The immunohistochemical localization of calcitonin gene-related peptid
e was examined, at both light and electron microscopic levels, in the
pancreas of various vertebrates, including the eel, bullfrog, turtle,
chicken, mouse, rat, guinea pig, dog, monkey, and human. Immunoreactiv
e staining was observed in nerve fibers in every animal species examin
ed, but positive endocrine cells were limited to the rat, monkey, and
human. The density of the positive endocrine cells varied considerably
among the three species (monkey > rat > human). Positive nerve fibers
were distributed throughout the parenchyma, being particularly rich a
round pancreatic ducts, and near large or small blood vessels. In four
species (eel, mouse, rat, and dog), positive nerve fibers formed a de
nse network in the islet region. There were positive varicose nerve fi
bers around exocrine cells. These fibers, varying in density in differ
ent species (relatively high in the eel, bullfrog, and rat), were some
times adjacent to acinar cells. At the electron microscopic level, pos
itive nerve terminals were often demonstrated in close apposition to t
he outer membrane of acinar cells. The eel pancreas revealed an except
ional pattern of staining in neuronal cell bodies that were scattered
in the interlobular connective tissue. Despite these anatomical differ
ences, the omnipresence of this peptide suggests its essential role(s)
in the pancreas.