Enhanced striatal glutamate release after the administration of rimonabant to 6-hydroxydopamine-lesioned rats

The Use of Compounds Derived from Cannabis sativa in the Treatment of Epilepsy, Painful Conditions, and Neuropsychiatric and Neurodegenerative Disorders

Neurological disorders present a wide range of symptoms and challenges in diagnosis and treatment. Cannabis sativa, with its diverse chemical composition, offers potential therapeutic benefits due to its anticonvulsive, analgesic, anti-inflammatory, and neuroprotective properties. Beyond cannabinoids, cannabis contains terpenes and polyphenols, which synergistically enhance its pharmacological effects. Various administration routes, including vaporization, oral ingestion, sublingual, and rectal, provide flexibility in treatment delivery. This review shows the therapeutic efficacy of cannabis in managing neurological disorders such as epilepsy, neurodegenerative diseases, neurodevelopmental disorders, psychiatric disorders, and painful pathologies. Drawing from surveys, patient studies, and clinical trials, it highlights the potential of cannabis in alleviating symptoms, slowing disease progression, and improving overall quality of life for patients. Understanding the diverse therapeutic mechanisms of cannabis can open up possibilities for using this plant for individual patient needs.

Therapeutic Molecular Insights into the Active Engagement of Cannabinoids in the Therapy of Parkinson's Disease: A Novel and Futuristic Approach

Parkinson's disease is a neurodegenerative disorder which is characterised mostly by loss of dopaminergic nerve cells throughout the nigral area mainly as a consequence of oxidative stress. Muscle stiffness, disorganised bodily responses, disturbed sleep, weariness, amnesia, and voice impairment are all symptoms of dopaminergic neuron degeneration and existing symptomatic treatments are important to arrest additional neuronal death. Some cannabinoids have recently been demonstrated as robust antioxidants that might protect the nerve cells from degeneration even when cannabinoid receptors are not triggered. Cannabinoids are likely to have property to slow or presumably cease the steady deterioration of the brain's dopaminergic systems, a condition for which there is now no treatment. The use of cannabinoids in combination with currently available drugs has the potential to introduce a radically new paradigm for treatment of Parkinson's disease, making it immensely useful in the treatment of such a debilitating illness.

Cannabinoids in movement disorders

INTRODUCTION

On the basis of both scientific progress and popular lore, there is growing optimism in the therapeutic potential of cannabis (marijuana) and cannabinoid-based chemicals for movement disorders. There is also notable skepticism regarding the scientific basis for this therapeutic optimism and significant concerns regarding the safety and regulation of cannabinoid products, particularly those available without prescription.

METHODS

In recognition of the high interest and controversial nature of this subject, the meeting committee of the International Parkinson and Movement Disorders Society arranged for a talk on cannabis at the 2019 annual meeting's Controversies in Movement Disorders plenary session. This paper summarizes the highlights of this session.

RESULTS

The endocannabinoid system is strongly tied to motor function and dysfunction, with basic research suggesting several promising therapeutic targets related to cannabinoids for movement disorders. Clinical research on cannabinoids for motor and nonmotor symptoms in Parkinson's disease, Huntington's disease, Tourette's syndrome, dystonia, and other movement disorders to date are promising at best and inconclusive or negative at worst. Research in other populations suggest efficacy for common symptoms like pain. While social campaigns against recreational cannabinoid use focus on cognitive changes in adolescents, the long-term sequelae of regulated medical use in older adults with movement disorders is unknown. The overall risks of cannabinoids may be similar to other commonly used medications and include falls and apathy.

CONCLUSION

Further research is greatly needed to better understand the actual clinical benefits and long-term side effects of medical cannabis products for movement disorders indications and populations.

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.

Is cannabidiol the ideal drug to treat non-motor Parkinson's disease symptoms?

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by motor symptoms such as bradykinesia, rest tremor, postural disturbances, and rigidity. PD is also characterized by non-motor symptoms such as sleep disturbances, cognitive deficits, and psychiatric disorders such as psychosis, depression, and anxiety. The pharmacological treatment for these symptoms is limited in efficacy and induce significant adverse reactions, highlighting the need for better treatment options. Cannabidiol (CBD) is a phytocannabinoid devoid of the euphoriant and cognitive effects of tetrahydrocannabinol, and preclinical and preliminary clinical studies suggest that this compound has therapeutic effect in non-motor symptoms of PD. In the present text, we review the clinical studies of cannabinoids in PD and the preclinical and clinical studies specifically on CBD. We found four randomized controlled trials (RCTs) involving the administration of agonists/antagonists of the cannabinoid 1 receptor, showing that these compounds were well tolerated, but only one study found positive results (reductions on levodopa-induced dyskinesia). We found seven preclinical models of PD using CBD, with six studies showing a neuroprotective effect of CBD. We found three trials involving CBD and PD: an open-label study, a case series, and an RCT. CBD was well tolerated, and all three studies reported significant therapeutic effects in non-motor symptoms (psychosis, rapid eye movement sleep behaviour disorder, daily activities, and stigma). However, sample sizes were small and CBD treatment was short (up to 6 weeks). Large-scale RCTs are needed to try to replicate these results and to assess the long-term safety of CBD.

Cannabinoids in Parkinson's Disease

The endocannabinoid system plays a regulatory role in a number of physiological processes and has been found altered in different pathological conditions, including movement disorders. The interactions between cannabinoids and dopamine in the basal ganglia are remarkably complex and involve both the modulation of other neurotransmitters (γ-aminobutyric acid, glutamate, opioids, peptides) and the activation of different receptors subtypes (cannabinoid receptor type 1 and 2). In the last years, experimental studies contributed to enrich this scenario reporting interactions between cannabinoids and other receptor systems (transient receptor potential vanilloid type 1 cation channel, adenosine receptors, 5-hydroxytryptamine receptors). The improved knowledge, adding new interpretation on the biochemical interaction between cannabinoids and other signaling pathways, may contribute to develop new pharmacological strategies. A number of preclinical studies in different experimental Parkinson's disease (PD) models demonstrated that modulating the cannabinoid system may be useful to treat some motor symptoms. Despite new cannabinoid-based medicines have been proposed for motor and nonmotor symptoms of PD, so far, results from clinical studies are controversial and inconclusive. Further clinical studies involving larger samples of patients, appropriate molecular targets, and specific clinical outcome measures are needed to clarify the effectiveness of cannabinoid-based therapies.

Marijuana Compounds: A Nonconventional Approach to Parkinson's Disease Therapy

Parkinson's disease (PD), a neurodegenerative disorder, is the second most common neurological illness in United States. Neurologically, it is characterized by the selective degeneration of a unique population of cells, the nigrostriatal dopamine neurons. The current treatment is symptomatic and mainly involves replacement of dopamine deficiency. This therapy improves only motor symptoms of Parkinson's disease and is associated with a number of adverse effects including dyskinesia. Therefore, there is unmet need for more comprehensive approach in the management of PD. Cannabis and related compounds have created significant research interest as a promising therapy in neurodegenerative and movement disorders. In this review we examine the potential benefits of medical marijuana and related compounds in the treatment of both motor and nonmotor symptoms as well as in slowing the progression of the disease. The potential for cannabis to enhance the quality of life of Parkinson's patients is explored.

Cannabinoid-dopamine interactions in the physiology and physiopathology of the basal ganglia

Endocannabinoids and their receptors play a modulatory role in the control of dopamine transmission in the basal ganglia. However, this influence is generally indirect and exerted through the modulation of GABA and glutamate inputs received by nigrostriatal dopaminergic neurons, which lack cannabinoid CB1 receptors although they may produce endocannabinoids. Additional evidence suggests that CB2 receptors may be located in nigrostriatal dopaminergic neurons, and that certain eicosanoid-related cannabinoids may directly activate TRPV1 receptors, which have been found in nigrostriatal dopaminergic neurons, thus allowing in both cases a direct regulation of dopamine transmission by specific cannabinoids. In addition, CB1 receptors form heteromers with dopaminergic receptors which provide another pathway to direct interactions between both systems, in this case at the postsynaptic level. Through these direct mechanisms or through indirect mechanisms involving GABA or glutamate neurons, cannabinoids may interact with dopaminergic transmission in the basal ganglia and this is likely to have important effects on dopamine-related functions in these structures (i.e. control of movement) and, particularly, on different pathologies affecting these processes, in particular, Parkinson's disease, but also dyskinesia, dystonia and other pathological conditions. The present review will address the current literature supporting these cannabinoid-dopamine interactions at the basal ganglia, with emphasis on aspects dealing with the physiopathological consequences of these interactions.

LINKED ARTICLES

This article is part of a themed section on Updating Neuropathology and Neuropharmacology of Monoaminergic Systems. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.13/issuetoc.

Promising cannabinoid-based therapies for Parkinson's disease: motor symptoms to neuroprotection

Parkinson’s disease (PD) is a slow insidious neurological disorder characterized by a loss of dopaminergic neurons in the midbrain. Although several recent preclinical advances have proposed to treat PD, there is hardly any clinically proved new therapeutic for its cure. Increasing evidence suggests a prominent modulatory function of the cannabinoid signaling system in the basal ganglia. Hence, use of cannabinoids as a new therapeutic target has been recommended as a promising therapy for PD. The elements of the endocannabinoid system are highly expressed in the neural circuit of basal ganglia wherein they bidirectionally interact with dopaminergic, glutamatergic, and GABAergic signaling systems. As the cannabinoid signaling system undergoes a biphasic pattern of change during progression of PD, it explains the motor inhibition typically observed in patients with PD. Cannabinoid agonists such as WIN-55,212-2 have been demonstrated experimentally as neuroprotective agents in PD, with respect to their ability to suppress excitotoxicity, glial activation, and oxidative injury that causes degeneration of dopaminergic neurons. Additional benefits provided by cannabinoid related compounds including CE-178253, oleoylethanolamide, nabilone and HU-210 have been reported to possess efficacy against bradykinesia and levodopa-induced dyskinesia in PD. Despite promising preclinical studies for PD, use of cannabinoids has not been studied extensively at the clinical level. In this review, we reassess the existing evidence suggesting involvement of the endocannabinoid system in the cause, symptomatology, and treatment of PD. We will try to identify future threads of research that will help in the understanding of the potential therapeutic benefits of the cannabinoid system for treating PD.

The therapeutic potential of cannabinoids for movement disorders

There is growing interest in the therapeutic potential of marijuana (cannabis) and cannabinoid-based chemicals within the medical community and, particularly, for neurological conditions. This interest is driven both by changes in the legal status of cannabis in many areas and increasing research into the roles of endocannabinoids within the central nervous system and their potential as symptomatic and/or neuroprotective therapies. We review basic science as well as preclinical and clinical studies on the therapeutic potential of cannabinoids specifically as it relates to movement disorders. The pharmacology of cannabis is complex, with over 60 neuroactive chemicals identified to date. The endocannabinoid system modulates neurotransmission involved in motor function, particularly within the basal ganglia. Preclinical research in animal models of several movement disorders have shown variable evidence for symptomatic benefits, but more consistently suggest potential neuroprotective effects in several animal models of Parkinson's (PD) and Huntington's disease (HD). Clinical observations and clinical trials of cannabinoid-based therapies suggests a possible benefit of cannabinoids for tics and probably no benefit for tremor in multiple sclerosis or dyskinesias or motor symptoms in PD. Data are insufficient to draw conclusions regarding HD, dystonia, or ataxia and nonexistent for myoclonus or RLS. Despite the widespread publicity about the medical benefits of cannabinoids, further preclinical and clinical research is needed to better characterize the pharmacological, physiological, and therapeutic effects of this class of drugs in movement disorders.

L-DOPA disrupts adenosine A(2A)-cannabinoid CB(1)-dopamine D(2) receptor heteromer cross-talk in the striatum of hemiparkinsonian rats: biochemical and behavioral studies

Long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA), still the most effective treatment in Parkinson's disease (PD), is associated with severe motor complications such as dyskinesia. Experimental and clinical data have indicated that adenosine A2A receptor antagonists can provide symptomatic improvement by potentiating L-DOPA efficacy and minimizing its side effects. It is known that the G-protein-coupled adenosine A2A, cannabinoid CB1 and dopamine D2 receptors may interact and form functional A2A-CB1-D2 receptor heteromers in co-transfected cells as well as in rat striatum. These data suggest that treatment with a combination of drugs or a single compound selectively acting on A2A-CB1-D2 heteromers may represent an alternative therapeutic treatment of PD. We investigated the expression of A2A-CB1-D2 receptor heteromers in the striatum of both naïve and hemiparkinsonian rats (HPD-rats) bearing a unilateral 6-hydroxydopamine (6-OHDA) lesion, and assessed how receptor heteromer expression and biochemical properties were affected by L-DOPA treatment. Radioligand binding data showed that A2A-CB1-D2 receptor heteromers are present in the striatum of both naïve and HPD-rats. However, behavioral results indicated that the combined administration of A2A (MSX-3 or SCH58261) and CB1 (rimonabant) receptor antagonists, in the presence of L-DOPA does not produce a response different from administration of the A2A receptor antagonist alone. These behavioral results prompted identification of heteromers in L-DOPA-treated animals. Interestingly, the radioligand binding results in samples from lesioned animals suggest that the heteromer is lost following acute or chronic treatment with L-DOPA.

Change in plasma levels of amino acid neurotransmitters and its correlation with clinical heterogeneity in early Parkinson's disease patients

BACKGROUND

The correlation between plasma amino acid (AA) neurotransmitters and clinical heterogeneity in early patients with Parkinson's disease (PD) is still poorly understood.

AIMS

To examine the plasma levels of AA neurotransmitters in early patients with PD and to evaluate their correlation with PD subtypes.

METHODS

Based on the predominant symptoms, fifty-one patients with PD were enrolled and divided into four subgroups: (1) akinetic-rigid type (ART), (2) tremor-dominant type (TDT), (3) postural instability/gait difficulty type (PIGD), and (4) mixed type (MT). Plasma levels of AA were measured by HPLC-RF, and their potential diagnostic practicality and their association with PD subtypes were evaluated by the receiver operating characteristic (ROC) and correlation analysis, respectively.

RESULTS

Patients with PD exhibited markedly lower levels of Asp, Glu, Tau, L-ser, and lower values of Glu/GABA ratio than healthy controls. The ROC analysis revealed their high sensitivity (77.1-87.5%) and specificity (58.8-88.2%). Furthermore, the glutamic acid (Glu), γ-aminobutyric acid (GABA) level in the PIGD subtype was increased as compared with other subtypes and was negatively correlated with the ART/PIGD ratio.

CONCLUSION

The decrease in plasma Asp, Glu, Tau, L-ser levels, and the value of Glu/GABA ratio may be helpful for early PD diagnosis. The elevated GABA level may be the biochemical basis for the specific symptoms of PIGD PD.

Cannabinoids and value-based decision making: implications for neurodegenerative disorders

In recent years, disturbances in cognitive function have been increasingly recognized as important symptomatic phenomena in neurodegenerative diseases, including Parkinson's Disease (PD). Value-based decision making in particular is an important executive cognitive function that is not only impaired in patients with PD, but also shares neural substrates with PD in basal ganglia structures and the dopamine system. Interestingly, the endogenous cannabinoid system modulates dopamine function and subsequently value-based decision making. This review will provide an overview of the interdisciplinary research that has influenced our understanding of value-based decision making and the role of dopamine, particularly in the context of reinforcement learning theories, as well as recent animal and human studies that demonstrate the modulatory role of activation of cannabinoid receptors by exogenous agonists or their naturally occurring ligands. The implications of this research for the symptomatology of and potential treatments for PD are also discussed.

Rimonabant for neurocognition in schizophrenia: a 16-week double blind randomized placebo controlled trial

OBJECTIVE

To examine the effect of rimonabant on neurocognitive impairments in people with schizophrenia.

METHODS

Participants entered a 16-week double-blind, placebo-controlled, randomized clinical trial. A neurocognitive battery was administered at baseline and end of study.

RESULTS

In comparison to rimonabant (20mg/day), placebo-treated participants exhibited a significant improvement on the Repeatable Battery for the Assessment of Neuropsychological Status total score. In contrast, rimonabant was associated with significant improvement on a probabilistic learning task. There were no other significant treatment effects.

CONCLUSIONS

Rimonabant did not improve global cognitive functioning, but did improve a specific learning deficit based on response to positive feedback.

Symptom-relieving and neuroprotective effects of the phytocannabinoid Δ⁹-THCV in animal models of Parkinson's disease

BACKGROUND AND PURPOSE

Previous findings have indicated that a cannabinoid, such as Δ(9)-THCV, which has antioxidant properties and the ability to activate CB(2) receptors but to block CB(1) , might be a promising therapy for alleviating symptoms and delaying neurodegeneration in Parkinson's disease (PD).

EXPERIMENTAL APPROACH

The ability of Δ(9)-THCV to reduce motor inhibition and provide neuroprotection was investigated in rats lesioned with 6-hydroxydopamine and in mice lesioned with lipopolysaccharide (LPS).

KEY RESULTS

Acute administration of Δ(9)-THCV attenuated the motor inhibition caused by 6-hydroxydopamine, presumably through changes in glutamatergic transmission. Moreover, chronic administration of Δ(9)-THCV attenuated the loss of tyrosine hydroxylase-positive neurones caused by 6-hydroxydopamine in the substantia nigra, through an effect related to its antioxidant properties (it was reproduced by cannabidiol -enriched botanical extract). In addition, CB(2) receptor-deficient mice responded to 6-hydroxydopamine in a similar manner to wild-type animals, and CB(2) receptors were poorly up-regulated in the rat substantia nigra in response to 6-hydroxydopamine. By contrast, the substantia nigra of mice that had been injected with LPS exhibited a greater up-regulation of CB(2) receptors. In these animals, Δ(9)-THCV also caused preservation of tyrosine hydroxylase-positive neurones. This effect probably involved CB(2) receptors as it was also elicited by the selective CB(2) receptor agonist, HU-308, and CB(2) receptor-deficient mice were more vulnerable to LPS lesions. CONCLUSIONS AND IMPLICATIONS Given its antioxidant properties and its ability to activate CB(2) but to block CB(1) receptors, Δ(9)-THCV has a promising pharmacological profile for delaying disease progression in PD and also for ameliorating parkinsonian symptoms.

Phytocannabinoids as novel therapeutic agents in CNS disorders

The Cannabis sativa herb contains over 100 phytocannabinoid (pCB) compounds and has been used for thousands of years for both recreational and medicinal purposes. In the past two decades, characterisation of the body's endogenous cannabinoid (CB) (endocannabinoid, eCB) system (ECS) has highlighted activation of central CB(1) receptors by the major pCB, Δ(9)-tetrahydrocannabinol (Δ(9)-THC) as the primary mediator of the psychoactive, hyperphagic and some of the potentially therapeutic properties of ingested cannabis. Whilst Δ(9)-THC is the most prevalent and widely studied pCB, it is also the predominant psychotropic component of cannabis, a property that likely limits its widespread therapeutic use as an isolated agent. In this regard, research focus has recently widened to include other pCBs including cannabidiol (CBD), cannabigerol (CBG), Δ(9)tetrahydrocannabivarin (Δ(9)-THCV) and cannabidivarin (CBDV), some of which show potential as therapeutic agents in preclinical models of CNS disease. Moreover, it is becoming evident that these non-Δ(9)-THC pCBs act at a wide range of pharmacological targets, not solely limited to CB receptors. Disorders that could be targeted include epilepsy, neurodegenerative diseases, affective disorders and the central modulation of feeding behaviour. Here, we review pCB effects in preclinical models of CNS disease and, where available, clinical trial data that support therapeutic effects. Such developments may soon yield the first non-Δ(9)-THC pCB-based medicines.

Effects of opioids, cannabinoids, and vanilloids on body temperature

Cannabinoid and opioid drugs produce marked changes in body temperature. Recent findings have extended our knowledge about the thermoregulatory effects of cannabinoids and opioids, particularly as related to delta opioid receptors, endogenous systems, and transient receptor potential (TRP) channels. Although delta opioid receptors were originally thought to play only a minor role in thermoregulation compared to mu and kappa opioid receptors, their activation has been shown to produce hypothermia in multiple species. Endogenous opioids and cannabinoids also regulate body temperature. Mu and kappa opioid receptors are thought to be in tonic balance, with mu and kappa receptor activation producing hyperthermia and hypothermia, respectively. A particularly intense research focus is TRP channels, where TRPV1 channel activation produces hypothermia whereas TRPA1 and TRPM8 channel activation causes hyperthermia. The marked hyperthermia produced by TRPV1 channel antagonists suggests these warm channels tonically control body temperature. A better understanding of the roles of cannabinoid, opioid, and TRP systems in thermoregulation may have broad clinical implications and provide insights into interactions among neurotransmitter systems involved in thermoregulation.

Effects of opioids, cannabinoids, and vanilloids on body temperature

Cannabinoid and opioid drugs produce marked changes in body temperature. Recent findings have extended our knowledge about the thermoregulatory effects of cannabinoids and opioids, particularly as related to delta opioid receptors, endogenous systems, and transient receptor potential (TRP) channels. Although delta opioid receptors were originally thought to play only a minor role in thermoregulation compared to mu and kappa opioid receptors, their activation has been shown to produce hypothermia in multiple species. Endogenous opioids and cannabinoids also regulate body temperature. Mu and kappa opioid receptors are thought to be in tonic balance, with mu and kappa receptor activation producing hyperthermia and hypothermia, respectively. A particularly intense research focus is TRP channels, where TRPV1 channel activation produces hypothermia whereas TRPA1 and TRPM8 channel activation causes hyperthermia. The marked hyperthermia produced by TRPV1 channel antagonists suggests these warm channels tonically control body temperature. A better understanding of the roles of cannabinoid, opioid, and TRP systems in thermoregulation may have broad clinical implications and provide insights into interactions among neurotransmitter systems involved in thermoregulation.

In vivo brain microdialysis: advances in neuropsychopharmacology and drug discovery

INTRODUCTION: Microdialysis is an important in vivo sampling technique, useful in the assay of extracellular tissue fluid. The technique has both pre-clinical and clinical applications but is most widely used in neuroscience. The in vivo microdialysis technique allows measurement of neurotransmitters such as acetycholine (ACh), the biogenic amines including dopamine (DA), norepinephrine (NE) and serotonin (5-HT), amino acids such as glutamate (Glu) and gamma aminobutyric acid (GABA), as well as the metabolites of the aforementioned neurotransmitters, and neuropeptides in neuronal extracellular fluid in discrete brain regions of laboratory animals such as rodents and non-human primates. AREAS COVERED: In this review we present a brief overview of the principles and procedures related to in vivo microdialysis and detail the use of this technique in the pre-clinical measurement of drugs designed to be used in the treatment of chemical addiction, neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) and as well as psychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD) and schizophrenia. This review offers insight into the tremendous utility and versatility of this technique in pursuing neuropharmacological investigations as well its significant potential in rational drug discovery. EXPERT OPINION: In vivo microdialysis is an extremely versatile technique, routinely used in the neuropharmacological investigation of drugs used for the treatment of neurological disorders. This technique has been a boon in the elucidation of the neurochemical profile and mechanism of action of several classes of drugs especially their effects on neurotransmitter systems. The exploitation and development of this technique for drug discovery in the near future will enable investigational new drug candidates to be rapidly moved into the clinical trial stages and to market thus providing new successful therapies for neurological diseases that are currently in demand.

Methamphetamine-induced dopamine-independent alterations in striatal gene expression in the 6-hydroxydopamine hemiparkinsonian rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)-denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (±1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.

Cannabinoid-dopamine interaction in the pathophysiology and treatment of CNS disorders

Endocannabinoids and their receptors, mainly the CB(1) receptor type, function as a retrograde signaling system in many synapses within the CNS, particularly in GABAergic and glutamatergic synapses. They also play a modulatory function on dopamine (DA) transmission, although CB(1) receptors do not appear to be located in dopaminergic terminals, at least in the major brain regions receiving dopaminergic innervation, e.g., the caudate-putamen and the nucleus accumbens/prefrontal cortex. Therefore, the effects of cannabinoids on DA transmission and DA-related behaviors are generally indirect and exerted through the modulation of GABA and glutamate inputs received by dopaminergic neurons. Recent evidence suggest, however, that certain eicosanoid-derived cannabinoids may directly activate TRPV(1) receptors, which have been found in some dopaminergic pathways, thus allowing a direct regulation of DA function. Through this direct mechanism or through indirect mechanisms involving GABA or glutamate neurons, cannabinoids may interact with DA transmission in the CNS and this has an important influence in various DA-related neurobiological processes (e.g., control of movement, motivation/reward) and, particularly, on different pathologies affecting these processes like basal ganglia disorders, schizophrenia, and drug addiction. The present review will address the current literature supporting these cannabinoid-DA interactions, with emphasis in aspects dealing with the neurochemical, physiological, and pharmacological/therapeutic bases of these interactions.

The endocannabinoid system as a target for the treatment of motor dysfunction

There is evidence that cannabinoid-based medicines that are selective for different targets in the cannabinoid signalling system (e.g. receptors, inactivation mechanism, enzymes) might be beneficial in basal ganglia disorders, namely Parkinson's disease (PD) and Huntington's disease (HD). These benefits not only include the alleviation of specific motor symptoms [e.g. choreic movements with cannabinoid receptor type 1 (CB(1))/transient receptor potential vanilloid type 1 agonists in HD; bradykinesia with CB(1) antagonists and tremor with CB(1) agonists in PD], but also the delay of disease progression due to the neuroprotective properties demonstrated for cannabinoids (e.g. CB(1) agonists reduce excitotoxicity; CB(2) agonists limit the toxicity of reactive microglia; and antioxidant cannabinoids attenuate oxidative damage). In addition, extensive biochemical, anatomical, physiological and pharmacological studies have demonstrated that: (i) the different elements of the cannabinoid system are abundant in basal ganglia structures and they are affected by these disorders; (ii) the cannabinoid system plays a prominent role in basal ganglia function by modulating the neurotransmitters that operate in the basal ganglia circuits, both in healthy and pathological conditions; and (iii) the activation and/or inhibition of the cannabinoid system is associated with important motor responses that are maintained and even enhanced in conditions of malfunctioning and/or degeneration. In this article we will review the available data regarding the relationship between the cannabinoid system and basal ganglia activity, both in healthy and pathological conditions and will also try to identify future lines of research expected to increase current knowledge about the potential therapeutic benefits of targeting this system in PD, HD and other basal ganglia disorders.

Cannabinoid CB1 receptors are early downregulated followed by a further upregulation in the basal ganglia of mice with deletion of specific park genes

This study was designed to examine the type of changes experienced by the CB1 receptor, a key element of the cannabinoid signaling system, in the basal ganglia of different mouse mutants generated by deletion of specific genes associated with the development of Parkinson's disease in humans [PARK1 (alpha-synuclein), PARK2 (parkin) or PARK6 (PINK1)]. We observed that CB1 receptor-mRNA levels were significantly reduced in the caudate-putamen in the three models under examination when animals were analyzed at early phases (< or = 12 months of age). This decrease was, in general, associated with a reduction in CB1 receptor binding in the substantia nigra and the globus pallidus, particularly in the case of alpha-synuclein-deficient mice. By contrast, both parameters, mRNA levels and binding for the CB1 receptor, showed an elevation in the same areas when animals were analyzed at older ages, mainly in the case of the CB1 receptor binding in the substantia nigra. In summary, our data revealed the existence of a biphasic response for CB1 receptors, with losses at early phases, when dopaminergic dysfunction is possibly the major event that takes place, followed by upregulatory responses at advanced phases characterized by the occurrence of evident nigrostriatal pathology including neuronal death in some cases.

High on habits

The neural circuits involved in learning and executing goal-directed actions, which are governed by action-outcome contingencies and sensitive to changes in the expected value of the outcome, have been shown to be different from those mediating habits, which are less dependent on action-outcome relations and changes in outcome value. Extended training, different reinforcement schedules, and substances of abuse have been shown to induce a shift from goal-directed performance to habitual performance. This shift can be beneficial in everyday life, but can also lead to loss of voluntary control and compulsive behavior, namely during drug seeking in addiction. Although the brain circuits underlying habit formation are becoming clearer, the molecular mechanisms underlying habit formation are still not understood. Here, we review a recent study where Hilario et al. (2007) established behavioral procedures to investigate habit formation in mice in order to investigate the molecular mechanisms underlying habit formation. Using those procedures, and a combination of genetic and pharmacological tools, the authors showed that endocannabinoid signaling is critical for habit formation.