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Amino Acid Neurotransmitters and Dopamine in Brain and Pituitary of the Goldfish: Involvement in the Regulation of Gonadotropin Secretion
Author(s) -
Sloley B. Duff,
Kah Olivier,
Trudeau Vance L.,
Dulka Joseph G.,
Peter Richard E.
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb10971.x
Subject(s) - taurine , medicine , endocrinology , glutamate decarboxylase , gonadotropin , glutamate receptor , dopamine , neurotransmitter , chemistry , pituitary gland , amino acid , biology , biochemistry , hormone , central nervous system , enzyme , receptor
An isocratic high–performance liquid chromatographic technique was developed to measure levels of γ–aminobutyric acid (GABA), glutamate, and taurine in the brain and pituitary of goldfish. Accuracy of this procedure for quantification of these compounds was established by evaluating anesthetic and postmortem effects and by selectively manipulating GABA concentrations by intraperitoneal administration of the glutamic acid decarboxylase (GAD) inhibitor 3–mercaptopropionic acid or the GABA transaminase inhibitor γ–vinyl GABA. The technique provided a simple, rapid, and reliable method for evaluating the concentrations of these amino acids without the use of complex gradient chromatographic systems. To investigate the relationship between neurotransmitter amino acids and the control of pituitary secretion of gonadotropin, the effects of injection of taurine, GABA, or monosodium glutamate on GABA, glutamate, taurine, and, in some instances, monoamine concentrations in the brain and pituitary were evaluated and related to serum gonadotropin levels. Injection of taurine caused an elevation in serum gonadotropin concentrations. In addition, injection of the taurine precursor hypotaurine but not the taurine catabolite isetheonic acid elevated serum gonadotropin levels. Intracerebroventricular injection of either GABA or taurine also elevated serum gonadotropin concentrations. Pretreatment of recrudescent fish with α–methyl– p –tyrosine reduced pituitary dopamine concentrations and also potentiated the serum gonadotropin response to taurine. Injection of monosodium glutamate caused an increase of glutamate content in the pituitary at 24 h; this was followed by a decrease at 72 h after administration. Pituitary GABA, taurine, and dopamine concentrations underwent a transient depletion after monosodium glutamate administration, and this was associated with an elevation of serum gonadotropin content. The increase in serum gonadotropin concentrations in response to a gonadotropin–releasing hormone analogue was potentiated by pretreatment with monosodium glutamate. This article demonstrates that procedures causing elevation in GABA and taurine concentrations stimulate gonadotropin release in a teleost fish.