精神分裂症患者颞上回的大麻素受体密度没有显著性变化

目的近年来研究发现,在精神分裂症患者的内源性大麻素递质系统会出现异常变化,而颞上回在精神分裂症的病理生理机制中和幻听症状密切相关。因此,对照正常人群,我们研究了精神分裂症患者颞上回大麻素CB-1受体的密度变化。方法采用定量放射自显影技术,通过[~3HJSR141716A(CB-1受体选择性拮抗剂)和[~3H]CP-55940(CB-1受体激动剂)检测颞上回CB-1受体密度水平。死后脑组织由澳大利亚新南威尔士州组织资源中心提供。结果先前研究发现,精神分裂症患者与认知功能失常相关的额前叶,前、后扣带回皮质的CB-1受体密度水平有异常改变.与此相反,本研究发现在精神分裂症患者的由[~3H]SR141716A和[~3H]CP-55940检测的颞上回大麻素受体密度水平和对照组比较没有显著变化。结论我们认为颞上回大麻素CB-1受体和精神分裂症患者的发病及幻听症状无关。     

精神分裂症患者颞上回的大麻素受体密度没有显著性变化

目的 近年来研究发现,在精神分裂症患者的内源性大麻素递质系统会出现异常变化,而颞上回在精神分裂症的病理生理机制中和幻听症状密切相关.因此,对照正常人群,我们研究了精神分裂症患者颞上回大麻素CB-1受体的密度变化.方法 采用定量放射自显影技术,通过[3H]SR141716A(CB-1受体选择性拮抗剂)和[3H]CP-55940(CB-1受体激动剂)检测颞上回CB-1受体密度水平.死后脑组织由澳大利亚新南威尔士州组织资源中心提供.结果 先前研究发现,精神分裂症患者与认知功能失常相关的额前叶,前、后扣带回皮质的CB-1受体密度水平有异常改变.与此相反,本研究发现在精神分裂症患者的由[3H]SR141716A和[3H]CP-55940检测的颞上回大麻素受体密度水平和对照组比较没有显著变化.结论 我们认为颞上回大麻素CB-1受体和精神分裂症患者的发病及幻听症状无关.     

Spinal anandamide inhibits nociceptive transmission via cannabinoid receptor activation in vivo

The endocannabinoid anandamide has affinity for cannabinoid and vanilloid receptors, which have opposing effects on nociceptive transmission. Effects of spinal administration of anandamide on innocuous and noxious evoked spinal neuronal responses in non-inflamed and carrageenin-inflamed rats were studied. Anandamide (0.1-50 microg/50 microl) had inconsistent effects in non-inflamed rats. Following carrageenin inflammation, anandamide (50 microg/50 microl) significantly reduced evoked neuronal responses, C-fibre mediated non-potentiated and post-discharge responses of neurones reduced to 65 +/- 5% and 57 +/- 10% of control, respectively. Effects of anandamide were blocked by SR141716A, a selective CB1 receptor antagonist. Spinal SR141716A (0.001-1 ng/50 microl) alone did not influence neuronal responses in inflamed rats. Spinal anandamide inhibited nociceptive transmission via CB1 receptors; following inflammation there is evidence for a loss of spinal endogenous cannabinoid tone.     

Neuroprotective cannabinoid receptor antagonist SR141716A prevents downregulation of excitotoxic NMDA receptors in the ischemic penumbra

Whether cannabinoids act as neuroprotectants or, on the contrary, even worsen neuronal damage after cerebral ischemia is currently under discussion. We have previously shown that treatment with the cannabinoid (CB1) receptor antagonist SR141716A reduces infarct volume by ∼40% after experimental stroke. Since it is suggested that SR141716A may exert neuroprotection besides its cannabinoid receptor-blocking effect, we addressed the question whether SR141716A may act via modulation of postischemic ligand binding to excitatory NMDA and/or α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid (AMPA) receptors. For this purpose, rats (n = 12) were treated with either intravenous saline (control) or CB1 receptor antagonist SR141716A (1 mg/kg) 30 min after permanent middle cerebral artery occlusion. Five hours after ischemia, quantitative receptor autoradiography was performed using [³H]CP 55,940, [³H]MK-801, and [³H]AMPA for labeling of CB1, NMDA, and AMPA receptors, respectively. Ligand binding was analyzed within the infarct core, cortical penumbra, and corresponding areas of the contralateral hemisphere and compared to that of sham-operated rats (n = 5). Both in ischemic controls and SR141716A-treated rats [³H]CP 55,940 ligand binding was not specifically regulated in the cortical penumbra or contralateral cortex. Importantly, reduced infarct volumes in SR141716A-treated rats were associated with maintained [³H]MK-801 binding to excitotoxic NMDA receptors in the penumbra, compared to a decrease in the control group. In summary, our data suggest that SR141716A may possess additional intrinsic neuroprotective properties independent of receptor-coupled pathways or due to action as a partial agonist.     

Cannabinoid CB1 receptor antagonism reduces conditioned reinstatement of ethanol-seeking behavior in rats

The endocannabinoid system is involved in a variety of effects of drugs of misuse, and blockade of the cannabinoid CB1 receptor by selective antagonists elicits marked reductions in opioid and alcohol self-administration. The present study was designed to extend our knowledge of the role of the cannabinoid CB1 receptor in the modulation of alcohol misuse vulnerability in rats. Accordingly, using nonselected Wistar rats and genetically selected Marchigian Sardinian alcohol-preferring (msP) rats, we investigated the effect of the CB1 antagonist SR141716A on operant alcohol self-administration and on reinstatement of alcohol-seeking behavior by environmental conditioning factors. In addition, in situ hybridization studies in both strains were performed to measure cannabinoid CB1 receptor mRNA in different brain areas of these animals. Results showed that intraperitoneal administration of SR141716A (0.03, 1.0 and 3.0 mg/kg) markedly inhibits ethanol self-administration and conditioned reinstatement of ethanol-seeking behavior in both strains of rats. ED50 analysis showed significantly higher sensitivity (P < 0.05) to the effect of SR141716A in msP rats than in heterogeneous Wistar rats. In situ hybridization studies revealed that, compared with Wistar rats, msP animals have consistently greater cannabinoid CB1 receptor mRNA expression in a number of brain areas, including the frontoparietal cortex, caudate-putamen and hippocampus (CA1 and dentate gyrus areas). In conclusion, we provide clear evidence that blockade of CB1 receptors reduces both ethanol self-administration and conditioned reinstatement of alcohol-seeking behavior in rats. In addition, current pharmacological and neuroanatomical data suggest that an altered function of the CB1 receptor system exists between genetically selected alcohol-preferring msP rats and a heterogeneous animal population.     

Neurokinin B, neurotensin, and cannabinoid receptor antagonists and Parkinson disease

The neuropeptides neurokinin B, neurotensin, and anandamide, the endogenous ligands of NK3, NT1, and CB1 receptors respectively, are known to interact with brain dopaminergic transmission. This study evaluated the effects of these three antagonists of the NK3 (SR 142801), neurotensin (SR 48692), and cannabinoid (SR 141716) receptors on the severity of motor symptoms and levodopa-induced dyskinesias after administration of a single dose of levodopa in 24 patients with Parkinson disease. In this exploratory randomized, double-blind, placebo-controlled study, at the dose used, the drugs tested were well tolerated and could not improve parkinsonian motor disability.     

Leptin receptor deficiency is associated with upregulation of cannabinoid 1 receptors in limbic brain regions

Leptin receptor dysfunction results in overeating and obesity. Leptin regulates hypothalamic signaling that underlies the motivation to hyperphagia, but the interaction between leptin and cannabinoid signaling is poorly understood. We evaluated the role of cannabinoid 1 receptors (CB(1)R) in overeating and the effects of food deprivation on CB(1)R in the brain. One-month-old Zucker rats were divided into unrestricted and restricted (fed 70% of unrestricted rats) diet groups and maintained until adulthood (4 months). Levels of relative binding sites of CB(1)R (CB(1)R binding levels) were assessed using [(3)H] SR141716A in vitro autoradiography. These levels were higher (except cerebellum and hypothalamus) at 4 months than at 1 month of age. One month CB(1)R binding levels for most brain regions did not differ between Ob and Lean (Le) rats (except in frontal and cingulate cortices in Le and in the hypothalamus in Ob). Four month Ob rats had higher CB(1)R binding levels than Le in most brain regions and food restriction was associated with higher CB(1)R levels in all brain regions in Ob, but not in Le rats. CB(1)R binding levels increased between adolescence and young adulthood which we believe was influenced by leptin and food availability. The high levels of CB(1)R in Ob rats suggest that leptin's inhibition of food-intake is in part mediated by downregulation of CB(1)R and that leptin interferes with CB(1)R upregulation under food-deprivation conditions. These results are consistent with prior findings showing increased levels of endogenous cannabinoids in the Ob rats corroborating the regulation of cannabinoid signaling by leptin.     

Changes in endocannabinoid levels in a rat model of behavioural sensitization to morphine

The opioid and cannabinoid systems co-operate to regulate physiological processes such as nociception and reward. The endocannabinoid system may be a component of the brain reward circuitry and thus play a role not only in cannabinoid tolerance/dependence, but also in dependence/withdrawal for other misused drugs. We provide evidence of a cannabinoid mechanism in an animal model of morphine drug-seeking behaviour, referred to as behavioural sensitization. The present study was designed to test the effects of the CB1 cannabinoid receptor antagonist SR141716A in two different phases of morphine sensitization (induction and expression) and to measure the brain contents of arachidonoylethanolamide (anandamide, AEA) and 2-arachidonoylglycerol (2-AG), the two main endogenous ligands for cannabinoid receptors in the different phases of morphine sensitization. The cannabinoid antagonist modified the signs of morphine sensitization when administered in the expression phase, whereas co-administration of SR141716A and morphine in the induction phase only slightly affected the behavioural responses, suggesting that CB1 receptor blockade attenuates the behavioural manifestations of morphine sensitization but not its development. AEA and 2-AG were affected differently by morphine during the two phases of behavioural sensitization. The alterations were in opposite directions and specific for the cerebral area analysed (caudate putamen, nucleus accumbens, hippocampus and prefrontal cortex). The results suggest that the endocannabinoid system undergoes profound changes during the different phases of sensitization to morphine in rats, providing a possible neurochemical basis for the previously observed cross-sensitization between opiates and cannabinoids.     

Cannabinoid receptor agonist-stimulated [35S]guanosine triphosphate gammaS binding in the brain of C57BL/6 and DBA/2 mice

The two inbred strains of mice C57BL/6 (alcohol-preferring) and DBA/2 (alcohol-avoiding) mice have been shown to differ significantly in their preference for alcohol (EtOH). We have previously demonstrated the differences in the density and the affinity of cannabinoid (CB1) receptors in the brains of the two inbred C57BL/6 and DBA/2 mouse strains. In the present study, we investigated the CB1 receptor agonist-stimulated guanosine-5'-O-(3-[(35)S]thio)-triphosphate ([(35)S]GTPgammaS) binding in plasma membranes (PM) from C57BL/6 and DBA/2 mice. The results indicate that the net CP55,940-stimulated [(35)S]GTPgammaS binding was increased with increasing concentrations of CB1 receptor agonists and GDP. The net CB1 receptor agonist (WIN55,212-2 or HU-210 or CP55,940)-stimulated [(35)S]GTPgammaS binding was reduced significantly (-10% to -12%, P < 0.05) in PM from DBA/2 mice; no significant differences were observed in basal [(35)S]GTPgammaS binding among these strains. Nonlinear regression analysis of net CP55,940-stimulated [(35)S]GTPgammaS binding showed that the B(max) of cannabinoid agonist-stimulated binding was significantly reduced (-24%) in DBA/2 mice (B(max) = 12.43 +/- 0.64 for C57BL/6 and 9.46 +/- 0.98 pmol/mg protein for DBA/2; P < 0.05) without any significant changes in the G protein affinity. The pharmacological specificity of CP55,940-stimulated [(35)S]GTPgammaS binding was examined with CB1 receptor antagonist SR141716A, and these studies indicated that CP55,940-stimulated [(35)S]GTPgammaS binding was blocked by SR141716A, with a decrease in the IC(50) values in the PM from the DBA/2 mouse strain. These results suggest that a signal transduction pathway(s) downstream from the CB1 receptor system may play an important role in controlling the voluntary EtOH consumption by these strains of mice.     

The cannabinoid CB1 receptor antagonist SR 141716A induces penile erection by increasing extra-cellular glutamic acid in the paraventricular nucleus of male rats

The cannabinoid CB1 receptor antagonist SR 141716A (0.1, 0.5 and 1 microg) induces penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats. The pro-erectile effect of SR 141716A occurs concomitantly with an increase in the concentration of glutamic acid in the paraventricular dialysate obtained by means of intra-cerebral microdialysis. Glutamic acid increase and penile erection did not occur when SR 141716A was given after tetrodotoxin, a voltage-dependent Na(+) channel blocker. Both penile erection and glutamic acid increases were also reduced by the cannabinoid CB1 receptor agonists WIN 55,212-2 or HU 210 given into the paraventricular nucleus before SR 141716A at doses unable to induce penile erection or to modify glutamic acid. In contrast, dizocilpine ((+)MK-801), an antagonist of excitatory amino acid receptors of the N-methyl-d-aspartic acid (NMDA) subtype, given into the paraventricular nucleus reduced penile erection, but was ineffective on the glutamic acid increase induced by the CB1 receptor antagonist. 6-Cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and (+/-)-2-amino-4-phosphono-butanoic acid (AP(4)), antagonists of the excitatory amino acid receptors of the AMPA subtype and of the metabotropic subtype, respectively, were ineffective on both penile erection and glutamic acid increase. SR 141716A responses were also reduced by muscimol, a GABA(A) receptor agonist, but not by baclofen, a GABA(B) receptor agonist, given into the paraventricular nucleus before SR 141716A. The present results show that SR 141716A induces penile erection by activating glutamic acid neurotransmission, which causes in turn the activation of paraventricular oxytocinergic neurons mediating penile erection.     

The role of the CB1 cannabinoid receptor and its endogenous ligands, anandamide and 2-arachidonoylglycerol, in amphetamine-induced behavioural sensitization

Cannabinoid receptors and their endogenous ligands (endocannabinoids) have been implicated in cocaine and amphetamine reward. Their role in psychostimulant-induced behavioural sensitization still has to be determined. The purpose of the present study was, for one, to compare the effects of a pharmacological and genetic manipulation of CB(1) cannabinoid receptors on amphetamine-induced locomotor sensitization in mice, and, secondly, to quantify the concentration of anandamide and 2-arachidonoylglycerol in different forebrain areas of behaviourally sensitized animals. The results can be summarized as follows: CB(1) knockout mice failed to sensitize to the locomotor stimulant effects of amphetamine. On the contrary, administration of the CB(1) receptor antagonist SR141716A (rimonabant; 3mg/kg; i.p.) increased amphetamine sensitization in wild-type animals, indicating that the difference between CB(1) knockouts and SR141716A treated animals could be due to the 'chronic' versus 'acute' loss of CB(1) receptor function, or, alternatively, that SR141716A could exert pharmacological effects beyond its proposed CB(1) antagonistic action. Furthermore, sensitized wild-type mice and animals, which had received a single amphetamine injection on the challenge day, both had increased anandamide concentrations in the dorsal striatum and decreased anandamide levels in the ventral striatum, comprising nucleus accumbens. 2-Arachidonoylglycerol levels were decreased in the ventral striatum of sensitized animals only. Together, these findings suggest that prolonged activation of dopamine receptors could alter endocannabinoid levels and support the proposed involvement of the CB(1) receptor in amphetamine sensitization.     

Activation of peripheral cannabinoid CB1 receptors inhibits mechanically evoked responses of spinal neurons in noninflamed rats and rats with hindpaw inflammation

The presence of cannabinoid1 (CB1) receptors on primary afferent fibres may provide a novel target for cannabinoid analgesics. The present study investigated the ability of peripheral CB1 receptors to modulate innocuous and noxious transmission in noninflamed rats and rats with peripheral carrageenan inflammation. Effects of peripheral injection of arachidonyl-2-choroethylamide (ACEA; 10 and 30 micro g in 50 micro L), a selective CB1 receptor agonist, on mechanically evoked responses of dorsal horn neurons were studied in noninflamed rats and rats with peripheral carrageenan inflammation. Peripheral injection of ACEA (30 micro g in 50 micro L) significantly inhibited innocuous (12 g) mechanically evoked responses of spinal neurons in noninflamed (27 +/- 4% of control; P < 0.01) and inflamed (12 +/- 8% of control; P < 0.05) rats. Similarly, noxious (80 g) mechanically evoked responses of spinal neurons were inhibited by peripheral injection of ACEA (30 micro g in 50 micro L) in noninflamed rats (51 +/- 9% of control; P < 0.01) and rats with peripheral carrageenan inflammation (21 +/- 8% of control; P < 0.01). Inhibitory effects of ACEA were significantly greater in rats with peripheral carrageenan inflammation than in noninflamed rats (P < 0.05). Inhibitory effects of ACEA were significantly blocked by coadministration of the CB1 receptor antagonist SR141716A in both groups of rats. Peripheral injection of SR141716A alone did not alter mechanically evoked responses of spinal neurons in either group of rats. These data demonstrate that activation of peripheral CB1 receptors can inhibit innocuous and noxious somatosensory processing. Furthermore, following peripheral inflammation there is an enhanced inhibitory effect of a peripherally administered CB1 receptor agonist on both innocuous and noxious mechanically evoked responses of spinal neurons.     

The effect of Delta9-tetrahydrocannabinol on sensorimotor gating in socially isolated rats

Rearing rats in isolation produces behavioural and neurochemical alterations similar to those observed in schizophrenia. Cannabinoids have also been implicated in inducing psychotic symptoms. In this study, we investigate the effect of the major psychoactive constituent of cannabis and partial cannabinoid CB(1) receptor agonist Delta(9)-tetrahydrocannabinol (THC) on prepulse inhibition (%PPI) of the acoustic startle reflex and on habituation in socially isolated and grouped rats. Deficits in %PPI are reminiscent of sensorimotor gating deficits observed in psychoses. Male Sprague-Dawley rat pups (21 days old) were housed in either single cages (isolated) or in group cages of six per cage (grouped). Eight weeks later the effect of vehicle, THC and the CB(1) receptor antagonist SR 141716 on %PPI was tested. Vehicle treated isolated rats exhibited significantly reduced PPI compared with grouped rats. Isolated rats treated with THC had significantly lower %PPI than vehicle treated groups. This further decrease of %PPI by THC was reversed by pre-treatment with SR 141716, indicating that this effect was mediated by CB(1) receptors. THC had no significant effect on %PPI in grouped rats. SR 141716 had no significant effect on %PPI in either grouped or isolated rats. Habituation did not significantly alter in any treatment group in any treatment group. These results suggest that THC produces significant decreases in sensorimotor gating in rats with already dysfunctional sensorimotor gating processes, but not in normal rats. The lack of effect of SR 141716 in either grouped or isolated rats suggests that normal endocannabinoid function is not critical in sensorimotor gating processes.     

'One-trial sensitization' to the anxiolytic-like effects of cannabinoid receptor antagonist SR141716A in the mouse elevated plus-maze

Significant variability in the effects of cannabinoid CB1 receptor ligands on emotional reactivity in animals and humans suggests that the endocannabinoid system may selectively modulate certain types of anxiety. In view of substantial evidence for qualitative differences in the nature of anxiety elicited on initial and subsequent exposures to the elevated plus-maze, the present studies contrasted the behavioural effects of the selective CB1 receptor antagonist SR141716A (0.1-10.0 mg/kg) and the reference benzodiazepine chlordiazepoxide (CDP, 15 mg/kg) both in maze-naive mice (trial 1) and in mice that had been given a single undrugged exposure to the maze 24 h prior to testing (trial 2). Results confirmed the anxioselective effect of CDP on trial 1 but a complete absence of such activity on trial 2 (i.e. one trial tolerance). In marked contrast, SR141716A had no behavioural effects in maze-naive mice but, at doses of 1.0-3.0 mg/kg (effect maximal at 1.0 mg/kg), significantly reduced anxiety-like responses in maze-experienced animals. Like the effect of CDP on trial 1, the antianxiety profile of SR141716A on plus-maze trial 2 was observed in the absence of any change in general activity levels. The apparent experientially induced 'sensitization' to the anxiolytic-like effects of SR141716A in the plus-maze contrasts markedly with the widely reported loss of benzodiazepine efficacy in test-experienced animals. Data are discussed in relation to the recently described phenotypes of CB1 receptor knockout mice and, in particular, to mounting evidence for the existence of a novel SR141716A-sensitive neuronal cannabinoid receptor.     

Distinct differences in the cannabinoid receptor binding in the brain of C57BL/6 and DBA/2 mice, selected for their differences in voluntary ethanol consumption

The two inbred strains of mice C57BL/6 and DBA/2 mice have been shown to differ significantly in their preference for alcohol (EtOH). These strains of mice have been employed to study various aspects of pharmacological and behavioral effects of EtOH. We have previously demonstrated that chronic EtOH exposure down-regulated cannabinoid receptors (CB1) in mouse synaptic plasma membranes and enhanced the synthesis of endogenous cannabimimetic compound anandamide (AnNH) in human neuroblastoma cells. The purpose of the present study was to investigate whether there were differences in the density and the affinity of CB1 receptors in the brains of the two inbred C57BL/6 (alcohol-preferring) and DBA/2 (alcohol avoiding) mice. The results indicate the presence of specific CB1 receptors in the brain membranes of both the strains. It was also found that the CB1 receptor densities (B(max)) were 25% lower in C57BL/6 (0.66 +/- 0.15 pmol/mg protein) compared with that of DBA/2 (0.88 +/- 0.08 pmol/mg protein) mice. Significant differences in the affinity were also observed between the two lines (K(d), 0.68 +/- 0.15 nM for C57BL/6 and 2.21 +/- 0.56 nM for DBA/2). The competition studies with SR141716A, a CB1 receptor antagonist, and 2-arachidonylglycerol (2-AG) and anandamide (AnNH), known CB1 receptor agonists, all showed a substantial decrease in [(3)H]CP-55,940 binding in both strains of mice with a higher K(i) values in the DBA/2 mice. These results suggest that CB1 receptor signal transduction may play an important role in controlling the voluntary EtOH consumption by these strains of mice.     

In vivo modulation of LPS-induced alterations in brain and peripheral cytokines and HPA axis activity by cannabinoids

This study investigated cannabinoid receptor-mediated regulation of brain and peripheral cytokines in vivo. The cannabinoid receptor agonist, HU210 attenuated lipopolysaccharide (LPS)-induced increases in IL-1beta and TNFalpha in rat brain and IL-1beta, TNFalpha, IL-6 and IFNgamma in plasma. The CB(1) receptor antagonist, SR141716A, attenuated the immunosupressive effects of HU210 on IL-1beta, but not TNFalpha. SR141716A or the CB(2) receptor antagonist, SR144528, alone attenuated LPS-induced cytokine increases. LPS and/or cannabinoids also reduced circulating lymphocyte numbers and increased corticosterone levels. These data provide evidence for modulation of pro-inflammatory cytokines in vivo by cannabinoid receptors and inform the development of cannabinoids for neuroinflammatory disorders.     

The effects of genetic and pharmacological blockade of the CB1 cannabinoid receptor on anxiety

The aim of this study was to compare the effects of the genetic and pharmacological disruption of CB1 cannabinoid receptors on the elevated plus-maze test of anxiety. In the first experiment, the behaviour of CB1-knockout mice and wild-type mice was compared. In the second experiment, the cannabinoid antagonist SR141716A (0, 1, and 3 mg/kg) was administered to both CB1-knockout and wild type mice. Untreated CB1-knockout mice showed a reduced exploration of the open arms of the plus-maze apparatus, thus appearing more anxious than the wild-type animals, however no changes in locomotion were noticed. The vehicle-injected CB1-knockout mice from the second experiment also showed increased anxiety as compared with wild types. Surprisingly, the cannabinoid antagonist SR141716A reduced anxiety in both wild type and CB1 knockout mice. Locomotor behaviour was only marginally affected. Recent evidence suggests the existence of a novel cannabinoid receptor in the brain. It has also been shown that SR141716A binds to both the CB1 and the putative novel receptor. The data presented here supports these findings, as the cannabinoid receptor antagonist affected anxiety in both wild type and CB1-knockout mice. Tentatively, it may be suggested that the discrepancy between the effects of the genetic and pharmacological blockade of the CB1 receptor suggests that the novel receptor plays a role in anxiety.     

Involvement of brain-derived neurotrophic factor in cannabinoid receptor-dependent protection against excitotoxicity

Cannabinoid type 1 (CB1) receptors play a central role in the protection against excitotoxicity induced by treatment of mice with kainic acid (KA). As inactivation of CB1 receptor function in mice blocks KA-induced increase of brain-derived neurotrophic factor (BDNF) mRNA levels in hippocampus, the notion was put forward that BDNF might be a mediator, at least in part, of CB1 receptor-dependent neuroprotection [Marsicano et al. (2003) Science, 302, 84-88]. To assess this signalling cascade in more detail, organotypic hippocampal slice cultures were used, as this in vitro system conserves morphological and functional properties of the hippocampus. Here, we show that both genetic ablation of CB1 receptors and pharmacological blockade with the specific CB1 receptor antagonist SR141716A increased the susceptibility of the in vitro cultures to KA-induced excitotoxicity, leading to extensive neuronal death. Next, we found that the application of SR141716A to hippocampal cultures from wild-type mice abolished the KA-induced increase in BDNF protein levels. Therefore, we tried to rescue these organotypic cultures from neuronal death by exogenously applied BDNF. Indeed, BDNF was sufficient to prevent KA-induced neuronal death after blockade of CB1 receptor signalling. In conclusion, our results strongly suggest that BDNF is a key mediator in CB1 receptor-dependent protection against excitotoxicity, and further underline the physiological importance of the endogenous cannabinoid system in neuroprotection.     

Differential stimulatory effects of cannabinoids on VIP release and NO synthase activity in synaptosomal fractions from rat ileum

Cannabinoid-1 (CB1) and CB2 receptors are present on neurons of the enteric nervous system. Our aim was to study whether cannabinoid receptor activation is involved in the regulation of VIP release and NO synthesis in isolated fractions of nerve terminals from rat ileum. VIP was measured by RIA and NO synthesis was analyzed using a L-[3H]arginine assay. Anandamide stimulated VIP release (basal: 245.9+/-12.4pg/mg, 10(-6)M: 307.6+/-11.7pg/mg, [n=6, P<0.05], 10(-7)M: 367.0+/-26.1pg/mg, [n=6, P<0.01]). The cannabinoid receptor agonist WIN 55,212-2 had similar effects (basal: 250.5+/-37.4pg/mg, 10(-6)M: 320.9+/-34.7pg/mg; [n=4, P<0.05]). The stimulatory effect of anandamide was blocked by the selective CB2 receptor antagonist, SR144528 (10(-7)M) (anandamide 10(-6)M: 307.6+/-11.7pg/mg; +SR144528: 249.0+/-26.3pg/mg, [n=6, P<0.05]), whereas the selective CB1 receptor antagonist SR141716 A had no effect. NO synthesis was stimulated by anandamide ([fmol/mg/min] basal: 0.08+/-0.01, 10(-6)M: 0.16+/-0.03; 10(-7)M: 0.13+/-0.02, n=4, P<0.05) and WIN 55,212-2 ([fmol/mg/min] basal: 0.05+/-0.01, 10(-6)M: 0.1+/-0.02, n=4, P<0.05). The anandamide reuptake inhibitor, AM 404 increased basal NOS activity ([fmol/mg/min] control: 0.1+/-0.04, 10(-6)M: 0.28+/-0.08, n=7, P<0.05). The stimulatory effect of anandamide on NO synthase was not antagonized by antagonists at the CB1, CB2 or TRPV1 receptor, respectively. In conclusion, in enteric nerves anandamide stimulates VIP release by activation of a CB2 receptor specific pathway, while the stimulation of NO production suggests the existence of an additional type of cannabinoid receptor in the enteric nervous system.     

Blockade of effects of smoked marijuana by the CB1-selective cannabinoid receptor antagonist SR141716

BACKGROUND: SR141716, a recently developed CB1 cannabinoid receptor antagonist, blocks acute effects of Delta-9-tetrahydrocannabinol (THC) and other CB1 cannabinoid agonists in vitro and in animals. These findings suggest that CB1 receptors mediate many of the effects of marijuana, but this has not been evaluated in humans. METHODS: Sixty-three healthy men with a history of marijuana use were randomly assigned to receive oral SR141716 or a placebo in an escalating dose (1, 3, 10, 30, and 90 mg) design. Each subject smoked an active (2.64% THC) or placebo marijuana cigarette 2 hours later. Psychological effects associated with marijuana intoxication and heart rate were measured before and after antagonist and marijuana administration. RESULTS: Single oral doses of SR141716 produced a significant dose-dependent blockade of marijuana-induced subjective intoxication and tachycardia. The 90-mg dose produced 38% to 43% reductions in visual analog scale ratings of "How high do you feel now?" "How stoned on marijuana are you now?" and "How strong is the drug effect you feel now?" and produced a 59% reduction in heart rate. SR141716 alone produced no significant physiological or psychological effects and did not affect peak THC plasma concentration or the area under the time x concentration curve. SR141716 was well tolerated by all subjects. CONCLUSIONS: SR141716 blocked acute psychological and physiological effects of smoked marijuana without altering THC pharmacokinetics. These findings confirm, for the first time in humans, the central role of CB1 receptors in mediating the effects of marijuana.