| The damages of alcohol dependence or alcohol addiction is severe for individual and society.The clarification of relevant mechanisms is beneficial to help addict.Previous studies had demonstrated that some nuclei(such as VTA,NAc and LHb)in the brain's reward pathway are involved in alcohol dependence or alcohol addiction.Recent studies had shown that epigenetic modifications may play a significant role in the formation of alcohol dependence.The present study focused on the key enzymes in methylation modification,including DNA methyltransferases(DNMTs),ten-eleven translocation(TETs)and protein-arginine methyltransferases(PRMTs),to investigate the possible roles of these enzymes in the NAc and the LHb in alcohol-dependent animal model.A set of animal model were prepared by drinking freely either water or 20% alcohol solution.On the basis of alcohol consumption,rats were divided two groups,low-alcohol-dependence group and high-alcohol-dependence group.The percentage of preference for alcohol in the low-alcohol-dependence group did not change with the number of drinking days,and remained generally between 10 and 20%.However,the preference for alcohol in rats with high-alcohol-dependence increased significantly with the increase of drinking days after the tenth day of drinking,the percentage of alcohol preference reached a relatively high level,which was stable between 20% and 30%.The alcohol preference in high-alcohol-dependent rats was significantly higher than that of low-alcohol-dependent rats.We hypothesized that the differences in alcohol dependence in rats may be related to the different levels of excitability of specific nucleus in the brain reward pathway.Therefore,we detected the expression of c-Fos protein in NAc and LHb of alcohol dependence rats before next alcohol drinking.The results showed that the numbers of c-Fos positive neuron in the NAc and LHb in both high-alcohol-dependent and low-alcohol-dependent rats were significantly increased as compared with normal control rats,indicating that alcohol dependence is related with the neuronal activity in the NAc and LHb.In addition,the numbers of c-Fos positive neuron in the LHb in high-alcohol-dependence rats were significantly higher than low-alcohol-dependence rats,indicating that the amount of c-Fos protein expression in the LHb is related to the degree of alcohol dependence.Camk2 a,Camk2b and GLT-1 are excitation-associated genes in the brain.We examined the expression of these excitatory-related genes.Compared with normal control rats,the expressions of Camk2 a and Camk2 b m RNA in both LHb and NAc of alcohol-dependent rats was significantly increased and the expression of GLT-1 m RNA was significantly decreased,suggesting that the LHb and NAc neurons in alcohol-dependent rats have higher excitability.Next,we examined the expression of key enzymes on methylation in the NAc and LHb in alcohol-dependent rats,including DNA methyltransferases(DNMT1 and DNMT3A),ten-eleven translocations(TET1 and TET2)and protein-arginine methyltransferases(PRMT1 and PRMT5).The results showed that the expression of DNMT1 m RNA was significantly decreased,the expression of PRMT1 m RNA was significantly increased and m RNA expressions of other enzymes were unchanged in LHb of alcohol-dependent rats,as compared with normal control rats.The results suggested that DNA methylation is decreased and histone methylation is increased in LHb of alcohol-dependent rats.In addition,the expressions of DNMT1 and PRMT1 m RNA were significantly higher than normal control rats and no changes were observed in other enzymes in NAc of alcohol-dependent rats,suggesting that DNA methylation and histone methylation in NAc of alcohol-dependent rats were increased.We speculate that changes of DNA and histone methylation in the LHb and NAc are associated with formation of alcohol-dependent. |
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