NITRIC-OXIDE INCREASES INTERSTITIAL EXCITATORY AMINO-ACID RELEASE IN THE RAT DORSOMEDIAL MEDULLA-OBLONGATA

In vivo microdialysis was employed to measure release of the neuroactive amino acids L-glutamate (Glu) and L-aspartate (Asp) in the dorsomedial medulla oblongata of the anaesthetised rat. Basal levels of endogenous extracellular Glu and Asp were increased over 5-fold and 3-fold, respectively, following perfusion with a depolarising stimulus of KCl. Intracerebral administration of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP, 30 muM) caused a 5-fold increase in extracellular Asp and a 2-fold increase in extracellular Glu, which was blocked by Methylene blue. These data suggest that NO, acting through guanylate cyclase, can affect excitatory amino acid neurotransmission in the dorsomedial medulla oblongata.