Abstract
Palatability of food is one of strong motivations to feeding behavior. Favorite food works as a natural reward, many reports suggest that the ventral tegmental area (VTA) is involved with hedonic responses to food. We studied the effects that lesions of dopamine cells in the VTA would have on preferences of tastes. After bilateral injections of 6-OHDA into the VTAs of rats (VTA rats), we tested the difference of preferences between VTA rats and sham surgical rats (sham rats) by the two-bottle choice test for 2 days with following taste fluids: saline (0.9% of NaCl), Sucrose (30, 60 and 120 mM) and umami substances monosodium glutamate (MSG, 30, 60, and 120 mM), inosine monophosphate (IMP, 15, 30 and 60 mM) and guanosine monophosphate (GMP, 15, 30 and 60 mM). There is no significant difference in% preference, only the consumption of sucrose was significantly decreased in the VTA rats, but the consumption of saline and umami tastants was not significantly. Second, we tested whether VTA rats could detect lysine (Lys) when they fed Lys deficient diet, in this condition Lys could have strong reward value for rats. After one week with a Lys deficient feed, both VTA and sham rats chose a Lys solution. These results suggest that dopaminergic cells in the VTA are related to sugar consumption but not to umami consumption. The consumption of an essential amino acid is not affected with the reward system even if it has a high reward value. The intake of essential nutrients might be regulated by another brain regions except the reward system. [J Physiol Sci. 2007;57 Suppl:S139]
