Biomedical Research

The dorsal raphe nucleus (DR), contains 60% serotonergic neurons, which appears to be involved in the control of endogenous pain sensation. MK-801, a non-competitive antagonist of N-methyl-D-aspartate receptors, inhibits spinal nociceptive neurons, however, little information is available about the effect of its administration on the DR. To evaluate the distribution of c-Fos and serotonin expression in the DR following experimental tooth movement in the rat upper molar and/or administration of MK-801. Fifty-six Wistar strain male rats underwent experimental tooth movement according to the Waldo’s method. Of all the rats, 28 were administrated MK-801 (3 mg/kg) intraperitoneally before initiating the experimental tooth movement (n=14). These animals were sacrificed 2 and 12 h after the experimental tooth movement. The sections including DR were dissected, and subjected to immunohistochemical staining with c-Fos and serotonin antibodies. In addition, 28 anesthesia control animals with or without administration of MK-801 were used as the controls. In the DR, the numbers of single-labeled (c-Fos) and double-labeled (c-Fos/serotonin) neurons were increased at 2 h and decreased by 12 h as compared with the controls. MK-801 decreased the numbers of double-labeled neurons at 2 h to the control level. The present results suggest that although blockage of NMDA receptors decreases neuronal activity with in the DR dur-ing experimental tooth movement, serotonergic DR neurons are not involved in the MK-801-induced analgesia

Author(s): Tatsunori Shibazaki, Yukiko Hattori, Eiji Tanaka, Mineo Watanabe, Mika Nishi, Kazuo Tanne
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