“The enigmatic saccus vasculossus. Characterization of this structure in Cichlasoma dimerus”.

SALLEMI JULIETA; DI YORIO, MARÍA PAULA; BERIOTTO, AGUSTINA C; PEREZ SIRKIN, DANIELA; BRECCIA, ANDRÉS; VISSIO, PAULA G.

Faro

Simposio; 9th INTERNATIONAL SYMPOSIUM ON FISH ENDOCRINOLOGY (30th CECE & 9th ISFE); 2022

European Society of Comparative Endocrinology/ International Society for Fish Endocrinology

The enigmatic saccus vasculossus. Characterization of this structure in Cichlasoma dimerusThe saccus vasculosus (SV) is a structure present only in fish, located on the floor of the hypothalamus, posterior to the pituitary gland. It is characterized by abundant sinusoidal vessels and a folded neuroepithelium which makes a chamber that connects to the third ventricle. The neuroepithelium consists of coronet cells and supporting cells, with interspersed liquor-contacting neurons. Regarding its function, it was suggested that SV responds to changes in the cerebrospinal fluid and a recent work proposes that it is homologous to the pars tuberalis, participating in the control of seasonal reproduction. In the SV of adults and juveniles Cichlasoma dimerus, we detected immunoreactive fibers of gonadotropin inhibitory hormone, and neuropeptide Y. The objective of this study is to characterize the SV of larvae, juvenile, and adults of C. dimerus, and to evaluate the presence of the beta-thyrotropin stimulating hormone (β-Tsh) and opsins (CER-982). Adult brains and larvae/juveniles, obtained from 3 independent spawning from hatching to 85 days post-hatching, were sampled and processed for histology, transfer electron microscopy (TEM), and immunohistochemistry. In this species, the SV starts developing by the time the adenohypophysis is observed. At first, two cell types connecting with the lumen can be distinguished, while blood capillaries associated to the outer layer of the SV at the beginning of juvenile stage. Then, blood capillaries invade the SV, and the cells acquire their typical morphology showing positive β-Tsh immunoreactivity during the gonadal differentiation period. In adults, all cell types are observed showing the typical morphology described for each one, and β-Tsh and rod-opsin immunoreactivity are detected in the crown of the coronet cells in both sexes. The present work proposes that the SV can be involved in the sensing of fish seasonality and comprises the starting point for future experiments about the role of SV in adulthood and during the development of this species.