Kawamura Yoshinobu, Fukaya Masahiro, Maejima Takashi, Yoshida Takayuki, Miura Eriko, Watanabe Masahiko, Ohno-Shosaku Takako, Kano Masanobu
Department of Cellular Neuroscience, Graduate School of Medicine, Osaka University, Suita 565-0871, Japan.
J Neurosci. 2006 Mar 15;26(11):2991-3001. doi: 10.1523/JNEUROSCI.4872-05.2006.
Endocannabinoids work as retrograde messengers and contribute to short-term and long-term modulation of synaptic transmission via presynaptic cannabinoid receptors. It is generally accepted that the CB1 cannabinoid receptor (CB1) mediates the effects of endocannabinoid in inhibitory synapses. For excitatory synapses, however, contributions of CB1, "CB3," and some other unidentified receptors have been suggested. In the present study we used electrophysiological and immunohistochemical techniques and examined the type(s) of cannabinoid receptor functioning at hippocampal and cerebellar excitatory synapses. Our electrophysiological data clearly demonstrate the predominant contribution of CB1. At hippocampal excitatory synapses on pyramidal neurons the cannabinoid-induced synaptic suppression was reversed by a CB1-specific antagonist, N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251), and was absent in CB1 knock-out mice. At climbing fiber (CF) and parallel fiber (PF) synapses on cerebellar Purkinje cells the cannabinoid-dependent suppression was absent in CB1 knock-out mice. The presence of CB1 at presynaptic terminals was confirmed by immunohistochemical experiments with specific antibodies against CB1. In immunoelectron microscopy the densities of CB1-positive signals in hippocampal excitatory terminals and cerebellar PF terminals were much lower than in inhibitory terminals but were clearly higher than the background. Along the long axis of PFs, the CB1 was localized at a much higher density on the perisynaptic membrane than on the extrasynaptic and synaptic regions. In contrast, CB1 density was low in CF terminals and was not significantly higher than the background. Despite the discrepancy between the electrophysiological and morphological data for CB1 expression on CFs, these results collectively indicate that CB1 is responsible for cannabinoid-dependent suppression of excitatory transmission in the hippocampus and cerebellum.
内源性大麻素作为逆行信使，通过突触前大麻素受体对突触传递进行短期和长期调节。人们普遍认为，CB1大麻素受体（CB1）介导内源性大麻素在抑制性突触中的作用。然而，对于兴奋性突触，有人提出了CB1、“CB3”和其他一些未明确的受体的作用。在本研究中，我们使用电生理和免疫组织化学技术，研究了在海马体和小脑兴奋性突触中发挥作用的大麻素受体类型。我们的电生理数据清楚地表明了CB1的主要作用。在海马体中锥体细胞上的兴奋性突触处，大麻素诱导的突触抑制可被CB1特异性拮抗剂N-（哌啶-1-基）-5-（4-碘苯基）-1-（2,4-二氯苯基）-4-甲基-1H-吡唑-3-甲酰胺（AM251）逆转，而在CB1基因敲除小鼠中则不存在这种抑制。在小脑浦肯野细胞上的攀缘纤维（CF）和平行纤维（PF）突触处，CB1基因敲除小鼠中不存在大麻素依赖性抑制。通过使用针对CB1的特异性抗体进行免疫组织化学实验，证实了突触前终末存在CB1。在免疫电子显微镜下，海马体兴奋性终末和小脑PF终末中CB1阳性信号的密度远低于抑制性终末，但明显高于背景。沿着PF的长轴，CB1在突触周围膜上的定位密度远高于突触外和突触区域。相比之下，CF终末中的CB1密度较低，且不显著高于背景。尽管CF上CB1表达的电生理和形态学数据存在差异，但这些结果共同表明，CB1负责海马体和小脑中大麻素依赖性的兴奋性传递抑制。
