The effect of low-level prenatal X-irradiation on postnatal development in the Wistar rat

The objective of this investigation was to determine the effect of low-dose prenatal X-irradiation on postnatal growth and neurobehavioral development, and whether alterations would manifest at dosages lower than those which produce anatomic malformations from exposure at the most sensitive period of organogenesis. Ninety-eight Wistar strain rats were exposed to 0.1, 0.2, or 0.4 Gy X-radiation of were sham irradiated on the 9th or 17th day of gestation. A conventional teratologic evaluation was completed on half of the animals (572 fetuses). The age of appearance of four physiologic markers and of acquisition of six reflexes was observed in 372 offspring. Exposure during early organogenesis at these levels had no effect on any of these parameters. Prenatal exposure to X-radiation on the 17th day of gestation at dosage levels greater than 0.1 Gy resulted in alterations in the appearance of three postnatal neurophysiologic parameters. Growth retardation throughout the postpartum period also was observed in the offspring. The induction of developmental and reflex alterations had a comparable threshold to the known threshold for anatomic malformations on the 9th day. These results indicate that all of the parameters studied had thresholds either at or above 0.2 Gy acute radiation, and that the postpartum developmental and reflex acquisition measures were not more sensitive indicators of exposure to X-radiation than growth parameters.     

Studies of the effect of 0.4-Gy and 0.6-Gy prenatal X-irradiation on postnatal adult behavior in the Wistar rat

Thirty-four pregnant Wistar rats were X-irradiated on the 9th or 17th day of gestation at a dosage level 0.4 Gy or 0.6 Gy or were sham-irradiated. All mothers were allowed to deliver their offspring, and litters were limited to a maximum of eight on day 2. On day 30, 224 offspring were weaned and raised until 60 days of age, at which time testing began. Each rat randomly received, in random order, three of the following six behavioral tests: Water T-maze, Conditioned Avoidance Response, Forelimb Hanging, Activity Wheel, Swimming, and Open Field. There were no statistically significant differences between the irradiated and control groups for maternal weight or weight gain or mean litter size, although the litter size of the 17th day 0.6-Gy group was slightly lower. Among offspring irradiated with 0.6 Gy on the 17th day, 3-day-old neonates' weights were significantly reduced. Offspring irradiated on the 17th day with 0.6 Gy exhibited higher Conditioned Avoidance Response 5th-day and retest avoidance scores than did the controls. There were also significant sex differences in responses within the irradiated and control groups for several tests, which were unrelated to radiation exposure. The results of this study indicate that low-level X-irradiation during the fetal period of rat gestation results in neonatal growth retardation and subtle behavioral alterations that may be manifested in adult life. Growth retardation may be the most sensitive indicator of subtle effects that result from low-level prenatal exposure to X-rays.     

Effects of 0.6-Gy prenatal X irradiation on postnatal neurophysiologic development in the Wistar rat

Forty-one pregnant Wistar strain rats were irradiated with 0.6-Gy X rays or were sham irradiated on the 9th or 17th days of gestation to determine if this dosage level would result in alterations in postnatal neurophysiologic development. Half of the mothers were sacrificed at term, and the developmental status of 221 newborns was evaluated. The remaining mothers delivered and raised their litters. The 161 offspring were observed for the age of attainment of the following physiologic parameters: pinna detachment, eye opening, testes opening. Offspring were also tested for the acquisition of the following selected reflexes: surface righting, negative geotaxis, auditory startle, air righting, and visual placing. Term fetal weight was lower than the controls in the group irradiated on the 9th day but was recuperable postnatally. None of the 9 developmental tests performed postnatally were abnormal in the animals irradiated on the 9th day. Thus, at least with regard to these measures, the surviving embryos exposed during the all-or-none period could not be differentiated from the controls. Offspring irradiated on the 17th day exhibited retarded growth which persisted during neonatal life. The three-day-mean neonatal weight was significantly lower in the group irradiated on the 17th day compared to controls. There were no significant maternal body weight or organ/weight differences between the groups. Rats exposed in utero on the 17th day had a significantly delayed acquisition of air righting. These results demonstrate that 0.6-Gy in utero irradiation on the 17th day of gestation can cause subtle alterations in growth and development of the Wistar strain rat during postnatal life.     

Studies concerning the effects of low level prenatal X-irradiation on postnatal growth and adult behaviour in the Wistar rat

Fifty-nine pregnant Wistar strain rats were sham irradiated or subjected to a 0.1 or 0.2 Gy exposure of X-radiation on the 9th or 17th day of gestation. Twenty-seven of the females were killed at term for teratologic analysis. The remaining mothers raised their young. At 60 days of age the 252 offsprings were randomly assigned three of six tests: open field, swimming, hanging, activity wheel, water T-maze, or conditioned avoidance response. Male offspring exposed at the 0.2 Gy level exhibited retarded growth only during the first few weeks of postnatal life. Female offspring exposed on the 17th day to 0.2 Gy X-radiation were growth retarded throughout the test period. Postnatal growth rates, however, were not significantly different between the irradiated and control groups. There were no significant alterations in adult behaviour due to prenatal X-irradiation. There were sex differences in activity wheel and forelimb hanging performance, unrelated to radiation exposure. These results indicate that prenatal low level X-irradiation on the 9th or 17th day of gestation does not result in significant alterations in adult behavioural performance in the rat, but prenatal growth retardation persists postnatally. Growth may be a more sensitive indicator of the effects of prenatal exposure to X-radiation than postnatal behaviour.     

Effects of prenatal X-irradiation on the 14th-18th days of gestation on postnatal growth and development in the rat

Thirty-nine pregnant adult Wistar strain rats were randomly assigned to one of three exposure groups: 0, 0.75, or 1.50 Gy X-radiation total exposure. Animals were exposed from the 14th to the 18th days of gestation at 0, 0.15, or 0.30 Gy per day. At term, 15 rats were killed and morphologic analyses were completed. Twenty-four rats were allowed to deliver their offspring. On the first day of postnatal life, litters were reduced to a maximum of eight pups per litter, with equal numbers of male and female offspring wherever possible. A total of 187 pups were observed for the age of acquisition of five reflexes (air righting, surface righting, visual placing, negative geotaxis, auditory startle) and the appearance of four physiologic markers (pinna detachment, eye opening, vaginal opening, testes descent). There was significant dose-related weight reduction in term fetuses and offspring throughout the 86-day postnatal period. Postnatal growth rate (g gained/day) was unaffected. Adult offspring brain and gonadal weight and organ weight:body weight ratios were reduced. Using the PAC50 methodology, dose-related alterations occurred in the acquisition of several reflexes. All physiologic markers exhibited a dose-related delay in appearance. These results indicate that fractionated exposure to X-radiation during the fetal period in the rat results in dose-dependent alterations in postnatal growth and physiologic development. These studies are important for our understanding of the long-range effects of prenatal exposure to ionizing radiation late in gestation.     

Effects of prenatal X-irradiation: studies on the mechanism of X-irradiation-induced inhibition of microsomal enzyme development in rat liver

Exposure of pregnant rats to 25 R of x-irradiation on the fourteenth gestation day has produced in the male offspring an impairment of the development of the hepatic microsomal enzyme system which metabolizes hexobarbital. However, irradiation did not suppress the increase of enzyme activity brought about by the administration of chemical inducers (pheno-barbital). Actinomycin, on the other hand, inhibited to varying degrees both the ontogenic and phenobarbital-induced increases in enzyme activity. The effects on the enzyme system have been supported by in vivo measurements of the duration of hexobarbital hypnosis. The ontogenic increase in enzyme activity is hormone-dependent, while that following phenobarbital administration is independent of hormonal regulation as evidenced by the response in hypophysectomized or sexually immature animals. It is concluded from these results that the inhibitory effect of x-irradiation on the hepatic enzyme system is mediated through an action on the hormonal regulation of enzyme activity. Evidence for this hypothesis is discussed.     

The effects of manganese deficiency during prenatal and postnatal development on mitochondrial structure and function in the rat

The influence of manganese deficiency on liver trace element concentration, MnSOD activity, and mitochondrial structure and function during postnatal development was determined in rats. In both normal and manganese-deficient animals, liver manganese concentration increased with time, but in deficient rats liver manganese was lower than in controls at all ages measured. At 9 mo of age, liver manganese concentration in the deficient rats was only 20% that of controls. The developmental pattern observed for MnSOD paralleled that of liver manganese concentration in normal and deficient rats; it was lower than in controls on days 20 and 60. However, at 9 mo of age, MnSOD levels were similar in the two groups. Although there were no differences at 9 mo of age in MnSOD activity between the groups, manganese-deficient rats showed mitochondrial abnormalities in liver. Despite mitochondrial abnormalities, however, oxygen uptake and P/O ratios were normal. We suggest that the mitochondrial damage apparent at 9 mo of age is, at least in part, the result of lower than normal MnSOD activity occurring earlier. The functional significance of the abnormalities remains to be established.     

Interactive effects of prenatal cocaine and nicotine exposure on maternal toxicity,postnatal development,and behavior in the rat

Two experiments were performed to investigate the interactive effects of prenatal coadministration of cocaine hydrochloride (C) and nicotine tartrate (N). Experiment I was designed to determine doses of C and N that could be coadministered without altering maternal gestational parameters and/or fetal viability. Exposure of Sprague-Dawley rats to combined high-dose C (20 mg/kg) and high-dose N (5.0 mg/kg) on gestation days 8–21 was not more toxic to dam or fetus than that of exposure to C alone. Experiment II investigated pregnancy outcome, postnatal development, and behavior of the offspring following drug exposure to either high-dose cocaine (20 mg/kg: CS), high-dose nicotine (5.0 mg/kg: NS), or both (NC) on gestation days 8–21. N was administered by osmotic minipump and C by sc injection. Saline-injected dams, fitted with saline-filled pumps (SS), and untreated dams, pair-fed (PF) to NC females, served as controls. Alterations in maternal variables were limited to a 10–15% decrease in food consumption in NC and CS groups. Pregnancy outcome and birth statistics were unaffected by prenatal treatment, as was offspring body weight during the first four postnatal weeks. However, the development of surface righting was delayed in CS pups, and only CS offspring were underresponsive to the stimulatory effects of dopamine agonists on activity and stereotypy. Behavioral responses to N challenge were similar in all groups. In addition, only CS offspring showed altered behavioral responses in a spontaneous alternation task. Treatment effects on dopamine D₁ and D₂ binding in the caudate nucleus were not observed. The combination of N and C did not exacerbate any of the behavioral changes seen in CS offspring. These results support the hypothesis that C is a behavioral teratogen in rodents, and suggest that in the present model, nicotine can mitigate some of the consequences ofin utero exposure to cocaine.     

Fetal hydantoin syndrome in rats: dose-effect relationships of prenatal phenytoin on postnatal development and behavior

Sprague-Dawley rats were gavaged once daily on days 7-18 of gestation with, 100, 150, or 200 mg/kg of phenytoin. Only the highest dose of phenytoin decreased maternal weight during gestation or increased offspring mortality up to weaning. Offspring were evaluated for activity prior to weaning (pivoting and photocell) and afterwards (figure 8, open-field, and hole-board), dynamic righting development, maze learning (Biel maze), and visual discrimination (Y maze), and for startle reaction to both auditory and tactile stimuli. The highest dose of phenytoin produced increased activity on all tests of activity, delayed dynamic righting development, impaired Biel maze and Y-maze learning, and inhibited tactile startle responses. The two lower doses of phenytoin generally showed a dose-effect relationship with values on most measures intermediate between values for controls and for the highest-dose group. Dose-effect relationships were most evident on measures of early activity (both tests), dynamic righting, and Biel maze learning, whereas only trends were evident on measures of later activity, Y maze, and startle. A dose-related rotational defect was found in a minority of phenytoin offspring, and although these individuals contributed to the behavioral abnormalities observed, they in no instance accounted for the overall pattern of effects seen in the phenytoin offspring. Maternal plasma phenytoin levels at the end of treatment were dose-related. Offspring showed no effects on postnatal growth, total brain weight, or brain protein content as adults. The data support the view that phenytoin is a potent behavioral teratogen at doses well below those causing any evidence of gross teratogenicity or embryotoxicity.     

Effect of prenatal hypoxia during organogenesis on albino rat behavior during postnatal period

The survival rate, physical development, and spontaneous behavior has been evaluated in pups of albino rats exposed to acute hypobaric hypoxia on the 9–10th day of gestation corresponding to the onset of organogenesis. Prenatal hypoxia increased the mortality among the offspring, delayed their physical development, and affected their spontaneous behavior up to the age of 2 months. The females exposed to intrauterine hypoxia proved to be more sensitive to hypoxia than males.     

Effects of postnatal corticosterone treatment on reproductive development in the rat

Reproductive development was studied in rats in which corticosterone (25 mg/100 g body wt) mixed with an equal amount of cholesterol was implanted i.p. at Days 3, 6, 12 or 18 after birth. Vaginal perforation in rats treated on Days 12 or 18 was advanced by 10 days but reproductive function in the treated animals was generally disrupted. A variable incidence of persistent vaginal oestrus was observed in adult females given implants on Days 3 and 6, and of prolonged vaginal dioestrus in those treated on Days 12 or 18. All treated females had lordosis quotients lower than those of untreated controls, the effect being most pronounced at the earlier ages of treatment. The results are believed to indicate two periods in reproductive development which are differentially affected by corticosterone.     

Change in expression of a 90-kDa glycoprotein GP90-MC301 during prenatal and postnatal testicular development: a differentiation marker for rat germ cells

GP90-MC301, a 90-kDa glycoprotein recognized by the monoclonal antibody MC301, is a reliable stage-specific marker for preleptotene to pachytene spermatocytes in adult rat testes. In this study we confirmed that the glycoprotein is also useful as a marker for germ cells in prenatal and postnatal testes. Immunohistochemical analysis showed a dramatic change in GP90-MC301 expression in germ cells during testis development. Strong expression was detected in primordial germ cells at embryonic day (E) 13 and in gonocytes at E16, and the expression was then markedly reduced at around the time (E18) gonocytes undergo G1/G0 arrest, and was not restored in gonocytes or spermatogonia afterward. Thereafter, it reappeared in primary spermatocytes in the prepubertal period. Testicular somatic cells such as Sertoli cells, Leydig cells, and peritubular myoid cells expressed GP90-MC301 during specific periods which were largely correlated with periods of active proliferation of these testicular somatic cells. Western blotting showed that GP90-MC301 was expressed during testis development without a change in its molecular size. Thus, GP90-MC301 is potentially useful for the analysis of not only spermatogenesis but also early testis development.     

Effects of chemically induced maternal toxicity on prenatal development in the rat

The hypothesis that chemically induced overt maternal toxicity induces a characteristic syndrome of adverse developmental effects in the rat was investigated. Pregnant animals (Sprague-Dawley strain) were dosed by oral gavage with one of a series of compounds on days 6-15 of gestation. These chemicals were diquat (DIQ), ethylene-bis-isothiocyanate (EBIS), toxaphene (TOX), styrene (STY), 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenol (2,4,5-Tr), triphenyl tin hydroxide (TPTH), and cacodylic acid (CAC). The compounds were chosen because they exhibited little or no developmental toxicity in previous studies. Dosage levels producing maternal weight loss and/or lethality were determined from preliminary toxicity studies. Significant maternal weight reductions were noted during the course of treatment with all compounds except CAC and 2,4,5-Tr. Maternal lethality was produced by EBIS, TOX, 2,4,-D, and 2,4,5-Tr. The main treatment-related developmental toxicity noted in litters at term consisted of increased lethality (EBIS, TPTH) and decreased fetal weight (EBIS and CAC). Treatment-related anomalies were seen in litters treated with 2,4-D and TOX (supernumerary ribs) and with EBIS and STY (enlarged renal pelvis). No significant developmental effects were produced with DIQ, or 2,4,5-Tr. This study indicates that overt maternal toxicity as defined by weight loss or mortality is not always associated with the same defined syndrome of adverse developmental effects in the rat.     

Effects of X-irradiation on rat hair follicles

The alterations of normal growth of hair follicles following irradiation of rat tails with X-rays have been analysed. The changes in follicle length are attributed to a series of deleterious events occurring in the hair matrix after irradiation. A dose-dependent reduction of length was demonstrated for a given post-irradiation interval. An approximate exponential response was obtained for all conditions excepting low doses for which a marked reduction of follicle length was observed a short time after irradiation and was ascribed to the depletion of highly radiosensitive cells. At later post-irradiation times this response was obscured by the resumption of follicle growth.     

Effects of prenatal and postnatal exposure to vitamin A on the development of the murine immune system

Vitamin A and its derivatives are known to enhance the immune system and affect embryogenesis. In this study, five daily subcutaneous injections of retinol palmitate (0.001 mg/kg body weight) were administered to eight female SW mice before mating. Six more weekly injections of retinol palmitate were given during pregnancy and lactation. Eight controls were similarly treated with saline. Four of the eight vitamin-A-treated females had litters, whereas seven of the eight saline-treated females had litters. Resultant litters did not differ in size or appearance. At 12 weeks of age, serum IgM and IgG1 levels were significantly higher in the progeny of vitamin-A-treated mothers before but not after immunization with a test antigen, sheep red blood cells (SRBC). This difference was not seen when other progeny were tested at the age of one year. Anti-SRBC titers did not differ in the two groups of progeny at the age of 12 weeks or one year. One-year-old progeny of vitamin-A-treated mothers weighed significantly more than did control progeny; significant enlargement of the heart, spleen, and kidneys was observed. However, organ-to-body-weight ratios did not differ significantly. In a separate experiment, adult female mice treated with varying doses of vitamin A (five daily doses of 0.0001, 0.0005, or 0.001 mg/kg body weight) showed a dose-dependent reduction of serum IgG1 and hematocrits, but no change in serum IgM levels or leukocyte counts. Resting untreated mice had IgM levels which were one-half those seen in saline-treated controls. These studies indicate that large doses of vitamin A can affect some aspects of the developing and mature murine immune system.     

Effects of lithocholic acid exposure throughout pregnancy on late prenatal and early postnatal development in rats

The effects of lithocholic acid (LCA) on late prenatal and early postnatal development were studied. LCA was given in the diet (0.8% by weight) or administered in the drinking water (0.8%) throughout the entire period of pregnancy. The addition of LCA to the drinking water caused a significant reduction in the weight of 20-day-old fetuses as well as their placentas and livers. Feeding LCA to pregnant rats affected postnatal growth of the offspring: their weight was significantly lower than control values until 6 weeks of age. The pattern of postnatal growth was similar in the experimental and control rats. The retardation in growth and development of the offspring was accompanied by microscopic and biochemical changes in their livers.     

Effects of pulsing electromagnetic fields on the prenatal and postnatal development in mice and rats: in vivo and in vitro studies

Electromagnetic fields (EMF) might have various biological effects on the developing embryo. We studied the effects of pulsing electromagnetic fields (PEMF) on the in vitro development of preimplantation mouse embryos and of early somite rat embryos as well as on the in vivo development of rat embryos. We used PEMF at frequencies of 1, 20, 50, 70, and 100 Hz with a tension of 0.6 V/m. The embryos were exposed to PEMF throughout the experimental period. PEMF at frequencies of 20 and 50 Hz were embryotoxic, inhibiting over 50% of blastocysts from hatching and further development, all within 72 h of culture. PEMF at frequencies of 50 and 70 Hz induced 22% and 30% incidence of malformations in 10.5 day old rat embryos after 48 h in culture. The main malformations were absence of telencephalic, optic, and otic vesicles and of forelimb buds. In addition, retarded growth and development manifested by fewer somites, reduction in crown-rump length, and retarded closure of the neural tube were found in many embryos. No significant pathological changes were found by TEM in PEMF-exposed embryos. Disappearance of microvilli and collapse of apical parts of endodermal cells were observed by SEM in many yolk sacs of embryos exposed to 50 and 70 Hz PEMF. A slightly reduced litter average, a reduction or increase of weight, and a delay in eye opening was observed among offspring of pregnant rats exposed throughout pregnancy to PEMF at frequencies of 20, 50, and 100 Hz. No malformations were observed among these offspring. The mechanism of PEMF-induced embryotoxicity and teratogeneity is unknown, as is the mechanism of the "protective effects" of the mother on the rat embryos exposed to PEMF in vivo.     

Influences of prenatal and postnatal fraternity size on ovarian development in the mouse

An experiment was conducted to test effects of prenatal and postnatal fraternity size (size of litter in which an individual develops prenatally or is reared postnatally) on ovarian development in mice. Fraternity size treatments were created by standardizing sizes of prenatal and postnatal fraternities in which mice were gestated and reared. Prenatal fraternity size was standardized by surgery on Day 9 of gestation to 6, 10, and 14 fetuses. Postnatal fraternity size was standardized by randomly assigning pups to litters of 5, 10, or 15 pups within 24 h of birth. Female pups were killed at either 3 or 20 wk of age and right ovaries were prepared for histology. Follicles were classified by size and morphology, and numbers of follicles in each class were tabulated. Interaction of postnatal fraternity size and age was observed for number of antral follicles (p less than 0.05). Mice reared in small postnatal fraternities had more antral follicles at weaning (3 wk) and fewer antral follicles at maturity (20 wk of age) than mice reared in large postnatal fraternities. No effect of either prenatal or postnatal fraternity size on other follicle populations was observed (p greater than 0.20). Numbers of Type 2 (primordial), Type 3a, and Type 3b follicles changed with age (p less than 0.01); numbers of primordial follicles declined with age, but numbers of Type 3a and 3b follicles increased. A hypothesis of a negative association between postnatal fraternity size and number of antral follicles at 3 wk of age was supported, but a hypothesis of a positive association between fraternity size and number of primordial follicles was not supported.