Effect of weaning time on the growth rate and food intake of the spiny mouse pup

The spiny mouse Acomys cahirinus produces well-developed pups although it is a relatively small mammal (45 g). We envisioned two opposing hypotheses on the effect of early weaning on the growth rate of pups. The first predicts little effect since the increase in energy intake of dams above non-reproducing females is relatively low, suggesting that pups consume a large portion of their energy as solid food, and the pups are very well developed at birth. The second predicts a substantial effect since the 'index of precociality', that is the energy intake for maintenance of a pup as a proportion of that predicted for a rodent of its body mass, falls within values for altricial rodents, suggesting an extended maternal dependence of the young. To test these hypotheses, we measured the growth rate and food intake of pups weaned after either 7, 14, 21 or 28 days. Only three of 12 pups weaned after 7 days survived and, consequently, the latter hypothesis was supported. All pups weaned at 14–28 days survived. There was a significant decrease in growth rate during the first day after weaning in pups weaned at 7, 14 and 21 days but not after 28 days, suggesting that pups did not require parental care by day 28. Peak growth rate in pups weaned at 14 days occurred in the second week but occurred in the third week in pups weaned at 21 and 28 days. In spite of these differences, pups in all treatments had similar body mass at 64 days, indicating compensatory growth. We concluded that pups of A. cahirinus are precocial from a morphological aspect in that they are well developed at birth but altricial from a nutritional aspect in that they require extended maternal support.     

Comparative Effects of Ethanol and Malnutrition on the Development of Catecholamine Neurons: Changes in Neurotransmitter Levels

Abstract: The comparative effects of exposure to ethanol and malnutrition on the concentrations of tyrosine and catecholamines in whole brain and selected regions of brain have been studied in the developing rat. These animals were the offspring of optimally nourished rats (control pups), of rats fed a diet with 35% of the calories supplied by ethanol (ETOH pups), or of animals fed a diet calorically equivalent to the latter but lacking ethanol (iso-caloric, 1C pups). These diets were administered to dams either during the last week of gestation (prenatal) or during lactation (postnatal). Tyrosine levels were elevated prior to birth in the prenatal ETOH or IC pups or at 1 and 2 weeks of age in postnatal ETOH or 1C pups as compared with values found in the control offspring. Dopamine concentration in whole brain was significantly lower in prenatal ETOH pups than in prenatal IC pups at 3 weeks of age. Levels in the brains of postnatal ETOH pups were lower than control values, but not relative to animals exposed to 1C diet. Investigation of corpus striatum showed a significant decrease in dopamine concentration compared with control or IC pup values as a result of postnatal exposure to ethanol. Norepinephrine levels in the whole brain of prenatal ETOH pups were consistently 30–40% lower than either control or matched 1C pups during development. At 3 weeks of age, the norepinephrine levels in the hypothalamus of animals exposed to ethanol pre or postnatally were 30–60% lower than values in the corresponding region in either control or 1C pups. In the rat model described, ethanol caused a decrease in catecholamine levels, perhaps solely by affecting the norepinephrine neurons.     

Effects of continuous gastric infusion of food dyes on developing rat pups

The consequences of chronic percutaneous gastric infusion of food dyes on the activity levels and shock avoidance performance of normal developing rats and those treated with 6-hydroxydo p-amine (6-OHDA) were investigated. All pups were artificially reared from four days of age and a liquid diet containing either food dyes (D) or no colorings (N) was infused into both 6-OHDA (T) and sham-treated pups (V). Pups receiving food dyes were significantly more active than comparable pups not receiving food dyes at all ages tested, an effect observed in both 6-OHDA and shamtreated pups. Pups treated with food dyes exhibited an impaired avoidance performance in a shuttle box at 28 days of age. VD and TN pups displayed an over 100% impairment in avoidance performance in comparison with VN pups. These results suggest that food dyes and/or their metabolites may exert deleterious effects on the behavioral repertoire of the developing rat pup.     

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.     

The effect of ambient temperature on body temperature and on ultrasonic behaviour in litters of albino laboratory mice deprived of their mothers

Litters of mouse pups of various ages when deprived of their mother and kept for one hour at ambient temperatures of 3°C, 12°C and 22°C lose heat less rapidly than pups isolated individually at similar temperatures. The litters are able to maintain constant body temperatures of 35–37°C by day 8 at 22°C, by day 19 at 12°C and by day 21 at 3°C. Very little ultrasound is detected from litters of any age up to 21 days at 22°C while at 12°C ultrasound is mainly detected from pups of 4 and 6 days; very few calls are produced by older pups at this temperature. Considerably more calls are emitted at 3°C than at either of the two higher temperatures. At 3°C the total number of calls emitted during the hour-long exposure period varied markedly with age. There were two peaks of calling, one on day 6 and the other on day 16. The temporal pattern of calling throughout the hour-long exposure period at 3°C was similar in pups of 4 and 6 days and in pups of 8, 10, 12, 14 and 16 days, but differed between these two groups. In the younger group of pups the rate of calling rose to a peak and then decreased to zero as the pups became comatose; in the older pups the rate of calling was low initially then either rose throughout the rest of the hour or rose to a high level that was maintained. It is suggested that the various patterns of ultrasonic calling can be associated with the physiological development of mouse litters.     

Role of huddling on the energetic of growth in a newborn altricial mammal

Huddling is considered as a social strategy to reduce thermal stress and promote growth in newborn altricial mammals. So far, the role of huddling on the allocation of saved energy has not been quantified nor have the related impacts on body temperature rhythms. To determine the energy partitioning of rabbit pups either raised alone or in groups of eight, four, or two individuals, when thermoregulatory inefficient (TI) and efficient (TE), we first investigated their total energy expenditure and body composition. We then monitored body temperature and activity rhythms to test whether huddling may impact these rhythms, centered on the suckling event. Pups in a group of eight utilized 40% less energy for thermogenesis when TI than did pups alone and 32% less energy when TE. Pups in groups of eight and four had significantly lower thermoregulatory costs in the TI period, whereas pups in groups of two, four, and eight had lower costs during the TE period. Huddling pups could therefore channel the energy saved into processes of growth and accrued more fat mass (on average 4.5 +/- 1.4 g) than isolated pups, which lost 0.7 g of fat. Pups in groups of four and eight had a body temperature significantly higher by 0.8 degrees C than pups in groups of two and one when TI, whereas no more differences were noted when the TE period was reached. Moreover, pups alone showed an endogenous circadian body temperature rhythm that differed when compared with that of huddling pups, with no rise before suckling. Thus huddling enables pups to invest the saved energy into growth and to regulate their body temperature to be more competitive during nursing, particularly at the early time when they are TI.     

Effects of excess methionine on collagen metabolism: a study on newborn rat skin

We studied the biochemical effects of excess methionine intake on the skin of newborn rats. Group 1 pups were intubated with methionine dissolved in 0.1 ml physiological saline solution in the amount of 0.1 g/100 body wt as a control using a gastric needle. Group 2 pups were given 0.2 g/100 g in the same manner as group 1 as an experimental group. They were intubated every other day from day 3 to 13. On Day 15, [14C]proline was injected intraperitoneally into pups and their skin was removed. 14C total and hydroxyproline uptake was examined in the tissue as well as in the sequential extracts. Although excess methionine intake by the pups did not alter the collagen content of their skin, it caused an increase in the content of type III collagen and a decrease in crosslinked collagen. In addition, newly synthesized collagen in the neutral salt extract increased in the excess methionine group, indicating that crosslinked collagen decreases as excess methionine was intubated. The present study demonstrated that excess methionine in the early lactational period altered the nature of the skin collagen of suckling newborn rat pups.     

Effect of mammillary body lesions in adult rats on the survival and development of their young

The lesion of the mammillary bodies in the adult female did not alter the oestrous cycle, sexual behavior, parturition, or the number and weight of pups at birth. Neither did it alter maternal behavior (nesting behavior, cleaning of the pups, placentophagia, nursing position, retrieving, etc.). Nevertheless, more than 30% of the pups born from the mothers with total lesions of the mammillary bodies died during the first 10 days after birth. The weight of the surviving pups was greatly impaired and the pups showed severe undernourishment. The effects of the lesion of the mammillary bodies on the survival and weight of the pups were dependent on the mass of tissue destroyed in that structure.     

Effect of maternal iron deficiency on GABA shunt pathway of developing rat brain

Iron deficiency during pregnancy and lactation (35 mg iron/kg diet) produced a significant reduction in liver nonheme iron in dams as well as in fetus and young ones. The body, liver and brain weights of fetus, new-born, and developing pups remained unaffected. However, the body weight and PCV were reduced only in 21-day-old pups. The enzyme activities of GDH, GAD, GABA-transaminase, and NAD(+)-linked ICDH were reduced in 14 and 21-day-old pups. The enzyme activities of NADP(+)-linked ICDH activities remained unaffected in the fetus and developing pups brain. Maternal rehabilitation on iron sufficient diet for 1 week from day 14 to 21 of lactation period did not reverse these changes. The maternal iron deficiency during lactation period alone did not cause any alteration in all parameters assayed, however, there was a reduction in liver non-heme iron of pups on days 14 and 21.     

Effect of preoptic region implants of dilute estradiol on the maternal behavior of ovariectomized, nulliparous rats

Estrogen implanted directly into the medial preoptic region of pregnant Charles River Sprague-Dawley rats hysterectomized and ovariectomized on Day 16 of gestation mimics the effects of systemic estrogen treatment at this time by reducing the latency to respond to foster pups with maternal behavior (Numan, Rosenblatt, and Komisaruk, 1977). The present report describes the pup-directed responses of ovariectomized, nulliparous Zivic-Miller Sprague-Dawley rats that received bilateral medial preoptic implants of either cholesterol (n = 11) or estradiol diluted 1:10 with cholesterol (n = 11). Two days after treatment these animals were housed with three foster pups: their responsivity to pups and quality of nests built were then assessed, at first hourly and then daily. Rats receiving intracranial estradiol required significantly shorter exposures to pups than did cholesterol-treated animals before initiating carrying and grouping of 3 dispersed pups in a maternal nest during a 15-min test. On other measures, however, the groups did not differ (e.g., proportion grouping pups overnight, time required to complete retrieval of pups to the nest, time required to rebuild a disrupted nest). Animals treated with cholesterol and animals with estradiol implants did not differ in uterine weight at the time of sacrifice, suggesting that estrogen did not leak, even from this well-vascularized implant site, into the circulation. Thus, as in the pregnant animal, the facilitating effects of estrogen on maternal behavior can be mediated through the medial preoptic region; however, the effects were evident only when a test requiring retrieval of several pups within an arbitrarily short interval was given.     

Influence of maternal mineral deficiency on the hepatic metallothionein and zinc in newborn rats

The effects of maternal Zn, Cu, or Fe deficiencies during late gestation on hepatic levels of metals and metallothionein (MT) and the binding of Zn and Cu to protein fractions were investigated in newborn rats. Timed pregnant rats were fed one of the following diets: Zn deficient (Zn-D), Cu-D, Fe-D, or control from day 12 of gestation until birth. The specific nutritional deficiency status of the dams was confirmed by low plasma levels of the deficient metal. Livers from pups were analyzed for MT, metal content, and metal-protein binding. Maternal Zn-D resulted in a greater than 50% reduction of hepatic MT levels in pups, whereas Cu-D and Fe-D had no significant effects. Pups in each deficient group showed a significant decrease in the hepatic levels of the respective metals. Fractionation of hepatic cytosols from the pups by Sephadex G-75 gel filtration showed that in both Fe-D and Cu-D pups the respective metals were depleted from the high molecular weight protein fraction, whereas in Zn-D pups the Zn was depleted mainly from the MT fraction (Ve/V0 approximately 2). Incorporation of [35S] cysteine into MT fractions was significantly lower in Zn-D pups as compared with control pups. These results indicate that there is a specific effect of the maternal Zn-D on the hepatic storage of Zn as MT in newborn rats.     

Effects of repeated pup exposure on behavioral,neural, and adrenocortical responses to pups in male California mice (Peromyscus californicus)

In biparental mammals, the factors facilitating the onset of male parental behavior are not well understood. While hormonal changes in fathers may play a role, prior experience with pups has also been implicated. We evaluated effects of prior exposure to pups on paternal responsiveness in the biparental California mouse (Peromyscus californicus). We analyzed behavioral, neural, and corticosterone responses to pups in adult virgin males that were interacting with a pup for the first time, adult virgin males that had been exposed to pups 3 times for 20 min each in the previous week, and new fathers. Control groups of virgins were similarly tested with a novel object (marble). Previous exposure to pups decreased virgins' latency to approach pups and initiate paternal care, and increased time spent in paternal care. Responses to pups did not differ between virgins with repeated exposure to pups and new fathers. In contrast, repeated exposure to a marble had no effects. Neither basal corticosterone levels nor corticosterone levels following acute pup or marble exposure differed among groups. Finally, Fos expression in the medial preoptic area, ventral and dorsal bed nucleus of the stria terminalis was higher following exposure to a pup than to a marble. Fos expression was not, however, affected by previous exposure to these stimuli. These results suggest that previous experience with pups can facilitate the onset of parental behavior in male California mice, similar to findings in female rodents, and that this effect is not associated with a general reduction in neophobia.     

The effect of overfeeding the young in early postnatal ontogeny on brown fatty tissue

We studied the effects of overfeeding of neonatal Wistar rats on O2 consumption by the interscapular brown adipose tissue and DNA content in the tissue. The overfeeding was induced by reducing the litter size to two to three pups per dam compared with standard litters of five to ten pups. All animals were allowed free access to water and forage and were kept at 24 +/- 1 degrees C. Newborn and 16-day-old rat pups were used in the experiments. The body weight of overfed pups was significantly higher than that of standard fed pups (p < 0.001). There were no differences between groups of 16-day-old rats in the resting metabolic rate. The mass of dried brown adipose tissue relative to the body mass in overfed pups was lower than in the control pups (p < 0.01). O2 consumption in the rats from small litters was 35% higher (p < 0.001). DNA content (mg/g brown adipose tissue) in overfed rats was 35% lower as compared to the control pups (p < 0.001). These results indicate that overfeeding at the preweaning stage of life affects growth, cellularity, and thermogenic function of brown adipose tissue.     

Effect of insulin and 2-deoxy-d-glucose on the food intake of infant rats

The effects of glucoprivation on the food intake have been determined in infant rats up to weaning. It was found that insulin reduced the milk intake of 9, 13 and 17-day-old males and females for three hours after treatment. In 24-day-old pups food intake increased for three hours after insulin administration, and decreased during the next 21-hour period. 2-deoxy-D-glucose increased the food intake in 28-day-old rat pups only. It was concluded that the inability of rat pups to correct glucoprivation by a subsequent increase of food intake is a consequence of the inadequate development of hypothalamic regulatory mechanisms. Glucoprivation stimuli are ineffective inducers of short-term hyperphagia of rat pups until the age of 24-28 days.     

卡麦角林处理哺乳期小鼠对子代存活和生长的影响

哺乳期是兽类繁殖成功的关键阶段之一,本实验以不同浓度卡麦角林油溶液对哺乳早期雌性小鼠连续灌胃3 d,检测雌性小鼠体重和幼鼠存活及体重变化,以此确定卡麦角林对哺乳雌性小鼠繁殖成功的影响。结果发现,卡麦角林对雌性小鼠在哺乳期的体重相对增长率无显著影响,但处理组幼鼠出现部分死亡,0 μg / kg、50 μg / kg、100 μg/ kg、200 μg/ kg、400 μg/ kg 组幼鼠死亡率分别为1.30% 、3.85% 、4. 08% 、7.38% 、21.19% ,幼鼠死亡数和剂量呈正相关,400 μg / kg 组幼鼠成活率显著下降到78 8% ,其他剂量组幼鼠成活率与对照组差异不显著;给药后7 d 存活幼鼠的生长发育显著被抑制,之后处理组幼鼠体重变化与对照组无显著差异。上述结果表明卡麦角林处理哺乳早期雌性小鼠可降低幼鼠成活率并抑制存活幼鼠的生长发育,进而有可能降低雌性小鼠及其子代的繁殖成功率。     

Effects of perinatal alcohol on sexual differentiation and open-field behavior in rats

Prenatal alcohol treatment prolonged the gestation period by 1 day in 5 out of 11 mothers and decreased the anogenital distance of pups of both sexes measured at birth. There were no effects on body weights of the pups at birth, total number of pups per litter, or sex ratio. The postnatally alcohol-treated males (pups nursed by alcohol-drinking mothers) had a significantly earlier preputial separation than animals treated with alcohol prenatally only or controls. There were no differences among the groups on the parameters of adult masculine sexual behavior, plasma testosterone, weights of sex accessory glands, or open-field behavior. Animals treated perinatally with alcohol showed a significant inhibition of penile reflexes. Repeated testing, however, abolished this effect.     

Tissue-specific effects of starvation and refeeding on the disposal of oral [1-14C]triolein in the rat during lactation and on removal of litter.

1. The effects of starvation and refeeding on the disposal of oral [14C]triolein between 14CO2 production and 14C-lipid accumulation in tissues of virgin rats, lactating rats and lactating rats with pups removed were studied. 2. Starvation (24 h) increased 14CO2 production in lactating rats and lactating rats with pups removed to values found in virgin rats. This increase was accompanied by decreases in 14C-lipid accumulation in mammary gland and pups of lactating rats and in white and brown adipose tissue of lactating rats with pups removed. 3. Short-term (2 h) refeeding ad libitum decreased 14CO2 production in lactating rats and lactating rats with pups removed, and restored the 14C-lipid accumulation in mammary glands plus pups and in white and brown adipose tissue respectively 4. Insulin deficiency induced with mannoheptulose inhibited the restoration of 14C-lipid accumulation in white adipose tissue on refeeding of lactating rats with pups removed, but did not prevent the restoration of 14C-lipid accumulation in mammary gland. 5. Changes in the activity of lipoprotein lipase in mammary gland and white adipose tissue paralleled the changes in 14C-lipid accumulation in these tissues. 6. It is concluded that 14C-lipid accumulation in mammary gland may not be affected by changes in plasma insulin concentration and that it is less sensitive to starvation than is lipogenesis or lactose synthesis. This has the advantage that the milk lipid content can still be maintained from hepatic very-low-density lipoprotein for a period after withdrawal of food. The major determinant of the disposal of oral 14C-triolein appears to be the total tissue activity of lipoprotein lipase. When this is high in mammary gland (fed lactating rats) or white adipose tissue (fed lactating rats with pups removed), less triacylglycerol is available for the muscle mass and consequently less is oxidized.     

Effects of mandibular gland ectomy and environmental temperature of dams on eyelid opening and body weight of pups in mice

Effects of the mandibular gland ectomy and environmental temperature to pups in Jcl: ICR mice were studied. In normal environmental animal room (A room; Tem. 23 +/- 2 degrees C, R. H. 50 +/- 10%), the mammary gland weights of lactating mothers and the body weights of pups in sialoadenectomized groups were slightly smaller than that of control groups during lactating period, whereas the eyelid opening of pups was not different between both groups and all pups exhibited complete eyelid opening on 14th day after birth. On the other hand, in cold environmental animal room (B room; Tem. 15 +/- 2 degrees C, R. H. 60 +/- 20%), the mammary gland weights of lactating mothers and the body weights of pups in sialoadenectomized groups were smaller than that of sialoadenectomized groups in A room and the eyelid opening of pups was considerably delayed when compared with that of control groups. The pups exhibited complete eyelid opening at 16th day after birth. These results were caused by mandibular gland ectomy and considered to be easily influenced by environmental conditions.     

Cross-generational effect of prenatal morphine exposure on neurobehavioral development of rat pups

Prenatal exposure to opiates can have devastating effects on the development of human fetuses and may induce long-term physical and neurobehavioral changes during postnatal maturation. The present study was aimed at identifying cross-generational effects of prenatal morphine exposure in Sprague-Dawley rats. Pregnant rats were injected subcutaneously with either saline or morphine (10 mg/kg) twice daily during gestational days 11-18. Litter size, percentage of males and females, anogenital distances (AGDs), righting reflex, and body weight were assessed in prenatally morphine-exposed pups (first generation) and their offspring (second generation). Both prenatally morphine-exposed pups and offspring of prenatally morphine-exposed dams exhibited an increased latency to right. Additionally, second generation pups were slower in righting than first generation pups. During the early postnatal period the second generation pups weighed less than the first generation regardless of drug exposure. The AGDs of second generation male pups were decreased relative to the first generation. Our data provide important novel information about the trans-generational effects of maternal opiate abuse that may be useful for understanding/evaluating the teratogenic effects of prenatal opiate exposure.     

The influence of tactile stimulation of nipples on the milk ejection reflex in the rat

Summary Changes of positive pressure exerted by pups on nipples during sucking were investigated using anesthetized, lactating dams. It was found that, every 50–60 s, individual pups performed bouts of pressure oscillations (3/s) of high amplitude which lasted about 10–12 s and coincided with periods of increased motor activity. During the intervals, when pups were quiet, series of low-amplitude oscillations (3/s) were also observed. Using a strain measuring method to record the activity of sucking pups, synchronization of activity of two or more pups was found to occur periodically every 25–30 s and, most frequently, 10–30 s before the reflex increase of milk pressure. In further experiments, artificial tactile stimulation was applied to the dam's nipples using the joint action of suction and positive pressure. Following a short-term (10–20 s) increase in frequency and amplitude of artificial nipple stimulation, 60%–80% of all reflexive peaks of milk pressure were elicited with a latency of 19 ± 5 s. This suggests that there are specific conditions under which the stimulation of nipples by pups may trigger the formation of the milk ejection reflex in the rat.Abbreviation MER milk ejection reflex