Brain Derived Neurotrophic Factor Stimulates Hypothalamic and Gonadal Reproductive Hormones and Oocyte Maturation in Zebrafish.

Brain-derived neurotrophic factor (BDNF) is a peptide widely known for its role in neurogenesis and synaptic plasticity. Its expression in non-neuronal tissues has been reported. In mammals, it is involved in ovarian development, follicle growth, oocyte maturation, and early embryonic development. In zebrafish, it was demonstrated that BDNF increases food intake and regulates metabolism. Reproduction and metabolism are tightly linked. We hypothesized that BDNF modulates reproductive hormones and reproductive functions in zebrafish. This study aimed to determine BDNF expression in the zebrafish reproductive axis and whether it modulates the reproductive endocrine milieu and oocyte biology in zebrafish. Our results show that bdnf and its receptor trkb, and BDNF-like immunoreactivity are detected in zebrafish gonads and liver cells. This suggests BDNF local production and possible actions within the gonads and liver. Intraperitoneal administration of 1, 10, or 100 ng/g bodyweight BDNF significantly (ANOVA, p<0.05) increased sgnrh/cgnrh-II, kiss1, and cyp19a1b mRNAs in the zebrafish brain; steroidogenic enzymes (star and cyp19a1a) and key receptors in the zebrafish gonads. In vitro incubation of zebrafish liver cells with BDNF significantly (ANOVA, p<0.05) increased estrogen receptor mRNAs and vitellogenin concentrations (ELISA) in the cells. BDNF (100 ng/mL) induced (ANOVA, p<0.05) oocyte maturation in vitro at 24 hours post-incubation and significantly upregulated cumulus-expansion related genes (ANOVA, p<0.05). Overall, our findings indicate a stimulatory role for BDNF in the reproductive axis of zebrafish. This provides impetus for future research on its mechanism of action and potential practical applications to enhance reproduction in aquaculture.