Modulatory effects of repeated psychophysical stress on masseter muscle nociception in the nucleus raphe magnus of rats

Psychophysical stress could increase nociception in the orofacial region including the masseter muscle, and neural changes in the brain contribute to increases in masseter muscle nociception under psychophysical stress conditions. The nucleus raphe magnus (NRM) located in the brain stem serves crucial roles to regulate nociception as descending pain controls. However, it remains unclear if neural activities in the NRM could be affected under psychophysical stress conditions. This study conducted experiments to assess (1) whether neural activity, indicated by Fos expression in the NRM evoked by masseter muscle injury, is modulated by the repeated forced swim stress (FST); (2) whether the selective serotonin reuptake inhibitor, fluoxetine, administered daily after FST could affect the number of Fos-positive neurons in the NRM. Results revealed that repeated forced swim stress significantly increased the number of Fos-positive neurons in the NRM evoked by masseter muscle injury. Fluoxetine inhibited increases in the number of Fos-positive neurons in the NRM in FST, but not in sham rats. These findings indicated that FST could increase in nociceptive neural activities in the NRM evoked by masseter muscle injury, which could be due to changes in serotonergic mechanisms at least, in part.

Journal of Oral Science. 2020, 62(2), 231-235.

新大院博(歯)甲第448号

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