Mechanisms for activation of aortic baroreceptor C-fibres in rabbits and rats.
Mechanisms for activation of aortic baroreceptor C-fibres in rabbits and rats.
复制标题
兔和大鼠主动脉压力感受器 C 纤维的激活机制。
DOI：
10.1046/j.1365-201x.1999.00556.x
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Brown,AM
中科院分区：
文献类型：
--
作者：
Thoren,P;Munch,PA;Brown,AM
在早期的研究中，我们检查了大鼠主动脉压力感受器与C纤维（无髓）传入的压力反应特性。与具有A纤维（有髓）传入的主动脉压力感受器纤维相比，C纤维在更高的压力下被激活，并且在稳定的压力水平下刺激时放电更不规则。在这里，我们研究放电和主动脉直径之间的关系，在这两种类型的传入大鼠和家兔。使用Anin vitroaortic arch/aortic nerve preparation来记录单纤维活动，同时记录主动脉弓压力和直径。使用高度灵敏的非接触式光电装置测量直径。压力感受器放电的特征是刺激神经末梢，以2 mmHg s-1的上升速率从阈下到200-250 mmHg的缓慢压力斜坡，或以110-180 mmHg的幅度从阈下到阈上水平的压力阶跃。 在对这些输入的反应中，兔子的C纤维（传导速度= 0.8-2.2 m s-1）表现得很像大鼠的C纤维。 与A纤维相比，C纤维的压力阈值明显更高（95 ± 3 mmHg vs. 53 ± 2 mmHg;平均值± SEM），阈值频率更低（2.4 ± 0.5 vs. 27.7 ± 1.8尖峰s-1），最大放电频率更低（22.7 ± 2.3 vs. 65 ± 5.8尖峰s-1），对压力阶跃的反应更不规则（传导速度为8-16m s-1）。 当与直径作图时，C纤维斜坡诱发放电首先逐渐增加，然后在主动脉直径变得相对恒定的越来越高的斜坡压力下急剧上升。相比之下，A纤维放电在很宽的压力范围内与直径线性相关。这些结果表明两种解释：（1）拉伸和C纤维放电之间的关系是高度非线性的，在大直径处敏感性显著增加。(2)C纤维是由壁内应力而不是拉伸的变化刺激的。
In an earlier study, we examined the pressure–response characteristics of rat aortic baroreceptors with C‐fibre (non‐medullated) afferents. Compared with aortic baroreceptor fibres with A‐fibre (medullated) afferents, the C‐fibres were activated at higher pressures and discharged more irregularly when stimulated with a steady level of pressure. Here we examine the relationship between discharge and the aortic diameter in these two types of afferents in rats and rabbits. Anin vitroaortic arch/aortic nerve preparation was used to record single‐fibre activity simultaneously with aortic arch pressure and diameter. Diameter was measured using a highly sensitive non‐contact photoelectric device. Baroreceptor discharge was characterized by stimulating the nerve endings with either slow pressure ramps from subthreshold to 200–250 mmHg, at a rate of rise of 2 mmHg s−1, or pressure steps from subthreshold to suprathreshold levels, at amplitudes of 110–180 mmHg. In response to these inputs, C‐fibres in rabbits (conduction velocities= 0.8–2.2 m s−1) behaved much like those in rats. The C‐fibres had significantly higher pressure thresholds (95 ± 3 mmHg vs. 53 ± 2 mmHg; mean ± SEM), lower threshold frequencies (2.4 ± 0.5 vs. 27.7 ± 1.8 spikes s−1), lower maximum discharge frequencies (22.7 ± 2.3 vs. 65 ± 5.8 spikes s−1) and more irregular discharge in response to a pressure step when compared with A‐fibres (conduction velocities of 8–16 m s−1). When plotted against diameter, C‐fibre ramp‐evoked discharge increased gradually at first, and then rose steeply at increasingly higher ramp pressures where aortic diameter became relatively constant. In contrast, A‐fibre discharge was linearly related to diameter over a wide range of pressure. These results suggest two interpretations: (1) The relation between stretch and C‐fibre discharge is highly non‐linear, with a marked increase in sensitivity at large diameters. (2) C‐fibres are stimulated by changes in intramural stress rather than stretch.