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Modulation of ATP-mediated contractions of the rat vas deferens through presynaptic cannabinoid receptors.

The effect of R-(+)-[2,3-dihydro-5-methyl-3-[(morpholiny)methyl]pyrolol[1,2,3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl)methanone mesylate (WIN 55,212-2; a cannabinoid receptor agonist) was investigated on contractions of the bisected (epididymal and prostatic portions) rat vas deferens to assess the role of cannabinoid receptors in sympathetic ATP neurotransmission. WIN 55,212-2 inhibited the electrically induced contractions in both portions of the rat vas deferens. In the presence of the alpha1-adrenoreceptor antagonist prazosin, electrical stimulation produces a contraction mediated exclusively by ATP. In this condition, WIN 55,212-2 in the prostatic portion elicited a concentration-dependent inhibition that was antagonized by N-piperidinyl-[8-chloro-1-(2,4-dichlorophenyl)-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide] (NESS 0327), a selective cannabinoid CB1 receptor antagonist. NESS 0327 caused a parallel dextral displacement of the WIN 55,212-2 concentration-response curve. It is suggested that activation of pre-junctional cannabinoid receptors on sympathetic nerves of the vas deferens modulates ATP neurotransmission.

Adenosine Triphosphate↗

Modulation of cytokine responses in Corynebacterium parvum-primed endotoxemic mice by centrally administered cannabinoid ligands.

The cannabinoid receptor agonists [(-)-11-hydoxy-Delta(8)tetrahydrocannabinol-dimethylheptyl] (HU-210) and [(R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl[pyrrolo[1,2,3-de]1,4-benzoxazin-6-yl](1-naphthalenyl) methanone] (WIN 55212-2) were previously shown to downregulate inflammatory cytokines (tumor necrosis factor alpha and interleukin-12) and to upregulate antiinflammatory interleukin-10 when administered intraperitoneally (i.p.) to mice before an endotoxin challenge. Cytokine modulation coincided with the onset of behavioral changes that are associated with cannabinoid agonist activated central cannabinoid CB(1) receptors. Both effects were antagonized by [N-(piperdin-1-yl)-5-(4-chloropheny)-1-(2,4-dichloropheny)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride] (SR141716A) a selective cannabinoid CB(1) receptor antagonist. In the present study, we have investigated further the apparent role of central CB(1) cannabinoid receptors in cytokine modulation by HU-210 and WIN 55212-2. When administered intracerebroventricularly (i.c.v.), the drugs modulated cytokine responses at doses that were threefold to fourfold lower than those found effective by the i.p. route. SR141716A blocked cytokine modulation when coadministered centrally with the agonists, while a selective cannabinoid CB(2) receptor antagonist, (N-[(1S)-endo-1,3,3-trimethylbicyclo[2.2.1]heptan-2-yl]5-(4-choro-3 methylphenyl)-1-(4-methylbenzyl)pyrazole-3-carboxamide) (SR144528) had no effect. Surprisingly, SR144528 was found to modulate cytokines itself when injected i.c.v.

Animals↗

Cannabinoid receptors are localized to noradrenergic axon terminals in the rat frontal cortex.

Cannabinoid agonists exert complex actions on modulatory neurotransmitters involved in attention and cognition. Previous studies have demonstrated that acute systemic administration of the synthetic cannabinoid agonist, WIN 55,212-2, increases norepinephrine efflux in the rat frontal cortex. In an effort to elucidate whether cannabinoid (CB1) receptors are positioned to presynaptically modulate norepinephrine release in the frontal cortex, immunocytochemical detection of the CB1 receptor and the catecholamine-synthesizing enzyme dopamine-beta-hydroxylase (DbetaH) was performed using confocal immunofluorescence microscopy and immunoelectron microscopy in rat brain. Fluorescence microscopy analysis of dually labeled tissue sections from the frontal cortex indicated that individual axonal processes exhibited both CB1 receptor and DbetaH immunoreactivities. Ultrastructural analysis confirmed that one-third of axon terminals containing CB1 immunolabeling also exhibited DbetaH labeling. Cortical neurons were also found to be targeted by separately labeled CB1- and DbetaH-containing axon terminals. In conclusion, the present neuroanatomical data suggest that cortical norepinephrine release may be modulated, in part, by CB1 receptors that are presynaptically distributed on noradrenergic axon terminals.

Animals↗

The endocannabinoid system: physiology and pharmacology.

The endogenous cannabinoid system is an ubiquitous lipid signalling system that appeared early in evolution and which has important regulatory functions throughout the body in all vertebrates. The main endocannabinoids (endogenous cannabis-like substances) are small molecules derived from arachidonic acid, anandamide (arachidonoylethanolamide) and 2-arachidonoylglycerol. They bind to a family of G-protein-coupled receptors, of which the cannabinoid CB(1) receptor is densely distributed in areas of the brain related to motor control, cognition, emotional responses, motivated behaviour and homeostasis. Outside the brain, the endocannabinoid system is one of the crucial modulators of the autonomic nervous system, the immune system and microcirculation. Endocannabinoids are released upon demand from lipid precursors in a receptor-dependent manner and serve as retrograde signalling messengers in GABAergic and glutamatergic synapses, as well as modulators of postsynaptic transmission, interacting with other neurotransmitters, including dopamine. Endocannabinoids are transported into cells by a specific uptake system and degraded by two well-characterized enzymes, the fatty acid amide hydrolase and the monoacylglycerol lipase. Recent pharmacological advances have led to the synthesis of cannabinoid receptor agonists and antagonists, anandamide uptake blockers and potent, selective inhibitors of endocannabinoid degradation. These new tools have enabled the study of the physiological roles played by the endocannabinoids and have opened up new strategies in the treatment of pain, obesity, neurological diseases including multiple sclerosis, emotional disturbances such as anxiety and other psychiatric disorders including drug addiction. Recent advances have specifically linked the endogenous cannabinoid system to alcoholism, and cannabinoid receptor antagonism now emerges as a promising therapeutic alternative for alcohol dependence and relapse.

Alcoholism↗

Cannabinoids on the brain.

Cannabis has a long history of consumption both for recreational and medicinal uses. Recently there have been significant advances in our understanding of how cannabis and related compounds (cannabinoids) affect the brain and this review addresses the current state of knowledge of these effects. Cannabinoids act primarily via two types of receptor, CB1 and CB2, with CB1 receptors mediating most of the central actions of cannabinoids. The presence of a new type of brain cannabinoid receptor is also indicated. Important advances have been made in our understanding of cannabinoid receptor signaling pathways, their modulation of synaptic transmission and plasticity, the cellular targets of cannabinoids in different central nervous system (CNS) regions and, in particular, the role of the endogenous brain cannabinoid (endocannabinoid) system. Cannabinoids have widespread actions in the brain: in the hippocampus they influence learning and memory; in the basal ganglia they modulate locomotor activity and reward pathways; in the hypothalamus they have a role in the control of appetite. Cannabinoids may also be protective against neurodegeneration and brain damage and exhibit anticonvulsant activity. Some of the analgesic effects of cannabinoids also appear to involve sites within the brain. These advances in our understanding of the actions of cannabinoids and the brain endocannabinoid system have led to important new insights into neuronal function which are likely to result in the development of new therapeutic strategies for the treatment of a number of key CNS disorders.

Animals↗

Differential roles of CB1 and CB2 cannabinoid receptors in mast cells.

Cannabinoid modulation of immune responses is a pathological consequence of marijuana abuse and a potential outcome of therapeutic application of the drug. Moreover, endogenous cannabinoids are physiological immune regulators. In the present report, we describe alterations in gene transcription that occur after cannabinoid exposure in a mast cell line, RBL2H3. Cannabinoid exposure causes marked changes in the transcript levels for numerous genes, acting both independently of and in concert with immunoreceptor stimulation via Fc epsilon RI. In two mast cell lines, we observed mRNA and protein expression corresponding to both CB1 and CB2 cannabinoid receptor isoforms, contrary to the prevailing view that CB1 is restricted to the CNS. We show that coexpression of the two isoforms is not functionally redundant in mast cells. Analysis of signaling pathways downstream of cannabinoid application reveals that activation of extracellular signal-regulated kinase, AKT, and a selected subset of AKT targets is accomplished by CB2 ligands and nonselective CB1/CB2 agonists in mast cells. CB1 inhibition does not affect AKT or extracellular signal-regulated kinase activation by cannabinoids, indicating that CB2 is the predominant regulatory receptor for these kinases in this cell context. CB1 receptors are, however, functional in these mast cells, since they can contribute to suppression of secretory responses.

Animals↗

Uptake blockade of endocannabinoids in the NTS modulates baroreflex-evoked sympathoinhibition.

Previous studies supporting a possible physiological role for an endogenous cannabinoid, arachidonylethanolamide (AEA, anandamide), showed a significant increase in AEA content in the nucleus tractus solitarius (NTS) after an increase in blood pressure (BP) and prolonged baroreflex inhibition of renal sympathetic nerve activity (RSNA) after exogenous AEA microinjections into the NTS. These results, along with other studies, support the hypothesis that endogenous AEA can modulate the baroreflex through cannabinoid CB(1) receptor activation within the NTS. This study was performed to characterize the physiological role of endogenously released cannabinoids (endocannabinoids) in regulating baroreflex control of RSNA through actions in the NTS. Endocannabinoid effects were assessed by measuring the RSNA baroreflex response to increased pressure after bilateral microinjections of AM404, an endocannabinoid transport inhibitor, into the NTS of adult male Sprague Dawley rats. AM404 blocks uptake of endocannabinoids and enhances the effects of any endocannabinoids released [M. Beltramo, et al., Functional role of high-affinity anandamide transport, as revealed by selective inhibition, Science 277 (5329) (1997) 1094-1097.] into the NTS. Therefore, it was hypothesized that microinjections of AM404 should exhibit effects similar to microinjections of exogenous AEA. In this study, AM404 microinjections into the NTS were found to significantly prolong baroreflex inhibition of RSNA compared to control, similar to effects of exogenous AEA. This effect is thought to result from an increased endocannabinoid presence in the NTS, leading to prolonged CB(1) receptor activation. These results indicate that endocannabinoids released in the NTS have the potential to modulate baroreflex control at this site in the central baroreflex pathway.

Animals↗

Cellular localization of cannabinoid receptors and activated G-proteins in rat anterior cingulate cortex.

Cannabinoid receptors are found in moderate density throughout the cerebral cortex. The anterior cingulate cortex (ACC) is of particular interest due its high level of cannabinoid receptors and role in behaviors known to be modulated by cannabinoids. These studies were conducted to determine the cellular localization of cannabinoid receptors and to compare the level of cannabinoid receptor binding with receptor-mediated G-protein activity in the rat ACC. Either ibotenic acid or undercut lesions were made in ACC, and brains were processed for [3H]WIN 55,212-2 and WIN 55,212-2-stimulated [35S]GTPgammaS autoradiography. Both cannabinoid receptors and receptor-activated G-proteins were highest in laminae I and VI of ACC in control tissue. Although similar levels of receptor binding were found in these laminae, significantly higher levels of receptor-activated G-proteins were found in lamina VI. Ibotenic acid lesions that destroyed ACC neurons decreased [3H]WIN 55,212-2 binding by 60-70% and eliminated WIN 55,212-2-stimulated [35S]GTPgammaS binding. In contrast, deafferentation of the ACC with undercut lesions had no significant effect on cannabinoid receptor binding or G-protein activation. These results indicate that cannabinoid receptors in laminae I and VI of the ACC are located on somatodendritic elements or axons intrinsic to the ACC. In addition, differences in the relative levels of cannabinoid binding sites and activated G-proteins between cortical laminae indicate that the efficiency of cannabinoid receptors for G-protein activation may vary within a specific brain region.

Animals↗

Endocannabinoids: endogenous cannabinoid receptor ligands with neuromodulatory action.

The existence of an endogenous cannabinoid system was demonstrated conclusively with the discovery of endogenous brain constituents capable of activating the cannabinoid receptors functionally. These compounds are synthesized by neuronal cells and inactivated through re-uptake and enzymatic hydrolysis by both neurons and astrocytes. In analogy with the endorphins they can be referred to as endocannabinoids. Apart from the identification of their metabolic pathways, research carried out in the past six years has focused on the possible cellular and molecular targets for the actions of endocannabinoids. These studies have confirmed a similarity between the endocannabinoids and the psychoactive substance in marijuana, delta9(-)-tetrahydrocannabinol, and have suggested a role for endocannabinoids in the modulation of neurotransmitter action and release.

Animals↗

Enhanced levels of endogenous cannabinoids in the globus pallidus are associated with a reduction in movement in an animal model of Parkinson's disease.

In recent years, cannabinoid receptors and their endogenous ligands (endocannabinoids) have been identified within the brain. The high density of CB1 cannabinoid receptors within the basal ganglia suggests a potential role for endocannabinoids in the control of voluntary movement and in basal ganglia-related movement disorders such as Parkinson's disease. However, whether endocannabinoids play a role in regulating motor behavior in health and disease is unknown. Here we report the presence in two regions of the basal ganglia, the globus pallidus and substantia nigra, of the endocannabinoids 2-arachidonoylglycerol (2AG) and anandamide. The levels of the latter compound are approximately threefold higher than those previously reported in any other brain region. In the reserpine-treated rat, an animal model of Parkinson's disease, suppression of locomotion is accompanied by a sevenfold increase in the levels of the 2AG in the globus pallidus, but not in the other five brain regions analyzed. Stimulation of locomotion in the reserpine-treated rat by either of the two selective agonists of D2 and D1 dopamine receptors, quinpirole and R-(+/-)-3-allyl-6-chloro-7, 8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (Cl-APB), respectively, results in the reduction of both anandamide and 2AG levels in the globus pallidus. Finally, full restoration of locomotion in the reserpine-treated rat is obtained by coadministration of quinpirole and the selective antagonist of the cannabinoid CB1 receptor subtype, SR141716A. These findings indicate a link between endocannabinoid signaling in the globus pallidus and symptoms of Parkinson's disease in the reserpine-treated rat, and suggest that modulation of the endocannabinoid signaling system might prove useful in treating this or other basal ganglia-related movement disorders.

Animals↗

Anandamide as an intracellular messenger regulating ion channel activity.

The endocannabinoid anandamide (N-arachidonoylethanolamine) was proposed to be an extracellular retrograde messenger, which regulates excitability of neurons by cannabinoid CB1 receptor-dependent inhibition of neurotransmitter release. Recent findings indicate that the neuromodulatory actions of anandamide might be more complex. Anandamide has been shown to directly modulate various ion channels, such as alpha7-nicotinic acetylcholine receptors, T-type Ca2+ channels, voltage-gated and background K+-channels and Transient Receptor Potential Vanilloid type 1 (TRPV1) channels. The binding site of anandamide at some of these ion channels appears to be intracellular or at the bilayer interface. This rises the intriguing possibility that anandamide, prior to its release into the synaptic cleft, may regulate ion homeostasis and excitability of neurons as an intracellular modulator of ion channels independent of its action at cannabinoid CB1 receptors. This possibility might extend the concept of anandamide as an endocannabinoid retrograde messenger and may have profound implications for its role in neurotransmission and neuronal function. Here, we will review the evidence for this hypothesis.

Animals↗

Endocannabinoids control spasticity in a multiple sclerosis model.

Spasticity is a complicating sign in multiple sclerosis that also develops in a model of chronic relapsing experimental autoimmune encephalomyelitis (CREAE) in mice. In areas associated with nerve damage, increased levels of the endocannabinoids, anandamide (arachidonoylethanolamide, AEA) and 2-arachidonoyl glycerol (2-AG), and of the AEA congener, palmitoylethanolamide (PEA), were detected here, whereas comparable levels of these compounds were found in normal and non-spastic CREAE mice. While exogenously administered endocannabinoids and PEA ameliorate spasticity, selective inhibitors of endocannabinoid re-uptake and hydrolysis-probably through the enhancement of endogenous levels of AEA, and, possibly, 2-arachidonoyl glycerol-significantly ameliorated spasticity to an extent comparable with that observed previously with potent cannabinoid receptor agonists. These studies provide definitive evidence for the tonic control of spasticity by the endocannabinoid system and open new horizons to therapy of multiple sclerosis, and other neuromuscular diseases, based on agents modulating endocannabinoid levels and action, which exhibit little psychotropic activity.

Amides↗

Antinociception and modulation of rostral ventromedial medulla neuronal activity by local microinfusion of a cannabinoid receptor agonist.

Systemic administration of a cannabinoid agonist produces antinociception through the activation of pain modulating neurons in the rostral ventromedial medulla (RVM). The aim of the present study was to determine how a cannabinoid receptor agonist acting directly within the RVM affects neuronal activity to produce behaviorally measurable antinociception. In lightly anesthetized rats, two types of RVM neurons have been defined based on changes in tail flick-related activity. On-cells increase firing (on-cell burst), whereas off-cells cease firing (off-cell pause), just prior to a tail flick. The cannabinoid receptor agonist WIN55,212-2 was microinfused directly into the RVM while monitoring tail flick latencies and on- and off-cell activity. Microinfusion of WIN55,212-2 (2.0 microg/microl and 0.4 microg/microl) reduced the tail flick-related on-cell burst, decreased the duration of the off-cell pause, and increased off-cell ongoing activity. These changes were prevented by co-infusing the CB1 receptor antagonist, SR141716A (0.35 microg/microl), with WIN55,212-2 (0.4 microg/microl). Furthermore, 2.0 microg/microl WIN55,212-2 delayed the onset of the off-cell pause and increased tail flick latencies. Microinfusion of WIN55,212-2 to brain regions caudal or lateral to the RVM had no effect on RVM neuronal activity or tail flick latencies. These results indicate that cannabinoids act directly within the RVM to affect off-cell activity, providing one mechanism by which cannabinoids produce antinociception.

Action Potentials↗

Cannabinoid receptors in microglia of the central nervous system: immune functional relevance.

Microglia, resident macrophages of the brain, function as immune effector and accessory cells. Paradoxically, they not only play a role in host defense and tissue repair but also have been implicated in a variety of neuropathological processes. Microglia, in addition to exhibiting phenotypic markers for macrophages, express CB1 and CB2 cannabinoid receptors. Recent studies suggest the existence of a third, yet-to-be cloned, non-CB1, non-CB2 cannabinoid receptor. These receptors appear to be functionally relevant within defined windows of microglial activation state and have been implicated as linked to cannabinoid modulation of chemokine and cytokine expression. The recognition that microglia express cannabinoid receptors and that their activation results in modulation of select cellular activities suggests that they may be amenable to therapeutic manipulation for ablating untoward inflammatory responses in the central nervous system.

Animals↗

Cannabinoid receptor messenger RNA levels decrease in a subset of neurons of the lateral striatum, cortex and hippocampus of transgenic Huntington's disease mice.

One of the earliest changes, at the molecular level, that occurs in human Huntington's disease patients is reduction in cannabinoid receptor ligand binding in the substantia nigra pars reticulata compared to neurologically normal controls. The loss of cannabinoid receptor binding is thought to occur early in or prior to the development of Huntington's disease neuropathology. We wish to determine whether cannabinoid receptor messenger RNA levels were altered in a mouse model of Huntington's disease. Transgenic mice hemizygous for the promoter sequence and exon 1 of the human Huntington's disease gene exhibit a progressive neurological phenotype with many of the features of Huntington's disease. This neurological phenotype develops in the absence of neural degeneration making these mice a model system to dissociate changes related to cell dysfunction from changes related to cell loss. We examine the steady-state levels and cellular distribution of the brain-specific cannabinoid receptor messenger RNA by northern blot and in situ hybridization. The cannabinoid receptor messenger RNA was expressed throughout the striatum, cortex and hippocampus of wild-type mice. At four and five weeks of age, there was no difference in the distribution of the cannabinoid receptor messenger RNA between the wild-type and transgenic Huntington's disease mice. At six, seven, eight and 10 weeks of age, however, the Huntington's disease mice exhibit reduced levels of cannabinoid receptor messenger RNA in the lateral striatum compared to age-matched controls. The Huntington's disease mice also showed a loss of cannabinoid receptor messenger RNA within a subset of neurons in the cortex and hippocampus. We did not observe any difference in the expression of cannabinoid receptor between the wild-type and Huntington's disease mice throughout Ammon's horn of the hippocampus or in the medial striatum. The decrease in cannabinoid receptor messenger RNA levels preceded the development of the Huntington's disease phenotype and neuronal degeneration and, therefore, these transgenic mice model early cellular changes observed in human patients. Our results demonstrate that the single copy cannabinoid receptor gene is subjected to cell-specific and time-dependent regulation of the steady-state level of its gene product as a result of the expression of the Huntington's disease gene. As the endogenous cannabinoid receptor agonist, anandimide, has been shown to modulate dopamine neurotransmission within the basal ganglia, the loss of cannabinoid receptors may contribute to the development of motor symptoms or cognitive decline or both seen in Huntington's disease patients.

Animals↗

Endocannabinoids and related fatty acid derivatives in pain modulation.

The brain produces at least five compounds that possess sub-micromolar affinity for cannabinoid receptors: anandamide, 2-arachidonoylglycerol, noladin ether, virodhamine, and N-arachidonoyldopamine (NADA). One function of these and/or related compounds is to suppress pain sensitivity. Much evidence supports a role of endocannabinoids in pain modulation in general, and some evidence points to the role of particular endocannabinoids. Related endogenous fatty acid derivatives such as oleamide, palmitoylethanolamide, 2-lineoylglycerol, 2-palmitoylglycerol, and a family of arachidonoyl amino acids may interact with endocannabinoids in the modulation of pain sensitivity.

Animals↗

Endocannabinoids and food consumption: comparisons with benzodiazepine and opioid palatability-dependent appetite.

The endocannabinoid system consists of several endogenous lipids, including anandamide and 2-arachidonoyl-glycerol (2-AG), and constitute a retrograde signalling system, which modulates neurotransmitter release and synaptic plasticity. Specific brain-type cannabinoid receptors (CB(1)) are widely distributed in the central nervous system, and are localized presynaptically. Mounting evidence, reviewed here, indicates that cannabinoids can act to increase food consumption, and cannabinoid CB(1) receptor antagonists/inverse agonists reduce food intake and suppress operant responding for food rewards. Hence, endocannabinoids provide the first example of a retrograde signalling system, which is strongly implicated in the control of food intake. Benzodiazepine and opioid palatability-dependent appetite are well-established processes supported by several sources of convergent evidence; they provide pharmacological benchmarks against which to evaluate the endocannabinoids. To date, evidence that endocannabinoids specifically modulate palatability as an affective evaluative process is insufficient and not compelling. Endocannabinoids may have important clinical utility in the treatment of human obesity and forms of eating disorders.

Animals↗

From cannabis to cannabinergics: new therapeutic opportunities.

The molecular basis of cannabinoid activity is better understood since the discovery of the CB(1) receptor in the mammalian brain and the CB(2) receptor in peripheral tissues. Subsequently, an endogenous CB(1) receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB(1) and CB(2) receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.

Amidohydrolases↗