Teratological studies of prenatal exposure of mice to a 20 kHz sawtooth magnetic field

In order to evaluate the importance of gestational age in possible effects due to exposure to a 20 kHz sawtooth magnetic field, pregnant ICR mice at gestational 2.5-15.5 days post-coitus, which is the most sensitive stage for the induction of major congenital malformations, were exposed in a carrousel irradiator. The mice were exposed to a 20 kHz intermediate frequency (IF) sawtooth magnetic field had a 6.5 microT peak intensity for 8 h/day. The animals were sacrificed on the 18th day of gestation; and the fetuses were examined for mortality, growth retardation, changes in head size, and other morphological abnormalities. From the above conditions, it is concluded that the exposure to a 20 kHz sawtooth magnetic field with 6.5 microT peak intensity does not inflict any adverse effect on fetuses of pregnant mice.     

Effect of a 20 kHz sawtooth magnetic field exposure on the estrous cycle in mice

Female mice post weaning were exposed to 20 kHz sawtooth electric and magnetic fields (EMF) with 6.25 microT peak intensity for 6 weeks. Estrous cycles were checked using vaginal smears over the last 10 days of the experimental period. The vaginal smears from EMF-exposed mice revealed an increase in the frequency of one or two phases persisting. The number of estrous cycles less than 1 was more in the EMF-exposed group than in the sham control group. Furthermore, in the EMF-exposed group, the duration of proestrous and metestrous stages of the estrous cycle was significantly increased compared with the control group. In conclusion, our results suggest that exposure to 20 kHz sawtooth EMF may affect normal cycling of the estrous cycle by disrupting the female reproductive endocrine physiology. We should not disregard the possible adverse reproductive effect of the 20 kHz sawtooth EMF generated under the occupational exposure situation in females.     

The mutagenic effects of low level sub-acute inhalation exposure to benzene in CD-1 mice.

Benzene is a widely used chemical and common environmental contaminant. It is carcinogenic in man and animals and is genotoxic in mice, rats, and occupationally exposed humans at doses above one part per million. In order to evaluate the genotoxic effects of prolonged exposures to very low concentrations of benzene, we exposed CD-1 mice to benzene by inhalation for 22 h per day, seven days per week for six weeks at 40, 100 and 1000 parts per billion (ppb). Additional groups were exposed to purified air or were housed in standard plastic cages. The effects of in vivo exposure to benzene were evaluated by using an autoradiographic assay to determine the frequency of mutants which represent mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in spleen lymphocytes. At the end of the six weeks exposure period lymphocytes were recovered from the spleens of the mice and cryopreserved prior to assay. Mutant cells were selected on the basis of their ability to incorporate tritiated thymidine in the presence of 6-thioguanine. The weighted mean variant (mutant) frequencies (Vf) of female mice (three per group) were 7.2 x 10(-6) at 0 ppb; 29.2 x 10(-6) at 40 ppb; 62.5 x 10(-6) at 100 ppb and 25.0 x 10(-6) at 1000 ppb. The Vf of unexposed mice housed in standard cages was 13.2 x 10(-6). In male mice the same pattern of response was observed, but the increases in Vf in response to benzene were not as great. In both sexes of mice, the increases at 40 and 100 ppb were significantly greater than at 0 ppb (P less than 0.05). The increase in Vf with exposure to 100 ppb and the decline at 1000 ppb parallel the results observed for chromosome damage in spleen lymphocytes from the same animals (Au et al., Mutation Res., 260 (1991) 219-224). These results indicate that sub-chronic exposure to benzene at levels below the current Occupational Safety and Health Administration Permitted Exposure Limit may induce gene mutations in lymphocytes in mice.     

Behavioral effects of long-term exposure to magnetic fields in rats

Male rats and pregnant and nonpregnant female rats of the Wistar strain were sham-exposed or exposed to static (0.49 T) or to extremely low frequency (50 Hz) magnetic fields (0.018 T) 2 h per day for 20 consecutive days. Measures of irritability, exploratory activity, and locomotion were made in that order before and after the 4th, 10th, and 17th 2-h exposures. A reliable decrease in the irritability of rats after repeated exposure to a static or undulating field was found. No significant effects of treatment conditions on open-field behavior and locomotor activity were observed. Pregnancy had no influence on the behavioral end points. These results indicate that irritability of rats may be used as a simple behavioral indicant of mammalian sensitivity to magnetic fields. © 1993 Wiley-Liss. Inc.     

The effects of repeated oral gavage on the health of male CD-1 mice

Oral gavage is a widely used method for administering substances to animals in pharmacological and toxicological studies. The authors evaluated whether oral gavage causes behavioral indicators of stress, increased mortality rate, alterations in food and water consumption and body weight or histological lesions in CD-1 mice. Gavage was carried out once per d for 5 d per week over 6 consecutive weeks. The mortality rate of mice in this study was 15%. Mice subjected to gavage did not undergo changes in food or water consumption during the study, and their mean body weights and relative organ weights were similar to those of mice in the control group. Serum cortisol levels at the time of euthanasia in mice in both groups were within the normal range. Histopathology showed acute esophagitis and pleurisy, indicative of perforation of the esophagus, in the two mice that died but no abnormalities in the other mice. The results suggest that animal stress and mortality related to oral gavage can be minimized when the procedure is carried out by an experienced technician.     

Adverse effects on female development and reproduction in CD-1 mice following neonatal exposure to the phytoestrogen genistein at environmentally relevant doses

Outbred female CD-1 mice were treated with genistein (Gen), the primary phytoestrogen in soy, by s.c. injections on Neonatal Days 1-5 at doses of 0.5, 5, or 50 mg/kg per day (Gen-0.5, Gen-5, and Gen-50). The day of vaginal opening was observed in mice treated with Gen and compared with controls, and although there were some differences, they were not statistically significant. Gen-treated mice had prolonged estrous cycles with a dose- and age-related increase in severity of abnormal cycles. Females treated with Gen-0.5 or Gen-5 bred to control males at 2, 4, and 6 mo showed statistically significant decreases in the number of live pups over time with increasing dose; at 6 mo, 60% of the females in the Gen-0.5 group and 40% in the Gen-5 group delivered live pups compared with 100% of controls. Mice treated with Gen-50 did not deliver live pups. At 2 mo, >60% of the mice treated with Gen-50 were fertile as determined by uterine implantation sites, but pregnancy was not maintained; pregnancy loss was characterized by fewer, smaller implantation sites and increased reabsorptions. Mice treated with lower doses of Gen had increased numbers of corpora lutea compared with controls, while mice treated with the highest dose had decreased numbers; however, superovulation with eCG/hCG yielded similar numbers of oocytes as controls. Serum levels of progesterone, estradiol, and testosterone were similar between Gen-treated and control mice when measured before puberty and during pregnancy. In summary, neonatal treatment with Gen caused abnormal estrous cycles, altered ovarian function, early reproductive senescence, and subfertility/infertility at environmentally relevant doses.     

The effects of long-term exposure to extremely low-frequency magnetic fields on bone formation in ovariectomized rats

The effects of long‐term extremely low‐frequency magnetic field (ELF‐MF) exposure on bone formation and biochemical markers were investigated in ovariectomized rats. Sixty mature female Sprague–Dawley rats were randomly divided into four different groups (n = 15): (i) unexposed control (CTL); (ii) ovariectomized only (OVX); (iii) non‐ovariectomized, exposed (SHAM + ELF‐MF); and (iv) ovariectomized, exposed (OVX + ELF‐MF). The third and fourth groups were exposed to 1.5 mT ELF‐MF for 4 h a day for 6 months. Bone mineral density (BMD) was determined using dual energy X‐ray absorption (DEXA) measurements. The formation and resorption of bone were evaluated using bone‐specific alkaline phosphatase (BAP), osteocalcin, osteoprotogerin, and N‐telopeptide. After 6 months of ELF‐MF therapy, BMD values were significantly lower in the OVX group and higher in the OVX + ELF‐MF and SHAM + ELF‐MF groups than they were before therapy (P < 0.001). Although there was no significant difference in BMD values among the groups before therapy, the BMD values increased significantly after 6 months in the OVX + ELF‐MF and SHAM + ELF‐MF groups and were reduced in the OVX group compared to the CTL group (P < 0.001). The concentrations of BAP, osteocalcin, osteoprotogerin, and N‐telopeptide in the three experimental groups also changed in a significant way compared to the CTL group. The results of the present study suggest that osteoporosis can be inhibited by ELF‐MF stimulation treatments. It was also concluded that ELF‐MF may be useful in the prevention of osteoporosis in ovariectomized rats. Bioelectromagnetics 33:543–549, 2012. © 2012 Wiley Periodicals, Inc.     

Biologic effects of prolonged exposure to ELF electromagnetic fields in rats: II. 50 Hz magnetic fields

To provide possible laboratory support to health risk evaluation associated with long-term, low-intensity magnetic field exposure, 256 male albino rats and an equal number of control animals (initial age 12 weeks) were exposed 22 h/day to a 50 Hz magnetic flux density of 5 μmT for 32 weeks (a total of about 5000 h). Hematology was studied from blood samples before exposure to the field and at 12 week intervals. Morphology and histology of liver, heart, mesenteric lymph nodes, and testes as well as brain neurotransmitters were assessed at the end of the exposure period. In two identical sets of experiments, no significant differences in the investigated variables were found between exposed and sham-exposed animals. It is concluded that continuous exposure to a 50 Hz magnetic field of 5 μT from week 12 to week 44, which makes up ?70% of the life span of the rat before sacrifice, does not cause changes in growth rate, in the morphology and histology of liver, heart, mesenteric lymph nodes, testes, and bone marrow, in hematology and hematochemistry, or in the neurotransmitters dopamine and serotonin. © 1995 Wiley-Liss, Inc.     

Residential exposure to 60-Hz magnetic fields from appliances.

A model has been developed that permits assessment of residential exposure to 60-Hz magnetic fields emitted by appliances. It is based on volume- and time-averaging of magnetic-dipole fields. The model enables the contribution of appliances in the total residential exposure to be compared with that of other sources in any residence under study. Calculations based on measurements reported in the literature on 98 appliances revealed that appliances are not a significant source of whole-body exposure, but that they may be the dominant source of exposure of the body's extremities.     

Development of the ventilatory response to hypoxia in Swiss CD-1 mice.

We examined developmental changes in breathing pattern and the ventilatory response to hypoxia (7.4% O(2)) in unanesthetized Swiss CD-1 mice ranging in age from postnatal day 0 to 42 (P(0)-P(42)) using head-out plethysmography. The breathing pattern of P(0) mice was unstable. Apneas were frequent at P(0) (occupying 29 +/- 6% of total time) but rare by P(3) (5 +/- 2% of total time). Tidal volume increased in proportion to body mass ( approximately 10-13 ml/kg), but increases in respiratory frequency (f) (55 +/- 7, 130 +/- 13, and 207 +/- 20 cycles/min for P(0), P(3), and P(42), respectively) were responsible for developmental increases in minute ventilation (690 +/- 90, 1,530 +/- 250, and 2,170 +/- 430 ml. min(-1). kg(-1) for P(0), P(3), and P(42), respectively). Between P(0) and P(3), increases in f were mediated by reductions in apnea and inspiratory and expiratory times; beyond P(3), increases were due to reductions in expiratory time. Mice of all ages showed a biphasic hypoxic ventilatory response, which differed in two respects from the response typical of most mammals. First, the initial hyperpnea, which was greatest in mature animals, decreased developmentally from a maximum, relative to control, of 2.58 +/- 0.29 in P(0) mice to 1. 32 +/- 0.09 in P(42) mice. Second, whereas ventilation typically falls to or below control in most neonatal mammals, ventilation remained elevated relative to control throughout the hypoxic exposure in P(0) (1.73 +/- 0.31), P(3) (1.64 +/- 0.29), and P(9) (1. 34 +/- 0.17) mice but not in P(19) or P(42) mice.     

Chronic exposure of primates to 60-Hz electric and magnetic fields: III. Neurophysiologic effects

The neurophysiologic effects of combined 60-Hz electric (E) and magnetic (B) fields, of magnitudes comparable to those produced by high-voltage powerlines, were investigated in 10 monkeys (Macaca nemestrina). Six animals (experimental group) were each exposed to three different levels of E and B fields: 3 kV/m and 0.1 G, 10 kV/m and 0.3 G, and 30 kV/m and 0.9 G. Field exposures were preceded and followed by sham exposures, during which factors of field generation were present (e.g., heat, vibration, noise, etc.) without E and B fields. Each of the five segments (i.e., the three exposure segments and the initial and final sham exposure segments) lasted 3 weeks. Animals were exposed for 18 h/day (fields on at 1600 h, off at 1000 h). Four other animals (external control group) were given sham exposure for the entire 15-week period. Auditory, visual, and somatosensory evoked potentials were recorded twice a week, during the daily 6-h field-off period. E- and B-field exposure had no effect on the early or mid-latency evoked potential components, suggesting that exposure at these levels has no effect on peripheral or central sensory afferent pathways. However, there was a statistically significant decrease in the amplitudes of late components of the somatosensory evoked potential during the 10kV/m and 0.3 G, and 30 kV/m and 0.9 G exposure levels. This result is possibly related to the opiate antagonist effect of electromagnetic field exposure reported by others.     

Chronic exposure of primates to 60-Hz electric and magnetic fields: II. Neurochemical effects

We exposed Macaca nemestrina (pig-tailed macaques) to electric (E) and magnetic (B) fields ranging in intensity from 3 kV/m and 0.1 G to 30 kV/m and 0.9 G for three 21-day (d) periods. Experimental animals were exposed to sham E and B fields for two 21-d periods, one prior to and one following actual exposure to E and B fields, resulting in a total of five 21-d periods. Control animals were exposed to sham E and B fields for the entire 105-d interval. At the end of each 21-d period cerebrospinal fluid (CSF) was obtained by lumbar puncture and analyzed for concentrations of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), metabolites of dopamine and serotonin neurotransmitters, respectively, by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). Results are based on an examination of six experimental and four control animals. Exposure to E and B fields at all strengths was associated with a significant decline in CSF concentrations of both HVA and 5-HIAA when statistical comparisons were made against values obtained at the end of the preexposure interval. However, HVA returned to preexposure levels during the postexposure period, while 5-HIAA did not. No significant change in the concentrations of HVA or 5-HIAA was noted in the control animals. These results strongly suggest that exposure of the nonhuman primate to E and B fields can significantly affect specific biochemical estimates of nervous system function. These effects may involve alterations either in neuronal activity or in the activity of enzymes that catabolize the neurotransmitters.     

Effects of prolonged simultaneous exposure of CD-1 mice to high pressures and inert gas narcosis

Addition of N2 to the heliox used in pressure conditioning exposures reduces or suppresses the increase in convulsion threshold pressure (Pc) as well as the change in compression rate effect resulting from pressure exposures in the absence of N2; 18 atm N2 neutralizes the effect of 80 ATA total pressure so that Pc remains at a constant level throughout the conditioning period. Since N2 habituation is much slower than pressure conditioning (t1/2 6 days vs. 12 h), this precludes mere addition of pressure and N2 effects in this situation. In contrast to Pc, anesthesia tolerance of mice exposed to 80 ATA in the presence of 18 atm N2 increases even more (25%) than at the same PN2 but at a total pressure of only 18 ATA, indicating that pressure reversal of anesthesia does not extend to the habituation events. The implications of the striking asymmetry between the effects of protracted high pressure and inert gas narcotic exposures for an understanding of the nature of the supposed IG/HP antagonism are discussed.     

Effects of paternal subacute exposure to Tordon 202c on fetal growth and development in CD-1 mice

Male CD-1 mice were exposed to Tordon 202c (a picloram and 2,4-D combination herbicide) in the drinking water at concentrations of 0.21, 0.42, and 0.84% solutions for 60 days prior to mating with untreated females. Subsequently there was no exposure to Tordon 202c during gestation. Fetal weight and crown-rump length were reduced in the highest dosage group. The incidence of malformed fetuses (e.g., ablepharon, cleft palate, and unilateral agenesis of the testes) was increased in the middle dosage group while the incidence of fetuses with variants was increased in the lowest (e.g., an extra pair of ribs) and the highest dosage groups (e.g., incomplete ossification of the skeleton). The frequency of pregnancy failure was increased in the middle dosage group. Indices of paternal toxicity included increased lethality and decreased water consumption in the highest dosage group and increased relative spleen weights in the lowest and middle dosage groups. The results suggest paternally mediated reproductive toxicity.     

Embryotoxicity of phenytoin in adrenalectomized CD-1 mice.

It has been proposed that the anticonvulsant drug phenytoin (PHT) and glucocorticoids induce orofacial clefting by the same mechanism. Previous work had demonstrated that PHT treatment significantly increased endogenous maternal corticosterone concentrations for approximately 48 hr after dosing in A/J mice. The purpose of the present investigation was to determine whether PHT is embryotoxic in the absence of endogenous maternal glucocorticoids. Maternal adrenal glands were removed on Day 7 of gestation, and the incidence of clefting after PHT treatment was determined. There was a high level of maternal toxicity following adrenalectomy (ADX) and PHT treatment at either 60 or 75 mg/kg. This increased toxicity did not appear to be due to altered maternal drug levels in ADX mice. There was a significant increase in the clefting incidence among offspring of ADX dams treated with PHT at 60 mg/kg. This dose of PHT did not elevate maternal corticosterone levels in ADX dams. These data suggest that PHT is capable of producing clefts in the absence of endogenous maternal corticosterone.     

Small integrating meter for assessing long-term exposure to magnetic fields.

A small, lightweight meter has been developed for magnetic-field measurements, particularly those needed for exposure-assessment purposes. This meter, known as the AMEX-3D, continuously measures all three axes of magnetic-flux density and electronically combines the data into a single estimate of cumulative exposure to the root-mean-square (rms) resultant flux density. The AMEX-3D weighs about 120 g, measures 2.7 cm x 5.1 cm x 10.2 cm, and is battery powered. Two panel-mounted jacks are provided for measuring battery voltage and for reading cumulative exposure data from the unit. The instrument has, within 3 dB, a flat response to magnetic flux densities at all frequencies in its 30-1,000 Hz bandwidth. A detailed analysis of error sources in the AMEX-3D leads to an estimate of +/- 20% as the accuracy of the instrument over its dynamic range, which extends from 0.02 to 15 microT. The AMEX-3D was tested in the field by asking electric-utility distribution linemen to wear AMEX-3D and EMDEX meters simultaneously while working. Agreement between the two measures of exposure was excellent.     

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: II. Postnatal development and behavior

To investigate the potential of magnetic fields to act as a behavioral teratogen, pregnant CD1 mice were exposed or sham-exposed for all of gestation to a 50 Hz/20 mT magnetic field. Maturation of offspring was assessed using a range of standard developmental indices (eye opening, pinna detachment, hair coat, tooth eruption, sexual maturity, and weight) and simple reflexive behaviors (air righting, surface righting, forepaw grasp, cliff avoidance, and negative geotaxis). Activity and coordination levels were explored in juvenile and adult mice using an open field arena, a head-dip board, an accelerating Rotarod, and a residential activity wheel. All assessments were carried out without knowledge of exposure condition. Results from 168 sham-exposed mice from 21 litters and from 184 exposed mice from 23 litters were compared using survival analysis techniques and multivariate regression methods. Three possible field-dependent effects were found: Exposed animals performed the air righting reflex earlier (P < 0.01); exposed males (but not females) were significantly lighter in weight (P = 0.008) at 30 days of age; and exposed animals remained on a Rota-rod for less time as juveniles (P = 0.03). Some of these results have not been reported in other studies and may reflect spurious statistical significance, although some effect of magnetic field exposure cannot be ruled out. Overall, these results suggest that prenatal exposure to a 50 Hz magnetic field does not engender any gross impairments in the postnatal development or behavior of mice. This does not preclude such exposure affecting more subtle aspects of behavior. Published 1994 by Wiley-Liss, Inc.     

Effects of gestational exposure to ethane dimethanesulfonate in CD-1 mice: microtia and preliminary hearing tests

BACKGROUND: Microtia is a reduction in pinna size, usually seen in humans in conjunction with other medical conditions. We report microtia in CD‐1 mice after gestational exposure to ethane dimethanesulfonate (EDS), an alkylating agent and adult rat Leydig cell toxicant. METHODS: Time‐pregnant CD‐1 mice were administered 0, 80, or 160 mg EDS/kg on gestation days (GD) 11–17, or 0 or 160 mg EDS/kg on GD 11–13, GD 13–15 or GD 15–17. Pinnae were measured on postnatal days (PND) 4, 8, 18, and 28; and were observed for detachment from birth through PND 8. Branchial‐arch derived skeletal structures and histology of the pinna was examined on PND 4 and 24. Brainstem auditory evoked response (BAER) tests were carried out at approximately PND 160 to determine possible effects on hearing. RESULTS: All offspring of EDS‐treated dams exhibited bilateral, dose‐related decreases in pinna size. Gestational exposure during GD 11–13 produced smaller ears than during GD 13–15 or 15–17, but not as small as the GD 11–17 regimen. Ossification of other pharyngeal arch derivatives was delayed whereas histology was unremarkable. BAER analysis showed a decrease in the proportion of adult offspring producing a quantifiable response to varied auditory stimuli among EDS‐treated litters. CONCLUSIONS: Gestational exposure to EDS affects pinna development in the mouse, with a broad period of sensitivity during the second half of gestation. Microtia induced by EDS may be associated with hearing deficits, suggesting functional importance of pinna size or additional effects of EDS on ear development not detected by morphological examination. Birth Defects Res B68:383–390, 2003. © 2003 Wiley‐Liss, Inc.     

Effects of preconceptional and gestational exposure to Tordon 202c on fetal growth and development in CD-1 mice

Female CD-1 mice were exposed to Tordon 202c (a picloram and 2,4-D combination herbicide) in the drinking water at concentrations of 0.21, 0.42, and 0.84% for 60 days prior to mating with untreated males. One-half of the pregnant females subsequently continued treatment throughout gestation while the remaining females were maintained on distilled water. Fetal weight, crown-rump length, placental weight, and maternal gestational weight gain were reduced in a dose-dependent manner following combined preconceptional and gestational exposure. The incidence of malformed fetuses (cleft palate, renal agenesis, hydronephrosis, unilateral testicular agenesis, and umbilical hernia) and fetuses with variants (especially incomplete ossification of the skeleton) were increased in a dose-dependent manner following combined exposure. Increased maternal mortality and decreased preconception weight gain were observed in the highest-dosage group. Relative maternal liver weight was increased in a dose-dependent manner. The results suggest that combined preconceptional and gestational exposure to Tordon 202c is required for teratogenesis and fetal growth depression. Preconceptional exposure alone is not effective in increasing the risk for embryotoxicity.     

Alcohol and smokeless tobacco effects on the CD-1 mouse fetus.

Tobacco products and alcohol are commonly used as nonmedicinal drugs by pregnant women, and both are known to cause various effects on the fetus and the newborn. The objective of this study was to examine the fetal effects of both drugs when administered individually and simultaneously to pregnant CD-1 mice at moderate dosages. Specifically, we wanted to determine whether or not the effect on the fetus of these two biologically active substances was additive, ameliorative, or synergistic. A total of 65 CD-1 dams were divided among four groups receiving either ST equivalent to 8 mg/kg nicotine, ethanol (ETOH) 1.8 g/kg, a combination of ST+ETOH in the same dosages, or D-glucose (controls and ST alone) to supply calories equivalent to the dose of ethanol. Mice were dosed three times per day on gestational days 6-15. On gestational day 17 all dams were killed, fetal and placental weights recorded, and the number of resorbed, dead, and malformed fetuses noted. The mean maternal plasma drug levels were: nicotine-321 ng/ml and ethanol-0.105 g%. No significant differences were observed in maternal weight gain, litter size, or in the incidence of resorptions, deaths and/or malformations. Fetal weights were reduced in all three treatment groups (P less than 0.05), with the greatest reduction (13% decrease) recorded in the ST group, followed by a 9% decrease in the ETOH group, and a 7% decrease in the ST+ETOH group. Placentas of the ST group weighed significantly less (P less than 0.05) than controls. Ossification of the fetal skeleton, observed in ten sites, was affected to the greatest extent in the ST group, followed by the ETOH and ST+ETOH groups. Craniofacial measurements were significantly affected (P less than 0.05) in all three treatment groups, compared to controls. We conclude that under these experimental conditions, in terms of fetal growth and ossification, ST had the greatest effect, followed by ETOH and ST+ETOH. The interaction of ST+ETOH was neither additive, synergistic, nor ameliorative.