Mori R L, Bergsman A E, Holmes M J, Yates B J
Departments of Otolaryngology and Neuroscience, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Brain Res. 2001 May 25;902(1):82-91. doi: 10.1016/s0006-8993(01)02370-8.
Changes in posture can affect the resting length of respiratory muscles, requiring alterations in the activity of these muscles if ventilation is to be unaffected. Recent studies have shown that the vestibular system contributes to altering respiratory muscle activity during movement and changes in posture. Furthermore, anatomical studies have demonstrated that many bulbospinal neurons in the medial medullary reticular formation (MRF) provide inputs to phrenic and abdominal motoneurons; because this region of the reticular formation receives substantial vestibular and other movement-related input, it seems likely that medial medullary reticulospinal neurons could adjust the activity of respiratory motoneurons during postural alterations. The objective of the present study was to determine whether functional lesions of the MRF affect inspiratory and expiratory muscle responses to activation of the vestibular system. Lidocaine or muscimol injections into the MRF produced a large increase in diaphragm and abdominal muscle responses to vestibular stimulation. These vestibulo-respiratory responses were eliminated following subsequent chemical blockade of descending pathways in the lateral medulla. However, inactivation of pathways coursing through the lateral medulla eliminated excitatory, but not inhibitory, components of vestibulo-respiratory responses. The simplest explanation for these data is that MRF neurons that receive input from the vestibular nuclei make inhibitory connections with diaphragm and abdominal motoneurons, whereas a pathway that courses laterally in the caudal medulla provides excitatory vestibular inputs to these motoneurons.
姿势的改变会影响呼吸肌的静息长度，如果要使通气不受影响，就需要改变这些肌肉的活动。最近的研究表明，前庭系统有助于在运动和姿势改变期间改变呼吸肌的活动。此外，解剖学研究表明，延髓内侧网状结构（MRF）中的许多延髓脊髓神经元向膈神经和腹部运动神经元提供输入；由于网状结构的这一区域接受大量前庭和其他与运动相关的输入，延髓内侧网状脊髓神经元似乎有可能在姿势改变期间调节呼吸运动神经元的活动。本研究的目的是确定MRF的功能性损伤是否会影响吸气和呼气肌对前庭系统激活的反应。向MRF注射利多卡因或蝇蕈醇会使膈肌和腹部肌肉对前庭刺激的反应大幅增加。在随后对延髓外侧下行通路进行化学阻断后，这些前庭-呼吸反应消失。然而，通过延髓外侧的通路失活消除了前庭-呼吸反应的兴奋性成分，但没有消除抑制性成分。对这些数据最简单的解释是，接受前庭核输入的MRF神经元与膈肌和腹部运动神经元形成抑制性连接，而在延髓尾部外侧走行的一条通路为这些运动神经元提供兴奋性前庭输入。
