The Effect of Water Temperature on the GABAergic and Reproductive Systems in Female and Male Goldfish (Carassius auratus)

• Published in: General and comparative endocrinology 2002-02, Vol.125 (2), p.163-175
• Main Authors: Fraser, E.J., Bosma, P.T., Trudeau, V.L., Docherty, K.
• Format: Article
• Language: English
• Subjects: amino acid neurotransmitters; Animals; Carassius auratus; Female; gamma-Aminobutyric Acid - biosynthesis; gamma-Aminobutyric Acid - physiology; Glutamate Decarboxylase - genetics; Glutamic Acid - metabolism; Goldfish - physiology; Gonadotropins, Pituitary - blood; hypothalamus; Hypothalamus - drug effects; Hypothalamus - enzymology; Hypothalamus - metabolism; Isoenzymes - genetics; luteinizing hormone; Male; pituitary; Polymerase Chain Reaction; Reproduction - physiology; RNA, Messenger - analysis; Sex Characteristics; Telencephalon - drug effects; Telencephalon - enzymology; Telencephalon - metabolism; Temperature; Vigabatrin - pharmacology; Water
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1006/gcen.2001.7714

This study investigated the effect of water temperature on the synthesis of the amino acid neurotransmitter γ-aminobutyric acid (GABA). In goldfish, GABA stimulates the release of pituitary gonadotropin-II (GTH-II), which regulates gonadal function. Fish were maintained in water of 11, 18, or 24°. In the female and male goldfish, GABA synthesis rates estimated following inhibition of GABA catabolism by γ-vinyl GABA (GVG) in both the telencephalon (TEL) and the hypothalamus (HYP) were increased in fish held at 24° compared to those at either 11 or 18° (P < 0.05). Additionally, GABA synthesis rates in the pituitary increased in a temperature-dependent manner. Glutamate is the precursor for GABA synthesis; however, no consistent pattern was seen between glutamate and GABA synthesis rates, indicating that glutamate is not a limiting factor in GABA synthesis. Both water temperature and GVG administration increased serum GTH-II levels in female goldfish. However, in male goldfish water temperature had no significant effect on serum GTH-II levels, and GVG injection increased serum GTH-II levels only in fish maintained at 24°. The effects of temperature on the levels of mRNA expression of the GABA-synthesizing enzymes glutamate decarboxylase 65 (GAD65) and GAD67 were measured by semiquantitative PCR. In the TEL and HYP of female goldfish, GAD65 was not affected, whereas temperature change from 11 to 18° increased (P < 0.05) GAD67 mRNA levels. These results demonstrate that central GABAergic systems in the goldfish are temperature sensitive.