Release of [3H]- and endogenous GABA from slices of the rat medulla oblongata: modification by 3-mercaptopropionic acid, nipecotic acid and diaminobutyric acid

Abstract

Slices of the rat medulla oblongata were superfused and electrically stimulated. The amount of [3H]- and endogenous GABA was determined. There was a stimulus-evoked release of [3H]- and endogenous GABA, which was Ca2+-dependent and tetrodotoxin-sensitive. 3-Mercaptopropionic acid (3-MP) reduced the release of endogenous GABA, whereas the release of [3H]-GABA was not affected by this agent. Nipecotic acid enhanced the spontaneous and stimulus-evoked release of both [3H]- and endogenous GABA. 3-MP, nipecotic acid and diaminobutyric acid modified the stimulus-evoked release of endogenous GABA from slices containing the rostral ventrolateral medulla, the caudal ventrolateral medulla or the nucleus tractus solitarii, regions responsible for blood pressure regulation. These results suggest that 3-MP inhibits the stimulus-evoked release of GABA without affecting its release process, whereas nipecotic acid enhances the release via its uptake inhibition action.