Sensory SystemResearch PaperAntagonism of metabotropic glutamate receptor 4 receptors by (RS)-α-cyclopropyl-4-phosphonophenylglycine alters the taste of amino acids in rats
Section snippets
Subjects
One hundred thirty-two naïve male Sprague–Dawley rats at least 90 days old at the start of testing were used for these experiments. The subjects were housed separately in cages within a colony on a 12-h light/dark schedule. The subjects were water deprived 22 h a day and received food ad libitum. Each animal was tested at the same time each day. All experimental procedures with animals conform to the Guide for the Care and Use of Laboratory Animals on the ethical use of animals. All methods
MSG/glycine CPPG experiments
When the rats were conditioned to avoid glycine, the LiCl-injected group drank significantly less glycine (F(1,14)=74.19, P<.001; Fig. 1, top panels) and less MSG (F(1,14)=42.24, P<.001) than saline-injected rats, indicating that the animals had developed the CTA for glycine and that it generalized to MSG. CPPG had no effect on the strength of the CTA to glycine or the generalization of this CTA to MSG. In addition, lick rates were not affected by either CPPG or 75 mM NaCl in water (Table 1).
Discussion
T1R1/T1R3 receptors are thought to be taste receptors for detection of MSG and other l-amino acids (Nelson et al 2002, Li et al 2002, Zhao et al 2003). We hypothesized that mGluR4 receptors expressed in taste specific tissues of the tongue might also contribute to the tastes of other amino acids. We tested this hypothesis by conditioning rats to avoid either MSG or one of three amino acids (glycine, l-serine, l-arginine) and then testing the strength of the CTA and its generalization between
Acknowledgments
This research was supported by NSF IOS 0549167 awarded to E.R.D.
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2016, NeuroscienceCitation Excerpt :To address this question, we recorded l-amino acid and IMP-elicited calcium responses of TSCs from T1r3-GFP-labeled mice and T1r3 KO mice to identify the involvement of different mGluRs in the detection of various l-amino acids and IMP. We used three l-amino acids: (1) monopotassium glutamate (MPG), (2) Ser, and (3) Arg – all of which are known to elicit different tastes in mice and humans, although CTA experiments with rats suggest these amino acids may also share some taste qualities (Schiffman et al., 1981; Delay et al., 2007; Eschle et al., 2009; Kawai et al., 2012). Additionally at high concentration, Ser elicits umami taste in humans (Kawai et al., 2012).
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2013, European Journal of PharmacologyCitation Excerpt :Further support for a role for mGlu4 in taste comes from a study investigating taste aversion. Here, the group III mGlu receptor antagonist CPPG decreased the amount of aversion for MSG and other amino acids when MSG served as the conditioned stimulus (Eschle et al., 2009). However, when CPPG was administrated in combination with these other amino acids, it reduced the intensity of the stimulus experience and also changed the sensory experience qualitatively (Eschle et al., 2009).