Neuroscience Center, Brigham Young University, Provo, UT 84602, USA.
Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA.
Molecules. 2019 Apr 3;24(7):1306. doi: 10.3390/molecules24071306.
The hippocampus is thought to encode information by altering synaptic strength via synaptic plasticity. Some forms of synaptic plasticity are induced by lipid-based endocannabinoid signaling molecules that act on cannabinoid receptors (CB1). Endocannabinoids modulate synaptic plasticity of hippocampal pyramidal cells and stratum radiatum interneurons; however, the role of endocannabinoids in mediating synaptic plasticity of stratum oriens interneurons is unclear. These feedback inhibitory interneurons exhibit presynaptic long-term potentiation (LTP), but the exact mechanism is not entirely understood. We examined whether oriens interneurons produce endocannabinoids, and whether endocannabinoids are involved in presynaptic LTP. Using patch-clamp electrodes to extract single cells, we analyzed the expression of endocannabinoid biosynthetic enzyme mRNA by reverse transcription and then real-time PCR (RT-PCR). The cellular expression of calcium-binding proteins and neuropeptides were used to identify interneuron subtype. RT-PCR results demonstrate that stratum oriens interneurons express mRNA for both endocannabinoid biosynthetic enzymes and the type I metabotropic glutamate receptors (mGluRs), necessary for endocannabinoid production. Immunohistochemical staining further confirmed the presence of diacylglycerol lipase alpha, an endocannabinoid-synthesizing enzyme, in oriens interneurons. To test the role of endocannabinoids in synaptic plasticity, we performed whole-cell experiments using high-frequency stimulation to induce long-term potentiation in somatostatin-positive cells. This plasticity was blocked by AM-251, demonstrating CB1-dependence. In addition, in the presence of a fatty acid amide hydrolase inhibitor (URB597; 1 µM) and MAG lipase inhibitor (JZL184; 1 µM) that increase endogenous anandamide and 2-arachidonyl glycerol, respectively, excitatory current responses were potentiated. URB597-induced potentiation was blocked by CB1 antagonist AM-251 (2 µM). Collectively, this suggests somatostatin-positive oriens interneuron LTP is CB1-dependent.
海马体被认为通过突触可塑性改变突触强度来编码信息。一些形式的突触可塑性是由作用于大麻素受体 (CB1) 的脂基内源性大麻素信号分子诱导的。内源性大麻素调节海马锥体细胞和放射层中间神经元的突触可塑性；然而，内源性大麻素在介导放射层中间神经元的突触可塑性中的作用尚不清楚。这些反馈抑制性中间神经元表现出突触前长时程增强（LTP），但确切的机制尚不完全清楚。我们研究了放射层中间神经元是否产生内源性大麻素，以及内源性大麻素是否参与突触前 LTP。我们使用膜片钳电极提取单个细胞，通过反转录和实时 PCR（RT-PCR）分析内源性大麻素生物合成酶 mRNA 的表达。钙结合蛋白和神经肽的细胞表达用于鉴定中间神经元亚型。RT-PCR 结果表明，放射层中间神经元表达内源性大麻素生物合成酶和 I 型代谢型谷氨酸受体 (mGluR) 的 mRNA，这是内源性大麻素产生所必需的。免疫组织化学染色进一步证实了二酰基甘油脂肪酶 alpha（一种内源性大麻素合成酶）存在于放射层中间神经元中。为了测试内源性大麻素在突触可塑性中的作用，我们使用高频刺激在生长抑素阳性细胞中诱导长时程增强，进行全细胞实验。这种可塑性被 CB1 拮抗剂 AM-251 阻断，表明其依赖于 CB1。此外，在脂肪酸酰胺水解酶抑制剂 (URB597；1µM) 和 MAG 脂肪酶抑制剂 (JZL184；1µM) 的存在下，分别增加内源性大麻素和 2-花生四烯酰甘油，兴奋性电流反应被增强。URB597 诱导的增强被 CB1 拮抗剂 AM-251（2µM）阻断。总之，这表明生长抑素阳性放射层中间神经元 LTP 依赖于 CB1。
