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

Ethanol enhances JWH-018-induced impairment of sensorimotor and memory functions in mice: From preclinical evidence to forensic implication in Driving Under the Influence of Drugs

BACKGROUND

Several new Synthetic Cannabinoids have appeared each year since their introduction into the illicit drug market as recreational drugs. Among these, naphtalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) is one of the most detected compounds in biological samples from patients involved in intoxication or death cases. Furthermore, consumption of JWH-018 has been linked to several cases of Driving Under the Influence of Drugs (DUID) suggesting that effects induced by this compound can affect individuals' ability to drive.

METHODS

Given the high spread of polydrug consumption and the wide number of alcohol-related traffic accidents, this study aims to investigate the acute effects induced by co-administration of JWH-018 with ethanol on sensorimotor and motor responses, grip strength and memory functions in CD-1 male mice. Acute impairments induced by JWH-018 and ethanol alone have also been investigated, in order to compare their effects with that induced by their concurrent administration.

RESULTS

In vivo behavioral experiments revealed a worsening of the cognitive and sensorimotor disruption after the co-administration of JWH-018 with ethanol compared to single compounds.

CONCLUSIONS

These animal-based findings suggest a potential increased impairment on psychomotor performances which could be related to driving abilities posed by poly-drug consumption involving SCs and ethanol.

Low-Dose Ethanol Has Impacts on Plasma Levels of Metabolites Relating to Chronic Disease Risk in SAMP8 mice

The effects of low-dose alcohol on experimental animals are unclear. This study examined plasma metabolites in senescence-accelerated mice 8 (SAMP8) given low-dose ethanol, and compared them with aging progress and skeletal muscle strength. Male SAMP8 mice (10-wk-old) were given drinking water containing 0% (control), 1%, 2%, or 5% (v/v) ethanol for 14 wk. Compared with the control group, only mice who consumed 1% ethanol experienced a lower senescence score at 18 and 23 wk, as well as an increased limb grip strength at 21 wk. Plasma metabolites of control, 1% and 2% ethanol groups were analyzed by capillary electrophoresis-time-of-flight mass spectrometry (CE-TOF/MS). Among the 7 metabolites affected by ethanol, notewhorthy is the positive association of the ethanol levels in drinking water with the levels of α-ketoglutarate (antioxidant and anti-inflammatory metabolite) and hippurate (antioxidant and microbial co-metabolite) (p<0.05). Intriguingly, the levels of 2-hydroxyisobutyrate (the biomarker of energy metabolism and microbial co-metabolite) were higher in the 1% ethanol group (p<0.05), but not in the 2% ethanol group as compared to the control. Furthermore, the levels of some of the metabolites affected were correlated with some variables in the grading score of senescence and muscle strength. This study provides a novel insight into how low-dose ethanol in SAMP8 mice modulates the levels of circulating metabolites relating to chronic disease risk.

Acute alcohol and cognition: Remembering what it causes us to forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders, it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact that acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified.

Changes in CREB activation in the prefrontal cortex and hippocampus blunt ethanol-induced behavioral sensitization in adolescent mice

Drug dependence is a major health problem in adults and has been recognized as a significant problem in adolescents. We previously demonstrated that repeated treatment with a behaviorally sensitizing dose of ethanol in adult mice induced tolerance or no sensitization in adolescents and that repeated ethanol-treated adolescents expressed lower Fos and Egr-1 expression than adult mice in the prefrontal cortex (PFC). In the present work, we investigated the effects of acute and repeated ethanol administration on cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) DNA-binding activity using the electrophoretic mobility shift assay (EMSA) and the phosphorylated CREB (pCREB)/CREB ratio using immunoblotting in both the PFC and hippocampus in adolescent and adult mice. Adult mice exhibited typical locomotor sensitization after 15 days of daily treatment with 2.0 g/kg ethanol, whereas adolescent mice did not exhibit sensitization. Overall, adolescent mice displayed lower CREB binding activity in the PFC compared with adult mice, whereas opposite effects were observed in the hippocampus. The present results indicate that ethanol exposure induces significant and differential neuroadaptive changes in CREB DNA-binding activity in the PFC and hippocampus in adolescent mice compared with adult mice. These differential molecular changes may contribute to the blunted ethanol-induced behavioral sensitization observed in adolescent mice.

A low concentration of ethanol impairs learning but not motor and sensory behavior in Drosophila larvae

Drosophila melanogaster has proven to be a useful model system for the genetic analysis of ethanol-associated behaviors. However, past studies have focused on the response of the adult fly to large, and often sedating, doses of ethanol. The pharmacological effects of low and moderate quantities of ethanol have remained understudied. In this study, we tested the acute effects of low doses of ethanol (∼7 mM internal concentration) on Drosophila larvae. While ethanol did not affect locomotion or the response to an odorant, we observed that ethanol impaired associative olfactory learning when the heat shock unconditioned stimulus (US) intensity was low but not when the heat shock US intensity was high. We determined that the reduction in learning at low US intensity was not a result of ethanol anesthesia since ethanol-treated larvae responded to the heat shock in the same manner as untreated animals. Instead, low doses of ethanol likely impair the neuronal plasticity that underlies olfactory associative learning. This impairment in learning was reversible indicating that exposure to low doses of ethanol does not leave any long lasting behavioral or physiological effects.

An opportunistic theory of cellular and systems consolidation

Memories are often classified as hippocampus dependent or independent, and sleep has been found to facilitate both, but in different ways. In this Opinion, we explore the optimal neural state for cellular and systems consolidation of hippocampus-dependent memories that benefit from sleep. We suggest that these two kinds of consolidation, which are ordinarily treated separately, overlap in time and jointly benefit from a period of reduced interference (during which no new memories are formed). Conditions that result in reduced interference include slow wave sleep (SWS), NMDA receptor antagonists, benzodiazepines, alcohol and acetylcholine antagonists. We hypothesize that the consolidation of hippocampal-dependent memories might not depend on SWS per se. Instead, the brain opportunistically consolidates previously encoded memories whenever the hippocampus is not otherwise occupied by the task of encoding new memories.

Ethanol inhibits persistent activity in prefrontal cortical neurons

Cognitive functions supported by neurons in the prefrontal cortex (PFC) are disrupted by acute and chronic exposure to alcohol, yet little is known about the mechanisms that underlie these effects. In the present study, in vivo and in vitro electrophysiology was used to determine the effects of ethanol on neuronal firing and network patterns of persistent activity in PFC neurons. In vivo, ethanol (0.375-3.5 g/kg) dose-dependently reduced spike activity in the PFC measured with multielectrode extracellular recording in the anesthetized rat. In an in vitro coculture system containing slices of PFC, hippocampus, and ventral tegmental area (VTA), ethanol (25-100 mM) decreased persistent activity of PFC neurons, but had little effect on firing evoked by direct current injection. Persistent activity was often enhanced after ethanol washout and this effect was maintained in cultures lacking the VTA. A low concentration of the NMDA antagonist APV (5 microM) mimicked the inhibition of ethanol of persistent activity with no change in activity after washout. Ethanol inhibition of spontaneous and VTA-evoked persistent activity was enhanced by the D1 dopamine receptor antagonist SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride]. The results of this study show that ethanol inhibits persistent activity and spike firing of PFC neurons and that the degree of ethanol inhibition may be influenced by D1 receptor tone. Ethanol-induced alterations in the activity of deep-layer cortical neurons may underlie some of the behavioral effects associated with ethanol intake.

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.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

The neurosteroid pregnenolone sulfate neutralized the learning impairment induced by intrahippocampal nicotine in alcohol-drinking rats

The effects of intrahippocampal administration of nicotine and the neurosteroids pregnenolone sulfate and allopregnanolone on acquiring the lever-press response and extinction in a Skinner box were examined using voluntary alcohol-drinking rats. A free-choice drinking procedure that implies early availability of the alcoholic solution (10% ethanol v/v+3% glucose w/v in distilled water) was used. Alcohol and control rats were deprived of food and assigned at random to six groups. Each group received two consecutive intrahippocampal (dorsal CA1) injections immediately after 1-h of drinking ethanol and before the free lever-press response shaping and extinction session. The groups were: saline-saline; saline-pregnenolone sulfate (5 ng, 24 microM); saline-allopregnanolone (0.2 microg, 1.26 microM); nicotine (4.6 microg, 20 mM)-saline; nicotine-pregnenolone sulfate; nicotine-allopregnanolone. Blood alcohol concentrations were assessed the day before conditioning. The combination of the oral self-administration of ethanol and the intrahippocampal injection of nicotine deteriorated the ability to acquire the lever-press response. This effect was neutralized by intrahippocampal pregnenolone sulfate (negative modulator of the GABA(A) receptor complex), and it was not affected by intrahippocampal allopregnanolone (positive GABA receptor complex A modulator). Pregnenolone sulfate and allopregnanolone had no effects per se on lever-press acquisition, neither in alcohol-drinking rats nor in controls. Alcohol consumption facilitated operant extinction just as anxiolytics that act as positive modulators of the GABA receptor complex A receptors do, possibly reducing the anxiety or aversion related to non-reinforcement. This effect was increased by intrahippocampal nicotine.

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.

Biphasic effects of ethanol on acetylcholine release in the rat prefrontal cortex

Low doses of ethanol (0.5 g/kg i.p.) increased, while higher doses (1 g/kg i.p.) reduced acetylcholine (ACh) release in the rat prefrontal cortex (PFC). Ethanol (50-300 mM) applied in the nucleus basalis through a second dialysis probe caused concentration-dependent biphasic changes in prefrontocortical ACh release. Ethanol apparently acts on cholinergic fibers to modulate ACh transmission in the PFC. These results could be of relevance for the bidirectional modulation of working memory by ethanol.

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.

Neurosteroids in learning and memory processes

The discovery that neurosteroids could be synthesized de novo in the brain independent from the periphery and display neuronal actions led to great enthusiasm for the study of their physiological role. Pharmacological studies suggest that neurosteroids may be involved in several physiological processes, such as learning and memory. This chapter summarizes the effects of the administration of neurosteroids on learning and memory capabilities in rodents and in models of amnesia. We address the central mechanisms involved in mediating the modulation of learning and memory processes by neurosteroids. In this regard, the neurosteroid-modulated neurotransmitter systems, such as gamma-aminobutyric acid type A, N-methyl-D-aspartate, and cholinergic and sigma opioid systems, appear to be potential targets for the rapid memory alteration actions of neurosteroids. Moreover, given that some neurosteroids affect neuronal plasticity, this neuronal change could be involved in the long-term modulation of learning and memory processes. To understand the role of endogeneous neurosteroids in learning and memory processes, we present some physiological studies in rodents and humans. However, the latter do not successfully prove a role of endogenous neurosteroids in age-related memory impairments. Finally, we discuss the relative implication of a given neurosteroid vs its metabolites. For this question, a new approach using the quantitative determination of traces of neurosteroids by mass spectrometry seems to have potential for examining the role of each neurosteroid in discrete brain areas in learning and memory alterations, as observed during aging.

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.

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.

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.

The ethanol metabolite acetaldehyde inhibits the induction of long-term potentiation in the rat dentate gyrus in vivo

1. Ethanol has been reported to inhibit the induction of long-term potentiation (LTP) in the hippocampus. However, the correlation between the effects of ethanol in vivo and in vitro remained unclear. In addition, previous works have little considered the possibility that the effect of ethanol is mediated by its metabolites. To solve these problems, we investigated the effects of ethanol and acetaldehyde, the first metabolite in the metabolism of ethanol, on the induction of LTP at medial perforant path-granule cell synapses in the dentate gyrus of anaesthetized rats in vivo. 2. Oral administration of 1 g kg-1 ethanol significantly inhibited the induction of LTP, confirming the effectiveness of ethanol in vivo. 3. A lower dose of ethanol (0.5 g kg-1) failed to inhibit the induction of LTP in intact rats, but significantly inhibited LTP in rats treated with disulfiram, an inhibitor of aldehyde dehydrogenase, demonstrating that LTP is inhibited by acetaldehyde accumulation following ethanol administration. 4. Intravenous injection of acetaldehyde (0.06 g kg-1) significantly inhibited the induction of LTP. 5. The inhibitory effect of acetaldehyde on LTP induction was also observed when it was injected into the cerebroventricules, suggesting that acetaldehyde has a direct effect on the brain. The intracerebroventricular dose of acetaldehyde effective in inhibiting LTP induction (0.1 - 0.15 mg brain-1) was approximately 10 fold lower than that of ethanol (1.0 - 1.5 mg brain-1). 6. It is possible that acetaldehyde is partly responsible for memory impairments induced by ethanol intoxication.

Inhibitory effects of anesthetics and ethanol on muscarinic receptors expressed in Xenopus oocytes

Anesthetics (and ethanol) are known to produce amnesia as well as immobilization. Recent identification of a nonimmobilizing (nonanesthetic) agent (F6 or 1,2-dichlorohexafluorocyclobutane) that impairs learning and memory suggests that distinct mechanisms may be responsible for these two actions of anesthetic agents. Muscarinic receptors are believed to play a role in memory and learning, and we asked if a specific subtype of these receptors is affected by anesthetics as well as the new nonanesthetic. We investigated the effects of halothane, a novel halogenated anesthetic compound F3 (1-chloro-1,2,2-trifluorocyclobutane) and ethanol on acetylcholine-induced current mediated by a muscarinic m1 receptor expressed in Xenopus oocytes. We also studied the effects of halogenated nonanesthetic compounds, F6 and F8 (2,3-chlorooctafluorobutane) on muscarinic m1 receptors. Halothane, F3, F6 and ethanol inhibited muscarinic m1 receptor-induced Ca2+-dependent Cl- currents at pharmacologically relevant concentrations. F8 had no effect on acetylcholine-induced muscarinic m1 receptor function. The protein kinase C inhibitor, bisindolylmaleimide I (GF109203X), enhanced the acetylcholine-induced current and the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), inhibited this current. GF109203X abolished the inhibitory effects of halothane, F3 and ethanol on muscarinic m1 receptors but had no effect on actions of F6. These results demonstrate that anesthetics and a nonanesthetic inhibit the function of muscarinic m1 receptors and suggest activation of protein kinase C as the mechanism of action of anesthetics and ethanol on these receptors.

Chronic ethanol ingestion-induced changes in open-field behavior and oxidative stress in the rat

The effects of chronic ethanol intoxication on the open-field behavior, on antioxidant enzyme activities, and the degree of lipid peroxidation were investigated. Rats consuming a liquid diet containing 7% ethanol for 4, 7, 14, or 21 days exhibited a significantly decreased ambulation activity, accompanied by a reduced frequency and duration of explorative rearing in an open-field task 4, 7, and 14 days after chronic ethanol ingestion, whereas presumed adaptation to the neurologic effects of ethanol was observed on day 21. Changes in the activities of glutathione peroxidase (GSH-Px): glutathione reductase (GSH-R), and catalase, and in the content of reduced glutathione (GSH) in blood samples were determined by means of biochemical methods. The degree of lipid peroxidation was measured via thiobarbituric acid assays. Chronic ethanol ingestion elicited a significant increase in GSH-Px activity (by a maximum of approximately 32% on day 14), whereas opposite alterations in GSH-R and catalase activities were recorded (49% of the control value on day 4 and 17% on day 21, respectively). Highly elevated contents of thiobarbituric acid reactive substances reflected extensive lipid peroxidation processes throughout the experiment. These changes indicate that ethanol toxicity induces profound changes in explorative behavior, mediated, at least partly, by changes in the free radical metabolism.

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.

Behavioral correlates of single units in the medial septal area: the effect of ethanol

Experimental manipulations that compromise the medial septal area consistently and selectively impair working memory. The electrophysiological and pharmacological properties of medial septal neurons have been studied extensively, but the relation between medial septal neuronal activity and ongoing behavior has not been systematically analysed. Working memory was assessed in a continuous conditional discrimination task, and behavioral performance was correlated with medial septal single unit activity. Operant performance and the activity of rhythmically active neurons were continuously monitored during a 90 min test session, and peri-event time histograms of unit activity were constructed around relevant task events. Rats received intraperitoneal injections of either saline or ethanol (0.75 g/kg) 5 min before testing. Of the 52 medial septal neurons recorded under saline conditions, approximately 80% had significant behavioral correlates. Thirty-five per cent of these neurons were selectively activated at the time of the response and 65% at the time of the reward. Response-related activity was not selective for responses to the right or left lever, or to a particular type of trial, but in 61% of the cases was correlated with the accuracy of the response. In ethanol-treated rats, working memory was impaired, single unit activity was disrupted, and the behavioral correlates were less frequent and robust, especially the response-related correlates that were accuracy-sensitive. The results suggest that the medial septal area is involved in guiding accurate responses and processing rewards, and may contribute to the ethanol-induced impairments in working memory.

Ethanol suppresses the induction of long-term potentiation in vivo

Long-term potentiation (LTP), a leading neural mechanism of memory, is profoundly affected by ethanol in vitro, but ethanol's effect on LTP in vivo has not been studied at doses known to impair memory. In this study, LTP was induced in the dentate hilus by theta-pattern stimulation of the perforant path. Dentate evoked responses were recorded during a 3 h session in which rats pressed a lever on a fixed interval (30 s) schedule of reinforcement. Following theta-pattern stimulation, rats pretreated with saline had significant LTP that was present throughout the session. LTP was measured as an increase in the initial slope and the population spike of the evoked response. The potentiation was no longer present 24 h after stimulation. Ethanol (0.5 g/kg and 1.0 g/kg) blocked LTP and attenuated short-term frequency potentiation in a dose-dependent fashion. Although ethanol produced a decrease in rewarded lever pressing, lever pressing was not correlated to any measure of the evoked response. Ethanol, when given 60 min after theta-pattern stimulation, did not alter the expression of LTP. The results demonstrate that low doses of ethanol selectively blocked the induction of LTP in vivo, an effect that may underlie ethanol's impairment of memory.

The attenuation of suppression of motility by triazolam in the conditioned fear stress task is exacerbated by ethanol in mice

We investigated whether triazolam attenuated the suppression of motility in the conditioned fear stress task in mice and whether ethanol modified the effects of triazolam. When mice were placed 24 hours later (retention test) in the same environment in which they had previously been exposed to an electric foot shock (training), they exhibited a marked suppression of motility (conditioned fear stress). Triazolam (0.01-0.1 mg/kg, s.c.), administered before training, attenuated the suppression of motility in the conditioned fear stress task in a dose-dependent manner, without affecting the sensitivity to an electric foot shock. The doses of triazolam that attenuated the suppression of motility were much lower that those of chlordiazepoxide (5-10 mg/kg, s.c.). Neither drug, administered before the retention test, attenuated the suppression of motility in the conditioned fear stress task. These results suggest that both benzodiazepines may inhibit the process of acquisition, but not the process of recall, of memory. Ethanol (1 g/kg, p.o.), which, by itself, did not affect either the suppression of motility or the sensitivity to an electric foot shock, exacerbated the attenuation of the suppression of motility in the conditioned fear stress task induced by both triazolam (0.01 mg/kg) and chlordiazepoxide (5 mg/kg). These results suggest that ethanol exacerbates the effects of benzodiazepines.

Ethanol affects context memory and long-term habituation in the crab Chasmagnathus

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus that habituates promptly and for a long period. The effect of acute ethanol treatment on this long-term memory was analyzed. A single injection of 0.01, 0.05, or 0.1 micrograms ethanol (ET)/g given 30 min before iterated presentation of a visual danger stimulus failed to affect short-term habituation. Posttraining ethanol (0.01 to 0.1 microgram/g) produces a dose-dependent impairment of long-term habituation, but pretraining ethanol had no amnestic effect. However, a retention deficit confined to context memory was disclosed with both pre- and posttraining ethanol. Results from experiments with double injection (posttraining and pretesting injections) account for the retention impairment in terms of true amnesia (failure to acquire memory) but not due to state-dependence or retrieval deficit. The nonamnestic effect of pretraining ethanol upon long-term habituation is explained by a nonespecific depressing effect caused by interaction between iterative presentation of the danger stimulus and drug-induced internal state during training.

Low doses of ethanol impair spatial working memory and reduce hippocampal theta activity

Low doses of ethanol can alter neural activity in the septohippocampal pathway, a pathway critical for spatial working memory. The present study was designed to determine whether acute ethanol induces impairments in working memory and disrupts septohippocampal function as measured by the hippocampal theta rhythm. Rats were preoperatively trained on delayed alternation. A within-subject design was used to evaluate the effects of ethanol (0.25, 0.5, 0.75 and 1.0 g/kg, intraperitoneally) on performance 10 min and 90 min after injection as compared with preinjection baseline. Ethanol produced dose-, delay-, and time-dependent impairments in working memory as indicated by a change in choice accuracy in the delayed alternation task. Ethanol did not affect performance time, the ability to complete the task, or response bias. Thus, the impairment does not appear to result from a decrement in general performance, but rather from an impairment in spatial working memory. Hippocampal theta activity was suppressed by ethanol at the same doses, 0.75 g/kg and 1.0 g/kg, that impaired working memory. The interaction of ethanol with functions of the septohippocampal pathway are discussed.