Contribution of a-gustducin to taste-guided licking responses of mice

We examined the necessity of a-gustducin, a G protein a-subunit expressed in taste cells, to taste-mediated licking responses of mice to sapid stimuli. To this end, we measured licking responses of a-gustducin knock-out (Gus/) mice and heterozygotic littermate controls (Gus+/) to a variety of bitter, umami, sweet, salty and sour taste stimuli. All previous studies of how Gus/ mice ingest taste stimuli have used long-term (i.e. 48 h) preference tests, which may be confounded by post-ingestive and/or experiential effects of the taste stimuli. We minimized these confounds by using a brief-access taste test, which quantifies immediate lick responses to extremely small volumes of sapid solutions. We found that deleting a-gustducin (i) dramatically reduced the aversiveness of a diverse range of bitter taste stimuli; (ii) moderately decreased appetitive licking to low and in-termediate concentrations of an umami taste stimulus (monosodium glutamate in the presence of 100 lM amiloride), but virtually eliminated the normal aversion to high concentrations of the same taste stimulus; (iii) slightly decreased appetitive licking to sweet taste stimuli; and (iv) modestly reduced the aversiveness of high, but not low or intermediate, concentrations of NaCl. There was no significant effect of deleting a-gustducin on licking responses to NH4Cl or HCl. Key words: task, a-gustducin, brief-access taste test, knock-out mic