Abstract
Artificial sexual maturation of eel (Anguilla japonica) involves rearing in seawater and injecting salmon pituitary extract (SPE). The salinity of seawater and components of SPE influence hormonal activities of the eel pituitary, leading to gonad development. This study investigated the direct effects of salinity change and SPE treatment on the eel pituitary gland using primary cell cultures. Pituitary cells were cultured into four experimental groups: control culture (control), SPE-treated culture (SPE), NaCl-treated culture (NaCl) and NaCl+SPE treated culture (NaCl+SPE). We investigated the expression of genes presumably related to reproduction and/or salinity, including luteinizing hormone (LHβ), follicle stimulating hormone (FSHβ), progesterone receptor-like (pgrl), prolactin (PRL), dopamine receptor D4 (drd4), neuropeptide B/W receptor 2 (NPBWR2) and relaxin family peptide receptor 3-2b (rxfp3-2b). Gene expression analysis revealed significant upregulation of LHβ in SPE and NaCl+SPE groups compared to control and NaCl (p<0.05). FSHβ expression did not show any significant changes. PRL showed a significant decrease in the NaCl group (p<0.05). Pgrl, NPBWR2, drd4, and rxfp3-2b displayed the highest expression in the control group, with downregulation observed in all treatment groups (NaCl, SPE, and NaCl+SPE) (p<0.05). This study demonstrated the direct effects of salinity changes and SPE treatment on the eel pituitary. Results from this study also suggest that salinity change is necessary but work together with SPE to induce reproductive process, and that LHβ, pgrl, PRL, drd4, NPBWR2, and rxfp3-2b genes are obviously associated with reproduction and salinity changes in eels.