An Examination of the Role of L-Glutamate and Inosine 5'-Monophosphate in Hedonic Taste-Guided Behavior by Mice Lacking the T1R1 + T1R3 Receptor.
The heterodimeric T1R1 + T1R3 receptor is considered critical for normal signaling of L-glutamate and 5'-ribonucleotides in the oral cavity. However, some taste-guided responsiveness remains in mice lacking one subunit of the receptor, suggesting that other receptors are sufficient to support some behaviors. Here, mice lacking both receptor subunits (KO) and wild-type (WT, both n = 13) mice were tested in a battery of behavioral tests. Mice were trained and tested in gustometers with a concentration series of Maltrin-580, a maltodextrin, in a brief-access test (10-s trials) as a positive control. Similar tests followed with monosodium glutamate (MSG) with and without the ribonucleotide inosine 5'-monophosphate (IMP), but always in the presence of the epithelial sodium channel blocker amiloride (A). Brief-access tests were repeated following short-term (30-min) and long-term (48-h) exposures to MSG + A + IMP and were also conducted with sodium gluconate replacing MSG. Finally, progressive ratio tests were conducted with Maltrin-580 or MSG + A + IMP, to assess appetitive behavior while minimizing satiation. Overall, MSG generated little concentration-dependent responding in either food-restricted WT or KO mice, even in combination with IMP. However, KO mice licked less to the amino acid stimuli, a measure of consummatory behavior in the brief-access tests. In contrast, both groups initiated a similar number of trials and had a similar breakpoint in the progressive ratio task, both measures of appetitive (approach) behavior. Collectively, these results suggest that while the T1R1 + T1R3 receptor is necessary for consummatory responding to MSG (+IMP), other receptors are sufficient to maintain appetitive responding to this "umami" stimulus complex in food-restricted mice.
Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, FL, USA.
Ginger D
GD
Blonde
Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, FL, USA.
Alan C
AC
Spector
D000818:Animals; D005260:Female; D018698:Glutamic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D007291:Inosine Monophosphate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010684:Philosophy; D043562:Receptors, G-Protein-Coupled / Q000172:deficiency*; D013649:Taste / Q000187:drug effects* / Q000502:physiology*
D043562:Receptors, G-Protein-Coupled; C431926:taste receptors, type 1; D007291:Inosine Monophosphate; C070346:inosine 5'-phosphosulfate; D018698:Glutamic Acid
MSG; amino acid; knockout mice; taste hedonics; umami