Department of Morphological Neuroscience, Division of Neuroscience, Gifu University Graduate School of Medicine, Japan.
Brain Res. 2011 Jul 11;1400:19-30. doi: 10.1016/j.brainres.2011.05.026. Epub 2011 May 19.
The amygdala is activated by fear and plays an important role in the emotional response to life-threatening situations. When rats feel threatened, they respond by biting fiercely. Bite strength is regulated by the trigeminal motor nucleus and the mesencephalic trigeminal nucleus (Me5). The Me5 relays proprioceptive signals from the masticatory muscles and the periodontal ligaments to the trigeminal motor and premotor nuclei. The amygdala projects to the trigeminal motor nucleus and the premotor reticular formation. However, it is unknown whether the amygdala projects directly to the Me5. In the present study, neurons of the central amygdaloid nucleus (ACe) were labeled following injection of a retrograde tracer, Fast Blue, into the caudal Me5, and fibers and terminal buttons from the ACe to the Me5 were examined after injections of an anterograde neuronal tracer, biotinylated dextran amine into the ACe. Furthermore, wheat germ agglutinin-conjugated to horseradish peroxidase was injected into the ACe, and labeled fibers and terminal buttons in the Me5 were examined by electron microscopy. Labeled terminal buttons on Me5 somata were more abundant in the caudal than the rostral Me5. Electron microscopic observation revealed that a part of these terminal buttons formed axo-somatic synapses. These results indicate that the ACe sends direct projections to the Me5, and suggest that the amygdala regulates bite strength by modifying neuronal activity in the Me5.
杏仁核被恐惧激活，在对危及生命的情况的情绪反应中起着重要作用。当老鼠感到威胁时，它们会猛烈地咬。咬合力由三叉神经运动核和中脑三叉神经核（Me5）调节。Me5 将咀嚼肌和牙周韧带的本体感觉信号传递到三叉神经运动核和前运动网状核。杏仁核投射到三叉神经运动核和前运动网状结构。然而，杏仁核是否直接投射到 Me5 尚不清楚。在本研究中，将逆行示踪剂 Fast Blue 注射到 Me5 的尾侧，随后在 ACe 中注射顺行神经元示踪剂生物素化葡聚糖胺，观察到来自 ACe 的纤维和终末按钮到 Me5。此外，将辣根过氧化物酶结合的麦胚凝集素注入 ACe，通过电子显微镜观察 Me5 中的标记纤维和终末按钮。Me5 体上的标记终末按钮在尾侧比在头侧更丰富。电子显微镜观察显示，这些终末按钮的一部分形成轴-体突触。这些结果表明杏仁核通过调节 Me5 中的神经元活动来直接投射到 Me5，并暗示杏仁核调节咬合力。
