An in vivo profile of beta-endorphin release in the arcuate nucleus and nucleus accumbens following exposure to stress or alcohol.

The aim of the present study was to determine the effects of distinct categories of stressors on beta-endorphin (beta-EP) release in the arcuate nucleus (ArcN) and nucleus accumbens (NAcb) using in vivo microdialysis. Adult male rats were implanted with a cannula aimed at either the NAcb or the ArcN. On the day of testing, a 2 mm microdialysis probe was inserted into the cannula, and artificial cerebrospinal fluid was infused at 2.0 microl/min. After three baseline collections, animals either had a clothespin applied to the base of their tail for 20 min (a physical/tactile stressor), were exposed to fox urine odour for 20 min (a psychological stressor/species-specific threat), or were administered 2.4 g ethanol/kg body weight, 16.5% w/v, i.p. (a chemical/pharmacological stressor) with control animals receiving an equivalent volume of saline. Both tail-pinch and fox odour significantly increased beta-EP release from the ArcN (P<0.05), whilst only tail-pinch enhanced beta-EP release from the NAcb (P<0.01). On the other hand, alcohol stimulated beta-EP release in the NAcb as compared with saline-treated controls (P<0.01), but not in the ArcN. Although the increase in extracellular beta-EP produced by the other stressors was relatively rapid, there was a 90-min delay before alcohol administration caused beta-EP levels to exceed that of saline-injected controls. In conclusion, the fact that physical and fear-inducing psychological stressors stimulate beta-EP release in the ArcN and only physical stressors stimulate beta-EP release in the NAcb, indicates that stressors with different properties are processed differently in the brain. Also, an injection of alcohol caused a delayed increase of beta-EP in the NAcb but not the ArcN, indicating that alcohol may recruit a mechanism that is, at least partially, distinct from stress-related pathways.

Influence of the endogenous opioid system on high alcohol consumption and genetic predisposition to alcoholism.

There is increasing evidence supporting a link between the endogenous opioid system and excessive alcohol consumption. Acute or light alcohol consumption stimulates the release of opioid peptides in brain regions that are associated with reward and reinforcement and that mediate, at least in part, the reinforcing effects of ethanol. However, chronic heavy alcohol consumption induces a central opioid deficiency, which may be perceived as opioid withdrawal and may promote alcohol consumption through the mechanisms of negative reinforcement. The role of genetic factors in alcohol dependency is well recognized, and there is evidence that the activity of the endogenous opioid system under basal conditions and in response to ethanol may play a role in determining an individual's predisposition to alcoholism. The effectiveness of opioid receptor antagonists in decreasing alcohol consumption in people with an alcohol dependency and in animal models lends further support to the view that the opioid system may regulate, either directly or through interactions with other neurotransmitters, alcohol consumption. A better understanding of the complex interactions between ethanol, the endogenous opioids and other neurotransmitter systems will help to delineate the neurochemical mechanisms leading to alcoholism and may lead to the development of novel treatments.

Ontogenesis of proopiomelanocortin and its processing to beta-endorphin by the fetal and neonatal rat brain.

A number of reports suggest that beta-endorphin (beta-END) may play an important role in the regulation of cell proliferation and neuronal differentiation. Proopiomelanocortin (POMC), the common precursor ofadrenocorticotropic hormone and beta-END, is detected very early in embryonic life in hypothalamic neurons of the developing rat. However, very little is known about the degree to which POMC is processed to beta-END during fetal and early postnatal life. Thus, it was the objective of the present study to estimate the hypothalamic content of POMC mRNA, as well as the biosynthesis and posttranslational processing of POMC by hypothalamic neurons on fetal day 20 and on days 1, 8 and 22 of postnatal life. Hypothalamic POMC mRNA, as determined by Northern blot analysis, was higher on fetal day 20 than on postnatal days 1, 8 and 22. A higher rate of incorporation of [(3)H]phenylalanine into beta-END immunoreactive peptides was observed on fetal day 20 than on postnatal day 1. However, the rate of incorporation was significantly increased by day 8 of postnatal life and was similar to that on day 22. POMC was processed to beta-lipotropin (beta-LPH) and beta-END at all ages examined, but the relative proportions of POMC:beta-LPH:beta-END changed during development. Thus, beta-END accounted only for 34.89 +/- 6.14% of the total [(3)H]phenylalanine-labeled beta-END immunoreactive peptides on fetal day 20, while it accounted for 57. 37 +/- 5.20, 62.81 +/- 1.38 and 79.25 +/- 6.57% on days 1, 8 and 22 of postnatal life, respectively. Thus, POMC is processed to a considerable extent into beta-END-sized peptides by the fetal hypothalamus and may influence brain development. Furthermore, the rate of processing of hypothalamic POMC into beta-END increases with development, probably due to the increased activity of the enzymes specific for POMC processing.

Effects of voluntary ethanol drinking on [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor binding in the mouse hippocampus and cerebellum.

Chronic exposure to ethanol can induce widespread cell loss in the brain, in some cases even causing dementia. Although the underlying mechanism associated with ethanol toxicity has not yet been established, it is suggested that one of the ways in which ethanol disrupts neuronal functioning/survival is by targeting the actions of mitogenic growth factors. Insulin-like growth factors-I and -II and insulin are structurally related polypeptides with potent mitogenic and metabolic effects on the central and peripheral nervous systems. These growth factors and their respective receptors are widely distributed throughout the brain, including the hippocampus and cerebellum. Evidence indicates that ethanol can decrease plasma levels of insulin-like growth factors and can also inhibit the growth-promoting and cell survival effects of these growth factors under in vitro conditions. The present study was designed to determine if voluntary ethanol consumption over a 21-day period could alter [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor-binding sites in the hippocampus and cerebellum-areas known to be severely affected following chronic exposure to ethanol. C57BL/6 mice were presented with either water only or a choice of water and a 10% v/v ethanol solution. Mice with access to the ethanol solution drank an average of 5.35+/-0.77 g of ethanol/kg body weight per day. [125I]Insulin-like growth factor-I receptor-binding sites were found to be significantly increased in all subfields of the hippocampal formation, but not in the cerebellum, of ethanol-treated mice compared to controls. [125I]Insulin-like growth factor-II and [125I]insulin receptor-binding sites, on the other hand, did not exhibit any alterations either in the hippocampus or cerebellum following chronic exposure to ethanol. These results, in keeping with earlier reports, suggest that hippocampal insulin-like growth factor-I is more sensitive to ethanol treatment than either insulin-like growth factor-II or insulin, and the observed increase in the [125I]insulin-like growth factor-I receptor levels possibly reflects an activity-dependent response to prevent/slow down neuronal degeneration and/or to regulate subtle functional alterations that follow chronic exposure to ethanol.

Opioid propeptide mRNA content and receptor density in the brains of AA and ANA rats.

Recent evidence has indicated an association between the rewarding effects of ethanol intake and endogenous opioid activity. The present studies examine the presence of differences in opioid peptide mRNA content and mu and kappa opioid receptor densities, between ethanol naive AA and ANA rats bred selectively for their high and low alcohol consumption, respectively. In situ hybridization was used to compare the content of proopiomelanocortin, proenkephalin and prodynorphin mRNA in distinct brain regions known to be involved in the reinforcing properties of addictive drugs, between rats from each line. Results indicated that AA rats had a significantly greater content of proopiomelanocortin mRNA in the arcuate nucleus of the hypothalamus, of proenkephalin mRNA in the prefrontal cortex and of prodynorphin mRNA in the mediodorsal nucleus of the thalamus (p < or = .05). Receptor autoradiography was performed using 3H-labeled ligands specific for mu and kappa opioid receptors. AA rats were found to have a greater density of mu opioid receptors in the shell region of the nucleus accumbens and prefrontal cortex, but a lower density of kappa opioid receptors in the ventromedial hypothalamus, compared to ANA rats. The present data demonstrate the presence of inherited differences in the activity of distinct components of the endogenous opioid system in some brain regions associated with the processes of reward and reinforcement; and as such, may play a role in determining differences in ethanol drinking between AA and ANA rats.

Comparison of the proopiomelanocortin and proenkephalin opioid peptide systems in brain regions of the alcohol-preferring C57BL/6 and alcohol-avoiding DBA/2 mice.

Differences in the activity of distinct components of the endogenous opioid system between ethanol-preferring and ethanol-avoiding animals may be important in controlling their voluntary alcohol consumption. The objective of the present studies was to compare the activity of two opioid peptide systems (enkephalin and beta-endorphin) in distinct regions of the brain, between the C57BL/6 and DBA/2 mice, using sensitive radioimmunoassays, in situ hybridization, and immunohistochemical techniques. The immunohistochemical studies indicated that there was no significant difference in the number of either beta-endorphin or enkephalin immunopositive cells between the C57BL/6 and DBA/2 mice. The in situ hybridization studies demonstrated a 27% higher content of proopiomelanocortin mRNA in the arcuate nucleus of the C57BL/6 than DBA/2 mice, p < 0.02. The content of proenkephalin mRNA was 25% higher in the nucleus accumbens, p < 0.005 and 23% higher in the caudate putamen, p < 0.01, of the C57BL/6 than DBA/2 mice. There was no significant difference in the content of beta-endorphin peptides in the distinct brain regions investigated. The content of met-enkephalin-arg6-phe7 in the nucleus accumbens and caudate was similar between the two strains of mice, while it was significantly lower in the amygdala, hippocampus, ventral tegmental area, and periaqueductal grey of the C57BL/6 than DBA/2 mice. Thus, there are significant differences in the activity of these two endogenous opioid peptide systems in distinct regions of the brain, between ethanol naive C57BL/6 and DBA/2 mice, which may play a role in controlling their alcohol consumption.

Alcohol-seeking behavior: the roles of the hypothalamic-pituitary-adrenal axis and the endogenous opioid system.

Both the hormones of the hypothalamic-pituitary-adrenal (HPA) axis and the endogenous opioid system are activated in response to stress as well as after alcohol consumption, supporting the hypothesis that stress can influence both alcohol consumption and craving for alcohoL Activation of the HPA axis by stress or alcohol results in the production of glucocorticoid hormones, such as cortisol. Those hormones, in turn, are important for the release of the brain chemical dopamine in certain brain areas that are associated with the rewarding and reinforcing effects of alcohol and other drugs. Alcohol-induced release of certain endogenous opioids similarly results in dopamine release in those brain regions. Through this mechanism, both the HPA axis and the endogenous opioid system may influence alcohol consumption. Consequently, genetically determined differences in the activities of the HPA axis and endogenous opioid system may help determine a person's alcohol consumption level and vulnerability to alcoholism.

Content of dynorphins and kappa-opioid receptors in distinct brain regions of C57BL/6 and DBA/2 mice.

Differences in the activity of various components of the endogenous opioid system under basal conditions and after ethanol exposure have been reported between strains and lines of animals showing either high or low ethanol consumption. The objective of the present studies was to investigate the presence of differences in (a) the density of kappa-opioid binding sites, (b) the content of prodynorphin mRNA, and (c) the content of dynorphin peptides in distinct brain regions between the C57BL/6 (ethanol-preferring) and the DBA/2 (ethanol-avoiding) mice. Results indicated that the C57BL/6 mice have a higher content of kappa-opioid binding sites and dynorphin A 1-13 in the amygdala, and dynorphin A 1-8 in the ventral tegmental area, whereas the DBA/2 mice presented a significantly higher content of kappa-opioid binding sites, prodynorphin mRNA, as well as dynorphin A 1-13 and dynorphin A 1-8 peptides in the nucleus accumbens and septum. In addition, the DBA/2 mice presented a higher content of kappa-opioid receptors in the periaqueductal gray and dynorphin A 1-13 and dynorphin A 1-8 in the caudate putamen. Because enhanced stimulation of the kappa-opioid receptors at the level of the nucleus accumbens has been associated with decreased dopamine release and aversive states, the higher content of kappa-opioid receptors, pro-dynorphin mRNA, and dynorphin peptides (the endogenous ligand of k-binding sites) in regions of the limbic system of the DBA/2 mice may play an important role in determining their low alcohol consumption.

Characterization of the mu and delta opioid receptors in the brain of the C57BL/6 and DBA/2 mice, selected for their differences in voluntary ethanol consumption.

Genetically determined differences in the activity of the hypothalamic beta-endorphin system have been demonstrated between the C57BL/6 (alcohol-preferring) and DBA/2 (alcohol-aversive) inbred strains of mice. The present studies examined the distribution and density of the mu and delta receptors in specific brain regions that may mediate the rewarding and reinforcing effects of ethanol, using quantitative autoradiography and the specific mu agonist FK 33-824 and delta agonist DPDPE, in their iodinated form. 125I-FK 33-824 recognizes a high affinity binding site in brain membrane preparations from both the C57BL/6 (Kd = 1.37 +/- 0.22 nM; Bmax = 80 +/- 12.3 fmol/mg protein) and DBA/2 mice (Kd = 1.02 +/- 0.16 nM; Bmax = 39.5 +/- 9.6 fmol/mg protein), whereas 125I-DPDPE binds to a high affinity binding site in brain membranes from both the C57BL/6 (Kd = 1.08 +/- 0.34 nM; Bmax = 24.4 +/- 4.5 fmol/mg protein) and DBA/2 mice (Kd = 0.68 +/- 0.24 nM; Bmax = 15.3 +/- 3.7 fmol/mg protein). The autoradiographic studies demonstrated differences in the density of the mu opioid receptors between the two strains of mice in brain nuclei that are not directly related to the brain reward system. However, strain-related differences in the density of delta opioid receptors were observed in regions of the limbic system known to mediate the positive reinforcing effects of many drugs of abuse. The density of delta receptors was significantly higher in the ventral tegmental area and nucleus accumbens of the C57BL/6 mice. The results of the present study support the hypothesis that genetically determined differences exist in the density of opioid receptors in distinct regions of the brain between the C57BL/6 and DBA/2 inbred strains of mice, which may play a role in controlling their voluntary ethanol consumption.

Increased plasma atrial natriuretic peptide after ingestion of low doses of ethanol in humans.

Previous studies have demonstrated that, in human, acute consumption of high doses of ethanol, administered in a large quantity of fluid, with or without volume-loading, induced either a decrease or an increase in the plasma content of atrial natriuretic peptide (ANP)--a substance that has a hypotensive effect. The objective of the present study was to examine the effect of low doses of ethanol (0, 0.25, and 0.50 g of ethanol/kg of body weight) administered to six normotensive individuals, in a small volume of fluid without prior volume-loading. Before and at various intervals after administration of the placebo or ethanol drinks, heart rate and blood pressure were measured and blood samples were taken for estimation of the plasma ANP, arginine vasopressin, and cortisol contents. Results indicated small changes in blood pressure and heart rate after ingestion of either the placebo or ethanol drinks. On the other hand, a significant increase in the plasma ANP content was observed at 15 min after ingestion of both the 0.25 and 0.50 g of ethanol/kg of body weight doses, but not after the placebo drink. Plasma ANP levels were still elevated at 45 min postethanol intake, but had returned to basal levels at 120 min after the ethanol drink. Interestingly, it was noticed that the higher dose of ethanol (0.50 g) did not induce a higher plasma ANP concentration than the lower dose (0.25 g) of ethanol; however, the plasma ANP content remained elevated for a longer period. Furthermore, the increase in plasma ANP content was not due to ethanol or stress-induced increases in the plasma arginine vasopressin and cortisol contents, because the plasma concentration of these hormones remained either at basal or below basal levels for the duration of the experiment. In conclusion, ingestion of low amounts of ethanol equivalent to 1 or 2 standard drinks induced an increase in plasma ANP content.

Alterations in brain levels of atrial and C-type natriuretic peptides after chronic moderate ethanol consumption in spontaneously hypertensive rats.

Atrial (ANP) and C-type (CNP) natriuretic peptides have been found in brain regions associated with fluid homeostasis and blood pressure. Since chronic moderate ethanol consumption has been shown to prevent the age-dependent increase in blood pressure in experimental animals, the objective of the present studies was to investigate the effect of ethanol (20% (v/v) for 8 months) on the total content and concentration of ANP and CNP in the brain of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Ethanol increased the content and concentration of both ANP and CNP in the hypothalamus, pons and medulla of SHR rats. In contrast, in the WKY rats ethanol had no effect on the levels of ANP in any of the brain regions studies, but enhanced the concentration of CNP in the hypothalamus and medulla. Thus, ethanol induced changes in the content of natriuretic peptides in distinct brain regions associated with control of cardiovascular activity. Such changes may be partially responsible for the effect of chronic moderate ethanol consumption on blood pressure.

Renal alterations of atrial natriuretic peptide receptors by chronic moderate ethanol treatment.

Previous studies have shown that chronic moderate ethanol (EtOH) consumption prevents the age-dependent increase in blood pressure. However, the physiological systems mediating the antihypertensive effects of EtOH are not known. The objective of the present studies was to investigate the effects of chronic (8 mo) moderate EtOH consumption on renal natriuretic receptors of spontaneously hypertensive (SHR) and normotensive (WKY) rats, using competitive binding assay and autoradiographic techniques. In the renal glomeruli, the maximal binding capacity (Bmax) of the heterogeneous atrial natriuretic peptide (ANP) receptor population (NPR-A and NPR-C) was significantly lower in EtOH-treated SHR and WKY rats compared with water-treated controls. Quantification of receptor subtypes showed that this decrease was primarily the result of NPR-C down-regulation. The apparent dissociation constant (Kd) was also decreased by the EtOH treatment. In the renal papilla, the Bmax of the homogeneous receptor population (NPR-A) was significantly elevated by long-term EtOH consumption in both strains compared with water-treated controls. However, the Kd was unaltered by the EtOH administration. Thus EtOH treatment induced specific alterations in renal natriuretic receptors that may play a role in the "protective" effect of moderate EtOH consumption on the age-dependent increase in blood pressure.

Ethanol-induced change in cardiac and endogenous opiate function and risk for alcoholism.

Susceptibility to alcoholism varies with age, gender, and familial background. Youthful nonalcoholic males with multigenerational family histories of male alcoholism seem at particular risk. Previous investigations suggest that such males are characterized by abnormal psychophysiological response, while sober and alcohol-intoxicated; additional recent studies indicate that the endogenous opiate systems are involved in mediating ethanol reinforcement and modulating intake. We first compared cardiac response to alcohol administration among young (mean = 22.8 years), nonalcoholic men and women with multigenerational, unigenerational, and negative family histories of alcohol dependence and abuse. Then, we compared the ethanol-induced cardiac response of the males in these three groups to that of currently alcohol-dependent older males and age-matched nonalcoholic male controls. Finally, we examined ethanol-induced change in plasma beta-endorphin and cortisol levels among a subset of the nonalcoholic males, divided into those with high and low levels of postethanol administration heart-rate increase. Nonalcoholic males with multigenerational family histories of male alcoholism were characterized by significantly higher [t(301) = 5.70, p < 0.0001, Cohen's d = 0.73] levels of ethanol-induced heart-rate increase than nonalcoholics from all other comparison groups. The magnitude of their increase matched that of current male alcohol-dependents. Nonalcoholic males with high levels of ethanol-induced heart-rate increase also produced significantly more plasma beta-endorphin after consuming alcohol. Peak production of beta-endorphin was highly correlated (r = 0.861, p < 0.001) with magnitude of heart-rate increase. A subset of those at risk for alcoholism may be characterized by sensitivity to ethanol-induced reward, marked by heightened ethanol-induced, heart-rate increase, mediated by ethanol stimulation of endogenous opiate production. This subset might contain those who, once alcoholic, would differentially benefit from treatment with opiate antagonists.

Effect of chronic ethanol consumption on the atrial natriuretic system of spontaneously hypertensive rats.

There is a lot of discussion on the effects of ethanol (ETOH) on blood pressure (BP). It has been suggested that chronic moderate ETOH consumption prevents the development of age-dependent hypertension in humans and spontaneously hypertensive rats (SHR). However, the mechanism mediating this effect is unknown. In the present studies, we hypothesized the implication of atrial natriuretic peptide (ANP), a BP-lowering hormone, on the antihypertensive effect of moderate ETOH consumption. A 20% v/v solution of alcohol was given as drinking fluid to SHR and normotensive Wistar-Kyoto (WKY) rats for up to 32 weeks. This treatment prevented, at least in part, the age-dependent increase of BP in SHR and WKY rats. The lower BP was associated with significantly lower levels of circulating atrial natriuretic peptide in both groups. After chronic ETOH administration, total ANP content and concentration were higher in the left and right atria of SHR and WKY rats than in water-treated controls. Despite the ETOH-induced increase in atrial ANP content, there was no significant change in atrial ANP mRNA, suggesting decreased atrial release. Chronic ETOH treatment significantly reduced ANP mRNA in the ventricles of SHR but not of WKY rats. Correspondingly, ventricular ANP content and concentration were lowered by ETOH in SHR only. Chronic ETOH administration induced a significant increase of plasma arginine vasopressin and a significant decrease of plasma aldosterone in SHR but not in WKY rats. Thus, chronic ETOH treatment prevented the age-dependent elevation of BP in both SHR and WKY rats and altered the activity of heart ANP as well as of the aldosterone and plasma arginine vasopressin systems.

Effect of chronic moderate ethanol consumption on heart brain natriuretic peptide.

There is experimental evidence indicating that chronic moderate ethanol consumption delays the age-dependent increase in blood pressure. Since the brain natriuretic peptide (BNP) is a potent hypotensive hormone, the effect of chronic ethanol treatment on the heart BNP system was investigated, using spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Chronic moderate ethanol consumption resulted in significantly lower circulating BNP levels for both SHR (206.9 +/- 18.5 vs. 306.9 +/- 28.1 pg/ml, n = 12, P < or = 0.05) and WKY rats (131.3 +/- 20.7 vs. 220.6 +/- 25.0 pg/ml, n = 12, P < or = 0.05). Left and right atrial BNP content and concentration in WKY rats and left atrial BNP content and concentration in SHR rats were augmented by the ethanol treatment, but not atrial BNP mRNA. In ventricular tissue, alcohol had no effect on total BNP content of either SHR or WKY rats, but it induced a significant elevation in ventricular BNP concentration (microgram/mg protein) and BNP mRNA in SHR, but not WKY rats. Thus, chronic ethanol treatment resulted in specific alterations in the activity of the heart BNP system.

Implications of endogenous opioids and dopamine in alcoholism: human and basic science studies.

We investigated the endogenous opioid system and its role in mediating the reinforcing effects of ethanol that lead to high ethanol consumption as a biochemical marker of an individual's vulnerability to excessive ethanol consumption. We performed studies using human subjects with [high risk (HR)] and without [low risk (LR)] a family history of alcoholism to supplement our studies with experimental animals bred selectively for high- or low-ethanol consumption. HR subjects had lower basal plasma beta-endorphin levels as compared with LR subjects, but they had a more pronounced release of beta-endorphin after exposure to ethanol. Findings from animal studies indicated that ethanol-preferring (C57BL/6) mice (analogous to the HR human subjects) had higher levels of hypothalamic beta-endorphin activity than did ethanol-avoiding (DBA/2) mice (analogous to the LR human subjects) under basal conditions. However, the C57BL/6 mice had a more pronounced release of hypothalamic beta-endorphin than did DBA/2 mice after exposure to ethanol. Thus, although hypothalamic beta-endorphin system activity in human and animal models of alcoholism differs under basal conditions, there is enhanced hypothalamic beta-endorphin system activity after exposure to ethanol in both models. We have also performed studies comparing the density and distribution of opioid receptors in brains of ethanol-preferring animals, such as C57BL/6 mice and ALKO-alcohol (AA) rats, and ethanol-avoiding animals, such as DBA/2 mice and ALKO-non-alcohol (ANA) rats. Interestingly, it was observed that in distinct brain regions known to be important for mediating the process of reinforcement, the C57BL/6 mice had a higher density of delta-opioid receptors than the DBA/2 mice, while the AA rats had a higher density of mu-opioid receptors than the ANA rats. Thus, in the ethanol-preferring animals, the increased release of beta-endorphin following exposure to ethanol was associated with a higher density of delta- or mu-opioid receptors in brain regions important for reinforcement, such as the nucleus accumbens and the ventral tegmental area, and may interact with the dopaminergic system and promote ethanol's reinforcing properties, leading to excessive drinking and alcoholism.

Enhanced sensitivity of pituitary beta-endorphin to ethanol in subjects at high risk of alcoholism.

BACKGROUND: Previous studies have demonstrated that a moderate dose of ethanol induced a significant increase in the plasma beta-endorphin content of subjects from families with a history of alcoholism (high risk (HR)), but not subjects from families without a history of alcoholism (low risk (LR)). The objective of this study was to examine the response of the pituitary beta-endorphin and adrenal cortisol systems to various concentrations of ethanol in male and female subjects at high and low risk of the future development of alcoholism. METHODS: All subjects participated in four experimental sessions. In each session the subjects were given a drink containing one of the following doses of ethanol: 0, 0.25, 0.50, and 0.75 g of ethanol per kilogram of body weight (for a 60- to 70-kg individual). Blood samples were taken at 0 minutes and at 15, 45, 120, and 180 minutes after the drink for estimation of the blood alcohol, plasma beta-endorphin, and plasma cortisol levels. RESULTS: The concentration of alcohol in the blood at various intervals after the drink was similar among the subjects, regardless of the risk group. Ethanol increased the plasma level of beta-endorphin-related peptides of the HR but not of the LR subjects in a dose-dependent manner. All subjects showed a small decrease in plasma cortisol level with time, but ethanol ingestion did not significantly alter the plasma cortisol levels. CONCLUSION: This study indicates that the pituitary beta-endorphin system, but not the adrenal cortisol system, of the HR subjects shows an enhanced sensitivity to ethanol, which may be an important factor in controlling ethanol consumption.

Implications of endogenous opioids and dopamine in alcoholism: human and basic science studies.

We investigated the endogenous opioid system and its role in mediating the reinforcing effects of ethanol that lead to high ethanol consumption as a biochemical marker of an individual's vulnerability to excessive ethanol consumption. We performed studies using human subjects with [high risk (HR)] and without [low risk (LR)] a family history of alcoholism to supplement our studies with experimental animals bred selectively for high- or low-ethanol consumption. HR subjects had lower basal plasma beta-endorphin levels as compared with LR subjects, but they had a more pronounced release of beta-endorphin after exposure to ethanol. Findings from animal studies indicated that ethanol-preferring (C57BL/6) mice (analogous to the HR human subjects) had higher levels of hypothalamic beta-endorphin activity than did ethanol-avoiding (DBA/2) mice (analogous to the LR human subjects) under basal conditions. However, the C57BL/6 mice had a more pronounced release of hypothalamic beta-endorphin than did DBA/2 mice after exposure to ethanol. Thus, although hypothalamic beta-endorphin system activity in human and animal models of alcoholism differs under basal conditions, there is enhanced hypothalamic beta-endorphin system activity after exposure to ethanol in both models. We have also performed studies comparing the density and distribution of opioid receptors in brains of ethanol-preferring animals, such as C57BL/6 mice and ALKO-alcohol (AA) rats, and ethanol-avoiding animals, such as DBA/2 mice and ALKO-non-alcohol (ANA) rats. Interestingly, it was observed that in distinct brain regions known to be important for mediating the process of reinforcement, the C57BL/6 mice had a higher density of delta-opioid receptors than the DBA/2 mice, while the AA rats had a higher density of mu-opioid receptors than the ANA rats. Thus, in the ethanol-preferring animals, the increased release of beta-endorphin following exposure to ethanol was associated with a higher density of delta- or mu-opioid receptors in brain regions important for reinforcement, such as the nucleus accumbens and the ventral tegmental area, and may interact with the dopaminergic system and promote ethanol's reinforcing properties, leading to excessive drinking and alcoholism.

Fetal ethanol exposure: hypothalamic-pituitary-adrenal and beta-endorphin responses to repeated stress.

Previous studies provide evidence that fetal ethanol exposure induces hypothalamic-pituitary-adrenal (HPA) and pituitary beta-endorphin (beta-EP) hyperresponsiveness to acute stressors. The present study demonstrates significant effects of in utero ethanol exposure on the parallel response patterns of the HPA axis and the pituitary beta-EP system to repeated exposures to a stressor, restraint stress, and indicates sex differences in response. Together, data from the two experiments indicate that, after repeated restraint exposures, fetal ethanol-exposed (E) males and females both show significantly increased plasma levels of adrenocorticotropin (ACTH), and E males also show significantly increased plasma levels of beta-endorphin-like immunoreactivity (beta-EPLIR), compared with their respective pair-fed and control counterparts. Marginal increases in the corticosterone response of E males and the beta-EPLIR response of E females, compared with their controls, were also observed. In addition, delayed or deficient habituation to restraint stress was observed in the beta-EPLIR response of E males and the ACTH response of E females. These data demonstrate that fetal E-exposed males and females both exhibit hormonal hyperresponsiveness and/or deficits in recovery after repeated exposures to restraint stress, but that the patterns of response may differ depending on the number and duration of restraint exposures, the time course measured, and whether the endpoint measured is corticosterone, ACTH, or beta-EPLIR. In addition, the finding that E and pair-fed animals both differed from their respective controls in certain developmental and hormonal measures suggests that prenatal nutritional factors may play a role in mediating some of the changes that are observed.

Implication of the endogenous opioid system in excessive ethanol consumption.

Numerous human and animal studies suggest that certain genetic factors may increase an individual's vulnerability to excessive alcohol consumption. Human and animal studies suggest that some of the reinforcing effects of ethanol may be mediated by the endogenous opioid system. In human studies, plasma levels of subjects genetically at high risk for excessive alcohol consumption showed lower basal activity of beta-endorphin, and more pronounced release of beta-endorphin in response to ethanol. In animal studies, the hypothalamus of mice bred for ethanol preference showed high basal activity of beta-endorphin and more pronounced release of beta-endorphin in response to ethanol than control mice. An important factor in the development of excessive ethanol consumption is the increase in opioidergic activity shortly after individuals begin drinking ethanol. Increased opioidergic activity could mediate the rewarding effects of ethanol, reinforce the act of drinking, and increase ethanol consumption. Human and animal studies, in which the administration of the opioid antagonists naloxone and naltrexone decreased ethanol consumption both by ethanol-preferring animals and by recovering alcoholics, support this hypothesis.