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Neuroendocrine gene expression reveals a decrease in dopamine D2B receptor with no changes in GnRH system during
Shan-Ru Jeng1, Wen-Shiun Yueh1, Yi-Ting Pen1
1Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan.
General and Comparative Endocrinology
|August 16, 2014
Summary
Silvering in female Japanese eels involves moderate gonad development, driven by increased estrogen and testosterone. A decrease in dopamine D2B receptor expression in the pituitary may reduce inhibition, aiding this reproductive preparation.
Area of Science:
- Endocrinology
- Neuroendocrinology
- Fish Biology
Background:
- Silvering is a crucial metamorphic stage in female eels, preceding oceanic migration and involving gonad development.
- Previous research indicates moderate ovarian growth during this transition from yellow to silver stages.
Purpose of the Study:
- To investigate the molecular endocrine mechanisms underlying ovarian development during silvering in Japanese eels.
- To elucidate the roles of the brain-pituitary-gonadal (BPG) axis and dopaminergic control in this process.
Main Methods:
- Quantification of gonad somatic index (GSI) and histological analysis of oocytes.
- Measurement of serum estradiol (E2) and testosterone (T) levels.
- Real-time quantitative PCR (qPCR) to analyze gene expression of gonadotropins (FSH-β, LH-β), GnRH system components, and dopamine receptors (D2A, D2B).
Main Results:
- Serum E2 and T significantly increased with ovarian development, indicating enhanced steroidogenesis.
- Pituitary FSH-β and LH-β transcript levels were elevated, supporting increased gonadotropin expression.
- Brain GnRH system gene expression remained unchanged, while tyrosine hydroxylase (dopamine synthesis) was maintained.
- A significant decrease in dopamine D2B receptor (DA-D2BR) expression was observed in the forebrain and pituitary.
Conclusions:
- Silvering involves significant activation of steroidogenesis and pituitary gonadotropin expression, correlating with ovarian development.
- The GnRH system gene expression does not appear to be upregulated during silvering.
- Reduced expression of the pituitary dopamine D2B receptor may alleviate dopaminergic inhibition, contributing to the activation of the pituitary-gonadal axis during eel silvering.
