Effects of Long-Term Ethanol Consumption on Learning-Memory Functions in Mice and the Mechanisms Involved

  Objective  To investigate the effect of long-term ethanol consumption on learning-memory functions in mice and the mechanisms involved.

  Methods  Thirty male C57BL6/J mice were randomly assigned to 3 groups, with 10 mice in each group. The three groups included a control group in which the mice were given water ad libitum for 30 days, a long-term ethanol consumption group, or the EtOH group, in which the mice were given 6% (volume fraction) ethanol ad libitum for 30 days, and a long-term alcoholism group, or the EtOH+G group, in which the mice were given 5% (volume fraction) ethanol ad libitum for 30 days plus intermittent intragastric gavage of 20% ethanol at 3.5 g per kilogram body mass once every three days. After 30 days, the learning-memory functions of the mice were evaluated. At the conclusion of the experiment, the brain tissue of the mice was collected in order to examine the oxygen consumption rate (OCR) of mitochondria, the levels of pan-acetylation and protein oxidative stress in the hippocampal tissue, and the expression of sirtuin-3 (SIRT3) in hippocampus.

  Results  Morris water maze test showed that, compared with those of the control group, the times of crossing the platform and the percentage of platform time in the EtOH group and the EtOH+G group were both lower, and the EtOH+G group had the lowest results (P<0.05). Western blot results showed that long-term ethanol intake increased the levels of protein oxidative stress and pan-acetylation in the hippocampal tissue and down-regulated SIRT3 expression of hippocampal mitochondria. The results of mitochondrial complex Ⅱ respiration showed that the brain mitochondrial 3-state respiration in the EtOH group and the EtOH+G group was lower than that in the control group (P<0.05). Compared that with the control group, the mitochondrial maximum respiration in EtOH+G group was decreased (P<0.05).

  Conclusions  Both long-term ethanol consumption and long-term alcoholism can reduce learning-memory functions and long-term alcoholism has the greater impact of the two. The potential mechanism may involve the down-regulation of the expression of SIRT3 protein in the hippocampus, which results in an increased level of pan-acetylation and enhanced expression of oxidative stress protein in the hippocampus, affects the mitochondrial functions of the brain, inhibits the oxidative phosphorylation capacity of mitochondrial complex Ⅱ, reduces the ATP energy supply of the brain tissue, and thus affects the learning-memory function.