Egr-1 was used to identity stress-responsive neurons, following 1-3 h of restraint. A large increase in nuclear Egr-1 immunolabeling was observed in several dorsomedial thalamic nuclei, and in a stream of neurons extending from below the mesencephalic central gray (overlapping the nucleus of Darkschewitsch at these levels) to just anterior to the nucleus of Edinger-Westphal. A more modest increase in neuronal nuclear Egr-1 was observed in the medial posterior hypothalamic area, the mesencephalic periventricular area, the ventral tegmental area, the inferior colliculus, the nucleus paramedianus of the midbrain, and the intercollicular nucleus. The distribution and abundance of urocortin-immunolabeled neurons coincided with that of the stress-responsive neurons below the mesencephalic periaqueductal gray, and about 50% of these urocortin neurons were activated by stress. These results suggest that, as in some mammals, the urocortinergic neurons of the paramedian subgriseal mesencephalon respond to stress. In those mammals, in which the boundaries of the nucleus of Edinger-Westphal are indistinct, the caudal part of the homologous field of urocortinergic neurons has been referred to as the nucleus of Edinger-Westphal. In pigeons, in which the nucleus of Edinger-Westphal is cytoarchitectonically well-defined, the caudal part of this urocortinergic field clearly does not include the nucleus of Edinger-Westphal.

The acute intoxicating effects of ethanol are not dependent on the vasopressin 1a or 1b receptors

Studies of the role of vasopressin (Avp) in mediating the effects of ethanol have focused on Avp's role in altering kidney function via its action through the vasopressin 2 receptor. However, alcohol consumption also has central effects that are poorly understood. There is evidence that Avp may mediate ethanol consumption as well as some of ethanol's behavioral effects. Centrally only two Avp receptor subtypes are expressed: the 1a receptor (Avpr1a) and the 1b receptor (Avpr1b). To determine the extent to which these receptors mediate the behavioral effects of alcohol, we used mice with targeted disruptions of either their Avpr1a or Avpr1b gene. We examined the effects of genotype on the acute intoxicating effects of ethanol as well as on voluntary ethanol consumption. Surprisingly, our findings indicate that there is no interaction between either the Avpr1a or Avpr1b and ethanol on motor coordination, hypothermia, mood, or voluntary ethanol consumption.

The urocortin 1 neurocircuit: Ethanol-sensitivity and potential involvement in alcohol consumption

One of the hallmarks of alcoholism is continued excessive consumption of alcohol-containing beverages despite the negative consequences of such behavior. The neurocircuitry regulating alcohol consumption is not well understood. Recent studies have shown that the neuropeptide urocortin 1 (Ucn1), a member of the corticotropin-releasing factor (CRF) family of peptides, could be an important player in the regulation of alcohol consumption. This evidence is accumulated along three directions of research: (1) Ucn 1-containing neurons are extremely sensitive to alcohol; (2) the Ucn1 neurocircuit may contribute to the genetic predisposition to high alcohol intake in mice and rats; (3) manipulation of the Ucn1 system alters alcohol consumption and sensitivity. This paper reviews the current knowledge of the Ucn1 neurocircuit and the evidence for its involvement in alcohol-related behaviors, and proposes a mechanism for its involvement in the regulation of alcohol consumption.

Ethanol-related behaviors in mice lacking the NMDA receptor NR2A subunit

RATIONALE

The ionotropic NMDA glutamate receptor is composed of NR1 and NR2 (NR2A-D) subunits. While there is compelling evidence that NMDA receptors modulate behavioral effects of ethanol, there is little understanding of how the subunit composition of the NMDA receptor mediates these effects.

OBJECTIVES

In the current study, we assessed the relative roles of NMDA subunits via phenotypic assessment of ethanol-related behaviors in NR2A knockout (KO) mice.

RESULTS

Results demonstrated that NR2A KO and heterozygous mice failed to show evidence of ethanol-induced conditioned place preference. As compared to wild-type (WT) controls, KO mice showed impaired motor coordination at baseline and, in some instances, following ethanol treatment on the accelerating rotarod, balance beam, and wire-hang tests. By contrast, open field locomotor-stimulant, sedative/hypnotic, and hypothermic responses to ethanol were not different between genotypes, nor was voluntary ethanol consumption and preference in a two-bottle choice paradigm. Blood ethanol concentrations were lower in KO than WT mice following intraperitoneal ethanol injection.

CONCLUSIONS

Results suggest that the loss of NR2A subunit-containing NMDA receptors impairs the ability to form or express learned reward-related responses to ethanol and causes deficits in motor coordination. However, the loss of NR2A does not alter other measures of acute ethanol intoxication or ethanol consumption, possibly implicating other NMDA subunits in these effects. These data provide novel insight into the role of NMDA receptors in modulating the behavioral effects of ethanol.

Distribution of corticotropin-releasing factor and urocortin 1 in the vole brain

Brain receptor patterns for the corticotropin-releasing factor (CRF) receptors, CRF1 and CRF2, are dramatically different between monogamous and promiscuous vole species, and CRF physiologically regulates pair bonding behavior in the monogamous prairie vole. However, it is uncertain whether species differences also exist in the neuroanatomical distribution of the endogenous ligands for the CRF1 and CRF2 receptors, such as CRF and urocortin-1 (Ucn1). We compared the expression of CRF and Ucn1 in four vole species, monogamous prairie and pine voles, and promiscuous meadow and montane voles, using in situ hybridization of CRF and Ucn1 mRNA. Our results reveal that CRF mRNA expression patterns in all four vole species appear highly conserved throughout the brain, including the olfactory bulb, nucleus accumbens, bed nucleus of the stria terminalis, medial preoptic area, central amygdala, hippocampus, posterior thalamus, and cerebellum. Similarly, Ucn1 mRNA primarily localized to the Edinger-Westphal nucleus in all four vole species. Immunocytochemistry in prairie and meadow voles confirmed localization of CRF and Ucn1 protein to these previously identified brain regions. These data demonstrate a striking dichotomy between the extraordinary species diversity of brain receptor patterns when compared to the highly conserved brain distributions of their respective ligands. Our findings generate novel hypotheses regarding the evolutionary mechanisms underlying the neural circuitry of species-typical social behaviors.

Brain Region-Specific Regulation of Urocortin 1 Innervation and Corticotropin-Releasing Factor Receptor Type 2 Binding by Ethanol Exposure

BACKGROUND

Ethanol administration and consumption selectively activates the urocortin 1 (Ucn1)-expressing neurons of the Edinger-Westphal nucleus. We investigated whether repeated ethanol exposure affects Ucn1 and Ucn1-responsive corticotropin-releasing factor type-2 receptors (CRF2).

METHODS

Male C57BL/6J and DBA/2J mice were exposed to 2 g/kg ethanol via intraperitoneal injection once per day for 14, seven, or zero days. Ucn1 immunoreactivity was measured in the lateral septum, dorsal raphe, and Edinger-Westphal nucleus. In a separate experiment, C57BL/6J mice were exposed to ethanol for seven, one, or zero days, and CRF2 receptor binding was measured in the lateral septum and dorsal raphe by receptor autoradiography.

RESULTS

Ethanol exposure induced parallel changes in Ucn1 immunoreactive terminal fibers in the lateral septum and dorsal raphe of both strains. Seven ethanol exposures but not one ethanol exposure significantly increased CRF2 receptor binding in the dorsal raphe and slightly increased CRF2 receptor binding in the lateral septum.

CONCLUSIONS

These results provide evidence that the Ucn1/CRF2 receptor system can be modified by ethanol exposure. They additionally suggest that this system may be involved in behavioral changes during alcoholism.

Ataxia and c-Fos expression in mice drinking ethanol in a limited access session

BACKGROUND

Although previous murine studies have demonstrated ethanol self-administration resulting in blood ethanol concentrations (BECs) believed to be pharmacologically relevant, to our knowledge, no study reported to date has demonstrated intoxication via ataxia after self-administration. Thus, the goal of this study was to demonstrate ataxia and to examine changes in c-Fos expression in mice after self-administration of intoxicating doses of ethanol.

METHODS

Male C57BL/6J mice were trained to drink a 10% ethanol solution during daily 30-min limited access sessions. Mice were exposed to increasing concentrations of ethanol until a 10% ethanol solution was reached. BEC and ataxia, measured as foot slips off of a balance beam, were examined after the limited access self-administration session. In a separate experiment, various brain structures from mice drinking water or ethanol were examined for changes in c-Fos expression two hr after the limited access session.

RESULTS

Mice drank between 1.5 and 2 g/kg of 10% ethanol during the daily 30-min session. BECs for these mice 15 min after the limited access session ranged between 0.52 and 2.13 mg/ml. A significant increase in foot slips off a balance beam was seen immediately after ethanol consumption during the limited access session. Among mice drinking ethanol, an increase in c-Fos expression was seen in the Edinger-Westphal nucleus, and a decrease in c-Fos expression was seen in the cingulate cortex, ventral tegmental area, lateral and medial septum, CA1 region of the hippocampus, and basolateral amygdala.

CONCLUSIONS

After this procedure in mice, BECs are achieved that are in a range considered pharmacologically relevant and intoxicating. Significant ataxia was observed after ethanol self-administration. Brain regions showing changes in c-Fos expression after voluntary intoxication were similar to those previously reported, suggesting that these brain regions are involved in regulating behavioral effects of alcohol intoxication.

Neuropeptide Y activates urocortin 1 neurons in the nonpreganglionic Edinger-Westphal nucleus

Central regulatory pathways promoting stress adaptation utilize various neurotransmitters/neuropeptides, such as urocortin 1 (Ucn1) and neuropeptide Y (NPY). Ucn1 is abundantly expressed in the nonpreganglionic Edinger-Westphal nucleus (npEW), where it is codistributed with NPY-immunoreactive (ir) terminals. A special role for both neuropeptides has been postulated in stress adaptation. Using double-labeling immunohistochemistry, we observed close appositions between NPY-ir terminals and neurons immunoreactive for Ucn1 in the rat, as well as in the human npEW. Therefore, we hypothesized that NPY might control the activity of Ucn1-positive neurons in the npEW. To test this hypothesis, NPY was injected into the lateral cerebral ventricle of rats, resulting in a strong activation of npEW Ucn1 neurons as revealed by Fos immunohistochemistry. Ucn1 mRNA was also upregulated in the npEW 2 hours after the injection of NPY. In a search for the type of NPY receptor that mediates this NPY-induced recruitment of npEW-Ucn1 cells, we found that the great majority of Ucn1 cells exhibited NPY Y5 receptor immunoreactivity, and only a few of the Ucn1 cells coexpressed the Y1 receptor. We concluded that NPY, via NPY Y5 and to a lesser extent via the Y1 receptors, exerts a stimulatory action on Ucn1 cells in the npEW. Further studies are currently in progress to elucidate the significance of this NPY-Ucn1 interaction in the npEW.