Effects of intraperitoneal injection of lipopolysaccharide-induced peripheral inflammation on dopamine neuron damage...

Current studies have documented neuroinflammation is implicated in Parkinson's disease. Recently, growing evidence indicated peripheral inflammation plays an important role in regulation of neuroinflammation and thus conferring protection against dopamine (DA) neuronal damage. However, the underlying mechanisms are not clearly illuminated.

The effects of intraperitoneal injection of LPS (LPS_[i.p.] )-induced peripheral inflammation on substantia nigra (SN) injection of LPS (LPS_[SN] )-elicited DA neuronal damage in rat midbrain were investigated. Rats were intraperitoneally injected with LPS (0.5 mg/kg) daily for 4 consecutive days and then given single injection of LPS (8 μg) into SN with an interval of 0 (LPS_(i.p.) 0 day ± LPS_(SN) ), 30 (LPS_(i.p.) 30 days ± LPS_(SN) ), and 90 (LPS_(i.p.) 90 days ± LPS_(SN) ) days after LPS_(i.p.) administration.

LPS_(i.p.) increased the levels of inflammatory factors in peripheral blood in (LPS_(i.p.) 0 day ± LPS_(SN) ). Importantly, in (LPS_(i.p.) 0 day ± LPS_(SN) ) and (LPS_(i.p.) 30 days ± LPS_(SN) ), LPS_(i.p.) attenuated LPS_(SN) -induced DA neuronal loss in SN. Besides, LPS_(i.p.) reduced LPS_(SN) -induced microglia and astrocytes activation in SN. Furtherly, LPS_(i.p.) reduced pro-inflammatory M1 microglia markers mRNA levels and increased anti-inflammatory M2 microglia markers mRNA levels. In addition, the increased T-cell marker expression and the decreased M1 microglia marker expression and more DA neuronal survival were discerned at the same area of rat midbrain in LPS_(SN) -induced DA neuronal damage 30 days after LPS_(i.p.) application.

This study suggested LPS_(i.p.) -induced peripheral inflammation might cause T cells to infiltrate the brain to regulate microglia-mediated neuroinflammation, thereby protecting DA neurons.