Cannabinoid-induced conditioned place preference in the spontaneously hypertensive rat-an animal model of attention deficit hyperactivity disorder

Age- and sex-dependent participation of the endocannabinoid system in locomotion and risk assessment of an ADHD rat model

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder affecting individuals across age groups. Impairments in executive function characterize ADHD and are often associated with elevated levels of risk-taking behaviors. The endocannabinoid system plays a crucial role in modulating prefrontal cortex circuits. Here, we assessed the effects of acute pharmacological manipulation of cannabinoid CB1 and CB2 receptors on locomotion and risk assessment/anxiety-like behaviors in an ADHD animal model during adolescence and adulthood. Further, we investigated the protein levels and gene expression of endocannabinoid system components (CB1, CB2, FAAH, MAGL) in the prefrontal cortex at both ages. During adolescence, activation of cannabinoid receptors aggravated the hyperactivity and risky behaviors of the ADHD model. These behavioral traits were more evident in female rats. In adulthood, manipulation of cannabinoid receptors did not alter hyperactivity but worsened risk assessment. Overall, gene expression levels of receptors and enzymes of the endocannabinoid system were increased in the ADHD model. Our findings suggest that the endocannabinoid system may operate differently in ADHD, and manipulating this system, especially in adolescents, could exacerbate deficits in inhibitory control.

Unlocking the age-old secrets of reward and substance use

Although substance use is widespread across the lifespan from early adolescence to older adulthood, the prevalence of substance use disorder (SUD) differs between age groups. These age differences in SUD rates necessitate an investigation into how age moderates reward sensitivity, and consequently influences the risks and consequences related to substance use. This theoretical review integrates evidence from the literature to address the dynamic interplay between age and reward in the context of substance use. Overall, increasing evidence demonstrates that age moderates reward sensitivity and underlying reward system neurobiology. Reward sensitivity undergoes a non-linear trajectory across the lifespan. Low levels of reward sensitivity are associated with childhood and late adulthood. In contrast, high levels are associated with early to late adolescence, followed by a decline in the twenties. These fluctuations in reward sensitivity across the lifespan contribute to complex associations with substance use. This lends support to adolescence and young adulthood as vulnerable periods for the risk of subsequent SUD. More empirical research is needed to investigate reward sensitivity during SUD maintenance and recovery. Future research should also involve larger sample sizes and encompass a broader range of age groups, including older adults.

Intrauterine and Postnatal Exposure to High Levels of Fluoride Is Associated with Motor Impairments, Oxidative Stress, and Morphological Damage in the Cerebellum of Offspring Rats

Fluoride (F) is abundantly present on Earth and plays a beneficial role in human health. However, exposure to high doses of F can be a risk, mainly in endemic fluorosis regions. In light of this, we investigated the effects of F exposure during the intrauterine and postnatal periods of rats, in doses similar to those recommended in drinking water and the levels of F in regions with endemic fluorosis, on the offspring rats’ cerebellum. Pregnant rats were divided into three groups: control (received ultrapure water only), 10 mg F/L, and 50 mg F/L for a period of 42 days (21 days gestation and 21 days lactation). At the end of the lactation period, the male pups were evaluated by behavioral tests, morphological markers, and biochemistry assays. The results pointed out that 50 mg F/L exposure during the intrauterine and lactational period of rats is capable of promoting oxidative stress in the cerebellum with a decrease in Purkinje cell density and myelin basic protein compromise, which could be associated with functional motor impairments. In addition, although 10 mg F/L exposure promoted redox alterations, it did not affect other parameters evaluated, highlighting the safe use of F in low doses.

Trace amine-associated receptor 1 modulates motor hyperactivity, cognition, and anxiety-like behavior in an animal model of ADHD

Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor that has recently been implicated in several psychiatric conditions related to monoaminergic dysfunction, such as schizophrenia, substance use disorders, and mood disorders. Although attention-deficit/hyperactivity disorder (ADHD) is also related to changes in monoaminergic neurotransmission, studies that assess whether TAAR1 participates in the neurobiology of ADHD are lacking. We hypothesized that TAAR1 plays an important role in ADHD and might represent a potential therapeutic target. Here, we investigate if TAAR1 modulates behavioral phenotypes in Spontaneously Hypertensive Rats (SHR), the most validated animal model of ADHD, and Wistar Kyoto rats (WKY, used as a control strain). Our results showed that TAAR1 is downregulated in ADHD-related brain regions in SHR compared with WKY. While intracerebroventricular (i.c.v.) administration of the selective TAAR1 antagonist EPPTB impaired cognitive performance in SHR, i.c.v. administration of highly selective TAAR1 full agonist RO5256390 decreased motor hyperactivity, novelty-induced locomotion, and induced an anxiolytic-like behavior. Overall, our findings show that changes in TAAR1 levels/activity underlie behavior in SHR, suggesting that TAAR1 plays a role in the neurobiology of ADHD. Although additional confirmatory studies are required, TAAR1 might be a potential pharmacological target for individuals with this disorder.

Early-life stress exacerbates the effects of WIN55,212-2 and modulates the cannabinoid receptor type 1 expression

Early-life stress induces an abnormal brain development and increases the risk of psychiatric diseases, including depression, anxiety and substance use disorders. We have developed a reliable model for maternal neglect, named maternal separation with early weaning (MSEW) in CD1 mice. In the present study, we evaluated the long-term effects on anxiety-like behaviours, nociception as well as the Iba1-positive microglial cells in this model in comparison to standard nest (SN) mice. Moreover, we investigated whether MSEW alters the cannabinoid agonist WIN55,212-2 effects regarding reward, spatial and emotional memories, tolerance to different cannabinoid responses, and physical dependence. Adult male offspring of MSEW group showed impaired responses on spatial and emotional memories after a repeated WIN55,212-2 treatment. These behavioural impairments were associated with an increase in basolateral amygdala and hippocampal CB1-expressing fibres and higher number of CB1-containing cells in cerebellum. Additionally, MSEW promotes a higher number of Iba1-positive microglial cells in basolateral amygdala and cerebellum. As for the cannabinoid-induced effects, rearing conditions did not influence the rewarding effects of WIN55,212-2 in the conditioned place preference paradigm. However, MSEW mice showed a delay in the development of tolerance to the cannabinoid effects. Moreover, CB1-positive fibres were reduced in limbic areas in MSEW mice after cannabinoid withdrawal precipitated with the CB1 antagonist SR141617A. These findings support that early-life stress promotes behavioural and molecular changes in the sensitivity to cannabinoids, which are mediated by alterations in CB1 signalling in limbic areas and it induces an increased Iba1-microglial marker which could interfere in emotional memories formation.

Attention-Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype/Presentation: Research Progress and Translational Studies

Research on the predominantly inattentive attention-deficit/hyperactivity disorder (ADHD-PI) subtype/presentation is important given its high prevalence, but paradoxically it is under-recognized and undertreated. The temporal stability of the inattention symptom could impact the high worldwide prevalence of ADHD-PI. Some evidence suggests differences in the nature of attentional deficit in ADHD-PI vs. that in other subtypes. Impairments in neuropsychological, neurocognitive, and social functioning are also evident in ADHD-PI, which could be specific to the subtype (e.g., processing speed, social perception, and skills), or differ from others in severity. Neuroimaging studies have also revealed ADHD-PI-specific neuropathological abnormalities and those that are shared with other subtypes. ADHD-PI is highly comorbid with learning and internalizing (e.g., anxiety and depression) disorders. There is no solid evidence for ADHD-PI-specific genetic etiologies and differential responses of subtypes to ADHD medications. Translational studies have used the Wistar Kyoto/NCrl substrain which requires further characterizations as an ADHD-PI model. Overall, ADHD-PI research has been conducted in the context of the Diagnostic and Statistical Manual, which arguably does not conform to the widely recognized "dimensional" view of ADHD. The Research Domain Criteria has been proposed to provide a novel framework for understanding the nature of neuropsychiatric illnesses and ultimately improve their diagnosis and treatment.

Organophosphate Agent Induces ADHD-Like Behaviors via Inhibition of Brain Endocannabinoid-Hydrolyzing Enzyme(s) in Adolescent Male Rats

Anticholinergic organophosphate (OP) agents act on the diverse serine hydrolases, thereby revealing unexpected biological effects. Epidemiological studies indicate a relationship between the OP exposure and development of attention-deficit/hyperactivity disorder (ADHD)-like symptoms, whereas no plausible mechanism for the OP-induced ADHD has been established. The present investigation employs ethyl octylphosphonofluoridate (EOPF) as an OP-probe, which is an extremely potent inhibitor of endocannabinoid (EC, anandamide and 2-arachidonoylglycerol)-hydrolyzing enzymes: that is, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). An ex vivo experiment shows that EOPF treatment decreases FAAH and MAGL activities and conversely increases EC levels in the rat brain. Subsequently, EOPF (treated intraperitoneally once at 0, 1, 2, or 3 mg/kg) clearly induces ADHD-like behaviors (in elevated plus-maze test) in both Wistar and spontaneously hypertensive rats. The EOPF-induced behaviors are reduced by a concomitant administration of cannabinoid receptor inverse agonist SLV-319. Accordingly, the EC system is a feasible target for OP-caused ADHD-like behaviors in adolescent rats.

Caffeine and cannabinoid receptors modulate impulsive behavior in an animal model of attentional deficit and hyperactivity disorder

Attention deficit and hyperactivity disorder (ADHD) is characterized by impaired levels of hyperactivity, impulsivity, and inattention. Adenosine and endocannabinoid systems tightly interact in the modulation of dopamine signaling, involved in the neurobiology of ADHD. In this study, we evaluated the modulating effects of the cannabinoid and adenosine systems in a tolerance to delay of reward task using the most widely used animal model of ADHD. Spontaneous Hypertensive Rats (SHR) and Wistar-Kyoto rats were treated chronically or acutely with caffeine, a non-selective adenosine receptor antagonist, or acutely with a cannabinoid agonist (WIN55212-2, WIN) or antagonist (AM251). Subsequently, animals were tested in the tolerance to delay of reward task, in which they had to choose between a small, but immediate, or a large, but delayed, reward. Treatment with WIN decreased, whereas treatment with AM251 increased the choices of the large reward, selectively in SHR rats, indicating a CB₁ receptor-mediated increase in impulsive behavior. An acute pre-treatment with caffeine blocked WIN effects. Conversely, a chronic treatment with caffeine increased the impulsive phenotype and potentiated the WIN effects. The results indicate that both cannabinoid and adenosine receptors modulate impulsive behavior in SHR: the antagonism of cannabinoid receptors might be effective in reducing impulsive symptoms present in ADHD; in addition, caffeine showed the opposite effects on impulsive behavior depending on the length of treatment. These observations are of particular importance to consider when therapeutic manipulation of CB1 receptors is applied to ADHD patients who consume coffee.

Highway to hell or magic smoke? The dose-dependence of Δ9-THC in place conditioning paradigms

The prerequisites for responsible cannabis use are at the heart of current inquiries into cannabis decriminalization by policy makers as well as academic and nonacademic stakeholders at a global scale. Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the prime psychoactive compound of the cannabis sativa, as well as cannabimimetics that resemble the pharmacological properties and psychological effects of Δ⁹-THC, lend themselves handsomely to the preclinical scrutiny of reward-related behavior because they carry marked translational value. Although a functional dichotomy of the psychological effects of Δ⁹-THC (rewarding versus aversive) has been abundantly reported in place conditioning (PC) paradigms, and might be best attributed to a dose-dependence of Δ⁹-THC, most PC studies with Δ⁹-THC feature no significant effects at all. Therefore, after decades of rigorous research, it still remains undetermined whether Δ⁹-THC generally exerts rewarding or aversive effects in rodents. Here, we set out to extrapolate the commonly alleged dose-dependence of the rewarding and aversive effects of Δ⁹-THC from the existing literature, at the behavioral pharmacological level of analysis. Specifically, our meta-analysis investigated: (i) the alleged bidirectional effects and dose-dependence of Δ⁹-THC in the PC test; (ii) methodological inconsistencies between PC studies; and (iii) other pharmacological studies on cannabinoids (i.e., dopamine release, anxiety, stress, conditioned taste aversion, catalepsy) to substantiate the validity of PC findings. Our findings suggest that: (i) Δ⁹-THC dose-dependently generates rewarding (1 mg/kg) and aversive (5 mg/kg) effects in PC; (ii) an inconsistent use of priming injections hampers a clear establishment of the rewarding effects of Δ⁹-THC in PC tests and might explain the seemingly contradictory plethora of nonsignificant THC studies in the PC test; and (iii) other pharmacological studies on Δ⁹-THC substantiate the dose-dependent biphasic effects of Δ⁹-THC in PC. A standardized experimental design would advance evidence-based practice in future PC studies with Δ⁹-THC and facilitate the pointed establishment of rewarding and aversive effects of the substance.

Tripping with Synthetic Cannabinoids ("Spice"): Anecdotal and Experimental Observations in Animals and Man

The phenomenon of consuming synthetic cannabinoids ("Spice") for recreational purposes is a fairly recent trend. However, consumption of cannabis dates back millennia, with numerous accounts written on the experience of its consumption, and thousands of scientific reports published on the effects of its constituents in laboratory animals and humans. Here, we focus on consolidating the scientific literature on the effects of "Spice" compounds in various behavioral assays, including assessing abuse liability, tolerance, dependence, withdrawal, and potential toxicity. In most cases, the behavioral effects of "Spice" compounds are compared with those of Δ9-tetrahydrocannabinol. Methodological aspects, such as modes of administration and other logistical issues, are also discussed. As the original "Spice" molecules never were intended for human consumption, scientifically based information about potential toxicity and short- and long-term behavioral effects are very limited. Consequently, preclinical behavioral studies with "Spice" compounds are still in a nascent stage. Research is needed to address the addiction potential and other effects, including propensity for producing tissue/organ toxicity, of these synthetic cannabimimetic "Spice" compounds.

Δ(9)-Tetrahydrocannabinol-like effects of novel synthetic cannabinoids in mice and rats

RATIONALE

Novel cannabinoid compounds continue to be marketed as "legal" marijuana substitutes, even though little is known about their molecular and behavioral effects.

OBJECTIVES

Six of these compounds (ADBICA, ADB-PINACA, THJ-2201, RCS-4, JWH-122, JWH-210) were tested for in vitro and in vivo cannabinoid-like effects to determine their abuse liability.

METHODS

Binding to and functional activity at CB1 cannabinoid receptors was tested. Locomotor activity in mice was tested to screen for behavioral activity and to identify behaviorally active dose ranges and times of peak effect. Discriminative stimulus effects of the six compounds were tested in rats trained to discriminate Δ(9)-tetrahydrocannabinol (Δ(9)-THC).

RESULTS

ADBICA, ADB-PINACA, THJ-2201, RCS-4, JWH-122, and JWH-210 showed high affinity binding at the CB1 receptor at nanomolar affinities (0.59 to 22.5 nM), and all acted as full agonists with nanomolar potencies (0.024 to 111 nM) when compared to the CB1 receptor full agonist CP 55940. All compounds depressed locomotor activity below 50 % of vehicle responding, with depressant effects lasting 1.5 to nearly 4 h. All compounds fully substituted (<80 % Δ(9)-THC-appropriate responding) for the discriminative stimulus effects of Δ(9)-THC. 3,4-Methylenedioxy-methamphetamine (MDMA) was tested as a negative control and did not substitute for Δ(9)-THC (11 % Δ(9)-THC-appropriate responding).

CONCLUSIONS

All six of the compounds acted at the CB1 receptor and produced behavioral effects common to abused cannabinoid compounds, which suggest that these compounds have substantial abuse liability common to controlled synthetic cannabinoid compounds.

Binge-like ingestion of a combination of an energy drink and alcohol leads to cognitive deficits and motivational changes

The combination of alcohol with an energy drink (ED) is believed to contribute to risky alcohol-drinking behaviors, such as binge drinking. However, the long-term effects on cognition and reward function that are caused by the repeated binge-like ingestion of alcohol and EDs are still poorly known. The present study examined the effects of a history of repeated exposure to alcohol and/or an ED on short-term memory and alcohol-seeking behavior. Male Wistar rats were given daily intragastric administration of alcohol (3.4g/kg) combined or not with an ED (10.71ml/kg) for 6 consecutive days. The rats were tested for locomotion 15min after the first intragastric treatment. Short-term memory was assessed in the novel object recognition and social discrimination tests 2-3days after the last intragastric administration. The rewarding effect of alcohol was tested 1-3weeks following the last intragastric administration in a conditioned place preference paradigm. The acute binge-like ingestion of alcohol decreased locomotor activity, whereas the combination of alcohol and an ED increased locomotion in the first minutes of assessment. Alcohol exposure produced cognitive deficits in both the object recognition and social discrimination tests, and adding the ED to the alcohol solution did not modify these effects. The combination of alcohol and the ED increased alcohol-induced conditioned place preference. Thus, a history of binge-like alcohol exposure combined with the ED caused subsequent cognitive deficits and increased alcohol seeking behavior, and such behavioral effects might contribute to the progression to alcohol abuse disorders.

Common prefrontal cortical gene expression profiles between adolescent SHR/NCrl and WKY/NCrl rats which showed inattention behavior

Factor analyses of attention-deficit/hyperactivity (ADHD) symptoms divide the behavioral symptoms of ADHD into two separate domains, one reflecting inattention and the other, a combination of hyperactivity and impulsivity. Identifying domain-specific genetic risk variants may aid in the discovery of specific biological risk factors for ADHD. In contrast with data available on genes involved in hyperactivity and impulsivity, there is limited information on the genetic influences of inattention. Transcriptional profiling analysis in animal models of disorders may provide an important tool to identify genetic involvement in behavioral phenotypes. To explore some of the potential genetic underpinnings of ADHD inattention, we examined common differentially expressed genes (DEGs) in the prefrontal cortex of SHR/NCrl, the most validated animal model of ADHD and WKY/NCrl, animal model of ADHD-inattentive type. In contrast with Wistar rats, strain representing the "normal" heterogeneous population, SHR/NCrl and WKY/NCrl showed inattention behavior in the Y-maze task. The common DEGs in the PFC of SHR/NCrl and WKY/NCrl vs. Wistar rats are those involved in transcription (e.g. Creg1, Thrsp, Zeb2), synaptic transmission (e.g. Atp2b2, Syt12, Chrna5), neurological system process (e.g. Atg7, Cacnb4, Grin3a), and immune response (e.g. Atg7, Ip6k2, Mx2). qRT-PCR analyses validated expression patterns of genes representing the major functional gene families among the DEGs (Grin3a, Thrsp, Vof-16 and Zeb2). Although further studies are warranted, the present findings indicate novel genes associated with known functional pathways of relevance to ADHD which are assumed to play important roles in the etiology of ADHD-inattentive subtype.

Emergence of sex differences in the development of substance use and abuse during adolescence

Substance use and abuse begin during adolescence. Male and female adolescent humans initiate use at comparable rates, but males increase use faster. In adulthood, more men than women use and abuse addictive drugs. However, some women progress more rapidly from initiation of use to entry into treatment. In animal models, adolescent males and females consume addictive drugs similarly. However, reproductively mature females acquire self-administration faster, and in some models, escalate use more. Sex/gender differences exist in neurobiologic factors mediating both reinforcement (dopamine, opioids) and aversiveness (CRF, dynorphin), as well as intrinsic factors (personality, psychiatric co-morbidities) and extrinsic factors (history of abuse, environment especially peers and family) which influence the progression from initial use to abuse. Many of these important differences emerge during adolescence, and are moderated by sexual differentiation of the brain. Estradiol effects which enhance both dopaminergic and CRF-mediated processes contribute to the female vulnerability to substance use and abuse. Testosterone enhances impulsivity and sensation seeking in both males and females. Several protective factors in females also influence initiation and progression of substance use including hormonal changes of pregnancy as well as greater capacity for self-regulation and lower peak levels of impulsivity/sensation seeking. Same sex peers represent a risk factor more for males than females during adolescence, while romantic partners increase risk for women during this developmental epoch. In summary, biologic factors, psychiatric co-morbidities as well as personality and environment present sex/gender-specific risks as adolescents begin to initiate substance use.

Animals with a schizophrenia-like phenotype are differentially sensitive to the motivational effects of cannabinoid agonists in conditioned place preference

Cannabis is the most consumed illicit drug worldwide, but among patients with a diagnosis of schizophrenia, this consumption is higher suggesting that they are differentially sensitive to cannabis. We chose to study this problematic using a neurodevelopmental model of schizophrenia: neonatal ventral hippocampus lesions (NVHL). In a first study, we compared the locomotor response to novelty, a mild stress and two doses of amphetamine (0.75 and 1.5 mg/kg) in sham and NVHL rats at post-natal day 35 (PD35) or 56 (PD56). In a second study, we investigated the valence of the motivational effect of Delta-9-tetrahydrocannabinnol (THC, 0.5 mg/kg, i.p.) and the cannabinoid receptor agonist, WIN55,212-2 (WIN, 1 mg/kg, i.p.), using the conditioned place preference paradigm; we used a biased procedure that comprised 12 days of testing with 3 paired-conditioning. The effects of this dose of WIN were also measured on locomotor activity. Results confirmed that the adult NVHL animals displayed a stronger locomotor response to the two doses of amphetamine, but not to novelty and a mild stress. In adult NVHL, but not sham animals, WIN stimulated locomotor activity and produced a conditioned place aversion. At the dose tested, THC tended to produce an aversion in adult sham but not NVHL animals. Taken together these findings show that adult animals with a schizophrenia-like phenotype are differentially sensitive to the motivational effect of cannabinoids.

Endocannabinoids underlie reconsolidation of hedonic memories in Wistar rats

RATIONALE

Drug addicts constantly relapse to drug seeking after recall of memories linked to the drug experience. It is believed that a successful application of therapies that block memory reconsolidation may end the continuous cycle of drug relapse.

OBJECTIVES

The purpose of this study is to investigate whether modulation of the endocannabinoid system would impact the reconsolidation of opioid-related hedonic memories in rats previously paired to morphine context.

METHODS

Male Wistar rats were trained to acquire a morphine-conditioned place preference (CPP). One week later, morphine-CPP memory was reactivated by a brief exposure to a drug-paired context. Immediately after the memory reactivation session, independent groups of morphine-trained rats received a single subcutaneous injection of different doses of cannabinoid CB1 receptor antagonist rimonabant, CB2-selective antagonist AM630, potent CB1/CB2 agonist WIN 55,212-2, inhibitor of enzyme fatty acid amide hydrolase URB597, or vehicle. Morphine-CPP was retested 1 and 2 weeks after reactivation.

RESULTS

Blockade of CB1 (but not CB2) cannabinoid receptors impaired CPP reconsolidation of morphine-CPP at both tests 1 and 2 weeks post-reactivation, whereas direct activation of cannabinoid receptors did not produce significant effects on morphine-induced CPP. However, boosting endocannabinoid signaling by inhibition of anandamide metabolism promoted a transient CB1-dependent enhancement of the CPP.

Endocannabinoid signaling in the etiology and treatment of major depressive illness

The purpose of this review is to examine human and preclinical data that are relevant to the following hypotheses. The first hypothesis is that deficient CB1R-mediated signaling results in symptoms that mimic those seen in depression. The second hypothesis is that activation of CB1R-mediated signaling results in behavioral, endocrine and other effects that are similar to those produced by currently used antidepressants. The third hypothesis is that conventional antidepressant therapies act through enhanced CB1R mediated signaling. Together the available data indicate that activators of CB1R signaling, particularly inhibitors of fatty acid amide hydrolase, should be considered for clinical trials for the treatment of depression.

Cannabinoid Regulation of Brain Reward Processing with an Emphasis on the Role of CB1 Receptors: A Step Back into the Future

Over the last decades, the endocannabinoid system has been implicated in a large variety of functions, including a crucial modulation of brain-reward circuits and the regulation of motivational processes. Importantly, behavioral studies have shown that cannabinoid compounds activate brain reward mechanisms and circuits in a similar manner to other drugs of abuse, such as nicotine, alcohol, cocaine, and heroin, although the conditions under which cannabinoids exert their rewarding effects may be more limited. Furthermore, there is evidence on the involvement of the endocannabinoid system in the regulation of cue- and drug-induced relapsing phenomena in animal models. The aim of this review is to briefly present the available data obtained using diverse behavioral experimental approaches in experimental animals, namely, the intracranial self-stimulation paradigm, the self-administration procedure, the conditioned place preference procedure, and the reinstatement of drug-seeking behavior procedure, to provide a comprehensive picture of the current status of what is known about the endocannabinoid system mechanisms that underlie modification of brain-reward processes. Emphasis is placed on the effects of cannabinoid 1 (CB1) receptor agonists, antagonists, and endocannabinoid modulators. Further, the role of CB1 receptors in reward processes is investigated through presentation of respective genetic ablation studies in mice. The vast majority of studies in the existing literature suggest that the endocannabinoid system plays a major role in modulating motivation and reward processes. However, much remains to be done before we fully understand these interactions. Further research in the future will shed more light on these processes and, thus, could lead to the development of potential pharmacotherapies designed to treat reward-dysfunction-related disorders.

Acute total sleep deprivation potentiates amphetamine-induced locomotor-stimulant effects and behavioral sensitization in mice

It has been demonstrated that a prolonged period (48 h) of paradoxical sleep deprivation (PSD) potentiates amphetamine (AMP)-induced behavioral sensitization, an animal model of addiction-related neuroadaptations. In the present study, we examined the effects of an acute short-term deprivation of total sleep (TSD) (6h) on AMP-induced behavioral sensitization in mice and compared them to the effects of short-term PSD (6 h). Three-month-old male C57BL/6J mice underwent TSD (experiment 1-gentle handling method) or PSD (experiment 2-multiple platforms method) for 6 h. Immediately after the sleep deprivation period, mice were tested in the open field for 10 min under the effects of saline or 2.0 mg/kg AMP. Seven days later, to assess behavioral sensitization, all of the mice received a challenge injection of 2.0 mg/kg AMP and were tested in the open field for 10 min. Total, peripheral, and central locomotion, and grooming duration were measured. TSD, but not PSD, potentiated the hyperlocomotion induced by an acute injection of AMP and this effect was due to an increased locomotion in the central squares of the apparatus. Similarly, TSD facilitated the development of AMP-induced sensitization, but only in the central locomotion parameter. The data indicate that an acute period of TSD may exacerbate the behavioral effects of AMP in mice. Because sleep architecture is composed of paradoxical and slow wave sleep, and 6-h PSD had no effects on AMP-induced hyperlocomotion or sensitization, our data suggest that the deprivation of slow wave sleep plays a critical role in the mechanisms that underlie the potentiating effects of TSD on both the acute and sensitized addiction-related responses to AMP.

Long-term cognitive impairments induced by chronic cannabinoid exposure during adolescence in rats: a strain comparison

RATIONALE

During cerebral development, adolescence is a critical phase in which the endocannabinoid system plays an important role in regulating various neurotransmitters. Moreover, evidence from both human and animal studies suggests that chronic cannabinoid exposure during this vulnerable period can induce persistent brain and behavioural alterations.

OBJECTIVES

The aim of this study was to compare the long-term cognitive consequences of chronic adolescence cannabinoid exposure between Lister Hooded rats and Wistar rats.

METHODS

Rats of both strains were injected daily throughout their adolescent or adult periods with vehicle or with incremental doses of the synthetic cannabinoid CB1 receptor agonist CP55,940 (CP). Short-term and spatial working memories were assessed using the object recognition and object location, tasks respectively. For both tasks, the effect of a 30- or 120-min delay between the learning and the testing phase was investigated.

RESULTS

In the object recognition task, adolescent CP exposure impaired short-term memory after both delays in both strains. In contrast, in the object location task, adolescent CP exposure impaired spatial working memory in the Wistar rats after a 30-min delay, whereas the Lister Hooded rats exhibited a similar effect only after a 120-min delay. In these tests, no long-term deleterious effects were found following adult CP exposure in either strain.

CONCLUSIONS

Our results confirm that adolescence is a critical period for the deleterious effects of cannabinoids on cognition and that these deleterious effects on spatial working memory are more strain-dependent than the effects observed on short-term memory.

Differential effects of intermittent and continuous exposure to novel environmental stimuli on the development of amphetamine-induced behavioral sensitization in mice: implications for addiction

BACKGROUND

Previous studies have demonstrated a preventive effect of continuous environmental enrichment during early development on the vulnerability of rodents to drug addiction-related behaviors. Recently, it was demonstrated that a continuous environmental enrichment could eliminate already established addiction-related behaviors in mice. The present study compared the effects of intermittent or continuous exposure to novel stimuli during repeated amphetamine (Amp) treatment on the development of behavioral sensitization (an animal model of addiction-related neuroadaptations) in adult mice.

METHODS

Three-month-old male Swiss mice were treated with 2.5mg/kg Amp every other day for 13 days in their home cages. Novel objects were presented in their home cages for 2h on non-drug treatment days (experiment 1) or for 24h/day during the 13 days of drug treatment (experiment 2). Seven days after the drug treatment had finished, the mice were challenged with 2.5mg/kg Amp, and their locomotor activity was quantified in a familiar open field for 10 min.

RESULTS

Intermittent exposure to the novel objects did not modify the acute Amp locomotor stimulatory effect but potentiated the development of Amp-induced locomotor sensitization. This enhanced sensitization was due to increased locomotion in the central squares of the apparatus, which suggests anxiolysis or increased impulsiveness. Conversely, continuous exposure to the novel objects potentiated the acute Amp locomotor stimulatory effect and blunted the development of Amp-induced locomotor sensitization.

CONCLUSIONS

We conclude that addiction-related behaviors can be differentially and critically modified depending on the schedule and period of the novelty exposure.

[Comorbidity between attention deficit/hyperactivity disorder and substance use disorders: evidence from animal models]

OBJECTIVE

To describe some recent theories regarding the comorbidity between attention deficit/hyperactivity disorder and substance use disorders and discuss the utility of using spontaneously hypertensive rats (an animal model of attention deficit/hyperactivity disorder) for the study of attention deficit/hyperactivity disorder and substance use disorders comorbidity.

METHOD

We compiled the main results of studies investigating the behavioral effects of drugs of abuse in spontaneously hypertensive rats.

RESULTS AND DISCUSSION

Spontaneously hypertensive rats, in addition to expressing the main features of attention deficit/hyperactivity disorder (impulsivity, hyperactivity, and attention deficit), appear to be more sensitive to psychostimulants, cannabinoids, and opioids and drink large amounts of alcohol. Repeated treatment of spontaneously hypertensive rats with methylphenidate (a first-choice drug for the treatment of attention deficit/hyperactivity disorder) or exposure to an enriched environment during adolescence resulted in an increase or decrease, respectively, in alcohol consumption in adulthood. These results suggest that environmental factors can either favor or confer resistance to attention deficit/hyperactivity disorder and substance use disorders comorbidity. Although research is at the very early stage in this field, spontaneously hypertensive rats appear to be a useful animal model for the study of attention deficit/hyperactivity disorder and substance use disorders comorbidity.

Direct intra-accumbal infusion of a beta-adrenergic receptor antagonist abolishes WIN 55,212-2-induced aversion

The cannabinoid system is known to interact with a variety of neuromodulators in the central nervous system and impacts diverse behaviors. Previous studies have demonstrated that limbic norepinephrine is a critical determinant in the behavioral expression of cannabinoid-induced aversion. The present study was carried out to define the adrenergic receptor subtype involved in mediating cannabinoid-induced behavioral responses. An acute microinjection of the β1-adrenergic receptor blocker, betaxolol, directly into the nucleus accumbens (Acb), was able to prevent WIN 55,212-2-induced aversion, but not lithium-induced aversion, as measured in a place conditioning paradigm. These results suggest that noradrenergic transmission in the Acb is important for cannabinoid-induced aversion and that beta-adrenergic antagonists may be effective in counteracting negative side effects of cannabinoid-based agents.

Iron-sulfur clusters: biogenesis, molecular mechanisms, and their functional significance

Iron-sulfur clusters [Fe-S] are small, ubiquitous inorganic cofactors representing one of the earliest catalysts during biomolecule evolution and are involved in fundamental biological reactions, including regulation of enzyme activity, mitochondrial respiration, ribosome biogenesis, cofactor biogenesis, gene expression regulation, and nucleotide metabolism. Although simple in structure, [Fe-S] biogenesis requires complex protein machineries and pathways for assembly. [Fe-S] are assembled from cysteine-derived sulfur and iron onto scaffold proteins followed by transfer to recipient apoproteins. Several predominant iron-sulfur biogenesis systems have been identified, including nitrogen fixation (NIF), sulfur utilization factor (SUF), iron-sulfur cluster (ISC), and cytosolic iron-sulfur protein assembly (CIA), and many protein components have been identified and characterized. In eukaryotes ISC is mainly localized to mitochondria, cytosolic iron-sulfur protein assembly to the cytosol, whereas plant sulfur utilization factor is localized mainly to plastids. Because of this spatial separation, evidence suggests cross-talk mediated by organelle export machineries and dual targeting mechanisms. Although research efforts in understanding iron-sulfur biogenesis has been centered on bacteria, yeast, and plants, recent efforts have implicated inappropriate [Fe-S] biogenesis to underlie many human diseases. In this review we detail our current understanding of [Fe-S] biogenesis across species boundaries highlighting evolutionary conservation and divergence and assembling our knowledge into a cellular context.

Methylphenidate treatment in adolescent rats with an attention deficit/hyperactivity disorder phenotype: cocaine addiction vulnerability and dopamine transporter function

Appropriate animal models of attention deficit/hyperactivity disorder (ADHD) and drug reinforcement allow investigation of possible underlying biological bases of ADHD and its comorbidity with cocaine addiction. Toward this end, spontaneously hypertensive rats (SHRs) exhibiting an ADHD phenotype were compared with Wistar-Kyoto (WKY) and Wistar (WIS) rats. Initially, 1.5 mg/kg oral methylphenidate or vehicle was administered between postnatal days 28 and 55, and acquisition of visual discrimination learning was examined. After discontinuing adolescent treatments, adult rats were evaluated for cocaine self-administration and dopamine transporter (DAT) function in the prefrontal cortex (PFC) and striatum. During adolescence, SHRs showed deficits in visual discrimination relative to WKY and WIS rats when non-medicated. Methylphenidate improved visual discrimination only in SHRs. Compared with WKY and WIS rats, SHRs with previous methylphenidate treatment acquired cocaine self-administration faster, identified cocaine as a highly efficacious reinforcer by displaying an upward shift in the cocaine dose-response function, and showed the greatest motivation to self-administer cocaine by exhibiting the highest progressive ratio breakpoints. In the PFC, the maximal dopamine uptake (V(max)) at DAT was decreased in SHRs and increased in WKY and WIS rats by previous methylphenidate treatment. The affinity (K(m)) for dopamine at DAT in the PFC was not different between strains, nor was V(max) or K(m) altered in the striatum by previous methylphenidate treatment in any strain. Methylphenidate-induced decreases in dopamine clearance by DAT in the PFC may underlie increased cocaine self-administration in SHRs. These preclinical findings suggest that caution should be exercised when methylphenidate is prescribed for first-time treatment of ADHD in adolescent patients, as cocaine addiction vulnerability may be augmented.

Reinforcing effects of methamphetamine in an animal model of attention-deficit/hyperactivity disorder--the spontaneously hypertensive rat

Substrains of the Spontaneously Hypertensive rat (SHR), a putative animal model of Attention-Deficit/Hyperactivity Disorder (ADHD), have demonstrated increased sensitivity to many drugs of abuse, including psychostimulants. Therefore, it was suggested that studies in SHR may help elucidate ADHD and comorbidity with substance use disorder (SUD). However, the drug intake profile of the SHR in the most relevant animal model of drug addiction, the self-administration (SA) test, and its response on the conditioned place preference (CPP) paradigm are not yet determined. In the present study, we employed SA and CPP tests to investigate the reinforcing effects of the psychostimulant methamphetamine in an SHR substrain obtained from Charles River, Japan (SHR/NCrlCrlj). Concurrent tests were also performed in Wistar rats, the strain representing "normal" heterogeneous population. To address if the presence of ADHD behaviors further increases sensitivity to the rewarding effect of methamphetamine during adolescence, a critical period for the onset of drug abuse, CPP tests were especially conducted in adolescent Wistar and SHR/NCrlCrlj. We found that the SHR/NCrlCrlj also acquired methamphetamine SA and CPP, indicating reinforcing effects of methamphetamine in this ADHD animal model. However, we did not observe increased responsiveness of the SHR/NCrlCrlj to methamphetamine in both SA and CPP assays. This indicates that the reinforcing effects of methamphetamine may be similar in strains and that the SHR/NCrlCrlj may not adequately model ADHD and increased sensitivity to methamphetamine.

Contribution of limbic norepinephrine to cannabinoid-induced aversion

RATIONALE

The cannabinoid system has risen to the forefront in the development of novel treatments for a number of pathophysiological processes. However, significant side effects have been observed in clinical trials raising concerns regarding the potential clinical utility of cannabinoid-based agents. Understanding the neural circuits and neurochemical substrates impacted by cannabinoids will provide a better means of gaging their actions within the central nervous system that may contribute to the expression of unwanted side effects.

OBJECTIVES

In the present study, we investigated whether norepinephrine (NE) in the limbic forebrain is a critical determinant of cannabinoid receptor agonist-induced aversion and anxiety in rats.

METHODS

An immunotoxin lesion approach was combined with behavioral analysis using a place conditioning paradigm and the elevated zero maze.

RESULTS

Our results show that the non-selective CB1/CB2 receptor agonist, WIN 55,212-2, produced a significant place aversion in rats. Further, NE in the nucleus accumbens was critical for WIN 55,212-2-induced aversion but did not affect anxiety-like behaviors. Depletion of NE from the bed nucleus of the stria terminalis was ineffective in altering WIN 55,212-2-induced aversion and anxiety.

CONCLUSIONS

These results indicate that limbic, specifically accumbal, NE is required for cannabinoid-induced aversion but is not essential to cannabinoid-induced anxiety.

The emergence of gonadal hormone influences on dopaminergic function during puberty

Adolescence is the developmental epoch during which children become adults-intellectually, physically, hormonally and socially. Brain development in critical areas is ongoing. Adolescents are risk-taking and novelty-seeking and they weigh positive experiences more heavily and negative experiences less than adults. This inherent behavioral bias can lead to risky behaviors like drug taking. Most drug addictions start during adolescence and early drug-taking is associated with an increased rate of drug abuse and dependence. The hormonal changes of puberty contribute to physical, emotional, intellectual and social changes during adolescence. These hormonal events do not just cause maturation of reproductive function and the emergence of secondary sex characteristics. They contribute to the appearance of sex differences in non-reproductive behaviors as well. Sex differences in drug use behaviors are among the latter. The male predominance in overall drug use appears by the end of adolescence, while girls develop the rapid progression from first use to dependence (telescoping) that represent a female-biased vulnerability. Sex differences in many behaviors including drug use have been attributed to social and cultural factors. A narrowing gap in drug use between adolescent boys and girls supports this thesis. However, some sex differences in addiction vulnerability reflect biologic differences in brain circuits involved in addiction. The purpose of this review is to summarize the contribution of sex differences in the function of ascending dopamine systems that are critical to reinforcement, to briefly summarize the behavioral, neurochemical and anatomical changes in brain dopaminergic functions related to addiction that occur during adolescence and to present new findings about the emergence of sex differences in dopaminergic function during adolescence.

Cannabinoid conditioned reward and aversion: behavioral and neural processes

The discovery that delta-9-tetrahydrocannabinol (Δ(9)-THC) is the primary psychoactive ingredient in marijuana prompted research that helped elucidate the endogenous cannabinoid system of the brain. Δ(9)-THC and other cannabinoid ligands with agonist action (CP 55,940, HU210, and WIN 55,212-2) increase firing of dopamine neurons and increase synaptic dopamine in brain regions associated with reward and drug addiction. Such changes in cellular processes have prompted investigators to examine the conditioned rewarding effects of the cannabinoid ligands using the place conditioning task with rats and mice. As reviewed here, these cannabinoid ligands can condition place preferences (evidence for rewarding effects) and place aversions (evidence for aversive qualities). Notably, the procedural details used in these place conditioning studies have varied across laboratories. Such variation includes differences in apparatus type, existence of procedural biases, dose, number of conditioning trials, injection-to-placement intervals, and pre-training drug exposure. Some differences in outcome across studies can be explained by these procedural variables. For example, low doses of Δ(9)-THC appear to have conditioned rewarding effects, whereas higher doses have aversive effects that either mask these rewarding effects or condition a place aversion. Throughout this review we highlight key areas that need further research.

Effect of adolescent exposure to WIN 55212-2 on the acquisition and reinstatement of MDMA-induced conditioned place preference

The present study employs a conditioned place preference procedure (CPP) to examine the effects of exposure to the cannabinoid agonist WIN 55212-2 (WIN) (0.1 and 0.5mg/kg) during adolescence on the reinforcing properties of +/-3,4-methylenedioxymetamphetamine hydrochloride (MDMA) (1.25 and 2.5mg/kg) in mice. On postnatal day (PD) 27, animals received a daily injection of the assigned treatment on 5 consecutive days, and three days later the place conditioning procedure was initiated (PD 35). The results suggest that pre-exposure to cannabinoids strengthens the properties of MDMA and favors reinstatement of the craving for the drug, which endorses the gateway hypothesis.

Environmental enrichment reduces the impact of novelty and motivational properties of ethanol in spontaneously hypertensive rats

The present study investigated the consequences of environmental enrichment on the impact of novelty and motivational properties of ethanol in spontaneously hypertensive rats (SHR), a validated model of attention deficit hyperactivity disorder (ADHD). This rat strain displays increased sensitivity to distinct classes of abused drugs, which makes it an interesting model for the study of the association between ADHD and drug abuse. Female SHR reared from weaning to adulthood in standard (SE) or enriched (EE) environment were tested on novelty-induced locomotion, saccharin consumption, ethanol consumption (forced and free-choice schedules) and ethanol-induced conditioned place preference (CPP). SHR reared in an EE showed reduced novelty-induced locomotion, consumed less saccharin and ethanol in a forced schedule and showed less ethanol preference in a free-choice schedule compared to SE rats. Moreover, EE rats did not develop CPP, whereas SE rats developed preference for ethanol (1.2g/kg). These results show that exposure to stimuli mimicking positive life experiences (environmental enrichment) induces persistent changes in the reward/motivational system of female SHR, suggesting an important role of the familiar environment during early stages of the neurodevelopment on the co-morbidity of ADHD and drug abuse.