Endocannabinoid Production Research Articles

Purine receptor‐mediated endocannabinoid production and retrograde synaptic signalling in the cerebellar cortex

Presynaptic CB₁ cannabinoid receptors can be activated by endogenous cannabinoids (endocannabinoids) synthesized by postsynaptic neurones. The hypothesis of the present work was that activation of calcium-permeable transmitter-gated ion channels in postsynaptic neurones, specifically of P2X purine receptors, can lead to endocannabinoid production and retrograde synaptic signalling. GABAergic inhibitory postsynaptic currents (IPSCs) were recorded with patch-clamp techniques in Purkinje cells in mouse cerebellar slices. Purine receptors on Purkinje cells were activated by pressure ejection of ATP from a pipette. ATP evoked an inward current in Purkinje cells, most likely due to P2X receptor activation. The ATP-evoked currents were accompanied by currents via voltage-gated calcium channels. ATP suppressed electrical stimulation-evoked IPSCs and miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin, and these effects were prevented by the CB₁ antagonist rimonabant and the calcium chelator BAPTA (applied into the Purkinje cell). ATP also suppressed mIPSCs when voltage-gated calcium channels were blocked by cadmium, and intracellular calcium stores were depleted by thapsigargin. However, ATP failed to suppress mIPSCs when the extracellular calcium concentration was zero. ATP elicits CB₁ receptor-dependent retrograde synaptic suppression, which is probably mediated by an endocannabinod released by the postsynaptic neurone. An increase in intracellular calcium concentration in the postsynaptic neurone is necessary for this retrograde signalling. We propose that ATP increases the calcium concentration by two mechanisms: calcium enters into the neurone via the P2X receptor ion channel and the ATP-evoked depolarization triggers voltage-gated calcium channels.

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.

Postsynaptic TRPV1 triggers cell type–specific long-term depression in the nucleus accumbens

Synaptic modifications in the nucleus accumbens (NAc) are important for adaptive and pathological reward-dependent learning. Medium spiny neurons (MSNs), the major cell type in the NAc, participate in two parallel circuits that subserve distinct behavioral functions, yet little is known about differences in their electrophysiological and synaptic properties. Using bacterial artificial chromosome transgenic mice, we found that synaptic activation of group I metabotropic glutamate receptors in NAc MSNs in the indirect, but not direct, pathway led to the production of endocannabinoids, which activated presynaptic CB1 receptors to trigger endocannabinoid-mediated long-term depression (eCB-LTD) as well as postsynaptic transient receptor potential vanilloid 1 (TRPV1) channels to trigger a form of LTD resulting from endocytosis of AMPA receptors. These results reveal a previously unknown action of TRPV1 channels and indicate that the postsynaptic generation of endocannabinoids can modulate synaptic strength in a cell type-specific fashion by activating distinct pre- and postsynaptic targets.

Cross-regulation of cannabinoid CB1 and CB2 receptors governs hepatic steatosis

Cross-regulation of cannabinoid CB1 and CB2 receptors governs hepatic steatosis

Endocannabinoid-mediated synaptically evoked suppression of GABAergic transmission in the cerebellar cortex

Presynaptic CB1 cannabinoid receptors are frequently targets of endogenous cannabinoids (endocannabinoids) released from postsynaptic neurons. It is known that the glutamatergic afferent input to a neuron can trigger endocannabinoid production and that the released endocannabinoid can suppress the glutamatergic input. We tested the hypothesis that activation of the glutamatergic input to a neuron leads to an endocannabinoid-mediated suppression of the GABAergic afferent input to the same neuron. Spontaneous postsynaptic currents (sPSCs) were recorded with patch-clamp techniques in Purkinje cells in mouse cerebellar brain slices. Activation of the climbing fiber-mediated glutamatergic input to Purkinje cells led to a suppression of the sPSCs by 34±3%. This suppression was mostly due to suppression of GABAergic spontaneous inhibitory postsynaptic current (sIPSCs), because 93% of the sPSCs recorded in Purkinje cells were GABAergic sIPSCs. Blockade of ionotropic, but not metabotropic glutamate receptors, prevented the suppression. The climbing fiber activation led to an increase in calcium concentration in the Purkinje cells, and this increase was necessary for the suppression of sPSCs, because the suppression did not occur when the calcium increase was prevented by BAPTA. No sPSC suppression was observed in the presence of the CB1 antagonist rimonabant or the diacylglycerol lipase inhibitor orlistat. In a further series of experiments GABAergic sIPSCs were recorded: these sIPSCs were also suppressed after climbing fiber activation, and the suppression was sensitive to the CB1 antagonist SLV319. Finally, the GABAergic synaptic transmission between molecular layer interneurons and Purkinje cells was directly studied on simultaneously patch-clamped neuron pairs. Climbing fiber activation led to suppression of the interneuron → Purkinje cell synaptic transmission. The results point to a novel form of endocannabinoid-mediated heterosynaptic plasticity. The endocannabinoid production in a neuron is triggered by its glutamatergic synaptic input and is dependent on an increase in intracellular calcium concentration. The produced endocannabinoid, in turn, suppresses the GABAergic synaptic input to the neuron by activating CB1 cannabinoid receptors.

Characterization of mice lacking candidate N-acyl ethanolamine biosynthetic enzymes provides evidence for multiple pathways that contribute to endocannabinoid production in vivo

The biosynthesis of the endocannabinoid anandamide (AEA) and related N-acyl ethanolamine (NAE) lipids is complex and appears to involve multiple pathways, including: (1) direct release of NAEs from N-acyl phosphatidyl ethanolamine (NAPE) precursors by the phosphodiesterase NAPE-PLD, and (2) double O-deacylation of NAPEs followed by phosphodiester bond hydrolysis of the resulting glycero-phospho (GP)-NAEs. We recently identified GDE1 as a GP-NAE phosphodiesterase that may be involved in the second pathway. Here, we report the generation and characterization of GDE1(-/-) mice, which are viable and overtly normal in their cage behavior. Brain homogenates from GDE1(-/-) mice exhibit a near-complete loss of detectable GP-NAE phosphodiesterase activity; however, bulk brain levels of AEA and other NAEs were unaltered in these animals. To address the possibility of compensatory pathways, we generated GDE1(-/-)/NAPE-PLD(-/-) mice. Conversion of NAPE to NAE was virtually undetectable in brain homogenates from these animals as measured under standard assay conditions, but again, bulk changes in brain NAEs were not observed. Interestingly, significant reductions in the accumulation of brain NAEs, including anandamide, were detected in GDE1(-/-)/NAPE-PLD(-/-) mice treated with a fatty acid amide hydrolase (FAAH) inhibitor that blocks NAE degradation. Finally, we determined that primary neurons from GDE1(-/-)/NAPE-PLD(-/-) mice can convert NAPEs to NAEs by a pathway that is not preserved following cell homogenization. In summary, combined inactivation of GDE1 and NAPE-PLD results in partial disruption of NAE biosynthesis, while also pointing to the existence of an additional enzymatic pathway(s) that converts NAPEs to NAEs. Characterization of this pathway should provide clarity on the multifaceted nature of NAE biosynthesis.

Therapeutic approach to eating disorders: the biological background

There is a great deal of uncertainty about response of eating disorders to treatment. This is in part due to the fact that not only their etiologic and pathogenetic bases, but also their classification, prevalence, course, comorbidities and prognosis are continually undergoing new appraisal and definition. Eating disorders are the expression of both psychological and physical pathologies, and each of these components has prevailed from time to time and from study to study, orienting toward different diagnoses and supporting different treatments. Today, the psychological component is considered the core of eating disorders, while the physical component is regarded as just the consequence of the aberrant eating behaviours. However, this is to some extent questionable, since some physical impairments are involved in the development of certain psychopathological aspects, contributing to their maintenance, prognosis and response to treatments. Genetic, biological, temperamental and family-social factors have been in turn considered as primary causes for the development of eating disorders, but they are probably effective only when they act all together as a concurrence of causes 1-4. This raises some intriguing questions about treatment of eating disorders: which etiopathogenetic factors must we confront in our treatments? Which should we address as first? Or should we confront all of them simultaneously? Unfortunately, at the moment we have no definitive answer to these questions. K. Halmi describes what can be considered today the optimal approach to the treatment of eating disorders. Why are the results of this approach not predictable and not always satisfactory? One reason could be that we do not know exactly what brain biological impairments are present in patients with eating disorders during the symptomatic phases of their disease, after recovery or when the disorder becomes chronic. Central neurotransmitter alterations have been reported in small groups of patients, with decreased serotonin, noradrenaline and brain-derived neurotrophic factor and increased neuropeptide Y and endocannabinoid production in anorexia nervosa and, in some cases, bulimia nervosa patients 5-7. As for dopamine, data are discordant, revealing either hypo- or hypersecretion of the amine in anorexia nervosa, and hypo- or normosecretion in bulimia nervosa 8,9. However, all these changes reflect mean values of study groups. We do not know whether these alterations occur in every patient or are limited to some of them, being responsible for the prognosis of eating disorders or for some aspects of psychopathology which characterize subgroups of patients. At the moment, we do not have enough data to settle this issue, but the possible biochemical variability from patient to patient or from time to time during the course of the disease may be one reason for the relatively inconsistent and unpredictable responses to treatments 10. Moreover, some of the neurotransmitter alterations are still present long after the recovery of eating disorders, possibly being responsible for relapses and chronicity. Increased 5-HT2A receptors in anorexia and bulimia nervosa, and reduced 5-HT1A receptors as well as increased D2/D3 receptors binding in anorexia nervosa have been observed in specific brain areas one year after recovery, and it has been suggested that a central serotonin and/or dopamine hyperactivity could represent a biological trait of vulnerability to eating disorders, needing correction to prevent relapses and/or recurrences 11-13. At present, no specific psychopharmacological trial has been conducted to verify this hypothesis. As Halmi outlines in a recent editorial 14, “it is unlikely that predictably effective treatment for anorexia nervosa (and, we believe, also for other eating disorders) will be available until we decipher the reinforcing neurobiological mechanisms sustaining the disorder”.

Metaplasticity of Hypothalamic Synapses following In Vivo Challenge

Neural networks that regulate an organism's internal environment must sense perturbations, respond appropriately, and then reset. These adaptations should be reflected as changes in the efficacy of the synapses that drive the final output of these homeostatic networks. Here we show that hemorrhage, an in vivo challenge to fluid homeostasis, induces LTD at glutamate synapses onto hypothalamic magnocellular neurosecretory cells (MNCs). LTD requires the activation of postsynaptic alpha2-adrenoceptors and the production of endocannabinoids that act in a retrograde fashion to inhibit glutamate release. In addition, both hemorrhage and noradrenaline downregulate presynaptic group III mGluRs. This loss of mGluR function allows high-frequency activity to potentiate these synapses from their depressed state. These findings demonstrate that noradrenaline controls a form of metaplasticity that may underlie the resetting of homeostatic networks following a successful response to an acute physiological challenge.

Neurotensin inhibition of GABAergic transmission via mGluR‐induced endocannabinoid signalling in rat periaqueductal grey

Neurotensin modulates pain via its actions within descending analgesic pathways which include brain regions such as the midbrain periaqueductal grey (PAG). The aim of this study was to examine the cellular actions of neurotensin on PAG neurons. Whole cell patch clamp recordings were made from rat midbrain PAG slices in vitro to examine the postsynaptic effects of neurotensin and its effects on GABA(A) mediated inhibitory postsynaptic currents (IPSCs). Neurotensin (100-300 nM) produced an inward current in subpopulations of opioid sensitive and insensitive PAG neurons which did not reverse over membrane potentials between -50 and -130 mV. The neurotensin induced current was abolished by the NTS1 and NTS1/2 antagonists SR48692 (300 nM) and SR142948A (300 nM). Neurotensin also produced a reduction in the amplitude of evoked IPSCs, but had no effect on the rate and amplitude of TTX-resistant miniature IPSCs. The neurotensin induced inhibition of evoked IPSCs was reduced by the mGluR5 antagonist MPEP (5microM) and abolished by the cannabinoid CB(1) receptor antagonist AM251 (3 microM). These results suggest that neurotensin produces direct neuronal depolarisation via NTS1 receptors and inhibits GABAergic synaptic transmission within the PAG. The inhibition of synaptic transmission is mediated by neuronal excitation and action potential dependent release of glutamate, leading to mGluR5 mediated production of endocannabinoids which activate presynaptic CB(1) receptors. Thus, neurotensin has cellular actions within the PAG which are consistent with both algesic and analgesic activity, some of which are mediated via the endocannabinoid system.

Depolarizing GABAergic synaptic input triggers endocannabinoid‐mediated retrograde synaptic signaling

Endocannabinoids released by postsynaptic neurons inhibit neurotransmitter release from presynaptic axon terminals. One typical stimulus of endocannabinoid production is an increase of calcium concentration in postsynaptic neurons. The aim of the present study was to clarify whether depolarizing GABAergic synaptic input, by increasing calcium concentration in postsynaptic neurons, can trigger endocannabinoid production. Spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) were recorded in Purkinje cells in mouse cerebellar slices with patch-clamp pipettes containing 151 mM chloride (a usual recording mode). sIPSCs were depolarizing inward currents under this condition. Combined electrophysiological and fluorometric calcium imaging experiments indicated that sIPSCs frequently triggered calcium spikes. After the calcium spikes, a short-term suppression of sIPSCs occurred. This suppression was prevented by the CB(1) cannabinoid receptor antagonist rimonabant and the diacylglycerol lipase inhibitor orlistat, but not changed by URB597, an inhibitor of anandamide degradation. It is, therefore, likely that CB(1) receptors and 2-arachidonoylglycerol were involved. For testing the physiological significance of the above observation, we carried out experiments on brains of 3- to 5-day-old mice. The gramicidin-induced perforated patch-clamp mode was used for preserving the physiological intracellular chloride concentration of the neurons. Depolarizing GABAergic sIPSCs occurred under this condition, but at a very low rate. Rimonabant did not change the frequency of these sIPSCs, arguing against the persistence of an endocannabinoid tone. The results point to a new kind of trigger of endocannabinoid production: depolarizing GABAergic synaptic input can elicit endocannabinoid production in postsynaptic neurons by activating calcium channels. The produced endocannabinoid suppresses GABA release from presynaptic axon terminals.

Regular firing of a single output neuron reduces its own inhibition through endocannabinoids in substantia nigra pars reticulata of juvenile mice

Depolarization-induced suppression of inhibition in substantia nigra pars reticulata suggests that burst-like activity but not regular firing suffices to activate presynaptic endocannabinoid CB1 receptors. To more closely determine the type of activity required, we applied gramicidin perforated patch recording under visual control to substantia nigra slices of juvenile mice. We found that evoked inhibitory postsynaptic currents (eIPSCs) were reduced in amplitude by the spontaneous firing of a neuron under study, whereas silencing this neuron enhanced inhibitory responses. Autonomous firing reduced eIPSCs to 78%±2% in a time- but not frequency-dependent manner. The phenomenon which we termed firing-induced suppression of inhibition was cannabinoid receptor subtype 1–dependent, whereas adenosine A1 receptors played only a minor role. Depletion of intracellular Ca2+ stores abolished the firing-induced suppression of inhibition suggesting that Ca2+ release from internal stores is necessary for the production of endocannabinoids during autonomous firing. We suggest that the Ca2+ influx during autonomous activity of pars reticulata neurons suffices to selectively dampen incoming inhibition from striatal neurons because it is amplified by ryanodine receptor-mediated Ca2+ release from intracellular stores.

Interactions between cannabinoids and alcohol

Event Abstract Back to Event Interactions between cannabinoids and alcohol Fernando Rodriguez-de-Fonseca1* 1 Hospital Carlos Haya, Avenida Carlos Haya 82, Laboratorio de Medicina Regenerativa, Fundación IMABIS, Spain The endogenous cannabinoid anandamide participates in the neuroadaptations associated with chronic ethanol exposure and serves as a link between exogenous cannabinoid administration and alcohol actions. While cannabinoid exposure favors alcohol intake, cannabinoid CB1 receptor antagonist reduces both alcohol intake and cue-induced relapse to alcohol selfadministration. Thus, intraperitoneal administration of the cannabinoid CB1 receptor antagonist SR141716A (0.03, 1.0 and 3.0 mg/kg) markedly inhibits ethanol selfadministration and conditioned reinstatement of ethanol-seeking behavior in both Wistar and Marchegian-Sardinian Alcohol preferring rats (mSp). ED50 analysis showed significantly higher sensitivity (p<0.05) to the effect of SR141716A in msP rats compared to heterogeneous Wistar rats. On the other side, acute peripheral administration of ethanol (4 gr/kg, i.p.) decreased anandamide in the cerebellum, the hippocampus and the ventral striatum, as well as in plasma and adipose tissue. Parallel decreases of a second acylethanolamide, palmithylethanolamide were observed in the brain. Effects were observed 45-90 min after ethanol administration. In vivo studies revealed that anandamide decreases were associated with a remarkable inhibition of the release of both anadamide and glutamate release in the ventral striatum. There were no changes in the expression and enzimatic activity of the main enzyme that degradates anandamide, the fatty acid amidohydrolase. Acute ethanol did not change neither the activity of n-acyltransferase, the enzyme that catalyzes the synthesis of the anandamide precursor, nor the expression of NAPE-PLD, the enzyme that releases anandamide from membrane phospholipid precursors. These results suggest that receptor-mediated release of acylethanolamide is inhibited by the acute administration of ethanol, and that this effect is not derived of increased fatty acid ethanolamide degradation. In conclusion, we provide clear evidence that the endogenous cannabinoid system participates in alcohol-seeking behavior in rats, and that alcohol directly modulates endocannabinoid production. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Oral Presentation Topic: Symposium 02 – Cannabinoids and brain reward processes Citation: Rodriguez-de-Fonseca F (2009). Interactions between cannabinoids and alcohol. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.009 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 Nov 2009; Published Online: 18 Nov 2009. * Correspondence: Fernando Rodriguez-de-Fonseca, Hospital Carlos Haya, Avenida Carlos Haya 82, Laboratorio de Medicina Regenerativa, Fundación IMABIS, 13331 Marseille, Spain, fernando.rodriguez@ibima.eu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Fernando Rodriguez-de-Fonseca Google Fernando Rodriguez-de-Fonseca Google Scholar Fernando Rodriguez-de-Fonseca PubMed Fernando Rodriguez-de-Fonseca Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The Endocannabinoid 2-Arachidonoylglycerol Is Responsible for the Slow Self-Inhibition in Neocortical Interneurons

In the CNS, endocannabinoids are identified mainly as two endogenous lipids: anandamide, the ethanolamide of arachidonic acid, and 2-arachidonoylglycerol (2-AG). Endocannabinoids are known to inhibit transmitter release from presynaptic terminals; however we have recently demonstrated that they are also involved in slow self-inhibition (SSI) of layer V low-threshold spiking (LTS) interneurons in rat somatosensory cortex. SSI is induced by repetitive firing in LTS cells, which can express either cholecystokinin or somatostatin. SSI is triggered by an endocannabinoid-dependent activation of a prolonged somatodendritic K(+) conductance and associated hyperpolarization in the same cell. The synthesis of both endocannabinoids is dependent on elevated [Ca(2+)](i) such as occurs during sustained neuronal activity. To establish whether 2-AG mediates autocrine LTS-SSI, we blocked its biosynthesis from phospholipase C (PLC) and diacylglycerol lipases (DAGLs). Current-clamp recordings from LTS interneurons in acute neocortical slices showed that inclusion of DAGL inhibitors in the whole-cell pipette prevented the long-lasting hyperpolarization triggered by LTS cell repetitive firing. Similarly, extracellular applications of a PLC inhibitor prevented SSI in LTS interneurons. Moreover, metabotropic glutamate receptor-dependent activation of PLC produced a long-lasting hyperpolarization which was prevented by the CB1 antagonist AM251, as well as by PLC and DAGL inhibitors. The loss of SSI in the presence of intracellular DAGL blockers confirms that endocannabinoid production occurs in the same interneuron undergoing the persistent hyperpolarization. Since DAGLs produce no endocannabinoid other than 2-AG, these results identify this compound as the autocrine mediator responsible for the postsynaptic slow self-inhibition of neocortical LTS interneurons.

Predominant expression of phospholipase Cβ1 in telencephalic principal neurons and cerebellar interneurons, and its close association with related signaling molecules in somatodendritic neuronal elements

Upon activation of receptors coupled to the Gq subclass of G proteins, phospholipase C (PLC)beta hydrolyses membrane phospholipid to yield a pair of second messengers, inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. Of four PLCbeta isoforms, PLCbeta1 is transcribed predominantly in the telencephalon and its gene inactivation in mice impairs metabotropic glutamate receptor- and muscarinic acetylcholine receptor-dependent hippocampal oscillations, endocannabinoid production in the hippocampus and barrel formation in the somatosensory cortex. Here we examined cellular and subcellular distributions of PLCbeta1 in adult mouse brains. In the telencephalon, high levels of PLCbeta1 were observed in principal neurons, including pyramidal cells in the cortex and hippocampus, granule cells and mossy cells in the dentate gyrus, and medium spiny neurons in the caudate-putamen, whereas most interneurons had low levels of or were negative for PLCbeta1 and, instead, expressed PLCbeta4. By immunofluorescence, tiny clusters of PLCbeta1 were distributed in somatodendritic compartments of principal neurons and positioned close to those of metabotropic glutamate receptor 5, muscarinic acetylcholine receptor M1 and diacylglycerol lipase-alpha, respectively. Immunoelectron microscopy revealed that PLCbeta1 was often associated with the smooth endoplasmic reticulum, cell membrane or postsynaptic density. In particular, it was highly accumulated at the perisynapse of dendritic spines forming asymmetrical synapses. In the cerebellum, PLCbeta1 was generally low but was enriched in axons and dendrites of basket cells. These results suggest that PLCbeta1 is the key effector in telencephalic principal neurons and cerebellar interneurons. Furthermore, the well-orchestrated molecular arrangement appears to be the anatomical basis for the specificity, efficiency and convergence of the neuronal phosphoinositide signaling system.

Critical Role of the Endocannabinoid System in the Regulation of Food Intake and Energy Metabolism, with Phylogenetic, Developmental, and Pathophysiological Implications

The endocannabinoid system (ECS) consists of two receptors (CB(1) and CB(2)), several endogenous ligands (primarily anandamide and 2-AG), and over a dozen ligand-metabolizing enzymes. The ECS has deep phylogenetic roots and regulates many aspects of embryological development and homeostasis, including neuroprotection and neural plasticity, immunity and inflammation, apoptosis and carcinogenesis, pain and emotional memory, and the focus of this review: hunger, feeding, and metabolism. The ECS controls energy balance and lipid metabolism centrally (in the hypothalamus and mesolimbic pathways) and peripherally (in adipocytes and pancreatic islet cells), acting through numerous anorexigenic and orexigenic pathways (e.g., ghrelin, leptin, orexin, adiponectin, endogenous opioids, and corticotropin-releasing hormone). Obesity leads to excessive endocannabinoid production by adipocytes, which drives CB(1) in a feed-forward dysfunction. Phylogenetic research suggests the genes for endocannabinoid enzymes, especially DAGLalpha and NAPE-PLD, may harbor mildly deleterious alleles that express disease-related phenotypes. Several CB(1) inverse agonists have been developed for the treatment of obesity, including rimonabant, taranabant, and surinabant. These drugs are efficacious at reducing food intake as well as abdominal adiposity and cardiometabolic risk factors. However, given the myriad beneficial roles of the ECS, it should be no surprise that systemic CB(1) blockade induces various adverse effects. Alternatives to systemic blockade include CB(1) partial agonists, pleiotropic drugs, peripherally restricted antagonists, allosteric antagonists, and endocannabinoid ligand modulation. The ECS offers several discrete targets for the management of obesity and its associated cardiometabolic sequelae.

Dietary Manipulation of Precursor Polyunsaturated Fatty Acids Modulates Eicosanoid and Endocannabinoid Synthesis: A Potential Tool to Control Tumor Development

The amount and type of dietary fats represent risk factors for several cancers. Essential PUFAs serve as precursors of several biologically active molecules, mainly endocannabinoids and eicosanoids, which participate in tumorigenic processes. However, their mechanisms still remain unclear. This article reviews the current knowledge and experimental results on the effects of dietary manipulation of n-3, n-6 essential fatty acids (EFA) including the conjugated linoleic acid (CLA), on eicosanoid and endocannabinoid production, and their correlation with cancer development. The oxidative pathways of Arachidonic acid (AA) when it is released from phospholipids as Lipoxygenases (LOXs), cyclooxygenases (COX) and Cytochrome P-450s (CYP450) to eicosanoids, and the non-oxidative pathway to endocannabinoid synthesis are summarized. COXs, LOXs, and CYP 450s, endocannabinoids, thereby generating oxygenated products that resemble eicosanoids with the slight difference that endocannabinoid-derived products retain amide or ester functionalities at C1. Competition between n – 3 and n – 6 FA families gives rise to a variation in the ratio of the eicosanoid products, but the significance of these changes are as yet poorly understood. Finally, we propose that the apparently contradictory results in the field of eicosanoids, endocannabionids and cancer should be considered due to difficulties arising from the lack of nutritional evaluation.

The ins and outs of endocannabinoid signaling in healthy and diseased brain

The endocannabinoid signaling system regulates neuronal activity and glial cell function. While numerous studies exist on the pharmacology and coupling of cannabinoid receptors, only recently have fundamental questions been addressed regarding endocannabinoid metabolism and physiopathological function. These lipids can be independently produced and differentially activate cannabinoid 1 and 2 receptors, a diversity that creates a unique level of control of neuronal activity and glial cell functions. This review outlines our current understanding of this diversity, focusing on the stimuli that control endocannabinoid production in the brain under healthy and pathological conditions. By increasing this understanding, new pharmacological targets are likely be identified, some of which might be valuable for the treatment of neurological disease.

Multiple Sclerosis, Cannabinoids, and Cognition

Multiple Sclerosis, Cannabinoids, and Cognition

Potentiation of Electrical and Chemical Synaptic Transmission Mediated by Endocannabinoids

Endocannabinoids are well established as inhibitors of chemical synaptic transmission via presynaptic activation of the cannabinoid type 1 receptor (CB1R). Contrasting this notion, we show that dendritic release of endocannabinoids mediates potentiation of synaptic transmission at mixed (electrical and chemical) synaptic contacts on the goldfish Mauthner cell. Remarkably, the observed enhancement was not restricted to the glutamatergic component of the synaptic response but also included a parallel increase in electrical transmission. This effect involved the activation of CB1 receptors and was indirectly mediated via the release of dopamine from nearby varicosities, which in turn led to potentiation of the synaptic response via a cAMP-dependent protein kinase-mediated postsynaptic mechanism. Thus, endocannabinoid release can potentiate synaptic transmission, and its functional roles include the regulation of gap junction-mediated electrical synapses. Similar interactions between endocannabinoid and dopaminergic systems may be widespread and potentially relevant for the motor and rewarding effects of cannabis derivatives.

Endocannabinoid signalling triggered by NMDA receptor‐mediated calcium entry into rat hippocampal neurons

Endocannabinoids are released from neurons in activity-dependent manners, act retrogradely on presynaptic CB(1) cannabinoid receptors, and induce short-term or long-term suppression of transmitter release. The endocannabinoid release is triggered by postsynaptic activation of voltage-gated Ca(2+) channels and/or G(q)-coupled receptors such as group I metabotropic glutamate receptors (I-mGluRs) and M(1)/M(3) muscarinic receptors. However, the roles of NMDA receptors, which provide another pathway for Ca(2+) entry into neurons, in endocannabinoid signalling have been poorly understood. In the present study, we investigated the possible contribution of NMDA receptors in endocannabinoid production by recording IPSCs in cultured hippocampal neurons. Under the conditions minimizing the activation of voltage-gated Ca(2+) channels, local application of NMDA (200 microm) transiently suppressed cannabinoid-sensitive IPSCs, but not cannabinoid-insensitive IPSCs. This NMDA-induced suppression was abolished by blocking NMDA receptors, CB(1) receptors and diacylglycerol lipase, but not by inhibiting voltage-gated Ca(2+) channels. When the postsynaptic neuron was dialysed with 30 mm BAPTA, the NMDA-induced suppression was reduced significantly. A lower dose of NMDA (20 microm) exerted little effect when applied alone, but markedly enhanced the cannabinoid-dependent suppression driven by muscarinic receptors or I-mGluRs. These data clearly indicate that the activation of NMDA receptors facilitates the endocannabinoid release either alone or in concert with the G(q)-coupled receptors.