Dried bonito dashi: a preferred fish broth without postoral reward actions in mice.

The flavor of dashi, the broth prepared from dried bonito tuna, is attractive to humans and rodents. The present experiments examined the ability of dashi to serve as an oral and/or postoral rewarding stimulus for conditioned flavor preferences in mice. In Experiment 1, C57BL/6J (B6) mice were infused intragastrically with dashi when they consumed a conditioned stimulus (CS)+ flavor and with water when they drank a CS- flavor on alternate days. Postoral dashi did not condition a CS+ preference. The combined effects of oral and postoral dashi exposure were examined in Experiment 2, in which B6 mice consumed a CS+ flavored dashi solution and CS- flavored water on alternate days. The mice did not prefer the CS+ to CS- when both flavors were presented in water. Yet, the B6 mice in both experiments preferred dashi to water in oral tests. Experiment 3 showed that taste-impaired Trpm5 knockout (KO) mice did not learn to prefer dashi after exposure to it, in contrast to previous findings with the umami prototype monosodium glutamate. This was not due to an inability to taste dashi, because Trpm5 KO mice learned a strong preference for dashi after it was mixed with glucose. The impact of dashi on reward may largely reflect an enhancement of association of oral and postoral effects of food.