Fan W, Reynolds P J, Andresen M C
Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland 97201-3098, USA.
Am J Physiol. 1996 Dec;271(6 Pt 2):H2218-27. doi: 10.1152/ajpheart.1996.271.6.H2218.
Dynamic cardiovascular regulation depends on baroreflexes and the processing of sensory information. We evaluated the influence of choice of anesthetic on the frequency-response characteristics of the baroreflex of rats by electrical stimulation of two major baroreceptor-containing nerves, the carotid sinus (CSN) and aortic depressor nerves (ADN). The ADN contains baroreceptors alone, and the CSN has both chemoreceptors and baroreceptors. Most studies were performed under pentobarbital sodium (PB; 65 mg/kg) anesthesia. We compared this to a combination of alpha-chloralose (80 mg/kg) and urethan (800 mg/kg) (CU). Stimulus trains were fixed at 60-s periods (0.1-ms shocks, supramaximal intensities, 1-200 Hz) and delivered in steady and burst patterns. Unilateral steady-frequency ADN stimulation in PB-anesthetized rats evoked reflex decreases in mean arterial pressure and heart rate that increased with frequencies between 1 and approximately 10 Hz before reaching a maximum. From 10 to 200 Hz, PB ADN reflex responses were sustained at these maximal levels. Cutting the opposite ADN or both CSNs did not alter ADN baroreflex relationships. Heart rate and mean arterial pressure depressor responses evoked by CSN stimulation in PB-anesthetized rats were smaller compared with ADN stimulation and were biphasic, with small pressor responses at 1 Hz. Maximal CSN depressor responses in PB-anesthetized rats occurred at approximately 20 Hz and were sustained at 20-200 Hz. Baroreflex responses for ADN stimulation in CU-anesthetized rats were similar to those in PB-anesthetized rats. In contrast, in CU-anesthetized rats, maximal CSN responses occurred at 20 Hz but declined at 50-200 Hz. Constant- and burst-stimulation responses were equivalent. The results suggest that rat aortic baroreflex responses are sustained even at very high input frequencies (> 100 Hz). The sustained high-frequency baroreflex responses seem to present a paradox in understanding central integration because other studies show substantial depression of sensory transmission at the first synapse in the nucleus tractus solitarius at frequencies as low as 10 Hz.
动态心血管调节依赖于压力反射和感觉信息的处理。我们通过电刺激两条主要的含压力感受器神经，即颈动脉窦神经（CSN）和主动脉减压神经（ADN），评估了麻醉剂的选择对大鼠压力反射频率响应特性的影响。ADN仅含压力感受器，而CSN既有化学感受器又有压力感受器。大多数研究在戊巴比妥钠（PB；65mg/kg）麻醉下进行。我们将其与α-氯醛糖（80mg/kg）和乌拉坦（800mg/kg）（CU）的组合进行了比较。刺激序列固定为60秒时段（0.1毫秒电击，超强强度，1 - 200Hz），并以稳定和爆发模式施加。在PB麻醉的大鼠中，单侧稳定频率的ADN刺激引起平均动脉压和心率的反射性降低，在达到最大值之前，在1至约10Hz之间随频率增加。从10至200Hz，PB ADN反射反应维持在这些最大水平。切断对侧ADN或双侧CSN不会改变ADN压力反射关系。与ADN刺激相比，PB麻醉的大鼠中CSN刺激引起的心率和平均动脉压降低反应较小，并且是双相的，在1Hz时有小的升压反应。PB麻醉的大鼠中CSN最大降压反应出现在约20Hz，并在20 - 200Hz维持。CU麻醉的大鼠中ADN刺激的压力反射反应与PB麻醉的大鼠相似。相比之下，在CU麻醉的大鼠中，CSN最大反应出现在20Hz，但在50 - 200Hz下降。恒定刺激和爆发刺激反应相当。结果表明，即使在非常高的输入频率（>100Hz）下，大鼠主动脉压力反射反应仍能维持。持续的高频压力反射反应在理解中枢整合方面似乎存在一个悖论，因为其他研究表明，在孤束核的第一个突触处，在低至10Hz的频率下感觉传递就会有显著抑制。
