Impairment of acquisition of a DRL schedule following prolonged ethanol consumption

Early life stress in fathers improves behavioural flexibility in their offspring

Traumatic experiences in childhood can alter behavioural responses and increase the risk for psychopathologies across life, not only in the exposed individuals but also in their progeny. In some conditions, such experiences can however be beneficial and facilitate the appraisal of adverse environments later in life. Here we expose newborn mice to unpredictable maternal separation combined with unpredictable maternal stress (MSUS) for 2 weeks and assess the impact on behaviour in the offspring when adult. We show that MSUS in male mice favours goal-directed behaviours and behavioural flexibility in the adult offspring. This effect is accompanied by epigenetic changes involving histone post-translational modifications at the mineralocorticoid receptor (MR) gene and decreased MR expression in the hippocampus. Mimicking these changes pharmacologically in vivo reproduces the behavioural phenotype. These findings highlight the beneficial impact that early adverse experiences can have in adulthood, and the implication of epigenetic modes of gene regulation.

Chronic Ethanol Consumption Impairs Learning and Memory After Cessation of Ethanol

Acute consumption of ethanol results in reversible changes in learning and memory whereas chronic ethanol consumption of six or more months produces permanent deficits and neural damage in rodents. The goal of the current paper was determine whether shorter durations of chronic ethanol ingestion in mice would produce long-term deficits in learning and memory after the cessation of ethanol. We first examined the effects of four and eight weeks of 20% ethanol followed by a three week withdrawal period on learning and memory in mice. We determined that three weeks after eight, but not four, weeks of 20% ethanol consumption resulted in deficits in learning and long-term memory (seven days) in T-maze footshock avoidance and Greek Cross brightness discrimination, step-down passive avoidance and shuttlebox active avoidance. Short-term memory (1 hr) was not affected. The deficit was not related to changes in thiamine status, caloric intake, or nonmnemonic factors, such as, activity or footshock sensitivity. Lastly, we examined if the mice recovered after longer durations of withdrawal. After eight weeks of ethanol, we compared mice after three and 12 weeks of withdrawal. Mice that had been off ethanol for both three and 12 weeks were impaired in T-maze footshock avoidance compared to the controls. The current results indicate that a duration of ethanol consumption as short as eight weeks produces deficits in learning and memory that are present 12 weeks after withdrawal.

Behavioral effects of intraventricular injections of low doses of ethanol, acetaldehyde, and acetate in rats: studies with low and high rate operant schedules

Although ethanol is typically classed as a sedative-hypnotic, low doses of ethanol have been shown to stimulate locomotor activity in mice. However, in rats the typical response to peripheral administration of ethanol is a dose-dependent suppression of motor activity and operant responding. The present study was undertaken to determine the effects of intraventricular (ICV) infusions of ethanol, acetaldehyde, and acetate on operant performance in rats. ICV injections of ethanol, acetaldehyde, or acetate were given to rats previously trained on either a differential-reinforcement-of-low-rates-of-responding (DRL) 30-s schedule, which generates low rates of responding, or a fixed ratio 5 (FR5) schedule, which generates relatively high rates. Ethanol, acetaldehyde, and acetate all produced a rate-increasing effect in rats on the DRL 30-s schedule at moderate doses (2.8 and 1.4 micromol, respectively). Acetate also produced a rate-decreasing effect on the DRL 30-s schedule at a larger dose (8.8 micromol). Performance on the FR5 schedule was unaltered by ethanol and acetaldehyde, even at doses as high as 17.6 micromol. However, acetate produced a rate-decreasing effect on the FR5 schedule at doses of 4.4, 5.6, and 8.8 micromol. Central administration of low doses of ethanol and its metabolites can increase operant responding on some schedules in rats. Acetate is the substance that is most potent for producing rate-suppressing effects. These results indicate that the major metabolites of ethanol are pharmacologically active when injected into the brain, and suggest that acetate may mediate some of the rate-suppressing effects of ethanol, such as sedation, ataxia or motor slowing.

Periadolescent alcohol alters adult behavioral characteristics in the rat

Long-Evans hooded rats were given 5% alcohol (EtOH), 10% EtOH or tap water as sole fluid from postnatal day 21 (P21) to P70. The 10% EtOH group drank 26% less and 10% EtOH males gained 7.6% less weight than the tap water control group. There were no significant consumption or weight differences between 5% EtOH and control subjects. At P105, 35 days after the conclusion of alcohol dosing, we conducted several behavioral tests. Males in the 10% group drank 67.8% more alcohol than controls in a two-bottle preference test. On a DRL-20-s operant reinforcement schedule, a difficult timing task dependent upon limbic structures, subjects in the 10% group had higher barpress rates, while those in the 5% group had lower barpress rates than controls. On this task, 10% females received fewer reinforcements, while both 5% and 10% males earned more reinforcements than controls. Efficiency ratios were lowest for 10% females and highest for 5% males. Males in the 5% group had shorter latencies than controls to find the platform in a Morris water maze and were significantly more likely than controls to initially find the platform. These data suggest that EtOH consumption during periadolescent development may have long-lasting neurobehavioral effects.

Synaptic reorganization in the hippocampal formation of alcohol-fed rats may compensate for functional deficits related to neuronal loss

We have examined the behavioral and neuroanatomical effects of long-term alcohol intake in rats ingesting a 20% solution of ethanol for 30 weeks. Previous studies have shown that this treatment provokes neuronal degeneration in the hippocampal formation, which occurs in parallel with remodeling processes. Spatial reference and working memory of alcohol-fed rats were evaluated during last 4 weeks of treatment by comparison of their performance with age-matched controls on the Morris water maze. Alcohol consumption did not affect the performance of rats in the reference memory task as indicated by the measures derived from the acquisition trials and from the probe-trial, which were highly similar for alcohol-fed and control animals. Also, performance in the working memory task was not significantly altered in alcohol-treated animals. No treatment-related changes in swim speed or impairments of sensorimotor abilities, tested in the visible platform task, were detected. Stereological methods were applied to evaluate the damage inflicted by alcohol intake in the structure of the hippocampal formation. In the alcohol-treated animals, there was a noticeable cell loss in the granular layer of the dentate gyrus (10%), and in CA3 (18%) and CA1 (19%) hippocampal subdivisions. In spite of the neuronal loss, the total number of synapses between mossy fibers and CA3 pyramids was unaffected by alcohol treatment suggesting that new synaptic contacts were formed between the surviving neurons. We show that, regardless the marked hippocampal cell loss in rats exposed to chronic alcohol intake, the reorganization that takes place at the synaptic level may alleviate the expected functional deficits.

Behavioral and neuroanatomical consequences of chronic ethanol intake and withdrawal

We have examined if long-term (13 months) alcohol consumption and the same treatment followed by a 6-week withdrawal period cause different neuropathological changes in rats. Spatial reference and working memory of alcohol-consuming and withdrawn rats were evaluated by comparison of their performance with age-matched controls in the Morris water maze. In the reference memory task we did not observe significant cognitive deficits in rats continuously exposed to ethanol, whereas withdrawn animals showed an obvious impairment of their overall performance. The reference memory deficit in withdrawn rats was evident in the spatial probe trial; these animals required significantly longer swimming distances to approach the former position of the platform when compared with controls and alcohol-consuming animals. In contrast, working memory was not significantly altered in either experimental group. Stereological methods were applied to compare the neurodegenerative changes produced by alcohol intake and withdrawal in the hippocampal formation. In the alcohol-consuming animals there was a significant cell loss in CA1 (18%) and CA3 (19%) hippocampal regions. Moreover, in withdrawn rats there was a further decay in the total number of pyramidal neurons, which amounted to 15% relative to nonwithdrawn animals. In the granular layer of the dentate gyrus there was a trend in the same direction, but it did not reach significance. Thus, our findings indicate that withdrawn rats are cognitively impaired relative to animals submitted to continuous alcohol consumption and to age-matched controls, which fits the morphological data showing that withdrawal aggravates ethanol-induced degenerative processes in the hippocampal formation.

Dissociable long-term cognitive deficits after frontal versus sensorimotor cortical contusions

Cognitive deficits are the most enduring and disabling sequelae of human traumatic brain injury (TBI), but quantifying the magnitude, duration, and pattern of cognitive deficits produced by different types of TBI has received little emphasis in preclinical animal models. The objective of the present study was to use a battery of behavioral tests to determine if different impact sites produce different patterns of behavioral deficits and to determine how long behavioral deficits can be detected after TBI. Prior to surgery, rats were trained to criteria on delayed nonmatching to position, radial arm maze, and rotarod tasks. Rats received sham surgery (controls), midline frontal contusions (frontal TBI, 2.25 m/sec impact), or unilateral sensorimotor cortex contusions (lateral TBI, 3.22 m/sec impact) at 12 months of age and were tested throughout the next 12 months. Cognitive deficits were more robust and more enduring than sensorimotor deficits for both lateral TBI and frontal TBI groups. Lateral TBI rats exhibited transient deficits in the forelimb placing and in the rotarod test of motor/ambulatory function, but cognitive deficits were apparent throughout the 12-month postsurgery period on tests of spatial learning and memory including: (1)reacquisition of a working memory version of the radial arm maze 6-7 months post-TBI, (2) performance in water maze probe trials 8 months post-TBI, and (3) repeated acquisition of the Morris water maze 8 and 11 months post-TBI. Frontal TBI rats exhibited a different pattern of deficits, with the most robust deficits in tests of attention/orientation such as: (1) the delayed nonmatching to position task (even with no delays) 1-11 weeks post-TBI, (2) the repeated acquisition version of the water maze--especially on the first "information" trial 8 months post-TBI, (3) a test of sensorimotor neglect or inattention 8.5 months post-TBI, and (4) a DRL20 test of timing and/or sustained attention 11 months after surgery. These results suggest that long-term behavioral deficits can be detected in rodent models of TBI, that cognitive deficits seem to be more robust than sensorimotor deficits, and that different TBI impact sites produce dissociable patterns of cognitive deficits in rats.

Chronic ethanol consumption in rats: correlation between memory performance and hippocampal acetylcholine release in vivo

The effects of chronic alcohol consumption on memory performance and hippocampal acetylcholine release in vivo were investigated in rats. Rats were allowed to drink 25% (v/v) ethanol solution as the only source of fluid for nine consecutive months, whereas control rats received only tap water. Memory performance was tested by the acquisition of shuttle box active and passive avoidance. Chronic ethanol-consuming rats were not impaired in the acquisition of the active avoidance response task, whereas in the passive avoidance task, latency scores of treated rats were significantly lower than in controls. The basal release of acetylcholine in freely moving rats, assessed by the microdialysis technique, was significantly decreased in ethanol-treated rats. Impairment in memory performance, as assessed in the passive avoidance task, was significantly correlated with hippocampal acetylcholine release in vivo.

Absence of impairments in spatial and temporal discrimination learning in Lewis rats after chronic ethanol consumption

Many studies reported that chronic ethanol consumption leads to cognitive dysfunction in rodents. It has been suggested that the effects of chronic ethanol consumption resemble those of aging because of the behavioral and neurochemical similarities between the two processes. The present study examined the effects of a chronic ethanol treatment (20% aqueous solution) in Lewis rats on performance in three different tasks: the Morris spatial navigation task, a cone-field task, and a temporal discrimination task. Although an age-related deficit was found in water escape learning, chronic ethanol consumption did not affect the performance of adult and old rats. The results of this experiment were, however, not conclusive. No differences between old control and ethanol-treated rats were found for spatial (cone-field task) and temporal discrimination learning. However, old ethanol-treated rats showed a transient tendency to perseverate in the temporal discrimination task. The present results are at variance with the generally found cognitive impairments after chronic ethanol consumption using aqueous solutions. It is suggested that the effects of ethanol could be related to strain of rat, task complexity, method of ethanol administering, and housing conditions and may explain the discrepancy between results.

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

The effects of chronic alcohol consumption or thiamin deficiency on radial-arm maze performance in the rat

Experiment 1 tested the hypothesis that chronic consumption of ethanol, in the presence of good nutrition, is associated with impairments in memory. Rats were fed a vitamin-fortified ethanol-Sustagen diet with 35% ethanol-derived calories for 150 days. Two control groups were used. The first was pair fed a Sustagen mix in which sucrose had been substituted for ethanol. The second control group received ad lib access to standard laboratory chow and water. All animals were then placed on the chow and water diet for six weeks prior to testing in an eight-arm radial maze. There was a significant, but modest, difference between groups in the number of trials to reach a criterion level of seven correct from the first eight choices and all eight correct in ten choices. However, there were no differences between the groups when delays (0, 5, 20, 60, 120 and 240 minutes) were imposed between the 4th and 5th choices. In Experiment 2, a thiamin-deficient group was compared with pair-fed and ad lib control groups on the same task. The thiamin-deficient group took more trials to reach criterion but the groups did not differ in the delay testing phase. The results are discussed in the context of reference/working memory distinctions, and the literature on remediation of cognitive deficits associated with alcoholism.

Effects of an alcohol diet on locomotor activity and the acquisition of brain self-stimulation in rats

Male rats (n = 45), implanted with stimulating electrodes in the lateral hypothalamus for intracranial self-stimulation (ICSS), were allocated to three groups equalized for body weights. One group was given an alcohol liquid diet (Lieber-DeCarli) diet as the sole source of food; a second group was given a control liquid diet in which carbohydrates were substituted for alcohol; and a third group was maintained on standard laboratory chow and water. After four weeks on these diets, all animals were tested during the fifth week of the diets for locomotor activity in five daily 15-min sessions, and their reactivity to handling was also measured. During the sixth and seventh weeks of the diets, animals were allowed to self-train for ICSS during daily 15-min sessions. In the eighth week blood alcohol levels were measured. There were no differences between groups in locomotor activity or reactivity to handling. However, when tested for the acquisition of ICSS, animals on the diet containing alcohol made fewer responses than did those receiving the two control diets (p less than 0.001). The mean blood level of alcohol in the alcohol-consuming group at the time of day of behavioral testing was 50.6 +/- 5.0 mg/dl. These results suggested that the chronic ingestion of an alcohol-containing diet which resulted in only moderate blood levels of alcohol may not affect simple behavior such as locomotor activity, but may produce decrements in the performance of a more complex task such as lever pressing for ICSS.

Chronic ethanol and chlordiazepoxide: contrasting effects on reward learning

Rats were exposed for one week to increasing concentrations of ethanol in a liquid diet, and were then maintained for a further 4 weeks on a 10% ethanol diet. Ten weeks after return to normal diet they were trained in a learning task in which three out of nine holes were consistently rewarded. The ex-ethanol-treated rats were slower to complete the task during the first week, compared with their control group and the differences were most marked on days 3 and 4, which were the days of most rapid improvement. On day 4 the ex-ethanol-treated rats made significantly more errors at rewarded holes. In contrast, rats that had been treated for 4 weeks with chlordiazepoxide (10 mg/kg/day) and then trained 10 weeks later on days 2 and 3 made significantly fewer errors of reference memory, and on day 2 made significantly fewer errors of working memory, compared with their control group.

Alcohol withdrawal-induced changes in brain biogenic amines in mice: influence of the genotype

Alterations in striatal and hippocampal dopamine (DA) and serotonin (5HT) activities were investigated in two inbred strains of mice (C57B1 and Balb/c) after 3 withdrawal periods following 5 months chronic ethanol administration. Two groups of animals with different levels of ethanol administration (15% and 30%, v/v) were examined. A striking strain dependency has been noted. Striatal dopaminergic mechanisms of the Balb/c strain are profoundly disturbed in both groups. In contrast no changes were noted for either transmitter activities in C57B1 mice at any withdrawal time studied. Strain dependency has also been noted for hippocampal serotonin neurotransmission, since only Balb/c mice showed a progressive decrease in 5HT levels. These impairments observed in striatum and hippocampus could be involved in motor incoordinations and convulsions often associated with the withdrawal syndrome. The differences in withdrawal effects we noted between the two strains may be linked to the specific chemical neuroanatomy of the strains. Such specificities could be implied in the well known variability of withdrawal induced behavior in man.

Long-lasting effects on habituation and passive avoidance performance of a period of chronic ethanol administration in the rat

Rats were fed a liquid diet to which an increasing concentration of ethanol was added over a period of 3 weeks; a concentration of 10% ethanol was then maintained for a further 4 weeks. The rats were then returned to a normal ad libitum diet of rat pellets. In order to assess the long-term effects of this ethanol diet, the performance of different groups of rats was assessed 3 and 5 months after the normal diet was resumed. At both times, the ex-ethanol-treated rats showed significantly impaired between-day habituation of exploratory head-dipping at holes that were empty, but normal between-day habituation of head-dipping at the hole with the same object underneath on all 3 days. The ex-ethanol-treated rats also showed a reduced response to the introduction of an object at a previously empty hole and, following this, a subsequent disruption of between-day habituation of head-dipping at this hole. Within-session habituation of head-dipping was unimpaired. There were no deficits in the acquisition or short-term retention of a passive avoidance response, but on retention testing 24 h after training the ex-ethanol-treated rats showed a decreased latency to enter the shocked compartment. On the trials 24 h and 48 h after training the rats tested 5 months after their ethanol treatment showed impaired extinction of the passive avoidance response.

Cholinergic system and memory in the rat: effects of chronic ethanol, embryonic basal forebrain brain transplants and excitotoxic lesions of cholinergic basal forebrain projection system

Oral administration of ethanol (20% v/v) to male Sprague-Dawley rats for different periods of time up to 28 weeks resulted in profound reductions of acetylcholine content, in vitro synthesis and release of acetylcholine, choline uptake, activities of choline acetyltransferase, acetylcholinesterase and pyruvate decarboxylase, content of noradrenaline, serotonin and, to a lesser extent, dopamine throughout the brain. Changes were fully and partially reversible by a 4 weeks' ethanol-free period following a treatment of 8 and 18 weeks, respectively. They remained persistent, however, after 28 weeks of treatment. Performance in an eight arm-radial maze revealed a severe impairment in both spatial and non-spatial reference and working memory. A similar pattern of memory impairment was obtained after ibotenate lesion of the cholinergic basal forebrain projection system. In order to test whether this memory impairment depends on cholinergic deafferentation of the cortex, cholinergic-rich fetal basal forebrain cell suspensions were transplanted into cortex, hippocampus or both these sites in ethanol treated rats. Cholinergic-rich transplants, but not cholinergic-poor transplants, were effective in ameliorating impaired memory function and measures of cholinergic activity in the basal forebrain projection system. The behavioural efficacy of the basal forebrain grafts was well correlated with measures of both transplant volume and the degree to which they restored acetylcholine content at the transplant site; these transplants had no effect, however, on brain monoamine levels. The effects of the cholinergic-rich transplants into cortical and hippocampal sites were additive in their amelioration of performance in the radial maze. Similarly, ibotenate lesions of the sites of origin of the cholinergic projections to neocortex (in the region of the nucleus basalis magnocellularis) and hippocampus (the medial septal areas and nucleus of the diagonal band), respectively, were additive in their deleterious effects on maze performance. There were no qualitative differences in the susceptibility of the four different types of memory performance measured (spatial and non-spatial reference and working memory) to the effects of ethanol, ibotenate lesions of the cholinergic projection system, or cholinergic-rich brain tissue transplants. Thus, overall, the results indicate that the forebrain cholinergic system acts as a whole, without major functional differences between the projections originating in the medial septal area/diagonal band complex and the basal nucleus, and that it discharges a very general function in cognitive processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated withdrawal from ethanol on radial arm acquisition in rats

Male rats were treated with ethanol (8.0-12.0 g/kg/day) for four 2 week periods interrupted every 2 weeks by a 2 week period of no drug treatment. Thus they experienced withdrawal from ethanol four times. Other rats were treated with ethanol for 8 weeks with no interruptions, to control for the total dose and duration of drug treatment. Acquisition of an eight-arm radial maze response when daily ethanol treatment was ended, was not affected by either the experience of four withdrawals from ethanol or by 8 weeks of ethanol treatment. The lack of withdrawal-induced impairment can be attributed to a lack of sensitivity in the maze task to possible withdrawal-induced deficits and to an insufficient duration of ethanol dependence.

The effect of repeated withdrawal episodes on acquisition and loss of tolerance to ethanol in ethanol-treated rats

Male rats were administered ethanol via an intragastric catheter (8.0-12.0 g/kg/day) either continuously for 8 weeks or on a binge schedule with four 2 week cycles of drug administration separated from each successive cycle by a 2 week period of no drug treatment. Older rats were administered ethanol for 2 weeks, to provide an age control for the binge-treated animals as age can alter an animal's sensitivity to ethanol. Acquisition and loss of tolerance to ethanol-induced motor impairment were measured on a dowel task while acquisition and loss of tolerance to ethanol-induced hypothermia were assessed by measuring rectal temperature. Acceleration of tolerance development to both ethanol-induced motor impairment and hypothermia was observed in animals subjected to repeated withdrawal episodes (binge-Study 1) but not in the controls for total dose and duration of drug treatment who experienced withdrawal only once (continuous-Study 2). Persistence of tolerance to ethanol-induced motor impairment occurred in both binge and continuously treated animals while persistence of tolerance to ethanol-induced hypothermia was seen only in the binge treated animals. Age (3 to 7 months) did not affect tolerance development or decay. After three cycles of drug treatment (three withdrawal episodes), binge treated animals showed an impairment in motor ability when blood ethanol levels were near zero. This impairment disappeared when the animals were administered ethanol, indicating a normalizing effect of ethanol on motor behavior in animals subjected to repeated episodes of withdrawal. A similar, but not significant, effect was seen in continuously treated animals. Thus, in an animal exposed to prolonged ethanol treatment, persistent changes in responding to the drug were found. The persistence of these changes was enhanced by the experience of withdrawal from ethanol.

Prolonged ethanol consumption influences shuttle box and passive avoidance performance in rats

Rats were chronically maintained on an ethanol liquid diet for 16 days. Three weeks after cessation of ethanol intake, animals were tested for the acquisition of shuttle box avoidance and the retention of passive avoidance behaviour. Alcohol consuming rats showed a significant impairment of acquisition in the shuttle box task, and a slight impairment in the retention of the passive avoidance response. It is concluded that ethanol or its metabolites can induce long-term effects on learning and memory processes, even after cessation of drug consumption.

Memory deficits subsequent to chronic consumption of alcohol in mice: an analysis based on spontaneous alternation behavior

Male mice of the BALB/c strain were given a solution of 15% ethanol as their only source of fluid for periods varying from 5 weeks to 8 months. For behavioral testing, they were compared with control groups which had received either an isocaloric solution of sucrose or tap water. Memory was tested by using spontaneous alternation behavior in a T maze. Each test consisted of two forced trials (acquisition) followed by a free trial (test) given at different acquisition--test intervals (from 30 s to 24 h). Results from two independent experiments showed that after 25 weeks of ethanol administration there was an accelerated rate of decay of spontaneous alternation as a function of the acquisition--test interval. Such a phenomenon persisted after ethanol was omitted from the diet. A third experiment showed that when tested on two successive sessions separated by a 5 h interval, experimental subjects exhibited a decreased ability to perform normally on the second test. Our data are interpreted as showing that long-term ethanol administration results in accelerated forgetting and increased vulnerability to proactive interference and, as such, they are compared to the memory dysfunctions observed in amnesic patients.

Comparative effects of long-term ethanol consumption and forebrain lesions on maze learning and active avoidance behavior in rats

Male rats consumed a liquid diet containing 10.7% ethanol as their only source of food and fluid for 6.5 months, beginning at 2 months of age. During withdrawal, there were no differences between the alcohol group and their pair-fed or free-fed controls on EEG, body temperature, irritability and tremor measures. In behavioral tests begun 4-5 weeks after withdrawal, the rats that had consumed alcohol acquired accurate spatial behavior in a cross maze task more slowly than controls, but were unimpaired in shuttle-avoidance learning. In concurrent studies with groups of rats that had sustained lesions of the dorsal hippocampus, the mamillary bodies (MMB), or the mediodorsal thalamus, the pattern of behavioral deficits after MMB lesions was found to be qualitatively similar to that observed after the cessation of long-term alcohol consumption. These findings provide renewed hope that a useful rodent model for studying the neuropsychology of cognitive deficits associated with human alcoholism can be developed.

The neurotoxicity of ethanol

Alterations in nervous system functioning following acute and chronic ethanol exposure have been studied in a great number of experimental investigations. Results from many of these investigations can be difficult to interpret, particularly since a variety of techniques and exposure models are employed. This review emphasizes those studies which, in the opinion of the author, fit into a pattern where results from studying one function of the nervous system is in accordance with results from studying another. Thus, the fluidizing effect of ethanol on the neuronal membrane - an effect which ethanol shares with anaesthetics - leads to a change in protein function which in turn affects ion transport such as Na+ and Ca++ across the membrane due to changes in the ion channels. Cation influx is probably directly coupled to neurotransmitter release which is in agreement with the finding that ethanol exposure results in inhibition of Na+ and Ca++ current as well as acetylcholine release. The sensitization of the dopaminergic system after ethanol exposure may also be related to the changes in cation flux, and the changes in this system probably play a crucial rôle in the development of tolerance and withdrawal symptoms. Other aspects such as impairment of protein synthesis, altered GABA function of impairment of neuron excitability and conduction are more difficult to place in proper perspective. The rôle of acetaldehyde in acute as well as chronic ethanol intoxication also remains a controversy. These may, however, be secondary phenomena to primary changes in different part of the nervous system not necessarily important in the clinical situation. Behavioural and anatomical studies particularly from recent years have shown that experimental animals develop memory disturbances following chronic exposure even when kept on sufficient diet. These findings argue strongly for a direct toxic effect of ethanol, and are furthermore compatible with behavioural changes in chronic alcoholics, dominated by memory impairment. Since it has been argued that the cholinergic system plays a significant rôle for memory function, a possible explanation for some of the psychological and anatomical deficits caused by ethanol is thus the changes in the function of the cholinergic system particularly in the hippocampal regions.

Electrophysiological analysis of synaptic distribution in CA1 of rat hippocampus after chronic ethanol exposure

This study investigated the long-lasting effects of chronic ethanol consumption on the distribution of Schaffer collateral-commissural (SCH/COM) afferents within stratum radiatum of rat hippocampal CA1. Experimental animals were fed an ethanol-containing liquid diet for 20 weeks but were withdrawn from the special diet for at least 8 weeks prior to acute electrophysiological recordings. Field potential laminar analyses were performed by stepping the recording electrode in 25 microns increments through CA1 and sampling evoked potentials at each point. One-dimensional current-source density (CSD) was calculated from the field potential laminar profiles to enhance spatial resolution of current sources and sinks. Stimulation of the SCH/COM afferents elicits short-latency, negative field potentials throughout the synaptic terminal zone (stratum radiatum). CSD analysis in normal animals revealed that the synaptic currents generated in stratum radiatum concentrate into bimodal yet overlapping components, peaking 71.3 microns and 228.3 microns from the pyramidal cell layer. Chronic ethanol treatment produced: (1) a 13.2% shrinkage of the overall extent of current sinks in stratum radiatum; (2) a 37.4% reduction in the spatial extent of the sink proximal to the cell layer; and (3) an increase in the amplitude of the more distal sink. We tentatively propose the proximal and distal sinks to reflect a separation of the COM and SCH afferents, respectively. Chronic ethanol thus appeared to have selectively produced persistent damage to the COM-CA1 pathway.

Augmentation of short-term plasticity in CA1 of rat hippocampus after chronic ethanol treatment

The neurotoxic effects of chronic ethanol exposure were investigated in rat hippocampus by electrophysiological analysis of the Schaffer collateral-commissural input to stratum radiatum of CA1. Experimental animals were fed an ethanol-containing liquid diet for 20 weeks but were withdrawn from the special diet at least eight weeks prior to acute electrophysiological recordings. Ethanol treatment had no effect on input-output relationships for either the population EPSP or the population spike (PS). During paired-pulse stimulation, the ethanol group exhibited a greater facilitation of the test pulse PS relative to the control group, although potentiation of the EPSP was unchanged. In addition, the ethanol group showed a trend toward greater facilitation of the PS during 5 and 10 Hz tetani. No differences between groups were observed in the magnitude or duration of the long-term potentiation produced by 5, 10 or 100 Hz stimulus trains. Ethanol treatment did significantly reduce the transient spike depression after low frequency stimulation. This pattern of results is similar to that found for treatments which reduce hippocampal recurrent inhibition. Thus, chronic ethanol treatment may produce a lasting disruption of intrinsic inhibitory neurotransmission in the rat hippocampus.

Neuronal loss in hippocampus induced by prolonged ethanol consumption in rats

Quantitative neurohistological techniques were used to examine the hippocampal complex of laboratory rats maintained on ethanol-containing or control diets for 5 months followed by a 2-month alcohol-free period. Chronic ethanol consumption resulted in a significant loss of hippocampal pyramidal and dentate gyrus granule cells. This study provides direct evidence that long-term ethanol consumption, in the absence of malnutrition, produces neuronal loss in the central nervous system.