Search

1 Department of Otorhinolaryngology Department of Anatomy 7Department of Physiology Yokohama City University School of Medicine, Yokohama 236-0004, Japan Department of Systems Physiology University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan Department of Medicine and Department of Neurosciences University of California San Diego, La Jolla, CA 92093, USA Department of Physiology Kitasato University School of Medicine, Sagamihara 228-8555, Japan

The carotid bodies are enlarged by several fold in rats exposed to chronic hypoxia; their volume increases and endothelial cells multiply (Barer et al. 1976; Heath et al. 1973; Laider and Kay 1975a, b). Recently, we examined the peptidergic innervation in the carotid body of the rats exposed to chronically isocapnic hypoxia (Kusakabe et al. 1998). The density of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive fibers in the chronically hypoxic carotid body decreased significantly to under 50%, the density of vasoactive intestinal polypeptide (VIP) immunoreactive fibers increased significantly 1.80 times, and the density of neuropeptide Y (NPY) immunoreactive fibers was unchanged in comparison with the controls. These findings suggest that altered peptidergic innervation of the chronically hypoxic carotid body is one feature of hypoxic adaptation, which may involve modulation of chemosensory mechanisms by modification of carotid body circulation. As far as we are aware, however, there are no immunohistochemical studies on the peptidergic innervation in the carotid body during deacclimatization after chronic hypoxia is terminated. In the present study, the distribution and abundance of neuropeptide

The amphibian carotid labyrinth has arterial chemoreceptor and baroreceptor functions analogous to those of the mammalian carotid body and carotid sinus (Ishii et al, 1966). In addition, it has been suggested that the carotid labyrinth functions in controlling the blood flow to the internal and external carotid arteries (Kusakabe et al, 1987). We have observed several neuropeptide-containing nerve fibers in the carotid labyrinth, and suggested that the peptidergic innervation may participate in the function of the labyrinth (Kusakabe et al, 1991). In the carotid labyrinth, the coexistence of substance P (SP) with calcitonin gene-related peptide (CGRP) was first supposed from two adjacent sections (Kusakabe et al, 1991). Later, this speculation was clarified using the double-labelling method with an individual filter system (Kusakabe et al, 1993, 1994). It is now necessary to consider whether this coexistence is in a single axon within a bundle, or whether the two immunoreactivities originate from separate neurons in the same bundle. To clarify this, the precise coexistence of SP, CGRP, vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and galanin (GAL) was examined using a combination of double immunofluorescence labelling and a multiple dye filter system.