Psychophysical stress can cause neural changes that increase nociception in the orofacial region, particularly the masseter muscle (MM). The nucleus raphe magnus (NRM), which is located in the brain stem, serves the crucial role of regulating nociception through descending modulatory pain control. However, it remains unclear if neural activities in the NRM are affected under psychophysical stress conditions. This study conducted experiments to assess (1) whether neural activity, indicated by Fos expression in an NRM that has experienced MM injury, is affected by the stress of repeated forced swim tests (FST); and (2) whether the selective serotonin reuptake inhibitor fluoxetine administered daily after an FST could affect the number of Fos-positive neurons in the NRM. Results revealed that the stress from repeated FSTs significantly increased the number of Fos-positive neurons in an NRM that had been affected by MM injury. Fluoxetine inhibited increases in the number of Fos-positive neurons in the NRM that occurred as a result of FSTs, but this was not observed in sham rats. These findings indicate that the stress from FSTs could increase nociceptive neural activity in an NRM that has experienced MM injury. This could be due, in part, to changes in serotonergic mechanisms.

中文翻译：

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反复心理生理压力对大鼠中缝大核中咬肌痛的调节作用。

心理生理压力会引起神经变化，从而增加口面部的伤害感受，尤其是咬肌（MM）。位于脑干中的中缝大核（NRM）通过降低调节性疼痛控制来发挥调节伤害感受的关键作用。但是，尚不清楚NRM中的神经活动是否在心理生理压力条件下受到影响。这项研究进行了实验，以评估（1）神经活动（由遭受MM损伤的NRM中的Fos表达指示）是否受到重复强迫游泳试验（FST）的压力的影响；（2）FST后每天服用选择性5-羟色胺再摄取抑制剂氟西汀是否会影响NRM中Fos阳性神经元的数量。结果显示，重复FST产生的压力显着增加了受MM损伤影响的NRM中Fos阳性神经元的数量。氟西汀可抑制由于FST引起的NRM中Fos阳性神经元数量的增加，但这在假大鼠中未观察到。这些发现表明，来自FST的压力可以增加遭受MM损伤的NRM的伤害性神经活动。这可能部分是由于血清素能机制的变化。这些发现表明，来自FST的压力可以增加遭受MM损伤的NRM的伤害性神经活动。这可能部分是由于血清素能机制的变化。这些发现表明，来自FST的压力可以增加遭受MM损伤的NRM的伤害性神经活动。这可能部分是由于血清素能机制的变化。