Bao H, Bradley R M, Mistretta C M
Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109-1078, USA.
Brain Res Dev Brain Res. 1995 May 26;86(1-2):143-54. doi: 10.1016/0165-3806(95)00020-e.
There is no current understanding of the nature or time course of maturation of intrinsic electrophysiological properties for neurons in the gustatory region of the nucleus of the solitary tract (NST). Therefore, we used whole cell recordings in an in vitro slice preparation of the rat brainstem to characterize development of resting membrane, action potential and repetitive discharge properties of cells in gustatory NST at postnatal days 5, 10, 15, 20, and 30, and adult ages. Neurons were filled with Biocytin to verify location and characterize morphology. Membranes from younger neurons demonstrated a steeper current-voltage relation or higher input resistance, and a longer time constant than mature cells. Action potentials in younger cells had a slower rate of rise and were longer in duration. The afterhyperpolarization that typically follows the spike discharge usually had one phase in younger neurons, but was characterized by two or more phases in an increasing proportion of older cells. The repetitive discharge frequency in response to a range of depolarizing current pulses increased during development, and frequency/current plots were steeper in older compared with younger neurons. However, in all age groups there was clear accommodation of the discharge frequency. The greatest changes in resting membrane, action potential, and discharge properties were observed between P5 and P15, and mature values were generally reached by P20. At each postnatal age, neurons could be categorized in four neuron groups, based on the discharge pattern in response to a hyperpolarizing/depolarizing current protocol. Anatomical reconstructions indicated that although cells increased in overall dendritic expanse during development, neurons became less complex as illustrated by decreases in number of dendritic branch points, and in number and density of spines. The timing of major developmental differences in intrinsic electrical characteristics observed here is associated with a period of previously reported maturational changes in extracellular taste responses to number and concentration of chemical stimuli. However, further alterations in extracellular taste responses proceed after apparent maturation of intrinsic neural properties.
目前对于孤束核（NST）味觉区域神经元内在电生理特性的成熟本质或时间进程尚无了解。因此，我们在大鼠脑干的体外脑片制备中使用全细胞记录，以表征出生后第5、10、15、20、30天以及成年期味觉NST中细胞的静息膜电位、动作电位和重复放电特性。用生物胞素填充神经元以验证其位置并表征形态。较年轻神经元的膜表现出比成熟细胞更陡峭的电流 - 电压关系或更高的输入电阻，以及更长的时间常数。较年轻细胞的动作电位上升速率较慢且持续时间更长。通常跟随动作电位发放的超极化后电位在较年轻神经元中通常有一个阶段，但在比例不断增加的较老细胞中其特征为两个或更多阶段。在发育过程中，对一系列去极化电流脉冲的重复放电频率增加，并且较老神经元的频率/电流图比年轻神经元更陡峭。然而，在所有年龄组中，放电频率都有明显的适应性变化。在静息膜电位、动作电位和放电特性方面观察到的最大变化发生在出生后第5天至第15天之间，并且通常在出生后第20天达到成熟值。在每个出生后年龄，根据对超极化/去极化电流方案的放电模式，神经元可分为四类。解剖重建表明，尽管在发育过程中细胞的总体树突范围增加，但神经元变得不那么复杂，这表现为树突分支点数量以及棘突数量和密度的减少。此处观察到的内在电特性主要发育差异的时间与先前报道的细胞外味觉对化学刺激数量和浓度的成熟变化时期相关。然而，在内在神经特性明显成熟后，细胞外味觉反应会进一步发生变化。
