Effects of continuous versus limited access to ethanol on ethanol self-administration

Eight male, experimentally naive Long-Evans rats were housed in operant chambers 23 h per day following initiation to self-administer ethanol. While housed in the chambers, the animals had continuous access to food pellets according to a fixed ratio 1 schedule of reinforcement, 10% ethanol (v/v) according to a fixed ratio 4 schedule of reinforcement and water in a drinking tube with licks recorded via a drinkometer. Over a series of experimental phases, daily availability of the ethanol solution was limited to 16, 6, 4, 2, or 1 30-min period per day. The 1 30-min period access was examined during the 12th hour or the second hour of the daily sessions. Over the course of the experiment, total responses on the lever that operated the dipper, g/kg per day and number of ethanol drinking bouts per day decreased significantly as the number of daily access periods decreased. On the other hand, the number of dippers presented per ethanol bout, g/kg per ethanol bout and ethanol bout duration increased, with significant increases in dippers per bout occurring when one 30-min access period per day was provided. These data indicate that the size of a single ethanol drinking bout can be increased somewhat by limiting the opportunity to obtain ethanol reinforcement and agrees with earlier research that has shown similar effects.