Department of Physical Therapy, University of Florida, Gainesville, Florida.
McKnight Brain Institute, University of Florida, Gainesville, Florida.
J Neurophysiol. 2020 Mar 1;123(3):993-1003. doi: 10.1152/jn.00708.2019. Epub 2020 Jan 15.
Phrenic long-term facilitation (LTF) is a sustained increase in phrenic motor output occurring after exposure to multiple (but not single) hypoxic episodes. Ampakines are a class of drugs that enhance AMPA receptor function. Ampakines can enhance expression of neuroplasticity, and the phrenic motor system is fundamentally dependent on excitatory glutamatergic currents. Accordingly, we tested the hypothesis that combining ampakine pretreatment with a single brief hypoxic exposure would result in phrenic motor facilitation lasting well beyond the period of hypoxia. Phrenic nerve output was recorded in urethane-anesthetized, ventilated, and vagotomized adult Sprague-Dawley rats. Ampakine CX717 (15 mg/kg iv; = 8) produced a small increase in phrenic inspiratory burst amplitude and frequency, but values quickly returned to predrug baseline. When CX717 was followed 2 min later by a 5-min exposure to hypoxia ( = 8; ~45 mmHg), a persistent increase in phrenic inspiratory burst amplitude (i.e., phrenic motor facilitation) was observed up to 60 min posthypoxia (103 ± 53% increase from baseline). In contrast, when hypoxia was preceded by vehicle injection (10% 2-hydroxypropyl-β-cyclodextrin; = 8), inspiratory phrenic bursting was similar to baseline values at 60 min. Additional experiments with another ampakine (CX1739, 15 mg/kg) produced comparable results. We conclude that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation. This targeted approach for enhancing respiratory neuroplasticity may have value in the context of hypoxia-based neurorehabilitation strategies. A single brief episode of hypoxia (e.g., 3-5 min) does not evoke long-lasting increases in respiratory motor output after the hypoxia is concluded. Ampakines are a class of drugs that enhance AMPA receptor function. We show that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation after the acute hypoxic episode.
膈神经长期易化(LTF)是在多次(但不是单次)低氧暴露后膈神经运动输出持续增加的现象。Ampakines 是一类增强 AMPA 受体功能的药物。Ampakines 可以增强神经可塑性的表达,而膈神经运动系统基本依赖兴奋性谷氨酸能电流。因此,我们假设在单次短暂低氧暴露前给予 Ampakine 预处理,会导致膈神经运动易化持续时间远超低氧期。在麻醉、通气和迷走神经切断的成年 Sprague-Dawley 大鼠中记录膈神经输出。Ampakine CX717(静脉注射 15 mg/kg;n=8)使膈神经吸气爆发幅度和频率略有增加,但很快恢复到预给药基线。当 CX717 在 2 分钟后紧接着进行 5 分钟的低氧暴露(n=8;~45mmHg)时,观察到膈神经吸气爆发幅度的持续增加(即膈神经运动易化),直至低氧后 60 分钟(基线增加 103±53%)。相比之下,当低氧前给予载体注射(10% 2-羟丙基-β-环糊精;n=8)时,60 分钟时吸气膈神经爆发与基线值相似。另一 Ampakine(CX1739,15mg/kg)的额外实验产生了类似的结果。我们得出结论,低剂量 Ampakine 治疗与单次短暂低氧暴露相结合可引发持续的膈神经运动易化。这种针对增强呼吸神经可塑性的靶向方法可能在基于低氧的神经康复策略中具有价值。单次短暂的低氧暴露(例如 3-5 分钟)在低氧结束后不会引起呼吸运动输出的持久增加。Ampakines 是一类增强 AMPA 受体功能的药物。我们表明,低剂量 Ampakine 治疗与单次短暂低氧暴露相结合,可以在急性低氧发作后引发持续的膈神经运动易化。