长时间抑制呼吸神经活动引起膈神经振幅的持久增加,称为不活动诱导膈运动促进(iPMF)。在不活动(iIMF)后,吸气肋间神经活动也会短暂发生促进作用。颈脊髓中的非典型PKC活性是iPMF和iIMF所必需的,但位点和相关PKC亚型未知。这里,我们使用RNA干扰来检验下述假设:膈运动神经元内的非典型PKCζ同工型对于iPMF是必需的,但是肋间运动神经元内的PKCζ对于短暂性iIMF是不必要的。在大鼠中进行胸膜内siRNA注射以敲除膈和肋间运动神经元PKCζmRNA(siPKCζ)。对照大鼠接受非靶向siRNA(NTsi)或siPKCθ;其他形式的呼吸运动可塑性需要PKCθ。在麻醉下测量膈神经和肋间外(T2)EMG活动,机械通气大鼠暴露于适度低碳酸血症引起的呼吸神经不活动(即神经呼吸暂停)30分钟,或类似的持续时间没有神经呼吸暂停(时间控制)。神经呼吸暂停后60分钟与时间对照(-3±3%)相比,NTsi(68±10%)和siPKCθ(57±8%)的膈爆发幅度从基线增加。相比之下,siPKCζ实际上废除了iPMF(5±4%)。虽然iIMF在所有组中都是短暂的,siPKCζ在神经呼吸暂停后5分钟(50±21%)与NTsi(97±22%)和siPKCθ(103±20%)减弱iIMF。神经不活动抬高膈,而不是肋间对高二氧化碳的反应-siPKCζ阻断了这种作用。我们得出结论,膈运动神经元PKCζ是持久iPMF所必需的,而肋间运动神经元PKCζ有助于,但对于暂时的iIMF不是必需的。
Prolonged inhibition of respiratory neural activity elicits a long-lasting increase in
phrenic nerve amplitude once respiratory neural activity is restored. Such long-lasting facilitation represents a form of respiratory motor plasticity known as inactivity-induced
phrenic motor facilitation (iPMF). Although facilitation also occurs in inspiratory intercostal nerve activity after diminished respiratory neural activity (iIMF), it is of shorter duration. Atypical PKC activity in the cervical spinal cord is necessary for iPMF and iIMF, but the site and specific isoform of the relevant atypical PKC are unknown. Here, we used RNA interference to test the hypothesis that the zeta atypical PKC isoform (PKCζ) within phrenic motor neurons is necessary for iPMF but PKCζ within intercostal motor neurons is unnecessary for transient iIMF. Intrapleural injections of siRNAs targeting PKCζ (siPKCζ) to knock down PKCζ mRNA within
phrenic and intercostal motor neurons were made in rats. Control rats received a nontargeting siRNA (NTsi) or an active siRNA pool targeting a novel PKC isoform, PKCθ (siPKCθ), which is required for other forms of respiratory motor plasticity. Phrenic nerve burst amplitude and external intercostal (T2) electromyographic (EMG) activity were measured in anesthetized and mechanically ventilated rats exposed to 30 min of respiratory neural inactivity (i.e., neural apnea) created by modest hypocapnia (20 min) or a similar recording duration without neural apnea (time control).
Phrenic burst amplitude was increased in rats treated with NTsi (68 ± 10% baseline) and siPKCθ (57 ± 8% baseline) 60 min after neural apnea vs. time control rats (-3 ± 3% baseline), demonstrating iPMF. In contrast, intrapleural siPKCζ virtually abolished iPMF (5 ± 4% baseline). iIMF was transient in all groups exposed to neural apnea; however, intrapleural siPKCζ attenuated iIMF 5 min after neural apnea (50 ± 21% baseline) vs. NTsi (97 ± 22% baseline) and siPKCθ (103 ± 20% baseline). Neural inactivity elevated the
phrenic, but not intercostal, responses to hypercapnia, an effect that was blocked by siPKCζ. We conclude that PKCζ within phrenic motor neurons is necessary for long-lasting iPMF, whereas intercostal motor neuron PKCζ contributes to, but is not necessary for, transient iIMF.NEW & NOTEWORTHY We report important new findings concerning the mechanisms regulating a form of spinal neuroplasticity elicited by prolonged inhibition of respiratory neural activity, inactivity-induced phrenic motor facilitation (iPMF). We demonstrate that the atypical PKC isoform PKCζ within phrenic motor neurons is necessary for long-lasting iPMF, whereas intercostal motor neuron PKCζ contributes to, but is not necessary for, transient inspiratory intercostal facilitation. Our findings are novel and advance our understanding of mechanisms contributing to phrenic motor plasticity.