Effect of a two bottle-choice nicotine self-administration assay on bottle preference, animal weight and daily fluid intake. A) Mice in both groups that were either implanted with saline pumps or nicotine pumps displayed significant increase in body weight from day 0 to day 20 over the course of the nicotine self-administration experiment. However, there was no significant difference in body weight between saline pump and nicotine pump mice either on day 0 or on day 20 of the experiment. B) There was no difference in daily fluid volume (totaled for both bottles, ml) consumed between the choice or abstinence periods in either the saline pump mice or the nicotine pump mice. Furthermore, there was no difference in fluid volumes consumed between saline pump mice and nicotine pump mice during choice or abstinence. C) Daily fluid intake normalized to animal body weight (totaled for both bottles, ml fluid/kg mouse) showed that nicotine pump mice consumed a significantly larger daily total fluid dose compared to saline pump mice during periods of choice and also during periods of abstinence, although neither the nicotine pump mice nor the saline pump mice consumed more fluid during choice as compared to during abstinence. D) Both the saline pump and nicotine pump mice showed a linear trend of decreased total fluid intake over the 20 days of the self-administration experiment (saline pump: dashed line, R2 = 0.61, *p = 0.0003, linear regression) (nicotine pump: solid line, R2 = 0.70, **p < 0.0001, linear regression).