Deficit in beta-endorphin peptide and tendency to alcohol abuse

β-Endorphin influences sedative and ataxic effects of alcohol

Beta-endorphin (β-E) is an opioid peptide linked to the behavioral effects of ethanol. For example, β-E provides negative feedback to inhibit the hypothalamic-pituitary-adrenal (HPA) stress axis, and neuroadaptation of this system to ethanol may facilitate sex differences in disordered drinking. Locomotor sensitivity to ethanol may also influence the risk for addiction; however, the role of β-E in psychomotor effects of ethanol is not fully understood. We examined the role of β-E and sex on locomotor effects of ethanol using adult male and female wild-type C57BL/6J and β-E deficient B6.129S2-Pomctm1Low/J mice in a parallel rod floor apparatus following 0.75 or 2.0 g/kg ethanol. Beginning 15 min after intraperitoneal injection, we recorded foot slips, distance traveled, slips per meter, first instance of immobility, and total time spent off-balance (lying on the floor) over 15 min, and collected blood for analysis of ethanol concentration 60 min after injection. Overall, β-E deficient mice were more sedated and ataxic following ethanol; at the lower dose they slipped more frequently and had a higher rate of slips per meter traveled. At the higher dose, β-E deficient mice were predominantly sedated, slipping less frequently, and traveling less, as well as spending more time off-balance and becoming immobile sooner. Genotype interacted with sex in that male β-E deficient mice slipped more frequently than their female counterparts, suggesting that β-E may elicit sex-dependent effects of ethanol-induced ataxia. Blood ethanol concentration did not differ between any group, suggesting that behavioral differences result from altered sensitivity to ethanol. Our data support the contention that β-E modulates the locomotor effects of ethanol and may influence ataxia in a sex-dependent manner. These findings help elucidate the role of β-E in diverging behavioral responses to ethanol and may aid the development of targeted treatments for alcohol use disorders.

The life and times of endogenous opioid peptides: Updated understanding of synthesis, spatiotemporal dynamics, and the clinical impact in alcohol use disorder

The opioid G-protein coupled receptors (GPCRs) strongly modulate many of the central nervous system structures that contribute to neurological and psychiatric disorders including pain, major depressive disorder, and substance use disorders. To better treat these and related diseases, it is essential to understand the signaling of their endogenous ligands. In this review, we focus on what is known and unknown about the regulation of the over two dozen endogenous peptides with high affinity for one or more of the opioid receptors. We briefly describe which peptides are produced, with a particular focus on the recently proposed possible synthesis pathways for the endomorphins. Next, we describe examples of endogenous opioid peptide expression organization in several neural circuits and how they appear to be released from specific neural compartments that vary across brain regions. We discuss current knowledge regarding the strength of neural activity required to drive endogenous opioid peptide release, clues about how far peptides diffuse from release sites, and their extracellular lifetime after release. Finally, as a translational example, we discuss the mechanisms of action of naltrexone (NTX), which is used clinically to treat alcohol use disorder. NTX is a synthetic morphine analog that non-specifically antagonizes the action of most endogenous opioid peptides developed in the 1960s and FDA approved in the 1980s. We review recent studies clarifying the precise endogenous activity that NTX prevents. Together, the works described here highlight the challenges and opportunities the complex opioid system presents as a therapeutic target.

Capsaicin Reduces Ethanol Consumption in C57BL/6 but not DBA/2 Mice

Objective

Capsaicin, the pungent analgesic substance of hot peppers which produces a burning sensation and pain is known to affect Substance P and central opioid activities. This experiment was designed to test the effect of capsaicin on alcohol consumption in C57BL/6 and DBA/2 mice. These two strains are known to differ in both their alcohol consumption and their endogenous opioid distribution and response to alcohol. It is hypothesized that this effect may be mediated by both increases Substance P and decreases beta-endorphin.

Methods

After i.p. administration of 0.01 and 0.001 mg/kg of capsaicin with a vehicle or the vehicle alone as the control for eight days in C57BL/6 and DBA/2 mice on limited access alcohol model, Capsaicin’s effects on 2-hour alcohol, 22-hours water, 24-hours food intake and body weight were studied.

Results

In this study, as expected, C57BL/6 mice drank significantly more alcohol than DBA/2 mice under baseline conditions. Capsaicin at both doses tested significantly reduced baseline alcohol consumption in C57BL/6 but not DBA/2 mice. These effects were selective for alcohol as capsaicin did not disrupt food or water consumption.

Conclusion

These results demonstrate that capsaicin differentially affects those mechanisms underlying alcohol consumption in two strains of mice known to differ in their preference for and consumption of alcohol. This effect is hypothesized to be related to differences in the response of the endogenous opioid system.

Deficit of β-endorphin neurons in the hypothalamus and high expression of MOR in mesolimbic structures are related to high alcohol consumption in outbred rats

Clinical studies have postulated that β-endorphin deficiency generates excessive alcohol consumption, and it has been shown that the reduction of β-endorphin neurons increases alcohol intake in animal models. The β-endorphin produce their rewarding effect when they act mainly on the μ-opioid receptors (MOR) located in mesolimbic structures. Thus, it is possible that individual differences in these components of the endogenous opioid system are related to different levels of alcohol consumption. The present study thus examines the relation between two levels of alcohol consumption and intrinsic characteristics of the components of the opioid system in outbred Wistar rats that were not genetically selected. We analyzed the number of β-endorphin-positive neurons in the arcuate nucleus (ArN) and the expression of μ-opioid receptors (MOR) in regions of the reward system, such as the nucleus accumbens (NAc), amygdala (Amy), and ventral tegmental area (VTA) in outbred rats with low (LC) or high (HC) voluntary alcohol consumption. Findings showed that the HC rats had a lower number of β-endorphin-positive neurons in the hypothalamic ArN and a higher expression of MOR in the NAc and VTA, compared to the LC rats. No changes in the expression of MOR in the Amy were observed between the two groups. Results suggest that intrinsic variability in the number of β-endorphin neurons and in the expression of MOR in the LC and HC rats could explain their different patterns for alcohol intake.

Roles of β-Endorphin in Stress, Behavior, Neuroinflammation, and Brain Energy Metabolism

β-Endorphins are peptides that exert a wide variety of effects throughout the body. Produced through the cleavage pro-opiomelanocortin (POMC), β-endorphins are the primarily agonist of mu opioid receptors, which can be found throughout the body, brain, and cells of the immune system that regulate a diverse set of systems. As an agonist of the body's opioid receptors, β-endorphins are most noted for their potent analgesic effects, but they also have their involvement in reward-centric and homeostasis-restoring behaviors, among other effects. These effects have implicated the peptide in psychiatric and neurodegenerative disorders, making it a research target of interest. This review briefly summarizes the basics of endorphin function, goes over the behaviors and regulatory pathways it governs, and examines the variability of β-endorphin levels observed between normal and disease/disorder affected individuals.

Brief Report: Relationship Between Cotinine Levels and Peripheral Endogenous Concentrations of Oxytocin, β-Endorphin, and Orexin in Individuals With Both Alcohol and Nicotine Use Disorders

BACKGROUND AND OBJECTIVES

In this secondary analysis of a pilot clinical trial with individuals with alcohol and nicotine use disorders, we investigate the relationship between serum concentrations of oxytocin, β-endorphin, melatonin, α-melanocyte-stimulating hormone, substance P, and orexin, with objective biomarkers (salivary cotinine and serum γ-glutamyl transferase [GGT]) as well as with self-reported smoking and alcohol drinking.

METHODS

Biomarkers for a total of N = 19 participants were analyzed using multiplexed, competitive format immune-assay (peptides) and enzyme competitive immunoassay (saliva). A regression analysis using Pearson's correlation coefficient was utilized to determine correlations. We controlled for multiple comparisons, checked for collinearities, and ran two-sided statistical tests.

RESULTS

We found significant positive correlations for cotinine and oxytocin (P = .002), β-endorphin (P = .008), and orexin (P < .001), but not for either GGT or self-reported smoking or alcohol drinking.

CONCLUSION AND SCIENTIFIC SIGNIFICANCE

These preliminary results suggest a relationship between cotinine and oxytocin, β-endorphin, and orexin, which opens up new potential hypotheses on the potential role of these endocrine pathways in tobacco smokers. (Am J Addict 2021;30:88-91).

A novel theory on the predictive value of variation in the β-endorphin system on the risk and severity of PTSD

Despite growing interest in genetic and psychosocial indicators of heightened susceptibility to posttraumatic stress disorder (PTSD), a predictive model, which explains why some individuals develop PTSD in response to life-threatening traumatic events, while others, when faced with the same or similar experiences, do not, has thus far remained out of reach. In this paper, we review the literature on gene-environment interactions in β-endorphin system functioning with regard to PTSD and suggest that variation, both genetic and with regard to environmental stimuli, in systems which, like the β-endorphin system, distort human perception of life-threatening traumatic experiences may account for some of the variance in resilience to the disorder. Given the role of β-endorphin in both social connections and physical exercise, this becomes especially relevant with regard to military selection, training, and leadership processes.

An overview of effective therapies and recent advances in biomarkers for chronic liver diseases and associated liver cancer

Chronic liver diseases (CLDs) such as hepatitis, alcoholic liver disease, nonalcoholic fatty liver, and their downstream effect cancer affect more than a billion of people around the world both symptomatically and asymptomatically. The major limitation for early detection and suitable medical management of CLDs and liver cancer is either the absent of symptoms or their similar manifestations as other diseases. This detection impediment has led to a steady increase in the number of people suffering from CLDs with an ultimate outcome of liver failure and undergoing transplantation. A better understanding of CLD pathogenesis has helped us to develop novel therapies for patients who are at greatest risk for CLD progression to the most serious disease cancer. With the discovery of aberrant molecular pathways in CLDs, it is now possible to delineate a road map for selecting targeted therapies for CLDs. Technological advances in imaging as well as the availability of several stable, sensitive, early, noninvasive biomarkers for distinguishing different stages of CLDs and cancer have greatly facilitated both drug target identification and real-time monitoring of response to therapy. Biomarkers are the most useful in clinical practice for liver diseases like hepatocellular carcinoma (HCC), which is associated with secretion of various tumor-related proteins or nucleotides in peripheral circulation. The need for the identification of CLD biomarkers remains high. This article reviews the etiologies of CLDs, the results of recent clinical trials of treatments for CLDs, and development of noninvasive methodologies for detecting CLDs and monitoring their progression toward HCC.

Voluntary alcohol consumption and plasma beta-endorphin levels in alcohol preferring rats chronically treated with lamotrigine

Several recent studies have indicated that lamotrigine, similarly to other antiepileptic drugs, may be useful in the therapy of alcohol dependence. The rationale for using lamotrigine in the treatment of alcohol addiction is based on its multiple mechanisms of action which include inhibition of voltage-sensitive sodium channels, modulation voltage-gated calcium currents and transient potassium outward current. However, the known mechanism of lamotrigine does not fully explain its efficacy in alcohol addiction therapy. For this reason we have decided to examine the effect of lamotrigine on the opioid system. Our previous studies showed that topiramate and levetiracetam (antiepileptic drugs) as well as the most effective drugs in alcohol addiction therapy i.e. naltrexone and acamprosate, when given repeatedly, all increased plasma beta endorphin (an endogenous opioid peptide) level, despite operating through different pharmacological mechanisms. It is known that low beta-endorphin level is often associated with alcohol addiction and also that alcohol consumption elevates the level of this peptide. This study aims to assess the effect of repeated treatment with lamotrigine on voluntary alcohol intake and beta-endorphin plasma level in alcohol preferring rats (Warsaw high preferring (WHP) rats). We observed a decrease in alcohol consumption in rats treated with lamotrigine. However we didn't observe significant changes in beta-endorphin level during withdrawal of alcohol, which may indicate that the drug does not affect the opioid system. We suppose that lamotrigine may be useful in alcohol dependence therapy and presents a potential area for further study.

Effect of repeated treatment with topiramate on voluntary alcohol intake and beta-endorphin plasma level in Warsaw alcohol high-preferring rats

RATIONALE

Pharmacological treatment currently used for alcohol dependence is not sufficient for the all patients, and there is a crucial need to find more effective treatments. Recent studies indicate that topiramate is likely the most promising new medication for alcohol dependence. The rationale for topiramate as treatment for alcohol addiction is based on its multifaceted neurochemical activity that targets multiple neural pathways.

OBJECTIVES

This study aims to assess the effect of repeated treatment with topiramate on voluntary alcohol intake and beta-endorphin plasma level in rats selectively bred for high alcohol preference.

METHODS

Initially, Warsaw high preferring rats (N = 50) were given a 24-h/day free choice between a 10 % (v/v) alcohol solution and water for three consecutive weeks. Subsequently, rats were administered with topiramate (40 or 80 mg/kg b.w.) or vehicle for 14 days and ethanol intake was measured daily. Subsequently, we examined the effects of topiramate on plasma beta-endorphin levels, while alcohol was available and when it was not available for an extended period time.

RESULTS

We observed significantly increase in the levels of beta-endorphin in rats with free access to alcohol both in a topiramate- or vehicle-treated group. However, in topiramate-treated group, a voluntary consumption of alcohol diminished in comparison with the vehicle-treated rats.

CONCLUSION

The results from this study indicated that topiramate reduces voluntary alcohol intake and support our previous findings that the increase of beta-endorphin level is responsible at least partly for the effectiveness of drugs in treating the alcohol addiction.

Identification of POMC exonic variants associated with substance dependence and body mass index

Background

Risk of substance dependence (SD) and obesity has been linked to the function of melanocortin peptides encoded by the proopiomelanocortin gene (POMC).

Methods and Results

POMC exons were Sanger sequenced in 280 African Americans (AAs) and 308 European Americans (EAs). Among them, 311 (167 AAs and 114 EAs) were affected with substance (alcohol, cocaine, opioid and/or marijuana) dependence and 277 (113 AAs and164 EAs) were screened controls. We identified 23 variants, including two common polymorphisms (rs10654394 and rs1042571) and 21 rare variants; 12 of which were novel. We used logistic regression to analyze the association between the two common variants and SD or body mass index (BMI), with sex, age, and ancestry proportion as covariates. The common variant rs1042571 in the 3′UTR was significantly associated with BMI in EAs (Overweight: P_adj = 0.005; Obese: P_adj = 0.018; Overweight+Obese: P_adj = 0.002) but not in AAs. The common variant, rs10654394, was not associated with BMI and neither common variant was associated with SD in either population. To evaluate the association between the rare variants and SD or BMI, we collapsed rare variants and tested their prevalence using Fisher’s exact test. In AAs, rare variants were nominally associated with SD overall and with specific SD traits (SD: P_FET,1df = 0.026; alcohol dependence: P_FET,1df = 0.027; cocaine dependence: P_FET,1df = 0.007; marijuana dependence: P_FET,1df = 0.050) (the P-value from cocaine dependence analysis survived Bonferroni correction). There was no such effect in EAs. Although the frequency of the rare variants did not differ significantly between the normal-weight group and the overweight or obese group in either population, certain rare exonic variants occurred only in overweight or obese subjects without SD.

Conclusion

These findings suggest that POMC exonic variants may influence risk for both SD and elevated BMI, in a population-specific manner. However, common and rare variants in this gene may exert different effects on these two phenotypes.

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.

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.

Ethanol exposure selectively alters beta-endorphin content but not [3H]-DAMGO binding in discrete regions of the rat brain

The dopaminergic mesocorticolimbic system plays an important role in the reinforcing effects of ethanol. Opioid peptides modulate the activity of this system and have been suggested to mediate, at least in part, the reinforcing properties of ethanol. Thus, beta-endorphin (beta-END) could participate in the development of ethanol reinforcement and addiction. The aim of this work was to investigate the acute and chronic ethanol effects on beta-END content in regions of the mesolimbic system and to examine if chronic ethanol treatment alters ligand binding to mu opioid receptor (muOR). Male Wistar rats received a single acute ethanol dose of 2.5 g/kg or water by intra-gastric administration. For chronic ethanol treatment experiments, one group of rats was given ethanol (10% v/v solution) to drink, two groups were given equivalent volumes of sucrose (14.14% isocaloric solution) or water, respectively, and a fourth group had ad libitum access to food and water. Treatment was followed for 4 weeks. Beta-endorphin content in brain regions was quantified by radioimmunoassay and ligand binding studies to muOR were performed by quantitative autoradiography using 8 nM [(3)H]-DAMGO as radioligand. Acute ethanol decreased beta-END content in the hypothalamus (26%) 1h after administration. No ethanol effects were observed in the midbrain, ventral tegmental area, substantia nigra, nucleus accumbens, nucleus accumbens-septum and prefrontal cortex. Chronic ethanol treatment neither changed beta-END levels nor [(3)H]-DAMGO binding to mu opioid receptors in any of the regions studied. However, beta-END levels in the sucrose group were significantly increased in the nucleus accumbens and substantia nigra, in comparison to all other groups. These findings suggest that different neural mechanisms and specific brain regions may be involved in the reinforcing effects of ethanol and sucrose.

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.

Morphine attenuates the expression of sensitization to ethanol, but opioid antagonists do not

Behavioral sensitization to ethanol is characterized by an increased locomotor activity after repeated exposure. A great variability exists among species and strains in the development of sensitization. There is a growing amount of evidence to indicate that the opioid system is involved in alcoholism; it is possible, therefore, that this system also modulates the sensitization to ethanol. In this study we evaluated the role of the opioid system in determining the variability of the sensitized response to ethanol. Mice received repeated administrations of ethanol (2.2 g/kg) or saline every other day for 10 days. According to their locomotor response on the last day of treatment, ethanol-treated animals were classified into two groups: sensitized or non-sensitized mice. After the treatment, mice were submitted to four challenges 48 h apart. In experiments 1 and 2, mice were challenged, respectively, with i.p. administration of opioid antagonists (naloxone or naltrexone) or an opioid agonist (morphine), followed immediately by 2.2 g/kg ethanol. In experiment 3, animals received morphine by i.c.v., followed by 2.2 g/kg of ethanol (i.p.). Pretreatment with opioid antagonists (naloxone or naltrexone) did not block the expression of ethanol sensitization; however pretreatment with morphine attenuated the increased locomotor activity after ethanol administration in sensitized mice. In experiment 4, after the ethanol or saline treatment, mice brains were processed and brain mu opioid binding was assessed by autoradiography using [3H]D-Ala2,N-mePhe4, Gly-ol5-enkephalin ([3H]DAMGO). No differences were seen between any of the groups of mice, so the agonist effect is not likely to be mediated by differences in binding to mu opioid receptors.

Pharmacogenetic treatments for drug addiction: alcohol and opiates

AIMS

Psychiatric pharmacogenetics involves the use of genetic tests that can predict the effectiveness of treatments for individual patients with mental illness such as drug dependence. This review aims to cover these developments in the pharmacotherapy of alcohol and opiates, two addictive drugs for which we have the majority of our FDA approved pharmacotherapies.

METHODS

We conducted a literature review using Medline searching terms related to these two drugs and their pharmacotherapies crossed with related genetic studies.

RESULTS

Alcohol's physiological and subjective effects are associated with enhanced beta-endorphin release. Naltrexone increases baseline beta-endorphin release blocking further release by alcohol. Naltrexone's action as an alcohol pharmacotherapy is facilitated by a putative functional single nucleotide polymorphism (SNP) in the opioid mu receptor gene (Al18G) which alters receptor function. Patients with this SNP have significantly lower relapse rates to alcoholism when treated with naltrexone. Caucasians with various forms of the CYP2D6 enzyme results in a 'poor metabolizer' phenotype and appear to be protected from developing opioid dependence. Others with a "ultra-rapid metabolizer" phenotype do poorly on methadone maintenance and have frequent withdrawal symptoms. These patients can do well using buprenorphine because it is not significantly metabolized by CYP2D6.

CONCLUSIONS

Pharmacogenetics has great potential for improving treatment outcome as we identify gene variants that affect pharmacodynamic and pharmacokinetic factors. These mutations guide pharmacotherapeutic agent choice for optimum treatment of alcohol and opiate abuse and subsequent relapse.

Beta-endorphin levels in longtailed and pigtailed macaques vary by abnormal behavior rating and sex

Frequent or severe abnormal behavior may be associated with the release of endorphins that positively reinforce the behavior with an opiate euphoria or analgesia. One line of research exploring this association involves the superhormone, proopiomelanocortin (POMC). The products of POMC appear to be dysregulated in some human subjects who exhibit self-injurious behavior (SIB). Macaque monkeys have POMC very similar to humans, and some laboratory macaques display SIB or frequent stereotypies. We investigated associations between plasma levels of three immunoreactive POMC fragments with possible opioid action and abnormal behavior ratings in macaques. In 58 adult male and female macaques (24 Macaca fascicularis and 34 Macaca nemestrina), plasma levels of intact beta-endorphin (betaE) and the N-terminal fragment (BEN) were significantly higher in animals with higher levels of abnormal behavior. The C-terminal fragment (BEC) was significantly higher in males but unrelated to ratings of abnormal behavior. Levels of ACTH, cortisol, and (betaE-ACTH)/betaE dysregulation index were unrelated to abnormal behavior. None of the POMC products differed significantly by subjects' species, age, or weight. The finding that intact beta-endorphin is positively related to abnormal behavior in two species of macaque is consistent with some previous research on human subjects and nonprimates. The positive relation of the N-terminal fragment of betaE to abnormal behavior is a new finding.

Effect of repeated treatment with topiramate on the beta-endorphin plasma level in rats selectively bred for high and low alcohol preference

Recent research indicates that topiramate has a role in the treatment of alcohol dependence. Topiramate has multiple mechanisms of action including enhancement of GABA-ergic inhibitory transmission and blocking excitatory glutamate neurotransmission, and modulating voltage-gated sodium and calcium ion channels and inhibiting carbonic anhydrase. In this study, we examined the effect of topiramate on endogenous opioid systems, which have an important role in the development of alcohol dependence. We investigated the beta-endorphin plasma level of animals with high- and low-risks of alcohol dependency after repeated treatment with topiramate. We used the Warsaw High Preferring (WHP) and Warsaw Low Preferring (WLP) rats, and treated them with topiramate at a dose of 80 mg/kg p.o. for 14 days. In WHP rats treatment with topiramate led to an increase in beta-endorphin plasma levels, which persisted at the same level even after a single injection of alcohol. The level of this peptide with topiramate was lower than in alcohol-injected WHP rats who did not receive topiramate. Beta-endorphin levels in WHP rats after topiramate or topiramate and ethanol treatment were similar to the basal level of this peptide in WLP rats. In WLP rats, topiramate did not prevent the ethanol-induced increase in beta-endorphin plasma level. We propose that administration of topiramate may have different effects on the opioid system involved in dependence according to genetic susceptibilities to alcoholism.