Persistent anxiogenic effects of a single or repeated doses of cocaine and methamphetamine: interactions with endogenous cannabinoid receptor ligands

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Differential effects of GABAA receptor activation in the prelimbic and orbitofrontal cortices on anxiety

RATIONALE

The development of effective anxiety treatments has been hindered by limited understanding of the neurobiological mechanisms involved in anxiety regulation. Whilst gamma-aminobutyric acid (GABA) neurotransmission in the prefrontal cortex (PFC) is one mechanism consistently implicated in anxiety regulation, PFC subregions may contribute uniquely.

OBJECTIVES

The present study examined the effects of inactivating the PFC subregions of the prelimbic cortex (PrL) or orbitofrontal cortex (OFC) through GABA_A receptor (GABA_AR) activation, on anxiety behaviours in male Wistar rats.

METHODS

Sixty-six male Wistar rats were surgically implanted with bilateral cannulae into the PrL (n = 33) or the OFC (n = 33). Rats then received a microinjection of either the GABA_A receptor agonist muscimol or vehicle prior to each experiment, conducted 1 week apart. Measures of anxiety were examined using the elevated plus maze (EPM) and the emergence test (ET). The effect on locomotor activity (baseline or methamphetamine-induced) was also tested.

RESULTS

Differential effects of brain region inactivation on anxiety-like behaviour were shown by measures in the EPM and ET; muscimol infused into the PrL-reduced anxiety-like behaviour, yet had no significant effect when infused into the OFC, compared with control treated rats. No effects on locomotor activity at baseline or following methamphetamine treatment were found.

CONCLUSIONS

This study highlights that activation of GABA_ARs specifically within the PrL, but not OFC, reduces anxiety behaviours in male rats. This suggests that activity of the PrL plays a more important role than the OFC in the neurobiological mechanisms of unconditioned anxiety and should be targeted for future therapies.

Antagonizing serotonin 2A (5-HT2A) receptors attenuates methamphetamine-induced reward and blocks methamphetamine-induced anxiety-like behaviors in adult male rats

BACKGROUND

Methamphetamine is a highly addictive and abused psychostimulant. Symptoms of methamphetamine withdrawal including drug craving and anxiety that can drive relapse. Currently, there is no FDA approved treatment for methamphetamine use disorder, highlighting the need for research examining the neural mechanisms underlying psychostimulant-induced behaviors. Research indicates that the 5-HT_2A receptor antagonist M100907 attenuates several psychostimulant-induced behaviors, including conditioned place preference (CPP). However, these findings have not been extended to methamphetamine. The present study investigated the effects of M100907 on acquisition of methamphetamine-CPP and methamphetamine-induced anxiety-like behavior.

METHODS

Adult male rats were tested across eight consecutive days. Prior to methamphetamine administration (0 or 1 mg/kg, i.p.), rats were pretreated with their assigned dose of M100907 (0, 0.0025 .025 or 0.25 mg/kg, i.p.) and were placed into their initially non-preferred chamber. After four methamphetamine conditioning sessions, the effects of M100907 on methamphetamine-induced CPP were assessed. Following CPP testing, rats were screened for anxiety-like behaviors in the elevated plus-maze.

RESULTS

Pretreatment with M100907 attenuated methamphetamine-induced CPP without producing any observable rewarding or aversive effects in methamphetamine naïve rats. Additionally, M100907 blocked methamphetamine-induced increases in anxiety-like behavior and attenuated some indices of anxiety in methamphetamine naïve rats.

CONCLUSIONS

Results suggest that blocking 5-HT_2A receptors with the selective antagonist M100907 attenuates the rewarding effects of methamphetamine and does not produce any rewarding or aversive effects alone. Further, M100907 pretreatment blocked the anxiety-inducing effects of methamphetamine. Collectively, these data suggest that the 5-HT_2A receptor subtype represents a novel target for treating methamphetamine use disorder.

What is the role of subcutaneous single injections on the behavior of adult male rats exposed to drugs?

Psychostimulants, as well as cannabinoids, have been shown to significantly affect a great variety of behaviors in both humans and laboratory animals. Our previous studies have repeatedly demonstrated that the application of the vehicle for psychostimulants, i.e. saline, to control groups, generated different behavioral test results compared to absolute naive controls (i.e. without any injection). Therefore, our present study has set three goals: (1) to evaluate the effect of three different psychostimulant drugs, (2) to evaluate the effect of three doses of delta 9-tetrahydrocannabinol (THC), and (3) to evaluate the effect of saline and ethanol injections vs sham injections and no injection on spontaneous behavior of adult male rats. The LABORAS test (Metris B.V., Netherlands) was used to examine spontaneous locomotor activity and exploratory behavior in an unknown environment over 1 h. In Experiment 1, psychostimulant drugs were tested: single subcutaneous (s.c.) injections of amphetamine (5 mg/kg), cocaine (5 mg/kg), and 3,4-methylenedioxymethamphetamine (MDMA) (5 mg/kg) were applied prior to testing. Control animals received the same volume (1 ml/kg) of s.c. saline. In Experiment 2, the effect of three doses of THC (1, 2, and 5 mg/kg, s.c.) were examined. An s.c. injection of vehicle (ethanol) was used as a control. In Experiment 3, injections of saline and ethanol were compared to the group receiving a sham s.c. injection and to a group of absolute "naive" controls. Our results demonstrated that (1) all psychostimulants increased locomotion time, distance traveled, and speed while decreasing immobility time of adult male rats relative to saline controls. The most prominent effect was associated with MDMA; (2) The effect of THC was dose-dependent and was most apparent within the first 10 min of the LABORAS test. (3) With regard to the effect of injection: absolute controls (without injection) compared to animals injected with ethanol, saline, or sham-injected displayed reduced immobility time, traveled longer distances, and had increased speed. In conclusion, our data showed drug dependent behavioral changes in adult male rats after application of psychostimulants and cannabinoids. Our findings also suggest that not only drugs but the actual single injection per se also affects the behavior of laboratory animals in an unknown environment. This effect seems to be associated with the acute stress associated with the injection.

LiCl Pretreatment Ameliorates Adolescent Methamphetamine Exposure-Induced Long-Term Alterations in Behavior and Hippocampal Ultrastructure in Adulthood in Mice

BACKGROUND

Adolescent methamphetamine exposure causes a broad range of neurobiological deficits in adulthood. Glycogen synthase kinase-3β is involved in various cognitive and behavioral processes associated with methamphetamine exposure. This study aims to investigate the protective effects of the glycogen synthase kinase-3β inhibitor lithium chloride on adolescent methamphetamine exposure-induced long-term alterations in emotion, cognition, behavior, and molecule and hippocampal ultrastructure in adulthood.

METHODS

A behavioral test battery was used to investigate the protective effects of lithium chloride on adolescent methamphetamine exposure-induced long-term emotional, cognitive, and behavioral impairments in mice. Western blotting and immunohistochemistry were used to detect glycogen synthase kinase-3β activity levels in the medial prefrontal cortex and dorsal hippocampus. Electron microscopy was used to analyze changes in synaptic ultrastructure in the dorsal hippocampus. Locomotor sensitization with a methamphetamine (1 mg/kg) challenge was examined 80 days after adolescent methamphetamine exposure.

RESULTS

Adolescent methamphetamine exposure induced long-term alterations in locomotor activity, novel spatial exploration, and social recognition memory; increases in glycogen synthase kinase-3β activity in dorsal hippocampus; and decreases in excitatory synapse density and postsynaptic density thickness in CA1. These changes were ameliorated by lithium chloride pretreatment. Adolescent methamphetamine exposure-induced working memory deficits in Y-maze spontaneous alternation test and anxiety-like behavior in elevated-plus maze test spontaneously recovered after long-term methamphetamine abstinence. No significant locomotor sensitization was observed after long-term methamphetamine abstinence.

CONCLUSIONS

Hyperactive glycogen synthase kinase-3β contributes to adolescent chronic methamphetamine exposure-induced behavioral and hippocampal impairments in adulthood. Our results suggest glycogen synthase kinase-3β may be a potential target for the treatment of deficits in adulthood associated with adolescent methamphetamine abuse.

Role of the endocannabinoid system in drug addiction

Drug addiction is a chronic relapsing disorder that produces a dramaticglobal health burden worldwide. Not effective treatment of drug addiction is currently available probably due to the difficulties to find an appropriate target to manage this complex disease raising the needs for further identification of novel therapeutic approaches. The endocannabinoid system has been found to play a crucial role in the neurobiological substrate underlying drug addiction. Endocannabinoids and cannabinoid receptors are widely expressed in the main areas of the mesocorticolimbic system that participate in the initiation and maintenance of drug consumption and in the development of compulsion and loss of behavioral control occurring during drug addiction. The identification of the important role played by CB1 cannabinoid receptors in drug addiction encouraged the possible used of an early commercialized CB1 receptor antagonist for treating drug addiction. However, the incidence of serious psychiatric adverse events leaded to the sudden withdrawal from the market of this CB1 antagonist and all the research programs developed by pharmaceutical companies to obtain new CB1 antagonists were stopped. Currently, new research strategies are under development to target the endocannabinoid system for drug addiction avoiding these side effects, which include allosteric negative modulators of CB1 receptors and compounds targeting CB2 receptors. Recent studies showing the potential role of CB2 receptors in the addictive properties of different drugs of abuse have open a promising research opportunity to develop novel possible therapeutic approaches.

17 β-Estradiol exacerbates methamphetamine-induced anxiety-like behavior in female mice

The present experiment investigated the effect of 17 β-estradiol (E₂) on anxiety-like behavior following methamphetamine administration in female, Swiss-Webster mice. Mice underwent bilateral ovariectomy (OVX) followed by a subcutaneous implantation of a Silastic capsule containing either sesame oil (OVX + Oil) or E₂ (36 μg/ml; OVX + E₂). One week later, mice were placed in an open-field chamber for an 8-h session. During the first 3 h of the session, mice were permitted to run in the absence of any drug (baseline). Then, mice were injected intraperitoneally with methamphetamine (0.25, 0.5 or 1.0 mg/kg) or vehicle (physiological saline) and returned to the open-field chamber for the remaining five hours of the session. Mice were injected with vehicle or a different methamphetamine dose once a week for 4 weeks. Four measures of anxiety were assessed: distanced traveled, vertical counts, time in the center, and time resting in the perimeter of the chamber. OVX + E₂ were less active and spent less time in the center than OVX + Oil mice during Hour 1 at certain doses, but not during remaining baseline hours (Hours 2-3). Furthermore, group differences were not observed during the Stimulant Phase (Hour 4) following injection of any methamphetamine dose (0.25, 0.5 or 1.0 mg/kg) or the vehicle. However, OVX + E₂ mice were less active, spent less time in the center, and spent more time resting in the perimeter of the chamber compared to OVX + Oil mice during certain hours of the Clearance Phase (Hours 5-8) following injection of the high (1.0 mg/kg), but not the low (0.25 mg/kg) or moderate (0.5 mg/kg), methamphetamine doses. These results suggest that E₂ exacerbates anxiety-like behavior during acute clearance from a high methamphetamine dose in OVX female mice, perhaps indicating that E₂ contributes to drug relapse in women by worsening anxiety-related withdrawal symptoms.

The effects of enriched environment on the behavioral and corticosterone response to methamphetamine in adolescent and adult mice

Methamphetamine alters behavior and the stress response system. Relatively little research has examined the effects of methamphetamine in adolescents and compared these effects to those in adults. Housing in enriched environments has been explored as one way to protect against the effects of methamphetamine, but the findings are conflicting and no study has examined how enriched environment may alter the behavioral and corticosterone responses to methamphetamine in adolescent and adult rodents. We examined the long-term effects of methamphetamine exposure on anxiety, social behavior, behavioral despair, and corticosterone levels in adolescent and adult mice housed in enriched or isolated environments. Enriched environment did not alter the behavioral or corticosterone response to methamphetamine. Methamphetamine exposure decreased anxiety and increased behavioral despair in adult mice, but methamphetamine did not alter behavior in adolescent mice. There was no effect of methamphetamine on social behavior or corticosterone levels. Our findings demonstrate that the specific environmental enrichment paradigm used in this study was not sufficient to mitigate the behavioral effects of methamphetamine and that adolescent mice are relatively resistant to the effects of methamphetamine compared to adult mice.

Epigenetic mechanisms associated with addiction-related behavioural effects of nicotine and/or cocaine: implication of the endocannabinoid system

The addictive use of nicotine (NC) and cocaine (COC) continues to be a major public health problem, and their combined use has been reported, particularly during adolescence. In neural plasticity, commonly induced by NC and COC, as well as behavioural plasticity related to the use of these two drugs, the involvement of epigenetic mechanisms, in which the reversible regulation of gene expression occurs independently of the DNA sequence, has recently been reported. Furthermore, on the basis of intense interactions with the target neurotransmitter systems, the endocannabinoid (ECB) system has been considered pivotal for eliciting the effects of NC or COC. The combined use of marijuana with NC and/or COC has also been reported. This article presents the addiction-related behavioural effects of NC and/or COC, based on the common behavioural/neural plasticity and combined use of NC/COC, and reviews the interacting role of the ECB system. The epigenetic processes inseparable from the effects of NC and/or COC (i.e. DNA methylation, histone modifications and alterations in microRNAs) and the putative therapeutic involvement of the ECB system at the epigenetic level are also discussed.

Blockade of TRPV1 Inhibits Methamphetamine-induced Rewarding Effects

Methamphetamine (MAP) is the most widely used psychostimulant in the world, but the exact mechanisms underlying MAP addiction are not yet fully understood. Recent studies have identified the distribution of TRPV1 in several brain regions that are related to drug addiction, including nucleus accumbens (NAc) and dorsal striatum (DSt). In the present study, we performed conditioned place preference (CPP) and self-administration tests to examine the effects of capsazepine (CPZ) and SB366791 (SB) on MAP reward. We found that both CPZ and SB significantly inhibited MAP-induced CPP and self-administration; in contrast, TRPV1 knock-out (KO) mice did not develop MAP-induced CPP. Real-time RT-PCR, Western blot and quantitative autoradiographic tests showed up-regulation of TRPV1 mRNA and protein expression in the NAc and/or DSt regions of mice exhibiting MAP-induced CPP. In addition, an in vivo microdialysis experiment showed that CPZ dramatically reduced dopamine (DA) levels in the NAc region of MAP-treated mice. Furthermore, attenuated dopamine transporter (DAT) binding levels in the NAc and DSt regions of MAP-induced CPP mice were reversed by CPZ. Together, these data suggest that TRPV1 plays an important role in MAP reward via the modulation of DA release and DAT density, thereby providing a novel therapeutic target for MAP addiction.

Effect of three different regimens of repeated methamphetamine on rats' cognitive performance

Neurocognitive impairment in response to methamphetamine (MA) has been proven in a variety of experimental and clinical studies. Elucidation of the underlying mechanisms of MA-induced cognitive deficits and finding preventive/therapeutic approaches need best-suited animal models. In modeling repeated MA exposure, while some believes that escalating doses simulate drug abuse conditions, others believe this regimen confers a preconditioning protection. The present study aimed to compare the effects of three different regimens of repeated MA administration on memory and cognitive function of adult rats. Rats in two different experimental groups were treated with escalating paradigms consisted of twice-daily i.p. injections; 1-4 mg/kg over 7 days or 1-10 mg/kg over 10 days. The third group received twice-daily doses of 15 mg/kg every other day over 14 days. Spatial working memory, novel object recognition task and anxiety-like behavior were measured sequentially in all MA-treated rats and vehicle-treated controls started from day 8 after last injection. All MA regimens decreased rates of spontaneous alternation in Y-maze and increased anxiety-like response. Short-term recognition memory was unchanged across all MA-treated animals, while long-term memory was impaired in the second and third MA regimen. Though MA deleterious effect especially in recognition memory is somehow dose dependent, preconditioning effect of increasing doses may be ruled out at least in the case of parameters measured here.

Endocannabinoid mechanism in amphetamine-type stimulant use disorders: A short review

Recent evidence shows that the endocannabinoid system is involved in amphetamine-type stimulants (ATS) use disorders. To elucidate the role of the endocannabinoid system in ATS addiction, we reviewed results of studies using cannabinoid receptor agonists, antagonists as well as knockout model. The endocannabinoid system seems to play a role in reinstatement and relapse of ATS addiction and ATS-induced psychiatric symptoms. The molecular mechanisms of this system remains unclear, the association with dopamine system in nucleus accumbens is most likely involved. However, the function of the endocannabinoid system in anxiety and anti-anxiety effects induced by ATS is more complicated. These findings suggest that the endocannabinoid system may play an important role in the mechanism of ATS addiction and provide new idea for treating ATS addiction.

Morphine decreases social interaction of adult male rats, while THC does not affect it

The aim of the present study was to compare effect of three low doses of morphine (MOR) and delta9-tetrahydrocannabinol (THC) on social behavior tested in Social interaction test (SIT). 45 min prior to testing adult male rats received one of the drugs or solvents: MOR (1; 2.5; 5 mg/kg); saline as a solvent for MOR; THC (0.5; 1; 2 mg/kg); ethanol as a solvent for THC. Occurrence and time spent in specific patterns of social interactions (SI) and non-social activities (locomotion and rearing) was video-recorded for 5 min and then analyzed. MOR in doses of 1 and 2.5 mg/kg displayed decreased SI in total. Detailed analysis of specific patterns of SI revealed decrease in mutual sniffing and allo-grooming after all doses of MOR. The highest dose (5 mg/kg) of MOR decreased following and increased genital investigation. Rearing activity was increased by lower doses of MOR (1 and 2.5 mg/kg). THC, in each of the tested doses, did not induce any specific changes when compared to matching control group (ethanol). However, an additional statistical analysis showed differences between all THC groups and their ethanol control group when compared to saline controls. There was lower SI in total, lower mutual sniffing and allo-grooming, but higher rearing in THC and ethanol groups than in saline control group. Thus, changes seen in THC and ethanol groups are seemed to be attributed mainly to the effect of the ethanol. Based on the present results we can assume that opioids affect SI more than cannabinoid.

Attenuation of the anxiogenic effects of cocaine by 5-HT1B autoreceptor stimulation in the bed nucleus of the stria terminalis of rats

RATIONALE

Cocaine produces significant aversive/anxiogenic actions whose underlying neurobiology remains unclear. A possible substrate contributing to these actions is the serotonergic (5-HT) pathway projecting from the dorsal raphé (DRN) to regions of the extended amygdala, including the bed nucleus of the stria terminalis (BNST) which have been implicated in the production of anxiogenic states.

OBJECTIVES

The present study examined the contribution of 5-HT signaling within the BNST to the anxiogenic effects of cocaine as measured in a runway model of drug self-administration.

METHODS

Male Sprague-Dawley rats were fitted with bilateral infusion cannula aimed at the BNST and then trained to traverse a straight alley once a day for a single 1 mg/kg i.v. cocaine infusion delivered upon goal-box entry on each of 16 consecutive days/trials. Intracranial infusions of CP 94,253 (0, 0.25, 0.5, or 1.0 μg/side) were administered to inhibit local 5-HT release via activation of 5-HT_1B autoreceptors. To confirm receptor specificity, the effects of this treatment were then challenged by co-administration of the selective 5-HT_1B antagonist NAS-181.

RESULTS

Intra-BNST infusions of the 5-HT_1B autoreceptor agonist attenuated the anxiogenic effects of cocaine as reflected by a decrease in runway approach-avoidance conflict behavior. This effect was reversed by the 5-HT_1B antagonist. Neither start latencies (a measure of the subject's motivation to seek cocaine) nor spontaneous locomotor activity (an index of motoric capacity) were altered by either treatment.

CONCLUSIONS

Inhibition of 5-HT_1B signaling within the BNST selectively attenuated the anxiogenic effects of cocaine, while leaving unaffected the positive incentive properties of the drug.

The Non-Peptide Arginine-Vasopressin v1a Selective Receptor Antagonist, SR49059, Blocks the Rewarding, Prosocial, and Anxiolytic Effects of 3,4-Methylenedioxymethamphetamine and Its Derivatives in Zebra Fish

3,4-Methylenedioxymethamphetamine (MDMA) and its derivatives, 2,5-dimethoxy-4-bromo-amphetamine hydrobromide (DOB) and para-methoxyamphetamine (PMA), are recreational drugs whose pharmacological effects have recently been attributed to serotonin 5HT_2A/C receptors. However, there is growing evidence that the oxytocin (OT)/vasopressin system can modulate some the effects of MDMA. In this study, MDMA (2.5-10 mg/kg), DOB (0.5 mg/kg), or PMA (0.005, 0.1, or 0.25 mg/kg) were administered intramuscularly to adult zebra fish, alone or in combination with the V_1a vasopressin antagonist, SR49059 (0.01-1 ng/kg), before carrying out conditioned place preference (CPP), social preference, novel tank diving, and light-dark tests in order to evaluate subsequent rewarding, social, and emotional-like behavior. The combination of SR49059 and each drug progressively blocked: (1) rewarding behavior as measured by CPP in terms of time spent in drug-paired compartment; (2) prosocial effects measured on the basis of the time spent in the proximity of a nacre fish picture; and (3) anxiolytic effects in terms of the time spent in the upper half of the novel tank and in the white compartment of the tank used for the light-dark test. Antagonism was obtained at SR49059 doses which, when given alone, did not change motor function. In comparison with a control group, receiving vehicle alone, there was a three to five times increase in the brain release of isotocin (the analog of OT in fish) after treatment with the most active doses of MDMA (10 mg/kg), DOB (0.5 mg/kg), and PMA (0.1 mg/kg) as evaluated by means of bioanalytical reversed-phase high-performance liquid chromatography. Taken together, these findings show that the OT/vasopressin system is involved in the rewarding, prosocial, and anxiolytic effects of MDMA, DOB, and PMA in zebra fish and underline the association between this system and the behavioral alterations associated with disorders related to substance abuse.

Effect of olfactory manganese exposure on anxiety-related behavior in a mouse model of iron overload hemochromatosis

Manganese in excess promotes unstable emotional behavior. Our previous study showed that olfactory manganese uptake into the brain is altered in Hfe(-/-) mice, a model of iron overload hemochromatosis, suggesting that Hfe deficiency could modify the neurotoxicity of airborne manganese. We determined anxiety-related behavior and monoaminergic protein expression after repeated intranasal instillation of MnCl2 to Hfe(-/-) mice. Compared with manganese-instilled wild-type mice, Hfe(-/-) mice showed decreased manganese accumulation in the cerebellum. Hfe(-/-) mice also exhibited increased anxiety with decreased exploratory activity and elevated dopamine D1 receptor and norepinephrine transporter in the striatum. Moreover, Hfe deficiency attenuated manganese-associated impulsivity and modified the effect of manganese on the expression of tyrosine hydroxylase, vesicular monoamine transporter and serotonin transporter. Together, our data indicate that loss of HFE function alters manganese-associated emotional behavior and further suggest that HFE could be a potential molecular target to alleviate affective disorders induced by manganese inhalation.

Acute total sleep deprivation potentiates cocaine-induced hyperlocomotion in mice

Sleep deprivation is common place in modern society. Nowadays, people tend to self-impose less sleep in order to achieve professional or social goals. In the social context, late-night parties are frequently associated with higher availability of recreational drugs with abuse potential. Physiologically, all of these drugs induce an increase in dopamine release in the mesolimbic dopaminergic system, which leads to hyperlocomotion in rodents. Sleep deprivation also seems to play an important role in the events related to the neurotransmission of the dopaminergic system by potentiating its behavioral effects. In this scenario, the aim of the present study was to investigate the effects of total sleep deprivation (6h) on the acute cocaine-induced locomotor stimulation in male mice. Animals were sleep deprived or maintained in their home cages and subsequently treated with an acute i.p. injection of 15mg/kg cocaine or saline and observed in the open field. Total sleep deprivation for 6h potentiated the hyperlocomotion induced by acute cocaine administration. In addition, the cocaine sleep deprived group showed a decreased ratio central/total locomotion compared to the cocaine control group, which might be related to an increase in the impulsiveness of mice. Our data indicate that acute periods of sleep loss should be considered risk factors for cocaine abuse.

Repeated cocaine enhances ventral hippocampal-stimulated dopamine efflux in the nucleus accumbens and alters ventral hippocampal NMDA receptor subunit expression

Dopaminergic neurotransmission in the nucleus accumbens is important for various reward-related cognitive processes including reinforcement learning. Repeated cocaine enhances hippocampal synaptic plasticity, and phasic elevations of accumbal dopamine evoked by unconditioned stimuli are dependent on impulse flow from the ventral hippocampus. Therefore, sensitized hippocampal activity may be one mechanism by which drugs of abuse enhance limbic dopaminergic activity. In this study, in vivo microdialysis in freely moving adult male Sprague-Dawley rats was used to investigate the effect of repeated cocaine on ventral hippocampus-mediated dopaminergic transmission within the medial shell of the nucleus accumbens. Following seven daily injections of saline or cocaine (20 mg/kg, ip), unilateral infusion of N-methyl-d-aspartate (NMDA, 0.5 μg) into the ventral hippocampus transiently increased both motoric activity and ipsilateral dopamine efflux in the medial shell of the nucleus accumbens, and this effect was greater in rats that received repeated cocaine compared to controls that received repeated saline. In addition, repeated cocaine altered NMDA receptor subunit expression in the ventral hippocampus, reducing the NR2A : NR2B subunit ratio. Together, these results suggest that repeated exposure to cocaine produces maladaptive ventral hippocampal-nucleus accumbens communication, in part through changes in glutamate receptor composition. A behaviorally sensitizing regimen of cocaine (20 mg/kg, ip 7 days) also sensitized ventral hippocampus (hipp)-mediated dopaminergic transmission within the nucleus accumbens (Nac) to NMDA stimulation (bolts). This was associated with reduced ventral hippocampal NR2A:NR2B subunit ratio, suggesting that repeated exposure to cocaine produces changes in hippocampal NMDA receptor composition that lead to enhanced ventral hippocampus-nucleus accumbens communication.

Limbic system mGluR5 availability in cocaine dependent subjects: a high-resolution PET [(11)C]ABP688 study

Cocaine self-administration decreases type 5 metabotropic glutamate receptor (mGluR5) tissue concentrations in laboratory rats during early abstinence. These changes are thought to influence the drug's reinforcing properties and the ability of drug-related cues to induce relapse. Here, our goal was to measure brain regional mGluR5 availability in recently abstinent cocaine dependent humans. Participants meeting DSM-IV diagnostic criteria for current cocaine dependence (n=9) were recruited from the general population. mGluR5 availability (binding potential, non-displaceable; BPND) was measured with high-resolution positron emission tomography (PET HRRT) and [(11)C]ABP688. Compared to age- and sex-matched healthy controls (n=9), cocaine dependent subjects showed significantly lower BPND values in the ventral (bilateral: -28.2%, p=0.011), associative (right: -21.4%, p=0.043), and sensorimotor striatum (bilateral: -21.7%, p=0.045), amygdala (left: -26%, p=0.046) and insula (right: -23.3%, p=0.041). Among the cocaine users, receptor availabilities were related to abstinence (range: 2 to 14days). The longer the duration of abstinence, the lower the BPND values in the sensorimotor striatum (r=-0.71, p=0.034), left amygdala (r=-0.73, p=0.026) and right insula (r=-0.67, p=0.046). Compared to healthy controls, BPND values were significantly reduced in those who tested negative for cocaine on the PET test session in the ventral (p=0.018) and sensorimotor striatum (p=0.017), left amygdala (p=0.008), and right insula (p=0.029), but not in those who tested positive. Together, these results provide evidence of time-related mGluR5 alterations in striatal and limbic regions in humans during early cocaine abstinence.

Stress system changes associated with marijuana dependence may increase craving for alcohol and cocaine

OBJECTIVE

To date, little research exists defining bio-behavioral adaptations associated with both marijuana abuse and risk of craving and relapse to other drugs of abuse during early abstinence.

METHOD

Fifty-nine treatment-seeking individuals dependent on alcohol and cocaine were recruited. Thirty of these individuals were also marijuana (MJ) dependent; 29 were not. Twenty-six socially drinking healthy controls were also recruited. All participants were exposed to three 5-min guided imagery conditions (stress, alcohol/cocaine cue and relaxing), presented randomly, one per day across three consecutive days. Measures of craving, anxiety, heart rate, blood pressure, plasma adrenocorticotrophic hormone and cortisol were collected at baseline and subsequent recovery time points.

RESULTS

The MJ-dependent group showed increased basal anxiety ratings and cardiovascular output alongside enhanced alcohol craving and cocaine craving, and dampened cardiovascular response to stress and cue. They also demonstrated elevated cue-induced anxiety and stress-induced cortisol and adrenocorticotrophic hormone levels, which were not observed in the non-MJ-dependent group or controls. Cue-related alcohol craving and anxiety were both predictive of a shorter number of days to marijuana relapse following discharge from inpatient treatment.

CONCLUSIONS

Findings provide some support for drug cross-sensitization in terms of motivational processes associated with stress-related and cue-related craving and relapse.

Noladin ether, a putative endocannabinoid, enhances motivation to eat after acute systemic administration in rats

BACKGROUND AND PURPOSE Endocannabinoid systems are strongly implicated in the physiological control of appetite and eating behaviour, with cannabinoid CB(1) receptor agonists and antagonists, respectively, increasing or decreasing food intake. This study examined the acute actions of the putative endocannabinoid noladin ether on food intake and eating motivation, assessing how it affects the amount of work expended by animals to obtain food. EXPERIMENTAL APPROACH Non-deprived male rats were injected systemically with noladin ether to assess its acute effects on ad libitum feeding of a standard laboratory diet. Additionally, the effects of noladin on lever pressing for palatable food were determined using a progressive ratio (PR) operant paradigm. KEY RESULTS Noladin dose dependently increased 2 h food intake, with a significant effect over 1 h after a dose of 0.5 mg·kg(-1). In the PR test, this hyperphagic dose of noladin ether promoted sustained high rates of responding and significantly increased the total number of lever presses and break-point. These latter effects were prevented by pretreatment with 1.0 mg·kg(-1) of the selective CB(1) antagonist surinabant (SR147778), that alone had no effect on responding. CONCLUSIONS AND IMPLICATIONS This is the first report of hyperphagia induced by acute noladin administration, and the first description of behavioural actions in rats. Consistent with prevailing notions about the role of endocannabinoids in appetite, a hyperphagic dose of noladin markedly increased efforts expended by animals to obtain food. Thus, noladin exerts a specific action on eating motivation; possibly promoting eating by increasing the incentive value of food.

Post-conditioning propranolol disrupts cocaine sensitization

Antagonists of β-adrenergic receptors (β-ARs) have previously been demonstrated to impair long-term memory in a variety of animal behavioral paradigms. Surprisingly little is known about the ability of β-ARs to modulate initial memory formation in drug conditioning paradigms. The current study examined whether the post-training administration of the β-AR antagonist, propranolol, would disrupt single-trial cocaine-induced sensitization. Rats received 10 mg/kg propranolol immediately following a 30-min cocaine or vehicle exposure in a conditioning context and were later tested for their locomotor response to a cocaine challenge. Rats that received propranolol following cocaine conditioning showed an impairment of locomotor sensitization during testing. However, this effect was only seen in animals with an initial sensitivity to the locomotor effects of cocaine. Rats that failed to show a locomotor response to cocaine during conditioning were not affected by propranolol. We discuss the implications of these findings as they relate to drug conditioning and memory consolidation studies.

Cannabinoid receptor stimulation increases motivation for nicotine and nicotine seeking

The cannabinoid system appears to play a critical facilitative role in mediating the reinforcing effects of nicotine and relapse to nicotine-seeking behaviour in abstinent subjects based on the actions of cannabinoid (CB) receptor antagonists. However, the effects of CB receptor stimulation on nicotine self-administration and reinstatement have not been systematically studied. Here, we studied the effects of WIN 55,212-2, a CB1/2 agonist, on intravenous nicotine self-administration under fixed-ratio (FR) and progressive-ratio (PR) schedules of reinforcement in rats. The effects of WIN 55,212-2 on responding for food under similar schedules were also studied. In addition, the effects of WIN 55,212-2 on nicotine- and cue-induced reinstatement of nicotine seeking were also studied, as well as the effects of WIN 55,212-2 on nicotine discrimination. WIN 55,212-2 decreased nicotine self-administration under the FR schedule. However, co-administration of WIN 55,212-2 with nicotine decreased responding for food, which suggests that this effect was non-selective. In contrast, WIN 55,212-2 increased both nicotine self-administration and responding for food under the PR schedule, produced dose-dependent reinstatement of nicotine seeking, and enhanced the reinstatement effects of nicotine-associated cues. Some of these effects were reversed by the CB1 antagonist rimonabant, but not by the CB2 antagonist AM630. In the drug discrimination tests between saline and 0.4 mg/kg nicotine, WIN 55,212-2 produced no nicotine-like discriminative effects but significantly potentiated discriminative stimulus effects of nicotine at the low dose through a CB1-receptor-dependent mechanism. These findings indicate that cannabinoid CB1-receptor stimulation increases the reinforcing effects of nicotine and precipitates relapse to nicotine-seeking behaviour in abstinent subjects. Thus, modulating CB1-receptor signalling might have therapeutic value for treating nicotine dependence.

Sex differences in anxiety-like behavior and locomotor activity following prenatal and postnatal methamphetamine exposure in adult rats

The aim of the present study was to investigate the impact of prenatal and postnatal methamphetamine (MA) exposure on behavior and anxiety in adult male and female rats. Mothers were daily exposed to injection of MA (5 mg/kg) or saline (S): prior to impregnation and throughout gestation and lactation periods. On postnatal day 1, pups were cross-fostered so that each mother raised 6 saline-exposed pups and 6 MA-exposed pups. Based on the prenatal and postnatal exposure 4 experimental groups (S/S, S/MA, MA/S, MA/MA) were tested in the Open field (OF) and in the Elevated plus maze (EPM) in adulthood. Locomotion, exploration, immobility and comforting behavior were evaluated in the OF, while anxiety was assessed in the EPM. While prenatal MA exposure did not affect behavior and anxiety in adulthood, postnatal MA exposure (i.e. MA administration to lactating mothers) induced long-term changes. Specifically, adult female rats in diestrus and adult males postnatally exposed to MA via breast milk (S/MA and MA/MA) had decreased locomotion and exploratory behavior in the OF and showed increased anxiety-like behavior in the EPM when compared to female rats in diestrus or males postnatally exposed to saline (S/S and MA/S). In adult females in proestrus, postnatal exposure to MA affected only exploratory behavior in the OF when compared to rats in proestrus postnatally exposed to saline. Thus, the present study shows that postnatal exposure to MA via breast milk impairs behavior in unfamiliar environment and anxiety-like behavior of adult male and female rats more than prenatal MA exposure.

Enhancement of endocannabinoid signaling with JZL184, an inhibitor of the 2-arachidonoylglycerol hydrolyzing enzyme monoacylglycerol lipase, produces anxiolytic effects under conditions of high environmental aversiveness in rats

Dysregulation in signaling of the endocannabinoid 2-arachidonoylglycerol (2-AG) is implicated in hyperresponsiveness to stress. We hypothesized that blockade of monoacylglycerol lipase (MGL), the primary enzyme responsible for 2-AG deactivation in vivo, would produce context-dependent anxiolytic effects in rats. Environmental aversiveness was manipulated by varying illumination of an elevated plus maze. Percentage open arm time and numbers of open and closed arm entries were measured in rats receiving a single intraperitoneal (i.p.) injection of either vehicle, the MGL inhibitor JZL184 (1-8mg/kg), the benzodiazepine diazepam (1mg/kg), the cannabinoid CB(1) receptor antagonist rimonabant (1mg/kg), or JZL184 (8mg/kg) coadministered with rimonabant (1mg/kg). JZL184 (8mg/kg) produced anxiolytic-like effects (i.e., increased percentage open arm time and number of open arm entries) under high, but not low, levels of environmental aversiveness. Diazepam produced anxiolytic effects in either context. Rimonabant blocked the anxiolytic-like effects of JZL184, consistent with mediation by CB(1). Anxiolytic effects of JZL184 were preserved following chronic (8mg/kg per day×6 days) administration. Chronic and acute JZL184 treatment similarly enhanced behavioral sensitivity to an exogenous cannabinoid (WIN55,212-2; 2.5mg/kg i.p.) 24 or 72h following the terminal injection, suggesting a pervasive effect of MGL inhibition on the endocannabinoid system. We attribute our results to alterations in emotion rather than locomotor activity as JZL184 did not alter the number of closed arm entries in the plus maze or produce motor ataxia in the bar test. Our results demonstrate that JZL184 has beneficial, context-dependent effects on anxiety in rats, presumably via inhibition of MGL-mediated hydrolysis of 2-AG. These data warrant further testing of MGL inhibitors to elucidate the functional role of 2-AG in controlling anxiety and stress responsiveness. Our data further implicate a role for 2-AG in the regulation of emotion and validate MGL as a therapeutic target.

Inactivation of the dorsal raphé nucleus reduces the anxiogenic response of rats running an alley for intravenous cocaine

Rats traversing a straight alley once a day for delivery of a single i.v. injection of cocaine develop over trials an ambivalence about entering the goal box. This ambivalence is characterized by the increasing occurrence of "retreat behaviors" where animals leave the start box and run quickly to the goal box, but then stop at the entry point and "retreat" back toward the start box. This unique pattern of retreat behavior has been shown to reflect a form of "approach-avoidance conflict" that stems from the animals' concurrent positive (cocaine reward) and negative (cocaine-induced anxiety) associations with the goal box. Cocaine blocks reuptake of the serotonergic (5-HT) transporter and serotonin has been implicated in the modulation of anxiety. It was therefore of interest to determine whether inactivation of the serotonergic cell bodies residing in the dorsal raphé nucleus (DRN) and projecting to brain areas critical for the modulation of anxiety, would alter the anxiogenic state exhibited by rats running an alley for single daily i.v. injections of 1.0mg/kg cocaine. Reversible inactivation of the DRN was accomplished by intracranial application of a mixed solution of the GABA agonists baclofen and muscimol. While DRN inactivation had no impact on the subjects' motivation to initiate responding (i.e., latencies to leave the start box were unaffected) it reliably reduced the frequency of approach-avoidance retreat behaviors (conflict behavior). These data suggest that inactivation of the dorsal raphé reduces the conflict/anxiety otherwise present in experienced cocaine-seeking animals.

(+)-Methamphetamine-induced monoamine reductions and impaired egocentric learning in adrenalectomized rats is independent of hyperthermia

Methamphetamine (MA) is widely abused and implicated in residual cognitive deficits. In rats, increases in plasma corticosterone and egocentric learning deficits are observed after a 1-day binge regimen of MA (10 mg/kg x 4 at 2-h intervals). The purpose of this experiment was to determine if adrenal inactivation during and following MA exposure would attenuate the egocentric learning deficits in the Cincinnati water maze (CWM). In the first experiment, the effects of adrenalectomy (ADX) or sham surgery (SHAM) on MA-induced neurotoxicity at 72 h were determined. SHAM-MA animals showed typical patterns of hyperthermia, whereas ADX-MA animals were normothermic. Both SHAM-MA- and ADX-MA-treated animals showed increased neostriatal glial fibrillary acidic protein and decreased monoamines in the neostriatum, hippocampus, and entorhinal cortex. In the second experiment, SHAM-MA- and ADX-MA-treated groups showed equivalently impaired CWM performance 2 weeks post-treatment (increased latencies, errors, and start returns) compared to SHAM-saline (SAL) and ADX-SAL groups with no effects on novel object recognition, elevated zero maze, or acoustic startle/prepulse inhibition. Post-testing, monoamine levels remained decreased in both MA-treated groups in all three brain regions, but were not as large as those observed at 72-h post-treatment. The data demonstrate that MA-induced learning deficits can be dissociated from drug-induced increases in plasma corticosterone or hyperthermia, but co-occur with dopamine and serotonin reductions.

Effects of cannabinoid CB1 receptor antagonist rimonabant in consolidation and reconsolidation of methamphetamine reward memory in mice

RATIONALE

Previous studies have shown that cannabinoid CB1 receptors play an important role in specific aspects of learning and memory, yet there has been no systematic study focusing on the involvement of cannabinoid CB1 receptors in methamphetamine-related reward memory.

OBJECTIVES

The purpose of this study was to examine whether rimonabant, a cannabinoid CB1 receptor antagonist, would disrupt the consolidation and reconsolidation of methamphetamine-related reward memory, using conditioned place preference paradigm (CPP).

MATERIALS AND METHODS

Separate groups of male Kunming mice were trained to acquire methamphetamine CPP. Vehicle or rimonabant (1 mg/kg or 3 mg/kg, i.p.) was given at different time points: immediately after each CPP training session (consolidation), 30 min before the reactivation of CPP (retrieval), or immediately after the reactivation of CPP (reconsolidation). Methamphetamine CPP was retested 24 h and 1 and 2 weeks after rimonabant administration.

RESULTS

Rimonabant at doses of 1 and 3 mg/kg significantly inhibited the consolidation of methamphetamine CPP. Only high-dose rimonabant (3 mg/kg) disrupted the retrieval and reconsolidation of methamphetamine CPP. Rimonabant had no effect on methamphetamine CPP in the absence of methamphetamine CPP reactivation.

CONCLUSIONS

Our findings suggest that cannabinoid CB1 receptors play a major role in methamphetamine reward memory, and cannabinoid CB1 receptor antagonists may be a potential pharmacotherapy to manage relapse associated with drug-reward-related memory.

Mirtazapine treatment after conditioning with methamphetamine alters subsequent expression of place preference

Methamphetamine (MP) is a widely abused psychostimulant. There are currently no FDA approved pharmacotherapies for the MP addict. The antidepressant, mirtazapine (Mirt) is a high affinity antagonist at several monoaminergic receptors that are affected by MP. This study evaluated the potential of Mirt as a therapeutic agent for MP addiction and described associated changes in neuronal signaling. A single pairing conditioned place preference (CPP) paradigm was utilized as a behavioral measure of MP-induced effects. Rats learned to associate unique environmental cues with the effects of 1.0 mg/kg (i.p.) MP (day 1) or saline (day 2). Mirt (5.0 mg/kg i.p.) was given in the home cage on day 3 and CPP was assessed on day 4. To evaluate signaling events that correlate with this behavior, brain tissue of these rats were dissected for immunoblot assays of extracellular signal-regulated kinase (ERK) and a transcriptional regulator, cAMP response element-binding protein (CREB) after the CPP test. During the CPP test, rats conditioned with MP spent more time in the environment associated with MP. Importantly, rats given Mirt did not express CPP. MP-induced CPP was associated with a decrease in phosphorylated CREB (pCREB) in the ventral tegmental area, and decreased phosphorylated ERK and pCREB in the nucleus accumbens and treatment with Mirt did not reverse these changes. No changes in signaling proteins were obtained from rats similarly treated with MP and Mirt, without exposure to cues of the conditioning paradigm. Overall, a post-conditioning treatment with Mirt can nullify MP-induced associative learning. However, additional studies are needed to ascertain the molecular events underlying this effect of Mirt.

The role of the CB1 receptor in the regulation of sleep

During the 1990s, transmembranal proteins in the central nervous system (CNS) that recognize the principal compound of marijuana, the delta-9-tetrahydrocannabinol (Delta9-THC) were described. The receptors were classified as central or peripheral, CB1 and CB2, respectively. To this date, it has been documented the presence in the CNS of specific lipids that bind naturally to the CB1/CB2 receptors. The family of endogenous cannabinoids or endocannabinoids comprises oleamide, arachidonoylethanolamine, 2-arachidonylglycerol, virodhamine, noladin ether and N-arachidonyldopamine. Pharmacological experiments have shown that those compounds induce cannabimimetic effects. Endocannabinoids are fatty acid derivates that have a variety of biological actions, most notably via activation of the cannabinoid receptors. The endocannabinoids have an active role modulating diverse neurobiological functions, such as learning and memory, feeding, pain perception and sleep generation. Experimental evidence shows that the administration of Delta9-THC promotes sleep. The activation of the CB1 receptor leads to an induction of sleep, this effect is blocked via the selective antagonist. Since the system of the endogenous cannabinoids is present in several species, including humans, this leads to the speculation of the neurobiological role of the endocannabinoid system on diverse functions such as sleep modulation. This review discusses the evidence of the system of the endocannabinoids as well as their physiological role in diverse behaviours, including the modulation of sleep.

Behavioural and neurotoxic long-lasting effects of MDMA plus cocaine in adolescent mice

The poly-drug pattern is the most common among MDMA users, with cocaine being a frequently associated drug. The aim of the present work was to evaluate the behavioural and neurotoxic long-term effects of exposure during adolescence to MDMA alone or plus cocaine. Mice of 28 to 30 days of age received a treatment of two daily injections of an identical dose of MDMA (5, 10 or 20 mg/kg), alone or plus cocaine (25 mg/kg), for 3 days (6 administrations). Three weeks after receiving MDMA, an increase in the time dedicated by the animals to social contacts with their conspecifics was observed, whilst their behaviour in the elevated plus maze showed no differences from that of non-treated mice. After being exposed to MDMA plus cocaine, mice spent more time in social contacts during the interaction test, as well as exhibiting an anxiolytic profile in the elevated plus maze, with an increase in the time and number of entries in the open arms. The activity of mice treated with cocaine alone or plus MDMA remained constant; the decrease observed among the rest of the animals after the second hour was absent in their case. The level of dopamine in the striatum was diminished in mice treated with 20 mg/kg of MDMA, but this neurotransmitter was not affected in animals exposed to the same dose plus cocaine. The present results highlight pronounced alterations in the behaviour of adult mice after exposure to MDMA and cocaine during adolescence, and demonstrate that these long-term effects can occur without the dopaminergic system becoming affected.

Anxiogenesis in adult rats treated chronically with cocaine during adolescence: effects of extended abstinence and 8-OH-DPAT treatment

Our laboratory has recently observed the development of an anxiogenic response after a short abstinence period ( approximately 10 days) in young adult rats treated repeatedly with cocaine during adolescence. The present study was conducted to determine if this effect persists into adulthood following extended durations of abstinence and whether it could be modulated with the 5-HT(1A) agonist (+/-)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT). Accordingly, 30-day-old rats were injected with either 10mg/kg cocaine or saline for 8 consecutive days. Approximately 8 weeks after the final injection, anxiety levels in subjects were assessed with an elevated zero maze with a second assessment performed 4 weeks thereafter. Shortly prior to each test session, half the subjects in each of the two adolescent drug conditions received injections of 300 microg/kg 8-OH-DPAT while the other half received injections of the vehicle. Based on total time spent in the open areas of the maze, the results obtained at the first abstinent duration indicated that adolescent cocaine treatment did not induce an anxiogenic response. Assessment of maze behavior at the second abstinent duration was aided with a digital tracking and computerized scoring system (LimeLight, Actimetrics). Similar to the results obtained at the first abstinent duration, the amount of time spent in the open areas of the maze was unrelated to prior cocaine treatment. However, cocaine-treated rats did show evidence of an anxiogenic response at this abstinent duration based on more frequent entries into and out of the open and enclosed areas of the maze, more frequent and longer durations of exploratory bouts beyond the perimeter of the maze, excessive number of cautious protrusions into the open areas, and faster running velocities through the open areas. These results were not artifacts of generalized motor activation in that comparable total distance traveled scores were noted for all subjects. Treatment with 8-OH-DPAT shortly prior to elevated zero maze testing normalized these behaviors induced by adolescent cocaine. It is concluded that the anxiogenic response produced by cocaine exposure during adolescence persists 12 weeks beyond cessation of drug treatment and that this effect is reversible with 8-OH-DPAT. In addition, the results underscore the importance of taking multiple measures when assessing anxiety in experimental animals. Implications for the neurobiology of drug abuse and the role of serotonin are discussed.

Subchronic cannabinoid agonist (WIN 55,212-2) treatment during cocaine abstinence alters subsequent cocaine seeking behavior

The co-abuse of marijuana with cocaine is widespread, but it has not been until recently that the relationship between the behavioral effects of cannabinoids and cocaine has begun to be unveiled in animal models. Male Wistar rats were trained to intravenously self-administer cocaine until a stable baseline was reached. Rats then were subjected to a 5-day cocaine deprivation period during which they were treated daily with 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 mesylate) (0, 0.3, 1, and 3 mg/kg; i.p.). Following this subchronic treatment, rats were tested, in counterbalanced order, in a test of anxiety (elevated plus-maze), as well as extinction and cue-induced reinstatement tests, the latter conducted according to a between-within procedure. Subchronic administration of WIN 55,212-2 was found to produce dose-dependent alterations of performance in the extinction, reinstatement, and anxiety tests with the lowest dose of WIN 55,212-2 producing the highest resistance to extinction and reinstatement, and the highest dose of WIN 55,212-2 producing the highest anxiolytic activity. Subchronic treatment with WIN 55,212-2 in rats without a history of cocaine self-administration did not affect anxiety levels. The results suggest an important role of the cannabinoid system in neuronal processes underlying cocaine seeking behavior. However, further studies will be necessary to understand possible implications of these findings for a role of the cannabinoid system as a treatment target for human cocaine abuse.

Chronologically overlapping occurrences of nicotine-induced anxiety- and depression-related behavioral symptoms: effects of anxiolytic and cannabinoid drugs

BACKGROUND

Anxiety and depression are among the most frequently-observed psychiatric symptoms associated with nicotine (NC). In addition to the similarity to other addictive drugs, these NC-induced symptoms are characteristic in that the opposite behavioral effects, i.e. anxiolytic and antidepressant effects, which may reinforce the habitual use of NC, have also been reported. In the present study, the time course of anxiety- and depression-related behavioral alterations was examined in mice. Furthermore, based on the reported similarity in the mechanisms responsible for NC-induced anxiety- and depression-related symptoms, as well as the contribution of brain cannabinoid (CB) receptors to these behavioral symptoms, the effects of anxiolytics and CB receptor ligands (CBs) against these behavioral symptoms were investigated.

RESULTS

Repeated subcutaneous NC treatments (0.3 mg/kg, 4 days), compared with a single treatment (0.5 mg/kg), caused both prolonged anxiogenic effects in the elevated plus-maze test, and prolonged depressive effects in the forced swimming test, even at 120 min time point after the last NC treatment. A transient anxiolytic preference for open arms was also observed in the elevated plus-maze test. Among the anxiolytics and CBs, the serotonin 1A (5-HT1A) antagonist WAY 100135 and the endogenous mixed CB agonist/antagonist virodhamine (VD), when administered intraperitoneally before each NC treatment, provided the strongest antagonistic effects against the anxiety-related symptoms. However, against the depression-related symptoms, only VD provided significant antagonistic effects in both single and repeated treatment groups.

CONCLUSION

The present results support the presence of a chronological overlap of NC-induced anxiety- and depression-related behavioral symptoms, and the contribution of brain CB receptors to these behavioral symptoms. The repeated NC-induced prolongation of these behavioral symptoms and the early transient anxiolytic behavioral alterations support an increased possibility of the habitual use of NC. Furthermore, based on the antagonistic effects of VD, one can predict that the characteristic effects on brain CB receptors as a mixed CB agonist/antagonist contributed to its therapeutic effects as both an anxiolytic and an antidepressant.

Neuropeptide S: a novel modulator of stress and arousal

Neuropeptide S (NPS) is a recently identified bioactive peptide that modulates stress and arousal. NPS is expressed in a few discrete nuclei in the brainstem, such as the pericoerulear (locus coeruleus (LC)) area and the parabrachial nucleus. NPS activates its cognate G protein-coupled receptor at low nanomolar agonist concentrations and induces elevation of intracellular Ca2+ and cAMP, therefore acting as an excitatory transmitter. The NPS receptor is widely expressed in the brain, including regions known to regulate stress responses such as hypothalamus, thalamus, amygdala and limbic cortex. We have recently reported that the NPS system can modulate stress responses and induce wakefulness based on a battery of behavioral tests. Activation of NPS receptors induces arousal and reduces all sleep stages. At the same time, NPS produces anxiolytic-like effects in rodents. These studies indicate that the NPS system has a unique pharmacological profile to promote both anxiolytic and arousal effects. NPS might interact with other hypothalamic neuropeptide systems that are known to be involved in stress and appetite control and thus might be a valuable target for development of a new class of drugs to treat anxiety disorders.

Mice with Decreased Cerebral Dopamine Function following a Neurotoxic Dose of MDMA (3,4-Methylenedioxymethamphetamine, “Ecstasy”) Exhibit Increased Ethanol Consumption and Preference

MDMA (3,4-methylenedioxymethamphetamine, "ecstasy") administration to mice produces relatively selective long-term neurotoxic damage to dopaminergic pathways. There is strong evidence indicating that the dopamine system plays a key role in the rewarding effects of ethanol and modulates ethanol intake. Using a two-bottle free-choice paradigm, we examined the voluntary consumption and preference for ethanol in mice deficient in cerebral dopamine concentration and dopamine transporter density by previous repeated MDMA administration. The current study shows that mice pre-exposed to a neurotoxic dose of MDMA exhibited a higher consumption of and preference for ethanol compared with saline-treated animals. The D(1) receptor full agonist SKF81297 [(6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide)] attenuated the enhanced ethanol intake, an effect that was reversed by SCH23390 [((R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], a D(1) receptor antagonist. MDMA-exposed mice also showed a reduced release of basal dopamine in the nucleus accumbens compared with saline-injected animals and a modest increase in D(1) receptor density in caudate-putamen and nucleus accumbens. Intraperitoneal administration of ethanol elevated extracellular dopamine release in the nucleus accumbens of saline-treated mice, but this effect was almost abolished in MDMA-treated mice. Differences between saline- and MDMA-treated animals did not appear to be secondary to changes in acute ethanol clearance. These results indicate that mice with reduced dopamine activity following a neurotoxic dose of MDMA exhibit increased ethanol consumption and preference and suggest that animals might need to consume more alcohol to reach the threshold for the rewarding effects of ethanol.

Effects of buspirone on the immediate positive and delayed negative properties of intravenous cocaine as measured in the conditioned place preference test

In prior work, we have demonstrated that the behavioral effects of cocaine adhere to the predictions of the opponent-process theory of drug action. Animals develop conditioned place preferences for distinct locations paired with the immediate effects of IV cocaine, but learn to avoid places paired with the effects present 15-min post-injection. It was of interest to assess the putative role of 5-HT in producing the negative properties of cocaine since cocaine acts to inhibit the reuptake of serotonin (5-HT) and since such actions have been associated with anxiogenic consequences. Male rats were administered a reinforcing dose of cocaine (1.0 mg/kg IV) and then placed - either immediately or after a 15-min delay - into one side of a two-compartment (black-white) conditioned place preference (CPP) box for 5-min. On alternate days, the animals received IV saline injections and were placed in the opposite side of the CPP box. This continued for eight days after which animals had experienced 4 pairings of cocaine with one side (black or white) of the CPP apparatus, and 4 saline pairings with the opposite side. Other groups of rats were treated identically except that 30-min prior to placement into the apparatus, these animals received an IP injection of saline or buspirone (a partial 5-HT1A agonist) at a dose that we have shown to be anxiolytic (2.5 mg/kg IP). Control animals experienced either buspirone or saline pretreatments without cocaine. Our results confirm that animals increase the time spent on the side paired with the immediate effects of cocaine (compared to baseline), but tend to avoid the side paired with effects present 15-min post-injection. Buspirone had no effect on the immediate rewarding properties of cocaine, but completely reversed the negative properties present 15-min post-cocaine. These results are consistent with the view that attenuation of 5-HT neurotransmission (via the autoreceptor agonist properties of buspirone) can reverse the negative impact of IV cocaine.

Runway self-administration of intracerebroventricular cocaine: evidence of mixed positive and negative drug actions

In previous work from our laboratory, animals running for intravenous cocaine developed a unique approach-avoidance 'retreat behavior' that was hypothesized to result from cocaine's well documented reinforcing (positive) and anxiogenic (negative) properties. To assess the role of central mechanisms in producing cocaine's positive and negative effects, we assessed whether or not animals running a straight alley for intracerebroventricular applications of cocaine would produce a similar behavioral profile to that previously observed with intravenous applications. Retreat frequency and location were measured in male Sprague-Dawley rats trained to run an alley for one of four doses of intracerebroventricular-administered cocaine (0, 25, 50 or 100 microg cocaine/infusion). Testing involved a single trial per day over 14 consecutive days with a single infusion of cocaine delivered upon goal box entry. The 100 and 50 microg intracerebroventricular cocaine groups exhibited significantly higher retreat frequencies than the 25 and 0 microg groups and the nature and magnitude of the behavior was comparable to that previously observed with intravenous cocaine. These results suggest that the intracerebroventricular self-administration of cocaine results in mixed positive and negative consequences and therefore likely stem from the drug's actions within the central nervous system.

Persistent generalized anxiety after brief exposure to the dopamine antagonist metoclopramide

The authors describe a 31-year-old woman who developed persistent generalized anxiety after brief exposure to the dopamine antagonist metoclopramide. Independently of that, she had experienced a panic attack followed by dystonias, shortly after a single dose of that drug, 17 years before. Both temporal association and recurrence of anxiety symptoms after re-challenge with metoclopramide suggest a causal relationship. The case might provide an initial piece of evidence that dopaminergic neurotransmission can be involved in the pathogenesis of generalized anxiety disorder.

Chronic cocaine or ethanol exposure during adolescence alters novelty-related behaviors in adulthood

Adolescence is a time of high-risk behavior and increased exploration. This developmental period is marked by a greater probability to initiate drug use and is associated with an increased risk to develop addiction and adulthood dependency and drug use at this time is associated with an increased risk. Human adolescents are predisposed toward an increased likelihood of risk-taking behaviors [Zuckerman M. Sensation seeking and the endogenous deficit theory of drug abuse. NIDA Res Monogr 1986;74:59-70.], including drug use or initiation. In the present study, adolescent animals were exposed to twenty days of either saline (0.9% sodium chloride), cocaine (20 mg/kg) or ethanol (1 g/kg) i.p. followed by a fifteen-day washout period. All animals were tested as adults on several behavioral measures including locomotor activity induced by a novel environment, time spent in the center of an open field, novelty preference and novel object exploration. Animals exposed to cocaine during adolescence and tested as adults exhibited a greater locomotor response in a novel environment, spent less time in the center of the novel open field and spent less time with a novel object, results that are indicative of a stress or anxiogenic response to novelty or a novel situation. Adolescent animals chronically administered ethanol and tested as adults, unlike cocaine-exposed were not different from controls in a novel environment, indicated by locomotor activity or time spent with a novel object. However, ethanol-exposed animals approached the novel object more, suggesting that exposure to ethanol during development may result in less-inhibited behaviors during adulthood. The differences in adult behavioral responses after drug exposure during adolescence are likely due to differences in the mechanisms of action of the drugs and subsequent reward and/or stress responsivity. Future studies are needed to determine the neural substrates of these long lasting drug-induced changes.