Neuronal Localization of Immunoreactive Adrenocorticotropin-like Substance in the Hypothalamus of Elasmobranch Fishes

The occurrence and localization of adrenocorticotropin (ACTH)-like material in the brain of two species of elasmobranch fishes, Scyliorhinus canicula and Squalus acanthias, were studied by immunohistochemical techniques using an antiserum generated against human ACTH1-24. In both species immunopositive neurons and fibers were recognized in the basal hypothalamus mainly distributed in the nucleus lateralis tuberis, in which many of these elements were of the liquor-contacting type. A few ACTH-like positive cells were also found in the nucleus lobi lateralis hypothalami. The features of this peptidergic system, its topographic distribution to form intrinsic circuits within the posterior hypothalamic area and probably connections with the pituitary, suggest implications in brain neuromodulatory activities and hypophyseal regulation for this peptide.