Hudson P M, Semenenko F M, Lumb B M
Department of Physiology, School of Medical Sciences, University of Bristol, BS8 1TD, Bristol, UK.
Neuroscience. 2000;99(3):541-7. doi: 10.1016/s0306-4522(00)00210-4.
The aim of the present study was to determine whether or not descending control of spinal dorsal horn neuronal responsiveness following neuronal activation at pressor sites in the rostral ventrolateral medulla is selective for nociceptive information. Extracellular single-unit activity was recorded from 49 dorsal horn neurons in the lower lumbar spinal cord of anaesthetized rats. The 30 Class 2 neurons selected for investigation responded to noxious (pinch and radiant heat) and non-noxious (prod, stroke and/or brush) stimulation within their cutaneous receptive fields on the ipsilateral hindpaw. The excitatory amino acid, DL-homocysteic acid, was microinjected into either the rostral or the caudal rostral ventrolateral medulla at sites that evoked increases in arterial blood pressure. Effects of neuronal activation at these sites were then tested on the responses of Class 2 neurons to noxious and non-noxious stimulation within their excitatory receptive fields. The noxious pinch and radiant heat responses of Class 2 neurons were depressed, respectively to 13+/-3.8% (n=23) and to 16+/-3.7% (n=18) of control, following stimulation at sites in the rostral rostral ventrolateral medulla. In contrast, the low-threshold (prod) responses of eight Class 2 neurons tested were not depressed following neuronal activation at the same sites. When tested, control injections of the inhibitory amino acid, GABA, at the same sites in the rostral rostral ventrolateral medulla had no significant effects on neuronal activity. Neither intravenous administration of noradrenaline (to mimic the pressor responses evoked by DL-homocysteic acid microinjections in the rostral ventrolateral medulla) nor activation at pressor sites in the caudal rostral ventrolateral medulla had any significant effect on neuronal responsiveness. With regard to sensory processing in the spinal cord, these data suggest that descending inhibitory control that originates from neurons in pressor regions of the rostral rostral ventrolateral medulla is highly selective for nociceptive inputs to Class 2 neurons. These data are discussed in relation to the role of the rostral ventrolateral medulla in executing the changes in autonomic and sensory functions that are co-ordinated by higher centres in the CNS.
本研究的目的是确定延髓头端腹外侧加压部位神经元激活后，脊髓背角神经元反应性的下行控制是否对伤害性信息具有选择性。在麻醉大鼠的腰下段脊髓中，记录了49个背角神经元的细胞外单单位活动。选择用于研究的30个2类神经元在同侧后爪的皮肤感受野内，对伤害性（夹捏和辐射热）和非伤害性（轻戳、抚摸和/或轻刷）刺激均有反应。将兴奋性氨基酸DL-高半胱氨酸微量注射到延髓头端或尾端头端腹外侧引起动脉血压升高的部位。然后测试这些部位神经元激活对2类神经元在其兴奋性感受野内对伤害性和非伤害性刺激反应的影响。在延髓头端头端腹外侧部位进行刺激后，2类神经元的伤害性夹捏和辐射热反应分别降至对照的13±3.8%（n = 23）和16±3.7%（n = 18）。相比之下，所测试的8个2类神经元的低阈值（轻戳）反应在相同部位神经元激活后并未受到抑制。当在延髓头端头端腹外侧相同部位注射抑制性氨基酸GABA作为对照时，对神经元活动没有显著影响。静脉注射去甲肾上腺素（以模拟延髓头端腹外侧微量注射DL-高半胱氨酸所诱发的加压反应）以及延髓尾端头端腹外侧加压部位的激活，均对神经元反应性没有显著影响。关于脊髓中的感觉处理，这些数据表明，源自延髓头端头端腹外侧加压区域神经元的下行抑制控制对2类神经元的伤害性输入具有高度选择性。结合延髓头端腹外侧在执行由中枢神经系统高级中枢协调的自主和感觉功能变化中的作用，对这些数据进行了讨论。
