Effect of untreated and NECA-treated astrocyte supernatants on survival of cultured cortical neurons against excitotoxicity. Primary cortical neurons were treated without or with recombinant mouse Leukemia inhibitory factor (rmLIF, 0.1 ng/mL), NECA (1 μM) or astrocyte supernatants (untreated or treated with 1 μM NECA for 4 hours; diluted 1:1 in neuronal culture medium) for 24 hours. Where indicated, rmLIF and NECA-treated astrocyte supernatants were treated with an anti-LIF neutralizing antibody (AF449; 100 ng/mL for 1.5 hours) before applying them to cultured neurons. Subsequently, the neurons were treated without or with glutamate (Glut.; 50 μM for 1 hour) and cell survival assessed 24 hours after glutamate treatment by a colorimetric MTT assay. The optical densities were measured at 570 nm, with a 630 nm and blank correction. Data are normalized to percent of control and presented as Mean ± S.E.M of four independent experiments. P < 0.05, when compared to glutamate-treated condition. NECA, 5′-N-ethylcarboxamide.