Coexistence of substance P and calcitonin gene-related peptide in the nerve fibers of the carotid labyrinth of the bullfrog, Rana catesbeiana.

Double immunohistochemical staining with fluorescein isothiocyanate (FITC)- and rhodamine-conjugated antisera revealed the coexistence of substance P (SP) and calcitonin gene-related peptide (CGRP) in most nerve fibers in the intervascular stroma of the carotid labyrinth of the bullfrog, Rana catesbeiana. A few fibers contained SP without CGRP. The results suggest that the vascular regulatory function, which is one of the possible functions of the carotid labyrinth, may be controlled in part by the interaction of SP and CGRP.