• Kouta Nagoya, Shiro Nakamura, Keiko Ikeda, Hiroshi Onimaru, Atsushi Yoshida, Kiyomi Nakayama, Ayako Mochizuki, Masaaki Kiyomoto, Fumihiko Sato, Kiyoshi Kawakami, Koji Takahashi, and Tomio Inoue.
• Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; Division of Oral Rehabilitation Medicine, Department of Special Needs Dentistry, Showa University School of Dentistry, 2-2-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan.
• Neuroscience. 2017 Sep 1; 358: 211-226.

AbstractPhox2b encodes a paired-like homeodomain-containing transcription factor essential for development of the autonomic nervous system. Phox2b-expressing (Phox2b+) neurons are present in the reticular formation dorsal to the trigeminal motor nucleus (RdV) as well as the nucleus of the solitary tract and parafacial respiratory group. However, the nature of Phox2b+ RdV neurons is still unclear. We investigated the physiological and morphological properties of Phox2b+ RdV neurons using postnatal day 2-7 transgenic rats expressing yellow fluorescent protein under the control of Phox2b. Almost all of Phox2b+ RdV neurons were glutamatergic, whereas Phox2b-negative (Phox2b-) RdV neurons consisted of a few glutamatergic, many GABAergic, and many glycinergic neurons. The majority (48/56) of Phox2b+ neurons showed low-frequency firing (LF), while most of Phox2b- neurons (35/42) exhibited high-frequency firing (HF) in response to intracellularly injected currents. All, but one, Phox2b+ neurons (55/56) did not fire spontaneously, whereas three-fourths of the Phox2b- neurons (31/42) were spontaneously active. K+ channel and persistent Na+ current blockers affected the firing of LF and HF neurons. The majority of Phox2b+ (35/46) and half of the Phox2b- neurons (19/40) did not respond to stimulations of the mesencephalic trigeminal nucleus, the trigeminal tract, and the principal sensory trigeminal nucleus. Biocytin labeling revealed that about half of the Phox2b+ (5/12) and Phox2b- RdV neurons (5/10) send their axons to the trigeminal motor nucleus. These results suggest that Phox2b+ RdV neurons have distinct neurotransmitter phenotypes and firing properties from Phox2b- RdV neurons and might play important roles in feeding-related functions including suckling and possibly mastication.Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

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