Endocannabinoid brain mechanisms and addiction

在2006年10月1日至2007年9月30日期间，该研究项目取得了重大进展。在所述报告期内，我们研究了一种新型高选择性大麻素CB 1受体拮抗剂AM 251对使用恢复动物模型的可卡因触发的药物寻求行为复发的影响，以及在恢复条件下对可卡因诱导的细胞外多巴胺，谷氨酸和γ-氨基丁酸（GABA）变化的影响。我们发现，全身给药的AM 251选择性抑制可卡因诱导的，但不是蔗糖加蔗糖线索诱导的，奖励寻求行为的恢复。AM 251本身并不能触发恢复。局部微灌注AM 251到边缘前脑或背侧纹状体的背侧核也抑制可卡因触发的恢复。单独的AM 251以电压依赖性钠通道依赖性方式剂量依赖性地升高谷氨酸盐核。AM 251不影响丘脑核多巴胺或GABA。预处理与AM 251剂量依赖性地抑制可卡因诱导的增加，但在多巴胺的脑桥核谷氨酸。LY 341495阻断丘脑核代谢型谷氨酸mGluR 2/3受体可轻微促进可卡因增强的谷氨酸释放，但阻断AM 251对可卡因触发的恢复的拮抗作用。我们的结论是：1）CB 1大麻素受体在可卡因消退条件下对延髓核谷氨酸释放产生紧张性抑制; 2）通过AM 251阻断CB 1大麻素受体抑制可卡因增强的延髓核谷氨酸释放和可卡因触发的恢复;和3）这些作用似乎是通过激活突触前mGluR 2/3自身受体介导的，继发于AM 251诱导的增加（去抑制）核谷氨酸释放。我们进一步发现，AM 251剂量依赖性地降低（30-70%）静脉内可卡因自我管理的断点在实验室大鼠进行比例强化条件下。CB 1受体拮抗剂SR 141716给药使折点降低了35%，但未达到统计学显著性。AM 251和SR 141716均未改变固定比例（FR 2）强化条件下的可卡因自我给药。AM 251还显著且剂量依赖性地抑制（25-90%）可卡因增强的脑刺激奖赏，而SR 141716仅在最高剂量的SR 141716测试下减弱可卡因的奖赏增强效应，并且仅产生40%的衰减。在所有测试剂量下，单独的AM 251对脑刺激奖赏没有影响，而单独的高剂量SR 141716显著抑制脑奖赏。这些数据表明，AM 251对CB 1受体的阻断剂量依赖性地抑制可卡因的奖励效应（通过渐进比静脉内可卡因自我给药和脑电刺激奖励评估），而SR 141716基本无效。我们认为，高剂量SR 141716产生的大脑奖赏抑制可能是接受SR 141716治疗的人中烦躁不安和/或抑郁症临床报告的基础。我们的结论是，AM 251或其他更有效和选择性的CB 1大麻素受体拮抗剂作为潜在的有效的抗可卡因药物值得进一步研究。

During the period 01 Oct 06 to 30 Sept 07, significant progress was made on this research project. During said reporting period, we studied the effects of AM251, a novel highly selective cannabinoid CB1 receptor antagonist, on cocaine-triggered relapse to drug-seeking behavior using the reinstatement animal model and on cocaine-induced changes in extracellular dopamine, glutamate, and gamma-aminobutyric acid (GABA) under reinstatement conditions. We found that systemic administration of AM251 selectively inhibited cocaine-induced, but not sucrose plus sucrose cue-induced, reinstatement of reward-seeking behavior. AM251 alone did not trigger reinstatement. Local micro-perfusion of AM251 into the nucleus accumbens of the limbic forebrain or the dorsal striatum also inhibited cocaine-triggered reinstatement. AM251 alone dose-dependently elevated nucleus accumbens glutamate in a voltage-dependent sodium-channel-dependent manner. AM251 did not affect nucleus accumbens dopamine or GABA. Pretreatment with AM251 dose-dependently inhibited cocaine-induced increases in nucleus accumbens glutamate but not in dopamine. Blockade of nucleus accumbens metabotropic glutamate mGluR2/3 receptors by LY341495 slightly facilitated cocaine-enhanced glutamate release but blocked the antagonism of cocaine-triggered reinstatement by AM251. We conclude that: 1) CB1 cannabinoid receptors exert tonic inhibition over nucleus accumbens glutamate release under cocaine-extinction conditions; 2) blockade of CB1 cannabinoid receptors by AM251 inhibits cocaine-enhanced nucleus accumbens glutamate release and cocaine-triggered reinstatement; and 3) these effects appear to be mediated by activation of presynaptic mGluR2/3 autoreceptors secondary to AM251-induced increase (disinhibition) of nucleus accumbens glutamate release. We further found that AM251 dose-dependently lowered (by 30-70%) the break-point for intravenous cocaine self-administration under progressive-ratio reinforcement conditions in laboratory rats. Administration of the CB1 receptor antagonist SR141716 lowered the break-point by 35%, which did not reach statistical significance. Neither AM251 nor SR141716 altered cocaine self-administration under fixed-ratio (FR2) reinforcement conditions. AM251 also significantly and dose-dependently inhibited (by 25-90%) cocaine-enhanced brain stimulation reward, while SR141716 attenuated cocaine's reward-enhancing effect only at the highest dose of SR141716 tested and only producing a 40% attenuation. AM251 alone, at all doses tested, had no effect on brain stimulation reward, while high doses of SR141716 alone significantly inhibited brain reward. These data suggest that blockade of CB1 receptors by AM251 dose-dependently inhibits cocaine's rewarding effects (as assessed by both progressive-ratio intravenous cocaine self-administration and by electrical brain stimulation reward), whereas SR141716 is largely ineffective. We believe that the inhibition of brain reward produced by high doses of SR141716 may underlie clinical reports of dysphoria and/or depression in humans treated with SR141716. We conclude that AM251 or other more potent and selective CB1 cannabinoid receptor antagonists deserve further study as potentially effective anti-cocaine medications.