Distribution of gamma-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.
In the catfish Heteropneustes fossilis, the hypothalamus and telencephalon showed seasonal variations in gamma-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 microgram/g BW) restored the levels to that of sham ovariectomized or parallel control group. Treatment with GABA (i.p.; 10 or 50 micrograms/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 micrograms) group. This stimulatory effect was not evident in other seasons. The results of the present study suggest that Estradiol-17 beta (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.
Joy
K P
KP
Department of Zoology, Banaras Hindu University, Varanasi, India. kpjoy@banaras.ernet.in
Tharakan
B
B
Goos
H J
HJ
D000818:Animals; D002397:Catfishes / Q000502:physiology; D004958:Estradiol / Q000008:administration & dosage*; D005260:Female; D006062:Gonadotropins / Q000097:blood*; D010052:Ovariectomy; D016548:Prosencephalon / Q000378:metabolism*; D015203:Reproducibility of Results; D012621:Seasons; D005680:gamma-Aminobutyric Acid / Q000008:administration & dosage / Q000378:metabolism*
D006062:Gonadotropins; D004958:Estradiol; D005680:gamma-Aminobutyric Acid