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Gonadotropin-releasing hormone (GnRH): expression during salmon migration
I S Parhar1, N Koibuchi, M Sakai
1National Research Institute of Aquaculture, Tochigi, Japan.
Neuroscience Letters
|May 19, 1994
Summary
Researchers found gonadotropin-releasing hormone (GnRH) neurons in chum salmon, with expression potentially linked to thyroid hormones. This suggests thyroid hormones may drive migratory behavior and GnRH expression during seaward migration.
Area of Science:
- Neuroendocrinology
- Fish Biology
- Reproductive Physiology
Background:
- Gonadotropin-releasing hormone (GnRH) regulates reproduction in vertebrates.
- Understanding GnRH neuron distribution and regulation is key to deciphering migratory behaviors in fish.
Purpose of the Study:
- To investigate the distribution of GnRH neurons in seaward migrating chum salmon.
- To explore the relationship between GnRH expression, thyroid hormones, and migratory behavior.
Main Methods:
- Immunocytochemistry and in situ hybridization were used to locate GnRH neurons.
- Plasma thyroid hormone levels were measured during the migratory period.
Main Results:
- GnRH neurons were identified in the nasal epithelium, nervus terminalis, olfactory bulb (rostroventral and caudalmost ganglia), and a novel ganglion at the cribriform bone.
- Increased GnRH mRNA in specific ganglia and a surge in plasma thyroid hormones were observed during migration.
- GnRH immunoreactivity, but not mRNA, was detected in midbrain neurons.
Conclusions:
- Thyroid hormones may play a crucial role in upregulating GnRH expression.
- Thyroid hormones are hypothesized to be essential for the migratory behavior of chum salmon.