Spinal cord stimulation modulates supraspinal centers of the descending antinociceptive system in rats with unilateral s
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RESEARCH
Spinal cord stimulation modulates supraspinal centers of the descending antinociceptive system in rats with unilateral spinal nerve injury Toshiharu Tazawa1,3, Yoshinori Kamiya2,3,4*, Ayako Kobayashi1, Kensuke Saeki2, Masahito Takiguchi2, Yusuke Nakahashi1,3, Hironobu Shinbori1, Kengo Funakoshi2 and Takahisa Goto1
Abstract Background: The descending antinociceptive system (DAS) is thought to play crucial roles in the antinociceptive effect of spinal cord stimulation (SCS), especially through its serotonergic pathway. The nucleus raphe magnus (NRM) in the rostral ventromedial medulla is a major source of serotonin [5-hydroxytryptamine (5-HT)] to the DAS, but the role of the dorsal raphe nucleus (DRN) in the ventral periaqueductal gray matter is still unclear. Moreover, the influence of the noradrenergic pathway is largely unknown. In this study, we evaluated the involvement of these serotonergic and noradrenergic pathways in SCS-induced antinociception by behavioral analysis of spinal nerve-ligated (SNL) rats. We also investigated immunohistochemical changes in the DRN and locus coeruleus (LC), regarded as the adrenergic center of the DAS, and expression changes of synthetic enzymes of 5-HT [tryptophan hydroxylase (TPH)] and norepinephrine [dopamine β-hydroxylase (DβH)] in the spinal dorsal horn. Results: Intrathecally administered methysergide, a 5-HT1- and 5-HT2-receptor antagonist, and idazoxan, an α2adrenergic receptor antagonist, equally abolished the antinociceptive effect of SCS. The numbers of TPH-positive serotonergic and phosphorylated cyclic AMP response element binding protein (pCREB)-positive neurons and percentage of pCREB-positive serotonergic neurons in the DRN significantly increased after 3-h SCS. Further, the ipsilateral-tocontralateral immunoreactivity ratio of DβH increased in the LC of SNL rats and reached the level seen in naïve rats, even though the number of pCREB-positive neurons in the LC was unchanged by SNL and SCS. Moreover, 3-h SCS did not increase the expression levels of TPH and DβH in the spinal dorsal horn. Conclusions: The serotonergic and noradrenergic pathways of the DAS are involved in the antinociceptive effect of SCS, but activation of the DRN might primarily be responsible for this effect, and the LC may have a smaller contribution. SCS does not potentiate the synthetic enzymes of 5HT and norepinephrine in the neuropathic spinal cord. Keywords: Descending antinociceptive system, Dorsal raphe nucleus, Locus coeruleus, Neuropathic pain, Noradrenergic pathway, Serotonergic pathway, Spinal cord, Spinal cord stimulation Background Spinal cord stimulation (SCS) is widely performed to manage intractable pain. The antinociceptive effect *Correspondence: [email protected] 4 Present Address: Division of Anesthesiology, Niigata University Graduate School of Medical and Dental Sciences, 1‑757 Asahimachi‑dori, Chuo‑ku, Niigata 951‑8510, Japan Full list of author information is available at the end of the article
of serotonin (5-HT) in the spinal cor
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