Post-oral and perioral stimulations during nursing enhance appetitive olfactory memory in neonatal rabbits

Nursing-suckling interactions facilitate olfactory learning in newborns as long as suckling and the olfactory stimulus temporally overlap. We tested the hypothesis that olfactory preferences would develop even with a long delay between odor presentation and nursing. Thyme was presented to 2-day-old rabbit pups by placing an odorized plate 2 cm above their nest box. Duration and time of nursing were controlled and occurred before, during, or after odor presentation. Controls were not nursed. When exposed to the odor for 15 min, control pups preferred thyme to a novel odor in a 2-choice test immediately after exposure but not 3 and 22 h later. When pups were nursed immediately before thyme exposure or during exposure, they preferred the familiar odorant until 22 h later. Identically, when nursing occurred 30 min before odor exposure, a preference for thyme was maintained up to 22 h. This was not observed when nursing occurred 60 min before odor presentation. We concluded that enhancement of olfactory memory occurs in neonates during nursing but also after post-oral stimulation by postprandial internal state.