Behavioral sensitization to amphetamine follows chronic administration of the CB1 agonist WIN 55,212-2 in Lewis rats

Psychotomimetic compensation versus sensitization

It is a paradox that psychotomimetic drugs can relieve symptoms that increase risk of and cooccur with psychosis, such as attention and motivational deficits (e.g., amphetamines), pain (e.g., cannabis) and symptoms of depression (e.g., psychedelics, dissociatives). We introduce the ideas of psychotomimetic compensation and psychotomimetic sensitization to explain this paradox. Psychotomimetic compensation refers to a short-term stressor or drug-induced compensation against stress that is facilitated by engagement of neurotransmitter/modulator systems (endocannabinoid, serotonergic, glutamatergic and dopaminergic) that mediate the effects of common psychotomimetic drugs. Psychotomimetic sensitization occurs after repeated exposure to stress and/or drugs and is evidenced by the gradual intensification and increase of psychotic-like experiences over time. Theoretical and practical implications of this model are discussed.

Comparative effects of cannabinoid CB1 receptor agonist and antagonist on timing impulsivity induced by d-amphetamine in a differential reinforcement of low-rate response task in male rats

RATIONALE

In human beings and experimental animals, maladaptive impulsivity is manifested by the acute injection of psychostimulants, such as amphetamine. Cannabinoid CB1 receptors have been implicated in the regulation of stimulant-induced impulsive action, but the role of CB1 receptors in timing-related impulsive action by amphetamine remains unknown.

METHODS

Male rats were used in evaluating the effects of CB1 receptor antagonist and agonist (SR141716A and WIN55,212-2, respectively) systemically administered individually and combined with d-amphetamine on a differential reinforcement of low-rate response (DRL) task, an operant behavioral test of timing and behavioral inhibition characterized as a type of timing impulsive action.

RESULTS

A distinct pattern of DRL behavioral changes was produced by acute d-amphetamine (0, 0.5, 1.0, and 1.5 mg/kg) treatment in a dose-dependent fashion, whereas no significant dose effect was detected for acute SR141716A (0, 0.3, 1, and 3 mg/kg) or WIN55,212-2 (0, 0.5, 1, and 2 mg/kg) treatment. Furthermore, DRL behavior altered by 1.5 mg/kg d-amphetamine was reversed by a noneffective dose of SR141716A (3 mg/kg) pretreatment. The minimally influenced DRL behavior by 0.5 mg/kg d-amphetamine was affected by pretreatment with a noneffective dose of WIN55,212-2 (1 mg/kg).

CONCLUSION

These findings reveal that the activation and blockade of CB1 receptors can differentially modulate the timing impulsive action of DRL behavior induced by acute amphetamine treatment. Characterizing how CB1 receptors modulate impulsive behavior will deepen our understanding of the cannabinoid psychopharmacology of impulsivity and may be helpful in developing an optimal pharmacotherapy for reducing maladaptive impulsivity in patients with some psychiatric disorders.

Adolescent cannabinoid exposure induces irritability-like behavior and cocaine cross-sensitization without affecting the escalation of cocaine self-administration in adulthood

Cannabis use is typically initiated during adolescence and is a significant risk factor for the development of cocaine use in adulthood. However, no preclinical studies have examined the effects of adolescent cannabinoid exposure on cocaine dependence in adulthood using the escalation model of cocaine self-administration and the assessment of negative emotional states. In the present study, we found that exposure to the cannabinoid receptor agonist WIN55,212-2 (WIN) in adolescence produced irritability-like behavior and psychomotor cross-sensitization to cocaine in adolescence. In adulthood, rats were allowed to self-administer cocaine. The acquisition of cocaine self-administration was lower in rats with adolescent WIN exposure compared with controls. However, both WIN-exposed and control rats escalated their cocaine intake at the same rate, had similar responding under a progressive-ratio schedule of reinforcement, and had similar psychomotor responses to cocaine. Interestingly, the increase in irritability-like behavior that was previously observed in adolescence after WIN exposure persisted into adulthood. Whether the persisting increase in irritability-like behavior after WIN exposure has translational relevance remains to be studied. In summary, these results suggest that psychoactive cannabinoid exposure during adolescence is unlikely to have a major effect on the escalation of cocaine intake or the development of compulsive-like responding per se in adulthood in a rat model of cocaine self-administration. However, whether the persisting irritability-like behavior may predispose an individual to mood-related impairments in adulthood or predict such impairments warrants further investigation.

Behavioral and neurochemical changes in mesostriatal dopaminergic regions of the rat after chronic administration of the cannabinoid receptor agonist WIN55,212-2

BACKGROUND

The endocannabinoid system interacts extensively with other neurotransmitter systems and has been implicated in a variety of functions, including regulation of basal ganglia circuits and motor behavior. The present study examined the effects of repeated administration of the nonselective cannabinoid receptor 1 agonist WIN55,212-2 on locomotor activity and on binding and mRNA levels of dopamine receptors and transporters and GABAA receptors in mesostriatal dopaminergic regions of the rat.

METHODS

Rats received systemic injections of WIN55,212-2 (0, 0.1, 0.3, or 1mg/kg, intraperitoneally) for 20 consecutive days. Locomotor activity was measured on days 1, 10, and 20. Following the last measurement, rats were euthanized and prepared for in vitro binding and in situ hybridization experiments.

RESULTS

Acutely, 0.3 and 1mg/kg of WIN55,212-2 produced hypolocomotion, which was sustained for the next 2 measurements, compared to vehicle. Repeated administration of WIN55,212-2 decreased the mRNA levels of the D2 autoreceptors in substantia nigra and ventral tegmental area and increased D1 receptor mRNA and binding in nucleus accumbens. Furthermore, both dopamine receptor and transporter binding and mRNA levels were decreased in substantia nigra. Moreover, repeated administration of WIN55,212-2 decreased GABAA receptor binding levels in dorsal striatum and substantia nigra.

CONCLUSIONS

Our data indicate that chronic WIN55,212-2 administration results in sustained effects on locomotor activity, similar to those observed after acute administration, and modulates the dopaminergic and GABAergic systems in a region-, dose-, and neurotransmitter-selective manner.

History of cannabis use is not associated with alterations in striatal dopamine D2/D3 receptor availability

Cannabis use in adolescence is emerging as a risk factor for the development of psychosis. In animal studies, Δ9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, modulates striatal dopaminergic neurotransmission. Alterations in human striatal dopaminergic function have also been reported both in psychosis and in stimulant use. We sought to examine whether striatal dopamine D(2)/D(3) receptor availability was altered in volunteers with a history of cannabis use using a database of previously acquired [(11)C]-raclopride positron emission tomography (PET) scans. Ten [(11)C]-raclopride scans from volunteers with a history of cannabis use were compared to ten control scans using a functional striatal subdivision region of interest (ROI) analysis. No significant differences in either overall striatal BP(ND) values or BP(ND) values in any functional striatal subdivision were found between the two groups. There was also no correlation between lifetime frequency of cannabis use and BP(ND) values. Limbic striatal BP(ND) values were ten percent lower in current nicotine cigarette smokers. These findings suggest that, unlike other drugs of abuse, a history of cannabis use is not associated with alterations in striatal dopamine D(2)/D(3) receptor availability.

Previous exposure to delta9-tetrahydrocannibinol enhances locomotor responding to but not self-administration of amphetamine

Previous exposure to amphetamine leads to enhanced locomotor and nucleus accumbens (NAcc) dopamine (DA) responding to the drug as well as enhanced amphetamine self-administration. Here, we investigated the effects of exposure to Δ(9)-tetrahydrocannibinol (Δ(9)-THC) on behavioral and biochemical responding to amphetamine. Rats in different groups received five exposure injections of vehicle or one of five doses of Δ(9)-THC (0.4, 0.75, 1.5, 3.0, and 6.0 mg/kg i.p.) and were tested 2 days and 2 weeks later. Exposure to all but the lowest and highest doses of Δ(9)-THC enhanced the locomotor response to amphetamine (0.75 mg/kg i.p.), but all failed to enhance NAcc DA overflow in response to the drug. Moreover, exposure to 3.0 mg/kg i.p. Δ(9)-THC increased forskolin-evoked adenylyl cyclase activity in the NAcc and rats' locomotor response to the direct DA receptor agonist apomorphine (1.0 mg/kg s.c.), suggesting that Δ(9)-THC sensitized locomotor responding to amphetamine by up-regulating postsynaptic DA receptor signaling in the NAcc. Finally, amphetamine self-administration (200 μg/kg/infusion i.v.) was enhanced in amphetamine (5 × 1.5 mg/kg i.p.)-exposed rats, but not in rats exposed to Δ(9)-THC (5 × 3.0 mg/kg i.p.). Previous exposure to this dose of Δ(9)-THC modestly increased apomorphine SA (0.5 mg/kg/infusion i.v.). Thus, unlike amphetamine exposure, exposure to Δ(9)-THC does not enhance the subsequent NAcc DA response to amphetamine or promote amphetamine self-administration. Although Δ(9)-THC leads to alterations in postsynaptic DA receptor signaling in the NAcc and these can affect the generation of locomotion, these neuroadaptations do not seem to be linked to the expression of enhanced amphetamine self-administration.

Differential treatment regimen-related effects of cannabinoids on D1 and D2 receptors in adolescent and adult rat brain

Animal studies suggest differential effects of cannabinoids on dopamine-related behaviours in adolescence and adulthood however few studies have investigated the underlying neurochemical effects of cannabinoids during adolescence. The aim of the present study was to compare the effects of treatment with the synthetic cannabinoid, HU210, on dopamine receptor density in adolescent and adult rats. Adolescent (postnatal day (PND) 35) and adult (PND 70) rats received a single dose of 100μg/kg HU210 or 25, 50 or 100μg/kg HU210 for 4 or 14 days. Dopamine D1 receptor (D1R) or D2 receptor (D2R) density was measured in the medial and lateral (CPUL) caudate putamen, nucleus accumbens, olfactory tubercle (TU) and substantia nigra (D1R only) using in vitro autoradiography. D1R and D2R densities were 1.6-1.7- and 1.1-1.4-fold higher respectively in adolescent control rats compared to adults. In adult rats, D1R density was increased by 1.2- and 1.3-fold (p<0.05) in CPUL and TU respectively compared to controls, after 14 days of HU210 treatment. A significant overall effect of treatment (p<0.05) on D2R density was also observed in adults after the single dose and 4 and 14 days administration of HU210. In adolescents, an overall effect of treatment on D1R density after a single exposure to HU210 was seen (p=0.0026) but no changes in D1R or D2R densities were observed in other treatment groups. These results suggest that the adolescent rat brain does not display the same compensatory mechanisms activated in the adult brain following cannabinoid treatment.

Methanandamide blocks amphetamine-induced behavioral sensitization in rats

Methanandamide acts at targets which modulate amphetamine-induced behaviors. Therefore, we investigated methanandamide effects on the acute hyperactivity produced by a single injection of amphetamine and behavioral sensitization induced by repeated amphetamine exposure in rats. Methanandamide (5mg/kg, i.p.) did not affect basal locomotor or stereotypical activity. Methanandamide (5mg/kg, i.p.) pretreatment did not alter the acute increase in locomotor or stereotypical activities produced by acute amphetamine (2mg/kg, i.p.). For chronic studies, rats injected with amphetamine (2mg/kg, i.p.) once daily for 3 consecutive days were then challenged with amphetamine (2mg/kg, i.p.) 5 days later. Expression of locomotor sensitization was blocked when methanandamide (5mg/kg, i.p.) was given once, just prior to amphetamine (2mg/kg, i.p.) challenge. In rats co-exposed to methanandamide (5mg/kg, i.p.) and amphetamine (2mg/kg, i.p.) on days 1-3 and then challenged with amphetamine (2mg/kg, i.p.) following 5 days of drug absence, the development of both locomotor and stereotypical sensitization was blocked. The ability of methanandamide to block amphetamine-sensitized behaviors suggests that this pharmacologically diverse lipid regulates signaling events impacted by repeated psychostimulant exposure.

Behavioural and dopaminergic alterations induced by a low dose of WIN 55,212-2 in a conditioned place preference procedure

AIMS

This study investigated the role of the cannabinoid CB1 receptor agonist, WIN 55,212-2, on motor activity. Subsequently, the effects of a low, stimulatory dose of WIN 55,212-2 and cocaine, as a positive control, were evaluated using a conditioned place preference (CPP) procedure. Upon completion of CPP, in rats that had been treated with WIN 55,212-2, dopaminergic status and spontaneous and d-amphetamine-induced motor activity were assessed.

MAIN METHODS

Sprague-Dawley rats were evaluated for habituated motor activity following WIN 55,212-2 (0, 0.1, 0.3, 1 mg/kg, i.p.) administration. A stimulatory dose of WIN 55,212-2 (0.1 mg/kg, i.p.) and cocaine (20 mg/kg, i.p.) was selected to assess CPP behaviour. Upon completion of CPP, in one group, tissue levels of dopamine and its metabolites were measured in distinct brain regions (dorsal striatum, nucleus accumbens, prefrontal cortex, amygdala, hippocampus) using High Performance Liquid Chromatography with electrochemical detection. In another group, spontaneous and D-amphetamine-induced motor activity was evaluated in an open-field apparatus.

KEY FINDINGS

The lowest dose of WIN 55,212-2 increased motor activity but did not produce CPP. As expected, cocaine induced clear CPP. Dopaminergic status was increased in a region-specific way and motor activity was enhanced following a challenge of D-amphetamine in rats that had been administered with WIN 55,212-2 during conditioning.

SIGNIFICANCE

A stimulatory effect of WIN 55,212-2 on motor activity was not accompanied by place preference. Upon completion of the CPP procedure, this dose was found to induce region-specific hyperdopaminergia along with a greater sensitivity to a subsequent challenge dose of D-amphetamine.

Attenuation of basal and cocaine-enhanced locomotion and nucleus accumbens dopamine in cannabinoid CB1-receptor-knockout mice

RATIONALE

Effect of cannabinoid CB1 receptor deletion on cocaine's actions is controversial. This is partly based on findings in CB1-receptor-knockout (CB1(-/-)) mice with CD1 genetic background.

OBJECTIVES

In the present study, we used CB1(-/-) mice with a C57BL/6J genetic background to further investigate the role of CB1 receptors in cocaine's action.

MATERIALS AND METHODS

Locomotor activity was assessed using AccuScan locomotor chambers. Brain extracellular dopamine (DA) levels were measured by in vivo microdialysis and by fast-scan cyclic voltammetry in the nucleus accumbens (NAc).

RESULTS

CB1(-/-) mice displayed a significant reduction in basal levels of locomotion and extracellular DA, as well as in cocaine-enhanced locomotion and extracellular DA, as compared to their wild-type (CB1(+/+)) littermates. The reduction in basal and cocaine-enhanced DA appears to be related to a reduction in basal DA release, not to an increase in DA clearance, as indicated by fast-scan cyclic voltammetry in brain slices. Pharmacological blockade of CB1 receptors by SR141716 inhibited locomotion and NAc DA release in CB1(+/+) mice.

CONCLUSIONS

The present findings suggest an important role for CB1 receptors in mediating cocaine's behavioral and neurochemical effects.

Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine

Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.

The role of CB1 receptors in psychostimulant addiction

Recent studies have implicated the endocannabinoid (eCB) system in the neuronal mechanisms underlying substance dependence. Here, we review results of studies using cannabinoid receptor subtype 1 (CB1) knockout mice as well as CB1 antagonists to elucidate the role of this neurotransmitter system in psychostimulant addiction. The overall picture is that CB1 receptors appear not to be involved in psychostimulant reward, nor in the development of dependence to such substances. In contrast, the eCB system appears to play a role in the persistence of psychostimulant addiction. In particular, CB1 receptors have been found to play a cardinal role in mediating reinstatement of previously extinguished drug-seeking behavior upon re-exposure to the drug or drug-associated cues. The anatomical loci as well as the neuronal mechanisms of the relapse-preventing effects of CB1 antagonists are still poorly understood, although interactions of the eCB system with afferent glutamatergic and possibly dopaminergic projections to the nucleus accumbens are most likely involved. In addition, CB1 receptors seem to modulate drug-related memories, in line with the hypothesized role of the eCB system in memory-related plasticity. Together, these findings suggest that modulators of the eCB system represent a promising novel type of therapy to treat drug addiction.

The role of the cannabinoid type 1 receptor and down-stream cAMP/DARPP-32 signal in the nucleus accumbens of methamphetamine-sensitized rats

Blockade of the cannabinoid type 1 (CB(1)) receptor could suppress methamphetamine self-administration; however, the cellular mechanism remains unclear. In this study, we intended to investigate the significance of brain CB(1) receptors on the development of behavioral sensitization to methamphetamine. Male Sprague-Dawley rats treated with chronic methamphetamine (4 mg/kg, i.p.) for either 7 or 14 days developed behavioral sensitization to methamphetamine (1 mg/kg) at withdrawal day 7. A progressive decrease in numbers of CB(1) receptor (both Bmax and mRNA) but increase in binding affinity (Kd) was noticed during withdrawal days 3 to 7. Microinjection of CB(1) antagonist [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] into the nucleus accumbens (NAc) at withdrawal day 7, significantly suppressed the behavioral sensitization to methamphetamine. In NAc brain slices preparation, acute incubation with CB(1) agonist (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55940) dose-dependently enhanced cAMP accumulation in sensitized rats; no change was noticed in control groups. Consequently, treatment of CP 55940 induced a dose-dependent (10 nmol/L-10 micromol/L) phosphorylation on down-stream dopamine and cAMP-regulated phosphoprotein of Mr 32 000 (DARPP-32)/Thr34 in sensitized rats, while only 10 micromol/L CP 55940 was able to enhance the phosphoDARPP-32/T34 in control groups. Alternatively, both basal activity of calcineurin (PP-2B) and CP 55940-induced changes in the amount of PP-2B in the NAc were both decreased in sensitized rats, but not in controls. Overall, we demonstrated that brain CB(1) receptor and its down-stream cAMP/DARPP-32/T34/PP-2B signaling are profoundly altered in methamphetamine-sensitized animals.

Modulation of the endocannabinoid system: therapeutic potential against cocaine dependence

Dependence on cocaine is still a main unresolved medical and social concern, and in spite of research efforts, no pharmacological therapy against cocaine dependence is yet available. Recent studies have shown that the endocannabinoid system participates in specific stages and aspects of drug dependence in general, and some of this evidence suggests an involvement of the cannabinoid system in cocaine effects. For example, cocaine administration has been shown to alter brain endocannabinoid levels, and the endocannabinoid system has been involved in long-term modifications of brain processes that might play a role in neuro/behavioral effects of psychostimulant drugs like cocaine. Human studies show that marijuana dependence is frequently associated with cocaine dependence, and that the cannabinoid receptor CNR1 gene polymorphism might be related to cocaine addiction. This article will review the main papers in the field showing how a modulation of different components of the cannabinoid system might interact with some of the neurobiological/behavioral effects of cocaine related to its reinforcing effects, evaluated in preclinical models or in clinical settings. The goal of this review will be to provide insights into the complex picture of cocaine abuse and addiction, and to extrapolate from such endocannabinoid-cocaine interactions useful information to test the therapeutic potential of cannabinoid ligands and endocannabinoid-level enhancers against cocaine dependence for future preclinical/clinical trials.

WIN-55,212-2 and SR-141716A alter nicotine-induced changes in locomotor activity, but do not alter nicotine-evoked [3H]dopamine release

Nicotine, the main psychoactive ingredient in tobacco, plays a key role in the development of cigarette smoking addiction. The endocannabinoid system has been demonstrated to have an important role in the motivational and reinforcing effects of drugs. The present study used behavioral and neurochemical techniques to study the interaction of cannabinoid receptors and nicotine pharmacology. In a locomotor activity experiment in rats, the CB(1)/CB(2) cannabinoid receptor agonist WIN-55,212-2 (0.28-2.8 mg/kg) attenuated nicotine (0.4 mg/kg)-induced hyperactivity, but did not alter nicotine (1.0 mg/kg)-induced hypoactivity. In contrast, the selective CB(1) cannabinoid receptor antagonist SR-141716A (1.0 mg/kg) diminished nicotine-induced hypoactivity, but did not alter nicotine-induced hyperactivity. In a neurochemical experiment, rat striatal slices preloaded with [(3)H]dopamine were superfused with WIN-55,212-2 or SR-141716A. A high concentration (100 microM) of WIN-55,212-2 evoked [(3)H]overflow, but this effect was not blocked by the cannabinoid receptor antagonist AM-251. SR-141716A did not evoke [(3)H]overflow, and neither WIN-55,212-2 nor SR-141716A altered nicotine-evoked [(3)H]overflow. Overall, these results indicate a behavioral interaction between cannabinoid receptors and nicotine pharmacology. Likely, WIN-55,212-2 and SR-141716A block nicotine-induced changes in behavior through an indirect mechanism, such as alteration in endocannabinoid regulation of motor circuits, rather than directly through blockade of nicotinic acetylcholine receptors.

Chronic treatment with Delta-9-tetrahydrocannabinol alters the structure of neurons in the nucleus accumbens shell and medial prefrontal cortex of rats

The potential of repeated exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) to produce long-lasting changes in synaptic connections in a manner similar to other drugs of abuse was evaluated in Sprague-Dawley rats. For 12 days, rats received two i.p. injections per day (8 h apart) of vehicle, a low dose of Delta(9)-THC (0.5 mg/kg), or escalating doses of Delta(9)-THC (0.5-4.0 mg/kg). Thirty days later, they were evaluated for sensitized locomotor activity (during the night cycle) for 60 min on each of three trials. Using a within-groups design, rats were tested following an injection of vehicle, 0.5 mg/kg Delta(9)-THC or 2.0 mg/kg Delta(9)-THC. The rats showed no evidence of sensitized locomotor activity in any group. Twenty-four hours after the final sensitization test, their brains were removed and then processed for Golgi-Cox staining. Prior exposure to Delta(9)-THC (both the low dose and the escalating doses) increased the length of the dendrites as well as the number of dendritic branches in the shell of the nucleus accumbens and in the medial prefrontal cortex, but not in the hippocampus, striatum, orbital frontal cortex, parietal cortex, or occipital cortex. These results are similar to those evident in brains of rats sensitized to amphetamine, and support previous findings that cannabinoids promote DA activity in the mesolimbic DA system.

Involvement of protein kinase A in ethanol-induced locomotor activity and sensitization

RATIONALE

Mutant mice lacking the RIIbeta subunit of protein kinase A (regulatory subunit II beta(-/-)) show increased ethanol preference. Recent evidence suggests a relationship between heightened ethanol preference and susceptibility to ethanol-induced locomotor sensitization. It is currently unknown if protein kinase A signaling modulates the stimulant effects and/or behavioral sensitization caused by ethanol administration. To address this question, we examined the effects of repeated ethanol administration on locomotor activity RIIbeta(-/-) and littermate wild-type (RIIbeta(+/+)) mice on multiple genetic backgrounds.

METHODS

Over three consecutive days, mice were given single i.p. saline injections and immediately placed in a locomotor activity apparatus to establish a composite baseline for locomotor activity. Next, mice maintained on a hybrid 129/SvEvxC57BL/6J or pure C57BL/6J genetic background were given 10 i.p. ethanol injections before being placed in the activity apparatus. Each ethanol injection was separated by 3-4 days. To determine if changes in behavior were specific to ethanol injection, naïve mice were tested following repeated daily saline injections. The effects of ethanol injection on locomotor behavior were also assessed using an alternate paradigm in which mice were given repeated ethanol injections in their home cage environment.

RESULTS

Relative to RIIbeta(+/+) mice, RIIbeta(-/-) mice, regardless of genetic background, consistently showed significantly greater ethanol-induced locomotor activation. RIIbeta(-/-) mice also showed increased sensitivity to ethanol-induced locomotor sensitization resulting from repeated administration, an effect that was dependent on genetic background and testing paradigm. Increased locomotor activity by RIIbeta(-/-) mice was specific to ethanol injections, and was not related to altered blood ethanol levels.

CONCLUSIONS

These data provide novel evidence implicating an influence of protein kinase A signaling on ethanol-induced locomotor activity and behavioral sensitization. The observation that RIIbeta(-/-) mice are more sensitive to the effects of repeated ethanol administration suggests that normal protein kinase A signaling limits, or is protective against, the stimulant effects of ethanol and the plastic alterations that underlie behavioral sensitization.

Cannabinoid CB1 receptor dependent effects of the NMDA antagonist phencyclidine in the social withdrawal model of schizophrenia

Clinical and laboratory findings suggest that cannabinoid signalling is implicated in schizophrenia. However, the interaction remains poorly understood, as data are often contradictory. Here we investigated wild-type (WT) and cannabinoid CB1 receptor-knockout (CB1-KO) mice in the phencyclidine-induced social withdrawal model of schizophrenia. N-methyl-D-aspartate (NMDA) antagonists (including phencyclidine) induce psychotic symptoms in humans, and are used to model schizophrenia in a variety of experimental conditions. In WTs, 5 mg/kg phencyclidine increased locomotion and stereotyped behaviours, and decreased social interactions. These changes are consistent with a schizophrenia-like effect. In CB1-KOs, phencyclidine decreased locomotion, enhanced ataxia and stereotypy more markedly than in WTs, but did not affect social interactions. Locomotion showed a significant negative correlation with both ataxia and stereotypy, suggesting that in CB1-KOs, the locomotor suppressive effect of phencyclidine was secondary to changes in these variables. Our findings demonstrate that CB1 gene disruption dramatically alters the behavioural effects of the NMDA antagonist phencyclidine, suggesting that the CB1 receptor is involved in schizophrenia. As social disruption and stereotypy respectively are believed to model negative and positive symptoms of schizophrenia, our findings tentatively suggest that cannabinoids are differentially involved in these two symptom categories. These findings require verification by experiments involving CB1 receptor blockers, as the genetic and pharmacological blockade of receptors may not always provide similar results.

A nonsynonymous polymorphism in the human fatty acid amide hydrolase gene did not associate with either methamphetamine dependence or schizophrenia

Genetic contributions to the etiology of substance abuse and dependence are topics of major interest. Acute and chronic cannabis use can produce drug-induced psychosis resembling schizophrenia and worsen positive symptoms of schizophrenia. The endocannabinoid system is one of the most important neural signaling pathways implicated in substance abuse and dependence. The fatty acid amide hydrolase (FAAH) is a primary catabolic enzyme of endocannabinoids. To clarify a possible involvement of FAAH in the etiology of methamphetamine dependence/psychosis or schizophrenia, we examined the genetic association of a nonsynonymous polymorphism of the FAAH gene (Pro129Thr) by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism with either disorder. Because the Pro129Thr polymorphism reduces enzyme instability, it is unlikely that dysfunction of FAAH and enhanced endocannabinoid system induce susceptibility to either methamphetamine dependence/psychosis or schizophrenia.

The CB receptor agonist WIN 55,212-2 fails to elicit disruption of prepulse inhibition of the startle in Sprague-Dawley rats

RATIONALE

A growing evidentiary body indicates cannabinoid exposure is conducive to cognitive impairment and psychotic phenomena in vulnerable individuals. In this respect, recent studies have displayed controversial results on the ability of cannabinoids to elicit sensorimotor gating alterations and attentional filtering, whose disruption is a distinctive feature of psychosis.

OBJECTIVES

The goal of this study was to investigate the effects of acute, subchronic, and chronic treatment with the synthetic CB receptor agonist WIN 55,212-2 (WIN) on prepulse inhibition (PPI) of the acoustic startle reflex (ASR), a powerful paradigm for evaluation of sensorimotor gating.

METHODS

Different groups of adult Sprague-Dawley rats were treated with 0.5, 1, and 2 mg/kg WIN (i.p.) acutely, as well as for 7 days and 21 days. All animals underwent testing 40 min after the last treatment and their evaluation was compared with that of animals treated with vehicle. In a separate group, the effects of WIN withdrawal were also analyzed, 24 h after discontinuation of a 21-day treatment.

RESULTS

No variation in PPI was detected in any of the test groups when compared with controls, whatever the dosage and the treatment.

CONCLUSIONS

These findings suggest WIN does not impair sensorimotor gating in Sprague-Dawley rats and confirm clinical evidence according to which cannabis is an unlikely causative of psychosis among non-vulnerable individuals. Nonetheless, since in other studies the same compound was shown to induce PPI alterations in Wistar rats, our results are also suggestive that genetic differences might be critical for the development of cannabis-induced cognitive disorders.

Human cannabinoid receptor 1: 5' exons, candidate regulatory regions, polymorphisms, haplotypes and association with polysubstance abuse

A number of lines of evidence make the gene that encodes the G-protein-coupled CB1/Cnr1 receptor a strong candidate to harbor variants that might contribute to individual differences in human addiction vulnerability. The CB1/Cnr1 receptor is the major brain site at which cannabinoid marijuana constituents are psychoactive as well as the principal brain receptor for endogenous anandamide ligands. It is densely expressed in brain circuits likely to be important for both the reward and mnemonic processes important for addiction. Altered drug effects in CB1/Cnr1 knockout mice and initial association studies also make variants at the CB1/Cnr1 locus candidates for roles in human vulnerabilities to addictions. However, many features of this gene's structure, regulation and variation remain poorly defined. This poor definition has limited the ability of previous association studies to adequately sample variation at this locus. We now report improved definition of the human CB1/Cnr1 locus and its variants. Novel exons 1-3, splice variant and candidate promoter region sequences add to the richness of the CB1/Cnr1 locus. Candidate promoter region sequences confer reporter gene expression in cells that express CB1/Cnr1. Common polymorphisms reveal patterns of linkage disequilibrium in European- and in African-American individuals. A 5' CB1/Cnr1 "TAG" haplotype displays significant allelic frequency differences between substance abusers and controls in European-American, African-American and Japanese samples. Post-mortem brain samples of heterozygous individuals contain less mRNA transcribed from the TAG alleles than from other CB1/Cnr1 haplotypes. CB1/ Cnr1 genomic variation thus appears to play roles in human addiction vulnerability.

The psychotomimetic effects of intravenous delta-9-tetrahydrocannabinol in healthy individuals: implications for psychosis

Recent advances in the understanding of brain cannabinoid receptor function have renewed interest in the association between cannabinoid compounds and psychosis. In a 3-day, double-blind, randomized, and counterbalanced study, the behavioral, cognitive, and endocrine effects of 0, 2.5, and 5 mg intravenous delta-9-tetrahydrocannabinol (Delta-9-THC) were characterized in 22 healthy individuals, who had been exposed to cannabis but had never been diagnosed with a cannabis abuse disorder. Prospective safety data at 1, 3, and 6 months poststudy was also collected. Delta-9-THC (1) produced schizophrenia-like positive and negative symptoms; (2) altered perception; (3) increased anxiety; (4) produced euphoria; (5) disrupted immediate and delayed word recall, sparing recognition recall; (6) impaired performance on tests of distractibility, verbal fluency, and working memory (7) did not impair orientation; (8) increased plasma cortisol. These data indicate that Delta-9-THC produces a broad range of transient symptoms, behaviors, and cognitive deficits in healthy individuals that resemble some aspects of endogenous psychoses. These data warrant further study of whether brain cannabinoid receptor function contributes to the pathophysiology of psychotic disorders.

Amphetamine effects on dopamine levels and behavior following cannabinoid exposure during adolescence

The cannabis gateway hypothesis purports that early exposure to cannabis is a risk factor for subsequent use of other addictive drugs, e.g., psychostimulants. Neurobiological sensitization, consistent with a gateway hypothesis, was currently studied in regard to amphetamine response. Rats were exposed to the cannabinoid receptor agonist WIN 55,212-2 [(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone] 1.25 mg/kg, intraperitoneally; i.p. for 5 days during early adolescence. Amphetamine (0.5 mg/kg, i.p.) or WIN 55,212-2 (1.25 mg/kg, i.p.) was administered in late adolescence and in vivo dopamine levels were simultaneously measured in the nucleus accumbens. Locomotor and stereotyped behaviors were also monitored in rats pretreated with WIN 55,212-2 (0.625, 1.25 or 2.5 mg/kg) or Delta-9-tetrahydrocannabinol (0.75, 1.5 or 3.0 mg/kg, i.p.) for 5 days during early adolescence and challenged with amphetamine (0.5 or 2.0 mg/kg) in late adolescence or as adults. Pretreatment with WIN 55,212-2 or Delta-9-tetrahydrocannabinol during early adolescence did not alter the dopaminergic or behavioral responses to amphetamine in adolescence or adulthood. In conclusion, these findings do not support the cannabis gateway hypothesis in regard to subsequent amphetamine exposure.

Reciprocal cross-sensitization between amphetamine and salt appetite

Previous work in our laboratory has demonstrated a potentiation of the psychomotor effects of amphetamine in animals with a history of sodium depletion, a process referred to as cross-sensitization. The present studies were done to further develop this finding by assessing multiple effects of amphetamine in rats with and without a history of sodium depletion. For Experiments 1-3, rats were depleted of sodium twice then subjected to one of three experimental procedures [open-field activity, conditioned place preference (CPP) and conditioned taste aversion (CTA)]. A history of depletion produced an elevation in the psychomotor effects of amphetamine. CPP, used to assess the rewarding properties of amphetamine, developed in rats with a history of depletion but not in controls. The aversive component of amphetamine as measured by CTA was unaffected by previous experience with sodium depletion. Finally, acute salt appetite after depletion was assessed in rats exposed to a sensitizing regimen of amphetamine. Animals with a drug history demonstrated a significant elevation in NaCl solution intake after depletion in comparison to controls. Together, the data provide strong evidence for the reciprocal cross-sensitization of salt appetite and response to amphetamine.

Adolescent exposure to cannabinoids induces long-lasting changes in the response to drugs of abuse of rat midbrain dopamine neurons

BACKGROUND

Recent studies have raised concerns about subtle long-lasting neurobiological changes that might be triggered by exposure to Cannabis derivatives, especially in a critical phase of brain maturation, such as puberty. The mesolimbic dopamine (DA) system, involved in the processing of drug-induced reward, is a locus of action of cannabinoids and endocannabinoids. Thus, we compared the effects of repeated cannabinoid administration in adolescent and adult rats on DA neuronal functions and responses to drugs of abuse.

METHODS

Single-unit extracellular recordings from antidromically identified mesoaccumbens DA neurons and from their target cells in the nucleus accumbens were carried out in urethane-anesthetized rats. Animals were pretreated during adolescence or adulthood, for 3 days, with the cannabinoid agonist WIN55212.2 (WIN) or vehicle and allowed a 2-week interval.

RESULTS

In cannabinoid-administered rats, DA neurons were significantly less responsive to the stimulating action of WIN, regardless of the age of pretreatment; however, in the adolescent group, but not in the adult, long-lasting cross-tolerance developed to morphine, cocaine, and amphetamine.

CONCLUSIONS

Our study suggests that an enduring form of neuronal adaptation occurs in DA neurons after subchronic cannabinoid intake at a young age, affecting subsequent responses to drugs of abuse.

The endocannabinoid system in the basal ganglia and in the mesolimbic reward system: implications for neurological and psychiatric disorders

To date, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best studied endocannabinoids and are thought to act as retrograde messengers in the central nervous system (CNS). By activating presynaptic cannabinoid CB1 receptors, they can reduce glutamate release in dorsal and ventral striatum (nucleus accumbens) and alter synaptic plasticity, thereby modulating neurotransmission in the basal ganglia and in the mesolimbic reward system. In this review, we will focus on the role of the endocannabinoid system within these neuronal pathways and describe its effect on dopaminergic transmission and vice versa. The endocannabinoid system is unlikely to directly affect dopamine release, but can modify dopamine transmission trough trans-synaptic mechanisms, involving gamma-aminobutyric acid (GABA)-ergic and glutamatergic synapses, as well as by converging signal transduction cascades of the cannabinoid and dopamine receptors. The dopamine and endocannabinoid systems exert a mutual control on each other. Cannabinergic signalling may lead to release of dopamine, which can act via dopamine D1-like receptors as a negative feedback mechanism to counteract the effects of activation of the cannabinoid CB1 receptor. On the other hand, dopaminergic signalling via dopamine D2-like receptors may lead to up-regulation of cannabinergic signalling, which is likely to represent a negative feedback on dopaminergic signalling. The consequences of these interactions become evident in pathological conditions in which one of the two systems is likely to be malfunctioning. We will discuss neurological and psychiatric disorders such as Parkinson's and Huntington's disease, drug addiction and schizophrenia. Furthermore, the possible role of the endocannabinoid system in disorders not necessarily depending on the dopaminergic system, such as eating disorders and anxiety, will be described.