Interaction between GABA, GnRH and Activin A in the Goldfish Neuroendocrine Brain

Abstract

The neurotransmitter gamma-aminobutyric acid (GABA) stimulates the release of luteinizing hormone (LH) by enhancing gonadotropin-releasing hormone (GnRH) release in the goldfish, Carassius auratus. Activin A is another protein that stimulates the release of LH. Activin A also stimulates the release of GnRH from the rat hypothalamus, but this effect has never been shown in fish. Using real-time RT-PCR, we have shown that an injection of baclofen, a GABAB receptor agonist, into sexually mature goldfish stimulates the expression of activin betaA subunits in the telencephalon and sGnRH in the hypothalamus. Baclofen also inhibits the expression of that activin receptor IIB and IB in the hypothalamus. Immunocytochemical studies show that activin betaA subunits and activin receptors are localised in the olfactory bulb, telencephalon, thalamus, hypothalamus and optic tectum. Activin receptors are colocalised with GnRH fibres in the hypothalamus. This study has provided further insight into the role of activin as a neuroendocrine factor controlling reproduction in the goldfish brain.