Morphofunctional Characteristics of the Hypothalamo-Hypophyseal Neurosecretory System (HHNS) in Round Goby, Gobius melanostomus Pallas, in Early Ontogenesis

Abstract

The development of the HHNS was studied in fry born in aquaria, from 1 to 60 days after hatching. Fixations of fish were done every 3–5 days. In newly hatched fry, certain parts of the HHNS were already formed. In the adenohypophysis (A), pro-, meso-, and meta-A are distinguished; chromophil cells are absent. In distal parts of the neurohypophysis (NH) there is some compact PAS-negative, Gomori-positive substance. However, the nucleuspreopticus neurosecretory cells and the preopticohypophyseal tract are not seen; neither are the nucleus-lateralis-tuberis cells. Individual capillaries are present in the NH of fry from the 1st day of life. Their number increases with age, indicating the possibility of release of neurosecretory material into the blood. In 7–10 days acidophilic cells of the meso-A associated with growth regulation are differentiated. At 15 days one sees acidophilic cells of the pro-A and, at 20–25 days, basophilic cells of the meso-A, which have a thyrotropic function. Before the beginning of morphologic differentiation of acidophilic and basophilic cells of the meso-A the contacts of the Gomori-positive fibers with corresponding cell types appear in the region of these cells. This fact suggests participation of Gomori-positive neurosecretion in the differentiation of adenohypophyseal cells. As fry develop, the amount of neurosecretory substance in the NH increases, as does the number of axoadenar contacts within the A. They are mostly found in the zone of basophilic cells. Since the first capillaries are observed in the meso-A only in 45-day-old gobies, it seems that neuronal adenocriny is one of the principal ways by which neurohormonal factors influence the A glandular cells of the round goby during its early ontogenesis .