Maternal Odor Exposure Modulates Acceptance of a Bitter Taste in Newborn and Infant Rats

Abstract

The acceptance of bitter, aversive, substances during early life is enhanced by stimulation with familiar, pre-exposed odors. Newborn rats exhibited heightened grasp responses toward an artificial nipple dispensing quinine, and drank more of this bitter solution, if concurrently stimulated with a lemon odor they had been exposed to shortly after birth. It yet unknown, however, if odors made familiar via normative developmental milestones also acquire modulatory influence upon seeking and intake of basic tastants. The current study assessed the influence of exposure to maternal odor on intake and grasp responses toward a surrogate nipple providing quinine, in 3-day (Experiment 1) or 12-day (Experiment 2) old, Wistar rat pups. The results revealed enhanced seeking and intake of the bitter solution, but not of water, in animals tested in the presence of the mother (and hence exposed to its odor cues), at both ages, compared to counterparts given either no explicit odor stimulation or stimulation to the odor of an unrelated dam. These results, obtained with a biologically relevant odor, are consistent with those previously found with a neutral, arbitrary odor. It seems that during the early stages of development, familiar odors regulate the acceptance of non-palatable, otherwise rejected, flavors.

Keywords: bitter; mother; odor; ontogeny; rats; taste.

FIGURE 1

Mean percentage (±SE) of (A) body weight gain, (B) total time of grasp, (C) number of grasp, (D) latency to grasp, and (E) mean grasp duration during the 6-min presentation of the artificial nipple containing quinine in the presence of the mother (black bars – Odor condition) or in the absence of the mother (white bars – No odor condition). ^∗Indicates p < 0.05.

FIGURE 2

Mean percentage (±SE) of body weight gain during the 6-min administration of quinine or water in the presence of the mother’s odor or in the presence of another lactating mother. ^∗Indicates p < 0.05.