Hippocampal-dependent learning and experience-dependent activation of the hippocampus are preferentially disrupted by ethanol

Environmental modulation of ethanol-induced locomotor activity: Correlation with neuronal activity in distinct brain regions of adolescent and adult Swiss mice

Drug abuse is a concerning health problem in adults and has been recognized as a major problem in adolescents. Induction of immediate-early genes (IEG), such as c-Fos or Egr-1, is used to identify brain areas that become activated in response to various stimuli, including addictive drugs. It is known that the environment can alter the response to drugs of abuse. Accordingly, environmental cues may trigger drug-seeking behavior when the drug is repeatedly administered in a given environment. The goal of this study was first to examine for age differences in context-dependent sensitization and then evaluate IEG expression in different brain regions. For this, groups of mice received i.p. ethanol (2.0 g/kg) or saline in the test apparatus, while other groups received the solutions in the home cage, for 15 days. One week after this treatment phase, mice were challenged with ethanol injection. Acutely, ethanol increased both locomotor activity and IEG expression in different brain regions, indistinctly, in adolescent and adult mice. However, adults exhibited a typical context-dependent behavioral sensitization following repeated ethanol treatment, while adolescent mice presented gradually smaller locomotion across treatment, when ethanol was administered in a paired regimen with environment. Conversely, ethanol-treated adolescents expressed context-independent behavioral sensitization. Overall, repeated ethanol administration desensitized IEG expression in both adolescent and adult mice, but this effect was greatest in the nucleus accumbens and prefrontal cortex of adolescents treated in the context-dependent paradigm. These results suggest developmental differences in the sensitivity to the conditioned and unconditioned locomotor effects of ethanol.

Varenicline ameliorates ethanol-induced deficits in learning in C57BL/6 mice

Ethanol is a frequently abused drug that impairs cognitive processes such as learning. Varenicline, an alpha4beta2 nicotinic receptor partial agonist and alpha7 nicotinic receptor full agonist prescribed for smoking cessation, has been shown to decrease ethanol consumption. The current study investigated whether varenicline could ameliorate ethanol-induced deficits in learning and whether varenicline alters blood alcohol concentration in C57BL/6 mice. Conditioning consisted of two auditory conditioned stimulus (CS; 30s, 85dB white noise)-foot shock unconditioned stimulus (US; 2s, 0.57mA) pairings. For all studies, saline or ethanol (1.0, 1.5, 2.0g/kg i.p.) was administered 15min before training, and saline or varenicline (0.05, 0.1, 0.2mg/kg i.p.) was administered 60min before either training or testing. For blood alcohol analysis, saline or varenicline (0.1mg/kg) was administered 60min before collection, and saline or ethanol (1.0, 1.5, 2.0g/kg) was administered 15min before collection. Varenicline dose-dependently ameliorated ethanol-induced conditioning deficits for all three doses of ethanol when administered before training but not when administered 24h later, before testing. In addition, varenicline did not alter blood alcohol concentration. The smoking cessation aid varenicline may have therapeutic uses for treating ethanol-associated disruptions in cognitive processes.

Effect of postnatal treadmill exercise on c-Fos expression in the hippocampus of rat pups born from the alcohol-intoxicated mothers

Maternal alcohol-intoxication during pregnancy exerts detrimental effects on fetal development and is known to influence learning ability and memory capability by altering neuronal activity in the hippocampus. c-Fos expression represents neuronal activity and plays a crucial role in the brain development. Physical exercise is known to enhance neuronal plasticity and activity. In the present study, we investigated the influence of postnatal treadmill running on the c-Fos expression in the hippocampus of rat pups born from the alcohol-intoxicated mothers. The results obtained show that maternal alcohol-intoxication suppressed c-Fos expression in the hippocampus of rat pups and that postnatal treadmill exercise enhanced c-Fos expression in the hippocampus of these rat pups. The present study suggests that exercise should be considered as a therapeutic means of countering the effects of maternal alcohol-intoxication, and that it may provide a useful strategy for enhancing the neuronal activity of children born from the mothers who abuse alcohol during pregnancy.

Interactive effects of ethanol and nicotine on learning in C57BL/6J mice depend on both dose and duration of treatment

OBJECTIVE AND RATIONALE

Alcohol and nicotine are commonly co-abused; one possible explanation for co-abuse is that each drug ameliorates the aversive effects of the other. Both drugs have dose-dependent effects on learning and memory. Thus, this study examined the interactive effects of acute ethanol and acute, chronic, or withdrawal from chronic nicotine on fear conditioning in C57BL/6J mice.

MATERIALS AND METHODS

Conditioning consisted of auditory conditioned stimulus-foot-shock unconditioned stimulus pairings. For acute studies, saline or ethanol, then saline or nicotine was administered before training, and saline or nicotine was also administered before testing. For chronic and withdrawal studies, saline or nicotine was administered chronically, and ethanol or saline was administered before training.

RESULTS

Acute nicotine (0.09 mg/kg) reversed ethanol-induced deficits (1.0 and 1.5 g/kg) in contextual and cued fear conditioning, whereas a low dose of ethanol (0.25 g/kg) reversed nicotine (6.3 mg kg(-1) day(-1)) withdrawal-induced deficits in contextual conditioning. Tolerance developed for the effects of nicotine on ethanol-induced deficits in conditioning and cross-tolerance between chronic nicotine and acute ethanol was seen for the enhancing effects of ethanol on conditioning.

CONCLUSIONS

The complex and sometimes polar actions of ethanol and nicotine on behavior may contribute to co-abuse of these drugs. Specifically, smoking may initially reduce the aversive effects of ethanol, but tolerance develops for this effect. In addition, low doses of alcohol may lessen nicotine withdrawal symptoms.

Acute ethanol has biphasic effects on short- and long-term memory in both foreground and background contextual fear conditioning in C57BL/6 mice

BACKGROUND

Ethanol is a frequently abused, addictive drug that impairs cognitive function. Ethanol may disrupt cognitive processes by altering attention, short-term memory, and/or long-term memory. Interestingly, some research suggests that ethanol may enhance cognitive processes at lower doses. The current research examined the dose-dependent effects of ethanol on contextual and cued fear conditioning. In addition, the present studies assessed the importance of stimulus salience in the effects of ethanol and directly compared the effects of ethanol on short-term and long-term memory.

METHODS

This study employed both foreground and background fear conditioning, which differ in the salience of contextual stimuli, and tested conditioning at 4 hours, 24 hours, and 1 week in order to assess the effects of ethanol on short-term and long-term memory. Foreground conditioning consisted of 2 presentations of a foot shock unconditioned stimulus (US) (2 seconds, 0.57 mA). Background conditioning consisted of 2 auditory conditioned stimulus (30 seconds, 85 dB white noise)-foot shock (US; 2 seconds, 0.57 mA) pairings.

RESULTS

For both foreground and background conditioning, ethanol enhanced short-term and long-term memory for contextual and cued conditioning at a low dose (0.25 g/kg) and impaired short-term and long-term memory for contextual and cued conditioning at a high dose (1.0 g/kg).

CONCLUSIONS

These results suggest that ethanol has long-lasting, biphasic effects on short-term and long-term memory for contextual and cued conditioning. Furthermore, the effects of ethanol on contextual fear conditioning are independent of the salience of the context.

Covalent Modification of DNA Regulates Memory Formation

DNA methylation is a covalent chemical modification of DNA catalyzed by DNA methyltransferases (DNMTs). DNA methylation is associated with transcriptional silencing and has been studied extensively as a lifelong molecular information storage mechanism put in place during development. Here we report that DNMT gene expression is upregulated in the adult rat hippocampus following contextual fear conditioning and that DNMT inhibition blocks memory formation. In addition, fear conditioning is associated with rapid methylation and transcriptional silencing of the memory suppressor gene PP1 and demethylation and transcriptional activation of the synaptic plasticity gene reelin, indicating both methyltransferase and demethylase activity during consolidation. DNMT inhibition prevents the PP1 methylation increase, resulting in aberrant transcription of the gene during the memory-consolidation period. These results demonstrate that DNA methylation is dynamically regulated in the adult nervous system and that this cellular mechanism is a crucial step in memory formation.

Repeated ethanol treatment in adolescent rats alters cortical NMDA receptor

Earlier we have reported that repeated ethanol treatment during adolescence causes long-lasting impairments in spatial learning and memory. The present study was undertaken to determine the cellular mechanisms underlying the persistent ethanol-induced cognitive dysfunction in adolescent male rats. Since in adult animals ethanol is known to affect the N-methyl-d-aspartate (NMDA) receptor-gated ion channel, the hypothesis tested here was that adolescent ethanol exposure modulates NMDA receptor (NR) regulation in the brain. Adolescent male rats were injected daily with ethanol (2g/kg intraperitoneally) for 5 consecutive days. Control rats received isovolumetric saline for the same number of days. Groups of control and experimental rats were sacrificed 7 days after the last ethanol/saline administration, and NR activity was measured in specific brain regions (frontal cortex, hippocampus) using the [(3)H]MK-801 binding assay. In addition, some rats were sacrificed and their brains were used to investigate changes in NR pharmacology by measuring specific NR2 subunits immunohistochemically. Compared to saline-treated controls, ethanol-treated rats showed significant increases in [(3)H]MK-801 maximal binding in the frontal cortex. This was associated with increased cortical NR2B subunit protein. [(3)H]MK-801 binding in the hippocampus was minimally affected. These results indicate that ethanol exposure during the adolescent period produces brain region-specific alterations in NR activity. These changes are different from those reported in literature for ethanol administration during the perinatal period or adulthood. Together, these data suggest that adolescence represents a unique stage in brain development in its long-term sensitivity to ethanol.

Context is a trigger for relapse to alcohol

The environment in which alcohol consumption occurs may trigger later relapse in alcohol abusers. In this study, we tested whether an alcohol-associated environment would induce alcohol-seeking behavior. Male rats were trained to lever press for oral alcohol reinforcement in a distinctive context. Responding was then extinguished in a context with different olfactory, visual and tactile properties. Placement of the rats back into the original context in which they self-administered alcohol induced, in the absence of alcohol availability, a significant increase in lever press responding on the alcohol lever as compared to extinction levels of responding. The ability of the alcohol context to support alcohol-seeking behavior was maintained over 3 weeks, with no significant diminution. A second group of rats was trained to lever press for sucrose reinforcement; this group also demonstrated context-dependent reinstatement, although the degree of reinstatement decreased over repeated tests, returning to extinction values after 3 weeks. These findings indicate that contextual conditioning has a long-term impact on ethanol-seeking behavior after ethanol withdrawal. This animal model may be useful to study the neural mechanisms underlying relapse induced by ethanol-associated contexts in humans.

Ataxia and c-Fos expression in mice drinking ethanol in a limited access session

BACKGROUND

Although previous murine studies have demonstrated ethanol self-administration resulting in blood ethanol concentrations (BECs) believed to be pharmacologically relevant, to our knowledge, no study reported to date has demonstrated intoxication via ataxia after self-administration. Thus, the goal of this study was to demonstrate ataxia and to examine changes in c-Fos expression in mice after self-administration of intoxicating doses of ethanol.

METHODS

Male C57BL/6J mice were trained to drink a 10% ethanol solution during daily 30-min limited access sessions. Mice were exposed to increasing concentrations of ethanol until a 10% ethanol solution was reached. BEC and ataxia, measured as foot slips off of a balance beam, were examined after the limited access self-administration session. In a separate experiment, various brain structures from mice drinking water or ethanol were examined for changes in c-Fos expression two hr after the limited access session.

RESULTS

Mice drank between 1.5 and 2 g/kg of 10% ethanol during the daily 30-min session. BECs for these mice 15 min after the limited access session ranged between 0.52 and 2.13 mg/ml. A significant increase in foot slips off a balance beam was seen immediately after ethanol consumption during the limited access session. Among mice drinking ethanol, an increase in c-Fos expression was seen in the Edinger-Westphal nucleus, and a decrease in c-Fos expression was seen in the cingulate cortex, ventral tegmental area, lateral and medial septum, CA1 region of the hippocampus, and basolateral amygdala.

CONCLUSIONS

After this procedure in mice, BECs are achieved that are in a range considered pharmacologically relevant and intoxicating. Significant ataxia was observed after ethanol self-administration. Brain regions showing changes in c-Fos expression after voluntary intoxication were similar to those previously reported, suggesting that these brain regions are involved in regulating behavioral effects of alcohol intoxication.

Adolescent Rats Exposed to Repeated Ethanol Treatment Show Lingering Behavioral Impairments

BACKGROUND

Repeated ethanol treatment has been reported to differentially affect water maze performance in adolescent and adult rats. The present study was undertaken to determine the age-specific reversal of ethanol-induced deficit in water maze performance.

METHODS

Adolescent and adult male rats were subjected to repeated ethanol or saline treatments. Experimental rats were injected daily with 2 g/kg ethanol (intraperitoneally) for five consecutive days (Days 1-5) and tested in the hidden platform task of the Morris water maze 30 minutes after ethanol treatment; control rats received isovolumetric saline. On the last training day, all rats were tested in the probe trial and in the cued visual task. After an ethanol-free period of 4-25 days, rats were retested in the water maze.

RESULTS

Adolescent ethanol-treated rats had significantly higher latencies and swam greater distances to find the hidden platform, compared to age-matched saline control rats. Ethanol rats also showed increased hug time, i.e., spent significantly more time near the periphery of the pool than control rats. In the probe trial, compared to adolescent saline rats, ethanol rats spent less time in the target quadrant. However, there was no difference between ethanol- and saline-treated rats in the swim speed or in the visual task performance. Experimental and control rats were retested in the water maze 4 days (Day 9), 7 days (Day 12), and 25 days (Day 30) after the last ethanol/saline treatment; no injections were given on those days. Ethanol-treated rats continued to do poorly on all retest days. Ethanol treatment in adult male rats acutely increased latency and distance to find the hidden platform, but unlike adolescent alcohol rats, their performance in the probe trial did not differ from adult saline rats. Also, swim speed and visual task performance of adult rats were significantly affected by ethanol exposure. During retesting, their performance did not differ from adult control rats.

CONCLUSIONS

Adolescent rats exposed to ethanol showed deficits in water maze performance, had increased hug time, and failed to catch up with control rats during the weeks after the ethanol treatment period was over. Adult alcohol rats showed some behavioral dysfunction (increased latency and distance to find the hidden platform) but had problems swimming, and in the probe trial they performed as well as control rats. Also, in adult rats, ethanol-induced impairments were quickly reversed after the ethanol treatment was over, a finding that suggests impaired motor coordination more than a true learning deficit. Together, these data indicate that repeated ethanol treatment in adolescent rats, but not adult rats, show long-term impairments in maze performance.

The effect of long context exposure on cued conditioning and c-fos expression in the rat forebrain

The c-fos expression was used to study the neural substrates of the cued fear conditioning acquisition, preceded by a short exposure versus a long exposure to the conditioning context. A long-context exposure (either during the night or during the day) prior to conditioning, was associated with low freezing in the learning test. Differences in the c-fos expression of CA1, CA3, BL Amygdala, LS and BNST were found between the short- or long-context groups with a pre-exposure before cued conditioning. Ce Amygdala showed no differences in the c-fos expression labeling. We reported the hippocampal c-fos activation during the cued fear conditioning acquisition. Specifically, the CA1 activation could be related with the context-US processing during the CS-US association acquisition, which might prove that the CS-US associations cannot be made without an integrated context participating. The results showed that a long-context exposure prior to cued conditioning produces an inhibition of the CR (freezing), and this phenomenon is related with a specific c-fos expression in CA1, CA3, BL Amygdala, LS and BNST during the fear acquisition.

The use of acute ethanol administration as a tool to investigate multiple memory systems

The discovery of multiple memory systems supported by discrete brain regions has been one of the most important advances in behavioral neuroscience. A wealth of studies have investigated the role of the hippocampus and related structures in supporting various types of memory classifications. While the exact classification that best describes hippocampal function is often debated, a specific subset of cognitive function that is focused on the use of spatial information to form hippocampal cognitive maps has received extensive investigation. These studies frequently employ a variety of experimental manipulations including brain lesions, temporary neural blockade due to cooling or discrete injections of specific drugs. While these studies have provided important insights into the function of the hippocampus, they are limited due to the invasive nature of the manipulation. Ethanol is a drug that is easily administered in a non-invasive fashion, is rapidly absorbed and produces effects only in specific brain regions. The hippocampus is one brain region affected by acute ethanol administration. The following review summarizes research from the last 20 years investigating the effects of acute ethanol administration on one specific type of hippocampal cognitive function, namely spatial memory. It is proposed that among its many effects, one specific action of acute ethanol administration is to produce similar cognitive and neurophysiological effects as lesions of the hippocampus. Based on these similarities and the ease of its use, it is concluded that acute ethanol administration is a valuable tool in studying hippocampal function and multiple memory systems.

Intermittent Ethanol Exposure in Adolescent Rats: Dose-Dependent Impairments in Trace Conditioning

BACKGROUND

Recent studies have revealed that the adolescent brain may be especially vulnerable to ethanol-induced toxicity. Corticolimbic regions are more severely damaged following ethanol exposure during adolescence than during adulthood. The consequences of adolescent ethanol exposure on cognition however, have only recently begun to be explored.

METHODS

Male and female rats were administered 0, 1.5, 2.5 or 4.5 g/kg ethanol (20% v/v) by acute intragastric gavage during adolescence (postnatal days [PD] 28, 30, 32 and 34). On PD 40, half of the subjects in each dose group were given 5 pairings of a 10-sec flashing light (CS; conditioned stimulus) immediately followed by mild footshock (US; unconditioned stimulus), a procedure known as delay conditioning. The other half were also given 5 CS-US pairings, but the US was presented 10 sec after CS offset, a procedure known as trace conditioning. All subjects were tested for CS-elicited freezing 24 h later.

RESULTS

There was no effect of adolescent ethanol exposure on delay conditioned responding, with all subjects demonstrating comparable levels of CS-elicited freezing. In contrast, the amount of freezing in the trace conditioned subjects was negatively correlated with prior ethanol dose. Specifically, exposure to 2.5 or 4.5 g/kg during adolescence resulted in a deficit in trace conditioned responding.

CONCLUSIONS

These data indicate that intermittent exposure to ethanol during adolescence results in impairment in hippocampal-dependent trace conditioning that persists beyond the period of ethanol exposure. Delay conditioning was unaffected by prior ethanol treatment, indicating that there was no difficulty in detecting the CS or US, or in the ability to engage in freezing behavior. These results suggest that the adolescent brain may be particularly vulnerable to the effects of repeated exposure to ethanol that can have consequences for nonspatial, hippocampal-dependent cognitive abilities.

Fear conditioning is impaired in adult rats by ethanol doses that do not affect periadolescents

Adolescent rats and humans exhibit physiological, behavioral, and cognitive differences compared to their adult counterparts. These differences are apparent also in reactions to psychoactive drugs, such as ethanol. Recent studies have shown that though less sensitive to several behavioral indices of intoxication by ethanol, adolescent rats are more sensitive to the cognition-impairing effects of ethanol. Ethanol's effects, in the present experiment, were assessed in terms of a fear conditioning test not previously used in comparison of adult and adolescent Sprague-Dawley albino rats. Separate groups of both ages were given intraperitoneal (i.p.) ethanol before or after tone-shock conditioning. This task features a hippocampus-independent component, learned freezing to a tone, and a hippocampus-dependent component, learned freezing to context. Post-training ethanol had no effect on retention in either age, but pre-acquisition ethanol impaired adult learning more than adolescent learning, as indexed by the expression of fear at the test. Blood alcohol was equivalent in adolescents and adults at a dose that produced cognitive discrepancies. Unlike other reports, these experiments demonstrate that adolescents may not be more sensitive to ethanol's effects in all cases of learning.

GABAA receptor-mediated inhibition by ethanol of long-term potentiation in the basolateral amygdala-dentate gyrus pathway in vivo

Although ethanol has been reported to inhibit the induction of long-term potentiation in hippocampal CA1 and dentate gyrus synapses of rats, very little is known about the effect of ethanol on synaptic plasticity in other brain regions. Therefore, in the present study, we investigated the effect of ethanol on long-term potentiation in synaptic pathway from the basolateral amygdala to the dentate gyrus by using anesthetized rats in vivo. I.v. (20-40% x 2 ml/kg) or i.c.v. (30-40% x 5 microl) administration of ethanol did not affect the basal amplitude of dentate gyrus field potential evoked by basolateral amygdala stimulation, but significantly inhibited the induction of long-term potentiation following application of tetanic stimulation. Since long-term potentiation in this pathway was independent of N-methyl-d-aspartate receptors, the inhibitory effect of ethanol is unlikely to be caused by suppression of N-methyl-d-aspartate receptor function. Alternatively, long-term potentiation in this pathway was significantly suppressed by the benzodiazepine agonist diazepam (2 mg/kg, i.p.), and the inhibitory effect of ethanol was abolished by the GABAA receptor channel blocker picrotoxin (1 mg/kg, i.p.). The present study demonstrates that ethanol inhibits the induction of long-term potentiation in the basolateral amygdala-dentate gyrus pathway by enhancing GABAA receptor-mediated neurotransmission.

A two-dimensional neuropsychology of defense: fear/anxiety and defensive distance

We present in this paper a picture of the neural systems controlling defense that updates and simplifies Gray's "Neuropsychology of Anxiety". It is based on two behavioural dimensions: 'defensive distance' as defined by the Blanchards and 'defensive direction'. Defensive direction is a categorical dimension with avoidance of threat corresponding to fear and approach to threat corresponding to anxiety. These two psychological dimensions are mapped to underlying neural dimensions. Defensive distance is mapped to neural level, with the shortest defensive distances involving the lowest neural level (periaqueductal grey) and the largest defensive distances the highest neural level (prefrontal cortex). Defensive direction is mapped to separate parallel streams that run across these levels. A significant departure from prior models is the proposal that both fear and anxiety are represented at all levels. The theory is presented in a simplified form that does not incorporate the interactions that must occur between non-adjacent levels of the system. It also requires expansion to include the dimension of escapability of threat. Our current development and these proposed future extensions do not change the core concepts originally proposed by Gray and, we argue, demonstrate their enduring value.

Nicotine enhances contextual fear conditioning and ameliorates ethanol-induced deficits in contextual fear conditioning

Nicotine and ethanol are 2 commonly used and abused drugs that have divergent effects on learning. The present study examined the effects of acute nicotine (0.25 mg/kg), ethanol (1.0 g/kg), and ethanol-nicotine coadministration on fear conditioning in C57BL/6 mice. Mice were assessed for contextual and cued fear conditioning at 1 day and 1 week posttraining. Ethanol disrupted acquisition but not consolidation of contextual fear conditioning; nicotine enhanced contextual fear conditioning and ameliorated ethanol-associated deficits in contextual fear conditioning. Mecamylamine antagonized this effect. Fear conditioning was reassessed 1 week after initial testing with no drug administered. At the 1-week retest, mice previously treated with nicotine continued to show enhanced contextual fear, and mice previously treated with ethanol continued to show contextual fear deficits. Thus, nicotine both produces a long-lasting enhancement of contextual fear conditioning and protects against ethanol-associated deficits.

Impairments in spatial learning and memory: ethanol, allopregnanolone, and the hippocampus

Acute ethanol administration impairs performance in many cognitive tasks that are dependent on hippocampal function. For example, acute ethanol administration produces dose-dependent impairments in spatial learning. Ethanol also decreases the spatial specificity of hippocampal place cells. Such findings raise the possibility that ethanol affects learning and memory by altering, either directly or indirectly, neuronal activity in the hippocampus and related structures. Acute ethanol administration induces a dose- and time-dependent increase in brain concentration of the neuroactive steroid allopregnanolone. Allopregnanolone is a potent GABAA receptor agonist and produces effects similar to the effects produced by ethanol. Blockade of de novo biosynthesis of allopregnanolone alters many of ethanol's effects including ethanol-induced suppression of spontaneous activity in medial septum/diagonal band of Broca neurons and hippocampal pyramidal neurons. These findings suggest that ethanol-induced increases in allopregnanolone levels might play a central role in the effects of acute ethanol on cognitive processing and hippocampal function. The impact of ethanol on spatial cognitive processing and hippocampal function will be reviewed. In addition, the possibility that ethanol-induced changes in neuroactive steroid levels contribute to the impact of ethanol on spatial learning and hippocampal function will be explored.

Acute ethanol administration selectively impairs spatial memory in C57BL/6J mice

It has been shown in rats that acute ethanol administration, via a single intraperitoneal injection, selectively impairs the memory of certain spatial tasks. It is unknown whether these same results can be produced in the C57BL/6J mouse strain. Male C57BL/6J mice were trained in a spatial task in the Morris water maze. After training, an ethanol test was administered in which each mouse was given an injection of one of four randomly assigned doses: ethanol, at a dose of 1.25, 1.75, or 2.25 g/kg, or a saline control dose that remained constant at 1.75 g/kg. Thirty minutes after injection, the mice were given the spatial task. Next, the same mice were given training for a nonspatial task in the Morris water maze. After training, another ethanol test was administered. Again, the mice were randomly assigned one of the aforementioned doses. Thirty minutes after injections, the mice were given the nonspatial task. Results from Study 1, by using latency, showed that acute ethanol administration selectively impaired spatial memory (P<.05) at 1.75 and 2.25 g/kg doses, yet it failed to significantly impair nonspatial memory except at the 2.25 g/kg dose. Results from Study 2, by using path lengths, showed similar effects, in that acute ethanol administration selectively impaired spatial memory (P<.05) at the 2.25 g/kg dose, yet it failed to impair nonspatial memory at any dose. These findings demonstrate that acute ethanol administration selectively impairs spatial memory in C57BL/6J mice.

Role of neuronal nicotinic receptors in the effects of nicotine and ethanol on contextual fear conditioning

Nicotine can enhance contextual learning while ethanol impairs some forms of learning. Nicotine can overcome some of the impairing effects of ethanol when the two drugs are co-administered. The specific brain nicotinic acetylcholine receptors (nAChRs) that mediate nicotine's effects on contextual learning and whether any of ethanol's actions are mediated by nAChRs are unknown. The potential roles of nAChRs in contextual and cued fear conditioning as well as the effects of nicotine, ethanol, or co-administration of nicotine and ethanol were examined in wild type and homozygous null mutant mice from alpha7, beta2, beta3, and beta4 mouse lines at 24 h after training. Nicotine was given prior to training and testing, whereas ethanol was given only before training. Nicotine enhanced contextual learning in both alpha7 wild types and mutants when mice were trained at 0.17 mA, but not 0.35 mA. Mutants lacking the alpha7 subunit were less sensitive to the memory impairing effects of ethanol trained at 0.35 mA. beta2 Null mutants receiving saline showed a small, but significant, impairment in contextual learning compared with wild type littermates when the shock stimulus was 0.35 mA. Beta2 Null mutant mice also did not respond to the cognitive enhancing effects of nicotine alone, or after ethanol administration. beta3 and beta4 null mutants did not differ from wild types either after saline or any of drug treatments. These results show that beta2-containing nAChRs, but not beta3- or beta4-containing receptors, mediate the enhancing effects of nicotine on contextual learning and confirm previous studies implicating beta2 in other forms of learning. A new role for alpha7 nAChRs in regulating sensitivity to the cognitive disrupting effects of ethanol is proposed.

Expression of hNP22 Is Altered in the Frontal Cortex and Hippocampus of the Alcoholic Human Brain

BACKGROUND

Human neuronal protein (hNP22) is a gene with elevated messenger RNA expression in the prefrontal cortex of the human alcoholic brain. hNP22 has high homology with a rat protein (rNP22). These proteins also share homology with a number of cytoskeleton-interacting proteins.

METHODS

A rabbit polyclonal antibody to an 18-amino acid epitope was produced for use in Western and immunohistochemical analysis. Samples from the human frontal and motor cortices were used for Western blots (n = 10), whereas a different group of frontal cortex and hippocampal samples were obtained for immunohistochemistry (n = 12).

RESULTS

The hNP22 antibody detected a single protein in both rat and human brain. Western blots revealed a significant increase in hNP22 protein levels in the frontal cortex but not the motor cortex of alcoholic cases. Immunohistochemical studies confirmed the increased hNP22 protein expression in all cortical layers. This is consistent with results previously obtained using Northern analysis. Immunohistochemical analysis also revealed a significant increase of hNP22 immunoreactivity in the CA3 and CA4 but not other regions of the hippocampus.

CONCLUSIONS

It is possible that this protein may play a role in the morphological or plastic changes observed after chronic alcohol exposure and withdrawal, either as a cytoskeleton-interacting protein or as a signaling molecule.

Alcohol-induced memory impairment in trace fear conditioning: a hippocampus-specific effect

It has been hypothesized that the amnesic effects of alcohol are through selective disruption of hippocampal function. Delay and trace fear conditioning are useful paradigms to investigate hippocampal-dependent and independent forms of memory. With delay fear conditioning, learning of explicit cues does not depend on normal hippocampal function, whereas learning explicit cues in trace fear conditioning does. In both delay and trace fear conditioning, the hippocampus is involved in learning to contextual cues, but it may not be entirely necessary. The present study investigates the effects of alcohol on the acquisition of delay and trace fear conditioning in mice, using freezing as a measure of learning. Male C57BL/6J mice were injected with 0.8 or 1.6 g/kg of 20% v/v alcohol and were immediately exposed to eight tone-footshock pairings in which the conditional stimulus (CS) either coterminated with a footshock unconditional stimulus (US) (delay conditioning) or was separated from the footshock by a 30-s trace interval (trace conditioning). During trace, but not delay fear conditioning, 0.8 g/kg alcohol impaired learning to a tone CS. This dose also impaired context-dependent learning in both procedures (although only slightly for trace fear conditioning). The 1.6 g/kg alcohol exerted a nonselective impairment on learning. The impairment by alcohol of learning to a tone CS when it is hippocampus-dependent, but not when it is hippocampus-independent provides further support for the hypothesis that alcohol exerts a selective effect on hippocampus-dependent learning.

Ethanol disrupts fear conditioning in C57BL/6 mice

Ethanol has been demonstrated to disrupt numerous forms of learning. For example, ethanol disrupts fear conditioning in rats. Surprisingly, the opposite result was reported for mice. Because of the importance of mouse models in ethanol research and the predominance of transgenic mice generated on a C57BL/6 background, the present study examined the effects of acute ethanol administration on fear conditioning in C57BL/6 mice. Fear conditioning was chosen because of the apparent contradiction in results between mice and rats, because of its popularity in assessing forebrain-dependent learning and because the task examines two types of learning: (i) the hippocampus-dependent contextual learning and (ii) the hippocampus-independent conditioned stimulus-unconditioned stimulus learning. Dose-response curves were generated for ethanol (0.5, 1.0 and 1.5 g/kg) given on either training day, testing day, or both days. Ethanol, in a dose-dependent manner, disrupted fear conditioning when given on training day or given on both training and testing days. Ethanol given on testing day only did not disrupt fear conditioning. The present results demonstrate that ethanol disrupts fear conditioning in C57BL/6 mice.

Effect of Puerariae radix on c-Fos expression in hippocampus of alcohol-intoxicated juvenile rats

Alcohol consumption is known to cause substantial neuronal loss in several regions of the brain. In Oriental medicine, medications based on Puerariae radix have been known to be of efficacy in the treatment of alcohol-related problems. In the present study, the effect of the aqueous extract of Puerariae radix on the expression of c-Fos, an immediate early gene whose expression is sometimes used as a marker for stimulus-induced changes in the metabolic activity of neurons, in the hippocampus of acutely alcohol-intoxicated juvenile rats was investigated via immunohistochemistry. In the first part of the experiment, Sprague-Dawley rats were divided into six groups: the control group, the alcohol-treated group, the alcohol- and 0.3 mg/kg Puerariae radix-treated group, the alcohol- and 3 mg/kg Puerariae radix-treated group, the alcohol- and 30 mg/kg Puerariae radix-treated group, and the alcohol- and 300 mg/kg Puerariae radix-treated group. In the second part of the experiment, animals were divided into four groups: the control group, the 30 mg/kg Puerariae radix-treated group, the alcohol-treated group, and the alcohol- and 30 mg/kg Puerariae radix-treated group. From the results, it was demonstrated that alcohol administration significantly decreases the number of Fos-positive cells in the various regions of the hippocampus, and Puerariae radix treatment inhibits the alcohol-induced suppression of the expression of Fos in the hippocampus in a dose-dependent manner. Puerariae radix exerted no significant effect on Fos expression in the hippocampus of normal rats. The results presented in this study suggest that Puerariae radix may alleviate alcohol-induced disruption of hippocampal functions.

Nimodipine prevents the effects of ethanol in tests of memory

The effects of acute administration of the dihydropyridine calcium channel antagonist, nimodipine, were studied on the actions of ethanol in the radial arm maze and the object recognition test. In the former test, the effects of the drugs were examined on the performance in finding the four baited arms, after previous training in this task. Ethanol, at 1 g/kg, increased both the number of re-entries into baited arms (counted as errors of working memory) and the total number of arm choices required to complete the task. Administration of nimodipine, 10 mg/kg, with the ethanol, completely prevented the deleterious effects on memory in this task, but had no effects on the performance when given in the absence of ethanol. In the object recognition task, ethanol, 1 g/kg, significantly decreased the differences in the time spent exploring novel and familiar objects. Nimodipine, 10 mg/kg, given with the ethanol, completely prevented this effect, but nimodipine alone had no effects. The lack of changes in total exploration times indicated that the effects of ethanol in these tests were not due to loss of motor co-ordination or of alertness. The results are discussed in the light of the known actions of the drugs on brain function.

Effects of acute alcohol administration on object recognition learning in C57BL/6J mice

The goal of the present study was to investigate effects of alcohol intoxication on the object recognition learning task. Male C57BL/6J mice habituated to saline injections and exploratory arena received different doses of ethanol (0, 1.6 or 2.4 g/kg) before or after a 10-min training session. During training, animals were exposed to a small object (a marble or a die). On the next day, during a 10-min testing session, animals were exposed to two objects: the familiar object from the previous day and a novel object. Analysis of behavior during testing showed that mice injected with 0 and 1.6 g/kg of ethanol before training spent more time exploring a novel than a familiar object during testing. In contrast, mice injected with 2.4 g/kg ethanol spent equal amounts of time exploring the novel and the familiar object. Mice injected with this dose of ethanol after training did not show a decreased ratio of object exploration during testing. Analysis of behavior during training showed that mice injected with this dose of ethanol spent less time exploring the object, although their locomotor activity was not decreased. Our results show that in C57BL/6J mice, ethanol intoxication interferes with exploratory activity during object exploration, but not with consolidation of memory.

The role of GABAergic neuroactive steroids in ethanol action, tolerance and dependence

This article reviews data on ethanol and neurosteroid interactions in the CNS. We discuss how GABAergic neurosteroids, including 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC, produced in response to systemic ethanol administration contribute to several of the effects of ethanol associated with modulation of GABA(A) receptors in rodents. There is an essential correlation between the time course of ethanol-induced 3alpha,5alpha-TH PROG production in the brain and specific behavioral and neural effects of ethanol. Furthermore, the anticonvulsant and inhibitory effects of ethanol on spontaneous neural activity were completely prevented by a key inhibitor of steroid biosynthesis. 3alpha,5alpha-TH PROG influences cognitive processing, spatial learning and memory and alters drinking behaviors in rats. Furthermore, ethanol induction of 3alpha,5alpha-TH PROG is diminished in tolerant and dependent animals. These effects are associated with increases in the sensitivity of GABA(A) receptors to neurosteroids and suggest an important role in ethanol withdrawal. Together, we suggest that 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC contribute to ethanol action and this interaction may represent a new mechanism of ethanol action. The identification of neurosteroid intermediaries involved in ethanol action may lead to important advances in the field and the development of novel therapeutics for alcoholism.

Age-related effects of moderate alcohol consumption on GAP-43 levels in rat hippocampus

The effects of moderate intake of ethanol and ageing were investigated on the levels of the growth-associated protein GAP-43, whose expression has been used as an indicator of axonal growth during development, regeneration and remodelling of synaptic connections. Groups of female Wistar rats (12 and 24 months of age), were alcohol-fed for one month while age-matched control groups received an isocaloric diet. A quantitative evaluation of GAP-43 was performed in hippocampus and in hippocampal selected areas in view of the vulnerability of this complex to alcohol aggression by means of two different methods, namely Western blot analysis and immunohistochemistry. While the former measures total extractable GAP-43, the latter allows visualisation of in situ changes in topographical distribution of GAP-43. Western blot analysis revealed an age-dependent reduction (-47%) and an ethanol-associated increase (81%) of GAP-43 demonstrated only in the old group. Conversely, quantitative immunohistochemistry of GAP-43 in the entire hippocampus showed a non-significant ethanol-related decrement in 24-month-old rats (-30%), although the age-dependent reduction was confirmed. Ageing was associated with a decrement of GAP-43 immunostaining in CA3 stratum radiatum (CA3) and in inner molecular layer of dentate gyrus (IML). Treatment determined a decrease of GAP-43 immunostaining in adult rat CA3 and IML and no change in CA1 stratum radiatum (CA1). Our results suggest that immunohistochemistry evaluation underestimates GAP-43 levels in ethanol-treated animals possibly as a consequence of conformational changes induced by alcohol, resulting in non-targeting of the specific antibody. Western blot analysis demonstrate that although there is a reduction of GAP-43 levels in hippocampus of aged rats, this structure retain a remarkable potential to compensate for ethanol toxicity during ageing.

Septohippocampal pathway as a site for the memory-impairing effects of ethanol

Ethanol affects behavior by interacting with synaptic sites at many levels of the nervous system. However, it targets most readily and at the lowest concentrations those sites mediating higher cognitive functions such as attention and memory. The memory-impairing effects of ethanol are thought to involve the hippocampus, a structure particularly vulnerable to the effects ethanol at low concentrations and early in the rising phase of the blood ethanol concentration curve. One of the early, low-dose effects of ethanol is an interruption of the normal physiological regulation of the hippocampus by the ascending septohippocampal pathway originating in the medial septal area (MSA). Ethanol enhances GABAergic transmission in the MSA, thereby reducing the regularity and vigor with which rhythmically bursting neurons of the MSA drive the hippocampal theta rhythm. Disruption of septohippocampal activity also has consequences on the response of the hippocampus to cortical inputs. Ethanol produces a loss of hippocampal responsivity that reduces the ability of the hippocampus to encode and retrieve relevant stimulus information necessary for accurate memory. This paper examines the behavioral and neural evidence for hippocampal vulnerability to ethanol and explores the hypothesis that these effects are due to ethanol disrupting septohippocampal modulation of the hippocampus, resulting in impairments of memory.

Effects of acute and chronic ethanol exposure on spatial cognitive processing and hippocampal function in the rat

Animals, including rats, have a predisposition to process and use spatial information to organize and guide behavior. The hippocampus and related structures are critically involved in this function, and, consequently, it has been proposed that one function of the hippocampus is to construct "spatial cognitive maps" of environments. Lesions to the hippocampus or its connections produce a pattern of alterations in behavior which include shifts from the use of spatial information to guide behavior to the use of cue- or taxon-based information to guide behavior. Recently it was demonstrated that ethanol interacts with a specific group of neurotransmitter systems, i.e., N-methyl-D-aspartate receptors and GABA(A) receptors that exist in high proportions in the hippocampus and related structures. In this review, we seek to summarize the literature demonstrating that one effect of acute and chronic ethanol exposure is to produce behavioral alterations that are strikingly similar to those found following lesions to the hippocampal system. Furthermore, cellular and anatomical alterations resulting from similar ethanol exposure paradigms will be reviewed and offered as possible mechanisms for producing the alterations in behavior. Finally, several unanswered questions concerning the interaction between ethanol and spatial cognitive processing will be identified.

Ethanol, memory, and hippocampal function: a review of recent findings

For well over a century, ethanol was believed to exert its effects on cognition and behavior by producing a ubiquitous depression of central nervous system activity. A general disruption in brain function was consistent with the belief that ethanol's effects on cognition and behavior were also quite general. Substantial evidence now indicates that ethanol produces a host of selective effects on neural activity, resulting in regional differences in ethanol's effects in the brain. Consistent with such evidence, recent research suggests that ethanol's effects on cognition and behavior are not as global as previously assumed. The present paper discusses evidence that many of ethanol's effects on learning and memory stem from altered cellular activity in the hippocampus and related structures. Potential mechanisms for ethanol's disruption of hippocampal function are reviewed. Evidence suggests that ethanol disrupts activity in the hippocampus by interacting directly with hippocampal neurons and by interacting with critical hippocampal afferents.

Alcohol drinking produces brain region-selective changes in expression of inducible transcription factors

Mapping the effects of alcohol consumption on neural activity could provide valuable information on mechanisms of alcohol's effects on behavior. The present study sought to identify effects of alcohol consumption on expression of inducible transcription factors (ITFs) in mouse brain. C57BL/6J mice were trained to consume 10% ethanol/10% sucrose solution during a 30-min limited access period. Control animals were given access to 10% sucrose solution or water. Following the final day of the procedure, animals were sacrificed and immunohistochemical analyses were performed for three ITFs (c-Fos, FosB, and Zif268). Alcohol-consuming animals had increased ITF expression in several brain areas. Specifically, c-Fos was significantly induced in the nucleus accumbens core (AcbC), the medial posteroventral portion of the central nucleus of the amygdala (CeMPV), and the Edinger-Westphal nucleus (EW). Expression of c-Fos was significantly lower in the dentate gyrus of alcohol-consuming animals vs. sucrose-consuming animals. However, it was not significantly different from the water controls. Induction of c-Fos in AcbC, CeMPV and EW was significantly related to blood alcohol concentrations (BAC). Furthermore, FosB expression in the CeMPV and the EW was also significantly higher in the alcohol-consuming animals vs. water controls. FosB expression in the EW was significantly related to BAC. The significance of these results is two-fold. First, our experiments demonstrate that ITF mapping is an effective strategy in identifying alcohol-induced changes following voluntary consumption. Second, they suggest a relationship between ITF expression in AcbC, CeMPV and EW and the level of alcohol intoxication.

Acute ethanol administration impairs spatial performance while facilitating nonspatial performance in rats

Acute ethanol administration produces learning and memory impairments similar to those found following lesions to the hippocampal system in rats. For example, both ethanol and hippocampal lesions impair performance on spatial learning and memory tasks while sparing performance on many nonspatial learning and memory tasks. Lesions to the hippocampal system can also alter the nature of the information that the animal uses to guide its behavior, from using spatial information to using individual cues. In the present experiment, rats were trained, while sober, to navigate on an eight-arm radial arm maze to a specific arm for food reward. During training, the rewarded arm was always in the same specific location and contained well-defined cues. After the rat learned the task, a memory test was conducted under different doses of ethanol (0.0 g/kg [saline control], 1.0, 1.5, or 2.0 g/kg, intraperitoneal). On the test day the maze was rotated so that the cued arm was 90 degrees to the right of its original position. During testing, intact rats showed a significant bias to approach the place where they had been previously rewarded, even though the cue was no longer located there. Acute ethanol administration dose dependently reduced approaches to the rewarded place. However, ethanol administration did not result in increases in random choices; rather, it resulted in a dose-dependent increase in approaches to the cued arm, now in a new location. These results extend previous research showing that acute ethanol administration and lesions to the hippocampal system produce similar effects on learning and memory in rats.

The "anxiety state" and its relation with rat models of memory and habituation

Rats selected as "anxious", "nonanxious," or normal according to their behavior in an elevated plus maze were submitted to memory tasks and the densities of central benzodiazepine receptors in the amygdala and the hippocampus were studied. Anxious rats exibited better retention scores in the inhibitory avoidance task while nonanxious rats exibited worse retention scores in inhibitory and two-way active avoidance tasks compared to normal rats. No significant differences were detected in the retention scores for habituation to an open field. Nonanxious rats presented a lower benzodiazepine receptor density in the hippocampus but not in the amygdala compared to the other groups. These data suggest that the benzodiazepine receptors are involved in the effect of "anxiety" or emotional states on memory storage processes.

Selective effects of alcohol drinking on restraint-induced expression of immediate early genes in mouse brain

BACKGROUND

Analysis of immediate early gene expression in brain is a common contemporary method for mapping changes in neuronal activation with cellular resolution. This method has been applied previously in models of involuntary alcohol exposure. In this study, immunohistochemical expression analysis of immediate early genes c-fos, fosB, and zif268 was performed in brain of C57BL/6J mice after voluntary alcohol consumption.

METHODS

Mice were trained to consume 10% ethanol/10% sucrose, using a 30-min limited-access paradigm. Animals consumed approximately 1.5 g/kg of ethanol per session. Control animals consumed 10% sucrose solution. Gene expression was determined in half of the animals 1.5 hr after the drinking session. Gene expression in the remaining animals was determined after 0.5 hr of restraint stress, which is known to elevate expression of immediate early genes in many brain regions. Analysis of the stressed animals was also performed 1.5 hr after the drinking session.

RESULTS

Blood alcohol concentrations were significantly reduced in animals exposed to restraint stress. However, stressed mice showed the greatest alcohol-induced changes in gene expression. Specifically, animals consuming ethanol/sucrose with subsequent exposure to restraint stress had lower c-Fos expression in the CA3 region of hippocampus, and higher c-Fos expression in nucleus accumbens than mice exposed to restraint stress after drinking the sucrose solution. Consumption of the ethanol/sucrose solution also significantly reduced FosB expression in the basolateral amygdala and lateral hypothalamus, and Zif268 expression in the CA1 region of the hippocampus of stressed animals.

CONCLUSIONS

These data confirm previous observations showing selective effects of alcohol administration on immediate early gene expression. Furthermore, the effects of voluntary alcohol self-administration on immediate early gene expression differ from involuntary alcohol exposure and suggest several brain regions as substrates for alcohol consumption.

Ethanol concentrations approaching minimum alveolar anesthetic concentration are required to suppress learning in a fear-potentiated startle paradigm in rats

We previously demonstrated that desflurane and two nonimmobilizers dose-dependently decrease learning and memory in rats. This suggests that although they do not suppress movement in response to noxious stimuli, nonimmobilizers act like inhaled anesthetics in their effects on learning and memory. Like most conventional anesthetics, nonimmobilizers have a greater affinity for lipid than for aqueous phases. In the present study, we examined the effect of ethanol on learning and memory to test the hypothesis that a large part of the capacity of anesthetics to affect learning depends on an action on a lipid (nonpolar) phase. Unlike volatile anesthetics and nonimmobilizers, ethanol has a greater affinity for water than for lipids. Thus, if our hypothesis is correct, ethanol should be relatively less potent in its suppression of memory. Rats receiving various doses of ethanol were conditioned to fear a light followed by a footshock. Fear conditioning to the light was subsequently assessed by measurement of potentiation of the acoustic startle reflex in the presence, compared with the absence, of light. Ethanol up to 0.54 minimum alveolar anesthetic concentration (MAC) did not abolish fear, but 0.82 MAC ethanol did abolish learning. Expressed as a fraction of MAC or predicted MAC, ethanol is less potent than desflurane or the nonimmobilizer 1,2-dichlorohexafluorocyclobutane in suppressing learning. This finding is consistent with the hypothesis that the capacity of anesthetics and nonimmobilizers to impair learning and memory depends mostly on an action at a nonpolar site.

IMPLICATIONS

Abolition of learning and memory is an important property of inhaled anesthetics. This effect primarily results from an action at a lipid (nonpolar) site, rather than a polar site or a water-lipid interface.

Reduced dorsal hippocampal glutamate release significantly correlates with the spatial memory deficits produced by benzodiazepines and ethanol

Memory deficits frequently occur after taking benzodiazepines and ethanol. We studied in vivo hippocampal presynaptic glutamate transmission in conjunction with memory deficits induced by benzodiazepines and ethanol in rats as an animal model of amnesia. These drugs potently impaired spatial memory formation as evaluated by the Morris water maze task, the rank order among tested treatments being the combination of triazolam (20 micrograms/kg) with ethanol (2 g/kg) > or = triazolam (100 micrograms/kg) > ethanol (2 g/kg) > or = triazolam (20 micrograms/kg) > rilmazafone (20 micrograms/kg). On the other hand, these drug treatments also reduced glutamate release in the dorsal hippocampus but not in the cerebellum measured by microdialysis: the combined administration of triazolam with ethanol potently inhibited glutamate release to 60% of basal output in the dorsal hippocampus. These decreases in hippocampal glutamate transmission closely correlated with the extent of impairment of spatial memory performance (r = 0.990). Thus, the present results strongly indicated that presynaptic dysfunction in dorsal hippocampal glutamatergic neurons would be critical for spatial memory deficits induced by benzodiazepines and ethanol.

The cerebral cortex is damaged in chronic alcoholics

There is some controversy in the literature concerning whether chronic alcohol consumption damages the cerebral cortex. While decreased neuronal density in specific cortical regions is well described in chronic alcoholics, a recent study by Badsberg Jensen and Pakkenberg using unbiased stereological methods questions whether neurodegeneration occurs. In order to assess selective neurodegeneration in the cerebral cortex of chronic alcoholics, regional volumes and unbiased estimates of regional neuronal number (including neuronal identification with calcium-binding proteins) were calculated for 14 chronic alcoholics and 21 controls. Cases were carefully screened to exclude any interfering pathologies. Lifetime and maximum daily alcohol consumption was determined, and homogeneous groups were identified (four chronic alcoholics with Wernicke's encephalopathy and Korsakoff's psychosis, four chronic alcoholics with Wernicke's encephalopathy alone, six chronic alcoholics without Wernicke's encephalopathy or Korsakoff's psychosis, and 21 controls). Brain volume analysis revealed that discrete regions were significantly smaller in the chronic alcoholics compared to controls. As previously shown, white matter regions (particularly in the frontal lobe) were the most significantly reduced in volume. Alcoholics with Wernicke's encephalopathy (either alone or in combination with Korsakoff's psychosis) had significantly smaller white matter volumes than controls or alcoholics without these complications. Medial temporal lobe regions and the thalamus were also reduced in volume. Regression analyses revealed that the volume of both the white matter and thalamus negatively correlated with alcohol consumption. Consistent with the interpretation of previous neuronal density studies, selective neuronal loss was found in the superior frontal association cortex of chronic alcoholics, while no loss occurred from the motor cortex. The number of parvalbumin-, calbindin- and calretinin-immunoreactive neurons was found to be unaltered in chronic alcoholics, suggesting that the neurodegeneration is confined to the non-GABAergic pyramidal neurons. As neurodegeneration was observed in all alcoholic groups, damage to the frontal association cortex is not restricted to alcoholics with the amnesia of Korsakoff's psychosis. These results are consistent with the notion that chronic alcohol consumption is associated with selective neuronal vulnerability. The selective frontal neurodegeneration and the frontal focus of white matter atrophy are supported by neuropsychological, regional blood flow, and magnetic resonance imaging studies of frontal lobe dysfunction in chronic alcoholics and may correlate with abnormalities in working memory.