Bile duct ligation increased dopamine levels in the cerebral cortex of rats partly due to induction of tyrosine hydroxylase

Abstract

Background and PurposeLiver failure is associated with psychiatric alterations, partly resulting from the increased brain dopamine levels. We investigated the relationship between increased dopamine levels and mental abnormalities using bile duct ligation (BDL) rats and the mechanism by which liver failure increased dopamine levels in SH‐SY5Y cells.Behavioural tests were carried out on day 13 and 27 following BDL, along with measurements of dopamine and metabolites, expressions of enzymes and transporters related to dopamine metabolism, and its transport into the cortex and the hippocampus. SH‐SY5Y cells were used to investigate whether NH4Cl, bile acids and bilirubin affected expression of tyrosine hydroxylase or not. Tyrosine hydroxylase (TH) expression in SH‐SY5Y cells co‐incubated with bilirubin and signal pathway inhibitors was measured.Key ResultsOpen‐field test results demonstrated BDL rats showed anxiety‐like behaviour, accompanied by increased dopamine levels and expression of TH protein in the cortex. Membrane bound long form (MB)‐COMT, slightly but significantly decreased. SH‐SY5Y cells indicated that increased bilirubin levels was a factor in inducing TH expression. Both inhibitor of NF‐κB pathway BAY 11‐7082 and silencing NF‐κB p65 reversed bilirubin‐induced upregulation of TH protein. NF‐κB activator TNF‐α increased expression of TH protein. Roles of bilirubin in increases of TH protein expressions and dopamine levels were measured using hyperbilirubinemia rats. Anxiety‐like behaviour, was associated with increased dopamine levels and TH protein expressions in hyperbilirubinemia rats.Conclusion and ImplicationsBDL significantly increased dopamine levels in rat cortex partly due to bilirubin‐mediated TH induction. Increased bilirubin induced TH expression via activating NF‐κB signalling pathway.