Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, USA.
J Comp Neurol. 2021 Aug 1;529(11):2842-2864. doi: 10.1002/cne.25130. Epub 2021 Feb 28.
The trigeminal blink reflex plays an important role in protecting the corneal surface from damage and preserving visual function in an unpredictable environment. The closing phase of the human reflex, produced by activation of the orbicularis oculi (ObOc) muscles, consists of an initial, small, ipsilateral R component, followed by a larger, bilateral R component. We investigated the circuitry that underlies this reflex in macaque (Macaca fascicularis and Macaca mulatta) monkeys by the use of single and dual tracer methods. Injection of retrograde tracer into the facial nucleus labeled neurons in the principal trigeminal nucleus, and in the spinal nucleus pars oralis and interpolaris, bilaterally, and in pars caudalis, ipsilaterally. Injection of anterograde tracer into the principal trigeminal nucleus labeled axons that directly terminated on ObOc motoneurons, with an ipsilateral predominance. Injection of anterograde tracer into pars caudalis of the spinal trigeminal nucleus labeled axons that directly terminated on ipsilateral ObOc motoneurons. The observed pattern of labeling indicates that the reticular formation ventromedial to the principal and spinal nuclei also contributes extensive bilateral input to ObOc motoneurons. Thus, much of the trigeminal sensory complex is in a position to supply a monosynaptic drive for lid closure, and the adjacent reticular formation can supply a disynaptic drive. These findings indicate that the assignment of the R and R components of the blink reflex to different parts of the trigeminal sensory complex cannot be exclusively based on subdivision connectional relationships with facial motoneurons. The characteristics of the R component may be due, instead, to other circuit properties.
眨眼反射的三叉神经发挥着重要的作用，在保护角膜表面免受损伤，并保持在不可预测的环境中的视觉功能。人类反射的关闭阶段，通过激活眼轮匝肌（ObOc）肌肉产生，包括初始的、小的、同侧的 R 分量，随后是更大的、双侧的 R 分量。我们通过使用单和双示踪剂方法研究了猕猴（Macaca fascicularis 和 Macaca mulatta）眨眼反射背后的电路。将逆行示踪剂注入面神经核标记了双侧的三叉神经主核、脊髓核前腹侧和中间核，以及同侧的尾侧核。将顺行示踪剂注入三叉神经主核标记了直接终止于 ObOc 运动神经元的轴突，具有同侧优势。将顺行示踪剂注入脊髓三叉神经核尾侧核标记了直接终止于同侧 ObOc 运动神经元的轴突。观察到的标记模式表明，位于主核和脊髓核腹内侧的网状结构也对 ObOc 运动神经元提供广泛的双侧输入。因此，三叉神经感觉复合体的大部分都能够提供闭眼的单突触驱动，而相邻的网状结构可以提供双突触驱动。这些发现表明，眨眼反射的 R 和 R 分量的分配不能仅仅基于与面运动神经元的细分连接关系来分配给三叉神经感觉复合体的不同部分。R 分量的特征可能归因于其他电路特性。
