Changes of dopamine transmission in the nucleus accumbens shell and core during ethanol and sucrose self-administration

Ethanol is a psychoactive compound of several beverage abused by humans and it is well known that, as well as other drugs of abuse, increases dopamine (DA) transmission preferentially in the nucleus accumbens (NAc) shell. The aim of our study was to investigate by microdialysis the role of the NAc shell and core DA in the response to ethanol and to ethanol-conditioned stimuli (ethanol-CS) using an instrumental conditioning paradigm with fixed-ratio 1 (FR1). Rats were trained to acquire sucrose and ethanol oral self-administration under a FR 1 paradigm (1 nose poke corresponds to 0.25 ml administration of 20% sucrose or 10% ethanol in 20% sucrose solutions). We found that oral ethanol, either self-administered or given passively, produces an increase of DA transmission in the shell and in the core, strengthened during the self-administration session, while ethanol-CS increased DA preferentially in the NAc shell. Sucrose oral self-administration and its conditioned cues affects DA exclusively in the shell, but the passive administration increases DA in the shell and in the core. These data suggest that the two compartments of the NAc are differently implicated in the responsiveness to natural and to pharmacological rewards. While DA transmission in the NAc shell seems to play a key role in the operant responding for both sucrose and ethanol, the DA core appears to be more involved in the responsiveness to ethanol.