Yajima Y, Hayashi Y
Department of Physiology, Hyogo College of Medicine, Nishinomiya, Japan.
Neuroscience. 1997 Aug;79(4):1079-88. doi: 10.1016/s0306-4522(97)00012-2.
GABA-sensitive ambiguus motoneurons were investigated by microiontophoretic application of GABAergic drugs including bicuculline and muscimol in alpha-chloralose- and urethane-anaesthetized rats. Ambiguus motoneurons were activated by recurrent laryngeal nerve stimulation through a small cuff electrode and identified as laryngeal motoneurons when they met the conventional criteria for antidromic activation. GABA(A) antagonist, bicuculline, and its agonist, muscimol, were iontophoretized on ambiguus motoneurons through a three-multibarrel electrode glued to the recording microelectrode. One-hundred and nineteen out of 155 neurons sampled from the loose formation and its vicinity were found to be respiratory neurons, most of which were inspiratory neurons. A small proportion (32 neurons) was classified as laryngeal motoneurons according to the criteria. A majority of laryngeal motoneurons was found to be GABA sensitive. Namely, application of GABA and its antagonist and agonist affected the antidromic spikes in a dose-dependent manner; GABA and muscimol usually decreased the amplitude and slowed the slope in the spike, whereas bicuculline, reversed these inhibitory effects. The dose-dependent relationships were limited exclusively to the measurements analysed in the negative-going phase but not in the positive-going phase in the antidromic spike. GABA and muscimol decreased but bicuculline increased the ratios to control in these measurements. The effects of distributions of the histograms shifting towards the opposite direction were statistically significant. The line of evidence suggests strongly that a majority of laryngeal motoneurons located in the nucleus ambiguus presumably possesses GABA(A) receptors on their postsynaptic membrane. These GABA-sensitive laryngeal motoneurons may receive inputs either from inhibitory interneurons subserving the reciprocal inhibition in the reflexive integration or from inhibitory respiratory interneurons which control the synchronized glottic movements during vocalization and respiration.
在α-氯醛糖和乌拉坦麻醉的大鼠中，通过微量离子电泳法施加包括荷包牡丹碱和蝇蕈醇在内的GABA能药物，对GABA敏感的疑核运动神经元进行了研究。通过一个小的袖带电极刺激喉返神经来激活疑核运动神经元，当它们符合逆向激活的传统标准时，被识别为喉运动神经元。通过粘贴在记录微电极上的三管电极，将GABA(A)拮抗剂荷包牡丹碱及其激动剂蝇蕈醇微量离子电泳到疑核运动神经元上。从松散结构及其附近采样的155个神经元中，有119个被发现是呼吸神经元，其中大多数是吸气神经元。根据标准，一小部分（32个神经元）被归类为喉运动神经元。发现大多数喉运动神经元对GABA敏感。也就是说，施加GABA及其拮抗剂和激动剂以剂量依赖性方式影响逆向动作电位；GABA和蝇蕈醇通常会降低动作电位的幅度并减缓其上升斜率，而荷包牡丹碱则会逆转这些抑制作用。剂量依赖性关系仅局限于逆向动作电位负向阶段的测量分析，而正向阶段则没有。在这些测量中，GABA和蝇蕈醇降低了与对照的比率，而荷包牡丹碱则增加了该比率。直方图分布向相反方向移动的影响具有统计学意义。这一系列证据有力地表明，位于疑核中的大多数喉运动神经元的突触后膜上可能存在GABA(A)受体。这些对GABA敏感的喉运动神经元可能接收来自在反射整合中起相互抑制作用的抑制性中间神经元的输入，或者来自在发声和呼吸过程中控制声门同步运动的抑制性呼吸中间神经元的输入。
