P-65
INCREASED REINFORCING AND MOTIVATIONAL PROPERTIES OF ALCOHOL IN SARDINIAN ALCOHOL-PREFERRING RATS AT THE END OF THE DARK PHASE

Extract

When exposed to daily drinking sessions of one hour, with concurrent availability of multiple alcohol concentrations, and unpredictability of time of alcohol access, Sardinian alcohol-preferring (sP) rats displayed high sensitivity to time schedule, consuming intoxicating amounts of alcohol when the drinking session occurred during the latter part of the dark phase of the light/dark cycle (Alcohol 48:301-311, 2014). More recently, we investigated whether sensitivity of sP rats to time schedule extended to operant procedures of alcohol self-administration. To this end, three different alcohol solutions (10%, 20%, and 30%, v/v) were concurrently available in daily 1-hour self-administration sessions under a Fixed Ratio 4 schedule of reinforcement and with unpredictable time schedule; water was available uncontingently. Number of lever-responses and amount of self-administered alcohol were positively correlated with time of alcohol access during the dark phase; when the self-administration session occurred at the first and latest hours of the dark phase, the amount of self-administered alcohol averaged 0.95-1.0 and 1.55-1.65 g/kg, respectively. Sensitivity of the motivational properties of alcohol to time schedule was evaluated in sP rats exposed to (i) self-administration sessions under the Progressive Ratio schedule of reinforcement and (ii) sessions of alcohol seeking under the extinction responding (ER) schedule. Values of breakpoint and ER for alcohol were approximately 50% higher when sessions occurred at the last rather than first hour of the dark phase. Together, these results suggest that the reinforcing and motivational properties of alcohol were sensitive to time schedule and stronger at the end of the dark phase.