Workman B J, Lumb B M
Department of Physiology, School of Medical Sciences, Bristol, United Kingdom.
J Neurophysiol. 1997 May;77(5):2831-5. doi: 10.1152/jn.1997.77.5.2831.
The aim of the present study was to examine the selectivity of descending control of nociceptive information in the spinal dorsal horn following neuronal activation at "pressor" sites in the anterior hypothalamus. Extracellular single-unit activity was recorded from 11 dorsal horn neurons in the lower lumbar spinal cord of anesthetized rats. Neurons selected for investigation were those that responded to noxious (pinch and radiant heat >46 degrees C) and nonnoxious (prod, stroke, and/or brush) stimulation within their cutaneous receptive fields on the ipsilateral hind paw. These are referred to as Class 2 neurons. Micropipettes were inserted stereotaxically into the anterior hypothalamus at sites where injection of the excitatory amino acid L-homocysteic acid (L-HCA) evoked increases in arterial blood pressure. The effects of microinjection of L-HCA at "pressor" sites in the anterior hypothalamus were then tested on the responses of Class 2 neurons to noxious and nonnoxious stimulation of their excitatory receptive fields. The high-threshold (pinch and/or radiant heat) responses of 7/7 Class 2 neurons tested were inhibited by an average of 66.3 +/- 8.8% (mean +/- SE) by neuronal activation at hypothalamic pressor sites. The low-threshold (prod) responses of 10/10 Class 2 neurons tested were not inhibited by neuronal activation at hypothalamic pressor sites; in 6 of these cells the response to low-intensity stimulation was increased by between 4 and 20%. Control injections of the inhibitory amino acid gamma-aminobutyric acid (GABA) at the same hypothalamic pressor sites had no significant effects on arterial blood pressure or neuronal activity. 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 anterior hypothalamus is highly selective for nociceptive inputs to Class 2 neurons.
本研究的目的是检测下丘脑前部“升压”位点神经元激活后，脊髓背角伤害性信息下行控制的选择性。在麻醉大鼠的下腰段脊髓，记录了11个背角神经元的细胞外单单位活动。被选作研究的神经元是那些在同侧后爪皮肤感受野内对伤害性刺激（夹捏和>46℃辐射热）和非伤害性刺激（轻戳、抚摸和/或刷擦）有反应的神经元。这些被称为2类神经元。将微电极立体定向插入下丘脑前部，在这些位点注射兴奋性氨基酸L-高半胱氨酸（L-HCA）可引起动脉血压升高。然后在下丘脑前部“升压”位点微量注射L-HCA，检测其对2类神经元兴奋性感受野伤害性和非伤害性刺激反应的影响。7个被检测的2类神经元中，有7个的高阈值（夹捏和/或辐射热）反应平均被下丘脑升压位点的神经元激活抑制了66.3±8.8%（平均值±标准误）。10个被检测的2类神经元中，有10个的低阈值（轻戳）反应未被下丘脑升压位点的神经元激活所抑制；其中6个细胞对低强度刺激的反应增强了4%至20%。在相同的下丘脑升压位点注射抑制性氨基酸γ-氨基丁酸（GABA）作为对照，对动脉血压或神经元活动没有显著影响。关于脊髓中的感觉处理，这些数据表明，源于下丘脑前部升压区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。
