Changes in the peptidergic innervation in the carotid body of rats chronically exposed to hypercapnic hypoxia: an effect of arterial CO2 tension

T. Kusakabe1, H. Hirakawa2, H. Matsuda3, Y. Yamamoto4, T. Nagai5, T. Kawakami6, T. Takenaka1 and Y. Hayashida2

1Laboratory for Anatomy and Physiology, Department of Sport and Medical Science, Kokushikan University, Tokyo, 2Department of Systems Physiology, University of Occupational and Environmental Health, Kitakyushu, 3Department of Otorhinolaryngology, Yokohama City University School of Medicine, Kanazawa-ku, Yokohama, 4Laboratory of Veterinary Anatomy, Department of Veterinary Science, Faculty of Agriculture, Gifu University, Gifu , 5Department of Legal Medicine, Kitasato University School of Medicine, Sagamihara, and 6Department of Physiology, Kitasato University School of Medicine, Sagamihara, Japan

Offprint requests to: Prof. Tatsumi Kusakabe, Laboratory for Anatomy and Physiology, Department of Sport and Medical Science, Kokushikan University, 7-3-1 Nagayama, Tama, Tokyo 206-8515, Japan. Fax: 81-42-339-7238. e-mail: kusakabe@kokushikan.ac.jp

Summary. The abundance of neuropeptide Y (NPY)-, vasoactive intestinal polypeptide (VIP)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers in the carotid body was examined in chronically hypercapnic hypoxic rats (10% O2 and 6-7% CO2 for 3 months), and the distribution and abundance of these four peptidergic fibers were compared with those of previously reported hypocapnic- and isocapnic hypoxic carotid bodies to evaluate the effect of arterial CO2 tension. The vasculature in the carotid body of chronically hypercapnic hypoxic rats was found to be enlarged in comparison with that of normoxic control rats, but the rate of vascular enlargement was smaller than that in the previously reported hypocapnic- and isocapnic hypoxic carotid bodies. In the chronically hypercapnic hypoxic carotid body, the density per unit area of parenchymal NPY fibers was significantly increased, and that of VIP fibers was unchanged, although the density of NPY and VIP fibers in the previously reportetd chronically hypocapnic and isocapnic hypoxic carotid bodies was opposite to that in hypercapnic hypoxia as observed in this study. The density of SP and CGRP fibers was decreased. These results along with previous reports suggest that different levels of arterial CO2 tension change the peptidergic innervation in the carotid body during chronically hypoxic exposure, and altered peptidergic innervation of the chronically hypercapnic hypoxic carotid body is one feature of hypoxic adaptation. Histol. Histopathol. 17, 21-29 (2002)

Key words: Carotid body, Systemic hypoxia (Hyper-, Iso-, and Hypocapnic hypoxia), Regulatory neuropeptides, Autonomic nervous system, Immunohistochemistry, Rat

DOI: 10.14670/HH-17.21