Acquisition and persistence of intermittent access-induced escalated sucrose intake in male rats.

Ad lib fed male rats with 23 h every third day access (E3DA) to 4% sucrose come to double the sucrose intake of rats with everyday access (EDA). These differences are maintained if all rats are then put on an alternate day schedule. In two experiments, we explored how initial patterns of sucrose availability influenced consumption when access conditions changed. In Phase I of a 2 by 2 experiment 1, rats given E3DA to 4% sucrose approximately doubled the intake of rats given EDA. In Phase II, half the EDA rats were shifted to E3DA and they rapidly increased their sucrose intake, but their sucrose consumption remained below that of the Phase I E3DA rats. Rats shifted from E3DA to EDA only gradually reduced their intake over the 40 days. In Phase III, all rats were shifted to alternate day access and the effects of prior phases were still evident. In experiment 2, rats given 40 days of EDA to 4% sucrose and then shifted to E3DA showed almost identical sucrose intake increases as age-matched rats with no previous sucrose experience. The period of EDA to sucrose did not influence the magnitude of the E3DA effect. In a third experiment, we found that older rats showed an intermittency effect similar to what we have found with younger rats. Limited or unpredictable availability of a food source, even after a period of abundance, can produce a profound positive change in an animal's evaluation of the item.