Response variability of ethanol-induced locomotor activation in mice

Reduced expression of ethanol sensitization by α3β4 nicotinic acetylcholine receptors in DBA/2J mice

Alcohol use disorder (AUD) is a leading cause of preventable death in the United States, however existing treatments are ineffective and produce aversive side effects such as nausea and fatigue. One potential therapeutic for AUD is the α3β4 nicotinic acetylcholine receptor (nAChR) antagonist 18-methoxycoronaridine (18-MC). Prior work has shown that 18-MC reduces ethanol consumption in rodent models. The present study sought to further examine the therapeutic potential of 18-MC by testing its effects on nonconsummatory behaviors. We examined 2 behavioral measures: ethanol-induced locomotor stimulation, which measures euphoric properties of the drug, and the expression of locomotor sensitization which models neuroadaptations in response to repeated exposure. We tested dose-dependent effects of 18-MC (0, 10, 20 and 30 mg/kg) administration on ethanol stimulation and locomotor sensitization in female and male DBA/2J mice. 18-MC had no effect on acute ethanol-induced stimulation, but the highest dose (30 mg/kg) significantly decreased the expression of locomotor sensitization. Our results support the involvement of α3β4 nAChR in the expression of ethanol-induced locomotor sensitization and suggest that 18-MC may be a therapeutic for AUD. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

A role for nucleus accumbens glutamate in the expression but not the induction of behavioural sensitization to ethanol

Mechanisms underlying differential sensitivity to behavioural sensitization to ethanol (EtOH) remain poorly understood, although accumulating evidence suggests a role for glutamatergic processes in the ventral striatum. Efforts to address this issue can benefit from the well-documented fact that in any given cohort, some of the mice (High sensitized; HS) show robust sensitization, while others (Low sensitized; LS) show little, if any, sensitization. Here, we examined whether this variability might be differentially associated with nucleus accumbens (NAc) glutamate processes. Male DBA mice received 5 EtOH (2.2g/kg) or saline injections twice a week and were challenged with EtOH (1.8g/kg) 2 weeks after injection 5. When an EtOH challenge was administered 2 weeks following the induction of sensitization, HS, but not LS, mice showed a robust increase in glutamate levels (67%, P<0.01) as measured by in vivo microdialysis. In a separate cohort, the mGlu2/3 agonist LY354740 (10mg/kg), given prior to the EtOH challenge, abolished the expression of sensitization. To ascertain whether enhanced release could also be observed during the induction of sensitization, glutamate levels were measured after the 1st and 5th EtOH injection and were found to be unchanged in HS mice, although briefly elevated in LS mice at injection 5. To further assess possible glutamate involvement during the induction of sensitization, sensitizing EtOH injections were co-administered with NMDAR antagonists. At the doses used, MK-801 (0.25mg/kg) and CGS 19755 (10mg/kg) blocked the expression of sensitization, but did not significantly interfere with the development of EtOH sensitization. Within the limitations of the present design, the results suggest an important role for EtOH-induced glutamate release in the NAc when sensitization is well established, but not necessarily during the development of sensitization.

Behavioral sensitization to ethanol: Neural basis and factors that influence its acquisition and expression

Ethanol-induced behavioral sensitization (EBS) was first described in 1980, approximately 10 years after the phenomenon was described for psychostimulants. Ethanol acts on γ-aminobutyric acid (GABA) and glutamate receptors as an allosteric agonist and antagonist, respectively, but it also affects many other molecular targets. The multiplicity of factors involved in the behavioral and neurochemical effects of ethanol and the ensuing complexity may explain much of the apparent disparate results, found across different labs, regarding ethanol-induced behavioral sensitization. Although the mesocorticolimbic dopamine system plays an important role in EBS, we provide evidence of the involvement of other neurotransmitter systems, mainly the glutamatergic, GABAergic, and opioidergic systems. This review also analyses the neural underpinnings (e.g., induction of cellular transcription factors such as cyclic adenosine monophosphate response element binding protein and growth factors, such as the brain-derived neurotrophic factor) and other factors that influence the phenomenon, including age, sex, dose, and protocols of drug administration. One of the reasons that make EBS an attractive phenomenon is the assumption, firmly based on empirical evidence, that EBS and addiction-related processes have common molecular and neural basis. Therefore, EBS has been used as a model of addiction processes. We discuss the association between different measures of ethanol-induced reward and EBS. Parallels between the pharmacological basis of EBS and acute motor effects of ethanol are also discussed.

Ethanol-related behaviors in mice lacking the sigma-1 receptor

RATIONALE

The Sigma-1 receptor (Sig-1R) is a chaperone protein that has been implicated in drug abuse and addiction. Multiple studies have characterized the role the Sig-1R plays in psychostimulant addiction; however, fewer studies have specifically investigated its role in alcohol addiction. We have previously shown that antagonism of the Sig-1R reduces excessive drinking and motivation to drink, whereas agonism induces binge-like drinking in rodents.

OBJECTIVES

The objectives of these studies were to investigate the impact of Sig-1R gene deletion in C57Bl/6J mice on ethanol drinking and other ethanol-related behaviors.

METHODS

We used an extensive panel of behavioral tests to examine ethanol actions in male, adult mice lacking Oprs1, the gene encoding the Sig-1R. To compare ethanol drinking behavior, Sig-1 knockout (KO) and wild type (WT) mice were subject to a two-bottle choice, continuous access paradigm with different concentrations of ethanol (3-20% v/v) vs. water. Consumption of sweet and bitter solutions was also assessed in Sig-1R KO and WT mice. Finally, motor stimulant sensitivity, taste aversion and ataxic effects of ethanol were assessed.

RESULTS

Sig-1R KO mice displayed higher ethanol intake compared to WT mice; the two genotypes did not differ in their sweet or bitter taste perception. Sig-1R KO mice showed lower sensitivity to ethanol stimulant effects, but greater sensitivity to its taste aversive effects. Ethanol-induced sedation was instead unaltered in the mutants.

CONCLUSIONS

Our results prove that the deletion of the Sig-1R increases ethanol consumption, likely by decreasing its rewarding effects, and therefore indicating that the Sig-1R is involved in modulation of the reinforcing effects of alcohol.

Changes in dendritic spine density in the nucleus accumbens do not underlie ethanol sensitization

Behavioral sensitization to various drugs of abuse has been shown to change dendritic spine density and/or morphology of nucleus accumbens (NAc) medium spiny neurons, an effect seen across drug classes. However, is it not known whether behavioral sensitization to ethanol (EtOH) is also associated with structural changes in this region. Here we compared dendritic spine density and morphology between mice showing High vs. Low levels of EtOH sensitization and found that high levels of EtOH sensitization were not associated with changes in dendritic spine density or spine type. Unexpectedly, however, a significant increase in the density of stubby-type spines was seen in mice that were resistant to sensitization. Since the presence of this spine type has been associated with long-term depression and cognitive/learning deficits this may explain why these mice fail to sensitize and why they show poor performance in conditioning tasks, as previously shown. A possible causal role for structural plasticity in behavioral sensitization to various drugs has been debated. In the case of EtOH sensitization, our results suggest that drug-induced changes in structural plasticity in the accumbens neurons may not be the cause of sensitized behavior.

Individual differences in ethanol locomotor sensitization are associated with dopamine D1 receptor intra-cellular signaling of DARPP-32 in the nucleus accumbens

In mice there are clear individual differences in the development of behavioral sensitization to ethanol, a progressive potentiation of its psychomotor stimulant effect. Variability in the behavioral responses to ethanol has been associated with alcohol preference. Here we investigated if the functional hyperresponsiveness of D1 receptors observed in ethanol sensitized mice leads to an increased activation of DARPP-32, a central regulatory protein in medium spiny neurons, in the nucleus accumbens - a brain region known to play a role in drug reinforcement. Swiss Webster mice received ethanol (2.2 g/kg/day) or saline i.p. administrations for 21 days and were weekly evaluated regarding their locomotor activity. From those treated with ethanol, the 33% with the highest levels of locomotor activity were classified as “sensitized” and the 33% with the lowest levels as "non-sensitized”. The latter presented similar locomotor levels to those of saline-treated mice. Different subgroups of mice received intra-accumbens administrations of saline and, 48 h later, SKF-38393, D1 receptor agonist 0.1 or 1 µg/side. Indeed, sensitized mice presented functional hyperresponsiveness of D1 receptors in the accumbens. Two weeks following the ethanol treatment, other subgroups received systemic saline or SKF 10 mg/kg, 20 min before the euthanasia. The nucleus accumbens were dissected for the Western Blot analyses of total DARPP-32 and phospho-Thr34-DARPP-32 expression. D1 receptor activation induced higher phospho-Thr34-DARPP-32 expression in sensitized mice than in non-sensitized or saline. The functionally hyperresponsiveness of D1 receptors in the nucleus accumbens is associated with an increased phospho-Thr34-DARPP-32 expression after D1 receptor activation. These data suggest that an enduring increase in the sensitivity of the dopamine D1 receptor intracellular pathway sensitivity represents a neurobiological correlate associated with the development of locomotor sensitization to ethanol.

Effect of fendiline on the maintenance and expression of methamphetamine-induced conditioned place preference in Sprague-Dawley rats

RATIONALE

Fendiline is a GABAB receptor-positive allosteric modulator and L-type Ca²⁺ channel blocker that is safe for human use. Based on these pharmacological properties, fendiline may be useful to disrupt associative memories that can drive relapse to drug use in drug-addicted individuals

OBJECTIVE

The current study evaluated the potential of fendiline to inhibit the maintenance and expression of learned associations between methamphetamine (meth) and an environmental context using conditioned place preference (CPP) in rats, to model for the associative learning that occurs during drug abuse by humans

METHODS

Following meth conditioning (1 mg/kg), fendiline (5 mg/kg) was administered at various post-conditioning times to ascertain if there was a temporal window during which fendiline would be effective.

RESULTS

Two once-daily injections of fendiline did not influence the maintenance of CPP regardless of the post-conditioning treatment time while 10 once-daily fendiline treatments inhibited CPP maintenance (p < 0.05). Fendiline administered immediately prior to the CPP test inhibited expression of meth-induced CPP in rats with a fendiline treatment history of 10 once-daily injections (p < 0.05) or those that received two injections that corresponded to the last 2 days of the 10-day treatment (p < 0.05). Fendiline did not produce preference or aversion on its own, nor did it alter motivated motor behavior.

CONCLUSION

Maintenance and expression of meth CPP is mitigated by repeated fendiline treatments when administered during the days that precede CPP testing. Reduction in the significance of meth-associated cues can reduce relapse; therefore, fendiline may be of value for addiction therapy in abstinent, meth-addicted humans.

Deciphering the relationship between vulnerability to ethanol-induced behavioral sensitization and ethanol consumption in outbred mice

Ethanol (EtOH)-induced behavioral sensitization (EIBS) is proposed to play a role in early and recurring steps of alcohol dependence, but its impact on alcohol abuse is not clear. EIBS development is dependent upon animal species, strain and also individual factors. We proposed here to decipher the co-expression of EIBS and EtOH intake in individual animals among outbred Swiss mice, which exhibit heterogeneity that parallels what may occur in humans. To do so, mice were exposed to a two-bottle choice with free access to water or 10% EtOH for 6 days just before and immediately after chronic intraperitoneal 2.5 g/kg ethanol injections once a day for 10 consecutive days. Based on their sensitization scores, mice were split into resistant and sensitized animals. First, we showed that individual susceptibility to EIBS is inversely correlated with voluntary EtOH consumption. Exposure to repeated EtOH during EIBS development increased subsequent EtOH intake among the entire population. Very interestingly, subsequent analyses suggested that the less the mice are sensitized the more they increase their EtOH intake; however, resistant mice were sensitive to EtOH adulteration with quinine, whereas sensitized ones maintained their EtOH intake levels, therefore exhibiting a compulsive-like drinking pattern. In addition, we showed that resistant mice do not exhibit a weaker sensitivity to the aversive properties of EtOH that may contribute to their higher level of EtOH intake compared to sensitized mice. This study confirms and extends previous data showing a deep relationship between propensity for EtOH consumption and susceptibility to EIBS in Swiss mice.

Differential patterns of expression of neuropeptide Y throughout abstinence in outbred Swiss mice classified as susceptible or resistant to ethanol-induced locomotor sensitization

Several studies have focused on the negative emotional state associated with drug abstinence. The peptide NPY plays an important role given its involvement in drug addiction, anxiety, and mood disorders. Interestingly, it is well established that outbred Swiss mice exhibit a prominent behavioral variability to ethanol-induced locomotor sensitization. Here, we investigated whether mice that were either susceptible or resistant to ethanol sensitization differed in their NPY expression during abstinence. The mice were treated daily with ethanol (2 g/kg, i.p.) or saline for 21 days. According to the locomotor activity after the last injection, the ethanol group was classified as sensitized (EtOH_High) or non-sensitized (EtOH_Low). To evaluate NPY expression, some of the mice were sacrificed at 18 h or 5 days of abstinence, and others were challenged at the 5th day of abstinence with ethanol (1.4 g/kg) and sacrificed after 1.5 h. At 5 days of abstinence, NPY expression increased in the orbital cortex, dorsomedial striatum, and dentate gyrus in the EtOH_High mice. These changes were counteracted by the ethanol challenge. In the EtOH_Low mice, NPY expression increased in the dentate gyrus only after 18 h of abstinence. Lastly, a decreased level of NPY was found in the prelimbic cortex of the EtOH_Low mice at 5 days of abstinence, and this was reversed by ethanol challenge. Therefore, behavioral variability in ethanol sensitization confers differential neurochemical features during the subsequent abstinence, including distinct patterns of NPY expression.

Expression of behavioral sensitization to ethanol is increased by energy drink administration

Alcohol abuse and dependence are important medical, social and economical problems, affecting millions of people. A relatively recent habit among young people is mixing alcohol with energy drinks (ED), in spite of the risks involved may be higher than those associated with alcohol consumption alone. The mixture of alcohol and energy drinks, both with stimulant properties, may alter the perception of intoxication and could lead individuals to believe they are less drunk and can drink more or for longer periods of time. In animals, the repeated administration of ethanol can lead to a progressive increase of the locomotor stimulant effect, known as behavioral sensitization, a drug-dependent behavioral plasticity associated with vulnerability to addiction. As well as for addiction, there are clear individual differences in the level of sensitization to ethanol among species and even among individuals from the same strain. The present study assessed how ED affects the expression of ethanol sensitization. Female mice chronically treated with ethanol (2.4 g/kg) were classified as low-sensitized or high-sensitized. Two days later, different groups of mice were submitted to saline+water, ethanol+water or ethanol+ED systemic challenges. As expected, only the high-sensitized group expressed clear sensitization after ethanol administration. However, the administration of ethanol+ED triggered the sensitization expression in the low-sensitized group. These data indicate that the combined use of ED and ethanol can potentiate the stimulant and, consequently, the reward effects of ethanol in previously treated mice. If a similar process occurs in human beings, the use of ED can increase the risk of developing alcohol abuse or dependence.

Quantification of locomotor activity in larval zebrafish: considerations for the design of high-throughput behavioral studies

High-throughput behavioral studies using larval zebrafish often assess locomotor activity to determine the effects of experimental perturbations. However, the results reported by different groups are difficult to compare because there is not a standardized experimental paradigm or measure of locomotor activity. To address this, we investigated the effects that several factors, including the stage of larval development and the physical dimensions (depth and diameter) of the behavioral arena, have on the locomotor activity produced by larval zebrafish. We provide evidence for differences in locomotor activity between larvae at different stages and when recorded in wells of different depths, but not in wells of different diameters. We also show that the variability for most properties of locomotor activity is less for older than younger larvae, which is consistent with previous reports. Finally, we show that conflicting interpretations of activity level can occur when activity is assessed with a single measure of locomotor activity. Thus, we conclude that although a combination of factors should be considered when designing behavioral experiments, the use of older larvae in deep wells will reduce the variability of locomotor activity, and that multiple properties of locomotor activity should be measured to determine activity level.

Temporal and behavioral variability in cannabinoid receptor expression in outbred mice submitted to ethanol-induced locomotor sensitization paradigm

BACKGROUND

There is a close relationship between the endocannabinoid system and alcoholism. This study investigated possible differential expression of cannabinoid receptors CB1 (CB1R) and CB2 (CB2R) in an outbred mice strain displaying behavioral variability to ethanol (EtOH)-induced locomotor sensitization.

METHODS

Male adult Swiss mice treated chronically with EtOH (2 g/kg, i.p., daily for 21 days) were classified as "EtOH_High" or "EtOH_Low" according to their locomotor activity after the 21st EtOH injection. A control group was similarly injected with saline. Temporal analysis of CB1R and CB2R immunoreactivity was performed in 3 different occasions: (i) at the end of chronic EtOH treatment, (ii) on the fifth day of EtOH withdrawal, and (iii) after EtOH challenge.

RESULTS

Overall, no differences were seen between experimental groups regarding the CB1R at the end of acquisition. However, there were decreases in CB2R in the prefrontal cortex and the hippocampus in EtOH_Low mice. On the fifth day of withdrawal, only EtOH_High mice presented increase in CB1R. Nonetheless, CB2R up-regulation was observed in both EtOH_High and EtOH_Low mice. EtOH challenge counteracted CB1R and CBR2 up-regulation, mainly in the EtOH_High, in structures related to emotionality, such as prefrontal cortex, ventral tegmental area, amygdala, striatum, and hippocampus.

CONCLUSIONS

There are different patterns of cannabinoid receptor expression during locomotor sensitization paradigm, at both temporal and behavioral perspectives. We hypothesize that CB2R down-regulation might be related to resilience to develop locomotor sensitization, while CB1R up-regulation relates to withdrawal aspects in sensitized mice.

Susceptibility to ethanol sensitization is differentially associated with changes in pCREB, trkB and BDNF mRNA expression in the mouse brain

Repeated exposure to ethanol in mice induces behavioural sensitization, a progressive increase in locomotor activity that is common to drugs of abuse. Not all mice however show sensitization to ethanol. The goal of the present study was to examine whether variability in the sensitization response to ethanol (EtOH) is differentially associated with regional brain changes in specific molecular markers associated with neuroplasticity, namely BDNF and its receptor trkB, and levels of phosphorylated cyclic AMP-regulated element-binding protein (pCREB), 14 days after withdrawal from chronic, intermittent EtOH exposure. Male DBA/2NCrl mice received 7 biweekly EtOH (2.2g/kg, i.p.) or saline (SAL) injections and were classified as Sensitized or Non-sensitized on the basis of final locomotor activity (LMA) scores. Brains were removed two weeks later for immunohistochemical and in situ hybridization analyses. Compared to SAL-treated and Non-sensitized mice, Sensitized animals showed a higher number of pCREB-immunoreactive cells in the nucleus accumbens shell (+68% and +50%, respectively) and in the bed nucleus of the stria terminalis (+61% and 46%, respectively), whereas SAL and Non-sensitized groups did not differ from each other. A different pattern was seen when BDNF and trkB mRNA levels were analyzed in the same groups. Non-sensitized mice displayed lower BDNF mRNA in several brain areas and significantly lower trkB levels throughout the brain when compared to either the Sensitized or to SAL groups, which did not differ from each other. These results indicate that sensitization to EtOH is differentially associated with increased pCREB levels in specific brain areas. The observed decrease in BDNF and trkB mRNA in the Non-sensitized group suggests the possibility that EtOH may have neurotoxic effects in a subpopulation of mice, which might in turn prevent the development of behavioural sensitization. The lack of a difference in BDNF and trkB mRNA expression between Sensitized and SAL mice suggests that EtOH sensitization may be mediated by mechanisms different from those mediating sensitization to other psychostimulants.

Expression of ethanol-induced behavioral sensitization is associated with alteration of chromatin remodeling in mice

BACKGROUND

Ethanol-induced behavioral sensitization (EIBS) is proposed to play a role in early and recurring steps of addiction. EIBS does not occur uniformly in all animals even from the same inbred strain. Since recent data demonstrate that epigenetic mechanisms are likely to be involved in the development and the persistence of ethanol-related behaviors, we explored the involvement of epigenetic mechanisms in ethanol response after EIBS development.

METHODOLOGY

DBA/2J mice were i.p. injected with saline or ethanol (2 g/kg) once a day for 10 consecutive days. At day 17, ethanol-treated mice were split in resistant and sensitized groups. Brains were then removed 30 min after a saline or 2 g/kg ethanol challenge to assess i) gene expression using PCR array targeting 84 epigenetic-related genes and ii) histone deacetylases (HDAC), histone acetylases (HAT) and DNA methyltransferases (DNMT) activities as well as H4K12 acetylation.

PRINCIPAL FINDINGS

Acute ethanol administration decreased dnmt1, esco2 and rps6ka5 genes expression. These genes were similarly altered in sensitized but not in resistant mice after an ethanol challenge, suggesting that resistant mice were tolerant to the transcriptional outcomes of an ethanol challenge. Whereas global HAT or DNMT activity was not affected, global HDAC activity was reduced after an acute ethanol injection. HDAC inhibition occurred in all ethanol-treated mice but with a lesser extent in sensitized animals. As a consequence, H4 acetylation was specifically potentiated in the core of the Nac proportionally to the striatal HDAC activity decrease.

CONCLUSIONS/SIGNIFICANCE

The present study highlights that the contrasted behavioral response to an ethanol challenge between resistant and sensitized mice may be mediated by epigenetic mechanisms occurring specifically in the striatum. Here we show that vulnerability to ethanol dependence and relapse could be, at least in part, due to individual variability in acute ethanol-induced epigenetic response.

Effects of group exposure on single injection-induced behavioral sensitization to drugs of abuse in mice

BACKGROUND

Behavioral sensitization in rodents is hypothesized to reflect neuronal adaptations that are related to drug addiction in humans. We evaluated the effects of group exposure on the acute hyperlocomotion and behavioral sensitization induced by four drugs of abuse in C57BL/6 mice: methylenedioxymethamphetamine (MDMA), d-amphetamine, morphine and ethanol.

METHODS

In the priming session, animals received an ip injection of one of the drugs of abuse and were exposed to an open field either individually or in groups of four. Seven days later, we assessed behavioral sensitization in the challenge session. All animals received an ip injection of the same drug and were exposed to the open field in the same social conditions described for the priming session. Locomotion and social interaction were quantified during each session.

RESULTS

Acute MDMA, morphine and ethanol, but not d-amphetamine, increased social interaction. However, group exposure only potentiated MDMA-induced hyperlocomotion. After a challenge injection of each drug, there was no sensitization to the facilitating effect of MDMA, morphine or ethanol on social interaction, but locomotion sensitization developed to all drugs of abuse except ethanol. This sensitization was potentiated by group exposure in MDMA-treated animals, attenuated in morphine-treated animals and not modified in d-amphetamine-treated animals. Acute MDMA enhanced body contact and peaceful following, while acute morphine and ethanol increased social sniffing.

CONCLUSIONS

These results provide preclinical evidence showing that while different drugs of abuse affect different components of social interaction, the neuronal adaptations related to drug dependence can be critically and specifically influenced by group exposure.

Accumbal dopamine D2 receptor function is associated with individual variability in ethanol behavioral sensitization

Striatal dopamine D2 receptors have been implicated in the development of behavioral sensitization after repeated exposure to drugs of abuse. There are clear individual differences in the level of sensitization to ethanol among species and even among individuals from the same strain. Albino Swiss mice treated with ethanol (2.2 g/kg) have been shown to present clear variations in the development of sensitization. While some mice developed ethanol (EtOH) induced sensitization, others did not. This variability was associated with differences in D2 dopaminergic receptor binding. In the present study, we evaluated the functional relevance of dopamine D2 receptor by measuring, in sensitized and non-sensitized mice, the locomotor response to a D2 receptor agonist (quinpirole, 0.5 and 2.0 mg/kg i.p. or 0.01 and 0.2 μg/side intra-accumbens) or antagonist (sulpiride, 10 or 50 mg/kg i.p. or 0.02 μg/side intra-accumbens + ethanol i.p.). Whereas the systemic administration of quinpirole decreased locomotor activity in a similar way in all the groups, intra-nucleus accumbens (NAc) administration induced significantly higher locomotor stimulation in the sensitized group alone. Our data show that functionally hyperresponsive D2 receptors are present in the NAcs of sensitized but not non-sensitized mice, suggesting that this could be a biomarker of behavioral sensitization. Furthermore, i.p. administration of sulpiride blocked the expression of sensitization in the sensitized group, and intra-NAc administration attenuated it, indicating that the activation of accumbal D2 receptors is essential for the expression of EtOH behavioral sensitization. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Acute neuroactive drug exposures alter locomotor activity in larval zebrafish

As part of the development of a rapid in vivo screen for prioritization of toxic chemicals, we have begun to characterize the locomotor activity of zebrafish (Danio rerio) larvae by assessing the acute effects of prototypic drugs that act on the central nervous system. Initially, we chose ethanol, d-amphetamine, and cocaine, which are known, in mammals, to increase locomotion at low doses and decrease locomotion at higher doses. Wild-type larvae were individually maintained in 96-well microtiter plates at 26 degrees C, under a 14:10 h light:dark cycle, with lights on at 0830 h. At 6 days post-fertilization, ethanol (1-4% v/v), d-amphetamine sulfate (0.1-20.0 microM) or cocaine hydrochloride (0.2-50.0 microM) were administered to the larvae by immersion. Beginning 20 min into the exposure, locomotion was assessed for each animal for 70 min using 10-minute, alternating light (visible light) and dark (infrared light) periods. Low concentrations of ethanol and d-amphetamine increased activity, while higher concentrations of all three drugs decreased activity. Because ethanol effects occurred predominately during the light periods, whereas the d-amphetamine and cocaine effects occurred during the dark periods, alternating lighting conditions proved to be advantageous. These results indicate that zebrafish larvae are sensitive to neuroactive drugs, and their locomotor response is similar to that of mammals.

Morphine attenuates the expression of sensitization to ethanol, but opioid antagonists do not

Behavioral sensitization to ethanol is characterized by an increased locomotor activity after repeated exposure. A great variability exists among species and strains in the development of sensitization. There is a growing amount of evidence to indicate that the opioid system is involved in alcoholism; it is possible, therefore, that this system also modulates the sensitization to ethanol. In this study we evaluated the role of the opioid system in determining the variability of the sensitized response to ethanol. Mice received repeated administrations of ethanol (2.2 g/kg) or saline every other day for 10 days. According to their locomotor response on the last day of treatment, ethanol-treated animals were classified into two groups: sensitized or non-sensitized mice. After the treatment, mice were submitted to four challenges 48 h apart. In experiments 1 and 2, mice were challenged, respectively, with i.p. administration of opioid antagonists (naloxone or naltrexone) or an opioid agonist (morphine), followed immediately by 2.2 g/kg ethanol. In experiment 3, animals received morphine by i.c.v., followed by 2.2 g/kg of ethanol (i.p.). Pretreatment with opioid antagonists (naloxone or naltrexone) did not block the expression of ethanol sensitization; however pretreatment with morphine attenuated the increased locomotor activity after ethanol administration in sensitized mice. In experiment 4, after the ethanol or saline treatment, mice brains were processed and brain mu opioid binding was assessed by autoradiography using [3H]D-Ala2,N-mePhe4, Gly-ol5-enkephalin ([3H]DAMGO). No differences were seen between any of the groups of mice, so the agonist effect is not likely to be mediated by differences in binding to mu opioid receptors.

Locomotor effects of ethanol and acetaldehyde after peripheral and intraventricular injections in Swiss and C57BL/6J mice

Several studies have suggested that acetaldehyde, the first product of ethanol metabolism, is involved in the locomotor stimulant effects of ethanol in mice, although it has never been formally tested whether acetaldehyde injected directly into the brain of mice has stimulant properties. Recently, it was also shown in rats that both ethanol and acetaldehyde can induce opposite locomotor effects according to the route of administration. Whereas peripheral administrations of ethanol and acetaldehyde induced locomotor depressant effects, their infusions directly into the brain produced locomotor stimulation. The aim of the present study was to characterize in mice the locomotor effects of ethanol and acetaldehyde injected either peripherally by the intraperitoneal route or centrally into the brain ventricles. Additionally, the effects of ethanol and acetaldehyde were compared in two strains of mice known for their differential sensitivity to the locomotor effects of ethanol, namely Swiss and C57BL/6J mice. Ethanol induced a biphasic effect on locomotor activity in Swiss mice, with stimulant effects at low to moderate doses and depressant effects at higher doses. Such a profile of effects was observed whatever the route of administration, peripheral or central. In C57BL/6J mice, ethanol only induced monophasic depressant effects. In this mouse strain, no evidence of the stimulant effects of ethanol was found after either an i.p. or an i.c.v. administration of ethanol. In contrast to ethanol, acetaldehyde yielded only depressant effects in both strains of mice after both peripheral and central administrations. These results indicate that the route of administration does not alter the locomotor effects of ethanol and acetaldehyde in mice. Additionally, the present study shows that the stimulant properties of acetaldehyde, even after direct infusion into the brain, are not as obvious as previously speculated.

Behavioral analysis of male rat sexual motivation and performance following acute ethanol treatment

To characterize the effects of acute ethanol treatment on sexual motivation and performance, 30 male Long-Evans rats were assigned to one of three treatment conditions: saline (n=9), 0.25 g/kg ethanol (n=10), or 1.0 g/kg ethanol (n=11). Males were injected intraperitoneally 30 min before behavioral testing. Male rats were placed in a multilevel testing chamber 5 min prior to the introduction of a receptive female rat and level changes were recorded as an index of sexual motivation. After the female rat was placed in the chamber, standard measures of sexual performance were recorded over three weekly tests. Results indicated that the highest dose of ethanol (1.0 g/kg) increased male rat level-changing behavior compared to the saline group. Although ethanol treatment failed to affect most measures of sexual performance, males administered 1.0 g/kg ethanol had fewer anogenital investigations and had longer postejaculatory intervals (PEIs) compared to control animals. The data from this experiment suggest that ethanol increases rodent sexual motivation but impairs specific parameters of sexual performance.

Differential propensity to ethanol sensitization is not associated with altered binding to D1 receptors or dopamine transporters in mouse brain

Behavioral sensitization to ethanol's stimulant effect has been proposed as a marker for individual abuse liability. In previous work we have demonstrated that mice showing an increased propensity to EtOH sensitization had higher levels of dopamine (DA) D2 receptor binding in localized brain areas compared to mice showing less sensitization. In the present study we examined whether altered binding to D1 or the DA transporter (DAT) might also be associated with differential propensity to develop EtOH sensitization. Male Swiss mice received 2.4 g/kg EtOH or saline intraperitoneally (i.p.) daily for 21 days, were tested weekly for locomotor activity, and then sacrificed. D1 and DAT binding were assessed by quantitative autoradiography using [(3)H]SCH-23390 and [(3)H]WIN 35,428, respectively. EtOH-treated mice were subdivided into sensitized and non-sensitized subgroups according to their locomotor activity during treatment. Analyses of brain D1 (19 regions) and DAT (12 regions) binding densities revealed no significant differences among EtOH-sensitized, -non-sensitized or saline groups in any of the regions measured (all p values > 0.32 for D1 and > 0.16 for DAT). These results suggest that brain D1 and DAT binding, unlike the recently reported changes in D2 binding, do not differentiate mice that develop behavioral sensitization to ethanol from those that do not.

Resistance to ethanol sensitization is associated with increased NMDA receptor binding in specific brain areas

Co-administration of N-methyl-D-aspartate (NMDA) receptor antagonists is known to block the development of behavioral sensitization to ethanol and other psychostimulants. Since ethanol sensitization in mice does not occur uniformly in all treated animals, the present study examined the possibility that NMDA receptor binding would be selectively altered in mice susceptible to ethanol sensitization. Mice received 2.4 g/kg ethanol or saline i.p. daily for 21 days and were sacrificed 24 h later. No differences in [3H]dizocilpine ([3H](+)MK-801) binding were found between sensitized and vehicle-treated mice in any of the brain regions analyzed. However, ethanol-treated mice that did not develop sensitization showed significantly higher binding in the nucleus accumbens core (+32% and +40% compared to controls and ethanol-sensitized mice, respectively; P<0.04) and the prefrontal cortex (+15% and +22%; P<0.02). In a separate experiment, sensitization resistant mice challenged with 0.25 mg/kg (+)MK 801 showed significantly less motor activation than saline-treated or ethanol-sensitized mice. These results point to a clear association between elevated NMDA receptor binding in specific brain regions and resistance to ethanol sensitization.

Combined effects of diethylpropion and alcohol on locomotor activity of mice: participation of the dopaminergic and opioid systems

The widespread consumption of anorectics and combined anorectic + alcohol misuse are problems in Brazil. In order to better understand the interactive effects of ethanol (EtOH) and diethylpropion (DEP) we examined the locomotion-activating effects of these drugs given alone or in combination in mice. We also determined whether this response was affected by dopamine (DA) or opioid receptor antagonists. A total of 160 male Swiss mice weighing approximately 30 g were divided into groups of 8 animals per group. The animals were treated daily for 7 consecutive days with combined EtOH + DEP (1.2 g/kg and 5.0 mg/kg, ip), EtOH (1.2 g/kg, ip), DEP (5.0 mg/kg, ip) or the control solution coadministered with the DA antagonist haloperidol (HAL, 0.075 mg/kg, ip), the opioid antagonist naloxone (NAL, 1.0 mg/kg, ip), or vehicle. On days 1, 7 and 10 after the injections, mice were assessed in activity cages at different times (15, 30, 45 and 60 min) for 5 min. The acute combination of EtOH plus DEP induced a significantly higher increase in locomotor activity (day 1: 369.5 +/- 34.41) when compared to either drug alone (day 1: EtOH = 232.5 +/- 23.79 and DEP = 276.0 +/- 12.85) and to control solution (day 1: 153.12 +/- 7.64). However, the repeated administration of EtOH (day 7: 314.63 +/- 26.79 and day 10: 257.62 +/- 29.91) or DEP (day 7: 309.5 +/- 31.65 and day 10: 321.12 +/- 39. 24) alone or in combination (day 7: 459.75 +/- 41.28 and day 10: 427. 87 +/- 33.0) failed to induce a progressive increase in the locomotor response. These data demonstrate greater locomotion-activating effects of the EtOH + DEP combination, probably involving DA and/or opioid receptor stimulation, since the daily pretreatment with HAL (day 1: EtOH + DEP = 395.62 +/- 11.92 and EtOH + DEP + HAL = 371.5 +/- 6.76; day 7: EtOH + DEP = 502.5 +/- 42.27 and EtOH + DEP + HAL = 281.12 +/- 16.08; day 10: EtOH + DEP = 445.75 +/- 16.64 and EtOH + DEP + HAL = 376.75 +/- 16.4) and NAL (day 1: EtOH + DEP = 553.62 +/- 38.15 and EtOH + DEP + NAL = 445.12 +/- 55.67; day 7: EtOH + DEP = 617.5 +/- 38.89 and EtOH + DEP + NAL = 418.25 +/- 61.18; day 10: EtOH + DEP = 541.37 +/- 32.86 and EtOH + DEP + NAL = 427.12 +/- 51.6) reduced the locomotor response induced by combined administration of EtOH + DEP. These findings also suggest that a major determinant of combined anorectic-alcohol misuse may be the increased stimulating effects produced by the combination.

Influence of novel and habituated testing conditions on cocaine sensitization

Female Swiss-Webster mice were treated daily for 10 days with cocaine (15 mg/kg i.p.) followed by 10 days with saline or ethanol (1.6 g/kg i.p.) or the reverse; following each injection in the experimental conditions locomotion was quantified in photocell cages. In animals given cocaine first, cocaine-induced locomotion was initially high and did not increase further with successive injections. In animals given prior saline or ethanol treatments, cocaine-induced locomotion was initially low but increased with successive cocaine treatments. There was no evidence of sensitization to the locomotor-stimulating effects of ethanol or of cross-sensitization between ethanol and cocaine. With respect to subsequent cocaine sensitization, the essential feature of prior saline or ethanol treatment appeared to be the handling and injection experience itself; a control group receiving prior saline injection in the home cage also showed a low level of cocaine-induced locomotion on the first day of cocaine testing but increasing locomotion with repeated cocaine testing. Thus, cocaine sensitization, rather than a progressive augmentation of motor function, may reflect a progressive reversal of the behavioral suppression caused by habituation to aspects of the testing situation or to some form of situational anxiety that precludes normal exploratory responses.

Genetic differences in tolerance and sensitization to the sedative/hypnotic effects of alcohol

Initial sensitivity to alcohol and the development of alcohol tolerance were examined in rats of the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines. All rats received two alcohol injections (3.0 g/kg b.wt., IP) separated by either 1 or 2 days. P rats were less sensitive to the behaviorally impairing effects of alcohol than were NP rats, as evidenced by a longer latency to lose righting reflex (RR) and a shorter time to recover RR following an initial alcohol injection. When 1 day separated the two alcohol injections, P rats recovered the RR more rapidly following a second injection compared to the first, indicating that the P rats developed tolerance to the sedative/hypnotic effects of alcohol. In contrast, the NP rats recovered the RR more slowly following the second injection compared to the first, indicating that the NP rats developed sensitization to alcohol. Tolerance in the P line and sensitization in the NP line disappeared when 2 days separated the two alcohol injections. Line differences in initial sensitivity and tolerance/sensitization to the behaviorally impairing effects of alcohol may contribute to the differences in alcohol consumption observed in the P and NP lines.

Conditioned activation induced by ethanol: role in sensitization and conditioned place preference

Previous studies of ethanol-induced activation and place preference conditioning have shown that repeated exposure to ethanol produces sensitization to ethanol's locomotor activating effect in mice. This experiment was designed to determine whether the behavioral sensitization to ethanol that occurs during place preference conditioning is due to development of a Pavlovian conditioned activity response. Mice (DBA/2J) in the experimental group (BEFORE) received four pairings of a distinctive floor stimulus with ethanol (2 g/kg, IP); a different floor stimulus was paired with saline (counterbalanced). Mice in two control groups were exposed equally to each floor stimulus and were handled and injected as often as experimental mice. One control group (AFTER) always received ethanol in the home cage 1 h after exposure to the floor stimulus, while the other control group (NO-DRUG) never received ethanol during conditioning. BEFORE group mice showed a significant conditioned place preference, whereas control mice did not. Activity tests after saline or ethanol indicated higher activity levels in BEFORE mice compared to control mice, regardless of floor stimulus. Moreover, BEFORE mice were more active on their CS+ floor than on their CS- floor during saline tests; activity was equally elevated on both floors during ethanol tests. These results support the hypothesis that sensitization to ethanol's activating effect is mediated by Pavlovian conditioning. Further, they suggest that place conditioning established-associative control by two kinds of stimuli; the specific tactile cues serving as CS+ and CS- and the general environmental cues common to both CS+ and CS- trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the hypothermic response to ethanol in rats selectively bred for oral ethanol preference and nonpreference

The duration of retention of tolerance to ethanol was tested in the alcohol-preferring (P) and alcohol-nonpreferring (NP) rats lines, using ethanol-induced hypothermia as a measure of tolerance. Rats received two injections of ethanol (3.5 g/kg) body wt, IP) and the time between the injections was 1, 2, or 3 days. When one day separated the two injections, tolerance to the hypothermic effect of a second "test" injection was found in both lines. When 2 or 3 days separated the two injections, the P line showed a loss of tolerance and the NP line showed sensitization to ethanol. Sensitization in the NP line grew stronger when the interval between injections was increased from 2 to 3 days. The duration of retention of tolerance to ethanol-induced hypothermia in the P line was shorter than has previously been reported for motor impairment in this line. It appears that the duration of tolerance retention in the P line depends on the test used to measure tolerance. Sensitization to ethanol in the NP line may be associated with low oral ethanol intake.

Amygdaloid kindling and kindled seizures in rats receiving chronic ethanol administration

The effects of chronic ethanol administration were studied in rats receiving amygdaloid kindling. Daily ethanol administration 10 min prior to kindling stimulation delayed acquisition of kindling without affecting the electrical afterdischarge. For the lowest tested dose of ethanol (0.5 g/kg), this delay was restricted to kindling stages 1 and 2. For the higher doses of ethanol (1.0 and 1.5 g/kg) this delay became more severe and stages 3 and 4 were blocked. Ethanol produced a clear dose-related anticonvulsant effect upon kindled seizures. After repeated exposure to kindling stimulation and ethanol this anticonvulsant effect vanished. After a 15-day interval without stimulation or ethanol application kindled animals were insensitive to ethanol's anticonvulsant effect. In conclusion, it is suggested that the anticonvulsant effects of low ethanol doses are restricted to kindling stages 1 and 2 and that anticonvulsant effects of high ethanol doses are limited by tolerance and by the level of consolidation of the kindled seizure. Finally, we suggest that the anticonvulsant properties of ethanol are not due to its general depressant effect but to some rather specific action.

Effects of ethanol on reinforced variations and repetitions by rats under a multiple schedule

Response sequences emitted by five Long-Evans rats were reinforced under a two-component multiple schedule. In the REPEAT component, food pellets were contingent upon completion of a left-left-right-right (LLRR) sequence on two levers. In the VARY component, pellets were contingent upon variable sequences (i.e., a sequence was reinforced only if it differed from each of the previous five sequences). The rats learned to emit LLRR sequences in the REPEAT component and variable sequences in VARY. Intraperitoneal injections of ethanol (1.25, 1.75, and 2.25 g/kg) significantly increased sequence variability in REPEAT, thereby lowering reinforcement probability, but had little effect on sequence variability in the VARY component. These results extend previous findings that alcohol impairs the performance of reinforced repetitions but not of reinforced variations in response sequences.

Increased stimulatory effect by the combined administration of cocaine and alcohol in mice

Locomotor activity was recorded after 5-30 mg/kg of cocaine in mice pretreated or not with a stimulant dose of ethanol (2.0 g/kg). The increase in locomotion induced by the association of cocaine plus ethanol was significantly larger when compared to either the group injected with only cocaine or only ethanol.

Ethanol-induced locomotor stimulation in C57BL/6 mice following RO15-4513 administration

The purpose of this study was to examine the effects of two partial benzodiazepine inverse agonists, RO15-4513 and FG-7142, alone and in combination with ethanol on locomotor activity in C57BL/6 mice. When administered alone, 1.5 g/kg ethanol did not significantly influence activity, confirming previous reports indicating this mouse strain is relatively insensitive to the excitatory properties of ethanol. RO15-4513 treatment also did not significantly influence locomotor activity when administered alone. However, coadministration of RO15-4513 (1.5-6 mg/kg) and ethanol markedly increased locomotor activity. Moreover, the unmasking of ethanol's stimulant action by RO15-4513 (6 mg/kg) was completely reversed by pretreatment with the benzodiazepine receptor antagonist RO15-1788. In contrast, FG-7142 (10-20 mg/kg) increased activity to the same extent in both saline and ethanol-injected mice. This effect was blocked by RO15-1788 pretreatment as well. Neither RO15-4513, FG-7142, nor RO15-1788 significantly influenced blood ethanol concentrations. It is suggested that RO15-4513 unmasked the stimulant effects of ethanol by virtue of its ability to antagonize the depressant properties of ethanol in C57BL/6 mice.