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Repeated anodal transcranial direct current stimulation (RA-tDCS) is a neuromodulatory technique consisting of stimulating the cerebral cortex with a weak electric anodal current in a non-invasive manner. RA-tDCS over the dorsolateral prefrontal cortex has antidepressant-like properties and improves memory both in humans and laboratory animals. However, the mechanisms of action of RA-tDCS remain poorly understood. Since adult hippocampal neurogenesis is thought to be involved in the pathophysiology of depression and memory functioning, the purpose of this work was to evaluate the impact of RA-tDCS on hippocampal neurogenesis levels in mice. RA-tDCS was applied for 20 min per day for five consecutive days over the left frontal cortex of young adult (2-month-old, high basal level of neurogenesis) and middle-aged (10-month-old, low basal level of neurogenesis) female mice. Mice received three intraperitoneal injections of bromodeoxyuridine (BrdU) on the final day of RA-tDCS. The brains were collected either 1 day or 3 weeks after the BrdU injections to quantify cell proliferation and cell survival, respectively. RA-tDCS increased hippocampal cell proliferation in young adult female mice, preferentially (but not exclusively) in the dorsal part of the dentate gyrus. However, the number of cells that survived after 3 weeks was the same in both the Sham and the tDCS groups. This was due to a lower survival rate in the tDCS group, which suppressed the beneficial effects of tDCS on cell proliferation. No modulation of cell proliferation or survival was observed in middle-aged animals. Our RA-tDCS protocol may, therefore, influence the behavior of naïve female mice, as we previously described, but its effect on the hippocampus is only transient in young adult animals. Future studies using animal models for depression in male and female mice should provide further insights into RA-tDCS detailed age- and sex-dependent effects on hippocampal neurogenesis.

Abtract Background Transcranial direct current stimulation (tDCS) is a non-invasive method increasingly popular for the treatment of several brain disorders, such as major depression. Despite great enthusiasm and promising results, some studies report discrepant findings and no consensus exists for the clinical use of tDCS. Objective The present study aims to (i) determine the most effective stimulation parameters to optimize antidepressant-like effect of tDCS in the forced-swim test in mice and (ii) identify brain regions recruited by tDCS and possibly involved in its behavioral effect using Fos immunohistochemistry. Results We reported that tDCS induced long-lasting antidepressant-like effect, which varied as a function of stimulation settings including number, duration, intensity and polarity of stimulation. Interestingly, the present study also demonstrated that tDCS reduced depressive-like behaviors induced by chronic corticosterone exposure. Furthermore, behavioral outcomes induced by a single stimulation were associated with neuronal activation in the prefrontal cortex, dorsal hippocampus, ventral tegmental area and nucleus accumbens, whereas no overexpression of c-fos was associated with 10 stimulations. Conclusion The strongest behavioral response was observed with an anodal stimulation of 200 μA during 20min. The repetition of this stimulation was necessary to induce long-lasting behavioral effects that are probably associated with plastic changes in the neuronal response.

Objectives: Vortioxetine has already shown its efficacy in the acute and long-term treatment of major depressive disorder (MDD) and its potential interest in the prevention of relapse. The aim of this study was to review the current status of knowledge regarding its cognitive effects. Methods: We conducted a review of key data obtained from preclinical behavioral models and clinical trials in MDD focusing on vortioxetine-induced cognitive changes. Results: In animals, acute and chronic administration of vortioxetine improves performance on objective measures that cover a broad range of cognitive domains. In human, vortioxetine appears to be a useful treatment option in MDD patients with cognitive dysfunction. Conclusion: Vortioxetine constitutes a promising treatment for treatment of cognitive impairment in MDD, but its place in the therapeutic armamentarium still needs to be determined.

Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability. This technique is a promising emerging tool to treat several neuropathologies, including addiction. We have previously shown in mice that repeated tDCS normalizes pathological behaviors associated with chronic nicotine exposure. Here, we evaluated, in adult female mice, the impact of tDCS on cocaine-induced behavior and gene regulation in corticostriatal circuits implicated in psychostimulant addiction. Anodal tDCS was applied transcranially over the frontal cortex. Three weeks after repeated tDCS, we investigated the induction of a gene expression marker (Zif268) by cocaine (25 mg/kg) in 26 cortical and 23 striatal regions using in situ hybridization histochemistry. We also assessed place preference conditioning by cocaine (5, 10 and 25 mg/kg). tDCS pretreatment increased basal expression and attenuated cocaine (25 mg/kg)-induced expression of Zif268 in specific corticostriatal circuits. Cocaine-induced locomotor activation (25 mg/kg) and place preference conditioning (5 and 25 mg/kg) were also reduced. These results demonstrate that tDCS can attenuate molecular and behavioral responses to cocaine for several weeks. Together, our findings provide pre-clinical evidence that such electrical brain stimulation may be useful to modify the psychostimulant addiction risk.

International audience; There is growing interest in non-invasive brain stimulation (NIBS) as a novel treatment option for substance-use disorders (SUDs). Recent momentum stems from a foundation of preclinical neuroscience demonstrating links between neural circuits and drug consuming behavior, as well as recent FDA-approval of NIBS treatments for mental health disorders that share overlapping pathology with SUDs. As with any emerging field, enthusiasm must be tempered by reason; lessons learned from the past should be prudently applied to future therapies. Here, an international ensemble of experts provides an overview of the state of transcranial-electrical (tES) and transcranial-magnetic (TMS) stimulation applied in SUDs. This consensus paper provides a systematic literature review on published data - emphasizing the heterogeneity of methods and outcome measures while suggesting strategies to help bridge knowledge gaps. The goal of this effort is to provide the community with guidelines for best practices in tES/TMS SUD research. We hope this will accelerate the speed at which the community translates basic neuroscience into advanced neuromodulation tools for clinical practice in addiction medicine.

In this symposium, we will tackle several examples of studies conducted in animal models to unravel the mode of action of different methods of non-invasive brain stimulation used to treat psychiatric disorders in human. First, Sylvie Gory-Faure will highlight the essential role of neural survival for short- and long-term efficacy of electroconvulsive stimulation in an animal model of depression (MAP6 KO mouse). Then, Vincent Van Waes will present behavioral and neurobiological data on the beneficial impact of repeated anodal transcranial direct stimulation on cognition, depression- and addiction-related behaviors in mice. Robrecht Dockx will describe a new accelerated high frequency (aHF) repetitive transcranial magnetic stimulation protocol tested in dogs. Finally, Dimitri De Bundel will talk about the effects of transcranial direct current stimulation to modulate fear extinction in a mouse model based on auditory fear conditioning. To conclude, the necessity to carry out translational studies to accelerate the development of brain stimulation techniques that have a strong therapeutic potential in human will be discussed.

Drug combinations that include the psychostimulant methylphenidate plus a selective serotonin reuptake inhibitor (SSRI) such as fluoxetine are increasingly used in children and adolescents. For example, this combination is indicated in the treatment of attention-deficit/hyperactivity disorder and depression comorbidity and other mental disorders. Such co-exposure also occurs in patients on SSRIs who use methylphenidate as a cognitive enhancer. The neurobiological consequences of these drug combinations are poorly understood. Methylphenidate alone can produce gene regulation effects that mimic addiction-related gene regulation by cocaine, consistent with its moderate addiction liability. We have previously shown that combining SSRIs with methylphenidate potentiates methylphenidate-induced gene regulation in the striatum. The present study investigated which striatal output pathways are affected by the methylphenidate + fluoxetine combination, by assessing effects on pathway-specific neuropeptide markers, and which serotonin receptor subtypes may mediate these effects. Our results demonstrate that a 5-day repeated treatment with fluoxetine (5 mg/kg) potentiates methylphenidate (5 mg/kg)-induced expression of both dynorphin (direct pathway marker) and enkephalin (indirect pathway). These changes were accompanied by correlated increases in the expression of the 5-HT1B, but not 5-HT2C, serotonin receptor in the same striatal regions. A further study showed that the 5-HT1B receptor agonist CP94253 (3-10 mg/kg) mimics the fluoxetine potentiation of methylphenidate-induced gene regulation. These findings suggest a role for the 5-HT1B receptor in the fluoxetine effects on striatal gene regulation. Given that 5-HT1B receptors are known to facilitate addiction-related gene regulation and behavior, our results suggest that SSRIs may enhance the addiction liability of methylphenidate by increasing 5-HT1B receptor signaling.

Use of psychostimulants such as methylphenidate (Ritalin) in medical treatments and as cognitive enhancers in the healthy is increasing. Methylphenidate produces some addiction-related gene regulation in animal models. Recent findings show that combining selective serotonin reuptake inhibitor (SSRI) antidepressants such as fluoxetine with methylphenidate potentiates methylphenidate-induced gene regulation. We investigated the endurance of such abnormal gene regulation by assessing an established marker for altered gene regulation after drug treatments - blunting (repression) of immediate-early gene (IEG) inducibility - 14 days after repeated methylphenidate+fluoxetine treatment in adolescent rats. Thus, we measured the effects of a 6-day repeated treatment with methylphenidate (5 mg/kg), fluoxetine (5 mg/kg) or their combination on the inducibility (by cocaine) of neuroplasticity-related IEGs (Zif268, Homer1a) in the striatum, by in situ hybridization histochemistry. Repeated methylphenidate treatment alone produced modest gene blunting, while fluoxetine alone had no effect. In contrast, fluoxetine given in conjunction with methylphenidate produced pronounced potentiation of methylphenidate-induced blunting for both genes. This potentiation was seen in many functional domains of the striatum, but was most robust in the lateral, sensorimotor striatum. These enduring molecular changes were associated with potentiated induction of behavioral stereotypies in an open-field test. For illicit psychostimulants, blunting of gene expression is considered part of the molecular basis of addiction. Our results thus suggest that SSRIs such as fluoxetine may increase the addiction liability of methylphenidate. Key words: cognitive enhancer, dopamine, serotonin, gene expression, psychostimulant, SSRI antidepressant, striatum.

Successful available treatments to quit smoking remain scarce. Recently, the potential of transcranial direct current stimulation (tDCS) as a tool to reduce craving for nicotine has gained interest. However, there is no documented animal model to assess the neurobiological mechanisms of tDCS on addiction-related behaviors. To address this topic, we have developed a model of repeated tDCS in mice and used it to validate its effectiveness in relieving nicotine addiction. Anodal repeated tDCS was applied over the frontal cortex of Swiss female mice. The stimulation electrode (anode) was fixed directly onto the cranium, and the reference electrode was placed onto the ventral thorax. A 2 × 20 min/day stimulation paradigm for five consecutive days was used (0.2 mA). In the first study, we screened for behaviors altered by the stimulation. Second, we tested whether tDCS could alleviate abnormal behaviors associated with abstinence from nicotine consumption. In naive animals, repeated tDCS had antidepressant-like properties 3 weeks after the last stimulation, improved working memory, and decreased conditioned place preference for nicotine without affecting locomotor activity and anxiety-related behavior. Importantly, abnormal behaviors associated with chronic nicotine exposure (ie, depression-like behavior, increase in nicotine-induced place preference) were normalized by repeated tDCS. Our data show for the first time in an animal model that repeated tDCS is a promising, non-expensive clinical tool that could be used to reduce smoking craving and facilitate smoking cessation. Our animal model will be useful to investigate the mechanisms underlying the effects of tDCS on addiction and other psychiatric disorders.

There is a growing use of psychostimulants such as methylphenidate (Ritalin; dopamine reuptake inhibitor) for medical treatments and as cognitive enhancers in the healthy. Methylphenidate is known to produce some addiction-related gene regulation. Recent findings in animal models show that selective serotonin reuptake inhibitors (SSRIs) including fluoxetine can potentiate acute induction of gene expression by methylphenidate, thus indicating an acute facilitatory role for serotonin in dopamine-induced gene regulation. We investigated whether repeated exposure to fluoxetine in conjunction with methylphenidate in adolescent rats facilitated a gene regulation effect well-established for repeated exposure to illicit psychostimulants such as cocaine - blunting (repression) of gene inducibility. We measured, by in situ hybridization histochemistry, the effects of a 5-day repeated treatment with methylphenidate (5 mg/kg), fluoxetine (5 mg/kg) or a combination on the inducibility (by cocaine) of neuroplasticity-related genes (Zif268, Homer1a) in the striatum. Repeated methylphenidate treatment alone produced minimal gene blunting, while fluoxetine alone had no effect. In contrast, fluoxetine added to methylphenidate robustly potentiated methylphenidate-induced blunting for both genes. This potentiation was widespread throughout the striatum, but was most robust in the lateral, sensorimotor striatum, thus mimicking cocaine effects. For illicit psychostimulants, blunting of gene expression is considered part of the molecular basis of addiction. Our results thus suggest that SSRIs such as fluoxetine may increase the addiction liability of methylphenidate.

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.

Concomitant therapies combining psychostimulants such as methylphenidate and selective serotonin reuptake inhibitors (SSRIs) are used to treat several mental disorders, including attention-deficit hyperactivity disorder/depression comorbidity. The neurobiological consequences of these drug combinations are poorly understood. Methylphenidate alone induces gene regulation that mimics partly effects of cocaine, consistent with some addiction liability. We previously showed that the SSRI fluoxetine potentiates methylphenidate-induced gene regulation in the striatum. The present study investigated which striatal output pathways are affected by the methylphenidate + fluoxetine combination, by assessing effects on pathway-specific neuropeptide markers. Results demonstrate that fluoxetine (5 mg/kg) potentiates methylphenidate (5 mg/kg)-induced expression of substance P and dynorphin, markers for direct pathway neurons. In contrast, no drug effects on the indirect pathway marker enkephalin were found. Because methylphenidate alone has minimal effects on dynorphin, the potentiation of dynorphin induction represents a more cocaine-like effect for the drug combination. On the other hand, the lack of an effect on enkephalin suggests a greater selectivity for the direct pathway compared with psychostimulants such as cocaine. Overall, the fluoxetine potentiation of gene regulation by methylphenidate occurs preferentially in sensorimotor striatal circuits, similar to other addictive psychostimulants. These results suggest that SSRIs may enhance the addiction liability of methylphenidate.

The psychostimulant methylphenidate (Ritalin) is used in conjunction with selective serotonin reuptake inhibitors (SSRIs) in the treatment of medical conditions such as attention-deficit hyperactivity disorder with anxiety/depression comorbidity and major depression. Co-exposure also occurs in patients on SSRIs who use psychostimulant 'cognitive enhancers'. Methylphenidate is a dopamine/norepinephrine reuptake inhibitor that produces altered gene expression in the forebrain; these effects partly mimic gene regulation by cocaine (dopamine/norepinephrine/serotonin reuptake inhibitor). We investigated whether the addition of SSRIs (fluoxetine or citalopram; 5 mg/kg) modified gene regulation by methylphenidate (2-5 mg/kg) in the striatum and cortex of adolescent rats. Our results show that SSRIs potentiate methylphenidate-induced expression of the transcription factor genes zif268 and c-fos in the striatum, rendering these molecular changes more cocaine-like. Present throughout most of the striatum, this potentiation was most robust in its sensorimotor parts. The methylphenidate + SSRI combination also enhanced behavioral stereotypies, consistent with dysfunction in sensorimotor striatal circuits. In so far as such gene regulation is implicated in psychostimulant addiction, our findings suggest that SSRIs may enhance the addiction potential of methylphenidate.

Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability. This technique is a promising emerging tool to treat several neuropathologies, including addiction. We have previously shown in mice that repeated tDCS normalizes pathological behaviors associated with chronic nicotine exposure. Here, we evaluated, in adult female mice, the impact of tDCS on cocaine-induced behavior and gene regulation in corticostriatal circuits implicated in psychostimulant addiction. Anodal tDCS was applied transcranially over the frontal cortex. Three weeks after repeated tDCS, we investigated the induction of a gene expression marker (Zif268) by cocaine (25 mg/kg) in 26 cortical and 23 striatal regions using in situ hybridization histochemistry. We also assessed place preference conditioning by cocaine (5, 10, and 25 mg/kg). tDCS pretreatment increased basal expression and attenuated cocaine (25 mg/kg)-induced expression of Zif268 in specific corticostriatal circuits. Cocaine-induced locomotor activation (25 mg/kg) and place preference conditioning (5 and 25 mg/kg) were also reduced. These results demonstrate that tDCS can attenuate molecular and behavioral responses to cocaine for several weeks. Together, our findings provide pre-clinical evidence that such electrical brain stimulation may be useful to modify the psychostimulant addiction risk.

Background There is growing use of psychostimulant cognitive enhancers such as methylphenidate (Ritalin). Methylphenidate differs from the psychostimulant cocaine because it does not enhance synaptic levels of serotonin. We investigated whether exposure to methylphenidate combined with a serotonin-enhancing medication, the prototypical selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac), would produce more "cocaine-like" molecular and behavioral changes. Methods We measured the effects of fluoxetine on gene expression induced by the cognitive enhancer methylphenidate in the striatum and nucleus accumbens of rats, by in situ hybridization histochemistry. We also determined whether fluoxetine modified behavioral effects of methylphenidate. Results Fluoxetine robustly potentiated methylphenidate-induced expression of the transcription factors c- fos and zif 268 throughout the striatum and to some degree in the nucleus accumbens. Fluoxetine also enhanced methylphenidate-induced stereotypical behavior. Conclusions Both potentiated gene regulation in the striatum and the behavioral effects indicate that combining the SSRI fluoxetine with the cognitive enhancer methylphenidate mimics cocaine effects, consistent with an increased risk for substance use disorder.

Psychostimulants such as methylphenidate (MPH) and antidepressants such as fluoxetine (FLX) are widely used in the treatment of various mental disorders or as cognitive enhancers. These medications are often combined, for example, to treat comorbid disorders. There is a considerable body of evidence from animal models indicating that individually these psychotropic medications can have detrimental effects on the brain and behavior, especially when given during sensitive periods of brain development. However, almost no studies investigate possible interactions between these drugs. This is surprising given that their combined neurochemical effects (enhanced dopamine and serotonin neurotransmission) mimic some effects of illicit drugs such as cocaine and amphetamine. Here, we summarize recent studies in juvenile rats on the molecular effects in the mid- and forebrain and associated behavioral changes, after such combination treatments. Our findings indicate that these combined MPH+FLX treatments can produce similar molecular changes as seen after cocaine exposure while inducing behavioral changes indicative of dysregulated mood and motivation, effects that often endure into adulthood.

Corticostriatal circuits mediate various aspects of goal-directed behavior and are critically important for basal ganglia-related disorders. Activity in these circuits is regulated by the endocannabinoid system via stimulation of CB1 cannabinoid receptors. CB1 receptors are highly expressed in projection neurons and select interneurons of the striatum, but expression levels vary considerably between different striatal regions (functional domains). We investigated CB1 receptor expression within specific corticostriatal circuits by mapping CB1 mRNA levels in striatal sectors defined by their cortical inputs in rats. We also assessed changes in CB1 expression in the striatum during development. Our results show that CB1 expression is highest in juveniles (P25) and then progressively decreases towards adolescent (P40) and adult (P70) levels. At every age, CB1 receptors are predominantly expressed in sensorimotor striatal sectors, with considerably lower expression in associative and limbic sectors. Moreover, for most corticostriatal circuits there is an inverse relationship between cortical and striatal expression levels. Thus, striatal sectors with high CB1 expression (sensorimotor sectors) tend to receive inputs from cortical areas with low expression, while striatal sectors with low expression (associative/limbic sectors) receive inputs from cortical regions with higher expression (medial prefrontal cortex). In so far as CB1 mRNA levels reflect receptor function, our findings suggest differential CB1 signaling between different developmental stages and between sensorimotor and associative/limbic circuits. The regional distribution of CB1 receptor expression in the striatum further suggests that, in sensorimotor sectors, CB1 receptors mostly regulate GABA inputs from local axon collaterals of projection neurons, whereas in associative/limbic sectors, CB1 regulation of GABA inputs from interneurons and glutamate inputs may be more important.

GPR88 is a putative G-protein-coupled receptor that is highly and almost exclusively expressed in the striatum. Its function remains unknown. We investigated GPR88 cellular localization and expression levels across development in different functional domains of the striatum in juvenile (P25), adolescent (P40), and adult (P70) rats, by in situ hybridization histochemistry. At all ages, GPR88 mRNA expression was most robust in the sensorimotor (lateral) striatum and was detected in virtually every neuron. Expression was highest in juveniles and decreased thereafter with regionally distinct trajectories. Thus, in the dorsal striatum, there was a progressive decrease from juveniles to adolescents to adults. In contrast, in the nucleus accumbens, the only (modest) decrease occurred between juveniles and adolescents. These findings indicate that GPR88 is expressed in all striatal neurons, but is differentially regulated across development in different striatal regions.

International audience; * Rationale / In rats, prenatal restraint stress (PRS) induces persistent behavioral and neurobiological alterations leading to a greater consumption of psychostimulants during adulthood. However, little is known about alcohol vulnerability in this animal model. * Objectives / We examined in adolescent and adult male Sprague Dawley rats the long-lasting impact of PRS exposure on alcohol consumption. * Methods / PRS rats were subjected to a prenatal stress (three daily 45-min sessions of restraint stress to the mothers during the last 10 days of pregnancy). Alcohol preference was assessed in a two-bottle choice paradigm (alcohol 2.5%, 5%, or 10% versus water), in both naïve adolescent rats and adult rats previously exposed to a chronic alcohol treatment. Behavioral indices associated with incentive motivation for alcohol were investigated. Finally, plasma levels of transaminases (marker of hepatic damages) and ΔFosB levels in the nucleus accumbens (a potential molecular switch for addiction) were evaluated following the chronic alcohol exposure. * Results / Alcohol preference was not affected by PRS. Contrary to our expectations, stressed and unstressed rats did not display signs of compulsive alcohol consumption. The consequences of the alcohol exposure on locomotor reactivity and on transaminase levels were more prominent in PRS group. Similarly, PRS potentiated alcohol-induced ΔFosB levels in the nucleus accumbens. * Conclusion / Our data suggest that negative events occurring in utero do not modulate alcohol preference in male rats but potentiate chronic alcohol-induced molecular neuroadaptation in the brain reward circuitry. Further studies are needed to determine whether the exacerbated ΔFosB upregulation in PRS rats could be extended to other reinforcing stimuli.

International audience; We examined the interaction between early life stress and vulnerability to alcohol in female rats exposed to prenatal restraint stress (PRS rats). First we studied the impact of PRS on ethanol preference during adolescence. PRS slightly increased ethanol preference per se, but abolished the effect of social isolation on ethanol preference. We then studied the impact of PRS on short- and long-term responses to ethanol focusing on behavioral and neurochemical parameters related to depression/anxiety. PRS or unstressed adolescent female rats received 10% ethanol in the drinking water for 4 weeks from PND30 to PND60. At PND60, the immobility time in the forced-swim test did not differ between PRS and unstressed rats receiving water alone. Ethanol consumption had no effect in unstressed rats, but significantly reduced the immobility time in PRS rats. In contrast, a marked increase in the immobility time was seen after 5 weeks of ethanol withdrawal only in unstressed rats. Hippocampal levels of neuropeptide Y (NPY) and mGlu1a metabotropic glutamate receptors were increased at the end of ethanol treatment only in unstressed rats. Ethanol treatment had no effect on levels of corticotropin-releasing hormone (CRH) in the hippocampus, striatum, and prefrontal cortex of both groups of rats. After ethanol withdrawal, hippocampal levels of mGlu1 receptors were higher in unstressed rats, but lower in PRS rats, whereas NPY and CRH levels were similar in the two groups of rats. These data indicate that early life stress has a strong impact on the vulnerability and responsiveness to ethanol consumption during adolescence.

International audience; Prenatal restraint stress (PRS) in rats is associated with hippocampal dysfunctions and several behavioural and endocrine disorders related to this brain area. Recently, we have reported that the PRS modifies the hypothalamic–pituitary–adrenal (HPA) response to an ethanol challenge in adolescent animals. Since hippocampus is particularly sensitive to the deleterious effects of ethanol during adolescence, we investigated in this study the combined effects of PRS and ethanol administration on the oxidative status in the hippocampus of 28-day-old male rats. Thirty minutes after an intraperitoneal (i.p.) injection of ethanol (1.5 g/kg), the activities of several antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) but also non-enzymatic antioxidant (reduced glutathione) were assayed. Thiobarbituric acid reactive substances (TBARS) levels were also measured as a marker of lipid peroxidation. Ethanol enhanced superoxide dismutase activity in control rats but not in PRS rats. At basal level, catalase activity was lower in PRS rats than in control rats, indicating a potentially higher sensitivity to oxidative damages after this early stress. However, the hippocampal TBARS levels were not significantly affected by the ethanol administration, showing that an acute ethanol exposure does not induce oxidative damage in adolescent male rats. In conclusion, our data suggest that PRS affects both basal antioxidant status in the hippocampus and antioxidant response after an acute ethanol exposure. These findings extend previous works showing that PRS leads to hippocampal dysfunctions and raise the question of the potential increase of the hippocampal oxidative damage in PRS rats after repeated exposure to ethanol.

The period of adolescence and environmental factors, such as stress, are important in determining ethanol vulnerability in both humans and rats. Ethanol is a powerful activator of the hypothalamic-pituitary-adrenal (HPA) axis but attenuated responses of the HPA axis to ethanol have been described in populations with a high risk of ethanol abuse. In rats, prenatal stress leads to prolonged stress-induced corticosterone secretion and increases the vulnerability to drugs of abuse, such as amphetamine and nicotine in adulthood and 3,4-methylenedioxymethamphetamine in adolescent rats. The aim of the present study was to assess the impact of a prenatal stress on HPA axis responsiveness to a moderate dose of ethanol (1.5 g/kg i.p.) in adolescent male rats (28 days old). The parameters evaluated were plasma adrenocorticotropic hormone, plasma corticosterone and mRNA expression of HPA axis central markers (mineralocorticoid receptor, glucocorticoid receptor, corticotropin-releasing hormone and pro-opiomelanocortin). Contrary to prior expectations, our results demonstrate that prenatal stress blunts the HPA axis responsiveness to a moderate dose of ethanol in adolescent rats in spite of similar blood ethanol levels. These data suggest that prenatal stress may have the opposite effect on the response to stress depending on the attributes of the stressor stimulus. They thus raise questions about the possible impact of prenatal stress on the further development of ethanol vulnerability.

This study was part of a wider translational project on the efficacy of tDCS in the treatment of major depression and in attempts to facilitate alcohol and smoking cessation. tDCS is a non- invasive, painless and safe brain stimulation procedure capable of modulating cortical excitability. Preliminary clinical studies have indicated that tDCS applied over the dorsal prefrontal cortex of chronically dependent smokers and alcohol users reduces their desire for smoking and drinking, respectively. The neurobiological mechanisms underlying these effects remain unknown. We have developed a model of tDCS in mice that mimics the experimental paradigms used in our clinical research. Anodal tDCS is applied transcranially over the frontal cortex (2 x 20 min/day current for 5 consecutive days, intensity = 0.2 mA). The control group undergoes the same procedure but no current is applied. We evaluated the effects of tDCS on nicotine and alcohol consumption as well as on the rewarding effects of these two drugs of abuse. We assessed the impact of tDCS on stress-related, anxiety-related and depression-related behaviors. We tested the effects of tDCS on mice that had been chronically exposed to nicotine during adolescence. Chronic exposure to nicotine induced depression-like behavior in adult mice. It is thought that this depression- like state may be a symptom of withdrawal that facilitates relapse after abstinence. Our data indicate that tDCS reversed behavioral anomalies. In conclusion, our animal model has potential value as a means for exploring the neurobiological changes that underlie the beneficial effects of tDCS on addiction-related behaviors.

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique in which a low current is delivered via electrodes on the scalp to modulate cortical excitability. lt is a promising tool in the treatment of various neurological and psychiatrie illnesses, yet the mechanisms underlying its beneficial effects remain unknown. The goal of my thesis was to describe the effects of repeated tDCS on behavior in mice, and to offer preliminary insights regarding the neurobiological mechanisms involved. Our data indicate that repeated tDCS over the frontal lobe (0.2 mA, 2x20 min/day, 5 consecutive days) has antidepressant prope11ies and improves memory. Interestingly, tDCS increased precursor cell proliferation in the hippocampus, suggesting that tDCS may increase neurogenesis levels in this brain area. Lastly, tDCS decreased the behavioral and/or the molecular effects of nicotine, alcohol and cocaïne. For example, tDCS attenuated cocaine-induced Zif268 expression in specific corticostriatal circuits. Altogether, our findings provide pre-clinical evidence that tDCS cou Id be a beneficial adjunct treatment for several psychiatrie disorders. Our animal mode! will be useful to further investigate the mechanisms underlying the beneficial effects of tDCS on behavior.; La stimulation transcrânienne par courant continu (tDCS) est une technique de neuromodulation non invasive qui permet de modifier l'excitabilité co11icale au moyen d'un faible courant électrique délivré à travers le crâne. Elle constitue une piste intéressante pour l'élaboration de nouveaux traitements de divers troubles psychiatriques ou neurologiques, mais les mécanismes qui sous-tendent ses effets sont méconnus. L'objectif de ma thèse a été d'évaluer chez la souris les comp011ements affectés par des sessions répétées de tDCS et d'étudier des pistes concernant ses mécanismes d'action. Nous avons montré un effet bénéfique de la tDCS anodique au niveau du lobe frontal (2x20 minutes/jour à 0.2 mA, 5 jours consécutifs) sur les comportements associés à la dépression et sur la mémoire. Nous avons par ailleurs quantifié la prolifération cellulaire au niveau de l'hippocampe et montré que celle-ci est plus importante chez les souris stimulées, suggérant que la tDCS pourrait augmenter la neurogenèse hippocampique. Enfin, nos études sur des souris exposées à différentes drogues (nicotine, alcool, cocaïne) dévoilent que la tDCS diminue certains de leurs effets comportementaux (ex: valeur hédonique) et/ou moléculaires (ex: induction de Zif268 dans les circuits cortico-striataux). Nos résultats sont en adéquation avec les données cliniques recueillies chez l'Homme et soutiennent l'hypothèse que la tDCS pourrait être un traitement additionnel pour diverses pathologies. Ils ouvrent la voie à différentes études complémentaires, pour lesquelles notre modèle animal constitue un outil intéressant.

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique in which a low current is delivered via electrodes on the scalp to modulate cortical excitability. It is a promising tool in the treatment of various neurological and psychiatric illnesses, yet the mechanisms underlying its beneficial effects remain unknown.The goal of my thesis was to describe the effects of repeated tDCS on behavior in mice, and to offer preliminary insights regarding the neurobiological mechanisms involved.Our data indicate that repeated tDCS over the frontal lobe (0.2 mA, 2x20 min/day, 5 consecutive days) has antidepressant properties and improves memory. Interestingly, tDCS increased precursor cell proliferation in the hippocampus, suggesting that tDCS may increase neurogenesis levels in this brain area. Lastly, tDCS decreased the behavioral and/or the molecular effects of nicotine, alcohol and cocaine. For example, tDCS attenuated cocaine-induced Zif268 expression in specific corticostriatal circuits.Altogether, our findings provide pre-clinical evidence that tDCS could be a beneficial adjunct treatment for several psychiatric disorders. Our animal model will be useful to further investigate the mechanisms underlying the beneficial effects of tDCS on behavior.; La stimulation transcrânienne par courant continu (tDCS) est une technique de neuromodulation non invasive qui permet de modifier l'excitabilité corticale au moyen d'un faible courant électrique délivré à travers le crâne. Elle constitue une piste intéressante pour l'élaboration de nouveaux traitements de divers troubles psychiatriques ou neurologiques, mais les mécanismes qui sous-tendent ses effets sont méconnus. L'objectif de ma thèse a été d'évaluer chez la souris les comportements affectés par des sessions répétées de tDCS et d’étudier des pistes concernant ses mécanismes d’action.Nous avons montré un effet bénéfique de la tDCS anodique au niveau du lobe frontal (2x20 minutes/jour à 0.2 mA, 5 jours consécutifs) sur les comportements associés à la dépression et sur la mémoire. Nous avons par ailleurs quantifié la prolifération cellulaire au niveau de l'hippocampe et montré que celle-ci est plus importante chez les souris stimulées, suggérant que la tDCS pourrait augmenter la neurogenèse hippocampique. Enfin, nos études sur des souris exposées à différentes drogues (nicotine, alcool, cocaïne) dévoilent que la tDCS diminue certains de leurs effets comportementaux (ex : valeur hédonique) et/ou moléculaires (ex : induction de Zif268 dans les circuits cortico-striataux).Nos résultats sont en adéquation avec les données cliniques recueillies chez l'Homme et soutiennent l'hypothèse que la tDCS pourrait être un traitement additionnel pour diverses pathologies. Ils ouvrent la voie à différentes études complémentaires, pour lesquelles notre modèle animal constitue un outil intéressant.