Rabbit pup response to the mammary pheromone: from automatism to prandial control

Rabbit pups display nipple-search behavior in response to maternal odor cues such as the Mammary Pheromone (MP). Here, we assessed in 3 steps whether the activity of the MP is influenced by prandial and/or rhythmic factors during early development. To address this point, the activity of the MP was tested in 690 pups varying in age (day 0, 2, 5 or 10), prandial state (sucked or un-nursed) and period of their 24-h cycle (-6 to +12 h after the daily sucking). In Experiment 1, the responsiveness of d0 pups was high and stable during the whole day, whether they are nursed or deprived of sucking. The MP activity was thus unaffected by colostrum ingestion. Experiment 2 revealed that some differences appear the next days: whereas the responsiveness of d2 pups was also very high during the 24-h cycle (>94%), it decreased in d5-d10 pups immediately after sucking (<48%), with a rapid recuperation in d5 pups. Experiment 3 showed that this postprandial drop in response to the MP disappeared in d5-d10 pups that missed the daily nursing, suggesting that it resulted from post-ingestive/post-absorptive events rather than from rhythm activity-related factors. Taken together, the results show a progressive change in the circadian dynamics of the MP-induced orocephalic response as a function of age modulated by prandial state. This indicates a transition from an automatic response to the MP to a response regulated by physiological factors associated with satiation.