Contribution of orosensory stimulation to strain differences in oil intake by mice

Little is known about why animals differ in daily intake of oils. Here, we tested the hypothesis that the oral acceptability of oil is a key determinant of daily intake. To this end, we examined short- and long-term ingestive responses of eight mouse strains (FVB/NJ, SWR/J, SM/J, C57BL/6J, BALB/cJ, 129P3/J, DBA/2J and AKR/J) to Intralipid™, a stable emulsion of soybean oil. In Experiment 1, we compared orosensory responsiveness (as indicated by initial licking rates) of eight mouse strains to a range of concentrations of Intralipid and sucrose. We included sucrose because there are two natural alleles of Tas1r3 (the gene that encodes the T1R3 sweet taste receptor), and strains with the Tas1r3Sac-b allele exhibit higher daily intake of sucrose and oil than strains with the Tas1r3Sac-d allele. All strains exhibited concentration-dependent increases in lick rates for both sucrose and Intralipid, but the extent of these increases varied greatly across strains. The strains with the Tas1r3Sac-b allele licked more vigorously for sucrose at concentrations ≤ 0.3 M, but not for Intralipid at any concentration. In Experiment 2, we ran the mice through 24-h preference tests, in which they had a choice between water and each of four concentrations of Intralipid (1, 5, 10 and 20%). The strains differed greatly in daily intake of Intralipid, particularly at the 1 and 5% concentrations. Regression analyses revealed that strain differences in orosensory responsiveness reliably predicted strain differences in daily intake of 1 and 5% Intralipid, but not 10 or 20% Intralipid. These findings indicate (i) that Tas1r3 genotype does not modulate orosensory stimulation from oil, (ii) that orosensory stimulation contributes to strain differences in daily intake of dilute oil emulsions, but not concentrated ones, and (iii) that daily intake of concentrated oil emulsions is controlled primarily by post-oral satiety mechanisms.