Distribution of adrenomedullin-like immunoreactivity in the brain of the adult sea lamprey

Adrenomedullin (AM) is a neuropeptide widely distributed in vertebrates. In jawed vertebrates it has been localized in distinct regions of the central nervous system by means of antisera against human AM because the molecule seems to be well conserved across species. In this study, we have analyzed the localization of AM-like immunoreactive (AM-ir) cell bodies and fibers throughout the brain of the adult sea lamprey Petromyzon marinus, by using immunohistochemistry. Several AM-ir cell populations were found in the basal plate of the secondary prosencephalon, being more numerous in the hypothalamus, as well as two in the diencephalon and one in the mesencephalon; in addition two cell populations were found in the rhombencephalic alar plate, one in the isthmic region and other in the nucleus of the solitary tract. Immunolabeled fibers were widespread throughout the lamprey brain, but were more abundant in the basal plate. Of particular interest was the conspicuous innervation of the striatum by AM-ir fibers. In addition, our results indicate that AM-ir cells and fibers are present in the lamprey hypothalamo-neurohypophyseal system, suggesting that AM plays some important role in the control of pituitary gland function.