Ontogeny of adenohypophyseal cells, pituitary gland development, and structure in adults of Astyanax lacustris (Teleostei, Characiformes): an emerging Neotropical model fish species.

Pituitary gland morphogenesis and the ontogeny of the adenohypophyseal (AH) cells of Astyanax lacustris are presented herein. This Characiformes species shows great ecological and commercial importance, and it has been increasingly used as animal model. For this study, A. lacustris specimens were collected from 0.5 to 120 days after hatching (dah) (adults). The entire animal or its head was appropriately fixed, and after histological processing, the sections were subjected to histochemical and immunohistochemical reactions, using homologous and heterologous antibodies. The first AH cells of A. lacustris were detected at 1 dah by the immunostaining of prolactin (PRL)-producing cells. The morphology of the gland presented changes in shape throughout the development, starting with elongation but more oval at the end. The neurohypophysis was differentiated at 3 dah, along with the identification of adrenocorticotropic hormone (ACTH), melanotropic hormone (MSH), thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH)-producing cells. Identification of the immunoreactive cells to anti-luteinizing hormone (LH), anti-somatolactin (SL), and anti-growth hormone (GH) antibodies occurred at 5 dah. At 20 dah, an increase in pituitary proportions and the presence of the pituitary stalk were observed. At 60 dah, the pituitary gland already had the same shape and distribution of AH cells seen in the adult. The ontogeny of adenohypophyseal cells in A. lacustris corroborates the heterogeneity in the appearance of these cell types in teleosts and suggests that these hormones actively participate during the post-hatching development of this species, even before the establishment of all endocrine axes. Our findings contribute to understanding the morphogenesis of the hypothalamic-pituitary axis in South American teleosts, providing essential data for the development of future studies related to pituitary gland morphophysiology under normal or experimental conditions.