Both micromolar and sub-picomolar concentrations of SN are neuroprotective against LPS-induced neurotoxicity. Rat primary mesencephalic neuron-glia cultures seeded in a 24-well culture plate with 5 × 105 rat midbrain cells, then pretreated with SN (10-17 to 10-5 M) for 30 min before the addition of 10 ng/ml LPS. Eight days later, the LPS-induced dopaminergic neurotoxicity was quantified by the [3H]-DA uptake assay (A); by immunocytochemical analysis, including TH-IR neuron counts (B); and by representative pictures of immunostained sections (C). Results are expressed as percentage of vehicle-treated control cultures and represent the mean ± SE. for four (A) or three (B, C) independent experiments in triplicate. The mean absolute values of [3H]-DA uptake for vehicle-treated cultures range from 5000 to 7000 cpm. *P < 0.05, **P < 0.01 compared with the LPS-treated cultures.