Distribution of calcitonin gene-related peptide in the rat peripheral nervous system with reference to its coexistence with substance P.

This immunocytochemical study, using a double-staining method, showed that calcitonin gene-related peptide-like immunoreactive structures are widely distributed in the peripheral nervous system and that many of them coexist with substance P-like immunoreactive structures in single sensory ganglion cells. Neurons positive for calcitonin gene-related peptide but negative for substance P were detected in sensory ganglia. These cells were large (about 30-45 micron in diameter); these primary sensory neurons containing calcitonin gene-related peptide can probably act independently of substance P. There were neurons containing calcitonin gene-related peptide without substance P in the pterygopalatine ganglion, although these cells were less numerous than in the sensory ganglia. In consecutive sections, calcitonin gene-related peptide-like structures occurred in thyroid parafollicular cells, which also contain calcitonin. This suggested that messenger RNA for producing calcitonin gene-related peptide is also present in the thyroid, and like calcitonin, calcitonin gene-related peptide may have a peripheral physiological role.