Nitric oxide produced during sublethal ischemia is crucial for the preconditioning-induced down-regulation of glutamate transporter GLT-1 in neuron/astrocyte co-cultures

In the brain, prior sublethal ischemia ( preconditioning, PC) produces tolerance of neurons to subsequent lethal ischemia. This study aims at elucidating whether and how nitric oxide ( NO) produced during PC is involved in the PC-induced ischemic tolerance of neurons in neuron/astrocyte co-cultures. The rise in the extracellular concentration of glutamate during ischemia caused by the reversed uptake of glutamate (Glu) by the astrocytic Glu transporter GLT-1 was markedly suppressed by the prior PC treatment, but the suppression was reversed by treatment with an inhibitor of nitric oxide synthase ( NOS) during PC. Immunocytochemical and Western blot analyses demonstrated that the expression of GLT-1 was down-regulated after the PC insult, and this down-regulation was also antagonized by treatment with NOS inhibitors during PC. Here we show that nNOS-derived NO produced during PC was crucial for the down-regulation of astrocytic GLT-1, and this down-regulation coincided with an increased survival rate of neurons.