Evaluating sex and line differences in successive negative contrast and ethanol consumption using alcohol preferring and high alcohol drinking rats

Background

The loss of a job or relationship are a couple of examples of unexpected reward loss. Life events, such as these can induce negative emotional reactions (e.g., anxiety and stress), which have been associated with increased alcohol consumption and in turn, an increased risk of developing an alcohol use disorder (AUD). The present study analyzed consummatory successive negative contrast (SNC) for the first time in alcohol preferring (P) and high alcohol drinking (HAD) rats that have been selectively bred to consume high amounts of ethanol. Following reward loss, animals were given free access to ethanol to determine whether consumption would increase as a possible indication of any negative emotional reaction.

Methods

Male and female P and HAD rats were split into shifted and unshifted groups receiving either 32% or 4% sucrose for 5 min across 10 preshift days. Subsequently, all animals received 4% sucrose for four postshift days, across which, animals were given access to 20% ethanol for 30 min after access to 4% sucrose.

Results

Male and female P rats demonstrated a longer contrast effect than HAD rats, indicated by a longer recovery time following the downshift in reward. Conversely, HAD males did not demonstrate a contrast effect following this downshift in reward unlike their female counterparts. Surprisingly, P rats who experienced a loss of reward consumed significantly less ethanol than animals who did not. Lastly, individual measure of contrast size, or shift ratio, was significantly associated with greater ethanol consumption in HAD males only, who did not display a contrast effect.

Conclusions

These data indicate different reactivity to SNC between these two lines and sexes, suggesting different genetic and sex-related mechanisms underlying sensitivity to an unexpected loss of reward and ethanol consumption following this loss.