Contribution of α-Gustducin to Taste-guided Licking Responses of Mice

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Abstract
We examined the necessity of α-gustducin, a G protein α-subunit expressed in taste cells, to taste-mediated licking responses of mice to sapid stimuli. To this end, we measured licking responses of α-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 α-gustducin (i) dramatically reduced the aversiveness of a diverse range of ‘bitter’ taste stimuli; (ii) moderately decreased appetitive licking to low and intermediate concentrations of an ‘umami’ taste stimulus (monosodium glutamate in the presence of 100 μM 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 α-gustducin on licking responses to NH4Cl or HCl.