Bitter avoidance in guinea pigs (Cavia porcellus) and mice (Mus musculus and Peromyscus leucopus).

Abstract

Rejection of bitter substances is common in many species and may function to protect an animal from ingestion of bitter-tasting toxins. Since many plants are bitter, it has been proposed that high tolerance for bitterness would be adaptive for herbivores. Earlier studies conducted on herbivorous guinea pigs (Cavia porcellus) have been used to support this proposal. We tested guinea pigs with bitter plant secondary metabolites (salicin, caffeine, quinine hydrochloride) and bitter protein hydrolysates (two types of hydrolyzed casein, hydrolyzed soy) in a series of two-choice preference tests. For comparison, we tested two non-herbivorous mouse species (Mus musculus and Peromyscus leucopus). Guinea pigs did show weaker avoidance of QHCl than did the mice, confirming predictions generated from earlier work. However, guinea pigs had similar responses to caffeine as did Peromyscus. Both of these species showed weaker avoidance responses than Mus to 10 mM caffeine. For salicin, guinea pigs were the only species to avoid it at 10 mM and their preference scores at this concentration were significantly lower than for the two mice species. Guinea pigs avoided all of the protein hydrolysates more strongly than the other species. Responses to the protein hydrolysates did not reflect the patterns observed with the simple bitter compounds, suggesting that other properties of these complex stimuli may be responsible for guinea pig avoidance of them. Our results suggest caution in accepting, without further empirical support, the premise that guinea pigs (and herbivores in general) have a generalized reduced bitter sensitivity.

The Bitter Taste Receptor TAS2R16 Achieves High Specificity and Accommodates Diverse Glycoside Ligands by using a Two-faced Binding Pocket

“…It is interesting to note that eight of the critical TAS2R16 residues identified here (I13, V77, R124, N148, L185, M200, W261, S273) are conserved between humans and guinea pigs (which have similar bitter taste sensitivity to salicin) but not in mice, which are indifferent to glucopyranosides but become responsive when expressing human TAS2R16 as a transgene 46 , 47 . This suggests that the ligand specificity of murine TAS2R16 may be significantly different than that of the human receptor.…”

The Taste of Caffeine

“…98 Guinea pigs, hamsters, and mice also avoid the taste of caffeine, suggesting that it is bitter (or elicits a negative taste quality) to these species as well. 17,99 Rhesus macaques generalize between quinine and caffeine (i.e., they do not discriminate between the taste of quinine and the taste of caffeine), again demonstrating its similarity to other bitter tastes, at least in primates. 100 In rodents, discrimination between caffeine and other chemicals that taste bitter to humans has not received enough attention.…”

Genetics of Taste Receptors

“…However, recent studies have shown that this relationship is more complex. For example, some bitter compounds (salicin and protein hydrolysates) evoked stronger avoidance in herbivores than in omnivores [145, 146]. Thus, bitter taste avoidance is species and stimulus dependent, and the premise that herbivores have a generalized reduced bitter sensitivity is not accurate.…”