Burns L L, Haigler H J
Exp Neurol. 1983 Mar;79(3):688-703. doi: 10.1016/0014-4886(83)90033-x.
Spontaneously firing neurons that were responsive to noxious face pinch or noxious heat were studied in the trigeminal spinal nucleus of the rat brain. These neurons responded with either an increase or decrease in firing rate. In these neurons serotonin (5-hydroxytryptamine; 5-HT) apparently acts through two mechanisms to attenuate the response to a noxious stimulus. One mechanism is mimicked by morphine; these two drugs block the response to the noxious stimuli without having a consistent effect on spontaneous firing. The effects of the two drugs were somewhat selective depending on the noxious stimulus used and the effect of the noxious stimulus; morphine and 5-HT were more effective in blocking the increase in firing rate evoked by the face pinch but 5-HT and morphine were more effective in blocking the decrease in firing rate evoked by the noxious heat stimulus. Interestingly, the direction of the response to a particular noxious stimulus frequently predicted whether or not both morphine and 5-HT would act on the same or different neurons. A second mechanism by which 5-HT, but not morphine, acted was to change the spontaneous firing in a direction opposite that evoked by the noxious stimulus. This type of effect apparently modulated the response to a noxious stimulus by changing the spontaneous firing rate such that a noxious stimulus had to be more intense before it could significantly alter the neuronal firing in the opposite direction. Morphine occasionally produced a change in firing pattern in neurons; this effect remains to be documented more extensively.
在大鼠脑的三叉神经脊髓核中，对有害的面部捏夹或有害热刺激有反应的自发放电神经元被进行了研究。这些神经元的放电频率会增加或减少。在这些神经元中，血清素（5-羟色胺；5-HT）显然通过两种机制来减弱对有害刺激的反应。一种机制可被吗啡模拟；这两种药物能阻断对有害刺激的反应，而对自发放电没有一致的影响。这两种药物的作用在一定程度上具有选择性，具体取决于所使用的有害刺激以及有害刺激的效果；吗啡和5-HT在阻断面部捏夹引起的放电频率增加方面更有效，但5-HT和吗啡在阻断有害热刺激引起的放电频率降低方面更有效。有趣的是，对特定有害刺激的反应方向常常能预测吗啡和5-HT是否会作用于相同或不同的神经元。5-HT起作用而吗啡不起作用的第二种机制是，使自发放电向与有害刺激所诱发的相反方向改变。这种类型的效应显然是通过改变自发放电频率来调节对有害刺激的反应，使得有害刺激必须更强烈才能显著改变神经元向相反方向的放电。吗啡偶尔会使神经元的放电模式发生变化；这种效应还有待更广泛地记录。
