The terminal nerve in turbot, Psetta maxima: a developmental immunocytochemical study

The ontogeny and organization of the terminal nerve (TN) during turbot development was studied using an antiserum to neuropeptide Y. First immunoreactive cells were detected in the olfactory placode at hatching time. At 1 day after hatching, a loose group of labeled neurons form an extracranial primordial ganglion of the TN. During the subsequent larval development, more perikarya displaying increased immunoreactivity were found along the course of the olfactory nerve. Moreover, labeled cells cross the meninx of the forebrain gathering in the olfactory bulb of larval turbot. Projections from these cells, directed both to the caudal brain and to the retina, develop when the cells become established in the olfactory bulb. The generation of immunoreactive cells in the olfactory organ extends into the metamorphic period, when a pronounced asymmetry affects the turbot morphology. At this time, the topological location of the immunoreactive cells in the TN becomes distorted. This developmental pattern was compared with those found in other teleosts and in other vertebrates. Preabsorption experiments of anti-neuropeptide Y serum with neuropeptide Y and FMRF-amide suggests that immunoreactive material observed in TN cells was not neuropeptide Y, and raises the possibility that other peptides, e.g. FMRF-amide-like peptides, exist in this neural system.