Hormonal and metabolic rhythms associated with the daily scheduled nursing in rabbit pups

Abstract

Young rabbits are nursed every 24 h for a period of 3-5 min. As a consequence, pups are synchronized to this nursing event; this synchronization is characterized by increased locomotor activity and a peaking of core temperature and plasma corticosterone in anticipation of the daily meal. Ghrelin is a hormone suggested to play a role in meal initiation and to promote food intake. The present study explored the role of ghrelin in food-entrained conditions. Newborn rabbits were maintained in constant darkness and nursed once daily at 1000 by the lactating dam. On postnatal day 7, rabbits were killed at six different time points to complete a 24-h cycle. All pups developed locomotor rhythms entrained by mealtime and exhibited anticipatory activity. Food-entrained rhythms in plasma corticosterone and free fatty acids were observed even if two meals were omitted. In contrast, daily food-driven rhythms in stomach weight, plasma glucose, liver glycogen, and ghrelin did not persist when two meals were omitted. Peak ghrelin levels were observed at the moment in the cycle when the stomach weight was lowest, i.e., before initiation of anticipation. The present data are in agreement with previous data from rabbit pups maintained in light-dark conditions and provide evidence that 7- to 9-day-old rabbits in constant darkness can exhibit metabolic and hormonal rhythms mainly driven by the restricted daily nursing.

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

“…Additionally, at this age, their circadian visual system is immature (Juárez et al, 2013) and the SCN is not necessary for food entrainment (Hernández-Campos et al, 2011). Accordingly, the synchronization of FAA and some brain structures shifts in parallel when nursing is scheduled either during the day or the night (Caba et al, 2008;Morgado et al, 2008Morgado et al, , 2010a, as well as the telencephalic regions of the present contribution, as indicated by PER1 protein, product of the Per1 clock gene in preliminary experiments (Moreno et al, 2012;Morgado et al, 2010b). Hence, the effects observed in the three telencephalic areas are indeed due mainly to ingestion of food and not to an influence of the SCN.…”

Rodent model of infant attachment learning and stress

“…Seymour Levine, one of the first to study the role of early experiences in shaping stress responses, has left a lasting legacy regarding the profound influence of the mother on the development of the stress system in numerous species (Levine, 1957, 1967; Lyons, Martel, Levine, Risch, & Schatzberg, 1999; Morgado et al, 2008; Schmidt et al, 2006; Stanton et al, 1987). The data outlined in this review indicate that functional changes in infant learning are modified by a unique interaction between the developing CORT system, the amygdala, and the learning context that depends on whether the mother is present or absent.…”

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

“…These behavioral and physiological parameters synchronized with mealtime are controlled by a putative food-entrainable oscillator (FEO; Stephan, 2002). Recently, we reported that Cort and free fatty acids (FFA) also seemed to be entrained by nursing scheduled at 10:00 h, in rabbit pups housed in constant dark conditions, but whose mothers were exposed to a 12h:12h light/dark cycle with lights on at 07:00 h. On the contrary, stomach weight and liver glycogen followed an exogenous rhythm as values increased only after nursing, but not in fasted pups (Morgado et al, 2008). In the same study, we also found that ghrelin was low at nursing and reached a peaked 12 h later, whereas this pattern was absent in fasted pups.…”

“…Thus, in rats and humans, the physiological consequences of food ingestion are critically dependent of the time of day at which feeding takes place (Belda et al, 2005; Goel et al, 2009; Yoshihara et al, 2005). In our previous study in the rabbit, pups were scheduled to suckle during the day, at 10:00 h (Morgado et al, 2008). However, rabbits mothers nurse their pups during the night, at around 02:00 h (González-Mariscal et al, 2009; Jilge, 1991, 1993; Szeto et al, 2004).…”

“…Ghrelin promotes hunger and meal initiation (Bodosi et al, 2004; Cummins et al, 2001; Sugino et al, 2002), whereas leptin decreases food intake and increase energy expenditure (Mercer et al, 1997; Sugino et al, 2002). Cort was measured as an indicator of physiological synchronization (Morgado et al, 2008; Rovirosa et al, 2005). FFA were also taken into account as they are proposed to have a relevant role in food entrainment, perhaps as part of the synchronizing signal of the putative FEO (Escobar et al, 2009; Martinez-Merlos et al, 2004).…”