Saleh T M, Bauce L G, Pittman Q J
Neuroscience Research Group, University of Calgary, Alberta, Canada.
Am J Physiol. 1997 May;272(5 Pt 2):R1631-40. doi: 10.1152/ajpregu.1997.272.5.R1631.
The parabrachial nucleus (PBN) is a regulatory nucleus that relays visceral information from the brain stem to the cortex. Immunohistochemical studies have shown that the levels of various neuropeptides in the PBN were changed after visceral afferent activation. Because the major transmitter relaying visceral information through the PBN is glutamate, the present study asked if glutamate release into the PBN also was changed after vagal afferent activation in anesthetized male rats. The distally crushed vagus was stimulated (50 Hz, 1-2 mA, 1 s on, 2 s off) for 2 h. Dialysates of the PBN were collected every 30 min and assayed for glutamate using high-performance liquid chromatography. Extracellular glutamate concentrations were reduced during the vagal stimulation, increased fourfold compared with prestimulated levels after the stimulation was terminated, and returned to prestimulated levels over the next 2 h poststimulation. These changes were not due to alterations in blood pressure because sodium nitroprusside infusion for the same interval resulted in a similar hypotension, but increased glutamate release. Phenylephrine and sodium nitroprusside were infused intravenously to measure the cardiac baroreflex before, during, and after vagal stimulation. The pressor (but not the depressor) response was elevated during the period of enhanced glutamate release, and the baroreflex curve was shifted to the right (increased threshold) without a change in gain. These changes in the cardiac baroreflex were reduced, but still seen, when the PBNs were dialyzed bilaterally with the glutamate antagonists MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione. Thus visceral activation alters glutamate release in the PBN and has enduring effects on cardiac baroreflex function.
臂旁核（PBN）是一个调节性核团，它将来自脑干的内脏信息传递至皮层。免疫组织化学研究表明，内脏传入激活后，PBN中多种神经肽的水平发生了变化。由于通过PBN传递内脏信息的主要递质是谷氨酸，因此本研究探讨了在麻醉雄性大鼠中，迷走神经传入激活后，谷氨酸释放到PBN中是否也会发生变化。对远端结扎的迷走神经进行刺激（50Hz，1 - 2mA，刺激1秒，间隔2秒），持续2小时。每隔30分钟收集PBN的透析液，并用高效液相色谱法检测谷氨酸。迷走神经刺激期间细胞外谷氨酸浓度降低，刺激终止后与刺激前水平相比增加了四倍，并在刺激后的接下来2小时内恢复到刺激前水平。这些变化并非由血压改变引起，因为在相同时间段内输注硝普钠会导致类似的低血压，但会增加谷氨酸释放。静脉注射去氧肾上腺素和硝普钠以测量迷走神经刺激前、期间和之后的心脏压力反射。在谷氨酸释放增强期间，升压（而非降压）反应升高，压力反射曲线向右移动（阈值增加），增益无变化。当用谷氨酸拮抗剂MK - 801和6 - 氰基 - 7 - 硝基喹喔啉 - 2,3 - 二酮双侧透析PBN时，心脏压力反射的这些变化有所减轻，但仍然可见。因此，内脏激活会改变PBN中的谷氨酸释放，并对心脏压力反射功能产生持久影响。
