The effects of long-term ethanol on brain receptors for dopamine, acetylcholine, serotonin and noradrenaline

Selective allosteric modulation of muscarinic acetylcholine receptors for the treatment of schizophrenia and substance use disorders

Muscarinic acetylcholine receptor (mAChRs) subtypes represent exciting new targets for the treatment of schizophrenia and substance use disorder (SUD). Recent advances in the development of subtype-selective allosteric modulators have revealed promising effects in preclinical models targeting the different symptoms observed in schizophrenia and SUD. M₁ PAMs display potential for addressing the negative and cognitive symptoms of schizophrenia, while M₄ PAMs exhibit promise in treating preclinical models predictive of antipsychotic-like activity. In SUD, there is increasing support for modulation of mesocorticolimbic dopaminergic circuitry involved in SUD with selective M₄ mAChR PAMs or M₅ mAChR NAMs. Allosteric modulators of these mAChR subtypes have demonstrated efficacy in rodent models of cocaine and ethanol seeking, with indications that these ligand may also be useful for other substances of abuse, as well as in various stages in the cycle of addiction. Importantly, allosteric modulators of the different mAChR subtypes may provide viable treatment options, while conferring greater subtype specificity and corresponding enhanced therapeutic index than orthosteric muscarinic ligands and maintaining endogenous temporo-spatial ACh signaling. Overall, subtype specific mAChR allosteric modulators represent important novel therapeutic mechanisms for schizophrenia and SUD.

Alcohol and basal ganglia circuitry: Animal models

Brain circuits that include the cortex and basal ganglia make up the bulk of the forebrain, and influence behaviors related to almost all aspects of affective, cognitive and sensorimotor functions. The learning of new actions as well as association of existing action repertoires with environmental events are key functions of this circuitry. Unfortunately, the cortico-basal ganglia circuitry is also the target for all drugs of abuse, including alcohol. This makes the circuitry susceptible to the actions of chronic alcohol exposure that impairs circuit function in ways that contribute to cognitive dysfunction and drug use disorders. In the present review, we describe the connectivity and functions of the associative, limbic and sensorimotor cortico-basal ganglia circuits. We then review the effects of acute and chronic alcohol exposure on circuit function. Finally, we review studies examining the roles of the different circuits and circuit elements in alcohol use and abuse. We attempt to synthesize information from a variety of studies in laboratory animals and humans to generate hypotheses about how the three circuits interact with each other and with the other brain circuits during exposure to alcohol and during the development of alcohol use disorders. This article is part of the Special Issue entitled "Alcoholism".

DRD2 Gene Transfer Into the Nucleus Accumbens Core of the Alcohol Preferring and Nonpreferring Rats Attenuates Alcohol Drinking

BACKGROUND

Transient overexpression of the dopamine D2 receptor (DRD2) gene in the nucleus accumbens (NAc) using an adenoviral vector has been associated with a significant decrease in alcohol intake in Sprague Dawley rats. This overexpression of DRD2 reduced alcohol consumption in a two-bottle-choice paradigm and supported the view that high levels of DRD2 may be protective against alcohol abuse.

METHODS

Using a limited access (1 hr) two-bottle-choice (water versus 10% ethanol) drinking paradigm, we examined the effects of the DRD2 vector in alcohol intake in the genetically inbred alcohol-preferring (P) and -nonpreferring (NP) rats. In addition, micro-positron emission tomography imaging was used at the completion of the study to assess in vivo the chronic (7 weeks) effects of ethanol exposure on DRD2 levels between the two groups.

RESULTS

P rats that were treated with the DRD2 vector (in the NAc) significantly attenuated their alcohol preference (37% decrease) and intake (48% decrease), and these measures returned to pretreatment levels by day 20. A similar pattern of behavior (attenuation of ethanol drinking) was observed in NP rats. Analysis of the [C]raclopride micro-positron emission tomography data after chronic (7 weeks) exposure to ethanol revealed clear DRD2 binding differences between the P and NP rats. P rats showed 16% lower [C]raclopride specific binding in striatum than the NP rats.

CONCLUSIONS

These findings further support our hypothesis that high levels of DRD2 are causally associated with a reduction in alcohol consumption and may serve as a protective factor against alcoholism. That this effect was seen in P rats, which are predisposed to alcohol intake, suggests that they are protective even in those who are genetically predisposed to high alcohol intake. It is noteworthy that increasing DRD2 significantly decreased alcohol intake but did not abolish it, suggesting that high DRD2 levels may specifically interfere with the administration of large quantities of alcohol. The significantly higher DRD2 concentration in NP than P rats after 7 weeks of ethanol therefore could account for low alcohol intake.

Ethanol drinking experience attenuates (-)sulpiride-induced increases in extracellular dopamine levels in the nucleus accumbens of alcohol-preferring (P) rats

BACKGROUND

The reinforcing properties of ethanol may be partly mediated through the mesolimbic dopamine (DA) system. This study examines the effects of local application of the DA D(2) receptor antagonist (-)sulpiride (SUL) on ethanol drinking of alcohol-preferring (P) rats, and extracellular DA levels in the nucleus accumbens (NAc) of P rats that were either ethanol-naive or had been chronically drinking ethanol.

METHODS

Microdialysis was used to sample NAc DA levels, and reverse microdialysis was used to locally administer the D(2) antagonist (-)sulpiride (SUL) into the NAc of adult female P rats that were either drinking ethanol (n = 17) or were ethanol-naive (n = 24). Stable intake of 15% (v/v) ethanol (>/=0.75 g/kg) was established for the ethanol-drinking group in daily 1-hr access periods over a minimum of 4 weeks before surgery. Naive and ethanol-drinking rats were implanted with bilateral guide cannulae aimed 4 mm above the NAc shell. After recovery from surgery, microdialysis probes (active area = 2 mm) were inserted bilaterally into the NAc. Two days later, rats in the ethanol-drinking and naive groups were each divided into two groups; one group was bilaterally perfused (1.0 microl/min) with artificial cerebrospinal fluid (aCSF) and the other group was further divided into three subgroups that were perfused with aCSF + either 50, 100, or 200 microM SUL for 240 min. During the last 60 min of perfusion, the ethanol-drinking rats were given their daily 1-hr ethanol access period. Following ethanol access, the aCSF + SUL subgroups were then given aCSF only. The entire perfusion procedure was repeated 24 hr later, but the aCSF only and aCSF + SUL group treatment conditions were transposed.

RESULTS

In ethanol-drinking rats, 100 and 200 microM SUL increased extracellular NAc DA levels to approximately 200% of basal values, but did not significantly alter ethanol intake. In ethanol-naive P rats, 100 and 200 microM SUL increased extracellular NAc DA levels significantly more (450% of basal; p < 0.05) than in the ethanol-drinking group.

CONCLUSIONS

The findings are consistent with the hypothesis that ethanol-drinking experience causes a desensitization or a down-regulation of D(2) autoreceptors in the NAc of P rats.

Changes in dopamine receptor responsivity during alcohol detoxification may predict relapse

In the search for clinical and biological variables that may predict relapse of alcohol dependent patients after detoxification, we followed up for 1 year male patients that had undergone successful detoxification. The patients had been tested earlier during their usual alcohol consumption and immediately after detoxification for the responsivity of D2 dopamine receptors (as measured by the increases in prolactin plasma levels caused by intramuscular administration of 5 mg of the dopamine receptor blocker haloperidol). Of the 18 patients, eight had not consumed alcohol for more than 6 months, and ten had relapsed within 6 months. Comparison of the clinical and neuroendocrine data for the two subgroups revealed no significant differences in age, amount of alcohol consumed during alcohol abuse, score in the Beck Depression Inventory, score in the Brief Michigan Alcoholism Screening Test, or prolactin responses to haloperidol before detoxification. In patients who relapsed, the duration of alcoholism was marginally shorter (P=0.055). Patients who did not relapse had significantly higher (P=0.003) prolactin responses to haloperidol in the test performed after detoxification as compared with patients who did relapse, and their responses were similar to those of a group of healthy male subjects. The results show that the increase in dopamine receptor responsivity that occurs after detoxification is a favourable factor for non-relapse; it may reflect recovery from down-regulation of the dopaminergic reward system caused by alcohol consumption.

Specific binding and laterality of human extrastriatal dopamine D2/D3 receptors in late onset type 1 alcoholic patients

Late onset type 1 alcoholism has been suggested to be associated with decreased dopaminergic transmission. Our hypothesis was that late onset type 1 alcoholics have also abnormal extrastriatal dopamine D(2)/D(3) receptor distribution. We performed binding, heterogeneity and laterality analysis of extrastriatal and striatal dopamine D(2)/D(3) receptors in nine late onset male alcoholics and in 12 age-matched healthy males. A radioligand, [(123)I]epidepride was used in high resolution single-photon emission tomography (SPET). Specific binding of epidepride in the left temporal pole was significantly (P<0.05) lower in type 1 alcoholics (0.74+/-0.14 ml/ml) than in controls (0.89+/-0.14 ml/ml). In alcoholics, there was no normal left-to-right asymmetry of the temporal cortical heterogeneity of epidepride distribution observed in control males (0.89+/-0.19 vs. 1.10+/-0.19; P<0.05). The results suggest that the specific binding of dopamine D(2)/D(3) receptors in late type 1 alcoholics is decreased and its laterality in the temporal brain is altered from normal.

Dopamine receptor responsivity in alcoholic patients before and after detoxification

OBJECTIVE

To assess central dopamine receptor responsivity in alcoholic patients during their usual alcohol consumption and after detoxification.

METHOD

Plasma prolactin levels were measured at 0, 30, 60, and 90 min after administration of 5 mg haloperidol i.m. in 21 hospitalized male alcoholic patients during usual alcohol consumption, and 13 days later (mean, range 7-17 days), after detoxification. The test was also performed in seven healthy male volunteers. The patterns of prolactin responses were compared using repeated measures analysis of variance.

RESULTS

The prolactin responses to haloperidol increased significantly after detoxification compared to those during usual alcohol consumption (state x time interaction P < 0.01; planned comparisons for times 0 and 90 min between states P = 0.03). Compared to controls, the responses of the patients before detoxification were lower (group-time interaction P = 0.001), and the difference was not significant after detoxification (P = 0.19). The magnitude of plasma prolactin (PRL) responses were not related to duration of alcohol abuse, score in the Brief Michigan Alcoholism Screening Test (BMAST) scale, or family history of alcoholism.

CONCLUSIONS

Alcohol detoxification is accompanied by a normalization of the low responsivity of central dopaminergic receptors during alcohol abuse. The data support the hypothesis of a participation of the central dopaminergic system in alcohol dependence.

Long-term effects of chronic ethanol on muscarinic receptor binding in rat brain

Effects of chronic ethanol treatment (CET) on muscarinic acetylcholine receptor (mAChR) binding properties were investigated via quantitative autoradiography in rats maintained on an ethanol-containing liquid diet for 28 weeks and withdrawn from ethanol for 8 weeks before harvesting of tissues. Controls received an identical diet in which sucrose was substituted isocalorically for ethanol. Maximal binding of the radiolabeled mAChR antagonist quinuclidinyl benzilate ([3H]QNB) was not reduced in hippocampal area CA1, dentate gyrus, neocortex, striatum, or thalamus, suggesting that CET results in no significant mAChR loss in these regions. Binding affinities of the cholinergic agonist carbachol to mAChRs were unaffected by CET in each of these regions, as determined by competitive displacement of [3H]QNB labeling. These results suggest that CET-induced functional deficits in brain cholinergic responses are not due to direct effects of CET on mAChR binding properties.

Modulation of serotonin2A/2C receptors and these receptor-linked phosphoinositide system by ethanol

Studies related to 5-HT2A/2C receptors and these receptor-linked phosphoinositide (PI) system in the rat brain during chronic ethanol treatment and withdrawal are discussed. Chronic ethanol treatment (60 days) has no effect on 5-HT2A/2C receptors in the cortex and the hippocampus but significantly decreased 5-HT-stimulated PI hydrolysis in the rat cortex. On the other hand, chronic ethanol treatment (60 days) significantly increased 5-HT2C receptors and 5-HT-stimulated PI hydrolysis in the rat choroid plexus. Ethanol withdrawal (24 h) after chronic ethanol consumption (15 days) results in the down-regulation of 5-HT2A receptors and in a decrease in 5-HT-stimulated PI hydrolysis in the rat cortex. Taken together, these results, along with other reports in the literature, suggest that 5-HT2A/2C receptors or their function are altered during chronic ethanol consumption and withdrawal. Further studies are needed to explore the role of 5-HT2A/2C receptors and the PI signal transduction system in the development of ethanol withdrawal symptoms after chronic ethanol consumption.

Ethanol enhances muscarinic cholinergic neurotransmission in rat hippocampus in vitro

Previous studies from our laboratory showed that ethanol enhances muscarinic excitatory responses in rat hippocampal neurons in vivo and, like muscarinic agonists, reduces the M-current (IM) in these neurons in vitro. Therefore, we used extracellular and intracellular recording techniques in the hippocampal slice preparation to examine the mechanisms underlying this ethanol-muscarinic interaction. Surprisingly, superfusion or local application of low concentrations of acetylcholine (ACh), carbachol (CCh) or muscarine reduced the amplitudes of CA1 field potentials evoked by stratum radiatum (SR) stimulation. This effect was blocked by 1 microM atropine but was independent of the method of agonist application, the site of application or the SR stimulus paradigm. In intracellular and extracellular single unit recordings, cholinergic depressions of field potentials were correlated with: (1) depolarization of pyramidal neurons; (2) spike discharge increases; (3) reduction of amplitudes of postsynaptic potentials and (4) reduction of late afterhyperpolarizations (AHPs). Superfusion of low ethanol concentrations (11-22 mM) alone had little effect on SR-evoked field potentials but enhanced (by 10-90%) both the depressions of evoked field potentials and depolarizations elicited by the muscarinic agonists. Ethanol (22-44 mM) also enhanced both the amplitude and duration of the muscarinic slow excitatory postsynaptic potentials (sEPSPs) recorded intracellularly in CA1 and CA3 neurons. This effect was enhanced by eserine and blocked by atropine, verifying involvement of muscarinic receptors. These results suggest that: (1) caution be used in interpreting results of field potential studies regarding drug-induced excitability changes; and (2) ethanol in just-intoxicating concentrations enhances endogenous muscarinic synaptic transmission as well as responses to exogenous muscarinic agonists.

Chronic ethanol consumption affects cholinoceptor- and purinoceptor-mediated contractions of the isolated rat bladder

Isolated bladder strips from 12-week ethanol-fed, pair-fed and control adult male rats were investigated. Contractile responses to carbachol (CCh; 0.1-300 microM) were statistically significantly potentiated in the ethanol-fed group compared to pair-fed and control. Contractions to beta,gamma-methylene ATP (beta,gamma-MeATP; 1-300 microM) were statistically significantly potentiated in the ethanol-fed group at the highest concentration tested (300 microM). Neurogenic contractions (0.5-32 pps) from the ethanol-fed group in the absence of atropine and after desensitisation by alpha,beta-methylene ATP (alpha,beta-MeATP; 3 microM), were significantly potentiated compared to the pair-fed and control groups; in the presence of atropine (1 microM), neurogenic contractions were significantly augmented at the higher frequencies. It is concluded that chronic ethanol treatment affects both cholinoceptor- and purinoceptor-mediated contractions of the rat bladder.

Relationship between concurrent substance abuse in psychiatric patients and neuroleptic dosage

The use of a structured diagnostic interview (The Schedule for Affective Disorders and Schizophrenia) with 58 consecutively admitted general adult psychiatric patients revealed that 62.1% of them abused alcohol and 58.6% had a substance use disorder. The drug abusers did not differ significantly from the nonabusers on mean psychoticism (Brief Psychiatric Rating Scale) scores. However, they received higher doses of antipsychotic agents (mean daily dose 1022 mg CPZ EQ (SD = 614) vs 609 mg CPZ EQ (SD = 481); z = 2.58, p < .01) to achieve stabilization. The clinical implications of this finding are discussed.

Striatal D2 dopamine receptor binding characteristics in vivo in patients with alcohol dependence

Striatal D2 dopamine receptor characteristics of nine male patients with alcohol dependence abstinent for 1-68 weeks and eight healthy male volunteers were studied in vivo with positron emission tomography. The selective D2 receptor ligand [11C]raclopride and equilibrium model was used for D2 receptor density (Bmax) and affinity (Kd) measurements. A trend for a decreased striatal D2 receptor density and for reduced D2 receptor affinity was observed in patients with alcohol dependence. These parameters were not statistically significantly different between alcoholics and controls, but the ratio between D2 receptor density and affinity (Bmax/Kd or the striatum/cerebellum ratio from the high specific activity scan) was highly significantly lower in alcoholics than that of controls. In conclusion, the low D2 dopamine receptor Bmax/Kd ratio (striatum/cerebellum ratio) indicates that specific aspects of striatal [11C]raclopride binding in vivo are deviant in alcoholics compared to controls. The result is compatible with a reduced avidity of striatal dopamine D2 receptors in alcoholics, which is in line with the idea that D2 dopaminergic mechanisms are involved in the biology of alcohol dependence in man.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Chronic effects of ethanol on central adenosine function of mice

Chronic ingestion of 5% ethanol had no significant effect on open field locomotor of NIH Swiss strain male mice, nor were the depressant effects of a non-selective adenosine receptor agonist, NECA, or the stimulant effects of a non-selective antagonist, caffeine significantly altered. The density of cerebral cortical A1-adenosine receptors and of nitrendipine binding sites on calcium channels were significantly increased after chronic ethanol, while the density of striatal A2a-adenosine receptors were unchanged. The locomotor stimulant effects of ethanol (2.5 g/kg) were slightly decreased after chronic ethanol, but were markedly reduced in mice after chronic caffeine ingestion. The results suggest some involvement of adenosine systems in the effects of ethanol.

Effects of chronic ethanol on cholinergic actions in rat hippocampus: electrophysiological studies and quantification of m1-m5 muscarinic receptor subtypes

The effects of chronic ethanol treatment (CET) on cholinergic modulation of CA1 evoked field potentials and recurrent inhibition were investigated in rat hippocampal slices. Densities of muscarinic receptor subtypes were quantified in remaining hippocampal tissue by immunoprecipitation. Iontophoretic application of ACh in stratum pyramidale results in facilitation of single evoked population spikes; application in stratum radiatum results in depression of field EPSPs. CET decreased cholinergic facilitation of population spikes, while cholinergic inhibition of field EPSPs remained unaffected. Integrity of feedback (recurrent) inhibitory circuitry was evaluated by paired-pulse stimulation. As previously demonstrated, recurrent inhibition was significantly reduced after CET; cholinergic disinhibition was also significantly reduced. Thus, CET appears to disrupt a subset of cholinergic effector systems within hippocampal neurons. The reductions in cholinergic function produced by CET does not appear to be due to receptor loss, since muscarinic receptor subtype densities were not found to be significantly altered in this tissue. These results support the hypothesis that muscarinic receptor function is impaired in CA1 pyramidal cells through a disruption of intracellular signal transduction mechanisms. While it is unclear whether cholinergic function is reduced in interneurons directly, these results suggest that modulation of neuronal firing in the hippocampus is markedly altered following CET due to impairment of both cholinergic and GABAergic systems.

Neurotoxic effects of gasoline and gasoline constituents

This overview was developed as part of a symposium on noncancer end points of gasoline and key gasoline components. The specific components included are methyl tertiary butyl ether, ethyl tertiary butyl ether, tertiary amyl methyl ether, butadiene, benzene, xylene, toluene, methyl alcohol, and ethyl alcohol. The overview focuses on neurotoxic effects related to chronic low-level exposures. A few general conclusions and recommendations can be made based on the results of the studies to date. a) All the compounds reviewed are neuroactive and, as such, should be examined for their neurotoxicity. b) For most of the compounds, there is a substantial margin of safety between the current permissible exposure levels and levels that would be expected to cause overt signs of neurotoxicity in humans. This is not the case for xylene, toluene, and methanol, however, where neurologic effects are observed at or below the current Threshold Limit Value. c) For most of the compounds, the relationship between chronic low-level exposure and subtle neurotoxic effects has not been studied. Studies therefore should focus on examining the dose-response relationship between chronic low-level exposure and subtle changes in central nervous system function.

Bidirectional changes in striatal D1-dopamine receptor density during chronic ethanol intake

Results of previous studies on the effects of ethanol consumption on the properties of D1 dopamine receptors appear contradictory and inconclusive. In this study we have examined the time course of the effects of dietary ethanol on the properties of striatal D1 dopamine receptors. Chronic ethanol intake led to bidirectional changes in the maximum number (Bmax) of [3H]SCH-23390 binding to striatal D1 dopamine receptors measured 10 hrs after termination of the ethanol intake. A significant decrease (80% of control), increase (159% of control), increase (122% of control), and decrease (85% of control) after 1, 2, 3, and 4 weeks of ethanol intake respectively was observed. The bidirectional changes disappeared after 6 and 10 weeks of continued ethanol intake and the Bmax returned back to the control level. The receptor affinity (Kd), however, remained unaltered in all cases. These data suggest that the duration of ethanol exposure may be an important determinant in regulating D1 dopamine receptor density.

Cholinergic mechanisms in physical dependence on barbiturates, ethanol and benzodiazepines

The aim of this review is to summarize the effects of acute and chronic treatment with barbiturates, ethanol and benzodiazepines on cholinergic mechanisms in the brains of experimental animals. A single dose of each of these substances reduces the turnover of ACh in the brain. Long-term treatment has the opposite effect; complicated interactions including decreased content of ACh are induced. Barbiturates have been shown to bind stereospecifically to muscarinic and nicotinic receptors in the brain, but this has not been observed for ethanol or the benzodiazepines. The effects on the cholinergic system are affected by the length of treatment and choice of treatment regimen. No effect on cholinergic parameters, such as muscarinic receptors, in the brain is observed on withdrawal of ethanol or barbiturate treatment when the animals are still tolerant towards the substances. The increase in the number of muscarinic receptors observed in several brain regions on withdrawal is seen as a sign of cholinergic supersensitivity. The number of receptors returns to normal when abstinence convulsions have occurred. The assumption of a cholinergic influence is supported by the finding that atropine, given as a single dose on the day of withdrawal of barbital, can prevent the muscarinic receptor changes. Furthermore, long-term barbital or ethanol treatment can induce permanent persistent changes in the cholinergic system in the brain. Cognitive defects and a significant permanent reduction in the content of ACh can be measured in rats which have had long-term barbital treatment. Similarly, a reduced number of muscarinic receptors has been measured in different brain regions of chronic alcoholics. Accumulating data support the role of the cholinergic system in expressing symptoms of physical dependence on barbiturates, ethanol and benzodiazepines as well as in the permanent long-term effects observed after end of treatment.

Adaptive changes of dopamine-D2 receptors in rat brain following ethanol withdrawal: a quantitative autoradiographic investigation

The effect of subchronic treatment with two doses of ethanol (5 and 10 vol% drinking fluid) on the density of dopamine-D2 receptors was investigated at two different phases of withdrawal, namely 24 h and 5 days after the cessation of the ethanol application. The number of dopamine-D2 receptors was affected in regions receiving projections from both the substantia nigra as well as the ventral tegmentum. Twenty-four hours after the replacement of the ethanol solution by water, a dose-dependent decrease of D2 receptors was found in all regions (N. caudatus dorsalis, medialis and ventralis, N. accumbens lateralis and medialis, tuberculum olfactorium) and most of the analyzed planes [interaural 7.7-10.2 according to the atlas of Paxinos and Watson (35)]. At day 5 of withdrawal, the number of dopamine-D2 receptors of the animals treated with 5 vol% ethanol reached the level of water controls in most planes. In contrast, two- to three-fold higher numbers were detected in animals treated with the higher dose. Only in the most caudal parts of the investigated regions, was the number of receptors decreased with the higher dose. The mesocorticolimbic system seems to be less sensitive to the effects of ethanol than the nigrostriatal neurones. The findings of the present study suggest an increased activity of dopaminergic neurons with an adaptive reduction of dopamine-D2 receptors during the subchronic treatment with ethanol during the first day(s) of withdrawal. This phase is followed by a reduced turnover rate for up to 7 days (21). The reduced activity of dopaminergic neurones induces a compensatory increase of the number of receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic ethanol consumption on the mesolimbic and nigrostriatal dopamine systems

Both the mesolimbic dopamine system, which is involved with the rewarding properties of several drugs of abuse, and the nigrostriatal dopamine system, which is involved with motor function, appear to be sensitive to the effects of ethanol. In order to determine which components of the mesolimbic and nigrostriatal dopamine systems are adversely affected by chronic ethanol consumption, we assessed dopamine and DOPAC (3,4-dihydroxyphenylacetic acid) concentration and D1 and D2 receptors in several dopaminergic brain areas. These studies demonstrated that consumption of a 6.6% (v/v) ethanol-containing lipid diet for 1 month affected several components of the mesolimbic dopamine system in 3-month-old Fisher 344 rats and fewer components of the nigrostriatal dopamine system. Specifically, there was a 1.6- to 2.6-fold increase in the concentration of DOPAC in the nucleus accumbens (NA), frontal cortex (FCX), ventral tegmental area (VTA), and substantia nigra (SN). While the increase in DOPAC in the FCX and VTA was paralleled by a similar increase in dopamine, there was a significant deficiency of dopamine in the SN. These results suggest that there is an increase in dopamine turnover in the FCX, VTA, NA, and SN, which is accompanied by increased dopamine synthesis in the former two regions. Studies of dopamine receptors in control and ethanol-fed rats demonstrated a 25% loss of D1 receptors in the NA. No significant differences were found in D1 receptors in the striatum or globus pallidus. In addition, there were no differences in the number of total D2 receptors or in the conversion of the high to low affinity state of D2 receptors in the nucleus accumbens and striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Bidirectional changes in striatal D2-dopamine receptor density during chronic ethanol intake

Results of previous studies on the effects of ethanol consumption for a single fixed period on the properties of D2 dopamine receptors appear contradictory and inconclusive. In this study, we have examined the time course of the effects of dietary ethanol on the properties of striatal D2 dopamine receptor. Ethanol intake led to a significant decrease in the maximum number (Bmax) after 1 (35% of control) and 2 weeks (48% of control), but not after 3 (93% of control) or 4 weeks (97% of control) of treatment. However, there was a significant increase in Bmax after 6 (118% of control) and 10 weeks (123% of control) of ethanol consumption. The affinity (Kd) of the receptor, however, remained unaltered in all cases. In conclusion, these data show that the duration of ethanol exposure may be an important determinant regulating D2-dopamine receptor density.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Ethanol intake and 3H-serotonin uptake I: A study in Fawn-Hooded rats

Ethanol intake and synaptosomal 3H-serotonin uptake were studied in male Fawn-Hooded and Sprague-Dawley rats. Fawn-Hooded rats consumed more alcohol and more water than Sprague-Dawley rats. Plasma alcohol levels of Sprague-Dawley rats were not detectable but were about 5 mg/dl in Fawn-Hooded rats. Ethanol intake increased the Vmax of serotonin uptake in Fawn-Hooded rats in hippocampus and cortex, but not in thalamus. In Fawn-Hooded rats, serotonin uptake (Vmax) was higher than in Sprague-Dawley rats cortex. Ethanol intake reduced the Vmax of serotonin uptake in Fawn-Hooded rats in hippocampus and cortex. In cortex, the carrier affinity for serotonin was increased in alcoholized Fawn-Hooded rats. These results indicate that synaptosomal 3H-serotonin uptake is affected by ethanol intake. In Fawn-Hooded rats, high ethanol consumption is associated with high serotonin uptake. In rats presenting high serotonin uptake, alcoholisation reduces 3H-serotonin internalisation in synaptosomes, indicating a specific sensitivity to alcohol intake of serotonin uptake system.

Altered pineal serotonin binding in some suicides

Serotonergic abnormalities have been regularly reported in the brains of suicide victims. Because of evidence that pineal function is altered in depressed subjects and that serotonin-releasing axons may innervate the pineal, we assayed tritiated serotonin binding in a series of control and suicide pineals. High affinity binding was present, and there were apparent differences between some suicides and controls.

Effects of chronic exposure to ethanol alone and in combination with desipramine on beta-adrenoceptors of rat brain

The effect of chronic ethanol exposure alone or in combination with desipramine on agonist and antagonist binding to beta-adrenoceptors was studied in membrane preparations from rat frontal cortex and hippocampus. Ten day exposure of animals to ethanol vapor (25 mg/l) in inhalation chambers had no effect on binding properties of antagonist iodocyanopindolol (ICYP) in either brain region. However, ethanol in combination with chronic desipramine treatment prevented the reduction of beta-adrenoceptor density in frontal cortex produced by desipramine administration. Similar to its effects on antagonist binding, chronic ethanol exposure did not change the agonist isoproterenol binding characteristics measured in membranes from either rat frontal cortex or hippocampus. However, the combination of ethanol plus desipramine reduced the dissociation constant of the low affinity state of the receptor (KL) in frontal cortex from 23.1 +/- 3.7 microM in controls to 11.2 +/- 1.7 microM. Moreover, ethanol plus desipramine produced a greater decrease in the percentage of cortical receptors in the high affinity state for agonist (%RH) than did desipramine alone. This suggests that ethanol enhances desipramine-induced desensitization of beta-adrenoceptors in frontal cortex in spite of the prevention of reduction in density of the receptors. In hippocampal membranes, ethanol together with desipramine prevented desipramine-induced changes in agonist binding characteristics, i.e. the decrease in KH (dissociation constant from high affinity state of the receptor) and the consequent enhancement in KL/KH ratio. Thus, chronic exposure to relatively low concentrations of ethanol partially prevents effects of desipramine on beta-adrenoceptors.

Ethanol administration does not alter dopamine D1 and D2 receptor characteristics in rat brain

The effects of 5 weeks' ethanol treatment on the number and affinity of cortical and striatal dopamine D1 receptors and striatal D2 receptors in rat brain were investigated. The ethanol and control diets were carried out using the pair-feeding technique. The number and affinity of dopamine D1 receptor sites in the frontal cortex and caudate-putamen or D2 receptors in the caudate-putamen were not significantly altered by the used ethanol dose regimen. This study demonstrates that if dietary factors related to ethanol consumption are carefully controlled no 'specific' ethanol-induced changes in striatal D1 and D2 or cortical D1 receptor characteristics can be observed after 5 weeks' ethanol consumption. Thus, changes in the central dopamine receptors are not likely to play any significant role in the effects of moderate ethanol consumption on neuronal function.

Ethanol potentiates serotonin stimulated inositol lipid metabolism in primary astroglial cell cultures

Serotonin-stimulated activation of phospholipase C in primary astroglial cell cultures was studied as a mean of evaluating the effect of acute ethanol exposition on this signal transduction system. The addition of 50-150 mM ethanol prior to stimulation with 10(-5) M serotonin led to a potentiation of the serotonin-induced [3H]-inositol phosphate formation and an increased incorporation of [3H]-inositol into the three phosphoinositides studied. This potentiating effect of ethanol was observed only when ethanol was added together with serotonin. No stimulatory effect of ethanol per se was found. Furthermore, ethanol had no effect on arginine-vasopressin, bradykinin or phenylephrine stimulated inositol lipid metabolism.

Ethanol does not affect serotonin receptor binding in rodent brain

The effects of ethanol on serotonin (5-hydroxytryptamine, 5-HT) receptor binding in rat and mouse brain were determined under in vitro conditions and in mouse brain following seven days of ethanol ingestion. 5-HT1A receptor characteristics were measured utilizing the agonist [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([ 3H]DPAT), and 5HT2 receptor-binding studies utilized the antagonist [3H]ketanserin. At the highest concentration of ethanol tested in vitro (680 mM), there was only 25% inhibition of [3H]DPAT binding in rat and mouse brain and 14% inhibition of [3H]ketanserin binding in rat brain. Effects of an anesthetic concentration of ethanol (100 mM) on agonist binding in the presence and absence of the guanine nucleotide GTP were also evaluated in vitro in mouse brain. In no case did ethanol (100 mM) significantly affect 5-HT1A or 5-HT2 receptor-binding characteristics. When 5-HT receptor characteristics were measured after mice consumed ethanol for seven days, there was no change in either 5-HT1A or 5-HT2 receptor-binding properties in any of the brain areas examined.

Anatomical mapping of tetrahydropapaveroline-reactive sites in brain mediating suppression of alcohol drinking in the rat

In a previous study, anatomically circumscribed sites were identified within limbic-midbrain and limbic-forebrain structures of the rat in which injections of tetrahydropapaveroline (THP) evoked the drinking of alcohol even at aversive concentrations. The purpose of the second part of this study was to identify specific sites in the same limbic structures which also were reactive to THP but which mediated the suppression of alcohol consumption. Cannulae for repeated microinjection of THP were implanted stereotaxically in male Sprague-Dawley rats at sites extending from the ventral tegmental-substantia nigra complex rostrally to the region of the olfactory tubercle. Postoperatively, the rats were tested for their self-selection of water versus alcohol offered in solutions increased over 10 consecutive days in 10 concentrations from 3 to 30%. THP was dissolved in a CSF vehicle containing Na2S2O5 or ascorbate and microinjected in a dose of 25, 50 or 250 ng contained in a volume of 1.5-2.0 microliters. Following a sequence of 5 microinjections of THP, given over 3 days, the same 10-day alcohol drinking test was repeated. Ordinarily, sites at three depths 1.0-1.5 mm beneath the tip of the guide tube were tested for their reactivity to the amine-aldehyde adduct. When injected at 21 sites within coronal planes 1.0-10.5, THP attenuated the intake of alcohol significantly. Structures sensitive to the inhibitory action of the aldehyde adduct included the substantia nigra, reticular formation, medial lemniscus, preoptic area, nucleus accumbens, olfactory tubercle, cingulate gyrus and rostral hippocampus. Within 65 loci contained within the same AP planes, little or no effect of alcohol intake was exerted by THP independent of the dose microinjected. Nonreactive loci were identified within fiber pathways including the corpus callosum and optic tract, motor systems of the caudate nucleus, and both sensory and motor relay nuclei of the thalamus. An analysis of the critical part played by the dose of THP revealed that 81% of reactive sites given the 25 ng dose mediated enhanced drinking of alcohol, as demonstrated in the first study. Conversely, the 50 and 250 ng doses injected at THP-sensitive loci reduced alcohol consumption three to seven times more often than they augmented drinking. Anatomical sites mediating an attenuation of alcohol consumption in response to the higher doses of THP overlapped with both enkephalinergic and dopaminergic systems which project from the ventral tegmentum and substantia nigra to the rostral limbic-forebrain.(ABSTRACT TRUNCATED AT 400 WORDS)

A neuroanatomical substrate for alcohol drinking: identification of tetrahydropapaveroline (THP)-reactive sites in the rat brain

Certain endogenously synthesized adducts, derived from a condensation reaction of a catechol- or indole-amine with a biogenic aldehyde, act in the brain to augment or suppress the drinking of ethyl alcohol. When infused directly into the cerebral ventricles, a tetrahydro-isoquinoline such as tetrahydropapaveroline (THP) can enhance markedly the consumption of alcohol even in noxious concentrations. The present study was undertaken to isolate and identify specific anatomical structures in the limbic-midbrain, limbic-forebrain which mediate the changes in the ingestion of alcohol induced by THP. In adult male Sprague-Dawley rats, a 23 ga guide tube was implanted stereotaxically either unilaterally or bilaterally in cerebral regions extending from coronal planes AP 1.0-10.0. Following recovery, each animal was tested by a standard screen for its self-selection of water versus an alcohol solution offered in 10 concentrations increased on each of 10 days from 3 to 30%. THP was dissolved in an artificial CSF vehicle containing Na2S2O5 or ascorbate and then microinjected in a volume of 1.5-2.0 microliters at a depth 1.0-1.5 mm beneath the tip of the guide. After a set of 5 microinjections of THP in a dose of 25, 50 or 250 ng was given over 3 days, the same 10-day alcohol preference sequence was repeated. In nearly all rats, the microinjection series was repeated at either one or two depths 1.0-1.5 mm ventral to the first, after which the same alcohol test was repeated. The results showed that THP induces or sustains significant increases in alcohol intake when the adduct was injected at 16 sites within caudal AP planes 1.0-5.0. Structures sensitive to THP included the substantia nigra, reticular formation, medial lemniscus, zona incerta and medial forebrain bundle. When injected at 21 sites located more rostrally within AP planes 6.5-10.0, THP also evoked significant increments in alcohol intake of a similar magnitude. The reactive loci included the N. accumbens, olfactory tubercle, lateral septum, preoptic area, stria terminalis, medial forebrain bundle and rostral hippocampus. In terms of the efficacy of the dose of THP microinjected, 25, 50 and 250 ng induced alcohol self-selection in 81%, 5% and 14% of the sites, respectively. Repeated microinjections following identical procedures of two control solutions at 46 homologous sites within corresponding coronal planes from AP 1.5-10.0 produced no significant alterations in g/kg or proportional intakes of alcohol. Composite anatomical maps of the THP-reactive sites revealed their integral overlap with dopaminergic pathways which originate in the ventral tegmentum and substantia nigra and project rostrally to s

Hippocampal and cerebellar beta-adrenergic receptors and adenylate cyclase are differentially altered by chronic ethanol ingestion

Chronic ethanol ingestion by mice resulted in the loss of high-affinity beta-adrenergic agonist binding sites and a significant decrease in activation of adenylate cyclase by guanine nucleotides and beta-adrenergic agonists in the hippocampus, although no significant change was noted in the total number of beta-adrenergic receptors, as defined by the binding of the antagonist [125]iodocyanopindolol. In cerebellum, chronic ethanol ingestion resulted in a 16% decrease in the total concentration of beta-adrenergic receptors and in a decrease in the affinity for agonist of the high-affinity beta-adrenergic agonist binding sites. However, neither the amount of the high-affinity agonist binding sites nor the activation of adenylate cyclase by agonist was affected. The different responses to ethanol in hippocampus and cerebellum may result from quantitative differences in distribution of beta 1- and beta 2-adrenergic receptors in the tested brain areas and/or differential effects of ethanol on stimulatory guanine nucleotide binding protein in these brain areas.

Effect of ethanol administration of striatal D1 and D2 dopamine receptors

Chronic in vivo exposure of rats to ethanol in a complete liquid diet for 14 or 21 days produced a behavioral tolerance to the acute injection of ethanol. After 21 days, but not 14 days, of chronic exposure, there was a significant increase in the maximum density of striatal D1 and D2 dopamine receptors without a change in these receptors' affinities. A 24-h withdrawal from the 21-day exposure did not alter the observed increase in density. Both the level and duration of ethanol exposure appear to be important variables for demonstration of an increase in striatal D1 and D2 dopamine receptors.

Decrease in the number of rat brain dopamine and muscarinic receptors after chronic alcohol intake

The effect of 32 weeks' alcohol treatment on the number and affinity of dopamine and muscarinic receptor sites in rat striatum were measured using 3H-spiperone and 3H-quinuclidinylbenzilate (3H-QNB) as radioligands. The number of dopamine receptor sites was 38 per cent and the number of muscarinic receptor sites 36 per cent lower in the alcohol group than in control rats. The differences in receptor affinities were less marked. In conclusion, a long-term alcohol intake with rather moderate doses seems to induce a pronounced down-regulation in dopamine and muscarinic receptor systems in rat striatum.

Castration and tolerance induces changes in the levels of the activity of acetylcholinesterase in the isolated vas deferens of the rat

Changes in the activity of acetylcholinesterase (AChE) of the isolated vas deferens from normal, castrated, morphine and ethanol-tolerant rats were studied. Three days after the termination of treatment with morphine and on the last day of treatment with ethanol, a significant inhibition of the activity of AChE was detected. This reduction in the enzymatic activity persisted in morphine-tolerant rats for 15 days, but not for 30 days, at which time the levels of AChE were determined to be normal. However, in ethanol-tolerant rats, there were no significant changes found at days 15 or 30. The activity of AChE was decreased significantly in castrated rats, but this effect was reversed by treatment with testosterone. During withdrawal from morphine or ethanol, the levels of AChE were significantly increased. The results indicate that morphine and ethanol may be inducing changes in the feedback mechanism which regulates the levels of AChE at post-synaptic sites, and these changes could play an important role in the development of tolerance to morphine and to ethanol.

The effect of ethanol and haloperidol on dopamine receptor (D2) density

The study was performed to investigate the influence of ethanol on haloperidol-induced changes of the dopamine (D2) receptors in rat striatal membrane preparations. Subchronic administration of the neuroleptic in the drinking water resulted in an increase of the number of binding sites in a dose-dependent manner. Simultaneous treatment with both haloperidol and ethanol prevented the rise of D2 receptors.

Influence of mouse genotype on responses of central biogenic amines to alcohol intoxication and aging

Dopamine and serotonin responses to various periods of alcohol treatment have been followed in striatum and hippocampus of two inbred strains of mice and related to the effect of aging. A striking strain dependency was noted for chronic alcohol effects and also for senescence. For both neurotransmitters studied the C57Bl strain loses tolerance to prolonged alcohol injury earlier than the Balb/c strain. This loss of tolerance accompanying aging may be indicative of more widespread changes in CNS adaptability in this strain. The unequal capacity to adapt also appears to depend on the nervous structure and the neurotransmitter considered. Alcohol and aging induced changes are not identical. In a given mouse strain, significant effects of either drug or aging induced disturbances are noted. A similar molecular process could operate in both aging and alcohol abuse, but the neurochemical effect might depend on the nervous structure or neurotransmitter involved. Such a phenomenon may be the basis of differences in behavioral changes observed in alcoholics.

Influence of mouse genotype on responses of central cholinergic neurotransmission to long term alcohol intoxication

Cholinergic neurotransmission has been followed in striatum and hippocampus in two inbred strains of mice (C57Bl/6 and Balb/c) during long term alcohol exposure (over a 25 month period) and with aging. Marked strain dependent differences in reactivity of pre- and postsynaptic cholinergic markers to chronic alcohol exposure and aging were demonstrated in both structures. The Balb/c strain exhibits a remarkable long lasting tolerance to alcohol injury for striatal and hippocampal cholinergic markers (choline acetyltransferase, high affinity choline uptake, muscarinic receptors affinity, acetyl cholinesterase), whereas C57Bl mice appear more sensitive to alcohol intoxication. Likewise aging affects the C57Bl mouse more severely than the Balb/c, a phenomenon which may be involved in the sensitivity of these mice to alcohol intoxication. Moreover long term alcohol exposure, in addition to aging show unequal effects on the diverse cholinergic markers studied. Also divergences of specific brain areas have been noted and should be related to their particular neuroanatomy. Such discrepancies may, in part, explain differences observed in the behavioral effects of chronic alcohol intoxication in alcoholics.

Genotypic differences in age and chronic alcohol exposure effects on somatostatin levels in hippocampus and striatum in mice

Somatostatin contents of striatum, hippocampus, and pons medulla have been followed in two inbred strains of mice (C57B1/6J and Balb/cJ) with aging and long term alcohol exposure (over a 25 month period of intoxication). Marked strain dependent differences in basic levels of somatostatin and genotypic variations in reactivity of this neuropeptide to aging processes and chronic alcohol exposure were demonstrated. The Balb/c strain exhibits a significant age dependent decrease in striatal and hippocampal somatostatin levels whereas the C57B1 mice remain unchanged until the 27 month. Moreover, only the Balb/c strain reacts to chronic alcohol exposure, showing a significant increase in somatostatin levels in those structures affected by the aging process. Such genotypic differences may be involved in man in specific pathologies in aged individuals and in alcohol induced behavioral alterations in alcoholics.

Alcoholism and epilepsy

There is a scarcity of population-based epidemiological investigations concerning the prevalence of epilepsy among alcoholics, and of alcoholism among epileptic patients. Available data seem to suggest that the prevalence of epilepsy among alcoholics is at least triple that in the general population, and that alcoholism may be more prevalent among epileptic patients than in the general population. The term "alcoholic epilepsy" has been used with varying definitions in different investigations. It is suggested that a uniform definition be adopted so as to minimize confusion when comparing data from different laboratories. Although there is general agreement that excessive alcohol intake can increase the frequency of seizures in epileptic patients, limited available data suggest that light to moderate social alcohol drinking may not affect seizure frequency. However, epileptic patients should be warned about the possible adverse effects of alcohol, especially those who have refractory forms of epilepsy. Except for a few anomalous cases, evidence for the direct seizure-provoking effect of alcohol is not strong. This is because it is difficult to pinpoint alcohol as the only etiology; more likely, alcohol is only one factor among others (e.g., head trauma, cerebral infarct, alcohol withdrawal, and metabolic effects of alcohol) in provoking seizures. Because seizures are a symptom and not a disease, it is often difficult to distinguish epileptic seizures from alcohol-withdrawal seizures. Patients with only the latter kind of seizures should not need chronic antiepileptic medication.

Inhibition by naloxone of the rise in hypothalamic dopamine and serum prolactin induced by ethanol

We investigated the effect of naloxone on the concentration of dopamine in the hypothalamus and on the concentration of prolactin in serum and anterior pituitary of male rats acutely treated with ethanol. Acute ethanol administration increased serum prolactin levels and hypothalamic dopamine concentration. Pituitary prolactin was not modified by this treatment. Naloxone administered 15 min before the animals were sacrificed decreased serum prolactin levels and hypothalamic dopamine concentration in ethanol-treated rats. These results suggest that ethanol increases prolactin secretion because it decreases the release of dopamine by the hypothalamus. Naloxone decreases prolactin release probably because it antagonizes the inhibitory action of opioids on dopaminergic neurons.

Changes in dopamine receptor sensitivity in humans after heavy alcohol intake

Dopamine (DA) sensitivity, assessed through maximal growth hormone (GH) response to stimulation by apomorphine (APO) (0.18-0.24 mg iv) was studied in 16 chronic alcoholics newly admitted after a period of heavy alcohol intake. Repeated hormonal tests were thereafter performed during a 2-month period under strictly controlled conditions to avoid relapse into alcohol consumption. Eight healthy volunteers with alcohol consumption slightly less than that of the general population were used as controls. It was found that DA sensitivity in the early abstinence phase was higher than later in the 2-month recovery period but not significantly different from control values. The relatively higher DA sensitivity in the early abstinence phase might be responsible for a lower threshold for psychotic symptoms and neuroleptic-induced extrapyramidal side effects. The results of this study give further evidence of a prolonged recovery phase after heavy alcohol intake.

Failure of amantadine and bromocriptine to counteract alcoholic inebriation in man

Oral amantadine 100 mg and bromocriptine 2.5 + 2.5 mg, alone and in combination with ethanol (1 g/kg), were investigated in two placebo-controlled, double-blind and cross-over trials. In the first trial the psychomotor effects of amantadine and bromocriptine were compared to those of placebo, and in the second trial ethanol was added to the treatment. Bromocriptine lowered serum prolactin levels, thus confirming its absorption. Amantadine and bromocriptine alone had no psychomotor effects but unpleasant sensations, nausea and dizziness were reported after bromocriptine. Ethanol impaired performance in terms of impaired coordinative and reactive skills, lowered tapping speed, prolonged critical flicker interval and reduced gaze nystagmus angle (P less than 0.05 to 0.001; two-way ANOVA). Subjectively, ethanol induced mental slowness, clumsiness and impairment of performance (P less than 0.05 to 0.001). Amantadine and bromocriptine failed to counteract any of these ethanol-induced changes. It is concluded that in man, an acute dopaminergic activation by amantadine or bromocriptine does not significantly modify the psychomotor effects of ethanol.

Dietary ascorbic acid deficiency in guinea pigs: no effect on ethanol preference, spiroperidol binding, or monoamine oxidase activity

Ascorbic acid levels are commonly reported to be decreased in alcoholics. Although this deficiency could be due to dietary factors, there is evidence that ascorbic acid may be involved in the metabolism and acute effects of ethanol, possibly related to the pathogenesis of alcoholism. Therefore, we examined ethanol preference in guinea pigs receiving an ascorbate deficient vs a normal diet. Brain and spleen ascorbic acid levels were dramatically decreased, but ethanol preference was not altered by the acute dietary deficiency of this vitamin. In addition, an acute stressor (cold water swim), alone or in combination with ascorbate deficiency, had no effect on ethanol preference. At termination of the experiment, two measures of brain aminergic function (MAO activity and 3H-spiroperidol binding), purportedly altered by ethanol or ascorbic acid or both, were not associated with tissue ascorbate levels.

Acquisition of behaviourally augmented tolerance to ethanol and its relationship to muscarinic receptors

Two groups of adult male rats were injected daily with ethanol (1.5 g/kg IP in 15% w/v solution) either before (the behaviourally augmented tolerant group) or after (the physiologically tolerant group) being placed in operant chambers. The control groups received daily isotonic saline injections either before or after the operant task. When challenged with ethanol (2.5 g/kg) on day 30 prior to the operant task, the control group was most impaired, while the behaviourally augmented tolerant group was significantly less impaired than the physiologically tolerant group. The two ethanol-treated groups were impaired to the same extent when challenged on day 60. Partial generalization of this behavioural tolerance to ethanol was observed, as the behaviourally augmented tolerant group was less impaired than the physiologically tolerant group for a tail flick response to painful stimuli after an ethanol challenge on day 30. However, the two ethanol-treated groups exhibited similar impairments of locomotor activity after an ethanol challenge on day 40. No differences in muscarinic receptor binding among the control and two ethanol-treated groups were found. These findings demonstrate that behaviourally augmented tolerance to ethanol may be partially generalizable but is unrelated to changes in muscarinic cholinergic receptors.

Prenatal exposure to ethanol alters [3h]naloxone binding in rat striatum

Pregnant rats were administered ethanol from day 8 of pregnancy until the day of delivery. Control rats were given isocaloric replacement of sucrose. [3H]Naloxone binding was determined in the striatum of pups of various ages in both groups. The binding was significantly lower in the pups of ethanol treated mothers than in pups of control mothers at all ages examined. The findings suggests an interference in the normal development of striatal receptors in rats prenatally exposed to ethanol.