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

Cannabis, a complex plant: different compounds and different effects on individuals

Cannabis is a complex plant, with major compounds such as delta-9-tetrahydrocannabinol and cannabidiol, which have opposing effects. The discovery of its compounds has led to the further discovery of an important neurotransmitter system called the endocannabinoid system. This system is widely distributed in the brain and in the body, and is considered to be responsible for numerous significant functions. There has been a recent and consistent worldwide increase in cannabis potency, with increasing associated health concerns. A number of epidemiological research projects have shown links between dose-related cannabis use and an increased risk of development of an enduring psychotic illness. However, it is also known that not everyone who uses cannabis is affected adversely in the same way. What makes someone more susceptible to its negative effects is not yet known, however there are some emerging vulnerability factors, ranging from certain genes to personality characteristics. In this article we first provide an overview of the biochemical basis of cannabis research by examining the different effects of the two main compounds of the plant and the endocannabinoid system, and then go on to review available information on the possible factors explaining variation of its effects upon different individuals.

WIN55, 212-2 promotes differentiation of oligodendrocyte precursor cells and improve remyelination through regulation of the phosphorylation level of the ERK 1/2 via cannabinoid receptor 1 after stroke-induced demyelination

In stroke, a common cause of neurological disability in adults is that the myelin sheaths are lost through the injury or death of mature oligodendrocytes, and the failure of remyelination may be often due to insufficient proliferation and differentiation of oligodendroglial progenitors. In the current study, we used middle cerebral artery occlusion (MCAO) to induced transient focal cerebral ischemia, and found that WIN55, 212-2 augmented actively proliferating oligodendrocytes measured by CC1 immunoreactive cells within the peri-infarct areas. To establish whether these effects were associated with changes in myelin formation, we analyzed the expression of myelin basic protein (MBP) and myelin ultrastructure. We found that WIN55, 212-2 showed more extensive remyelination than vehicle at 14 days post injection (dpi). The extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway may be involved in OPCs differentiation. To determine the regulatory effect of WIN55, 212-2 post-treatment on phospho-ERK 1/2 (p-ERK 1/2) after ischemia/reperfusion, Western blot analysis was performed. We found that WIN55, 212-2 regulated the phosphorylation level of the ERK 1/2 to promote OPCs survival and differentiation. Notably, cannabinoid receptor 1 is coupled to the activation of the ERK cascade. Following rimonabant combined treatment, the effect of WIN55, 212-2 on regulating the phosphorylation level of the ERK 1/2 was reversed, and the effect of accelerated myelin formation was partially inhibited. Together, we first found that WIN55, 212-2 promoted OPCs differentiation and remyelination through regulation of the level of the p-ERK 1/2 via cannabinoid receptor 1.

Cannabinoids, multiple sclerosis and neuroprotection

The cannabinoid signaling system participates in the control of cell homeostasis in the CNS, which explains why, in different neurodegenerative diseases including multiple sclerosis (MS), alterations in this system have been found to serve both as a pathogenic factor (malfunctioning of this system has been found at early phases of these diseases) and as a therapeutic target (the management of this system has beneficial effects). MS is an autoimmune disease that affects the CNS and it is characterized by inflammation, demyelination, remyelination, gliosis and axonal damage. Although it has been considered mainly as an inflammatory disorder, recent studies have recognized the importance of axonal loss both in the progression of the disorder and in the appearance of neurological disability, even in early stages of the disease. In recent years, several laboratories have addressed the therapeutic potential of cannabinoids in MS, given the experience reported by some MS patients who self-medicated with marijuana. Most of these studies focused on the alleviation of symptoms (spasticity, tremor, anxiety and pain) or on the inflammatory component of the disease. However, recent data also revealed the important neuroprotective action that could be exerted by cannabinoids in this disorder. The present review will be precisely centered on this neuroprotective potential, which is based mainly on antioxidant, anti-inflammatory and anti-excitotoxic properties, exerted through the activation of CB1 or CB2 receptors or other unknown mechanisms.

Type-1 cannabinoid receptor signaling in neuronal development

The type-1 cannabinoid receptor (CB1R) was initially identified as the neuronal target of Δ(9)-tetrahydrocannabinol (THC), the major psychoactive substance of marijuana. This receptor is one of the most abundant G-protein-coupled receptors in the adult brain, the target of endocannabinoid ligands and a well-characterized retrograde synaptic regulator. However, CB1Rs are also highly and often transiently expressed in neuronal populations in the embryonic and early postnatal brain, even before the formation of synapses. This suggests important physiological roles for CB1Rs during neuronal development. Several recent reviews have summarized our knowledge about the role of the endocannabinoid (eCB) system in neurodevelopment and neurotransmission by focusing on the metabolism of endocannabinoid molecules. Here, we review current knowledge about the effects of the modulation of CB1R signaling during the different phases of brain development. More precisely, we focus on reports that directly implicate CB1Rs during progenitor cell migration and differentiation, neurite outgrowth, axonal pathfinding and synaptogenesis. Based on theoretical considerations and on the reviewed experimental data, we propose a new model to explain the diversity of experimental findings on eCB signaling on neurite growth and axonal pathfinding. In our model, cell-autonomus and paracrine eCBs acting on CB1Rs are part of a global inhibitory network of cytoskeletal effectors, which act in concert with positive-feedback local-excitation loops, to ultimately yield highly polarized neurons.

G-protein-coupled receptors in adult neurogenesis

The importance of adult neurogenesis has only recently been accepted, resulting in a completely new field of investigation within stem cell biology. The regulation and functional significance of adult neurogenesis is currently an area of highly active research. G-protein-coupled receptors (GPCRs) have emerged as potential modulators of adult neurogenesis. GPCRs represent a class of proteins with significant clinical importance, because approximately 30% of all modern therapeutic treatments target these receptors. GPCRs bind to a large class of neurotransmitters and neuromodulators such as norepinephrine, dopamine, and serotonin. Besides their typical role in cellular communication, GPCRs are expressed on adult neural stem cells and their progenitors that relay specific signals to regulate the neurogenic process. This review summarizes the field of adult neurogenesis and its methods and specifies the roles of various GPCRs and their signal transduction pathways that are involved in the regulation of adult neural stem cells and their progenitors. Current evidence supporting adult neurogenesis as a model for self-repair in neuropathologic conditions, adult neural stem cell therapeutic strategies, and potential avenues for GPCR-based therapeutics are also discussed.

Cannabidiol protects oligodendrocyte progenitor cells from inflammation-induced apoptosis by attenuating endoplasmic reticulum stress

Cannabidiol (CBD) is the most abundant cannabinoid in Cannabis sativa that has no psychoactive properties. CBD has been approved to treat inflammation, pain and spasticity associated with multiple sclerosis (MS), of which demyelination and oligodendrocyte loss are hallmarks. Thus, we investigated the protective effects of CBD against the damage to oligodendrocyte progenitor cells (OPCs) mediated by the immune system. Doses of 1 μM CBD protect OPCs from oxidative stress by decreasing the production of reactive oxygen species. CBD also protects OPCs from apoptosis induced by LPS/IFNγ through the decrease of caspase 3 induction via mechanisms that do not involve CB1, CB2, TRPV1 or PPARγ receptors. Tunicamycin-induced OPC death was attenuated by CBD, suggesting a role of endoplasmic reticulum (ER) stress in the mode of action of CBD. This protection against ER stress-induced apoptosis was associated with reduced phosphorylation of eiF2α, one of the initiators of the ER stress pathway. Indeed, CBD diminished the phosphorylation of PKR and eiF2α induced by LPS/IFNγ. The pro-survival effects of CBD in OPCs were accompanied by decreases in the expression of ER apoptotic effectors (CHOP, Bax and caspase 12), and increased expression of the anti-apoptotic Bcl-2. These findings suggest that attenuation of the ER stress pathway is involved in the ‘oligoprotective' effects of CBD during inflammation.

Effect of long-term cannabis use on axonal fibre connectivity

Cannabis use typically begins during adolescence and early adulthood, a period when cannabinoid receptors are still abundant in white matter pathways across the brain. However, few studies to date have explored the impact of regular cannabis use on white matter structure, with no previous studies examining its impact on axonal connectivity. The aim of this study was to examine axonal fibre pathways across the brain for evidence of microstructural alterations associated with long-term cannabis use and to test whether age of regular cannabis use is associated with severity of any microstructural change. To this end, diffusion-weighted magnetic resonance imaging and brain connectivity mapping techniques were performed in 59 cannabis users with longstanding histories of heavy use and 33 matched controls. Axonal connectivity was found to be impaired in the right fimbria of the hippocampus (fornix), splenium of the corpus callosum and commissural fibres. Radial and axial diffusivity in these pathways were associated with the age at which regular cannabis use commenced. Our findings indicate long-term cannabis use is hazardous to the white matter of the developing brain. Delaying the age at which regular use begins may minimize the severity of microstructural impairment.

CD200-CD200R1 interaction contributes to neuroprotective effects of anandamide on experimentally induced inflammation

The endocannabinoid anandamide (AEA) is released by macrophages and microglia on pathological neuroinflammatory conditions such as multiple sclerosis (MS). CD200 is a membrane glycoprotein expressed in neurons that suppresses immune activity via its receptor (CD200R) mainly located in macrophages/microglia. CD200-CD200R interactions contribute to the brain immune privileged status. In this study, we show that AEA protects neurons from microglia-induced neurotoxicity via CD200-CD200R interaction. AEA increases the expression of CD200R1 in LPS/IFN-γ activated microglia through the activation of CB(2) receptors. The neuroprotective effect of AEA disappears when microglial cells derive from CD200R1(-/-) mice. We also show that engagement of CD200R1 by CD200Fc decreased the production of the proinflammatory cytokines IL-1β and IL-6, but increased IL-10 in activated microglia. In the chronic phases of Theiler's virus-induced demyelinating disease (TMEV-IDD) the expression of CD200 and CD200R1 was reduced in the spinal cord. AEA-treated animals up-regulated the expression of CD200 and CD200R1, restoring levels found in sham animals together with increased expression of IL-10 and reduced expression of IL-1β and IL-6. Treated animals also improved their motor behavior. Because AEA up-regulated the expression of CD200R1 in microglia, but failed to enhance CD200 in neurons we suggest that AEA-induced up-regulation of CD200 in TMEV-IDD is likely due to IL-10 as this cytokine increases CD200 in neurons. Our findings provide a new mechanism of action of AEA to limit immune response in the inflamed brain.

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.

Role of the cellular prion protein in oligodendrocyte precursor cell proliferation and differentiation in the developing and adult mouse CNS

There are numerous studies describing the signaling mechanisms that mediate oligodendrocyte precursor cell (OPC) proliferation and differentiation, although the contribution of the cellular prion protein (PrP^c) to this process remains unclear. PrP^c is a glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein involved in diverse cellular processes during the development and maturation of the mammalian central nervous system (CNS). Here we describe how PrP^c influences oligodendrocyte proliferation in the developing and adult CNS. OPCs that lack PrP^c proliferate more vigorously at the expense of a delay in differentiation, which correlates with changes in the expression of oligodendrocyte lineage markers. In addition, numerous NG2-positive cells were observed in cortical regions of adult PrP^c knockout mice, although no significant changes in myelination can be seen, probably due to the death of surplus cells.

The decrease of dopamine D₂/D₃ receptor densities in the putamen and nucleus caudatus goes parallel with maintained levels of CB₁ cannabinoid receptors in Parkinson's disease: a preliminary autoradiographic study with the selective dopamine D₂/D₃ antagonist [³H]raclopride and the novel CB₁ inverse agonist [¹²⁵I]SD7015

Cannabinoid type-1 receptors (CB₁Rs) modulate synaptic neurotransmission by participating in retrograde signaling in the adult brain. Increasing evidence suggests that cannabinoids through CB₁Rs play an important role in the regulation of motor activities in the striatum. In the present study, we used human brain samples to examine the relationship between CB₁R and dopamine receptor density in case of Parkinson's disease (PD). Post mortem putamen, nucleus caudatus and medial frontal gyrus samples obtained from PD patients were used for CB₁R and dopamine D₂/D₃ receptor autoradiography. [¹²⁵I]SD7015, a novel selective CB₁R inverse agonist, developed by a number of the present co-authors, and [³H]raclopride, a dopamine D₂/D₃ antagonist, were used as radioligands. Our results demonstrate unchanged CB₁R density in the putamen and nucleus caudatus of deceased PD patients, treated with levodopa (L-DOPA). At the same time dopamine D₂/D₃ receptors displayed significantly decreased density levels in case of PD putamen (control: 47.97 ± 10.00 fmol/g, PD: 3.73 ± 0.07 fmol/g (mean ± SEM), p<0.05) and nucleus caudatus (control: 30.26 ± 2.48 fmol/g, PD: 12.84 ± 5.49 fmol/g, p<0.0005) samples. In contrast to the putamen and the nucleus caudatus, in the medial frontal gyrus neither receptor densities were affected. Our data suggest the presence of an unaltered CB₁R population even in late stages of levodopa treated PD. This further supports the presence of an intact CB₁R population which, in line with the conclusion of earlier publications, may be utilized as a pharmacological target in the treatment of PD. Furthermore we found discrepancy between a maintained CB₁R population and a decreased dopamine D₂/D₃ receptor population in PD striatum. The precise explanation of this conundrum requires further studies with simultaneous examination of the central cannabinoid and dopaminergic systems in PD using higher sample size.

The endocannabinoid system: a revolving plate in neuro-immune interaction in health and disease

Studies of the last 40 years have brought to light an important physiological network, the endocannabinoid system. Endogenous and exogenous cannabinoids mediate their effects through activation of specific cannabinoid receptors. This modulatory homoeostatic system operates in the regulation of brain function and also in the periphery. The cannabinoid system has been shown to be involved in regulating the immune system. Studies examining the effect of cannabinoid-based drugs on immunity have shown that many cellular and cytokine mechanisms are modulated by these agents, thus raising the hypothesis that these compounds may be of value in the management of chronic inflammatory diseases. The special properties of endocannabinoids as neurotransmitters, their pleiotropic effects and the impact on immune function show that the endocannabinoid system represents a revolving plate of neural and immune interactions. In this paper, we outline current information on immune effects of cannabinoids in health and disease.

Cannabinoid receptor agonists modulate oligodendrocyte differentiation by activating PI3K/Akt and the mammalian target of rapamycin (mTOR) pathways

BACKGROUND AND PURPOSE

The endogenous cannabinoid system participates in oligodendrocyte progenitor differentiation in vitro. To determine the effect of synthetic cannabinoids on oligodendrocyte differentiation, we exposed differentiating cultures of oligodendrocytes with cannabinoid CB(1), CB(2) and CB(1)/CB(2) receptor agonists and antagonists. The response of the PI3K/Akt and the mammalian target of rapamycin (mTOR) signalling pathways were studied as effectors of cannabinoid activity.

EXPERIMENTAL APPROACH

Purified oligodendrocyte progenitor cells (OPC) obtained from primary mixed glial cell cultures were treated for 48 h with CB(1), CB(2) and CB(1) /CB(2) receptor agonists (ACEA, JWH133 and HU210, respectively) in the presence or absence of the antagonists AM281 (CB(1) receptor) and AM630 (CB(2) receptor). Moreover, inhibitors of the phosphatidylinositol 3-kinase (PI3K)/Akt and mTOR pathways (LY294002 and rapamycin, respectively) were used to study the involvement of these pathways on cannabinoid-induced OPC maturation.

KEY RESULTS

ACEA, JWH133 and HU-210 enhanced OPC differentiation as assessed by the expression of stage specific antigens and myelin basic protein (MBP). Moreover, this effect was blocked by the CB receptor antagonists. ACEA, JWH133 and HU210 induced a time-dependent phosphorylation of Akt and mTOR, whereas the inhibitors of PI3K/Akt (LY294002) or of mTOR (rapamycin) reversed the effects of HU-210 on oligodendrocyte differentiation and kinase activation.

CONCLUSIONS AND IMPLICATIONS

Activation of cannabinoid CB(1) or CB(2) receptors with selective agonists accelerated oligodendrocyte differentiation through the mTOR and Akt signalling pathways.

Prolonged oral cannabinoid administration prevents neuroinflammation, lowers β-amyloid levels and improves cognitive performance in Tg APP 2576 mice

Background

Alzheimer's disease (AD) brain shows an ongoing inflammatory condition and non-steroidal anti-inflammatories diminish the risk of suffering the neurologic disease. Cannabinoids are neuroprotective and anti-inflammatory agents with therapeutic potential.

Methods

We have studied the effects of prolonged oral administration of transgenic amyloid precursor protein (APP) mice with two pharmacologically different cannabinoids (WIN 55,212-2 and JWH-133, 0.2 mg/kg/day in the drinking water during 4 months) on inflammatory and cognitive parameters, and on ¹⁸F-fluoro-deoxyglucose (¹⁸FDG) uptake by positron emission tomography (PET).

Results

Novel object recognition was significantly reduced in 11 month old Tg APP mice and 4 month administration of JWH was able to normalize this cognitive deficit, although WIN was ineffective. Wild type mice cognitive performance was unaltered by cannabinoid administration. Tg APP mice showed decreased ¹⁸FDG uptake in hippocampus and cortical regions, which was counteracted by oral JWH treatment. Hippocampal GFAP immunoreactivity and cortical protein expression was unaffected by genotype or treatment. In contrast, the density of Iba1 positive microglia was increased in Tg APP mice, and normalized following JWH chronic treatment. Both cannabinoids were effective at reducing the enhancement of COX-2 protein levels and TNF-α mRNA expression found in the AD model. Increased cortical β-amyloid (Aβ) levels were significantly reduced in the mouse model by both cannabinoids. Noteworthy both cannabinoids enhanced Aβ transport across choroid plexus cells in vitro.

Conclusions

In summary we have shown that chronically administered cannabinoid showed marked beneficial effects concomitant with inflammation reduction and increased Aβ clearance.

CB2 cannabinoid receptors promote neural progenitor cell proliferation via mTORC1 signaling

The endocannabinoid system is known to regulate neural progenitor (NP) cell proliferation and neurogenesis. In particular, CB(2) cannabinoid receptors have been shown to promote NP proliferation. As CB(2) receptors are not expressed in differentiated neurons, CB(2)-selective agonists are promising candidates to manipulate NP proliferation and indirectly neurogenesis by overcoming the undesired psychoactive effects of neuronal CB(1) cannabinoid receptor activation. Here, by using NP cells, brain organotypic cultures, and in vivo animal models, we investigated the signal transduction mechanism involved in CB(2) receptor-induced NP cell proliferation and neurogenesis. Exposure of hippocampal HiB5 NP cells to the CB(2) receptor-selective agonist HU-308 led to the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin complex 1 (mTORC1) pathway, which, by inhibiting its downstream target p27Kip1, induced NP proliferation. Experiments conducted with the CB(2) receptor-selective antagonist SR144528, inhibitors of the PI3K/Akt/mTORC1 axis, and CB(2) receptor transient-transfection vector further supported that CB(2) receptors control NP cell proliferation via activation of mTORC1 signaling. Likewise, CB(2) receptor engagement induced cell proliferation in an mTORC1-dependent manner both in embryonic cortical slices and in adult hippocampal NPs. Thus, HU-308 increased ribosomal protein S6 phosphorylation and 5-bromo-2'-deoxyuridine incorporation in wild-type but not CB(2) receptor-deficient NPs of the mouse subgranular zone. Moreover, adult hippocampal NP proliferation induced by HU-308 and excitotoxicity was blocked by the mTORC1 inhibitor rapamycin. Altogether, these findings provide a mechanism of action and a rationale for the use of nonpsychotomimetic CB(2) receptor-selective ligands as a novel strategy for the control of NP cell proliferation and neurogenesis.

Cannabinoid receptor type 1 protects nigrostriatal dopaminergic neurons against MPTP neurotoxicity by inhibiting microglial activation

This study examined whether the cannabinoid receptor type 1 (CB(1)) receptor contributes to the survival of nigrostriatal dopaminergic (DA) neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. MPTP induced significant loss of nigrostriatal DA neurons and microglial activation in the substantia nigra (SN), visualized with tyrosine hydroxylase or macrophage Ag complex-1 immunohistochemistry. Real-time PCR, ELISA, Western blotting, and immunohistochemistry disclosed upregulation of proinflammatory cytokines, activation of microglial NADPH oxidase, and subsequent reactive oxygen species production and oxidative damage of DNA and proteins in MPTP-treated SN, resulting in degeneration of DA neurons. Conversely, treatment with nonselective cannabinoid receptor agonists (WIN55,212-2 and HU210) led to increased survival of DA neurons in the SN, their fibers and dopamine levels in the striatum, and improved motor function. This neuroprotection by cannabinoids was accompanied by suppression of NADPH oxidase reactive oxygen species production and reduced expression of proinflammatory cytokines from activated microglia. Interestingly, cannabinoids protected DA neurons against 1-methyl-4-phenyl-pyridinium neurotoxicity in cocultures of mesencephalic neurons and microglia, but not in neuron-enriched mesencephalic cultures devoid of microglia. The observed neuroprotection and inhibition of microglial activation were reversed upon treatment with CB(1) receptor selective antagonists AM251 and/or SR14,716A, confirming the involvement of the CB(1) receptor. The present in vivo and in vitro findings clearly indicate that the CB(1) receptor possesses anti-inflammatory properties and inhibits microglia-mediated oxidative stress. Our results collectively suggest that the cannabinoid system is beneficial for the treatment of Parkinson's disease and other disorders associated with neuroinflammation and microglia-derived oxidative damage.

N-arachidonoyl-L-serine is neuroprotective after traumatic brain injury by reducing apoptosis

N-arachidonoyl-L-serine (AraS) is a brain component structurally related to the endocannabinoid family. We investigated the neuroprotective effects of AraS following closed head injury induced by weight drop onto the exposed fronto-parietal skull and the mechanisms involved. A single injection of AraS following injury led to a significant improvement in functional outcome, and to reduced edema and lesion volume compared with vehicle. Specific antagonists to CB2 receptors, transient receptor potential vanilloid 1 (TRPV1) or large conductance calcium-activated potassium (BK) channels reversed these effects. Specific binding assays did not indicate binding of AraS to the GPR55 cannabinoid receptor. N-arachidonoyl-L-serine blocked the attenuation in phosphorylated extracellular-signal-regulated kinase 1/2 (ERK) levels and led to an increase in pAkt in both the ipsilateral and contralateral cortices. Increased levels of the prosurvival factor Bcl-xL were evident 24 hours after injury in AraS-treated mice, followed by a 30% reduction in caspase-3 activity, measured 3 days after injury. Treatment with a CB2 antagonist, but not with a CB1 antagonist, reversed this effect. Our results suggest that administration of AraS leads to neuroprotection via ERK and Akt phosphorylation and induction of their downstream antiapoptotic pathways. These protective effects are related mostly to indirect signaling via the CB2R and TRPV1 channels but not through CB1 or GPR55 receptors.

Wirkung von Cannabinoiden auf das Gehirn: Ein Überblick über MRI Befunde

Ziel: Übersicht über aktuelle Magnetresonanztomographie (MRI) Studien zur Wirkung von Cannabis auf das Gehirn. Methodik: Systematische Literaturrecherche mit Pubmed. Ergebnisse: Es wurden 37 Originalarbeiten gefunden, von denen 97 % zwischen 2004 und 2010 publiziert wurden. Je sechs Studien zur Volumetrie und Konnektivität beschreiben minimale Veränderungen der Hirnstrukturen, vor allem in Hippocampus und Amygdala, sowie die Integrität der weißen Substanz betreffend. Zwei neurometabolische Studien mit 1H-MR-Spektroskopie zeigen Veränderungen im dorsolateralen präfrontalen Cortex (DLPFC) und den Basalganglien. In vier placebo-kontrollierten funktionellen MRI Studien (fMRI) verminderte THC die Aktivierung in Hirnregionen, die zur Inhibition und zum Lernen benötigt werden, und CBD hemmte die Angst-assoziierte Aktivierung der Amygdala. Weitere 19 fMRI-Studien an chronischen Cannabiskonsumenten ergaben widersprüchliche Ergebnisse bzgl. Arbeitsgedächtnis, hippocampalem Gedächtnis, Gewinn/Verlust-Erwartung, Cannabis Cues, Emotionen, Inhibition, Motorik und Aufmerksamkeit. Schlussfolgerungen: Ein belastbarer Informationszuwachs wurde vor allem durch die getrennte, plazebo-kontrollierte Verabreichung von THC oder CBD in fMRI-Studien erreicht. Die widersprüchlichen Ergebnisse in fMRI Hirnaktivierungs-Mustern von Cannabiskonsumenten zeigen eine veränderte neuronale Plastizität, ohne dass eine Aussage getroffen werden kann, ob dies günstige oder ungünstige Auswirkungen hat. Für zukünftige Studien ist eine Bestimmung von CBD und THC z. B. durch Haaranalyse dringend anzuraten.

Tissue plasminogen activator prevents white matter damage following stroke

Tissue plasminogen activator (tPA) is the only available treatment for acute stroke. In addition to its vascular fibrinolytic action, tPA exerts various effects within the brain, ranging from synaptic plasticity to control of cell fate. To date, the influence of tPA in the ischemic brain has only been investigated on neuronal, microglial, and endothelial fate. We addressed the mechanism of action of tPA on oligodendrocyte (OL) survival and on the extent of white matter lesions in stroke. We also investigated the impact of aging on these processes. We observed that, in parallel to reduced levels of tPA in OLs, white matter gets more susceptible to ischemia in old mice. Interestingly, tPA protects murine and human OLs from apoptosis through an unexpected cytokine-like effect by the virtue of its epidermal growth factor-like domain. When injected into aged animals, tPA, although toxic to the gray matter, rescues white matter from ischemia independently of its proteolytic activity. These studies reveal a novel mechanism of action of tPA and unveil OL as a target cell for cytokine effects of tPA in brain diseases. They show overall that tPA protects white matter from stroke-induced lesions, an effect which may contribute to the global benefit of tPA-based stroke treatment.

Cannabinoid receptor 1 gene polymorphisms and marijuana misuse interactions on white matter and cognitive deficits in schizophrenia

Marijuana exposure during the critical period of adolescent brain maturation may disrupt neuro-modulatory influences of endocannabinoids and increase schizophrenia susceptibility. Cannabinoid receptor 1 (CB1/CNR1) is the principal brain receptor mediating marijuana effects. No study to-date has systematically investigated the impact of CNR1 on quantitative phenotypic features in schizophrenia and inter-relationships with marijuana misuse. We genotyped 235 schizophrenia patients using 12 tag single nucleotide polymorphisms (tSNPs) that account for most of CB1 coding region genetic variability. Patients underwent a high-resolution anatomic brain magnetic resonance scan and cognitive assessment. Almost a quarter of the sample met DSM marijuana abuse (14%) or dependence (8%) criteria. Effects of CNR1 tSNPs and marijuana abuse/dependence on brain volumes and neurocognition were assessed using ANCOVA, including co-morbid alcohol/non-marijuana illicit drug misuse as covariates. Significant main effects of CNR1 tSNPs (rs7766029, rs12720071, and rs9450898) were found in white matter (WM) volumes. Patients with marijuana abuse/dependence had smaller fronto-temporal WM volumes than patients without heavy marijuana use. More interestingly, there were significant rs12720071 genotype-by-marijuana use interaction effects on WM volumes and neurocognitive impairment; suggestive of gene-environment interactions for conferring phenotypic abnormalities in schizophrenia. In this comprehensive evaluation of genetic variants distributed across the CB1 locus, CNR1 genetic polymorphisms were associated with WM brain volume variation among schizophrenia patients. Our findings suggest that heavy cannabis use in the context of specific CNR1 genotypes may contribute to greater WM volume deficits and cognitive impairment, which could in turn increase schizophrenia risk.

Hyperactivation of anandamide synthesis and regulation of cell-cycle progression via cannabinoid type 1 (CB1) receptors in the regenerating liver

The mammalian liver regenerates upon tissue loss, which induces quiescent hepatocytes to enter the cell cycle and undergo limited replication under the control of multiple hormones, growth factors, and cytokines. Endocannabinoids acting via cannabinoid type 1 receptors (CB(1)R) promote neural progenitor cell proliferation, and in the liver they promote lipogenesis. These findings suggest the involvement of CB(1)R in the control of liver regeneration. Here we report that mice lacking CB(1)R globally or in hepatocytes only and wild-type mice treated with a CB(1)R antagonist have a delayed proliferative response to two-thirds partial hepatectomy (PHX). In wild-type mice, PHX leads to increased hepatic expression of CB(1)R and hyperactivation of the biosynthesis of the endocannabinoid anandamide in the liver via an in vivo pathway involving conjugation of arachidonic acid and ethanolamine by fatty-acid amide hydrolase. In wild-type but not CB(1)R(-/-) mice, PHX induces robust up-regulation of key cell-cycle proteins involved in mitotic progression, including cyclin-dependent kinase 1 (Cdk1), cyclin B2, and their transcriptional regulator forkhead box protein M1 (FoxM1), as revealed by ultrahigh-throughput RNA sequencing and pathway analysis and confirmed by real-time PCR and Western blot analyses. Treatment of wild-type mice with anandamide induces similar changes mediated via activation of the PI3K/Akt pathway. We conclude that activation of hepatic CB(1)R by newly synthesized anandamide promotes liver regeneration by controlling the expression of cell-cycle regulators that drive M phase progression.

Role of cannabinoids in multiple sclerosis

Although extracts from the cannabis plant have been used medicinally for thousands of years, it is only within the last 2 decades that our understanding of cannabinoid physiology and the provision of evidence for therapeutic benefit of cannabinoids has begun to accumulate. This review provides a background to advances in our understanding of cannabinoid receptors and the endocannabinoid system, and then considers how cannabinoids may help in the management of multiple sclerosis (MS). The relative paucity of treatments for MS-related symptoms has led to experimentation by patients with MS in a number of areas including the use of cannabis extracts. An increasing amount of evidence is now emerging to confirm anecdotal reports of symptomatic improvement, particularly for muscle stiffness and spasms, neuropathic pain and sleep and bladder disturbance, in patients with MS treated with cannabinoids. Trials evaluating a role in treating other symptoms such as tremor and nystagmus have not demonstrated any beneficial effects of cannabinoids. Safety profiles of cannabinoids seem acceptable, although a slow prolonged period of titration improves tolerability. No serious safety concerns have emerged. Methodological issues in trial design and treatment delivery are now being addressed. In addition, recent experimental evidence is beginning to suggest an effect of cannabinoids on more fundamental processes important in MS, with evidence of anti-inflammation, encouragement of remyelination and neuroprotection. Trials are currently under way to test whether cannabinoids may have a longer term role in reducing disability and progression in MS, in addition to symptom amelioration, where indications are being established.

[Cannabinoid applications in glaucoma]

INTRODUCTION

Glaucoma is a slowly progressive optic neuropathy that is one of the leading causes of legal blindness throughout the world. Currently there is a limited group of topical drugs for the medical treatment of glaucoma is currently limited, and research needs to be focused on new therapeutic horizons, such as the potential usefulness of the cannabinoid agonists for the treatment of glaucoma.

AIM

To review the current scientific literature related to the beneficial effects derived from the different ways of administration of cannabinoids indicated for the glaucomatous optic neuropathy.

DEVELOPMENT

Cannabinoid receptors have shown an intense expression in ocular tissues implicated in the regulation of the intraocular pressure, as well as inner layers of the retina. Through activation of CB1 and CB1 specific receptors and through other still unknown pathways, the cannabinoid agonists have shown both a clear hypotensive, as well as an experimentally proved neuroprotective effect on retinal ganglion cells.

CONCLUSIONS

Some cannabinoid agonists (WIN 55212-2, anandamide) have demonstrated, in experimental studies, to act as «ideal drugs» in the management of glaucoma, as they have been shown to have good tolerability after topical application, efficiently reduce intraocular pressure, and behave as neuroprotectors on retinal ganglion cells. Further studies as regards the safety and clinical assays must be carried out in order to examine the effectiveness of these drugs for the treatment of glaucoma in our daily clinical practice.

Cannabinoid receptor and N-acyl phosphatidylethanolamine phospholipase D--evidence for altered expression in multiple sclerosis

Cannabinoids have been shown to have a beneficial effect in both animal models of multiple sclerosis (MS) and human disease, although the mechanisms of action are unclear. We examined expression of the major cannabinoid receptors [(CBRs) cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2)] and a key enzyme involved in synthesis of the endocannabinoid anandamide [N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD)] in autopsy brain samples from patients with MS. CB1 was expressed in neurons, injured axons, oligodendrocytes, macrophages/microglia, some astrocytes, endothelial cells, smooth muscle cells and pericytes. CB2 and NAPE-PLD were localized to cerebral endothelial cells, pericytes, smooth muscle cells, astrocytes and macrophages/microglia. NAPE-PLD immunoreactivity was also seen in neurons. Endothelial CB2 expression was greatest in chronic inactive plaques, and in areas was seen in segments of endothelium where the endothelial expression of adhesion molecules (VCAM-1 and ICAM-1) was focally undetectable, and was often expressed in areas of blood-brain barrier damage. Vascular density was increased in chronic active plaques and normal-appearing white matter compared with controls. These data support findings from animal models which suggest a role for the endocannabinoid system in the MS, particularly in the regulation of endothelial leukocyte adhesion and the cellular response to injury.

Inverse agonism of cannabinoid CB1 receptor blocks the adhesion of encephalitogenic T cells in inflamed brain venules by a protein kinase A-dependent mechanism

It is well known that the cannabinoid system has a significant role in the regulation of the immune responses. Cannabinoid receptors CB1 and CB2 are expressed on T lymphocytes and mediate the immunomodulatory effects of cannabinoids on T cell functions. Here we show that the treatment of proteolipid protein (PLP)139-151-specific T cells with SR141716A, a CB1 inverse agonist and prototype of the diarylpyrazoles series, induced a strong inhibition of firm adhesion in inflamed brain venules in intravital microscopy experiments. In contrast, SR144528, a potent CB2 inverse agonist, had no significant effect on both rolling and arrest of activated T cells. In addition, two analogs of SR141716A and CB1 inverse agonists, AM251 and AM281 inhibited encephalitogenic T cell adhesion suggesting that selective CB1 inverse agonism interfere with lymphocyte trafficking in the CNS. Flow cytometry experiments showed that CB1 inverse agonists have no effect on adhesion molecule expression suggesting that CB1 blockade interferes with signal transduction pathways controlling T cell adhesion in inflamed brain venules. In addition, integrin clustering was not altered after treatment with CB1 inverse agonists suggesting that adhesion blockade is not due to the modulation of integrin valency. Notably, the inhibitory effect exerted by AM251 and AM281 on the adhesive interactions was completely reverted in the presence of protein kinase A (PKA) inhibitor H89, suggesting that cAMP and PKA activation play a key role in the adhesion blockade mediated by CB1 inverse agonists. To further strengthen these results and unveil a previously unknown inhibitory role of cAMP on activated T cell adhesion in vivo in the context of CNS inflammation, we showed that intracellular increase of cAMP induced by treatment with Bt2cAMP, a permeable analog of cAMP, and phosphodiesterase (PDE) inhibitor theophylline efficiently blocked the arrest of encephalitogenic T cells in inflamed brain venules. Our data show that modulation of CB1 function has anti-inflammatory effects and suggests that inverse agonism of CB1 block signal transduction mechanisms controlling encephalitogenic T cells adhesion in inflamed brain venules by a PKA-dependent mechanism.

The constitutive production of the endocannabinoid 2-arachidonoylglycerol participates in oligodendrocyte differentiation

Endocannabinoids have recently emerged as instructive cues in the developing central nervous system, and, based on the expression of their receptors, we identified oligodendrocytes as potential targets of these molecules. Here, we show that the enzymes responsible for the synthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG), diacylglycerol lipase alpha (DAGLα) and beta (DAGLβ), and degradation, monoacylglycerol lipase (MAGL), can be found in oligodendrocytes at different developmental stages. Moreover, cultured oligodendrocyte progenitor cells (OPCs) express DAGLα and β abundantly, resulting in the stronger production of 2-AG than in differentiated oligodendrocytes. The opposite is observed with MAGL. CB1 and CB2 receptor antagonists (SR141716 and AM630) impaired OPC differentiation into mature oligodendrocytes and likewise, inhibiting DAGL activity with RHC-80267 or tetrahydrolipstatin also blocked oligodendrocyte maturation, an effect reversed by the addition of exogenous 2-AG. Likewise, 2-AG synthesis disruption using specific siRNAs against DAGLα and DAGLβ significantly reduced myelin protein expression in vitro, whereas a pharmacological gain-of-function approach by using cannabinoid agonists or MAGL inhibition had the opposite effects. ERK/MAPK pathway is implicated in oligodendrocyte differentiation because PD98059, an inhibitor of MEK1, abrogated oligodendrocyte maturation. The cannabinoid receptor antagonists and RHC-80267 all diminished basal ERK1/2 phosphorylation, effects that were partially reversed by the addition of 2-AG. Overall, our data suggest a novel role of endocannabinoids in oligodendrocyte differentiation such that constitutive release of 2-AG activates cannabinoid receptors in an autocrine/paracrine way in OPCs, stimulating the ERK/MAPK signaling pathway.

The cannabinoid WIN55212-2 promotes neural repair after neonatal hypoxia-ischemia

BACKGROUND AND PURPOSE

The endocannabinoid system has been involved in the modulation of neural stem cells proliferation, survival and differentiation as well as in the generation of new oligodendrocyte progenitors in the postnatal brain. The present work aims to test the effect of the synthetic Type 1 and Type 2 cannabinoid receptor agonist WIN55212-2 on these processes in the context of neonatal rat brain hypoxia-ischemia (HI).

METHODS

P7 Wistar rats were subjected to HI and treated either with WIN55212-2 (1 mg/kg) or vehicle twice daily for 7 days after HI and euthanized at 1, 2, 7, 14, or 28 days to explore white matter injury progression and the neurogenic response in the subventricular zone after HI.

RESULTS

Our findings reveal that WIN55212-2 promotes remyelination of the injured external capsule, increasing the number of NG2+ early oligodendrocyte progenitors 7 days after HI in this area and the number of APC+ mature oligodendrocytes in the injured striatum 14 and 28 days after HI. WIN55212-2 also increases cell proliferation and protein expression of the neuroblast marker doublecortin in the subventricular zone 7 days after neonatal HI as well as the number of newly generated neuroblasts (5-bromodeoxyuridine+/doublecortin+ cells) in the ipsilateral striatum 14 days after HI.

CONCLUSIONS

Our results suggest that the activation of the endocannabinoid system promotes white and gray matter recovery after neonatal HI injury.

Diffusion tensor imaging in the early phase of schizophrenia: what have we learned?

The dysconnectivity model suggests that disturbed integration of neural communication is central to schizophrenia. The integrity of macro-structural brain circuits can be examined with diffusion tensor imaging (DTI), an MRI application sensitive to microstructural abnormalities of brain white matter. DTI studies in first-episode schizophrenia patients and individuals at high-risk of psychosis can provide insight into the role of structural dysconnectivity in the liability, onset and early course of psychosis. This review discusses (i) views on the role of white matter abnormalities in schizophrenia, (ii) DTI and its application in schizophrenia, (iii) DTI findings in first-episode patients and subjects at high-risk of psychosis; their timing, anatomical location and early course, (iv) the hypothesized underlying pathological substrate and possible causes of DTI white matter alterations, including effects of adolescent cannabis use, and (v) some methodological issues and future recommendations. In summary, there is evidence that DTI abnormalities convey a liability for psychosis and additional abnormalities occur around onset of psychosis. However, findings in first-episode patients are less robust than in chronic patients, and progression of disturbances may occur in the early course of poor-outcome patients. In addition, acceleration of the normal aging process may occur. Adolescent cannabis use has specific effects on DTI measures. An unresolved issue is the underlying pathology of DTI abnormalities, and combining DTI with other MRI indices can provide more insight. More research is needed on which genetic and environmental factors play a role in the variability of current results.

Overexpression of CB2 cannabinoid receptors results in neuroprotection against behavioral and neurochemical alterations induced by intracaudate administration of 6-hydroxydopamine

The role of CB2 cannabinoid receptors in the behavioral and neurochemical changes induced by intracaudate administration of 6-hydroxydopamine (6-OHDA) was evaluated. 6-OHDA (12 μg/4 μL) or its vehicle was injected in the caudate-putamen (CPu) of mice overexpressing the CB2 cannabinoid receptor (CB2xP) and wild type (WT) mice. Motor impairment, emotional behavior, and cognitive alterations were evaluated. Tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were measured by immunocytochemistry in the CPu and/or substantia nigra (SN) of CB2xP mice and WT mice. Oxidative/nitrosative and neuroinflammatory parameters were also measured in the CPu and cortex of 6-OHDA-treated and sham-treated mice. 6-OHDA-treated CB2xP mice presented significantly less motor deterioration than 6-OHDA-treated WT mice. Immunocytochemical analysis of tyrosine hydroxylase in the SN and CPu revealed significantly fewer lesions in CB2xP mice than in WT mice. GFAP and Iba-1 immunostaining revealed less astrocyte and microglia recruitment to the treated area of the CPu in CB2xP mice. Malonyldialdehyde (MDA) concentrations were lower in the striatum and cerebral cortex of sham-treated CB2xP mice than in sham-treated WT mice. The administration of 6-OHDA increased MDA levels in both WT mice and CB2xP mice; it increased the oxidized (GSSG)/reduced (GSH) glutathione ratio in the striatum in WT mice alone compared with matched sham-treated controls. The results revealed that overexpression of CB2 cannabinoid receptors decreased the extent of motor impairment and dopaminergic neuronal loss, reduced the recruitment of astrocytes and microglia to the lesion, and decreased the level of various oxidative parameters. These results suggest that CB2 receptors offer neuroprotection against dopaminergic injury.

The endocannabinoid system as a target for the treatment of neurodegenerative disease

The Cannabis sativa plant has been exploited for medicinal, agricultural and spiritual purposes in diverse cultures over thousands of years. Cannabis has been used recreationally for its psychotropic properties, while effects such as stimulation of appetite, analgesia and anti-emesis have lead to the medicinal application of cannabis. Indeed, reports of medicinal efficacy of cannabis can been traced back as far as 2700 BC, and even at that time reports also suggested a neuroprotective effect of the cultivar. The discovery of the psychoactive component of cannabis resin, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) occurred long before the serendipitous identification of a G-protein coupled receptor at which Delta(9)-THC is active in the brain. The subsequent finding of endogenous cannabinoid compounds, the synthesis of which is directed by neuronal excitability and which in turn served to regulate that excitability, further widened the range of potential drug targets through which the endocannabinoid system can be manipulated. As a result of this, alterations in the endocannabinoid system have been extensively investigated in a range of neurodegenerative disorders. In this review we examine the evidence implicating the endocannabinoid system in the cause, symptomatology or treatment of neurodegenerative disease. We examine data from human patients and compare and contrast this with evidence from animal models of these diseases. On the basis of this evidence we discuss the likely efficacy of endocannabinoid-based therapies in each disease context.

Endocannabinoid signaling directs differentiation of trophoblast cell lineages and placentation

In most mammals, placentation is critical for fetal development and pregnancy success. Exposure to marijuana during pregnancy has adverse effects, but whether the placenta is a target of cannabinoid/endocannabinoid signaling is not known. Using mice as a model system, we found that the endocannabinoid system is present in the ectoplacental cone and spongiotrophoblast cells. We also observed that aberrant endocannabinoid signaling confers premature trophoblast stem cell differentiation, and defective trophoblast development and invasion. These defects are reflected in retarded fetal development and compromised pregnancy outcome. Because the endocannabinoid system is conserved in mice and humans, our study suggests that endocannabinoid signaling is critical to placentation and pregnancy success in humans and implicates its potential significance in stem cell biology.

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.

Regulation of neural progenitor cell fate by anandamide

Exogenous application of neural progenitor cells (NPCs) has successful implications in treating brain disorders, and research is beginning to identify ways to mimic this exogenous application by activating endogenous stem cell compartments. The recent discovery of a functional endocannabinoid system in murine NPCs (mNPCs) represents one potential therapeutic means to influence endogenous stem cell compartments. High levels of the endogenous cannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) persist during CNS inflammation and infection. The goal of this study was to assess the influence of AEA on mNPCs to identify how the endocannabinoid system influences mNPCs in vitro, a potential model to investigate effects of endocannabinoids on endogenous stem cell compartments. Our results show that AEA affects mNPC cell fate determination. Initial glial differentiation was observed, followed by induction of neuronal differentiation with AEA treatment. Cell survival and apoptosis was not affected by AEA. These effects were coupled by an increased phosphorylation of cAMP-responsive element (CRE) binding protein (CREB).

Therapeutic Potential of Non-Psychotropic Cannabidiol in Ischemic Stroke

Cannabis contains the psychoactive component delta⁹-tetrahydrocannabinol (delta⁹-THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta⁹-THC and other cannabinoid CB₁ receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta⁹-THC also mediates psychological effects through the activation of the CB₁ receptor in the central nervous system. In addition to the CB₁ receptor agonists, cannabis also contains therapeutically active components which are CB₁ receptor independent. Of the CB₁ receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB₁ receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.

Endogenous cannabinoid signaling is required for voluntary exercise-induced enhancement of progenitor cell proliferation in the hippocampus

Voluntary exercise and endogenous cannabinoid activity have independently been shown to regulate hippocampal plasticity. The aim of the current study was to determine whether the endocannabinoid system is regulated by voluntary exercise and if these changes contribute to exercise-induced enhancement of cell proliferation. In Experiment 1, 8 days of free access to a running wheel increased the agonist binding site density of the cannabinoid CB(1) receptor; CB(1) receptor-mediated GTPgammaS binding; and the tissue content of the endocannabinoid anandamide in the hippocampus but not in the prefrontal cortex. In Experiment 2, the CB(1) receptor antagonist AM251 (1 mg kg(-1)) was administered daily to animals given free access to a running wheel for 8 days, after which cell proliferation in the hippocampus was examined through immunohistochemical analysis of the cell cycle protein Ki-67. Voluntary exercise increased proliferation of progenitor cells, as evidenced by the increase in the number of Ki-67 positive cells in the granule cell layer of the dentate gyrus (DG) in the hippocampus. However, this effect was abrogated by concurrent treatment with AM251, indicating that the increase in endocannabinoid signaling in the hippocampus is required for the exercise-induced increase in cell proliferation. These data demonstrate that the endocannabinoid system in the hippocampus is sensitive to environmental change and suggest that it is a mediator of experience-induced plasticity.

Anandamide enhances IL-10 production in activated microglia by targeting CB(2) receptors: roles of ERK1/2, JNK, and NF-kappaB

The endocannabinoid system exhibits anti-inflammatory properties by regulating cytokine production. Anandamide (AEA) down-regulates proinflammatory cytokines in a viral model of multiple sclerosis (MS). However, little is known about the mechanisms by which AEA exerts these effects. Microglial cells are the main source of cytokines within the brain and the first barrier of defense against pathogens by acting as antigen presenting cells. IL-10 is a key physiological negative regulator of microglial activation. In this study we show that AEA enhances LPS/IFNgamma-induced IL-10 production in microglia by targeting CB(2) receptors through the activation of ERK1/2 and JNK MAPKs. AEA also inhibits NF-kappaB activation by interfering with the phosphorylation of IkappaBalpha, which may result in an increase of IL-10 production. Moreover, endogenously produced IL-10 negatively regulates IL-12 and IL-23 cytokines, which in its turn modify the pattern of expression of transcription factors involved in Th commitment of splenocytes. This suggests that by altering the cytokine network, AEA could indirectly modify the type of immune responses within the central nervous system (CNS). Accordingly, pharmacological modulation of AEA uptake and degradation might be a useful tool for treating neuroinflammatory diseases.

The endocannabinoid 2-arachidonoylglycerol reduces lesion expansion and white matter damage after spinal cord injury

A series of pathological events secondary to spinal cord injury (SCI) contribute to the spread of the damage, which aggravates neurological deficits. Here we report that a single dose of the neuroprotective endocannabinoid 2-arachidonoyl glycerol (2-AG) administered early after SCI reduces lesion expansion, which was prevented by simultaneous blockade of both CB1 and CB2 receptors but not by blockade of either receptor alone. Treatment with 2-AG also preserves the white matter around the epicenter of the injury. Moreover, in the preserved white matter, 2-AG protects myelin from damage and reduces oligodendrocyte loss. In addition to these protective actions at the epicenter region, 2-AG also inhibits the myelin damage and delayed oligodendrocyte loss induced at 10mm from the epicenter. Interestingly, the early protective action of 2-AG is maintained 28 days after injury, when the lesion size is still smaller and the preservation of white matter is better in 2-AG-treated animals. Therefore, our results show that 2-AG protects from the expansion of the lesion and white matter damage, which suggest that this endogenous cannabinoid may be useful as a protective treatment for acute SCI.

CB1 cannabinoid receptors increase neuronal precursor proliferation through AKT/glycogen synthase kinase-3beta/beta-catenin signaling

The endocannabinoid system is involved in the regulation of many physiological effects in the central and peripheral nervous system. Recent findings have demonstrated the presence of a functional endocannabinoid system within neuronal progenitors located in the hippocampus and ventricular/subventricular zone that participates in the regulation of cell proliferation. It is presently unknown whether the endocannabinoid system exerts a widespread effect on neuronal precursors from different neurogenic regions, and very little is known about the signaling by which it regulates neuronal precursor proliferation. Herein, we demonstrate the presence of cannabinoid CB(1) receptors in granule cell precursors (GCPs) during early cerebellar development. Activation of CB(1) receptors by HU-210 promoted GCP proliferation in vitro, an effect that was prevented by a selective CB(1) antagonist. Accordingly, in vivo experiments showed that GCP proliferation was increased by chronic HU-210 treatment and that in CB(1)-deficient mice cell proliferation was significantly lower than in wild-type littermates, indicating that the endocannabinoid system is physiologically involved in regulation of GCP proliferation. The pro-proliferative effect of cannabinoids in GCPs was mediated through the CB(1)/AKT/glycogen synthase kinase-3beta/beta-catenin pathway. Involvement of this pathway was also observed in cultures of neuronal precursors from the subventricular zone, suggesting that this pathway may be a general mechanism by which endocannabinoids regulate proliferation of neuronal precursors. These observations suggest that endocannabinoids constitute a new family of lipid signaling cues that may exert a widespread effect on neuronal precursor proliferation during brain development.

Cannabinoids and the immune system: an overview

Cannabinoids can influence the immune network. Data on the impact of exogenous cannabinoid ligands on immune function serve not only to understand how the endocannabinoid system modulates immune phenomena associated with infection or inflammation, but also to identify therapeutic targets for immune diseases. Cannabinoids can modulate immune reactions in the periphery but also in the brain, influence T cell subset balance and cytokine expression and play a role in the balance between neuroinflammation and neurodegeneration. Immune cells can synthesize endocannabinoids and also be influenced by cannabinoid analogues. Cannabinoid receptors show different expression on immune cells depending on activation status and stimuli. The complexity of relation between cannabinoid ligands of various classes and cannabinoid receptors brought the need to refine the simple conceptual frame of agonist-antagonists and offered potential implications for understanding interactions in pathological conditions. The immune influence of cannabinoid ligands is not fully elucidated. However, aspects of their immunomodulatory effects provide the basis for a context-dependent targeted therapeutic approach, thus leading to the possibility for the use of cannabinoids in the treatment of inflammatory disease.

The cannabinoid receptor 1 gene (CNR1) and multiple sclerosis: an association study in two case-control groups from Spain

Different studies point to the implication of the endocannabinoid system in multiple sclerosis (MS) and animal models of MS. The purpose of this study was to evaluate a possible association of MS with polymorphic markers at the CNR1 gene, encoding the cannabinoid 1 (CB1) receptor. We have performed a genetic analysis of an AAT repeat microsatellite localized in the downstream region of the CNR1 gene, in two case—control groups of MS patients and healthy controls (HC) from Spain (Madrid and Bilbao). MS patients with primary progressive MS (PPMS) had more commonly long ((AAT) ≥13) alleles and genotypes with a significant difference for genotype 7/8 in Madrid (p = 0.043) and in the sum of both groups (p = 0.016); short alleles were less frequently found in PPMS with a significant difference for allele 5 in the analysis of both groups together (p = 0.039). In patients with relapsing MS, no consistent differences in allele and genotype distribution were found. Disease severity and progression was unrelated to AAT repeat variations. In conclusion, long (AAT) ≥13 CNR1 genotypes could behave as risk factors for PPMS.

c/EBPbeta is a major regulatory element driving transcriptional activation of the CXCL12 promoter

CXCL12 is considered a constitutively expressed chemokine with homeostatic functions. However, induction of CXCL12 expression and its potential role in several pathologic conditions have been reported, suggesting that CXCL12 gene expression can be induced by different stimuli. To elucidate the molecular mechanisms involved in the regulation of CXCL12 gene expression, we aim to define the molecular factors that operate at the transcriptional level. Basal, constitutive expression of CXCL12 was dependent on basic helix-loop-helix factors. Transcriptional up-regulation of the CXCL12 gene was induced by cellular confluence or inflammatory stimuli such as interleukin-1 and interleukin-6, in a CCAAT/enhancer binding protein beta (c/EBPbeta)-dependent manner. Chromatin immunoprecipitation assays confirmed c/EBPbeta binding to a specific response element located at -1171 of the promoter region of CXCL12. Our data show that c/EBPbeta is a major regulatory element driving transcription of the CXCL12 gene in response to cytokines and cell confluence.

Altered white matter microstructure in adolescent substance users

Chronic marijuana use during adolescence is frequently comorbid with heavy alcohol consumption and associated with CNS alterations, yet the influence of early cannabis and alcohol use on microstructural white matter integrity is unclear. Building on evidence that cannabinoid receptors are present in myelin precursors and affect glial cell processing, and that excessive ethanol exposure is associated with persistently impaired myelination, we used diffusion tensor imaging (DTI) to characterize white matter integrity in heavy substance using and non-using adolescents. We evaluated 36 marijuana and alcohol-using (MJ+ALC) adolescents (ages 16-19) and 36 demographically similar non-using controls with DTI. The diffusion parameters fractional anisotropy (FA) and mean diffusivity (MD) were subjected to whole-brain voxelwise group comparisons using tract-based spatial statistics (Smith, S.M., Jenkinson, M., Johansen-Berg, H., Rueckert, D., Nichols, T.E., Mackay, C.E., Watkins, K.E., Ciccarelli, O., Cader, M.Z., Matthews, P.M., Behrens, T.E., 2006. Tract-based spatial statistics: voxelwise analysis of multi-subject diffusion data. Neuroimage 31, 1487-1505). MJ+ALC teens had significantly lower FA than controls in 10 regions, including left superior longitudinal fasciculus (SLF), left postcentral gyrus, bilateral crus cerebri, and inferior frontal and temporal white matter tracts. These diminutions occurred in the context of increased FA in right occipital, internal capsule, and SLF regions. Changes in MD were less distributed, but increased MD was evident in the right occipital lobe, whereas the left inferior longitudinal fasciculus showed lower MD in MJ+ALC users. Findings suggest that fronto-parietal circuitry may be particularly impacted in adolescent users of the most prevalent intoxicants: marijuana and alcohol. Disruptions to white matter in this young group could indicate aberrant axonal and myelin maturation with resultant compromise of fiber integrity. Findings of increased anisotropic diffusion in alternate brain regions suggest possible neuroadaptive processes and can be examined in future studies of connectivity to determine how aberrancies in specific tracts might influence efficient cognitive processing.

Cannabinoids and experimental models of multiple sclerosis

The inflammatory response is a hallmark in the development of autoimmune-mediated neurodegenerative diseases of the central nervous system (CNS). Research on these pathological phenomena is being extensively undertaken and experimental autoimmune encephalomyelitis (EAE) serves as a valuable animal model. Studies from this model have generated interesting insights into biological effects of cannabinoids and may, at least to a certain extent, reflect the cannabinoid-mediated protective mechanisms also in human diseases with similar characteristics, such as multiple sclerosis (MS). Cannabinoids are involved in regulation of the immune system. These effects comprise modulation of inflammatory reaction through components of the innate and adaptive immune responses. Cannabinoids also confer neuroprotection and assist neuroregeneration, thus maintaining a balance within the delicate CNS microenvironment and restoring function following pathological condition, commonly driven by neuroinflammation. Continued studies of cannabinoid actions in EAE pathogenesis should be beneficial for the better understanding of the mechanisms governing such a vast array of physiological effects and in development of new therapeutic strategies for the treatment of human neuroinflammatory and neurodegenerative diseases.