Masuda N, Terui N, Koshiya N, Kumada M
Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki-ken, Japan.
J Auton Nerv Syst. 1991 Jun 15;34(2-3):103-17. doi: 10.1016/0165-1838(91)90077-g.
Participation of the caudal ventrolateral medulla in the arterial baroreceptor reflex was examined in urethane-anesthetized, vagotomized and immobilized rabbits whose aortic nerve was cut bilaterally. The extent of the caudal ventrolateral medulla was mapped by decreases in the renal sympathetic nerve activity and arterial pressure following a local microinjection of a neuroexcitatory amino acid, sodium glutamate (0.075-1.5 nmol). It extended between the levels 1.3 mm rostral and 3.0 mm caudal to the obex. An injection of sodium glutamate into the caudal ventrolateral medulla also diminished spontaneous activity of barosensitive reticulospinal neurons in the rostral ventrolateral medulla. In the 'split medulla preparation' in which the medulla was split along the midsagittal plane to disrupt fiber connections associating both sides, a neurotoxic agent, kainic acid, was injected unilaterally into the rostral ventrolateral medulla. This treatment markedly attenuated responses of renal sympathetic nerve activity and arterial pressure induced by a sodium glutamate injection into the ipsilateral caudal ventrolateral medulla, whereas responses to an injection into the contralateral caudal ventrolateral medulla were totally preserved. In four separate experiments, three to five injections of kainic acid were made unilaterally to cover the whole extent of the caudal ventrolateral medulla. The sympathoinhibitory and depressor responses to stimulation of the ipsilateral aortic nerve were then totally abolished. Simultaneously, the cardiac cycle-related rhythmic fluctuation of renal sympathetic nerve activity, which represented activity of the carotid sinus baroreceptor reflex, was attenuated to the noise level. These results, together with our previous electrophysiological demonstration of barosensitive caudal ventrolateral medulla neurons with axonal projections to the rostral ventrolateral medulla, strongly support the hypothesis that neurons in the caudal ventrolateral medulla mediate the arterial baroreceptor-vasomotor reflex through inhibition of barosensitive reticulospinal neurons in the rostral ventrolateral medulla.
在双侧切断主动脉神经的氨基甲酸乙酯麻醉、迷走神经切断并固定的家兔中，研究了延髓尾端腹外侧区在动脉压力感受器反射中的作用。通过局部微量注射神经兴奋性氨基酸谷氨酸钠（0.075 - 1.5 nmol）后肾交感神经活动和动脉血压的降低，描绘出延髓尾端腹外侧区的范围。它延伸至闩前方1.3 mm和后方3.0 mm之间的水平。向延髓尾端腹外侧区注射谷氨酸钠也会减少延髓头端腹外侧区压力敏感网状脊髓神经元的自发活动。在“延髓切开制备”中，沿矢状中线切开延髓以破坏两侧之间的纤维连接，将神经毒性剂 kainic 酸单侧注射到延髓头端腹外侧区。这种处理显著减弱了向同侧延髓尾端腹外侧区注射谷氨酸钠所诱导的肾交感神经活动和动脉血压反应，而对向对侧延髓尾端腹外侧区注射的反应则完全保留。在四个独立实验中，单侧进行三到五次 kainic 酸注射以覆盖延髓尾端腹外侧区的整个范围。然后，对同侧主动脉神经刺激的交感抑制和降压反应完全消失。同时，代表颈动脉窦压力感受器反射活动的肾交感神经活动的心动周期相关节律波动减弱至噪声水平。这些结果，连同我们之前对具有轴突投射至延髓头端腹外侧区的压力敏感延髓尾端腹外侧区神经元的电生理学证明，有力地支持了以下假设：延髓尾端腹外侧区的神经元通过抑制延髓头端腹外侧区的压力敏感网状脊髓神经元来介导动脉压力感受器 - 血管运动反射。
