Neonatal Body Weight Research Articles

The effects of maternal murine cytomegalovirus infection on the mouse conceptus at different gestational stages.

The effects of murine cytomegalovirus (MCMV) on the prenatal development of the CD-1 mouse were investigated. Two sets of experiments were performed. In the first, mice were inoculated with different doses of MCMV on gestational day 7, and in the second, pregnant animals were inoculated with a subacute injection dose at different gestational stages. The effects of maternal infection on pregnancy in terms of maternal sickness, embryo lethality, date of parturition, litter size, postnatal death, and pups' body weight on d 1 and d 3 postpartum were investigated. High-dose MCMV infection on d 7 of pregnancy resulted in a significant increase in early embryo resorption and also in a reduction of the neonatal body weight of surviving pups. Two gestational stages were identified as being especially susceptible to MCMV infection. Most embryonic death as indicated by resorption rates was found after treatment on d 9, whereas perinatal death was most frequent when treatment was done on d 13 of gestation. Still births and neonatal death within 24 h of birth were found commonly in this latter group, which also showed the most pronounced growth retardation. The phenomenon of delay in time of parturition was noted and found to be most significant in groups of animals that were inoculated on d 3 or d 13. This investigation suggests that the effects of MCMV on the CD-1 mouse vary greatly with the age of the embryo and the course of the infection.

Influences of maternal ethanol intake on maternal and perinatal hepatic heme and drug metabolizing enzymes in rats.

The effect of ethanol on maternal and neonatal hepatic heme and drug metabolizing systems was determined. Ethanol (16%, w/v) was administered orally as drinking solution to pregnant or lactating rats at different pre- and post-natal stages. The dams and pups were sacrificed on days 7, 14 and 21 after parturition, respectively. Ethanol administration to lactating rats from just after birth caused an appreciable decrease in the maternal and neonatal body and liver weights. In addition, the activities of nicotinamide adenine dinucleotide phosphate-cytochrome c reductase, nicotinamide adenine dinucleotide-cytochrome b5 reductase and heme oxygenase were significantly enhanced in the livers of neonates whose mothers were exposed to the ethanol during only first week of lactation, but those activities were not altered in the maternal livers. However, no remarkable alterations were observed in the contents of cytochrome P-450 and b5, and the activities of aminopyrine demethylase, aniline hydroxylase and delta-aminolevulinic acid synthetase in the livers of neonates from mothers who had received ethanol during lactation period or last week of gestation, although the activities of aminopyrine demethylase and aniline hydroxylase were enhanced significantly in lactating dams by ethanol consumption for 14 d after parturition.

Poids des nouveau-nés et stratégies reproductrices des vipères européennes

The reproductive strategies of six species and two subspecies of European vipers are compared. Eighty eight clutches were examined. The reproductive effort, defined as the ratio of total litter weight over body weight of the female just after parturition, varies widely among individuals. This individual variation is in part due to the variable amount of fat accumulated by pregnant females during vitellogenesis, and therefore is associated with their nutrition during the gestation period. However, a genetic polymorphism cannot be ruled out in certain populations. The average reproductive effort of the various species studied is 0.476 ; it does not significantly differ between the species concerned. Among the taxa studied, the average female body weight, just after parturition, ranges from 12.1 to 139.0 g, whereas that of the neonates ranges from 2.74 to 7.4 g, and their number from 2.0 to 8.9 per litter. Therefore the variation in neonatal body weight is smaller than that of the number of newborn per litter. Broadly speaking, small viper species bear fewer offsprings than larger ones, but these offspring are proportionately bigger. The distribution of the reproductive effort not only varies with the body size of the individual adult female ; it also depends on the species concerned, more particularly on the feeding habits and feeding opportunities of the newborn. Those which feed on invertebrates and, to a lesser extent, on small lizards, can afford to be small and numerous. This is not the case for the species whose young feed mostly on small mammals. Within a given taxon, the size of a litter generally increases with the body weight of the mother, whereas there is no correlation between the individual body weight of the newborn and that of their mother. The mortality rate of the young vipers during their first ten months of life varies greatly within the species concerned, at least in captivity. However, within a given species, the larger the newborn, the lower the mortality rate. In conclusion, the individual body weight of the newborn, and the variability of the reproductive effort among the various species of European vipers studied, depend on a number of different factors : female body size, feeding habits of the newborn, availability of prey, and mortality rates of the young in the postnatal period. The values observed under natural conditions obviously result from a compromise between different and often conflicting selective pressures.

In utero alcohol heightens juvenile reactivity

The behavioral teratogenicity of ethanol was studied in a laboratory model of the fetal alcohol syndrome. Pregnant rats were placed in one of three groups: Ethanol (4 g ethanol/kg intubated twice daily; Purina Chow ad lib.); Sucrose (7 g sucrose/kg intubated instead of ethanol; Untreated (no intubations; Purina Chow ad lib.). Ethanol offspring did not differ from either control group in neonatal body weight or developmental measures. On Day 35, 2 female offspring per litter were tested for reactivity to acoustic startle stimuli. Activity was measured during the pre-stimulus foreperiod and during inter-stimulus intervals. Ethanol pups displayed heightened startle reactivity in the absence of hyperactivity or disrupted habituation. These data indicate that ethanol in utero produces hyperrectivity in the absence of morphological, body weight or developmental abberations.

Prenatal stress reduces maternal aggression by mice offspring

Pregnant mice were subjected to the simultaneous stress of heat, restraint and bright lights during the last trimester of gestation whereas control mothers remained unhandled in the home cage. As adults, prenatally-stressed and nonstressed mice were mated and tested for maternal aggression. Compared with nonstressed controls, prenatally-stressed females bit intruder males on significantly fewer occasions. Prenatal stress therefore reduced maternal aggression by mice offspring. Prenatal stress also significantly reduced maternal and neonatal body weight. Because the appearance of maternal aggression characteristically has been associated with the postpartum period, prenatal stress may reduce maternal aggression in mice by disrupting gonadotropin secretions (possibly prolactin) associated with the lactational phase.

Correlations between neonatal body weight and adolescent brain development in rats.

Correlations between neonatal body weight, and body weight and several brain parameters at 30 days of age were studied in normal rats. At 30 days ('adolescence') cortex has already reached its final thickness and the rat exhibits long-term memory. Brain parameters included cerebral weight, DNA, protein and cholesterol contents and densities, as well as cortical and cerebral dimensions (cerebral sections). As expected, most of these parameters in 30-day-old animals were significantly correlated with each other. Unexpectedly, neonatal body weight was also significantly correlated with cholesterol content and density at 30 days, as well as with cortical and cerebral dimensions at 30 days. Thus, statistically, neonatal body weight already predetermines the extent of neuronal (cerebral) development at adolescence (30 days). This finding also makes it possible to make at birth statistical predictions about future brain development without having to sacrifice neonatal animals.

Effects of thyroid deficiency and sympathectomy on cardiac enzymes

The effects of thyroid deficiency (Td) and of chemical sympathectomy (Sx) were studied on marker enzymes of energy metabolism in cardiac muscle of neonatal and of adult rats. Td prevented the normal development of neonatal body weight, relative heart mass, and cardiac levels of cytochrome c (-22%), citrate synthase (-27%), phosphofructokinase (-20%) and Mg2+- and Ca2+-ATPase activity of purified myofibrils (-33%, -44%). Exogenous thyroxin replacement restored those parameters studied to normal with the exception that it persistently elevated citrate synthase activity significantly above normal control levels. Responses similar to those of Td neonates occurred when adult rats were similarly treated. Sx produced no consistent effects on respiratory and glycogenolytic marker enzymes, but caused a 20% reduction in Ca2+-ATPase activity of both neonatal and adult cardiac myofibrils. These findings suggest that cardiac muscle cells require thyroxin for normal growth and enzyme development. Also, Sx may impair cardiac functional capacity by altering Ca2+ activity of actomyosin ATPase.

Chronic toxicity and reproduction studies of hexachlorobutadiene in rats.

Hexachlorobutadiene (HCBD), while not produced commercially in the United States, may be encountered as an unwanted by-product of certain processes associated with the chlorination of hydrocarbons. Studies were conducted to assess the potential long-term toxicity of HCBD. In a reproduction study conducted in rats, dose levels of 20 or 2.0 mg/kg-day of HCBD induced slight maternal toxicity (primarily of the kidney) but caused no adverse effects on reproductive parameters-percent pregnancy and neonatal survival/development. A decreased neonatal body weight was noted at the highest dose level of 20 mg/kg-day of HCBD. No toxicologic effects were observed among the adults at a dose level of 0.2 mg/kg-day or among the neonates at dose levels of 0.2 or 2.0 mg/kg-day of HCBD. In a chronic toxicity study in rats, ingestion of 20 mg/kg-day for up to 2 years caused multiple toxicologic effects, primarily of the kidney, including the development of renal tubular adenomas and adenocarcinomas. Ingestion of the intermediate dose level of 2 mg/kg-day caused lesser degrees of toxicity, but no evidence of neoplasia. Ingestion of the lowest dose level of 0.2 mg/kg-day of HCBD caused no effects that could be attributed to treatment. These data indicate a dose-response relationship for HCBD-induced toxicity affecting primarily the kidney. HCBD-induced neoplasms occurred only at a dose level higher than that causing discernible renal injury.

Chronic Toxicity and Reproduction Studies of Hexachlorobutadiene in Rats

Hexachlorobutadiene (HCBD), while not produced commercially in the United States, may be encountered as an unwanted by-product of certain processes associated with the chlorination of hydrocarbons. Studies were conducted to assess the potential long-term toxicity of HCBD. In a reproduction study conducted in rats, dose levels of 20 or 2.0 mg/kg-day of HCBD induced slight maternal toxicity (primarily of the kidney) but caused no adverse effects on reproductive parameters—percent pregnancy and neonatal survival/development. A decreased neonatal body weight was noted at the highest dose level of 20 mg/kg-day of HCBD. No toxicologic effects were observed among the adults at a dose level of 0.2 mg/kg-day or among the neonates at dose levels of 0.2 or 2.0 mg/kg-day of HCBD. In a chronic toxicity study in rats, ingestion of 20 mg/kg-day for up to 2 years caused multiple toxicologic effects, primarily of the kidney, including the development of renal tubular adenomas and adenocarcinomas. Ingestion of the intermediate dose level of 2 mg/kg-day caused lesser degrees of toxicity, but no evidence of neoplasia. Ingestion of the lowest dose level of 0.2 mg/kg-day of HCBD caused no effects that could be attributed to treatment. These data indicate a dose-response relationship for HCBD-induced toxicity affecting primarily the kidney. HCBD-induced neoplasms occurred only at a dose level higher than that causing discernible renal injury.

Results of a reproduction study in rats fed diets containing hexachlorobutadiene

Hexachlorobutadiene (HCBD) is a by-product of certain processes associated with the chlorination of hydrocarbons. Very small amounts of HCBD may also be produced in chlorine cells. This study evaluated the effects of HCBD on reproduction in rats. Groups of male and female adult rats were fed diets containing HCBD at dose levels of 0, 0.2, 2.0, or 20 mg/kg/day for 90 days prior to mating, 15 days during mating, and subsequently throughout gestation and lactation. Signs of toxicity among the adult rats were observed at the two higher dose levels and included decreased weight gain and food consumption as well as alterations in kidney structure. There was no effect on pregnancy or neonatal survival and development. The body weight of neonates at the time of weaning, 21 days of age, was slightly but significantly less than that of control litters. This effect was found only at the high dose level. No toxic effects were observed among the adults at a dose level of 0.2 mg/kg/day or among the neonates at dose levels of 0.2 or 2.0 mg/kg/day.

Relation of Gestation Time to Brain Weight for Placental Mammals: Implications for the Theory of Vertebrate Growth

Duration of gestation in homothermic placental mammals has a much more precise alaxensis relation to neonatal brain size than to neonatal body size or any of three other neonatal or maternal dimensions. This was shown by a multivariate analysis of data on gestation time, neonatal and adult brain and body weight, and litter size for 91 species. These results can be explained by a theory of kinetics of fetal growth based on three hypotheses: (1) the brain is the slowest-growing organ in the fetal mammal; (2) it is also the pacemaker for growth of other tissues, which are held to its rate of growth; and (3) brain growth proceeds at the maximum rate allowed by its intrinsic growth law, so that the growth of all mammalian brains is governed in great degree by a single functional relation of attained size and time. The invariant rate constant for mammalian brain growth could be due to nutritional limitations or to the existence of an upper limit on rate of information flow during development.

Study of possible correlations between body weights and brain parameters in neonatal and mature rats.

Correlations between body weight, cerebral weight, cerebral DNA (cell number) and cerebral protein have been studied in a population of 249 neonatal (29 litters) and 107 adult normal rats. It was found that, on a statistical basis, an individual with a heavier neonatal body weight is also likely to have a higher cerebral weight, neonatal cerebral DNA (cell number) and neonatal cerebral protein. For a sample of this size, each pair of these parameters was significantly correlated. In adult animals the significance of correlations with body weights disappears, but the correlations between each pair of cerebral parameters remain significant.