Distribution of γ-aminobutyric acid in catfish (Heteropneustes fossilis) forebrain in relation to season, ovariectomy and E2 replacement, and effects of GABA administration on plasma Gonadotropin-II level |
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Authors: | K P Joy B Tharakan H J Th Goos |
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Institution: | a Department of Zoology, Banaras Hindu University, Varanasi 221005, India;b Department of Experimental Zoology, University of Utrecht, P.O. Box 80058, 3508 TB Utrecht, The Netherlands |
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Abstract: | In the catfish Heteropneustes fossilis, the hypothalamus and telencephalon showed seasonal variations in γ-aminobutyric acid (GABA) with high levels in prespawning and spawning phases and low levels in preparatory and postspawning phases. Ovariectomy for 4 and 5 weeks reduced significantly the GABA contents only in the hypothalamus. Replacement with E2 (1 μg/g BW) restored the levels to that of sham ovariectomized or parallel control group. Treatment with GABA (i.p.; 10 or 50 μg/g body weight (BW)) alone did not produce any significant effect on plasma gonadotropin-II (GTH-II) level in any of the seasons. Injection of GABA, but not baclofen (a GABAB agonist), stimulated GTH-II secretion in pimozide or GnRH analogue-pimozide pretreated fish at both 0.5 and 2 h in early prespawning phase except at 0.5 h in the pimozide—GABA (10 μg) group. This stimulatory effect was not evident in other seasons. The results of the present study suggest that Estradiol-17β (E2) seems to stimulate GABA which may account for its high level in the recrudescent phase. GABA seems to have a permissive role in GTH-II secretion when dopamine receptor function is inhibited. |
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Keywords: | Catfish Hypothalamic GABA Gonadotropin-II Ovariectomy GnRH analogue Pimozide Baclofen GABAA receptor |
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