King M S, Wang L, Bradley R M
Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109-1078.
Brain Res. 1993 Aug 13;619(1-2):120-30. doi: 10.1016/0006-8993(93)91603-p.
Whole-cell patch recordings of neurons in the rostral (gustatory) nucleus tractus solitarius (rNTS) were performed in a brain slice preparation from rat medulla. Neural responses to brief applications (10-45 s) of substance P (SP), via a constant superfusion apparatus, were recorded. SP transiently depolarized 80 of 117 (68%) rNTS neurons in a dose-dependent manner. Sub-micromolar concentrations of SP had potent excitatory effects, and the half maximal response occurred at 0.6 microM. The depolarizing effect of SP was accompanied by an increase in input resistance in 81% of the responsive neurons. The excitatory effects of SP persisted in low Ca2+ (0.2 mM) and high Mg2+ (12 mM) saline as well as in the presence of 2 microM TTX (n = 5 for each), suggesting direct postsynaptic action on the recorded neurons. SP also hyperpolarized 4 neurons (4%) and had no effect on 33 neurons (28%). Each of the 4 neurons which were hyperpolarized by SP showed a decrease in input resistance. A more detailed assessment of the types of neurons in the rNTS which respond to SP was also conducted. Neurons were separated into 4 electrophysiological groups on the basis of their repetitive firing pattern induced by a hyperpolarizing and depolarizing current injection paradigm. Neurons belonging to each of the 4 electrophysiological groups responded to SP. Eighteen neurons, which were filled with 1% biocytin during recording, were categorized as ovoid, multipolar or fusiform based on their morphological characteristics. SP excited all 3 morphological types of neurons in similar proportion. These results suggest that SP is an excitatory neurotransmitter in the rNTS. The effects of SP are not restricted to a particular neuron type defined either biophysically or morphologically. The implications of these results on the possible role of SP in processing gustatory and somatosensory information within the rNTS are discussed.
在大鼠延髓脑片标本上，对吻侧（味觉）孤束核（rNTS）中的神经元进行全细胞膜片钳记录。通过恒流灌注装置，记录对短暂施加（10 - 45秒）P物质（SP）的神经反应。SP以剂量依赖性方式使117个rNTS神经元中的80个（68%）发生瞬时去极化。亚微摩尔浓度的SP具有强大的兴奋作用，半数最大反应出现在0.6微摩尔时。SP的去极化作用伴随着81%的反应性神经元输入电阻增加。SP的兴奋作用在低钙（0.2毫摩尔）和高镁（12毫摩尔）盐溶液中以及存在2微摩尔河豚毒素（每种情况n = 5）时依然存在，提示对记录的神经元有直接的突触后作用。SP还使4个神经元（4%）发生超极化，对33个神经元（28%）无影响。被SP超极化的4个神经元中的每一个都表现出输入电阻降低。还对rNTS中对SP有反应的神经元类型进行了更详细的评估。根据由超极化和去极化电流注入模式诱导的重复放电模式，将神经元分为4个电生理组。属于4个电生理组中的每一组的神经元都对SP有反应。在记录过程中用1%生物胞素填充的18个神经元，根据其形态特征被分类为卵圆形、多极形或梭形。SP以相似比例兴奋所有3种形态类型的神经元。这些结果表明SP是rNTS中的一种兴奋性神经递质。SP的作用不限于通过生物物理或形态学定义的特定神经元类型。讨论了这些结果对SP在rNTS内处理味觉和躯体感觉信息中可能作用的意义。
