Nitric Oxide Produced During Ischemia Is Toxic but Crucial to Preconditioning-Induced Ischemic Tolerance of Neurons in Culture

Abstract

The present study investigated the roles of nitric oxide (NO) in preconditioning (PC)-induced neuronal ischemic tolerance in cortical cultures. Ischemia in vitro was simulated by subjecting cultures to both oxygen and glucose deprivation (OGD). A sublethal OGD (PC) significantly increased the survival rate of neurons when cultures were exposed to a lethal OGD 24 hr later. Both the inhibition of nitric oxide synthase (NOS) and scavenging of NO during PC significantly attenuated the PC-induced neuronal tolerance. In addition, exposure to an NO donor emulated the PC. In contrast, the inhibition of NOS and the scavenging of NO during lethal OGD tended to increase the survival rate of neurons. This study suggested that NO produced during ischemia was fundamentally toxic, but critical to the development of PC-induced neuronal tolerance.

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 addition, we also demonstrated the possibility that nitric oxide (NO) produced during PC is involved in the development of the PC-induced ischemic tolerance of neurons (10). Therefore, we first investigated whether the PC-induced suppression of the rise in the concentration of extracellular Glu was antagonized by the inhibition of NO production during PC in neuron/astrocyte co-cultures (Fig.…”

“…In addition, Yun et al (24) have recently demonstrated that the activation of p21 RAS induced by NO derived from nNOS is responsible for the PC-induced tolerance of neurons, suggesting that NO is a key mediator in the process leading to resistance against lethal ischemia. We have previously demonstrated that the enhanced production of NO is crucial to the development of PC-induced ischemic tolerance of neurons in neuron/astrocyte co-cultures (10).…”

“…Culture methods were described previously in detail (3,4,10,11). In brief, both neurons and astrocytes were prepared from 17-day old embryonic rat cortices and grown in Dulbecco's modified Eagle's medium (DMEM, Gibco, Grand Island, NY) which was supplemented with 10% heat-inactivated fetal bovine serum (FBS), 10%…”

“…We have previously revealed that the production of nitric oxide (NO) is 3 increased during PC, and this enhanced NO production is crucial to the development of PC-induced neuronal ischemic tolerance in cultured neurons (10). In addition, we have recently revealed that in neuron/astrocyte co-cultures the expression of the astrocytic glutamate transporter GLT-1 is transiently down-regulated after PC treatment, and the ischemia-induced rise in the extracellular concentration of glutamate via a reversed uptake of glutamate by GLT-1 is significantly suppressed (3).…”

Reversed Actrocytic GLT-1 during Ischemia is Crucial to Excitotoxic Death of Neurons, but Contributes to the Survival of Astrocytes themselves

“…Neuron/astrocyte co-culture Culture methods were described previously in detail (11)(12)(13). In brief, neurons/astrocytes were prepared from 17-day-old embryonic rat cortices and grown in Dulbecco's modified Eagle's medium (DMEM, Gibco, Grand Island, NY) which was supplemented with 10% heat-inactivated fetal bovine serum (FBS), 10% Ham's F12, and 0.24% penicillin/streptomycin (culture medium) and maintained in a 5% CO 2 incubator at 37 °C.…”