GABAERGIC CONTROL OF PROLACTIN-RELEASE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) PITUITARIES IN-VITRO

The involvement of gamma-aminobutyric acid (GABA) in the control of pr olactin (PRL) release was investigated in rainbow trout using both per ifused pituitary fragments and pituitary cells in primary culture. In our perifusion system, infusion of GABA (10(-6) to 10(-4) M) caused an inhibition of PRL release (between 20 and 40%). Administration on per ifused pituitary fragments of 3APS, a GABAa agonist, mimicked this inh ibitory effect. Moreover, bicuculline, a specific antagonist of GABAa receptors, totally abolished GABA effect. When tested on cultured pitu itary cells during 40h exposure, GABA (10(-5) M) caused a significant decrease in PRL release (24.5 %). Baclofen, a specific agonist for GAB Ab receptor tested at 10(-6) and 10(-5) M, also inhibited PRL released from cultured pituitary cells. These results demonstrate that GABA in hibits PRL release by acting directly on pituitary cells and that prob ably both types of GABA receptor (a and b) are involved in this regula tion.