Capsaicin and carbon dioxide act by distinct mechanisms on sensory nerve terminals in the cat cornea
Capsaicin and carbon dioxide act by distinct mechanisms on sensory nerve terminals in the cat cornea
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DOI：
10.1016/s0304-3959(96)03256-3
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发表时间：
1997-03-01
期刊：
影响因子：
7.4
通讯作者：
Rang, HP
中科院分区：
文献类型：
--
作者：
Chen, XJ;Belmonte, C;Rang, HP
通过记录麻醉猫混合睫状神经纤维中单个传入单位的放电情况，来研究二氧化碳、辣椒素以及辣椒素拮抗剂卡唑嗪对角膜感觉神经末梢的影响。根据对二氧化碳的敏感性（在潮湿气流中向角膜施加98.5%的二氧化碳，持续30秒）来选择单位。在这些单位中，约50%（38个中的18个）对辣椒素也有反应（以液滴形式施加0.1μM辣椒素，20秒后冲洗掉），其放电幅度与二氧化碳产生的相似。其他对二氧化碳敏感的单位（38个中的20个）对辣椒素没有反应。对辣椒素敏感的单位对二氧化碳的反应更快（首次放电的平均潜伏期为0.7±0.2秒），比对辣椒素不敏感的单位（首次放电的平均潜伏期为5.1±1.2秒）快。根据传导速度，对辣椒素敏感和不敏感的两组都包括A纤维和C纤维。向角膜施加卡唑嗪（10μM，持续5 - 20分钟）可可逆性地阻断单位对辣椒素的反应，但不影响对二氧化碳的反应。通过暴露于辣椒素（0.1μM）30秒而急性脱敏的单位（在此期间辣椒素诱发的放电降至零）仍然对二氧化碳有反应，尽管与对照组相比反应降低了44%。结论是，辣椒素和二氧化碳对猫角膜感觉传入神经的激活似乎涉及不同的机制，因为：（a）许多对二氧化碳敏感的单位不会被辣椒素兴奋；（b）卡唑嗪选择性地阻断辣椒素的兴奋作用而不影响对二氧化碳的反应；（c）对辣椒素的脱敏仅部分损害对二氧化碳的反应性。（C）1997年国际疼痛研究协会。
The discharge of single afferent units recorded from filaments of the mixed ciliary nerve of anaesthetised cats was used to study the effects of CO2, capsaicin and the capsaicin antagonist, capsazepine, on sensory nerve terminals in the cornea. Units were selected on the basis of their sensitivity to CO2 (98.5% applied to the cornea for 30 s in a moist gas stream). Of these units, about 50% (18/38) also responded to capsaicin (0.1 mu M applied as droplet and washed off after 20 a), with a discharge of similar magnitude to that produced by CO2. The other CO2-sensitive units (20/38) did not respond to capsaicin. Capsaicin-sensitive units responded more rapidly to CO2 (mean latency to first spike 0.7 +/- 0.2 s) than capsaicin-insensitive units (mean latency to first spike 5.1 +/- 1.2 s). On the basis of their conduction velocity, both the capsaicin-sensitive and the capsaicin-insensitive groups included both A- and C-fibres. Application of capsazepine (10 mu M for 5-20 min) to the cornea reversibly blocked the response of the units to capsaicin without affecting responses to CO2. Units that were acutely desensitised by exposure to capsaicin (0.1 mu M) for 30 s, during which time the discharge evoked by capsaicin declined to zero, still responded to CO2, though the response was reduced by 44% compared with controls. It is concluded that activation of sensory afferents in the cat cornea by capsaicin and by CO2 appear to involve distinct mechanisms, since: (a) many CO2-sensitive units are not excited by capsaicin; (b) capsazepine selectively blocks excitation by capsaicin without affecting responses to CO2; and (c) desensitisation to capsaicin impairs only partially the responsiveness to CO2. (C) 1997 International Association for the Study of Pain.