Nitrogen oxides (NO) such as nitric oxide have been suggested to potentiate neurotransmitter release in a variety of neuronal cells. In this study, we showed that NO donors stimulate the release of noradrenaline (NA) from rat hippocampus both in vivo and in vitro. Co-addition of NO donors (sodium nitroprusside [SNP] or S-nitroso-N-acetylpenicillamine [SNAP]) and thiol compounds (dithiothreitol [DTT] or L-cysteine) stimulated [3H]NA release from prelabeled hippocampal slices. Microdialysis in freely moving rats was used to ascertain the role of NO in control of NA release from the hippocampus in vivo. Co-addition of SNAP and L-cysteine stimulated endogenous NA release within 30 min. The concentration of NA peaked between 30-60 min to almost 3 times basal level. Another thiol compound, glutathione, had no effect on [3H]NA release in the presence of SNP or SNAP. In the presence of SNAP, the effect of L-cysteine was much higher than that of the D-isomer, although SNAP did not show stereospecificity. The effect of SNAP/L-cysteine was rapid and the maximal increase in [3H]NA release was attained 0-1 min after application, which was similar in time course to the effect of KCI. Unlike the release by KCI, SNAP/L-cysteine-stimulated NA release was independent of extracellular CaCl2. However, pretreatment with the calmodulin antagonists W-7 or trifluoperazine significantly reduced the SNAP/L-cysteine-stimulated [3H]NA release. Formation of nitric oxide and activation of guanylate cyclase by nitric oxide were not responsible for SNAP/L-cysteine-stimulated NA release. These findings suggest that NO donors stimulate NA release from the hippocampus in the presence of thiol compounds such as L-cysteine in vivo and in vitro in a calmodulin-dependent, Ca(2+)-and cyclic GMP-independent manner. The physiological roles of thiol compounds such as L-cysteine or glutathione as intermediates of NO are discussed.
Animals Calmodulin