Zhuo M, Gebhart G F
Department of Pharmacology, College of Medicine, The University of Iowa, Iowa City 52242, USA.
J Neurophysiol. 1997 Aug;78(2):746-58. doi: 10.1152/jn.1997.78.2.746.
The modulatory effects of electrical and chemical (glutamate) stimulation in the rostral ventromedial medulla (RVM) on spinal nociceptive transmission and a spinal nociceptive reflex were studied in rats. Electrical stimulation at a total 86 sites in the RVM in the medial raphe nuclei (n = 54) and adjacent gigantocellular areas (n = 32) produced biphasic (facilitatory and inhibitory, n = 43) or only inhibitory (n = 43) modulation of the tail-flick (TF) reflex. At these 43 biphasic sites in the RVM, facilitation of the TF reflex was produced at low intensities of stimulation (5-25 microA) and inhibition was produced at greater intensities of stimulation (50-200 microA). At 43 sites in the RVM, electrical stimulation only produced intensity-dependent inhibition of the TF reflex. Activation of cell bodies in the RVM by glutamate microinjection reproduced the biphasic modulatory effects of electrical stimulation. At biphasic sites previously characterized by electrical stimulation, glutamate at a low concentration (5 nmol) produced facilitation of the TF reflex; a greater concentration (50 nmol) only inhibited the TF reflex. In electrophysiological experiments, electrical stimulation at 62 sites in the RVM produced biphasic (n = 26), only inhibitory (n = 26), or only facilitatory (n = 10) modulation of responses of lumbar spinal dorsal horn neurons to noxious cutaneous thermal (50 degrees C) or mechanical (75.9 g) stimulation. Facilitatory effects were produced at lesser intensities of stimulation and inhibitory effects were produced at greater intensities of stimulation. The apparent latencies to stimulation-produced facilitation and inhibition, determined with the use of a cumulative sum method and bin-by-bin analysis of spinal neuron responses to noxious thermal stimulation of the skin, were 231 and 90 ms, respectively. The spinal pathways conveying descending facilitatory and inhibitory influences were found to be different. Descending facilitatory influences on the TF reflex were conveyed in ventral/ventrolateral funiculi, whereas inhibitory influences were conveyed in dorsolateral funiculi. The results indicate that descending inhibitory and facilitatory influences can be simultaneously engaged throughout the RVM, including nucleus raphe magnus, and that such influences are conveyed in different spinal funiculi.
在大鼠中研究了延髓头端腹内侧区（RVM）的电刺激和化学（谷氨酸）刺激对脊髓伤害性信息传递及脊髓伤害性反射的调节作用。对中缝内侧核（n = 54）和相邻巨细胞区（n = 32）的RVM共86个位点进行电刺激，对甩尾（TF）反射产生双相（易化和抑制，n = 43）或仅抑制（n = 43）调节。在RVM的这43个双相位点，低强度刺激（5 - 25微安）时产生TF反射的易化，高强度刺激（50 - 200微安）时产生抑制。在RVM的43个位点，电刺激仅产生强度依赖性的TF反射抑制。通过谷氨酸微量注射激活RVM中的细胞体可重现电刺激的双相调节作用。在先前用电刺激表征的双相位点，低浓度（5纳摩尔）谷氨酸产生TF反射的易化；较高浓度（50纳摩尔）仅抑制TF反射。在电生理实验中，对RVM的62个位点进行电刺激，对腰段脊髓背角神经元对有害皮肤热刺激（50℃）或机械刺激（75.9克）的反应产生双相（n = 26）、仅抑制（n = 26）或仅易化（n = 10）调节。较低强度刺激产生易化作用，较高强度刺激产生抑制作用。使用累积总和法和对脊髓神经元对皮肤有害热刺激反应的逐点分析确定，刺激产生易化和抑制的明显潜伏期分别为231和90毫秒。发现传递下行易化和抑制影响的脊髓通路不同。对TF反射的下行易化影响通过腹侧/腹外侧索传导，而抑制影响通过背外侧索传导。结果表明，下行抑制和易化影响可在整个RVM（包括中缝大核）同时起作用，且这些影响通过不同的脊髓索传导。
