Metabolic correlates of the circadian pattern of suckling-associated arousal in young rabbits

Abstract

Young rabbits (Oryctolagus cuniculus) are only nursed for 3-5 min every 24 h. They show a circadian increase in activity in anticipation of this, which is entrained by suckling. Our aim was to determine whether serum and liver metabolites show diurnal fluctuations which could act to regulate this circadian pattern. Stomach weight, liver glycogen and serum metabolites were measured every 3 h in 7- to 8-day-old pups when normally nursed (up to 24 h after suckling) and fasted (up to 48 h after suckling). The results suggest: 1. Energy balance between feeds was maintained by a cascade in the use of fuels, first glucose from the milk, then glycogen stores and gluconeogenesis from circulating products of proteins and triglycerides, and finally, in late-fasted animals, the mobilization of free fatty acids. 2. The empty stomach and depletion of glycogen 23-24 h after the last feed could act to trigger anticipatory arousal in normally nursed pups, and the release of free fatty acids 45 48 h after the last feed could trigger this in fasted pups. 3. Unmasking of rhythmicity by fasting in serum levels of glucose and proteins suggests their regulation by endogenous oscillators, which may also be the case for the mobilization of free fatty acids.

Food entrainment modifies the c-Fos expression pattern in brain stem nuclei of rats

“…Also, the stomach of RF rats exhibits a slow emptying rate that allows food absorption for a prolonged interval (24). This adaptive process was also observed in young rabbits, which are nursed only once a day by their lactating dams (17). This indicates that NST plays an important role receiving specific signals elicited during food entrainment that are transmitted to the brain and possibly to the food-entrained system.…”

Metabolic adaptations in neonatal mother-deprived rabbits

“…Newborn rabbits rely on a daily milk supply from suckling for their postnatal growth (Blumberg and Sokoloff, 1998). Usually, nursing occurs once a night and lasts only a few minutes (Zarrow et al, 1965;Hudson and Distel, 1982;González-Mariscal, 2007), but the doe's high milk fat content and the kits' gradual gastric emptying (Escobar et al, 2000) allow newborn rabbits to endure fasting between each nursing (Coureaud et al, 2000;Rödel et al, 2008). In the case of DLS, the two-day separation means that young rabbits miss two successive nursings.…”

“…limited to a few minutes a day during the single suckling episode (Escobar et al, 2000). Additionally, as a consequence of the DLS-provoked imbalance between energy intake and expenditure, kits lost 20% of their body weight, which was only partially recovered at weaning (Bonanno et al, 2004;Brecchia et al, 2009).…”

Mother-Young and Within-Litter Relations in the European Rabbit Oryctolagus cuniculus

“…This enables them to reach the doe's ventrum unhindered and to start the rapid search for nipples the moment she stands over them (see below). This anticipatory arousal is accompanied by a rise in the pups' (and mothers') body temperature (Jilge et al 2000;2001), and in fasted pups, in elevated serum concentrations of free fatty acids (Escobar et al 2000), presumably in preparation for the competitive nursing situation soon to follow (see below). This state of arousal may also explain the interesting finding that newborn pups briefly exposed to the smell of a human hand around nursing time show less fear of humans post weaning Altbäcker 1999, 2003).…”