[Alcohol consumption during the COVID-19 pandemic among French-speaking Belgian students : uncertainty and psychological distress]. / Face à la COVID-19. Consommation d'alcool pendant la pandémie de COVID-19 chez les étudiants belges francophones : incertitude et détresse psychologique.

The COVID-19 pandemic has had a deleterious impact on students. Studies showed an increase in anxiety-depressive symptoms and changes in certain health behaviours (smoking, drugs, etc.). The aim of the present study is to measure whether students' alcohol consumption changed during the third confinement (frequency and quantity) in relation to the factor of intolerance to uncertainty. The study was conducted on a sample of 273 French-speaking Belgian students (Universities and High Schools). The students answered questionnaires measuring their psycho-emotional state, alcohol consumption and intolerance of uncertainty and its mechanisms. Results showed that 65 % of the students had anxiety symptoms. Alcohol consumption remained moderate, with 85 % having not changed the frequency of consumption and 89 % their quantity of alcohol. Finally, the results indicated that the increase in alcohol consumption was essentially linked to positive expectations about the effects of alcohol, but not to measures of anxiety or intolerance of uncertainty. The study highlights the need for national prevention strategies to detect psychological distress in post-pandemic students.

La pandémie de COVID-19 a eu un impact délétère sur les étudiants. Les études montrent une augmentation de symptômes anxio-dépressifs et la modification de certains comportements de santé (tabac, drogue, etc.). L'objectif de la présente étude est de mesurer si la consommation d'alcool des étudiants a changé durant le troisième confinement (fréquence et quantité) en lien avec le facteur d'intolérance à l'incertitude. L'étude a été menée sur un échantillon de 273 étudiants belges francophones (Universités et Hautes Ecoles). Les étudiants ont répondu à des questionnaires mesurant leur état psycho-émotionnel, la consommation d'alcool et l'intolérance à l'incertitude et ses mécanismes. Les résultats montrent que 65 % des étudiants ont des symptômes anxieux. La consommation d'alcool reste modérée avec 85 % n'ayant pas modifié la fréquence de consommation et 89 % leur quantité d'alcool. Enfin, les résultats indiquent que l'augmentation de la consommation d'alcool était essentiellement liée aux attentes d'effets positifs de l'alcool, mais pas en lien avec les mesures d'anxiété ou d'intolérance à l'incertitude. L'étude met en évidence l'importance de mettre en place des stratégies nationales de prévention pour détecter la détresse psychologique des étudiants post-pandémie.

Using 360-degree immersive videos to assess multiple transdiagnostic symptoms: A study focusing on fear of negative evaluation, paranoid thoughts, negative automatic thoughts, and craving.

Over the last 20 years, virtual reality (VR) has gained a great interest for both assessment and treatment of various psychopathologies. However, due to high costs and material specificity, VR remains disadvantageous for clinicians. Adopting a multiple transdiagnostic approach, this study aims at testing the validity of a 360-degree immersive video (360IV) for the assessment of five common psychological symptoms (fear of negative evaluation, paranoid thoughts, negative automatic thoughts, craving for alcohol and for nicotine). A 360IV was constructed in the Darius Café and included actors behaving naturally. One hundred and fifty-eight adults from the general population were assessed in terms of their proneness towards the five symptoms, were then exposed to the 360IV and completed measures for the five state symptoms, four dimensions of presence (place, plausibility, copresence and social presence illusions) and cybersickness. Results revealed that the five symptoms occurred during the immersion and were predicted by the participants' proneness towards these symptoms. The 360IV was also able to elicit various levels of the four dimensions of presence while producing few cybersickness. The present study provides evidence supporting the use of the 360IV as a new accessible, ecological, and standardized tool to assess multiple transdiagnostic symptoms. Supplementary Information: The online version contains supplementary material available at 10.1007/s10055-023-00779-y.

Voluntary alcohol binge-drinking in adolescent C57Bl6 mice induces delayed appearance of behavioural defects in both males and females.

Adolescence is a developmental period characterized by significant changes in brain architecture and behaviour. The immaturity of the adolescent brain is associated with heightened vulnerability to exogenous agents, including alcohol. Alcohol is the most consumed drug among teenagers, and binge-drinking during adolescence is a major public health concern. Studies have suggested that adolescent alcohol exposure may interfere with the maturation of frontal brain regions and lead to long-lasting behavioural consequences. In this study, by using a slightly modified version of the Drinking in the Dark paradigm, adolescent C57Bl6 mice reach high blood alcohol concentration after voluntary binge-drinking. In order to assess short- and long-term consequences of adolescent alcohol exposure (AAE), a battery of behavioural tests was performed during late adolescence and during adulthood. We showed that AAE had no short-term effect on young mice behaviour but rather increased anxiety- and depressive-like behaviours, as well as alcohol consumption during adulthood. Moreover, alcohol binge-drinking during adolescence dramatically decreased recognition memory performances and behavioural flexibility in both adult males and females. Furthermore, we showed that voluntary consumption of alcohol during adolescence did not trigger any major activation of the innate immune system in the prefrontal cortex. Together, our data suggest that voluntary alcohol binge-drinking in adolescent mice induces a delayed appearance of behavioural impairments in adulthood.

Using 360° immersive videos to assess paranoia in a non-clinical population.

Introduction: For the past two decades, virtual reality (VR) has proven to be an innovative approach for the assessment of state paranoia. However, the use of VR remains costly, and avatars are still far from realistic in terms of facial and bodily expressions. The present study aimed to test the validity of three 360° immersive videos (360IVs) as an accessible and realistic alternative for the assessment of non-clinical state paranoia.Method: Three 360IVs were created (a Lift, a Library and a Bar) and included actors behaving naturally. One hundred and fifty healthy students were assessed in terms of their proneness towards trait paranoia, were then exposed to one of the three 360IVs, and finally completed measures of state paranoia, sense of presence and cybersickness.Results: Results revealed the presence of various interpretations about the actor's attitudes in the three 360IVs. Also, paranoid thoughts were predicted by proneness towards trait paranoia in two out of the three 360IVs. Furthermore, moderate levels of sense of presence and low levels of cybersickness were observed for each 360IV.Conclusion: The present study provides evidence in favour of the use of 360IVs as a new accessible, realistic, and standardised tool to assess state paranoia in non-clinical samples.

Relative stability of alexithymia and openness to emotions in one psychiatric day hospital setting.

Alexithymia (literally, difficulty finding words for emotions) and openness to emotions (OE: referring to the cognitive representation, communication, regulation, perception of internal and external bodily sensations, and social restriction of emotions) are strongly linked to psychopathology. The absolute and relative stability hypotheses were tested in order to determine whether significant changes occurred on these constructs after therapy, a condition where changes were expected for both constructs. Negative attitudes toward treatment (NTI) and perceived social support (PSS) were expected to significantly predict alexithymia and OE. Patients (N = 179) who participated in this longitudinal study filled in the Toronto Alexithymia Scale, the Dimensions of Openness to Emotions Scale, the NTI subscale, the Multidimensional Scale of Perceived Social Support, and the Social Desirability Scale. After treatment, we observed significant decrease of all alexithymia scores and significant increases of three OE scores, that is, cognitive representation, communication, and regulation of emotions. Regression analyses revealed that gender, age, NTI, and PSS were significant predictors of alexithymia and OE. NTI strongly predicted lower OE levels and higher alexithymia levels, whereas PSS had opposite predicting effects on these constructs. In conclusion, the significant changes, and the moderate to high correlational levels observed between before and after alexithymia and OE scores, strengthen the relative stability hypothesis for both constructs. In addition, PSS represents a protective factor and NTI a vulnerability indicator for therapists. Our aim is to optimize treatment by providing therapists treating emotion difficulties a more concrete array of variables that potentially either promote or subvert recovery.

Accurate Control of 17ß-Estradiol Long-Term Release Increases Reliability and Reproducibility of Preclinical Animal Studies.

Estrogens are the subject of intensive researches aiming to elucidate their mechanism of action on the various tissues they target and especially on mammary gland and breast cancer. The use of ready-to-use slow releasing devices to administer steroids, especially estrogens, to small experimental animals remains the method of choice in terms of animal well-being and of safety for both the researcher and the animal. In this study, we evaluated and compared, in vitro and in vivo, the release kinetic of estradiol (E2) over sixty days from two different slow-releasing systems: the matrix pellet (MP) and the reservoir implant (RI). We compared the impact of these systems in three E2-sensitive mouse models : mammary gland development, human MCF7 adenocarcinoma xenograft and mouse melanoma progression. The real amount of E2 that is released from both types of devices could differ from manufacturer specifications due to inadequate release for MP and initial burst effect for RI. Compared to MP, the interindividual variability was reduced with RI thanks to a superior control of the E2 release. Depending on the dose-dependent sensitivity of the physiological or pathological readout studied, this could lead to an improvement of the statistical power of in vivo experiments and thus to a reduction of the required animal number. Altogether, our data draw attention on the importance to adequately select the slow-releasing device that is the most appropriated to a specific experiment to better fulfill the 3Rs rule (Replacement, Reduction, Refinement) related to animal welfare and protection.

Differential effects of context on psychomotor sensitization to ethanol and cocaine.

Repeated drug injections lead to sensitization of their stimulant effects in mice, a phenomenon sometimes referred to as drug psychomotor sensitization. Previous studies showed that sensitization to cocaine is context dependent as its expression is reduced in an environment that was not paired with cocaine administration. In contrast, the effects of the test context on ethanol sensitization remain unclear. In the present study, female OF1 mice were repeatedly injected with 1.5 g/kg ethanol to test for both the effects of context novelty/familiarity and association on ethanol sensitization. A first group of mice was extensively pre-exposed to the test context before ethanol sensitization and ethanol injections were paired with the test context (familiar and paired group). A second group was not pre-exposed to the test context, but ethanol injections were paired with the test context (nonfamiliar and paired group). Finally, a third group of mice was not pre-exposed to the test context and ethanol was repeatedly injected in the home cage (unpaired group). Control groups were similarly exposed to the test context, but were injected with saline. In a second experiment, cocaine was used as a positive control. The same behavioral procedure was used, except that mice were injected with 10 mg/kg cocaine instead of ethanol. The results show a differential involvement of the test context in the sensitization to ethanol and cocaine. Cocaine sensitization is strongly context dependent and is not expressed in the unpaired group. In contrast, the expression of ethanol sensitization is independent of the context in which it was administered, but is strongly affected by the relative novelty/familiarity of the environment. Extensive pre-exposure to the test context prevented the expression of ethanol sensitization. One possible explanation is that expression of ethanol sensitization requires an arousing environment.

Correlation between ethanol behavioral sensitization and midbrain dopamine neuron reactivity to ethanol.

Repeated ethanol injections lead to a sensitization of its stimulant effects in mice. Some recent results argue against a role for ventral tegmental area (VTA) dopamine neurons in ethanol behavioral sensitization. The aim of the present study was to test whether in vivo ethanol locomotor sensitization correlates with changes in either basal- or ethanol-evoked firing rates of dopamine neurons in vitro. Female Swiss mice were daily injected with 2.5 g/kg ethanol (or saline in the control group) for 7 days and their locomotor activity was recorded. At the end of the sensitization procedure, extracellular recordings were made from dopaminergic neurons in midbrain slices from these mice. Significantly higher spontaneous basal firing rates of dopamine neurons were recorded in ethanol-sensitized mice relative to control mice, but without correlations with the behavioral effects. The superfusion of sulpiride, a dopamine D2 antagonist, induced a stronger increase of dopamine neuron firing rates in ethanol-sensitized mice. This shows that the D2 feedback in dopamine neurons is preserved after chronic ethanol administration and argues against a reduced D2 feedback as an explanation for the increased dopamine neuron basal firing rates in ethanol-sensitized mice. Finally, ethanol superfusion (10-100 mM) significantly increased the firing rates of dopamine neurons and this effect was of higher magnitude in ethanol-sensitized mice. Furthermore, there were significant correlations between such a sensitization of dopamine neuron activity and ethanol behavioral sensitization. These results support the hypothesis that changes in brain dopamine neuron activity contribute to the behavioral sensitization of the stimulant effects of ethanol.

Validation of the Marijuana Effect Expectancies Questionnaire (MEEQ) in a Non-Clinical French-Speaking Adolescent Sample.

Teenagers commonly use cannabis. Expectancies related to the effects of cannabis play an important role in its consumption and are frequently measured with the Marijuana Effect Expectancies Questionnaire (MEEQ). This study aims to assess the psychometric properties (factor structure, internal consistency reliability, criterion validity) of the French MEEQ. A sample of 1,343 non-clinical teenagers (14-18 years) were recruited to answer a self-report questionnaire; 877 of them responded twice (one-year interval). A four-factor structure was obtained: Cognitive Impairment and Negative, Relaxation and Social Facilitation, Perceptual Enhancement and Craving and Negative Behavioral Effect Expectancies. It is concluded that the French MEEQ constitutes an appropriate tool to measure cannabis effect expectancies among adolescents.

Brain Activation Associated with Automatic Processing of Alcohol-Related Cues in Young Heavy Drinkers and Its Modulation by Alcohol Administration.

BACKGROUND: While the automatic processing of alcohol-related cues by alcohol abusers is well established in experimental psychopathology approaches, the cerebral regions involved in this phenomenon and the influence of alcohol intake on this process remain unknown. The aim of this functional magnetic resonance imaging (fMRI) study was to investigate the neural mechanisms underlying the processing of task-irrelevant alcohol-related stimuli in young heavy drinkers and their modulation by alcohol administration. METHODS: Twelve heavy drinking male participants were scanned on 2 separate days; once after a low dose of alcohol intake (0.4 g/kg), and once after a placebo intake, in balanced order. Images of alcoholic drinks, soft drinks, or neutral objects were shown while participants' neural activity was recorded through fMRI. Moreover, participants' attentional focus was manipulated using a task which required them to process the central images of interest (focus alcohol condition) or a center unattended task (focus not on alcohol condition). RESULTS: Results indicated that an explicit judgment on beverage-related cues increased activation in the prefrontal area compared with the judgment of neutral objects. By comparison with that of task-irrelevant neutral cues, the processing of task-irrelevant alcohol-related cues increased the activation in a large network of cerebral areas including visual and temporal regions, the bilateral anterior cingulate cortex, the posterior cingulate cortex, and the putamen. Moreover, in the condition with focus not on alcohol, the ventral tegmental area (VTA) was particularly activated by the presentation of (task-irrelevant) alcohol-related cues compared to task-irrelevant soft-drink-related cues. CONCLUSIONS: The VTA was especially involved in the automatic processing of alcohol-related cues in young heavy drinkers. Low dose of alcohol did not modulate the neural substrates involved in the processing of salient alcohol-related cues.

Efficacy of Heroin-assisted Treatment In Belgium: A Randomised Controlled Trial.

BACKGROUND/AIMS: Heroin-assisted treatment (HAT) can improve the condition of heroin addicts still using street heroin after a methadone treatment. In Belgium, a new trial compared the efficacy of a HAT to existing methadone maintenance treatment. METHODS: In this randomised controlled trial, HAT was limited to 12 months. Participants were assessed every 3 months. They were responders if they showed improvement on the level of street heroin use, health or criminal involvement. RESULTS: 74 participants were randomised in the trial. The experimental group (n = 36) counted 30% of responders more than the control group (n = 38) at each assessment point (p < 0.05), except at 12 months where the difference (11%) was no longer significant (p = 0.35). Still, after 12 months, participants in the experimental group reported significantly greater improvements (p < 0.05) than the control group on the level of street heroin use and on the level of physical and mental health. Both groups reported significantly less criminal acts after 12 months (p < 0.001), but with no significant difference between the groups. CONCLUSIONS: This trial confirms the short-term efficacy of HAT for severe heroin addicts, who already failed methadone treatment.

A longitudinal study of cannabis use initiation among high school students: Effects of social anxiety, expectancies, peers and alcohol.

This study identified protective and risk factors of cannabis use initiation, including expectancies and social anxiety. A questionnaire was completed twice by 877 teenagers. Logistic regressions, mediation and moderation analyses were performed. Significant risk factors were alcohol use, peer users, perceptual enhancement, and craving expectancies. Protective factors were negative behavior expectancies and social anxiety. Social anxiety protected from initiation through the mediating role of perceptual enhancement and craving expectancies, whatever the role of peer users and alcohol use. Findings are discussed in terms of risk and protection, in an overall approach including internalizing factors. Results support the identification of an internalizing profile of adolescents for prevention or treatment and the importance of social anxiety and expectancies in intervention.

Impact of a pre-test measurement of alcohol craving in cue-exposure studies: Relationship with social desirability and demand effects.

Craving is one of the most studied concepts in the field of addiction. It is often investigated with repeated-measure experimental designs using self-reported scales. However, the explicit nature of self-reported craving scales may make them vulnerable to social desirability and demand effects. The aim of the present study was to test whether a pre-experimental measurement of craving affects its post-experimental assessment after an alcohol video exposure and whether these changes relate to social desirability, demand effects, and alcohol consumption. Seventy-five healthy volunteers aged 18-30 years were randomly assigned to two experimental groups: a pre-post and a post-only craving assessment group. They were invited to watch an alcohol-related video. Social desirability, demand effects, engagement toward the video, and severity of alcohol consumption were assessed in all participants. The results showed a significant effect of alcohol consumption (p < .001, η2p = .09) on post-experimental craving. The main effect of the repeated measure of craving was also significant (p = .04, η2p = .001), together with the interaction between these two variables (p = .03, η2p = .06). The pre-experimental craving measurement increased its post-experimental levels, but only in heavy drinkers. However, no evidence was found that these changes were related to social desirability or demand effects. Additional exploratory analyses indicated that craving increase in high alcohol drinkers was mediated by a stronger engagement toward the alcohol-related video. In summary, the repeated measurement of craving with explicit scales has a significant impact on the results of alcohol craving studies and may not always be desirable, especially when the true purpose of the study needs to be hidden from the participants. However, the present results also suggest that the pre-post experimental design is advisable when the experimenters seek to maximize the relationship between the individual levels of alcohol consumption and alcohol cue-exposure craving changes.

Effects of social housing conditions on ethanol-induced behavioral sensitization in Swiss mice.

RATIONALE: In previous animal model studies, it was shown that drug sensitization is dependent upon physical environmental conditions. However, the effects of social housing conditions on drug sensitization is much less known. OBJECTIVE: The aim of the present study was to investigate the effects of social conditions, through the size of housing groups, on ethanol stimulant effects and ethanol-induced behavioral sensitization in mice. MATERIALS AND METHODS: Male and female Swiss mice were housed in groups of different sizes (isolated mice, two mice per cage, four mice per cage and eight mice per cage) during a six-week period. A standard paradigm of ethanol-induced locomotor sensitization was then started with one daily injection of 2.5 g/kg ethanol for 8 consecutive days. RESULTS: The results show that social housing conditions affect the acute stimulant effects of ethanol. The highest stimulant effects were observed in socially isolated mice and then gradually decreased as the size of the group increased. Although the rate of ethanol sensitization did not differ between groups, the ultimate sensitized levels of ethanol-induced stimulant effects were significantly reduced in mice housed in groups of eight. CONCLUSIONS: These results are consistent with the idea that higher levels of acute and sensitized ethanol stimulant effects are observed in mice housed in stressful housing conditions, such as social isolation.

Age-related differences in perceptuomotor procedural learning in children.

Procedural learning is generally considered to proceed in a series of phases, with cognitive resources playing an important role during the initial step. From a developmental perspective, little is known about the development of procedural learning or the role played by explicit cognitive processes during learning. The main objectives of this study were (a) to determine whether procedural learning performance improves with age by comparing groups of 7-year-old children, 10-year-old children, and adults and (b) to investigate the role played by executive functions during the acquisition in these three age groups. The 76 participants were assessed on a computerized adaptation of the mirror tracing paradigm. Results revealed that the youngest children had more difficulty in adapting to the task (they were slower and committed more errors at the beginning of the learning process) than 10-year-olds, but despite this age effect observed at the outset, all children improved performance across trials and transferred their skill to a different figure as well as adults. Correlational analyses showed that inhibition abilities play a key role in the performance of 10-year-olds and adults at the beginning of the learning but not in that of 7-year-olds. Overall, our results suggest that the age-related differences observed in our procedural learning task are at least partly due to the differential involvement of inhibition abilities, which may facilitate learning (so long as they are sufficiently developed) during the initial steps of the learning process; however, they would not be a necessary condition for skill learning to occur.

Social context in school: its relation to adolescents' depressive mood.

This study examined the impact of various school-related factors on adolescents' depressive mood, including prosocial behavior, verbal aggression, and relationships with teachers. The data used in this study were collected in the context of a larger survey on victimization in secondary schools from the French Community of Belgium. Participants were 2896 secondary school students (1520 males; 1376 females) aged 12-18 years. Results showed that for both genders, the three strongest predictors of depressive mood were age, feeling of exclusion, and verbal aggression. This study focusing on school-related predictors of depressive mood confirmed the importance of the social context in school as a predictor of depression in both girls and boys.

Alcohol Craving in Heavy and Occasional Alcohol Drinkers After Cue Exposure in a Virtual Environment: The Role of the Sense of Presence.

The development of new technologies, and more specifically the opportunity to immerse participants in virtual controlled environments, provides a new ecological framework for researchers to study complex behaviors. This experiment aimed to compare post-immersion craving in occasional and heavy alcohol drinkers. Twenty-two occasional drinkers and eighteen heavy drinkers were recruited and immersed in a virtual bar, including alcoholic beverages. After the exposure, heavy drinkers reported a significantly higher craving than occasional drinkers. Post-immersion alcohol craving was significantly related to the levels of perceived ecological validity of the virtual environment. Finally, a moderation analysis suggested that the levels of craving more strongly increased with perceived ecological validity in heavy drinkers than in occasional drinkers. Therefore, the perceived ecological validity was an important experimental parameter to study craving in a virtual environment. These results further suggested that virtual reality might be a useful tool for both the scientific study of alcohol addiction and the treatment of alcohol dependence and relapse.

Acetaldehyde and the hypothermic effects of ethanol in mice.

BACKGROUND: Acetaldehyde, the first metabolite of ethanol, has been suggested to be involved in many behavioral effects of ethanol. However, few studies have investigated the hypothermic effects of acetaldehyde or the contribution of acetaldehyde to ethanol-induced hypothermia. The aim of the present study is to better understand the hypothermic effects of acetaldehyde and the possible contribution of acetaldehyde in ethanol-induced hypothermia, especially under conditions leading to acetaldehyde accumulation. METHODS: Female Swiss mice were injected intraperitoneally with ethanol and acetaldehyde and their rectal temperatures were measured with a digital thermometer at various time points after the injections. Experiment 1 compared the hypothermic effects of various acetaldehyde doses (0 to 300 mg/kg) with a reference dose of ethanol (3 g/kg). Experiment 2 tested the effects of a pretreatment with the aldehyde dehydrogenase (ALDH) inhibitor cyanamide (25 mg/kg) on ethanol- and acetaldehyde-induced hypothermia. In experiments 3 and 4, mice received a combined pretreatment with cyanamide and the alcohol dehydrogenase (ADH) inhibitor 4-Methylpyrazole (10 mg/kg) before the injection of ethanol or acetaldehyde. RESULTS: Acetaldehyde at doses between 100 and 300 mg/kg induced significant hypothermic effects, but of shorter duration than ethanol-induced hypothermia. The inhibition of ALDH enzymes by cyanamide induced a strong potentiation of both ethanol- and acetaldehyde-induced hypothermia. The pretreatment with 4-MP prevented the potentiation of ethanol-induced hypothermia by cyanamide, but slightly increased the potentiation of acetaldehyde-induced hypothermia by cyanamide. CONCLUSIONS: The results of the present study clearly show that acetaldehyde has hypothermic properties in mice at least at relatively high concentrations. Furthermore, the accumulation of acetaldehyde following ALDH inhibition strongly enhanced the hypothermic effects of ethanol. These latter results confirm the hypothermic properties of acetaldehyde and show that acetate, the next step in ethanol metabolism, is not involved in these hypothermic effects. Finally, the experiment with 4-MP indicates that the potentiating effects of cyanamide are mediated by the peripheral accumulation of acetaldehyde, which then reaches the brain to induce a severe hypothermia.

Long-term exposure to daily ethanol injections in DBA/2J and Swiss mice: Lessons for the interpretation of ethanol sensitization.

Most mice ethanol sensitization studies focused on neurobiology at the expense of its behavioral characterization. Furthermore, relatively short ethanol exposures (10 to 20 injections) were used in these studies. The first aim of the present study is to better characterize the development and expression of ethanol sensitization after an extended exposure of 45 daily injections. In some previous studies, mice were classified as "respondent" and "resistant" to ethanol sensitization. The second aim of the present study is to test the long-term reliability of such categorizations and the consequences of their use on the interpretation of the ethanol sensitization results. Swiss and DBA/2J female mice received 45 consecutive daily ethanol administrations (respectively 2.5 and 2.0 g/kg) and their locomotor activity was daily recorded to test the development of ethanol sensitization. At the end of the procedure, a challenge test assessed the inter-group ethanol sensitization.The results of the present study show that ethanol sensitization continues to develop beyond 20 days to reach maximal levels after about 25 injections in DBA/2J mice and 40 injections in Swiss mice, although the core phase of the development of ethanol sensitization occurred in both strains during the first 20 days. Remarkably, ethanol sensitization after such a long daily ethanol treatment resulted in both an upward shift of the magnitude of ethanol stimulant effects and a prolongation of these effects in time (up to 30 minutes). Mice classified as "resistant to ethanol sensitization" according to previous studies developed very significant levels of ethanol sensitization when tested after 45 ethanol injections and are best described as showing a delayed development of ethanol sensitization. Furthermore, mice classified as respondent or resistant to ethanol sensitization also differ in their acute response to ethanol, such that it is difficult to ascertain whether these classifications are specifically related to the sensitization process.