Treating a novel plasticity defect rescues episodic memory in Fragile X model mice.

Episodic memory, a fundamental component of human cognition, is significantly impaired in autism. We believe we report the first evidence for this problem in the Fmr1-knockout (KO) mouse model of Fragile X syndrome and describe potentially treatable underlying causes. The hippocampus is critical for the formation and use of episodes, with semantic (cue identity) information relayed to the structure via the lateral perforant path (LPP). The unusual form of synaptic plasticity expressed by the LPP (lppLTP) was profoundly impaired in Fmr1-KOs relative to wild-type mice. Two factors contributed to this defect: (i) reduced GluN1 subunit levels in synaptic NMDA receptors and related currents, and (ii) impaired retrograde synaptic signaling by the endocannabinoid 2-arachidonoylglycerol (2-AG). Studies using a novel serial cue paradigm showed that episodic encoding is dependent on both the LPP and the endocannabinoid receptor CB1, and is strikingly impaired in Fmr1-KOs. Enhancing 2-AG signaling rescued both lppLTP and learning in the mutants. Thus, two consequences of the Fragile-X mutation converge on plasticity at one site in hippocampus to prevent encoding of a basic element of cognitive memory. Collectively, the results suggest a clinically plausible approach to treatment.

Remote memories are enhanced by COMT activity through dysregulation of the endocannabinoid system in the prefrontal cortex.

The prefrontal cortex (PFC) is a crucial hub for the flexible modulation of recent memories (executive functions) as well as for the stable organization of remote memories. Dopamine in the PFC is implicated in both these processes and genetic variants affecting its neurotransmission might control the unique balance between cognitive stability and flexibility present in each individual. Functional genetic variants in the catechol-O-methyltransferase (COMT) gene result in a different catabolism of dopamine in the PFC. However, despite the established role played by COMT genetic variation in executive functions, its impact on remote memory formation and recall is still poorly explored. Here we report that transgenic mice overexpressing the human COMT-Val gene (COMT-Val-tg) present exaggerated remote memories (>50 days) while having unaltered recent memories (<24 h). COMT selectively and reversibly modulated the recall of remote memories as silencing COMT Val overexpression starting from 30 days after the initial aversive conditioning normalized remote memories. COMT genetic overactivity produced a selective overdrive of the endocannabinoid system within the PFC, but not in the striatum and hippocampus, which was associated with enhanced remote memories. Indeed, acute pharmacological blockade of CB1 receptors was sufficient to rescue the altered remote memory recall in COMT-Val-tg mice and increased PFC dopamine levels. These results demonstrate that COMT genetic variations modulate the retrieval of remote memories through the dysregulation of the endocannabinoid system in the PFC.

Specific skeletal muscle sphingolipid compounds in energy expenditure regulation and weight gain in Native Americans of Southwestern heritage.

BACKGROUND/OBJECTIVES: In animal models, a role in the regulation of energy expenditure (EE) has been ascribed to sphingolipids, active components of cell membranes participating in cellular signaling. In humans, it is unknown whether sphingolipids have a role in the modulation of EE and, consequently, influence weight gain. The present study investigated the putative association of EE and weight gain with sphingolipid levels in the human skeletal muscle, a component of fat-free mass (the strongest determinant of EE), in adipose tissue and plasma. SUBJECTS/METHODS: Twenty-four-hour EE, sleeping metabolic rate (SMR) and resting metabolic rate (RMR) were assessed in 35 healthy Native Americans of Southwestern heritage (24 male; 30.2±7.73 years). Sphingolipid (ceramide, C; sphingomyelin, SM) concentrations were measured in skeletal muscle tissue, subcutaneous adipose tissue and plasma samples. After 6.68 years (0.26-12.4 years), follow-up weights were determined in 16 participants (4 females). RESULTS: Concentrations of C24:0, SM18:1/26:1 and SM18:0/24:1 in muscle were associated with 24-h EE (r=-0.47, P=0.01), SMR (r=-0.59, P=0.0008) and RMR (r=-0.44, P=0.01), respectively. Certain muscle sphingomyelins also predicted weight gain (for example, SM18:1/23:1, r=0.74, P=0.004). For specific muscle sphingomyelins that correlated with weight gain and EE (SM18:1/23:0, SM18:1/23:1 and SMR, r=-0.51, r=-0.41, respectively, all P<0.03; SM18:1/24:2 and RMR, r=-0.36, P=0.03), associations could be reproduced with SMR in adipose tissue (all r<-0.46, all P<0.04), though not in plasma. CONCLUSIONS: This study provides preliminary, novel evidence, that specific muscle and adipose tissue sphingolipid compounds are associated with EE and weight gain in Native Americans of Southwestern heritage. Further studies are warranted to investigate whether sphingolipids of different body compartments act in concert to modulate energy balance in humans.

An Important Role for N-Acylethanolamine Acid Amidase in the Complete Freund's Adjuvant Rat Model of Arthritis.

The endogenous lipid amides, palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), exert marked antinociceptive and anti-inflammatory effects in animal models by engaging nuclear peroxisome proliferator-activated receptor-α. PEA and OEA are produced by macrophages and other host-defense cells and are deactivated by the cysteine amidase, N-acylethanolamine acid amidase (NAAA), which is highly expressed in macrophages and B-lymphocytes. In the present study, we examined whether a) NAAA might be involved in the inflammatory reaction triggered by injection of complete Freund's adjuvant (CFA) into the rat paw and b) administration of 4-cyclohexylbutyl-N-[(S)-2-oxoazetidin-3-yl]-carbamate (ARN726), a novel systemically active NAAA inhibitor, attenuates such reaction. Injection of CFA into the paw produced local edema and heat hyperalgesia, which were accompanied by decreased PEA and OEA content (assessed by liquid chromatography/mass spectrometry) and increased NAAA levels (assessed by Western blot and ex vivo enzyme activity measurements) in paw tissue. Administration of undec-10-ynyl-N-[(3S)-2-oxoazetidin-3-yl] carbamate (ARN14686), a NAAA-preferring activity-based probe, revealed that NAAA was catalytically active in CFA-treated paws. Administration of ARN726 reduced NAAA activity and restored PEA and OEA levels in inflamed tissues, and significantly decreased CFA-induced inflammatory symptoms, including pus production and myeloperoxidase activity. The results confirm the usefulness of ARN726 as a probe to investigate the functions of NAAA in health and disease and suggest that this enzyme may provide a new molecular target for the treatment of arthritis.

Effects of peripheral FAAH blockade on NTG-induced hyperalgesia--evaluation of URB937 in an animal model of migraine.

BACKGROUND: Systemic nitroglycerin (NTG) activates brain nuclei involved in nociceptive transmission as well as in neuroendocrine and autonomic functions in rats. These changes are considered relevant for migraine because NTG consistently provokes spontaneous-like migraine attacks in migraineurs. Several studies have suggested a relationship between the endocannabinoid levels and pain mediation in migraine. URB937, a peripheral inhibitor of fatty acid amide hydrolase (FAAH)-the enzyme that degrades anandamide, produces analgesia in animal models of pain, but there is no information on its effects in migraine. AIM: We evaluated whether URB937 alters nociceptive responses in the animal model of migraine based on NTG administration in male rats, using the tail flick test and the plantar and orofacial formalin tests, under baseline conditions and after NTG administration. Furthermore, we investigated whether URB937 affects NTG-induced c-Fos expression in the brain. RESULTS: During the tail flick test, URB937 showed an antinociceptive effect in baseline conditions and it blocked NTG-induced hyperalgesia. URB937 also proved effective in counteracting NTG-induced hyperalgesia during both the plantar and orofacial formalin tests. Mapping of brain nuclei activated by NTG indicates that URB937 significantly reduces c-Fos expression in the nucleus trigeminalis caudalis and the locus coeruleus. CONCLUSIONS: The data suggest that URB937 is capable of changing, probably via indirect mechanisms, the functional status of central structures that are important for pain transmission in an animal model of migraine.

Elevated brain cannabinoid CB1 receptor availability in post-traumatic stress disorder: a positron emission tomography study.

Endocannabinoids and their attending cannabinoid type 1 (CB1) receptor have been implicated in animal models of post-traumatic stress disorder (PTSD). However, their specific role has not been studied in people with PTSD. Herein, we present an in vivo imaging study using positron emission tomography (PET) and the CB1-selective radioligand [(11)C]OMAR in individuals with PTSD, and healthy controls with lifetime histories of trauma (trauma-exposed controls (TC)) and those without such histories (healthy controls (HC)). Untreated individuals with PTSD (N=25) with non-combat trauma histories, and TC (N=12) and HC (N=23) participated in a magnetic resonance imaging scan and a resting PET scan with the CB1 receptor antagonist radiotracer [(11)C]OMAR, which measures the volume of distribution (VT) linearly related to CB1 receptor availability. Peripheral levels of anandamide, 2-arachidonoylglycerol, oleoylethanolamide, palmitoylethanolamide and cortisol were also assessed. In the PTSD group, relative to the HC and TC groups, we found elevated brain-wide [(11)C]OMAR VT values (F(2,53)=7.96, P=0.001; 19.5% and 14.5% higher, respectively), which were most pronounced in women (F(1,53)=5.52, P=0.023). Anandamide concentrations were reduced in the PTSD relative to the TC (53.1% lower) and HC (58.2% lower) groups. Cortisol levels were lower in the PTSD and TC groups relative to the HC group. Three biomarkers examined collectively--OMAR VT, anandamide and cortisol--correctly classified nearly 85% of PTSD cases. These results suggest that abnormal CB1 receptor-mediated anandamide signaling is implicated in the etiology of PTSD, and provide a promising neurobiological model to develop novel, evidence-based pharmacotherapies for this disorder.

Arachidonic acid in cell signaling.

Important advances have recently been made in our understanding of the arachidonic acid cascade. The molecular characterization of different forms of phospholipase A2 indicates that multiple pathways are involved in the release of arachidonic acid evoked by physiological or pathological stimuli. Moreover, studies on the expression of enzymes that metabolize arachidonic acid reveal the potential participation of the eicosanoids in central aspects of cell regulation, such as control of mitogenesis. Finally, cloning of the first eicosanoid receptors is a major step towards elucidating the diverse cellular functions exerted by these bioactive lipids.

Pharmacokinetic and pharmacodynamic properties of aerosolized ("vaped") THC in adolescent male and female rats.

RATIONALE: Adolescent exposure to ∆9-tetrahydrocannabinol (THC), the psychotropic constituent of cannabis, might affect brain development, and in rodent models leads to long-term behavioral and physiological alterations. Yet, the basic pharmacology of this drug in adolescent rodents, especially when ingested via ecologically relevant routes like aerosol inhalation, commonly referred to as "vaping," is still poorly characterized. Moreover, sex differences exist in THC metabolism, kinetics, and behavioral effects, but these have not been rigorously examined after vapor dosing in adolescents. OBJECTIVES: We investigated the pharmacokinetics and pharmacodynamics of aerosolized THC (30 min inhalation exposure, 25 or 100 mg/ml) in adolescent Wistar rats of both sexes. METHODS: Liquid chromatography/mass spectrometry analysis of THC and its major metabolites was conducted on blood plasma and brain tissue at 5, 30, 60, and 120 min following a 30-min aerosol dosing session. Effects on activity in a novel environment for 120 min after aerosol, and temperature, were measured in separate rats. RESULTS: We found sex-dependent differences in the pharmacokinetics of THC and its active (11-OH-THC) and inactive (11-COOH-THC) metabolites in the blood and brain, along with dose- and sex-dependent effects on anxiety-like and exploratory behaviors; namely, greater 11-OH-THC levels accompanied by greater behavioral effects in females at the low dose but similar hypothermic effects in both sexes at the high dose. CONCLUSIONS: These results provide a benchmark for dosing adolescent rats with aerosolized (or "vaped") THC, which could facilitate adoption by other labs of this potentially human-relevant THC exposure model to understand cannabis effects on the developing brain.

FAAH deficiency promotes energy storage and enhances the motivation for food.

RATIONALE: Fatty acid amide hydrolase (FAAH) is the main degrading enzyme of the fatty acid ethanolamides anandamide (AEA) and oleoylethanolamide (OEA), which have opposite effects on food intake and energy balance. AEA, an endogenous ligand of CB(1) cannabinoid receptors, enhances food intake and energy storage, whereas OEA binds to peroxisome proliferator-activated receptors-alpha to reduce food intake and promoting lipolysis. To elucidate the role of FAAH in food intake and energy balance, we have evaluated different metabolic and behavioral responses related to feeding in FAAH-deficient (FAAH(-/-)) mice and their wild-type littermates. METHODOLOGY AND RESULTS: Total daily food intake was similar in both genotypes, but high-fat food consumption was enhanced during the dark hours and decreased during the light hours in FAAH(-/-) mice. The reinforcing and motivational effects of food were also enhanced in FAAH(-/-) mice as revealed by operant behavioral paradigms. These behavioral responses were reversed by the administration of the selective CB(1) cannabinoid antagonist rimonabant. Furthermore, body weight, total amount of adipose tissue, plasma-free fatty acids and triglyceride content in plasma, liver, skeletal muscle and adipose tissue, were increased in FAAH(-/-) mice. Accordingly, leptin levels were increased and adiponectin levels decreased in these mutants, FAAH(-/-) mice also showed enhanced plasma insulin and blood glucose levels revealing an insulin resistance. As expected, both AEA and OEA levels were increased in hypothalamus, small intestine and liver of FAAH(-/-) mice. CONCLUSION: These results indicate that the lack of FAAH predominantly promotes energy storage by food intake-independent mechanisms, through the enhancement of AEA levels rather than promoting the anorexic effects of OEA.

Functional role of high-affinity anandamide transport, as revealed by selective inhibition.

Anandamide, an endogenous ligand for central cannabinoid receptors, is released from neurons on depolarization and rapidly inactivated. Anandamide inactivation is not completely understood, but it may occur by transport into cells or by enzymatic hydrolysis. The compound N-(4-hydroxyphenyl)arachidonylamide (AM404) was shown to inhibit high-affinity anandamide accumulation in rat neurons and astrocytes in vitro, an indication that this accumulation resulted from carrier-mediated transport. Although AM404 did not activate cannabinoid receptors or inhibit anandamide hydrolysis, it enhanced receptor-mediated anandamide responses in vitro and in vivo. The data indicate that carrier-mediated transport may be essential for termination of the biological effects of anandamide, and may represent a potential drug target.

The FAAH inhibitor URB-597 interferes with cisplatin- and nicotine-induced vomiting in the Suncus murinus (house musk shrew).

Considerable evidence implicates the endocannabinoid system as a neuromodulator of nausea and vomiting. The action of anandamide (AEA) can be prolonged by inhibiting its degradation, through the use of URB597 (URB), a Fatty Acid Amide Hydrolase (FAAH) enzyme inhibitor. Here we present evidence that the FAAH inhibitor, URB, interferes with cisplatin- and nicotine-induced vomiting in the Suncus murinus. In Experiment 1, shrews were injected with URB (0.9 mg/kg) or vehicle 120 min prior to the behavioral testing. They received a second injection of AEA (5 mg/kg) or vehicle 15 min prior to being injected with cisplatin (20 mg/kg) or saline and the number of vomiting episodes were counted for 60 min. In Experiment 2, shrews were injected with vehicle or URB (0.9 mg/kg) 120 min prior to receiving an injection of nicotine (5 mg/kg) or saline and the number of vomiting episodes were counted for 15 min. Experiment 3 evaluated the potential of the CB(1) antagonist, SR141716, to reverse the effect of URB on nicotine-induced vomiting. URB attenuated vomiting produced by cisplatin and nicotine and the combination of URB+AEA suppressed vomiting produced by cisplatin. The effect of URB on nicotine-induced vomiting was reversed by SR141716. These data suggest that the EC system plays a tonic role in the regulation of toxin-induced vomiting.

AM404, an anandamide transport inhibitor, reduces plasma extravasation in a model of neuropathic pain in rat: role for cannabinoid receptors.

Neuropathic pain consequent to peripheral nerve injury has been associated with local inflammation. Following noxious stimulation afferent fibres release substance P (SP) and calcitonin-gene related peptide (CGRP), which are closely related to oedema formation and plasma leakage. The effect of the anandamide transport blocker AM404 has been studied on plasma extravasation after chronic constriction injury (CCI) which consists in a unilateral loose ligation of the rat sciatic nerve (Bennett and Xie, 1988). AM404 (1-3-10 mg kg(-1)) reduced plasma extravasation in the legated paw, measured as mug of Evans Blue per gram of fresh tissue. A strong effect on vascular permeability was also produced by the synthetic cannabinoid agonist WIN 55,212-2 (0.1-0.3-1 mg kg(-1)). Using specific antagonists or enzyme inhibitors, we demonstrate that cannabinoids act at several levels: data on the 3rd day suggest a strong involvement of substance P (SP) and calcitonin gene-related peptide (CGRP) in the control of vascular tone, whereas at the 7th and 14th days the major role seems to be played by prostaglandins (PGs) and nitric oxide (NO). Capsaicin injection in ligated paws of AM404- or WIN 55,212-2-treated rats resulted in an increase of Evans Blue extravasation, suggesting the involvement of the cannabinergic system in the protective effect of C fibres of ligated paws. Taken together, these data demonstrate the efficacy of cannabinoids in controlling pain behaviour through the modulation of several pain mediators and markers of vascular reactivity, such as SP, CGRP, PGs and NO.

The endocannabinoid system in brain reward processes.

Food, drugs and brain stimulation can serve as strong rewarding stimuli and are all believed to activate common brain circuits that evolved in mammals to favour fitness and survival. For decades, endogenous dopaminergic and opioid systems have been considered the most important systems in mediating brain reward processes. Recent evidence suggests that the endogenous cannabinoid (endocannabinoid) system also has an important role in signalling of rewarding events. First, CB(1) receptors are found in brain areas involved in reward processes, such as the dopaminergic mesolimbic system. Second, activation of CB(1) receptors by plant-derived, synthetic or endogenous CB(1) receptor agonists stimulates dopaminergic neurotransmission, produces rewarding effects and increases rewarding effects of abused drugs and food. Third, pharmacological or genetic blockade of CB(1) receptors prevents activation of dopaminergic neurotransmission by several addictive drugs and reduces rewarding effects of food and these drugs. Fourth, brain levels of the endocannabinoids anandamide and 2-arachidonoylglycerol are altered by activation of reward processes. However, the intrinsic activity of the endocannabinoid system does not appear to play a facilitatory role in brain stimulation reward and some evidence suggests it may even oppose it. The influence of the endocannabinoid system on brain reward processes may depend on the degree of activation of the different brain areas involved and might represent a mechanism for fine-tuning dopaminergic activity. Although involvement of the various components of the endocannabinoid system may differ depending on the type of rewarding event investigated, this system appears to play a major role in modulating reward processes.

Dopamine activation of endogenous cannabinoid signaling in dorsal striatum.

We measured endogenous cannabinoid release in dorsal striatum of freely moving rats by microdialysis and gas chromatography/mass spectrometry. Neural activity stimulated the release of anandamide, but not of other endogenous cannabinoids such as 2-arachidonylglycerol. Moreover, anandamide release was increased eightfold over baseline after local administration of the D2-like (D2, D3, D4) dopamine receptor agonist quinpirole, a response that was prevented by the D2-like receptor antagonist raclopride. Administration of the D1-like (D1, D5) receptor agonist SKF38393 had no such effect. These results suggest that functional interactions between endocannabinoid and dopaminergic systems may contribute to striatal signaling. In agreement with this hypothesis, pretreatment with the cannabinoid antagonist SR141716A enhanced the stimulation of motor behavior elicited by systemic administration of quinpirole. The endocannabinoid system therefore may act as an inhibitory feedback mechanism countering dopamine-induced facilitation of motor activity.

Role of endocannabinoids and their analogues in obesity and eating disorders.

Fatty acids ethanolamides (FAEs) are a family of lipid mediators. A member of this family, anandamide, is an endogenous ligand for cannabinoid receptors targeted by the marijuana constituent Delta-9-tetrahydrocannabinol. Anandamide is now established as a brain endocannabinoid messenger and multiple roles for other FAEs have also been proposed. One emerging function of these lipid mediators is the regulation of feeding behavior and body weight. Anandamide causes overeating in rats because of its ability to activate cannabinoid receptors. This action is of therapeutic relevance: cannabinoid agonists are currently used to alleviate anorexia and nausea in AIDS patients, whereas the cannabinoid receptor CB1 antagonist rimonabant was recently found to be effective in the treatment of obesity. In contrast to anandamide, its monounsatured analogue, oleoylethanolamide (OEA), decreases food intake and body weight gain through a cannabinoid receptor-independent mechanism. In the rat proximal small intestine, endogenous OEA levels decrease during fasting and increase upon refeeding. These periprandial fluctuations may represent a previously undescribed signal that modulates between-meal satiety. Pharmacological studies have shown, indeed, that, as a drug, OEA produces profound anorexiant effects in rats and mice, due to selective prolongation of feeding latency and post-meal interval. The effects observed after chronic administration of OEA to different animal models of obesity, clearly indicate that inhibition of eating is not the only mechanism by which OEA can control energy metabolism. In fact, stimulation of lipolysis is responsible for the reduced fat mass and decrease of body weight gain observed in these models. Although OEA may bind to multiple receptors, several lines of evidence indicate that peripheral PPAR-alpha mediates the effects of this compound. The pathophysiological significance of OEA in the regulation of eating and body weight is further evidenced by preliminary clinical results, showing altered levels of this molecule in the cerebrospinal fluid and plasma of subjects recovered from eating disorders. These results complete previous observation on anandamide content, which resulted altered in plasma of women affected by anorexia nervosa or binge-eating disorder.

Adolescent cannabinoid exposure effects on natural reward seeking and learning in rats.

RATIONALE: Adolescence is characterized by endocannabinoid (ECB)-dependent refinement of neural circuits underlying emotion, learning, and motivation. As a result, adolescent cannabinoid receptor stimulation (ACRS) with phytocannabinoids or synthetic agonists like "Spice" cause robust and persistent changes in both behavior and circuit architecture in rodents, including in reward-related regions like medial prefrontal cortex and nucleus accumbens (NAc). OBJECTIVES AND METHODS: Here, we examine persistent effects of ACRS with the cannabinoid receptor 1/2 specific agonist WIN55-212,2 (WIN; 1.2 mg/kg/day, postnatal day (PD) 30-43), on natural reward-seeking behaviors and ECB system function in adult male Long Evans rats (PD 60+). RESULTS: WIN ACRS increased palatable food intake, and altered attribution of incentive salience to food cues in a sign-/goal-tracking paradigm. ACRS also blunted hunger-induced sucrose intake, and resulted in increased anandamide and oleoylethanolamide levels in NAc after acute food restriction not seen in controls. ACRS did not affect food neophobia or locomotor response to a novel environment, but did increase preference for exploring a novel environment. CONCLUSIONS: These results demonstrate that ACRS causes long-term increases in natural reward-seeking behaviors and ECB system function that persist into adulthood, potentially increasing liability to excessive natural reward seeking later in life.

Progress in the development of ß-lactams as N-Acylethanolamine Acid Amidase (NAAA) inhibitors: Synthesis and SAR study of new, potent N-O-substituted derivatives.

The anti-inflammatory effects resulting from raising the levels of palmitoylethanolamide (PEA), an endogenous bioactive lipid, led to envisage N-Acylethanolamine Acid Amidase (NAAA), the cysteine hydrolase mainly responsible for PEA degradation, as an attractive target for small molecule inhibitors. Previous work in our group identified serine-derived ß-lactams as potent and systemically active inhibitors of NAAA activity. Aiming to expand the SAR study around this class of compounds, we investigated the effect of the substitution on the endocyclic nitrogen by designing and synthesizing a series of N-substituted ß-lactams. The present work describes the synthesis of new N-O-alkyl and N-O-aryl substituted ß-lactams and reports the results of the structure activity relationship (SAR) study leading to the discovery of a novel, single-digit nanomolar NAAA inhibitor (37). Compound 37 was shown in vitro to inhibit human NAAA via S-acylation of the catalytic cysteine, and to display very good selectivity vs. human Acid Ceramidase, a cysteine amidase structurally related to NAAA. Preliminary in vivo studies showed that compound 37, administered topically, reduced paw edema and heat hyperalgesia in a carrageenan-induced inflammation mouse model. The high in vitro potency of 37 as NAAA inhibitor, and its encouraging in vivo activity qualify this compound as a new tool for the study of the role of NAAA in inflammatory and pain states.

The cannabinoid receptor agonist WIN 55,212-2 attenuates the effects induced by quinolinic acid in the rat striatum.

The ability of CB(1) receptors to regulate the release of glutamate in the striatum, together with the finding that, in experimental models of Huntington disease (HD), both endocannabinoid levels and CB(1) receptor densities are reduced, has prompted the investigation on the neuroprotective role of the cannabinoids in HD. Quinolinic acid (QA) is an excitotoxin that, when injected in the rat striatum reproduces many features of HD and that acts by stimulating glutamate outflow. The aim of the present study was to test the ability of the cannabinoid receptor agonist WIN 55,212-2 to prevent the effects induced by QA in the rat striatum. In microdialysis experiments, probe perfusion with WIN 55,212-2 significantly and dose-dependently prevented the increase in extracellular glutamate induced by QA. In electrophysiological recordings in corticostriatal slices, the application of WIN 55,212-2 prevented QA-induced reduction of the field potential amplitude. Both effects of WIN 55,212-2 were prevented by the CB(1) receptor antagonist AM 251. In in vivo experiments, intrastriatal WIN 55,212-2 significantly attenuated the striatal damage induced by QA, although no significant effects were observed on a behavioural ground. These data demonstrate that the stimulation of CB(1) receptors might lead to neuroprotective effects against excitotoxic striatal toxicity.