Dopamine (DA)-induced learning and memory impairment is well documented in minimal hepatic encephalopathy (MHE), but the contribution of DA to neurodegeneration and the involved underlying mechanisms are not fully understood. In this study, the effect of DA on neuronal apoptosis was initially detected. The results showed that MHE/DA (10 mug)-treated rats displayed neuronal apoptosis. However, we found that DA (10 muM) treatment did not induce evident apoptosis in primary cultured neurons (PCNs) but did produce TNF-alpha in primary cultured astrocytes (PCAs). Furthermore, co-cultures between PCAs and PCNs exposed to DA exhibited increased astrocytic TNF-alpha levels and neuronal apoptosis compared with co-cultures exposed to the vehicle, indicating the attribution of the neuronal apoptosis to astrocytic TNF-alpha. We also demonstrated that DA enhanced TNF-alpha production from astrocytes by activation of the TLR4/MyD88/NF-kappaB pathway, and secreted astrocytic TNF-alpha-potentiated neuronal apoptosis through inactivation of the PI3K/Akt/mTOR pathway. Overall, the findings from this study suggest that DA stimulates substantial production and secretion of astrocytic TNF-alpha, consequently and indirectly triggering progressive neurodegeneration, resulting in cognitive decline and memory loss in MHE.
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