Pharmacological separation of cannabinoid sensitive receptors on hippocampal excitatory and inhibitory fibers
Pharmacological separation of cannabinoid sensitive receptors on hippocampal excitatory and inhibitory fibers
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DOI：
10.1016/s0028-3908(02)00157-0
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发表时间：
2002-09-01
影响因子：
4.7
通讯作者：
Freund, TF
中科院分区：
文献类型：
--
作者：
Hájos, N;Freund, TF
我们早期的研究表明，在海马体中，大麻素通过CB 1大麻素受体抑制抑制性突触传递，而一种新的大麻素敏感受体调节兴奋性突触（Katona，I.例如，Journal of Neuroscience 19（1999）4544; Hajos，N.例如，European Journal of Neuroscience 12（2000）3239; Hajos，N.例如，Neuroscience 106（2001）1）。新受体不对应于CB 2，因为这种受体类型不在脑中表达（Munro，S.例如，Nature 365（1993）61）。最近的结合实验显示，合成大麻素WIN 55，212 -2以较低的亲和力结合到CB 1受体敲除小鼠的脑膜，表明海马中这两种类型的大麻素受体之间存在药理学差异（Breivogel等人，Molecular Pharmacology 60（2001）155）。为了详细分析这种差异，我们首先使用全细胞膜片钳记录确定了WIN 55，212 -2在大鼠海马切片中兴奋性和抑制性传递的EC 50值。在CA 1锥体细胞电刺激诱发的抑制性突触后电流（IPSC）的估计EC 50值为0.24 μ M，而兴奋性突触后电流（EPSC），它是2.01 μ M，分别。大麻素拮抗剂AM 251阻断了WIN 55，212 -2诱导的对诱发的IPSC的抑制，但不阻断对EPSC的抑制，这为其对CB 1的选择性提供了证据。然后，我们测试了大麻素对海马兴奋性神经传递的作用是否是通过对香草素配体具有亲和力的受体介导的假设。香草素受体拮抗剂辣椒平（10 μ M）与大麻素（WIN 55，212-2或CP 55，940）的共同应用防止了EPSC的减少，但没有IPSC。辣椒素（10 μ M）的灌流也抑制了诱发的EPSCs的振幅，辣椒素也可以拮抗这种作用。相比之下，辣椒素并没有改变诱发的IPSC的振幅。这些结果表明，WIN 55，212 -2在减少通过CB 1的GABA能电流方面比抑制通过新CB受体的谷氨酸能传递方面更有效一个数量级。新CB受体（和EPSC）对香草素配体的敏感性，但对大麻素拮抗剂AM 251的敏感性，代表了区分这两种受体的另一种药理学工具，因为CB 1（及其对IPSC的作用）不受香草素调节，但被AM 251拮抗。(C)2002爱思唯尔科技有限公司版权所有。
Our earlier studies demonstrated that in the hippocampus, cannabinoids suppress inhibitory synaptic transmission via CB1 cannabinoid receptors, whereas a novel cannabinoid-sensitive receptor modulates excitatory synapses (Katona, I. et al., Journal of Neuroscience 19 (1999) 4544; Hajos, N. et al., European Journal of Neuroscience 12 (2000) 3239; Hajos, N. et al., Neuroscience 106 (2001) 1). The novel receptor does not correspond to CB2, since this receptor type is not expressed in the brain (Munro, S. et al., Nature 365 (1993) 61). Recent binding experiments revealed that the synthetic cannabinoid WIN 55,212-2 binds with lower affinity to brain membranes of CB1 receptor-knockout mice indicating that pharmacological differences exist between these two types of cannabinoid receptors in the hippocampus (Breivogel et al., Molecular Pharmacology 60 (2001) 155). To analyze this difference in detail, we first determined the EC50 values of WIN 55,212-2 for excitatory and inhibitory transmission in rat hippocampal slices using whole-cell patch-clamp recordings. The estimated EC50 value for inhibitory postsynaptic currents (IPSC) evoked by electrical stimulation in CA1 pyramidal cells was 0.24 muM, whereas for excitatory postsynaptic currents (EPSC) it was 2.01 muM, respectively. The cannabinoid antagonist, AM251, blocked the WIN 55,212-2-induced inhibition of evoked IPSCs, but not of EPSCs, providing evidence for its selectivity for CB1. We then tested the hypothesis of whether the cannabinoid effect on hippocampal excitatory neurotransmission is mediated via receptors with an affinity for vanilloid ligands. Co-application of the vanilloid receptor antagonist capsazepine (10 muM) with cannabinoids (WIN55,212-2 or CP55,940) prevented the reduction of EPSCs, but not of IPSCs. The amplitude of evoked EPSCs was also suppressed by superfusion of the vanilloid receptor agonist capsaicin (10 muM), an effect which could also be antagonized by capsazepine. In contrast, capsaicin did not change the amplitude of evoked IPSCs.These results demonstrate that WIN 55,212-2 is an order of magnitude more potent in reducing GABAergic currents via CB1 than in inhibiting glutamatergic transmission via the new CB receptor. The sensitivity of the new CB receptor (and EPSCs) to vanilloid ligands, but not to the cannabinoid antagonist AM251, represents another pharmacological tool to distinguish the two receptors, since CB1 (and its effect on IPSCs) is not modulated by vanilloids, but is antagonized by AM251. (C) 2002 Elsevier Science Ltd. All rights reserved.