Study of verification and origin of a novel medullary respiratory neuron group (para-facial respiratory group)

本研究的目的是揭示新的延髓呼吸神经元群（para-facial respiratory group，pFRG ; Onimaru & Homma，2003）的细胞水平实体（例如，分布、形态、生理和药理学特征）和功能。对于该分析，我们使用从新生大鼠分离的脑干-脊髓制备物。结果表明：（1）pFRG主要由吸气前（Pre-I）神经元组成。2)pFRG/Pre-I神经元的细胞索马位于面神经核水平，靠近腹侧面，软脑膜下方。3)μ-阿片受体激动剂DAMGO不抑制pFRG/Pre-I神经元的活动。4)pFRG/Pre-I神经元的活动反映在面神经活动中。5)在适当的实验条件下，将延髓横切于pFRG和前Botzinger复合体（PBC）之间，每一节段的延髓均能产生自发节律性活动。6)这些节律性活动对应于pFRG/Pre-I（在吻侧阻滞中）和PBC/吸气（在尾侧阻滞中）神经元活动。7)通过增加细胞外钾离子浓度、应用持久性钠通道阻滞剂（利鲁唑）或降低CO2压力来抑制pFRG/Pre-I神经元的节律，而PBC/吸气活动对这些操作更具抵抗力。8)当延髓被切断通过中线，节律活动的pFRG/前I神经元在右侧和左侧的延髓独立维持，但PBC-吸气活动停止。这些结果表明，pFRG/Pre-I神经元产生节律的机制与PBC-吸气神经元有本质的不同，并提示在正常（或较低）外钾浓度的正常实验条件下，pFRG/Pre-I神经元决定基本的呼吸节律。

Aim of this study was to reveal cellular level entity (e.g. distribution, morphology, physiological and pharmacological characteristics) and the function of novel medullary respiratory neuron group (para-facial respiratory group, pFRG ; Onimaru ＆ Homma, 2003). For this analysis, we used the brainstem-spinal cord preparation isolated form newborn rats. The present study revealed the following : 1)The pFRG consisted predominantly of pre-inspiratory (Pre-I) neurons. 2)Cell soma of the pFRG/Pre-I neuron was located close to the ventral surface, immediately below the pia membrane, at the level of the facial nucleus. 3)Activity of the pFRG/Pre-I neurons was not inhibited by μ-opiate agonist, DAMGO. 4)Activity of the pFRG/Pre-I neurons was reflected in the facial nerve activity. 5)When the medulla was transversely cut between the pFRG and the pre-Botzinger complex (PBC), each block of the medulla could produced spontaneous rhythmic activity under the appropriate experimental conditions. 6)These rhythmic activity corresponded to the pFRG/Pre-I (in the rostral block) and PBC/inspiratory (in the caudal block) neuron activity. 7)Rhythm of the pFRG/Pre-I neurons was depressed by increasing extracellular potassium ion concentration, application of a persistent sodium channel blocker (riluzole) or lowering CO2 pressure, whereas the PBC/inspiratory activity was more resistant to these manipulations. 8)When the medulla was cut through the midline, rhythmic activity of the pFRG/Pre-I neurons was maintained independently in the right and left medulla, but PBC-inspiratory activity was stopped. These findings showed that mechanism of rhythm generation by the pFRG/Pre-I neurons are essentially different from that of PBC-inspiratory neurons and suggested that the pFRG/Pre-I neurons determine basic respiratory rhythm under normal experimental condition with normal (or lower) external potassium concentration.