Graded and dynamic reflex summation of myelinated and unmyelinated rat aortic baroreceptors
Graded and dynamic reflex summation of myelinated and unmyelinated rat aortic baroreceptors
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DOI：
10.1152/ajpregu.1999.277.3.r748
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发表时间：
1999-09-01
影响因子：
2.8
通讯作者：
Andresen, MC
中科院分区：
文献类型：
--
作者：
Fan, W;Schild, JH;Andresen, MC
无髓鞘(C)和有髓鞘(A)压力受体（BR）轴突存在于大鼠主动脉降压神经（ADN）中。采用ADN分级电激活和阳极传导阻断，通过平均动脉压（MAP）和心率（HR）的变化来评估麻醉大鼠的反射反应。我们测试了c型BR输入在低频时有效的假设，因为它们的数量超过a型。阳极电流（I-an）可逆地消除了所有MAP和HR对a选择性刺激的反应。高强度激活所有ADN axone (A + C)，并在较低频率（10 hz ADN刺激）下降低MAP。尽管每秒的电击次数相同，但脉冲模式显著增强了A-选择性反射反应，而不是c -选择性反射反应。a选择性刺激即使在200hz时也不能引起明显的心动过缓。最大强度刺激加I-an （C选择性）比不加I-an （A+C）诱发的心动过缓更少，表明MAP反应的超加性和不同于闭塞性和。然而，C型BRs与所有a型BRs的激活数量减少表明反射性心动过缓反应中a - C之间存在强烈的相互作用。令人惊讶的是，尽管有C传导和抑制反应，但a型传导阻滞消除了这种次极大强度下的所有反射性心动过缓。A型和c型BRs协同作用，A型活性在心脏通路中是绝对必需的，而在抑制通路中则不需要。因此，更多的数量似乎不能解释c型BR的疗效，这两种感觉亚型之间的关键相互作用似乎在心脏和全身压力反射效应通路中发生差异。
Unmyelinated (C) and myelinated (A) baroreceptor (BR) axons are present in rat aortic depressor nerve (ADN). With graded ADN electrical activation and anodal conduction blockade, reflex responses in anesthetized rats were assessed as changes in mean arterial pressure (MAP) and heart rate (HR). We tested the hypothesis that C-type BR inputs are effective at low frequencies because they outnumber A-type. Anodal current (I-an) reversibly eliminated all MAP and HR responses to A-selective stimuli. High intensities activated all ADN axone (A + C) and decreased MAP at lower frequencies (10-Hz ADN stimulation. Burst patterns significantly augmented A- but not C-selective reflex responses despite identical numbers of shocks per second. A-selective stimuli failed to evoke significant bradycardia even at 200 Hz. Maximum intensity stimuli plus I-an (C selective) evoked less bradycardia than without I-an (A+C), indicating supra-additive summation unlike the occlusive summation for MAP responses. However, activation of reduced numbers of C-type BRs with all A-type BRs suggests a strong A to C interaction in reflex bradycardia responses. Surprisingly, I-an block of A-type conduction eliminated all reflex bradycardia at such submaximal intensities despite C conduction and depressor responses. A- and C-type BRs act synergistically, and A-type activity is absolutely required in cardiac but not in depressor pathways. Thus greater numbers do not appear to account for C-type BR efficacy, and critical interactions between these two sensory subtypes appear to occur differentially across cardiac and systemic baroreflex effector pathways.