Vanilloid VR1 receptor is involved in rimonabant-induced neuroprotection

Expression of the Transient Receptor Potential Vanilloid 1 ion channel in the supramammillary nucleus and the antidepressant effects of its antagonist AMG9810 in mice

The Transient Receptor Potential Vanilloid 1 (TRPV1) non-selective cation channel predominantly expressed in primary sensory neurons of the dorsal root and trigeminal ganglia mediates pain and neurogenic inflammation. TRPV1 mRNA and immunoreactivity were described in the central nervous system (CNS), but its precise expression pattern and function have not been clarified. Here we investigated Trpv1 mRNA expression in the mouse brain using ultrasensitive RNAScope in situ hybridization. The role of TRPV1 in anxiety, depression-like behaviors and memory functions was investigated by TRPV1-deficient mice and pharmacological antagonism by AMG9810. Trpv1 mRNA is selectively expressed in the supramammillary nucleus (SuM) co-localized with Vglut2 mRNA, but not with tyrosine hydroxylase immunopositivity demonstrating its presence in glutamatergic, but not dopaminergic neurons. TRPV1-deleted mice exhibited significantly reduced anxiety in the Light-Dark box and depression-like behaviors in the Forced Swim Test, but their performance in the Elevated Plus Maze as well as their spontaneous locomotor activity, memory and learning function in the Radial Arm Maze, Y-maze and Novel Object Recognition test were not different from WTs. AMG9810 (intraperitoneal injection 50 mg/kg) induced anti-depressant, but not anxiolytic effects. It is concluded that TRPV1 in the SuM might have functional relevance in mood regulation and TRPV1 antagonism could be a novel perspective for anti-depressant drugs.

The Association between Spicy Food Consumption and Psychological Health in Chinese College Students: A Cross-Sectional Study

BACKGROUND

Capsaicin is the main active ingredient in chili peppers and spicy food. Animal studies provide contradictory results on the role of capsaicin in psychiatric disorders. There are no epidemiological studies to investigate the relationship between spicy food consumption and psychological health.

METHODS

A cross-sectional online survey was conducted. Psychological health was assessed with the Depression Anxiety Stress Scale, and spicy food consumption was assessed as frequency, strength, and duration of consumption. Multivariable logistic regression was conducted to determine the associations between spicy food consumption and psychological symptoms.

RESULTS

Our sample comprised 1771 participants (male = 674, mean age = 21.97 years). The odds of having depressive, anxiety, and stress symptoms were 34.0%, 46.5%, and 19.1% in Chinese college students, respectively. After adjusting for a series of covariates, compared with non-consumers, the odds ratios (ORs) of depressive symptoms across spicy food consumption were 1.13 (95% CI: 0.87-1.46) for 1-2 days/week and 1.38 (95% CI: 1.02-1.86) for ≥3 days/week. With regard to anxiety symptoms, the ORs were 0.99 (95% CI: 0.78, 1.27) for 1-2 days/week and 1.50 (95% CI: 1.13-1.99) for ≥3 days/week. For stress symptoms, the ORs were 0.90 (95% CI: 0.66-1.23) for 1-2 days/week and 1.27 (95% CI: 0.89-1.80) for ≥3 days/week. The ORs for the depressive symptoms associated with different intensities of spicy food consumption were 1.00 (reference) for the reference group (non-consumers), 1.17 (95% CI: 0.90-1.52) for eating weakly spicy food, and 1.34 (95% CI: 1.01-1.78) for moderately to strongly spicy food.

CONCLUSION

The findings suggested a positive association between frequently spicy food consumption and depressive/anxiety symptoms in adolescents, and no such association was found for stress symptoms.

Neuroprotective Effects of Cannabidiol but Not Δ9-Tetrahydrocannabinol in Rat Hippocampal Slices Exposed to Oxygen-Glucose Deprivation: Studies with Cannabis Extracts and Selected Cannabinoids

(1) Background: Over the past 10 years, a number of scientific studies have demonstrated the therapeutic potential of cannabinoid compounds present in the Cannabis Sativa and Indica plants. However, their role in mechanisms leading to neurodegeneration following cerebral ischemia is yet unclear. (2) Methods: We investigated the effects of Cannabis extracts (Bedrocan, FM2) or selected cannabinoids (Δ⁹-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabigerol) in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation (OGD), an in vitro model of forebrain global ischemia. Cell death in the CA1 subregion of slices was quantified by propidium iodide fluorescence, and morphological analysis and tissue organization were examined by immunohistochemistry and confocal microscopy. (3) Results: Incubation with the Bedrocan extract or THC exacerbated, whereas incubation with the FM2 extract or cannabidiol attenuated CA1 injury induced by OGD. Δ⁹-THC toxicity was prevented by CB1 receptor antagonists, the neuroprotective effect of cannabidiol was blocked by TRPV2, 5-HT1A, and PPARγ antagonists. Confocal microscopy confirmed that CBD, but not THC, had a significant protective effect toward neuronal damage and tissue disorganization caused by OGD in organotypic hippocampal slices. (4) Conclusions: Our results suggest that cannabinoids play different roles in the mechanisms of post-ischemic neuronal death. In particular, appropriate concentrations of CBD or CBD/THC ratios may represent a valid therapeutic intervention in the treatment of post-ischemic neuronal death.

Cannabinoid Receptor 1 Inhibition in Chronic Kidney Disease: A New Therapeutic Toolbox

Chronic kidney disease (CKD) concerns millions of individuals worldwide, with few therapeutic strategies available to date. Recent evidence suggests that the endocannabinoid system (ECS) could be a new therapeutic target to prevent CKD. ECS combines receptors, cannabinoid receptor type 1 (CB1R) and type 2 (CB2R), and ligands. The most prominent receptor within the kidney is CB1R, its endogenous local ligands being anandamide and 2-arachidonoylglycerol. Therefore, the present review focuses on the therapeutic potential of CB1R and not CB2R. In the normal kidney, CB1R is expressed in many cell types, especially in the vasculature where it contributes to the regulation of renal hemodynamics. CB1R could also participate to water and sodium balance and to blood pressure regulation but its precise role remains to decipher. CB1R promotes renal fibrosis in both metabolic and non-metabolic nephropathies. In metabolic syndrome, obesity and diabetes, CB1R inhibition not only improves metabolic parameters, but also exerts a direct role in preventing renal fibrosis. In non-metabolic nephropathies, its inhibition reduces the development of renal fibrosis. There is a growing interest of the industry to develop new CB1R antagonists without central nervous side-effects. Experimental data on renal fibrosis are encouraging and some molecules are currently under early-stage clinical phases (phases I and IIa studies). In the present review, we will first describe the role of the endocannabinoid receptors, especially CB1R, in renal physiology. We will next explore the role of endocannabinoid receptors in both metabolic and non-metabolic CKD and renal fibrosis. Finally, we will discuss the therapeutic potential of CB1R inhibition using the new pharmacological approaches. Overall, the new pharmacological blockers of CB1R could provide an additional therapeutic toolbox in the management of CKD and renal fibrosis from both metabolic and non-metabolic origin.

Neuropsychiatric implications of transient receptor potential vanilloid (TRPV) channels in the reward system

Neuropsychiatric disorders (NPDs) exert a devastating impact on an individual's personal and social well-being, encompassing various conditions and brain anomalies that influence affect, cognition, and behavior. Because the pathophysiology of NPDs is multifactorial, the precise mechanisms underlying the development of such disorders remain unclear, representing a unique challenge in current neuropsychopharmacotherapy. Transient receptor potential vanilloid (TRPV) type channels are a family of ligand-gated ion channels that mainly include sensory receptors that respond to thermal, mechanical and chemical stimuli. TRPV channels are abundantly present in dopaminergic neurons, thus playing a pivotal role in the modulation of the reward system and in pathophysiology of diseases such as stress, anxiety, depression, schizophrenia, neurodegenerative disorders and substance abuse/addiction. Recent evidence has highlighted TRPV channels as potential targets for understanding modulation of the reward system and various forms of addiction (opioids, cocaine, amphetamines, alcohol, nicotine, cannabis). In this review, we discuss the distribution, physiological roles, ligands and therapeutic importance of TRPV channels with regard to NPDs and addiction biology.

Neuroprotection in Oxidative Stress-Related Neurodegenerative Diseases: Role of Endocannabinoid System Modulation

SIGNIFICANCE

Redox imbalance may lead to overproduction of reactive oxygen and nitrogen species (ROS/RNS) and subsequent oxidative tissue damage, which is a critical event in the course of neurodegenerative diseases. It is still not fully elucidated, however, whether oxidative stress is the primary trigger or a consequence in the process of neurodegeneration. Recent Advances: Increasing evidence suggests that oxidative stress is involved in the propagation of neuronal injury and consequent inflammatory response, which in concert promote development of pathological alterations characteristic of most common neurodegenerative diseases.

CRITICAL ISSUES

Accumulating recent evidence also suggests that there is an important interplay between the lipid endocannabinoid system [ECS; comprising the main cannabinoid 1 and 2 receptors (CB1 and CB2), endocannabinoids, and their synthetic and metabolizing enzymes] and various key inflammatory and redox-dependent processes.

FUTURE DIRECTIONS

Targeting the ECS to modulate redox state-dependent cell death and to decrease consequent or preceding inflammatory response holds therapeutic potential in a multitude of oxidative stress-related acute or chronic neurodegenerative disorders from stroke and traumatic brain injury to Alzheimer's and Parkinson's diseases and multiple sclerosis, just to name a few, which will be discussed in this overview. Antioxid. Redox Signal. 29, 75-108.

Surprising outcomes in cannabinoid CB1/CB2 receptor double knockout mice in two models of ischemia

AIMS

We tested the hypothesis that CB1/CB2 receptor double knockout would produce significant increases in infarct size and volume and significant worsening in clinical score, using two mouse models, one of permanent ischemia and one of ischemia/reperfusion.

MAIN METHODS

Focal cerebral infarcts were created using either photo induced permanent injury or transient middle cerebral artery occlusion. Infarct volume and motor function were evaluated in cannabinoid receptor 1/cannabinoid receptor 2 double knockout mice.

KEY FINDINGS

The results surprisingly revealed that CB1/CB2 double knockout mice showed improved outcomes, with the most improvements in the mouse model of permanent ischemia.

SIGNIFICANCE

Although the number of individuals suffering from stroke in the United States and worldwide will continue to grow, therapeutic intervention for treatment following stroke remains frustratingly limited. Both the cannabinoid 1 receptor (CB1R) and the cannabinoid 2 receptor (CB2R) have been studied in relationship to stroke. Deletion of the CB2R has been shown to worsen outcome, while selective CB2R agonists have been demonstrated to be neuroprotective following stroke. Although initial studies of CB1R knockout mice demonstrated increased injury following stroke, indicating that activation of the CB1R was neuroprotective, later studies of selective antagonists of the CB1R also demonstrated a protective effect. Surprisingly the double knockout animals had improved outcome. Since the phenotype of the double knockout is not dramatically changed, significant changes in the contribution of other homeostatic pathways in compensation for the loss of these two important receptors may explain these apparently contradictory results.

N-stearoyltyrosine protects primary cortical neurons against oxygen-glucose deprivation-induced apoptosis through inhibiting anandamide inactivation system

N-stearoylthrosine (NST), a synthesized anandamide (AEA) analogue, plays a neuroprotective role in neurodegenerative diseases and cerebrovascular diseases. Several studies have demonstrated that the endocannabinoids systems (ECS) are involved in the neuroprotective effects against cerebral ischemic injury. Oxygen-glucose deprivation (OGD)-induced neuronal injury elevated the levels of endocannabinoids and activated ECS. This research was conducted to investigate the neuroprotective effect of NST against OGD-induced neuronal injury in cultured primary cortical neurons and the potential mechanism involved. Cortical neurons were treated with NST at indicate concentrations for 30min prior to injury and OGD injured neurons were incubated with normal conditions for 0-24h. The best neuroprotective effect of NST against OGD-induced injury occurred at 10μM. All data indicated that the neuroprotective effect of NST against OGD-induced injury resulted from blocking anandamide membrane transporter (AMT) (IC₅₀=11.74nM) and inhibiting fatty acid amide hydrolase activity (FAAH) (IC₅₀=16.54nM). Our findings demonstrated that NST has an important role in cerebral ischemic injury pathological progression through activating cannabinoid receptors by inhibiting AEA inactivation system. These data suggested a potential role for NST in the therapeutic consideration of cerebral ischemic injury. However, inhibition of AEA inactivation system may provide a neuroprotective effect during cerebral ischemic injury.

Psychiatric Disorders and TRP Channels: Focus on Psychotropic Drugs

Psychiatric and neurological disorders are mostly associated with the changes in neural calcium ion signaling pathways required for activity-triggered cellular events. One calcium channel family is the TRP cation channel family, which contains seven subfamilies. Results of recent papers have discovered that calcium ion influx through TRP channels is important. We discuss the latest advances in calcium ion influx through TRP channels in the etiology of psychiatric disorders. Activation of TRPC4, TRPC5, and TRPV1 cation channels in the etiology of psychiatric disorders such as anxiety, fear-associated responses, and depression modulate calcium ion influx. Evidence substantiates that anandamide and its analog (methanandamide) induce an anxiolytic-like effect via CB1 receptors and TRPV1 channels. Intracellular calcium influx induced by oxidative stress has an significant role in the etiology of bipolar disorders (BDs), and studies recently reported the important role of TRP channels such as TRPC3, TRPM2, and TRPV1 in converting oxidant or nitrogen radical signaling to cytosolic calcium ion homeostasis in BDs. The TRPV1 channel also plays a function in morphine tolerance and hyperalgesia. Among psychotropic drugs, amitriptyline and capsazepine seem to have protective effects on psychiatric disorders via the TRP channels. Some drugs such as cocaine and methamphetamine also seem to have an important role in alcohol addiction and substance abuse via activation of the TRPV1 channel. Thus, we explore the relationships between the etiology of psychiatric disorders and TRP channel-regulated mechanisms. Investigation of the TRP channels in psychiatric disorders holds the promise of the development of new drug treatments.

Perspectives of TRPV1 Function on the Neurogenesis and Neural Plasticity

The development of new strategies to renew and repair neuronal networks using neural plasticity induced by stem cell graft could enable new therapies to cure diseases that were considered lethal until now. In adequate microenvironment a neuronal progenitor must receive molecular signal of a specific cellular context to determine fate, differentiation, and location. TRPV1, a nonselective calcium channel, is expressed in neurogenic regions of the brain like the subgranular zone of the hippocampal dentate gyrus and the telencephalic subventricular zone, being valuable for neural differentiation and neural plasticity. Current data show that TRPV1 is involved in several neuronal functions as cytoskeleton dynamics, cell migration, survival, and regeneration of injured neurons, incorporating several stimuli in neurogenesis and network integration. The function of TRPV1 in the brain is under intensive investigation, due to multiple places where it has been detected and its sensitivity for different chemical and physical agonists, and a new role of TRPV1 in brain function is now emerging as a molecular tool for survival and control of neural stem cells.

Fatty acid binding protein deletion suppresses inflammatory pain through endocannabinoid/N-acylethanolamine-dependent mechanisms

Background

Fatty acid binding proteins (FABPs) serve as intracellular carriers that deliver endocannabinoids and N-acylethanolamines to their catabolic enzymes. Inhibition of FABPs reduces endocannabinoid transport and catabolism in cells and FABP inhibitors produce antinociceptive and anti-inflammatory effects in mice. Potential analgesic effects in mice lacking FABPs, however, have not been tested.

Findings

Mice lacking FABP5 and FABP7, which exhibit highest affinities for endocannabinoids, possessed elevated levels of the endocannabinoid anandamide and the related N-acylethanolamines palmitoylethanolamide and oleoylethanolamide. There were no compensatory changes in the expression of other FABPs or in endocannabinoid-related proteins in the brains of FABP5/7 knockout mice. These mice exhibited reduced nociception in the carrageenan, formalin, and acetic acid tests of inflammatory and visceral pain. The antinociceptive effects in FABP5/7 knockout mice were reversed by pretreatment with cannabinoid receptor 1, peroxisome proliferator-activated receptor alpha, and transient receptor potential vanilloid 1 receptor antagonists in a modality specific manner. Lastly, the knockout mice did not possess motor impairments.

Conclusions

This study demonstrates that mice lacking FABPs possess elevated levels of N-acylethanolamines, consistent with the idea that FABPs regulate the endocannabinoid and N-acylethanolamine tone in vivo. The antinociceptive effects observed in the knockout mice support a role for FABPs in regulating nociception and suggest that these proteins should serve as targets for the development of future analgesics.

The combination of oral L-DOPA/rimonabant for effective dyskinesia treatment and cytological preservation in a rat model of Parkinson's disease and L-DOPA-induced dyskinesia

Parkinson's disease is the second most prevalent neurodegenerative disease in the world. Its treatment is limited so far to the management of parkinsonian symptoms with L-DOPA (LD). The long-term use of LD is limited by the development of L-DOPA-induced dyskinesias and dystonia. However, recent studies have suggested that pharmacological targeting of the endocannabinoid system may potentially provide a valuable therapeutic tool to suppress these motor alterations. In the present study, we have explored the behavioral (L-DOPA-induced dyskinesias severity) and cytological (substantia nigra compacta neurons and striatum neuropil preservation) effects of the oral coadministration of LD and rimonabant, a selective antagonist of CB1 receptors, in the 6-hydroxydopamine rat model of Parkinson's disease. Oral coadministration of LD (30 mg/kg) and rimonabant (1 mg/kg) significantly decreased abnormal involuntary movements and dystonia, possibly through the conservation of some functional tyrosine hydroxylase-immunoreactive dopaminergic cells, which in turn translates into a well-preserved neuropil of a less denervated striatum. Our results provide anatomical evidence that long-term coadministration of LD with cannabinoid antagonist-based therapy may not only alleviate specific motor symptoms but also delay/arrest the degeneration of striatal and substantia nigra compacta cells.

Δ9-tetrahydrocannabinol prevents methamphetamine-induced neurotoxicity

Methamphetamine (METH) is a potent psychostimulant with neurotoxic properties. Heavy use increases the activation of neuronal nitric oxide synthase (nNOS), production of peroxynitrites, microglia stimulation, and induces hyperthermia and anorectic effects. Most METH recreational users also consume cannabis. Preclinical studies have shown that natural (Δ9-tetrahydrocannabinol, Δ9-THC) and synthetic cannabinoid CB1 and CB2 receptor agonists exert neuroprotective effects on different models of cerebral damage. Here, we investigated the neuroprotective effect of Δ9-THC on METH-induced neurotoxicity by examining its ability to reduce astrocyte activation and nNOS overexpression in selected brain areas. Rats exposed to a METH neurotoxic regimen (4×10 mg/kg, 2 hours apart) were pre- or post-treated with Δ9-THC (1 or 3 mg/kg) and sacrificed 3 days after the last METH administration. Semi-quantitative immunohistochemistry was performed using antibodies against nNOS and Glial Fibrillary Acidic Protein (GFAP). Results showed that, as compared to corresponding controls (i) METH-induced nNOS overexpression in the caudate-putamen (CPu) was significantly attenuated by pre- and post-treatment with both doses of Δ9-THC (−19% and −28% for 1 mg/kg pre- and post-treated animals; −25% and −21% for 3 mg/kg pre- and post-treated animals); (ii) METH-induced GFAP-immunoreactivity (IR) was significantly reduced in the CPu by post-treatment with 1 mg/kg Δ9-THC1 (−50%) and by pre-treatment with 3 mg/kg Δ9-THC (−53%); (iii) METH-induced GFAP-IR was significantly decreased in the prefrontal cortex (PFC) by pre- and post-treatment with both doses of Δ9-THC (−34% and −47% for 1 mg/kg pre- and post-treated animals; −37% and −29% for 3 mg/kg pre- and post-treated animals). The cannabinoid CB1 receptor antagonist SR141716A attenuated METH-induced nNOS overexpression in the CPu, but failed to counteract the Δ9-THC-mediated reduction of METH-induced GFAP-IR both in the PFC and CPu. Our results indicate that Δ9-THC reduces METH-induced brain damage via inhibition of nNOS expression and astrocyte activation through CB1-dependent and independent mechanisms, respectively.

TRPV1 in the central nervous system: synaptic plasticity, function, and pharmacological implications

The function of TRPV1 in the peripheral nervous system is increasingly being investigated for its anti-inflammatory and antinociceptive properties in an effort to find a novel target to fight pain that is nonaddictive. However, in recent years, it was discovered that TRPV1 is also associated with a wide array of functions and behaviors in the central nervous system, such as fear, anxiety, stress, thermoregulation, pain, and, more recently, synaptic plasticity, the cellular mechanism that allows the brain to adapt to its environment. This suggests a new role for brain TRPV1 in areas such as learning and memory, reward and addiction, and development. This wide array of functional aspects of TRPV1 in the central nervous system (CNS) is in part due to its multimodal form of activation and highlights the potential pharmacological implications of TRPV1 in the brain. As humans also express a TRPV1 homologue, it is likely that animal research will be translational to humans and therefore worthy of exploration. This review outlines the basic expression patterns of TRPV1 in the CNS along with what is known regarding its signaling mechanisms and its role in the aforementioned brain functions. As TRPV1 involvement in synaptic plasticity has never been fully reviewed elsewhere, it will be a focus of this review. The chapter concludes with some of the potential pharmaceutical implications of further TRPV1 research.

Neuroinflammation in ischemic brain injury as an adaptive process

Cerebral ischaemia triggers various physiological processes, some of which have been considered deleterious and others beneficial. These processes have been characterized in one influential model as being part of a transition from injury to repair processes. We argue that another important distinction is between dysregulated and regulated processes. Although intervening in the course of dysregulated processes may be neuroprotective, this is unlikely to be true for regulated processes. This is because from an evolutionary perspective, regulated complex processes that are conserved across many species are likely to be adaptive and provide a survival advantage. We argue that the neuroinflammatory cascade is an adaptive process in this sense, and contrast this with a currently popular theory which we term the maladaptive immune response theory. We review the evidence from clinical and preclinical pharmacology with respect to this theory, and deduced that the evidence is inconclusive at best, and probably falsifies the theory. We argue that this is why there are no anti-inflammatory treatments for cerebral ischaemia, despite 30 years of seemingly promising preclinical results. We therefore propose an opposing theory, which we call the adaptive immune response hypothesis.

Disruption of ion homeostasis in the neurogliovascular unit underlies the pathogenesis of ischemic cerebral edema

Cerebral edema is a major cause of morbidity and mortality following ischemic stroke, but its underlying molecular pathophysiology is incompletely understood. Recent data have revealed the importance of ion flux via channels and transporters expressed in the neurogliovascular unit in the development of ischemia-triggered cytotoxic edema, vasogenic edema, and hemorrhagic conversion. Disruption of homeostatic mechanisms governing cell volume regulation and epithelial/endothelial ion transport due to ischemia-associated energy failure results in the thermodynamically driven re-equilibration of solutes and water across the CSF-blood and blood-brain barriers that ultimately increases the brain's extravascular volume. Additionally, hypoxia, inflammation, and other stress-triggered increases in the functional expression of ion channels and transporters normally expressed at low levels in the neurogliovascular unit cause disruptions in ion homeostasis that contribute to ischemic cerebral edema. Here, we review the pathophysiological significance of several molecular mediators of ion transport expressed in the neurogliovascular unit, including targets of existing FDA-approved drugs, which might be potential nodes for therapeutic intervention.

The biarylpyrazole compound AM251 alters mitochondrial physiology via proteolytic degradation of ERRα

The orphan nuclear receptor estrogen-related receptor alpha (ERRα) directs the transcription of nuclear genes involved in energy homeostasis control and the regulation of mitochondrial mass and function. A crucial role for controlling ERRα-mediated target gene expression has been ascribed to the biarylpyrazole compound 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) through direct binding to and destabilization of ERRα protein. Here, we provide evidence that structurally related AM251 analogs also have negative impacts on ERRα protein levels in a cell-type-dependent manner while having no deleterious actions on ERRγ. We show that these off-target cellular effects of AM251 are mediated by proteasomal degradation of nuclear ERRα. Cell treatment with the nuclear export inhibitor leptomycin B did not prevent AM251-induced destabilization of ERRα protein, whereas proteasome inhibition with MG132 stabilized and maintained its DNA-binding function, indicative of ERRα being a target of nuclear proteasomal complexes. NativePAGE analysis revealed that ERRα formed a ∼220-kDa multiprotein nuclear complex that was devoid of ERRγ and the coregulator peroxisome proliferator-activated receptor γ coactivator-1. AM251 induced SUMO-2,3 incorporation in ERRα in conjunction with increased protein kinase C activity, whose activation by phorbol ester also promoted ERRα protein loss. Down-regulation of ERRα by AM251 or small interfering RNA led to increased mitochondria biogenesis while negatively impacting mitochondrial membrane potential. These results reveal a novel molecular mechanism by which AM251 and related compounds alter mitochondrial physiology through destabilization of ERRα.

Unique effects of compounds active at both cannabinoid and serotonin receptors during stroke

We reported previously that both a cannabinoid receptor 2 (CB2R) agonist and a cannabinoid receptor 1 (CB1R) antagonist were protective in the treatment of transient middle cerebral artery occlusion/reperfusion injury (MCAO/R) and that they acted in a synergistic manner when administered in combination. The goal of the current study was to determine which of the potential cannabinoid receptors participate in the protective effects of this drug combination in a mouse model of MCAO/R. The effects of administration of the CB2R agonist/CB1R antagonist combination on infarct size and cerebral blood flow during a 1-h occlusion were tested in CB1R-deficient animals, CB2R-deficient animals, and animals treated with capsazepine, the antagonist for the vanilloid receptor type I (TRPV1) and WAY100135, the antagonist for the hydroxytryptamine1A receptor (5-HT1A). The protective effect of the CB2R agonist/CB1R antagonist combination on infarct size was not influenced by the absence of the CB1R nor by blocking the TRPV1 receptor, but was attenuated by the absence of CB2R and by blocking the 5-HT1A receptor. Increases in cerebral blood flow and arteriolar diameter were also found to be independent of the CB1R and TRPV1 receptor. In conclusion, administration of the CB2R agonist/CB1R antagonist combination causes a significant reduction in infarct size in the MCAO/R model. The protective effect involves both the CB2R and the 5-HT1A receptor. Neither the CB1R nor the TRPV1 receptors appear to participate in this response.

Long-term depression of nociceptive synapses by non-nociceptive afferent activity: role of endocannabinoids, Ca²+, and calcineurin

Activity in non-nociceptive afferents is known to produce long-lasting decreases in nociceptive signaling, often referred to as gate control, but the cellular mechanisms mediating this form of neuroplasticity are poorly understood. In the leech, activation of non-nociceptive touch (T) mechanosensory neurons induces a heterosynaptic depression of nociceptive (N) synapses that is endocannabinoid-dependent. This heterosynaptic, endocannabinoid-dependent long-term depression (ecLTD) is observed where the T- and N-cells converge on a common postsynaptic target, in this case the motor neuron that innervates the longitudinal muscles (L-cells) that contributes to a defensive withdrawal reflex. Depression in the nociceptive synapse required both presynaptic and postsynaptic increases in intracellular Ca²⁺. Activation of the Ca²⁺-sensitive protein phosphatase calcineurin was also required, but only in the presynaptic neuron. Heterosynaptic ecLTD was unaffected by antagonists for NMDA or metabotropic glutamate receptors, but was blocked by the 5-HT₂ receptor antagonist ritanserin. Depression was also blocked by the CB1 receptor antagonist rimonabant, but this is thought to represent an effect on a TRPV-like receptor. This heterosynaptic, endocannabinoid-dependent modulation of nociceptive synapses represents a novel mechanism for regulating how injury-inducing or painful stimuli are transmitted to the rest of the central nervous system.

Update on the role of cannabinoid receptors after ischemic stroke

Cannabinoids are considered as key mediators in the pathophysiology of inflammatory diseases, including atherosclerosis. In particular, they have been shown to reduce the ischemic injury after acute cardiovascular events, such as acute myocardial infarction and ischemic stroke. These protective and anti-inflammatory properties on peripheral tissues and circulating inflammatory have been demonstrated to involve their binding with both selective cannabinoid type 1 (CB₁) and type 2 (CB₂) transmembrane receptors. On the other hands, the recent discoveries of novel different classes of cannabinoids and receptors have increased the complexity of this system in atherosclerosis. Although only preliminary data have been reported on the activities of novel cannabinoid receptors, several studies have already investigated the role of CB₁ and CB₂ receptors in ischemic stroke. While CB₁ receptor activation has been shown to directly reduce atherosclerotic plaque inflammation, controversial data have been shown on neurotransmission and neuroprotection after stroke. Given its potent anti-inflammatory activities on circulating leukocytes, the CB₂ activation has been proven to produce protective effects against acute poststroke inflammation. In this paper, we will update evidence on different cannabinoid-triggered avenues to reduce inflammation and neuronal injury in acute ischemic stroke.

TRPV1: a stress response protein in the central nervous system

The transient receptor potential (TRP) family comprises a diverse group of cation channels that regulate a variety of intracellular signaling pathways. The TRPV1 (vanilloid 1) channel is best known for its role in nociception and sensory transmission. First studied in the dorsal root ganglia as the receptor for capsaicin, TRPV1 is now recognized to have a broader distribution and function within the central nervous system (CNS). Because it can be activated by a range of potentially noxious stimuli, TRPV1's polymodal nature and ability to interact with other receptor pathways make it a candidate for a stress response protein. As a result, TRPV1 is emerging as a key mediator of CNS function through modulation of both glial and neuronal activity. Growing evidence has suggested that TRPV1 can mediate a variety of pathways from glial reactivity and cytokine release to synaptic transmission and plasticity. This review highlights the increasing importance of TRPV1 as a regulator of CNS function in response to stress.

Orally administered oleoylethanolamide protects mice from focal cerebral ischemic injury by activating peroxisome proliferator-activated receptor α

Oleoylethanolamide (OEA) is a high-affinity agonist of peroxisome proliferator-activated receptor α (PPARα) which may act as an endogenous neuroprotective factor. However, it is not clear whether orally administered OEA is effective against ischemic brain injury. In our study, transient focal cerebral ischemia was induced by middle cerebral artery occlusion for 90 min followed by reperfusion. To evaluate its preventive effects, OEA (10, 20 or 40 mg/kg, ig) was administered for 3 days before ischemia. To evaluate its therapeutic effects, OEA (40 mg/kg, ig) was administered at 0.5 or 1h before reperfusion or at 0 or 1h after reperfusion. In some experiments, the PPARα antagonist MK886 (10mg/kg, ig) was administered 0.5h before OEA. Neurological deficit score, infarct volume and brain edema degree were determined at 24h after reperfusion. Blood-brain barrier (BBB) disruption was evaluated by Evans blue (EB) leakage at 6h after reperfusion. Real-time RT-PCR and western blot were performed to detect PPARα mRNA and protein expression. Oral OEA pretreatment improved neurological dysfunction reduced infarct volume and alleviated brain edema in a dose-dependent manner; the most effective dose was 40 mg/kg. The therapeutic time is within 1h after reperfusion. OEA also increased PPARα mRNA and protein expression in the ischemic brain. The PPARα antagonist MK886 abolished the protective effects of OEA. In conclusion, our results indicate that orally administered OEA protects against acute cerebral ischemic injury in mice, at least in part by activating PPARα.

The inverse agonist effect of rimonabant on G protein activation is not mediated by the cannabinoid CB1 receptor: evidence from postmortem human brain

Rimonabant (SR141716) was the first potent and selective cannabinoid CB1 receptor antagonist synthesized. Several data support that rimonabant behaves as an inverse agonist. Moreover, there is evidence suggesting that this inverse agonism may be CB1 receptor-independent. The aim of the present study was to elucidate whether the effect of rimonabant over G protein activation in postmortem human brain is CB1 dependent or independent. [(35)S]GTPγS binding assays and antibody-capture [(35)S]GTPγS scintillation proximity assays (SPA) were performed in human and mice brain. [(3)H]SR141716 binding characteristics were also studied. Rimonabant concentration-dependently decreased basal [(35)S]GTPγS binding to human cortical membranes. This effect did not change in the presence of either the CB1 receptor agonist WIN 55,212-2, the CB1 receptor neutral antagonist O-2050, or the CB1 allosteric modulator Org 27569. [(35)S]GTPγS binding assays performed in CB1 knockout mice brains revealed that rimonabant inhibited the [(35)S]GTPγS binding in the same manner as it did in wild-type mice. The SPA combined with the use of specific antibody-capture of G(α) specific subunits showed that rimonabant produces its inverse agonist effect through G(i3), G(o) and G(z) subtypes. This effect was not inhibited by the CB1 receptor antagonist O-2050. Finally, [(3)H]SR141716 binding assays in human cortical membranes demonstrated that rimonabant recognizes an additional binding site other than the CB1 receptor orthosteric binding site recognized by O-2050. This study provides new data demonstrating that at least the inverse agonist effect observed with >1μM concentrations of rimonabant in [(35)S]GTPγS binding assays is not mediated by the CB1 receptor in human brain.

Cannabinoid type 2 receptor activation downregulates stroke-induced classic and alternative brain macrophage/microglial activation concomitant to neuroprotection

BACKGROUND AND PURPOSE

Ischemic stroke continues to be one of the main causes of death worldwide. Inflammation accounts for a large part of damage in this pathology. The cannabinoid type 2 receptor (CB2R) has been proposed to have neuroprotective properties in neurological diseases. Therefore, our aim was to determine the effects of the activation of CB2R on infarct outcome and on ischemia-induced brain expression of classic and alternative markers of macrophage/microglial activation.

METHODS

Swiss wild-type and CB2R knockout male mice were subjected to a permanent middle cerebral artery occlusion. Mice were treated with either a CB2R agonist (JWH-133), with or without a CB2R antagonist (SR144528) or vehicle. Infarct outcome was determined by measuring infarct volume and neurological outcome. An additional group of animals was used to assess mRNA and protein expression of CB2R, interleukin (IL)-1β, IL-6, tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide (MIP) -1α, RANTES, inducible nitric oxide synthase (iNOS), cyclooxygenase-2, IL-4, IL-10, transforming growth factor β (TGF-β), arginase I, and Ym1.

RESULTS

Administration of JWH-133 significantly improved infarct outcome, as shown by a reduction in brain infarction and neurological impairment. This effect was reversed by the CB2R antagonist and was absent in CB2R knockout mice. Concomitantly, administration of JWH-133 led to a lower intensity of Iba1+ microglia/macrophages and a decrease in middle cerebral artery occlusion-induced gene expression of both classic (IL-6, TNF-α, MCP-1, MIP-1α, RANTES, and iNOS) and alternative mediators/markers (IL-10, TGF-β, and Ym1) of microglial/macrophage activation after permanent middle cerebral artery occlusion.

CONCLUSIONS

The inhibitory effect of CB2R on the activation of different subpopulations of microglia/macrophages may account for the protective effect of the selective CB2R agonist JWH-133 after stroke.

CB1 receptors and post-ischemic brain damage: studies on the toxic and neuroprotective effects of cannabinoids in rat organotypic hippocampal slices

Cannabinoids (CBs) are implicated in a number of physiological and pathological mechanisms in the central nervous system, but their exact role in post-ischemic brain injury is unclear. The toxic and neuroprotective effects of synthetic and endogenous CBs were evaluated in rat organotypic hippocampal slices exposed to 20 min oxygen-glucose deprivation (OGD) and in gerbils subjected to bilateral carotid occlusion for 5 min. When present in the incubation medium, the synthetic CB agonists WIN 55212-2 and CP 55940 (1-30 μM) and the CB1 agonist ACEA exacerbated CA1 injury induced by OGD, whereas the CB1 receptor antagonists AM 251 and LY 320135 were neuroprotective with maximal activity at 1 μM. AM 251 (at 3 mg/kg, i.p.) also attenuated CA1 pyramidal cell death in gerbils in vivo. The endocannabinoid 2-arachidonoylglycerol (2-AG) reduced OGD injury in hippocampal slices at 0.1-1 μM, whereas anandamide (AEA) was neurotoxic at the same concentrations. The effects of WIN 55212-2, AEA and 2-AG in slices were all dependent on the activation of CB1 but not CB2 receptors, except for the toxic effects of AEA that were also dependent on vanilloid TRPV1 receptors. Our results suggest that exogenous administration of CB1 agonists and the production of endocannabinoids "on demand" may produce different, if not opposite, effects on the fate of neurons following cerebral ischemia.

Effect of rimonabant, the cannabinoid CB1 receptor antagonist, on peripheral nerve in streptozotocin-induced diabetic rat

The aim of this study is to investigate the effect of rimonabant, which has antiatherosclerotic and antiinflammatory properties, on peripheral neuropathy in a diabetic rat. Diabetic rat models were induced by treatment with streptozotocin and then either normal or diabetic rats were treated with an oral dose of 10mg/kg/day rimonabant or placebo for 24 weeks. We quantified the densities of intraepidermal (PGP9.5+) nerve fiber and total skin (RECA-1+) capillary length. We also measured the current perception threshold, as defined by the intensity of sine-wave stimulus, skin blood flow after treadmill running and TNF-alpha level in spinal cord tissue or plasma. After 24 weeks, rimonabant reduced the body weight and food intake in both diabetic and normal rats, but it had no effect on blood sugar levels. In addition, rimonabant treatment significantly improved the decreased intraepidermal nerve fiber density (5.53+/-0.12 vs. 4.36+/-0.27/mm, P<0.05) and alleviated the increased current perception threshold in rimonabant-treated versus control diabetic rats. These responses were closely associated with the attenuation of skin capillary loss (1.98+/-0.07 vs. 1.67+/-0.10 mm/mm(2), P<0.05), increase in skin blood flow (14.93+/-1.08 vs. 12.07+/-0.87 TPU, P<0.05) and reduction in TNF-alpha level in tissue (70.10+/-4.99 vs. 91.18+/-3.34 pg/mg, P<0.05) in rimonabant-treated diabetic rats compared with placebo. These findings suggest that rimonabant can be beneficial for treatment of diabetic peripheral neuropathy, possibly due to its potential role in micro- and macrovessel protection and its anti-inflammatory properties.

Modulation of the endocannabinoid system: neuroprotection or neurotoxicity?

There is now a large volume of data indicating that compounds activating cannabinoid CB(1) receptors, either directly or indirectly by preventing the breakdown of endogenous cannabinoids, can protect against neuronal damage produced by a variety of neuronal "insults". Given that such neurodegenerative stimuli result in increased endocannabinoid levels and that animals with genetic deletions of CB(1) receptors are more susceptible to the deleterious effects of such stimuli, a case can be made for an endogenous neuroprotective role of endocannabinoids. However, this is an oversimplification of the current literature, since (a) compounds released together with the endocannabinoids can contribute to the neuroprotective effect; (b) other proteins, such as TASK-1 and PPARalpha, are involved; (c) the CB(1) receptor antagonist/inverse agonist rimonabant has also been reported to have neuroprotective properties in a number of animal models of neurodegenerative disorders. Furthermore, the CB(2) receptor located on peripheral immune cells and activated microglia are potential targets for novel therapies. In terms of the clinical usefulness of targeting the endocannabinoid system for the treatment of neurodegenerative disorders, data are emerging, but important factors to be considered are windows of opportunity (for acute situations such as trauma and ischemia) and the functionality of the target receptors (for chronic neurodegenerative disorders such as Alzheimer's disease).

The paradoxical role of the transient receptor potential vanilloid 1 receptor in inflammation

The transient potential receptor vanilloid 1 (TRPV1) receptor is a non-selective cation channel that is chemically activated by capsaicin, the pungent component of hot peppers. In addition, endogenous compounds, in particular the endogenous cannabinoid receptor activator, anandamide, have been demonstrated to activate TRPV1 in vivo. TRPV1 receptors are also activated by temperatures within the noxious range (>43 degrees C) and low pH (<pH 6.0). TRPV1 receptors are predominantly expressed in primary afferent fibres which are peptidergic sensory neurones, such as the thinly myelinated A-delta and unmyelinated C-fibres. TRPV1 receptors have also been demonstrated to be present in non-neuronal cells. Historically, TRPV1 has been considered as a pro-inflammatory receptor due to its key role in several conditions, including neuropathic pain, joint inflammation and inflammatory bowel disease, amongst others. However, the purpose of this review is to underline the emerging new evidence which demonstrate paradoxical, protective functions for this unique receptor in vivo. For example, in experimentally induced sepsis, TRPV1 null mice demonstrated elevated levels of pathological markers in comparison to wild-type mice. In addition to the pro-inflammatory and protective roles of TRPV1 in pathophysiological states, TRPV1 has also been shown to have important functions under normal physiological conditions, for example in urinary bladder function, thermoregulation and neurogenesis. The emerging functions of TRPV1 highlight the necessity for further research in light of increasing reports of potential TRPV1 antagonists undergoing pre-clinical experimentations.

CB2 receptor activation attenuates microcirculatory dysfunction during cerebral ischemic/reperfusion injury

Previous studies from our laboratory indicated that selective cannabinoid CB(2) agonists were able to attenuate cerebral ischemia/reperfusion (I/R) injury. The goal of current study is to further test whether this attenuation involves cerebral microcirculatory function during I/R injury. Middle cerebral artery occlusion with reperfusion (MCAO/R) was performed in male mice. A selective CB(2) agonist was administered at different dosages and different times. Cerebral infarction volume, neurological function and cerebral microcirculatory function (leukocyte/endothelial interactions, cell adhesion molecule expression and blood-brain barrier disruption) were examined in vivo and in vitro. CB(2) knockout mice were subjected to MCAO/R following same procedures. Administration of the CB(2) agonist at middle dosage exerted optimal effects in reducing cerebral infarction and improving neurological function compared with other dosage groups and control group. Treatment with the CB(2) agonist at the optimal dose was still effective when given 3 h after MCAO. Transient ischemia significantly increased leukocyte/endothelial interactions, adhesion molecules expression and blood-brain barrier disruption which were all attenuated by pre-treatment with a CB(2) agonist. CB(2) knockout mice showed larger cerebral infarction and worse neurological function compared to wide type. In conclusion, CB(2) activation contributed to protecting the brain through the attenuation of cerebral microcirculatory dysfunction during cerebral I/R injury.

Role of ionotropic cannabinoid receptors in peripheral antinociception and antihyperalgesia

Despite the wealth of information on cannabinoid-induced peripheral antihyperalgesic and antinociceptive effects in many pain models, the molecular mechanism(s) for these actions remains unknown. Although metabotropic cannabinoid receptors have important roles in many pharmacological actions of cannabinoids, recent studies have led to the recognition of a family of at least five ionotropic cannabinoid receptors (ICRs). The known ICRs are members of the family of transient receptor potential (TRP) channels and include TRPV1, TRPV2, TRPV4, TRPM8 and TRPA1. Cannabinoid activation of ICRs can result in desensitization of the TRPA1 and TRPV1 channel activities, inhibition of nociceptors and antihyperalgesia and antinociception in certain pain models. Thus, cannabinoids activate both metabotropic and ionotropic mechanisms to produce peripheral analgesic effects. Here, we provide an overview of the pharmacology of TRP channels as ICRs.

Cannabinoids and capsaicin improve liver function following thioacetamide-induced acute injury in mice

OBJECTIVES

We have shown the beneficial effects of cannabinoids in a murine model of hepatic encephalopathy following thioacetamide and now report their effects on the liver injury.

METHODS

Fulminant hepatic failure (FHF) was induced by administration of 200 mg/kg thioacetamide to wild-type (WT) and CB2 Knockout (KO) mice. Twenty-four hours later, mice were injected with 2-arachidonoylglycerol (CB1, CB2, and TRPV1 agonist), HU308 (CB2 agonist), SR141716 A (CB1 receptor blocker), SR141716 A+2-AG, and SR144528 (CB2 receptor blocker), capsaicin and capsazepine (TRPV1 agonist and antagonist receptors). Mice were sacrificed 2 days after thioacetamide administration (day 3) and liver biochemistry and histopathology as well as evaluation of 2-arachidonoylglycerol levels were performed on liver tissue.

RESULTS

Liver histopathology undertaken 48 h after thioacetamide showed evidence of necrosis and inflammation. SR141716 A, HU308, and 2-arachidonoylglycerol reduced inflammation and promoted regeneration 1 day after their administration. Liver enzymes increased after thioacetamide administration and were reversed after SR141716 A and 2-arachidonoylglycerol administered alone or combined, HU-308, but not SR144528. Thus, the beneficial effects mediated through CB2 receptors. However, CB2 KO mice still modulated liver function via the TRPV1 receptors. Capsaicin improved both liver pathology and function in WT thioacetamide-treated mice, while capsazepine impaired it.

CONCLUSIONS

The similar pattern found between the effect of cannabinoids and their antagonists on brain and liver indicated that the therapeutic effect might be directed by the improvement in both organs through CB2 receptors and/or TRPV1 receptors. Modulation of these systems may have therapeutic potential.

Role of cannabinoids and endocannabinoids in cerebral ischemia

The human costs of stroke are very large and growing; it is the third largest cause of death in the United States and survivors are often faced with loss of ability to function independently. There is a large need for therapeutic approaches that act to protect neurons from the injury produced by ischemia and reperfusion. The goal of this review is to introduce and discuss the available data that endogenous cannabinoid signaling is altered during ischemia and that it contributes to the consequences of ischemia-induced injury. Overall, the available data suggest that inhibition of CB1 receptor activation together with increased CB2 receptor activation produces beneficial effects.

Protection of capsaicin against hypoxia–reoxygenation-induced apoptosis of rat hippocampal neurons

The aim of this study was to investigate the effect of capsaicin on hypoxia–reoxygenation (H/R)-induced apoptosis in primary rat hippocampal neurons. Three hours of hypoxia (1% O2) and subsequent reoxygenation for 24 h significantly increased the apoptotic death of hippocampal neurons, as evidenced by increases in both TUNEL-positive cell number and caspase-3 activity. Pretreatment with capsaicin (3–30 µmol/L) or the caspase-3-specific inhibitor acetyl-DEVD-CHO (100 µmol/L) markedly attenuated H/R-induced apoptosis in hippocampal neurons. Capsaicin also markedly induced the phosphorylation of Akt. The phosphoinositide 3-kinase (PI3K) inhibitor LY294002 (10 µmol/L) prevented any capsaicin-induced survival effect in hippocampal neurons. Intracellular levels of reactive oxygen species (ROS), which were greatly increased after H/R, were significantly inhibited by capsaicin, pyrrolidine dithiocarbamate (PDTC) (50 µmol/L), and LY294002. Taken together, these data suggest that capsaicin protects against H/R-induced apoptosis of hippocampal neurons via the PI3K/Akt-mediated signaling pathway, which is related to the inhibition of oxidative stress and caspase-3 activation.

Brain TRPV1: a depressing TR(i)P down memory lane?

On sensory neurons, the capsaicin receptor TRPV1 (transient receptor potential, vanilloid subfamily, member 1) functions as a molecular integrator of noxious stimuli and represents a novel target for analgesic drugs. The presence of TRPV1 in the brain is now well established but, despite intensive research, its function is only beginning to be understood. New evidence implies an unexpected role for hippocampal TRPV1 in neuropsychiatric disorders. For instance, it was hypothesized that the effects of the cannabinoid-receptor antagonist rimonabant on mood might be due to its capability to antagonize TRPV1 receptors at high doses. Most studies, however, imply a positive (e.g. anxiolytic) outcome for TRPV1 antagonism. With potent small-molecule TRPV1 antagonists undergoing clinical trials, the effect of brain TRPV1 blockade might determine the future of this class of novel analgesic drugs. Clearly, more research is needed to delineate the biological role of brain TRPV1 receptors.

Drug therapies for stroke and traumatic brain injury often display U-shaped dose responses: occurrence, mechanisms, and clinical implications

This article explores the occurrence of U-shaped dose responses induced by neuroprotective agents in animal stroke and traumatic brain injury (TBI) screening/preclinical studies. The assessment was stimulated by suggestions that U-shaped dose responses may be common for neuroprotective agents in stroke and TBI models, and its lack of both recognition and understanding may be a factor contributing to the failure of many promising drugs to be protective in clinical trials. Over 30 agents with neuroprotective properties in animal stroke/TBI models were identified that act via U-shaped dose responses in a broad range of experimental protocols. These findings suggest that U-shaped dose responses in animal stroke/TBI models may be a general occurrence and have significant implications for drug discovery, drug development, and clinical practice.

TRPV1 channels mediate long-term depression at synapses on hippocampal interneurons

TRPV1 receptors have classically been defined as heat-sensitive, ligand-gated, nonselective cation channels that integrate nociceptive stimuli in sensory neurons. TRPV1 receptors have also been identified in the brain, but their physiological role is poorly understood. Here we report that TRPV1 channel activation is necessary and sufficient to trigger long-term synaptic depression (LTD). Excitatory synapses onto hippocampal interneurons were depressed by either capsaicin, a potent TRPV1 channel activator, or the endogenously released eicosanoid, 12-(S)-HPETE, whereas neighboring excitatory synapses onto CA1 pyramidal cells were unaffected. TRPV1 receptor antagonists also prevented interneuron LTD. In brain slices from TRPV1-/- mice, LTD was absent, and neither capsaicin nor 12-(S)-HPETE elicited synaptic depression. Our results suggest that, in the hippocampus, TRPV1 receptor activation selectively modifies synapses onto interneurons. Like other forms of hippocampal synaptic plasticity, TRPV1-mediated LTD may have a role in long-term changes in physiological and pathological circuit behavior during learning and epileptic activity.

Roles of transient receptor potential vanilloid subtype 1 and cannabinoid type 1 receptors in the brain: neuroprotection versus neurotoxicity

Transient receptor potential vanilloid subtype 1 (TRPV1), also known as vanilloid receptor 1 (VR1), is a nonselective cation channel that is activated by a variety of ligands, such as exogenous capsaicin (CAP) or endogenous anandamide (AEA), as well as products of lipoxygenases. Cannabinoid type 1 (CB1) receptor belongs to the G protein-coupled receptor superfamily and is activated by cannabinoids such as AEA and exogenous Delta-9-tetrahydrocannabinol (THC). TRPV1 and CB1 receptors are widely expressed in the brain and play many significant roles in various brain regions; however, the issue of whether TRPV1 or CB1 receptors mediate neuroprotection or neurotoxicity remains controversial. Furthermore, functional crosstalk between these two receptors has been recently reported. It is therefore timely to review current knowledge regarding the functions of these two receptors and to consider new directions of investigation on their roles in the brain.

Changes in brain levels of N-acylethanolamines and 2-arachidonoylglycerol in focal cerebral ischemia in mice

The N-acylethanolamines (NAEs) and 2-arachidonoylglycerol (2-AG) are bioactive lipids that can modulate inflammatory responses and protect neurons against glutamatergic excitotoxicity. We have used a model of focal cerebral ischemia in young adult mice to investigate the relationship between focal cerebral ischemia and endogenous NAEs. Over the first 24 h after induction of permanent middle cerebral artery occlusion, we observed a time-dependent increase in all the investigated NAEs, except for anandamide. Moreover, we found an accumulation of 2-AG at 4 h that returned to basal level 12 h after induction of ischemia. Accumulation of NAEs did not depend on regulation of N-acylphosphatidylethanolamine-hydrolyzing phospholipase D or fatty acid amide hydrolase. Treatment with the fatty acid amide hydrolase inhibitor URB597 (cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester; 1 mg/kg; i.p.) 1.5 h before arterial occlusion decreased the infarct volume in our model system. Our results suggest that NAEs and 2-AG may be involved in regulation of neuroprotection during focal cerebral ischemia in mice.

Delta9-tetrahydrocannabinol (THC) and AM 404 protect against cerebral ischaemia in gerbils through a mechanism involving cannabinoid and opioid receptors

BACKGROUND AND PURPOSE

It has been suggested that the endocannabinoid system elicits neuroprotection against excitotoxic brain damage. In the present study the therapeutic potential of AM 404 on ischaemia-induced neuronal injury was investigated in vivo and compared with that of the classical cannabinoid receptor type 1 (CB1) agonist, delta 9-tetraydrocannabinol (THC), using a model of transient global cerebral ischaemia in the gerbil.

EXPERIMENTAL APPROACH

The effects of AM 404 (0.015-2 mg kg(-1)) and THC (0.05-2 mg kg(-1)), given 5 min after ischaemia, were measured from 1 h to 7 days in terms of electroencephalographic (EEG) total spectral power, spontaneous motor activity, memory function, rectal temperature and hippocampal CA1 neuronal count.

KEY RESULTS

Over the dose range tested, AM 404 (2 mg kg(-1)) and THC (1 mg kg(-1)) completely reversed the ischaemia-induced behavioural, EEG and histological damage. Only THC (1 and 2 mg kg(-1)) induced a decrease of body temperature. Pretreatment with the selective CB1 receptor antagonist, AM 251 (1 mg kg(-1)) and the opioid antagonist, naloxone (2 mg kg(-1)) reversed the protective effect induced by both AM 404 and THC while the TRPV1 vanilloid antagonist, capsazepine (0.01 mg kg(-1)), was ineffective.

CONCLUSIONS AND IMPLICATIONS

Our findings demonstrate that AM 404 and THC reduce neuronal damage caused by bilateral carotid occlusion in gerbils and that this protection is mediated through an interaction with CB1 and opioid receptors. Endocannabinoids might form the basis for the development of new neuroprotective drugs useful for the treatment of stroke and other neurodegenerative pathologies.

Short- and long-term plasticity of the endocannabinoid system in neuropsychiatric and neurological disorders

The activity of the endocannabinoid system, in terms of the levels of the endocannabinoids and of cannabinoid receptors, or of the functional coupling of the latter to a biological response, undergoes to remodelling during pathological conditions. In the CNS, these changes, depending also on the nature of the disorder, can be transient or long-lasting, occur only in those tissues involved in the pathological condition and usually aim at restoring the physiological homeostasis by reducing excitotoxicity, inflammation and neuronal death. However, during chronic disorders, prolonged activation of the endocannabinoid system might also contribute to the symptoms of the pathology. Whilst acute changes of the tissue levels of the endocannabinoids reflect the "on demand" nature of their biosynthesis and release, and hence are effected mostly through regulation of the biosynthetic enzymes, chronic changes seem to be mostly due to longer-lasting alterations in the expression of anabolic and catabolic enzymes. The possibility of obtaining therapeutic advantage from endocannabinoid plasticity in neuropsychiatric and neurological disorders is discussed in this review article.

Cytotoxic edema: mechanisms of pathological cell swelling

✓Cerebral edema is caused by a variety of pathological conditions that affect the brain. It is associated with two separate pathophysiological processes with distinct molecular and physiological antecedents: those related to cytotoxic (cellular) edema of neurons and astrocytes, and those related to transcapillary flux of Na+and other ions, water, and serum macromolecules. In this review, the authors focus exclusively on the first of these two processes. Cytotoxic edema results from unchecked or uncompensated influx of cations, mainly Na+, through cation channels. The authors review the different cation channels that have been implicated in the formation of cytotoxic edema of astrocytes and neurons in different pathological states. A better understanding of these molecular mechanisms holds the promise of improved treatments of cerebral edema and of the secondary injury produced by this pathological process.

Cannabinoid modulation of neuronal function after oxygen/glucose deprivation in area CA1 of the rat hippocampus

Endocannabinoids released during cerebral ischemia have been implicated as neuroprotective agents. We assessed the role of cannabinoid receptors in modulating the response of neurons to oxygen/glucose deprivation (OGD), a model for in vitro ischemia, in rat hippocampal slices using extracellular recording techniques. Under control conditions, 15 min OGD resulted in only 50% recovery of CA1 field excitatory postsynaptic potentials (fEPSPs) 60 min post-insult. This post-OGD depression of function was primarily NMDA receptor-dependent as the NMDA receptor antagonist MK-801 (50 microM) promoted recovery of synaptic transmission to 76% of the baseline. Treatment with the CB1 receptor antagonist AM251 (1 microM), which prevented the depression of excitatory synaptic transmission caused by WIN55,212-2 (1 microM), also markedly enhanced recovery of function (71% of control). The enhanced recovery after OGD in the presence of AM251 was independent of both GABA(A) receptors and NMDA receptors since co-application of AM251 with either bicuculline (10 microM) or MK-801 (50 microM) did not alter recovery, or further improved recovery, respectively. These results suggest endocannabinoids released during OGD may modulate synaptic transmission and post-OGD neuronal outcome via activation of an AM251-sensitive cannabinoid receptor.

Non-selective cation channels, transient receptor potential channels and ischemic stroke

Several pathways to neural cell death are involved in ischemic stroke, and all require monovalent or divalent cation influx, implicating non-selective cation (NC) channels. NC channels are also likely to be involved in the dysfunction of vascular endothelial cells that leads to formation of edema following cerebral ischemia. Two newly described NC channels have emerged as potential participants in ischemic stroke, the acid sensing ion channel (ASIC), and the sulfonylurea receptor-1 (SUR1)-regulated NC(Ca-ATP) channel. Non-specific blockers of NC channels, including pinokalant (LOE 908 MS) and rimonabant (SR141716A), have beneficial effects in rodent models of ischemic stroke. Evidence is accumulating that NC channels formed by members of the transient receptor potential (TRP) family are also up-regulated in ischemic stroke and may play a direct role in calcium-mediated neuronal death. The nascent field of NC channels, including TRP channels, in ischemic stroke is poised to provide novel mechanistic insights and therapeutic strategies for this often devastating human condition.

Transient receptor potential cation channels in disease

The transient receptor potential (TRP) superfamily consists of a large number of cation channels that are mostly permeable to both monovalent and divalent cations. The 28 mammalian TRP channels can be subdivided into six main subfamilies: the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and the TRPA (ankyrin) groups. TRP channels are expressed in almost every tissue and cell type and play an important role in the regulation of various cell functions. Currently, significant scientific effort is being devoted to understanding the physiology of TRP channels and their relationship to human diseases. At this point, only a few channelopathies in which defects in TRP genes are the direct cause of cellular dysfunction have been identified. In addition, mapping of TRP genes to susceptible chromosome regions (e.g., translocations, breakpoint intervals, increased frequency of polymorphisms) has been considered suggestive of the involvement of these channels in hereditary diseases. Moreover, strong indications of the involvement of TRP channels in several diseases come from correlations between levels of channel expression and disease symptoms. Finally, TRP channels are involved in some systemic diseases due to their role as targets for irritants, inflammation products, and xenobiotic toxins. The analysis of transgenic models allows further extrapolations of TRP channel deficiency to human physiology and disease. In this review, we provide an overview of the impact of TRP channels on the pathogenesis of several diseases and identify several TRPs for which a causal pathogenic role might be anticipated.