Isradipine and Other Calcium Channel Antagonists Attenuate Ethanol Consumption in Ethanol-Preferring Rats

The present work is concerned with studying of the ability of different calcium channel antagonists to modify voluntary ethanol ingestion by rats selectively bred for high ethanol preference. The compounds were given s.c. thrice daily for 5 days at doses that did not produce locomotor impairment. While nifedipine, darodipine, and verapamil (each at the dose of 20 mg/kg thrice daily) produced a modest reduction in ethanol intake, isradipine (at the dose of 1 mg/kg three times a day) reduced ethanol intake by over 70%. For all compounds, the reduction in ethanol intake was compensated by a proportional increase in water consumption and the inhibitory effect persisted throughout the 5 days of treatment. The data indicate that calcium channel antagonists exhibit quite different potency in reducing ethanol preference, however this action is a general property of this class of compounds.     

Naltrexone Reduces Ethanol- and/or Water-Reinforced Responding in Rhesus Monkeys: Effect Depends Upon Ethanol Concentration

BACKGROUND: The opioid antagonist naltrexone reduces responding for ethanol. If naltrexone produces this effect by blocking ethanol-induced opioid activity, then naltrexone should reduce responding for ethanol regardless of level of the ethanol responding relative to an alternatively available reinforcer. In addition, if naltrexone competitively blocks ethanol-induced opioid activity, then the naltrexone effect may be surmountable by increasing ethanol concentration and, thus, ethanol intake (g/kg). This study was conducted to determine whether naltrexone will selectively reduce ethanol-reinforced responding when the ethanol concentration is varied such that ethanol fluid deliveries are less than, greater than, or equal to the fluid deliveries of concurrently available water. METHODS: Four adult male rhesus monkeys were allowed to respond for ethanol or water concurrently for 2 hr per day. Ethanol concentration was either 2%, 8%, or 32%. On various days, either saline or naltrexone (0.1 mg/kg) was given intramuscularly 30 min before the drinking session. RESULTS: When ethanol fluid deliveries were greater than those of water (at 2% ethanol), naltrexone reduced responding for ethanol. When the ethanol and water fluid deliveries were approximately equal (at 8% ethanol), naltrexone reduced both ethanol and water fluid deliveries. When water fluid deliveries were greater than those of ethanol (at 32% ethanol), naltrexone reduced responding for water. CONCLUSIONS: Thus, naltrexone reduced responding for the preferred fluid, either ethanol or water, depending on ethanol concentration. The effect was not surmountable by increasing ethanol concentration and, therefore, ethanol intake (g/kg). Naltrexone may reduce ethanol-reinforced responding by a mechanism other than that of blocking ethanol-induced opioid activity. Naltrexone may be inducing an aversive interoceptive state.     

Differential Changes in Sucrose/Ethanol and Sucrose Maintained Responding by Independently Altering Ethanol or Sucrose Concentration

Increased reinforcing efficacy of sucrose/ethanol solutions in comparison to sucrose solutions has been previously demonstrated. However, the contribution of the components of the sucrose/ethanol solution is not well defined. The present study used a multiple schedule of reinforcement to evaluate the differential changes in reinforcer presentations as sucrose or ethanol concentrations were altered. Male Long-Evans rats were trained to press a lever on a multiple fixed ratio 4-fixed ratio 4 schedule which was composed of alternating 2-min components. During one component, 5% sucrose/10% ethanol was presented as the reinforcer and, in the second component, 5% sucrose was presented. Independent manipulations of the ethanol concentration (0,5, and 20%) in the sucrose/ethanol solution or sucrose concentration (0, 10, and 20%) in the sucrose solution were then performed. Increasing the ethanol concentration in the sucrose/ethanol solution resulted in decreases in reinforcer delivery but increases in ethanol intake (grams per kilogram) and total session caloric intake. Increasing the sucrose concentration in the sucrose solution resulted in significant increases in sucrose reinforcer delivery and total session caloric intake. During the concentration manipulations, the number of reinforcers presented of the unchanged reinforcer was not affected. Differential changes in the pattern of reinforcer presentation after ethanol and sucrose concentration manipulations during successive access periods suggest that sucrose and sucrose/ethanol maintained responding are differentially regulated. Changes in sucrose maintained responding after increases in the sucrose concentration were observed early in the session suggesting a strong influence of taste in regulating intake. Changes in sucrose/ethanol maintained responding after increases in the ethanol concentration occurred later in the session and suggest that postingestive effects (i.e., pharmacology) play a major role in the regulation of sucrose/ethanol intake. In addition, the differential patterns of sucrose/ethanol and sucrose maintained behavior suggest that the ethanol component of the sucrose/ethanol solution plays an important role in maintaining sucrose/ethanol reinforced behavior.     

Responding for Oral Ethanol after Naloxone Treatment by Alcohol-Preferring AA Rats

The present study examined the effect of a relatively nonselective opioid antagonist, naloxone, on lever pressing for oral ethanol by the alcohol-preferring AA rats. The AAs, housed continually in operant chambers with free access to food and water, learned to respond for 10% oral ethanol during daily 60-min alcohol access periods indicated by a stimulus light. The rats developed stable ethanol responding, resulting in mean ethanol intakes of 1.2 g/kg/60 min and measurable blood alcohol levels. In the first experiment, single systemic injections of naloxone (0.05–2.5 mg/kg) had no effect on the initial rate of responding; dose-dependent decreases were observed later during the alcohol access. The second experiment examined the effects of repeated injections of 0.5 and 2.5 mg/kg naloxone on 5 consecutive days. Naloxone suppressed responding dose-relatedly over the treatment days. In contrast to the effects of single injections, repeated injections with 2.5 mg/kg naloxone produced progressive decreases within the first minutes of access. The results suggest that naloxone may attenuate the reinforcing actions of ethanol.     

Effects of Ethanol, MK-801, and Chlordiazepoxide on Locomotor Activity in Different Rat Lines: Dissociation of Locomotor Stimulation from Ethanol Preference

Several lines of research have suggested a link between the reward value of a drug and its ability to stimulate locomotion. One goal of the present study was to determine whether ethanol preferentially stimulates locomotor activity in lines of rat that show a preference for ethanol. A secondary goal was to determine the extent to which the benzodiazepine-like and NMDA antagonistic action of ethanol accounted for its effect on locomotor activity. To meet these goals, the effects of varying doses of ethanol (0.125-1.0 g/kg), MK-801 (0.1-0.3 mg/kg), and chlordiazepoxide (0.3-3 mg/kg) on locomotor activity were studied in several lines of rats that had been habituated to the testing procedure. The effect of low doses of ethanol on motor activity in the Alcohol-Preferring (P) and Fawn-Hooded rats, which show a strong ethanol preference, were similar to those of the alcohol-nonpreferring (NP), Flinders Sensitive Line, and Flinders Resistant Line rats. Only the Flinder Resistant Line rats showed a small, but significant increase in locomotor activity after the administration of ethanol. The highest dose of ethanol (1.0 g/kg) produced locomotor depression in all lines except the P and NP lines, which were not tested at this dose. These findings do not support a link between locomotor stimulation by ethanol and ethanol preference. In contrast, all lines exhibited locomotor stimulation after moderate (0.1-0.3 mg/kg) doses of MK-801, but did not exhibit increases in activity following any dose of chlordiazepoxide. These data indicate that the profiles of activity after MK-801 and chlordiazepoxide were distinct from that of ethanol in the various rat lines. Therefore, the effects of ethanol on locomotor activity cannot be accounted for by reference solely to its antagonist-like action at NMDA receptors and/or its agonist-like action at GABA/benzodiazepine receptors.     

Effect of Pentylenetetrazole on Ethanol Intake, Ethanol Kinetics, and Social Behavior in Male Wistar Rats

Stress and anxiety are often implicated in excessive alcohol use. The nature of this interaction, however, is not understood. The aim of this study was to examine the effect of the anxiogenic agent, pentylenetetrazole (PTZ), on the acquisition and maintenance of ethanol drinking behavior in male Wistar rats. In rats maintained on a limited access procedure, with a choice between a 12% w/v ethanol (ETOH) solution and water available for 30 min each day, acute PTZ administration (1.5 to 15.0 mg/kg) did not modify ETOH intake. Chronic PTZ administration elicited a significant suppression in ETOH intake; however, this effect developed gradually over time. During the acquisition phase, chronic PTZ treatment also suppressed ETOH consumption. Chronic, but not acute, treatment with PTZ seemed to enhance water consumption. To assess whether the effect of PTZ on ETOH intake was due to either alterations in ETOH kinetics or behavior, blood ETOH levels and social interaction behaviour were examined. PTZ (15.0 mg/kg) produced a significant suppression in social interaction behavior, although tolerance developed to this effect on chronic PTZ administration. Both acute and chronic PTZ treatment (15 mg/kg) resulted in lower blood ETOH levels achieved after administration of 1.0 g/kg po of ETOH. Because the anxiogenic effect of PTZ was not maintained on repeated administration, yet the suppression of ETOH intake was only observed after chronic treatment, this suggests a dissociation between the processes regulating these behaviors.     

The Discriminative Stimulus Properties of Acute Ethanol Withdrawal (Hangover) in Rats

Twenty male Sprague-Dawley rats were trained to discriminate pentylenetetrazole (PTZ, 15 mg/kg, intraperitoneally) from saline (SAL) under a drug discrimination procedure. Test sessions were conducted with 10 randomly selected subjects. Tests with various doses of PTZ resulted in a dose-dependent increase in the percentage of total session responses emitted on the PTZ-appropriate lever without a significant change in response rates across a wide range of test PTZ doses. Rats did not generalize the PTZ stimulus to ethanol (ETOH) up to ETOH test doses that completely suppressed responding. High acute ETOH doses (2, 3, and 4 g/kg) administered at various time points prior to discrimination test sessions engendered responding on the PTZ-appropriate level in a quantitative fashion, that was dose- and time-dependent. This acute ETOH delayed effect from these high doses replicates our previously published study using a Drug 1-Drug 2 discrimination task with Chlordiazepoxide and PTZ. More importantly, we suggest that the present behavioral assay may be a sensitive animal analogue of human "hangover" phenomena.     

The α1-Adrenergic Receptor Antagonist, Prazosin, Reduces Alcohol Drinking in Alcohol-Preferring (P) Rats

Background:  Preliminary evidence suggest that noradrenergic signaling may play a role in mediating alcohol drinking behavior in both humans and rats. Accordingly, we tested the hypothesis that blockade of α₁-adrenergic receptors will suppress alcohol drinking in rats selectively bred for alcohol preference (P line).
Methods:  Adult male P rats were given 24-hour access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 hours daily. Rats were injected IP with the α₁-adrenergic receptor antagonist, prazosin (0, 0.5, 1.0, 1.5, or 2.0 mg/kg body weight), once a day at 15 minutes prior to onset of the daily 2-hour 2-bottle choice, alcohol versus water, access period for 2 consecutive days and then 3 weeks later for 5 consecutive days.
Results:  Prazosin significantly reduced ( p  < 0.01) alcohol intake during the initial 2 daily administrations, and this reduction of alcohol intake was maintained for 5 consecutive days by daily prazosin treatment in the subsequent more prolonged trial ( p  < 0.05). The prazosin-induced reduction of alcohol intake was not dependent upon drug-induced motor impairment since increases in water drinking ( p  < 0.05) were exhibited during the 2-hour access periods during both 2- and 5-day prazosin treatment.
Conclusions:  The results indicate that the noradrenergic system plays a role in mediating alcohol drinking in rats of the P line and suggest that prazosin—a safe, well-characterized, and well-tolerated drug—may be an effective pharmacotherapeutic agent for the treatment of alcohol use disorders.     

Increased Anxiety-Like Behavior and Ethanol Self-Administration in Dependent Rats: Reversal via Corticotropin-Releasing Factor-2 Receptor Activation

BACKGROUND: Corticotropin-releasing factor (CRF) has been hypothesized to be one of the main regulators of the stress response observed during alcohol withdrawal. The CRF receptor subtypes seem to have a differential role in the regulation of stress-related behavior. Given the behavioral characterization of these receptors, the objective of the following experiments was to characterize the role of CRF2 receptors in the interaction between alcohol and stress by examining the effects of CRF2 receptor activation in the behavioral stress response and ethanol self-administration during early ethanol withdrawal in dependent rats. METHODS: Male Wistar rats were made dependent on ethanol via chronic exposure to an ethanol containing liquid diet. Behavior in the elevated plus maze and ethanol self-administration were measured at 2 hr after removal of the diet. The role of the CRF2 receptor in the regulation of these behaviors during the early stages of withdrawal was examined via central injection of the highly selective CRF2 receptor agonist urocortin 3. RESULTS: Rats showed decreased exploration of the open arms of the elevated plus maze, an indication of a heightened behavioral stress response, after chronic ethanol exposure. This effect was attenuated by central injection of urocortin 3. In addition, urocortin 3 injections reversed the increase in ethanol self-administration observed during early withdrawal in dependent rats. CONCLUSIONS: Reversal of the increased stress-related behavior in the elevated plus maze observed after injections of urocortin 3 indicates that the decreased responding for ethanol also seen after urocortin 3 administration is likely due to a diminished anxiety-like state. These data suggest that activation of the CRF2 receptor may provide a novel target in the attenuation of the stress response characteristic of the early stages of ethanol withdrawal.     

Zinc Administration Improves Gastric Alcohol Dehydrogenase Activity and First-Pass Metabolism of Ethanol in Alcohol-Fed Rats

The effects of zinc on first-pass metabolism (FPM) of ethanol and gastric and hepatic alcohol dehydrogenase (ADH) activities have been investigated in two groups of male Wistar rats fed a liquid ethanol diet with normal zinc content (7.6 mg/liter), or zinc supplemented (76 mg/liter), for 21 days, and in two pair-fed groups receiving the same diets without ethanol. Alcoholic rats with normal dietary zinc had lower FPM (1.64 ± 0.25 vs. 2.43 ± 0.20 mM ± hr, p < 0.05) and gastric ADH activity (184 ± 7 vs. 335 ± 41 μmol/min/mg protein, p < 0.01) than control rats. Zinc supplementation did not produce any change in FPM or in gastric ADH activity in control rats. By contrast, in alcoholic rats, the zinc supplement increased gastric ADH activity (247 ± 31 vs. 184 ± 7 μmol/min/mg protein, p < 0.05) and decreased the areas under the curve of blood ethanol concentrations after the intragastric administration of 0.25 g/kg of body weight of ethanol (0.78 ± 0.07 vs. 1.71 ± 0.24 mM ± hr, p < 0.05), thereby increasing the FPM. In conclusion, in alcohol-fed rats, the administration of zinc supplements restores gastric ADH activity and improves the FPM of ethanol. These effects may be one of the mechanisms in which zinc has a beneficial role in preventing the development of alcoholic hepatic lesions.     

Appetitive and Consummatory Behaviors in the Control of Ethanol Consumption: A Measure of Ethanol Seeking Behavior

Models of ethanol self-administration in animals have demonstrated that ethanol can reinforce a variety of behaviors, independent of ethanol's caloric or fluid properties. However, the processes that control self-administration remain unclear. Determining factors related to ethanol seeking behavior, independent of consumption, Is central to the concepts of intake regulation. The model described in this article proposes a method to separate the initial appetitive (seeking) behavior from the following consummatory (drinking) behavior to assess each behavior type. Rats were trained to lever press to gain access to a drinking tube connected to a fluid bottle containing either 10Y0 ethanol or 3% sucrose for 20 min. When the response requirement to obtain access to the tube was increased, it was found that both solutions supported the same amount of responding (breakpoint was at approximately a fixed ratio 32 requirement), indicating equal reinforcer strength. However, regardless of the response requirement, if access to the fluids occurred, intakes were not changed. This suggests that factors besides those of reinforcer efficacy are important in controlling the size of the consummatory bout. Based on these findings, we believe that this model will be useful in determining factors related to seeking behaviors and the control of drinking bout size.     

A Retinoic Acid Receptor Antagonist Suppresses Brain Retinoic Acid Receptor Overexpression and Reverses a Working Memory Deficit Induced by Chronic Ethanol Consumption in Mice

BACKGROUND: Chronic ethanol consumption induces disorders in the biosynthesis of retinoic acid, an active derivative of vitamin A. Recent evidence suggests that an alteration in the retinoic acid signaling pathway leads to impairments in learning and memory in adult mice. We have previously shown that chronic ethanol consumption in mice produces an increased expression of the brain retinoic acid receptor beta (RARbeta) mRNA. These results prompted us to examine whether suppressing the overexpression of retinoid receptors in alcohol-treated mice by RAR antagonist administration would reverse their cognitive impairment. METHODS: After 10 months of ethanol consumption (12% v/v in drinking water), C57BL/6 mice were submitted to a working memory task in a T-maze. Then, mice of the control and the ethanol-treated groups received an RARbeta antagonist (CD2665 0.6 mg/kg) for 22 days. The behavioral effect of CD2665 administration was evaluated on a spontaneous alternation task and the neurochemical effect was measured by quantifying the mRNA expression of RARalpha, RARbeta, retinoid X receptor (RXRbeta/gamma) and tissue transglutaminase (tTG; a retinoic acid-target gene). RESULTS: Mice submitted to ethanol treatment exhibited a progressive decrease in spontaneous alternation rates over successive trials. Moreover, these mice displayed an increased expression of brain RARbeta and RXRbeta/gamma mRNA, together with an increased level of tTG mRNA and enzymatic activity. The administration of CD2665 to alcohol-treated mice totally reversed the working memory deficit and suppressed the overexpression of brain RARbeta, RXRbeta/gamma and tTG mRNA, whereas the same treatment in control mice decreased only the RARbeta mRNA level without affecting memory performance. CONCLUSION: These data point to the potential role of the retinoid signaling pathway in memory processes and suggest that the overexpression of brain RARbeta and RXRbeta/gamma could be responsible, at least in part, for some memory impairments observed during chronic ethanol consumption.     

Effects of Chronic Ethanol Exposure on Cardiac Receptor-Adenylyl Cyclase Coupling: Studies in Cultured Embryonic Chick Myocytes and Ethanol Fed Rats

Ethanol effects in the brain appear to be mediated at least in part by an alteration in receptor-effector coupling via guanine nucleotide-binding regulatory proteins (G proteins). To test the hypothesis that a similar pathway participates in the cardiotoxic effects of ethanol, we assessed the effects of chronic ethanol on two commonly used experimental models: embryonic chick myocytes in culture and ventricular myocardium from chronically fed rats. Ethanol had no effect on either the function or quantity of G proteins as assessed by effector-stimulated adenylyl cyclase activity and the levels of ADP-ribosylation substrates. In contrast, effector-stimulated adenylyl cyclase activity was significantly altered in the liver of ethanol-fed rats. These results suggest that receptor-effector coupling via G proteins in our two cardiac models is insensitive to ethanol and that ethanol effects may be species or organ specific.     

A Single, Moderate Ethanol Exposure Alters Extracellular Dopamine Levels and Dopamine D2 Receptor Function in the Nucleus Accumbens of Wistar Rats

Background: The nucleus accumbens (NAc) has been implicated in the neurochemical effects of ethanol (EtOH). Evidence suggests that repeated EtOH exposures and chronic EtOH drinking increase dopamine (DA) neurotransmission in the NAc due, in part, to a reduction in D₂ autoreceptor function. The objectives of the current study were to evaluate the effects of a single EtOH pretreatment and repeated EtOH pretreatments on DA neurotransmission and D₂ autoreceptor function in the NAc of Wistar rats. Methods: Experiment 1 examined D₂ receptor function after a single intraperitoneal (i.p.) injection or repeated i.p. injections of 0.0, 0.5, 1.0, or 2.0 g/kg EtOH to female Wistar rats. Single EtOH pretreatment groups received 1 daily i.p. injection of 0.9% NaCl (saline) for 4 days, followed by 1 day of saline or EtOH administration; repeated EtOH pretreatment groups received 5 days of saline or EtOH injections. Reverse microdialysis experiments were conducted to determine the effects of local perfusion with the D₂‐like receptor antagonist (‐)sulpiride (SUL; 100 uM), on extracellular DA levels in the NAc. Experiment 2 evaluated if pretreatment with a single, moderate (1.0 g/kg) dose of EtOH would alter levels and clearance of extracellular DA in the NAc, as measured by no‐net‐flux (NNF) microdialysis. Subjects were divided into the EtOH‐naïve and the single EtOH pretreated groups from Experiment 1. Results: Experiment 1: Changes in extracellular DA levels induced with SUL perfusion were altered by the EtOH dose (p < 0.001), but not the number of EtOH pretreatments (p > 0.05). Post‐hoc analyses indicated that groups pretreated with single or repeated 1.0 g/kg EtOH showed significantly attenuated DA response to SUL, compared with all other groups (p < 0.001). Experiment 2: Multiple linear regression analyses yielded significantly (p < 0.05) higher extracellular DA concentrations in the NAc of rats receiving EtOH pretreatment, compared with their EtOH‐naïve counterparts (3.96 ± 0.42 nM and 3.25 ± 0.23 nM, respectively). Extraction fractions were not significantly different between the 2 groups. Conclusions: The present results indicate that a single EtOH pretreatment at a moderate dose can increase DA neurotransmission in the NAc due, in part, to reduced D₂ autoreceptor function.     

Ethanol Consumption by Fawn-Hooded Rats Following Abstinence Effect of Naltrexone and Changes in μ-Opioid Receptor Density

BACKGROUND: Relapse after abstinence can be modelled in rats using an alcohol deprivation effect (ADE) of enhanced ethanol consumption after a period of enforced abstinence from ethanol; however, not all rat strains display such an effect. We wanted to examine the effect of naltrexone on ethanol consumption by ethanol-preferring Fawn-Hooded (FH) rats using such a model. METHODS: FH rats were given continual free-choice access to a 5% ethanol solution or water (4 weeks) followed by 2 weeks of water alone. At the end of this abstinence period, osmotic minipumps were implanted subcutaneously to deliver saline (n = 4) or naltrexone (n = 4; 8.4 mg/kg/day for 4 weeks). After recovery from surgery, the rats were again given access to 5% ethanol under the same free-choice conditions (4 weeks). A third group of age-matched controls drank only water during the behavioral trial. At the end of the behavioral trial, the rats were decapitated and an autoradiographic examination was made of micro-opioid receptor density through the forebrain using the ligand [125I]FK-33824. RESULTS: First, a period of enforced abstinence from ethanol consumption caused a significant (p < 0.05) and prolonged increase in ethanol preference (+18%) and decrease in water consumption (-53%), although the volume of ethanol consumed (ml/day) did not vary, indicating an atypical ADE in this rat strain. Second, naltrexone significantly (p < 0.05) decreased ethanol consumption by the FH rats in terms of absolute amount of ethanol consumed and preference for ethanol solution, but this effect of naltrexone diminished over time, concurrent with a robust and significant elevation in micro-opioid receptor density in all brain regions examined (p < 0.05). Finally, ethanol consumption alone also upregulated micro-opioid receptor density relative to nondrinking controls in a number of brain regions, which included the nucleus accumbens (+29%) and caudate-putamen (+15%,p < 0.05), but decreased micro-opioid receptor density in other regions including the substantia nigra pars reticulata, which was suggestive of an indirect effect on micro-opioid receptors. CONCLUSIONS: The data suggest that continual long-term naltrexone treatment may not be effective in the treatment of alcoholism, possibly because of the induced increase in micro-opioid receptor density.     

Sex Differences in Rats in the Development of and Recovery From Ethanol Dependence Assessed by Changes in Seizure Susceptibility

BACKGROUND: Previous investigations have found sex differences in rats in response to chronic ethanol exposure. The most dramatic differences were observed with anticonvulsant treatment during ethanol withdrawal, when seizure susceptibility is significantly increased. Sex differences in this response were found for both GABAergic and glutamatergic compounds. This study was aimed at exploring whether sex also influences the timing for the development of and recovery from ethanol dependence. METHODS: Ethanol was administered in a liquid diet, with pair-fed animals receiving dextrose, substituted isocalorically for the ethanol. Ethanol dependence and withdrawal were assessed by measurement of seizure thresholds after abrupt removal of the ethanol diet. Seizure thresholds were determined by slow, tail vein infusion of the gamma-aminobutyric acidA-receptor antagonist bicuculline. RESULTS: Male and female rats displayed differences in timing for both onset and recovery from ethanol dependence, as determined by changes in ethanol withdrawal seizure susceptibility. Female rats were slower to develop dependence and quicker to recover compared with male rats. Furthermore, acute ethanol administration did not alter seizure susceptibility in pair-fed control animals, but it was anticonvulsant in ethanol-withdrawn rats. Ethanol-withdrawn female rats showed a greater response to acute ethanol administration than did male rats. CONCLUSIONS: This set of experiments uncovered additional sex differences in one measure of ethanol dependence and withdrawal. Proposed mechanisms for the development of ethanol dependence involve alterations in subunit assembly of gamma-aminobutyric acidA and NMDA receptors or various posttranslational modifications. In consideration of these findings, whatever mechanisms underlie the development of ethanol dependence, there is a different sequence of events in male compared with female rats. Studies are ongoing to determine associations between behavioral measures of ethanol dependence/withdrawal and selective neuronal adaptations.     

A Critical Evaluation of Influence of Ethanol and Diet on Salsolinol Enantiomers in Humans and Rats

Background: (R/S)‐Salsolinol (SAL), a condensation product of dopamine (DA) with acetaldehyde, has been speculated to have a role in the etiology of alcoholism. Earlier studies have shown the presence of SAL in biological fluids and postmortem brains from both alcoholics and nonalcoholics. However, the involvement of SAL in alcoholism has been controversial over several decades, since the reported SAL levels and their changes after ethanol exposure were not consistent, possibly due to inadequate analytical procedures and confounding factors such as diet and genetic predisposition. Using a newly developed mass spectrometric method to analyze SAL stereoisomers, we evaluated the contribution of ethanol, diet, and genetic background to SAL levels as well as its enantiomeric distribution. Methods: Simultaneous measurement of SAL enantiomers and DA were achieved by high performance liquid chromatography‐tandem mass spectrometry (HPLC/MS/MS). Plasma samples were collected from human subjects before and after banana (a food rich in SAL) intake, and during ethanol infusion. Rat plasma and brain samples were collected at various time points after the administration of SAL or banana by gavage. The brain parts including nucleus accumbens (NAC) and striatum (STR) were obtained from alcohol‐non‐preferring (NP) or alcohol‐preferring (P) rats as well as P‐rats which had a free access to ethanol (P‐EtOH). Results: Plasma SAL levels were increased significantly after banana intake in humans. Consistently, administration of banana to rats also resulted in a drastic increase of plasma SAL levels, whereas brain SAL levels remained unaltered. Acute ethanol infusion did not change SAL levels or R/S ratio in plasma from healthy humans. The levels of both SAL isomers and DA were significantly lower in the NAC of P rats in comparison to NP rats. The SAL levels in NAC of P rats remained unchanged after chronic free‐choice ethanol drinking. There were decreasing trends of SAL in STR and DA in both brain regions. No changes in enantiomeric ratio were observed after acute or chronic ethanol exposure. Conclusions: SAL from dietary sources is the major contributor to plasma SAL levels. No significant changes of SAL plasma levels or enantiomeric distribution after acute or chronic ethanol exposure suggest that SAL may not be a biomarker for ethanol drinking. Significantly lower SAL and DA levels observed in NAC of P rats may be associated with innate alcohol preference.