Developmental mechanisms from tetal to neonatal type of respiratory center as a functional neuron network

我们分析了大鼠胎儿髓质呼吸神经元的内在爆发特性。在显示胎儿型c4吸气爆发模式的E17-20制剂中，约60%的吸气神经元表现出电压依赖性的爆发活动。在E19制剂中，破裂神经元的输入电阻明显高于非破裂细胞。与非破裂细胞相比，破裂神经元的膜电容更低（但不显著）。由于在低Ca2+/高Mg2+溶液中，爆发神经元仍然保持爆发活性，我们认为它们具有内在的爆发特性。利用光学记录，用电压敏感染料染色，分析胎儿腹侧髓质呼吸神经元网络的活动。在E20/21制剂中，呼吸神经元活动出现在吻侧腹外侧髓质（面旁呼吸组，pFRG）的有限区域，并主要在尾侧传播。然后，在吸气期，活动高峰出现在尾侧腹外侧髓质（CVLM），并在吻侧主要出现在面核的外侧和内侧区域。这种模式与新生大鼠制剂基本相同。相比之下，在所有El7和大部分El8制剂中，呼吸活动首先出现在CVLM区域，与吸气爆发的开始一致，然后向体侧传播。依次在整个面核区域出现强活动，并在C4吸气活动终止后持续1-3秒。在一半的E19制剂中，呼吸活动从pFRG（新生儿型）开始，而在其他（胎儿型）中，呼吸活动从CVLM开始。然而，即使在显示新生儿型-网络活动模式的制剂中，C4吸气活动为胎儿型，显示短的爆发持续时间。我们认为，初级节律产生网络和时空模式先于产生吸气活动的神经元网络发展到新生儿类型。少

We analyzed intrinsic burst generating property of respiratory neurons in the medulla of the rat fetus. In the E17-20 preparations that showed the fetal type-C4 inspiratory burst pattern, about 60% of inspiratory neurons exhibited voltage-dependent burst activity. In E19 preparations, the input resistance of the bursting neurons was significantly higher than that of non-bursting cells. Membrane capacitance tended to be lower (but not significant) in the bursting neurons than in the non-bursting cells. Since the bursting neurons still kept the bursting activity in the low Ca2+/high Mg2+ solution, we concluded that they possess intrinsic burst generating properties.Using optical recordings, we analyzed respiratory neuron network activity in the ventral medulla of fetus stained with voltage-sensitive dye. In E20/21 preparations, respiratory neuron activity appeared in the limited area of the rostral ventrolateral medulla (para-facial respiratory group, pFRG), and propagated mainly caudall … More y. Then, during the inspiratory phase, the peak of activity was detected, caudally, in the caudal ventrolateral medulla (CVLM) and, rostrally, in the mainly lateral and medial region of the facial nucleus. Such pattern was basically identical to that of neonatal rat preparations. In contrast, in all of El7 and most of El8 preparations, respiratory activity first appeared in the CVLM region, coincidently with the start of inspiratory burst, and then propagated rostrally. Successively, strong activity appeared in the whole region of the facial nucleus and continued 1-3 sec after termination of C4 inspiratory activity. In half of E19 preparations, respiratory activity started from the pFRG (neonatal type), whereas it started from the CVLM inothers (fetal type). However, even in the preparations that showed the neonatal type-network activity pattern, C4 inspiratory activity was the fetal type showing short burst duration. We suggest that the primary rhythm generating network and the spatio-temporal pattern develops to the neonatal type before the neuron network generating inspiratory activity does. Less