Zhang W, Mifflin S W
Department of Pharmacology, University of Texas Health Science Center, San Antonio 78284-7764.
Am J Physiol. 1993 Aug;265(2 Pt 2):H770-3. doi: 10.1152/ajpheart.1993.265.2.H770.
The nucleus tractus solitarius (NTS) is the primary site of termination of arterial baroreceptor and chemoreceptor afferent fibers. Excitatory amino acid (EAA) receptors within NTS have been shown to play an important role in the mediation of arterial baroreceptor reflexes; however, the importance of EAA receptors within NTS in the mediation of arterial chemoreceptor reflexes remains controversial. Therefore, in chloralose-urethan-anesthetized, mechanically ventilated, paralyzed rats, 4 nmol of the broad-spectrum EAA receptor antagonist kynurenic acid (Kyn) was injected into the NTS to observe the effects of EAA receptor blockade on the pressor responses evoked by either activation of ipsilateral carotid body chemoreceptors (by close arterial injection of CO2-saturated bicarbonate) or electrical stimulation of ipsilateral carotid sinus nerve (CSN). Under control conditions, activation of carotid body chemoreceptors and CSN stimulation evoked increases in arterial pressure of 27 +/- 2 (n = 24 sites) and 28 +/- 3% (n = 8), respectively. Kyn microinjection into NTS significantly reduced the pressor responses evoked by activation of carotid body chemoreceptors and electrical stimulation of the CSN for 20 and 25 min, respectively. Attenuation of pressor responses evoked by chemoreceptor activation were maximal at 20 min post-Kyn injection (13 +/- 2%), whereas CSN-evoked pressor responses were maximally attenuated at 15 min (6 +/- 4%). Microinjection into NTS of 4 nmol of xanthurenic acid, a structural analogue of Kyn with no EAA receptor antagonist properties, had no effect on chemoreceptor reflexes. We conclude that EAA receptors within NTS play an important role in the mediation of arterial chemoreceptor reflexes.
孤束核（NTS）是动脉压力感受器和化学感受器传入纤维的主要终末部位。已证明NTS内的兴奋性氨基酸（EAA）受体在介导动脉压力感受器反射中起重要作用；然而，NTS内的EAA受体在介导动脉化学感受器反射中的重要性仍存在争议。因此，在氯醛糖-氨基甲酸乙酯麻醉、机械通气、麻痹的大鼠中，将4 nmol广谱EAA受体拮抗剂犬尿喹啉酸（Kyn）注入NTS，以观察EAA受体阻断对同侧颈动脉体化学感受器激活（通过动脉内注射CO2饱和碳酸氢盐）或同侧颈动脉窦神经（CSN）电刺激所诱发的升压反应的影响。在对照条件下，颈动脉体化学感受器激活和CSN刺激分别引起动脉血压升高27±2（n = 24个部位）和28±3%（n = 8）。向NTS内微量注射Kyn可分别在20分钟和25分钟内显著降低由颈动脉体化学感受器激活和CSN电刺激所诱发的升压反应。化学感受器激活所诱发的升压反应减弱在注射Kyn后20分钟时最大（13±2%），而CSN诱发的升压反应在15分钟时最大程度减弱（6±4%）。向NTS内微量注射4 nmol黄尿酸（一种无EAA受体拮抗特性的Kyn结构类似物）对化学感受器反射无影响。我们得出结论，NTS内的EAA受体在介导动脉化学感受器反射中起重要作用。
