Modest Long-Term Ethanol Consumption Affects Expression of Neurotransmitter Receptor Genes in the Rat Nucleus Accumbens
Over 100 million people worldwide are affected by alcohol use disorders. These conditions usually take years to develop where an initial, voluntary consumption is gradually replaced by a compulsive intake of alcohol. The exact mechanisms behind this transition remain unknown. However, ethanol (EtOH) is known to interact with several neurotransmitters and receptors in the central nervous system, and chronic EtOH consumption causes alterations in these neurotransmitter systems, proposed to contribute to the development of dependence. This study aimed to repeat previous findings that animals after long-term voluntary EtOH consumption spontaneously increase their intake. That the initial encounter with EtOH causes an elevation of dopamine in the nucleus accumbens (nAc), inducing feelings of well-being and creating an incentive to continue the behavior, has been repeatedly reported in both animals and humans. The effects of chronic EtOH consumption on this region are not as well investigated.
We examined both long-term EtOH consumption behavior and its consequences on expression of neurotransmitter-related genes in the nAc of the Wistar rat using quantitative polymerase chain reaction.
In general, the EtOH consumption of the animals in this study was modest with an average intake of 0.9 g/kg/d, and only 1 of the 24 rats consuming EtOH for 10 months drastically increased its intake in line with the results of Wolffgramm and Heyne (1995). Expression of the genes for dopamine receptor 2, μ-opioid receptor, and somatostatin receptor 4 were down-regulated in animals after 2 and/or 4, but not 10, months of EtOH consumption.
Chronic consumption even of modest amounts of alcohol seems to affect regulation of expression of these genes, possibly leading to changes in neurotransmitter signaling. Studies are ongoing to investigate whether these alterations are specific for the nAc.