Site of action of acute alcohol administration in stimulating the rat hypothalamic-pituitary-adrenal axis: comparison between the effect of systemic and intracerebroventricular injection of this drug on pituitary and hypothalamic responses

Sex-Specific Impact of Fkbp5 on Hippocampal Response to Acute Alcohol Injection: Involvement in Alterations of Metabolism-Related Pathways

High levels of alcohol intake alter brain gene expression and can produce long-lasting effects. FK506-binding protein 51 (FKBP51) encoded by Fkbp5 is a physical and cellular stress response gene and has been associated with alcohol consumption and withdrawal severity. Fkbp5 has been previously linked to neurite outgrowth and hippocampal morphology, sex differences in stress response, and epigenetic modification. Presently, primary cultured Fkbp5 KO and WT mouse neurons were examined for neurite outgrowth and mitochondrial signal with and without alcohol. We found neurite specification differences between KO and WT; particularly, mesh-like morphology was observed after alcohol treatment and confirmed higher MitoTracker signal in cultured neurons of Fkbp5 KO compared to WT at both naive and alcohol-treated conditions. Brain regions that express FKBP51 protein were identified, and hippocampus was confirmed to possess a high level of expression. RNA-seq profiling was performed using the hippocampus of naïve or alcohol-injected (2 mg EtOH/Kg) male and female Fkbp5 KO and WT mice. Differentially expressed genes (DEGs) were identified between Fkbp5 KO and WT at baseline and following alcohol treatment, with female comparisons possessing a higher number of DEGs than male comparisons. Pathway analysis suggested that genes affecting calcium signaling, lipid metabolism, and axon guidance were differentially expressed at naïve condition between KO and WT. Alcohol treatment significantly affected pathways and enzymes involved in biosynthesis (Keto, serine, and glycine) and signaling (dopamine and insulin receptor), and neuroprotective role. Functions related to cell morphology, cell-to-cell signaling, lipid metabolism, injury response, and post-translational modification were significantly altered due to alcohol. In summary, Fkbp5 plays a critical role in the response to acute alcohol treatment by altering metabolism and signaling-related genes.

Stress and gonadal steroid influences on alcohol drinking and withdrawal, with focus on animal models in females

Sexually dimorphic effects of alcohol, following binge drinking, chronic intoxication, and withdrawal, are documented at the level of the transcriptome and in behavioral and physiological responses. The purpose of the current review is to update and to expand upon contributions of the endocrine system to alcohol drinking and withdrawal in females, with a focus on animal models. Steroids important in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes, the reciprocal interactions between these axes, the effects of chronic alcohol use on steroid levels, and the genomic and rapid membrane-associated effects of steroids and neurosteroids in models of alcohol drinking and withdrawal are described. Importantly, comparison between males and females highlight some divergent effects of sex- and stress-steroids on alcohol drinking- and withdrawal-related behaviors, and the distinct differences in response emphasize the importance of considering sex in the development of novel pharmacotherapies for the treatment of alcohol use disorder.

Blunted neural reward response to alcohol and greater alcohol motivation in binge drinkers in a randomized clinical experiment

BACKGROUND

Alcohol stimulates cerebral blood flow (CBF) in brain reward regions. However, neural processes that support sustained alcohol motivation after the first drink are not well understood.

METHODS

Using a novel placebo-controlled, randomized, crossover experiment, 27 individuals who binge drink (BD; 15 M, 12 F) and 25 social drinkers (SD; 15 M, 10 F) underwent a behavioral test of self-motivated alcohol consumption using an Alcohol Taste Test (ATT) involving alcoholic and nonalcoholic beer on separate days. The test was followed immediately by perfusion functional magnetic resonance imaging (fMRI). On both days, participants then engaged in a post-scan ATT with placebo beer to assess sustained alcohol self-motivation without active alcohol effects. Linear mixed effects models were used to examine the effects of drinking group on the placebo-controlled effect of initial alcohol motivation on brain perfusion (whole brain corrected p < 0.001, cluster corrected p < 0.025) and on the relationship between placebo-controlled brain perfusion and sustained alcohol motivation.

RESULTS

Initial alcohol self-motivation in the alcohol relative to placebo session led to markedly decreased activation in the medial orbitofrontal cortex (OFC) and the ventral striatum in BD relative to SD, indicative of neural reward tolerance. The BD group also showed an enhanced neural response in behavioral intention regions of the supplementary motor area (SMA) and inferior frontal gyrus (IFG) regions. Moreover, there was greater sustained alcohol motivation in BD than SD in the post-scan ATT in the alcohol relative to placebo session. Correspondingly, only in BD and only in the alcohol session, lower alcohol-induced OFC response correlated with concurrent sensitized SMA response, and each predicted the subsequent sustained higher alcohol motivation in the post-scan ATT.

CONCLUSIONS

Alcohol-related OFC tolerance may play an important role in sustained alcohol motivation. Furthermore, both specific alcohol-related neural reward tolerance and premotor sensitization responses may contribute to escalating alcohol motivation to drive excessive alcohol intake, even in individuals without alcohol use disorder.

An opponent process for alcohol addiction based on changes in endocrine gland mass

Consuming addictive drugs is often initially pleasurable, but escalating drug intake eventually recruits physiological anti-reward systems called opponent processes that cause tolerance and withdrawal symptoms. Opponent processes are fundamental for the addiction process, but their physiological basis is not fully characterized. Here, we propose an opponent processes mechanism centered on the endocrine stress response, the hypothalamic-pituitary-adrenal (HPA) axis. We focus on alcohol addiction, where the HPA axis is activated and secretes β-endorphin, causing euphoria and analgesia. Using a mathematical model, we show that slow changes in the functional mass of HPA glands act as an opponent process for β-endorphin secretion. The model explains hormone dynamics in alcohol addiction and experiments on alcohol preference in rodents. The opponent process is based on fold-change detection (FCD) where β-endorphin responses are relative rather than absolute; FCD confers vulnerability to addiction but has adaptive roles for learning. Our model suggests gland mass changes as potential targets for intervention in addiction.

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Addiction involves tolerance and withdrawal over weeks

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Model of the HPA-axis and β-endorphins explains tolerance and withdrawal

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Effects due to changes in the functional mass of endocrine glands

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Fold-change detection makes circuit prone to addiction but boosts learning

Epigenetic landscape of stress surfeit disorders: Key role for DNA methylation dynamics

Chronic exposure to stress throughout lifespan alters brain structure and function, inducing a maladaptive response to environmental stimuli, that can contribute to the development of a pathological phenotype. Studies have shown that hypothalamic-pituitary-adrenal (HPA) axis dysfunction is associated with various neuropsychiatric disorders, including major depressive, alcohol use and post-traumatic stress disorders. Downstream actors of the HPA axis, glucocorticoids are critical mediators of the stress response and exert their function through specific receptors, i.e., the glucocorticoid receptor (GR), highly expressed in stress/reward-integrative pathways. GRs are ligand-activated transcription factors that recruit epigenetic actors to regulate gene expression via DNA methylation, altering chromatin structure and thus shaping the response to stress. The dynamic interplay between stress response and epigenetic modifiers suggest DNA methylation plays a key role in the development of stress surfeit disorders.

Alcohol Use Disorder, Neurodegeneration, Alzheimer's and Parkinson's Disease: Interplay Between Oxidative Stress, Neuroimmune Response and Excitotoxicity

Alcohol use disorder (AUD) has been associated with neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Prolonged excessive alcohol intake contributes to increased production of reactive oxygen species that triggers neuroimmune response and cellular apoptosis and necrosis via lipid peroxidation, mitochondrial, protein or DNA damage. Long term binge alcohol consumption also upregulates glutamate receptors, glucocorticoids and reduces reuptake of glutamate in the central nervous system, resulting in glutamate excitotoxicity, and eventually mitochondrial injury and cell death. In this review, we delineate the following principles in alcohol-induced neurodegeneration: (1) alcohol-induced oxidative stress, (2) neuroimmune response toward increased oxidants and lipopolysaccharide, (3) glutamate excitotoxicity and cell injury, and (4) interplay between oxidative stress, neuroimmune response and excitotoxicity leading to neurodegeneration and (5) potential chronic alcohol intake-induced development of neurodegenerative diseases, including Alzheimer's and Parkinson's disease.

The Endocrine System and Alcohol Drinking in Females

Sexually dimorphic effects of alcohol exposure throughout life have been documented in clinical and preclinical studies. In the past, rates of alcohol use disorder (AUD) were higher in men than in women, but over the past 10 years, the difference between sexes in prevalence of AUD and binge drinking has narrowed. Recent evidence adds to historical data regarding the influence of sex steroids on alcohol drinking and the interaction with stress-related steroids. This review considers the contribution of the endocrine system to alcohol drinking in females, with a focus on the hypothalamic pituitary gonadal axis and the hypothalamic pituitary adrenal axis and their reciprocal interactions. Emphasis is given to preclinical studies that examined genomic and rapid membrane effects of estrogen, progesterone, glucocorticoids, and GABAergic neurosteroids for their effects on alcohol drinking and models of relapse. Pertinent comparisons to data in males highlight divergent effects of sex and stress steroids on alcohol drinking and emphasize the importance of considering sex in the development of novel pharmacotherapeutic targets for the treatment of AUD. For instance, pharmacological strategies targeting the corticotropin releasing factor and glucocorticoid receptor systems may be differentially effective in males and females, whereas strategies to enhance GABAergic neurosteroids may represent a biomarker of treatment efficacy in both sexes.

Chronic alcohol disrupts hypothalamic responses to stress by modifying CRF and NMDA receptor function

The chronic inability of alcoholics to effectively cope with relapse-inducing stressors has been linked to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and corticotropin-releasing factor (CRF) signaling. However, the cellular mechanisms responsible for this dysregulation are yet to be identified. After exposure of male Sprague Dawley rats to chronic intermittent ethanol (CIE; 5-6 g/kg orally for 35 doses over 50 days) or water, followed by 40-60 days of protracted withdrawal, we investigated CIE effects on glutamatergic synaptic transmission, stress-induced plasticity, CRF- and ethanol-induced NMDAR inhibition using electrophysiological recordings in parvocellular neurosecretory cells (PNCs) of the paraventricular nucleus. We also assessed CIE effects on hypothalamic mRNA expression of CRF-related genes using real-time polymerase chain reaction, and on HPA axis function by measuring stress-induced increases in plasma adrenocorticotropic hormone, corticosterone, and self-grooming. In control rats, ethanol-mediated inhibition of NMDARs was prevented by CRF1 receptor (CRFR1) blockade with antalarmin, while CRF/CRFR1-mediated NMDAR blockade was prevented by intracellularly-applied inhibitor of phosphatases PP1/PP2A, okadaic acid, but not the selective striatal-enriched tyrosine protein phosphatase inhibitor, TC-2153. CIE exposure increased GluN2B subunit-dependent NMDAR function of PNCs. This was associated with the loss of both ethanol- and CRF-mediated NMDAR inhibition, and loss of stress-induced short-term potentiation of glutamatergic synaptic inputs, which could be reversed by intracellular blockade of NMDARs with MK801. CIE exposure also blunted the hormonal and self-grooming behavioral responses to repeated restraint stress. These findings suggest a cellular mechanism whereby chronic alcohol dysregulates the hormonal and behavioral responses to repetitive stressors by increasing NMDAR function and decreasing CRFR1 function.

Dynamic Adaptation in Neurosteroid Networks in Response to Alcohol

The term neurosteroid refers to rapid membrane actions of steroid hormones and their derivatives that can modulate physiological functions and behavior via their interactions with ligand-gated ion channels. This chapter will highlight recent advances pertaining to the modulatory effects of a select group of neurosteroids that are primarily potent positive allosteric modulators of γ-aminobutyric acid_A receptors (GABA_ARs). Nanomolar concentrations of neurosteroids, which occur in vivo, potentiate phasic and tonic forms of GABA_AR-mediated inhibition, indicating that both synaptic and extrasynaptic GABA_ARs possess sensitivity to neurosteroids and contribute to the overall ability of neurosteroids to modulate central nervous system excitability. Common effects of alcohol and neurosteroids at GABA_ARs have stimulated research on the ability of neurosteroids to modulate alcohol's acute and chronic effects. Background on neurosteroid pharmacology and biosynthetic enzymes will be provided as it relates to experimental findings. Data will be summarized on alcohol and neurosteroid interactions across neuroanatomical regions and models of intoxication, consumption, dependence, and withdrawal. Evidence supports independent regulation of neurosteroid synthesis between periphery and brain as well as across brain regions following acute alcohol administration and during withdrawal. Local mechanisms for fine-tuning neuronal excitability via manipulation of neurosteroid synthesis exert predicted behavioral and electrophysiological responses on GABA_AR-mediated inhibition. Collectively, targeting neurosteroidogenesis may be a beneficial treatment strategy for alcohol use disorders.

Synaptic adaptations in the central amygdala and hypothalamic paraventricular nucleus associated with protracted ethanol abstinence in male rhesus monkeys

Alcohol use disorder is a significant global burden. Stress has been identified as an etiological factor in the initiation and continuation of ethanol consumption. Understanding adaptations within stress circuitry is an important step toward novel treatment strategies. The effects of protracted abstinence following long-term ethanol self-administration on the central nucleus of the amygdala (CeA) and the hypothalamic paraventricular nucleus (PVN) were evaluated in male rhesus monkeys. Using whole-cell patch-clamp electrophysiology, inhibitory GABAergic transmission in the CeA and excitatory glutamatergic transmission in the PVN were measured. CeA neurons from abstinent drinkers displayed an elevated baseline spontaneous inhibitory postsynaptic current (sIPSC) frequency compared with controls, indicating increased presynaptic GABA release. Application of acute ethanol significantly increased the frequency of sIPSCs in controls, but not in abstinent drinkers, suggesting a tolerance to ethanol-enhanced GABA release in abstinent rhesus monkeys with a history of chronic ethanol self-administration and repeated abstinence. In the PVN, the frequency of spontaneous excitatory postsynaptic currents (sEPSC) was elevated in abstinent drinkers compared with controls, indicating increased presynaptic glutamate release. Notably, acute ethanol decreased presynaptic glutamate release onto parvocellular PVN neurons in both controls and abstinent drinkers, suggesting a lack of tolerance to acute ethanol among PVN neurons. These results are the first to demonstrate distinct synaptic adaptations and ethanol sensitivity in both the extrahypothalamic and hypothalamic stress circuits in abstinent rhesus males. Importantly, our findings describe adaptations in stress circuitry present in the brain at a state during abstinence, just prior to relapse to ethanol drinking.

Stress vulnerability and alcohol use and consequences: From human laboratory studies to clinical outcomes

It is well known that vulnerability to stress is a risk factor for alcohol use disorder (AUD). Chronic alcohol use can result in neuroadaptations in cortico-striatal pathways and hypothalamic pituitary adrenal (HPA) axis function that are manifested in altered behavioral and cognitive control functions contributing to alcohol craving, compulsive motivation, consumption, and consequences. This symposium brings together studies utilizing novel approaches to help improve our understanding of stress - past, acute, and chronic - on alcohol seeking and consumption and related outcomes using a combination of human laboratory models, neuroimaging, and clinical measures. Examining factors that determine vulnerability as well as resilience to stress are of particular interest in the study of AUD because, in addition to increasing our understanding of the risk factors for AUD, such knowledge can be used to develop more effective treatments. Dr. Stangl presented a novel human experimental model that demonstrates, for the first time, stress-induced increases in alcohol self-administration in binge drinkers using a guided imagery paradigm combined with intravenous alcohol self-administration (IV-ASA). Dr. Blaine presented data demonstrating that glucocorticoid response to stress drives compulsive alcohol motivation and intake in binge/heavy drinkers. Dr. Plawecki presented data examining sex differences in the effect of two distinct stress paradigms - mood induction and abstinence - on IV-ASA in moderate drinkers. Dr. Schwandt presented clinical data providing a new perspective on the relationship between childhood trauma and AUD by suggesting possible underlying mechanisms that confer resilience, rather than vulnerability, to severe early life stress exposure.

The influence of adolescent nicotine exposure on ethanol intake and brain gene expression

Nicotine and alcohol are often co-abused. Adolescence is a vulnerable period for the initiation of both nicotine and alcohol use, which can lead to subsequent neurodevelopmental and behavioral alterations. It is possible that during this vulnerable period, use of one drug leads to neurobiological alterations that affect subsequent consumption of the other drug. The aim of the present study was to determine the effect of nicotine exposure during adolescence on ethanol intake, and the effect of these substances on brain gene expression. Forty-three adolescent female C57BL/6J mice were assigned to four groups. In the first phase of the experiment, adolescent mice (PND 36-41 days) were exposed to three bottles filled with water or nicotine (200 μg/ml) for 22 h a day and a single bottle of water 2 h a day for six days. In the second phase (PND 42-45 days), the 4-day Drinking-in-the-Dark paradigm consisting of access to 20% v/v ethanol or water for 2h or 4h (the last day) was overlaid during the time when the mice did not have nicotine available. Ethanol consumption (g/kg) and blood ethanol concentrations (BEC, mg %) were measured on the final day and whole brains including the cerebellum, were dissected for RNA sequencing. Differentially expressed genes (DEG) were detected with CuffDiff and gene networks were built using WGCNA. Prior nicotine exposure increased ethanol consumption and resulting BEC. Significant DEG and biological pathways found in the group exposed to both nicotine and ethanol included genes important in stress-related neuropeptide signaling, hypothalamic-pituitary-adrenal (HPA) axis activity, glutamate release, GABA signaling, and dopamine release. These results replicate our earlier findings that nicotine exposure during adolescence increases ethanol consumption and extends this work by examining gene expression differences which could mediate these behavioral effects.

Targeted overexpression of CRH receptor subtype 1 in central amygdala neurons: effect on alcohol-seeking behavior

RATIONALE

The corticotropin-releasing hormone (CRH) system is a key mediator of stress-induced responses in alcohol-seeking behavior. Recent research has identified the central nucleus of the amygdala (CeA), a brain region involved in the regulation of fear and stress-induced responses that is especially rich in CRH-positive neurons, as a key player in mediating excessive alcohol seeking. However, detailed characterization of the specific influences that local neuronal populations exert in mediating alcohol responses is hampered by current limitations in pharmacological and immunohistochemical tools for targeting CRH receptor subtype 1 (CRHR1).

OBJECTIVE

In this study, we investigated the effect of cell- and region-specific overexpression of CRHR1 in the CeA using a novel transgenic tool.

METHODS

Co-expression of CRHR1 in calcium-calmodulin-dependent kinase II (αCaMKII) neurons of the amygdala was demonstrated by double immunohistochemistry using a Crhr1-GFP reporter mouse line. A Cre-inducible Crhr1-expressing adeno-associated virus (AAV) was site-specifically injected into the CeA of αCaMKII-Cre^ERT2 transgenic rats to analyze the role of CRHR1 in αCaMKII neurons on alcohol self-administration and reinstatement behavior.

RESULTS

Forty-eight percent of CRHR1-containing cells showed co-expression of αCaMKII in the CeA. AAV-mediated gene transfer in αCaMKII neurons induced a 24-fold increase of Crhr1 mRNA in the CeA which had no effect on locomotor activity, alcohol self-administration, or cue-induced reinstatement. However, rats overexpressing Crhr1 in the CeA increased responding in the stress-induced reinstatement task with yohimbine serving as a pharmacological stressor.

CONCLUSION

We demonstrate that CRHR1 overexpression in CeA-αCaMKII neurons is sufficient to mediate increased vulnerability to stress-triggered relapse into alcohol seeking.

Influence of stress associated with chronic alcohol exposure on drinking

Stress is commonly regarded as an important trigger for relapse and a significant factor that promotes increased motivation to drink in some individuals. However, the relationship between stress and alcohol is complex, likely changing in form during the transition from early moderated alcohol use to more heavy uncontrolled alcohol intake. A growing body of evidence indicates that prolonged excessive alcohol consumption serves as a potent stressor, producing persistent dysregulation of brain reward and stress systems beyond normal homeostatic limits. This progressive dysfunctional (allostatic) state is characterized by changes in neuroendocrine and brain stress pathways that underlie expression of withdrawal symptoms that reflect a negative affective state (dysphoria, anxiety), as well as increased motivation to self-administer alcohol. This review highlights literature supportive of this theoretical framework for alcohol addiction. In particular, evidence for stress-related neural, physiological, and behavioral changes associated with chronic alcohol exposure and withdrawal experience is presented. Additionally, this review focuses on the effects of chronic alcohol-induced changes in several pro-stress neuropeptides (corticotropin-releasing factor, dynorphin) and anti-stress neuropeptide systems (nocicepton, neuropeptide Y, oxytocin) in contributing to the stress, negative emotional, and motivational consequences of chronic alcohol exposure. Studies involving use of animal models have significantly increased our understanding of the dynamic stress-related physiological mechanisms and psychological underpinnings of alcohol addiction. This, in turn, is crucial for developing new and more effective therapeutics for treating excessive, harmful drinking, particularly stress-enhanced alcohol consumption. This article is part of the Special Issue entitled "Alcoholism".

Studies using macaque monkeys to address excessive alcohol drinking and stress interactions

The use of non-human primates (NHPs) in studies of volitional, oral self-administration of alcohol can help address the complex interplay between stress and excessive alcohol consumption. There are aspects to brain, endocrine and behavior of NHPs, particularly macaques, that provide a critical translational link towards understanding the risks and consequences of alcohol use disorders (AUDs) in humans. These include wide individual differences in escalating daily alcohol intake, accurate measures of hypothalamic-pituitary-adrenal (HPA) axis hormonal interactions, neuroanatomical specificity of synaptic adaptations to chronic alcohol, genetic similarities to humans, and the ability to conduct in vivo brain imaging. When placed in a framework that alcohol addiction is a sequence of dysregulations in motivational circuitry associated with severity of AUD, the NHP can provide within-subject information on both risks for and consequences of repeatedly drinking to intoxication. Notably, long-term adaptations in neurocircuitry that mediate behavioral reinforcement, stress responses and executive functions are possible with NHPs. We review here the substantial progress made using NHPs to address the complex relationship between alcohol and stress as risk factors and consequences of daily drinking to intoxication. This review also highlights areas where future studies of brain and HPA axis adaptations are needed to better understand the mechanisms involved in stress leading to excessive alcohol consumption. This article is part of the Special Issue entitled "Alcoholism".

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.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

Effects of prolonged alcohol exposure on somatotrophs and corticotrophs in adult rats: Stereological and hormonal study

Exposure to alcohol alters many physiological processes, including endocrine status. The present study examined whether prolonged alcohol (A) exposure could modulate selected stereological and hormonal aspects of pituitary somatotrophs (growth hormone-GH cells) and corticotrophs (adrenocorticotropic hormone-ACTH cells) in adult rats. Changes in pituitary gland volume; the volume density, total number and volume of GH and ACTH cells following alcohol exposure were evaluated using a stereological system (newCAST), while peripheral GH and ACTH levels were determined biochemically. Our results demonstrated the reduction (p<0.05) of the volume density (37%) and volume of GH cells (29%) in the group A. Also, there was a tendency for the total number of GH cells to be smaller in the group A. Serum GH level was significantly decreased (p<0.05; 70%) in the group A when compared to control values. Moreover, prolonged alcohol exposure induced declines (p<0.05) in volume density (24%) and volume of ACTH cells (29%). The total number of ACTH cells and ACTH level were higher (p<0.05; 42%) in the group A than in control rats. Collectively, these results indicate that prolonged alcohol exposure leads not only to changes in GH and ACTH hormone levels, but also to alterations of the morphological aspects of GH and ACTH cells within the pituitary.

Alcohol Effects on Stress Pathways: Impact on Craving and Relapse Risk

A significant amount of neurobiological research regarding the development of alcohol use disorders (AUDs) has focused on alcohol-related activation and long-term alterations in the mesocortical dopaminergic reward pathways. However, alcohol does not only interact with brain reward systems. Many of its acute and chronic effects may be related to allostatic adaptations in hypothalamic and extrahypothalamic stress regulation pathways. For example, acute binge intoxication is associated with hypothalamically driven increases in blood cortisol, norepinephrine, and sex steroid metabolite levels. This may contribute to the development of mesocortical sensitization to alcohol. Furthermore, chronic alcohol exposure is associated with systemic dysregulation of the hypothalamic pituitary adrenal axis, sympathetic adrenal medullary system, and sex steroid systems. This dysregulation appears to manifest as neuroendocrine tolerance. In this review, we first summarize the literature suggesting that alcohol-induced alterations in these hypothalamic systems influence craving and contribute to the development of AUDs. We note that for women, the effects of alcohol on these neuroendocrine stress regulation systems may be influenced by the rhythmic variations of hormones and steroids across the menstrual cycle. Second, we discuss how changes in these systems may indicate progression of AUDs and increased risk of relapse in both sexes. Specifically, neuroendocrine tolerance may contribute to mesocortical sensitization, which in turn may lead to decreased prefrontal inhibitory control of the dopaminergic reward and hypothalamic stress systems. Thus, pharmacological strategies that counteract alcohol-associated changes in hypothalamic and extrahypothalamic stress regulation pathways may slow the development and progression of AUDs.

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.

Acute oral administration of the novel, competitive and selective glucocorticoid receptor antagonist ORG 34517 reduces the severity of ethanol withdrawal and related hypothalamic-pituitary-adrenal axis activation

BACKGROUND

The development of ethanol dependence is associated with alterations in hypothalamic-pituitary-adrenal (HPA) axis and activation of type II glucocorticoid receptors (GR). These effects may contribute to withdrawal-associated anxiety, craving and relapse to drinking. The present studies examined acute and oral administration of the novel, selective and competitive GR antagonist ORG 34517 on the severity of ethanol withdrawal.

METHODS

Adult, male Sprague-Dawley rats were administered ethanol (4g/kg/i.g.) twice daily for 5 days followed by 2 days of withdrawal for 1, 2 or 3 consecutive cycles. Blood ethanol levels (BELs) were determined at 0930 on Day 4 of each week, while blood corticosterone levels (BCLs) were obtained at 11:00hours on the first day of each ethanol withdrawal. During early withdrawal, subjects received oral administration of ORG 345617 (60mg/kg/i.g.) or a placebo and withdrawal was monitored.

RESULTS

Peak BELs of 225.52mg/dl were observed during the third week. Withdrawal from three cycles of the regimen produced marked behavioral abnormalities (e.g., aggression, rigidity, and hypoactivity) and significant increases in BCLs of ethanol-dependent subjects. Acute, oral administration of ORG 34517 during early withdrawal significantly reduced both the severity of ethanol withdrawal, as reflected in reduced rigidity, aggression, and hypoactivity, and elevations in BCL without producing any sedative-like effects.

CONCLUSIONS

The present findings demonstrate that repeated ethanol exposure and withdrawal is associated with significant behavioral abnormalities and dysregulation of HPA axis activation. Further these data suggest that selective GR antagonists should be further considered as putative pharmacotherapies for treatment of ethanol dependence.

An ultrastructural analysis of the effects of ethanol self-administration on the hypothalamic paraventricular nucleus in rhesus macaques

A bidirectional relationship between stress and ethanol exists whereby stressful events are comorbid with problematic ethanol use and prolonged ethanol exposure results in adaptations of the physiological stress response. Endocrine response to stress is initiated in the hypothalamic paraventricular nucleus (PVN) with the synthesis and release of corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Alterations in CRH and AVP following long-term ethanol exposure in rodents is well demonstrated, however little is known about the response to ethanol in primates or the mechanisms of adaptation. We hypothesized that long-term ethanol self-administration in nonhuman primates would lead to ultrastructural changes in the PVN underlying adaptation to chronic ethanol. Double-label immunogold electron microscopy (EM) was used to measure presynaptic gamma-aminobutyric acid (GABA) and glutamate density within synaptic terminals contacting CRH- and AVP-immunoreactive dendrites. Additionally, pituitary-adrenal hormones (ACTH, cortisol, DHEA-s and aldosterone) under two conditions (low and mild stress) were compared before and after self-administration. All hormones were elevated in response to the mild stressor independent of ethanol consumption. The presynaptic glutamate density in recurrent (i.e., intra-hypothalamic) CRH terminals was highly related to ethanol intake, and may be a permissive factor in increased drinking due to stress. Conversely, glutamate density within recurrent AVP terminals showed a trend-level increase following ethanol, but was not related to average daily consumption. Glutamate density in non-recurrent AVP terminals was related to aldosterone under the low stress condition while GABAergic density in this terminal population was related to water consumption. The results reveal distinct populations of presynaptic terminals whose glutamatergic or GABAergic density were uniquely related to water and ethanol consumption and circulating hormones.

Environmental stressors influence limited-access ethanol consumption by C57BL/6J mice in a sex-dependent manner

Exposure to stress contributes to ethanol consumption in humans, but it produces inconsistent effects on ethanol drinking in rodent models. Therefore, the present study examined the influence of different stressors (restraint, tail suspension, predator odor, foot shock, and tail pinch) on 2-h access to water and 10% ethanol by male and female C57BL/6J mice and determined whether there were sex-dependent differences in response to stress. Plasma corticosterone (CORT) and allopregnanolone (ALLO) were assessed as indexes of hypothalamic-pituitary-adrenal axis activity and of endogenous neurosteroid levels, respectively, following restraint, tail suspension, and predator odor. These stressors increased plasma CORT and ALLO levels, and produced a greater increase in CORT and ALLO levels in females versus males. Ethanol intake was decreased following restraint, tail suspension, foot shock, and tail pinch in both sexes, with stressor-related differences in the duration of the suppression. Predator odor significantly increased ethanol intake on the following two days in females and on the second day after stress in males. Notably, there was a significant positive correlation between CORT levels immediately after predator odor stress and ethanol intake on the following day. In summary, the type of stressor influenced ethanol consumption, with subtle sex differences in the magnitude and persistence of the effect. These findings are the first to demonstrate that a single, acute exposure to restraint, tail suspension, and predator odor stress increased plasma CORT and ALLO levels in animals with a history of ethanol consumption and that female mice were more responsive than males to the ability of stress to increase CORT and ALLO levels as well as to increase ethanol intake following predator odor stress. Because predator odor stress is a model of post-traumatic stress disorder (PTSD), the present sex differences have important implications for preclinical studies modeling the comorbidity of PTSD and alcohol use disorders.

Allopregnanolone modulation of HPA axis function in the adult rat

RATIONALE

GABAergic neuronal circuits regulate neuroendocrine stress response, and the most potent positive endogenous modulator of GABAA receptor function is allopregnanolone. This neurosteroid acts in a nongenomic manner to selectively increase the inhibitory signal meditated by GABAA receptors; in addition, it also induces long-lasting changes in the expression of specific GABAA receptor subunits in various brain regions, with consequent changes in receptor function.

OBJECTIVE

The objective of this review is to summarize our findings on emotional state and stress responsiveness in three animal models in which basal brain concentrations of allopregnanolone differ. It is postulated that individual differences in allopregnanolone levels can influence general resilience.

RESULTS

The results showed that there is an apparent correlation between endogenous levels of brain allopregnanolone and basal and stress-stimulated HPA axis activity.

CONCLUSION

The relationship between endogenous brain levels of allopregnanolone and HPA axis activity and function sustains the therapeutic potential of this neurosteroid for the treatment of stress-associated disorders.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Sex differences in neuroadaptation to alcohol and withdrawal neurotoxicity

Recent work suggests that sex differences exist with regard to both the nature of neuroadaptation to alcohol during the development of dependence, and possibly, the neurodegenerative consequences of alcohol dependence. Volumetric studies in human samples show that females may demonstrate increased volumetric brain loss with equal or lesser dependence histories than males. Furthermore, animal studies demonstrate sex differences in glutamatergic, GABAergic, and adenosinergic receptor signaling and endocrine responses following prolonged alcohol exposure. These differences may influence the development of dependence, neuronal function, and viability, particularly during alcohol withdrawal. The present review discusses the current state of knowledge in this regard. It is concluded that there exists a clear need for a more extensive examination of potential sex differences in neurodegenerative consequences of alcohol dependence in men and women, particularly with regard to the role that alterations in amino acid signaling and hypothalamic-pituitary-adrenal axis function may play. Furthermore, we note the need for expanded examination of the unique role that alcohol withdrawal-associated neuronal activity may have in the development of dependence-associated neurotoxicity.

Social rank, chronic ethanol self-administration, and diurnal pituitary-adrenal activity in cynomolgus monkeys

RATIONALE

Dominance hierarchies affect ethanol self-administration, with greater intake among subordinate animals compared to dominant animals. Excessive ethanol intake disrupts circadian rhythms. Diurnal rhythms of the hypothalamic-pituitary-adrenal axis have not been characterized in the context of ethanol self-administration with regard to social rank.

OBJECTIVE

This study aimed to determine whether diurnal pituitary-adrenal hormonal rhythms account for differences between social ranks in ethanol self-administration or are differentially affected by ethanol self-administration between social ranks.

METHODS

During alternating individual (n = 11-12) and social (n = 3 groups) housing of male cynomolgus monkeys (Macaca fascicularis), diurnal measures of cortisol and adrenocorticotropic hormone (ACTH) were obtained from plasma samples three times per week. Social rank was determined, ethanol (4 %, w/v) self-administration was induced, and then the monkeys were allowed a choice of water or ethanol for 22 h/day for 49 weeks.

RESULTS

For all social ranks, plasma ACTH was elevated during social housing, but cortisol was stable, although greater among dominant monkeys. Ethanol self-administration blunted the effect of social housing, cortisol, and the diurnal rhythm for both hormones, regardless of daily ethanol intake (1.2-4.2 g/kg/day). Peak ACTH and cortisol were more likely to be observed in the morning during ethanol access. Ethanol, not vehicle, intake was lower during social housing across social ranks. Only dominant monkeys showed significantly lower blood-ethanol concentration during social housing.

CONCLUSIONS

There was a low threshold for disruption of diurnal pituitary rhythms by ethanol drinking, but sustained adrenal corticosteroid rhythms. Protection against heavy drinking among dominant monkeys may have constrained ethanol intoxication, possibly to preserve dominance rank.

Direct central nervous system effect of alcohol alters synthesis and degradation of skeletal muscle protein

AIMS

Alcohol can directly impair protein synthesis in cultured myocytes as well as in in situ perfused skeletal muscle. However, alcohol in the general circulation diffuses rapidly into the central nervous system (CNS). Therefore, this study determined whether localized elevation of alcohol within the CNS is capable of decreasing muscle protein synthesis.

METHODS

Conscious unstrained male rats received a continuous intracerebroventricular (ICV) infusion of ethanol and skeletal muscle protein synthesis and degradation were assessed.

RESULTS

ICV alcohol decreased protein synthesis in the gastrocnemius after 6 and 24 h, compared with the time-matched controls. The reduction was equivalent for both sarcoplasmic and myofibrillar proteins and was reversible. The inhibitory effect of alcohol was not prevented by the catalase inhibitor 3-amino-1,2,4-triazole and was mimicked by ICV-administered t-butanol. The alcohol-induced decrease in muscle protein synthesis was associated with a concomitant reduction in phosphorylation of 4E-binding protein and ribosomal S6 kinase-1, suggesting impaired mammalian target of rapamycin kinase activity. ICV alcohol also impaired the ability of leucine to stimulate protein synthesis. Conversely, ICV alcohol increased muscle proteasome activity and muscle RING-finger protein-1 mRNA content. Altered muscle protein metabolism was not associated with changes in muscle mRNA content for tumor necrosis factor α, interleukin-6 or insulin-like growth factor (IGF)-I or circulating insulin or IGF-I.

CONCLUSION

Selective elevation of alcohol within the CNS is capable of decreasing protein synthesis and increasing protein degradation in muscle in the absence of alcohol in the general circulation, thus revealing a previously unrecognized central neural mechanism, which may account for part of the inhibitory effect of ingested alcohol on muscle protein homeostasis.

Neurocircuitry for modeling drug effects

The identification and functional understanding of the neurocircuitry that mediates alcohol and drug effects that are relevant for the development of addictive behavior is a fundamental challenge in addiction research. Here we introduce an assumption-free construction of a neurocircuitry that mediates acute and chronic drug effects on neurotransmitter dynamics that is solely based on rodent neuroanatomy. Two types of data were considered for constructing the neurocircuitry: (1) information on the cytoarchitecture and neurochemical connectivity of each brain region of interest obtained from different neuroanatomical techniques; (2) information on the functional relevance of each region of interest with respect to alcohol and drug effects. We used mathematical data mining and hierarchical clustering methods to achieve the highest standards in the preprocessing of these data. Using this approach, a dynamical network of high molecular and spatial resolution containing 19 brain regions and seven neurotransmitter systems was obtained. Further graph theoretical analysis suggests that the neurocircuitry is connected and cannot be separated into further components. Our analysis also reveals the existence of a principal core subcircuit comprised of nine brain regions: the prefrontal cortex, insular cortex, nucleus accumbens, hypothalamus, amygdala, thalamus, substantia nigra, ventral tegmental area and raphe nuclei. Finally, by means of algebraic criteria for synchronizability of the neurocircuitry, the suitability for in silico modeling of acute and chronic drug effects is indicated. Indeed, we introduced as an example a dynamical system for modeling the effects of acute ethanol administration in rats and obtained an increase in dopamine release in the nucleus accumbens-a hallmark of drug reinforcement-to an extent similar to that seen in numerous microdialysis studies. We conclude that the present neurocircuitry provides a structural and dynamical framework for large-scale mathematical models and will help to predict chronic drug effects on brain function.

Glucocorticoid and polyamine interactions in the plasticity of glutamatergic synapses that contribute to ethanol-associated dependence and neuronal injury

Stress contributes to the development of ethanol dependence and is also a consequence of dependence. However, the complexity of physiological interactions between activation of the hypothalamic-pituitary-adrenal (HPA) axis and ethanol itself is not well delineated. Emerging evidence derived from examination of corticotropin-releasing factor systems and glucocorticoid receptor systems in ethanol dependence suggests a role for pharmacological manipulation of the HPA axis in attenuating ethanol intake, though it is not clear how activation of the HPA axis may promote ethanol dependence or contribute to the neuroadaptative changes that accompany the development of dependence and the severity of ethanol withdrawal. This review examines the role that glucocorticoids, in particular, have in promoting ethanol-associated plasticity of glutamatergic synapses by influencing expression of endogenous linear polyamines and polyamine-sensitive polypeptide subunits of N-methyl-D-aspartate (NMDA)-type glutamate receptors. We provide evidence that interactions among glucocorticoid systems, polyamines and NMDA receptors are highly relevant to both the development of ethanol dependence and to behavioral and neuropathological sequelae associated with ethanol withdrawal. Examination of these issues is likely to be of critical importance not only in further elucidating the neurobiology of HPA axis dysregulation in ethanol dependence, but also with regard to identification of novel therapeutic targets that may be exploited in the treatment of ethanol dependence.

Roles of the locus coeruleus and adrenergic receptors in brain-mediated hypothalamic-pituitary-adrenal axis responses to intracerebroventricular alcohol

BACKGROUND

Alcohol activates the hypothalamic-pituitary-adrenal (HPA) axis through its actions in both the periphery and the central nervous system (CNS). The studies presented here were designed to test the CNS-specific noradrenergic mechanisms by which alcohol stimulates HPA activity in the male rat.

METHODS

We used an experimental paradigm in which a small, nontoxic amount (5 μl) of alcohol was slowly microinfused intracerebroventricularly (icv). Alcohol was administered icv to animals with lesions of the locus coeruleus (LC) or in animals pretreated with α- or β-adrenergic receptor antagonists. Hormonal HPA activation was determined by measuring secretion of the pituitary stress hormone adrenocorticotropin (ACTH). Neuronal activation was determined by quantification of the expression of the transcription factor c-fos (Fos).

RESULTS

As expected, icv alcohol stimulated ACTH secretion from the pituitary and Fos expression in the paraventricular nucleus of the hypothalamus (PVN). Bilateral electrolytic LC lesions blocked the ability of icv alcohol to stimulate ACTH secretion. Pretreatment with icv propranolol increased basal ACTH secretion levels, but icv alcohol did not increase this effect. Propranolol also blunted icv alcohol-induced PVN Fos expression. A low dose of phenoxybenzamine, an α-adrenergic receptor antagonist, did not affect the ability of icv alcohol to stimulate ACTH release. However, a higher dose of the drug was able to block the ACTH response to icv alcohol. Despite this, phenoxybenzamine did not inhibit alcohol-induced Fos expression. Icv pretreatment with corynanthine, a selective α-1 adrenergic receptor antagonist, modestly raised basal ACTH levels and blocked the icv alcohol-induced secretion of this hormone.

CONCLUSIONS

These results indicate that the LC and norepinephrine play important roles in HPA activation caused by icv alcohol administration, but that the specific adrenergic receptor subtypes involved in this phenomenon still need to be identified.

Stress and the HPA axis: role of glucocorticoids in alcohol dependence

Stress has long been suggested to be an important correlate of uncontrolled drinking and relapse. An important hormonal response system to stress-the hypothalamic-pituitary-adrenal (HPA) axis-may be involved in this process, particularly stress hormones known as glucocorticoids and primarily cortisol. The actions of this hormone system normally are tightly regulated to ensure that the body can respond quickly to stressful events and return to a normal state just as rapidly. The main determinants of HPA axis activity are genetic background, early-life environment, and current life stress. Alterations in HPA axis regulation are associated with problematic alcohol use and dependence; however, the nature of this dysregulation appears to vary with respect to stage of alcohol dependence. Much of this research has focused specifically on the role of cortisol in the risk for, development of, and relapse to chronic alcohol use. These studies found that cortisol can interact with the brain's reward system, which may contribute to alcohol's reinforcing effects. Cortisol also can influence a person's cognitive processes, promoting habit-based learning, which may contribute to habit formation and risk of relapse. Finally, cortisol levels during abstinence may be useful clinical indicators of relapse vulnerability in alcohol-dependent people.

Neurosteroid influences on sensitivity to ethanol

This review will highlight a variety of mechanisms by which neurosteroids affect sensitivity to ethanol, including physiological states associated with activity of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes, and the effects of chronic exposure to ethanol, in addition to behavioral implications. To date, γ-aminobutyric acid (GABA(A)) receptor mechanisms are a major focus of the modulation of ethanol effects by neuroactive steroids. While NMDA receptor mechanisms are gaining prominence in the literature, these complex data would be best discussed separately. Accordingly, GABA(A) receptor mechanisms are emphasized in this review with brief mention of some NMDA receptor mechanisms to point out contrasting neuroactive steroid pharmacology. Overall, the data suggest that neurosteroids are virtually ubiquitous modulators of inhibitory neurotransmission. Neurosteroids appear to affect sensitivity to ethanol in specific brain regions and, consequently, specific behavioral tests, possibly related to the efficacy and potency of ethanol to potentiate the release of GABA and increase neurosteroid concentrations. Although direct interaction of ethanol and neuroactive steroids at common receptor binding sites has been suggested in some studies, this proposition is still controversial. It is currently difficult to assign a specific mechanism by which neuroactive steroids could modulate the effects of ethanol in particular behavioral tasks.

Immediate and prolonged effects of alcohol exposure on the activity of the hypothalamic-pituitary-adrenal axis in adult and adolescent rats

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis. Part of this influence is likely exerted directly at the level of the corticotropin-releasing factor (CRF) gene, but intermediates may also play a role. Here we review the effect of alcohol on this axis, provide new data on the effects of binge drinking during adolescence, and argue for a role of catecholaminergic circuits. Indeed, acute injection of this drug activates brain stem adrenergic and noradrenergic circuits, and their lesion, or blockade of α1 adrenergic receptors significantly blunts alcohol-induced ACTH release. As alcohol can influence the HPA axis even once discontinued, and alcohol consumption in young people is associated with increased adult drug abuse (a phenomenon possibly mediated by the HPA axis), we determined whether alcohol consumption during adolescence modified this axis. The number of CRF-immunoreactive (ir) cells/section was significantly decreased in the central nucleus of the amygdala of adolescent self-administering binge-drinking animals, compared to controls. When another group of adolescent binge-drinking rats was administered alcohol in adulthood, the number of colocalized c-fos-ir and PNMT-ir cells/brain stem section in the C3 area was significantly decreased, compared to controls. As the HPA axis response to alcohol is blunted in adult rats exposed to alcohol vapors during adolescence, a phenomenon which was not observed in our model of self-administration, it is possible that the blood alcohol levels achieved in various models play a role in the long-term consequences of exposure to alcohol early in life. Collectively, these results suggest an important role of brain catecholamines in modulating the short- and long-term consequences of alcohol administration.

Brain stem catecholamines circuitry: activation by alcohol and role in the hypothalamic-pituitary-adrenal response to this drug

Although the stimulatory effect of alcohol on the rat hypothalamic-pituitary-adrenal (HPA) axis is well known, the mechanisms underlying this influence remain poorly understood. In the present study, we tested the hypothesis that brain catecholamines play an important role in this response. As expected, the acute intragastric administration of alcohol to adult male rats elevated plasma adrenocorticotrophic hormone (ACTH) levels and activated hypothalamic corticotrophin-releasing factor neurones. Novel findings pertain to the effect of alcohol on, and the role played by, brain adrenergic circuits. We first observed that alcohol up-regulated c-fos signals in the locus coeruleus, the main noradrenergic brain cell group; and that it activated (nor)adrenergic medullary cells (A1-A2/C1-C3). Evidence for the role played by these catecholaminergic circuits then came from the observation that blockade of α(1) -, but not β-, adrenergic receptors interfered with alcohol-induced ACTH secretion; and that depletion of catecholaminergic input to the paraventricular nucleus (PVN) by the toxin 6-hydroxydopamine significantly decreased the ACTH response to alcohol. Finally, destruction of the A1-A2/C1-C3 region with the immunotoxin anti-dopamine-B-hydroxylase-saporin interfered with the catecholaminergic input to the PVN. Collectively, our work extends our knowledge of the ability of this drug to up-regulate catecholamine circuitry in the rat brain. It also shows that medullary catecholamine innervation of the hypothalamus plays an important role in modulating the stimulatory effect of alcohol on the HPA axis, an effect exerted through activation of α(1) -adrenergic receptors.

Adolescent alcohol exposure alters the central brain circuits known to regulate the stress response

Adolescent alcohol exposure (AAE) may exert long-term effects on the adult brain. Here, we tested the hypothesis that the brain regions affected include the rat hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined the consequences of AAE [postnatal days (PND) 28-42] on the HPA axis-related brain circuitry of male rats challenged with an intragastric (ig) administration of alcohol in young adulthood (PND 61-62). Adolescent rats were exposed to alcohol vapors, while controls did not receive the drug. The mean blood alcohol level in adolescence on PND 40 was 212.8±5.7 mg %. Using immunohistochemistry and in situ hybridization procedures, we measured signals for c-fos and corticotropin releasing factor (CRF) in the paraventricular nucleus (PVN) of the hypothalamus, as well as signals for c-fos and phenylethanolamine N-methyltransferase (PNMT) in the adrenergic brain stem regions (C1 and C2). PVN CRF mRNA expression was significantly blunted in AAE rats tested at PND 61-62, compared to their controls. These animals also displayed a significant increase in the mean number of PNMT-ir cells/brain stem section in the C2 area. Collectively, these results suggest that exposure to alcohol vapors during adolescence exerts long-term effects on the ability of the PVN to mount a response to an acute alcohol administration in young adulthood, possibly mediated by medullary catecholamine input to the PVN.

The importance of glucocorticoids in alcohol dependence and neurotoxicity

Alterations in hypothalamo-pituitary adrenal (HPA) function have been described in alcoholics and in rodents after chronic alcohol consumption but the role of glucocorticoids in alcohol consumption, and the mechanisms involved, has received little attention until recently. Both alcohol consumption and withdrawal from chronic alcohol intake raise circulating glucocorticoid levels, and prolonged high concentrations of glucocorticoids are known to have detrimental effects on neuronal function and cognition. This minireview covers the ways in which glucocorticoids may be involved in drinking behavior, from social drinking to dependence, and the negative consequences of alcohol consumption seen during withdrawal which may have a detrimental effect on treatment outcome. Research shows prolonged increases in brain glucocorticoid concentrations and decreased brain glucocorticoid receptor availability (consistent with increased levels of endogenous ligand) after withdrawal from chronic alcohol treatment. Evidence suggests that increased glucocorticoid levels in the brain after chronic alcohol treatment are associated with the cognitive deficits seen during abstinence which impact on treatment efficacy and quality of life. Studies on organotypic cultures also demonstrate the importance of glucocorticoids in the neuropathological consequences of alcohol dependence.

Activation of the hypothalamic-pituitary-adrenal axis by addictive drugs: different pathways, common outcome

Addictive drugs (opiates, ethanol, cannabinoids (CBs), nicotine, cocaine, amphetamines) induce activation of the hypothalamic-pituitary-adrenal (HPA) axis, with the subsequent release of adrenocorticotropic hormone and glucocorticoids. The sequence of events leading to HPA activation appears to start within the brain, suggesting that activation is not secondary to peripheral homeostatic alterations. The precise neurochemical mechanisms and brain pathways involved are markedly dependent on the particular drug, although it is assumed that information eventually converges into the hypothalamic paraventricular nucleus (PVN). Whereas some drugs may act on the hypothalamus or directly within PVN neurons (i.e. ethanol), others exert their primary action outside the PVN (i.e. CBs, nicotine, cocaine). Corticotropin-releasing hormone (CRH) has a critical role in most cases, but the changes in c-fos and CRH gene expression in the PVN also reveal differences among drugs. More studies are needed to understand how addictive drugs act on this important neuroendocrine system and their functional consequences.

Type 7 adenylyl cyclase-mediated hypothalamic-pituitary-adrenal axis responsiveness: influence of ethanol and sex

Although ethanol has been considered to be an anxiolytic agent, consumption of ethanol has also been shown to increase plasma adrenocorticotropin and glucocorticoids. The corticotrophin-releasing factor (CRF) receptor 1alpha (CRF-R1) is a G protein-coupled receptor that activates adenylyl cyclase (AC), leading to adrenocorticotropin (and subsequently glucocorticoid) release into the circulation. There are nine members of the membrane-bound AC family, and the type 7 AC (AC7) is most sensitive to ethanol, which enhances the responsiveness of AC7 to G protein-coupled receptor activation. We determined the time course of ethanol's effect on plasma adrenocorticotropin and corticosterone levels in male and female AC7 transgenic (Adcy7(huTG)) mice (in which AC7 is overexpressed in neural tissue) and AC7 heterozygous knockdown [Adcy7(+/-)] mice (in which AC7 is underexpressed in neural tissue), and their respective littermate controls [wild type (WT)]. CRF-R1 mRNA and mRNA and protein for different forms of ACs were measured by using gene expression arrays, quantitative reverse transcription-polymerase chain reaction, and immunoblotting in pituitaries of all animals. Our results demonstrated increased levels of AC7 in pituitary of Adcy7(huTG) mice and decreased levels in pituitary of Adcy7(+/-) mice compared with WT animals. Male and female Adcy7(huTG) mice displayed higher plasma adrenocorticotropin and corticosterone levels than WT and/or Adcy7(+/-) mice after ethanol injection. Female mice displayed higher adrenocorticotropin and corticosterone levels after ethanol injection than males, regardless of genotype. The data provide evidence for an integral role of AC7 in the increase of plasma adrenocorticotropin and corticosterone levels during alcohol intoxication.

Human and laboratory rodent low response to alcohol: is better consilience possible?

If people are brought into the laboratory and given alcohol, there are pronounced differences among individuals in many responses to the drug. Some participants in alcohol challenge protocols show a cluster of 'low level of responses to alcohol' determined by observing post-drinking-related changes in subjective, motor and physiological effects at a given dose level. Those individuals characterized as having low level of response (LR) to alcohol have been shown to be at increased risk for a lifetime diagnosis of alcohol dependence (AD), and this relationship between low LR and AD appears to be in part genetic. LR to alcohol is an area where achieving greater consilience between the human and the rodent phenotypes would seem to be highly likely. However, despite extensive data from both human and rodent studies, few attempts have been made to evaluate the human and animal data systematically in order to understand which aspects of LR appear to be most directly comparable across species and thus the most promising for further study. We review four general aspects of LR that could be compared between humans and laboratory animals: (1) behavioral measures of subjective intoxication; (2) body sway; (3) endocrine responses; and (4) stimulant, autonomic and electrophysiological responses. None of these aspects of LR provide completely face-valid direct comparisons across species. Nevertheless, one of the most replicated findings in humans is the low subjective response, but, as it may reflect either aversively valenced and/or positively valenced responses to alcohol as usually assessed, it is unclear which rodent responses are analogous. Stimulated heart rate appears to be consistent in animal and human studies, although at-risk subjects appear to be more rather than less sensitive to alcohol using this measure. The hormone and electrophysiological data offer strong possibilities of understanding the neurobiological mechanisms, but the rodent data in particular are rather sparse and unsystematic. Therefore, we suggest that more effort is still needed to collect data using refined measures designed to be more directly comparable in humans and animals. Additionally, the genetically mediated mechanisms underlying this endophenotype need to be characterized further across species.

Ethanol modulates corticotropin releasing hormone release from the rat hypothalamus: does acetaldehyde play a role?

BACKGROUND AND METHODS

Ethanol (EtOH) activates hypothalamic-pituitary-adrenal (HPA) axis, resulting in adrenocorticotropin hormone, glucocorticoid release, and in modifications of the response of the axis to other stressors. The initial site of EtOH action within the HPA system seems to be the hypothalamus. Thus, to determine the mechanisms responsible for these effects, we investigated: (i) whether EtOH was able to release corticotrophic releasing hormone (CRH) from incubated hypothalamic explants; (ii) whether acetaldehyde (ACD), its first metabolite formed in the brain by catalase activity, might play a role in EtOH activity. To this aim, rat hypothalamic explants were incubated with: (i) medium containing EtOH at 32.6 x 10(3) microM; (ii) different concentration of ACD (1, 3, 10, and 30 microM); (iii) EtOH plus 3amino-1,2,4-triazole (3AT, 32 x 10(3) microM) an inhibitor of cerebral catalase; (iv) ACD plus D-penicillamine (DP, 50.3 x 10(3) microM) an ACD-trapping agent. CRH levels were evaluated by a radioimmunoassay.

RESULTS

Incubation with EtOH induced a 7-fold increase in CRH secretion, with respect to basal levels; ACD was able to stimulate CRH release in a dose-dependent manner; the inhibition of cerebral catalase by 3AT blocked EtOH-induced CRH outflow; the inactivation of ACD by DP reverted the ACD-stimulating effect on CRH secretion.

CONCLUSIONS

These data show that both EtOH and acetaldehyde are able to increase hypothalamic CRH release from the rat hypothalamus and that acetaldehyde itself appears to be the mediator of EtOH activity.

The role of oestradiol in sexually dimorphic hypothalamic-pituitary-adrena axis responses to intracerebroventricular ethanol administration in the rat

Systemic ethanol (EtOH) administration activates the hypothalamic-pituitary-adrenal (HPA) axis of rats in a sexually dimorphic manner. The present studies tested the role played by the central nervous system (CNS) in this phenomenon. To localise the effects of the drug to the brain, we utilised an experimental paradigm whereby a small, nontoxic amount of the drug was delivered via intracerebroventricular (i.c.v.) injection. EtoH administered i.c.v. rapidly diffuses throughout the cerebrospinal fluid and brain, and does not cause neuronal damage or have any long-term physiological or behavioural effects. Experimental groups included intact males, intact cycling females, and ovariectomised (OVX) animals with or without replacement oestradiol (E(2)). Intracerebroventricular EtOH-induced HPA hormonal activation was determined by measuring plasma adrenocorticotrophin (ACTH) levels. Activation of brain areas that both regulate HPA function and are responsive to gonadal hormones was determined using expression of the transcription factor c-fos (Fos) as a marker of neuronal activity. We observed sex- and oestrous cycle- dependent differences in HPA activation by EtOH as measured by both these parameters. ACTH secretion was highest in females in pro-oestrus or oestrus, just prior to or after the endogenous peak of E(2), as was Fos expression in the paraventricular nucleus of the hypothalamus (PVN) and the locus coreuleus (LC) of the brainstem. In OVX animals, E(2) replacement caused an increase in PVN and LC Fos expression in response to i.c.v. EtOH compared to OVX controls, but a decrease in ACTH secretion. Taken together, these results indicate that at the level of the CNS, EtOH stimulates HPA activity more robustly at times when the effects of E(2) are high, but that E(2) alone is not responsible for this effect. The data further suggest that the LC plays an important role in the circuitry, which appears to be different from that activated following the systemic administration of EtOH.

Ethanol induction of steroidogenesis in rat adrenal and brain is dependent upon pituitary ACTH release and de novo adrenal StAR synthesis

The mechanisms of ethanol actions that produce its behavioral sequelae involve the synthesis of potent GABAergic neuroactive steroids, specifically the GABAergic metabolites of progesterone, (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha,5alpha-THP), and deoxycorticosterone, (3alpha,5alpha)-3,21-dihydroxypregnan-20-one. We investigated the mechanisms that underlie the effect of ethanol on adrenal steroidogenesis. We found that ethanol effects on plasma pregnenolone, progesterone, 3alpha,5alpha-THP and cortical 3alpha,5alpha-THP are highly correlated, exhibit a threshold of 1.5 g/kg, but show no dose dependence. Ethanol increases plasma adrenocorticotropic hormone (ACTH), adrenal steroidogenic acute regulatory protein (StAR), and adrenal StAR phosphorylation, but does not alter levels of other adrenal cholesterol transporters. The inhibition of ACTH release, de novo adrenal StAR synthesis or cytochrome P450 side chain cleavage activity prevents ethanol-induced increases in GABAergic steroids in plasma and brain. ACTH release and de novo StAR synthesis are independently regulated following ethanol administration and both are necessary, but not sufficient, for ethanol-induced elevation of plasma and brain neuroactive steroids. As GABAergic steroids contribute to ethanol actions and ethanol sensitivity, the mechanisms of this effect of ethanol may be important factors that contribute to the behavioral actions of ethanol and risk for alcohol abuse disorders.

Role of various neurotransmitters in mediating the long-term endocrine consequences of prenatal alcohol exposure

Adult rats and mice born to dams exposed to alcohol (fetal alcohol-exposed [FAE]) exhibit enhanced activity of their hypothalamic-pituitary-adrenal (HPA) axis when exposed to stressors. However, the mechanisms responsible for this phenomenon remain incompletely understood. Here two possibilities are reviewed: one that pertains to nitric oxide (NO), an unstable gas that stimulates the HPA axis; and one that focuses on catecholamines, which also stimulate this axis. Significant alterations were not observed in levels of NO synthase, the enzyme responsible for NO formation, in the paraventricula nucleus (PVN) of FAE rats. However, the stimulatory influence of this gas on the hypothalamic-pituitary-adrenal (HPA) axis was enhanced in these animals, thereby providing a mechanism likely to participate in the neuroendocrine hyperactivity that is the hallmark of this model. It was also recently shown that, while the ability of catecholamines to release adrenocorticotropic hormone (ACTH) was comparable in control rats and rats exposed to alcohol during embryonic development, there was a significant upregulation of the C1 brain-stem region when these latter animals were exposed to mild footshocks. Since this region sends prominent projections to the PVN, its increased activity may participate in the HPA axis hyperactivity observed in FAE offspring. Finally, microarray technology was used to search for potential differences in genes present in the brains of control and FAE mice. When these brains were collected on day 17.5 of embryonic development, several genes were upregulated, while others were downregulated, which may provide potential new candidates that mediate the influence of prenatal alcohol on the HPA axis of adult offspring.

Stress, alcohol and drug interaction: an update of human research

A challenging question that continues unanswered in the field of addiction is why some individuals are more vulnerable to substance use disorders than others. Numerous risk factors for alcohol and other drugs of abuse, including exposure to various forms of stress, have been identified in clinical studies. However, the neurobiological mechanisms that underlie this relationship remain unclear. Critical neurotransmitters, hormones and neurobiological sites have been recognized, which may provide the substrates that convey individual differences in vulnerability to addiction. With the advent of more sophisticated measures of brain function in humans, such as functional imaging technology, the mechanisms and neural pathways involved in the interactions between drugs of abuse, the mesocorticolimbic dopamine system and stress systems are beginning to be characterized. This review provides a neuroadaptive perspective regarding the role of the hormonal and brain stress systems in drug addiction with a focus on the changes that occur during the transition from occasional drug use to drug dependence. We also review factors that contribute to different levels of hormonal/brain stress activation, which has implications for understanding individual vulnerability to drug dependence. Ultimately, these efforts may improve our chances of designing treatment strategies that target addiction at the core of the disorder.