CO2 STIMULATION OF THE CORNEA - A COMPARISON BETWEEN HUMAN SENSATION AND NERVE ACTIVITY IN POLYMODAL NOCICEPTIVE AFFERENTS OF THE CAT
CO2 STIMULATION OF THE CORNEA - A COMPARISON BETWEEN HUMAN SENSATION AND NERVE ACTIVITY IN POLYMODAL NOCICEPTIVE AFFERENTS OF THE CAT
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DOI：
10.1111/j.1460-9568.1995.tb01105.x
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发表时间：
1995-06-01
影响因子：
3.4
通讯作者：
BELMONTE, C
中科院分区：
文献类型：
--
作者：
CHEN, XJ;GALLAR, J;BELMONTE, C
已经提出低pH对伤害感受器的激发是组织损伤后疼痛的原因。在这里，我们已经研究了pH值的降低所造成的应用CO2脉冲角膜上的猫的角膜传入神经的活动和人类的疼痛感觉的大小。记录麻醉猫角膜传入纤维的单位活动。A-δ或C多模态伤害性单位的角膜感受野暴露于空气中具有不同浓度的CO2（0、35、50、65、80和98.5%）的气体混合物30 s。在40 +/-3%CO2的平均阈值浓度下诱发对CO2的反应。它们由一种逐渐衰减到紧张水平的冲动放电组成。在15%的装置中，不存在初始爆破。CO2浓度和点火频率数据可以拟合为指数为1.12的幂函数。二氧化碳脉冲也应用于16名志愿者的角膜。通过视觉模拟量表和口头描述量表测量所经历的感觉。将流量调节至低于机械刺激阈值（2.8 +/- 0.5 mg）。当以5%的步长施加含有10- 90%CO2的混合物作为3 s脉冲时，在33.5 +/-4.0%CO2下诱发阈值感觉，描述为轻度刺痛。随着CO2浓度升高（47.5 +/-3.6%CO2），这种感觉变得明显疼痛。对于同一个受试者，感觉阈值是非常恒定的，尽管它随着暴露时间的延长而变化。CO2浓度和疼痛幅度之间的关系可以调整为幂指数为1.12的幂函数。猫的二氧化碳浓度与神经放电的曲线和人类的心理物理感觉的曲线非常相似。这些结果表明，角膜多模态伤害感受器响应质子，并编码CO2浓度的变化，可能反映pH值的变化。同样的刺激引起角膜疼痛的感觉在人类中，从而打开了使用CO2作为一种有效的刺激角膜的感觉的可能性。
Excitation of nociceptors by low pH has been proposed as a cause of pain following tissue injury. Here we have studied the effect of pH reductions caused by application of CO2 pulses to the cornea on the activity of corneal afferent nerves of the cat and on the magnitude of pain sensations in humans. Single-unit activity was recorded from corneal afferent fibres in anaesthetized cats. The corneal receptive field of A-delta or C polymodal nociceptive units was exposed for 30 s to a gas mixture with different concentrations of CO2 in air (0, 35, 50, 65, 80 and 98.5%). Responses to CO2 were evoked at a mean threshold concentration of 40 +/- 3% CO2. They consisted of a discharge of impulses that decayed gradually to a tonic level. In 15% of the units the initial burst was absent. The CO2 concentration and firing frequency data could be fitted to a power function with an exponent of 1.12. Pulses of CO2 were also applied to the cornea of 16 human volunteers. Sensations experienced were measured by means of a visual analogue scale and a verbal descriptor scale. Flow was adjusted below the mechanical stimulation threshold (2.8 +/- 0.5 mg). When mixtures containing 10-90% CO2 in 5% steps were applied as 3 s pulses, threshold sensation, described as a mild stinging pain, was evoked at 33.5 +/- 4.0% CO2. This sensation became overtly painful with higher CO2 concentrations (47.5 +/- 3.6% CO2). For the same subject the sensory threshold was remarkably constant, though it changed with longer exposure times. The relationship between CO2 concentration and magnitude of pain could be adjusted to a power function with a power exponent of 1.12. Curves of CO2 concentration versus neural discharges in the cat and versus psychophysical sensation in humans were very similar. These results show that corneal polymodal nociceptors respond to protons, and encode changes in CO2 concentration presumably reflecting pH changes. The same stimulus evokes corneal pain sensations in humans, thus opening the possibility of using CO2 as an effective stimulus for corneal aesthesiometry.