Stimulation Of Cannabinoid CB1 Receptors Research Articles

Cross-Talk between the (Endo)Cannabinoid and Renin-Angiotensin Systems: Basic Evidence and Potential Therapeutic Significance.

This review is dedicated to the cross-talk between the (endo)cannabinoid and renin angiotensin systems (RAS). Activation of AT1 receptors (AT1Rs) by angiotensin II (Ang II) can release endocannabinoids that, by acting at cannabinoid CB1 receptors (CB1Rs), modify the response to AT1R stimulation. CB1R blockade may enhance AT1R-mediated responses (mainly vasoconstrictor effects) or reduce them (mainly central nervous system-mediated effects). The final effects depend on whether stimulation of CB1Rs and AT1Rs induces opposite or the same effects. Second, CB1R blockade may diminish AT1R levels. Third, phytocannabinoids modulate angiotensin-converting enzyme-2. Additional studies are required to clarify (1) the existence of a cross-talk between the protective axis of the RAS (Ang II—AT2 receptor system or angiotensin 1-7—Mas receptor system) with components of the endocannabinoid system, (2) the influence of Ang II on constituents of the endocannabinoid system and (3) the (patho)physiological significance of AT1R-CB1R heteromerization. As a therapeutic consequence, CB1R antagonists may influence effects elicited by the activation or blockade of the RAS; phytocannabinoids may be useful as adjuvant therapy against COVID-19; single drugs acting on the (endo)cannabinoid system (cannabidiol) and the RAS (telmisartan) may show pharmacokinetic interactions since they are substrates of the same metabolizing enzyme of the transport mechanism.

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.

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. 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. To this end, female dopamine D1 receptor-deficient mice and wild-type littermates were treated with HU-210, a potent synthetic cannabinoid agonist. 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. These results support for a role of dopamine D1 receptors in the acute, chronic, and withdrawal actions of spice drugs.

Targeting Endocannabinoid Signaling: FAAH and MAG Lipase Inhibitors.

Inspired by the medicinal properties of the plant Cannabis sativa and its principal component (-)-trans-Δ9-tetrahydrocannabinol (THC), researchers have developed a variety of compounds to modulate the endocannabinoid system in the human brain. Inhibitors of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), which are the enzymes responsible for the inactivation of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, respectively, may exert therapeutic effects without inducing the adverse side effects associated with direct cannabinoid CB1 receptor stimulation by THC. Here we review the FAAH and MAGL inhibitors that have reached clinical trials, discuss potential caveats, and provide an outlook on where the field is headed.

Microstructure analysis of the effects of the cannabinoid agents HU-210 and rimonabant in rats licking for sucrose

Stimulation of cannabinoid CB1 receptors generally increases ingestion. However, the non-selective cannabinoid receptor agonist HU-210 exerts the opposite effect. The first objective of this study was to investigate the role of CB1 receptors in this “atypical” effect. Studies on the endocannabinoid system investigating the microstructure of licking for palatable solutions reported inconsistent results as for the role of CB1 receptors in “liking” and “wanting”. The second objective was to deal with these inconsistencies investigating the within-session time-course of licking-burst number. The microstructure of licking for a 10% sucrose solution in 30-min sessions was analysed in two experiments. In Experiment 1, the effect of the CB1 receptor antagonist-inverse agonist rimonabant (0.5, 1 mg/kg) on HU-210 effect (100 μg/kg) was investigated. A dose range of HU-210 (25, 50, 100 μg/kg) was examined in Experiment 2. In Experiment 1, both HU-210 and rimonabant reduced licking due to reduced burst number. Moreover, HU-210 reduced the intra-burst lick rate, an index of motor competence. HU-210 effects were antagonised by rimonabant, and vice versa. Rimonabant decreased burst number late in the session at 0.5 mg/kg, and since the beginning of the session at 1 mg/kg. In Experiment 2, HU-210 failed to affect overall ingestion. These results suggest that HU-210 effect – when present – depends on CB1 receptor stimulation, possibly leading to impairment of the motor competence necessary for licking. The reduction of burst number late in the session observed with rimonabant 0.5 mg/kg, which resembles the effect of reward devaluation, might suggest reduced “liking”.

Δ9-THC and related cannabinoids suppress substance P- induced neurokinin NK1-receptor-mediated vomiting via activation of cannabinoid CB1 receptor

Δ9-THC suppresses cisplatin-induced vomiting through activation of cannabinoid CB1 receptors. Cisplatin-evoked emesis is predominantly due to release of serotonin and substance P (SP) in the gut and the brainstem which subsequently stimulate their corresponding 5-HT3-and neurokinin NK1-receptors to induce vomiting. Δ9-THC can inhibit vomiting caused either by the serotonin precursor 5-HTP, or the 5-HT3 receptor selective agonist, 2-methyserotonin. In the current study, we explored whether Δ9-THC and related CB1/CB2 receptor agonists (WIN55,212–2 and CP55,940) inhibit vomiting evoked by SP (50 mg/kg, i.p.) or the NK1 receptor selective agonist GR73632 (5 mg/kg, i.p.). Behavioral methods were employed to determine the antiemetic efficacy of cannabinoids in least shrews. Our results showed that administration of varying doses of Δ9-THC (i.p. or s.c.), WIN55,212–2 (i.p.), or CP55,940 (i.p.) caused significant suppression of SP-evoked vomiting in a dose-dependent manner. When tested against GR73632, Δ9-THC also dose-dependently reduced the evoked emesis. The antiemetic effect of Δ9-THC against SP-induced vomiting was prevented by low non-emetic doses of the CB1 receptor inverse-agonist/antagonist SR141716A (<10 mg/kg). We also found that the NK1 receptor antagonist netupitant can significantly suppress vomiting caused by a large emetic dose of SR141716A (20 mg/kg). In sum, Δ9-THC and related cannabinoids suppress vomiting evoked by the nonselective (SP) and selective (GR73632) neurokinin NK1 receptor agonists via stimulation of cannabinoid CB1 receptors.

Cannabinoidergic Regulation of the Functional State of the Heart. The Role of the Autonomic Nervous System

Cannabinoids have been shown to induce long-lasting hypotension and bradycardia, which can be preceded by transient tachycardia and hypertension associated with activation of vanilloid TRPV1 receptors. Prolonged hypotension and bradycardia are consequences of the stimulation of cannabinoid CB1 receptors. Endogenous cannabinoids are not involved in regulating heart rate or arterial blood pressure in intact animals. Cannabinoid-induced bradycardia results from the sympatholytic and vagotonic actions of cannabinoids. Prolonged hypotension results from cannabinoid-induced vasorelaxation. Activation of presynaptic CB1 receptors located on sympathetic terminals innervating the heart and arteries leads to inhibition of noradrenaline release from these terminals. Endogenous cannabinoids have cardioprotective effects in coronary occlusion, inhibiting sympathetic influences on the myocardium. Anandamide, which activates TRPV1 receptors, can induce the Bezold–Jarisch reflex. Stimulation of presynaptic CB1 receptors promotes reductions in CGRP (calcitonin gene-related peptide) release from the afferent terminals of the vagus nerve. Stimulation of vanilloid TRPV1 receptors, conversely, induces CGRP release from the sensory fibers of the vagus nerve. The brainstem nuclei may take part in the cardiovascular effects of cannabinoids seen on i.v. administration of CB agonists.

Antidote to cannabinoid intoxication: the CB1 receptor inverse agonist, AM251, reverses hypothermic effects of the CB1 receptor agonist, CB-13, in mice.

Cannabis is a recreational drug leading to intoxication, following stimulation of cannabinoid CB1 receptors. However, more recently, herbs mixed with synthetic cannabinoids sometimes known as 'Spice' and 'Black Mamba' have been increasingly used, and their high CB1 receptor affinity has led not only to marked intoxication but also life-threatening complications and an increasing number of deaths. Although many studies have indicated that prophylactic treatment with CB1 receptor antagonists can block cannabimimetic effects in animals and humans, the aim of this study was to determine whether CB1 receptor antagonism could reverse physical cannabimimetic effects. Cannabimimetic effects, measured by the hypothermic response following sedation and hypomotility, were induced by the synthetic CB1 receptor agonist CB-13 (1-naphthalenyl[4-(pentyloxy)-1-naphthalenyl]methanone) in Biozzi Antibody High mice. The CB1 receptor antagonist/inverse agonist AM251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) was administered 20 min after the injection of CB-13 and its effects on the cannabimimetic responses were assessed. In this study, the CNS-related cannabimimetic effects, as measured by the hypothermic effect, induced by the CB1 receptor agonist were therapeutically treated and were rapidly reversed by the CB1 receptor antagonist/inverse agonist. There was also a subjective reversal of visually evident sedation. Cannabinoid receptor antagonists have been widely used and so may provide an acceptable single-dose antidote to cannabinoid intoxication. This use may save human life, where the life-threatening effects are mediated by cannabinoid receptors and not off-target influences of the synthetic cannabinoids or non-cannabinoids within the recreational drug mixture.

Stimulation of cannabinoid CB1 receptors prevents nerve-mediated airway hyperreactivity in NGF-induced inflammation in mouse airways

Cannabinoids are known to inhibit neuronal activity and have significant immunomodulatory effects which suggest a role in inflammatory airway diseases. In the present study, we tested the hypothesis that cannabinoids have both acute and chronic modulatory effects on nerve-mediated contractions in NGF-induced airway inflammation. Contractions induced by electrical field stimulation (EFS) were examined in tracheal segments isolated from male BALB/c mice. Tissues were both used fresh or after four days of culture with NGF to induce airway inflammation, and further exposed to cannabinoid receptor agonists. In order to evaluate nerve density, tracheal segments were also examined by immunohistochemistry after in vitro treatments. The CB1 receptor agonists ACEA and ACPA inhibited the constant train EFS-induced contractions in both fresh and NGF-exposed tracheas, an effect that could be blocked by the CB1 receptor antagonist AM251. Culturing the tissues with NGF up-regulated the frequency-dependent EFS-contractions in isolated tracheas. This up-regulation could be inhibited by concomitant treatment with ACEA or ACPA. The treatment with NGF and/or ACEA did not affect the potency or the maximum response to carbachol. In histological sections, it was recognized that the enhanced effect induced by NGF was associated with an increase in nerve density, which, similarly, could be prevented by ACEA treatment. This study shows that stimulation of cannabinoid CB1 receptors modifies the increase of neuronal activity and density in NGF-induced airway inflammation and directly inhibits cholinergic contractions in the airways by a presynaptic mechanism. These findings indicate a protective role of CB1 receptors in airway inflammation.

Effect of nucleus accumbens shell 5-HT4 receptors on the impairment of ACPA-induced emotional memory consolidation in male Wistar rats.

The present study investigates the effects of 5-HT4 receptors of the nucleus accumbens (NAc) shell on the impairment of emotional memory consolidation induced by cannabinoid CB1 receptor stimulation. The elevated plus maze test-retest paradigm was used to assess memory in adult male Wistar rats. Intra-NAc shell administration of ACPA (selective cannabinoid CB1 receptor agonist 0.006 µg/rat) and RS23597 (5-HT4 receptor antagonist 0.01 µg/rat), immediately after training, decreased emotional memory consolidation, suggesting a drug-induced amnesia, whereas post-training intra-NAc shell microinjections of RS67333 (5-HT4 receptor agonist 0.016 µg/rat) increased emotional memory consolidation. Interestingly, RS67333 exerted a dual effect on ACPA-induced behaviors, potentiating and restoring amnesia caused by the subthreshold and effective doses of ACPA, respectively. However, neither RS23597 nor AM251 (CB1 receptor antagonist 30, 60 and 120 ng/rat) affected emotional memory consolidation. Nonetheless, a subthreshold dose of AM251 (120 ng/rat) reversed the amnesia induced by ACPA (0.006 µg/rat) and RS23597 (0.01 µg/rat). None of the above doses altered the locomotor activity. In conclusion, our results suggest that the NAc-shell 5-HT4 receptors are involved in the modulation of ACPA-induced amnesia.

CB1 receptor affects cortical plasticity and response to physiotherapy in multiple sclerosis.

Objectives:Therapeutic effects of physical therapy in neurologic disorders mostly rely on the promotion of use-dependent synaptic plasticity in damaged neuronal circuits. Genetic differences affecting the efficiency of synaptic plasticity mechanisms could explain why some patients do not respond adequately to the treatment. It is known that physical exercise activates the endocannabinoid system and that stimulation of cannabinoid CB1 receptors (CB1Rs) promotes synaptic plasticity in both rodents and humans. We thus tested whether CB1R genetic variants affect responsiveness to exercise therapy.Methods:We evaluated the effect of a genetic variant of the CB1R associated with reduced receptor expression (patients with long AAT trinucleotide short tandem repeats in the CNR1 gene) on long-term potentiation (LTP)–like cortical plasticity induced by transcranial magnetic theta burst stimulation (TBS) of the motor cortex and, in parallel, on clinical response to exercise therapy in patients with multiple sclerosis.Results:We found that patients with long AAT CNR1 repeats do not express TBS-induced LTP-like cortical plasticity and show poor clinical benefit after exercise therapy.Conclusions:Our results provide the first evidence that genetic differences within the CB1R may influence clinical responses to exercise therapy, and they strengthen the hypothesis that CB1Rs are involved in the regulation of synaptic plasticity and in the control of spasticity in humans. This information might be of great relevance for patient stratification and personalized rehabilitation treatment programs.

Complex interaction between anandamide and the nitrergic system in the dorsolateral periaqueductal gray to modulate anxiety-like behavior in rats

Stimulation of cannabinoid CB1 receptors or inhibition of nitric oxide synthase (NOS) in the dorsolateral periaqueductal gray (dlPAG) decreases anxiety-like behavior. Moreover, activation of CB1 receptors attenuates flight responses induced by nitric oxide (NO) donors in the dlPAG, suggesting that endocannabinoids and NO could interact to control defensive responses such as anxiety-like behavior. To test this hypothesis male Wistar rats received intra-dlPAG microinjections of anandamide (AEA) or NO inhibitors and were tested in the elevated plus maze (EPM). Combined administration of low and ineffective doses of AEA and the NO scavenger (c-Ptio), the nNOS inhibitor (NPA) or the soluble guanylate cyclase inhibitor (ODQ) induced anxiolytic-like effects. The CB1 receptor antagonist AM251, but not the GABAA receptor antagonist bicuculline, attenuated the effect induced by AEA + c-Ptio combination. No effect, however, was found when anxiolytic doses of these same drugs were administered together. Combination of higher, ineffective doses of AEA and c-Ptio, NPA or ODQ was again anxiolytic. The effect of the former combination was prevented by low and ineffective doses of the GABAA receptor antagonist bicuculline or the GABA synthesis inhibitor l-allilglycine, suggesting that they depend on GABAA-mediated neurotransmission. AM251 was also able to attenuate this effect, indicating that in the presence of NO inhibition, the resultant anxiolytic-like effect could be due to AEA action on CB1 receptors. The present results suggest that the AEA and nitrergic systems exert a complex functional interaction in the dlPAG to modulate anxiety behavior, probably interfering, in addition to glutamate, also with GABAergic mechanisms.

Phencyclidine-Induced Social Withdrawal Results from Deficient Stimulation of Cannabinoid CB1 Receptors: Implications for Schizophrenia

The neuronal mechanisms underlying social withdrawal, one of the core negative symptoms of schizophrenia, are not well understood. Recent studies suggest an involvement of the endocannabinoid system in the pathophysiology of schizophrenia and, in particular, of negative symptoms. We used biochemical, pharmacological, and behavioral approaches to investigate the role played by the endocannabinoid system in social withdrawal induced by sub-chronic administration of phencyclidine (PCP). Pharmacological enhancement of endocannabinoid levels via systemic administration of URB597, an inhibitor of endocannabinoid degradation, reversed social withdrawal in PCP-treated rats via stimulation of CB1 receptors, but reduced social interaction in control animals through activation of a cannabinoid/vanilloid-sensitive receptor. In addition, the potent CB agonist CP55,940 reversed PCP-induced social withdrawal in a CB₁-dependent manner, whereas pharmacological blockade of CB₁ receptors by either AM251 or SR141716 reduced the time spent in social interaction in control animals. PCP-induced social withdrawal was accompanied by a decrease of anandamide (AEA) levels in the amygdala and prefrontal cortex, and these deficits were reversed by URB597. As CB₁ receptors are predominantly expressed on GABAergic interneurons containing the anxiogenic peptide cholecystokinin (CCK), we also examined whether the PCP-induced social withdrawal resulted from deficient CB₁-mediated modulation of CCK transmission. The selective CCK2 antagonist LY225910 blocked both PCP- and AM251-induced social withdrawal, but not URB597 effect in control rats. Taken together, these findings indicate that AEA-mediated activation of CB₁ receptors is crucial for social interaction, and that PCP-induced social withdrawal results from deficient endocannabinoid transmission.

Stimulation of accumbens shell cannabinoid CB1 receptors by noladin ether, a putative endocannabinoid, modulates food intake and dietary selection in rats

Stimulation of cannabinoid CB1 receptors in nucleus accumbens shell has been shown to stimulate feeding and enhance positive ‘liking’ reactions to intraoral sucrose. This study examined the behavioural effects of noladin ether and 2-arachidonoylglycerol following infusion into accumbens shell, on chow intake and food preference in high-carbohydrate and high-fat preferring rats. Noladin ether, potently and dose-dependently stimulated chow intake as compared with 2-arachidonoylglycerol in free-feeding rats. In the diet preference paradigm, in which rats were given free access to both, high-carbohydrate (HC) and high-fat (HF) diets simultaneously, an intra-accumbens administration of noladin ether as well as 2-arachidonoylglycerol, preferentially enhanced fat consumption over carbohydrate in both HF- and HC-preferring rats. These effects were significantly attenuated by the CB1 receptor antagonist, AM 251. These results suggesting that, the endocannabinoids through CB1 receptors, affects appetite for specific dietary components. Both these agents exert a specific action on eating motivation and possibly promoting eating by enhancing the incentive value of food. Altogether these findings reinforce the idea that the endogenous cannabinoid system in the accumbens shell may be important to augment reward-driven feeding via modulation of CB1 receptor signalling pathways.

Cannabinoid receptor stimulation increases motivation for nicotine and nicotine seeking

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

Effects of caffeine on striatal neurotransmission: Focus on cannabinoid CB1 receptors

Caffeine is the most commonly self-administered psychoactive substance worldwide. At usual doses, the effects of caffeine on vigilance, attention, mood and arousal largely depend on the modulation of central adenosine receptors. The present review article describes the action of caffeine within the striatum, to provide a possible molecular mechanism at the basis of the psychomotor and reinforcing properties of this pharmacological agent. The striatum is in fact a subcortical area involved in sensorimotor, cognitive, and emotional processes, and recent experimental findings showed that chronic caffeine consumption enhances the sensitivity of striatal GABAergic synapses to the stimulation of cannabinoid CB1 receptors. The endocannabinoid system is involved in the psychoactive effects of many compounds, and adenosine A2A receptors (the main receptor target of caffeine) elicit a permissive effect towards CB1 receptors, thus suggesting that A2A-CB1 receptor interaction plays a major role in the generation and maintenance of caffeine reinforcing behavior. Aim of this review is to describe the effects of caffeine on striatal neurotransmission with special reference to the modulation of the endocannabinoid system.

Abnormal sensitivity of cannabinoid CB1 receptors in the striatum of mice with experimental amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that primarily affects motor neurons. However, additional neuronal systems are also involved, and the aim of this study was to investigate the involvement of the nucleus striatum. By means of neurophysiological recordings in slices, we have investigated both excitatory and inhibitory synaptic transmission in the striatum of G93A-SOD1 ALS mice, along with the sensitivity of these synapses to cannabinoid CB1 receptor stimulation. We have observed reduced frequency of glutamate-mediated spontaneous excitatory postsynaptic currents (EPSCs) and increased frequency of GABA-mediated spontaneous inhibitory postsynaptic currents (IPSCs) recorded from striatal neurons of ALS mice, possibly due to presynaptic defects in transmitter release. The sensitivity of cannabinoid CB1 receptors controlling both glutamate and GABA transmission was remarkably potentiated in ALS mice, indicating that adaptations of the endocannabinoid system might be involved in the pathophysiology of ALS. In conclusion, our data identify possible physiological correlates of striatal dysfunction in ALS mice, and suggest that cannabinoid CB1 receptors might be potential therapeutic targets for this dramatic disease.

Exercise attenuates the clinical, synaptic and dendritic abnormalities of experimental autoimmune encephalomyelitis

Voluntary exercise is beneficial in models of primarily neurodegenerative disorders. Whether exercise also affects inflammatory neurodegeneration is unknown. In the present study, we evaluated the clinical, synaptic and neuropathological effects of voluntary wheel running in mice with myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. Exercising EAE mice exhibited less severe neurological deficits compared to control EAE animals. The sensitivity of striatal GABA synapses to the stimulation of cannabinoid CB1 receptors was dramatically downregulated following EAE induction, and was rescued by exercise in EAE mice with access to a running wheel. Finally, we found that exercise was able to contrast dendritic spine loss induced by EAE in striatal neurons, although the degree of inflammatory response was similar in the two experimental groups. Our work suggests that life style and experiences can impact the clinical course of inflammatory neurodegenerative diseases by affecting their synaptic bases.

Caffeine drinking potentiates cannabinoid transmission in the striatum: Interaction with stress effects

Caffeine, the psychoactive ingredient of coffee and of many soft drinks, is frequently abused by humans especially during stressful live events. The endocannabinoid system is involved in the central effects of many psychoactive compounds and of stress. Whether caffeine alters the cannabinoid system and interferes with stress-induced synaptic alterations is however unknown. We have studied electrophysiologically the sensitivity of cannabinoid receptors modulating synaptic transmission in the striatum of mice exposed to caffeine in their drinking solution. Chronic caffeine assumption sensitized GABAergic synapses to the presynaptic effect of cannabinoid CB1 receptor stimulation by exo- and endocannabinoids. Caffeine was conversely unable to affect the sensitivity of cannabinoid receptors modulating glutamate transmission. The synaptic effects of caffeine were slowly reversible after its removal from the drinking solution. Furthermore, although exposure to caffeine for only 24 h did not produce measurable changes of the sensitivity of cannabinoid CB1 receptors, it was able to contrast the down-regulation of CB1 receptor-mediated responses after social defeat stress. Our data suggest that the cannabinoid system is implicated in the psychoactive properties of caffeine and in the ability of caffeine to reduce the pathological consequences of stress.

Cannabinoid CB1 receptor stimulation affords neuroprotection in MPTP-induced neurotoxicity by attenuating S100B up-regulation in vitro

In this study, we investigated the mechanism of S100B neurotoxicity and the effect of cannabinoids, in C6 cells treated with 1-methyl-4-phenyl 1,2,3,6 tetrahydropyridine (MPTP) and co-cultured with differentiated PC12 cells. MPTP concentration- and time-dependently increased S100B density in C6 cells. This effect was followed by increased C6 cell proliferation and decreased cell viability of co-cultured PC12 cells. An antibody against S100B, given to PC12 cells before co-culture, led to their survival. Treatment with arachidonyl-2-chloroethylamide, a CB1 agonist, significantly inhibited MPTP-induced S100B density in C6 cells and protected co-cultured PC12 cells from cell death. Because MPTP selectively increased the levels of anandamide in C6 cells, the involvement of the endocannabinoid system was investigated by using selective inhibitors of endocannabinoid inactivation (cellular re-uptake or enzymatic hydrolysis) and selective cannabinoid CB1 and CB2 receptor antagonists and by silencing the CB1 receptor. Our data suggest that selective activation of CB1 receptors by either exogenous or endogenous cannabinoids might afford neuroprotection in MPTP-induced neurotoxicity also by controlling S100B up-regulation in activated glial cells.

Chronic cocaine sensitizes striatal GABAergic synapses to the stimulation of cannabinoid CB1 receptors

Behavioural studies indicate that cannabinoid receptors are implicated in cocaine addiction. The synaptic underpinning of cocaine-cannabinoid receptor interaction is however, obscure. We have studied electrophysiologically the sensitivity of cannabinoid receptors modulating synaptic transmission in the striatum of rats exposed to cocaine. One-day treatment with cocaine did not modify the synaptic response to HU210, a cannabinoid CB1 receptor agonist. Seven days cocaine-treatment, conversely, caused conditioned place preference, and sensitized striatal GABAergic synapses to the presynaptic effect of cannabinoid CB1 receptor stimulation. The cannabinoid receptor-induced modulation of glutamate transmission was unaltered by cocaine. Furthermore, the effects of chronic cocaine on cannabinoid-mediated regulation of striatal GABA synapses were attenuated one week after the discontinuation of cocaine, and absent two weeks later, indicating the progressive reversibility of the adaptations of cannabinoid system during abstinence of drug consumption. Our data support the concept that modulation of cannabinoid receptors might be useful against drug abuse.