Effects of scheduled access on ethanol intake by the alcohol-preferring (P) line of rats

Abstract

The effects of scheduling the availability of ethanol on its voluntary consumption by the selectively bred alcohol-preferring P rats were examined under three conditions: unrestricted 24 hr/day access (Condition A), access limited to a continuous 4 hr/day (Condition B), and access limited to 1 hr every 3 hr, 4 times/day (Condition C). Food and water were always available. Daily alcohol intakes (mean±SEM) with Conditions A, B and C were 6.9±0.2, 2.1±0.2 and 4.4±0.2 g/kg, respectively, while the intake per hour of availability increased from 0.3±0.03 under Condition A to 1.1±0.4 g/kg under condition C. The amount of ethanol consumed per drinking episode under Conditions A, B and C were 1.1±0.1, 2.1±0.2 and 1.1±0.03 g/kg, respectively. Mean blood alcohol concentrations (BACs), determined periodically during the dark cycle of Condition A and five minutes after drinking episodes under Conditions B and C, were 59±10, 61±7 and 62±7 mg%, respectively. When unlimited access was reinstated after Condition C, daily alcohol consumption returned to a level similar to that under the initial Condition A (7.2±0.5 g/kg). When the ethanol concentration was increased from 5 to 20% (v/v) under Condition C, the amount of ethanol consumed per episode at 5% was significantly less than at the 10, 15 and 20% concentrations, and the volume consumed was significantly lower at the 20% concentration than at the 5, 10 and 15% concentrations. However, mean BAC measured five minutes after cessation of drinking did not differ across the four concentrations (rnage: 50±7 to 62±7 mg%). The findings indicate that BAC is a major factor that limits ethanol intake in P rats Scheduling the availability of ethanol to one episode per day for four hours enhances alcohol intake when calculated per drinking episode but not per day. Scheduling also does not increase intake during subsequent unrestricted access in the P rats.