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

本研究旨在揭示新型髓质呼吸神经元群（para-facial respiratory group, pFRG; Onimaru & Homma, 2003）的细胞水平实体（如分布、形态、生理和药理特征）和功能。为了进行分析，我们使用了从新生大鼠身上分离的脑干-脊髓制备物。本研究发现：1)pFRG主要由吸气前神经元（Pre-I）组成。2) pFRG/Pre-I神经元的胞体位于靠近腹面、紧靠虹膜下方的面核水平。3) μ-阿片激动剂DAMGO未抑制pFRG/Pre-I神经元的活性。4) pFRG/Pre-I神经元的活性反映在面神经活动中。5)当髓质在pFRG和pre-Botzinger复合物（PBC）之间横切时，在适当的实验条件下，每一块髓质都能产生自发的节律性活动。6)这些节律性活动与pFRG/Pre-I（在吻侧区）和PBC/吸气（在尾侧区）神经元活动相对应。7)增加细胞外钾离子浓度、应用持续性钠通道阻滞剂（利鲁唑）或降低CO2压力均可抑制pFRG/Pre-I神经元的节律，而PBC/吸气活动对这些操作的抵抗力更强。8)髓质中线切开后，左右髓质pFRG/Pre-I神经元的节律性活动保持独立，pbc -吸气活动停止。这些结果表明pFRG/Pre-I神经元的节律产生机制与pbc -吸气神经元的节律产生机制有本质区别，提示pFRG/Pre-I神经元在正常（或较低）外钾浓度的正常实验条件下决定基本呼吸节律。

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.