Nature's food anticipatory experiment: entrainment of locomotor behavior, suprachiasmatic and dorsomedial hypothalamic nuclei by suckling in rabbit pups

Abstract

In nature and under laboratory conditions, dams nurse rabbit pups once daily for a duration of fewer than 5 min. The present study explored neural mechanisms mediating the timing of nursing in this natural model of food anticipatory activity, focussing on the suprachiasmatic nucleus (SCN), the locus of the master circadian clock and on the dorsomedial hypothalamic nucleus (DMH), a region implicated in timing of food-entrained behavior. Rabbit pups are born in the dark, with eyelids closed. Nursing visits to the litters also occurs during the dark phase. To explore the effect of the timing of feeding, pups were maintained in constant darkness, while females housed in a light-dark cycle were permitted to nurse their pups either during the night (night-fed group) or day (day-fed group). All pups exhibited anticipatory locomotor activity before daily nursing. In the SCN, PER1 and FOS peaked during the night in both groups, with a longer duration of elevated protein expression in the night-fed group. In contrast, DMH peak PER1 expression occurred 8 h after pups were fed, corresponding to the shift in timing of nursing. Comparison of nursed and 48 h fasted pups indicates that the timing of PER1 expression was similar in the SCN and DMH, with fewer PER1-positive cells in the latter group. The results indicate that rabbit pups show food anticipatory activity, and that timing of nursing differentially affects PER1 expression in the SCN and DMH.

Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

“…Thus, a 6-h shift on P3 in the time of nursing resulted in a corresponding shift in the pattern of expression of both sets of measures by P7 (see Caldelas et al 2007 for a comparison with the pattern of gene expression in nonshifted \control" pups on P7). In a methodological improvement on previous studies (Jilge et al, 2000Caldelas et al, 2007;Caba et al, 2008), this occurred even after ensuring complete separation of mothers and young between nursing visits to prevent possible vibrational cues associated with the mother's restlessness in From postnatal days 1 to 3 (P3) pups were nursed at 09:30 h and from P4 to P7 (P7) nursing was delayed 6-15:30 h. anticipation of nursing from triggering anticipatory responses in the pups. As nursing occurred in dim red light, we consider it most unlikely that the pups were entrained even partially by this weak photic cue.…”

“…Nevertheless, it is increasingly clear that to fully understand circadian function, and particularly in complex natural contexts, nonphotic input must also be considered (Hastings et al, 1997;Challet et al, 2003;Caldelas et al, 2005a). Although biologically relevant nonphotic stimuli are typically more difficult to identify, define and to administer than photic cues, a promising approach used increasingly in mammalian research is to study the develop-ment of circadian systems in previsual altricial young (Reppert, 1989;Escobar et al, 2000;Davis and Reppert, 2001;Jilge and Hudson, 2001;Shimomura et al, 2001;Ohta et al, 2002Ohta et al, , 2003Sládek et al, 2004;Caldelas et al, 2005aCaldelas et al, , 2007Kováîcikova et al, 2005Kováîcikova et al, , 2006Caba et al, 2008;reviewed in Caldelas et al, in press).…”

“…However, we still know very little about the neural regulation of the newborn rabbit's circadian system (but see Allingham et al, 1998;Caba et al, 2008). As part of an on-going program investigating this we recently reported diurnal patterns in the expression of the clock genes Per1, Per2, Cry1, and Bmal1 in the suprachiasmatic nuclei of the hypothalamus (SCN; the main circadian pacemaker in mammals) (Caldelas et al, 2007).…”

Behavioral, Physiological, and Neuroendocrine Circadian Rhythms During Lactation

“…A serum shock, administration of various compounds such as cAMP, protein kinase C, glucocorticoid hormones, or Ca 2+ to a cultured rat-1 fi broblast cell line, can all trigger a surge of Per1 transcription and elicit and shift circadian expression of clock genes and other genes (Balsalobre et al 2000 ). In adult rats, exposure to stressors (Takahashi et al 2001 ) or scheduled feeding (Caba et al 2008 ;Feillet et al 2008 ) also induces a similar effect in several brain nuclei. Overall we consider that suckling seems to be the main stimulus that entrains clock gene oscillations in neuroendocrine cells in the rabbit.…”

Research Article Analysis of melanopsin gene expression in the rabbit retina at different ages.

“…The female rabbit breastfeeds kits once a day, they suckle up to 35% of their body weight every 24 h for 3-5 min and the mother keeps in darkness throughout the lactation (Caba et al, 2008). When young rabbits leave the burrow at 2 weeks of age, is when they are exposed to light and as a result, they open their eyelids.…”