Anatomical distribution of galanin-like immunoreactivity in the brain and pituitary of teleost fishes.

Immunohistochemical study of brains of five teleost fishes (molly, sea bass, killifish, flounder, tilapia) revealed similar extensive systems of galanin immunoreactive (GAL-ir) neurons. Cell bodies were located in the anterior preoptic recess (where coexistence with corticotrophin-releasing factor-like-ir was found), posterior tuberal hypothalamus and vagal lobe of the medulla oblongata. Fibres in the fingers of neurohypophysial tissue penetrating the pituitary pars distalis suggested an anatomical relationship between GAL-ir terminals and the hormone secreting cells. Electron microscopic studies on sea bass pituitary revealed contacts of GAL-ir fibres with growth hormone cells and gonadotrophs. Thus a GAL-like peptide may be released from nerve terminals in the teleost pituitary, where it may act locally to modulate the secretion of one or more pituitary hormones.