Cannabinoid Type 1 Antagonist Research Articles

Interrelated involvement of the endocannabinoid/endovanilloid (TRPV1) systems and epigenetic processes in anxiety- and working memory impairment-related behavioural effects of nicotine as a stressor.

The addictive use of nicotine contained in tobacco is associated with stressor-like emotional and cognitive effects such as anxiety and working memory impairment, and the involvement of epigenetic mechanisms such as histone acetylation has recently been reported. Although the precise nature of behavioural plasticity remains unclear, both anxiogenic- and working memory impairment-like effects were observed in the present experimental model of mice treated with repeated subcutaneous nicotine and/or immobilization stress, and these effects were commonly attenuated by the histone deacetylase (HDAC) inhibitors that induce histone acetylation. Such HDAC inhibitor-induced resilience was mimicked by ligands for the endocannabinoid (ECB) system, a neurotransmitter system that is closely associated with nicotine-induced addiction-related behaviours: the anxiogenic-like effects were mitigated by the cannabinoid type 1 (CB1) agonist arachidonylcyclopropylamide (ACPA), whereas the working memory impairment-like effects were mitigated by the CB1 antagonist SR 141716A. Moreover, the effects of the HDAC inhibitors were also mimicked by ligands for the endovanilloid (transient receptor potential vanilloid 1 [TRPV1]) system, a system that shares common characteristics with the ECB system: the anxiogenic-like effects were mitigated by the TRPV1 antagonist capsazepine, whereas the working memory impairment-like effects were mitigated by the TRPV1 agonist olvanil. Notably, the HDAC inhibitor-induced anxiolytic-like effects were attenuated by SR 141716A, which were further counteracted by capsazepine, whereas the working memory improvement-like effects were attenuated by capsazepine, which were further counteracted by SR 141716A. These results suggest the contribution of interrelated control of the ECB/TRPV1 systems and epigenetic processes such as histone acetylation to novel therapeutic approaches.

Experimental and computational studies of 1,5-diphenyl-pyrazole-3-carboxamide compounds as potential Cannabinoid receptor type 1

Cannabinoid type 1 (CB1) receptors play an important role in the pathophysiology of many diseases because of their regulatory roles in the central nervous system and peripheral organs. In this study, firstly, four new pyrazole-3-carboxamide derivatives with a structure similar to that of Rimonabant were synthesized. These compounds were identified by IR, 1H NMR, 13C NMR, HRMS and XRD analysis. Then, theoretical studies were carried out for the synthesized compounds. The electrophilic and nucleophilic attack sites of the four compounds were comprehensibly determined and evaluated using theoretical MEP analysis applied to the optimized structures. Additionally, the possible hydrogen bondings within the crystal structure were investigated by Hirsfeld surface analysis. Later, the theoretical best binding affinities of newly synthesized target compounds including thiazole (3a and 3c) and thiadiazole (3b and 3d) four molecules with four different targets such as 5TGZ (CB1 antagonist), 5ZTY (CB2), 1MMB (batimastat) and 4YXD (succinate dehydrogenase) proteins were performed using molecular docking simulations with AutoDockVina program in this report. Lastly, drug-likeness, ADME properties and the evaluation of toxicity parameters of newly synthesized molecules using smile codes were performed in detail. The findings revealed that the studied molecules may show potential bioactivity, especially as CB1 antagonists.

Mu-opioid and CB1 cannabinoid receptors of the dorsal periaqueductal gray interplay in the regulation of fear response, but not antinociception

Evidence indicates that periaqueductal gray matter (PAG) plays an important role in defensive responses and pain control. The activation of cannabinoid type-1 (CB1) or mu-opioid (MOR) receptors in the dorsal region of this structure (dPAG) inhibits fear and facilitates antinociception induced by different aversive stimuli. However, it is still unknown whether these two receptors work cooperatively in order to achieve these inhibitory actions. This study investigated the involvement and a likely interplay between CB1 and MOR receptors localized into the dPAG on the regulation of fear-like defensive responses and antinociception (evaluated in tail-flick test) evoked by dPAG chemical stimulation with N-methyl-d-aspartate (NMDA). Before the administration of NMDA, animals were first intra-dPAG injected with the CB1 agonist ACEA (0.5 pmol), or with the MOR agonist DAMGO (0.5 pmol) in combination with the respective antagonists AM251 (CB1 antagonist, 100 pmol) or CTOP (MOR antagonist, 1 nmol). To investigate the interplay between these receptors, microinjection of CTOP was combined with ACEA, or microinjection of AM251 was combined with DAMGO. Our results showed that both the intra-PAG treatments with ACEA or DAMGO inhibited NMDA-induced freezing expression, whereas only the treatment with DAMGO increased antinociception induced with NMDA, which are completely blocked by its respective antagonists. Interestingly, the inhibitory effects of ACEA or DAMGO on freezing was blocked by CTOP and AM251, respectively, indicating a functional interaction between these two receptors in the mediation of defensive behaviors. However, this cooperative interaction was not observed during the NMDA-induced antinociception. Our findings indicate that there is a cooperative action between the MOR and CB1 receptors within the dPAG and it is involved in the mediation of NMDA-induced defensive responses. Additionally, the MORs into the dPAG are involved in the modulation of the antinociceptive effects that follow a fear-like defense-reaction induced by dPAG chemical stimulation with NMDA.

2-Linoleoylglycerol Is a Partial Agonist of the Human Cannabinoid Type 1 Receptor that Can Suppress 2-Arachidonolyglycerol and Anandamide Activity.

Introduction: The cannabinoid type 1 (CB1) receptor and cannabinoid type 2 (CB2) receptor are widely expressed in the body and anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are their best characterized endogenous ligands. The diacylglycerol lipases (diacylglycerol lipase alpha and diacylglycerol lipase beta) not only synthesize essentially all the 2-AG in the body but also generate other monoacylglycerols, including 2-linoleoylglycerol (2-LG). This lipid has been proposed to modulate endocannabinoid (eCB) signaling by protecting 2-AG from hydrolysis. However, more recently, 2-LG has been reported to be a CB1 antagonist. Methods: The effect of 2-LG on the human CB1 receptor activity was evaluated in vitro using a cell-based reporter assay that couples CB1 receptor activation to the expression of the β-lactamase enzyme. Receptor activity can then be measured by a β-lactamase enzymatic assay. Results: When benchmarked against 2-AG, AEA, and arachidonoyl-2'-chloroethylamide (a synthetic CB1 agonist), 2-LG functions as a partial agonist at the CB1 receptor. The 2-LG response was potentiated by JZL195, a drug that inhibits the hydrolysis of monoacylglycerols. The 2-LG response was also fully inhibited by the synthetic CB1 antagonist AM251 and by the natural plant derived antagonist cannabidiol. 2-LG did not potentiate, and only blunted, the activity of 2-AG and AEA. Conclusions: These results support the hypothesis that 2-LG is a partial agonist at the human CB1 receptor and capable of modulating the activity of the established eCBs.

The Roles of Anandamide, Fatty Acid Amide Hydrolase, and Leukemia Inhibitory Factor on the Endometrium during the Implantation Window.

We investigated the role of the endocannabinoid system (ECS) in the endometrium of unexplained infertility (UI) patients, and effect of anandamide (AEA) on leukemia inhibitory factor (LIF). Patients were divided into UI and control groups. Endometrium samples were collected at the midluteal phase. Levels of cannabinoid type 1 (CB1), fatty acid amide hydrolase (FAAH), and LIF were examined. LIF productions were measured after AEA, CB1 antagonist AM251, and CB2 antagonist AM630 stimulation. Rates of available embryo, successful implantation and pregnancy, and the endometrial thickness of UI group were significantly lower than control, suggesting uterine receptivity was decreased in UI group. FAAH and LIF levels were significantly decreased, whereas endometrial CB1 was slightly increased in UI group. LIF production was promoted by low amount of AEA administration (1-10 μM), while the promotion was reduced by higher concentration of AEA (50 μM). LIF levels were decreased by AM251 or AM630, compared with AEA alone. Expressions of FAAH and LIF were closely associated with uterus receptivity and implantation rate of UI patients. Different concentrations of AEA could stimulate dynamic changes in LIF production. Our data indicated the important role of the ECS in human fertility, which may promote new strategies for successful implantation and treatments for reproductive diseases.

Blockade of Cannabinoid CB1 Receptors in the Dorsal Periaqueductal Gray Unmasks the Antinociceptive Effect of Local Injections of Anandamide in Mice.

Divergent results in pain management account for the growing number of studies aiming at elucidating the pharmacology of the endocannabinoid/endovanilloid anandamide (AEA) within several pain-related brain structures. For instance, the stimulation of both Transient Receptor Potential Vanilloid type 1 (TRPV1) and Cannabinoid type 1 (CB1) receptors led to paradoxical effects on nociception. Here, we attempted to propose a clear and reproducible methodology to achieve the antinociceptive effect of exogenous AEA within the dorsal periaqueductal gray (dPAG) of mice exposed to the tail-flick test. Accordingly, male Swiss mice received intra-dPAG injection of AEA (CB1/TRPV1 agonist), capsaicin (TRPV1 agonist), WIN (CB1 agonist), AM251 (CB1 antagonist), and 6-iodonordihydrocapsaicin (6-IODO) (TRPV1 selective antagonist) and their nociceptive response was assessed with the tail-flick test. In order to assess AEA effects on nociception specifically at vanilloid or cannabinoid (CB) substrates into the dPAG, mice underwent an intrinsically inactive dose of AM251 or 6-IODO followed by local AEA injections and were subjected to the same test. While intra-dPAG AEA did not change acute pain, local injections of capsaicin or WIN induced a marked TRPV1- and CB1-dependent antinociceptive effect, respectively. Regarding the role of AEA specifically at CB/vanilloid substrates, while the blockade of TRPV1 did not change the lack of effects of intra-dPAG AEA on nociception, local pre-treatment of AM251, a CB1 antagonist, led to a clear AEA-induced antinociception. It seems that the exogenous AEA-induced antinociception is unmasked when it selectively binds to vanilloid substrates, which might be useful to address acute pain in basic and perhaps clinical trials.

Effects of Cannabinoid Agonists and Antagonists on Sleep and Breathing in Sprague-Dawley Rats

There are no pharmacological treatments for obstructive sleep apnea syndrome, but dronabinol showed promise in a small pilot study. In anesthetized rats, dronabinol attenuates reflex apnea via activation of cannabinoid (CB) receptors located on vagal afferents; an effect blocked by cannabinoid type 1 (CB1) and/or type 2 (CB2) receptor antagonists. Here, using a natural model of central sleep apnea, we examine the effects of dronabinol, alone and in combination with selective antagonists in conscious rats chronically instrumented to stage sleep and measure cessation of breathing. Adult male Sprague-Dawley rats were anesthetized and implanted with bilateral stainless steel screws into the skull for electroencephalogram recording and bilateral wire electrodes into the nuchal muscles for electromyogram recording. Each animal was recorded by polysomnography on multiple occasions separated by at least 3 days. The study was a fully nested, repeated measures crossover design, such that each rat was recorded following each of 8 intraperitoneal injections: vehicle; vehicle and CB1 antagonist (AM 251); vehicle and CB2 antagonist (AM 630); vehicle and CB1/CB2 antagonist; dronabinol; dronabinol and CB1 antagonist; dronabinol and CB2 antagonist; and dronabinol and CB1/CB2 antagonist. Dronabinol decreased the percent time spent in rapid eye movement (REM) sleep. CB receptor antagonists did not reverse this effect. Dronabinol also decreased apneas during sleep, and this apnea suppression was reversed by CB1 or CB1/CB2 receptor antagonism. Dronabinol's effects on apneas were dependent on CB1 receptor activation, while dronabinol's effects on REM sleep were CB receptor-independent.

Involvement of CB1 and TRPV1 receptors located in the ventral medial prefrontal cortex in the modulation of stress coping behavior

Cannabinoid type-1 (CB1) and transient receptor potential vanilloid type-1 (TRPV1) receptors may have opposite roles in modulating neural activity and, consequently, in regulating the stress response. These receptors are widely expressed in several brain structures, including the ventral medial prefrontal cortex (vmPFC). The functional consequences of the interaction between CB1 and TRPV1, however, have scarcely been explored. Therefore, we investigated if CB1 and TRPV1 receptors located in the vmPFC would be involved in the behavioral changes induced by the stress of the forced swim test (FST). Rats with cannulae implanted into the vmPFC were given the dual blocker of TRPV1 receptors and fatty acid amide hydrolase (FAAH), Arachidonyl serotonin (AA-5HT, 0.125/0.25/0.5nmol), TRPV1 antagonist, SB366791 (0.5/1/10nmol), FAAH inhibitor, URB597 (0.001/0.01/0.1/1nmol), or vehicle and were submitted to the FST, or to the open-field test. Another group received intra-vmPFC injection of SB366791 or vehicle, followed by a second injection of URB597 or vehicle, and was submitted to the FST. Lastly, a group received intra-vmPFC injection of a CB1 antagonist, in sub-effective dose or vehicle, followed by AA-5HT, SB366791 or vehicle. The results showed that AA-5HT, SB366791 and URB597 significantly reduced the immobility time without changing the locomotor activity. Furthermore, the co-administration of URB597 and SB366791 in sub-effective doses induced an antidepressant-like effect in the FST. Additionally, the antidepressant-like effect of AA-5HT was prevented by the CB1 antagonist. Together, these results suggest that both, CB1 and TRPV1 receptors located in the vmPFC are involved in the behavioral responses to stress, although in opposite ways.

Putative Epigenetic Involvement of the Endocannabinoid System in Anxiety- and Depression-Related Behaviors Caused by Nicotine as a Stressor.

Like various stressors, the addictive use of nicotine (NC) is associated with emotional symptoms such as anxiety and depression, although the underlying mechanisms have not yet been fully elucidated due to the complicated involvement of target neurotransmitter systems. In the elicitation of these emotional symptoms, the fundamental involvement of epigenetic mechanisms such as histone acetylation has recently been suggested. Furthermore, among the interacting neurotransmitter systems implicated in the effects of NC and stressors, the endocannabinoid (ECB) system is considered to contribute indispensably to anxiety and depression. In the present study, the epigenetic involvement of histone acetylation induced by histone deacetylase (HDAC) inhibitors was investigated in anxiety- and depression-related behavioral alterations caused by NC and/or immobilization stress (IM). Moreover, based on the contributing roles of the ECB system, the interacting influence of ECB ligands on the effects of HDAC inhibitors was evaluated in order to examine epigenetic therapeutic interventions. Anxiety-like (elevated plus-maze test) and depression-like (forced swimming test) behaviors, which were observed in mice treated with repeated (4 days) NC (subcutaneous 0.8 mg/kg) and/or IM (10 min), were blocked by the HDAC inhibitors sodium butyrate (SB) and valproic acid (VA). The cannabinoid type 1 (CB1) agonist ACPA (arachidonylcyclopropylamide; AC) also antagonized these behaviors. Conversely, the CB1 antagonist SR 141716A (SR), which counteracted the effects of AC, attenuated the anxiolytic-like effects of the HDAC inhibitors commonly in the NC and/or IM groups. SR also attenuated the antidepressant-like effects of the HDAC inhibitors, most notably in the IM group. From these results, the combined involvement of histone acetylation and ECB system was shown in anxiety- and depression-related behaviors. In the NC treatment groups, the limited influence of SR against the HDAC inhibitor-induced antidepressant-like effects may reflect the characteristic involvement of histone acetylation within the NC-related neurotransmitter systems other than the ECB system.

Dorsolateral periaqueductal gray matter CB1 and TRPV1 receptors exert opposite modulation on expression of contextual fear conditioning

Cannabinoid type 1 (CB1) and Transient Potential Vanilloid type 1 (TRPV1) receptors in the dorsolateral periaqueductal gray (dlPAG) matter are involved in the modulation of conditioned response. Both CB1 and TRPV1 receptors are related to glutamate release and nitric oxide (NO) synthesis. It was previously demonstrated that both NMDA glutamate receptors and NO are involved in the conditioned emotional response. Therefore, one aim of this work was to verify whether dlPAG CB1 and TRPV1 receptors modulate the expression of contextual conditioned emotional response. Moreover, we also investigated the involvement of NMDA receptors and the NO pathway in this response. Male Wistar rats with local dlPAG guide cannula were submitted to contextual fear conditioning. Following 24 h, a polyethylene catheter was implanted in the femoral artery for cardiovascular recordings. After an additional 24 h, drugs were administered in the dlPAG and freezing behavior and autonomic responses were recorded during chamber re-exposure. Both a CB1 antagonist (AM251) and a TRPV1 agonist (Capsaicin; CPS) increased the expression of a conditioned emotional response. This response was prevented by an NMDA antagonist, a preferential neuronal NO synthase inhibitor, an NO scavenger and a soluble guanylate cyclase inhibitor (sGC). Furthermore, pretreatment with a TRPV1 antagonist also prevented the increased conditioned emotional response induced by AM251. Considering that GABA can counterbalance glutamate effects, we also investigated whether GABAA receptors were involved in the effect of a higher dose of AM251. Pretreatment with a GABAA receptor antagonist caused an increased conditioned emotional response by AM251. Our results support the possibility that dlPAG CB1 and TRPV1 receptors are involved in the expression of conditioned emotional response through the NMDA/NO/sGC pathway. Moreover, the opposite effects exerted by GABA and glutamate could produce different outcomes of drugs modulating eCBs.

Spinal neuronal cannabinoid receptors mediate urodynamic effects of systemic fatty acid amide hydrolase (FAAH) inhibition in rats.

To test if urodynamic effects from systemic Fatty Acid Amide Hydrolase (FAAH) inhibition involve sacral spinal cannabinoid type 1 (CB1) or type 2 (CB2) receptors. Male rats with or without partial urethral obstruction were used for cystometry or immunohistochemistry. Urodynamic effects of intravenous (IV) 0.3 mg/kg Oleoyl Ethyl Amide (OEtA; FAAH inhibitor), and intrathecal (IT) 5 μg rimonabant (CB1 antagonist) or 5 μg SR144528 (CB2 antagonist) were studied in awake rats. After administration of rimonabant or SR144528, non-obstructed rats with normal bladder function developed bladder overactivity (BO), which was counteracted by OEtA. OEtA also counteracted BO in obstructed rats. SR144528 did not affect bladder function in obstructed rats but counteracted the urodynamic effects of OEtA. Surprisingly, rimonabant (and AM251, another CB1 antagonist) reduced BO in obstructed rats, whereafter OEtA produced no additional urodynamic effects. CB1 expression increased in the sacral spinal cord of obstructed rats whereas no changes were observed for CB2 or FAAH. Urodynamic effects of systemic FAAH inhibition involve activities at spinal neuronal CB1 and CB2 receptors in normal and obstructed rats. Endogenous spinal CB receptor ligands seem to regulate normal micturition and BO. Altered spinal CB receptor functions may be involved in the pathogenesis of obstruction-induced BO. Neurourol. Urodynam. 35:464-470, 2016. © 2015 Wiley Periodicals, Inc.

CB1 receptor signaling regulates social anxiety and memory

The endocannabinoid (eCB) system regulates emotion, stress, memory and cognition through the cannabinoid type 1 (CB1 ) receptor. To test the role of CB1 signaling in social anxiety and memory, we utilized a genetic knockout (KO) and a pharmacological approach. Specifically, we assessed the effects of a constitutive KO of CB1 receptors (CB1 KOs) and systemic administration of a CB1 antagonist (AM251; 5 mg/kg) on social anxiety in a social investigation paradigm and social memory in a social discrimination test. Results showed that when compared with wild-type (WT) and vehicle-treated animals, CB1 KOs and WT animals that received an acute dose of AM251 displayed anxiety-like behaviors toward a novel male conspecific. When compared with WT animals, KOs showed both active and passive defensive coping behaviors, i.e. elevated avoidance, freezing and risk-assessment behaviors, all consistent with an anxiety-like profile. Animals that received acute doses of AM251 also showed an anxiety-like profile when compared with vehicle-treated animals, yet did not show an active coping strategy, i.e. changes in risk-assessment behaviors. In the social discrimination test, CB1 KOs and animals that received the CB1 antagonist showed enhanced levels of social memory relative to their respective controls. These results clearly implicate CB1 receptors in the regulation of social anxiety, memory and arousal. The elevated arousal/anxiety resulting from either total CB1 deletion or an acute CB1 blockade may promote enhanced social discrimination/memory. These findings may emphasize the role of the eCB system in anxiety and memory to affect social behavior.

The cannabinoid Δ9-tetrahydrocannabivarin (THCV) ameliorates insulin sensitivity in two mouse models of obesity

Background:Cannabinoid type-1 (CB1) receptor inverse agonists improve type 2 diabetes and dyslipidaemia but were discontinued due to adverse psychiatric effects. Δ9-Tetrahydrocannabivarin (THCV) is a neutral CB1 antagonist producing hypophagia and body weight reduction in lean mice. We investigated its effects in dietary-induced (DIO) and genetically (ob/ob) obese mice.Methods:We performed two dose-ranging studies in DIO mice; study 1: 0.3, 1, 2.5, 5 and 12.5 mg kg−1, oral twice daily for 30 days and study 2: 0.1, 0.5, 2.5 and 12.5 mg kg−1, oral, once daily for 45 days. One pilot (study 3: 0.3 and 3 mg kg−1, oral, once daily) and one full dose-ranging (study 4: 0.1, 0.5, 2.5 and 12.5 mg kg−1, oral, once daily) studies in ob/ob mice for 30 days. The CB1 inverse agonist, AM251, oral, 10 mg kg−1 once daily or 5 mg kg−1 twice daily was used as the positive control. Cumulative food and water intake, body weight gain, energy expenditure, glucose and insulin levels (fasting or during oral glucose tolerance tests), plasma high-density lipoprotein and total cholesterol, and liver triglycerides were measured. HL-5 hepatocytes or C2C12 myotubes made insulin-resistant with chronic insulin or palmitic acid were treated with 0, 1, 3 and 10 μℳ THCV or AM251.Results:THCV did not significantly affect food intake or body weight gain in any of the studies, but produced an early and transient increase in energy expenditure. It dose-dependently reduced glucose intolerance in ob/ob mice and improved glucose tolerance and increased insulin sensitivity in DIO mice, without consistently affecting plasma lipids. THCV also restored insulin signalling in insulin-resistant hepatocytes and myotubes.Conclusions:THCV is a new potential treatment against obesity-associated glucose intolerance with pharmacology different from that of CB1 inverse agonists/antagonists.

Role of TRPV1 receptors on panic-like behaviors mediated by the dorsolateral periaqueductal gray in rats

The transient receptors potential vanilloid type 1 channels (TRPV1) are expressed in several brain regions related to defensive behaviors, including the dorsolateral periaqueductal gray (dlPAG). The endocannabinoid anandamide, in addition to its agonist activity at cannabinoid type 1 (CB1), is also proposed as an endogenous agonist of these receptors, through which it could facilitate anxiety-like responses. The aim of this work was to test the hypothesis that TRPV1 in the dlPAG of rats would mediate panic-like responses in two models, namely the escape responses induced by chemical stimulation of this structure or by exposure to the elevated T-Maze (ETM). Antagonism of TRPV1 with capsazepine injected into the dlPAG reduced the defense response induced by local NMDA-injection, suggesting an anti-aversive effect. In the ETM, capsazepine inhibited escape response, suggesting a panicolytic-like effect. Interestingly, this effect was prevented by a CB1 antagonist (AM251). The present study showed that antagonism of TRPV1 in the dlPAG induces panicolytic-like effects, which can be prevented by a CB1 antagonist. Therefore, these antiaversive effects of TRPV1 blockade may ultimately occur due to a predominant action of anandamide through CB1 receptors.

Nicotine reinforcement is reduced by cannabinoid CB1 receptor blockade in the ventral tegmental area

Cannabinoid type 1 (CB1) receptors control the motivational properties and reinforcing effects of nicotine. Indeed, peripheral administration of a CB1 receptor antagonist dramatically decreases both nicotine taking and seeking. However, the neural substrates through which the cannabinoid CB1 receptors regulate the voluntary intake of nicotine remain to be elucidated. In the present study, we sought to determine whether central injections of a CB1 receptor antagonist delivered either into the ventral tegmental area (VTA) or the nucleus accumbens (NAC) may alter nicotine intravenous self-administration (IVSA). Rats were first trained to self-administer nicotine (30 μg/kg/0.1 ml). The effect of central infusions of the CB1 antagonist AM 251 (0, 1 and 10 μg/0.5 μl/side) on nicotine-taking behavior was then tested. Intra-VTA infusions of AM 251 dose dependently reduced IVSA with a significant decrease for the dose 10 μg/0.5 μl/side. Moreover, operant responding for water was unaltered by intra-VTA AM 251 at the same dose. Surprisingly, intra-NAC delivery of AM 251 did not alter nicotine behavior at all. These data suggest that in rats chronically exposed to nicotine IVSA, the cannabinoid CB1 receptors located in the VTA rather than in the NAC specifically control nicotine reinforcement and, subsequently, nicotine-taking behavior.

Differential effects of TRPV1 receptor ligands against nicotine-induced depression-like behaviors

BackgroundThe contributions of brain cannabinoid (CB) receptors, typically CB1 (CB type 1) receptors, to the behavioral effects of nicotine (NC) have been reported to involve brain transient receptor potential vanilloid 1 (TRPV1) receptors, and the activation of candidate endogenous TRPV1 ligands is expected to be therapeutically effective. In the present study, the effects of TRPV1 ligands with or without affinity for CB1 receptors were examined on NC-induced depression-like behavioral alterations in a mouse model in order to elucidate the "antidepressant-like" contributions of TRPV1 receptors against the NC-induced "depression" observed in various types of tobacco abuse.ResultsRepeated subcutaneous NC treatments (NC group: 0.3 mg/kg, 4 days), like repeated immobilization stress (IM) (IM group: 10 min, 4 days), caused depression-like behavioral alterations in both the forced swimming (reduced swimming behaviors) and the tail suspension (increased immobility times) tests, at the 2 h time point after the last treatment. In both NC and IM groups, the TRPV1 agonists capsaicin (CP) and olvanil (OL) administered intraperitoneally provided significant antidepressant-like attenuation against these behavioral alterations, whereas the TRPV1 antagonist capsazepine (CZ) did not attenuate any depression-like behaviors. Furthermore, the endogenous TRPV1-agonistic CB1 agonists anandamide (AEA) and N-arachidonyldopamine (NADA) did not have any antidepressant-like effects. Nevertheless, a synthetic "hybrid" agonist of CB1 and TRPV1 receptors, arvanil (AR), caused significant antidepressant-like effects. The antidepressant-like effects of CP and OL were antagonized by the TRPV1 antagonist CZ. However, the antidepressant-like effects of AR were not antagonized by either CZ or the CB1 antagonist AM 251 (AM).ConclusionsThe antidepressant-like effects of TRPV1 agonists shown in the present study suggest a characteristic involvement of TRPV1 receptors in NC-induced depression-like behaviors, similar to those caused by IM. The strong antidepressant-like effects of the potent TRPV1 plus CB1 agonist AR, which has been reported to cause part of its TRPV1-mimetic and cannabimimetic effects presumably via non-TRPV1 or non-CB1 mechanisms support a contribution from other sites of action which may play a therapeutically important role in the treatment of NC abuse.

P.1.d.012 Role of the endocannabinoid system and vanilloid TRPV1 channels in the phenotype of dopamine D3 receptor knock-out mice

Cannabinoid type-1 (CB1) and transient receptor potential vanilloid type-1 (TRPV1) receptors may have opposite roles in modulating neural activity and, consequently, in regulating the stress response. These receptors are widely expressed in several brain structures, including the ventral medial prefrontal cortex (vmPFC). The functional consequences of the interaction between CB1 and TRPV1, however, have scarcely been explored. Therefore, we investigated if CB1 and TRPV1 receptors located in the vmPFC would be involved in the behavioral changes induced by the stress of the forced swim test (FST). Rats with cannulae implanted into the vmPFC were given the dual blocker of TRPV1 receptors and fatty acid amide hydrolase (FAAH), Arachidonyl serotonin (AA-5HT, 0.125/0.25/0.5 nmol), TRPV1 antagonist, SB366791 (0.5/1/10 nmol), FAAH inhibitor, URB597 (0.001/0.01/0.1/1 nmol), or vehicle and were submitted to the FST, or to the open-field test. Another group received intra-vmPFC injection of SB366791 or vehicle, followed by a second injection of URB597 or vehicle, and was submitted to the FST. Lastly, a group received intra-vmPFC injection of a CB1 antagonist, in sub-effective dose or vehicle, followed by AA-5HT, SB366791 or vehicle. The results showed that AA-5HT, SB366791 and URB597 significantly reduced the immobility time without changing the locomotor activity. Furthermore, the co-administration of URB597 and SB366791 in sub-effective doses induced an antidepressant-like effect in the FST. Additionally, the antidepressant-like effect of AA-5HT was prevented by the CB1 antagonist. Together, these results suggest that both, CB1 and TRPV1 receptors located in the vmPFC are involved in the behavioral responses to stress, although in opposite ways.

P.4.b.004 Stimulation of the lateral habenula inhibits a panic-like behaviour by activation of serotonin-1A receptors in the rat dorsal periaqueductal gray

The transient receptors potential vanilloid type 1 channels (TRPV1) are expressed in several brain regions related to defensive behaviors, including the dorsolateral periaqueductal gray (dlPAG). The endocannabinoid anandamide, in addition to its agonist activity at cannabinoid type 1 (CB1), is also proposed as an endogenous agonist of these receptors, through which it could facilitate anxiety-like responses. The aim of this work was to test the hypothesis that TRPV1 in the dlPAG of rats would mediate panic-like responses in two models, namely the escape responses induced by chemical stimulation of this structure or by exposure to the elevated T-Maze (ETM). Antagonism of TRPV1 with capsazepine injected into the dlPAG reduced the defense response induced by local NMDA-injection, suggesting an anti-aversive effect. In the ETM, capsazepine inhibited escape response, suggesting a panicolytic-like effect. Interestingly, this effect was prevented by a CB1 antagonist (AM251). The present study showed that antagonism of TRPV1 in the dlPAG induces panicolytic-like effects, which can be prevented by a CB1 antagonist. Therefore, these antiaversive effects of TRPV1 blockade may ultimately occur due to a predominant action of anandamide through CB1 receptors.

Tilting the Balance

Cortical function depends on the proper balance between excitation and inhibition: If the balance tilts toward excitation, a seizure may occur, whereas if the balance shifts too far toward inhibition, network activity may shut down. GABA (γ-aminobutyric acid) is the major inhibitory transmitter in the adult brain; however, GABA is excitatory during early development, leading Bernard et al. to investigate the possible inhibitory role of endocannabinoids in regulating network activity in the developing brain. After using immunocytochemistry to localize cannabinoid type 1 (CB1) receptors to the terminals of hippocampal GABAergic interneurons, the authors combined electrophysiology with pharmacological analysis to show that endocannabinoids released from pyramidal cells and interneurons in rat pup hippocampal slices could act through CB1 receptors to inhibit GABA release. Pharmacological analysis in the presence of glutamate antagonists indicated that CB1 receptors were tonically activated in hippocampal slices and that CB1 blockade enhanced the amplitude of spontaneous GABAergic postsynaptic currents and stimulated the appearance of spontaneous epileptiform discharges, whereas endocannabinoid accumulation decreased the spontaneous firing rate of interneurons. In the absence of glutamatergic antagonists, CB1 blockade stimulated network activity and CB1 stimulation inhibited network activity. A CB1 antagonist triggered epileptic discharges in 5-day-old rat pups in vivo, whereas pharmacological activation of CB1 receptors decreased spontaneous neuronal activity. Thus, the authors conclude that endocannabinoid signaling acts to regulate network activity in the developing brain and that its disruption could have major functional consequences. C. Bernard, M. Milh, Y. M. Morozov, Y. Ben-Ari, T. F. Freund, H. Gozlan, Altering cannabinoid signaling during development disrupts neuronal activity. Proc. Natl. Acad. Sci. U.S.A. 102 , 9388-9393 (2005). [Abstract] [Full Text]