The enigmatic saccus vasculosus: Characterization of this structure in Cichlasoma dimerus

SALLEMI, JULIETA; DI YORIO, MARÍA PAULA; BERIOTTO, AGUSTINA; PÉREZ SIRKIN, DANIELA IRINA; BRECCIA, ANDRÉS; VISSIO, PAULA GABRIELA

Faro

Congreso; 9th INTERNATIONAL SYMPOSIUM ON FISH ENDOCRINOLOGY; 2022

The saccus vasculosus (SV) is a structure present only in fish, located on the floor of the hypothalamus, posteriorto the pituitary gland. It is characterized by abundant sinusoidal vessels and a folded neuroepithelium which makesa 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 changesin the cerebrospinal fluid and a recent work proposes that it is homologous to the pars tuberalis, participating inthe control of seasonal reproduction. In the SV of adults and juveniles Cichlasoma dimerus, we detectedimmunoreactive fibers of gonadotropin inhibitory hormone, and neuropeptide Y. The objective of this study is tocharacterize the SV of larvae, juvenile, and adults of C. dimerus, and to evaluate the presence of the betathyrotropin stimulating hormone (β-Tsh) and opsins (CER-982). Adult brains and larvae/juveniles, obtained from3 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 theouter layer of the SV at the beginning of juvenile stage. Then, blood capillaries invade the SV, and the cellsacquire their typical morphology showing positive β-Tsh immunoreactivity during the gonadal differentiationperiod. In adults, all cell types are observed showing the typical morphology described for each one, and β-Tshand rod-opsin immunoreactivity are detected in the crown of the coronet cells in both sexes. The present workproposes that the SV can be involved in the sensing of fish seasonality and comprises the starting point for futureexperiments about the role of SV in adulthood and during the development of this species.