Abstract
Ethanol, like other substances of abuse, preferentially increases dopamine (DA) transmission in the rat nucleus accumbens (NAc) following passive administration. It remains unclear, however, whether ethanol also increases NAc DA transmission following operant oral self-administration (SA). The NAc is made-up of a ventro-medial compartment, the shell and a dorso-lateral one, the core, where DA transmission responds differentially following exposure to drugs of abuse. Previous studies from our laboratory investigated changes in dialysate DA in the NAc shell and core of rats responding for sucrose pellets and for drugs of abuse. As a follow up to these studies, we recently investigated the changes in NAc shell and core DA transmission associated to oral SA of a 10% ethanol solution. For the purpose of comparison with literature studies utilizing sucrose + ethanol solutions, we also investigated the changes in dialysate DA associated to SA of 20% sucrose and 10% ethanol + 20% sucrose solutions. Rats were trained to acquire oral SA of the solutions under a Fixed Ratio 1 (FR1) schedule of nose-poking. After training, rats were monitored by microdialysis on three consecutive days under response contingent (active), reward omission (extinction trial) and response non-contingent (passive) presentation of ethanol, sucrose or ethanol + sucrose solutions. Active and passive ethanol administration produced a similar increase in dialysate DA in the two NAc subdivisions, while under extinction trial DA increased preferentially in the shell compared to the core. Conversely, under sucrose SA and extinction DA increased exclusively in the shell. These observations provide unequivocal evidence that oral SA of 10% ethanol increases dialysate DA in the NAc, and also suggest that stimuli conditioned to ethanol exposure contribute to the increase of dialysate DA observed in the NAc following ethanol SA. Comparison between the pattern of DA changes detected in the NAc subdivisions under sucrose and ethanol SA likewise suggests that the NAc shell and core DA play different roles in sucrose as compared to ethanol reinforcement.
Highlights
Drinking of alcohol plays an important social role in numerous cultures, with alcoholic beverages being legally available throughout the majority of countries worldwide
This study investigated by microdialysis the responsiveness of nucleus accumbens (NAc) shell and core DA transmission to 10% ethanol solution compared to 10% ethanol + 20% sucrose and 20% sucrose solutions; each solution was administered under three different conditions in rats previously trained to respond on a continuous reinforcement (FR1) schedule
Under these conditions, responding for 20% sucrose solution was associated with a selective increase of DA in the shell, while responding for ethanol and ethanol + sucrose solutions was associated with increased dialysate DA both in the shell and core
Summary
Drinking of alcohol plays an important social role in numerous cultures, with alcoholic beverages being legally available throughout the majority of countries worldwide. A further point of uncertainty in the paradigm adopted in the above studies arises from the failure of sucrose SA to increase dialysate DA in any subdivision of the NAc (Howard et al, 2009) This observation is in contrast with a large number of studies showing that sucrose SA increases dialysate DA, depending on the experimental conditions, in the NAc shell, or in both the shell and core (Bassareo and Di Chiara, 1997, 1999; Brown et al, 2011; Cacciapaglia et al, 2012; Bassareo et al, 2015a,b,c)
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