Role of the endogenous cannabinoid system as a modulator of dopamine transmission: implications for Parkinson's disease and schizophrenia

Maternal Cannabis Use during Lactation and Potential Effects on Human Milk Composition and Production: A Narrative Review

Cannabis use has increased sharply in the last 20 y among adults, including reproductive-aged women. Its recent widespread legalization is associated with a decrease in risk perception of cannabis use during breastfeeding. However, the effect of cannabis use (if any) on milk production and milk composition is not known. This narrative review summarizes current knowledge related to maternal cannabis use during breastfeeding and provides an overview of possible pathways whereby cannabis might affect milk composition and production. Several studies have demonstrated that cannabinoids and their metabolites are detectable in human milk produced by mothers who use cannabis. Due to their physicochemical properties, cannabinoids are stored in adipose tissue, can easily reach the mammary gland, and can be secreted in milk. Moreover, cannabinoid receptors are present in adipocytes and mammary epithelial cells. The activation of these receptors directly modulates fatty acid metabolism, potentially causing changes in milk fatty acid profiles. Additionally, the endocannabinoid system is intimately connected to the endocrine system. As such, it is probable that interactions of exogenous cannabinoids with the endocannabinoid system might modify release of critical hormones (e.g., prolactin and dopamine) that regulate milk production and secretion. Nonetheless, few studies have investigated effects of cannabis use (including on milk production and composition) in lactating women. Additional research utilizing robust methodologies are needed to elucidate whether and how cannabis use affects human milk production and composition.

Effects of selective orexin receptor-2 and cannabinoid receptor-1 antagonists on the response of medial prefrontal cortex neurons to tramadol

Tramadol is widely used to control pain in various diseases, but the relevant mechanisms are less known despite the severe risks of abuse. The medial prefrontal cortex (mPFC) is one of the critical centers of the reward system. Studies have shown that orexins and endocannabinoids are likely to play an important role in addiction. In this study, the effect of orexin receptor-2 (OX2R) and endocannabinoid receptor-1 (CB1R) blockade on the neuronal activity of mPFC was investigated in response to tramadol in male rats. Tramadol was injected intraperitoneally, and its effects on the firing of mPFC pyramidal neurons were investigated using in vivo extracellular single-unit recording. Tramadol affected the pyramidal neuronal activity of the mPFC. AM251 (18 nmol/4 μl), as a selective CB1R antagonist, and TCS-OX2-29 (50 nmol/4 μl), as a selective OX2R antagonist, individually or simultaneously were microinjected into the lateral ventricle of the brain (intracerebroventricular, ICV). The results showed that the ratio of neurons with the excitatory/inhibitory or no responses was significantly changed by tramadol (p < .05). These changes were prevented by blockade of CB1Rs alone or blockade of OX2Rs and CB1Rs simultaneously (p < .05). However, blockade of these receptors in the vehicle group had no significant effect on neuronal activity. The findings of this study indicate the potential role of orexin and endocannabinoid systems in mediating the effects of tramadol in mPFC and the possible interaction between the two systems via OX2 and CB1 receptors. However, further studies are needed to identify these effects by examining intracellular signaling.

Marijuana Is Associated With a Hormonal Imbalance Among Several Habits Related to Male Infertility: A Retrospective Study

Marijuana is one of the most consumed drugs worldwide. There is increasing evidence of an association between marijuana and male infertility. This study intends to assess the repercussion of marijuana smoking and other habits (sedentary lifestyle, alcohol, and tobacco use) in the testicular function of infertile men seeking andrological evaluation. A retrospective study was performed using medical records data of men aged 18-59 years from 2009 to 2017. Complete semen analyses, sperm functional tests, SHBG, and hormonal levels, testosterone-to-estradiol ratio (T/E2), and testis volume were evaluated. Exclusion criteria included cryptorchidism, infertility caused by genetic or infectious diseases, and cancer. A multiple linear regression analysis was performed to investigate which habit could predict certain parameters using the software SPSS 23.0 (P < 0.05). In a sample of 153 men, semen parameters, testosterone levels, and testis volume were not significantly influenced. Marijuana use had the broader hormonal changes since it influences estradiol (P = 0.000; B = -11.616), prolactin (P = 0.000; B = 3.211), SHBG levels (P = 0.017; B = 7.489), and T/E2 (P = 0.004; B = 14.030). Sedentary lifestyle (P = 0.028; B = 1.279) and tobacco smoking (P = 0.031; B = -2.401) influenced the prolactin levels. Marijuana is associated with hormonal imbalance in this infertile cohort by lowering estradiol levels and inhibiting aromatase function.

Genetic deletion of dopamine D1 receptors increases the sensitivity to cannabinoid CB1 receptor antagonist-precipitated withdrawal when compared with wild-type littermates: studies in female mice repeatedly exposed to the Spice cannabinoid HU-210

RATIONALE

The emergence of the consumption of highly potent synthetic cannabinoid receptor agonists (spice drugs) that produce important neurological symptoms has prompted the research on the consequences of acute and chronic use of these new psychoactive substances. Most studies on cannabinoid dependence have been performed in male animals, and there is a need of studies using female subjects.

OBJECTIVES

In the present study, we evaluated only in female animals the role of dopamine D1 receptors in the behavioral responses induced by acute and repeated stimulation of cannabinoid CB1 receptors, including the development of physical dependence, since cannabinoid CB1 receptors are co-localized with dopamine D1 receptors on GABAergic neurons projecting to the substantia nigra.

METHODS

To this end, female dopamine D1 receptor-deficient mice and wild-type littermates were treated with HU-210, a potent synthetic cannabinoid agonist.

RESULTS

Mutant mice displayed an enhanced response to acute motor and hypothermic effects to HU-210 when compared with wild-type females. The administration of SR141716A precipitated behavioral signs of withdrawal in mice treated subchronically with HU-210. Severity of cannabinoid withdrawal syndrome was potentiated in dopamine D1-deficient female mice. Indeed, 4 of 6 abstinence signs were increased in mutant mice.

CONCLUSIONS

These results support for a role of dopamine D1 receptors in the acute, chronic, and withdrawal actions of spice drugs.

Dopamine Related Genes Differentially Affect Declarative Long-Term Memory in Healthy Humans

In humans, monetary reward can promote behavioral performance including response times, accuracy, and subsequent recognition memory. Recent studies have shown that the dopaminergic system plays an essential role here, but the link to interindividual differences remains unclear. To further investigate this issue, we focused on previously described polymorphisms of genes affecting dopaminergic neurotransmission: DAT1 40 base pair (bp), DAT1 30 bp, DRD4 48 bp, and cannabinoid receptor type 1 (CNR1). Specifically, 669 healthy humans participated in a delayed recognition memory paradigm on two consecutive days. On the first day, male vs. female faces served as cues predicting an immediate monetary reward upon correct button presses. Subsequently, participants performed a remember/know recognition memory task on the same day and 1 day later. As predicted, reward increased accuracy and accelerated response times, which were modulated by DAT 30 bp. However, reward did not promote subsequent recognition memory performance and there was no interaction with any genotype tested here. Importantly, there were differential effects of genotype on declarative long-term memory independent of reward: (a) DAT1 40 bp was linked to the quality of memory with a more pronounced difference between recollection and familiarity in the heterozygous and homozygous 10-R as compared to homozygous 9-R; (b) DAT1 30 bp was linked to memory decay, which was most pronounced in homozygous 4-R; (c) DRD4 48 bp was linked to overall recognition memory with higher performance in the short allele group; and (d) CNR1 was linked to overall memory with reduced performance in the homozygous short group. These findings give new insights into how polymorphisms, which are related to dopaminergic neuromodulation, differentially affect long-term recognition memory performance.

Distinctive Evidence Involved in the Role of Endocannabinoid Signalling in Parkinson's Disease: A Perspective on Associated Therapeutic Interventions

Current pharmacotherapy of Parkinson's disease (PD) is symptomatic and palliative, with levodopa/carbidopa therapy remaining the prime treatment, and nevertheless, being unable to modulate the progression of the neurodegeneration. No available treatment for PD can enhance the patient's life-quality by regressing this diseased state. Various studies have encouraged the enrichment of treatment possibilities by discovering the association of the effects of the endocannabinoid system (ECS) in PD. These reviews delineate the reported evidence from the literature on the neuromodulatory role of the endocannabinoid system and expression of cannabinoid receptors in symptomatology, cause, and treatment of PD progression, wherein cannabinoid (CB) signalling experiences alterations of biphasic pattern during PD progression. Published papers to date were searched via MEDLINE, PubMed, etc., using specific key words in the topic of our manuscript. Endocannabinoids regulate the basal ganglia neuronal circuit pathways, synaptic plasticity, and motor functions via communication with dopaminergic, glutamatergic, and GABAergic signalling systems bidirectionally in PD. Further, gripping preclinical and clinical studies demonstrate the context regarding the cannabinoid compounds, which is supported by various evidence (neuroprotection, suppression of excitotoxicity, oxidative stress, glial activation, and additional benefits) provided by cannabinoid-like compounds (much research addresses the direct regulation of cannabinoids with dopamine transmission and other signalling pathways in PD). More data related to endocannabinoids efficacy, safety, and pharmacokinetic profiles need to be explored, providing better insights into their potential to ameliorate or even regress PD.

Contrast sensitivity and motion discrimination in cannabis users

RATIONALE

Cannabis use impairs visual attention; however, it is unclear whether cannabis use also impairs low level visual processing or whether low level visual deficits can be related to lower dopaminergic functioning found in cannabis users.

OBJECTIVES

To investigate whether spatiotemporal contrast sensitivity and motion discrimination under normal and low luminance conditions differ in cannabis users and non-users.

METHODS

Control (n = 20) and cannabis (n = 21) participants completed a visual acuity test, a saliva test and self-report measures. Spatial and temporal contrast thresholds, motion coherence thresholds for translational and radial motion and the spontaneous eye blink rate were then collected.

RESULTS

Cannabis users showed decreased spatial contrast sensitivity under low luminance conditions and increased motion coherence thresholds under all luminance levels tested compared to non-users. No differences in temporal contrast sensitivity were found between the groups. Frequency of cannabis use correlated significantly and negatively with contrast sensitivity, both spatial and temporal, in the cannabis group and higher motion coherence thresholds for radial motion were also associated with more frequent cannabis use in this group. The eye blink rate was significantly lower in cannabis users compared to non-users.

CONCLUSIONS

The present study shows that cannabis use is associated with deficits in low level visual processing. Such deficits are suggested to relate to lower dopamine, in a similar manner as in clinical populations. The implications for driving safety under reduced visibility (e.g. night) in abstaining cannabis users are discussed.

The interactive role of CB1 receptors and L-type calcium channels in hippocampal long-term potentiation in rats

Long-term potentiation (LTP) of synaptic responses is a widely researched model of synaptic plasticity that occurs during learning and memory. The cannabinoid system is an endogenous system that modulate this kind of synaptic plasticity. In addition, voltage dependent calcium channels is essential for induction of LTP at some synapses in the hippocampus. However, there is currently debate over the interaction between L-type calcium channels and cannabinoid system on the synaptic plasticity. In this study, we examined the effects of an acute administration of the cannabinoid antagonist AM251 following a chronic administration of the Ca²⁺ channel blocker verapamil on LTP induction in the hippocampal dentate gyrus(DG) of rats. Male Wistar rats were administered verapamil(10,25,50mg/kg) or saline intraperitoneally(IP) daily for 13days(n=10/group). After this treatment period, animals were anesthetized with an IP injection of urethane; the recording and stimulating electrodes were positioned in the DG and the perforant pathway. After obtaining a steady state baseline response, a single IP injection of saline or AM251(1 or 5mg/kg) was administered. LTP was induced by high-frequency stimulation(HFS). The population spike(PS) amplitude and the slope of excitatory postsynaptic potentials(EPSP) were compared between the experimental groups. The acute administration of the CB1 antagonist AM251 increased LTP induction. The EPSP slopes and PS amplitude in the verapamil and AM251 groups differed after HFS, such that AM251 increased LTP, whereas verapamil decreased LTP induction. These findings suggest that there are functional interactions between the L-type calcium channels and cannabinoid system in this model of synaptic plasticity in the hippocampus.

Gastric Bypass Surgery Recruits a Gut PPAR-α-Striatal D1R Pathway to Reduce Fat Appetite in Obese Rats

Bariatric surgery remains the single most effective long-term treatment modality for morbid obesity, achieved mainly by lowering caloric intake through as yet ill-defined mechanisms. Here we show in rats that Roux-en-Y gastric bypass (RYGB)-like rerouting of ingested fat mobilizes lower small intestine production of the fat-satiety molecule oleoylethanolamide (OEA). This was associated with vagus nerve-driven increases in dorsal striatal dopamine release. We also demonstrate that RYGB upregulates striatal dopamine 1 receptor (D1R) expression specifically under high-fat diet feeding conditions. Mechanistically, interfering with local OEA, vagal, and dorsal striatal D1R signaling negated the beneficial effects of RYGB on fat intake and preferences. These findings delineate a molecular/systems pathway through which bariatric surgery improves feeding behavior and may aid in the development of novel weight loss strategies that similarly modify brain reward circuits compromised in obesity.

Genetic association analysis of CNR1 and CNR2 polymorphisms with schizophrenia in a Korean population

Located on 6q15 and 1p36.11, cannabinoid receptor 1 (CNR1) and cannabinoid receptor 2 (CNR2) genes are considered to be a positional and functional candidate gene for the development of mental disorders such as schizophrenia because CNR1 is known as a regulator of dopamine signaling in the hippocampus and the cerebral cortex. However, few genetic studies have been carried out to investigate an association of CNR1 and CNR2 polymorphisms and the risk of schizophrenia. In this study, although the result indicates that CNR1 and CNR2 variations are unlikely to influence schizophrenia susceptibility in a Korean population, the findings would provide meaningful information for further genetic studies.

Behavioural, biochemical and molecular changes induced by chronic crack-cocaine inhalation in mice: The role of dopaminergic and endocannabinoid systems in the prefrontal cortex

Crack-cocaine addiction has increasingly become a public health problem worldwide, especially in developing countries. However, no studies have focused on neurobiological mechanisms underlying the severe addiction produced by this drug, which seems to differ from powder cocaine in many aspects. This study investigated behavioural, biochemical and molecular changes in mice inhaling crack-cocaine, focusing on dopaminergic and endocannabinoid systems in the prefrontal cortex. Mice were submitted to two inhalation sessions of crack-cocaine a day (crack-cocaine group) during 11 days, meanwhile the control group had no access to the drug. We found that the crack-cocaine group exhibited hyperlocomotion and a peculiar jumping behaviour ("escape jumping"). Blood collected right after the last inhalation session revealed that the anhydroecgonine methyl ester (AEME), a specific metabolite of cocaine pyrolysis, was much more concentrated than cocaine itself in the crack-cocaine group. Most genes related to the endocannabinoid system, CB1 receptor and cannabinoid degradation enzymes were downregulated after 11-day crack-cocaine exposition. These changes may have decreased dopamine and its metabolites levels, which in turn may be related with the extreme upregulation of dopamine receptors and tyrosine hydroxylase observed in the prefrontal cortex of these animals. Our data suggest that after 11 days of crack-cocaine exposure, neuroadaptive changes towards downregulation of reinforcing mechanisms may have taken place as a result of neurochemical changes observed on dopaminergic and endocannabinoid systems. Successive changes like these have never been described in cocaine hydrochloride models before, probably because AEME is only produced by cocaine pyrolysis and this metabolite may underlie the more aggressive pattern of addiction induced by crack-cocaine.

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.

Involvement of the endocannabinoid system in osteoarthritis pain

Osteoarthritis is a degenerative joint disease associated with articular cartilage degradation. The major clinical outcome of osteoarthritis is a complex pain state that includes both nociceptive and neuropathic mechanisms. Currently, the therapeutic approaches for osteoarthritis are limited as no drugs are available to control the disease progression and the analgesic treatment has restricted efficacy. Increasing evidence from preclinical studies supports the interest of the endocannabinoid system as an emerging therapeutic target for osteoarthritis pain. Indeed, pharmacological studies have shown the anti-nociceptive effects of cannabinoids in different rodent models of osteoarthritis, and compelling evidence suggests an active participation of the endocannabinoid system in the pathophysiology of this disease. The ubiquitous distribution of cannabinoid receptors, together with the physiological role of the endocannabinoid system in the regulation of pain, inflammation and even joint function further support the therapeutic interest of cannabinoids for osteoarthritis. However, limited clinical evidence has been provided to support this therapeutic use of cannabinoids, despite the promising preclinical data. This review summarizes the promising results that have been recently obtained in support of the therapeutic value of cannabinoids for osteoarthritis management.

Changes in endocannabinoid and N-acylethanolamine levels in rat brain structures following cocaine self-administration and extinction training

Preclinical investigations have demonstrated that drugs of abuse alter the levels of lipid-based signalling molecules, including endocannabinoids (eCBs) and N-acylethanolamines (NAEs), in the rodent brain. In addition, several drugs targeting eCBs and/or NAEs are implicated in reward and/or seeking behaviours related to the stimulation of dopamine systems in the brain. In our study, the brain levels of eCBs (anandamide (AEA) and 2-arachidonoylglycerol (2-AG)) and NAEs (oleoylethanolamide (OEA) and palmitoylethanolamide (PEA)) were analyzed via an LC-MS/MS method in selected brain structures of rats during cocaine self-administration and after extinction training according to the "yoked" control procedure. Repeated (14days) cocaine (0.5mg/kg/infusion) self-administration and yoked drug delivery resulted in a significant decrease (ca. 52%) in AEA levels in the cerebellum, whereas levels of 2-AG increased in the frontal cortex, the hippocampus and the cerebellum and decreased in the hippocampus and the dorsal striatum. In addition, we detected increases (>150%) in the levels of OEA and PEA in the limbic areas in both cocaine treated groups, as well as an increase in the tissue levels of OEA in the dorsal striatum in only the yoked cocaine group and increases in the tissue levels of PEA in the dorsal striatum (both cocaine groups) and the nucleus accumbens (yoked cocaine group only). Compared to the yoked saline control group, extinction training (10days) resulted in a potent reduction in AEA levels in the frontal cortex, the hippocampus and the nucleus accumbens and in 2-AG levels in the hippocampus, the dorsal striatum and the cerebellum. The decreases in the limbic and subcortical areas were more apparent for rats that self-administered cocaine. Following extinction, there was a region-specific change in the levels of NAEs in rats previously injected with cocaine; a potent increase (ca. 100%) in the levels of OEA and PEA was detected in the prefrontal cortex and the hippocampus, whilst a drop was noted in the striatal areas versus yoked saline yoked animals. Our findings support the previous pharmacological evidence that the eCB system and NAEs are involved in reinforcement and extinction of positively reinforced behaviours and that these lipid-derived molecules may represent promising targets for the development of new treatments for drug addiction.

Effects of cannabinoid and vanilloid drugs on positive and negative-like symptoms on an animal model of schizophrenia: the SHR strain

Studies have suggested that the endocannabinoid system is implicated in the pathophysiology of schizophrenia. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs display hyperlocomotion - reverted by atypical and typical antipsychotics. These results suggest that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia and the effects of potential drugs with an antipsychotic profile. The aim of this study was to investigate the effects of WIN55-212,2 (CB1/CB2 agonist), ACEA (CB1 agonist), rimonabant (CB1 inverse agonist), AM404 (anandamide uptake/metabolism inhibitor), capsaicin (agonist TRPV1) and capsazepine (antagonist TRPV1) on the social interaction and locomotion of control animals (Wistar rats) and SHRs. The treatment with rimonabant was not able to alter either the social interaction or the locomotion presented by Wistar rats (WR) and SHR at any dose tested. The treatment with WIN55-212,2 decreased locomotion (1mg/kg) and social interaction (0.1 and 0.3mg/kg) of WR, while the dose of 1mg/kg increased social interaction of SHR. The treatment with ACEA increased (0.3mg/kg) and decreased (1mg/kg) locomotion of both strain. The administration of AM404 increased social interaction and decreased locomotion of SHR (5mg/kg), and decreased social interaction and increased locomotion in WR (1mg/kg). The treatment with capsaicin (2.5mg/kg) increased social interaction of both strain and decreased locomotion of SHR (2.5mg/kg) and WR (0.5mg/kg and 2.5mg/kg). In addition, capsazepine (5mg/kg) decreased locomotion of both strains and increased (5mg/kg) and decreased (10mg/kg) social interaction of WR. Our results indicate that the schizophrenia-like behaviors displayed by SHR are differently altered by cannabinoid and vanilloid drugs when compared to control animals and suggest the endocannabinoid and the vanilloid systems as a potential target for the treatment of schizophrenia.

Cannabinoid transmission in the prelimbic cortex bidirectionally controls opiate reward and aversion signaling through dissociable kappa versus μ-opiate receptor dependent mechanisms

Cannabinoid, dopamine (DA), and opiate receptor pathways play integrative roles in emotional learning, associative memory, and sensory perception. Modulation of cannabinoid CB1 receptor transmission within the medial prefrontal cortex (mPFC) regulates the emotional valence of both rewarding and aversive experiences. Furthermore, CB1 receptor substrates functionally interact with opiate-related motivational processing circuits, particularly in the context of reward-related learning and memory. Considerable evidence demonstrates functional interactions between CB1 and DA signaling pathways during the processing of motivationally salient information. However, the role of mPFC CB1 receptor transmission in the modulation of behavioral opiate-reward processing is not currently known. Using an unbiased conditioned place preference paradigm with rats, we examined the role of intra-mPFC CB1 transmission during opiate reward learning. We report that activation or inhibition of CB1 transmission within the prelimbic cortical (PLC) division of the mPFC bidirectionally regulates the motivational valence of opiates; whereas CB1 activation switched morphine reward signaling into an aversive stimulus, blockade of CB1 transmission potentiated the rewarding properties of normally sub-reward threshold conditioning doses of morphine. Both of these effects were dependent upon DA transmission as systemic blockade of DAergic transmission prevented CB1-dependent modulation of morphine reward and aversion behaviors. We further report that CB1-mediated intra-PLC opiate motivational signaling is mediated through a μ-opiate receptor-dependent reward pathway, or a κ-opiate receptor-dependent aversion pathway, directly within the ventral tegmental area. Our results provide evidence for a novel CB1-mediated motivational valence switching mechanism within the PLC, controlling dissociable subcortical reward and aversion pathways.

Cannabidiol reduces cigarette consumption in tobacco smokers: preliminary findings

The role of the endocannabinoid system in nicotine addiction is being increasingly acknowledged. We conducted a pilot, randomised double blind placebo controlled study set out to assess the impact of the ad-hoc use of cannabidiol (CBD) in smokers who wished to stop smoking. 24 smokers were randomised to receive an inhaler of CBD (n=12) or placebo (n=12) for one week, they were instructed to use the inhaler when they felt the urge to smoke. Over the treatment week, placebo treated smokers showed no differences in number of cigarettes smoked. In contrast, those treated with CBD significantly reduced the number of cigarettes smoked by ~40% during treatment. Results also indicated some maintenance of this effect at follow-up. These preliminary data, combined with the strong preclinical rationale for use of this compound, suggest CBD to be a potential treatment for nicotine addiction that warrants further exploration.

Hyperactivity induced by the dopamine D2/D3 receptor agonist quinpirole is attenuated by inhibitors of endocannabinoid degradation in mice

The present study was designed to investigate the effect of pharmacological inhibition of endocannabinoid degradation on behavioural actions of the dopamine D2/D3 receptor agonist quinpirole in male C57Bl/6J mice. In addition, we studied the effects of endocannabinoid degradation inhibition on both cocaine-induced psychomotor activation and behavioural sensitization. We analysed the effects of inhibition of the two main endocannabinoid degradation enzymes: fatty acid amide hydrolase (FAAH), using inhibitor URB597 (1 mg/kg); monoacylglycerol lipase (MAGL), using inhibitor URB602 (10 mg/kg). Administration of quinpirole (1 mg/kg) caused a temporal biphasic response characterized by a first phase of immobility (0-50 min), followed by enhanced locomotion (next 70 min) that was associated with the introduction of stereotyped behaviours (stereotyped jumping and rearing). Pretreatment with both endocannabinoid degradation inhibitors did not affect the hypoactivity actions of quinpirole. However, this pretreatment resulted in a marked decrease in quinpirole-induced locomotion and stereotyped behaviours. Administration of FAAH or MAGL inhibitors did not attenuate the acute effects of cocaine. Furthermore, these inhibitors did not impair the acquisition of cocaine-induced behavioural sensitization or the expression of cocaine-induced conditioned locomotion. Only MAGL inhibition attenuated the expression of an already acquired cocaine-induced behavioural sensitization. These results suggest that pharmacological inhibition of endocannabinoid degradation might exert a negative feedback on D2/D3 receptor-mediated hyperactivity. This finding might be relevant for therapeutic approaches for either psychomotor disorders (dyskinesia, corea) or disorganized behaviours associated with dopamine-mediated hyperactivity.

Interactions between the cannabinoid and dopaminergic systems: evidence from animal studies

There is a prominent role of the cannabinoid system to control basal ganglia function, in respect to reward, psychomotor function and motor control. Cannabinoid dysregulations might have a pathogenetic role in dopamine- and basal ganglia related neuropsychiatric disorders, such as drug addiction, psychosis, Parkinson's disease and Huntington's disease. This review highlights interactions between cannabinoids, and dopamine, to modulate neurotransmitter release and synaptic plasticity in the context of drug addiction, psychosis and cognition. Modulating endocannabinoid function, as a plasticity based therapeutic strategy, in the above pathologies with particular focus on cannabinoid receptor type 1 (CB1 receptor) antagonists/inverse agonists, is discussed. On the basis of the existing literature and of new experimental evidence presented here, CB1 receptor antagonists might be beneficial in disease states associated with hedonic dysregulation, and with cognitive dysfunction in particular in the context of psychosis. It is suggested that this effects might be mediated via a hyperglutamatergic state through metabotropic glutamate activation. Indications for endocannabinoid catabolism inhibitors in psychiatric disorders, that might be CB1 receptor independent and might involve TRPV1 receptors, are also discussed.

Site-specific and time-dependent activation of the endocannabinoid system after transection of long-range projections

Background

After focal neuronal injury the endocannabinioid system becomes activated and protects or harms neurons depending on cannabinoid derivates and receptor subtypes. Endocannabinoids (eCBs) play a central role in controlling local responses and influencing neural plasticity and survival. However, little is known about the functional relevance of eCBs in long-range projection damage as observed in stroke or spinal cord injury (SCI).

Methods

In rat organotypic entorhino-hippocampal slice cultures (OHSC) as a relevant and suitable model for investigating projection fibers in the CNS we performed perforant pathway transection (PPT) and subsequently analyzed the spatial and temporal dynamics of eCB levels. This approach allows proper distinction of responses in originating neurons (entorhinal cortex), areas of deafferentiation/anterograde axonal degeneration (dentate gyrus) and putative changes in more distant but synaptically connected subfields (cornu ammonis (CA) 1 region).

Results

Using LC-MS/MS, we measured a strong increase in arachidonoylethanolamide (AEA), oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) levels in the denervation zone (dentate gyrus) 24 hours post lesion (hpl), whereas entorhinal cortex and CA1 region exhibited little if any changes. NAPE-PLD, responsible for biosynthesis of eCBs, was increased early, whereas FAAH, a catabolizing enzyme, was up-regulated 48hpl.

Conclusion

Neuronal damage as assessed by transection of long-range projections apparently provides a strong time-dependent and area-confined signal for de novo synthesis of eCB, presumably to restrict neuronal damage. The present data underlines the importance of activation of the eCB system in CNS pathologies and identifies a novel site-specific intrinsic regulation of eCBs after long-range projection damage.

Differential treatment regimen-related effects of HU210 on CB(1) and D(2)-like receptor functionality in the rat basal ganglia

BACKGROUND/AIMS

Functional linkages between the cannabinoid CB(1) and the dopaminergic systems have been reported although the observations and the mechanisms hypothesizing their interactions at the G protein-coupled receptor (GPCR) functionality level are conflicting.

METHODS

Administration of a potent cannabinoid agonist, HU210, at various doses (25-100 μg/kg) and treatment regimens (1- to 14-day treatment) in rats was carried out to investigate the effect of HU210 treatment on the CB(1) and D(2)-like agonist-mediated GPCR activation.

RESULTS

The desensitizations (reduced coupling) of both D(2) agonist- and CB(1) agonist-mediated GPCR activation was found to be treatment duration dependent and region specific, suggesting implication of receptor tolerance and adaptation due to the cannabinoid treatment. The effect of HU210 on the CB(1) agonist-mediated GPCR desensitization in all treatment groups was not dose dependent.

CONCLUSIONS

The desensitization of D(2)-like receptors found after a cannabinoid treatment in this study strengthens the evidence that the two neurotransmitter systems interact at the intercellular level; this interaction might occur via multiple mechanisms, which also vary according to region.

Distribution of diacylglycerol lipase alpha, an endocannabinoid synthesizing enzyme, in the rat forebrain

1,2-diacylglycerol lipase alpha (DAGLα) is responsible for the biosynthesis and release of 2-arachidonoyl-glycerol (2-AG), the most abundant endocannabinoid in the brain. Although its expression has been detected in discrete regions, we showed here an integrated description of the distribution of DAGLα mRNA and protein in the rat forebrain using in situ hybridization histochemistry and immunohistochemistry. As novelty, we described the distribution of DAGLα protein expression in the olfactory system, the rostral migratory stream, neocortex, septum, thalamus, and hypothalamus. Similar DAGLα immunostaining pattern was also found in the brain of wild-type, but not of DAGLα knockout mice. Immunohistochemical data were correlated by the identification of DAGLα mRNA expression, for instance, in the somata of specific cells in olfactory structures, rostral migratory stream and neocortex, cells in some septal-basal-amygdaloid areas and the medial habenula, and magnocellular cells of the paraventricular hypothalamic nucleus. This widespread neuronal distribution of DAGLα is consistent with multiple roles for endocannabinoids in synaptic plasticity, including presynaptic inhibition of neurotransmitter release. We discuss our comparative analysis of the forebrain expression patterns of DAGLα and other components of the endocannabinoid signaling system, including the CB(1) receptor, monoacylglyceride lipase (MAGL), and fatty acid amide hydrolase (FAAH), providing some insight into the potential physiological and behavioral roles of this system.

Periadolescent exposure to cannabinoids alters the striatal and hippocampal dopaminergic system in the adult rat brain

In a previous work, we have shown that chronic administration of the cannabinoid agonist CP 55,940 (CP) during periadolescence increases cocaine self-administration in adult female rats, while it produces no such effect in males (Higuera-Matas et al., 2008). To extend these findings, we have analysed here the brains of the rats used as subjects in this previous work to evaluate the impact of the interaction between CP exposure and cocaine self-administration on dopaminergic parameters. We evaluated the levels of the dopamine transporter (DAT), and the D1- (D1R) and D2-type (D2R) dopaminergic receptors, as well as tyrosine hydroxylase (TH) mRNA in dopaminergic areas of the adult, cocaine self-administered, rat brain that had been chronically exposed to CP or vehicle (VH) during periadolescence. Control groups with CP/VH exposure and no self-administration experience were also included. In adult females, CP administration induced an up-regulation of DAT in the caudate-putamen that was maintained after cocaine self-administration. In males, CP induced an increase in the D1Rs content in the nucleus accumbens shell, which was not evident after cocaine self-administration. CP also reduced the expression of D2Rs in CA1 irrespective of sex. Finally, an increase in D1Rs was observed in the substantia nigra following cocaine self-administration. These findings suggest that a dopaminergic component modulated by cannabinoids may underlie the enhanced cocaine self-administration previously observed in adult female rats.

Adolescent cannabis use and psychosis: epidemiology and neurodevelopmental models

Cannabis is one of the most widely used illicit drugs among adolescents, and most users first experiment with it in adolescence. Adolescence is a critical phase for brain development, characterized by neuronal maturation and rearrangement processes, such as myelination, synaptic pruning and dendritic plasticity. The endocannabinoid system plays an important role in fundamental brain developmental processes such as neuronal cell proliferation, migration and differentiation. Therefore changes in endocannabinoid activity during this specific developmental phase, induced by the psychoactive component of marijuana, Delta(9)-tetrahydrocannabinol, might lead to subtle but lasting neurobiological changes that can affect brain functions and behaviour. In this review, we outline recent research into the endocannabinoid system focusing on the relationships between adolescent exposure to cannabinoids and increased risk for certain neuropsychiatric diseases such as schizophrenia, as highlighted by both human and animal studies. Particular emphasis will be given to the possible mechanisms by which adolescent cannabis consumption could render a person more susceptible to developing psychoses such as schizophrenia.

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.

Psychomotor performance in relation to acute oral administration of Delta9-tetrahydrocannabinol and standardized cannabis extract in healthy human subjects

Abnormalities in psychomotor performance are a consistent finding in schizophrenic patients as well as in chronic cannabis users. The high levels of central cannabinoid (CB(1)) receptors in the basal ganglia, the cerebral cortex and the cerebellum indicate their implication in the regulation of motor activity. Based on the close relationship between cannabis use, the endogenous cannabinoid system and motor disturbances found in schizophrenia, we expected that administration of cannabinoids may change pattern of psychomotor activity like in schizophrenic patients. This prospective, double-blind, placebo-controlled cross-over study investigated the acute effects of cannabinoids on psychomotor performance in 24 healthy right-handed volunteers (age 27.9 +/- 2.9 years, 12 male) by comparing Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and standardized cannabis extract containing Delta(9)-THC and cannabidiol. Psychomotor performance was assessed by using a finger tapping test series. Cannabis extract, but not Delta(9)-THC, revealed a significant reduction of right-hand tapping frequencies that was also found in schizophrenia. As to the pure Delta(9)-THC condition, left-hand tapping frequencies were correlated with the plasma concentrations of the Delta(9)-THC metabolite 11-OH-THC. These effects are thought to be related to cannabinoid actions on CB(1) receptors in the basal ganglia, the cerebral cortex and the cerebellum. Our data further demonstrate that acute CB(1) receptor activation under the cannabis extract condition may also affect intermanual coordination (IMC) as an index of interhemispheric transfer. AIR-Scale scores as a measure of subjective perception of intoxication were dose-dependently related to IMC which was shown by an inverted U-curve. This result may be due to functional changes involving GABAergic and glutamatergic neurotransmission within the corpus callosum.

The effects of cannabinoids on serum cortisol and prolactin in humans

BACKGROUND

Cannabis is one of the most widely used illicit substances, and there is growing interest in the therapeutic applications of cannabinoids. While known to modulate neuroendocrine function, the precise acute and chronic dose-related effects of cannabinoids in humans are not well-known. Furthermore, the existing literature on the neuroendocrine effects of cannabinoids is limited by small sample sizes (n = 6-22), heterogeneous samples with regard to cannabis exposure (lumping users and nonusers), lack of controlling for chronic cannabis exposure, differing methodologies, and limited dose-response data. Delta-9-tetrahydrocannabinol (Delta-9-THC) was hypothesized to produce dose-related increases in plasma cortisol levels and decreases in plasma prolactin levels. Furthermore, relative to controls, frequent users of cannabis were hypothesized to show altered baseline levels of these hormones and blunted Delta-9-THC-induced changes of these hormones.

MATERIALS AND METHODS

Pooled data from a series of laboratory studies with multiple doses of intravenous Delta-9-THC in healthy control subjects (n = 36) and frequent users of cannabis (n = 40) was examined to characterize the acute, chronic, and acute on chronic effects of cannabinoids on plasma cortisol and prolactin levels. Hormone levels were measured before (baseline) and 70 min after administration of each dose of Delta-9-THC. Data were analyzed using linear mixed models with +70 min hormonal levels as the dependant variable and baseline hormonal level as the covariate.

RESULTS

At socially relevant doses, Delta-9-THC raised plasma cortisol levels in a dose-dependent manner but frequent users showed blunted increases relative to healthy controls. Frequent users also had lower baseline plasma prolactin levels relative to healthy controls.

CONCLUSIONS

These group differences may be related to the development of tolerance to the neuroendocrine effects of cannabinoids. Alternatively, these results may reflect inherent differences in neuroendocrine function in frequent users of cannabis and not a consequence of cannabis use.

Cannabinoid receptor 1 gene (CNR1) and susceptibility to a quantitative phenotype for hebephrenic schizophrenia

Functional alterations of components of the endogenous cannabinoid system, in particular of the cannabinoid receptor 1 protein (CB1), are hypothetical contributors to many of the symptoms seen in schizophrenia. Variants within the cannabinoid receptor 1 gene (CNR1) have been shown to be directly associated with the hebephrenic form of schizophrenia in a Japanese population. This finding, however, has yet to be replicated. In the present study we sought to study the same (AAT)n-repeat microsatellite of the CNR1 gene which showed association to hebephrenic schizophrenia in Japan, and to investigate whether this microsatellite showed association to a hebephrenic type of schizophrenia in a family-based association study in a population of the Central Valley of Costa Rica. The Lifetime Dimensions of Psychosis Scale and a best estimate consensus process were utilized to identify subjects with schizophrenia who had an elevated lifetime dimensional score for negative and disorganized symptoms, which we used as a proxy for "hebephrenia." Using the Family Based Association Test we found association of these hebephrenic subjects and the (AAT)n-repeat marker of the CNR1 (multi-allelic P = 0.0368). Our hypothesis that an association with the (AAT)n-repeat marker of CNR1 would not be found with the more general type of schizophrenia was also confirmed. Schizophrenic subjects with prominent lifetime scores for disorganization and negative symptoms (dimension for hebephrenia) are associated with the CNR1 gene and present a type of symptomatology that resembles chronic cannabinoid-induced psychosis. The current finding points to the possibility of different genetic and pathophysiologic mechanisms underlying different types of schizophrenia.

Neonatal basolateral amygdala lesions affect monoamine and cannabinoid brain systems in adult rats

There is evidence for neurodevelopment disturbances in schizophrenia. In rats, a neonatal basolateral amygdala lesion induces behavioural features in adults reminiscent of the symptomatology of schizophrenia. Dopamine plays a key role in the pathogenesis of schizophrenia, and cannabis use has been implicated in the risk for developing schizophrenia. The effects of an excitotoxic, bilateral basolateral amygdala lesion on postnatal days 7 or 21 were compared when the rats were adult. The behavioural response to a novelty challenge and the level of dopamine receptors and cannabinoid receptors in the brain using in-vitro autoradiography was determined. In brain tissue punches concentrations of monoamines and metabolites were determined by high-performance liquid chromatography. The neonatal lesion, but not the later lesion induced behavioural hyperactivity and biochemical effects. The neonatal lesion reduced the density of dopamine D2-like, but not D3-, and less markely D1-like receptors and increased dopamine turnover. These effects were observed in the mesolimbic, but not in the striatal regions. In contrast, density of cannabinoid receptors was increased in the striatal, but not the mesolimbic regions of these animals. Noradrenergic neurotransmission was reduced in both regions. The present findings contribute to the idea that the neonatal basolateral amygdala lesion induces features in adults reminiscent of the neurodevelopmental disturbances in schizophrenia, with a focus on the amygdala-prefrontal cortex-nucleus accumbens circuit.

Supraspinal modulation of pain by cannabinoids: the role of GABA and glutamate

Recent physiological, pharmacological and anatomical studies provide evidence that one of the main roles of the endocannabinoid system in the brain is the regulation of gamma-aminobutyric acid (GABA) and glutamate release. This article aims to review this evidence in the context of its implications for pain. We first provide a brief overview of supraspinal regulation of nociception, followed by a review of the evidence that the brain's endocannabinoid system modulates nociception. We look in detail at regulation of supraspinal GABAergic and glutamatergic neurons by the endocannabinoid system and by exogenously administered cannabinoids. Finally, we review the evidence that cannabinoid-mediated modulation of pain involves modulation of GABAergic and glutamatergic neurotransmission in key brain regions.

Influences of an acoustic signal with ultrasound components on the acquisition of a defensive conditioned reflex in Wistar rats

The effects of short (90 sec) exposures to a complex acoustic signal with ultrasound components on the acquisition of a defensive conditioned two-way avoidance reflex using an electric shock as the unconditioned stimulus in a shuttle box were studied in female Wistar rats. This stimulus induced audiogenic convulsions of different severities in 59% of the animals. A scale for assessing the ability of rats to acquire the conditioned two-way avoidance reflex was developed. Presentation of the complex acoustic signal was found to be a powerful stressor for Wistar rats, preventing the acquisition of the reflex in the early stages (four and six days) after presentation. This effect was independent of the presence and severity of audiogenic convulsions in the rats during presentation of the acoustic signal. On repeat training nine days after the acoustic signal (with the first session after four days), acquisition of the reflex was hindered (as compared with controls not presented with the acoustic signal). However, on repeat training at later time points (1.5 months after the complex acoustic signal, with the first session after six days), the rats rapidly achieved the learning criterion (10 correct avoidance responses in a row). On the other hand, if the acoustic signal was presented at different times (immediately or at three or 45 days) after the first training session, the animals' ability to acquire the reflex on repeat training was not impaired at either the early or late periods after exposure to the stressor. These results suggest that the complex acoustic signal impairs short-term memory (the process of acquisition of the conditioned two-way avoidance reflex at the early post-presentation time point) but has no effect on long-term memory or consolidation of the memory trace.

Cannabinoid CB1 receptor antagonism markedly increases dopamine receptor-mediated stereotypies

The contribution of the endocannabinoid system to dopamine-mediated disorganized behavior in schizophrenia is discussed. We used a model of concurrent stimulation of dopamine D1 and D2 receptors to evaluate the role of this system in dopamine-mediated stereotypies measured in a hole-board test. Pretreatment with the cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A; 1 mg/kg) potentiated stereotyped behavior induced by coadministration of the dopamine D1 receptor agonist SKF 38393 (0.05, 0.1 and 1 mg/kg) and the dopamine D2 receptor agonist quinpirole (0.25 mg/kg). Thus, the endocannabinoid system acts as a brake for abnormal behavior associated with dopaminergic overactivation.

Feasibility of central cannabinoid CB1 receptor imaging with [124I]AM281 PET demonstrated in a schizophrenic patient

We studied central cannabinoid CB1 receptors in a schizophrenic patient using the pyrazole derivative AM281 labelled with the positron-emitting nuclide iodine-124. A dynamic positron emission tomography (PET) acquisition with simultaneous blood sampling was performed up to 1.5 h post-injection. The classical Logan plot analysis was applied to generate a three-dimensional map of distribution volume (DV). The map was spatially normalised into the Montreal Neurological Institute stereotactic space. Using a volume of interest (VOI) template, mean values of DV were extracted from multiple grey matter regions and white matter (as a reference). As a measure of regional receptor availability, ratios of DV in grey matter to DV in white matter minus one (DVR-1) were calculated. The highest receptor binding was observed in the striatum and the pallidum (DVR-1: 0.35-0.37). Binding in basal ganglia regions was lower on the left than the right side. Moderately high binding was seen in the frontal cortex (0.22), the temporal cortex (0.18) and the cerebellum (0.15). In conclusion, 124I-AM281 PET can be used to reveal areas with prominent CB1 receptor binding. Nevertheless, limited image contrast and relatively high radiation exposure (physical half-life of 124I: 4 days) have to be taken into account. Asymmetric receptor binding may possibly reflect pathologic changes in schizophrenia.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Endocannabinoids activate transient receptor potential vanilloid 1 receptors to reduce hyperdopaminergia-related hyperactivity: therapeutic implications

BACKGROUND

Knockout (KO) mice invalidated for the dopamine transporter (DAT) constitute a powerful animal model of neurobiological alterations associated with hyperdopaminergia relevant to schizophrenia and attention-deficit/hyperactivity disorder (ADHD).

METHODS

Because of continuously increasing evidence for a neuromodulatory role of endocannabinoids in dopamine-related pathophysiological responses, we assessed endocannabinoid signaling in DAT KO mice and evaluated the ability of endocannabinoid ligands to normalize behavioral deficits, namely spontaneous hyperlocomotion in these mice.

RESULTS

In DAT KO mice, we found markedly reduced anandamide levels, specifically in striatum, the dopamine nerve terminal region. Furthermore, three distinct indirect endocannabinoid agonists, the selective anandamide reuptake inhibitors AM404 and VDM11 and the fatty acid amidohydrolase inhibitor AA5HT, attenuated spontaneous hyperlocomotion in DAT KO mice. The hypolocomotor effects of AM404, VDM11, and AA5HT were significantly attenuated by co-administration of the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine but not the selective cannabinoid type 1 (CB1)receptor antagonist AM251. Interestingly, TRPV1 binding was increased in the striatum of DAT KO mice, while CB1 receptor binding was unaffected.

CONCLUSIONS

These data indicate a dysregulated striatal endocannabinoid neurotransmission associated with hyperdopaminergic state. Restoring endocannabinoid homeostasis in active synapses might constitute an alternative therapeutic strategy for disorders associated with hyperdopaminergia. In this process, TRPV1 receptors seem to play a key role and represent a novel promising pharmacological target.

Molecular mapping of striatal subdivisions in juvenile Macaca Mulata

The striatum of the primate brain can be subdivided into three distinct anatomical subregions: caudate (CAU), putamen (PUT), and ventral striatum (VS). Although these subregions share several anatomical connections, cell morphological, and histochemical features, they differ considerably in their vulnerability to different neurological and psychiatric diseases, and these brain regions have significantly different functions in health and disease. In order to better understand the molecular underpinnings of the different disease and functional vulnerabilities, transcriptional profiles were generated from the CAU, PUT, and VS of five juvenile rhesus macaques (Macaca mulatta) using human cDNA neuromicroarrays containing triplicate spots of 1227 cDNAs. Differences in microarray gene expression were assessed using z score analysis and 1.5-fold change between paired subregions. Clustering of genes based on dissimilarity of expression patterns between regions revealed subregion specific expression profiles encoding G-protein-coupled receptor signaling transcripts, transcription factors, kinases and phosphatases, and cell signaling and signal transduction transcripts. Twelve transcripts were examined using quantitative real-time PCR (qPCR), and 81% demonstrated alterations similar to those seen with microarray analysis, some of which were statistically significant. Subregion specific transcription profiles support the anatomical differentiation and potential disease vulnerabilities of the respective subregions.

Interpreting the association between cannabis use and increased risk for schizophrenia

Recent longitudinal studies from Sweden, the Netherlands, New Zealand, and Israel report that cannabis use during childhood and adolescence doubles the risk of later appearance of psychosis or schizophrenia, These data have been interpreted as indicating that cannabis has a causal effect along the pathway to psychosis. In this paper, we will offer an alternative explanation of these data. Recent investigations of patients with schizophrenia found increased density of cannabinoid receptors in the dorsolateral prefrontal cortex and the anterior cingulate cortex. Others reported higher levels of endogenous cannabinoids in the blood and cerebrospinal fluid of patients; these findings were independent of possible cannabis use. Several genetic studies have reported an association between genes encoding the cannabinoid receptor and schizophrenia. Thus, an alternative explanation of the association between cannabis use and schizophrenia might be that pathology of the cannabinoid system in schizophrenia patients is associated with both increased rates of cannabis use and increased risk for schizophrenia, without cannabis being a causal factor for schizophrenia.

Distribution of cannabinoid receptor 1 in the CNS of zebrafish

The cannabinoid receptor 1 (Cb1) mediates the psychoactive effect of marijuana. In mammals, there is abundant evidence advocating the importance of cannabinoid signaling; activation of Cb1 exerts diverse functions, chiefly by its ability to modulate neurotransmission. Thus, much attention has been devoted to understand its role in health and disease and to evaluate its therapeutic potential. Here, we have cloned zebrafish cb1 and investigated its expression in developing and adult zebrafish brain. Sequence analysis showed that there is a high degree of conservation, especially in residues demonstrated to be critical for function in mammals. In situ hybridization revealed that zebrafish cb1 appears first in the preoptic area at 24 hours post-fertilization. Subsequently, transcripts are detected in the dorsal telencephalon, hypothalamus, pretectum and torus longitudinalis. A similar pattern of expression is recapitulated in the adult brain. While cb1 is intensively stained in the medial zone of the dorsal telencephalon, expression elsewhere is weak by comparison. In particular, localization of cb1 in the telencephalic periventricular matrix is suggestive of the involvement of Cb1 in neurogenesis, bearing strong resemblance in terms of expression and function to the proliferative mammalian hippocampal formation. In addition, a gradient-like expression of cb1 is detected in the torus longitudinalis, a teleost specific neural tissue. In relation to dopaminergic neurons in the diencephalic posterior tuberculum (considered to be the teleostean homologue of the mammalian midbrain dopaminergic system), both cb1 and tyrosine hydroxylase-expressing cells occupy non-overlapping domains. However there is evidence that they are co-localized in the caudal zone of the hypothalamus, implying a direct modulation of dopamine release in this particular region. Collectively, our data indicate the propensity of zebrafish cb1 to participate in multiple neurological processes.

Subcellular localization of type 1 cannabinoid receptors in the rat basal ganglia

Endocannabinoids, acting via type 1 cannabinoid receptors (CB1), are known to be involved in short-term synaptic plasticity via retrograde signaling. Strong depolarization of the postsynaptic neurons is followed by the endocannabinoid-mediated activation of presynaptic CB1 receptors, which suppresses GABA and/or glutamate release. This phenomenon is termed depolarization-induced suppression of inhibition (DSI) or excitation (DSE), respectively. Although both phenomena have been reported to be present in the basal ganglia, the anatomical substrate for these actions has not been clearly identified. Here we investigate the high-resolution subcellular localization of CB1 receptors in the nucleus accumbens, striatum, globus pallidus and substantia nigra, as well as in the internal capsule, where the striato-nigral and pallido-nigral pathways are located. In all examined nuclei of the basal ganglia, we found that CB1 receptors were located on the membrane of axon terminals and preterminal axons. Electron microscopic examination revealed that the majority of these axon terminals were GABAergic, giving rise to mostly symmetrical synapses. Interestingly, preterminal axons showed far more intense staining for CB1, especially in the globus pallidus and substantia nigra, whereas their terminals were only faintly stained. Non-varicose, thin unmyelinated fibers in the internal capsule also showed strong CB1-labeling, and were embedded in bundles of myelinated CB1-negative axons. The majority of CB1 receptors labeled by immunogold particles were located in the axonal plasma membrane (92.3%), apparently capable of signaling cannabinoid actions. CB1 receptors in this location cannot directly modulate transmitter release, because the release sites are several hundred micrometers away. Interestingly, both the CB1 agonist, WIN55,212-2, as well as its antagonist, AM251, were able to block action potential generation, but via a CB1 independent mechanism, since the effects remained intact in CB1 knockout animals. Thus, our electrophysiological data suggest that these receptors are unable to influence action potential propagation, thus they may not be functional at these sites, but are likely being transported to the terminal fields. The present data are consistent with a role of endocannabinoids in the control of GABA, but not glutamate, release in the basal ganglia via presynaptic CB1 receptors, but also call the attention to possible non-CB1-mediated effects of widely used cannabinoid ligands on action potential generation.

A role for endocannabinoids in the generation of parkinsonism and levodopa-induced dyskinesia in MPTP-lesioned non-human primate models of Parkinson's disease

Endocannabinoids and cannabinoid CB1 receptors play a role in the control of movement by modulating GABA, glutamate, and other neurotransmitters throughout the basal ganglia. Roles for abnormalities in endocannabinoid signaling in Parkinson's disease (PD) and the major side effect of current treatments, levodopa-induced dyskinesia (LID), have been suggested by rodent studies. Here we show that signaling by endocannabinoids contributes to the pathophysiology of parkinsonism and LID in MPTP-lesioned, non-human primate models of Parkinson's disease. In MPTP-lesioned marmosets previously treated with levodopa to establish LID, attenuation of CB1 signaling by systemic administration of rimonabant (1 and 3 mg/kg) had anti-parkinsonian actions, equivalent to a 71% increase in motor activity at 3 mg/kg. Rimonabant did not elicit dyskinesia. Co-administration of levodopa (8 mg/kg) and rimonabant (1 and 3 mg/kg) resulted in significantly less dyskinesia than levodopa alone, without significantly affecting the anti-parkinsonian action of levodopa. These data suggest that enhanced endocannabinoid signaling may be involved in the pathophysiology of both parkinsonism and LID. To define potential mechanisms by which such a role might be mediated, we determined the levels of the endocannabinoids anandamide and 2-arachidonyl glycerol (2-AG) throughout the basal ganglia in normal and three groups of MPTP-lesioned cynomolgus monkeys (untreated; acutely treated with L-DOPA, non-dyskinetic; long-term treated, with levodopa-induced dyskinesia). In the untreated, MPTP-lesioned primate, parkinsonism was associated with increases in both 2-AG (+88%) and anandamide (+49%) in the striatum, and of 2-AG (+97%) in the substantia nigra, changes that are consistent with the previously suggested role for endocannabinoids in mechanisms attempting to compensate for loss of dopamine in untreated parkinsonism. Increased levels of anandamide (+34%) in the external globus pallidus of MPTP-lesioned animals were normalized by levodopa treatment and may contribute to the generation of parkinsonian symptoms. However, no clear alteration in endocannabinoid levels could be correlated with the expression of LID. These data highlight the potential roles played by endocannabinoids and CB1 in PD and LID and suggest the need for further research to pursue the multiple therapeutic opportunities for manipulating this system in movement disorders.

Role of endocannabinoid system in mental diseases

In the last decade, a large number of studies using Delta9-tetrahydrocannabinol (THC), the main active principle derivative of the marijuana plant, or cannabinoid synthetic derivatives have substantially contributed to advance the understanding of the pharmacology and neurobiological mechanisms produced by cannabinoid receptor activation. Cannabis has been historically used to relieve some of the symptoms associated with central nervous system disorders. Nowadays, there are anecdotal evidences for the use of cannabis in many patients suffering from multiple sclerosis or chronic pain. Following the historical reports of the use of cannabis for medicinal purposes, recent research has highlighted the potential of cannabinoids to treat a wide variety of clinical disorders. Some of these disorders that are being investigated are pain, motor dysfunctions or psychiatric illness. On the other hand, cannabis abuse has been related to several psychiatric disorders such as dependence, anxiety, depression, cognitive impairment, and psychosis. Considering that cannabis or cannabinoid pharmaceutical preparations may no longer be exclusively recreational drugs but may also present potential therapeutic uses, it has become of great interest to analyze the neurobiological and behavioral consequences of their administration. This review attempts to link current understanding of the basic neurobiology of the endocannabinoid system to novel opportunities for therapeutic intervention and its effects on the central nervous system.

Biosynthesis of endocannabinoids and their modes of action in neurodegenerative diseases

Endocannabinoids are thought to function as retrograde messengers, which modulate neurotransmitter release by activating presynaptic cannabinoid receptors. Anandamide and 2-arachidonoylglycerol (2-AG) are the two best studied endogenous lipids which can act as endocannabinoids. Together with the proteins responsible for their biosynthesis, inactivation and the cannabinoid receptors, these lipids constitute the endocannabinoid system. This system is proposed to be involved in various neurodegenerative diseases such as Parkinson's and Huntington's diseases as well as Multiple Sclerosis. It has been demonstrated that the endocannabinoid system can protect neurons against glutamate excitotoxicity and acute neuronal damage in both in vitro and in vivo models. In this paper we review the data concerning the involvement of the endocannabinoid system in neurodegenerative diseases in which neuronal cell death may be elicited by excitotoxicity. We focus on the biosynthesis of endocannabinoids and on their modes of action in animal models of these neurodegenerative diseases.