GABAergic MODULATION OF GONADOTROPIN (GtH2) SECRETION FROM CARP (Cyprinus carpio L.) HYPOPHYSIS

Mirosława Sokołowska-Mikołajczyk; Jarosław Chyb; Tomasz Mikołajczyk; Piotr Epler; Krzysztof Bieniarz; Włodzimierz Popek

Mirosława Sokołowska-Mikołajczyk
Jarosław Chyb
Tomasz Mikołajczyk
Piotr Epler
Krzysztof Bieniarz
Włodzimierz Popek

Keywords: GABA, COMMON CARP, SUBTYPES OF GABA RECEPTORS, GtH2

Abstract

Experiments in vivo and in vitro concerned the influence of GABA, agonists and antagonists of GABA_A and GABA_B receptor subtypes (isonipecotic acid - INIP, bicuculline - BIC, baclofen - BAC, 5-aminovaleric acid- AVA, muscimol - MUS) on gonadotropin (GtH2) secretion stimulated by GnRH-A analog in sexually mature carp around the spawning period. Influence of dopaminergic system on GtH2 release in fish was taken into account and that is why some experiments were carried out with the fish injected with pimozide - a dopamine antagonist.

These experiments demonstrated that GABA affected the GtH2 secretion from carp pituitary gland through the type A as well as type B receptors. It inhibited GtH2 secretion through the type A receptors at the level of hypothalamus (via inhibition of GnRH release). It also stimulated GtH2 release (at the hypothalamus level) by means of B type of GABA receptors due to impeding dopamine release, whereas at the level of hypophysis it inhibited GtH2 release through inhibition of GnRH secretion from the nerve endings.