Changes in the Peptidergic Innervation of the Rat Carotid Body a Month After the Termination of Chronic Hypoxia

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-