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Updated: Nov 10, 2025
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Published on: February 28, 2025
Food Entrainment, Arousal, and Motivation in the Neonatal Rabbit Pup
Mario Caba1, Michael N Lehman2, Mario Daniel Caba-Flores3
1Centro de Investigaciones Biomédicas, Universidad Veracruzana, Xalapa, Mexico.
Insights
Newborn rabbits develop food anticipatory activity (FAA) synchronized to daily nursing. This study explores the neurobiological basis of this circadian rhythm, including brain structures and physiological changes in young rabbits.
Area of Science:
- Circadian Biology
- Neuroscience
- Animal Models
Background:
- Newborn rabbit circadian systems are immature, relying on daily nursing for timing.
- Food anticipatory activity (FAA) and synchronized physiological rhythms occur in pups before nursing.
- Rhythmic parameters persist in the brain and periphery, including the olfactory bulb, even under fasting.
Purpose of the Study:
- To provide an overview of physiological and neurobiological changes related to circadian entrainment in newborn rabbits.
- To examine the roles of the OVLT and MnPO in fluid homeostasis and arousal.
- To investigate the neural substrates of FAA, including the corticolimbic system and amygdala.
- To review the function of oxytocinergic cells in the PVN linking to autonomic responses for meal anticipation.
Main Methods:
- Review of existing literature on circadian rhythms, FAA, and neurobiology in newborn rabbits.
- Analysis of physiological and metabolic parameters under fasting conditions.
- Examination of protein expression (Fos, Per1), glial markers (GFAP), and enzyme activity (cytochrome oxidase).
- Focus on specific brain regions: OVLT, MnPO, amygdala, extended amygdala, and PVN.
Main Results:
- The immature circadian system in newborn rabbits is entrained by the daily nursing schedule.
- FAA and synchronized physiological rhythms demonstrate anticipatory behavior in pups.
- Specific brain structures (e.g., olfactory bulb, OVLT, MnPO, amygdala, PVN) show rhythmic changes and are implicated in FAA and arousal.
- Oxytocinergic cells in the PVN play a role in mediating autonomic responses preceding meals.
Conclusions:
- The rabbit model is valuable for understanding food entrainment and circadian rhythm development.
- The study highlights the complex interplay of physiological and neurobiological mechanisms underlying anticipatory behaviors.
- Further research is needed to fully elucidate the roles of specific brain nuclei in FAA and related homeostatic processes.
Abstract:
In the newborn rabbit, the light entrainable circadian system is immature and once a day nursing provides the primary timing cue for entrainment. In advance of the mother's arrival, pups display food anticipatory activity (FAA), and metabolic and physiological parameters are synchronized to this daily event. Central structures in the brain are also entrained as indicated by expression of Fos and Per1 proteins, GFAP, a glial marker, and cytochrome oxidase activity. Under fasting conditions, several of these rhythmic parameters persist in the periphery and brain, including rhythms in the olfactory bulb (OB). Here we provide an overview of these physiological and neurobiological changes and focus on three issues, just beginning to be examined in the rabbit. First, we review evidence supporting roles for the organum vasculosum of lamina terminalis (OVLT) and median preoptic nucleus (MnPO) in homeostasis of fluid ingestion and the neural basis of arousal, the latter which also includes the role of the orexigenic system. Second, since FAA in association with the daily visit of the mother is an example of conditioned learning, we review evidence for changes in the corticolimbic system and identified nuclei in the amygdala and extended amygdala as part of the neural substrate responsible for FAA. Third, we review recent evidence supporting the role of oxytocinergic cells of the paraventricular hypothalamic nucleus (PVN) as a link to the autonomic system that underlies physiological events, which occur in preparation for the upcoming next daily meal. We conclude that the rabbit model has contributed to an overall understanding of food entrainment.
