INTERACTION BETWEEN GLUTAMATE AND GABA ON H-3 NORADRENALINE RELEASE FROM RAT HYPOTHALAMUS

Glutamate has been shown to stimulate noradrenaline (NA) release from hypothalamic nerve terminals. In the present study, we evaluated the p ossible interaction between the excitatory amino acid glutamate and ga mma-aminobutyric acid (GABA), an inhibitory transmitter, on noradrenal ine (NA) release from mediobasal hypothalamus (MBH) of adult male rats . Hypothalamic slices loaded in vitro with H-3-NA were superfused and exposed to glutamate, N-methyl-D-aspartic acid (NMDA), or kainate (KA) . We found that 3H-NA release evoked by the excitatory amino acids glu tamate and NMDA was dramatically decreased by GABA. The facilitatory e ffects of NMDA and KA were prevented concentration-dependently by the GABA(B) receptor antagonist 2-hydroxy saclofen which restored the NMDA effect. In addition, baclofen blocked K+-induced H-3-NA release. Acti vation of GABA(A) receptors by muscimol and THlP was ineffective. In c onclusion, glutamate and GABA, through GABA(B) receptors, may interact to modulate NA release from the rat mediobasal hypothalamus.