Does ethanol stimulate brain opiate receptors? Studies on receptor binding and naloxone inhibition of ethanol-induced effects

The Dopamine System in Mediating Alcohol Effects in Humans

Brain-imaging studies show that the development and maintenance of alcohol use disorder (AUD) is determined by a complex interaction of different neurotransmitter systems and multiple psychological factors. In this context, the dopaminergic reinforcement system appears to be of fundamental importance. We focus on the excitatory and depressant effects of acute versus chronic alcohol intake and its impact on dopaminergic neurotransmission. Furthermore, we describe alterations in dopaminergic neurotransmission as associated with symptoms of alcohol dependence. We specifically focus on neuroadaptations to chronic alcohol consumption and their effect on central processing of alcohol-associated and reward-related stimuli. Altered reward processing, complex conditioning processes, impaired reinforcement learning, and increased salience attribution to alcohol-associated stimuli enable alcohol cues to drive alcohol seeking and consumption. Finally, we will discuss how the neurobiological and neurochemical mechanisms of alcohol-associated alterations in reward processing and learning can interact with stress, cognition, and emotion processing.

Neurobiological aspects of pain in the context of alcohol use disorder

Alcohol is an effective and widely utilized analgesic. However, the chronic use of alcohol can actually facilitate nociceptive sensitivity over time, a condition known as hyperalgesia. Excessive and uncontrollable alcohol drinking is also a hallmark feature of alcohol use disorder (AUD). Both AUD and chronic pain are typically accompanied by negative affective states that may underlie reinforcement mechanisms contributing to AUD maintenance or progression. Frequent utilization of alcohol to relieve pain in individuals suffering from AUD or other chronic pain conditions may thus represent a powerful negative reinforcement construct. This chapter will describe ties between alcohol-mediated pain relief and potential exacerbation of AUD. We describe neurobiological systems engaged in alcohol analgesia as well as systems recruited in the development and maintenance of AUD and hyperalgesia. Although few effective therapies exist for either chronic pain or AUD, the common interaction of these conditions will likely lead the way for promising new discoveries of more effective and even simultaneous treatment of AUD and co-morbid hyperalgesia. An abundance of neurobiological findings from multiple laboratories has implicated a potentiation of central amygdala (CeA) signaling in both pain and AUD, and these data also suggest that attenuation of stress-related systems (including corticotropin-releasing factor, vasopressin, and glucocorticoid receptor activity) would be particularly effective and comprehensive therapeutic strategies targeting the critical intersection of somatic and motivational mechanisms driving AUD, including alcohol-induced hyperalgesia.

The arousal effect of hyperbaric oxygen through orexin/hypocretin an upregulation on ketamine/ethanol-induced unconsciousness in male rats

Approaches that facilitate the recovery from coma would have enormous impacts on patient outcomes and medical economics. Orexin-producing neurons release orexins (also known as hypocretins) energy-dependently to maintain arousal. Hyperbaric oxygen (HBO) could increase ATP levels by preserving mitochondrial function. We investigated, for the first time, the arousal effects of HBO and orexins mechanisms in a rat model of unconsciousness induced by ketamine or ethanol. A total of 120 Sprague-Dawley male rats were used in this study. Unconsciousness was induced either by intraperitoneal injection of ketamine or ethanol. The HBO treatment (100% O2 at 3 ATA) was administered immediately after unconsciousness induction for 1 hr. SB334867, orexin-1 receptor (OX1R) inhibitor, or JNJ10397049, orexin-2 receptor (OX2R) inhibitor was administered 30 min intraperitoneally before unconsciousness induction. Loss of righting reflex test (LORR) and Garcia test were used to evaluate the unconsciousness duration and neurological deficits after recovering from unconsciousness, respectively. Enzyme-linked immunosorbent assay was used to measure brain tissue ATP and orexin A levels. Ketamine or ethanol injection resulted in LORR immediately and neurological deficits 6 hr after unconsciousness induction. HBO treatment significantly reduced the LORR duration, improved Garcia scores and unregulated ATP and orexin A levels in the brain tissue. Administration of OX1R inhibitor or OX2 R inhibitor abolished arousal and neurological benefits of HBO. In conclusion, HBO exerted arousal-promoting effects on unconscious rats induced by ketamine or ethanol. The underlying mechanism was via, at least in part, ATP/orexin A upregulation. HBO may be a practical clinical approach to accelerate unconsciousness recovery in patients.

Analgesic Effects of Alcohol: A Systematic Review and Meta-Analysis of Controlled Experimental Studies in Healthy Participants

Despite the long-standing belief in the analgesic properties of alcohol, experimental studies have produced mixed results. This meta-analysis aimed to clarify whether alcohol produces a decrease in experimentally-induced pain and to determine the magnitude of any such effect. PubMed, PsycINFO, and Embase databases were searched from inception until April 21, 2016 for controlled studies examining the effect of quantified dosages of alcohol on pain response to noxious stimulation. Eighteen studies involving 404 participants were identified providing alcohol versus no-alcohol comparisons for 13 tests of pain threshold (n = 212) and 9 tests of pain intensity ratings (n = 192). Random effects meta-analysis of standardized mean difference (SMD) provided robust support for analgesic effects of alcohol. A mean blood alcohol content (BAC) of approximately .08% (3-4 standard drinks) produced a small elevation of pain threshold (SMD [95% CI] = .35 [.17-.54], P = .002), and a moderate to large reduction in pain intensity ratings (SMD [95% CI] = .64 [.37-.91], P < .0001), or equivalently, a mean reduction of 1.25 points on a 0- to 10-point pain rating scale. Furthermore, increasing BAC resulted in increasing analgesia, with each .02% BAC increment producing an increase of SMD = .11 for pain threshold and SMD = .20 for reduced pain intensity. Some evidence of publication bias emerged, but statistical correction methods suggested minimal impact on effect size. Taken together, findings suggest that alcohol is an effective analgesic that delivers clinically-relevant reductions in ratings of pain intensity, which could explain alcohol misuse in those with persistent pain despite its potential consequences for long-term health. Further research is needed to corroborate these findings for clinical pain states.

PERSPECTIVE

This meta-analysis provides robust evidence for the analgesic properties of alcohol, which could potentially contribute to alcohol misuse in pain patients. Strongest analgesia occurs for alcohol levels exceeding World Health Organization guidelines for low-risk drinking and suggests raising awareness of alternative, less harmful pain interventions to vulnerable patients may be beneficial.

Effects of ethanol on deep pain evoked by formalin injected in TMJ of rat

It has been reported that ethanol can alter nociceptive sensitivity from superficial tissues, such as skin and subcutaneous region. However, the influence of ethanol on deep pain conditions is not understood. The aim of this study was to demonstrate the acute, chronic and ethanol withdrawal effects on nociceptive behavioral responses induced by the injection of formalin into the temporomandibular joint (TMJ) region of rats. In experiment 1, rats were injected with ethanol (2,5 g/Kg, i.p.) or an equal volume of saline 15 min before the administration of formalin (1.5%) into the TMJ. Rats pretreated with ethanol showed a decrease in nociceptive behavioral responses. In experiment 2, rats were given an ethanol solution (6.5%) or tap water to drink for 4 and 10 days. On day 4, the animals (ethanol group) showed amounts of analgesia when submitted to the TMJ formalin test. Tolerance to the antinociceptive effects was observed on day 10. Behavioral hyperalgesia was verified 12 hr after withdrawal in another group that drank ethanol for 10 days. These results show that ethanol can affect the nociceptive responses related to deep pain evoked by the TMJ formalin test.

Antagonism of the non-opioid component of ethanol-induced analgesia by the NMDA receptor antagonist MK-801

Recent evidence from our laboratory suggests that the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (dizocilpine) selectively antagonizes non-opioid (i.e. naloxone-insensitive) mechanisms of stress-induced analgesia in mice. For example, we have recently demonstrated that a low dose of MK-801 (0.075 mg/kg, i.p.) antagonizes the non-opioid component of a mixed opioid/non-opioid swim stress-induced analgesia (SSIA) resulting from forced swimming for 3 min in 20 degrees C water. Since ethanol-induced analgesia (EIA) has been found to be only partially attenuated by naloxone, we hypothesized that MK-801 would similarly block the non-opioid component of EIA. The effects of MK-801 and of the opioid receptor antagonist naloxone (10 mg/kg, i.p.) on analgesia produced by ethanol (2.5 g/kg in 20% vol/vol, i.p.) were studied in control mice and in mice selectively bred for high (HA) or low (LA) SSIA. HA mice showed significantly more, and LA mice significantly less, EIA than controls. Naloxone and MK-801 significantly attenuated EIA in control and HA mice, and in these lines the combined administration of both antagonists blocked EIA completely. In LA mice, which displayed very little EIA, naloxone but not MK-801 reversed EIA completely. These findings provide additional evidence for the role of the NMDA receptor in non-opioid mechanisms of analgesia. The finding that mice selectively bred for high and low SSIA, also display high and low EIA suggests common mediation of the effects of stress and ethanol on antinociceptive processes.

Morphine-ethanol interaction on body temperature

1. The interaction between ethanol and morphine on core temperature was investigated in Swiss Webster mice. 2. Morphine (2.5-30 mg/kg) and ethanol (0.5-3.0 mg/g) administered individually resulted in a dose dependent decrease in body temperature. 3. When both drugs were injected simultaneously, body temperature decreased less than it would be expected to if the effects were additive. 4. Naloxone antagonized the hypothermic effect of morphine, but the hypothermic effect of ethanol and that of the combination of morphine plus ethanol was only reversed with high doses of naloxone (10 mg/kg). 5. Individual morphine and ethanol plasma levels were not significantly altered by their concomitant administration. 6. Binding of tritiated naloxone to opiate receptors in mouse brain membrane preparations was unchanged by pretreatment with ethanol (0.5 and 2 mg/g). 7. The interaction between morphine and ethanol was found to be less than additive and not related to pharmacokinetic changes of either drug.

Ethanol and opioid receptor signalling

Ethanol may modulate endogenous opioid systems by disrupting opioid receptor signalling. Low concentrations of ethanol slightly potentiate mu-opioid receptor binding by increasing receptor Bmax, and, in some cases, chronic ethanol exposure decreases the density or affinity of the mu-opioid receptors. By contrast, high concentrations of ethanol acutely decrease delta-opioid receptor binding by decreasing receptor affinity, whereas chronic exposure of animals and neuronal cell lines to lower concentrations of ethanol leads to possibly adaptive increases in the density or affinity of the delta-opioid receptors. In the neuronal cell line NG108-15, ethanol does not up-regulate the delta-opioid receptor by blocking receptor degradation or endocytosis, but protein synthesis is required for this response. Up-regulation of the delta-opioid receptor renders ethanol-treated NG108-15 cells 3.5-fold more sensitive to opioid inhibition of adenylyl cyclase. Long-term treatment with ethanol also increases maximal opioid inhibition in NG108-15 cells, possibly by decreasing levels of G alpha s and its mRNA. Ethanol differentially modulates signal transduction proteins in three additional neuronal cell lines, N18TG2, N4TG1, and N1E-115. Ethanol-treated N18TG2 cells show the least up-regulation of the delta-opioid receptor, little heterologous desensitization of adenylyl cyclase, and no changes in G alpha s or G alpha i. By contrast, ethanol-treated N1E-115 cells show the largest up-regulation of the delta-opioid receptor, the most heterologous desensitization of adenylyl cyclase, and concentration-dependent decreases in G alpha s and increases in G alpha i. Further analysis of these related neuronal cell lines may help to identify the molecular elements that endow some, but not all, neuronal cells with the capacity to adapt to ethanol.

New differences between the Wistar rat and Octodon degus, a putative laboratory animal resistant to morphine

1. The effects of CNS depressants (methadone and alcohol) and natural neurotransmitters (NA and ACh) are studied in O. degus. 2. O. degus shows resistance to methadone in the formalin algesiometric test and EEG. 3. Ethanol elimination profile suggest the presence of an atypical alcohol dehydrogenase in O. degus 4. O. degus is extremely resistant to the pressor effects of noradrenaline 5. the isolated atrium of this rodent is 40 times more sensitive to the negative chronotropic effect of methadone, than the rat atrium. 6. These effects could be explained in terms of an important catecholamine and endorphin co-secretion from adrenal glands in O. degus.

Mode of potentiating action of cocaine in morphine analgesia

The mechanism of antinociceptive interactions among morphine, cocaine and alcohol was studied in mice, guinea pigs and rabbits. In the tail-pressure test in mice, cocaine and alcohol alone showed almost no antinociceptive effects at doses up to 8 mg/kg, s.c., and 4 g/kg, respectively. Alcohol at 2 g/kg, i.g., also did not influence the effect of morphine, while cocaine at 4 mg/kg, s.c., significantly potentiated the antinociceptive effects of not only morphine but also pentazocine. In an analysis of serum and brain concentration levels of morphine in mice, when morphine and cocaine were simultaneously administered at 2 mg/kg, s.c., and 4 mg/kg, s.c., respectively, both serum and brain levels of morphine showed neither increase nor decrease in comparison with the levels in mice administered morphine alone. In myenteric plexus-longitudinal muscle preparations of isolated guinea pig ileum, 1 microM cocaine enhanced the agonistic effects of both pentazocine and ethylketocyclazocine. Furthermore, cocaine as well as ethylketocyclazocine showed naloxone-reversible agonistic effects in isolated rabbit vas deferens. These results indicate that cocaine may potentiate the antinociceptive effects of morphine and pentazocine by acting on the kappa-opioid receptors as an agonist.

Narcotic antagonism of seizures induced by a dopamine-derived tetrahydroisoquinoline alkaloid

This paper describes experiments designed to evaluate whether the narcotic antagonist naloxone significantly interferes with seizures induced by tetrahydroisoquinolines (TIQs). In these experiments we found that naloxone significantly reduced seizure scores induced by intra-cranially infusing mice with 50 micrograms of the dopamine-derived tetrahydroisoquinoline (TIQ) alkaloid, 6,7-dihydroxy TIQ. These findings support an opioid involvement in the actions of TIQs and may lead to further understanding of opioid-mediated novel excitatory receptors.

Selective effects of ethanol on opiate receptor subtypes in brain

Large concentrations of ethanol in vitro decreased ligand binding to mu and delta opiate receptors in the frontal cortex of the C57BL mouse, but did not alter binding to kappa opiate receptors. Mu and delta receptors were equally sensitive to the inhibitory effect of ethanol. Since the effects of ethanol were significant only in large concentrations, ethanol may alter opiate binding through its membrane lipid-perturbing actions, and the selectivity of the effects of ethanol may reflect differences in the microenvironments of the opiate receptor subtypes in membranes. After chronic ingestion of ethanol by mice, in vivo, there was a selective decrease in the number of mu receptors in the frontal cortex. This change may result from indirect effects of ethanol on the opiate receptor and may contribute to specific central effects of ethanol.

The contribution of classical conditioning to tolerance to the antinociceptive effects of ethanol

In rats, ethanol increases the latency of the tail-flick reflex to radiant heat. Three experiments examined the contribution of classical conditioning to the acquisition of tolerance to this antinociception. Experiment 1 showed that the antinociception produced by ethanol was dose dependent. The results of Experiment 2 demonstrated that rats exposed to a series of ethanol injections paired with a distinctive environment developed tolerance to this antinociception. In Experiment 3, tolerance was more pronounced in animals that had been exposed to ethanol and tested in the distinctive environment than in animals that had received ethanol in a nondistinctive environment. In contrast to previous reports in the literature, these results show that animals need not practice the tail-flick reflex while intoxicated in order to develop tolerance. Additionally, the data suggest that classical conditioning may contribute to tolerance to the antinociceptive effects of ethanol.

Antagonism by naltrexone of voluntary alcohol selection in the chronically drinking macaque monkey

An opiate receptor antagonist can reduce excessive alcohol drinking in the rat previously given intracerebroventricular (ICV) infusions of a tetrahydroisoquinoline. Recently, it was found that cerebrospinal fluid (CSF) obtained from volunteers or human patients and subsequently injected ICV in macaque monkeys markedly alters the voluntary consumption of ethyl alcohol in certain of these primates. The purpose of the present study was to determine whether an opioid antagonist would affect the pattern of alcohol intake in selected monkeys which drank excessive amounts of alcohol. Initially, the preferred concentration of alcohol was determined individually for each monkey which consistently drank from 3.0-6.0 g/kg alcohol per day. Subsequently, the single concentration, which ranged from 5-15%, was offered together with water during three consecutive periods as follows: (1) 4-day control baseline period; (2) a 3-day interval during which a saline control vehicle or 0.6 or 1.2 mg/kg naltrexone was administered subcutaneously at 0900 and 1700 hours; and (3) a final 4-day post-injection period during which the alcohol-water preference test was continued. The results showed that both doses of naltrexone significantly attenuated voluntary alcohol drinking up to 60% of the baseline intake during the 3 days of its administration. In two monkeys, alcohol drinking continued to be suppressed up to 50% of basal intake during all or a part of the 4-day post-naltrexone interval. These findings suggest that an opiate receptor mechanism in the brain could be partially involved in the action of the chemical constituents of the human's CSF which serve to induce an abnormally high intake of alcohol in the infra-human primate.

Ethanol-induced hypothermia in rats: possible involvement of opiate kappa receptors

The effect of the opiate antagonists naloxone and MR2266 on ethanol-induced hypothermia and changes in Ca2+-stimulated Mg2+-ATPase activity in brain regions were investigated in the present study. Administration of different doses of ethanol (0.5-2 g/kg, IP) produced a dose-dependent hypothermia. Ca2+/Mg2+-ATPase activity in the hypothalamus was stimulated at 30 min and 2 hr after ethanol (2 g/kg, IP) treatment. In cortex, enzyme activity was inhibited by ethanol at 30 min with no change seen at 2 hr. Naloxone (7.5 mg/kg, SC) at a dose which did not affect body temperature or enzyme activity, partially inhibited ethanol-induced hypothermia and enzyme activity at the earliest time (30 min) but not at 2 hours. The opiate Kappa antagonist MR2266 (5 mg/kg, SC), however, significantly protected against ethanol hypothermia and enzyme activation measured at 30-120 min. This evidence suggests that ethanol-induced hypothermia and subsequent activation changes of Ca2+/Mg2+-ATPase in the hypothalamus may be regulated by opiate Kappa receptors, and that Ca2+ ions play an important role in mediating the effects of ethanol.

Evidence from behavioural and in vitro receptor binding studies that the enkephalinergic system does not mediate acute ethanol effects

The behavioural disturbances produced by acute exposure to ethanol have been related to changes in function of the opioid systems in the CNS. However, evidence in the literature is conflicting. The present report concerns the possible role of the enkephalinergic system in the mediation of acute ethanol effects. We used rats to study the ability of a selective opioid delta receptor antagonist (ICI 154129) to prevent the effect of ethanol on pain sensitivity, body temperature, sensorimotor performance and level of consciousness. Furthermore, in vitro receptor binding was measured to investigate whether or not ethanol, within a non-lethal concentration range, would change the binding parameters of the delta receptor ligand [3H][D-ala2, D-Leu5]enkephalin. ICI 154129 did not significantly influence the effects of ethanol in the behavioural experiments. Ethanol did not significantly change the binding parameters whether saturation or competition was measured in the receptor binding experiments. Thus, there was no evidence that the enkephalinergic system mediated the acute ethanol effects.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Narcan inhibition of human liver alcohol dehydrogenase

Narcan, the pharmaceutical agent for the administration of naloxone, has been reported to antagonize ethanol intoxication. In addition to naloxone, Narcan contains the antioxidant esters methyl- and propylparaben. Pure naloxone and these two esters were examined for their capacity to inhibit ethanol oxidation by purified isozymes of human liver alcohol dehydrogenase (ADH). Naloxone (400 micromolar) fails completely to inactivate any of the three ADH isozyme classes. In contrast, methyl- and propylparaben, and some related esters, competitively inhibit the oxidation of ethanol and reduction of acetaldehyde by all isozymes examined. The reported effects of Narcan on ethanol-intoxicated animals or cells cannot be attributed to the action of naloxone.

Naloxone does not reverse ethanol analgesia in man

The effects of intravenously administered ethanol and morphine on pain threshold, reaction time, motor skills and short-term memory were investigated, and the ability of naloxone to reverse any changes was studied. Morphine (loading dose 0.2 mg/kg with an infusion of 0.004 mg/kg per min) and ethanol (loading dose 0.75 ml/kg with an infusion of 0.0025 ml/kg per min) produced a similar increase in pain threshold of 6.3 (s.e.m. = 1.5, n = 8) pain units and 7.7 (s.e.m. = 1.9, n = 8) pain units, respectively. Naloxone 0.015 mg/kg produced a significant reduction in pain threshold in the morphine group, but not in the ethanol group, and there was a significant difference between the groups following naloxone (P less than 0.05, t-test, 7 d.f.). Ethanol produced a significantly greater deterioration in motor skills than did morphine (P less than 0.05, t-test, 7 d.f.) and performance in both groups was improved following naloxone (P less than 0.05, t-test, 7 d.f.). There was no significant change in the other modalities studied. It is concluded that the reversal of ethanol effects by naloxone is probably due to a non-specific analeptic action rather than blockade of opioid receptors.

Stereospecific interaction between alcohol and opiates mediated by the mu high-affinity binding receptor

Experiment 1 revealed that preexposure to morphine blocked ethanol-induced CTA, and that conversely, preexposure to ethanol blocked morphine-induced CTA. In experiment 2, naloxazone injected 4.5 hr before the preexposure drug significantly reversed the interaction between morphine and ethanol. The results of Experiment 3 showed that preexposure to levorphanol blocked both morphine- and ethanol-induced CTAs while dextrorphan at the same dose did not affect the CTAs. These findings are discussed in terms of the involvement of the opiate receptors and their ligands in opiate-ethanol interaction.

Receptor stereospecificity in opiate-ethanol interaction using the preexposure-conditioned taste aversion (CTA) paradigm

In the first experiment, rats were conditioned with different doses of levorphanol or dextrorphan to a novel tasting saccharin solution. In the second experiment, rats were either preexposed to levorphanol or dextrorphan and conditioned with either morphine or ethanol to the saccharin solution. The results showed that levorphanol, but not dextrorphan, at 1, 5 and 10 mg/kg doses effectively induced a CTA. Preexposure to the 5 mg/kg dose of levorphanol blocked both morphine- and ethanol-induced CTAs. Dextrorphan at the same dose did not affect the CTAs. These findings are discussed in terms of the involvement of the opiate receptors in opiate-ethanol interaction.

Attenuation of ethanol-induced conditioned taste aversion by naloxazone: behavioral evidence for an opiate receptor-mediated morphine-ethanol interaction

When rats are presented with a novel saccharin solution and immediately injected with either morphine or ethanol, they subsequently develop a conditioned taste aversion (CTA) to the saccharin solution which reflects the aversive component of the conditioning drug. The present study provides evidence which suggests that both morphine-induced and ethanol-induced CTAs can be blocked by the specific high-affinity binding opiate antagonist, naloxazone.

Ethanol modulation of opiate receptors in cultured neural cells

The mouse neuroblastoma-rat glioma hybrid cell line NG108-15 was used to study the acute and chronic interaction of ethanol with intact neural cells. In the short term, ethanol inhibited opiate receptor binding, but after long-term exposure the cells exhibited an apparent adaptive increase in the number of opiate binding sites; this was reversible when ethanol was withdrawn. High concentrations of ethanol (200 mM) increased opiate binding after 18 to 24 hours, whereas lower concentrations (25 to 50 mM) produced similar changes after 2 weeks. This model system has potential for exploring the cellular and molecular mechanisms underlying ethanol intoxication, tolerance, and withdrawal.

Chronic ethanol alters the receptor binding characteristics of the delta opioid receptor ligand, D-Ala2-D-Leu5 enkephalin in mouse brain

The binding characteristics of the delta opioid receptor ligand, 3H-D-Ala2-D-Leu5 enkephalin, were markedly altered in brains obtained from mice fed an ethanol-containing diet for five days. Control mice exhibited both a high and low affinity site for 3H-D-Ala2-D-Leu5 enkephalin, whereas those consuming the ethanol diet were found to possess only one binding site. This singular site has an intermediate KD value with an increase in receptor number when compared to the high and low affinity sites observed in control mice. The in vitro addition of ethanol to a brain membrane preparation obtained from untreated mice, at a concentration equivalent to that found in the blood of the ethanol-treated mice, did not markedly affect D-Ala2-D-Leu5 enkephalin binding characteristics. No alteration in the binding characteristics of 3H-naloxone, a mu receptor ligand, was noted following five days of ethanol consumption. Mice maintained on the ethanol-containing diet were tolerant to the activity-stimulating effects of acute ethanol administration. These results suggest that mice consuming an ethanol diet in sufficient quantities to render them tolerant exhibit a specific loss of a 3H-D-Ala2-D-Leu5 enkephalin binding site, while the binding of 3H-naloxone was unchanged.

Symmetrical effect of pre-exposure between alcohol and morphine on conditioned taste aversion

It has previously been reported that pre-exposure to a psychoactive drug can block the conditioned taste aversion associated with that drug. This study was an attempt to investigate alcohol-morphine interactions using this pre-exposure paradigm. After two weeks of adaptation to a schedule of daily 30-minute access to water, rats were pre-exposed to morphine, ethanol, or the respective vehicle control every second day for three days before (Days 1, 3, 5) and after the first conditioning day (Days 8, 10, 12). On conditioning days (Days 7, 14), animals were first presented with a saccharin solution for 30 minutes following which animals that were pre-exposed to morphine were injected with ethanol while those pre-exposed to ethanol were administered with morphine. Saccharin was again presented on three more occasions (Days 21, 28, 35) without drug injection. Using the percent change in saccharin consumed from the first presentation as a measure of aversion, it was found that pre-exposure to morphine blocked ethanol conditioned taste aversion. Similarly, animals pre-exposed to ethanol showed less aversion to the saccharin paired with morphine. This is the first demonstration of a symmetrical relationship between alcohol and the opiates.

Naloxone and alcohol intoxication in the dog

1 The effects of naloxone upon ethanol-induced coma have been investigated in dogs. In a double blind study, 15 mongrel dogs received ethanol i.v. (4 g/kg) followed by a single dose of naloxone (12 micrograms/kg). 2 Naloxone failed to affect either the duration of respiratory arrest or the time to recovery of motor coordination. In similar animals treated with the narcotic analgesic, fentanyl, naloxone induced a dramatic and complete reversal of the narcotic effects within 30 seconds. 3 It is concluded that, if naloxone has any effect in alcoholic coma, it is not comparable with its dramatic action in narcotic coma.

Alcohol interactions with brain opiate receptors

Ethanol, added in vitro to mouse caudate membranes, inhibited high-affinity binding of 0.2 nM 3H-dihydromorphine (3H-DHM) over an ethanol concentration range of 250-1,000 mM. At lower, physiologically-attainable ethanol concentrations (e.g.: 50 mM), 3H-DHM binding was significantly increased. Over the concentration range of 50-1,000 mM, ethanol inhibited 0.5 nM 3H-[D-Ala2,D-Leu5]enkephalin (3H-ENK) binding to mouse caudate tissue, and no stimulation of 3H-ENK binding was noted at any of these concentrations of ethanol. Ethanol inhibits opiate binding in a pseudo-competitive manner and, therefore, the concentration of ligand used to assess the effects of ethanol is of major importance. Results obtained with other alcohols which differ in their membrane:water partition coefficients suggest that alcohol effects on opiate binding are not solely dependent on the membrane-disordering properties of the alcohols.

Antagonism of the behavioral effects of ethanol by naltrexone in BALB/c, C57BL/6, and DBA/2 mice

The effects of naltrexone on the increase in locomotor activity induced by a low dose (1.35 g/kg IP) of ethanol and on the duration of loss of righting reflex after a high dose (3.5 g/kg) of ethanol were studied in BALB/c, DBA/2, and C57BL/6 mice. Ethanol increased locomotor activity in DBA and BALB mice, but not in C57BL mice. Naltrexone, at a dose of 0.1 mg/kg, antagonized the ethanol-induced increase in locomotion similarly in DBA and BALB mice. The duration of loss of righting reflex was, however, differentially affected in all three strains by naltrexone. The BALB mice affected in all three strains by naltrexone. The BALB mice were the most sensitive strain (1 mg/kg naltrexone significantly counteracted ethanol hypnosis), the C57BL mice were intermediate (8 mg/kg naltrexone required to antagonize this effect of ethanol), and the DBA mice were least sensitive (no effect evident even at the highest dose of 8 mg/kg) to naltrexone. Thus, naltrexone could antagonize the behavioral effects of a low and high dose of ethanol, but the three strains, which differ in their behavioral response to ethanol, also were differentially sensitive to the effect of naltrexone in reversing ethanol-induced hypnosis and ethanol-induced changes in locomotor activity.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.