The Dopamine Response in the Nucleus Accumbens Core–Shell Border Differs From That in the Core and Shell During Operant Ethanol Self-Administration

Background:  Ethanol self-administration has been shown to increase dopamine in the nucleus accumbens; however, dopamine levels in the accumbal subregions (core, shell, and core–shell border) have not yet been measured separately in this paradigm. This study was designed to determine if dopamine responses during operant ethanol self-administration are similar in the core, core–shell border, and shell, particularly during transfer from the home cage to the operant chamber and during consumption of the drinking solution.
Methods:  Six groups of male Long–Evans rats were trained to lever-press for either 10% sucrose (10S) or 10% sucrose + 10% ethanol (10S10E) (with a guide cannula above the core, core–shell border, or shell of the accumbens). On experiment day, 5-minute microdialysis samples were collected from the core, core–shell border, or shell before, during, and after drinking. Dopamine and ethanol concentrations were analyzed in these samples.
Results:  A significant increase in dopamine occurred during transfer of the rats from the home cage into the operant chamber in all 6 groups, with those trained to drink 10S10E exhibiting a significantly higher increase than those trained to drink 10S in the core and shell. No significant increases were observed during drinking of either solution in the core or shell. A significant increase in dopamine was observed during consumption of ethanol in the core–shell border.
Conclusions:  We conclude that dopamine responses to operant ethanol self-administration are subregion specific. After operant training, accumbal dopamine responses in the core and shell occur when cues that predict ethanol availability are presented and not when the reinforcer is consumed. However, core–shell border dopamine responses occur at the time of the cue and consumption of the reinforcer.