刺激家兔腹部迷走神经外周端降压效应中枢机制的研究

应用电解损毁和脑室内注射药物的方法研究了刺激家兔腹部迷走神经外周端所致降压效应的中枢机制。结果表明:1.电刺激延脑闩部尾侧1.5—2mm、中线旁开0.25mm、深1—2mm 处主要引起降压反应。2.电解损毁该部位可以使刺激腹部迷走神经外周端所引起的降压效应显著减弱(n=20,P<0.001),但对刺激减压神经所致降压反应无影响。3.在延脑闩部水平电解损毁减压神经纤维在孤束核的主要投射区可以使刺激减压神经所致降压反应显著减弱,而对刺激腹部迷走神经外周端所致降压反应无影响。4.第四脑室注射5,6-双羟色胺的动物较之注射人工脑脊液的动物颈、胸髓5-羟色胺含量明显降低、动物动脉压增高、心率明显增快、刺激减压神经所致降压反应未见减弱,而刺激腹部迷走神经外周端所致降压反应却明显减小。因此,我们认为家兔腹部迷走神经外周端所致降压效应依赖于延脑闩下部的中缝隐核及连合核等结构,而与减压神经的投射部位无关。延脑中缝核至脊髓的下行性5-HT能神经纤维抑制脊髓交感节前神经元的活动,是这个降压效应的中枢机制之一。

STUDY ON THE CENTRAL MECHANISMS OF DEPRESSOR EFFECT INDUCED BY STIMULATION OF PERIPHERAL END OF ABDOMINAL VAGUS IN THE RABBIT

The central mechanism of the depressor effect produced by stimulation ofthe peripheral end of the abdominal vagal nerve in anesthetized rabbits was studiedby means of electrolytic lesion and intracisternal injection of 5,6-dihydroxytry-ptamine. The result of the experiments showed: 1. Electric stimulation of the area1.5 to 2 mm caudal to obex in the chloralosed rabbit caused depressor response. 2.The depressor response induced by stimulation of the peripheral end of the ab-dominal vagal nerve was attenuated following electrolytic lesion of the area 1.5 to2 mm caudal to obex. This procedure did not affect the depressor response causedby stimulation of the aortic nerve. 3. After lesion of the area at the level of theobex where the buffer nerves terminated, the depressor response induced by stim-ulation of the aortic nerve was significantly attenuated, but that induced by stim-ulation of the peripheral end of the abdominal vagal nerve was not affected. 4.By injecting 5, 6-dihydroxytryptamine into the fourth ventricle, 5 - HT contents inthe cervical and thoracic cords were decreased obviously, arterial pressure and heartrate increased, the depressor response induced by stimulation of the peripheral endof the abdominal vagal nerve was attenuated significantly. The results obtainedsuggest that the depressor response induced by stimulation of the peripheral end orthe abdominal vagal nerve depends on the structural integrity of a special area inthe lower part of the medulla which is separated from the buffer nerve terminatedarea. This area mainly includes nucleus commisuralis and nucleus raphe ob-nascurus. The inhibitory effect of the serotonergic descending system which origi-tes in the nucleus raphe on the activities of the spinal sympathetic preganglionicneurons may be one of the central mechanisms of the vagal stimulation-induceddepressor response.