Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, FL 32610, USA.
Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, FL 32610, USA.
Exp Neurol. 2021 Apr;338:113609. doi: 10.1016/j.expneurol.2021.113609. Epub 2021 Jan 15.
Although cervical spinal cord injury (cSCI) disrupts bulbo-spinal serotonergic projections, partial recovery of spinal serotonergic innervation below the injury site is observed after incomplete cSCI. Since serotonin contributes to functional recovery post-injury, treatments to restore or accelerate serotonergic reinnervation are of considerable interest. Intermittent hypoxia (IH) was reported to increase serotonin innervation near respiratory motor neurons in spinal intact rats, and to improve function after cSCI. Here, we tested the hypotheses that spontaneous serotonergic reinnervation of key respiratory (phrenic and intercostal) motor nuclei: 1) is partially restored 12 weeks post C2 hemisection (C2Hx); 2) is enhanced by IH; and 3) results from sprouting of spared crossed-spinal serotonergic projections below the site of injury. Serotonin was assessed via immunofluorescence in male Sprague Dawley rats with and without C2Hx (12 wks post-injury); individual groups were exposed to 28 days of: 1) normoxia; 2) daily acute IH (dAIH28: 10, 5 min 10.5% O2 episodes per day; 5 min normoxic intervals); 3) mild chronic IH (IH28-5/5: 5 min 10.5% O2 episodes; 5 min intervals; 8 h/day); or 4) moderate chronic IH (IH28-2/2: 2 min 10.5% O2 episodes; 2 min intervals; 8 h/day), simulating IH experienced during moderate sleep apnea. After C2Hx, the number of ipsilateral serotonergic structures was decreased in both motor nuclei, regardless of IH protocol. However, serotonergic structures were larger after C2Hx in both motor nuclei, and total serotonin immunolabeling area was increased in the phrenic motor nucleus but reduced in the intercostal motor nucleus. Both chronic IH protocols increased serotonin structure size and total area in the phrenic motor nuclei of uninjured rats, but had no detectable effects after C2Hx. Although the functional implications of fewer but larger serotonergic structures are unclear, we confirm that serotonergic reinnervation is substantial following injury, but IH does not affect the extent of reinnervation.
尽管颈脊髓损伤 (cSCI) 破坏了延髓-脊髓 5-羟色胺能投射，但在不完全性 cSCI 后，损伤部位以下的脊髓 5-羟色胺能神经支配会部分恢复。由于 5-羟色胺有助于损伤后的功能恢复，因此恢复或加速 5-羟色胺再支配的治疗方法具有相当大的意义。间歇性低氧 (IH) 已被报道可增加脊髓完整大鼠呼吸运动神经元附近的 5-羟色胺神经支配，并改善 cSCI 后的功能。在这里，我们测试了以下假设：1）在 C2 半切（C2Hx）后 12 周，关键呼吸（膈神经和肋间肌）运动核中的自发 5-羟色胺能再支配部分恢复；2）IH 增强；3）损伤部位以下交叉脊髓 5-羟色胺能投射的发芽导致。通过免疫荧光评估雄性 Sprague Dawley 大鼠有无 C2Hx（损伤后 12 周）的 5-羟色胺；单独的组接受 28 天的：1）常氧；2）每日急性 IH（dAIH28：每天 10.5%O2 发作 10 次，每次 5 分钟；5 分钟常氧间隔）；3）轻度慢性 IH（IH28-5/5：5 分钟 10.5%O2 发作；5 分钟间隔；每天 8 小时）；或 4）中度慢性 IH（IH28-2/2：2 分钟 10.5%O2 发作；2 分钟间隔；每天 8 小时），模拟中度睡眠呼吸暂停期间经历的 IH。在 C2Hx 后，无论 IH 方案如何，两个运动核中的同侧 5-羟色胺结构数量均减少。然而，在两个运动核中，C2Hx 后 5-羟色胺结构更大，膈神经运动核中的总 5-羟色胺免疫标记面积增加，但肋间肌运动核中的面积减少。两种慢性 IH 方案均增加了未受伤大鼠膈神经运动核中 5-羟色胺结构的大小和总面积，但在 C2Hx 后没有可检测到的影响。虽然结构数量较少但较大的 5-羟色胺结构的功能意义尚不清楚，但我们确认损伤后 5-羟色胺能再支配是大量的，但 IH 不会影响再支配的程度。
