Rats with intermittent access to sugar release DA in response to drinking sucrose for 60 min on day 21. Dopamine, as measured by in vivo microdialysis, increases for the Daily Intermittent Sucrose and Chow rats (open circles) on days 1, 2 and 21; in contrast, DA release was attenuated on day 21 in four control groups as follows: a group that only had 1-h access to sucrose on day 1 and 21 with ad libitum chow in the interim (Sucrose Twice), Ad libitum Sucrose and Chow group, and Daily Intermittent Chow group (bottom panel). The bar on the ordinate indicates the hour (0-60 min) that sucrose or chow was available for the tests. *p<0.05. From Rada et al., 2005.