Effect of weaning on the activities of glycogen synthase and phosphorylase in rat liver

The effects of weaning on the level of glycogen and the activities of glycogen synthase and phosphorylase were determined in rat liver. Glycogen levels in rat liver increased at the start of the weaning period and reached a plateau on postnatal day 20. The active form of glycogen synthase increased until postnatal day 19 and then declined. Total glycogen synthase (active + inactive) remained high during the suckling period and declined to a new low level during the weaning period. The activity ratio (active/total) increased from day 16 to days 18-22 and then decreased to the same level as found during the suckling period. At the onset of weaning the active form of phosphorylase decreased, whereas total phosphorylase initially increased and then decreased after postnatal day 20. Both forms of phosphorylase increased again at the end of the weaning period. The activity ratio decreased at the start of weaning and remained low throughout the rest of the weaning period. The effects of premature weaning were similar to those observed in normally weaned animals, but the changes occurred sooner and were more pronounced.     

Candidate chemosensory cells in the stomach mucosa of young postnatal mice during the phases of dietary changes

The complex physiology of the gastrointestinal (GI) tract must permanently be adjusted according to the composition of ingested food, which requires continuous monitoring by appropriate sensory systems. Sensing the dietary constituents is thought to be mediated by chemosensory cells residing in the mucosa of the GI tract. We have examined the appearance and differentiation of candidate chemosensory cells at distinct postnatal stages and visualized cells that express gustducin or TRPM5. Two critical stages have been considered: the suckling period when the neonates are nourished exclusively on milk and the weaning period when the diet gradually changes to solid food. At early postnatal stages, only a few gustducin- or TRPM5-expressing cells have been found; they display an immature morphology. At the time of weaning, numerous gustducin- or TRPM5-positive cells are present in the gastric mucosa and are isomorphic to adult candidate chemosensory cells. The typical accumulation of gustducin and TRPM5 cells at the border between the forestomach and corpus region and the characteristic tissue fold or “limiting ridge” have not been observed at early postnatal stages but are complete at the time of weaning. The appearance of candidate chemosensory cells at the strategic position occurs within the last few days before weaning but after the formation of the limiting ridge. Thus, both the topographic arrangement of the cells and the limiting ridge seem to be important features for the processing of solid food in the mouse stomach.     

Effect of milk deprivation during the lactation period on performance and digestive enzyme activities of the piglets following weaning

Post-weaning performance of piglets from systems where lactation is disrupted (e.g. from multisuckling systems) is superior to conventionally reared piglets. The objective of this study was to establish whether restricted growth prior to weaning caused by disruption of suckling was an important factor in post-weaning performance and also whether there were related changes in gastro-intestinal development. Ten litters of eight piglets were used in a split-plot design. Half of each litter (limited suckling, LS) had suckling disrupted by separation from their dam for 7 h/day from day 14 to 28 after farrowing. The remainder of each litter was allowed to suck normally (normal suckling, NS). The same amount of creep feed was offered to LS piglets as consumed by NS littermates on the previous day. There were no differences in weight between LS and NS piglets at 14 days of age, but restricting access to the sow reduced weaning weight at 28 days of age (7.96 v. 9.00 kg; LS v. NS; P < 0.01; s.e.d. 0.23). Feed intakes were greater for LS than NS piglets over the first 28 days post weaning, particularly in the 1st week after weaning when feed efficiency was also improved (0.91 v. 0.62 kg gain per kg feed; P < 0.01; s.e.d. 0.08). As a result, LS piglets grew more rapidly in the first 28 days post weaning, particularly in the first 7 days after weaning. Subsequent performance to 8 weeks was similar for both groups. Digestive organ weights were not different at 2 and 9 days after weaning; nor were small intestine specific enzyme activities significantly different ( P>0.05). Pancreatic trypsin activity was, however, greater ( P < 0.01) for LS pigs on both days 2 and 9 post weaning. In conclusion the restriction of growth as a result of limited suckling itself is an important factor in determining post-weaning performance and may be related to development of pancreatic trypsin activity.     

Regulation of succinyl-CoA:3-oxoacid CoA-transferase in developing rat brain: responsiveness associated with prenatal but not postnatal hyperketonemia

Activities of ketone body-metabolizing enzymes in rat brain rise 3- to 5-fold during the suckling period, then fall more than 50% after weaning. Our purpose was to determine the mechanism of the developmental changes in activity of 3-oxoacid CoA-transferase in rat brain and to study its regulation by dietary modification. Purified rat brain 3-oxoacid CoA-transferase was used to generate specific antibody. Immunotitrations of the enzyme from brains of 4-, 24-, and 90-day-old rats indicated that changes in 3-oxoacid CoA-transferase activity during development are due to changes in content of the enzyme protein. Pulse-labeling studies showed that changes in enzyme specific activity reflected changes in its relative rate of synthesis, which increased 2.5-fold between the nineteenth day of gestation and the third postnatal day, remained at this high level until the twelfth postnatal day, and declined thereafter, returning by Day 38 to the level observed in utero. The enzyme is apparently degraded very slowly during early postnatal life. Fetal hyperketonemia induced by feeding pregnant rats a high-fat diet was associated with an increase in the relative rate of synthesis of 3-oxoacid CoA-transferase in brains of 19-day-old fetuses and newborn rats and with an increase in the specific activity of the enzyme at birth. To examine the role of postnatal hyperketonemia in the development of the enzyme in brains of suckling rats, neonates received intragastric cannulas and were fed, for up to 13 days, a modified milk formula low in fat. Postnatal hyperketonemia was abolished but cerebral 3-oxoacid CoA-transferase specific activity on Days 10 and 17 was not significantly affected. Thus, the physiological hyperketonemia caused by the high fat content of rat milk is not required for the normal development of 3-oxoacid CoA-transferase in rat brain.     

Postnatal Methylmercury Exposure Induces Hyperlocomotor Activity and Cerebellar Oxidative Stress in Mice: Dependence on the Neurodevelopmental Period

During the early postnatal period the central nervous system (CNS) is extremely sensitive to external agents. The present study aims at the investigation of critical phases where methylmercury (MeHg) induces cerebellar toxicity during the suckling period in mice. Animals were treated with daily subcutaneous injections of MeHg (7 mg/kg of body weight) during four different periods (5 days each) at the early postnatal period: postnatal day (PND) 1–5, PND 6–10, PND 11–15, or PND 16–20. A control group was treated with daily subcutaneous injections of a 150 mM NaCl solution (10 ml/kg of body weight). Subjects exposed to MeHg at different postnatal periods were littermate. At PND 35, behavioral tests were performed to evaluate spontaneous locomotor activity in the open field and motor performance in the rotarod task. Biochemical parameters related to oxidative stress (levels of glutathione and thiobarbituric acid reactive substances, as well as glutathione peroxidase and glutathione reductase activity) were evaluated in cerebellum. Hyperlocomotor activity and high levels of cerebellar thiobarbituric acid reactive substances were observed in animals exposed to MeHg during the PND 11–15 or PND 16–20 periods. Cerebellar glutathione reductase activity decreased in MeHg-exposed animals. Cerebellar glutathione peroxidase activity was also decreased after MeHg exposure and the lowest enzymatic activity was found in animals exposed to MeHg during the later days of the suckling period. In addition, low levels of cerebellar glutathione were found in animals exposed to MeHg during the PND 16–20 period. The present results show that the postnatal exposure to MeHg during the second half of the suckling period causes hyperlocomotor activity in mice and point to this phase as a critical developmental stage where mouse cerebellum is a vulnerable target for the neurotoxic and pro-oxidative effects of MeHg.     

The fatty liver dystrophy (fld) mutation. A new mutant mouse with a developmental abnormality in triglyceride metabolism and associated tissue-specific defects in lipoprotein lipase and hepatic lipase activities

An autosomal recessive mutation, termed fatty liver dystrophy (fld), can be identified in neonatal mice by their enlarged and fatty liver (Sweet, H. O., Birkenmeier, E. H., and Davisson, M. T. (1988) Mouse News Letter 81, 69). We have examined the underlying metabolic abnormalities in fld/fld mice from postnatal days 3-40. Serum and hepatic triglyceride levels were elevated 5-fold in suckling fld/fld mice compared to their +/? littermates but abruptly resolved at the suckling/weaning transition. Blot hybridization analysis of liver and intestinal RNAs revealed a liver-specific increase in apolipoprotein (apo) A-IV and C-II mRNA concentrations (100- and 6-fold, respectively) that was limited to the suckling and early weaning stages in fld/fld mice. Resolution of these differences during the weaning period could not be delayed by prolonging suckling to the 20th postnatal day nor could the mutant phenotype be elicited in young adult animals with a high fat diet. Lipoprotein lipase (LPL) activity was reduced 16-fold in the white adipose tissue of fld/fld mice until the onset of weaning. Heart activity was decreased less than 2-fold, but there were no deficits in brown adipose tissue or liver. Hepatic lipase (HL) mRNA levels and activity were significantly reduced in fld/fld livers and sera, respectively, during the suckling period. Mapping studies show the fld locus to be distinct from loci encoding LPL, HL, and apoA-IV, and those responsible for the combined lipase deficiencies in cld/cld and W/Wv mice. These data suggest that the fld mutation is associated with developmentally programmed tissue-specific defects in the neonatal expression of LPL and HL activities and provide evidence for a new regulatory locus which affects these lipase activities. This mutation could serve as a useful model for (i) analyzing the homeostatic mechanisms controlling lipid metabolism in newborn mice and (ii) understanding and treating certain inborn errors in human triglyceride metabolism.     

Colonization of segmented filamentous bacteria and its interaction with the luminal IgA level in conventional mice

Segmented filamentous bacteria (SFB) colonize in the ileum. They promote the development of intraepithelial lymphocytes and immunoglobulin A (IgA)-producing cells in the small intestine. In SFB-monoassociated mice, changes in SFB colonization of the small intestine were related to the level of IgA derived from maternal milk during the suckling period and self-produced in the small intestine after weaning. In this study, we investigated whether or not maternal and neonatal IgA influence the colonization of SFB in conventional mice from 18 to 105 days old. The pups were forcedly weaned at 20 days old. SFB could be detected in the distal small intestine after day 22, and their number rapidly reached a maximum on day 28. Thereafter, they gradually declined to one-fourth of the maximum level. The lowest concentrations of IgA in the small intestinal and cecal contents were detected on day 22. Thereafter, they increased as the age of the mice increased. The expression of the polymeric immunoglobulin receptor gene in the distal small intestine increased after weaning. These results suggested that the colonization of SFB in the pre-weaning and post-weaning periods might be prevented with IgA derived from maternal milk and self-produced IgA, respectively.     

Suckling effects in sows: importance for mammary development and productivity

An understanding of the mechanisms regulating milk yield in sows is crucial for producers to make the best management decisions during lactation. Suckling of mammary glands by piglets is one factor that is essential for development of these glands during lactation and for the maintenance of lactation in sows. The process of mammary development is not static as the majority of it takes place in the last third of gestation, continues during lactation, is followed by involution at weaning and starts over again in the next gestation. During involution, the mammary glands undergo a rapid and drastic regression in parenchymal tissue, and this can also occur during lactation if a gland is not suckled regularly. Indeed, the pattern of regression is similar for glands that involute at weaning or during lactation. Suckling during 12 to 14 h postpartum is insufficient to maintain lactation and the process of involution that occurs in early lactation is reversible within 1 day of farrowing but is irreversible if a gland is not used for 3 days. However, milk yield from a gland which is ‘rescued’ within the first 24 h remains lower throughout lactation. Suckling does not only affect milk yield in the ongoing lactation, but it also seems to affect that of the next lactation. Indeed, non-suckling of a mammary gland in first-parity sows decreased development and milk yield of that gland in second parity. Nursing behaviour of piglets in early lactation was also affected, where changes were indicative of piglets in second parity being hungrier when suckling glands that were not previously used. It is not known, however, if the same effects would be seen between the second and third lactation. Furthermore, the minimum suckling period required to ensure maximal milk yield from a gland in the next lactation is not known. This review provides an update on our current knowledge of the importance of suckling for mammary development and milk yield in swine.     

Blood dopamine beta-hydroxylase activity and noradrenaline levels in the developing white rat.

Dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating) (EC 1.14.17.1) activity in serum of blood obtained by decapitation of white rats at 19, 20, and 21 days in utero, immediately after birth, and postnatally to 70 days, was measured. Noradrenaline (NA) and DBH in plasma from undisturbed, cannulated, postweaning rats were also assayed. During the last few days in utero and the first 2 postnatal days serum DBH activity tripled and then remained elevated during the suckling period. Upon weaning, serum DBH activity declined at first precipitously and then more slowly, until the adult level was reached around 70 days of age. This postweaning decrease in DBH activity was also observed with the cannulated animals. In contrast, plasma NA levels remained low and constant throughout the postweaning period. In suckling rats treated with 6-hydroxydopamine from 2 to 12 days of age, serum DBH activity decreased to less than half its initial value by day 8. It is suggested that the observed changes in serum DBH activity in fetal and postnatal rats reflect ontogenetic changes in sympathetic nerve terminals and that they are probably not correlated with release of NA.     

Spontaneous milk ejection during lactation and its possible relevance to success of breast-feeding.

In a woman suckling twins it became apparent that both suckling-induced and precisely timed, spontaneous bursts of milk ejection were occurring. Observations on days 14, 28, 56, and 112 of lactation disclosed highly significnat increases in intervals between episodes of spontaneous milk ejection. Furthermore, at all stages of lactation the interval between a feed and the next episode of spontaneous ejection was significantly longer than the interval between spontaneous ejections. The decrease in frequency of episodes of spontaneous milk ejection during lactation may be related to the decreasing release of prolactin in response to suckling. Spontaneous milk-ejection episodes are felt only when the breast is full and may signal its readiness for a further suckling episode. Such bursts of milk ejection may stimulate the suckling response in babies, suggesting that rigid three- or four-hour feeding regimens may be unphysiological and pose a threat to the success of breast-feeding in the early postnatal period.     

Characterization of serum apolipoprotein patterns in rats during suckling and post-weaning periods

Changes of serum apolipoprotein patterns during the suckling and post-weaning periods were studied in rats. Concentrations of apolipoprotein A-IV and the high-molecular-weight form of apolipoprotein B were markedly high during the early suckling periods and decreased at weaning. Secretion of apolipoprotein A-IV into the mesenteric lymph in 2-week-old rats was as high as that in adult rats into which the high-fat diet was infused constantly. Apolipoprotein A-IV was found both in high-density lipoprotein and lipoprotein-free fractions, and the relative distribution in the latter decreased developmentally. The concentration of apolipoprotein A-I was low for 1 week after birth, after which it increased to the adult level. The apolipoprotein E level during the suckling and post-weaning periods was similar to or above that of adult rats. The newly formed apolipoprotein B in very-low-density lipoproteins secreted by the isolated liver and by the primary culture hepatocytes of suckling rats was predominantly a high-molecular-weight form. Overnight fasting and early weaning caused a remarkable alteration of the serum apolipoprotein profile. It therefore appears that frequent ingestion of dam's milk as well as ontogenic development are relevant to the serum apolipoprotein patterns characteristic for suckling rats.     

Postnatal development of galanin-like peptide mRNA expression in rat hypothalamus

We examined the developmental change of GALP mRNA in male and female rat hypothalamus during postnatal day 1 to 60, using in situ hybridization histochemistry. Neuropeptide Y (NPY) and proopiomelanocortin (POMC) mRNA in the hypothalamus were also examined because they are important in the regulation of food intake. GALP mRNA was first detected in the arcuate nucleus (ARC) on day 8. GALP mRNA was gradually increased between day 8 and 14 and markedly increased between day 14 and 40, which is the weaning and pubertal period in rats. After day 40, there were no significant differences in GALP mRNA. In contrast to GALP, NPY and POMC mRNAs were detected in the ARC from day 1 and lasted to day 60. There was no sexual dimorphism in GALP, NPY and POMC mRNAs during postnatal development. Next, we examined the effect of the milk deprivation for 24 h on GALP, NPY and POMC mRNA in pups. GALP mRNA did not change by milk deprivation on day 9 and 15, while milk deprivation had a significant effect on NPY and POMC mRNA on day 15. These results suggest that the development of GALP may be associated with developmental changes such as weaning, feeding and maturation of reproductive functions. The regulatory mechanism of GALP mRNA is different from that of the NPY and POMC genes during postnatal development.     

Expression of thrombospondin-1 and CD36 and CD47 receptors in the rat brain after exposure to damaging factors in the early postnatal period

The expression of thrombospondin-1 (TS-1) and its receptors CD47 and CD36 in the cerebral cortex and hippocampus of rats under damaging factors in the early postnatal period was studied. After hypoxia on the 7th day of postnatal development, an increase in the number of CD47-expressing cerebral endothelial cells (days of postnatal development: P28–P70) and reduction in the number of TS-1-expressing astrocytes in the cortex at P28 were observed. In animals subjected to early postnatal stress at the age of P2–P15, a decrease in TS-1-expressing astrocytes in the cortex and hippocampus was registered (predominantly at the age of P28). It was noted that these changes characterize the period of long-term effects (P28–P70) of early stress that is relevant to the processes of reparative angiogenesis and arresting of neurological deficits.     

Diurnal rhythms of hepatic carbohydrate metabolism during development of the rat

The ;8+16' feeding schedule (8h feeding and 16h without food in each 24h cycle) was applied to nursing mother rats to study enzyme development in neonatal rats in the absence of solid food. A ;16+8' suckling schedule (16h with the mother and 8h while the mother is fed in a separate cage) was used to show that the increases in pyruvate kinase, glucokinase and aldolase B activities that occur in the late suckling period of liver development do not require the intake of solid food at this time. Their activities may, however, be modulated by the composition of the diet at the time of weaning. Adaptation to the composition of the diet can occur within one feeding period, and to the periodicity of food provision in one or two feeding periods. In the early neonatal period, diurnal rhythms of tyrosine aminotransferase, liver glycogen and glucokinase are either greatly suppressed or absent, but develop rapidly after weaning. Food-dependent rhythms of glycogen and tyrosine aminotransferase were included in the late suckling period (day 14).     

26Al incorporation into the brain of suckling rats through maternal milk

Aluminium inhibits prenatal and postnatal brain development. However, aluminium incorporation into the brain of sucklings through maternal milk has not yet been well clarified because aluminium lacks a suitable isotope for radioactive tracer experiments. Using 26Al (26AlCl(3)) as a tracer, we measured 26Al incorporation into the brain of suckling rats by accelerator mass spectrometry. Lactating rats were subcutaneously injected with 26AlCl(3) from day 1 to day 20 postpartum. Suckling rats were weaned from day 21 postpartum. From day 5 to day 20 postpartum, the amounts of 26Al measured in the cerebrum, cerebellum, spinal cord, liver, and kidneys of suckling rats increased significantly. After weaning, the amounts of 26Al in the liver and kidneys decreased remarkably. Alternatively, in the cerebrum, cerebellum, and spinal cord, as much as 12 to 20% of the 26Al amounts present on day 20 postpartum remained in the tissues on day 730 postpartum. As the life span of rats is about 2 years, we conclude that considerable amounts of the 26Al taken up into the brain of suckling rats through maternal milk remained in their brain throughout their lifetime.     

Changes of colon epithelium proliferation due to individual aging with cyclin proliferating cell nuclear antigen (PCNA/cyclin) immunostaining compared to [3H]-thymidine radioautography

We report a change in the proliferative activity of mouse colonic epithelium due to development and aging. In order to measure the proliferative activity, colonic epithelium was immunostained for cyclin proliferating cell nuclear antigen (PCNA/cyclin), which appears from the Gl to the S phase of the cell cycle, and compared with labeling obtained by [³H]-thymidine radioautography. Litter mice of six age groups from the fetal period (embryonic day 19), newborn period (postnatal day 1), suckling period (postnatal day 5), weaning period (postnatal dy 21), adult period (2 month old) to the senescent period (11 month old) were examined by immunohistochemistry. The descending colons were fixed in methacarn (method-Carnoy) and embedded in paraffin. Sections were stained for PCNA/cyclin activity using 19A2 monoclonal antibody and the avidin-biotin peroxidase complex (ABC) technique. For radioautography, litter mice of nine age groups using in vivo intraperitoneal administration of [³H]-thymidine. The labeling indices of colonic epithelial cells in the proliferative zone were then analyzed and compared between the two investigative methods. Our results show that the prliferative activity of mice colon was high in the fetal and newborn periods and almost constant from the suckling period to senescence, as demonstrated by both PCNA/cyclin immunohistochemistry and [³H]-thymidine radioautography. The labeling index seen by PCNA/cyclin immunohistochemistry was, however, higher than that seen by [³H]-thymidine radioautography.     

Mucosal IgA increase in rats by continuous CLA feeding during suckling and early infancy

The aim of this work was to establish the effect of the cis9,trans11 conjugated linoleic acid (CLA) isomer on mucosal immunity during early life in rats, a period when mucosal immunoglobulin production is poorly developed, as is also the case in humans. CLA supplementation was performed during three life periods: gestation, suckling, and early infancy. The immune status of supplemented animals was evaluated at two time points: at the end of the suckling period (21-day-old rats) and 1 week after weaning (28-day-old rats). Secretory IgA was quantified in intestinal washes from 28-day-old rats by ELISA technique. IgA, TGFbeta, and PPARgamma mRNA expression was measured in small intestine and colon by real time PCR, using Taqman specific probes and primers. IgA mucosal production was enhanced in animals supplemented with CLA during suckling and early infancy: in 28-day-old rats, IgA mRNA expression was increased in small intestine and colon by approximately 6- and 4-fold, respectively, and intestinal IgA protein by approximately 2-fold. TGFbeta gene expression was independent of age and type of tissue considered, and was not modified by dietary CLA. Gene expression of PPARgamma, a possible mediator of CLA's effects was also upregulated in animals receiving CLA during early life. In conclusion, dietary supplementation with CLA during suckling and extended to early infancy enhances development of the intestinal immune response in rats.