An analysis of some effects of ethanol on performance in a passive avoidance task

Cross state-dependent memory retrieval between tramadol and ethanol: involvement of dorsal hippocampal GABAA receptors

RATIONALE

Tramadol and ethanol, as psychoactive agents, are often abused. Discovering the molecular pathways of drug-induced memory creation may contribute to preventing drug addiction and relapse.

OBJECTIVE

The tramadol- and ethanol-induced state-dependent memory (SDM) and cross-SDM retrieval between tramadol and ethanol were examined in this study. Moreover, because of the confirmed involvement of GABAA receptors and GABAergic neurotransmission in memory retrieval impairment, we assessed cross-SDM retrieval between tramadol and ethanol with a specific emphasis on the role of the GABAA receptors. The first hypothesis of this study was the presence of cross-SDM between tramadol and ethanol, and the second hypothesis was related to possible role of GABAA receptors in memory retrieval impairment within the dorsal hippocampus. The cannulae were inserted into the hippocampal CA1 area of NMRI mice, and a step-down inhibitory avoidance test was used to evaluate state dependence and memory recovery.

RESULTS

The post-training and/or pre-test administration of tramadol (2.5 and 5 mg/kg, i.p.) and/or ethanol (0.5 and 1 g/kg, i.p.) induced amnesia, which was restored after the administration of the drugs 24 h later during the pre-test period, proposing ethanol and tramadol SDM. The pre-test injection of ethanol (0.25 and 0.5 g/kg, i.p.) with tramadol at an ineffective dose (1.25 mg/kg) enhanced tramadol SDM. Moreover, tramadol injection (1.25 and 2.5 mg/kg) with ethanol at the ineffective dose (0.25 g/kg) promoted ethanol SDM. Furthermore, the pre-test intra-CA1 injection of bicuculline (0.0625, 0.125, and 0.25 μg/mouse), a GABAA receptor antagonist, 5 min before the injection of tramadol (5 mg/kg) or ethanol (1 g/kg) inhibited tramadol- and ethanol-induced SDM dose-dependently.

CONCLUSION

The findings strongly confirmed cross-SDM between tramadol and ethanol and the critical role of dorsal hippocampal GABAA receptors in the cross-SDM between tramadol and ethanol.

Insights into the adverse effects of prepubertal chronic ethanol exposure on adult female reproduction

Heavy drinking in women is known to adversely affect pregnancy and fertility. However, pregnancy is a complex process, and the adverse effects of ethanol on pregnancy does not mean that ethanol will have adverse effects on all stages from gamete to fetal formation. Similarly, the adverse effects of ethanol before and after adolescence cannot be generalized. To focus on the effects of prepubertal ethanol on female reproductive ability, we established a mouse model of prepubertal ethanol exposure by changing drinking water to 20% v/v ethanol. Some routine detections were performed on the model mice, and details such as mating, fertility, reproductive organ and fetal weights were recorded day by day after discontinuation of ethanol exposure. Prepubertal ethanol exposure resulted in decreased ovarian weight and significantly reduced oocyte maturation and ovulation after sexual maturation, however, normal morphology oocytes with discharged polar body showed normal chromosomes and spindle morphology. Strikingly, oocytes with normal morphology from ethanol exposed mice showed reduced fertilization rate, but once fertilized they had the ability to develop to blastocysts. RNA-seq analysis showed that the gene expression of the ethanol exposed oocytes with normal morphology had been altered. These results show the adverse effects of prepubertal alcohol exposure on adult female reproductive health.

Effects of ethanol and caffeine on behavior in C57BL/6 mice in the plus-maze discriminative avoidance task

INTRODUCTION

Caffeine is frequently consumed concurrent to or immediately following ethanol consumption. Identifying how caffeine and ethanol interact to modulate behavior is essential to understanding the co-use of these drugs. The plus-maze discriminative avoidance task (PMDAT) allows within-subject measurement of learning, anxiety, and locomotion.

METHODS

For training, each mouse was placed in the center of the plus-maze for 5 min, and each time that the mouse entered the aversive enclosed arm, a light and white noise were turned on. At testing, each mouse was returned to the center of the maze for 3 min. No cues were turned on during testing.

RESULTS

Ethanol (1.0-1.4 g/kg) dose-dependently decreased anxiety and learning, and increased locomotion. Caffeine (5.0-40.0 mg/kg) dose-dependently increased anxiety and decreased locomotion and learning. Caffeine failed to reverse ethanol-induced learning deficits. However, 1.4 g/kg ethanol blocked the anxiogenic effect of caffeine.

DISCUSSION

Although caffeine and ethanol interact to modulate behavior in the PMDAT, caffeine does not reverse ethanol-induced learning deficits. Ethanol-induced anxiolysis may contribute to alcohol consumption, while ethanol's blockade of caffeine-induced anxiogenesis may contribute to co-use.

Interactive effects of ethanol and nicotine on learning, anxiety, and locomotion in C57BL/6 mice in the plus-maze discriminative avoidance task

INTRODUCTION

Alcohol and nicotine both alter learning, locomotion, and anxiety, yet no study has directly examined the interactive effects of these drugs across these behaviors within subjects. Such a comparison would determine if the drugs produce independent effects on each behavior. The plus-maze discriminative avoidance task (PMDAT) allows within-subject measurement of these behaviors.

METHODS

For training, each mouse explored the elevated plus-maze for 5 min and each time a mouse entered the aversive enclosed arm, a light and white noise were turned on. For testing, each mouse was returned to the center of the maze and, for 3 min, the time in each arm or in the center area was recorded. No cues were turned on during testing. The effects of ethanol (0.6-2.6 g/kg 15 min before training) and nicotine (0.045-0.18 mg/kg 5 min before training), alone or in combination, on behavior were examined.

RESULTS

Ethanol dose-dependently decreased anxiety, increased locomotion, and decreased learning but different doses altered each behavior. Nicotine dose-dependently increased anxiety and locomotion and decreased learning but different doses altered each behavior. Nicotine (0.09 mg/kg) reversed ethanol-associated changes in learning (1.0 and 1.4 g/kg), locomotion (1.4 g/kg), and anxiety (1.4 g/kg).

CONCLUSIONS

The effects of nicotine or ethanol on learning occurred at different doses than those that altered anxiety or locomotion, suggesting that the drug effects on learning are independent of the effects on anxiety and locomotion. With combined administration, nicotine reduced ethanol-associated deficits in learning and changes in anxiety and locomotion.

The Effects of Puerariae Flos on Stress-induced Deficits of Learning and Memory in Ovariectomized Female Rats

Puerariae flos (PF) is a traditional oriental medicinal plant and has clinically been prescribed for a long time. The purpose of the present study was to examine the effect of PF on repeated stress-induced alterations of learning and memory on a Morris water maze (MWM) test in ovariectomized (OVX) female rats. The changes in the reactivity of the cholinergic system were assessed by measuring the immunoreactive neurons of choline acetyltransferase (ChAT) in the hippocampus after behavioral testing. The female rats were randomly divided into four groups: the nonoperated and nonstressed group (normal), the sham-operated and stressed group (control), the ovariectomized and stressed group (OS), and the ovariectomized, stressed and PF treated group (OSF). Rats were exposed to immobilization stress (IMO) for 14 d (2 h/d), and PF (400 mg/kg, p.o.) was administered 30 min before IMO stress. Results showed that treatments with PF caused significant reversals of the stress-induced deficits in learning and memory on a spatial memory task, and also increased the ChAT immunoreactivities. In conclusion, administration of PF improved spatial learning and memory in OVX rats, and PF may be useful for the treatment of postmenopausal-related dementia.

Acute ethanol ingestion impairs appetitive olfactory learning and odor discrimination in the honey bee

Invertebrates are valuable models for increasing our understanding of the effects of ethanol on the nervous system, but most studies on invertebrates and ethanol have focused on the effects of ethanol on locomotor behavior. In this work we investigate the influence of an acute dose of ethanol on appetitive olfactory learning in the honey bee (Apis mellifera), a model system for learning and memory. Adult worker honey bees were fed a range of doses (2.5%, 5%, 10%, or 25%) of ethanol and then conditioned to associate an odor with a sucrose reward using either a simple or differential conditioning paradigm. Consumption of ethanol before conditioning significantly reduced both the rate of acquisition and the asymptotic strength of the association. Honey bees also exhibited a dose dependent reduction in arousal/attention during conditioning. Consumption of ethanol after conditioning did not affect recall 24h later. The observed deficits in acquisition were not due to the affect of ethanol on gustatory sensitivity or motor function. However, honey bees given higher doses of ethanol had difficulty discriminating amongst different odors suggesting that ethanol consumption influences olfactory processing. Taken together, these results demonstrate that an acute dose of ethanol affects appetitive learning and olfactory perception in the honey bee.

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.

Dissociation of the effects of ethanol on memory, anxiety, and motor behavior in mice tested in the plus-maze discriminative avoidance task

RATIONALE

Several studies have shown the amnestic effects of ethanol (ETOH). However, while memory tasks in rodents can be markedly influenced by anxiety-like behavior and motor function, ETOH induces anxiolysis and different effects on locomotion, depending on the dose.

OBJECTIVE

Verify the effects of ETOH in mice tested in the plus-maze discriminative avoidance task (PMDAT) concomitantly evaluating memory, anxiety-like behavior, and motor behavior.

METHODS

ETOH acutely or repeatedly treated mice were submitted to the training session in a modified elevated plus-maze with two open and two enclosed arms, aversive stimuli in one of the enclosed arms, and tested 24 h later without aversive stimuli. Learning/memory, locomotion, and anxiety-related behavior were evaluated by aversive arm exploration, number of entries in all the arms and open arms exploration, respectively.

RESULTS

Acute ETOH: (1) either increased (1.2-1.8 g/kg) or decreased (3.0 g/kg) locomotion; (2) decreased anxiety levels (1.2-3.0 g/kg); and (3) induced learning deficits (1.2-3.0 g/kg) and memory deficits (0.3-3.0 g/kg). After repeated treatment, sensitization and tolerance to hyperlocomotion and anxiolysis induced by 1.8 g/kg ETOH were observed, respectively, and tolerance to the amnestic effect of 0.6 (but not 1.8) g/kg ETOH occurred.

CONCLUSION

Neither the anxiolytic nor the locomotor effects of ETOH seem to be related to its amnestic effect in the PMDAT. Additionally, data give support to the effectiveness of the PMDAT in simultaneously evaluating learning, memory, anxiety-like behavior, and motor activity by different parameters. Possible relationships between the behavioral alterations found are discussed.

Role of test activity in ethanol-induced disruption of place preference expression in mice

RATIONALE

Reduced expression of a drug-induced conditioned place preference (CPP) may reflect a decrease in the drug's conditioned rewarding effects. However, CPP is also open to disruption by processes unrelated to the underlying motivation. In unpublished studies, we previously observed that ethanol pretreatment before testing disrupted expression of ethanol-induced CPP in DBA/2J mice. We hypothesized that this interference effect was due to large ethanol-induced increases in activity.

OBJECTIVE

The present studies were designed to examine the relationship between test activity and expression of ethanol-induced CPP both in the presence and absence of ethanol. To assess the generality of this relationship, we examined these effects both in DBA/2J (which are highly activated by ethanol) and in NZB/B1NJ mice (which show similar CPP, but less ethanol-induced activation).

MATERIALS AND METHODS

In separate experiments, inbred mice from each strain underwent ethanol (2 g/kg) place conditioning. Saline or ethanol was then administered immediately before the test.

RESULTS

Ethanol, given immediately before the test, blocked the expression of ethanol CPP in DBA/2J, but not in NZB/B1NJ mice. Moreover, ethanol significantly increased test activity levels in DBA/2J and to a much lesser degree in NZB/B1NJ mice. Correlation analyses showed an inverse phenotypic relationship between preference and test activity, reflecting stronger preferences in less active mice.

CONCLUSIONS

Disruption of ethanol-CPP observed in DBA/2J mice may be a consequence of high ethanol-induced activity levels. More generally, these studies suggest that competing behaviors can affect expression of a drug-induced CPP independent of affecting the conditioned rewarding effects of the drug.

Effects of an aqueous extract of Puerariae flos (Thomsonide) on impairment of passive avoidance behavior in mice

The effects of an aqueous extract of Puerariae flos (Thomsonide) on ethanol-induced learning and memory impairment and scopolamine-induced amnesia were investigated. Thomsonide exerted an ameliorating effect on the impairment of both memory registration and memory retrieval induced by ethanol. These results indicate that Thomsonide has an antiamnesic effect on the central nervous system in alcoholic intoxication and support the traditional use of Puerariae flos for the treatment of alcoholic intoxication. Thomsonide also improved the scopolamine-induced impairment of memory registration in passive avoidance behavior in mice. The results of this study suggest that it may be possible to use Thomsonide for the treatment of age-related memory impairment and dementia.

EFFECT OF ETHANOL ON MORPHINE STATE-DEPENDENT LEARNING IN THE MOUSE: INVOLVEMENT OF GABAERGIC, OPIOIDERGIC AND CHOLINERGIC SYSTEMS

AIMS

We have studied the effect of acute administration of ethanol when it replaced morphine in step-down passive avoidance task on the test day and the effects of antagonists of GABAergic, opioidergic and cholinergic systems on ethanol actions.

METHODS

Morphine (5 mg/kg, s.c.) was administered as pre-training and 24 h later as pre-test drug, and the latencies were measured in mice. Ethanol (0.125, 0.25, 1 and 2 g/kg, i.p.) was administered instead of pre-test morphine. Antagonists of GABAergic (bicuculline 0.5, 1 and 2 mg/kg, i.p.), opioidergic (naloxone 0.06, 0.25 and 1 mg/kg, i.p.) and cholinergic (atropine 0.625 and 1.25 mg/kg, i.p. and mecamylamine 0.5, 1 and 2 mg/kg, i.p.) systems were co-administered with ethanol (0.25 g/kg, i.p.) on the test day. Locomotor activity was measured as well.

RESULTS

Pre-training morphine impaired the memory on the test day which was restored when the same dose of morphine was used as pre-test drug. All four doses of ethanol replaced pre-test morphine and enhanced the memory. This effect was prevented by all of the above antagonists. No significant changes were seen in the locomotor activity of the animals treated with ethanol or antagonists compared to the proper controls.

CONCLUSIONS

GABAergic, endogenous opioidergic and cholinergic systems are involved in the memory recall improvement by ethanol when it replaced morphine on the test day. A review of the literature suggests other possibilities such as the release of intermediate neurotransmitters.

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.

Multiple binge alcohol consumption during rat adolescence increases anxiety but does not impair retention in the passive avoidance task

We investigated the effect of binge alcohol consumption on anxiety-related behavior and memory in adolescent male Wistar rats. Three consecutive daily sessions of ethanol administration (5 g/kg) were repeated weekly for 4 weeks. The retention of passive avoidance was measured weekly, 48 h following the treatment. Three days after the last memory test a novel object exploration test was done. There was no significant difference in step-through latency between the groups, but the ethanol-treated group displayed a significantly higher incidence of defecation, and an increased number of boluses during the passive avoidance test. The latency to explore a novel object was also higher, while the duration of exploration was significantly lower. Together, these data suggest that binge alcohol consumption in adolescent rats does not impair their memory in passive avoidance tasks, but may significantly increase their anxiety.

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.

Effects of MK-801 and ethanol combinations on memory consolidation in CD1 mice: involvement of GABAergic mechanisms

In the present research the effect of the noncompetitive N-methyl-d-aspartate receptor antagonist MK-801 and ethanol combinations on memory consolidation and the involvement of GABAergic mechanisms in this effect were investigated in CD1 mice injected intraperitoneally with the drugs immediately or 120 min after training in a one-trial inhibitory avoidance apparatus and tested for retention 24 h later. The results showed that (a) the retention performances of mice were impaired in a dose-dependent manner by immediate posttraining MK-801 (0.2 and 0.3, but not 0.1 mg/kg) and ethanol (1 and 2, but not 0.5 g/kg) administrations; (b) an otherwise ineffective dose of MK-801 (0.1 mg/kg) enhanced the deleterious effect exerted by ethanol (1 and 2 g/kg); (c) an otherwise ineffective dose of muscimol (0.5 mg/kg) enhanced, while otherwise ineffective doses of picrotoxin (0.25 mg/kg) or bicuculline (0.1 mg/kg) antagonized, this effect; and (d) no effect was observed when the treatments were carried out 120 min after training, suggesting that the effects observed following immediate posttraining administrations were due to the influence on the consolidation of memory. From these experiments it is evident that (a) MK-801 enhances ethanol's effects on memory consolidation and (b) GABAergic mechanisms are involved in this effect.

Automated analysis of foot-shock sensitivity and concurrent freezing behavior in mice

Foot-shock is used in a variety of behavioral tasks either as a motivational stimulus, a way to characterize different rodents, or to test various pharmacological agents for their antinociceptive or analgesic effects. All these procedures need to assess foot-shock sensitivity either to rule out possible differences (when the shock is used as a motivational stimulus) or to use the differences to compare animals or treatments. In addition, many of the procedures that utilize foot-shock as a motivational stimulus evaluate freezing as an index of anxiety or fear. In the present study, data obtained by an automated computer system was compared with data obtained by human observers to validate the automated system for examining foot-shock sensitivity in mice. The different computer measures obtained for foot-shock sensitivity exhibited high correlations with human scoring at shock levels as low as 0.2 mA. The computer controlled analysis provided a non-subjective, quantifiable measurement of the foot-shock-induced response as well as freezing behavior. Automated data collection is an improvement over the methods of human visual observation in that the data collection is more standardized, efficient and consistent.

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.

Synthesis of 2-amino-5-sulfanyl-1,3,4-thiadiazole derivatives and evaluation of their antidepressant and anxiolytic activity

Recently a series of 2-amino-5-sulfanyl-1,3,4-thiadiazole derivatives bearing different substituents were synthesized and screened pharmacologically in order to evaluate their central nervous system activity. The purpose of this study was to evaluate the effects of the title compounds on CNS activity by varying the substituents in the thiadiazole moiety. It was found that some of these compounds possess marked antidepressant and anxiolytic properties comparable in efficiency to the reference drugs Imipramine and Diazepam. The most potent compound 3k was further investigated to complete its pharmacological profile with respect to undesired side effects. Behavioral results showed that 3k is a very promising compound, characterized by a mixed antidepressant-anxiolytic activity accompanied by a therapeutic dose range that is essentially 2 orders of magnitude less than that at which side effects such as sedation and amnesia are evident.

Attenuation of the acute amnestic effect of ethanol by ifenprodil: comparison with ondansetron and dizocilpine

The aim of the present study was to examine the influence of ifenprodil, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist which also blocks 5-HT3 receptors, on the amnestic effect of ethanol in a passive avoidance task in mice. The anti-amnestic action of ifenprodil was compared with the effects of the 5-HT3 receptor antagonist ondansetron and the non-competitive NMDA-receptor antagonist dizocilpine (MK-801). Ethanol, 2 g/kg and dizocilpine 0.1 mg/kg significantly impaired the passive avoidance response. In contrast, ifenprodil (0.1-10 mg/kg), ondansetron (0.03-0.3 mg/kg) and dizocilpine (0.01 and 0.03 mg/kg) did not alter passive avoidance by themselves. Dizocilpine did not diminish the amnestic action of ethanol when administered at doses of 0.03-0.1 mg/kg. However, the amnestic effect of ethanol was partially restored towards normal by ifenprodil 0.3 mg/kg and by ondansetron 0.03 mg/kg (alone or together with dizocilpine 0.01 mg/kg) but it was not affected by other doses of ifenprodil (0.1, 1 and 10 mg/kg) and ondansetron (0.1 and 0.3 mg/kg). In conclusion, ifenprodil at an appropriate dose reduced ethanol-induced amnesia in a step-through passive avoidance task. The results are compatible with the assumption that the anti-amnestic action of ifenprodil may be (at least partially) due to an antagonism at 5-HT3 receptors.

Effects of nefiracetam on amnesia animal models with neuronal dysfunctions

The effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide (nefiracetam; DM-9384), on learning and memory in several amnesia animal models with neuronal dysfunctions were investigated. Nefiracetam improved scopolamine-, bicuculline-, picrotoxin-, ethanol-, chlordiazepoxide- and cycloheximide-induced amnesia. Anti-amnesic action of nefiracetam on scopolamine model was antagonized by nifedipine and flunarizine, but not by diltiazem. Repeated administration of nefiracetam to AF64A-treated animals improved impairment of learning and memory as well as the alterations in cholinergic and monoaminergic neurotransmitters in the hippocampus. Basal forebrain (BF) lesioned rats induced by excitotoxin or by thermal coagulation showed impairment of learning accompanied by a marked reduction in choline acetyltransferase (ChAT) and acetylcholine esterase activities. Nefiracetam improved the learning deficit of the BF-lesioned rats. Nefiracetam also improved the carbon monoxide-induced delayed and acute amnesia. Nefiracetam stimulated acetylcholine release in the frontal cortex. Repeated administration of nefiracetam increased ChAT activity, gamma-aminobutyric acid (GABA) turnover and glutamic acid decarboxylase activity, and facilitated the Na(+)-dependent high-affinity GABA uptake. Nefiracetam activated the high voltage-activated (N/L-type) Ca2+ channel. The dose-response curves of nefiracetam were bell-shaped in both behavioral and biochemical studies. Therefore, it is suggested that nefiracetam improves the dysfunction of cholinergic, GABAergic and/or monoaminergic neuronal function by acting at Ca2+ channel and enhancing the release of neurotransmitters, and modifies impairment of memory processes induced by drugs and hypoxia.

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

A classical fear conditioning paradigm was used to examine the effect of acute ethanol on the acquisition of context conditioning, a hippocampal-dependent associative task, and tone conditioning, a hippocampal-independent task. Administration of ethanol before the presentation of seven tone-shock pairings severely disrupted the acquisition of context conditioning, but had only a slight effect on tone conditioning, when conditioned fear was measured 48 h later. This effect was dose dependent: a dose of 0.5 g/kg had no effect on either context or tone conditioning, while doses of 1.0 and 1.5 g/kg disrupted context conditioning by 78-86%, and tone conditioning by 9-17%. Subsequent experiments indicated that ethanol's preferential effect on context conditioning could not be attributed to the fact that context conditioning is weaker than tone conditioning, ethanol-induced changes in motivational state or state-dependent learning. The effect of ethanol on stimulus-induced increases in hippocampal and neocortical expression of c-fos mRNA, a marker for changes in metabolic neuronal activity, was also examined. Ethanol completely blocked the induction of hippocampal c-fos mRNA by exposure to the conditioning context alone or seven tone-shock pairings, but only attenuated neocortical responses to these stimuli. Together, these results suggest that ethanol disrupts hippocampal-dependent learning by preferentially impairing stimulus processing at the level of the hippocampus.

Involvement of benzodiazepine/GABA-A receptor complex in ethanol-induced state-dependent learning in rats

State-dependent learning (SDL) induced by ethanol (EtOH) was investigated on the step-through passive avoidance task in rats. Pretraining injection of EtOH dose-dependently reduced step-through latency in the test session 24 h after the training. Injection of EtOH (1.0 g/kg) before both the training and test sessions, however, failed to reduce the latency. These results show that EtOH produces SDL. The failure of learning performance in SDL (dissociation in SDL) induced by EtOH was blocked by bicuculline, Ro15-4513 and picrotoxin injected before the training session. The success of learning performance in SDL (non-dissociation in SDL) induced by EtOH was also blocked by bicuculline, Ro15-4513 and picrotoxin injected before the test session. The antagonism of Ro15-4513 against EtOH was blocked by flumazenil. In the substitution test, pretest injection of EtOH produced non-dissociation in SDL in the both of pretraining diazepam-and muscimol-treated rats. On the other hand, neither pretest injection of diazepam nor muscimol produced non-dissociation in the pretraining EtOH-treated rats: asymmetrical cross-substitution between EtOH and diazepam and between EtOH and muscimol was observed. These results suggest that the EtOH-induced SDL is partially mediated by the benzodiazepine (BDZ)/GABA-A receptor complex.

Muscimol induces state-dependent learning in Morris water maze task in rats

Effects of muscimol on the place learning in Morris water maze task were investigated in rats. Rats were given 4 training trials per day with the submerged platform at a fixed location in the maze for 4 days. On day 4, rats were required to swim in the pool without the platform after 4 training trials (probe test). Compared to the saline-treated rats, the rats treated with muscimol on day 1-4 showed no modifications of place learning in the training trials and the probe test. However, in the rats treated with muscimol on day 1-3 and treated with saline on day 4, there was increased latency to reach the platform and reduced duration in the quadrant where the platform had been located on day 4. The increased latency in the training trials and reduced duration in the probe test on day 4 was blocked by bicuculline, when bicuculline and muscimol were co-administered on day 1-3, and saline was injected on day 4. Moreover, in the rats treated with muscimol on day 1-3, co-administration of bicuculline and muscimol on day 4 blocked place learning: increased latency in the training trials and reduced duration in the probe test was observed. These results suggest that muscimol induces state-dependent learning (SDL) in Morris water maze task, and that muscimol-induced SDL is mediated by GABAA receptors.

Ameliorating effect of clentiazem (TA-3090), a new Ca antagonist, on the impaired learning ability of poststroke SHRSP

We investigated the influence of clentiazem (8-chloro-diltiazem, (+)(2S,3S)-3-acetoxy-8-chloro-5-[2-(dimethyl-amino)ethyl]-2,3-dihydro-2- (4-methoxyphenyl)-1,5-benzothiazepin-4(5H)-one maleate, TA-3090) and other Ca antagonists on the impaired learning ability in poststroke spontaneous hypertensive rats stroke prone (SHRSP) using a shuttle box. SHRSP were given 1% NaCl solution as drinking water until the development of stroke (poststroke SHRSP). Active avoidance task was started from the fourth day after the onset of stroke. Over a period of 20 sessions (15 trials/session/day), the mean avoidance rate of the poststroke SHRSP was significantly lower than that of the nonstroke control group that was not given the salt solution. Clentiazem (1, 3, and 10 mg/kg/day) administered orally for 23 days after the development of stroke increased the avoidance rate in a dose-dependent manner. Nimodipine (1 and 10 mg/kg/day) also increased the avoidance rate, but its effect was not dose dependent. We also investigated the influence of clentiazem and other Ca antagonists on the passive avoidance performance by mice using a light-dark box. Clentiazem (3, 10, and 30 mg/kg) and other Ca antagonists, nimodipine (1 mg/kg) and nicardipine (10 mg/kg), all failed to protect either CO2- or electroconvulsive shock (ECS)-induced avoidance deficit when administered orally 1 h before the acquisition or retention trial. These results may be explained by the possibility that the Ca antagonists may ameliorate the impaired learning ability in poststroke SHRSP through their improving effect on the cerebral circulation disturbance.

A low dose of ethanol impairs working memory in mice in a win-shift foraging paradigm

Using a test of working memory which is not influenced by learning, the win-shift foraging paradigm, ethanol was found to produce amnesia in mice. This effect was produced by very low doses of ethanol, 0.5 and 1.5 g/kg, which did not alter motivation as measured by latency to leave the start box. These doses of ethanol also did not alter performance in the maze as measured by the time to traverse the maze. These data indicate that low doses of ethanol directly impair working memory--that is, the effects are not due to an alteration in learning. The win-shift foraging paradigm, which is free of some of the problems inherent in passive avoidance paradigms, may be useful in exploring the mechanism of this effect of ethanol.

Involvement of the cholinergic neuronal system and benzodiazepine receptors in alcohol-induced amnesia

We investigated the involvement of the GABAergic and cholinergic neuronal systems and benzodiazepine (BZP) receptors in ethanol-induced amnesia using a passive avoidance task. Pretraining administration of ethanol impaired the passive avoidance response. The BZP agonist chlordiazepoxide potentiated the amnesia, while the GABA antagonists bicuculline and picrotoxin failed to affect it. The acetylcholine esterase inhibitor physostigmine partially attenuated the ethanol-induced amnesia. These results suggest that ethanol-induced amnesia is related to BZP receptors and a dysfunction of the cholinergic neuronal system.

Ethanol effects in an anxiety/defense test battery

Two tests, components of an Anxiety/Defense Test Battery, have been designed to measure risk assessment, inhibition of nondefensive behaviors, and movement arrest, all of which occur in the natural defense patterns of rats to threatening stimuli. In these tests, which used a nonpainful threat stimulus (a cat), ethanol (0.6 and 1.2 g/kg) increased two risk assessment behaviors on an initial test day, and produced a wider pattern of changes in all three patterns on a retest (no cat) day, 5 days later. The pattern of results obtained is compatible with a view that defensive behaviors occur in a fixed sequence with the decreasing intensity of threat an important factor in the transition from one defensive behavior to the next, and with ethanol at these doses producing a mild and relatively nonspecific anxiolytic effect. Comparison of male and female subjects on these tasks also suggested that females are more defensive than males, a finding which agrees with a variety of human anxiety studies but is at variance with previous rodent literature.

Effects of DM-9384, a pyrrolidone derivative, on alcohol- and chlordiazepoxide-induced amnesia in mice

The effects of N-(2,6-dimethyl-phenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide (DM-9384), a new pyrrolidone derivative, were investigated on ethanol- and chlordiazepoxide (CDP)-induced amnesia animal model using the passive avoidance task in comparison with aniracetam, another pyrrolidone derivative. Pretraining administration of DM-9384 attenuated ethanol- and CDP-induced amnesia, whereas aniracetam failed to do so. The effects of DM-9384 on CDP-induced amnesia were antagonized by bicuculline, a GABAA receptor antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist and flumazenil, a benzodiazepine receptor antagonist. These results suggest that DM-9384 attenuates CDP-induced amnesia by interacting with the GABAergic neuronal system.

Enhancement of pavlovian conditioned suppression by mild ethanol intoxication

Rats were trained to bar-press for food and then received aversive Pavlovian conditioning following low doses of ethanol (0-1600 mg/kg in different groups). They were tested for Pavlovian conditioned suppression of bar-pressing 48 h, 7 days, and 14 days later following no additional differential treatments. The results showed that very low doses of ethanol (approximately 200 mg/kg) during training enhanced later conditioned suppression, whereas more moderate doses (800-1600 mg/kg) disrupted Pavlovian conditioning. These results parallel earlier observations that very low ethanol doses enhance Pavlovian conditioned eyeblink and heart rate responses in rabbits, and suggest that facilitation of Pavlovian conditioning may be a general effect of mild ethanol intoxication.

Contributions of hippocampus and neocortex to the expression of ethanol effects

The distinctive effects of ethanol on behavior suggest that certain parts of the CNS may be especially sensitive to it. One of the primary candidates is the hippocampal formation. Damage to this structure mimics acute ethanol treatment across a wide variety of behavioral tasks and processes. The possibility of a hippocampal basis for ethanol psychopharmacology was examined in the present experiments. Chosen for behavioral analysis were relatively complex eight-arm radial maze tasks which have independently been shown to be sensitive to ethanol administration and hippocampal lesions. Measures included arm selection predictability, vigilance, and retardation of extinction. Bilateral hippocampal lesions or ethanol injection (1.5 g/kg, IP) produced similar effects. However, hippocampectomy did not disrupt ethanol's influence on any task. Comparatively, neocortical ablation, especially prefrontal, was quite effective in this respect. It blocked or reduced two of the drug's three behavioral effects examined here, without any strong influence of its own, and without altering blood alcohol concentration.

Reversal of alcohol-induced amnesia by the benzodiazepine inverse agonist Ro 15-4513

We investigated the effects of benzodiazepine inverse agonists on ethanol-induced amnesia using a passive avoidance task. Pretraining treatment of mice with ethanol significantly impaired the passive avoidance response: there was a significant reduction in the % retention and step-down latency. The benzodiazepine inverse agonists, Ro 15-4513 and beta-CCM, significantly increased the % retention and prolonged the step-down latencies in mice treated with ethanol, but FG 7142 did not. The anti-amnesic effects of Ro 15-4513 were completely antagonized by co-administration of Ro 15-1788, a benzodiazepine antagonist. These results suggest that the anti-amnesic effect of Ro 15-4513 on alcohol-induced amnesia is mediated by benzodiazepine receptors.

Effects of ethanol on passive avoidance behavior in the mouse: involvement of GABAergic mechanisms

A passive avoidance methodology was used to test the effect of ethanol, and its interference with GABAergic mechanisms, on memory in male CD1 mice. Retention performance was reduced in a dose-related manner, by ethanol and by muscimol, a GABA agonist, while it was increased by the GABA antagonists picrotoxin and bicuculline. These effects were evident when treatments were carried out immediately, but not 120 min, after training, suggesting that they were due to a specific action of the drugs on the time-dependent memory consolidation process. The ethanol-induced reduction of retention performance was enhanced by muscimol and decreased by picrotoxin and bicuculline administrations. Taken together the results confirm the involvement of a GABAergic mechanism in memory consolidation and demonstrate that it underlies the negative effect of ethanol on passive avoidance behavior in the mouse.

Voluntary ethanol consumption in rats: an examination of blood/brain ethanol levels and behavior

The temporal pattern of food, water, and ethanol consumption was examined in rats maintained on a 24-hr ethanol access schedule. These data demonstrated that rats consume ethanol in discrete, short bouts mainly during the lights-out cycle. Simulation of a single ethanol drinking bout was carried out by limiting ethanol access to a short time period each day. Detectable levels of blood and brain ethanol were observed following these individual drinking bouts. Behavioral evidence is provided indicating that rats drink ethanol in quantities sufficient to produce pharmacological effects.

The effect of home or novel environment on the facilitation of passive avoidance by post-training ethanol

Passive avoidance behavior of mice is improved when mice are injected with ethanol immediately after footshock training. Further study has shown that avoidance can be affected by ethanol injections given within 1 h, but not at 90 or 180 min, after training. The present study was conducted to investigate the possibility that events which occur in the homecage during this sensitive period may influence the effect of ethanol on subsequent avoidance. Male Swiss-Webster mice were housed either singly in a novel environment for 90 min or returned to their (group) homecage following one-trial, step-through, passive avoidance training (0.1 mA footshock) and intraperitoneal injection of 3.0 g/kg ethanol (15% v/v) or saline. As in previous studies, when ethanol-treated mice were returned to their homecage, avoidance was significantly increased at 24 h compared to the behavior of saline-treated mice. However, when mice were isolated in the novel environment for 90 min immediately following treatment, the memory facilitating effects of ethanol were not observed. The avoidance behavior of mice injected with saline was the same regardless of their post-training environment. Also, the number of mice (6 or 10) housed per homecage did not significantly influence the effects of ethanol or post-training environment on avoidance. These findings indicate that environmental factors may interact with the effects of ethanol to modify avoidance behavior. The possible influence of variables such as aggression, thermoregulation, and behavioral arousal on the effects of ethanol in this paradigm are discussed.

Ethanol enhancement of Pavlovian conditioning: comparison with instrumental conditioning

Yoked pairs of rabbits received conditioning and extinction of eyeblink and heart rate responses using aversive Pavlovian versus instrumental avoidance contingencies. A low dose of ethanol (375 mg/kg) increased the amplitude of conditioned eyeblink responses during training and during subsequent extinction following either ethanol or water; this effect was more pronounced in the Pavlovian than the instrumental contingency groups. Ethanol treatment did not affect the cardiac component of the Orienting Reflex to novel tones or heart rate conditioned responses to tone signals, but did bias heart rate responses to tone-shock stimulus pairs in a parasympathetic direction; this effect occurred in both contingency groups but appeared to involve associative factors. These results support the conclusion that mild ethanol intoxication enhances the acquisition of Pavlovian conditioned reflexes, and impairs the ability to modify these responses when stimulus contingencies later change.

Ethanol changes patterns of defensive behavior in wild rats

Wild-trapped R. rattus under saline or four ethanol doses were run in tasks designed to measure a range of defensive reactions to nonpainful threat stimuli. Results suggest that at higher doses (1.2 g/kg and above) ethanol reduces defense, with effects ranging from slight reductions to near abolition, depending on the behavior measured. Low and moderate ethanol (0.3 and 0.6 g/kg) doses, however, had divergent effects, tending to enhance components of the defensive attack pattern (vocalization, jump attacks, bites), while not altering other aspects of defensiveness. This pattern of results suggest that an ethanol-based potentiation of defensive attack may be one of the factors involved in the phenomenon of aggression increases following alcohol consumption.

Pharmacological investigations of neurotransmitter involvement in passive avoidance responding: a review and some new results

The roles of acetylcholine (ACh), noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in passive avoidance responding are examined by reviewing previous studies of the effects on this task of drugs which alter the functioning of these neurotransmitter systems and also by presenting the results of a new study. This new study includes a number of drugs which do not seem to have been examined before, namely pilocarpine, pempidine, pentolinium, tetrabenazine, desipramine, clonidine, isoprenaline, pimozide, fluoxetine, L-tryptophan, methysergide and cyproheptadine. Because there is large variability in the effects of any one drug or class of drugs on passive avoidance responding, it is difficult to determine the exact involvement of the various neurotransmitter systems. There is also little good evidence that drug effects on performance of the passive avoidance response are caused by drug-induced changes in learning and memory processes or by state-dependent effects. Three other factors which may influence performance of the passive avoidance response-shock sensitivity, the biochemical response to stress and locomotor activity-are discussed and may be responsible for many of the drug-induced changes in passive avoidance responding.