ABSTRACT
It has been generally accepted that glutamate mediates the ischemic brain damage, excitotoxicity, and induces release of neurotransmitters, including norepinephrine (NE), in ischemic milieu. In the present study, the role of nitric oxide (NO) in the ischemia-induced (3H)norepinephrine((3H)NE) release from cortex slices of the rat was examined. Ischemia, deprivation of oxygen and glucose from Mg2+/-free artificial cerebrospinal fluid, induced significant release of (3H)NE from cortex slices. This ischemia-induced (3H)NE release was significantly attenuated by glutamatergic neurotransmission modifiers. NG-nitro-L-arginine methyl ester (L-NAME), NG-monomethyl-L-arginine (L-NMMA) or 7-nitroindazole, nitric oxide synthase inhibitors attenuated the ischemia-evoked (3H)NE release. Hemoglobin, a NO chelator, and 5, 5-dimethyl-L-pyrroline-N-oxide (DMPO), an electron spin trap, inhibited (3H)NE release dose-dependently. Ischemia-evoked (3H)NE release was inhibited by methylene blue, a soluble guanylate cyclase inhibitor, and potentiated by 8-bromo-cGMP, a cell permeable cGMP analog, zaprinast, a cGMP phosphodiesterase inhibitor, and S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide generator. These results suggest that the ischemia-evoked (3H)NE release is mediated by NMDA receptors, and activation of NO system is involved.