皮下注射福尔马林对猫初级传入单位反应的影响──电生理学研究

EFFECTS OF SUBCUTANEOUS FORMALIN ON RESPONSES OF IDENTIFIED PRIMARY AFFERENT UNITS IN THE CAT: AN ELECTROPHYSIOLOGICAL STUDY

作者以前的研究曾显示：皮下注射福尔马林引起的背角伤害感受性单位长时程反应主要取决于周围传入。当阻断坐骨神经时可以使广动力型神经元的这种反应被完全抑制。为了进一步阐明福尔马林引起的伤害性感受的周围机制，本文用细胞外记录技术记录了在乌拉坦—氯醛糖麻醉下猫的Ｌ７背根神经节的初级传入单位．与背角完全一致，皮下注射福尔马林引起非伤害性感受性单位短时程的峰放电增加，例如Ａβ－毛囊型，Ａβ－快适应型，Ａβ－慢适应Ⅰ型，Ａβ－慢适应Ⅱ型，Ａδ－Ｄ毛发型以及Ｃ－低阈值机械感受性单位等，其放电均低于１０分钟；而使伤害感受性单位的放电有长时程的增加，例如Ａδ－高阈值机械伤害感受性单位放电为３０～７０分。令人感到意外的是，在单位放电终止时，检测实验中所有初级传入单位对其相应注射部位的任何机械刺激都失去反应．将此结果与以前的实验结果一起分析时可以得出结论；福尔马林引起的中枢神经改变主要取决于上传的周围传入影响，而福尔马林引起的背角单位放电的时程，则取决于外周传入纤维的分布．本文还提出和讨论了关于福尔马林引起伤害性感受机制的新见解。

In our previous study, we have demonstrated that subcutaneous formalin-induced long-lasting response of dorsal horn nociceptive units is primarily dependent upon the ongoing peripheral afferent as blockade ofthe sciatic nerve results in complete suppress ion of the formalin-induced responses in wide dynamic range neurons.In order to further elucidate peripheral neural mechanisms underlying formalin-induced nociception, we recordedprimary afferent units from L7 dorsal root ganglia in urethane-chloralose anesthetized cats by means of extracellularsingle unit recording technique. In good correspondence with dorsal horn units, subcutaneous formalin resulted ina short-lasting increase in spike discharges of non-nociceptive units, such as Aβ-hair follicle, Aβ-rapidly adapting,Aβ-slowly adapting type Ⅰ, Aβ-slowly adapting type Ⅱ, Aδ-D hair and C-low threshold mechanoreceptive units,for less than 10 min; however, a long-lasting increase in spike discharges of nociceptive units such as Aδ-highthreshold mechanonociceptive units for 30～70 min. Unexpectedly, all primary afferent units in the present experiment showed a complete loss of responsiveness to any kind of mechanical stimuli applied to the injection site whentested at cease of unit firing. Taken together with our previous study, we conclude that formalin-induced centralneuronal changes are Primarily dependent upon ongoing peripheral afferent barrages and duration of formalin-induced firings of dorsal horn units are determined and mediated by peripheral afferent fibers innervated. A new notion about mechanisms underlying formalin-induced nociception was proposed and discussed.