DEVELOPMENT OF MELANIN-CONCENTRATING HORMONE-IMMUNOREACTIVE ELEMENTS IN THE BRAIN OF GILTHEAD SEABREAM (SPARUS-AURATUS)

The development of the hypothalamic melanin-concentrating hormone (MCH ) system of the teleost Sparus auratus has been studied by immunocytoc hemistry using an anti-salmon MCH serum. Immunoreactive perikarya and fibers are found in embryos, larvae, and juvenile specimens. In juveni les, most labeled neurons are present in the nucleus lateralis tuberis ; some are dispersed in the nucleus recessus lateralis and nucleus per iventricularis posterior. From the nucleus lateralis tuberis, MCH neur ons project a conspicuous tract of fibers to the ventral hypothalamus; this penetrates the pituitary stalk and reaches the neurohypophysis. Most fibers end close to the cells of the pars intermedia, and some re ach the adenohypophysial rostral pars distalis, Immunoreactive fibers can also be seen in extrahypophysial localizations, such as the preopt ic region and the nucleus sacci vasculosi. In embryos, MCH-immunoreact ive neurons first appear at 36 h post-fertilization in the ventrolater al margin of the developing hypothalamus. In larvae, at 4 days post-ha tching, perikarya can be observed in the ventrolateral border of the h ypothalamus and in the mid-hypothalamus, near the ventricle. At 26 day s post-hatching, MCH perikarya are restricted to the nucleus lateralis tuberis. The neurohypophysis possesses MCH-immunoreactive fibers from the second day post-hatching. The results indicate that MCH plays a r ole in larval development with respect to skin melanophores and cells that secrete melanocyte-stimulating hormone.