Release-regulating GABAA receptors are present on noradrenergic nerve terminals in selective areas of the rat brain.

The effects of gamma-aminobutyric acid (GABA) on the spontaneous release of [3H]-norepinephrine ([3H]-NE) were investigated by means of superfused synaptosomes prepared from different areas of the rat brain and prelabeled with [3H]-NE. GABA increased in a concentration-dependent way (1-300 microM) the release of [3H]-NE in hippocampal synaptosomes. The effect of GABA was mimicked in part by muscimol. Similar effects were observed in cerebral cortex synaptosomes where GABA and muscimol were however less potent than in hippocampus. No effect could be observed in hypothalamic synaptosomes. Bicuculline antagonized the effect of muscimol and that of low concentrations of GABA (below 10 microM). Above 10 microM, the [3H]-NE releasing effects of GABA became progressively less sensitive to bicuculline. (-)-Baclofen did not affect the spontaneous release of [3H]-NE. It is concluded that release-regulating receptors of the GABAA subtype are present on NE nerve terminals in selective areas of the rat brain.