Development of the caudal neurosecretory system of the Nile tilapiaOreochromis niloticus: An immunohistochemical and electron microscopic study

Abstract

The development of the caudal neurosecretory system (CNSS) of the Nile tilapia, Oreochromis niloticus, has been investigated by means of UI/oCRF (urotensin I/ovine corticotropin-releasing factor) immunohistochemistry and transmission electron microscopy. UI-like immunoreactive perikarya and fibers are first detected in the caudal spinal cord of larval fish about 4 days after hatching (stage 21). In the region of the future urophysis two bundles of strongly immunoreactive neurosecretory fibers are observed. At this stage, neurosecretory axons terminate on the meninx sheath of the spinal cord with immature neurosecretory terminals. The histogenesis of the urophysis begins at stage 24. The future neurohemal organ consists of a small ventral swelling of the spinal cord, which is associated with dilated vessels. At this stage, neurosecretory axons terminate on the basal lamina of the ingrowing blood vessels. Further development occurs by means of progressive branching of vessels and the concomitant increase in the number of neurosecretory terminals. In the caudal spinal cord, immunoreactive neurons also increase in number and progressively differentiate morphologically. Typical features of the mature CNSS are recognizable in 4-month-old juveniles. Data suggest that in tilapia both the synthesis and the release of urophysial hormones begin before morphogenesis of the neurohemal organ takes place.

Expression Pattern of nos1 in the Developing Nervous System of Ray-Finned Fish

“…In this structure, NO acts as a local synchronizer for the neighboring neurosecretory cells [51]. The onset of the CNSS starts during early development stages, as demonstrated for Nile tilapia, Oreochromis niloticus [52], and chum salmon, Oncorhyncus keta [53]. Therefore, the presence and distribution of neuronal nos1 in medaka tailbud could be related to this neurosecretory system, but further experimental evidence is needed to test this hypothesis.…”

The distinctive morphology of caudal neurosecretory system and its impact on Pampus argenteus throughout the breeding season

“…Our findings revealed a unique structural adaptation in P. argenteus, where a marked concavity in the last vertebra corresponds with a pronounced enlargement of the ventral side of the tail spinal cord, forming the neurohypophysis concealed within this concavity. Additionally, the size of the neurohypophysis varied significantly across species, with dimensions in the North American blueback herring averaging 1.0 mm × 1.3 mm × 0.5 mm (Richard et al, 1979), in the channel catfish approximately 1.5 mm in length and 1.0 mm in diameter (Kriebel, 1980), and in Nile tilapia (Oreochromis niloticus) around 4.0 mm in length and 0.3 mm in width (Cioni et al, 2000). In this study, the neurohypophysis in both morphologies of P. argenteus was found to be relatively smaller, a trait possibly attributed to the slender vertebral bones in their tail region.…”

Le système neurosécréteur caudal, l’autre système « neurohypophysaire » des poissons

“…De ces études, il ressort toutefois que la morphogénèse du SNSC est très tardive et ne s'achève généralement que plusieurs semaines voire même plusieurs mois après l'éclosion des alevins (Fridberg & Bern, 1968). Deux études plus récentes réalisées chez le saumon Onchorynchus keta (Oka et al, 1993) et chez le tilapia Oreochromis nilotica (Cioni et al, 2000) confirment ces données en montrant que l'urophyse n'acquiert ses caractéristiques définitives qu'au bout de 5 et 4 mois de vie libre, respectivement. Chez ces deux espèces, il est toutefois intéressant de noter que l'UI et/ou l'UII peuvent être détectées par immunohistochimie dès la période de l'éclosion (juste avant ou peu après), ce qui suggère que la détermination des cellules de Dahlgren se produit beaucoup plus précocement.…”