Greenspan J D, Vierck C J, Ritz L A
J Neurosci. 1986 Feb;6(2):380-90. doi: 10.1523/JNEUROSCI.06-02-00380.1986.
Four Macaca nemestrina monkeys were trained to pull a manipulandum to escape electrocutaneous stimulation (ES) applied to either leg. The intensities of stimulation which the monkeys chose to escape were those that humans identify as painful. The duration of escape trials was inversely related to stimulus intensity, and the force of escape responses was directly related to ES intensity. Reflexive responses were elicited by stimulus intensities below and above the escape threshold, and the force of the flexion reflexes was a negatively accelerating function of stimulus magnitude. The monkeys were also trained to respond, for water reinforcement, to cued, low-intensity ES. The stimulus intensities detected for water reinforcement were 50-100 X less than the escape thresholds. Following unilateral, anterolateral chordotomy, all monkeys demonstrated a large reduction in percentage of escape responding to stimulation of the contralateral leg. When the animals did escape contralateral stimulation, the latencies to respond were longer than preoperatively. The percentage and latency of escape responses to stimulation of the ipsilateral leg were not changed following chordotomy. Despite the depression of contralateral pain reactivity, the animals continued to respond to low levels of stimulation on the detection task, demonstrating that anterolateral chordotomy reduced the painfulness of strong stimulation without eliminating sensibility for low levels of stimulation. However, postoperative detection thresholds were consistently higher contralaterally than ipsilaterally. This effect resulted from slight contralateral decreases and significant ipsilateral increases in sensitivity to low levels of ES (relative to preoperative values). Thus, contralateral axons in the anterolateral column contribute to detection of light cutaneous stimulation, and chordotomy appears to disinhibit inputs from large myelinated afferent fibers to ipsilateral neurons in the spinal gray matter caudal to the lesion. The strictly contralateral slowing and reduction in percentage of pain reactivity by chordotomy correlated with reports from human patients. However, reflexive measures did not suffice as indicants of pain sensitivity. The chordotomies produced bilateral attenuations of reflexive amplitudes. Also, the force of operant escape responses was reduced with stimulation of either side. Thus, the disfacilitation of motoric reactions extended both rostral and caudal to the spinal lesions that interrupted propriospinal axons in the vicinity of the ventral horns.
对4只猪尾猕猴进行训练，使其拉动操作手柄以逃避施加于任一条腿上的皮肤电刺激（ES）。猴子选择逃避的刺激强度是人类认定为疼痛的强度。逃避试验的持续时间与刺激强度呈负相关，逃避反应的力量与ES强度呈正相关。低于和高于逃避阈值的刺激强度均可引发反射性反应，屈曲反射的力量是刺激强度的负加速函数。还训练猴子对提示的低强度ES做出反应以获取水奖励。检测到的用于水奖励的刺激强度比逃避阈值小50 - 100倍。单侧前外侧脊髓切开术后，所有猴子对侧腿刺激的逃避反应百分比大幅降低。当动物确实逃避对侧刺激时，反应潜伏期比术前更长。脊髓切开术后，同侧腿刺激的逃避反应百分比和潜伏期未发生变化。尽管对侧疼痛反应性降低，但动物在检测任务中仍对低水平刺激做出反应，表明前外侧脊髓切开术降低了强刺激的疼痛程度，但并未消除对低水平刺激的感觉能力。然而，术后对侧的检测阈值始终高于同侧。这种效应是由于对低水平ES的敏感性对侧略有降低而同侧显著增加（相对于术前值）所致。因此，前外侧柱中的对侧轴突有助于对轻度皮肤刺激的检测，脊髓切开术似乎解除了来自大的有髓传入纤维对损伤尾侧脊髓灰质同侧神经元的输入抑制。脊髓切开术严格的对侧减慢和疼痛反应百分比降低与人类患者的报告相符。然而，反射性测量不足以作为疼痛敏感性的指标。脊髓切开术导致反射幅度双侧减弱。此外，对任一侧的刺激都会降低操作性逃避反应的力量。因此，运动反应的去易化作用在脊髓损伤的头端和尾端均有延伸，该脊髓损伤中断了腹角附近的脊髓固有轴突。
