Flupirtine protects neurons against excitotoxic or ischemic damage and inhibits the increase in cytosolic Ca2+ concentration

We tested the effect of flupirtine against ischemic and excitotoxic neuronal damage as well as on the glutamate-induced rise in cytosolic calcium ion concentration (= [Ca2+](i)). For in vivo experiments we used a model of focal cerebral ischemia in mice. The middle cerebral artery was permanently occluded and 48 h afterwards brain tissue was stained with neutral red, perfusion-fixed and the infarct surface was determined planimetrically. Pretreatment with flupirtine significantly reduced the infarct area (controls: 24.3 +/- 4.8 mm(2), 1 mg/kg flupirtine: 20.1 +/- 3.6 mm(2) and 10 mg/kg flupirtine: 19.5 +/- 3.9 mm(2); P < 0.05), whereas postischemic application of flupirtine failed to reduce the infarct area. For in vitro studies, primary neuronal cultures were prepared from the hippocampi of newborn rats and excitotoxic damage was induced by exposing the cells to 500 mu M L-glutamate for 30 min. We could demonstrate that flupirtine (1-10 mu M) was capable of protecting neurons against glutamate-induced cytotoxicity. In order to elucidate the underlying mechanism of action, we tested the effect of flupirtine on the glutamate-induced rise in [Ca2+](i) using the Ca2+-indicator fura-2. L-Glutamate added in a final concentration of 100 mu M to the cultured cells for 16 s caused a rise in [Ca2+](i) from about 100 nM to 900 nM. Flupirtine (0.1-10 mu M) reduced the glutamate-induced rise in [Ca2+](i), concentration dependently.