Preweaning Stage Research Articles

Neonatal Systemic Glucocorticoids Alter the Body Weight Gain Pattern during the Pre-Weaning Stages of Development

Neonatal Systemic Glucocorticoids Alter the Body Weight Gain Pattern during the Pre-Weaning Stages of Development

Ontogeny of cocaine hyperactivity and conditioned place preference in mice.

Conditioned place preference (CPP) procedures using jointly visual and tactile cues (white compartment with a wide-mesh metal floor versus black compartment with a narrow-mesh floor) were employed to assess the ontogenetic pattern of cocaine reinforcing properties in outbred CD1 mice. A classical 11-day-long schedule, in which the drug experience occurred in the initially less-preferred compartment ("biased" procedure, Spyraki 1988), served to study cocaine (0, 1, 5, or 25 mg/kg IP repeated four times at 48 h intervals) during the early postweaning stage (21-32 days). The result was a fully-fledged CPP at all cocaine doses. A subsequent experiment used a shortened (4-day) "unbiased" CPP schedule (animals assigned at random to drug experience in one or the other compartment); this enabled an assessment of the ontogenetic pattern of the drug action (single treatment, same dose range) in pups of both sexes at three different developmental ages (14-17, 21-24, or 28-31 days). At the 25 mg/kg dose, CPP developed in animals of all ages, while the 5 mg/kg dose was effective only in 21-24 day pups and the 1 mg/kg dose was ineffective. No significant sex differences were found, but the use of the unbiased procedure enabled a demonstration of an interaction between treatment, age, and type of CS. At the preweaning stage, CPP was due mainly to an increased preference for the black/narrow-mesh compartment, while at the early postweaning stage it consisted mainly of an increased preference for the white/wide-mesh compartment; at the late postweaning stage the cue and the treatment factor did not interact.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of docking and shearing on growth and carcass traits of fat-tailed Ossimi sheep

SummaryThirty Ossimi lambs were used in an experiment to compare those whose tail was docked shortly after birth with controls. After weaning at 4 months of age the groups were further subdivided and two of the four groups closely shorn according to a 2 × 2 factorial design.Male lambs at 20 kg were subjected to intensive finishing until the age of 50 weeks and nine were then slaughtered to determine carcass characteristics.There was a trend for increased live-weight gain in the docked lambs in the preweaning stage (up to 16 weeks).This trend was also present, although not statistically significant, in the final phase of intensive feeding from 20 kg weight to 50 weeks. Shearing significantly improved daily gain in this final period (P < 0·05). These increases in gain were also apparently associated with improvements in efficiency, as judged on a group basis.Docking and shearing also tended to cause increases in body measurements: height, chest girth and abdomen girth in the case of docking (P < 0·05) and chest girth, chest depth and abdomen girth in the case of shearing (P < 0–05).Carcass characteristics, measured on a relatively small sample, indicated several effects of docking and shearing on carcass traits although most of these were consistent with the expected differences stemming from the higher carcass weights acheived at 50 weeks of age by docked and sheared lambs.

Effects of neonatal methylmercury exposure on adrenergic receptor binding sites in peripheral tissues of the developing rat

Neonatal exposure to methylmercury produces changes in patterns of tissue growth and function, in part, due to alterations in adrenergic neuronal input. To explore the mechanisms by which these changes come about, newborn rats were exposed to methylmercury (1 or 2.5 mg/kg per day) throughout the preweaning stage and the ontogeny of adrenergic receptor binding sites evaluated in liver, kidney, heart and lung, using [ 3H]prazosin ( α 1-receptors), [ 3H]rauwolscine ( α 2-receptors) and [ 125I]pindolol (β-receptors). In the kidney, methylmercury caused decreases in β- and α 1-receptor binding and increases in α 2-binding; previous work has shown that β-receptor-mediated responses are generally enhanced in methylmercury-exposed pups, and the down-regulation of β-receptor binding thus probably represents a compensatory action secondary to alterations in post-receptor coupling mechanisms. The effects of methylmercury on hepatic adrenergic receptors were different from those seen in the kidney, with substantial elevations in β- and α 1-receptor binding apparent in the preweaning stage; this agrees also with the differences in effects of the mercurial on trophic reactivity and growth in the 2 tissues. Despite the fact that methylmercury causes activation of neonatal cardiac sympathetic nerves, β-receptor binding sites in the heart were unaffected by methylmercury exposure; the failure to down-regulate cardiac postsynaptic receptors in the face of increased nerve activity again represents an anomaly of synaptic regulatory function. These results indicate that methylmercury alters adrenergic responsiveness, in part, through actions on the development of receptor binding sites, and further, that the organ-specificity and receptor subtype-selectivity are consistent with subsequent effects of the organomercurial on adrenergic participationin target organ growth; however, changes in receptor binding alone do not account for all of the effects of methylmercury on synaptic activity or trophic responses.

Effects of lactation on circulating plasma metabolites in 'cafeteria-fed' rats.

1. The effects of 'cafeteria feeding' on primiparous Wistar rats during lactation have been studied by measuring circulating levels of glucose, amino acids, lactate, urea and ammonia as well as glycogen levels in liver and muscle. 2. No significant changes in glucose levels were observed despite alterations in blood glucose compartmentation. 3. Compared with controls, the dams given the cafeteria diet had higher liver glycogen stores which were more easily mobilized at the peak of lactation. 4. Rats given the cafeteria diet showed a lower amino acid utilization than controls and adequately maintained circulating levels, as determined by the lower circulating levels of ammonia and urea. 5. No significant differences in body-weight were observed in the period studied despite increasing dam weight after weaning in the cafeteria-fed group. 6. The size of pups of cafeteria-fed dams was greater than that of controls, and the differences were marked after weaning, when the metabolic machinery of the cafeteria pup maintained high protein accretion and body build-up using fat as the main energy substrate characteristic of the preweaning stage. The controls, however, changed to greater utilization of amino acids as an energy substrate and adapted to high-protein (low-biological-quality) diets with a significantly different pattern of circulating nitrogen distribution.

Relationships between growth parameters and scrotal circumference in young beef bulls

Scrotal circumferences of 119 young bulls of four distinct breeding groups were measured at the end of a feedlot performance test and at the beginning of the breeding season when the bulls were approximately 14 months old, to study the relationships of weight and growth parameters with testes size. Scrotal circumference was positively correlated with body weight at the end of feedlot test in the four breeding groups. The association between scrotal circumference and body weight was much stronger in the breeding group which had been selected for low yeariing weight than in the other three breeding groups which had been selected for high growth rate. The relationships between scrotal circumference and preweaning and postweaning gain differed among the four breeding groups. Preweaning gain was the most important factor in the association between body weight and scrotal circumference among the three beef breeding groups. The results indicated that the preweaning stage was a critical period for testicular development and that the probability of finding beef bulls with smaller than average testes among the bulls selected for weaning weight would be relatively small. Scrotal circumference was reduced (2.5–11%) from the end of feedlot test until the beginning of the breeding season.

Organ specificity of neonatal methyl mercury hydroxide poisoning in the rat: Effects on ornithine decarboxylase activity in developing tissues

To determine the organ specificity of neonatal methyl mercury hydroxide (CH 3HgOH) exposure on biochemical development of its potential target tissues, effects on rat brain, liver, heart and kidney were compared utilizing the ontogenetic pattern of ornithine decarboxylase (ODC) activity, an early index of perturbation of cellular maturation. CH 3HgOH was given daily beginning at birth for up to 21 days, using three dose levels (1, 2.5 or 5 mg/kg s.c.). In the brain, CH 3HgOH treatment resulted in an initial reduction in ODC followed by a subsequent elevation of activity, a maturational pattern known to be associated with delayed cellular development. In contrast to the effects of CH 3HgOH on brain, the pattern obtained in the liver, an initial elevation followed by a subsequent decline, is usually associated with compression of the time course of cellular development. In the heart and kidney, CH 3HgOH produced sustained elevations of ODC representing prolongation of the developmental period of rapid tissue growth and development; these patterns were associated with tissue hypertrophy which was sustained through the preweaning stage for both tissues and well into the postweaning period for the kidney. The results obtained with ODC clearly demonstrate that neonatal CH 3HgOH poisoning causes organ-specific biochemical lesions which can play a role in subsequent effects on overall tissue development.

The effect of protein malnutrition on the copulatory behavior of the male rat

The copulatory behavior of male Sprague-Dawley rats reared under four dietary conditions was measured in three experiments at ages ranging from 95 to 325 days. Rats malnourished in preweaning stages of development were born to dams fed an 8% casein diet from 5 weeks before mating until weaning. Well-nourished rats were born to dams maintained on a 25% casein diet. At weaning half of the offspring in each group were switched to the other diet. In all three experiments rats subjected to the protein restriction in both pre- and postweaning periods, or in one period or the other only, were more effective copulators than well-nourished rats. The major differences between the protein-deprived and well-nourished rats were related to a diminished ability to intromit in the high-protein animals. Protein or protein—calorie malnutrition may enhance copulatory behavior in the male rat by retarding or prolonging several aspects of development, including body growth and changes in sex hormones.

The development, inhibition and disinhibition of pup-cannibalism in the Mongolian gerbil

The responses of juvenile and adult gerbils towards newborn test pups were investigated. Young animals of both sexes are less likely to attack the test pup than are older animals. Mature females are more likely to attempt to cannibalize pups than are mature males. Attempted cannibalism by adult males is inhibited when their mate becomes pregnant. If the pregnant female is removed from the cage for one to three days, however, attempted cannibalism is disinhibited. On the other hand, males which have reared a previous litter will not harm test pups when the female is removed. Experience of a pregnant female and of young pups during the pre-weaning stage does not influence the incidence of attempted cannibalism in adulthood. These data suggest that gerbils take full advantage of changing social conditions.

Chronic ingestion of cadmium and/or tritium in rats: I. Accumulation and distribution of cadmium in two generations

Sprague-Dawley rats continuously ingested low levels of Cd (0.1–5.1 ppm) from conception of the F 1 through delivery of the F 2 generation. Analyses of tissues at various ages during treatment showed that (1) blood is a poor indicator of chronic exposure history; (2) the placenta was an efficient barrier to Cd transfer to the fetus, permitting detectable levels of Cd in neonatal organs only at the highest exposure level; (3) milk does not appear to be an important source of neonatal exposure; (4) the postnatal accumulation rate of the metal appeared highest during preweaning stages; and (5) during prolonged ingestion, Cd levels in liver and kidney were roughly proportional to exposure while little accumulation was noted in brain and testes.

Epithelial cell migration in the intestine of the young mouse

Autoradiographs were made of sections of the duodenal region of the intestine from 3 stages of preweaning mice, sacrificed at intervals after injection of thymidine- 3H. The results clearly show that significant cell migration does occur in the intestinal epithelium of the duodenum at stages when dramatic cytodifferentiative changes are taking place in this tissue. The rate of epithelial cell migration (in terms of distance, in μ-traveled in 48 hours) is, in all of the 3 preweaning stages examined, lower than in the adult duodenum. Although the villi elongate, reaching a length equivalent to that of adult villi by 20–24 days after birth. the rate of epithelial cell migration does not increase during the preweaning period. As the villi lengthen, the time required for a cell to migrate from the intestinal crypt to the villus tip becomes increasingly greater. The observations in this study tend to support the idea that the process of villus elongation prior to weaning is regulated in the mouse duodenum by variation of the rate of cell extrusion from the villus tip.