Role Of Cannabinoid Receptor Type Research Articles

Cannabinoid Receptor‐Mediated Synaptic Signaling and Neural Plasticity in Central Olfactory Neurons

Our studies aim to understand integrative and computational mechanisms that allow main olfactory bulb neurons to respond to afferent input and synaptic or feedback signals. The endocannabinoid (eCB) signaling system has been functionally implicated in many brain regions but our understanding of the role of cannabinoid receptor type 1 (CB1R) in olfactory processing remains limited. Endocannabinoids are known to mediate retrograde signaling at synapses in several brain regions through a form of short‐term neural plasticity. Endocannabinoids are released from depolarized principal neurons and rapidly diffuse to presynaptic inhibitory interneurons to transiently reduce presynaptic firing and neurotransmitter (GABA) release (Depolarization‐Induced Suppression of Inhibition, DSI).We study the function of the endocannabinoid system in regulating neural activity at synapses in the main olfactory bulb, the first central relay station in the brain for the processing of olfactory information coming from the nose. Our experimental approach uses electrophysiological recording techniques, specifically whole cell patch‐clamp recordings. Previously, using anatomical approaches, we showed that CB1R is present in periglomerular processes of a GAD65‐positive population of interneurons but not in mitral cells, key output neurons. We detected eCBs in the mouse main olfactory bulb as well as the expression of CB1R and other genes associated with the cannabinoid signaling system.Output neurons such as mitral cells and tufted cells in the olfactory bulb are computational elements in brain circuits that integrate incoming signals with membrane properties to generate behaviorally relevant synaptic output. Our data support the notion that retrograde signaling is present in neural circuits involving mitral and tufted cells. Mitral and tufted cells release endocannabinoids and, through retrograde signaling, inhibit presynaptic interneurons such as periglomerular cells, which controls the GABA release of these presynaptic neurons. This, in turn, allows mitral and tufted cells to temporarily regulate their synaptic input and relieve them from synaptic inhibition. Endocannabinoids function as retrograde messengers to regulate neural signaling and mediate plasticity at olfactory bulb synapses with potential effects on olfactory threshold and behavior.

Induction of Liver Size Reduction in Zebrafish Larvae by the Emerging Synthetic Cannabinoid 4F-MDMB-BINACA and Its Impact on Drug Metabolism.

Zebrafish (ZF; Danio rerio) larvae have become a popular in vivo model in drug metabolism studies. Here, we investigated the metabolism of methyl 2-[1-(4-fluorobutyl)-1H-indazole-3-carboxamido]-3,3-dimethylbutanoate (4F-MDMB-BINACA) in ZF larvae after direct administration of the cannabinoid via microinjection, and we visualized the spatial distributions of the parent compound and its metabolites by mass spectrometry imaging (MSI). Furthermore, using genetically modified ZF larvae, the role of cannabinoid receptor type 1 (CB1) and type 2 (CB2) on drug metabolism was studied. Receptor-deficient ZF mutant larvae were created using morpholino oligonucleotides (MOs), and CB2-deficiency had a critical impact on liver development of ZF larva, leading to a significant reduction of liver size. A similar phenotype was observed when treating wild-type ZF larvae with 4F-MDMB-BINACA. Thus, we reasoned that the cannabinoid-induced impaired liver development might also influence its metabolic function. Studying the metabolism of two synthetic cannabinoids, 4F-MDMB-BINACA and methyl 2-(1-(5-fluoropentyl)-1H-pyrrolo[2,3-b]pyridine-3-carboxamido)-3,3-dimethylbutanoate (7′N-5F-ADB), revealed important insights into the in vivo metabolism of these compounds and the role of cannabinoid receptor binding.

P046 Effects of CB2 and TRPV1 stimulation on osteoclast overactivity induced by iron in pediatric inflammatory bowel disease

Abstract Background The reduction of bone mineral density and osteoporosis (OP) has an high impact on inflammatory bowel disease (IBD) patients’ health. We have previously shown that a dysregulated iron metabolism occurs in IBD and leads to a decrease in circulating iron concentration and an excessive intracellular sequestration of iron. Studies suggest that iron overload affects the bone, accelerating osteoclasts (OCs) differentiation and activation with consequent bone resorption. The aim of this study was to evaluate the role of Cannabinoid Receptor type 2 (CB2) and transient receptor potential vanilloid type-1 (TRPV1) and of the iron in the development of osteoporosis in pediatric IBD. Methods We enrolled 21 young subjects aged less than 18 years stratified into 3 groups on the basis of the clinical diagnosis: 7 with Ulcerative Colitis (UC) 7 with Crohn’s disease (CD) and 7 were non-IBD controls (CTR). We evaluated the role of CB2 and TRPV1 receptors and of iron in the development of OP in pediatric IBD at diagnosis and analyzed the effects of the pharmacological modulation of CB2 and TRPV1 receptors on osteoclast activity and on iron metabolism by Western Blotting, Tartrate-resistant acid phosphatase assay (TRAP assay) and Iron Assay Kit. We evaluated bone resorption through a commercially available kit visualizing and counting the resorption pits with the optical microscope. Results We observed higher levels of TRPV1 and lower levels of CB2 in the OCs from UC and CD patients compared to CTR. In IBD patients we found a significant up-regulation of osteoclast markers TRAP and Cathepsin K and a consequent osteoclast hyper-activation. The treatments of OCs from IBD patients with the CB2 agonist JWH-133 and the TRPV1 agonist Resinferatoxin, RTX, led to a significant reduction of osteoclastic hyper-activation affecting bone markers expression, number and size of active OCs, and bone resorption area. We also analyzed the [Fe3+] concentration and the expression of iron metabolism modulators, ferroportin1(FPN-1) and divalent metal transporter1(DMT1), in OCs derived from IBD patients. We demonstrated an increase of [Fe3+] and accordingly a decrease of FPN-1 in both groups of patients and an increase of DMT1 levels. After 48h of exposure to JWH-133 and RTX we observed a significant reduction of DMT1 expression in OCs from IBD patients together with a strong increase of FPN-1. Conclusion Our data confirm the well-known role of CB2 and TRPV1 receptors in bone metabolism and suggest that their stimulation can reduce the osteoclast overactivity induced by iron, thus providing new insights into the pathogenesis and in the treatment of pediatric IBD-related bone resorption.

Hippocampal astrocytes in juvenile rats with persistent epilepsy: the role of cannabinoid receptor type 2 in regulating MAPK pathway

Hippocampal astrocytes in juvenile rats with persistent epilepsy: the role of cannabinoid receptor type 2 in regulating MAPK pathway

The Role of Cannabinoid Receptor Type 2 in the Bone Loss Associated With Pediatric Celiac Disease.

In this study, we investigated the role of the cannabinoid receptor type 2 (CB2) in the bone loss associated with celiac disease (CD) evaluating the effect of its pharmacological modulation on osteoclast activity. We previously demonstrated a significant association between the CB2 Q63R variant and CD, suggesting it as a possible disease biomarker. Moreover, CB2 stimulation is beneficial for reducing osteoclast activity in several bone pathologic conditions. In vitro osteoclasts (OCs) were differentiated from peripheral blood mononuclear cells of healthy donors, CD children at diagnosis and after 1 year of gluten-free diet (GFD) and characterized by real-time PCR and western blot for the expression of CB2 and specific osteoclastic markers, TRAP and Cathepsin K. TRAP assay and Bone Resorption assay were performed to evaluate osteoclast activity before and after 48 h exposure to CB2 selective drugs (JWH-133 and AM630) and Vitamin D. We found in CD patients an osteoclast hyperactivation and low levels of CB2. CB2 stimulation with JWH-133 agonist is more effective than Vitamin D in reducing osteoclast activity whereas CB2 blockade with AM630 increases osteoclast activation. The anti-osteoporotic effect of JWH-133 decreases when used in co-treatment with vitamin D. GFD reduces osteoclast activity without restore CB2 expression. CB2 could be a molecular marker to predict the risk of bone alterations in CD and a pharmacological target to reduce bone mass loss in patients who need a direct intervention on bone metabolism, in addition to the GFD.

Cannabinoid receptor-mediated modulation of inhibitory inputs to mitral cells in the main olfactory bulb.

The endocannabinoid (eCB) signaling system has been functionally implicated in many brain regions. Our understanding of the role of cannabinoid receptor type 1 (CB1) in olfactory processing remains limited. Cannabinoid signaling is involved in regulating glomerular activity in the main olfactory bulb (MOB). However, the cannabinoid-related circuitry of inputs to mitral cells in the MOB has not been fully determined. Using anatomical and functional approaches we have explored this question. CB1 was present in periglomerular processes of a GAD65-positive subpopulation of interneurons but not in mitral cells. We detected eCBs in the mouse MOB as well as the expression of CB1 and other genes associated with cannabinoid signaling in the MOB. Patch-clamp electrophysiology demonstrated that CB1 agonists activated mitral cells and evoked an inward current, while CB1 antagonists reduced firing and evoked an outward current. CB1 effects on mitral cells were absent in subglomerular slices in which the olfactory nerve layer and glomerular layer were removed, suggesting the glomerular layer as the site of CB1 action. We previously observed that GABAergic periglomerular cells show the inverse response pattern to CB1 activation compared with mitral cells, suggesting that CB1 indirectly regulates mitral cell activity as a result of cellular activation of glomerular GABAergic processes . This hypothesis was supported by the finding that cannabinoids modulated synaptic transmission to mitral cells. We conclude that CB1 directly regulates GABAergic processes in the glomerular layer to control GABA release and, in turn, regulates mitral cell activity with potential effects on olfactory threshold and behavior.NEW & NOTEWORTHY Cannabinoid signaling with cannabinoid receptor type 1 (CB1) is involved in the regulation of glomerular activity in the main olfactory bulb (MOB). We detected endocannabinoids in the mouse MOB. CB1 was present in periglomerular processes of a GAD65-positive subpopulation of interneurons. CB1 agonists activated mitral cells. CB1 directly regulates GABAergic processes to control GABA release and, in turn, regulates mitral cell activity with potential effects on olfactory threshold and behavior.

Role of Cannabinoid Receptor Type 1 in Insulin Resistance and Its Biological Implications.

Endogenous cannabinoids (ECs) are lipid-signaling molecules that specifically bind to cannabinoid receptor types 1 and 2 (CB1R and CB2R) and are highly expressed in central and many peripheral tissues under pathological conditions. Activation of hepatic CB1R is associated with obesity, insulin resistance, and impaired metabolic function, owing to increased energy intake and storage, impaired glucose and lipid metabolism, and enhanced oxidative stress and inflammatory responses. Additionally, blocking peripheral CB1R improves insulin sensitivity and glucose metabolism and also reduces hepatic steatosis and body weight in obese mice. Thus, targeting EC receptors, especially CB1R, may provide a potential therapeutic strategy against obesity and insulin resistance. There are many CB1R antagonists, including inverse agonists and natural compounds that target CB1R and can reduce body weight, adiposity, and hepatic steatosis, and those that improve insulin sensitivity and reverse leptin resistance. Recently, the use of CB1R antagonists was suspended due to adverse central effects, and this caused a major setback in the development of CB1R antagonists. Recent studies, however, have focused on development of antagonists lacking adverse effects. In this review, we detail the important role of CB1R in hepatic insulin resistance and the possible underlying mechanisms, and the therapeutic potential of CB1R targeting is also discussed.

Role of cannabinoid receptor type 1 in rostral ventrolateral medulla in high-fat diet-induced hypertension in rats.

Stimulation of cannabinoid type 1 (CB1) receptor in the rostral ventrolateral medulla (RVLM) increases renal sympathetic activity (RSNA) and blood pressure (BP) in rats. Thus, we hypothesized that CB1 receptor in the RVLM may play a critical role in the development of obesity-induced hypertension. To this end, we evaluated the levels of endocannabinoids and CB1 receptors in the RVLM in high-fat diet (HFD)-induced hypertensive rats. We then used pharmacological and molecular methods to examine the role of RVLM CB1 receptors in regulation of BP, heart rate (HR), and RSNA in obesity-induced hypertensive rats. We found that HFD-fed rats exhibited higher basal BP, HR, and RSNA than standard diet-fed rats, which were associated with increased levels of endocannabinoids and CB1 receptor expression in the RVLM. Furthermore, unilateral intra-RVLM microinjections of AM251 (0, 100, or 500 nM/0.5 μl/site) dose-dependently decreased BP, HR, and RSNA to a greater extent in HFD-fed rats than in standard diet-fed rats. Finally, siRNA-mediated knockdown of CB1 receptor expression in the RVLM robustly decreased BP, HR, and RSNA in HFD-fed rats. Taken together, our results suggested that enhanced CB1 receptor-mediated neurotransmissions in the RVLM may play a role in the development of obesity-induced hypertension.

Activation of cannabinoid receptor type 2 by JWH133 alleviates bleomycin-induced pulmonary fibrosis in mice.

Activation of cannabinoid receptor type 2 has been shown to have anti-fibrosis function in skin and heart. However, whether activating cannabinoid receptor type 2 inhibits pulmonary fibrosis remains elusive. Lung fibroblasts and TGF-β1 are key players in the pathogenesis of pulmonary fibrosis. In this research, we aimed to investigate the role of cannabinoid receptor type 2 in pulmonary fibrosis in vitro and in vivo. In lung fibroblasts stimulated by TGF-β1, preincubated by cannabinoid receptor type 2 agonist JWH133 not only reduced the elevated levels of collagen I and α-SMA, but also inhibited fibroblasts’ proliferation and migration. The dosage of JWH133 had no clear cytotoxic activity, and all these JWH133 effects were partially abrogated by cannabinoid receptor type 2 antagonist SR144528. In bleomycin-induced mice pulmonary fibrosis model, CT images of the lung tissue revealed an extensive ground-glass opacity, reticular pattern and fibrosis stranding. Notably, JWH133 treatment controlled the ongoing fibrotic process (showed by decreased lung density and fibrosis score). Meanwhile, lung histological results revealed that JWH133 treatment suppressed both the inflammatory response and extracellular collagen deposition. SR144528 may increase the pulmonary fibrosis, but no statistically significant difference was proved. Importantly, JWH133 reduced serum profibrotic cytokines levels of TGF-β1 and inhibited TGF-β1/Smad2 pathway in vitro and in vivo. Our research indicated that activating cannabinoid receptor type 2 by a pharmacological method might be a potential strategy for pulmonary fibrosis.

The cannabinoid CB2 receptor-specific agonist AM1241 increases pentylenetetrazole-induced seizure severity in Wistar rats

The potential efficacy of cannabinoid receptor ligands for the treatment of epilepsy remains controversial; cannabis components that act via cannabinoid type 1 (CB1) receptors produce anticonvulsant effects in animal models despite treatment with the CB receptor agonist reliably inducing convulsions in various species. Moreover, the potential role of cannabinoid receptor type 2 (CB2) to modulate seizures remains under-investigated. This study assessed the effects of the selective CB2 receptor agonist, AM1241, on pentylenetetrazole (PTZ)-induced seizures in rats. A stereotactically placed guide cannula was surgically implanted into the right lateral ventricle in adult Wistar rats which, 5–6days later, received an acute intracerebroventricular (i.c.v.) microinfusion of AM1241 (0.01, 1 or 10μg/2μl or vehicle) 5min before intraperitoneal (i.p.) injection of PTZ (70mg/kg). Rats were observed for 30min and the seizure severity behavior measured using a modified Racine's scale. Additional groups of rats were pretreated with a single low dose of the selective CB2 receptor antagonist, AM630 (dose 1mg/kg; i.p.), or vehicle, 30min prior to i.c.v. microinfusion of AM1241 (1μg/2μl). AM1241 administration significantly increased tonic-clonic seizure incidence and severity while also decreasing the onset of generalized seizures (AM1241 1 and 10μg/2μl). Pretreatment with AM630 prevented the proconvulsant effects of AM1241. This study shows, for the first time, that selective activation of CB2 receptors can increase generalized seizure susceptibility and suggests that pathological hyperexcitability phenomena can be differentially regulated by targeting CB1 and CB2 receptors.

Anti-inflammatory role of cannabinoid receptor type 1 antagonist AM251 in high fat diet-induced obesity— a focus on microRNAs.

Abstract Obesity is a major health problem in the U.S. that continues to increase in prevalence. Excessive calorie consumption leads to expansion of adipose tissue through both hypertrophy and hyperplasia. As a result, adipocytes die and macrophages infiltrate into the adipose tissue to repair damage. Activation and infiltration of immune cells contribute to the chronic low-grade inflammation present in obesity. Immune cells express cannabinoid receptors that regulate inflammation. In this study, a mouse model of high fat diet-induced obesity was used to determine the effect the CB1 receptor antagonist AM251 has on adipose tissue inflammation. C57BL6 mice were fed a high fat diet (HFD) for twelve weeks to induce obesity and then given AM251 (10mg/kg/day) oral gavage for four weeks while continuing HFD. Treatment improved metabolic parameters while reducing fat mass and pro-inflammatory cytokine production. To further investigate the anti-inflammatory effects of AM251, infiltrating F4/80+ cells were isolated from epididymal fat and used for microRNA microarray. Nine miRNAs were differentially expressed as a result of AM251 treatment. These miRNAs were analyzed using Ingenuity Pathway Analysis software (Qiagen) and were found to significantly affect the “Inflammatory Disease and Inflammatory Response” pathways. Upregulated miRNAs such as miR-466i-3p were found to target macrophage polarization genes including Pik3r1. The current study suggests that CB1 antagonists may mediate anti-inflammatory effects and amelioration of obesity through regulation of miRNA expression. (Supported in parts by NIH grants P01AT003961, R01AT006888, R01ES019313, R01MH094755, P20GM103641, and Veterans Affairs Merit Award BX001357.)

Cannabinoid Receptor 2 Suppresses Leukocyte Inflammatory Migration by Modulating the JNK/c-Jun/Alox5 Pathway

The role of cannabinoid receptor type 2 (Cnr2) in regulating immune function had been widely investigated, but the mechanism is not fully understood. Cnr2 activation down-regulates 5-lipoxygenase (Alox5) expression by suppressing the JNK/c-Jun activation. The Cnr2-JNK-Alox5 axis modulates leukocyte inflammatory migration. Linking two important regulators in leukocyte inflammatory migration and providing a potential therapeutic strategy for treating human inflammation-associated diseases. Inflammatory migration of immune cells is involved in many human diseases. Identification of molecular pathways and modulators controlling inflammatory migration could lead to therapeutic strategies for treating human inflammation-associated diseases. The role of cannabinoid receptor type 2 (Cnr2) in regulating immune function had been widely investigated, but the mechanism is not fully understood. Through a chemical genetic screen using a zebrafish model for leukocyte migration, we found that both an agonist of the Cnr2 and inhibitor of the 5-lipoxygenase (Alox5, encoded by alox5) inhibit leukocyte migration in response to acute injury. These agents have a similar effect on migration of human myeloid cells. Consistent with these results, we found that inactivation of Cnr2 by zinc finger nuclease-mediated mutagenesis enhances leukocyte migration, while inactivation of Alox5 blocks leukocyte migration. Further investigation indicates that there is a signaling link between Cnr2 and Alox5 and that alox5 is a target of c-Jun. Cnr2 activation down-regulates alox5 expression by suppressing the JNK/c-Jun activation. These studies demonstrate that Cnr2, JNK, and Alox5 constitute a pathway regulating leukocyte migration. The cooperative effect between the Cnr2 agonist and Alox5 inhibitor also provides a potential therapeutic strategy for treating human inflammation-associated diseases.

Multipotent to Pluripotent Properties of Adult Stem Cells

Stem cells have captured the attention of both researchers and the public alike because of the promise of tissue regeneration, drug screening, and organogenesis. Stem cells are broadly classified as embryonic or adult with differentiation capacities ranging from pluripotent and multipotent to unipotent. In general, pluripotent stem cells are ascribed to cells derived from the inner cell mass of blastocyst stage embryos or to those generated experimentally using reprogramming factors. Adult stem or progenitor cells are generally tissue-restricted but reside in most organs. While the use of pluripotent stem cells has been limited to a few clinical trials due to safety concerns, adult stem cells have shown evidence of safety and are broadly employed in both clinical trials (http://www.clinicaltrial.gov/) and clinical practice. Transplantation of adult bone marrow hematopoietic stem cells, for example, represents a standard method of clinical care for autoimmune diseases and hematological disorders. While hematopoietic stem cells cannot be expanded in vitro, other stem cells such as mesenchymal stem cells (MSCs) can be easily expanded from autologous and allogeneic sources for clinical testing. Moreover, adult-derived testicular spermatogonial stem cells (SSCs) have been reported to be the only cells in the body that can be dedifferentiated/reprogrammed to a pluripotent state in vitro and grown into ES-like colonies. It has been advocated that adult stem cells have remarkable plasticity, transdetermination, and transdifferentiation ability. These properties have raised hope that adult stem cells could become a universal source of stem cells for tissue/organ repair in lieu of embryonic stem cells, which can easily form tumors. MSCs, for example, can be isolated from various tissues like bone marrow, gut, lungs, liver, blood, adipose tissue, umbilical cord Wharton's jelly, dental pulp, amniotic fluid, and so forth and have the ability to form bone, cartilage, adipose tissue, skeletal muscle, liver, neurons, skin, pancreatic islets, endothelial cells, intestine, renal, epithelial, and germ cells. More importantly, MSCs can be given across allogeneic barriers. Nevertheless, many trials with MSCs have shown only marginal benefits and some have proposed that the effects may be more paracrine in nature than being regenerative. This special issue, comprised of 10 articles, focuses on adult stem cells that examine the following claims: Why are MSCs ubiquitous? Are they indeed stem cells or just stromal cells which constitute the somatic niche for tissue specific stem cells in various body organs? Have we looked carefully at MSCs growing in a culture dish? Are ES-like colonies observed only from testicular biopsy but also from ovarian and endometrial biopsies? The article by D. Bhartiya addresses these issues and reviews the available literature on the presence of novel pluripotent very small ES-like stem cells (VSELs) as a subgroup among MSCs. It also highlights that Oct-4A transcripts need to be studied to conclude pluripotent state rather than Oct-4. An article by Dr. P. Rameshwar's group studied the safety issue of MSCs since these stem cells have been shown to support tumor growth. Other papers have discussed various sources of adult stem cells including dental pulp stem cells (S. Arrifin et al.), satellite stem cells in skeletal muscles (S. Fujimaki et al.), and bone marrow stem cells (I. Catacchio et al.) and their multipotent properties and transdifferentiation potential. Further characterization of these stem cells and their functional potential is essential. The role of cannabinoid receptor type I in differentiation and survival of MSCs is discussed by A. Gowran et al. M. Akita et al. show that CD133 positive cells have the capacity to form endothelial capillary tubes in 3D culture. Cultures of cardiac explants result in the formation of cardiospheres which contain both stem and progenitor cells implicated in cardiac regeneration (L. Barile et al.). Y. Togo et al. have reviewed the literature on the use of MSCs as a nonviral gene carrier for gene transfer in vitro. Finally, N. Sakayori et al. discuss how neural stem/progenitor cells function is regulated by lipids. The diverse areas of the manuscripts in this issue underscore the wide field of adult stem cell biology. The papers indicate that more in-depth research and functional studies are required to take adult stem cells safely to the clinic for regenerative medicine. Deepa Bhartiya Kenneth R. Boheler Pranela Rameshwar

Protective Role of Cannabinoid Receptor Type 2 in a Mouse Model of Diabetic Nephropathy

OBJECTIVEThe cannabinoid receptor type 2 (CB2) has protective effects in chronic degenerative diseases. Our aim was to assess the potential relevance of the CB2 receptor in both human and experimental diabetic nephropathy (DN).RESEARCH DESIGN AND METHODSCB2 expression was studied in kidney biopsies from patients with advanced DN, in early experimental diabetes, and in cultured podocytes. Levels of endocannabinoids and related enzymes were measured in the renal cortex from diabetic mice. To assess the functional role of CB2, streptozotocin-induced diabetic mice were treated for 14 weeks with AM1241, a selective CB2 agonist. In these animals, we studied albuminuria, renal function, expression of podocyte proteins (nephrin and zonula occludens-1), and markers of both fibrosis (fibronectin and transforming growth factor-β1) and inflammation (monocyte chemoattractant protein-1 [MCP-1], CC chemokine receptor 2 [CCR2], and monocyte markers). CB2 signaling was assessed in cultured podocytes.RESULTSPodocytes express the CB2 receptor both in vitro and in vivo. CB2 was downregulated in kidney biopsies from patients with advanced DN, and renal levels of the CB2 ligand 2-arachidonoylglycerol were reduced in diabetic mice, suggesting impaired CB2 regulation. In experimental diabetes, AM1241 ameliorated albuminuria, podocyte protein downregulation, and glomerular monocyte infiltration, without affecting early markers of fibrosis. In addition, AM1241 reduced CCR2 expression in both renal cortex and cultured podocytes, suggesting that CB2 activation may interfere with the deleterious effects of MCP-1 signaling.CONCLUSIONSThe CB2 receptor is expressed by podocytes, and in experimental diabetes, CB2 activation ameliorates both albuminuria and podocyte protein loss, suggesting a protective effect of signaling through CB2 in DN.

Role of Cannabinoid Receptor Type 1 Desensitization in Greater Tetrahydrocannabinol Impairment of Memory in Adolescent Rats

Adolescence is a well defined developmental period during which marijuana use is common. However, little is known about the response to marijuana in adolescents compared with adults. We have shown previously that adolescent rats are more impaired than adults by Δ(9)-tetrahydrocannabinol (THC), the main psychoactive compound in marijuana, in a spatial learning task, but the mechanism responsible for this differential impairment is not understood. We determined the role of THC tolerance and cannabinoid receptor type 1 (CB1) regulation in THC-induced spatial learning impairment in adolescent and adult rats. We measured the development of tolerance to THC-induced learning impairment in adolescent (postnatal days 30-35) and adult (postnatal days 70-75) rats. We pretreated them for 5 days with 10 mg/kg THC, and then evaluated the effects of vehicle or THC treatment on learning during training in the Morris water maze. We also determined CB1 number and functional coupling in the hippocampus of adolescents and adults. Finally, we measured the time course of hippocampal CB1 desensitization in adolescents and adults during treatment with 10 mg/kg THC or vehicle. Our results indicate that adults, but not adolescents, become tolerant to the effects of THC during water maze training after 5 days of pretreatment. CB1s in adolescent hippocampus are less functionally coupled to G proteins and desensitize more slowly in response to THC treatment than those of adults. THC may impair learning in adolescents more than in adults because of delayed activation of cellular homeostatic adaptive mechanisms underlying cannabinoid tolerance in the hippocampus.

Functional blockage of the cannabinoid receptor type 1 evokes a kappa‐opiate‐dependent analgesia

Progress in the control and treatment of pain may be facilitated by a better understanding of mechanisms underlying nociceptive processing. Cannabinoids and opioids are endogenous modulator of pain sensation, but therapies based in these compounds are not completely exploited because of their side effects. To test the role of cannabinoid receptor type 1 (CB1-R) inhibition in nociception, we performed a subchronic administration of the CB1-R antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM281) in mice. This treatment provoked analgesia in peripheral thermal and visceral models of pain. Analysis of genes encoded for the opioid system in the spinal cord showed an increase in the expression of genes encoded for the κ-opioid system in AM281-injected mice compared with vehicle-injected ones. Furthermore, systemic administration of nor-binaltorphimine, a κ-opioid receptor antagonist, blocked AM281-induced analgesia. Finally, c-fos expression in the dorsal spinal cord and higher centers of pain processing after noxious stimulation were significantly lower in AM281-injected mice than in vehicle-injected animals, indicating that dynorphin could block nociceptive information transmission at the spinal cord level. These results indicate the existence of a cross-talk between opioid and cannabinoid systems in nociception. Furthermore, the results suggest that CB1-R antagonists could be useful as a new therapeutic approach for pain relief.

Impaired cannabinoid receptor type 1 signaling interferes with stress-coping behavior in mice

Dysregulation of the endocannabinoid system is known to interfere with emotional processing of stressful events. Here, we studied the role of cannabinoid receptor type 1 (CB1) signaling in stress-coping behaviors using the forced swim test (FST) with repeated exposures. We compared effects of genetic inactivation with pharmacological blockade of CB1 receptors both in male and female mice. In addition, we investigated potential interactions of the endocannabinoid system with monoaminergic and neurotrophin systems of the brain. Naive CB1 receptor-deficient mice (CB1-/-) showed increased passive stress-coping behaviors as compared to wild-type littermates (CB1+/+) in the FST, independent of sex. These findings were partially reproduced in C57BL/6N animals and fully reproduced in female CB1+/+ mice by pharmacological blockade of CB1 receptors with the CB1 receptor antagonist SR141716. The specificity of SR141716 was confirmed in female CB1-/- mice, where it failed to affect behavioral performance. Sensitivity to the antidepressants desipramine and paroxetine was preserved, but slightly altered in female CB1-/- mice. There were no genotype differences between CB1+/+ and CB1-/- mice in monoamine oxidase A and B activities under basal conditions, nor in monoamine content of hippocampal tissue after FST exposure. mRNA expression of vesicular glutamate transporter type 1 was unaffected in CB1-/- mice, but mRNA expression of brain-derived neurotrophic factor (BDNF) was reduced in the hippocampus. Our results suggest that impaired CB1 receptor function promotes passive stress-coping behavior, which, at least in part, might relate to alterations in BDNF function.