蛋白激酶C参与内源性大麻素1型受体对心肌L型钙电流的抑制作用

目的研究激活心肌内源性大麻素1型(CB1)受体是否通过改变蛋白激酶C(PKC)活性从而抑制L型钙电流,探讨激活CB1受体导致PKC活性变化的信号途径。方法利用酶解法制备大鼠心室肌细胞,分别单独应用CB1受体特异性激动剂2-氯乙胺花生四烯酸(ACEA)100 nmol·L-1、CB1受体阻断剂AM251 100 nmol·L-1或PKC非特异性激动剂十四烷酸乙酸大戟二萜醇酯(PMA)500 nmol·L-1孵育细胞10 min;此外提前应用AM251或PMA孵育细胞5 min后,再用ACEA孵育细胞10 min。应用全细胞膜片钳技术记录单个心肌细胞的L型钙电流;应用Pep Tag非放射性蛋白激酶C检测系统检测细胞PKC活性;ELISA试剂盒测定细胞中二酰甘油(DAG)的含量;Western蛋白印迹法测定磷脂酶Cβ(PLCβ)和磷酸化磷脂酶Cβ(p-PLCβ)表达。结果给予ACEA激动大鼠心肌细胞的CB1受体,可显著抑制L型钙电流,最大峰值电流密度由11.4±0.8降至(6.4±1.5)p A·p F-1;预先给予AM251或PMA可以完全阻断此抑制效应。检测心肌细胞PKC活性发现,与正常对照组(1.59±0.50)μmol·min-1·L-1相比,ACEA组心肌细胞PKC活性为(0.69±0.48)μmol·min-1·L-1,明显降低;同样预先给予AM251或PMA完全阻断ACEA对PKC活性的抑制效应。而给予ACEA没有影响心肌细胞DAG含量和PLCβ的磷酸化。结论激活心肌细胞CB1受体后抑制细胞PKC的活性,从而抑制L型钙电流,此过程没有PLCβ-DAG途径参与。     

N-花生四烯酰乙醇胺及其类似物的神经保护作用

N-花生四烯酰乙醇胺（anandamide,AEA）属于内源性大麻素类长链脂肪酸衍生物,可通过大麻素受体（CB1/CB2）和（或）非CB1/CB2受体途径发挥神经保护作用。AEA类似物包括脂氨基酸类、脂肪酰乙醇胺类和甲基氟膦酸酯类化合物等。AEA类似物在生物活性及化学结构上与AEA相似,但作用靶点及作用机制并不完全相同,非CB1/CB2受体途径介导的神经保护活性及对脂肪酸酰胺水解酶活性的调节作用为该类化合物的重要特征。由于AEA作用于多靶点所致的许多副作用,给其临床试验和应用带来一定困难,而AEA类似物可能既具备AEA的神经保护活性又避免其毒副作用,因此研究AEA类似物的神经保护作用具有重要的理论意义和应用价值。本文主要对AEA及其类似物的神经保护活性和其作用机制进行综述。     

花生四烯乙醇胺对大鼠心功能与心肌一氧化氮水平及一氧化氮合酶活性的影响

目的 观察大麻素类物质花生四烯乙醇胺（anandamide，Ana）对大鼠体外心脏左心室心肌中一氧化氮(NO)含量和一氧化氮合酶(NOS)活性的影响。方法 采用Langendorff方法观察Ana对大鼠体外心脏心率（HR）、冠脉流量（CF）、冠脉灌注压(CPP)、左室压最大上升速率(＋dp/dtmax)、左室压最大下降速率( dp/dtmax)、左室收缩峰压(LVSP)、左室舒张末压(LVEDP)及左室发展压(LVDP)的影响；NO含量和NOS活性采用联苯胺荧光分光光度法测定。结果 Ana可使体外心脏心率、CPP、＋dp/dtmax、 dp/dtmax、LVSP、LVDP降低，使LVEDP升高，CF增加。选择性大麻素CB1受体拮抗药AM251(1 μmol·L 1)可阻断 Ana的部分心脏效应；另一选择性大麻素CB2受体拮抗药AM630(1 μmol·L 1)对Ana的心脏效应无显著影响。NOS抑制药L N 硝基精氨酸甲酯（L NAME）(100 μmol·L 1)对Ana的心脏效应也无显著影响。Ana能增强原生型NOS(cNOS)活性，抑制诱生型NOS(iNOS)活性，促进心肌NO的释放。结论 Ana使离体大鼠心肌收缩力降低，心率减慢，表现出负性肌力和负性频率作用；Ana可舒张冠脉，增加冠脉流量；大麻素CB2受体可能不参与Ana的这些心脏效应，内源性NO也可能不参与调节Ana的心脏效应；可能存在其他新的作用位点调节Ana的心脏效应。Ana调节心肌NOS同工酶活性，增加cNOS活性，降低iNOS活性，促进NO的释放，可能发挥心肌保护作用，在心肌缺血和高血压治疗中有潜在应用前景。     

大麻素及大麻受体与系统性红斑狼疮疾病治疗的相关研究进展

研究大麻受体在免疫细胞上的表达情况以及可能对系统性红斑狼疮发病产生的影响,进而研究对自身免疫病发生与发展的调节机制。系统性红斑狼疮（SLE）是一种较为常见的由于免疫系统异常、反应过激造成的全身性自身免疫病。最近已有研究表明,大麻素受体在免疫细胞表面有表达,且大麻素通过与免疫细胞表面的大麻素受体（CB1和CB2）结合对免疫系统可能有一定的抑制效果,进而发挥免疫调节的作用影响自身免疫病的进程。     

内源性大麻素CB2受体拮抗剂AM630对电针镇痛作用的影响

目的：研究内源性大麻素2型受体（CB2受体）拮抗剂AM630对电针镇痛作用的影响。方法：本课题组采用健康成年雄性SD大鼠共50只，随机分为五组：空白对照组（n=10）；炎症组（n=10）；电针治疗组（n=10）；电针＋CB2拮抗剂AM630组（n=10）：电针＋溶媒对照组（n=10）。除空白对照组外其它各组大鼠于左后肢外踝关节皮下注射完全弗式佐剂50μl，制备单发局限性佐剂关节炎模型，     

CB1拮抗剂利莫那班可能影响胚胎发育

已有研究表明，作用于大麻素1型受体（CB1）的药物，如Sanofi-Aventis公司开发的CB1拮抗剂利莫那班（rimonahant，Acomplia），会损害孕妇的胚胎发育。动物模型实验显示，正常的胚胎发育、输卵管运输、植入和妊娠均需要内大麻素anandamide达到一定水平。     

大麻素受体及其Ⅰ型抑制剂的研究进展

目前已经确认的大麻素(cannabinoid,CB)受体有两种亚型:CB1和CB2,它们的分布与生理功能各不相同,其选择性抑制剂的研究也是近年来的一个热点。研究表明,CB1受体抑制剂具有良好的抗肥胖活性。本文综述了CB受体及其Ⅰ型抑制剂的研究进展。     

内源性大麻素系统与老年性痴呆

老年性痴呆即阿尔茨海默病（Alzheimer’Sdisease,AD）是一种慢性进行性的神经退行性病变,其特征性病理改变为β-淀粉样蛋白（β-amy-loidpeptide,Aβ）沉积形成的细胞外老年斑和tau蛋白过度磷酸化形成的神经细胞内神经原纤维缠结,以及神经元丢失伴随胶质细胞增生等。最近的研究发现内源性大麻素系统对AD的病程有预防治疗作用,主要基于其对神经的保护作用和抗炎功效。本文综述了内源性大麻素对AD的保护作用的几个方面,旨在为AD的治疗开辟新的策略和思路。     

Ⅰ型大麻素受体调控焦亡通路介导抗精神病药心肌毒性的机制

目的研究常见抗精神病药诱导心肌毒性机制并提出有效的防治靶点。方法选取与临床维持治疗剂量等效的抗精神病药(氯氮平、奥氮平、喹硫平)分别ip给予小鼠7,14和21 d。经心脏超声检测心脏功能,组织形态学比较小鼠心脏病理改变。二代测序及蛋白质组学筛选信号通路,并通过基因敲除小鼠、稳转心肌细胞系等研究具体机制。结果奥氮平2.5 mg·kg~(-1)处理小鼠后,心肌炎症和纤维化重构呈时间依赖性改变。作用21 d后,奥氮平可引起18.3%小鼠猝死,并显著升高心脏内炎症因子及促纤维因子的表达及沉积。NLRP3炎性小体介导的细胞焦亡通路显著富集。敲除焦亡通路经典分子Gsdmd后,心脏功能显著改善。组学数据显示内源性大麻素系统是心肌细胞焦亡的重要因素。Ⅰ型大麻素受体(CB1R)的拮抗剂显著地抑制了心肌细胞焦亡的多个分子进程。在稳定敲除CB1R的心肌细胞中,奥氮平几乎不引起细胞焦亡。腹腔注射CB1R选择性拮抗剂(AM251,AM281或Rimonabant)可显著改善奥氮平慢性心肌毒性,提高小鼠生存。结论焦亡是抗精神病药慢性心肌毒性的新的病理特征;CB1R的拮抗剂可作为细胞焦亡的广谱性抑制剂,可用于抗精神病药慢性心肌毒性的防治。     

大麻素受体2激动剂AM1241对TGF-β1诱导的HSC-T6增殖、活化及凋亡的影响

目的 探究大麻素受体2激动剂AM1241对转化生长因子（TGF）-β1诱导的大鼠肝星状细胞（HSC-T6）增 殖、活化与凋亡的影响及其作用机制。方法 体外培养HSC-T6,采用CCK-8法检测AM1241对空白对照组（空白培 养基）、阴性对照组（未加药品）、TGF-β1 组（5 μg/L TGF-β1）及 20、40、80、160 μmol/L AM1241 组（5 μg/L TGF-β1+ 20、40、80、160 μmol/L AM1241）HSC-T6增殖的影响,计算半数抑制浓度（IC50）。采用流式细胞术检测阴性对照组、 TGF-β1组、30 μmol/L AM1241组、60 μmol/L AM1241组HSC-T6凋亡情况;采用Western blot检测阴性对照组、TGF- β1 组、27 μmol/L AM1241 组 α-平滑肌肌动蛋白（α-SMA）、碱性成纤维细胞生长因子（bFGF）、凋亡相关蛋白 Bax、 cleaved caspase-3、JNK及磷酸化c-Jun氨基末端激酶（p-JNK）蛋白表达水平。结果 与TGF-β1组比较,AM1241可 抑制HSC-T6增殖能力,且呈剂量依赖性（P＜0.05）。AM1241的IC50为27 μmol/L。30、60 μmol/L AM1241组HSC-T6 凋亡率较TGF-β1组明显上升,且60 μmol/L AM1241组高于30 μmol/L AM1241组（P＜0.05）。27 μmol/L AM1241组 α-SMA 和 bFGF 蛋白表达水平较 TGF-β1 组降低,Bax、cleaved caspase-3、p-JNK 蛋白表达水平较 TGF-β1 组升高 （P＜0.05）。结论 大麻素受体2激动剂AM1241能抑制TGF-β1诱导的HSC-T6的增殖与活化,并促进其凋亡,其作 用机制可能与JNK通路有关。     

Cannabinoid CB1 receptors mediate the effects of dipyrone

Dipyrone is a non‐steroidal anti‐inflammatory drug used primarily as an analgesic and antipyretic. Some hypothesize that dipyrone activity can modulate other pathways, including endocannabinoid signalling. Thus, the aim of the present study was to evaluate the possible role of endocannabinoids in mediating dipyrone activity. This study is based on the tetrad effects of cannabinoids, namely an antinociceptive and cataleptic state, hypolocomotion and hypothermia. Dipyrone (500 mg/kg, i.p.) treatment decreased locomotor activity, increased the latency to a thermal analgesic response and induced a cataleptic and hypothermic state. These reactions are similar to the tetrad effects caused by the cannabinoid agonist WIN 55,212‐2 (3 mg/kg, i.p.). The cannabinoid CB₁ receptor antagonist AM251 (10 mg/kg, i.p.) reversed the effects of dipyrone on locomotor activity, the cataleptic response and thermal analgesia. Both AM251 (10 mg/kg, i.p.) and the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine (10 mg/kg, i.p.) accentuated the reduction in body temperature caused by dipyrone. However, the CB₂ receptor antagonist AM630 did not alter the hypothermic response to dipyrone. These results indicate involvement of the endocannabinoid system, especially CB₁ receptors, in the analgesic and cataleptic effects of dipyrone, as well as hypolocomotion. However, cannabinoid receptors and TRPV1 were not involved in the hypothermic effects of dipyrone. We hypothesize that the mechanism of action of dipyrone may involve inhibition of cyclo‐oxygenase and fatty acid amide hydrolase, which together provide additional arachidonic acid as substrate for endocannabinoid synthesis or other related molecules. This increase in endocannabinoid availability enhances CB₁ receptor stimulation, contributing to the observed effects.     

内源性大麻素样物质的可能作用机制

内源性大麻素样物质是大麻素受体的内源性配体 ,在脑内有其特定的合成、转运、代谢途径 ,在生理状态下可调节某些神经递质如谷氨酸、GABA等的释放。因此对其作用机制的阐明不仅有利于进一步探讨大麻成瘾的机制 ,还有助于新药的研发     

Latest advances in the discovery of fatty acid amide hydrolase inhibitors

Introduction: Fatty acid amide hydrolase (FAAH) is the major catabolic enzyme of the endocannabinoid N-arachidonoylethanolamine (anandamide) that, with different degrees of efficiency, also hydrolyzes other endogenous fatty acid ethanolamides. FAAH is increasingly being considered a relevant therapeutic target, especially in models of inflammatory pain. The opportunity to selectively increase the endocannabinoid tone only in those tissues where such an enhancement can be beneficial might result in a therapeutic benefit with more limited side effects, compared to the use of direct agonists of anandamide-binding receptors. Thus the research for selective FAAH inhibitors has become a hot topic in current drug discovery.

Areas covered: This review highlights the advances in the development of different compounds belonging to different chemical families that have been proposed as FAAH inhibitors. Several classes of inhibitors have been reported so far, and they may be classified into two major classes: reversible and irreversible compounds. These inhibitors are reviewed herein with an emphasis on their potency and selectivity.

Expert opinion: In recent years, tremendous efforts have been made to develop the FAAH inhibitors, and consequently many novel chemical templates have been discovered. It is still a major challenge to identify the first inhibitor of FAAH suitable for clinical exploitation that satisfies the requirements of potency, selectivity versus proteins related to anandamide activity as well as other potential off-targets, reversibility versus irreversibility, and efficacy toward rat versus human FAAH.     

The CB1 cannabinoid receptor C-terminus regulates receptor desensitization in autaptic hippocampal neurones

BACKGROUND AND PURPOSE

The cannabinoid CB₁ receptor is the chief mediator of the CNS effects of cannabinoids. In cell culture model systems, CB₁ receptors both desensitize and internalize on activation. Previous work suggests that the extreme carboxy-terminus of this receptor regulates internalization via phosphorylation of residues clustered within this region. Mutational analysis of the carboxy-terminus of CB₁ receptors has demonstrated that the last six serine/threonine residues are necessary for agonist-induced internalization. However, the structural determinants of CB₁ receptor internalization are also dependent on the local cellular environment. The importance of cell context on CB₁ receptor function calls for an investigation of the functional roles of these residues in neurones.

EXPERIMENTAL APPROACH

To determine the structural requirements of CB₁ internalization in neurones, we evaluated the signalling properties of carboxy-terminal mutated CB₁ receptors expressed in cultured autaptic hippocampal neurones, using electrophysiological methods.

KEY RESULTS

CB₁ receptors transfected into CB₁ knockout neurones signalled and desensitized as did wild-type neurones, allowing us to test specific CB₁ receptor mutations. Deletion of the last 13 residues yielded a CB₁ receptor that inhibited excitatory postsynaptic currents but did not desensitize. Furthermore, mutation of the final six serine and threonine residues to alanines resulted in a non-desensitizing receptor. In contrast, CB₁ receptors lacking residues 419–460, leaving the last 14 residues intact, did desensitize.

CONCLUSIONS AND IMPLICATIONS

The distal thirteen residues of CB₁ receptors are crucial for their desensitization in cultured neurones. Furthermore, this desensitization is likely to follow phosphorylation of serines and threonines within this region.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7     

The Cannabinoid 1–Receptor Silent Antagonist O-2050 Attenuates Preference for High-Fat Diet and Activated Astrocytes in Mice

Endocannabinoids have been shown to activate reward-related feeding and to promote astrocytic differentiation. We investigated whether high-fat diet (HFD) intake produced a preference for HFD via an endocannabinoid-dependent mechanism. In the conditioned place preference test, the 2-week HFD–intake group showed preference for HFD and had increased expression of a marker for reactive astrocytes, glial fibrillary acid protein (GFAP), in the hypothalamus. The cannabinoid CB₁–receptor antagonist O-2050 reduced the preference for HFD and expression of GFAP in the hypothalamus. These results suggested that HFD intake led to the development of a preference for HFD via astrocytic CB₁ receptors in the hypothalamus.     

Discovery of PF-04457845: A Highly Potent, Orally Bioavailable, and Selective Urea FAAH Inhibitor

Fatty acid amide hydrolase (FAAH) is an integral membrane serine hydrolase that degrades the fatty acid amide family of signaling lipids, including the endocannabinoid anandamide. Genetic or pharmacological inactivation of FAAH leads to analgesic and anti-inflammatory phenotypes in rodents without showing the undesirable side effects observed with direct cannabinoid receptor agonists, indicating that FAAH may represent an attractive therapeutic target for the treatment of inflammatory pain and other nervous system disorders. Herein, we report the discovery and characterization of a highly efficacious and selective FAAH inhibitor PF-04457845 (23). Compound 23 inhibits FAAH by a covalent, irreversible mechanism involving carbamylation of the active-site serine nucleophile of FAAH with high in vitro potency (k(inact)/K(i) and IC(50) values of 40300 M(-1) s(-1) and 7.2 nM, respectively, for human FAAH). Compound 23 has exquisite selectivity for FAAH relative to other members of the serine hydrolase superfamily as demonstrated by competitive activity-based protein profiling. Oral administration of 23 at 0.1 mg/kg results in efficacy comparable to that of naproxen at 10 mg/kg in a rat model of inflammatory pain. Compound 23 is being evaluated in human clinical trials.     

Associations between Cannabinoid Receptor-1 (CNR1) Variation and Hippocampus and Amygdala Volumes in Heavy Cannabis Users

Heavy cannabis users display smaller amygdalae and hippocampi than controls, and genetic variation accounts for a large proportion of variance in liability to cannabis dependence (CD). A single nucleotide polymorphism in the cannabis receptor-1 gene (CNR1), rs2023239, has been associated with CD diagnosis and intermediate phenotypes, including abstinence-induced withdrawal, cue-elicited craving, and parahippocampal activation to cannabis cues. This study compared hippocampal and amygdalar volumes (potential CD intermediate phenotypes) between heavy cannabis users and healthy controls, and analyzed interactions between group, rs2023239 variation, and the volumes of these structures. Ninety-four heavy cannabis users participated, of whom 37 (14 men, 23 women; mean age=27.8) were matched to 37 healthy controls (14 men, 23 women; mean age=27.3) for case-control analyses. Controlling for total intracranial volume and other confounding variables, matched cannabis users had smaller bilateral hippocampi (left, p=0.002; right, p=0.001) and left amygdalae (p=0.01) than controls. When genotype was considered in the case-control analyses, there was a group by genotype interaction, such that the rs2023239 G allele predicted lower volume of bilateral hippocampi among cannabis users relative to controls (both p<0.001). This interaction persisted when all 94 cannabis users were compared to controls. There were no group by genotype interactions on amygdalar volume. These data replicate previous findings of reduced hippocampal and amygdalar volume among heavy cannabis users, and suggest that CNR1 rs2023239 variation may predispose smaller hippocampal volume after heavy cannabis use. This association should be tested in future studies of brain volume differences in CD.     

Inhibition of fatty acid amide hydrolase produces PPAR-alpha-mediated analgesia in a rat model of inflammatory pain

Background and purpose:

We have previously demonstrated antinociceptive effects of fatty acid amide hydrolase (FAAH) inhibition that were accompanied by increases in the levels of endocannabinoids (ECs) in the hind paw. Here, the effects of the FAAH inhibitor URB597 (3′-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) on responses of spinal neurons were studied.

Experimental approach:

Extracellular single-unit recordings of dorsal horn neurons were made in anaesthetized rats with hind paw inflammation induced by λ-carrageenan. Effects of intraplantar pre-administration of URB597, or vehicle, on carrageenan-evoked expansion of peripheral receptive fields of spinal neurons and mechanically evoked responses of neurons were studied. The cannabinoid receptor type 1 (CB₁) antagonist AM251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) and the peroxisome proliferator-activated receptor (PPAR)-α antagonist GW6471 ([(2S)-2-[[(1Z)-1-methyl-3-oxo-3-[4-(trifluoromethyl)phenyl]-1-propenyl]amino]-3-[4-[2-(5-methyl-2-phenyl-4-oxa zolyl)ethoxy]phenyl]propyl]-carbamic acid ethyl ester) were used to investigate the roles of these receptors in mediating the effects of URB597.

Key results:

URB597 (25 μg in 50 μL) pretreatment significantly inhibited carrageenan-evoked receptive field expansion and this was significantly reversed by co-administration of the PPAR-α antagonist but not the CB₁ antagonist. Pretreatment with the PPAR-α receptor agonist WY14643 ([[4-chloro-6-[(2,3-dimethylphenyl)amino]-2-pyrimidinyl]thio]acetic acid) also significantly inhibited receptive field expansion. URB597 (25 or 100 μg in 50 μL) had no significant effect on mechanically evoked responses of spinal neurons.

Conclusions and implications:

URB597 inhibited receptive field expansions but not mechanically evoked responses of spinal neurons in rats with hind paw inflammation. These effects were blocked by PPAR-α receptor antagonism. These data support the contention that URB597 exerts its antinociceptive effects by indirect inhibition of sensitization of neuronal responses at least partly through PPAR-α activation due to enhanced EC levels.     

The cannabinoid receptor-1 antagonist rimonabant inhibits platelet activation and reduces pro-inflammatory chemokines and leukocytes in Zucker rats

BACKGROUND AND PURPOSE: We investigated the effect of rimonabant on inflammation and enhanced platelet reactivity in type 2 diabetic Zucker rats, an experimental model of impaired glucose tolerance and the metabolic syndrome. EXPERIMENTAL APPROACH: Rimonabant (10 mg kg(-1) by gavage) was fed for 2 weeks to 3-month-old male obese Zucker rats as an impaired glucose tolerance model and for 10 weeks to 6-month-old male obese Zucker rats as a model of the metabolic syndrome. RANTES (Regulated upon Activation, Normal T cell Expressed, and Secreted) and MCP-1 (monocyte chemotactic protein-1) serum levels were determined by ELISA. Leukocyte populations were quantitatively assessed using a veterinary differential blood cell counter. Platelet activation was assessed by flow-cytometry, platelet aggregation, and adhesion of isolated platelets to immobilized fibrinogen. KEY RESULTS: RANTES and MCP-1 serum levels were increased in obese vs lean Zucker rats and significantly reduced by long-term treatment with rimonabant, which slowed weight gain in rats with the metabolic syndrome. Neutrophils and monocytes were significantly increased in young and old obese vs lean Zucker rats and lowered by rimonabant. Platelet-bound fibrinogen was significantly enhanced in obese vs lean Zucker rats of both age, and was reduced by rimonabant. Platelets from obese rats were more sensitive to thrombin-induced aggregation and adhesion to fibrinogen, which were both attenuated by rimonabant therapy. CONCLUSIONS AND IMPLICATIONS: We demonstrate positive modulation of circulating neutrophil and monocyte numbers, reduced platelet activation and lower RANTES and MCP-1 levels by rimonabant in Zucker rats. This may potentially contribute to a reduction of cardiovascular risk.     

Phencyclidine-Induced Social Withdrawal Results from Deficient Stimulation of Cannabinoid CB1 Receptors: Implications for Schizophrenia

The neuronal mechanisms underlying social withdrawal, one of the core negative symptoms of schizophrenia, are not well understood. Recent studies suggest an involvement of the endocannabinoid system in the pathophysiology of schizophrenia and, in particular, of negative symptoms. We used biochemical, pharmacological, and behavioral approaches to investigate the role played by the endocannabinoid system in social withdrawal induced by sub-chronic administration of phencyclidine (PCP). Pharmacological enhancement of endocannabinoid levels via systemic administration of URB597, an inhibitor of endocannabinoid degradation, reversed social withdrawal in PCP-treated rats via stimulation of CB₁ receptors, but reduced social interaction in control animals through activation of a cannabinoid/vanilloid-sensitive receptor. In addition, the potent CB agonist CP55,940 reversed PCP-induced social withdrawal in a CB₁-dependent manner, whereas pharmacological blockade of CB₁ receptors by either AM251 or SR141716 reduced the time spent in social interaction in control animals. PCP-induced social withdrawal was accompanied by a decrease of anandamide (AEA) levels in the amygdala and prefrontal cortex, and these deficits were reversed by URB597. As CB₁ receptors are predominantly expressed on GABAergic interneurons containing the anxiogenic peptide cholecystokinin (CCK), we also examined whether the PCP-induced social withdrawal resulted from deficient CB₁-mediated modulation of CCK transmission. The selective CCK2 antagonist {"type":"entrez-nucleotide","attrs":{"text":"LY225910","term_id":"1257563185","term_text":"LY225910"}}LY225910 blocked both PCP- and AM251-induced social withdrawal, but not URB597 effect in control rats. Taken together, these findings indicate that AEA-mediated activation of CB₁ receptors is crucial for social interaction, and that PCP-induced social withdrawal results from deficient endocannabinoid transmission.