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Psychopharmacology (Berl). 2015 Oct;232(19):3585-95. doi: 10.1007/s00213-015-4010-2. Epub 2015 Jul 7.

Elevated reinforcing and motivational properties of alcohol at the end of the nocturnal period in sP rats.

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Neuroscience Institute, Section of Cagliari, National Research Council of Italy, S.S. 554, km. 4,500, I-09042, Monserrato (CA), Italy.



Sardinian alcohol-preferring (sP) rats displayed high sensitivity to time schedule and consumed intoxicating amounts of alcohol during the last portion of the dark phase of the light/dark cycle when exposed to daily drinking sessions of 1 h, with concurrent availability of multiple alcohol concentrations and unpredictability of time of alcohol access.


The present study investigated whether sensitivity of sP rats to time schedule extended to operant procedures of alcohol self-administration.


In experiment 1, three different alcohol solutions (10, 20, and 30%, v/v) were concurrently available under a fixed ratio 4 schedule of reinforcement and with unpredictable time schedule; water was available uncontingently. Experiments 2 and 3 assessed the sensitivity of the motivational properties of alcohol to time schedule; rats were exposed to (a) self-administration sessions under the progressive ratio (PR) schedule of reinforcement and (b) sessions of alcohol seeking under the extinction responding (ER) schedule.


In experiment 1, 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. In experiments 2 and 3, values of breakpoint and ER for alcohol were approximately 50% higher when the sessions occurred at the last than first hour of the dark phase.


The reinforcing and motivational properties of alcohol were sensitive to time schedule and stronger at the end of the dark phase.

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