Fu Congrui, Xue Jinyu, Wang Ri, Chen Jinting, Ma Lan, Liu Yixian, Wang Xuejiao, Guo Fang, Zhang Yi, Zhang Xiangjian, Wang Sheng
Department of Physiology, Hebei Medical University, Shijiazhuang, Hebei, China.
Department of Respiration, Hebei Chest Hospital, Shijiazhuang, Hebei, China.
J Physiol. 2017 Jul 15;595(14):4973-4989. doi: 10.1113/JP274437. Epub 2017 Jun 16.
Central hypercapnic hypoventilation is highly prevalent in children suffering from congenital central hypoventilation syndrome (CCHS). Mutations of the gene for paired-like homeobox 2b (Phox2b) are aetiologically associated with CCHS and Phox2b is present in central components of respiratory chemoreflex, such as the nucleus tractus solitarius (NTS). Injection of the neurotoxin substance P-saporin into NTS destroys Phox2b-expressing neurons. Impaired hypercapnic ventilatory response caused by this neurotoxin is attributable to a loss of CO -sensitive Phox2b-expressing NTS neurons. A subgroup of Phox2b-expressing neurons exhibits intrinsic chemosensitivity. A background K channel-like current is partially responsible for such chemosensitivity in Phox2b-expressing neurons. The present study helps us better understand the mechanism of respiratory deficits in CCHS and potentially locates a brainstem site for development of precise clinical intervention.
The nucleus tractus solitarius (NTS) neurons have been considered to function as central respiratory chemoreceptors. However, the common molecular marker defined for these neurons remains unknown. The present study investigated whether paired-like homeobox 2b (Phox2b)-expressing NTS neurons are recruited in hypercapnic ventilatory response (HCVR) and whether these neurons exhibit intrinsic chemosensitivity. HCVR was assessed using whole body plethysmography and neuronal chemosensitivity was examined by patch clamp recordings in brainstem slices or dissociated neurons from Phox2b-EGFP transgenic mice. Injection of the neurotoxin substance P-saporin (SSP-SAP) into NTS destroyed Phox2b-expressing neurons. Minute ventilation and tidal volume were both reduced by 13% during exposure to 8% CO in inspired air when ∼13% of the Phox2b-expressing neurons were eliminated. However, a loss of ∼18% of these neurons was associated with considerable decreases in minute ventilation by ≥18% and in tidal volume by≥22% when challenged by ≥4% CO . In both cases, breathing frequency was unaffected. Most CO -activated neurons were immunoreactive to Phox2b. In brainstem slices, ∼43% of Phox2b-expressing neurons from Phox2b-EGFP mice displayed a sustained or transient increase in firing rate during physiological acidification (pH 7.0 or 8% CO ). Such a response was also present in dissociated neurons in favour of an intrinsic property. In voltage clamp recordings, a background K channel-like current was found in a subgroup of Phox2b-expressing neurons. Thus, the respiratory deficits caused by injection of SSP-SAP into the NTS are attributable to proportional lesions of CO /H -sensitive Phox2b-expressing neurons.
中枢性高碳酸血症性通气不足在患有先天性中枢性通气不足综合征（CCHS）的儿童中非常普遍。配对样同源盒2b（Phox2b）基因突变在病因上与CCHS相关，并且Phox2b存在于呼吸化学反射的中枢成分中，如孤束核（NTS）。将神经毒素P物质 - 皂草素注射到NTS中会破坏表达Phox2b的神经元。这种神经毒素引起的高碳酸血症通气反应受损归因于对CO2敏感的表达Phox2b的NTS神经元的丧失。表达Phox2b的神经元亚群表现出内在化学敏感性。一种背景钾通道样电流部分负责表达Phox2b的神经元中的这种化学敏感性。本研究有助于我们更好地理解CCHS中呼吸缺陷的机制，并可能确定一个脑干部位用于精确临床干预的开发。
孤束核（NTS）神经元被认为起着中枢呼吸化学感受器的作用。然而，为这些神经元定义的共同分子标记仍然未知。本研究调查了表达配对样同源盒2b（Phox2b）的NTS神经元是否参与高碳酸血症通气反应（HCVR），以及这些神经元是否表现出内在化学敏感性。使用全身体积描记法评估HCVR，并通过脑干切片或来自Phox2b - EGFP转基因小鼠的解离神经元的膜片钳记录来检查神经元化学敏感性。将神经毒素P物质 - 皂草素（SSP - SAP）注射到NTS中会破坏表达Phox2b的神经元。当约13%的表达Phox2b的神经元被消除时，在吸入空气中暴露于8% CO2期间，分钟通气量和潮气量均降低了13%。然而，当受到≥4% CO2刺激时，这些神经元丧失约18%与分钟通气量≥18%和潮气量≥22%的显著降低相关。在这两种情况下，呼吸频率均未受影响。大多数CO2激活的神经元对Phox2b具有免疫反应性。在脑干切片中，来自Phox2b - EGFP小鼠的约43%表达Phox2b的神经元在生理酸化（pH 7.0或8% CO2）期间表现出放电率的持续或短暂增加。这种反应在解离神经元中也存在，支持其内在特性。在电压钳记录中，在表达Phox2b的神经元亚群中发现了一种背景钾通道样电流。因此，将SSP - SAP注射到NTS中引起的呼吸缺陷归因于对CO2 / H +敏感的表达Phox2b的神经元的成比例损伤。
