Distribution of gastrin-releasing peptide/bombesin-like immunoreactivity in the rainbow trout brain.

The distribution of gastrin-releasing peptide (14-27)/bombesin-like immunoreactivity was studied in the brain of the teleost Oncorhynchus mykiss using an indirect immunoperoxidase technique. Cell bodies were only found in the hypothalamic nuclei posterioris periventricularis, the anterior part of the recessus lateralis, and in the recessus posterioris. Immunoreactive fibers were widely distributed in the diencephalon, midbrain, and hindbrain. The highest density of immunoreactive fibers was found in the hypothalamus, whereas a moderate to low density of fibers was visualized in the periventricular thalamus. In the midbrain, a moderate density of fibers was observed at the level of the nuclei lateralis and centralis of the torus semicircularis, the stratum album centrale of the optic tectum, the nucleus of the rostral mesencephalic tegmentum, the nuclei lateralis valvulae, the lemnisci lateralis, istmi and locus coeruleus, as well as in the hindbrain at the level of the nuclei gustatorius secundarius, cerebelli, descendens nervi trigemini, and funiculi lateralis. These data suggest that the peptide could be involved in neuroendocrine (LT, nRL, nRP), visual (OT, nRTM, TS, Is), auditory (TS), and nociceptive (Vd, nufl) mechanisms.