Organization of vasoactive intestinal peptide-like immunoreactive system in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development

The localization of vasoactive intestinal peptide (VIP)-like immunoreactivi ty was investigated in the brain, olfactory system and retina of the zebraf ish, Danio rerio, during development and in juvenile specimens, by using th e indirect immunofluorescence and the peroxidase-antiperoxidase methods. In 24 h post fertilization (hpf) embryos,VIP-like immunoreactive cells were p resent in the olfactory pit, the retina, and several regions of the brain, including the dorsal telencephalon, the diencephalon, the tegmentum of the mesencephalon, the caudal rhombencephalon and the anterior pituitary. In 48 hpf embryos, additional VIP-like immunoreactive cell bodies were found in the ventral telencephalon, whereas in the diencephalon VIP-like immunoposit ive cells were more concentrated within the ventro-caudal hypothalamus. Dur ing the 7 day larval period, a dense plexus of VIP-like immunoreactive fibe rs first appeared in the olfactory bulbs. In 15-day-old larvae, two new gro ups of positive cells were observed in the periventricular preoptic nucleus and in the dorsal rhombencephalon. In 1 month/2 months old animals,VIP-lik e immunoreactive elements were confined to the olfactory organ, the olfacto ry bulbs, the periventricular preoptic nucleus and the pituitary, pars dist alis. At 3 months stage, a large number of cells was observed in the perive ntricular preoptic nucleus. Western immunoblot analysis confirmed that VIP- like peptides, with molecular weight similar to that of synthetic VIP. are present early during the development of zebrafish. These results show that VIP-like immunoreactive structures appear early during ontogeny both in the olfactory pit, retina and brain. Transient expression of positive cells wa s found in the retina, telencephalon, diencephalon and brainstem. The locat ion of VIP-like immunoreactivity indicates that, during development, VIP co uld be involved in several neuromodulatory functions, including the process ing of visual and olfactory informations, as well as growth or survival pro motion activities. The presence of VIP-like immunopositive cells in the pit uitary, pars distalis, suggest that, during development, VIP may influence the secretion of pituitary hormones. (C) 2001 Elsevier Science B.V. All rig hts reserved.