The central medial (CMT) and paraventricular (PVT) thalamic nuclei project strongly to the basolateral amygdala (BL). Similarities between the responsiveness of CMT, PVT, and BL neurons suggest that these nuclei strongly influence BL activity. Supporting this possibility, an electron microscopic study reported that in contrast with other extrinsic afferents, CMT and PVT axon terminals form very few synapses with BL interneurons. However, since limited sampling is a concern in electron microscopic studies, the present investigation was undertaken to compare the impact of CMT and PVT thalamic inputs on principal and local-circuit BL neurons using optogenetic methods and whole-cell recordings in vitro. Optogenetic stimulation of CMT and PVT axons elicited glutamatergic EPSPs or EPSCs in principal cells and interneurons, but they generally had a longer latency in interneurons. Moreover, after blockade of polysynaptic interactions with tetrodotoxin (TTX), a lower proportion of interneurons (50%) than principal cells (90%) remained responsive to CMT and PVT inputs. While the presence of TTX-resistant responses in some interneurons indicates that CMT and PVT inputs directly contact some local-circuit cells, their lower incidence and amplitude after TTX suggest that CMT and PVT inputs form fewer synapses with them than with principal BL cells. Together, these results indicate that CMT and PVT inputs mainly contact principal BL neurons such that when CMT or PVT neurons fire, limited feed-forward inhibition counters their excitatory influence over principal BL cells. However, CMT and PVT axons can also recruit interneurons indirectly, via the activation of principal cells, thereby generating feedback inhibition.

中文翻译：

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中央内侧和室旁丘脑投射到基底外侧杏仁核的光遗传学研究


中央内侧 (CMT) 和室旁 (PVT) 丘脑核强烈投射到基底外侧杏仁核 (BL)。 CMT、PVT 和 BL 神经元的反应性之间的相似性表明这些细胞核强烈影响 BL 活性。一项电子显微镜研究支持了这种可能性，报告称与其他外在传入神经相比，CMT 和 PVT 轴突末端与 BL 中间神经元形成的突触非常少。然而，由于电子显微镜研究中的采样有限，因此本研究采用光遗传学方法和体外全细胞记录来比较 CMT 和 PVT 丘脑输入对主回路 BL 神经元和局部回路 BL 神经元的影响。 CMT 和 PVT 轴突的光遗传学刺激在主细胞和中间神经元中引发谷氨酸能 EPSP 或 EPSC，但它们通常在中间神经元中具有较长的潜伏期。此外，在阻断与河豚毒素 (TTX) 的多突触相互作用后，中间神经元 (50%) 的比例低于主细胞 (90%)，仍然对 CMT 和 PVT 输入做出反应。虽然一些中间神经元中 TTX 抵抗反应的存在表明 CMT 和 PVT 输入直接接触一些局部电路细胞，但 TTX 后它们的较低发生率和幅度表明 CMT 和 PVT 输入与它们形成的突触比与主要 BL 细胞形成的突触要少。总之，这些结果表明 CMT 和 PVT 输入主要接触主要 BL 神经元，因此当 CMT 或 PVT 神经元放电时，有限的前馈抑制抵消了它们对主要 BL 细胞的兴奋性影响。然而，CMT 和 PVT 轴突也可以通过主细胞的激活间接募集中间神经元，从而产生反馈抑制。