[Decreased dopaminergic activity in hepatic encephalopathy in rats with galactosamine-induced acute liver failure]

Hepatic encephalopathy might be related to the failure of the liver to remove some toxic substances that were endogenously produced. The amino acid imbalance theory focuses on an increase of false neurotransmitters and a decrease of noradrenaline and dopamine. Therefore, we examined the activities of the dopaminergic neurons of the substantia nigra pars compacta electrophysiologically in control rats and in rats with hepatic encephalopathy induced by galactosamine. The mean firing rates of the dopaminergic neurons in rats with hepatic encephalopathy was 138.5 +/- 77.8 spikes/min. This was significantly lower than the mean value for the control rats which was 220.1 +/- 105.7 spikes/min. The terminal excitability of the dopaminergic neurons in rats with hepatic encephalopathy was also decreased significantly compared with the excitability in the control rats. Following the administration of the BCAA-rich amino acid preparation (GO-80) to rats with hepatic encephalopathy, the firing rates and the terminal excitability of the dopaminergic neurons were increased. The results of this study indicate that hepatic encephalopathy in rats with galactosamine-induced acute liver failure is associated with a decreased activity of the dopaminergic neurotransmitter system.