Anandamide and WIN 55212-2 inhibit cyclic AMP formation through G-protein-coupled receptors distinct from CB1 cannabinoid receptors in cultured astrocytes

The Acute Activation of the CB1 Receptor in the Hippocampus Decreases Neurotoxicity and Prevents Spatial Memory Impairment in Rats Lesioned with β-Amyloid 25-35

Given their anti-inflammatory properties, cannabinoids have been shown to be neuroprotective agents and to reduce excitotoxicity, through the activation of the Cannabinoid receptor type 1 (CB1r). These properties have led to CB1r being proposed as pharmacological targets for the treatment of various neurodegenerative diseases. Amyloid-β 25-35 (Aβ_25-35) induces the expression of inducible nitric oxide synthase (iNOS) and increases nitric oxide (NO●) levels. It has been observed that increased NO● concentrations trigger biochemical pathways that contribute to neuronal death and cognitive damage. This study aimed to evaluate the neuroprotective effect of an acute activation of CB1r on spatial memory and its impact on iNOS protein expression, NO● levels, gliosis and the neurodegenerative process induced by the injection of Aβ_(25-35) into the CA1 subfield of the hippocampus. ACEA [1 μM/1 μL] and Aβ_(25-35) [100 μM/1 μL] and their respective vehicle groups were injected into the CA1 subfield of the hippocampus. The animals were tested for spatial learning and memory in the eight-arm radial maze, with the results revealing that the administration of ACEA plus Aβ_(25-35) improves learning and memory processes, in contrast with the Aβ_(25-35) group. Moreover, ACEA plus Aβ_(25-35) prevented both the increase in iNOS protein and NO● levels and the reactive gliosis induced by Aβ_(25-35). Importantly, neurodegeneration was significantly reduced by the administration of ACEA plus Aβ_(25-35) in the CA1 subfield of the hippocampus. The data obtained in the present research suggest that the acute early activation of CB1r is crucial for neuroprotection.

The Neuroglial Dialog Between Cannabinoids and Hemichannels

The formation of gap junctions was initially thought to be the central role of connexins, however, recent evidence had brought to light the high relevance of unopposed hemichannels as an independent mechanism for the selective release of biomolecules during physiological and pathological conditions. In the healthy brain, the physiological opening of astrocyte hemichannels modulates basal excitatory synaptic transmission. At the other end, the release of potentially neurotoxic compounds through astroglial hemichannels and pannexons has been insinuated as one of the functional alterations that negatively affect the progression of multiple brain diseases. Recent insights in this matter have suggested encannabinoids (eCBs) as molecules that could regulate the opening of these channels during diverse conditions. In this review, we discuss and hypothesize the possible interplay between the eCB system and the hemichannel/pannexon-mediated signaling in the inflamed brain and during event of synaptic plasticity. Most findings indicate that eCBs seem to counteract the activation of major neuroinflammatory pathways that lead to glia-mediated production of TNF-α and IL-1β, both well-known triggers of astroglial hemichannel opening. In contrast to the latter, in the normal brain, eCBs apparently elicit the Ca²⁺-activation of astrocyte hemichannels, which could have significant consequences on eCB-dependent synaptic plasticity.

Modulation of Astrocyte Activity by Cannabidiol, a Nonpsychoactive Cannabinoid

The astrocytes have gained in recent decades an enormous interest as a potential target for neurotherapies, due to their essential and pleiotropic roles in brain physiology and pathology. Their precise regulation is still far from understood, although several candidate molecules/systems arise as promising targets for astrocyte-mediated neuroregulation and/or neuroprotection. The cannabinoid system and its ligands have been shown to interact and affect activities of astrocytes. Cannabidiol (CBD) is the main non-psychotomimetic cannabinoid derived from Cannabis. CBD is devoid of direct CB1 and CB2 receptor activity, but exerts a number of important effects in the brain. Here, we attempt to sum up the current findings on the effects of CBD on astrocyte activity, and in this way on central nervous system (CNS) functions, across various tested models and neuropathologies. The collected data shows that increased astrocyte activity is suppressed in the presence of CBD in models of ischemia, Alzheimer-like and Multiple-Sclerosis-like neurodegenerations, sciatic nerve injury, epilepsy, and schizophrenia. Moreover, CBD has been shown to decrease proinflammatory functions and signaling in astrocytes.

Spatial distribution of cannabinoid receptor type 1 (CB1) in normal canine central and peripheral nervous system

The endocannabinoid system is a regulatory pathway consisting of two main types of cannabinoid receptors (CB₁ and CB₂) and their endogenous ligands, the endocannabinoids. The CB₁ receptor is highly expressed in the central and peripheral nervous systems (PNS) in mammalians and is involved in neuromodulatory functions. Since endocannabinoids were shown to be elevated in cerebrospinal fluid of epileptic dogs, knowledge about the species specific CB receptor expression in the nervous system is required. Therefore, we assessed the spatial distribution of CB₁ receptors in the normal canine CNS and PNS. Immunohistochemistry of several regions of the brain, spinal cord and peripheral nerves from a healthy four-week-old puppy, three six-month-old dogs, and one ten-year-old dog revealed strong dot-like immunoreactivity in the neuropil of the cerebral cortex, Cornu Ammonis (CA) and dentate gyrus of the hippocampus, midbrain, cerebellum, medulla oblongata and grey matter of the spinal cord. Dense CB₁ expression was found in fibres of the globus pallidus and substantia nigra surrounding immunonegative neurons. Astrocytes were constantly positive in all examined regions. CB₁ labelled neurons and satellite cells of the dorsal root ganglia, and myelinating Schwann cells in the PNS. These results demonstrate for the first time the spatial distribution of CB₁ receptors in the healthy canine CNS and PNS. These results can be used as a basis for further studies aiming to elucidate the physiological consequences of this particular anatomical and cellular distribution.

Cannabinoids prevent the amyloid β-induced activation of astroglial hemichannels: A neuroprotective mechanism

The mechanisms involved in Alzheimer's disease are not completely understood and how astrocytes and their gliotransmission contribute to this neurodegenerative disease remains to be fully elucidated. Previous studies have shown that amyloid-β peptide (Aβ) induces neuronal death by a mechanism that involves the excitotoxic release of ATP and glutamate associated to astroglial hemichannel opening. We have demonstrated that synthetic and endogenous cannabinoids (CBs) reduce the opening of astrocyte Cx43 hemichannels evoked by activated microglia or inflammatory mediators. Nevertheless, whether CBs could prevent the astroglial hemichannel-dependent death of neurons evoked by Aβ is unknown. Astrocytes as well as acute hippocampal slices were treated with the active fragment of Aβ alone or in combination with the following CBs: WIN, 2-AG, or methanandamide (Meth). Hemichannel activity was monitored by single channel recordings and by time-lapse ethidium uptake while neuronal death was assessed by Fluoro-Jade C staining. We report that CBs fully prevented the hemichannel activity and inflammatory profile evoked by Aβ in astrocytes. Moreover, CBs fully abolished the Aβ-induced release of excitotoxic glutamate and ATP associated to astrocyte Cx43 hemichannel activity, as well as neuronal damage in hippocampal slices exposed to Aβ. Consequently, this work opens novel avenues for alternative treatments that target astrocytes to maintain neuronal function and survival during AD. GLIA 2016 GLIA 2017;65:122-137.

Rising stars: modulation of brain functions by astroglial type-1 cannabinoid receptors

The type-1-cannabinoid (CB1 ) receptor is amongst the most widely expressed G protein-coupled receptors in the brain. In few decades, CB1 receptors have been shown to regulate a large array of functions from brain cell development and survival to complex cognitive processes. Understanding the cellular mechanisms underlying these functions of CB1 is complex due to the heterogeneity of the brain cell types on which the receptor is expressed. Although the large majority of CB1 receptors act on neurons, early studies pointed to a direct control of CB1 receptors over astroglial functions including brain energy supply and neuroprotection. In line with the growing concept of the tripartite synapse highlighting astrocytes as direct players in synaptic plasticity, astroglial CB1 receptor signaling recently emerged as the mediator of several forms of synaptic plasticity associated to important cognitive functions. Here, we shortly review the current knowledge on CB1 receptor-mediated astroglial functions. This functional spectrum is large and most of the mechanisms by which CB1 receptors control astrocytes, as well as their consequences in vivo, are still unknown, requiring innovative approaches to improve this new cannabinoid research field.

The role of endocannabinoids in pain modulation

The endocannabinoid system (ES) is comprised of cannabinoid (CB) receptors, their endogenous ligands (endocannabinoids), and proteins responsible for their metabolism. Endocannabinoids serve as retrograde signaling messengers in GABAergic and glutamatergic synapses, as well as modulators of postsynaptic transmission, that interact with other neurotransmitters. Physiological stimuli and pathological conditions lead to differential increases in brain endocannabinoids that regulate distinct biological functions. Furthermore, endocannabinoids modulate neuronal, glial, and endothelial cell function and exert neuromodulatory, anti-excitotoxic, anti-inflammatory, and vasodilatory effects. Analgesia is one of the principal therapeutic targets of cannabinoids. Cannabinoid analgesia is based on the suppression of spinal and thalamic nociceptive neurons, but peripheral sites of action have also been identified. The chronic pain that occasionally follows peripheral nerve injury differs fundamentally from inflammatory pain and is an area of considerable unmet therapeutic need. Over the last years, considerable progress has been made in understanding the role of the ES in the modulation of pain. Endocannabinoids have been shown to behave as analgesics in models of both acute nociception and clinical pain such as inflammation and painful neuropathy. The framework for such analgesic effects exists in the CB receptors, which are found in areas of the nervous system important for pain processing and in immune cells that regulate the neuro-immune interactions that mediate the inflammatory hyperalgesia. The purpose of this review is to present the available research and clinical data, up to date, regarding the ES and its role in pain modulation, as well as its possible therapeutic perspectives.

International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid receptors and their ligands: beyond CB₁ and CB₂

There are at least two types of cannabinoid receptors (CB(1) and CB(2)). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ(9)-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB(1), non-CB(2) established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB(1) and/or CB(2) receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel "CB(3)" cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB(1), non-CB(2) pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB(3) receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB(1) receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB(1)/CB(2) receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB(1), non-CB(2) cannabinoid receptors; and 4) current cannabinoid receptor nomenclature.

Cannabinoid and cannabinoid-like receptors in microglia, astrocytes, and astrocytomas

CB1 and CB2 receptors are activated by a plethora of cannabinoid compounds, be they endogenously-produced, plant-derived or synthetic. These receptors are expressed by microglia, astrocytes and astrocytomas, and their activation regulates these cells' differentiation, functions and viability. Recent studies show that glial cells also express cannabinoid-like receptors, and that their activation regulates different cell functions, but also control cell viability. This review summarizes this evidence, and discusses how selective compounds targeting cannabinoid-like receptors constitute promising therapeutics to manage neuroinflammation and eradicate malignant astrocytomas. Importantly, the selective targeting of cannabinoid-like receptors should provide therapeutic relieve without inducing the typical psychotropic effects and possible addictive properties associated with the use of Delta9-tetrahydrocannabinol, the main psychotropic ingredient produced by the plant Cannabis sativa.

The endocannabinoid anandamide inhibits potassium conductance in rat cortical astrocytes

Endocannabinoids are a family of endogenous signaling molecules that modulate neuronal excitability in the central nervous system (CNS) by interacting with cannabinoid (CB) receptors. In spite of the evidence that astroglial cells also possess CB receptors, there is no information on the role of endocannabinoids in regulating CNS function through the modulation of ion channel-mediated homeostatic mechanisms in astroglial cells. We provide electrophysiological evidence that the two brain endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG) markedly depress outward conductance mediated by delayed outward rectifier potassium current (IK(DR)) in primary cultured rat cortical astrocytes. Pharmacological experiments suggest that the effect of AEA does not result from the activation of known CB receptors. Moreover, neither the production of AEA metabolites nor variations in free cytosolic calcium are involved in the negative modulation of IK(DR). We show that the action of AEA is mediated by its interaction with the extracellular leaflet of the plasma membrane. Similar experiments performed in situ in cortical slices indicate that AEA downregulates IK(DR) in complex and passive astroglial cells. Moreover, IK(DR) is also inhibited by AEA in NG2 glia. Collectively, these results support the notion that endocannabinoids may exert their modulation of CNS function via the regulation of homeostatic function of the astroglial syncytium mediated by ion channel activity.

Role of cannabinoids in the management of neuropathic pain

The treatment of pain, particularly neuropathic pain, is one of the therapeutic applications of cannabis and cannabinoids that is currently under investigation and that stimulates interest among clinicians and basic researchers. Animal pain models, including models of acute, antinociceptive, inflammatory and neuropathic pain, have demonstrated the antinociceptive efficacy of cannabinoids without causing serious alterations in animal behaviour. These data, together with the historic and current empiric use of cannabinoids, support the interest in the analysis of their effectiveness in treating neuropathic pain. The evaluation of controlled trials that focus on the effect of cannabinoids on neuropathic pain reveals that this class of drugs is able to significantly reduce pain perception. Nevertheless, this effect is generally weak and clinical relevance remains under evaluation. Moreover, there is a lack of controlled trials and, in particular, comparisons with other drugs generally used in the treatment of neuropathic pain. Despite the fact that further research is required to achieve a definitive assessment, current data obtained from basic research and from analysis of the available controlled trials indicate that cannabinoids can be accepted as a useful option in the treatment of neuropathic pain.

The pharmacology of the cannabinoid system--a question of efficacy and selectivity

Our knowledge of the function of the cannabinoid system in the body has been aided by the availability of pharmacological agents that affect its function. This has been achieved by the design of agents that either directly interact with the receptor (agonists and antagonist/inverse agonists) and agents that indirectly modulate the receptor output by changing the levels of the endogenous cannabinoids (endocannabinoids). In this review, examples of the most commonly used receptor agonists, antagonists/inverse agonists, and indirectly acting agents (anandamide uptake inhibitors, fatty acid amide hydrolase inhibitors, monoacylglycerol lipase inhibitors) are given, with particular focus upon their selectivity and, in the case of the directly acting compounds, efficacy. Finally, the links between the endocannabinoid and cyclooxygenase pathways are explored, in particular, with respect to agents whose primary function is to inhibit cyclooxygenase activity, but which also interact with the endocannabinoid system.

Anandamide-mediated CB1/CB2 cannabinoid receptor--independent nitric oxide production in rabbit aortic endothelial cells

We have previously shown that the endocannabinoid anandamide and its metabolically stable analog (R)-methanandamide produce vasorelaxation in rabbit aortic ring preparations in an endothelium-dependent manner that could not be mimicked by other CB(1) cannabinoid receptor agonists (Am J Physiol 282: H2046-H2054, 2002). Here, we show that (R)-methanandamide and abnormal cannabidiol stimulated nitric oxide (NO) production in rabbit aortic endothelial cells (RAEC) in a dose-dependent manner but that other CB(1) and CB(2) receptor agonists, such as cis-3R-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4R-3(3-hydroxypropyl)-1R-cyclohexanol (CP55940) and (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo-[1,2,3-d,e]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone (WIN55212-2), failed to do so. CB(1) antagonists rimonabant [also known as SR141716; N-piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and 6-methoxy-2-(4-methoxyphenyl)benzo[b]-thien-3-yl][4-cyanophenyl]methanone (LY320135) and CB(2) antagonist N-[(1S)-endo-1,3,3,-trimethylbicyclo[2.2.1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) failed to block (R)-methanandamide-mediated NO production in RAEC. However, anandamide receptor antagonist (-)-4-(3-3,4-trans-p-menthadien-(1,8)-yl)-orcinol (O-1918) blocked (R)-methanandamide-mediated NO production in RAEC. Reverse transcriptase-polymerase chain reaction and Western blot analyses failed to detect the CB(1) receptor in RAEC, making this a good model to study non-CB(1) responses to anandamide. (R)-Methanandamide produced endothelial nitric-oxide synthase (eNOS) phosphorylation via the activation of phosphoinositide 3-kinase-Akt signaling. Inhibition of G(i) signaling with pertussis toxin, or phosphatidylinositol 3-kinase activity with 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), resulted in a decrease in (R)-methanandamide-induced Akt phosphorylation and NO production. Results from this study suggest that in RAEC, (R)-methanandamide acts on a novel non-CB(1) and non-CB(2) anandamide receptor and signals through G(i) and phosphatidylinositol 3-kinase, leading to Akt activation, eNOS phosphorylation, and NO production.

Agonists of cannabinoid receptor 1 and 2 inhibit experimental colitis induced by oil of mustard and by dextran sulfate sodium

Oil of mustard (OM) is a potent neuronal activator that is known to elicit visceral hyperalgesia when given intracolonically, but the full extent to which OM is also proinflammatory in the gastrointestinal tract is not known. We have previously shown that male CD-1 mice given a single administration of 0.5% OM develop a severe colitis that is maximum at day 3 and that gradually lessens until essentially absent by day 14. OM-induced neuronal stimulation is reported to be reduced by cannabinoid agonists, and cannabinoid receptor 1 (CB1R)-/- mice have exacerbated experimental colitis. Therefore, we examined the role of cannabinoids in this OM-induced 3-day model of colitis in CD-1 mice and in a 7-day dextran sulfate sodium (DSS) colitis model in BALB/c mice. In OM colitis, the CB1R-selective agonist ACEA and the CB2R-selective agonist JWH-133 reduced (P < 0.05) colon weight gain (means +/- SE; 82 +/- 13% and 47 +/- 15% inhibition, respectively), colon shrinkage (98 +/- 24% and 42 +/- 12%, respectively), colon inflammatory damage score (49 +/- 11% and 40 +/- 12%, respectively), and diarrhea (58 +/- 12% and 43 +/- 11%, respectively). Histological damage was similarly reduced by these treatments. Likewise, CBR agonists attenuated DSS colitis, albeit at higher doses; ACEA at 10 mg/kg, twice daily, inhibited (P < 0.05) macroscopic and microscopic scores (46 +/- 9% and 63 +/- 7%, respectively); whereas 20 mg/kg, twice daily, of JWH-133 was required to diminish (P < 0.05) macroscopic and microscopic scores (29 +/- 7% and 43 +/- 5%, respectively). CB1R and CB2R immunostaining of colon sections revealed that CB1R in enteric neurons was more intense in colitic vs. control mice; however, CB1R was also increased in the endothelial layer in OM colitis only. CB2R immunostaining was more marked in infiltrated immune cells in OM colitis. These findings validate the OM colitis model with respect to the DSS model and provide strong support to the emerging idea that cannabinoid receptor activation mediates protective mechanisms in experimental colitis. The demonstration of CB1R agonist effects in colitis support the neurogenic nature of the OM-induced colitis model and reinforce the importance of neuronal activation in intestinal inflammation.

R(+)-methanandamide and other cannabinoids induce the expression of cyclooxygenase-2 and matrix metalloproteinases in human nonpigmented ciliary epithelial cells

Prostaglandins (PGs) and matrix metalloproteinases (MMP) have been implicated in lowering intraocular pressure (IOP) by facilitating aqueous humor outflow. A possible role of cyclooxygenase-2 (COX-2) in this process was emphasized by findings showing an impaired COX-2 expression in the nonpigmented ciliary epithelium (NPE) of patients with primary open-angle glaucoma. Using human NPE cells, the present study therefore investigated the effect of the IOP-lowering cannabinoid R(+)-methanandamide [R(+)-MA] on the expression of COX-2 and different MMPs and tissue inhibitors of MMPs (TIMPs). R(+)-MA led to a concentration- and time-dependent increase of COX-2 mRNA expression. R(+)-MA-induced COX-2 expression was accompanied by time-dependent phosphorylations of p38 mitogen-activated protein kinase (MAPK) and p42/44 MAPK and was abrogated by inhibitors of both pathways. Moreover, R(+)-MA increased the mRNA and protein expression of MMP-1, MMP-3, MMP-9, and TIMP-1 but not that of MMP-2 and TIMP-2. Inhibition of COX-2 activity with NS-398 [N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide] was associated with a virtually complete suppression of R(+)-MA-induced MMP-9 and TIMP-1 expression. Consistent with these data, MMP-9 and TIMP-1 expression was also induced by PGE2, a major COX-2 product. Two other COX-2-inducing cannabinoids, anandamide and Delta9-tetrahydrocannabinol, caused the same pattern of MMP and TIMP expression as R(+)-MA both in the absence and presence of NS-398. Altogether, cannabinoids induce the production of several outflow-facilitating mediators in the human NPE. Our results further imply an involvement of COX-2-dependent PGs in MMP-9 and TIMP-1 expression. In conclusion, stimulation of intraocular COX-2 and MMP expression may represent a potential mechanism contributing to the IOP-lowering action of different cannabinoids.

The Synthetic Cannabinoid R(+)WIN 55,212-2 Inhibits the Interleukin-1 Signaling Pathway in Human Astrocytes in a Cannabinoid Receptor-independent Manner

R(+)WIN 55,212-2 is a synthetic cannabinoid that controls disease progression in models of multiple sclerosis. This is associated with its ability to reduce migration of leukocytes into the central nervous system. Because leukocyte migration is dependent on induction of adhesion molecules and chemokines by pro-inflammatory cytokines, we examined the effects of R(+)WIN 55,212-2 on their expression. Using 1321N1 astrocytoma and A-172 glioblastoma as cell models we show that R(+)WIN 55,212-2, but not its inactive chiral form S(-)WIN 55,212-2, strongly inhibits the interleukin-1 (IL-1) induction of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and the chemokine IL-8. This inhibition is not mediated via the CB1 or CB2 cannabinoid receptors, because their selective antagonists and pertussis toxin failed to affect the inhibitory effects of R(+)WIN 55,212-2. Furthermore reverse transcription-PCR analysis did not detect the expression of either receptor in 1321N1 cells. R(+)WIN 55,212-2 was shown to inhibit adhesion molecule and chemokine expression at the level of transcription, because it strongly inhibited the IL-1 induction of ICAM-1, VCAM-1, and IL-8 mRNAs and blocked the IL-1 activation of their promoters. The NFkappaB pathway was then assessed as a lead target for R(+)WIN 55,212-2. NFkappaB was measured by expression of a transfected NFkappaB-regulated reporter gene. Using this assay, R(+)WIN 55,212-2 strongly inhibited IL-1 activation of NFkappaB. Furthermore R(+)WIN 55,212-2 inhibited the ability of overexpressed Myd88, Tak-1, and IKK-2 to induce the reporter gene suggesting that R(+)WIN 55,212-2 acts at or downstream of IKK-2 in the IL-1 pathway. However R(+)WIN 55,212-2 failed to inhibit IL-1-induced degradation of IkappaBalpha, excluding IKK-2 as a direct target. In addition electrophoretic mobility shift and chromatin immunoprecipitation assays showed that R(+)WIN 55,212-2 does not regulate the IL-1-induced nuclear translocation of NFkappaB or the ability of the latter to bind to promoters regulating expression of ICAM-1 and IL-8. These data suggest that R(+)WIN 55,212-2 blocks IL-1 signaling by inhibiting the transactivation potential of NFkappaB.

Endocannabinoids Part I: molecular basis of endocannabinoid formation, action and inactivation and development of selective inhibitors

The discovery of specific receptors for Delta9-tetrahydrocannabinol, the major psychoactive component of marijuana, opened new horizons for the possible therapeutic exploitation of Cannabis sativa and the cannabinoids. Endogenous ligands of cannabinoid receptors, the 'endocannabinoids', were found and the molecular mechanisms underlying their biological effects and the regulation of their levels are now being identified. Cause/effect relationships between alterations of cannabinoid receptor/endocannabinoid levels in tissues and the symptoms of various pathological states are starting to be revealed. These studies may open the way to the possible use of substances that manipulate endocannabinoid levels and actions, such as inhibitors of the biosynthesis and inactivation and receptor antagonists, as cannabinoid-based therapeutic agents with little or no psychotropic side effect, thus potentially fulfilling an ambition nurtured for almost two centuries.

Differential effects of endocannabinoids on [(3)H]-GABA uptake in the rat globus pallidus

In the globus pallidus, cannabinoid CB(1) receptors are localized pre-synaptically on GABAergic neurons. We assessed the influence of the endocannabinoids, anandamide, 2-arachidonoyl-glycerol (2-AG) and noladin ether, on the uptake of [(3)H]-GABA in pallidal slices from rat. Both 2-AG and noladin ether increased [(3)H]-GABA uptake (by 40.8 +/- 8.0% and 38.4 +/- 12.5%). The effect of 2-AG was blocked by the cannabinoid CB(1) receptor antagonist AM 251. In contrast, neither anandamide nor the agonist WIN 55,212-2 had an effect on [(3)H]-GABA uptake. Different roles might be played by different endocannabinoids, both physiologically and in basal ganglia disorders, such as Parkinson's disease.

Cannabinoid signaling in glial cells

The cannabinoid signaling system is composed of cannabinoid (CB) receptors, their endogenous ligands, the endocannabinoids, and the enzymes that produce and inactivate them. It is well known that neurons communicate between each other through this signaling system. Delta 9-tetrahydrocannabinol, the main psychoactive compound of marijuana, interacts with CB receptors, impinging on this communication and inducing profound behavioral effects such as memory impairment and analgesia. Recent evidence suggests that glial cells also express components of the cannabinoid signaling system and marijuana-derived compounds act at CB receptors expressed by glial cells, affecting their functions. This review summarizes this evidence, discusses how glial cells might use the cannabinoid signaling system to communicate with neighboring cells, and argues that nonpsychotropic cannabinoids, both marijuana-derived and synthetic, likely constitute lead compounds for therapy aimed at reducing acute and chronic neuroinflammation, such as occurs in multiple sclerosis.

The biosynthesis, fate and pharmacological properties of endocannabinoids

The finding of endogenous ligands for cannabinoid receptors, the endocannabinoids, opened a new era in cannabinoid research. It meant that the biological role of cannabinoid signalling could be finally studied by investigating not only the pharmacological actions subsequent to stimulation of cannabinoid receptors by their agonists, but also how the activity of these receptors was regulated under physiological and pathological conditions by varying levels of the endocannabinoids. This in turn meant that the enzymes catalysing endocannabinoid biosynthesis and inactivation had to be identified and characterized, and that selective inhibitors of these enzymes had to be developed to be used as (1) probes to confirm endocannabinoid involvement in health and disease, and (2) templates for the design of new therapeutic drugs. This chapter summarizes the progress achieved in this direction during the 12 years following the discovery of the first endocannabinoid.

Cardiovascular pharmacology of cannabinoids

Cannabinoids and their synthetic and endogenous analogs affect a broad range of physiological functions, including cardiovascular variables, the most important component of their effect being profound hypotension. The mechanisms of the cardiovascular effects of cannabinoids in vivo are complex and may involve modulation of autonomic outflow in both the central and peripheral nervous systems as well as direct effects on the myocardium and vasculature. Although several lines of evidence indicate that the cardiovascular depressive effects of cannabinoids are mediated by peripherally localized CB1 receptors, recent studies provide strong support for the existence of as-yet-undefined endothelial and cardiac receptor(s) that mediate certain endocannabinoid-induced cardiovascular effects. The endogenous cannabinoid system has been recently implicated in the mechanism of hypotension associated with hemorrhagic, endotoxic, and cardiogenic shock, and advanced liver cirrhosis. Furthermore, cannabinoids have been considered as novel antihypertensive agents. A protective role of endocannabinoids in myocardial ischemia has also been documented. In this chapter, we summarize current information on the cardiovascular effects of cannabinoids and highlight the importance of these effects in a variety of pathophysiological conditions.

Neuroprotective effects of the synthetic cannabinoid HU-210 in primary cortical neurons are mediated by phosphatidylinositol 3-kinase/AKT signaling

Cannabinoids (CBs) are neuroprotective in vivo and in vitro, but the mechanisms of their actions are unknown. The aim of this study was to elucidate the signaling pathways that mediate the protective effect of CBs on primary cultured neurons. The neurotoxin S-AMPA induced significant death of rat primary cortical neurons, which was inhibited by the CB agonist HU-210. Antagonists selective for CB(1) or CB(2) receptors (AM 281 or AM 630, respectively) reversed the neuroprotective effect of HU-210 on S-AMPA-induced cell death. HU-210 triggered activation of AKT, but not activation of the ERK1/2, JNK or p38 signaling pathways. The phosphatidylinositol 3-kinase (PI 3-K) inhibitors LY294002 and wortmannin prevented phosphorylation of AKT in response to HU-210, and reversed the neuroprotective effect of HU-210 on S-AMPA-induced excitotoxicity. Thus the PI 3-K/AKT signaling pathway mediates the neuroprotective effect of exogenous cannabinoids such as HU-210 in primary CNS neurons.

R(+)-methanandamide-induced cyclooxygenase-2 expression in H4 human neuroglioma cells: possible involvement of membrane lipid rafts

Cannabinoids induce the expression of the cyclooxygenase-2 (COX-2) isoenzyme in H4 human neuroglioma cells via a pathway independent of cannabinoid- or vanilloid receptor activation. The underlying mechanism was recently shown to involve increased synthesis of ceramide, which in turn leads to activation of p38 and p42/44 mitogen-activated protein kinases (MAPKs). The present study investigates a possible contribution of membrane lipid rafts to cannabinoid-induced COX-2 expression. To address this issue, we tested the influence of methyl-beta-cyclodextrin (MCD), a membrane cholesterol depletor, on COX-2 expression by the endocannabinoid analogue R(+)-methanandamide (R(+)-MA). Incubation of H4 cells with MCD was associated with a loss of lipid raft integrity and a substantial inhibition of R(+)-MA-induced COX-2 expression and subsequent formation of prostaglandin E2. Moreover, MCD was shown to suppress signal transduction steps upstream to COX-2 induction by R(+)-MA. Accordingly, the cholesterol depletor suppressed R(+)-MA-induced formation of ceramide as well as phosphorylation of p38 and p42/44 MAPKs. Together, our results suggest that R(+)-MA induces COX-2 expression in human neuroglioma cells via a pathway linked to lipid raft microdomains.

[Endocannabinoids in the central nervous system]

The major psychoactive component of cannabis derivatives, delta9-THC, activates two G-protein coupled receptors: CB1 and CB2. Soon after the discovery of these receptors, their endogenous ligands were identified: lipid metabolites of arachidonic acid, named endocannabinoids. The two major main and most studied endocannabinoids are anandamide and 2-arachidonyl-glycerol. The CB1 receptor is massively expressed through-out the central nervous system whereas CB2 expression seems restricted to immune cells. Following endocannabinoid binding, CB1 receptors modulate second messenger cascades (inhibition of adenylate cyclase, activation of mitogen-activated protein kinases and of focal-adhesion kinases) as well as ionic conductances (inhibition of voltage-dependent calcium channels, activation of several potassium channels). Endocannabinoids transiently silence synapses by decreasing neurotransmitter release, play major parts in various forms of synaptic plasticity because of their ability to behave as retrograde messengers and activate non-cannabinoid receptors (such as vanilloid receptor type-1), illustrating the complexity of the endocannabinoid system. The diverse cellular targets of endocannabinoids are at the origin of the promising therapeutic potentials of the endocannabinoid system.

Cannabinoids reduce cAMP levels in the striatum of freely moving rats: an in vivo microdialysis study

The cannabinoid receptor subtype 1 (CB1R) is a member of the G(i)-protein-coupled receptor family and cannabinoid signaling is largely dependent on the suppression of adenylyl cyclase-catalyzed cAMP production. In cell lines transfected with the CB1R or in native tissue preparations, treatment with cannabinoid agonists reduces both basal and forskolin-stimulated cAMP synthesis. We measured extracellular cAMP concentrations in the striatum of freely moving rats utilizing microdialysis to determine if changes in cAMP concentrations in response to CB1R agonists can be monitored in vivo. Striatal infusion of the CB1R agonist WIN55,212-2 (100 microM or 1 mM), dose-dependently decreased basal and forskolin-stimulated extracellular cAMP. These effects were reversed by co-infusion of the CB1R antagonist SR141716A (30 microM), which alone had no effect up to the highest concentration tested (300 microM). These data indicate that changes in extracellular cAMP concentrations in response to CB1R stimulation can be monitored in vivo allowing the study of cannabinoid signaling in the whole animal.

The "dark side" of endocannabinoids: a neurotoxic role for anandamide

Endocannabinoids, including 2-arachidonoylglycerol and anandamide (N-arachidonoylethanolamine; AEA), have neuroprotective effects in the brain through actions at CB1 receptors. However, AEA also binds to vanilloid (VR1) receptors and induces cell death in several cell lines. Here we show that anandamide causes neuronal cell death in vitro and exacerbates cell loss caused by stretch-induced axonal injury or trophic withdrawal in rat primary neuronal cultures. Administered intracerebroventricularly, AEA causes sustained cerebral edema, as reflected by diffusion-weighted magnetic resonance imaging, regional cell loss, and impairment in long-term cognitive function. These effects are mediated, in part, through VR1 as well as through calpain-dependent mechanisms, but not through CB1 receptors or caspases. Central administration of AEA also significantly upregulates genes involved in pro-inflammatory/microglial-related responses. Thus, anandamide produces neurotoxic effects both in vitro and in vivo through multiple mechanisms independent of the CB1 receptor.

Multiple actions of anandamide on neonatal rat cultured sensory neurones

1. We have investigated the effects of the endocannabinoid anandamide (AEA) on neuronal excitability and vanilloid TRPV1 receptors in neonatal rat cultured dorsal root ganglion neurones. 2. Using whole-cell patch-clamp electrophysiology, we found that AEA inhibits high-voltage-activated Ca(2+) currents by 33+/-9% (five out of eight neurones) in the absence of the CB(1) receptor antagonist SR141716A (100 nM) and by 32+/-6% (seven out of 10 neurones) in the presence of SR141716A. 3. Fura-2 fluorescence Ca(2+) imaging revealed that AEA produced distinct effects on Ca(2+) transients produced by depolarisation evoked by 30 mM KCl. In a population of neurones of larger somal area (372+/-20 microM(2)), it significantly enhanced Ca(2+) transients (80.26+/-13.12% at 1 microM), an effect that persists after pertussis toxin pretreatment. In a population of neurones of smaller somal area (279+/-18 microM(2)), AEA significantly inhibits Ca(2+) transients (30.75+/-3.54% at 1 microM), an effect that is abolished by PTX pretreatment. 4. Extracellular application of 100 nM AEA failed to evoke TRPV1 receptor inward currents in seven out of eight neurones that responded to capsaicin (1 microM), with a mean inward current of -0.94+/-0.21 nA. In contrast, intracellular application of 100 nM AEA elicited robust inward currents in approximately 62% of neurones, the mean population response was -0.85+/-0.21 nA. When AEA was applied to the intracellular environment with capsazepine (1 microM), the mean population inward current was -0.01+/-0.01 nA. Under control conditions, mean population current fluctuations of -0.09+/-0.05 nA were observed.

Cannabinoids and neuroinflammation

Growing evidence suggests that a major physiological function of the cannabinoid signaling system is to modulate neuroinflammation. This review discusses the anti-inflammatory properties of cannabinoid compounds at molecular, cellular and whole animal levels, first by examining the evidence for anti-inflammatory effects of cannabinoids obtained using in vivo animal models of clinical neuroinflammatory conditions, specifically rodent models of multiple sclerosis, and second by describing the endogenous cannabinoid (endocannabinoid) system components in immune cells. Our aim is to identify immune functions modulated by cannabinoids that could account for their anti-inflammatory effects in these animal models.

The endocannabinoid system: a general view and latest additions

After the discovery, in the early 1990s, of specific G-protein-coupled receptors for marijuana's psychoactive principle Delta(9)-tetrahydrocannabinol, the cannabinoid receptors, and of their endogenous agonists, the endocannabinoids, a decade of investigations has greatly enlarged our understanding of this altogether new signalling system. Yet, while the finding of the endocannabinoids resulted in a new effort to reveal the mechanisms regulating their levels in the brain and peripheral organs under physiological and pathological conditions, more endogenous substances with a similar action, and more molecular targets for the previously discovered endogenous ligands, anandamide and 2-arachidonoylglycerol, or for some of their metabolites, were being proposed. As the scenario becomes subsequently more complicated, and the experimental tasks to be accomplished correspondingly more numerous, we briefly review in this article the latest 'additions' to the endocannabinoid system together with earlier breakthroughs that have contributed to our present knowledge of the biochemistry and pharmacology of the endocannabinoids.

Cannabinoids and gene expression during brain development

Cannabis is the most commonly used illicit drug in western societies, in particular among young people. It is consumed even by women during pregnancy and lactation, which result in a variety of disturbances in the development of their offspring, because, like other habit-forming drugs, cannabinoids, the psychoactive ingredients of marijuana, can cross the placental barrier and be secreted in the maternal milk. Through this way, cannabinoids affect the ontogeny of various neurotransmitter systems leading to changes in different behavioral patterns. Dopamine and endogenous opioids are among the neurotransmitters that result more affected by perinatal cannabinoid exposure, which, when animals mature, produce changes in motor activity, drug-seeking behavior, nociception and other processes. These disturbances are likely originated by the capability of cannabinoids to influence the expression of key genes for both neurotransmitters, in particular, the enzyme tyrosine hydroxylase and the opioid precursor proenkephalin. In addition, cannabinoids seem to be also able to influence the expression of genes encoding for neuron-glia cell adhesion molecules, which supports a potential influence of cannabinoids on the processes of cell proliferation, neuronal migration or axonal elongation in which these proteins are involved. In support of this possibility, CB1 receptors, which represent the major targets for the action of cannabinoids, are abundantly expressed in certain brain regions, such as the subventricular areas, which have been involved in these processes during brain development. Finally, cannabinoids might also be involved in the apoptotic death that occurs during brain development, possibly by influencing the expression of Bcl-2/Bax system. Also in support of this option, CB1 receptors are transiently expressed during brain development in different group of neurons which do not contain these receptors in the adult brain. This paper will review all evidence relating cannabinoids to the expression of key genes for neural development, trying to establish the future research addressed to elucidate the mechanisms involved in the epigenetic action of cannabinoids during brain development.

The endocannabinoid system in the basal ganglia and in the mesolimbic reward system: implications for neurological and psychiatric disorders

To date, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best studied endocannabinoids and are thought to act as retrograde messengers in the central nervous system (CNS). By activating presynaptic cannabinoid CB1 receptors, they can reduce glutamate release in dorsal and ventral striatum (nucleus accumbens) and alter synaptic plasticity, thereby modulating neurotransmission in the basal ganglia and in the mesolimbic reward system. In this review, we will focus on the role of the endocannabinoid system within these neuronal pathways and describe its effect on dopaminergic transmission and vice versa. The endocannabinoid system is unlikely to directly affect dopamine release, but can modify dopamine transmission trough trans-synaptic mechanisms, involving gamma-aminobutyric acid (GABA)-ergic and glutamatergic synapses, as well as by converging signal transduction cascades of the cannabinoid and dopamine receptors. The dopamine and endocannabinoid systems exert a mutual control on each other. Cannabinergic signalling may lead to release of dopamine, which can act via dopamine D1-like receptors as a negative feedback mechanism to counteract the effects of activation of the cannabinoid CB1 receptor. On the other hand, dopaminergic signalling via dopamine D2-like receptors may lead to up-regulation of cannabinergic signalling, which is likely to represent a negative feedback on dopaminergic signalling. The consequences of these interactions become evident in pathological conditions in which one of the two systems is likely to be malfunctioning. We will discuss neurological and psychiatric disorders such as Parkinson's and Huntington's disease, drug addiction and schizophrenia. Furthermore, the possible role of the endocannabinoid system in disorders not necessarily depending on the dopaminergic system, such as eating disorders and anxiety, will be described.

Endothelin-1 increases 2-arachidonoyl glycerol (2-AG) production in astrocytes

Astrocytes play an important role in neuroprotective responses. Recent studies indicate that endothelin-1, a neuropeptide upregulated during brain injury, increases levels of the endocannabinoid anandamide, a lipid with neuroprotective properties, in astrocytes in primary cultures. However, whether this neuropeptide also alters levels of 2-arachidonoyl glycerol (2-AG), the most abundant endocannabinoid in the CNS, in astrocytes remains unknown. In addition, 2-AG levels in astrocytes have never been measured. In this report we use chemical ionization gas chromatography/mass spectrometry to quantify picomole amounts of 2-AG in primary cultures of mouse astrocytes. We also demonstrate that endothelin-1 increases 2-AG production by 5-fold in these cells, a response that requires extracellular calcium and endothelin-1(A) receptor engagement. Immunocytochemistry showed that although cultured mouse neurons and microglia express cannabinoid receptors, cultured astrocytes do not. The data suggest that endothelin-1 modulates 2-AG production in astrocytes and that this endocannabinoid may participate in paracrine signaling toward neurons and microglia.

Cannabinoids inhibit the release of [3H]glutamate from rodent hippocampal synaptosomes via a novel CB1 receptor-independent action

In this study we investigated the effect of cannabinoids on [3H]glutamate release from hippocampal synaptosomes of rat and CB1-null mutant mouse. In the rat, cannabinoid receptor agonists, i.e. CP55,940 (EC50, 0.84 microm), WIN55,212-2 (EC50, 3.47 microm), ACEA (EC50, 17.8 microm), and R-(+)-methanandamide (EC50, 19.8 microm) concentration-dependently inhibited the 25-mm-K+ depolarization-evoked release of [3H]glutamate and, among them, WIN55,212-2 displayed the greatest efficacy. The CB1 receptor antagonists SR141716A (1-5 microm) and AM251 (1 microm) and the VR1 vanilloid receptor antagonist capsazepine (10 microm) did not antagonize the effect of the agonists. SR141716A by itself attenuated the evoked [3H]glutamate release. WIN55,212-2 inhibited the release of [3H]glutamate in CB1 -/- mice as well. These data demonstrate that the action of cannabinoids on glutamate release in the hippocampus is pharmacologically distinct and independent from the cloned CB1 receptor.

Heterogeneity of claudin expression by alveolar epithelial cells

Claudins are proteins that participate in epithelial barrier function and regulate paracellular permeability. By immunohistochemistry of adult rat lung sections, claudin-3, claudin-4, and claudin-5 were found to be co-expressed by type II alveolar epithelial cells. Claudin-3 and claudin-4 were also co-expressed by some alveolar epithelial cells adjacent to type II cells. In contrast, claudin-5 was expressed throughout the alveolus. Isolated primary rat alveolar epithelial cells in culture also expressed claudin-3, claudin-4, and claudin-5, but showed little claudin-1 and claudin-2 expression. Claudin expression by isolated cells at both the mRNA and protein level varied with time in culture. In particular, claudin-3 and claudin-5 co-localized and were distributed around the alveolar cell periphery, but claudin-4 expression was heterogeneous. We also found that paracellular permeability was increased when cultured alveolar epithelial cells were treated with a fatty acid amide, methanandamide. Methanandamide did not alter cell viability. Claudin-3, claudin-4, claudin-5, occludin, and zona occludens 1 remained localized to cell-cell contact sites at the plasma membrane in methanandamide-treated cells, suggesting that plasma membrane localization of these junction proteins is not sufficient for maintaining barrier function. However, methanandamide-treated cells showed a 12-fold increase in claudin-5 expression and a 2- to 3-fold increase in claudin-3, consistent with the notion that specific changes in claudin expression levels may correlate with changes in alveolar epithelial barrier function.

Cannabinoids ablate release of TNFalpha in rat microglial cells stimulated with lypopolysaccharide

Upon activation, brain microglial cells release proinflammatory mediators, such as TNFalpha, which may play an important role in eliciting neuroinflammatory processes causing brain damage. As cannabinoids have been reported to exert anti-inflammatory and neuroprotective actions in the brain, we here examined the effect of both synthetic and endogenous cannabinoids on TNFalpha release elicited by bacterial endotoxin lypopolysaccharide (LPS) in cultured microglia. Exposure of primary cultures of rat cortical microglial cells to LPS significantly stimulated TNFalpha mRNA expression and release. The endogenous cannabinoids anandamide and 2-arachidonylglycerol (2-AG), as well as the synthetic cannabinoids (+)WIN 55,212-2, CP 55,940, and HU210, inhibited in a concentration-dependent manner (1-10 microM) the LPS-induced TNFalpha release. Unlike the high-affinity cannabinoid receptor agonist (+)WIN 55,212-2, the low-affinity stereoisomer (-)WIN 55,212-2 did not exert any significant inhibition on TNFalpha release. Given this stereoselectivity, the ability of (+)WIN 55,212-2 to inhibit LPS-induced TNFalpha release from microglia is most likely receptor-mediated. By RT-PCR we found that the two G(i/o) protein-coupled cannabinoid receptors (type 1 and 2) are both expressed in microglial cultures. However, selective antagonists of type 1 (SR141716A and AM251) and type 2 (SR144528) cannabinoid receptors did not affect the effect of (+)WIN 55,212-2. Consistent with this finding is the observation that the ablative effect of (+)WIN 55,212-2 on LPS-evoked release of TNFalpha was not sensitive to the G(i/o) protein inactivator pertussis toxin. In addition, the cAMP elevating agents dibutyryl cAMP and forskolin both abolished LPS-induced TNFalpha release, thus rendering unlikely the possibility that (+)WIN 55,212-2 could ablate TNFalpha release through the inhibition of adenylate cyclase via the G(i)-coupled cannabinoid receptors type 1 and 2. In summary, our data indicate that both synthetic and endogenous cannabinoids inhibit LPS-induced release of TNFalpha from microglial cells. By showing that such effect does not appear to be mediated by either CB receptor type 1 or 2, we provide evidence suggestive of the existence of yet unidentified cannabinoid receptor(s) in brain microglia.

Plant-derived, synthetic and endogenous cannabinoids as neuroprotective agents. Non-psychoactive cannabinoids, 'entourage' compounds and inhibitors of N-acyl ethanolamine breakdown as therapeutic strategies to avoid pyschotropic effects

There is good evidence that plant-derived and synthetic cannabinoids possess neuroprotective properties. These compounds, as a result of effects upon CB(1) cannabinoid receptors, reduce the release of glutamate, and in addition reduce the influx of calcium following NMDA receptor activation. The major obstacle to the therapeutic utilization of such compounds are their psychotropic effects, which are also brought about by actions on CB(1) receptors. However, synthesis of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, which also have neuroprotective properties, are increased under conditions of severe inflammation and ischemia, raising the possibility that compounds that prevent their metabolism may be of therapeutic utility without having the drawback of producing psychotropic effects. In this review, the evidence indicating neuroprotective actions of plant-derived, synthetic and endogenous cannabinoids is presented. In addition, the pharmacological properties of endogenous anandamide-related compounds that are not active upon cannabinoid receptors, but which are also produced during conditions of severe inflammation and ischemia and may contribute to a neuroprotective action are reviewed.

The quest for a vascular endothelial cannabinoid receptor

This review examines pharmacological and biochemical evidence that suggests the existence of an as yet undefined endothelial receptor that mediates endocannabinoid-induced vasodilation. The signaling mechanisms triggered through this receptor and its potential physiological role are also discussed. Since vasodilation is often associated with hypotension, mechanisms involved in the hypotensive actions of cannabinoids, including the endocannabinoids anandamide and 2-arachidonoylglycerol, are also briefly reviewed.

Cannabinoids promote oligodendrocyte progenitor survival: involvement of cannabinoid receptors and phosphatidylinositol-3 kinase/Akt signaling

Cannabinoids exert pleiotropic actions in the CNS, including the inhibition of inflammatory responses and the enhancement of neuronal survival after injury. Although cannabinoid receptors are distributed widely in brain, their presence has not been investigated previously in oligodendrocytes. This study examined the expression of cannabinoid type 1 (CB1) receptors in rat oligodendrocytes in vivo and in culture and explored their biological function. Expression of CB1 receptors by oligodendrocytes was demonstrated immunocytochemically in postnatal and in adult white matter as well as in oligodendrocyte cultures. Reverse transcription-PCR and Western blotting further confirmed the presence of CB1 receptors. Oligodendrocyte progenitors undergo apoptosis with the withdrawal of trophic support, as determined by TUNEL assay and caspase-3 activation, and both the selective CB1 agonist arachidonyl-2'-chloroethylamide/(all Z)-N-(2-cycloethyl)-5,8,11,14-eicosatetraenamide (ACEA) and the nonselective cannabinoid agonists HU210 and (+)-Win-55212-2 enhanced cell survival. To investigate intracellular signaling involved in cannabinoid protection, we focused on the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. HU210, (+)-Win-55212-2, and ACEA elicited a time-dependent phosphorylation of Akt. Pertussis toxin abolished Akt activation, indicating the involvement of G(i)/G(o)-protein-coupled receptors. The CB1 receptor antagonist SR141716A partially inhibited Akt phosphorylation in response to HU210 and (+)-Win-55212-2 and abolished the effects of ACEA. Trophic support deprivation downregulated Akt activity, and cannabinoids recovered phospho-Akt levels. Inhibition of PI3K abrogated the survival action and the recovery of Akt activity in response to cannabinoids. SR141716A prevented only the protection conferred by ACEA. Nevertheless, SR141716A and the selective CB2 receptor antagonist SR144528 in combination inhibited the prosurvival action of HU210, which is in accordance with the finding of CB2 receptor expression by oligodendroglial cells. These data identify oligodendrocytes as potential targets of cannabinoid action in the CNS.

Acute neuronal injury, excitotoxicity, and the endocannabinoid system

The endocannabinoid system is a valuable target for drug discovery, because it is involved in the regulation of many cellular and physiological functions. The endocannabinoid system constitutes the endogenous lipids anandamide, 2-arachidonoylglycerol and noladin ether, and the cannabinoid CB1 and CB2 receptors as well as the proteins for their inactivation. It is thought that (endo)cannabinoid-based drugs may potentially be useful to reduce the effects of neurodegeneration. This paper reviews recent developments in the endocannabinoid system and its involvement in neuroprotection. Exogenous (endo)cannabinoids have been shown to exert neuroprotection in a variety of in vitro and in vivo models of neuronal injury via different mechanisms, such as prevention of excitotoxicity by CB1-mediated inhibition of glutamatergic transmission, reduction of calcium influx, and subsequent inhibition of deleterious cascades, TNF-alpha formation, and anti-oxidant activity. It has been suggested that the release of endogenous endocannabinoids during neuronal injury might be a protective response. However, several observations indicate that the role of the endocannabinoid system as a general endogenous protection system is questionable. The data are critically reviewed and possible explanations are given.

Neuronal and astrocytic localization of the cannabinoid receptor-1 in the dorsal horn of the rat spinal cord

Cannabinoids are involved in the control of pain at the spinal level through the cannabinoid receptor-1 (CB1) localized pre- and postsynaptically on primary afferent fibres and dorsal horn interneurones, respectively. Using immunocytochemistry, we show that in addition to its neuronal localization, CB1 is also expressed in numerous astrocytes in laminae I and II of the rat dorsal horn. This ubiquitous localization may account for the complex role played by cannabinoids in antinociception. CB1 receptors in astrocytes may be involved in the anti-hyperalgesic action of exogenous cannabinoids.

Astrocytes in culture produce anandamide and other acylethanolamides

Anandamide (arachidonylethanolamide) is an endocannabinoid that belongs to the acylethanolamide lipid family. It is produced by neurons in a calcium-dependent manner and acts through cannabinoid CB1 receptors. Other members of the acylethanolamide lipid family are also produced by neurons and act through G-protein-coupled receptors: homo-gamma-linolenylethanolamide (HEA) and docosatetraenylethanolamide (DEA) act through CB1 receptors, palmitylethanolamide (PEA) acts through CB2-like receptors, and oleylethanolamide (OEA) acts through receptors that have not yet been cloned. Although it is clear that anandamide and other acylethanolamides play a major role in neuronal signaling, whether astrocytes also produce these lipids is unknown. We developed a chemical ionization gas chromatography/mass spectrometry method that allows femtomole detection and quantification of anandamide and other acylethanolamides. Using this method, we unambiguously detected and quantified anandamide, HEA, DEA, PEA, and OEA in mouse astrocytes in culture. Stimulation of mouse astrocytes with ionomycin, a calcium ionophore, enhanced the production of anandamide, HEA, and DEA, whereas PEA and OEA levels were unchanged. Endothelin-1, a peptide known to act on astrocytes, enhanced the production of anandamide, without affecting the levels of other acylethanolamides. These results show that astrocytes produce anandamide, HEA, and DEA in a calcium-dependent manner and that anandamide biosynthesis can be selectively stimulated under physiologically relevant conditions. The relative levels of acylethanolamides in astrocytes from rat and human were different from the relative levels of acylethanolamides in mouse astrocytes, indicating that the production of these lipids differs between species. Because astrocytes are known to express CB1 receptors and inactivate endocannabinoids, our finding strongly suggests the existence of a functional endocannabinoid signaling system in these cells.

Exposure to cannabinoids in the development of endogenous cannabinoid system

New data strengthen the idea of a prominent role for endocannabinoids in the modulation of a wide variety of neurobiological functions. Among these, two functions, control of movement and antinociception, have attracted the maximal interest because of the possibility that cannabinoids and related compounds might be used with a therapeutic purpose. However, the functions of endocannabinoids in the brain, and also in the periphery, are large and involve, not only the adulthood, but also the period of prenatal and postnatal development, when endocannabinoids have been reported to be significantly present and to play a role in processes of brain development as neuronal proliferation and migration, axonal elongation, synaptogenesis and/or myelinogenesis. The present review article will summarize the different studies carried out on this topic and will suggest future lines of research to clarify the role of endocannabinoids and their receptors in the development.