The orexinergic synaptic innervation of serotonin- and orexin 1-receptor-containing neurons in the dorsal raphe nucleus |
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Authors: | Wang Qing-Ping Koyama Yoshimasa Guan Jian-Lian Takahashi Kazumi Kayama Yukihiko Shioda Seiji |
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Affiliation: | Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan. |
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Abstract: | Orexin/hypocretin has been well demonstrated to excite the serotonergic neurons in the dorsal raphe nucleus (DRN). We studied the morphological relationships between orexin-containing axon terminals and serotonin- as well as orexin-receptor-containing neurons in the dorsal raphe nucleus. Using immunohistochemical techniques at the light microscopic level, orexin A (OXA)-like immunoreactive neuronal fibers in the DRN were found to make close contact with serotonergic neurons, while some of the serotonergic neurons also expressed the orexin 1 receptor (OX1R). At the electron microscopic level, double-immunostaining experiments showed that the orexin A-like immunoreactive fibers were present mostly as axon terminals that made synapses on the serotonin- and orexin 1-receptor-containing neurons. While only axodendritic synapses between orexin A-containing axon terminals and serotonergic neurons were detected, the synapses made by orexin A-containing axon terminals on the orexin 1-receptor-containing neurons were both axodendritic and axosomatic. The present study suggests that excitation effect of orexin A on dorsal raphe serotonergic neurons is via synaptic communication through orexin 1 receptor. |
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