Participation of the Olfactory Bulb in Circadian Organization during Early Postnatal Life in Rabbits.

Experimental evidence indicates that during pre-visual stages of development in mammals, circadian regulation is still not under the control of the light-entrainable hypothalamic pacemaker, raising the possibility that the circadian rhythmicity that occurs during postnatal development is under the control of peripheral oscillators, such as the main olfactory bulb (MOB). We evaluated the outcome of olfactory bulbectomy on the temporal pattern of core body temperature and gross locomotor activity in newborn rabbits. From postnatal day 1 (P1), pups were randomly assigned to one of the following conditions: intact pups (INT), intact pups fed by enteral gavage (INT+ENT), sham operated pups (SHAM), pups with unilateral lesions of the olfactory bulb (OBx-UNI), and pups with bilateral lesions of the olfactory bulb (OBx-BI). At the beginning of the experiment, from P1-8, the animals in all groups were fed at 11:00, from P9-13 the feeding schedule was delayed 6 h (17:00), and finally, from P14-15 the animals were subjected to fasting conditions. The rabbit pups of the INT, INT+ENT, SHAM and OBx-UNI groups exhibited a clear circadian rhythmicity in body temperature and locomotor activity, with a conspicuous anticipatory rise hours prior to the nursing or feeding schedule, which persisted even during fasting conditions. In addition, phase delays in the nursing or feeding schedule induced a clear phase shift in both parameters. In contrast, the OBx-BI group exhibited atypical rhythmicity in both parameters under entrained conditions that altered the anticipatory component, as well as deficient phase control of both rhythms. The present results demonstrate that the expression of circadian rhythmicity at behavioral and physiological levels during early stages of rabbit development largely depends on the integrity of the main olfactory bulb

Misadjustment of diurnal expression of core temperature and locomotor activity in lactating rabbits associated with maternal over-nutrition before and during pregnancy.

Metabolic parameters ranging from circulating nutrient levels and substrate utilization to energy expenditure and thermogenesis are temporally modulated by the circadian timing system. During critical embryonic developmental periods, maternal over-nutrition could alter key elements in different tissues associated with the generation of circadian rhythmicity, compromising normal rhythmicity development. To address this issue, we determine whether maternal over-nutrition leads to alterations in the development of circadian rhythmicity at physiological and behavioral levels in the offspring. For this, female rabbits were fed a standard diet (SD) or high-fat and carbohydrate diet (HFCD) before mating and during gestation. Core body temperature and gross locomotor activity were continuously recorded in newborn rabbits, daily measurements of body weight and the amount of milk ingested was carried out. At the end of lactation, tissue samples, including brown adipose tissue (BAT) and white adipose tissue (WAT), were obtained for determining the expression of uncoupling protein-1 (UCP1) and cell death-inducing DNA fragmentation factor-like effector A (CIDEA) genes. HFCD pups exhibited conspicuous differences in the development of the daily rhythm of temperature and locomotor activity compared to the SD pups, including a significant increase in the daily mean core temperature, changes in the time when temperature or activity remains above the average, shifts in the acrophase, decrease in the duration and intensity of the anticipatory rise previous to nursing, and changes in frequency of the rhythms. HFCD pups exhibited a significant increase in BAT thermogenesis markers, and a decrease of these markers in WAT, indicating more heat generation by brown adipocytes and alterations in the browning process. These results indicate that maternal over-nutrition alters offspring homeostatic and chronostatic regulation at the physiological and behavioral levels. Further studies are needed to determine whether these alterations are associated with the changes in the organization of the circadian system of the progeny

Metabolites temporal pattern.

<p>Temporal profile of: liver weight (Liver) and serum levels of glucose (GLU), free fatty acids (FFA), tryacylglycerides (TAG), cholecystokinin (CCK) and cholesterol (CHO) of newborn rabbits on postnatal day 8, that were maintained under constant light, and received one of the following treatments: had access to a lactating doe (NAT) once every 24-h (indicated by the vertical gray bar) or olfactory stimulated with rabbit maternal milk (M-Milk), with the pheromone 2-methyl-but-2enal (2MB2) or with water (H₂O). Mean ± SEM, and the lines showed the fitted Cosinor function (see text for details). Mesor is indicated by the horizontal dotted line.</p

Duration and magnitude of the anticipatory component, in body temperature and locomotor activity.

<p>Graphics of the duration of the anticipation in core body temperature (A) and gross locomotor activity (C) of the newborn rabbits on postnatal day 7. Pups were maintained under constant light and received one of the following treatments: once every 24-h had access to a lactating doe (NAT), or olfactory stimulated with rabbit maternal milk (M-Milk), or with the pheromone 2-methyl-but-2enal (2MB2) or with water (H₂O). Graphics of the intensity of the anticipatory increase in relationship to the daily mean core temperature (B) and locomotor activity (D) for each group examined. Mean ± SEM. Scheffe * <i>p</i><0.01 vs. NAT.</p

Daily average of core body temperature and gross locomotor activity.

<p>The daily core body temperature (top panel) and gross locomotor activity (bottom panel) of newborn rabbits that were maintained under constant light and received one of the following treatments: once every 24-h had access to a lactating doe (NAT), or fed artificially and were olfactory stimulated with either rabbit maternal milk (M-Milk), pheromone 2-methyl-but-2enal (2MB2) or with water (H₂O) from postnatal day 2-7. Mean ± SEM. For body temperature: NAT, r² = 0.79; M-Milk, r² = 0.32; 2MB2, r² = 0.69; H₂O, r² = 0.63. For locomotor activity: NAT, r² = 0.99; M-Milk, r² = 0.97; 2MB2, r² = 0.94; H₂O, r² = 0.56.</p

Diurnal rhythm of gross locomotor activity.

<p>Representative temporal profiles of gross locomotor activity as measured using biotelemetry of newborn rabbits on postnatal day 7, maintained under constant light conditions and receiving the following treatment: pups that once every 24-h (indicated by the vertical grey bar) had access to a lactating doe (NAT), or olfactory stimulated with rabbit maternal milk (M-Milk) or with the pheromone 2-methyl-but-2enal (2MB2) or with water (H₂O). At the bottom, the mean diurnal pattern of body temperature and standard error (SEM), of each experimental condition from postnatal days 5 to 7 for all of the pups (eight animals per group) examined.</p

Temporal patterns of core body temperature.

<p>Representative daily profiles of temperature as measured using biotelemetry in newborn intact rabbit pups (INT), intact pups fed by enteral gavage (INT+ENT), sham operated pups (SHAM), pups with unilateral lesions of the olfactory bulb (OBx-UNI) and pups with bilateral lesions of the olfactory bulb (OBx-BI). From postnatal day 6–8, the pups were nursed or fed artificially every 24 h at 11:00 (indicated by the vertical red bar), from postnatal day 9–13 the feeding schedule was delayed 6 h (17:00), and from P14-15 the pups were maintained under fasting conditions (see text for details). The dotted red line indicates the daily mean temperature.</p

Temporal patterns of gross locomotor activity.

<p>Representative daily profiles of activity in newborn rabbits as measured using biotelemetry, in intact pups (INT), intact pups fed by enteral gavage (INT+ENT), sham operated pups (SHAM), pups with unilateral lesions of the olfactory bulb (OBx-UNI) and pups with bilateral lesions of the olfactory bulb (OBx-BI). From postnatal day 6–8, the pups were nursed or fed artificially every 24 h at 11:00 (indicated by the vertical red bar), from postnatal day 9–13 the feeding schedule was delayed 6 h (17:00), and from P14-15 the pups were maintained under fasting conditions (see text for details). The red dotted line indicates the daily mean activity.</p