Melis Miriam, Pistis Marco, Perra Simona, Muntoni Anna Lisa, Pillolla Giuliano, Gessa Gian Luigi
Centre of Excellence, Neurobiology of Addiction, University of Cagliari, Monserrato, 09042 Italy.
J Neurosci. 2004 Jan 7;24(1):53-62. doi: 10.1523/JNEUROSCI.4503-03.2004.
The endogenous cannabinoid system has been shown to play a crucial role in controlling neuronal excitability and synaptic transmission. In this study we investigated the effects of a cannabinoid receptor (CB-R) agonist WIN 55,212-2 (WIN) on excitatory synaptic transmission in the rat ventral tegmental area (VTA). Whole-cell patch clamp recordings were performed from VTA dopamine (DA) neurons in an in vitro slice preparation. WIN reduced both NMDA and AMPA EPSCs, as well as miniature EPSCs (mEPSCs), and increased the paired-pulse ratio, indicating a presynaptic locus of its action. We also found that WIN-induced effects were dose-dependent and mimicked by the CB1-R agonist HU210. Furthermore, two CB1-R antagonists, AM281 and SR141716A, blocked WIN-induced effects, suggesting that WIN modulates excitatory synaptic transmission via activation of CB1-Rs. Our additional finding that both AM281 and SR141716A per se increased NMDA EPSCs suggests that endogenous cannabinoids, released from depolarized postsynaptic neurons, might act retrogradely on presynaptic CB1-Rs to suppress glutamate release. Hence, we report that a type of synaptic modulation, previously termed depolarization-induced suppression of excitation (DSE), is present also in the VTA as a calcium-dependent phenomenon, blocked by both AM281 and SR141716A, and occluded by WIN. Importantly, DSE was partially blocked by the D2DA antagonist eticlopride and enhanced by the D2DA agonist quinpirole without changing the presynaptic cannabinoid sensitivity. These results indicate that the two pathways work in a cooperative manner to release endocannabinoids in the VTA, where they play a role as retrograde messengers for DSE via CB1-Rs.
内源性大麻素系统已被证明在控制神经元兴奋性和突触传递中起关键作用。在本研究中，我们研究了大麻素受体（CB-R）激动剂WIN 55,212-2（WIN）对大鼠腹侧被盖区（VTA）兴奋性突触传递的影响。在体外脑片制备中，对VTA多巴胺（DA）神经元进行全细胞膜片钳记录。WIN降低了NMDA和AMPA介导的兴奋性突触后电流（EPSCs）以及微小兴奋性突触后电流（mEPSCs），并增加了双脉冲比率，表明其作用位点在突触前。我们还发现WIN诱导的效应具有剂量依赖性，并且CB1-R激动剂HU210可模拟该效应。此外，两种CB1-R拮抗剂AM281和SR141716A可阻断WIN诱导的效应，表明WIN通过激活CB1-Rs来调节兴奋性突触传递。我们的另一项发现是，AM281和SR141716A本身均可增加NMDA EPSCs，这表明从去极化的突触后神经元释放的内源性大麻素可能逆行作用于突触前CB1-Rs以抑制谷氨酸释放。因此，我们报告，一种先前称为去极化诱导的兴奋抑制（DSE）的突触调制类型，在VTA中也作为一种钙依赖性现象存在，被AM281和SR141716A阻断，并被WIN掩盖。重要的是，DSE被D2多巴胺拮抗剂依替必利部分阻断，并被D2多巴胺激动剂喹吡罗增强，而不改变突触前大麻素敏感性。这些结果表明，这两条途径以协同方式在VTA中释放内源性大麻素，在那里它们通过CB1-Rs作为DSE的逆行信使发挥作用。
