Univ. of Pittsburgh School of Medicine, Dept. of Otolaryngology, Eye and Ear Institute, Rm. 519, Pittsburgh, PA 15213, USA.
J Appl Physiol (1985). 2011 Jun;110(6):1699-707. doi: 10.1152/japplphysiol.00180.2011. Epub 2011 Apr 14.
The responses to vestibular stimulation of brain stem neurons that regulate sympathetic outflow and blood flow have been studied extensively in decerebrate preparations, but not in conscious animals. In the present study, we compared the responses of neurons in the rostral ventrolateral medulla (RVLM), a principal region of the brain stem involved in the regulation of blood pressure, to whole body rotations of conscious and decerebrate cats. In both preparations, RVLM neurons exhibited similar levels of spontaneous activity (median of ∼17 spikes/s). The firing of about half of the RVLM neurons recorded in decerebrate cats was modulated by rotations; these cells were activated by vertical tilts in a variety of directions, with response characteristics suggesting that their labyrinthine inputs originated in otolith organs. The activity of over one-third of RVLM neurons in decerebrate animals was altered by stimulation of baroreceptors; RVLM units with and without baroreceptor signals had similar responses to rotations. In contrast, only 6% of RVLM neurons studied in conscious cats exhibited cardiac-related activity, and the firing of just 1% of the cells was modulated by rotations. These data suggest that the brain stem circuitry mediating vestibulosympathetic reflexes is highly sensitive to changes in body position in space but that the responses to vestibular stimuli of neurons in the pathway are suppressed by higher brain centers in conscious animals. The findings also raise the possibility that autonomic responses to a variety of inputs, including those from the inner ear, could be gated according to behavioral context and attenuated when they are not necessary.
延髓头端腹外侧区（RVLM）神经元对调节血压的脑于区的交感传出和血流的前庭刺激的反应，在去大脑动物中已进行了广泛的研究，但在清醒动物中尚未进行研究。在本研究中，我们比较了参与血压调节的脑于主要区域 RVLM 神经元对清醒和去大脑猫全身体旋转的反应。在这两种制剂中，RVLM 神经元表现出相似水平的自发活动（中位数约为 17 个脉冲/s）。大约一半在去大脑猫中记录的 RVLM 神经元的放电被旋转调制；这些细胞被各种方向的垂直倾斜激活，其反应特征表明它们的迷路输入源自耳石器官。超过三分之一在去大脑动物中 RVLM 神经元的活动被压力感受器刺激改变；具有和不具有压力感受器信号的 RVLM 单位对旋转有相似的反应。相比之下，在清醒猫中研究的只有 6%的 RVLM 神经元表现出与心脏相关的活动，只有 1%的细胞的放电被旋转调制。这些数据表明，介导前庭 - 交感反射的脑于回路对空间中身体位置的变化非常敏感，但该通路上神经元对前庭刺激的反应被清醒动物的高级脑中枢抑制。研究结果还提出了这样一种可能性，即对各种输入（包括来自内耳的输入）的自主反应可以根据行为背景进行门控，并在不需要时减弱。
