title: Elevated reinforcing and motivational properties of alcohol at the end of the nocturnal period in sP rats.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  The present study investigated whether sensitivity of sP rats to time schedule extended to operant procedures of alcohol self-administration.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  The reinforcing and motivational properties of alcohol were sensitive to time schedule and stronger at the end of the dark phase.
authors.affiliation: Neuroscience Institute, Section of Cagliari, National Research Council of Italy, S.S. 554, km. 4,500, I-09042, Monserrato (CA), Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Maccioni
authors.forename: Irene
authors.initials: I
authors.lastname: Lorrai
authors.forename: Maria Francesca
authors.initials: MF
authors.lastname: Marras
authors.forename: Andrea
authors.initials: A
authors.lastname: Contini
authors.forename: Alessandro
authors.initials: A
authors.lastname: Capra
authors.forename: Gessica
authors.initials: G
authors.lastname: Piras
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Caboni
authors.forename: Gian Luigi
authors.initials: GL
authors.lastname: Gessa
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Colombo
mesh_terms: D000428:Alcohol Drinking / Q000523:psychology*; D000818:Animals; D000431:Ethanol / Q000008:administration & dosage*; D008297:Male; D009042:Motivation / Q000187:drug effects* / Q000502:physiology; D017440:Photoperiod; D051381:Rats; D012055:Reinforcement Schedule; D012646:Self Administration
chemical_list: D000431:Ethanol