Localization by immunofluorescence of a gastrin-like substance in the brain of the rainbow trout, Salmo gairdneri.

With the aid of an indirect immunofluorescence technique neurons containing a gastrin-like substance were identified in the brain of Salmo gairdneri. The perikarya of these neurones appear to be located along the periventricular part of the nucleus lateralis tuberis between the hypophysial stalk and the most rostral tip of the saccus vasculosus. The fibres of these perikarya run rostrally toward the hypophysis, where they can be followed in the protrusions of the neurohypophysis into the proximal pars distalis. Here the bundle of immunoreactive fibres divides into numerous smaller bundles and into single fibres. Immunohistochemical specificity test have shown this immunoreactive substance to belong to the gastrin group, sharing an antigenic determinant with cholecystokinin (CCK) and pentagastrin (common amino-acid sequence Trp-Met-Asp-Phe). A possible function of these gastrin (or CCK)-containing neurones in the rainbow trout is discussed.