Bilateral dopaminergic lesions in the ventral tegmental area of rats influence sucrose intake, but not umami and amino acid intake

The role of the dopaminergic cells in the ventral tegmental area (VTA) in response to natural rewards is important in understanding palatability-induced feeding behavior. In this study, we first investigated whether dopaminergic lesions in the VTA would influence the taste preferences of rats for sodium chloride (NaCl), monosodium glutamate (MSG), disodium inosine-5′-monophosphate (IMP), disodium guanine-5′-monophosphate (GMP) and sucrose. Among these taste stimuli, only the preference of sucrose solutions decreased significantly in the VTA lesioned rats, preferences for the other taste stimuli were unaffected. Secondly, we tested whether VTA lesioned rats made slightly deficient in the amino acid lysine (by feeding rats a lysine deficient diet for five days) would detect the deficient amino acid in a choice test. Both the VTA lesioned rats and the control rats chose to consume the lysine solution and there was no difference between these two groups. These results suggest that the dopaminergic neurons in the VTA influence sucrose consumption, but do not alter the consumption of palatable umami compounds and salt. They also do not inhibit the animal's ability to recognize the essential amino acid lysine when the animal is deficient in it. Different central pathways must underlie sucrose preference and preferences for these amino acids and ribonucleotides.