Persistence of hormonal and metabolic rhythms during fasting in 7- to 9-day-old rabbits entrained by nursing during the night

Abstract

Rabbit does nurse their litter once every 24 h during the night. We hypothesized that corticosterone, ghrelin, leptin and metabolites like glucose, liver glycogen and free fatty acids could be affected in the pups by the time at which does nurse them. Therefore, we measured these parameters in pups nursed at 02:00 h (nighttime for the doe) to compare them with results from a previous study where does nursed at 10:00 h, during daytime. From postnatal day 7, pups were sacrificed either just before their scheduled time of nursing or at 4, 8, 12, 16 or 20 h after nursing (n = 6 at each time point); additional pups were sacrificed at 4 h intervals between 48 and 72 h after nursing to study the persistence of oscillations during fasting. All pups developed locomotor anticipatory activity to nursing. Corticosterone, ghrelin and free fatty acids exhibited a rhythm that persisted in fasted pups. Glucose concentrations were lower in fasted than in nursed pups, and glycogen was only detected in nursed subjects. Leptin values were stable and low in nursed subjects but increased significantly in fasted subjects up to 72 h after the expected nursing time. The rhythm of ghrelin persisted during fasting, contrary to our previous findings in pups nursed during daytime (i.e. outside the natural time of nursing for this species). Therefore, in 7-day-old rabbit pups, night nursing is a strong zeitgeber for corticosterone, ghrelin, free fatty acids and energy metabolites but not for leptin.

Circadian feeding entrains anticipatory metabolic activity in piriform cortex and olfactory tubercle, but not in suprachiasmatic nucleus

“…A similar pattern in neuronal activity has been observed with c-Fos immunohistochemistry in the rabbit pup (Nolasco et al, 2012) and in the adult rat (Caba et al, in press). In this last study, under a restricted feeding schedule, a parallel pattern of activation was found in the piriform cortex and bed nucleus of the accessory olfactory tract, which are main targets of OB.…”

“…Recently, it was shown that the main OB of neonatal rabbits expresses circadian oscillations of both c-Fos and Per1 proteins, which were entrained by circadian nursing (Nolasco et al, 2012). This result shows a possible functional significance of OB oscillations, suggesting that olfactory signals during nursing might be the primary entraining cue.…”

“…With exception of the daily visit of the mother for $5 min, pups remained undisturbed in constant darkness in the nest compartment for the entire experiment. 24-h locomotor activity of the pups was monitored by detectors located in the ceiling of each nest, tested to be sensitive to pups' movement through the infrared radiations (λ ¼5-14 mm) (Morgado et al, 2010). To determinate that the pups were behaviorally synchronized to the daily nursing, doubleplotted actograms and activity profiles were built with the transduced signal detected by the sensors with the circadian recording system SPAD9 (Omnialva M.R., Mexico).…”

“…However, the neural components of this conditioned system, its inputs and how food sets its phase are not well understood (Carneiro and Araujo, 2012;Silver et al, 2011). A natural, experimentally accessible example of FAA is displayed by the rabbit pup (Caba et al, 2008;Morgado et al, 2010). Nursing in the rabbit is a naturally circadian event: after parturition, dams visit the nest and nurse their pups once every 24 h, for only $ 5 min (Zarrow et al, 1965).…”

Activation of Organum Vasculosum of Lamina Terminalis, Median Preoptic Nucleus, and Medial Preoptic Area in Anticipation of Nursing in Rabbit Pups

“…Rabbit pups show clear locomotor anticipatory behavior and a significant increase of corticosterone before the arrival of the nursing mother (Caba et al, 2008;Jilge, 1995;Morgado et al, 2010a), which occurs with circadian periodicity (González-Mariscal et al, 2013;Jilge, 1995). Besides, the diffuse part of the dorsomedial nucleus (DMN; Caba et al, 2008) and parabrachial nucleus (PBN; Juárez et al, 2012) are entrained by the timing of feeding, but not the SCN (Caba et al, 2008), similar to rodents (Mistlberger, 2011).…”