Efficacy of providing nicotine in a liquid diet to rats

To determine if rats would consume nicotine at psychoactive levels, a nutri tionally balanced diet with 0, 20, 60, or 200 mg of nicotine tartrate per k g of diet was provided. Diet consumption and body weight differences were r ecorded for 14 days after which, following 16 hr of withdrawal, animals wer e given access to a two-bottle choice of the previously presented diet and a nicotine-free diet. Spontaneous horizontal motor activity was recorded 8, 16, and 24 hr after withdrawal. By Day 14, all animals showed a significan t increase in diet consumption and significant weight gain compared to Day 1, Animals consumed an average of 2.1, 6.8, or 19.5 mg/kg/day of nicotine o n the low, medium, and high-nicotine diets, respectively. However, animals receiving the high-nicotine diet consumed less diet and gained less weight than the control, low, and medium nicotine groups. During only the first 4 hr of the two-bottle choice (16-20 hr postwithdrawal), the high-nicotine gr oup consumed significantly higher amounts of nicotine base than the other g roups, but also consumed more of the control diet during the first 2 hr, In a replicate experiment, animals receiving the medium-nicotine diet showed an increased consumption of the nicotine diet and increased preference for nicotine following a 14-day exposure compared to the control-fed animals an d compared to a baseline preference test. Also, this group showed differenc es in locomotor activity consistent with other studies using an injection r egimen or subcutaneous pumps to induce dependence, Finally, animals in all three groups exhibited high plasma nicotine and cotinine (a major nicotine metabolite) levels. Because animals in all groups tolerated the diet well, gained weight, selected the nicotine diet in a choice test, and showed with drawal symptoms, we conclude that the liquid diet proved to be a satisfacto ry method of inducing nicotine dependence in rats.