Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki, Japan.
Neuroscience. 2010 Feb 17;165(4):1377-89. doi: 10.1016/j.neuroscience.2009.11.054. Epub 2009 Dec 1.
Retrograde synaptic signaling by endogenous cannabinoids (endocannabinoids) is a recently discovered form of neuromodulation in various brain regions. In hippocampus, it is well known that endocannabinoids suppress presynaptic inhibitory neurotransmitter release in CA1 region. However, endocannabinoid signaling in CA3 region remains to be examined. Here we investigated whether presynaptic inhibition can be caused by activation of postsynaptic group I metabotropic glutamate receptors (mGluRs) and following presynaptic cannabinoid receptor type 1 (CB1 receptor) using mechanically dissociated rat hippocampal CA3 pyramidal neurons with adherent functional synaptic boutons. Application of group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) reversibly suppressed spontaneous inhibitory postsynaptic currents (IPSCs). In the presence of tetrodotoxin (TTX), frequency of miniature IPSCs was significantly reduced by DHPG, while there were no significant changes in minimum quantal size and sensitivity of postsynaptic GABA(A) receptors to the GABA(A) receptor agonist muscimol, indicating that this suppression was caused by a decrease in GABA release from presynaptic nerve terminals. Application of CB1 synthetic agonist WIN55212-2 (mesylate(R)-(+)-2,3-dihydro-5-methyl-3-[4-morpholino)methyl]pyrrolo-[1,2,3-de]-1,4-benzoxazin-6-ylmethanone) or endocannabinoid 2-arachidonoylglycerol also suppressed the spontaneous IPSC. The inhibitory effect of DHPG on spontaneous IPSCs was abolished by SR-141716 (5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide), a CB1 receptor antagonist. Furthermore, postsynaptic application of GDP-betaS blocked the DHPG-induced inhibition of spontaneous IPSCs, indicating the involvement of endcannabinoid-mediated retrograde synaptic signaling. These results provide solid evidence for retrograde signaling from postsynaptic group I mGluRs to presynaptic CB1 receptors, which induces presynaptic inhibition of GABA release in rat hippocampal CA3 region.
内源性大麻素（内源性大麻素）的逆行突触信号传递是各种脑区中最近发现的一种神经调质形式。在海马体中，众所周知，内源性大麻素会抑制 CA1 区域的突触前抑制性神经递质释放。然而，CA3 区域的内源性大麻素信号传递仍有待研究。在这里，我们使用机械分离的具有粘附性功能突触小泡的大鼠海马 CA3 锥体神经元，研究了激活突触后 I 型代谢型谷氨酸受体 (mGluRs) 后是否可以引起突触前抑制，以及随后的 CB1 受体。应用 I 型 mGluR 激动剂 (RS)-3,5-二羟基苯甘氨酸 (DHPG) 可可逆地抑制自发性抑制性突触后电流 (IPSCs)。在加入河豚毒素 (TTX) 的情况下，DHPG 可显著降低微小 IPSC 的频率，而 GABA(A) 受体对 GABA(A) 受体激动剂 muscimol 的后突触 GABA(A) 受体的最小量子大小和敏感性没有明显变化，表明这种抑制是由于从突触前神经末梢释放 GABA 减少所致。应用 CB1 合成激动剂 WIN55212-2（甲磺酸盐（R）-[2,3-二氢-5-甲基-3-[4-吗啉基）甲基]吡咯烷-[1,2,3-de]-1,4-苯并恶嗪-6-基]（1-萘基）甲酮）或内源性大麻素 2-花生四烯酰甘油也可抑制自发性 IPSC。DHPG 对自发性 IPSC 的抑制作用被 CB1 受体拮抗剂 SR-141716（5-(4-氯苯基)-1-(2,4-二氯苯基)-4-甲基-N-(哌啶-1-基)-1H-吡唑-3-甲酰胺）消除。此外，DHPG 诱导的自发性 IPSC 抑制作用被突触后 GDP-βS 阻断，表明存在内源性大麻素介导的逆行突触信号传递。这些结果为从突触后 I 型 mGluRs 到突触前 CB1 受体的逆行信号传递提供了确凿的证据，这导致了大鼠海马 CA3 区域 GABA 释放的突触前抑制。
