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-Aminobutyric Acid Up-Regulates the Expression of a Novel Secretogranin-II Messenger Ribonucleic Acid in the Goldfish Pituitary¹

Department of Zoology (M.B., P.T.B., V.L.T.), University of Aberdeen, Aberdeen, AB24 2TZ, United Kingdom; Department of Biological Sciences (J.P.C.), University of Alberta, Edmonton, Alberta, T6G 2E9, Canada; and Department of Molecular and Cellular Biology (M.B., P.T.B., K.D.), Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, United Kingdom

Address all correspondence and requests for reprints to: Vance L. Trudeau, Department of Biology, University of Ottawa. P.O. Box 450, Station A. Ottawa, Ontario K1N 6N5, Canada. E-mail: vtrudeau{at}science.uottawa.ca

An RNA-arbitrarily primed PCR differential display strategy was used to identify candidate genes in the pituitary that are up-regulated by endogenously activated -aminobutyric acid (GABA) systems that may also be involved in the control of reproduction. Goldfish were injected with the GABA metabolism inhibitor -vinyl-GABA (GVG), known for its high efficiency to specifically increase endogenous brain and pituitary GABA levels in this species, resulting in higher levels of circulating gonadotropin-II (GTH-II). Several transcripts related to hormone secretion, signal transduction pathways, and messenger RNA (mRNA) editing were shown to be up-regulated after GVG injection. Among these transcripts we characterized an mRNA coding for the secretory vesicle protein secretogranin-II (SgII), a member of the chromogranin family, which is the precursor of a novel 34 amino acid neuropeptide, goldfish secretoneurin (SN). A semiquantitative PCR developed to measure pituitary SgII mRNA levels showed a 5-fold increase in GVG treated fish vs. control fish. Moreover, GVG treatment specifically increased SgII mRNA levels in gonadotrophs, concomitant with a decrease in GTH-II cell content. In addition, ip injection of synthetic goldfish SN increased GTH-II release in goldfish pretreated with the dopamine antagonist domperidone. Activation of GABAergic neurons has two effects, enhancing in vivo GTH-II release and up-regulating SgII mRNA specifically in goldfish gonadotrophs. Together with our SN bioactivity data, this suggests the existence in the pituitary of an autocrine or paracrine mechanism linked to the regulated secretory pathway in the gonadotrophs.

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