José Miñarro

Role of CB2 cannabinoid receptors in the rewarding, reinforcing, and physical effects of nicotine.

This study was aimed to evaluate the involvement of CB2 cannabinoid receptors (CB2r) in the rewarding, reinforcing and motivational effects of nicotine. Conditioned place preference (CPP) and intravenous self-administration experiments were carried out in knockout mice lacking CB2r (CB2KO) and wild-type (WT) littermates treated with the CB2r antagonist AM630 (1 and 3u2009mg/kg). Gene expression analyses of tyrosine hydroxylase (TH) and α3- and α4-nicotinic acetylcholine receptor subunits (nAChRs) in the ventral tegmental area (VTA) and immunohistochemical studies to elucidate whether CB2r colocalized with α3- and α4-nAChRs in the nucleus accumbens and VTA were performed. Mecamylamine-precipitated withdrawal syndrome after chronic nicotine exposure was evaluated in CB2KO mice and WT mice treated with AM630 (1 and 3u2009mg/kg). CB2KO mice did not show nicotine-induced place conditioning and self-administered significantly less nicotine. In addition, AM630 was able to block (3u2009mg/kg) nicotine-induced CPP and reduce (1 and 3u2009mg/kg) nicotine self-administration. Under baseline conditions, TH, α3-nAChR, and α4-nAChR mRNA levels in the VTA of CB2KO mice were significantly lower compared with WT mice. Confocal microscopy images revealed that CB2r colocalized with α3- and α4-nAChRs. Somatic signs of nicotine withdrawal (rearings, groomings, scratches, teeth chattering, and body tremors) increased significantly in WT but were absent in CB2KO mice. Interestingly, the administration of AM630 blocked the nicotine withdrawal syndrome and failed to alter basal behavior in saline-treated WT mice. These results suggest that CB2r play a relevant role in the rewarding, reinforcing, and motivational effects of nicotine. Pharmacological manipulation of this receptor deserves further consideration as a potential new valuable target for the treatment of nicotine dependence.

Neuroimmune Activation and Myelin Changes in Adolescent Rats Exposed to High-Dose Alcohol and Associated Cognitive Dysfunction: A Review with Reference to Human Adolescent Drinking

AIMSnThe aim of the study was to assess whether intermittent ethanol administration to adolescent rats activates innate immune response and TLRs signalling causing myelin disruption and long-term cognitive and behavioural deficits.nnnMETHODSnWe used a rat model of intermittent binge-like ethanol exposure during adolescence.nnnRESULTSnBinge-like ethanol administration to adolescent rats increased the gene expression of TLR4 and TLR2 in the prefrontal cortex (PFC), as well as inflammatory cytokines TNFα and IL-1β. Up-regulation of TLRs and inflammatory mediators were linked with alterations in the levels of several myelin proteins in the PFC of adolescent rats. These events were associated with previously reported long-term cognitive dysfunctions. Conversely, the same ethanol treatment did not cause significant changes in either inflammatory mediators or myelin changes in the brain of adult rats.nnnCONCLUSIONnActivation of innate immune receptors TLRs in the PFC appears to be involved in the neuroinflammation and demyelination processes induced by ethanol exposure during adolescence. The findings support the vulnerability of the juvenile brain to the effects of ethanol and the long-term cognitive consequences of binge drinking. In addition, ethanol-induced PFC dysfunctions might underlie the propensity of adolescents for impulsivity and to ignore the negative consequences of their behaviour, both of which could increase the risk of substance abuse.

Plasma profile of pro-inflammatory cytokines and chemokines in cocaine users under outpatient treatment: influence of cocaine symptom severity and psychiatric co-morbidity.

The treatment for cocaine use constitutes a clinical challenge because of the lack of appropriate therapies and the high rate of relapse. Recent evidence indicates that the immune system might be involved in the pathogenesis of cocaine addiction and its co‐morbid psychiatric disorders. This work examined the plasma pro‐inflammatory cytokine and chemokine profile in abstinent cocaine users (nu2009=u200982) who sought outpatient cocaine treatment and age/sex/body mass‐matched controls (nu2009=u200965). Participants were assessed with the diagnostic interview Psychiatric Research Interview for Substance and Mental Diseases according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM‐IV‐TR). Tumor necrosis factor‐alpha, chemokine (C‐C motif) ligand 2/monocyte chemotactic protein‐1 and chemokine (C‐X‐C motif) ligand 12 (CXCL12)/stromal cell‐derived factor‐1 (SDF‐1) were decreased in cocaine users, although all cytokines were identified as predictors of a lifetime pathological use of cocaine. Interleukin‐1 beta (IL‐1β), chemokine (C‐X3‐C motif) ligand 1 (CX3CL1)/fractalkine and CXCL12/SDF‐1 positively correlated with the cocaine symptom severity when using the DSM‐IV‐TR criteria for cocaine abuse/dependence. These cytokines allowed the categorization of the outpatients into subgroups according to severity, identifying a subgroup of severe cocaine users (9–11 criteria) with increased prevalence of co‐morbid psychiatric disorders [mood (54%), anxiety (32%), psychotic (30%) and personality (60%) disorders]. IL‐1β was observed to be increased in users with such psychiatric disorders relative to those users with no diagnosis. In addition to these clinical data, studies in mice demonstrated that plasma IL‐1β, CX3CL1 and CXCL12 were also affected after acute and chronic cocaine administration, providing a preclinical model for further research. In conclusion, cocaine exposure modifies the circulating levels of pro‐inflammatory mediators. Plasma cytokine/chemokine monitoring could improve the stratification of cocaine consumers seeking treatment and thus facilitate the application of appropriate interventions, including management of heightened risk of psychiatric co‐morbidity. Further research is necessary to elucidate the role of the immune system in the etiology of cocaine addiction.

The Novelty-Seeking Phenotype Modulates the Long-Lasting Effects of Intermittent Ethanol Administration during Adolescence

The aim of the present study was to investigate if a novelty-seeking phenotype mediates the long-lasting consequences of intermittent EtOH intoxication during adolescence. The hole board test was employed to classify adolescent mice as High- or Low-Novelty Seekers. Subsequently, animals were administered ethanol (1.25 or 2.5 g/kg) on two consecutive days at 48-h intervals over a 14-day period. Anxiety levels - measured using the elevated plus maze- spontaneous motor activity and social interaction test were studied 3 weeks later. A different set of mice underwent the same procedure, but received only the 2.5 g/kg dose of ethanol. Three weeks later, in order to induce CPP, the same animals were administered 1 or 6 mg/kg of cocaine or 1 or 2.5 mg/kg MDMA. The results revealed a decrease in aggressive behaviors and an anxiolytic profile in HNS mice and longer latency to explore the novel object by LNS mice. Ethanol exposure enhanced the reinforcing effects of cocaine and MDMA in both groups when CPP was induced with a sub-threshold dose of the drugs. The extinguished cocaine-induced CPP (1 and 6 mg/kg) was reinstated after a priming dose in HNS animals only. Our results confirm that intermittent EtOH administration during adolescence induces long-lasting effects that are manifested in adult life, and that there is an association between these effects and the novelty-seeking phenotype.

CB1 cannabinoid receptor-mediated aggressive behavior.

This study examined the role of cannabinoid CB1 receptors (CB1r) in aggressive behavior. Social encounters took place in grouped and isolated mice lacking CB1r (CB1KO) and in wild-type (WT) littermates. Cognitive impulsivity was evaluated in the delayed reinforcement task (DRT). Gene expression analyses of monoaminooxidase-A (MAO-A), catechol-o-methyl-transferase (COMT), 5-hydroxytriptamine transporter (5-HTT) and 5-HT1B serotonergic receptor (5HT1Br) in the median and dorsal raphe nuclei (MnR and DR, respectively) and in the amygdala (AMY) were performed by real time-PCR. Double immunohistochemistry studies evaluated COMT and CB1r co-localization in the raphe nuclei and in the cortical (ACo), basomedian (BMA) and basolateral (BLA) amygdaloid nuclei. The behavioral effects of the CB1r agonist ACEA (1 and 2xa0mg/kg) on aggression were also evaluated in isolated OF1 mice. CB1KO mice housed in groups showed higher levels of offensive aggression. Isolation increased aggressive behavior only in WT. In grouped CB1KO mice COMT gene expression was significantly higher in the MnR and DR, while MAO-A gene expression was lower in the MnR. Gene expression of 5HT1Br, COMT and MAO-A was higher in the amygdala of CB1KO mice. CB1r double-immunohistochemistry revealed cytoplasmic-labeled COMT-ir cells in the raphe nuclei and in the ACo, BMA and BLA. CB1r immunolabeling was observed only in ACo, BMA and BLA, where it was localized in axons and buttons. The density of labeled processes increased in BLA. Acute administration of the CB1 agonist ACEA (2xa0mg/kg) significantly decreased the aggression levels of OF1 mice. These results suggest that CB1r plays an important role in social interaction and aggressive behavior.

Capacity of novelty-induced locomotor activity and the hole-board test to predict sensitivity to the conditioned rewarding effects of cocaine

Novelty-seeking in rodents, defined as enhanced specific exploration of novel situations, is considered to predict the response of animals to drugs of abuse and, thus, allow drug-vulnerable individuals to be identified. The main objective of this study was to assess the predictive ability of two well-known paradigms of the novelty-seeking trait - novelty-induced locomotor activity (which distinguishes High- and Low-Responder mice, depending on their motor activity) and the hole-board test (which determines High- and Low-Novelty Seeker mice depending on the number of head dips they perform) - to identify subjects that would subsequently be more sensitive to the conditioned rewarding effects of cocaine in a population of young adult (PND 56) and adolescent (PND 35) OF1 mice of both sexes. Conditioned place preference (CPP), a useful tool for evaluating the sensitivity of individuals to the incentive properties of addictive drugs, was induced with a sub-threshold dose of cocaine (1 mg/kg, i.p.). Our results showed that novelty-induced motor activity had a greater predictive capacity to identify vulnerable-drug individuals among young-adult mice (PND 56), while the hole-board test was more effective in adolescents (PND 35). High-NR young-adults, which presented higher motor activity in the first ten minutes of the test (novelty-reactivity), were 3.9 times more likely to develop cocaine-induced CPP than Low-NR young-adults. When total activity (1h) was evaluated (novelty-habituation), only High-R (novelty-non-habituating) young-adult male and Low-R (novelty-habituating) female mice produced a high conditioning score. However, only High-Novelty Seeker male and female adolescents and Low-Novelty Seeker female young-adult animals (according to the hole-board test), acquired cocaine-induced CPP. These findings should contribute to the development of screening methods for identifying at-risk human drug users and prevention strategies for those with specific vulnerabilities.

Higher sensitivity to the conditioned rewarding effects of cocaine and MDMA in High-Novelty-Seekers mice exposed to a cocaine binge during adolescence

RationaleExposure to drugs during adolescence can induce alterations in the central nervous system. The novelty-seeking personality trait influences differences observed among individuals exposed to drugs of abuse.ObjectivesLong-term effects of intensive pre-treatment with cocaine during adolescence or adulthood were evaluated in High- and Low-Novelty Seeker (HNS and LNS) mice. It was hypothesized that a cocaine binge during adolescence would increase sensitivity to the rewarding effects of cocaine and MDMA, especially in HNS animals, and modify the spontaneous behaviour of adult animals.MethodsAdolescent (PND 33) and adult (PND 60) mice were identified as HNS or LNS according to their performance in the hole-board test. Subsequently, they received pre-treatment with cocaine (three injections per day of an increasing dose for 10xa0days) or saline. Three weeks later, the mice performed the hole-board, elevated plus maze, spontaneous locomotor activity and cocaine- (1xa0mg/kg) or MDMA- (1.25xa0mg/kg) induced conditioning place preference (CPP) tests. In another set of mice, the effects of pre-treatment of cocaine during adulthood on MDMA- or cocaine-induced CPP were also evaluated 3xa0weeks later.ResultsOnly HNS mice treated with cocaine during adolescence acquired MDMA- or cocaine-induced CPP in adulthood. Moreover, pre-exposure to cocaine during adolescence caused subsequent behavioural alterations, including reduced exploratory behaviour and increased locomotor reactivity.ConclusionsCocaine binge administration during adolescence induces a higher sensitivity to the rewarding effects of MDMA and cocaine in HNS mice in adulthood. This may explain the greater vulnerability often seen among individuals exposed early in life to drugs of abuse.

Effects of acute social stress on the conditioned place preference induced by MDMA in adolescent and adult mice.

Exposure to social defeat stress increases the rewarding effects of psychostimulants in animal models, but its effect on 3,4-methylenedioxymethylamphetamine (MDMA) reward has received little attention. In the present study, we evaluated the influence of social defeat on the rewarding effects of MDMA in adolescent [postnatal day (PND) 29–40] and adult (PND 50–61) male mice using the conditioned place preference paradigm. Experimental mice were exposed to social defeat in an agonistic encounter before each session of conditioning with 1.25 or 10u2009mg/kg of MDMA. The effects of social defeat on corticosterone levels and the motor or the anxiogenic effects of MDMA were also evaluated. Mice exposed to social defeat during adulthood did not show conditioned place preference after conditioning with either dose of MDMA. Conversely, social defeat did not affect the anxiogenic and motor effects of MDMA. Adult mice exposed to social defeat showed higher levels of corticosterone than their controls and adolescent mice. Social stress did not induce behavioural effects in adolescent mice. Our results show that stress induced by social defeat decreases the sensitivity of adult mice to the rewarding effects of MDMA.

Impact of social stress in addiction to psychostimulants: what we know from animal models.

Psychostimulant addiction, most notably cocaine and amphetamine - type stimulants are an important public health problem worldwide. It appears that social factors may influence the initiation, maintenance and recovery from addictions. Several animal models have been developed to study addiction, highlighting drug self-administration (SA) and the conditioned place preference (CPP) paradigms. These models have been modified to accurately reflect the characteristics of drug addiction in its different stages. One factor that clearly plays a major role in addiction is stress, which is a risk factor not only for the initiation, maintenance and escalation of drug consumption, but also for relapse. In animal models, stress for itself can provoke reinstatement of self-administration or CPP. The relationship between stress and addiction is very tight. One example is the close anatomical relationship of some areas that share these two phenomena. It seems obvious to think that the main source of stress in humans is social interaction. The aim of the present review is to gather the current information regarding the role of social stress in the addiction to psychostimulant drugs in animal models. First, we briefly describe the mechanisms by which stress exerts its effects and the basic concepts of addiction. We will try to establish common pathways of stress and addiction, to address later social stress effects on different stages of addiction. Then, we will address pharmacological therapies and preventive factors that counteract the enhancing effects of social stress in addiction. Finally, we will analyze how negative environmental conditions may induce individuals to increased vulnerability to drugs, and how favorable environmental conditions may have protective and curative effects against addiction. In this sense, we also analyze the importance of social interactions and their ability to modulate the different stages of addiction. As a conclusion, and despite the scarcity of the research, social stress exposure increases the initiation of psychostimulant consumption and the vulnerability to relapse in animal models of addiction. Studies on the mechanisms underlying the effects of social stress and how it can be counteracted pharmacologically, are research areas that should be explored in the future. At the same time, translational research on the effects of environmental conditions and positive social interactions, which have been shown to have a critical role in addictions, should be encouraged.

Sex-dependent effects of early maternal deprivation on MDMA-induced conditioned place preference in adolescent rats: possible neurochemical correlates.

The early neonatal stage constitutes a sensitive period during which exposure to adverse events can increase the risk of neuropsychiatric disorders. Maternal deprivation (MD) is a model of early life stress that induces long-term behavioural and physiological alterations, including susceptibility to different drugs of abuse. In the present study we have used the conditioned place preference (CPP) paradigm to address the influence of MD on the rewarding effects of 3,4-methylenedioxymetamphetamine (MDMA) in adolescent animals of both sexes. We have previously observed in adolescent rats that MD induces modifications in the serotonergic and endocannabinoid systems, which play a role in the rewarding effects of MDMA. In light of this evidence, we hypothesized that MD would alter the psychobiological consequences of exposure to MDMA. Neonatal Wistar rats underwent MD (24h, on PND 9) or were left undisturbed (controls). The animals were conditioned with 2.5mg/kg MDMA during the periadolescent period (PND 34-PND 43) and were tested in the open-field test at the end of adolescence (PND 60). Animals were sacrificed on PND 68-75 and levels of serotonin (5-HT) and its metabolite 5-hydroxyindole acetic acid were measured in the striatum, hippocampus and cortex, while the expression of hippocampal CB1 cannabinoid receptor (CB1R) and circulating levels of corticosterone and leptin were also measured. Control males showed CPP after administration of MDMA. However, no MDMA-induced CPP was detected in control females or MD males, and MD had no effect on open field activity in any group. A reduction in striatal and cortical 5-HT levels, increased expression of hippocampal CB1R and a marked trend towards higher circulating leptin levels were observed in MDMA-treated MD males. Our results demonstrate for the first time that MD reduces the rewarding effects of MDMA in a sex-dependent manner. We propose that this effect is related, at least in part, with alterations of the serotonergic and cannabinoid systems.