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The Journal of Neuroscience, November 26, 2008, 28(48):12845-12850; doi:10.1523/JNEUROSCI.3625-08.2008

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Brief Communications
CO₂-Sensitive Preinspiratory Neurons of the Parafacial Respiratory Group Express Phox2b in the Neonatal Rat

Hiroshi Onimaru,¹ Keiko Ikeda,² and Kiyoshi Kawakami²

¹Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142, Japan, and ²Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi 329-0498, Japan

Correspondence should be addressed to Dr. Hiroshi Onimaru at the above address. Email: oni{at}med.showa-u.ac.jp

Phox2b protein is a specific marker for neurons in the parafacial region of the ventral medulla, which are proposed to play a role in central chemoreception and postnatal survival. Mutations of PHOX2B cause congenital central hypoventilation syndrome. However, there have been no reports concerning electrophysiological characteristics of these Phox2b-expressing neurons in the parafacial region of the neonate immediately after birth. This region overlaps with the parafacial respiratory group (pFRG) composed predominantly of preinspiratory (Pre-I) neurons that are involved in respiratory rhythm generation. We studied (1) whether pFRG neurons are Phox2b immunoreactive or not and (2) whether they show intrinsic CO₂ chemosensitivity. We found that most pFRG/Pre-I neurons were Phox2b immunoreactive and depolarized upon increase in CO₂ concentration under condition of action potential-dependent synaptic transmission blockade by tetrodotoxin. We also confirmed that these pFRG neurons expressed neurokinin-1 receptor. They were tyrosine hydroxylase negative and presumed to be glutamatergic. Our findings suggest that Phox2b-expressing parafacial neurons play a role in respiratory rhythm generation as well as central chemoreception and thus are essential for postnatal survival.

Key words: Phox2b; central chemoreceptors; parafacial neurons; respiratory rhythm; congenital central hypoventilation syndrome; medulla oblongata

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Received July 31, 2008; revised Oct. 7, 2008; accepted Oct. 23, 2008.

Correspondence should be addressed to Dr. Hiroshi Onimaru at the above address. Email: oni{at}med.showa-u.ac.jp

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