Mantilla Carlos B, Gransee Heather M, Zhan Wen-Zhi, Sieck Gary C
Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; and
Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota.
J Neurophysiol. 2017 Sep 1;118(3):1732-1738. doi: 10.1152/jn.00345.2017. Epub 2017 Jun 28.
Incomplete cervical spinal cord hemisection at C2 (SH) disrupts descending excitatory drive to phrenic motoneurons, paralyzing the ipsilateral diaphragm muscle. Spontaneous recovery over time is associated with increased phrenic motoneuron expression of glutamatergic -methyl-d-aspartate (NMDA) and serotonergic 5-HT2A receptors. We hypothesized that NMDA and 5-HT2A receptor-mediated neurotransmission play a role in ipsilateral diaphragm muscle activity post-SH. Adult male Sprague-Dawley rats were implanted with bilateral diaphragm EMG electrodes for chronic EMG recordings up to 28 days post-SH (SH 28D). The extent of recovery was calculated by peak root-mean-square (RMS) EMG amplitude. In all animals, absence of ipsilateral activity was verified at 3 days post-SH. Diaphragm EMG activity was also recorded during exposure to hypoxia-hypercapnia (10% O-5% CO). In SH animals displaying recovery of ipsilateral diaphragm EMG activity at SH 28D, cervical spinal cord segments containing the phrenic motor nucleus (C3-C5) were surgically exposed and either the NMDA receptor antagonist d-2-amino-5-phosphonovalerate (d-AP5; 100 mM, 30 μl) or 5-HT2A receptor antagonist ketanserin (40 mM, 30 μl) was instilled intrathecally. Following d-AP5, diaphragm EMG amplitude was reduced ipsilaterally, during both eupnea (42% of pre-d-AP5 value; = 0.007) and hypoxia-hypercapnia (31% of pre-d-AP5 value; = 0.015), with no effect on contralateral EMG activity or in uninjured controls. Treatment with ketanserin did not change ipsilateral or contralateral RMS EMG amplitude in SH animals displaying recovery at SH 28D. Our results suggest that spinal glutamatergic NMDA receptor-mediated neurotransmission plays an important role in ipsilateral diaphragm muscle activity after cervical spinal cord injury. Spontaneous recovery following C2 spinal hemisection (SH) is associated with increased phrenic motoneuron expression of glutamatergic and serotonergic receptors. In this study, we show that pharmacological inhibition of glutamatergic -methyl-d-aspartate (NMDA) receptors blunts ipsilateral diaphragm activity post-SH. In contrast, pharmacological inhibition of serotonergic 5-HT2A receptors does not change diaphragm EMG activity post-SH. Our results suggest that NMDA receptor-mediated glutamatergic neurotransmission plays an important role in enhancing rhythmic respiratory-related diaphragm activity after spinal cord injury.
C2节段的不完全颈脊髓半横断损伤（SH）会破坏对膈运动神经元的下行兴奋性驱动，导致同侧膈肌麻痹。随着时间的推移，自发恢复与膈运动神经元中谷氨酸能N-甲基-D-天冬氨酸（NMDA）和5-羟色胺能5-HT2A受体的表达增加有关。我们假设NMDA和5-HT2A受体介导的神经传递在SH后同侧膈肌活动中起作用。成年雄性Sprague-Dawley大鼠植入双侧膈肌肌电图电极，用于在SH后长达28天（SH 28D）进行慢性肌电图记录。通过肌电图峰值均方根（RMS）幅度计算恢复程度。在所有动物中，在SH后3天证实同侧无活动。在暴露于低氧-高碳酸血症（10% O₂-5% CO₂）期间也记录膈肌肌电图活动。在SH 28D时显示同侧膈肌肌电图活动恢复的SH动物中，手术暴露包含膈运动核的颈脊髓节段（C3-C5），并鞘内注入NMDA受体拮抗剂D-2-氨基-5-磷酸戊酸（D-AP5；100 mM，30 μl）或5-HT2A受体拮抗剂酮色林（40 mM，30 μl）。注入D-AP5后，在平静呼吸（为注入D-AP5前值的42%；P = 0.007）和低氧-高碳酸血症期间（为注入D-AP5前值的31%；P = 0.015），同侧膈肌肌电图幅度均降低，对侧肌电图活动或未受伤对照无影响。在SH 28D时显示恢复的SH动物中，用酮色林治疗未改变同侧或对侧RMS肌电图幅度。我们的结果表明，脊髓谷氨酸能NMDA受体介导的神经传递在颈脊髓损伤后同侧膈肌活动中起重要作用。C2脊髓半横断损伤（SH）后的自发恢复与膈运动神经元中谷氨酸能和5-羟色胺能受体的表达增加有关。在本研究中，我们表明，药理学抑制谷氨酸能N-甲基-D-天冬氨酸（NMDA）受体会减弱SH后同侧膈肌活动。相反，药理学抑制5-羟色胺能5-HT2A受体不会改变SH后膈肌肌电图活动。我们的结果表明，NMDA受体介导的谷氨酸能神经传递在增强脊髓损伤后与呼吸相关的节律性膈肌活动中起重要作用。
