Expression and function of CB1 receptor in the rat striatum: localization and effects on D1 and D2 dopamine receptor-mediated motor behaviors

Low-dose cannabidiol treatment prevents chronic stress-induced phenotypes and is associated with multiple synaptic changes across various brain regions

Major Depressive Disorder (MDD) is a heterogeneous and debilitating mood disorder often associated with stress. Although current treatments are available, they remain ineffective for approximately 30% of affected individuals and are frequently accompanied by undesirable side effects. Cannabidiol (CBD) has emerged as a potential and safe therapeutic option for alleviating depressive symptoms; however, the underlying molecular mechanisms through which this compound exerts its beneficial effects are not yet fully understood. In this study, we demonstrate that a very low dose of CBD (1 mg/kg) can partially reverse some sequelae induced by chronic stress, a well-established mouse model used to simulate depressive-like symptoms. Using mass spectrometry to analyze different brain regions, we observed several improvements following CBD treatment, particularly in the medial prefrontal cortex (mPFC), across multiple neurotransmission systems (including glutamatergic and serotonergic pathways). Microstructural experiments, utilizing double-labeling of F-Actin and VGlut1-positive clusters, revealed a complete restoration of mature synapses in the mPFC of mice treated with CBD. In conclusion, our findings indicate that a very low dose of CBD is effective in counteracting the adverse effects of chronic stress, possibly through the synaptic remodeling of excitatory synapses in the mPFC.

Influence of solvent, sex, and age on pharmacokinetic and acute behavioral effects of vaporized cannabis extract in mice

The legalization of cannabis in several states across the US has increased the need to better understand its effects on the body, brain, and behavior, particularly in different populations. Rodent models are particularly valuable in this respect because they provide precise control over external variables. Previous rodent studies have found age and sex differences in response to injected Δ9-tetrahydrocannabinol (THC), the major psychoactive component of cannabis. However, this route of administration does not mimic the most common way humans consume cannabis, i.e. through inhalation. Here, we sought to address this gap by investigating age and sex differences in pharmacokinetics and the acute behavioral effects of vaporized cannabis extract in mice. Adolescent (postnatal day [P] 35-50) and adult (≥ P70) mice of both sexes received noncontingent exposure to 0 mg/ml, 150 mg/ml, or 300 mg/ml vaporized cannabis extract diluted in either 80% propylene glycol/20% vegetable glycerol (PG/VG) or 100% polyethylene glycol 400 (PEG). Immediately after exposure, body temperature, hot plate withdrawal latency, and locomotion were assessed. Blood was collected at 0, 30, and 60 min after vapor exposure, and plasma THC and its metabolites were analyzed. Measured THC levels were higher in both the plasma of vapor-exposed mice and the cannabis extract solutions themselves when PEG was the solvent compared to PG/VG. Vaporized cannabis (dissolved in PEG) at the highest dose tested induced hypothermic, antinociceptive, and locomotor-suppressing effects in all groups of mice. We found a dose-dependent age difference in locomotion, indicating that adolescents were less sensitive to the locomotor-suppressing effects of vaporized cannabis, which may be related to the plasma THC levels achieved. Although we found no significant sex differences in the acute behavioral effects of vaporized cannabis, there were significant sex differences in plasma THC metabolites indicating that female mice may metabolize vaporized cannabis more slowly than male mice. Taken together, the current findings add to a growing number of studies implementing vaporized cannabinoid delivery approaches by revealing PEG as the superior solvent for studies involving cannabis extract.

Multi-modal and bi-directional effects of a synthetic Δ9-Tetrahydrocannabinol (THC) analogue, Nabilone, on spatio-temporal binding windows: Evidence from the projected hand illusion

Abnormally widened spatial and temporal binding windows (SBW/TBWs; length of space/time whereby stimuli are considered part of the same percept) are observed in schizophrenia. TBW alterations have been associated with altered sense of agency (hereafter referred to as agency), and an associative relationship between embodiment (body ownership) and agency has been proposed. SBWs/TBWs are investigated separately, but no evidence exists of these being separate in mechanism, system or function. The underlying neural substrate of schizophrenia remains unclear. The literature claims either pro-psychotic or anti-psychotic effects of Δ9-Tetrahydrocannabinol (THC) in patients and healthy individuals, but major support for cannabis in the aetiology of schizophrenia is associative, not causal. To clarify if THC is pro- or anti-psychotic, this single-blind, placebo-controlled within-subjects cross-over study tested several hypotheses. 1) Competing hypotheses that a synthetic THC analogue, Nabilone (NAB, 1-2 mg), would alter measures of agency and embodiment in healthy volunteers (n = 32) similarly, or opposite, to that of in patients with schizophrenia. 2) That there would be significant associations between any NAB-induced alterations in individual agency and embodiment measures in the Projected Hand Illusion (PHI). 3) That there is a unitary spatio-temporal binding window (STBW). A large proportion of individuals did not experience the PHI. Multimodal and bi-directional effects of NAB on the PHI were observed. Evidence of a unitary spatio-temporal binding window (STBW) was observed. NAB widened the STBW in some but narrowed it in others as a function of space and delay. No associations were found between agency and embodiment.

Using caffeine as a chemical means to induce flow states

Flow is an intrinsically rewarding state characterised by positive affect and total task absorption. Because cognitive and physical performance are optimal in flow, chemical means to facilitate this state are appealing. Caffeine, a non-selective adenosine receptor antagonist, has been emphasized as a potential flow-inducer. Thus, we review the psychological and biological effects of caffeine that, conceptually, enhance flow. Caffeine may facilitate flow through various effects, including: i) upregulation of dopamine D1/D2 receptor affinity in reward-associated brain areas, leading to greater energetic arousal and 'wanting'; ii) protection of dopaminergic neurons; iii) increases in norepinephrine release and alertness, which offset sleep-deprivation and hypoarousal; iv) heightening of parasympathetic high frequency heart rate variability, resulting in improved cortical stress appraisal, v) modification of striatal endocannabinoid-CB1 receptor-signalling, leading to enhanced stress tolerance; and vi) changes in brain network activity in favour of executive function and flow. We also discuss the application of caffeine to treat attention deficit hyperactivity disorder and caveats. We hope to inspire studies assessing the use of caffeine to induce flow.

Synthesis and Preclinical Evaluation of Fluorinated 5-Azaindoles as CB2 PET Radioligands

Several classes of cannabinoid receptor type 2 radioligands have been evaluated for imaging of neuroinflammation, with successful clinical translation yet to take place. Here we describe the synthesis of fluorinated 5-azaindoles and pharmacological characterization and in vivo evaluation of 18F-radiolabeled analogues. [18F]2 (hCB2 Ki = 96.5 nM) and [18F]9 (hCB2 Ki = 7.7 nM) were prepared using Cu-mediated 18F-fluorination with non-decay-corrected radiochemical yields of 15 ± 6% and 18 ± 2% over 85 and 80 min, respectively, with high radiochemical purities (>97%) and molar activities (140-416 GBq/μmol). In PET imaging studies in rats, both [18F]2 and [18F]9 demonstrated specific binding in CB2-rich spleen after pretreatment with CB2-specific GW405833. Moreover, [18F]9 exhibited higher brain uptake at later time points in a murine model of neuroinflammation compared with a healthy control group. The results suggest further evaluation of azaindole based CB2 radioligands is warranted in other neuroinflammation models.

An enquiry to the role of CB1 receptors in neurodegeneration

Neurodegenerative disorders are debilitating conditions that impair patient quality of life and that represent heavy social-economic burdens to society. Whereas the root of some of these brain illnesses lies in autosomal inheritance, the origin of most of these neuropathologies is scantly understood. Similarly, the cellular and molecular substrates explaining the progressive loss of brain functions remains to be fully described too. Indeed, the study of brain neurodegeneration has resulted in a complex picture, composed of a myriad of altered processes that include broken brain bioenergetics, widespread neuroinflammation and aberrant activity of signaling pathways. In this context, several lines of research have shown that the endocannabinoid system (ECS) and its main signaling hub, the type-1 cannabinoid (CB1) receptor are altered in diverse neurodegenerative disorders. However, some of these data are conflictive or poorly described. In this review, we summarize the findings about the alterations in ECS and CB1 receptors signaling in three representative brain illnesses, the Alzheimer's, Parkinson's and Huntington's diseases, and we discuss the relevance of these studies in understanding neurodegeneration development and progression, with a special focus on astrocyte function. Noteworthy, the analysis of ECS defects in neurodegeneration warrant much more studies, as our conceptual understanding of ECS function has evolved quickly in the last years, which now include glia cells and the subcellular-specific CB1 receptors signaling as critical players of brain functions.

Levodopa-Induced Dyskinesias in Parkinson's Disease: An Overview on Pathophysiology, Clinical Manifestations, Therapy Management Strategies and Future Directions

Since its first introduction, levodopa has become the cornerstone for the treatment of Parkinson's disease and remains the leading therapeutic choice for motor control therapy so far. Unfortunately, the subsequent appearance of abnormal involuntary movements, known as dyskinesias, is a frequent drawback. Despite the deep knowledge of this complication, in terms of clinical phenomenology and the temporal relationship during a levodopa regimen, less is clear about the pathophysiological mechanisms underpinning it. As the disease progresses, specific oscillatory activities of both motor cortical and basal ganglia neurons and variation in levodopa metabolism, in terms of the dopamine receptor stimulation pattern and turnover rate, underlie dyskinesia onset. This review aims to provide a global overview on levodopa-induced dyskinesias, focusing on pathophysiology, clinical manifestations, therapy management strategies and future directions.

Oleoylethanolamide attenuates cocaine-primed reinstatement and alters dopaminergic gene expression in the striatum

The lipid oleoylethanolamide (OEA) has been shown to affect reward-related behavior. However, there is limited experimental evidence about the specific neurotransmission systems OEA may be affecting to exert this modulatory effect. The aim of this study was to evaluate the effects of OEA on the rewarding properties of cocaine and relapse-related gene expression in the striatum and hippocampus. For this purpose, we evaluated male OF1 mice on a cocaine-induced CPP procedure (10 mg/kg) and after the corresponding extinction sessions, we tested drug-induced reinstatement. The effects of OEA (10 mg/kg, i.p.) were evaluated at three different timepoints: (1) Before each cocaine conditioning session (OEA-C), (2) Before extinction sessions (OEA-EXT) and (3) Before the reinstatement test (OEA-REINST). Furthermore, gene expression changes in dopamine receptor D1 gene, dopamine receptor D2 gene, opioid receptor µ, cannabinoid receptor 1, in the striatum and hippocampus were analyzed by qRT-PCR. The results obtained in the study showed that OEA administration did not affect cocaine CPP acquisition. However, mice receiving different OEA treatment schedules (OEA-C, OEA-EXT and OEA-REINST) failed to display drug-induced reinstatement. Interestingly, the administration of OEA blocked the increase of dopamine receptor gene D1 in the striatum and hippocampus caused by cocaine exposure. In addition, OEA-treated mice exhibited reduced striatal dopamine receptor gene D2 and cannabinoid receptor 1. Together, these findings suggest that OEA may be a promising pharmacological agent in the treatment of cocaine use disorder.

Class A and C GPCR Dimers in Neurodegenerative Diseases

Neurodegenerative diseases affect over 30 million people worldwide with an ascending trend. Most individuals suffering from these irreversible brain damages belong to the elderly population, with onset between 50 and 60 years. Although the pathophysiology of such diseases is partially known, it remains unclear upon which point a disease turns degenerative. Moreover, current therapeutics can treat some of the symptoms but often have severe side effects and become less effective in long-term treatment. For many neurodegenerative diseases, the involvement of G proteincoupled receptors (GPCRs), which are key players of neuronal transmission and plasticity, has become clearer and holds great promise in elucidating their biological mechanism. With this review, we introduce and summarize class A and class C GPCRs, known to form heterodimers or oligomers to increase their signalling repertoire. Additionally, the examples discussed here were shown to display relevant alterations in brain signalling and had already been associated with the pathophysiology of certain neurodegenerative diseases. Lastly, we classified the heterodimers into two categories of crosstalk, positive or negative, for which there is known evidence.

Acute cannabinoids impair association learning via selectively enhancing synaptic transmission in striatonigral neurons

Background

Cannabinoids and their derivatives attract strong interest due to the tremendous potential of their psychoactive effects for treating psychiatric disorders and symptoms. However, their clinical application is restricted by various side-effects such as impaired coordination, anxiety, and learning and memory disability. Adverse impact on dorsal striatum-dependent learning is an important side-effect of cannabinoids. As one of the most important forms of learning mediated by the dorsal striatum, reinforcement learning is characterized by an initial association learning phase, followed by habit learning. While the effects of cannabinoids on habit learning have been well-studied, little is known about how cannabinoids influence the initial phase of reinforcement learning.

Results

We found that acute activation of cannabinoid receptor type 1 (CB1R) by the synthetic cannabinoid HU210 induced dose-dependent impairment of association learning, which could be alleviated by intra-dorsomedial striatum (DMS) injection of CB1R antagonist. Moreover, acute exposure to HU210 elicited enhanced synaptic transmission in striatonigral “direct” pathway medium spiny neurons (MSNs) but not indirect pathway neurons in DMS. Intriguingly, enhancement of synaptic transmission that is also observed after learning was abolished by HU210, indicating cannabinoid system might disrupt reinforcement learning by confounding synaptic plasticity normally required for learning. Remarkably, the impaired response-reinforcer learning was also induced by selectively enhancing the D1-MSN (MSN that selectively expresses the dopamine receptor type 1) activity by virally expressing excitatory hM3Dq DREADD (designer receptor exclusively activated by a designer drug), which could be rescued by specifically silencing the D1-MSN activity via hM4Di DREADD.

Conclusion

Our findings demonstrate dose-dependent deleterious effects of cannabinoids on association learning by disrupting plasticity change required for learning associated with the striatal direct pathway, which furthers our understanding of the side-effects of cannabinoids and the underlying mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01307-1.

Roles of the Cannabinoid System in the Basal Ganglia in Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease usually caused by neuroinflammation, oxidative stress and other etiologies. Recent studies have found that the cannabinoid system present in the basal ganglia has a strong influence on the progression of PD. Altering the cannabinoid receptor activation status by modulating endogenous cannabinoid (eCB) levels can exert an anti-movement disorder effect. Therefore, the development of drugs that modulate the endocannabinoid system may be a novel strategy for the treatment of PD. However, eCB regulation is complex, with diverse cannabinoid receptor functions and the presence of dopaminergic, glutamatergic, and γ-aminobutyric signals interacting with cannabinoid signaling in the basal ganglia region. Therefore, the study of eCB is challenging. Here, we have described the function of the cannabinoid system in the basal ganglia and its association with PD in three parts (eCBs, cannabinoid receptors, and factors regulating the cannabinoid metabolism) and summarized the mechanisms of action related to the cannabinoid analogs currently aimed at treating PD. The shortcomings identified from previous studies and the directions that should be explored in the future will provide insights into new approaches and ideas for the future development of cannabinoid-based drugs and the treatment of PD.

Striatonigrostriatal Spirals in Addiction

A biological reward system is integral to all animal life and humans are no exception. For millennia individuals have investigated this system and its influences on human behavior. In the modern day, with the US facing an ongoing epidemic of substance use without an effective treatment, these investigations are of paramount importance. It is well known that basal ganglia contribute to rewards and are involved in learning, approach behavior, economic choices, and positive emotions. This review aims to elucidate the physiological role of striatonigrostriatal (SNS) spirals, as part of basal ganglia circuits, in this reward system and their pathophysiological role in perpetuating addiction. Additionally, the main functions of neurotransmitters such as dopamine and glutamate and their receptors in SNS circuits will be summarized. With this information, the claim that SNS spirals are crucial intermediaries in the shift from goal-directed behavior to habitual behavior will be supported, making this circuit a viable target for potential therapeutic intervention in those with substance use disorders.

On the Biomedical Properties of Endocannabinoid Degradation and Reuptake Inhibitors: Pre-clinical and Clinical Evidence

The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.

Cannabidiol prevents amphetamine relapse and modulates D1- and D2-receptor levels in mesocorticolimbic brain areas of rats

Amphetamine (AMPH) is an addictive psychostimulant highly used worldwide and its consumption is related to neurotoxic effects. Currently, there is no pharmacotherapy approved for treating AMPH or other psychostimulant drug addiction. Different studies have shown promising properties of cannabidiol (CBD) for treating many neurological and psychiatric diseases, and recently, CBD is being considered a potential strategy for the treatment of drug addiction disorders. Thus, we investigated possible CBD beneficial effects on relapse symptoms following AMPH re-exposure considering drug relapse is the most difficult clinical factor to control during addiction treatment. Rats received d,l-AMPH (4 mg/kg, i.p.) or vehicle in the conditioned place preference (CPP) paradigm (8 days), when each experimental group was re-assigned to receive CBD at two different doses (5 or 10 mg/kg, i.p) or control, for 5 days. Subsequently, animals were re-exposed to AMPH-CPP (4 mg/kg, i.p.) for 3 additional days to assess relapse behavior. Besides locomotor and anxiety-like behaviors, dopaminergic molecular parameters were quantified in both prefrontal cortex and ventral striatum. Regarding molecular levels, CBD modulated at basal levels the dopaminergic targets (D1R, D2R, DAT, and TH) in the assessed brain areas, preventing AMPH relapse and decreasing anxiety-like behavior per se and in AMPH-CPP animals. The current findings give evidence about CBD-induced AMPH-relapse prevention, which may be linked to dopaminergic mesocorticolimbic system modulation. Although future and clinical studies are needed, our outcomes show that CBD may be a useful alternative to prevent AMPH relapse.

In vivo Bidirectional Modulation of Cannabinoid on the Activity of Globus Pallidus in Rats

Endocannabinoids are bioactive substances which participate in central motor control. The globus pallidus (GP) is a major nucleus in the basal ganglia circuit, which plays an important function in movement regulation. Both cannabinoid receptor type 1 (CB₁R) and cannabinoid receptor type 2 (CB₂R) are expressed in the GP suggesting GP as a main action area of endocannabinoids. To investigate the direct electrophysiological and behavioral effects of cannabinoids in GP, in vivo single unit extracellular recordings and behavioral tests were performed in rats. Administration of WIN 55,212-2 exerted three neuronal response patterns from all sampled neurons of GP, including (1) increase of the firing rate; (2) decrease of the firing rate; (3) increase and then decrease of the firing rate. Selectively blocking CB₁R by AM 251 decreased the firing rate and increased the firing rate. Selectively blocking CB₂R by AM 630 did not change the firing rate significantly, which suggested that endocannabinoids modulated the spontaneous firing activity of pallidal neurons mainly via CB₁R. Furthermore, co-application of AM 251, but not AM 630, blocked WIN 55,212-2-induced modulation of firing activity of pallidal neurons. Finally, both haloperidol-induced postural behavioral test and elevated body swing test (EBST) showed that unilateral microinjection of WIN 55,212-2 mainly induced contralateral-biased swing and deflection behaviors. Meanwhile, AM 251 produced opposite effect. The present in vivo study revealed that cannabinoids produced complicated electrophysiological and behavioral effects in the GP, which further demonstrated that the GP is a major functional region of endocannabinoid.

Marijuana improved motor impairments and changes in synaptic plasticity-related molecules in the striatum in 6-OHDA-treated rats

Using marijuana has become popular and is allowed for medical purposes in some countries. The effect of marijuana on Parkinson's disease is controversial and Medical marijuana may benefit for motor and non-motor symptoms of patients with Parkinson's disease. No research has been conducted to fully prove the benefits, risks, and uses of marijuana as a treatment for patients with Parkinson's disease. In the present study, several different approaches, including behavioral measures and the western blot method for protein level assay, were used to investigate whether exposure to marijuana affects the motor and synaptic plasticity impairment induced by 6-OHDA. Marijuana consumption significantly decreased apomorphine-induced contralateral rotation, beam travel time, beam freeze time, and catalepsy time, but significantly increased latency to fall in the rotarod test, balance time, and protein level of PSD-95 and dopamine receptor D1 in the 6-OHDA + marijuana group. These results suggest that marijuana may be helpful for motor disorders and synaptic changes in patients with Parkinson's disease.

Mechanistic insights into the protective effect of paracetamol against rotenone-induced Parkinson's disease in rats: Possible role of endocannabinoid system modulation

Parkinson's disease (PD) is a disabling progressive neurodegenerative disease. So far, PD's treatment remains symptomatic with no curative effects. Aside from its blatant analgesic and antipyretic efficacy, recent studies highlighted the endowed neuroprotective potentials of paracetamol (PCM). To this end: the present study investigated: (1) Possible protective role of PCM against rotenone-induced PD-like neurotoxicity in rats, and (2) the mechanisms underlying its neuroprotective actions including cannabinoid receptors' modulation. A dose-response study was conducted using three doses of PCM (25, 50, and 100 mg/kg/day, i.p.) and their effects on body weight changes, spontaneous locomotor activity, rotarod test, tyrosine hydroxylase (TH) and α-synuclein expression, and striatal dopamine (DA) content were evaluated. Results revealed that PCM (100 mg/kg/day, i.p.) halted PD motor impairment, prevented rotenone-induced weight loss, restored normal histological tissue structure, reversed rotenone-induced reduction in TH expression and striatal DA content, and markedly decreased midbrain and striatal α-synuclein expression in rotenone-treated rats. Accordingly, PCM (100 mg/kg/day, i.p.) was selected for further mechanistic investigations, where it ameliorated rotenone-induced oxidative stress, neuro-inflammation, apoptosis, and disturbed cannabinoid receptors' expression. In conclusion, our findings imply a multi-target neuroprotective effect of PCM in PD which could be attributed to its antioxidant, anti-inflammatory and anti-apoptotic activities, in addition to cannabinoid receptors' modulation.

Mechanism for differential recruitment of orbitostriatal transmission during actions and outcomes following chronic alcohol exposure

Psychiatric disease often produces symptoms that have divergent effects on neural activity. For example, in drug dependence, dysfunctional value-based decision-making and compulsive-like actions have been linked to hypo- and hyperactivity of orbital frontal cortex (OFC)-basal ganglia circuits, respectively; however, the underlying mechanisms are unknown. Here we show that alcohol-exposed mice have enhanced activity in OFC terminals in dorsal striatum (OFC-DS) associated with actions, but reduced activity of the same terminals during periods of outcome retrieval, corresponding with a loss of outcome control over decision-making. Disrupted OFC-DS terminal activity was due to a dysfunction of dopamine-type 1 receptors on spiny projection neurons (D1R SPNs) that resulted in increased retrograde endocannabinoid signaling at OFC-D1R SPN synapses reducing OFC-DS transmission. Blocking CB1 receptors restored OFC-DS activity in vivo and rescued outcome-based control over decision-making. These findings demonstrate a circuit-, synapse-, and computation-specific mechanism gating OFC activity in alcohol-exposed mice.

Crosstalk between the transcriptional regulation of dopamine D2 and cannabinoid CB1 receptors in schizophrenia: Analyses in patients and in perinatal Δ9-tetrahydrocannabinol-exposed rats

Perinatal exposure to Δ9-tetrahydrocannabinol (THC) affects brain development and might increase the incidence of psychopathology later in life, which seems to be related to a dysregulation of endocannabinoid and/or dopaminergic systems. We here evaluated the transcriptional regulation of the genes encoding for the cannabinoid CB1 receptor (Cnr1) and the dopamine D2 receptor (Drd2) in perinatal THC-(pTHC) exposed male rats, focusing on the role of DNA methylation analyzed by pyrosequencing. Simultaneously, the molecular and behavioral abnormalities at two different time points (i.e., neonatal age and adulthood) and the potential preventive effect of peripubertal treatment with cannabidiol, a non-euphoric component of Cannabis, were assessed. The DRD2 methylation was also evaluated in a cohort of subjects with schizophrenia. We observed an increase in both Cnr1 and Drd2 mRNA levels selectively in the prefrontal cortex of adult pTHC-exposed rats with a consistent reduction in DNA methylation at the Drd2 regulatory region, paralleled by social withdrawal and cognitive impairment which were reversed by cannabidiol treatment. These adult abnormalities were preceded at neonatal age by delayed appearance of neonatal reflexes, higher Drd2 mRNA and lower 2-arachidonoylglycerol (2-AG) brain levels, which persisted till adulthood. Alterations of the epigenetic mark for DRD2 were also found in subjects with schizophrenia. Overall, reported data add further evidence to the dopamine-cannabinoid interaction in terms of DRD2 and CNR1 dysregulation which could be implicated in the pathogenesis of schizophrenia spectrum disorders, suggesting that cannabidiol treatment may normalize pTHC-induced psychopathology by modulating the altered dopaminergic activity.

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.

Behavioral sensitization and cellular responses to psychostimulants are reduced in D2R knockout mice

Repeated cocaine exposure causes long-lasting neuroadaptations that involve alterations in cellular signaling and gene expression mediated by dopamine in different brain regions, such as the striatum. Previous studies have pointed out to the dopamine D1 receptor as one major player in psychostimulants-induced behavioral, cellular, and molecular changes. However, the role of other dopamine receptors has not been fully characterized. Here we used dopamine D2 receptor knockout (D2^-/- ) mice to explore the role of D2 receptor (D2R) in behavioral sensitization and its associated gene expression after acute and chronic cocaine and amphetamine administration. We also studied the impact of D2R elimination in D1R-mediated responses. We found that cocaine- and amphetamine-induced behavioral sensitization is deficient in D2^-/- mice. The expression of dynorphin, primarily regulated by D1R and a marker of direct-pathway striatal neurons, is attenuated in naïve- and in cocaine- or amphetamine-treated D2^-/- mice. Moreover, c-Fos expression observed in D2^-/- mice was reduced in acutely but not in chronically treated animals. Interestingly, inactivation of D2R increased c-Fos expression in neurons of the striatopallidal pathway. Finally, elimination of D2R blunted the locomotor and striatal c-Fos response to the full D1 agonist SKF81297. In conclusion, D2R is critical for the development of behavioral sensitization and the associated gene expression, after cocaine administration, and it is required for the locomotor responses promoted by D1R activation.

A novel allosteric modulator of the cannabinoid CB1 receptor ameliorates hyperdopaminergia endophenotypes in rodent models

The endocannabinoid system (eCBs) encompasses the endocannabinoids, their synthetic and degradative enzymes, and cannabinoid (CB) receptors. The eCBs mediates inhibition of neurotransmitter release and acts as a major homeostatic system. Many aspects of the eCBs are altered in a number of psychiatric disorders including schizophrenia, which is characterized by dysregulation of dopaminergic signaling. The GluN1-Knockdown (GluN1KD) and Dopamine Transporter Knockout (DATKO) mice are models of hyperdopaminergia, which display abnormal psychosis-related behaviors, including hyperlocomotion and changes in pre-pulse inhibition (PPI). Here, we investigate the ability of a novel CB₁ receptor (CB₁R) allosteric modulator, ABM300, to ameliorate these dysregulated behaviors. ABM300 was characterized in vitro (receptor binding, β-arrestin2 recruitment, ERK1/2 phosphorylation, cAMP inhibition) and in vivo (anxiety-like behaviors, cannabimimetic effects, novel environment exploratory behavior, pre-pulse inhibition, conditioned avoidance response) to assess the effects of the compound in dysregulated behaviors within the transgenic models. In vitro, ABM300 increased CB₁R agonist binding but acted as an inhibitor of CB₁R agonist induced signaling, including β-arrestin2 translocation, ERK phosphorylation and cAMP inhibition. In vivo, ABM300 did not elicit anxiogenic-like or cannabimimetic effects, but it decreased novelty-induced hyperactivity, exaggerated stereotypy, and vertical exploration in both transgenic models of hyperdopaminergia, as well as normalizing PPI in DATKO mice. The data demonstrate for the first time that a CB₁R allosteric modulator ameliorates the behavioral deficits in two models of increased dopamine, warranting further investigation as a potential therapeutic target in psychiatry.

Dopaminergic denervation impairs cortical motor and associative/limbic information processing through the basal ganglia and its modulation by the CB1 receptor

The basal ganglia (BG) are involved in cognitive/motivational functions in addition to movement control. Thus, BG segregated circuits, the sensorimotor (SM) and medial prefrontal (mPF) circuits, process different functional domains, such as motor and cognitive/motivational behaviours, respectively. With a high presence in the BG, the CB1 cannabinoid receptor modulates BG circuits. Furthermore, dopamine (DA), one of the principal neurotransmitters in the BG, also plays a key role in circuit functionality. Taking into account the interaction between DA and the endocannabinoid system at the BG level, we investigated the functioning of BG circuits and their modulation by the CB1 receptor under DA-depleted conditions. We performed single-unit extracellular recordings of substantia nigra pars reticulata (SNr) neurons with simultaneous cortical stimulation in sham and 6-hydroxydopamine (6-OHDA)-lesioned rats, together with immunohistochemical assays. We showed that DA loss alters cortico-nigral information processing in both circuits, with a predominant transmission through the hyperdirect pathway in the SM circuit and an increased transmission through the direct pathway in the mPF circuit. Moreover, although DA denervation does not change CB1 receptor density, it impairs its functionality, leading to a lack of modulation. These data highlight an abnormal transfer of information through the associative/limbic domains after DA denervation that may be related to the non-motor symptoms manifested by Parkinson's disease patients.

Δ 9-Tetrahydrocannabinol Toxicity and Validation of Cannabidiol on Brain Dopamine Levels: An Assessment on Cannabis Duplicity

Δ9-tetrahydrocannabinol (THC) of cannabis is the main psychoactive component which is a global significant concern to human health. Evaluation on THC reported its drastic effect on the brain dopaminergic (DAergic) system stimulating mesolimbic DA containing neurons thereby increasing the level of striatal DA. Cannabidiol (CBD), with its anxiolytic and anti-psychotic property, is potent to ameliorate the THC-induced DAergic variations. Legal authorization of cannabis use and its analogs in most countries led to a drastic dispute in the elicitation of cannabis products. With a recent increase in cannabis-induced disorder rates, the present review highlighted the detrimental effects of THC and the effects of CBD on THC induced alterations in DA synthesis and release. Alongside the reported data, uses of cannabis as a therapeutic medium in a number of health complications are also being briefly reviewed. These evaluated reports led to an anticipation of additional research contradictory to the findings of THC and CBD activity in the brain DAergic system and their medical implementations as therapeutics.

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.

Depression of Accumbal to Lateral Hypothalamic Synapses Gates Overeating

Overeating typically follows periods of energy deficit, but it is also sustained by highly palatable foods, even without metabolic demand. Dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs) of the nucleus accumbens shell (NAcSh) project to the lateral hypothalamus (LH) to authorize feeding when inhibited. Whether plasticity at these synapses can affect food intake is unknown. Here, ex vivo electrophysiology recordings reveal that D1-MSN-to-LH inhibitory transmission is depressed in circumstances in which overeating is promoted. Endocannabinoid signaling is identified as the induction mechanism, since inhibitory plasticity and concomitant overeating were blocked or induced by CB1R antagonism or agonism, respectively. D1-MSN-to-LH projectors were largely non-overlapping with D1-MSNs targeting ventral pallidum or ventral midbrain, providing an anatomical basis for distinct circuit plasticity mechanisms. Our study reveals a critical role for plasticity at D1-MSN-to-LH synapses in adaptive feeding control, which may underlie persistent overeating of unhealthy foods, a major risk factor for developing obesity.

The therapeutic role of cannabinoid receptors and its agonists or antagonists in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease and its characteristic is the progressive degeneration of dopaminergic neurons within the substantia nigra (SN) of the midbrain. There is hardly any clinically proven efficient therapeutics for its cure in several recent preclinical advances proposed to treat PD. Recent studies have found that the endocannabinoid signaling system in particular the comprised two receptors, CB1 and CB2 receptors, has a significant regulatory function in basal ganglia and is involved in the pathogenesis of PD. Therefore, adding new insights into the biochemical interactions between cannabinoids and other signaling pathways may help develop new pharmacological strategies. Factors of the endocannabinoid system (ECS) are abundantly expressed in the neural circuits of basal ganglia, where they interact interactively with glutamatergic, γ-aminobutyric acid-ergic (GABAergic), and dopaminergic signaling systems. Although preclinical studies on PD are promising, the use of cannabinoids at the clinical level has not been thoroughly studied. In this review, we evaluated the available evidence and reviewed the involvement of ECS in etiologies, symptoms and treatments related to PD. Since CB1 and CB2 receptors are the two main receptors of endocannabinoids, we primarily put the focus on the therapeutic role of CB1 and CB2 receptors in PD. We will try to determine future research clues that will help understand the potential therapeutic benefits of the ECS in the treatment of PD, aiming to open up new strategies and ideas for the treatment of PD.

Delta-9-tetrahydrocannabinol potentiates fear memory salience through functional modulation of mesolimbic dopaminergic activity states

Chronic or acute exposure to delta-9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, has been associated with numerous neuropsychiatric side-effects, including dysregulation of emotional processing and associative memory formation. Clinical and preclinical evidence suggests that the effects of THC are due to the ability to modulate mesolimbic dopamine (DA) activity states in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Nevertheless, the mechanisms by which THC modulates mesolimbic DA function and emotional processing are not well understood. Using an olfactory associative fear memory procedure combined with in vivo neuronal electrophysiology, we examined the effects of direct THC microinfusions targeting the shell region of the NAc (NASh) and examined how THC may modulate the processing of fear-related emotional memory and concomitant activity states of the mesolimbic DA system. We report that intra-NASh THC dose-dependently potentiates the emotional salience of normally subthreshold fear conditioning cues. These effects were dependent upon intra-VTA transmission through GABAergic receptor mechanisms and intra-NASh DAergic transmission. Furthermore, doses of intra-NASh THC that potentiated fear memory salience were found to modulate intra-VTA neuronal network activity by increasing the spontaneous firing and bursting frequency of DAergic neurones whilst decreasing the activity levels of a subpopulation of putative GABAergic VTA neurones. These findings demonstrate that THC can act directly in the NASh to modulate mesolimbic activity states and induce disturbances in emotional salience and memory formation through modulation of VTA DAergic transmission.

Beyond drug-induced alteration of glutamate homeostasis, astrocytes may contribute to dopamine-dependent intrastriatal functional shifts that underlie the development of drug addiction: A working hypothesis

The transition from recreational drug use to compulsive drug‐seeking habits, the hallmark of addiction, has been shown to depend on a shift in the locus of control over behaviour from the ventral to the dorsolateral striatum. This process has hitherto been considered to depend on the aberrant engagement of dopamine‐dependent plasticity processes within neuronal networks. However, exposure to drugs of abuse also triggers cellular and molecular adaptations in astrocytes within the striatum which could potentially contribute to the intrastriatal transitions observed during the development of drug addiction. Pharmacological interventions aiming to restore the astrocytic mechanisms responsible for maintaining homeostatic glutamate concentrations in the nucleus accumbens, that are altered by chronic exposure to addictive drugs, abolish the propensity to relapse in both preclinical and, to a lesser extent, clinical studies. Exposure to drugs of abuse also alters the function of astrocytes in the dorsolateral striatum, wherein dopaminergic mechanisms control drug‐seeking habits, associated compulsivity and relapse. This suggests that drug‐induced alterations in the glutamatergic homeostasis maintained by astrocytes throughout the entire striatum may interact with dopaminergic mechanisms to promote aberrant plasticity processes that contribute to the maintenance of maladaptive drug‐seeking habits. Capitalising on growing evidence that astrocytes play a fundamental regulatory role in glutamate and dopamine transmission in the striatum, we present an innovative model of a quadripartite synaptic microenvironment within which astrocytes channel functional interactions between the dopaminergic and glutamatergic systems that may represent the primary striatal functional unit that undergoes drug‐induced adaptations eventually leading to addiction.

Altered brain cannabinoid 1 receptor mRNA expression across postnatal development in the MAM model of schizophrenia

Altered cannabinoid 1 receptor (CB1R) expression has been reported in the brain of subjects with schizophrenia, a developmental mental illness that usually emerges in late adolescence/early adulthood. However, the developmental period at which changes in the CB1R expression appear in schizophrenia is unknown. To gain insight into this factor, we assessed the postnatal developmental trajectory of CB1R expression in the methylazoxymethanol (MAM) model of schizophrenia. Using in situ hybridization with film and grain analyses, CB1R messenger RNA (mRNA) levels were quantified in multiple brain regions, including the medial prefrontal cortex (mPFC), secondary motor cortex, dorsomedial and dorsolateral striatum, dorsal subregions and ventral subiculum of the hippocampus, of MAM-treated rats and normal controls at three developmental periods [juvenile - postnatal day (PD) 30; adolescence - PD45; and adulthood - PD85]. In all brain regions studied, CB1R mRNA levels were highest in juveniles and then decreased progressively toward adolescent and adult levels in control and MAM-treated rats. However, in MAM-treated rats, CB1R mRNA levels were lower in the mPFC at PD85 and higher in the dorsolateral striatum at PD45 and PD85 relative to controls. Cellular analyses confirmed the changes in CB1R mRNA expression in MAM-treated rats. These findings are in accordance with previous studies showing a decrease in the CB1R mRNA expression from juvenile period to adolescence to adulthood in cortical, striatal, and hippocampal regions. Additionally, similar to most of the schizophrenia-like signs observed in the MAM model, embryonic exposure to MAM leads to schizophrenia-related changes in CB1R mRNA expression that only emerge later in development.

G protein-coupled receptor heteromers are key players in substance use disorder

G protein-coupled receptors (GPCR) represent the largest family of membrane proteins in the human genome. Physical association between two different GPCRs is linked to functional interactions which generates a novel entity, called heteromer, with specific ligand binding and signaling properties. Heteromerization is increasingly recognized to take place in the mesocorticolimbic pathway and to contribute to various aspects related to substance use disorder. This review focuses on heteromers identified in brain areas relevant to drug addiction. We report changes at the molecular and cellular levels that establish specific functional impact and highlight behavioral outcome in preclinical models. Finally, we briefly discuss selective targeting of native heteromers as an innovative therapeutic option.

Downregulation of thioredoxin-1 in the ventral tegmental area delays extinction of methamphetamine-induced conditioned place preference

BACKGROUND

Drug addiction is characterized by compulsive drug use and relapse. Thioredoxin-1 is emerging as an important modulator involved in the cellular protective response against a variety of toxic stressors. Previous study has reported that thioredoxin-1 overexpression prevents the acquisition of methamphetamine-conditioned place preference. Here, we aimed to investigate the effect of thioredoxin-1 on methamphetamine-conditioned place preference extinction and the possible mechanism.

METHODS

(a) An extinction procedure in mice was employed to investigate the effect of thioredoxin-1 on the extinction of methamphetamine-conditioned place preference. After the acquisition of methamphetamine-conditioned place preference, mice underwent the following procedures: the injection of thioredoxin-1 small interfering RNA in the ventral tegmental area followed by the post-conditioned place preference test, four days of extinction training followed by four days of recovery after surgery. (b) The levels of thioredoxin-1, dopamine D1 receptor, tyrosine hydroxylase, phosphorylated extracellular regulated kinase, and phosphorylated cyclic adenosine monophosphate response element binding protein were examined by using Western blot analysis.

RESULTS

Thioredoxin-1 downregulation in the ventral tegmental area delayed methamphetamine-conditioned place preference extinction. The expression of thioredoxin-1 was decreased in the ventral tegmental area of mice in control and negative groups after methamphetamine-conditioned place preference extinction, but not in the thioredoxin-1 siRNA group. The levels of dopamine D1 receptor, tyrosine hydroxylase, phosphorylated extracellular regulated kinase, and phosphorylated cyclic adenosine monophosphate response element binding protein were decreased in the ventral tegmental area, nucleus accumbens, and prefrontal cortex of mice in the control and negative groups after methamphetamine-conditioned place preference extinction, but were inversely increased in thioredoxin-1 siRNA group.

CONCLUSIONS

The results suggest that downregulation of thioredoxin-1 in the ventral tegmental area may delay methamphetamine-conditioned place preference extinction by regulating the mesocorticolimbic dopaminergic signaling pathway.

The cannabinoid-1 receptor is abundantly expressed in striatal striosomes and striosome-dendron bouquets of the substantia nigra

Presynaptic cannabinoid-1 receptors (CB₁-R) bind endogenous and exogenous cannabinoids to modulate neurotransmitter release. CB₁-Rs are expressed throughout the basal ganglia, including striatum and substantia nigra, where they play a role in learning and control of motivated actions. However, the pattern of CB₁-R expression across different striatal compartments, microcircuits and efferent targets, and the contribution of different CB₁-R-expressing neurons to this pattern, are unclear. We use a combination of conventional techniques and novel genetic models to evaluate CB₁-R expression in striosome (patch) and matrix compartments of the striatum, and in nigral targets of striatal medium spiny projection neurons (MSNs). CB₁-R protein and mRNA follow a descending dorsolateral-to-ventromedial intensity gradient in the caudal striatum, with elevated expression in striosomes relative to the surrounding matrix. The lateral predominance of striosome CB₁-Rs contrasts with that of the classical striosomal marker, the mu opioid receptor (MOR), which is expressed most prominently in rostromedial striosomes. The dorsolateral-to-ventromedial CB₁-R gradient is similar to Drd2 dopamine receptor immunoreactivity and opposite to Substance P. This topology of CB₁-R expression is maintained downstream in the globus pallidus and substantia nigra. Dense CB₁-R-expressing striatonigral fibers extend dorsally within the substantia nigra pars reticulata, and colocalize with bundles of ventrally extending, striosome-targeted, dendrites of dopamine-containing neurons in the substantia nigra pars compacta (striosome-dendron bouquets). Within striatum, CB₁-Rs colocalize with fluorescently labeled MSN collaterals within the striosomes. Cre recombinase-mediated deletion of CB₁-Rs from cortical projection neurons or MSNs, and MSN-selective reintroduction of CB₁-Rs in knockout mice, demonstrate that the principal source of CB₁-Rs in dorsolateral striosomes is local MSN collaterals. These data suggest a role for CB₁-Rs in caudal dorsolateral striosome collaterals and striosome-dendron bouquet projections to lateral substantia nigra, where they are anatomically poised to mediate presynaptic disinhibition of both striosomal MSNs and midbrain dopamine neurons in response to endocannabinoids and cannabinomimetics.

PET Molecular Imaging Research of Levodopa-Induced Dyskinesias in Parkinson's Disease

Purpose of Review

To review the current status of positron emission tomography (PET) molecular imaging research of levodopa-induced dyskinesias (LIDs) in Parkinson’s disease (PD).

Recent Findings

Recent PET studies have provided robust evidence that LIDs in PD are associated with elevated and fluctuating striatal dopamine synaptic levels, which is a consequence of the imbalance between dopaminergic and serotonergic terminals, with the latter playing a key role in mishandling presynaptic dopamine release. Long-term exposure to levodopa is no longer believed to solely induce LIDs, as studies have highlighted that PD patients who go on to develop LIDs exhibit elevated putaminal dopamine release before the initiation of levodopa treatment, suggesting the involvement of other mechanisms, including altered neuronal firing and abnormal levels of phosphodiesterase 10A.

Summary

Dopaminergic, serotonergic, glutamatergic, adenosinergic and opioid systems and phosphodiesterase 10A levels have been shown to be implicated in the development of LIDs in PD. However, no system may be considered sufficient on its own for the development of LIDs, and the mechanisms underlying LIDs in PD may have a multisystem origin. In line with this notion, future studies should use multimodal PET molecular imaging in the same individuals to shed further light on the different mechanisms underlying the development of LIDs in PD.

Acute Δ-9-tetrahydrocannabinol administration in female rats attenuates immediate responses following losses but not multi-trial reinforcement learning from wins

Δ-9-Tetrahydrocannabinol (THC) is the main psychoactive component of marijuana and has potent effects on decision-making, including a proposed reduction in cognitive flexibility. We demonstrate here that acute THC administration differentially affects some of the processes that contribute to cognitive flexibility. Specifically, THC reduces lose-shift responding in which female rats tend to immediately shift choice responses away from options that result in reward omission on the previous trial. THC, however, did not impair the ability of rats to flexibly bias responses toward feeders with higher probability of reward in a reversal task. This response adaptation developed over several trials, suggesting that THC did not impair slower forms of reinforcement learning needed to choose among options with unequal utility. This dissociation of THC's effects on innate/rapid and learned/gradual decision-making processes was unexpected, but is supported by emerging evidence that lose-shift responding is mediated by neural mechanisms distinct from those involved in other forms of reinforcement learning. The present data suggest that, at least in some tasks, the apparent reductions in cognitive flexibility by THC may be explained by the immediate effects on loss sensitivity, rather than impairments of all processes used for choice adaptation.

Consequence of dopamine D2 receptor blockade on the hyperphagic effect induced by cannabinoid CB1 and CB2 receptors in layers

1. Endocannabinoids (ECBs) and their receptors play a regulatory function on several physiological processes such as feed-intake behaviour, mainly in the brain. This study was carried out in order to investigate the effects of the dopaminergic D1 and D2 receptors on CB1/CB2 ECB receptor-induced hyperphagia in 3-h feed-deprived neonatal layer chickens. 2. A total of 8 experiments were designed to explore the interplay of these two modulatory systems on feed intake in neonatal chickens. In Experiment 1, chickens were intracerebroventricular (ICV) injected with control solution, l-DOPA (levo-dihydroxyphenylalanine as precursor of dopamine; 125 nmol), 2-AG (2-arachidonoylglycerol as CB₁ receptor agonist; 2 µg) and co-administration of l-DOPA (125 nmol) plus 2-AG (2 µg). Experiments 2-4 were similar to Experiment 1 except birds were injected with either 6-OHDA (6-hydroxydopamine as dopamine synthesis inhibitor; 150 nmol), SCH23390 (D1 receptor antagonist; 5 nmol) and AMI-193 (D2 receptor antagonist; 5 nmol) instead of l-DOPA, respectively. Additionally, Experiments 5-8 followed the previous ones using the same dose of l-DOPA, 6-OHDA and dopamine antagonists except that birds were injected with CB65 (CB2 receptor agonist; 5 µg) instead of 2-AG. Coadministrations were at the same dose for each experiment. Cumulative feed intakes were measured until 120 min after each injection. 3. ICV administration of 6-OHDA and AMI-193 significantly attenuated 2-AG-induced hyperphagia. Interestingly, the hyperphagic effect of CB65 was significantly attenuated by administration of l-DOPA, whereas the administration of 6-OHDA and AMI-193 together amplified the hyperphagic effect of CB65. 4. It was concluded that cannabinoid-induced feeding behaviour is probably modulated by dopamine receptors in neonatal layer-type chickens. It seems that their interaction may be mediated by the D2-dopamine receptor.

Neurotransmission systems in Parkinson’s disease

Parkinson’s disease (PD) is histologically characterized by the accumulation of α-synuclein particles, known as Lewy bodies. The second most common neurodegenerative disorder, PD is widely known because of the typical motor manifestations of active tremor, rigidity, and postural instability, while several prodromal non-motor symptoms including REM sleep behavior disorders, depression, autonomic disturbances, and cognitive decline are being more extensively recognized. Motor symptoms most commonly arise from synucleinopathy of nigrostriatal pathway. Glutamatergic, γ-aminobutyric acid (GABA)ergic, cholinergic, serotoninergic, and endocannabinoid neurotransmission systems are not spared from the global cerebral neurodegenerative assault. Wide intrabasal and extrabasal of the basal ganglia provide enough justification to evaluate network circuits disturbance of these neurotransmission systems in PD. In this comprehensive review, English literature in PubMed, Science direct, EMBASE, and Web of Science databases were perused. Characteristics of dopaminergic and non-dopaminergic systems, disturbance of these neurotransmitter systems in the pathophysiology of PD, and their treatment applications are discussed.

Synaptic functions of endocannabinoid signaling in health and disease

Endocannabinoids (eCBs) are a family of lipid molecules that act as key regulators of synaptic transmission and plasticity. They are synthetized "on demand" following physiological and/or pathological stimuli. Once released from postsynaptic neurons, eCBs typically act as retrograde messengers to activate presynaptic type 1 cannabinoid receptors (CB₁) and induce short- or long-term depression of neurotransmitter release. Besides this canonical mechanism of action, recent findings have revealed a number of less conventional mechanisms by which eCBs regulate neural activity and synaptic function, suggesting that eCB-mediated plasticity is mechanistically more diverse than anticipated. These mechanisms include non-retrograde signaling, signaling via astrocytes, participation in long-term potentiation, and the involvement of mitochondrial CB₁. Focusing on paradigmatic brain areas, such as hippocampus, striatum, and neocortex, we review typical and novel signaling mechanisms, and discuss the functional implications in normal brain function and brain diseases. In summary, eCB signaling may lead to different forms of synaptic plasticity through activation of a plethora of mechanisms, which provide further complexity to the functional consequences of eCB signaling. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Endocannabinoid modulation of dopamine neurotransmission

Dopamine (DA) is a major catecholamine neurotransmitter in the mammalian brain that controls neural circuits involved in the cognitive, emotional, and motor aspects of goal-directed behavior. Accordingly, perturbations in DA neurotransmission play a central role in several neuropsychiatric disorders. Somewhat surprisingly given its prominent role in numerous behaviors, DA is released by a relatively small number of densely packed neurons originating in the midbrain. The dopaminergic midbrain innervates numerous brain regions where extracellular DA release and receptor binding promote short- and long-term changes in postsynaptic neuron function. Striatal forebrain nuclei receive the greatest proportion of DA projections and are a predominant hub at which DA influences behavior. A number of excitatory, inhibitory, and modulatory inputs orchestrate DA neurotransmission by controlling DA cell body firing patterns, terminal release, and effects on postsynaptic sites in the striatum. The endocannabinoid (eCB) system serves as an important filter of afferent input that acts locally at midbrain and terminal regions to shape how incoming information is conveyed onto DA neurons and to output targets. In this review, we aim to highlight existing knowledge regarding how eCB signaling controls DA neuron function through modifications in synaptic strength at midbrain and striatal sites, and to raise outstanding questions on this topic. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Deficits in striatal dopamine release in cannabis dependence

Most drugs of abuse lead to a general blunting of dopamine release in the chronic phase of dependence, which contributes to poor outcome. To test whether cannabis dependence is associated with a similar dopaminergic deficit, we examined striatal and extrastriatal dopamine release in severely cannabis-dependent participants (CD), free of any comorbid conditions, including nicotine use. Eleven CD and 12 healthy controls (HC) completed two positron emission tomography scans with [11C]-(+)-PHNO, before and after oral administration of d-amphetamine. CD stayed inpatient for 5-7 days prior to the scans to standardize abstinence. Magnetic resonance spectroscopy (MRS) measures of glutamate in the striatum and hippocampus were obtained in the same subjects. Percent change in [11C]-(+)-PHNO-binding potential (ΔBPND) was compared between groups and correlations with MRS glutamate, subclinical psychopathological and neurocognitive parameters were examined. CD had significantly lower ΔBPND in the striatum (P=0.002, effect size (ES)=1.48), including the associative striatum (P=0.003, ES=1.39), sensorimotor striatum (P=0.003, ES=1.41) and the pallidus (P=0.012, ES=1.16). Lower dopamine release in the associative striatum correlated with inattention and negative symptoms in CD, and with poorer working memory and probabilistic category learning performance in both CD and HC. No relationships to MRS glutamate and amphetamine-induced subclinical positive symptoms were detected. In conclusion, this study provides evidence that severe cannabis dependence-without the confounds of any comorbidity-is associated with a deficit in striatal dopamine release. This deficit extends to other extrastriatal areas and predicts subclinical psychopathology.

The CB1 receptor is required for the establishment of the hyperlocomotor phenotype in developmentally-induced hypothyroidism in mice

Alterations in motor functions are well-characterized features observed in humans and experimental animals with thyroid hormone dysfunctions during development. We have previously suggested the implication of the endocannabinoid system in the hyperlocomotor phenotype observed in developmentally induced hypothyroidism in rats. In this work we have further analyzed the implication of endocannabinoids in the effect of hypothyroidism on locomotor activity. To this end, we evaluated the locomotor activity in adult mice lacking the cannabinoid receptor type 1 (CB1R^-/-) and in their wild type littermates (CB1R^+/+), whose hypothyroidism was induced in day 12 of gestation and maintained during the experimental period. Our results show that hypothyroidism induced a hyperlocomotor phenotype only in CB1R^+/+, but not in CB1R^-/- mice. In contrast with our previous results in rats, the expression of CB1R in striatum and the motor response to the cannabinoid agonist HU210 was unaltered in hypothyroid CB1R^+/+ mice suggesting that the cannabinoid system is not altered by hypothyroidism. Also, no effect of HU210 was observed in locomotion of CB1R^-/- mice. Finally, since the dopaminergic system plays a major role in the control of locomotor activity we studied its function in hypothyroid wild type and knockout animals. Our results show no alteration in the behavioral response induced by the dopamine D1 receptor agonist SKF38393. However we observed a decreased response to the dopamine D2 receptor antagonist haloperidol only in hypothyroid CB1R^+/+ mice, which might indicate potential alterations in D2R signaling in these animals. In conclusion, our data suggest that the cannabinoid system is necessary for the induction of hyperlocomotor phenotype in mice with developmentally induced hypothyroidism.

Targeting anandamide metabolism rescues core and associated autistic-like symptoms in rats prenatally exposed to valproic acid

Autism spectrum disorders (ASD) are characterized by altered sociability, compromised communication and stereotyped/repetitive behaviors, for which no specific treatments are currently available. Prenatal exposure to valproic acid (VPA) is a known, although still underestimated, environmental risk factor for ASD. Altered endocannabinoid activity has been observed in autistic patients, and endocannabinoids are known to modulate behavioral traits that are typically affected in ASD. On this basis, we tested the hypothesis that changes in the endocannabinoid tone contribute to the altered phenotype induced by prenatal VPA exposure in rats, with focus on behavioral features that resemble the core and associated symptoms of ASD. In the course of development, VPA-exposed rats showed early deficits in social communication and discrimination, compromised sociability and social play behavior, stereotypies and increased anxiety, thus providing preclinical proof of the long-lasting deleterious effects induced by prenatal VPA exposure. At the neurochemical level, VPA-exposed rats displayed altered phosphorylation of CB1 cannabinoid receptors in different brain areas, associated with changes in anandamide metabolism from infancy to adulthood. Interestingly, enhancing anandamide signaling through inhibition of its degradation rescued the behavioral deficits displayed by VPA-exposed rats at infancy, adolescence and adulthood. This study therefore shows that abnormalities in anandamide activity may underlie the deleterious impact of environmental risk factors on ASD-relevant behaviors and that the endocannabinoid system may represent a therapeutic target for the core and associated symptoms displayed by autistic patients.

Pharmacogenetics of tardive dyskinesia: an updated review of the literature

Tardive dyskinesia (TD) is a serious and potentially irreversible side effect of long-term exposure to antipsychotic medication characterized by involuntary trunk, limb and orofacial muscle movements. Various mechanisms have been proposed for the etiopathophysiology of antipsychotic-induced TD in schizophrenia patients with genetic factors playing a prominent role. Earlier association studies have focused on polymorphisms in CYP2D6, dopamine-, serotonin-, GABA- and glutamate genes. This review highlights recent advances in the genetic investigation of TD. Recent promising findings were obtained with the HSPG2, DPP6, MTNR1A, SLC18A2, PIP5K2A and CNR1 genes. More research, including collection of well-characterized samples, enhancement of genome-wide strategies, gene–gene interaction and epigenetic analyses, is needed before genetic tests with clinical utility can be made available for TD.