Proopiomelanocortin messenger RNA is decreased in the mediobasal hypothalamus of rats made dependent on ethanol

Alcohol Withdrawal and the Associated Mood Disorders-A Review

Recreational use of alcohol is a social norm in many communities worldwide. Alcohol use in moderation brings pleasure and may protect the cardiovascular system. However, excessive alcohol consumption or alcohol abuse are detrimental to one's health. Three million deaths due to excessive alcohol consumption were reported by the World Health Organization. Emerging evidence also revealed the danger of moderate consumption, which includes the increased risk to cancer. Alcohol abuse and periods of withdrawal have been linked to depression and anxiety. Here, we present the effects of alcohol consumption (acute and chronic) on important brain structures-the frontal lobe, the temporal lobe, the limbic system, and the cerebellum. Apart from this, we also present the link between alcohol abuse and withdrawal and mood disorders in this review, thus drawing a link to oxidative stress. In addition, we also discuss the positive impacts of some pharmacotherapies used. Due to the ever-rising demands of life, the cycle between alcohol abuse, withdrawal, and mood disorders may be a never-ending cycle of destruction. Hence, through this review, we hope that we can emphasise the importance and urgency of managing this issue with the appropriate approaches.

Acupuncture Alleviates Anxiety and 22-kHz Ultrasonic Vocalizations in Rats Subjected to Repeated Alcohol Administration by Modulating the Brain-Derived Neurotrophic Factor/Corticotropin-Releasing Hormone Signaling Pathway

The Shenmen point (acupuncture point heart 7: HT7), located in the heart meridian, is frequently used to treat mental disorders, including drug addiction, anxiety, and depression. This study aimed to determine how HT7 regulates anxiety and negative emotions caused by repeated alcohol administration, focusing on the amygdala and paraventricular nucleus (PVN). Repeated administration of alcohol (ETOH; 2 g/kg, i.p. injection, 16% v/v) for 14 days increased the corticosterone (CORT) levels, and HT7 stimulation reduced the plasma CORT levels. HT7 stimulation mitigated anxiety-like behaviors and reduced 22-kHz ultrasonic vocalizations in rats receiving repeated ETOH injections. HT7 stimulation increased the amygdala expression of mature brain-derived neurotropic factor (mBDNF) and phosphorylated tropomyosin receptor kinase B (pTrkB) and decreased the PVN corticotropin-releasing hormone (CRH) expression. Amygdala microinjections of the TrkB antagonist ANA-12 (0.1 pmol/1 μL) reversed the increase in PVN CRH levels. The reduced PVN CRH levels were regulated by CRH-expressing neurons in the amygdala, and the increased amygdala CRH levels were affected by the HT7-stimulation induced increases in mBDNF. HT7 stimulation alleviates increased stress hormone levels and mitigates anxiety and negative emotions caused by repeated ETOH administration. These results provide scientific support for the clinical use of acupuncture to treat various alcoholism-induced diseases.

HPA axis responses to acute exercise differ in smokers and non-smokers

Physical exercise has been proposed as an adjunct in addiction treatment, including tobacco cigarette smoking. The physiological and biochemical mechanisms that could be affected by physical exercise in smokers and that could help quit smoking have not been investigated yet.

OBJECTIVE

To investigate whether the effects of acute exercise on smoking behavior and HPA axis activation in smokers are intensity-dependent.

METHODS

Healthy, non-systematically exercising individuals [25 smokers (age: 33±1.4 years) and 10 non-smokers (age: 34±2.1 years)] underwent three trials [moderate intensity (MI), high intensity (HI) exercise, control (C)] in a counterbalanced order, after an overnight fast and smoking abstinence, separated by at least six days. MI involved cycling at 50-60% of Heart Rate Reserve (HRR) for 30 min, HI involved cycling at 65-75% HRR for 30 min, while in C participants rested for 30 min. Time till the first cigarette following each trial was recorded. Smoking urge was evaluated and blood samples, [analyzed for β-endorphin (β-E), adrenocorticotropic hormone (ACTH), cortisol and catecholamines], were obtained prior to and immediately after each trial.

RESULTS

β-E, ACTH, catecholamines and cortisol responses to exercise were intensity-dependent and differed in smokers and non-smokers. Resting β-E levels were 2-2.5 times lower in smokers compared to non-smokers. HI resulted in increased β-E levels in both groups, with smokers exhibiting similar levels to that observed in non-smokers. Although smoking urge did not change post-exercise in smokers, time till first cigarette increased following both MI (64.6%) and HI (77.9%) compared to C.

CONCLUSIONS

HPA axis activation in response to exercise may differ between smokers and non-smokers. Smokers have lower resting levels of β-E compared to non-smokers and, since HI exercise increases β-E to similar levels to those of non-smokers and delays smoking, this may be used as an adjunct in smoking cessation.

The Role of Melanocortin Plasticity in Pain-Related Outcomes After Alcohol Exposure

The global COVID-19 pandemic has shone a light on the rates and dangers of alcohol misuse in adults and adolescents in the US and globally. Alcohol exposure during adolescence causes persistent molecular, cellular, and behavioral changes that increase the risk of alcohol use disorder (AUD) into adulthood. It is established that alcohol abuse in adulthood increases the likelihood of pain hypersensitivity and the genesis of chronic pain, and humans report drinking alcohol to relieve pain symptoms. However, the longitudinal effects of alcohol exposure on pain and the underlying CNS signaling that mediates it are understudied. Specific brain regions mediate pain effects, alcohol effects, and pain-alcohol interactions, and neural signaling in those brain regions is modulated by neuropeptides. The CNS melanocortin system is sensitive to alcohol and modulates pain sensitivity, but this system is understudied in the context of pain-alcohol interactions. In this review, we focus on the role of melanocortin signaling in brain regions sensitive to alcohol and pain, in particular the amygdala. We also discuss interactions of melanocortins with other peptide systems, including the opioid system, as potential mediators of pain-alcohol interactions. Therapeutic strategies that target the melanocortin system may mitigate the negative consequences of alcohol misuse during adolescence and/or adulthood, including effects on pain-related outcomes.

Acupuncture attenuates alcohol dependence through activation of endorphinergic input to the nucleus accumbens from the arcuate nucleus

A withdrawal-associated impairment in β-endorphin neurotransmission in the arcuate nucleus (ARC) of the hypothalamus is associated with alcohol dependence characterized by a chronic relapsing disorder. Although acupuncture activates β-endorphin neurons in the ARC projecting to the nucleus accumbens (NAc), a role for ARC β-endorphin neurons in alcohol dependence and acupuncture effects has not been examined. Here, we show that acupuncture at Shenmen (HT7) points attenuates behavioral manifestation of alcohol dependence by activating endorphinergic input to the NAc from the ARC. Acupuncture attenuated ethanol withdrawal tremor, anxiety-like behaviors, and ethanol self-administration in ethanol-dependent rats, which are mimicked by local injection of β-endorphin into the NAc. Acupuncture also reversed the decreased β-endorphin levels in the NAc and a reduction of neuronal activity in the ARC during ethanol withdrawal. These results suggest that acupuncture may provide a novel, potential treatment strategy for alcohol use disorder by direct activation of the brain pathway.

Exploring Sex Differences in the Attenuation of Ethanol Drinking by Naltrexone in Dependent Rats During Early and Protracted Abstinence

BACKGROUND

Despite considerable efforts, few drugs are available for the treatment of alcohol (ethanol [EtOH]) use disorder (AUD). EtOH directly or indirectly modulates several aspects of the central nervous system, including neurotransmitter/neuromodulator systems. Relapse vulnerability is a challenge for the treatment of EtOH addiction. EtOH withdrawal symptoms create motivational states that lead to compulsive EtOH drinking and relapse even after long periods of abstinence. Among the therapeutics to treat AUD, naltrexone (NTX) is a pharmacological treatment for relapse. The present study evaluated the effect of NTX on EtOH drinking in male and female EtOH-dependent rats during abstinence.

METHODS

Wistar rats (males and females) were first trained to orally self-administer 10% EtOH. Half of the rats were then made dependent by chronic intermittent EtOH (CIE) vapor exposure, and the other half were exposed to air. Using this model, rats exhibit somatic and motivational signs of withdrawal. At the end of EtOH vapor (or air) exposure, the rats were tested for the effects of NTX (10 mg/kg, oral) on EtOH self-administration at 3 abstinence time points: acute abstinence (A-Abst, 8 hours), late abstinence (L-Abst, 2 weeks), and protracted abstinence (P-Abst, 6 weeks).

RESULTS

NTX decreased EtOH intake in nondependent rats, regardless of sex and abstinence time point. In postdependent rats, NTX decreased EtOH intake only at a delayed abstinence time point (P-Abst) in males, whereas it similarly reduced EtOH drinking in females at all abstinence time points.

CONCLUSIONS

The therapeutic efficacy of NTX depends on the time of intervention during abstinence and is different between males and females. The data further suggest that EtOH dependence causes different neuroadaptations in male and female rats, reflected by differential effects of NTX. The results underscore the significance of considering the duration of EtOH abstinence and sex as a biological variable as important factors when developing pharmacotherapies for AUD.

Hypothalamic neuropeptide signaling in alcohol addiction

The hypothalamus is now known to regulate alcohol intake in addition to its established role in food intake, in part through neuromodulatory neurochemicals termed neuropeptides. Certain orexigenic neuropeptides act in the hypothalamus to promote alcohol drinking, although they affect different aspects of the drinking response. These neuropeptides, which include galanin, the endogenous opioid enkephalin, and orexin/hypocretin, appear to stimulate alcohol intake not only through mechanisms that promote food intake but also by enhancing reward and reinforcement from alcohol. Moreover, these neuropeptides participate in a positive feedback relationship with alcohol, whereby they are upregulated by alcohol intake to promote even further consumption. They contrast with other orexigenic neuropeptides, such as melanin-concentrating hormone and neuropeptide Y, which promote alcohol intake under limited circumstances, are not consistently stimulated by alcohol, and do not enhance reward. They also contrast with neuropeptides that can be anorexigenic, including the endogenous opioid dynorphin, corticotropin-releasing factor, and melanocortins, which act in the hypothalamus to inhibit alcohol drinking as well as reward and therefore counter the ingestive drive promoted by orexigenic neuropeptides. Thus, while multiple hypothalamic neuropeptides may work together to regulate different aspects of the alcohol drinking response, excessive signaling from orexigenic neuropeptides or inadequate signaling from anorexigenic neuropeptides can therefore allow alcohol drinking to become dysregulated.

Nicotine withdrawal and stress-induced changes in pain sensitivity: a cross-sectional investigation between abstinent smokers and nonsmokers

Chronic smoking has been linked with alterations in endogenous pain regulation. These alterations may be pronounced when individuals quit smoking because nicotine withdrawal produces a variety of psychological and physiological symptoms. Smokers interested in quitting (n = 98) and nonsmokers (n = 37) completed a laboratory session including cold pressor test (CPT) and heat thermal pain. Smokers set a quit date and completed the session after 48 h of abstinence. Participants completed the pain assessments once after rest and once after stress. Cardiovascular and nicotine withdrawal measures were collected. Smokers showed blunted cardiovascular responses to stress relative to nonsmokers. Only nonsmokers had greater pain tolerance to CPT after stress than after rest. Lower systolic blood pressure was related to lower pain tolerance. These findings suggest that smoking withdrawal is associated with blunted stress response and increased pain sensitivity.

Targeting central melanocortin receptors: a promising novel approach for treating alcohol abuse disorders

The melanocortin (MC) peptides are produced centrally by propiomelanocortin (POMC) neurons within the arcuate nucleus of the hypothalamus and act through five seven-transmembrane G-protein coupled melanocortin receptor (MCR) subtypes. The MC3R and MC4R subtypes, the most abundant central MCRs, are widely expressed in brain regions known to modulate neurobiological responses to ethanol, including regions of the hypothalamus and extended amygdala. Agouti-related protein (AgRP), also produced in the arcuate nucleus, is secreted in terminals expressing MCRs and functions as an endogenous MCR antagonist. This review highlights recent genetic and pharmacological findings that have implicated roles for the MC and AgRP systems in modulating ethanol consumption. Ethanol consumption is associated with significant alterations in the expression levels of various MC peptides/protein, which suggests that ethanol-induced perturbations of MC/AgRP signaling may modulate excessive ethanol intake. Consistently, MCR agonists decrease, and AgRP increases, ethanol consumption in mice. MCR agonists fail to blunt ethanol intake in mutant mice lacking the MC4R, suggesting that the protective effects of MCR agonists are modulated by the MC4R. Interestingly, recent evidence reveals that MCR agonists are more effective at blunting binge-like ethanol intake in mutant mice lacking the MC3R, suggesting that the MC3R has opposing effects on the MC4R. Finally, mutant mice lacking AgRP exhibit blunted voluntary and binge-like ethanol drinking, consistent with pharmacological studies. Collectively, these preclinical observations provide compelling evidence that compounds that target the MC system may provide therapeutic value for treating alcohol abuse disorders and that the utilization of currently available MC-targeting compounds- such as those being used to treat eating disorders- may be used as effective treatments to this end.

Decreased immunoreactivity of the polypeptide precursor pro-opiomelanocortin (POMC) and the prohormone convertase pc1/3 after chronic ethanol exposure in Sprague-Dawley rats

BACKGROUND

The melanocortin (MC) peptides and opioid peptide β-endorphin are cleaved from the polypeptide precursor pro-opiomelanocortin (POMC). POMC-derived peptides are generated by extensive posttranslational processing that involves several enzymes including prohormone convertase 1/3 and 2 (PC1/3 and PC2). Because ethanol (EtOH) decreases POMC mRNA levels, we determined whether the exposure to an EtOH-containing diet (ED) would significantly reduce central immunoreactivity (IR) of POMC, PC1/3, PC2, and β-endorphin.

METHODS

Male Sprague-Dawley rats were given 18 days of access to a normal rodent chow or a control diet (CD), or short-term (4 days) or long-term (18 days) access to an ED. At the end of the study, rats were perfused with 4% paraformaldehyde, and their brains were sectioned into sets for processing with POMC, PC1/3, PC2, and β-endorphin IR.

RESULTS

Rats exposed to an ED for 18 days (ED18) exhibited significant reductions of POMC and PC1/3 IR in the arcuate nucleus of the hypothalamus (Arc) relative to rats pair-fed a CD. On the other hand, rats exposed to an ED did not show any changes of central β-endorphin or PC2 IR relative to rats pair-fed a CD, regardless of length of exposure. Because there were no differences in body weights or caloric intake between the CD and ED groups, reductions of POMC and PC1/3 IR in ED-treated rats are best explained by EtOH exposure rather than altered energy balance.

CONCLUSIONS

This study shows that EtOH site-specifically reduces POMC and PC1/3 IR in rat brain. These observations are consistent with EtOH-induced reductions of α-melanocyte-stimulating hormone (α-MSH) and POMC IR that were previously reported. As MC agonists have been shown to blunt EtOH intake in rodents, exogenous MC receptor agonists, as well as targets that may increase the synthesis of endogenous α-MSH (e.g., PC1/3), may have therapeutic value for treating alcohol abuse disorders and alcoholism.

Locomotor sensitization to EtOH: contribution of β-Endorphin

Alcohol use disorders, like all drug addictions, involve a constellation of adaptive changes throughout the brain. Neural activity underlying changes in the rewarding properties of alcohol reflect changes in dopamine transmission in mesolimbic and nigrostriatal pathways and these effects are modulated by endogenous opioids such as β-Endorphin. In order to study the role of β-Endorphin in the development of locomotor sensitization to repeated EtOH exposure, we tested transgenic mice that vary in their capacity to synthesize this peptide as a result of constitutive modification of the Pomc gene. Our results indicate that mice deficient in β-Endorphin show attenuated locomotor activation following an acute injection of EtOH (2.0 g/kg) and, in contrast to wildtype mice, fail to demonstrate locomotor sensitization after 12 days of repeated EtOH injections. These data support the idea that β-Endorphin modulates the locomotor effects of EtOH and contributes to the neuroadaptive changes associated with chronic use.

Enhanced pain perception prior to smoking cessation is associated with early relapse

Accumulated evidence suggests that nicotine induces analgesia, and endogenous pain regulatory mechanisms may be altered by chronic smoking. The extent to which individual differences in pain perception are related to smokers' ability to abstain from smoking has not been directly examined. Seventy-one smokers who were interested in quitting completed a pre-cessation laboratory session which included the cold pressor test (CPT). Pain ratings were collected during and after CPT. Also, mood changes, cardiovascular measures, and salivary cortisol samples were evaluated prior to, during, and after CPT. Participants attended 4 weekly follow-up assessment sessions after their quit day. Cox regression analysis revealed that higher pain ratings during and after CPT predicted greater risk for smoking relapse. These results remained significant after affective and physiological responses to CPT were controlled, suggesting that pain ratings prior to smoking cessation are potentially useful in identifying smokers who are at greater risk of early smoking relapse and may reflect underlying putative risk for nicotine dependence and relapse.

Beta-endorphin mediates behavioral despair and the effect of ethanol on the tail suspension test in mice

BACKGROUND

The opioid peptide beta-endorphin (beta-E) is synthesized and released in response to stressful stimuli as well as acute alcohol administration. The release of beta-E following exposure to an inescapable aversive situation may mediate behaviors that contribute to allostasis of the stress response. The present study examines the effects of beta-E on immobility in assays involving inescapable stress, both under basal conditions and after acute administration of EtOH.

METHODS

Female and male transgenic mice with varying capacities to translate beta-E were subjected to either the forced swim (FST, Experiment 1) or the tail suspension test (TST, Experiment 2). In Experiment 3, mice were divided into three groups based on hormonal status (male, female-estrous, and female-nonestrous) and injected with either 1 g/kg EtOH or equivolume saline 14 minutes prior to behavioral assessment on the TST.

RESULTS

Experiments 1 and 2 demonstrated a direct relationship between beta-E levels and immobility. There were also sex differences in behavior in these tests, with males displaying more immobility than females. A main effect of genotype in Experiment 3 replicated findings in Experiments 1 and 2. There was also an effect of EtOH (increasing immobility) and a significant interaction reflecting a particularly robust effect of the drug in mice with low beta-E. In addition, there were interactions between beta-E, EtOH effects, and hormonal status.

CONCLUSIONS

These findings support the contention that beta-E moderates behavioral responses to stressful stimuli and suggest a role for this peptide in coping behavior. Furthermore, the effects of EtOH on the response to stress may be mediated by beta-E. Sex differences in this influence may contribute to sex differences in disease susceptibility and expression.

CB1 receptor blockade decreases ethanol intake and associated neurochemical changes in fawn-hooded rats

BACKGROUND

This study was undertaken to identify the neurochemical changes underlying the attenuation of voluntary ethanol intake induced by the cannabinoid CB1 receptor antagonist AM251 in fawn-hooded rats.

METHODS

Rats were exposed to the 2-bottle-choice paradigm (ethanol 10% v/v or water) for 15 days. After this period, rats received AM251 (3 to 6 mg/kg, i.p.) or vehicle.

RESULTS

Voluntary ethanol intake decreased (30%) with the administration of incremental dosages of AM251 (3 mg/kg, 5 days and 6 mg/kg, 5 days) in rats with acquired high preferring ethanol consumption (>3.5 g of ethanol/kg/d). Ethanol intake significantly decreased proopiomelanocortin expression in the arcuate nucleus (38.31%) and micro-opioid-DAMGO-stimulated [(35)S]-GTPgamma binding in the caudate-putamen (40%), nucleus accumbens core (AccC) (32.87%), and shell (AccS) (34.21%). Moreover, ethanol intake increased tyrosine hydroxylase (TH) gene expression in the substantia nigra (24%) and ventral tegmental area (23%) and corticotrophin-releasing gene expression in the paraventricular hypothalamic nucleus (41.6%). The reduction of ethanol intake induced by AM251 was associated with blockade or significant reduction of the changes produced by ethanol in the expression of these genes in key regions related to drug dependence. Interestingly, treatment with AM251 reduced (20%) TH gene expression in rats drinking only water. In this respect, the action of AM251 in reducing TH gene expression may not be specific.

CONCLUSION

Taken together, these results revealed that blockade of cannabinoid CB1 receptors (CB1r) decreased voluntary ethanol intake in ethanol-habituated rats by normalizing the neurochemical alterations induced by ethanol.

Influence of beta-Endorphin on anxious behavior in mice: interaction with EtOH

RATIONALE

The opioid peptide beta-endorphin (beta-E) is synthesized by the pro-opiomelanocortin gene in response to environmental stressors and alcohol administration and is implicated in the behavioral sequelae associated with these stimuli.

OBJECTIVES

We sought to determine the influence of beta-E on the stress response by evaluating basal measures of anxiety as well as on EtOH-induced anxiolytic behavior using transgenic mice that differ with respect to beta-E.

METHODS

Anxious behavior was evaluated for male and female heterozygous, wild-type, and beta-E knockout mice using the Light-Dark Box and Plus Maze assays. Subsequent tests evaluated behavior 20 min after administration of intraperitoneal saline or EtOH (0.5, 1.0, and 1.5 g/kg).

RESULTS

We observed a direct relationship between beta-E levels and the percentage of entries into open arms of the Plus Maze as well as the time spent in either the open arms or the light compartment of the Light-Dark box during basal conditions, suggesting that this peptide normally inhibits anxious behavior. However, mice lacking beta-E demonstrated an exaggerated anxiolytic response to EtOH in these assays.

CONCLUSIONS

These data suggest that beta-E moderates the response to stressful stimuli and supports the hypothesis that this peptide influences the behavioral effects of EtOH.

Attenuated beta endorphin response to acute stress is associated with smoking relapse

Stress has been cited as an important precipitator of smoking relapse. Dysregulation of neurobiological pathways related to stress might mediate effects of stress on smoking relapse. This study assessed the extent to which beta endorphin response to stress is associated with early smoking relapse. Forty-five smokers interested in smoking cessation were recruited and attended a laboratory session 24 h following the beginning of their abstinence period. During this session beta endorphin samples were collected before and after performing two acute stressors (public speaking and cognitive tasks). Participants also attended four weekly follow-up sessions to assess their smoking status. Results were compared between smokers who relapsed within the 4-week follow-up period and those who maintained abstinence over the same period. The acute stressors were associated with significant increases in measures of craving and withdrawal symptoms (ps<0.01). While baseline measures of beta endorphin did not differ between relapsers and successful abstainers (F<1), results demonstrated that smokers who relapsed exhibited attenuated beta endorphin response to the two stressors relative to those who maintained abstinence over the same period (ps<05). These results support recent evidence indicating that a dysregulated stress response is a key component in predicting smoking relapse.

Decreased immunoreactivity of the melanocortin neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) after chronic ethanol exposure in Sprague-Dawley rats

BACKGROUND

The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor proopiomelanocortin (POMC). Recent pharmacologic and genetic evidence suggests that MC receptor (MCR) signaling modulates neurobiologic responses to ethanol and ethanol intake. Because ethanol decreases POMC mRNA levels, we determined if exposure to an ethanol-containing diet (ED) would significantly reduce central immunoreactivity of the MC peptide alpha-MSH in rats. We also determined if ethanol exposure would alter the immunoreactivity of agouti-related protein (AgRP), an endogenous MCR antagonist.

METHODS

Male Sprague-Dawley rats were given 18 days of access to normal rodent chow or a control diet (CD), or short-term (4 days) or long-term (18 days) access to an ED. At the end of the study, rats were perfused with 4% paraformaldehyde and their brains were sectioned into two sets for processing with alpha-MSH or AgRP immunohistochemistry.

RESULTS

Rats exposed to an ED showed significant reductions of central alpha-MSH immunoreactivity relative to rats exposed to a control diet (CD) or normal rodent chow. Ethanol-induced reductions of alpha-MSH immunoreactivity were site-specific and were noted in regions of the hypothalamus and extended amygdala, as well as the paraventricular nucleus of the thalamus. Because there were no differences in body weights or caloric intake between the CD and ED groups, reductions of alpha-MSH immunoreactivity in ED-treated rats are best explained by ethanol exposure rather than altered energy balance. No significant ethanol-induced alterations in hypothalamic AgRP immunoreactivity were detected.

CONCLUSIONS

The present study shows that ethanol site specifically reduces alpha-MSH immunoreactivity in rat brain. These observations, in tandem with recent pharmacologic and genetic studies, suggest that the endogenous MC system modulates neurobiologic responses to ethanol. Thus, compounds which target MCRs may prove to have therapeutic value in the treatment of excessive ethanol consumption and/or the symptoms associated with ethanol withdrawal.

Differences in the Peripheral Levels of ??-endorphin in Response to Alcohol and Stress as a Function of Alcohol Dependence and Family History of Alcoholism

BACKGROUND

Evidence indicates that both genetic and environmental factors, such as stress, may play an important role for the development of alcoholism, while beta-endorphin may be implicated in the control of alcohol consumption. The objective of the present studies was to test the hypothesis that there are differences in the response of the pituitary beta-endorphin system to stress as a function of family history of alcoholism and alcohol dependence.

METHODS

The response of the pituitary beta-endorphin to a placebo or an alcohol (0.50 g ethanol/kg) drink and to a stress task performed 30 min following ingestion of either the placebo or the alcohol drink was measured in social and heavy drinkers with [high risk (HR)] and without [low risk (LR)] a family history of alcoholism. Thus, each subject participated in 4 experimental sessions given on different days in a randomized order. Four groups of subjects were investigated: 1) low risk nonalcoholics (LRNA); 2) high risk nonalcoholics (HRNA), 3) low risk alcoholics (LRA); and 4) high risk alcoholics (HRA). Plasma beta-endorphin was estimated prior to and for 3.5 hr post-stress. Changes in the concentration of plasma beta-endorphin following ingestion of either the placebo or alcohol drink without performance of the stress task served as controls to compare the stress-induced changes.

RESULTS

Basal plasma beta-endorphin levels were higher in LRNA than LRA, HRNA and HRA participants, while basal plasma beta-endorphin levels were higher in LRA than those in HRNA and HRA participants. Furthermore, there was no significant difference in the plasma beta-endorphin levels between HRNA and HRA participants. Stress, induced a significant increase in plasma beta-endorphin concentration in all four groups of participants. However, the stress-induced increase in plasma beta-endorphin levels was more pronounced in LRNA than HRNA, LRA and HRA participants. Thus, alcohol dependence decreased the basal plasma beta-endorphin levels in LR only, as well as the stress induced increase in plasma beta-endorphin levels of participants without, but not of those with, a family history of alcoholism. Alcohol prior to stress attenuated the stress-induced increase in plasma beta-endorphin levels of all four groups of participants.

CONCLUSIONS

The present data indicates that there are differences in both, the basal plasma beta-endorphin levels as well as the response of the pituitary beta-endorphin to stress as a function of family history of alcoholism and alcohol dependence. Thus, in HR individuals a dysfunction in the activity of the pituitary beta-endorphin system predates the development of alcoholism, while in LR individuals it develops following alcohol dependence. Furthermore, alcohol dependence did not alter the alcohol-induced attenuation of beta-endorphin response to stress.

Peripheral influences on central melanocortin neurons

The melanocortins are peptide products of post-translational processing of the pro-opiomelanocortin precursor protein. Melanocortin-expressing neurons are found in the arcuate nucleus of the hypothalamus and the nucleus of the solitary tract in the brain stem. The central melanocortin system is involved in a number of biological functions, including regulation of energy homeostasis. Hypothalamic and brain stem circuits interpret and integrate a number of peripheral inputs to provide a coordinated central response. This review examines the effect of these peripheral signals on central melanocortin signaling.

The opioidergic-alcohol link : implications for treatment

Preclinical and clinical data implicate the endogenous opioid system in alcohol dependence. In vitro studies show that rodent pituitary and hypothalamic tissue responds to acute exposure to alcohol by releasing beta-endorphins. In vivo studies suggest differential activity of endogenous opioid receptors in rodents with high and low alcohol preference. Similarly, humans with a family history of alcohol dependence also show a heightened endorphin response to an acute challenge of alcohol compared with those with no family history of alcohol dependence.The effects of opioid agonists and antagonists on rodent and human alcohol consumption further support the opioid-alcohol link. In rodents and humans, small doses of opioid agonists increase alcohol consumption, while pretreatment with large doses decreases consumption. The opioid antagonist naltrexone decreases rodent alcohol consumption, particularly in low doses under acute and intermittent schedules. Most clinical trials in patients with alcohol dependence support modest therapeutic effects of naltrexone in decreasing alcohol consumption. Efforts to identify subgroups of alcohol-dependent patients responsive to naltrexone, as well as psychosocial and pharmacological augmentation strategies, may further improve the clinical usefulness of the drug.

Vasoactive intestinal peptide and corticotropin-releasing hormone increase beta-endorphin release and proopiomelanocortin messenger RNA levels in primary cultures of hypothalamic cells: effects of acute and chronic ethanol treatment

BACKGROUND

beta-Endorphin (beta-EP) neurons are involved in ethanol's action on a variety of brain functions, including positive reinforcement. These neurons are innervated by vasoactive intestinal peptide (VIP)-containing and corticotropin-releasing hormone (CRH)-containing neurons in the hypothalamus. Whether these neuropeptides affect beta-EP neuronal function in the presence or absence of ethanol has not previously been determined.

METHODS

The authors determined the effects of VIP and CRH on gene expression and peptide release from beta-EP neurons in primary cultures of mediobasal hypothalamic cells. The effects of receptor antagonists on VIP- and CRH-induced beta-EP release was determined. Furthermore, the authors studied the effects of acute and chronic treatment with ethanol on the response of beta-EP neurons to VIP and CRH. Real-time reverse-transcription polymerase chain reaction was used for messenger RNA (mRNA) detection, and radioimmunoassay was used for hormone measurements.

RESULTS

We show that beta-EP neurons responded concentration dependently to VIP and CRH treatments by increasing both beta-EP release and proopiomelanocortin mRNA expression. Simultaneous treatment with a nonspecific receptor antagonist reduced the ability of CRH or VIP to induce beta-EP release from mediobasal hypothalamic cells. Acute treatment with ethanol increased beta-EP neuronal gene expression and the secretory response to CRH and VIP. However, previous exposure to chronic ethanol reduced the CRH and VIP responses of these neurons.

CONCLUSIONS

These results indicate that VIP and CRH stimulate beta-EP release from hypothalamic cells in primary cultures and that the stimulatory and adaptive responses of beta-EP neurons to ethanol may involve alteration in the responsiveness of beta-EP-secreting neurons to CRH and VIP.

Alcohol and gene expression in the central nervous system

AIMS

To describe recent research focusing on the analysis of gene and protein expression relevant to understanding ethanol consumption, dependence and effects, in order to identify common themes.

METHODS

A selective literature search was used to collate the relevant data.

RESULTS

Over 160 genes have been individually assessed before or after ethanol administration, as well as in genetically selected lines. Techniques for studying gene expression include northern blots, differential display, real time reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. More recently, high throughput functional genomic technology, such as DNA microarrays, has been used to examine gene expression. Recent gene expression analyses have dramatically increased the number of candidate genes (nine array papers have illuminated 600 novel gene transcripts that may contribute to alcohol abuse and alcoholism).

CONCLUSIONS

Although functional genomic experiments (transcriptome analysis) have failed to identify a single alcoholism gene, they have illuminated important pathways and gene products that may contribute to the risk of alcohol abuse and alcoholism.

Opioids and alcoholism

Although far from conclusive, evidence implicating the endogenous opioid system in the development and maintenance of alcoholism is growing. Currently available data suggest that ethanol increases opioid neurotransmission and that this activation is part of the mechanism responsible for its reinforcing effects. Findings from preclinical research indicate that ethanol consumption and ethanol-induced dopamine (DA) release are both reduced by opioid antagonists. Individual differences in endogenous opioid activity have been linked to inherited risks for alcoholism in studies comparing ethanol-preferring and nonpreferring rats, as well as in studies using targeted gene mutation (knockout) strategies. To a large extent, findings from human studies have paralleled those from the preclinical work. Persons who differ in family history of alcoholism have been shown to also differ in basal beta-endorphin activity, beta-endorphin response to alcohol, and subjective and HPA axis hormonal response to opioid antagonists. Findings from clinical trials indicate that opioid antagonists may reduce ethanol consumption in alcoholics, particularly in persons who have resumed drinking. Nevertheless, many questions remain unanswered about the use of opioid antagonists in alcoholism treatment and about the exact role of the opioid system in ethanol preference and reward. The progression of knowledge in this field suggests that many of these questions are imminently answerable, as our ability to characterize relationships between opioid activity and human behavior continues to develop. This paper summarizes both the progress that has been made and the gaps that remain in our understanding of the interactions between the endogenous opioid system and risk for alcoholism.

Effect of chronic alcohol consumption on the activity of the hypothalamic-pituitary-adrenal axis and pituitary beta-endorphin as a function of alcohol intake, age, and gender

BACKGROUND

Experimental evidence indicates that components of the hypothalamic-pituitary-adrenal (HPA) axis and of the endogenous opioid system, such as beta-endorphin (beta-END), influence alcohol consumption, whereas chronic alcohol abuse alters the activity of both systems. Furthermore, gender and age differences have been reported in the activity of the HPA axis under basal conditions, in response to stress and acute alcohol challenge. The objective of the present studies was to investigate the hypothesis that chronic alcohol consumption alters the activity of the HPA axis and pituitary beta-END as a function of severity of alcohol abuse, gender, and age.

METHODS

Three age groups of each gender (18-29, 30-44, and 45-60 years old) were recruited. Each age and gender group included four subgroups: (a) nondrinkers, (b) light drinkers, (c) heavy drinkers, and (d) alcoholics in treatment. Demographic characteristics, alcohol consumption, and presence of alcohol dependence were recorded by using a structured interview. Blood samples were taken on the day of the interview. The levels of plasma adrenal corticotropic hormone (ACTH), cortisol, and beta-END were estimated as an index of the activity of the HPA-axis and pituitary beta-END.

RESULTS

Plasma ACTH and beta-END levels were significantly lower in females than males of all age and drinking category groups. Plasma cortisol levels were higher in 18- to 29-year-old female subjects compared with the 18- to 29-year-old male subjects. The plasma ACTH and beta-END levels were lower whereas plasma cortisol levels were higher in heavy drinkers than nondrinkers. This decrease in plasma ACTH and beta-END levels with heavy drinking was more pronounced in female than male subjects of the 30-44 and 45-60 age groups.

CONCLUSIONS

Chronic drinking, gender, and age influence the activity of the HPA-axis and pituitary beta-END, which in turn may influence drinking behavior.

Naltrexone and alcohol drinking in mice lacking beta-endorphin by site-directed mutagenesis

Alcohol-induced activation of the opioid system may contribute to the reinforcing properties of alcohol. This study investigated whether elimination of beta-endorphin (BE) synthesis via site-directed mutagenesis in embryonic stem cells would alter alcohol intake in mice. Both BE-deficient and wildtype (WT) mice generated from the targeted stem cells were backcrossed for nine generations onto a C57BL/6 background, and were maintained with ad libitum food and water. Mice had access to alcohol (10% v/v) under the following conditions: 24 h, scheduled access for 2 h/day, following acute (1 or 2 days) or chronic (5 weeks) alcohol deprivation, and scheduled access following six doses of naltrexone (0.125-16.0 mg/kg BW, ip) or saline treatment. Alcohol intake was similar in BE-deficient and WT mice given chronic access to alcohol, but greater in BE-deficient compared with WT mice during the first 10 days of scheduled access to alcohol, but not after more extensive experience with scheduled access. BE-deficient, but not WT mice, increased alcohol intake following 2 days, but not 1 day or 5 weeks, of deprivation. Naltrexone reduced alcohol drinking both in BE-deficient and WT mice, suggesting that drinking is mediated, in part, by activation of opioid receptors in both genotypes.

Ethanol oral self-administration is increased in mutant mice with decreased beta-endorphin expression

The relationship between ethanol (EtOH) administration and the endogenous opioid system has been studied for many years and a considerable body of evidence supports the contention that EtOH modulates the production and/or release of endogenous opioid peptides. However, substantially less is known about the converse influence: the effect that opioids have on EtOH sensitivity. In this study, we used the beta-endorphin deficient mutant mouse line C57BL/6-Pomc1(tm1Low) to investigate the possible role of a specific opioid peptide on EtOH consumption. Homozygous knockout mice (entirely lacking beta-endorphin), heterozygous mice (50% beta-endorphin expression) and sibling wildtype mice from the same strain were evaluated in a two-bottle free choice paradigm for oral self-administration of EtOH. Across varying EtOH concentrations only the heterozygous mice were found to consistently drink more than wildtype mice. These data support the hypothesis that beta-endorphin modulates the response to EtOH.

The effect of repeated administration of morphine, cocaine and ethanol on mu and delta opioid receptor density in the nucleus accumbens and striatum of the rat

The present study was carried out to evaluate the effect of morphine, cocaine and ethanol on the density of opioid receptors in the nucleus accumbens and striatum of rat brain. The animals were injected i.p. with morphine in a single dose 20 mg/kg, or twice daily for 10 days in increasing doses of 20-100 mg/kg. Cocaine was administered in a dose of 60 mg/kg/day following the "binge" paradigm, every hour for 3 h, one day (single treatment) or five days (chronic treatment). Ethanol was administered in drinking water at increasing concentrations of 1-6% v/v, for one month. As shown by receptor autoradiography, single morphine and cocaine administration did not influence the binding density of the selective ligand of delta2 receptors [3H]Ile5,6deltorphin b, but single administration of cocaine decreased binding density of a highly selective antagonist of delta receptors, [3H]H-Tyr-Tic psi[CH2-NH]Phe-Phe-OH. Repeated morphine administration decreased the receptor density after both ligands of the delta receptor in the nucleus accumbens after 3, 24 and 48 h, and in the striatum after 24 and 48 h. The density of [3H]Ile5,6deltorphin b binding remained unchanged in both structures following repeated cocaine administration. After repeated cocaine administration either no changes (3 h) or a decrease in the binding of [3H]H-Tyr-Tic psi[CH2-NH]Phe-Phe-OH in the nucleus accumbens and striatum were observed after 24 and 48 h. Ethanol did not influence the binding density of [3H]H-Tyr-Tic psi[CH2-NH]Phe-Phe-OH and [3H]Ile5,6deltorphin b in the nucleus accumbens and striatum at any time-point studied. In the nucleus accumbens and striatum, no changes were found in the binding density of [3H]Tyr-D-Ala-Gly-MePhe-Gly-ol following single or repeated morphine administration. At 3 h after single or repeated "binge" cocaine administration, the binding of [3H]Tyr-D-Ala-Gly-MePhe-Gly-ol was not changed in either structure, but after 24 h the density of mu opioid receptors was decreased in both structures. Ethanol given to rats in drinking water decreased the binding of [3H]Tyr-D-Ala-Gly-MePhe-Gly-ol at the time of exposure to ethanol, yet in the nucleus accumbens only. Ethanol withdrawal decreased the density of the mu receptor in both structures after 24, 48 and 96 h. The above data indicate that repeated administration of morphine evokes a long-lasting down-regulation of the density of delta1 and delta2 opioid receptors, whereas cocaine affects in a similar way only the delta1 subtype in the nucleus accumbens, and to a lesser extent in the striatum. A long-term intake of ethanol solution down-regulates mu opioid receptors in both structures, but has no effect on any type of delta receptors. Thus changes in the particular opioid receptor depend on the type of drug used. Furthermore, the most profound changes are observed after late withdrawal, which may play some role in maintaining the state of dependence.

Effects of ethanol on basal and adenosine-induced increases in beta-endorphin release and intracellular cAMP levels in hypothalamic cells

Recently we have shown that the cAMP system is involved in ethanol-regulated beta-endorphin (beta-EP) release from rat hypothalamic neurons in primary cultures. The cascade of events that leads to activation of cAMP following ethanol treatment in hypothalamic beta-EP neurons is not apparent. In this study the role of adenosine, a cAMP regulator, in ethanol-regulated beta-EP release was determined by measuring the cellular incorporation of [3H]adenosine, intracellular cAMP levels and media immunoreactive (IR) beta-EP levels in cultures of rat hypothalamic cells following ethanol treatments in the presence and absence of an adenosine agonist and antagonist. Acute exposure to a 50 mM dose of ethanol for a period of 1 h increased media levels of IR-beta-EP and cellular contents of cAMP, but the ethanol treatment decreased [3H]adenosine uptake. Constant exposure to a 50 mM dose of ethanol for a period of 48 h, failed to alter media levels of IR-beta-EP, cell content of cAMP and [3H]adenosine uptake. The media level of IR-beta-EP was elevated following treatment with adenosine receptor agonist phenyl-isopropyl adenosine (PIA) and was reduced following treatment with adenosine receptor antagonist isobutylmethylxanthine (IBMX) or with adenosine uptake inhibitor adenosine deaminase. The level of cellular cAMP was also increased by PIA but was decreased by IBMX and adenosine deaminase. The stimulatory actions of the adenosine agonist PIA on IR-beta-EP release and on cAMP production were potentiated by simultaneous incubation with ethanol for 1 h. However, chronic ethanol exposure reduced PIA-induced IR-beta-EP release and cAMP production. Additionally, both IBMX and adenosine deaminase reduced ethanol-induced IR-beta-EP release and cAMP levels. These results suggest that ethanol inhibits adenosine uptake in IR-beta-EP neurons in the hypothalamus, thereby increasing extracellular levels of adenosine and leading to activation of membrane adenosine receptors, cAMP production and IR-beta-EP secretion from these neurons. Chronic ethanol desensitizes the adenosine-regulated cAMP production and IR-beta-EP release from hypothalamic neurons.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

The effect of an acute ethanol exposure on the rat brain POMC opiopeptide system

Endogenous peptides with a high affinity for opiate receptors located in the central nervous system have been postulated to play a role in the etiology of alcoholism or in other addictive diseases. Effects of different doses of ethanol (EtOH) at different time points post-EtOH administration on hypothalamic and hindbrain beta-endorphin-like peptide (beta-EPLP) content in male rats were measured by radioimmunoassay (RIA). A single EtOH exposure resulted in an increase in hypothalamic and a decrease in the hindbrain beta-EPLP levels. In another set of experiments, proopiomelanocortin (POMC) synthesis in the hypothalamus was measured by assaying both POMC primary transcript and mature mRNA. No changes in primary transcript or mature POMC hypothalamic mRNA were detected. Based on the results from this experiment we conclude that an acute EtOH exposure affects the rat hypothalamic POMC opiopeptide system by increasing levels of beta-EPLP and this increase in levels is not related to an increase in synthesis.

Effect of mu opioid receptor blockade on alcohol intake in rats bred for high alcohol drinking

Beta-funaltrexamine (beta-FNA), a selective mu opioid receptor antagonist, when administered in doses of 10.0, 15.0, and 20.0 mg/kg b.wt., decreased alcohol but not water intake in a dose-dependent manner in rats selectively bred for high alcohol intake (HAD line). Beta-FNA also suppressed the intake of a saccharin solution containing alcohol without altering the intake of a similar solution without alcohol. The results suggest that beta-FNA may prove useful as a pharmacotherapeutic agent for the treatment of alcohol dependence. In a second study, pituitary beta-endorphin gene expression (proopiomelanocortin or POMC messenger ribonucleic acid-mRNA) was compared in another pair of rat lines selectively bred for high or low alcohol intake (alcohol-preferring or P and alcohol-nonpreferring or NP lines). A repeated alcohol challenge (1.0 g/kg b.wt./day, IP for 4 days) produced a greater increase in POMC mRNA in the anterior and neurointermediate lobes of the pituitary of P rats compared with NP rats. The results suggest that a genetic predisposition toward high alcohol drinking may be associated with increased responsiveness of the opioid system to alcohol.

Enhanced activity of the brain beta-endorphin system by free-choice ethanol drinking in C57BL/6 but not DBA/2 mice

The objective of the present studies was to investigate the effect of voluntary ethanol consumption for 21 days on the brain beta-endorphin system of C57BL/6 (alcohol-preferring) and DBA/2 (alcohol-avoiding) strains of mice. As expected, C57BL/6 mice consumed a significantly higher quantity of the 10% ethanol solution than the DBA/2 mice. Under basal conditions the content of beta-endorphin like peptides differed only in the nucleus accumbens, higher levels being found in the DBA/2 mice. Voluntary ethanol consumption induced an increase in the hypothalamic content of mRNA coding for proopiomelanocortin, associated with a significant increase in the tissue content of beta-endorphin-like peptides in the arcuate nucleus and septum of the C57BL/6 mice, but did not alter the activity of the brain beta-endorphin system of the DBA/2 mice. Since voluntary ethanol consumption was not associated with nutritional deficits and stress, the ethanol-induced enhanced activity of the brain beta-endorphin system of the C57BL/6 mice must be a direct effect of ethanol and may be important in controlling the voluntary ethanol consumption by this strain of mice.

Genetics of alcoholism: role of the endogenous opioid system

At the present time alcoholism is recognized as a metabolic disease exhibiting the clinical features of craving for alcohol, loss of control over drinking, tolerance and physical dependence on alcohol, while both epidemiological and experimental studies have demonstrated that genetic factors may be important in determining whether an individual has a high or low vulnerability to develop alcoholism. Evidence also indicates that alcoholism is not characterized by a single gene single allele inheritance. Instead it seems that multiple genes and environmental factors interact to increase or decrease an individual's vulnerability to become an alcoholic. Current research is aimed at investigating whether certain behavioral, physiological and biochemical markers are highly associated with the incidence of alcoholism. Among the biochemical markers currently under investigation is the endogenous opioid system and its implication in mediating the reinforcing effects of ethanol. It is the objective of this manuscript to review current research on: (a) the interactions of ethanol with the endogenous opioid system at the molecular level; (b) the existence of genetically determined differences in the response of the endogenous opioid system to ethanol between subjects at high and low risk for excessive ethanol consumption, as well as between lines of animals showing preference or aversion for ethanol solutions; (c) the decrease of alcohol consumption following pretreatment with opioid antagonists; and (d) the possible use of specific opioid receptor antagonists together with behavioral therapy to modify drinking behavior, to control craving and to prevent relapse.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.