Function of opioidergic and dopaminergic antagonists on both spatial and object novelty detection deficits induced in rodent model of hepatic encephalopathy.

Liver disease has been known for a long time to affect brain function. We now report the function of opioidergic and dopaminergic antagonists on both spatial and object novelty detection deficits induced by hepatic encephalopathy (HE) following bile duct ligation (BDL), a model of chronic liver disease. Assessment of spatial and object novelty detection memories was carried out in the non-associative task. It consists of placing mice in an open field containing five objects and, after three sessions of habituation, examining their reactivity to object displacement (spatial novelty) and object substitution (object novelty). Both spatial and object novelty detection memories were impaired by BDL after 4 weeks. In the BDL mice, pre-test intraperitoneal administration of naloxone (μ-opioidergic receptor antagonist) at dose of 0.9mg/kg restored while sulpiride (D2-like dopamine receptor antagonist) at dose of 40mg/kg potentiated object novelty detection memory deficit. However, SCH23390 (D1-like dopamine receptor antagonist) at dose of 0.04mg/kg or sulpiride (20mg/kg) restored spatial novelty detection memory deficit. Moreover, SCH23390 or sulpiride impaired while naloxone did not alter both memories in sham-operated mice. Furthermore, subthreshold dose co-administration of dopaminergic antagonists together or each one plus naloxone did not alter both memory impairments in BDL mice, while all of three co-administration groups impaired object novelty detection and co-administration of naloxone plus sulpiride impaired spatial detection memory in sham-operated mice. In conclusion, we suggest that opioidergic and dopaminergic systems through separate pathways may contribute in memory impairments induced by BDL in the non-associative task.