Chemical Senses Advance Access originally published online on August 31, 2005
Chemical Senses 2005 30(7):601-614; doi:10.1093/chemse/bji054
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Initial Licking Responses of Mice to Sweeteners: Effects of Tas1r3 Polymorphisms
Department of Biological Sciences, Barnard College, Columbia University, New York, NY 10027, USA
Correspondence to be sent to: John I. Glendinning, Department of Biological Sciences, Barnard College, Columbia University, 3009 Broadway, New York, NY 10027, USA. e-mail: jglendinning{at}barnard.edu
Recent studies have established that the T1R3 receptor plays a central role in the taste-mediated ingestive response to sweeteners by mice. First, transgenic mice lacking the gene for T1R3, Tas1r3, show dramatically reduced lick responsiveness to most sweeteners. Second, strains with the taster allele of Tas1r3 (T strains) are more sensitive to low sweetener concentrations than strains with the nontaster allele (NT strains) and consume greater quantities of low- to midrange concentrations of sweeteners during 24-h tests. We asked how Tas1r3 polymorphisms influence the initial licking responses of four T strains (FVB/NJ, SWR/J, SM/J, and C57BL/6J) and four NT strains (BALB/cJ, 129P3/J, DBA/2J, and C3H/HeJ) to two sweeteners (sucrose and SC-45647, an artificial sweetener). We used the initial licking response as a measure of the taste-mediated ingestive response because its brief duration minimizes the potential contribution of nontaste factors (e.g., negative and positive postingestive feedback). Further, we used two complimentary short-term intake tests (the brief-access taste test and a novel 1-min preference test) to reduce the possibility that our findings were an epiphenomenon of a specific testing procedure. In both tests, the T strains were more responsive than the NT strains to low concentrations of each sweetener. At higher concentrations, however, there was considerable overlap between the T and NT strains. In fact, the initial licking response of several NT strains was more vigorous than (or equivalent to) that of several T strains. There was also considerable variation among strains with the same Tas1r3 allele. We conclude that Tas1r3 polymorphisms contribute to strain differences in initial lick responsiveness to low but not high concentrations of sweeteners.
Key words: initial licking response, mice, sweet taste, Tas1r3
1 We use the term "sweetener" to denote natural and artificial compounds that taste sweet to humans.
2 According to G. DuBois (personal communication, The Coca-Cola Company, Altanta, GA), the literature on SC-45647 is confusing because most of the studies that used this compound did not provide its chemical identity. SC-45647 is N-carboxymethyl-N'-(S)-a-phenethyl-N''-(4-cyanophenyl)-guanidine and was originally described by Nofre et al. (1990) without any common name or abbreviation. Since this original report, SC-45647 has been referred to as GUA-ac by Hellekant and Walters (1993), Compound 1 by Nagaranjan et al. (1996), and GA-1 (with reference to Nagarajan et al., 1996) by Nelson et al. (2001).
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