Behavioural NeuroscienceDeficits of mesolimbic dopamine neurotransmission in rat dietary obesity
Section snippets
Animals
Female albino Sprague–Dawley rats (Taconic, Hudson, NY, USA), were matched for a body weight of 300 g each at the age of 3 months. Female animals were chosen because, in contrast to male rats, the body weight of laboratory-chow fed females is relatively stable over time. Animals were housed individually in the same room under a 12-h reverse light/dark cycle (lights on: 6 pm, lights off: 6 am). Under these conditions we observed no impact of the estrous cycle phase on mesolimbic dopamine release
Dietary obese rats have a strong preference for highly palatable food
Cafeteria DIO rats showed a strong preference for sweet milk (74.4±6.4 g; 241±21 kcal) and the 32% sucrose solution (31.4±4.1 g; 40±5 kcal) (Fig. 1A, B,F(9,127)=116.9854, P<0.01). In addition, these animals ate significantly less of the Purina chow (5.66±1.02 g) compared to the laboratory chow fed animals (54.7±2.3 g; F(1,27)=419.681, P<0.01). After 14 weeks on the cafeteria diet, rats gained 53.7% of their initial body weight to a final weight of 444.9±19.0 g. After the same period, rats on
Discussion
In this study, rats became overweight from eating a cafeteria diet with a preference for high-carbohydrate foods. In their overweight state, they had lower basal extracellular dopamine as well as chow-stimulated or amphetamine-stimulated dopamine in the nucleus accumbens. In studies using drugs of abuse, animals will work to keep dopamine levels in the nucleus accumbens above a certain level (Wise et al 1995a, Wise et al 1995b, Ranaldi et al 1999). In the present study, the abused “substance”
Conclusion
In conclusion, the findings in this study show that the mesolimbic dopamine system plays a critical role in preference for high-energy diets, hyperphagia and the resulting dietary obesity. The nucleus accumbens and dorsal striatum dopaminergic neurotransmission are depressed in dietary obese rats. The animals can temporarily restore dopamine levels by eating highly palatable, high-energy food. These results suggest that selective targeting of presynaptic regulators of the mesolimbic dopamine
Acknowledgments
This work was supported by DK065872 (ENP), F31 DA023760 (BMG, ENP), a Smith Family Foundation Award of Excellence in Biomedical Research (ENP) and P30 NS047243 (Tufts Center for Neuroscience Research).
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