CB1 and CB2 cannabinoid receptor expression during development and in epileptogenic developmental pathologies

Recent data support the involvement of the endocannabinoid signaling in early brain development, as well as a key role of cannabinoid receptors (CBR) in pathological conditions associated with unbalanced neuronal excitability and inflammation. Using immunocytochemistry, we explored the expression and cellular pattern of CBR 1 and 2 (CB1 and CB2) during prenatal human cortical development, as well as in focal malformations of cortical development associated with intractable epilepsy (focal cortical dysplasia; cortical tubers in patients with the tuberous sclerosis complex and glioneuronal tumors). Strong CB1 immunoreactivity was detected in the cortical plate in developing human brain from the earliest stages tested (gestational week 9) and it persisted throughout prenatal development. Both cannabinoid receptors were not detected in neural progenitor cells located in the ventricular zone. Only CB1 was expressed in the subventricular zone and in Cajal–Retzius cells in the molecular zone of the developing neocortex. CB2 was detected in cells of the microglia/macrophage lineage during development. In malformations of cortical development, prominent CB1 expression was demonstrated in dysplastic neurons. Both CBR were detected in balloon/giant cells, but CB2 appeared to be more frequently expressed than CB1 in these cell types. Reactive astrocytes were mainly stained with CB1, whereas cells of the microglia/macrophage lineage were stained with CB2. These findings confirm the early expression pattern of cannabinoid receptors in the developing human brain, suggesting a function for CB1 in the early stages of corticogenesis. The expression patterns in malformations of cortical development highlight the role of cannabinoid receptors as mediators of the endocannabinoid signaling and as potential pharmacological targets to modulate neuronal and glial cell function in epileptogenic developmental pathologies.     

Expression of scavenger receptor class B, type I, by astrocytes and vascular smooth muscle cells in normal adult mouse and human brain and in Alzheimer's disease brain

In Alzheimer's disease (AD), fibrillar beta-amyloid protein (fAbeta) accumulates in the walls of cerebral vessels associated with vascular smooth muscle cells (SMCs), endothelium, and pericytes, and with microglia and astrocytes in plaques in the brain parenchyma. Scavenger receptor class A (SR-A) and class B, type I (SR-BI) mediate binding and ingestion of fAbeta by cultured human fetal microglia, microglia from newborn mice, and by cultured SMCs. Our findings that SR-BI participates in the adhesion of cultured microglia from newborn SR-A knock-out mice to fAbeta-coated surfaces, and that microglia secrete reactive oxygen species when they adhere to these surfaces prompted us to explore expression of SR-BI in vivo. We report here that astrocytes and SMCs in normal adult mouse and human brains and in AD brains express SR-BI. In contrast, microglia in normal adult mouse and human brains and in AD brains do not express SR-BI. These findings indicate that SR-BI may mediate interactions between astrocytes or SMCs and fAbeta, but not of microglia and fAbeta, in AD, and that expression of SR-BI by rodent microglia is developmentally regulated. They suggest that SR-BI expression also is developmentally regulated in human microglia.     

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

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

Glial expression of cannabinoid CB(2) receptors and fatty acid amide hydrolase are beta amyloid-linked events in Down's syndrome

Recent data suggest that the endocannabinoid system (ECS) may be involved in the glial response in different types of brain injury. Both acute and chronic insults seem to trigger a shift in the pattern of expression of some elements of this system from neuronal to glial. Specifically, data obtained in human brain tissue sections from Alzheimer's disease patients showed that the expression of cannabinoid receptors of the CB(2) type is induced in activated microglial cells while fatty acid amide hydrolase (FAAH) expression is increased in reactive astrocytes. The present study was designed to determine the time-course of the shift from neuronal to glial induction in the expression of these proteins in Down's syndrome, sometimes referred to as a human model of Alzheimer-like beta-amyloid (Abeta) deposition. Here we present immunohistochemical evidence that both CB(2) receptors and FAAH enzyme are induced in Abeta plaque-associated microglia and astroglia, respectively, in Down's syndrome. These results suggest that the induction of these elements of the ECS contributes to, or is a result of, amyloid deposition and subsequent plaque formation. In addition, they confirm a striking differential pattern of distribution of FAAH and CB(2) receptors.     

Targeting CB(2) receptor as a neuroinflammatory modulator in experimental autoimmune encephalomyelitis

During immune mediated demyelinating lesions, the endocannabinoid system is involved in the pathogenesis of both neuroinflammation and neurodegeneration through different mechanisms. Here, we explored the cellular distribution of cannabinoid 2 receptor (CB(2)R) in the central nervous system (CNS) and detected the level of CB(2)R expression during experimental autoimmune encephalomyelitis (EAE) by RT-PCR, Western blot and immunostaining. Our results show that CB(2)R was expressed in neurons, microglia and astrocytes. During EAE, the expression of CB(2)R in spinal cord rose slowly at days 9 and 17 post immunization (p.i.), and elevated rapidly at day 28 p.i., while the expression of CB(2)R in spleen elevated rapidly and got a plateau at days 17 and 28 p.i. Only the increase of CB(2)R expression in spinal cord demonstrated a significant difference when compared to control mice immunized with complete Freund's adjuvant (CFA). The selective CB(2)R antagonist (SR144528) exacerbated EAE clinical severity accompanied by weight loss. SR144528 inhibited the expression of CB(2)R, but increased the expression of CB(1)R in brain, spinal cord and spleen. The administration of SR144528 declined interferon-γ, IL-17, IL-4, IL-10, IL-1β, IL-6 and tumor necrosis factor-α, but increased CX3CL1 in brain and/or spinal cord. In contrast, IL-17 and MCP-1 were increased, while CX3CL1 was decreased in splenic mononuclear cells as compared to vehicle controls. These results indicate that manipulation of CB(2)R may have therapeutic value in MS, but its complexity remains to be considered and studied for further clinical application.     

Expression of intercellular adhesion molecule-1 in atherosclerotic plaques.

Immunohistochemistry of human atherosclerotic arteries demonstrates expression of the intercellular adhesion molecule-1 (ICAM-1) on endothelial cells, macrophages, and smooth muscle cells of the plaques. Normal arterial endothelial cells and intimal smooth muscle outside plaques give weaker or negative reactions; these differ from the strong endothelial expression in small vessels. Quantitative color-image analysis of the endothelial layer shows increased expression of ICAM-1 in all subtypes of atherosclerotic lesions, except fibrous plaques. Endothelial expression of ICAM-1 may be involved in the recruitment of monocytes to the lesion, as suggested by its role in the entry of leukocytes, including monocytes, into foci of inflammation. Collaboration with other mechanisms, particularly chemoattractant factors, may be important for this effect. ICAM-1 enhanced monocyte recruitment is a potential mechanism for the growth of an atherosclerotic plaque.     

Cannabinoid receptor stimulation is anti-inflammatory and improves memory in old rats

The number of activated microglia increase during normal aging. Stimulation of endocannabinoid receptors can reduce the number of activated microglia, particularly in the hippocampus, of young rats infused chronically with lipopolysaccharide (LPS). In the current study we demonstrate that endocannabinoid receptor stimulation by administration of WIN-55212-2 (2 mg/kg day) can reduce the number of activated microglia in hippocampus of aged rats and attenuate the spatial memory impairment in the water pool task. Our results suggest that the action of WIN-55212-2 does not depend upon a direct effect upon microglia or astrocytes but is dependent upon stimulation of neuronal cannabinoid receptors. Aging significantly reduced cannabinoid type 1 receptor binding but had no effect on cannabinoid receptor protein levels. Stimulation of cannabinoid receptors may provide clinical benefits in age-related diseases that are associated with brain inflammation, such as Alzheimer's disease.     

Cerebral hypoxia-ischemia and middle cerebral artery occlusion induce expression of the cannabinoid CB2 receptor in the brain

Until recently the cannabinoid CB2 receptor was believed to be absent from the central nervous system. In this study we have identified CB2 expressing cells that appear in the rat brain following stroke and hypoxic-ischemia. At 3 days following surgery CB2-positive macrophages, deriving from resident microglia and/or invading monocytes appear on the lesioned side of the brain. By day 7, a mixed population of CB2-positive cells is present. Microglia-derived macrophages are the key cells in the first stages of brain inflammation, and a pivotal step in the neurodegeneration that follows the acute stage of injury. Thus, CB2 may be important in the brain during injury, and in inflammatory neurodegenerative disorders. The presence of CB2-positive cells in the brain following stroke may provide a novel strategy for cannabinoid-mediated intervention into stroke induced neurodegeneration without the psychoactive effects of CB1 receptor stimulation.     

Immune system associated antigens expressed by cells of the human central nervous system

HLA-DR, HLA-DQ and HLA-DP are class II major histocompatibility complex (MHC) antigens necessary for T cell binding and antigen presentation. Interleukin-2 is a lymphokine used by the immune system to signal proliferation of cells in the immune response. Using unfixed tissue and free-floating immunohistochemistry, we show profuse immunoreactivity for these immune antigens in white and gray matter samples from normal and Alzheimer's (AD) disease patients. On morphologic grounds, immunoreactive cell types appear to include astrocytes, microglia, macrophages, and endothelial cells or pericytes.     

Hematopoietic stem cells provide repair functions after laser-induced Bruch's membrane rupture model of choroidal neovascularization

Vascular repair by adult hematopoietic stem cells (HSCs) is well-appreciated because these cells are known for their plasticity. We have shown that adult HSCs differentiate into endothelial cells and participate in both retinal and choroidal neovascularization. We asked whether HSCs participated in the wounding response by forming astrocytes, retinal pigment epithelia (RPE), macrophages, and pericytes. Lethally irradiated C57BL6/J mice were reconstituted with HSCs from mice homozygous for green fluorescent protein (GFP) and then subjected to laser-induced rupture of Bruch's membrane. After immunohistochemical examination of ocular tissue, GFP(+) astrocytes were observed concentrated along the edge of the laser wound, where they and mural cells closely ensheathed the neovasculature. GFP(+) vascular endothelial cells and macrophages/microglia were also evident. Large irregularly shaped GFP(+) RPE cells constituted approximately 93% of RPE cells adjacent to the edge of the denuded RPE area. In regions farther away from the wound, GFP(+) RPE cells were integrated among the GFP(-) host RPE. Thus, postnatal HSCs can differentiate into cells expressing markers specific to astrocytes, macrophages/microglia, mural cells, or RPE. These studies suggest that HSCs could serve as a therapeutic source for long-term regeneration of injured retina and choroid in diseases such as age-related macular degeneration and retinitis pigmentosa.     

Glutamate receptor expression in multiple sclerosis lesions

Blockade of receptors for the excitatory neurotransmitter glutamate ameliorates neurological clinical signs in models of the CNS inflammatory demyelinating disease multiple sclerosis (MS). To investigate whether glutamate excitoxicity may play a role in MS pathogenesis, the cellular localization of glutamate and its receptors, transporters and enzymes was examined. Expression of glutamate receptor (GluR) 1, a Ca(++)-permeable ionotropic AMPA receptor subunit, was up-regulated on oligodendrocytes in active MS lesion borders, but Ca(++)-impermeable AMPA GluR2 subunit levels were not increased. Reactive astrocytes in active plaques expressed AMPA GluR3 and metabotropic mGluR1, 2/3 and 5 receptors and the GLT-1 transporter, and a subpopulation was immunostained with glutamate antibodies. Activated microglia and macrophages were immunopositive for GluR2, GluR4 and NMDA receptor subunit 1. Kainate receptor GluR5-7 immunostaining showed endothelial cells and dystrophic axons. Astrocyte and macrophage populations expressed glutamate metabolizing enzymes and unexpectedly the EAAC1 transporter, which may play a role in glutamate uptake in lesions. Thus, reactive astrocytes in MS white matter lesions are equipped for a protective role in sequestering and metabolizing extracellular glutamate. However, they may be unable to maintain glutamate at levels low enough to protect oligodendrocytes rendered vulnerable to excitotoxic damage because of GluR1 up-regulation.     

Association between lipid accumulation and the cannabinoid system in Huh7 cells expressing HCV genes

Evidence from clinical and laboratory studies has accumulated indicating that the activation of the cannabinoid system is crucial for steatosis, especially in non-alcoholic fatty liver disease. However, the association between hepatitis C virus (HCV) infection and the cannabinoid system has not been well investigated and it is unclear whether steatosis in chronic hepatitis C develops via activation of the endocannabinoid/cannabinoid receptor signaling pathway. In this study, we examined the expression of a cannabinoid receptor (CB1) and the lipid accumulation in the hepatic Huh7 cell line, expressing HCV genes. We utilized Huh7/Rep-Feo-1b cells stably expressing HCV non-structural proteins (NS) 3, NS4, NS5A, and NS5B, as well as Tet-On Core-2 cells, in which the HCV core protein expression is inducible. Significantly higher levels of stored triglycerides were found in Huh7/Rep-Feo-1b cells compared to Huh7 cells. Also, triglyceride accumulation and CB1 receptor expression were down-regulated in Huh7/Rep-Feo-1b cells after HCV reduction by IFNα. Moreover, lipid accumulation appeared to increase after CB1 agonist treatment, while it decreased after CB1 antagonist treatment, although significant differences were not found compared to untreated cells. In Tet-On Core-2 cells, induction of HCV core protein expression did not affect CB1 expression or triglyceride accumulation. The results of this study in cultured cells suggest that HCV infection may activate the cannabinoid system and precede steatosis, but the core protein by itself may not have any effect on the cannabinoid system.     

中枢神经大麻素受体分布的细胞类型研究

目的研究不同脑区大麻素CB1、CB2受体分布的细胞类型,探索大麻素受体在中枢神经系统中的可能作用。方法运用免疫荧光单标、双标的方法研究2种大麻素受体在成年大鼠不同脑区、不同类型细胞中的表达分布情况。结果成年大鼠不同脑区的神经元中有CB1、CB2受体的表达,海马、大脑皮层、脑干以及小脑的浦肯野细胞层的神经元有较高表达,且2种大麻素受体的表达差异较小,基底神经节区有中等表达,而胼胝体区未发现有神经元表达。少突胶质细胞及星型胶质细胞中发现CB1、CB2受体的表达。结论大麻素受体CB1、CB2在中枢神经系统多种类型的细胞中均有分布,可能通过多种途径参与神经系统功能调节。     

Isolation and preliminary in vitro characterization of the porcine pulmonary intravascular macrophage

Porcine intravascular macrophages were isolated by perfusion of the pulmonary vasculature with 0.1% collagenase solution. The isolated cells formed intercellular adhesion plaques with endothelial cells when incubated with porcine pulmonary artery, aorta, and corneal cups. Intercellular adhesion plaques were focal junctionlike membrane specializations consisting of paired submembranous amorphous densities subjacent to 15-20 nm gaps between parallel apposing cell membranes. The intermembranous space was filled with moderately electron dense, finely granular material. Adhesion plaques formed in 4-8 hours and resembled the adhesion plaques formed between pulmonary intravascular macrophages and endothelium in vivo. Alveolar macrophages and peripheral blood monocytes did not form intercellular adhesion plaques with endothelial cells. Intravascular macrophages had histologic and ultrastructural features of macrophages, were alpha naphthyl butyrate esterase positive, adhered to plastic coverslips after 1 hour of incubation, and were smaller than alveolar macrophages and endothelial cells. The formation of intercellular adhesion plaques in vivo and in vitro by cells with morphologic and histochemical features of macrophages distinguishes intravascular macrophages from monocytes and alveolar macrophages.     

Redistribution of CB1 cannabinoid receptors during evolution of cholinergic basal forebrain territories and their cortical projection areas: a comparison between the gray mouse lemur (Microcebus murinus, primates) and rat

Endocannabinoid signaling, mediated by presynaptic CB1 cannabinoid receptors on neurons, is fundamental for the maintenance of synaptic plasticity by modulating neurotransmitter release from axon terminals. In the rodent basal forebrain, CB1 cannabinoid receptor-like immunoreactivity is only harbored by a subpopulation of cholinergic projection neurons. However, endocannabinoid control of cholinergic output from the substantia innominata, coincident target innervation of cholinergic and CB1 cannabinoid receptor-containing afferents, and cholinergic regulation of endocannabinoid synthesis in the hippocampus suggest a significant cholinergic-endocannabinergic interplay. Given the functional importance of the cholinergic modulation of endocannabinoid signaling, here we studied CB1 cannabinoid receptor distribution in cholinergic basal forebrain territories and their cortical projection areas in a prosimian primate, the gray mouse lemur. Perisomatic CB1 cannabinoid receptor immunoreactivity was unequivocally present in non-cholinergic neurons of the olfactory tubercule, and in cholecystokinin-containing interneurons in layers 2/3 of the neocortex. Significantly, CB1 cannabinoid receptor-like immunoreactivity was localized to cholinergic perikarya in the magnocellular basal nucleus. However, cortical cholinergic terminals lacked detectable CB1 cannabinoid receptor levels. A dichotomy of CB1 cannabinoid receptor distribution in frontal (suprasylvian) and parietotemporal (subsylvian) cortices was apparent. In the frontal cortex, CB1 cannabinoid receptor-containing axons concentrated in layers 2/3 and layer 6, while layer 4 and layer 5 were essentially devoid of CB1 cannabinoid receptor immunoreactivity. In contrast, CB1 cannabinoid receptors decorated axons in all layers of the parietotemporal cortex with peak densities in layer 2 and layer 4. In the hippocampus, CB1 cannabinoid receptor-containing terminals concentrated around pyramidal cell somata and proximal dendrites in the CA1-CA3 areas, and granule cell dendrites in the molecular layer of the dentate gyrus. CB1 cannabinoid receptors frequently localized to inhibitory GABAergic terminals while leaving glutamatergic boutons unlabeled. Aging did not affect either the density or layer-specific distribution of CB1 cannabinoid receptor-immunoreactive processes. We concluded that organizing principles of CB1 cannabinoid receptor-containing neurons and their terminal fields within the basal forebrain are evolutionarily conserved between rodents and prosimian primates. In contrast, the areal expansion and cytoarchitectonic differentiation of neocortical subfields in primates is associated with differential cortical patterning of CB1 cannabinoid receptor-containing subcortical and intracortical afferents.     

Expression of major histocompatibility complex class I molecules on the different cell types in multiple sclerosis lesions

Multiple sclerosis is considered to be an immune-mediated disease of the central nervous system, characterized by chronic inflammation, primary demyelination and axonal damage. The mechanisms of demyelination and axonal injury are heterogeneous and complex. One possible mechanism is direct damage of oligodendrocytes and neurons by Class I MHC restricted cytotoxic T-cells. In this study we analyzed the expression of functional MHC class I molecule complex, consisting of alpha-chain and beta2-microglobulin, in a large sample of human autopsy material, containing 10 cases of acute MS, 10 cases of chronic active MS, 10 cases of chronic inactive MS and 21 controls. To examine the expression of MHC class I and II molecules on the different cell-types in brain, we used quantitative immunohistochemical techniques, double staining and confocal laser microscopy scans on paraffin embedded sections. We found constitutive expression of MHC class I molecule on microglia and endothelial cells. A hierarchical up-regulation of MHC class I was present on astrocytes, oligodendrocytes, neurons and axons, depending upon the severity of the disease and the activity of the lesions. MHC class II molecules were expressed on microglia and macrophages, but not on astrocytes. These data indicate that in MS lesions all cells of the central nervous system are potential targets for Class I MHC restricted cytotoxic T-cells.     

Distinct changes in all major components of the neurovascular unit across different neuropathological stages of Alzheimer's disease

In the brain capillaries, endothelial cells, pericytes, astrocytes and microglia form a structural and functional complex called neurovascular unit (NVU) which is critically involved in maintaining neuronal homeostasis. In the present study, we applied a comprehensive immunohistochemical approach to investigate the structural alterations in the NVU across different Alzheimer''s disease (AD) neuropathological stages. Post‐mortem human cortical and hippocampal samples derived from AD patients and non‐demented elderly control individuals were immunostained using a panel of markers representing specific components of the NVU including Collagen IV (basement membrane), PDGFR‐β (pericytes), GFAP (astrocytes), Iba1 (microglia), MRC1 (perivascular macrophages) and lectin as an endothelial cell label. Astrocytes (GFAP) and microglia (Iba1) were quantified both in the whole visual‐field and specifically within the NVU, and the sample set was additionally analyzed using anti‐tau (AT8) and three different anti‐Aβ (clones G2‐10, G2‐11, 4G8) antibodies. Analyses of lectin labeled sections showed an altered vascular distribution in AD patients as revealed by a reduced nearest distance between capillaries. Within the NVU, a Braak‐stage dependent reduction in pericyte coverage was identified as the earliest structural alteration during AD progression. In comparison to non‐demented elderly controls, AD patients showed a significantly higher astrocyte coverage within the NVU, which was paralleled by a reduced microglial coverage around capillaries. Assessment of perivascular macrophages moreover demonstrated a relocation of these cells from leptomeningeal arteries to penetrating parenchymal vessels in AD patients. Collectively, the results of our study represent a comprehensive first in‐depth analysis of AD‐related structural changes in the NVU and suggest distinct alterations in all components of the NVU during AD progression.     

Atheromatous plaque macrophages produce plasminogen activator inhibitor type-1 and stimulate its production by endothelial cells and vascular smooth muscle cells.

The capacity of macrophages to influence directly and indirectly fibrinolytic processes in atherosclerosis was studied using macrophages isolated from atherosclerotic plaques of patients undergoing surgical repair of distal aortic and femoral arteries. These cells were characterized by their morphology, adherence, esterase positivity, and expression of CD14 antigen. Production of plasminogen activator inhibitor type-1 (PAI-1) by plaque macrophages (6.7 +/- 2.7 ng/10(5) cells/24 hours [mean +/- SEM]) was significantly greater than PAI-1 production by blood monocytes isolated simultaneously from the same patients (1.8 +/- 1.5 ng/10(5) cells/24 hours). Production of tissue type plasminogen activator and urokinase type was not augmented compared to blood monocytes. Conditioned medium from cultured plaque macrophages significantly increased production of PAI-1 by endothelial cells (85 +/- 11% above basal) and vascular smooth muscle cells (25 +/- 10%) in vitro. This response was significantly greater than the response to monocyte-conditioned medium (endothelial cells 38 +/- 11%, vascular smooth muscle cells 2.5 +/- 2.0%). Stimulation of endothelial cell PAI-1 production by macrophage-conditioned medium was partially inhibitable by a monoclonal antibody to transforming growth factor-beta. Tissue type plasminogen activator production by endothelial cells and vascular smooth muscle cells was not affected by plaque macrophage- or monocyte-conditioned medium. Urokinase type plasminogen activator production by endothelial cells and vascular smooth muscle cells was undetectable in control medium and was augmented to similar levels in response to plaque macrophage- and monocyte-conditioned media. These results demonstrate upregulation of PAI-1 production by macrophages in atheromatous plaques and the capacity of soluble products from plaque macrophages to upregulate PAI-1 production by endothelial cells and vascular smooth muscle cells in vitro. These data suggest that macrophages in atherosclerotic plaques may inhibit thrombolysis both directly and indirectly by effects of their soluble products on endothelial cells and vascular smooth muscle cells.     

Identification of differential protein expression associated with development of unstable human carotid plaques

Rupture-prone unstable arterial plaques develop concomitantly with the appearance of intraplaque hemorrhage and tissue ulceration, in association with deregulation of smooth muscle cell mitogenesis and leakage of newly formed blood vessels. Using microarray technology, we have identified novel protein deregulation associated with unstable carotid plaque regions. Overexpression of proapoptotic proteins caspase-9 and TRAF4 was seen in endothelial cells and smooth muscle cells from unstable hemorrhagic and ulcerated plaque regions. Topoisomerase-II-alpha (TOPO-II-alpha), which is associated with DNA repair mechanisms, was also overexpressed by these cells. Cell signaling molecules c-src, G-protein-coupled receptor kinase-interacting protein (GIT1), and c-jun N-terminal kinase (JNK) were up-regulated in endothelial cells from the same areas, whereas an increase in expression of junctional adhesion molecule-1 (JAM-1) in blood vessels and infiltrating macrophages from inflammatory regions might form part of a leukocyte rolling response, increasing the plaque volume. Grb2-like adaptor protein (Gads), responsible for differentiation of monocytes into macrophages, was expressed by macrophages from unstable plaques, suggesting a potential mechanism through which increased scavenging could occur in rupture-prone areas. We conclude that modulation of novel cell signaling intermediates, such as those described here, could be useful in the therapy of angiogenesis and apoptosis, designed to reduce unstable plaque formation.     

The endocannabinoid system in the physiology and pathophysiology of the gastrointestinal tract

Numerous investigations have recently demonstrated the important roles of the endocannabinoid system in the gastrointestinal (GI) tract under physiological and pathophysiological conditions. In the GI tract, cannabinoid type 1 (CB1) receptors are present in neurons of the enteric nervous system and in sensory terminals of vagal and spinal neurons, while cannabinoid type 2 receptors are located in immune cells. Activation of CB1 receptors was shown to modulate several functions in the GI tract, including gastric secretion, gastric emptying and intestinal motility. Under pathophysiological conditions induced experimentally in rodents, the endocannabinoid system conveys protection to the GI tract (e.g. from inflammation and abnormally high gastric and enteric secretions). Such protective activities are largely in agreement with anecdotal reports from folk medicine on the use of Cannabis sativa extracts by subjects suffering from various GI disorders. Thus, the endocannabinoid system may serve as a potentially promising therapeutic target against different GI disorders, including frankly inflammatory bowel diseases (e.g. Crohns disease), functional bowel diseases (e.g. irritable bowel syndrome) and secretion- and motility-related disorders. As stimulation of this modulatory system by CB1 receptor agonists can lead to unwanted psychotropic side effects, an alternative and promising avenue for therapeutic applications resides in the treatment with CB1 receptor agonists that are unable to cross the blood–brain barrier, or with compounds that inhibit the degradation of endogenous ligands (endocannabinoids) of CB1 receptors, hence prolonging the activity of the endocannabinoid system.