Lipopolysaccharide preconditioning induces protection against lipopolysaccharide-induced neurotoxicity in organotypic midbrain slice culture.

OBJECTIVE: To identify the protective effect of lipopolysaccharide (LPS) preconditioning against LPS-induced inflammatory damage in dopaminergic neurons of midbrain slice culture and the possible mechanisms.
METHODS: After cultured in vitro for 14 d, the rat organotypic midbrain slices were pretreated with different concentrations (0, 1, 3, 6 or 10 ng/mL) of LPS for 24 h followed by treatment with 100 ng/mL LPS for 72 h. The whole slice viability was determined by measurement of the activity of lactic acid dehydrogenase (LDH). Tyrosine hydroxylase-immunoreactive (TH-IR) neurons and CD11b/c equivalent-immunoreactive (OX-42-IR) microglia in the slices were observed by immunohistochemical method, and tumor necrosis factor-alpha (TNF-alpha) levels in the culture media were detected by enzyme-linked immunosorbent assays (ELISA).
RESULTS: In the slices treated with 100 ng/mL LPS for 72 h, the number of TH-IR neurons reduced from 191+/-12 in the control slices to 46+/-4, and the LDH activity elevated obviously (P < 0.01), along with remarkably increased number of OX-42-IR cells and production of TNF-alpha (P < 0.01). Preconditioning with 3 or 6 ng/mL LPS attenuated neuron loss (the number of TH-IR neurons increased to 126+/-12 and 180+/-13, respectively) and markedly reduced LDH levels (P < 0.05), accompanied by significant decreases of OX-42-IR microglia activation and TNF-alpha production (P < 0.05).
CONCLUSION: Low-dose LPS preconditioning could protect dopaminergic neurons against inflammatory damage in rat midbrain slice culture, and inhibition of microglial activation and reduction of the proinflammatory factor TNF-alpha production may contribute to this protective effect. Further understanding the underlying mechanism of LPS preconditioning may open a new window for treatment of Parkinson's disease.