Mouse Dams Research Articles

Prenatal Nicotine Exposure Modifies Behavior of Mice Through Early Development

Studies in humans and animal models (including rodents) have revealed lasting behavioral and cognitive impairments in offspring prenatally exposed to nicotine. Offspring of pregnant mouse dams prenatally subjected to 9–10 daily subcutaneous injections into the nape of the neck during pregnancy have been postnatally subjected to several developmental and behavioral tests to investigate the effects of prenatal nicotine exposure on those offspring at various stages of their life. The prenatal exposure to nicotine has resulted in significant reduced postnatal body weight gain, as well as in significant delay in eye opening, in the appearance of body hairs, and in sensory motor reflexes. However, motor activity was significantly stimulated in early adulthood of mouse pups prenatally exposed to nicotine, and such exposure proved to have long-lasting hyperactive effects on mice. Thus, exposure to nicotine during a critical prenatal period of brain development deduced from the present study in mice raises the alarm of the possible hazard of prenatal exposure to nicotine in humans. Hence, smoking by pregnant women might constitute a serious hazard to their in utero developing children.

Neurobehavioral alteration in rodents following developmental exposure to aluminum.

Aluminum (Al) is one of the most abundant metals in the earth's crust, and humans can be exposed to it from several sources. It is present in food, water, pharmaceutical compounds, and in the environment, e.g., as a result of acid rain leaching it from the soil. Exposure to Al has recently been implicated in a number of human pathologies, but it has not yet been definitely proved that it plays a major causal role in any of them. In this paper we review the effects of developmental exposure of laboratory animals to Al salts as a model for human pathological conditions. The data presented show behavioral and neurochemical changes in the offspring of AL-exposed mouse dams during gestation, which include alterations in the pattern of ultrasonic vocalizations and a marked reduction in central nervous system (CNS) choline acetyltransferase activity. Prenatal Al also affects CNS cholinergic functions under Nerve Growth Factor (NGF) control, as shown by increased central NGF levels and impaired performances in a maze learning task in young-adult mice. The need for more detailed studies to evaluate the risks for humans associated with developmental exposure to Al, as well as the importance of using more than one strain of laboratory animal in the experimental design, is emphasized.

Immunogenicity and protective efficacy of the alpha C protein of group B streptococci are inversely related to the number of repeats.

Infection by group B streptococci (GBS) is an important cause of bacterial disease in neonates. Alpha C protein is a protective cell surface-associated protein of GBS. This protein contains a repeat region flanked by N and C termini. Variable expression of tandem repeating units of alpha C proteins had been found among clinical isolates of GBS. We examined the effect of the number of repeats on the immunogenicity of the alpha C protein and its ability to elicit protection from GBS infection in a neonatal mouse model. Mice were immunized with purified alpha C proteins of constructs containing various numbers of repeats (n = 1, 2, 9, and 16) and the N- and C-terminal regions. Both the N-terminal and the repeat regions contain protective and opsonic epitopes. Antibody responses to the alpha C protein constructs with various numbers of repeats were tested with enzyme-linked immunosorbent assay plates coated with either native, nine-repeat alpha C protein or "repeatless" N-terminal antigen. An inverse relationship was found between the number of repeats and the immunogenicity of the alpha C protein; this effect was most pronounced on titers of antibody to the N-terminal region. An inverse relationship was also observed between the number of repeats and protective efficacy, i.e., mouse dams immunized with 5 microg of one- or nine-repeat alpha C protein transferred protective immunity to 65 or 11% of their pups, respectively (P < 0.0001). Thus, the presence of multiple repeats appears to lessen the antibody response to the complete alpha C protein, and especially the antibody response to its N-terminal region, and suggests a mechanism whereby repeat elements contribute to the evasion of host immunity.

Developmental toxicity evaluation of methyl tertiary-butyl ether (MTBE) by inhalation in mice and rabbits.

Pregnant CD-1 mice (30 per group) and female New Zealand White rabbits (15 per group) were exposed by inhalation to 0, 1000, 4000 and 8000 ppm methyl tertiary-butyl ether (MTBE) vapor for 6 h a day during gestational days (GD) 6-15 and 6-18, respectively. Maternal body weights, clinical observations and food consumption were recorded throughout gestation for both species. At scheduled euthanization (GD 18 for mice and GD 29 for rabbits), fetuses were weighed, sexed and examined for external, visceral (including craniofacial) and skeletal alterations. For both species, the pregnancy rate was high and equivalent across all groups; no pregnant animals died or aborted. There were no does that delivered early, but there were three mouse dams in the control group and two dams in the 4000 ppm group that delivered early and were removed from the study. In mice, maternal body weights, body weight gain, corrected maternal gestational weight change and food consumption were significantly reduced in mice at 8000 ppm. Hypoactivity and ataxia were observed in dams exposed to 4000 and 8000 ppm. Gestational parameters affected at 8000 ppm included post-implantation loss (due to increased late resorptions and dead fetuses) and altered sex ratio (decreased males); fetal body weights per litter were reduced at 4000 and 8000 ppm. There was a significantly increased incidence of cleft palate at 8000 ppm; this resulted in increased incidences of pooled external and visceral malformations and of total malformations at this exposure concentration. There were also treatment-related increases in the incidence of individual skeletal variations at 4000 and 8000 ppm. In rabbits, maternal weight gain and food consumption were significantly reduced at 4000 and 8000 ppm. Relative liver weights were also reduced at 8000 ppm. All gestational parameters were equivalent across all groups, including pre- and post-implantation loss, fetal sex ratios, litter size and fetal weights/litter. There was no evidence of treatment-related teratogenicity observed at any dose tested in rabbits. The no-observed-effect levels (NOELs) for maternal and developmental toxicity were both 1000 ppm in mice and 1000 ppm and at least 8000 ppm, respectively, in rabbits.

Prior Cocaine Exposure in Different Environments Affects the Behavioral Responses of Mouse Dams

The present study evaluated the behavioral repertoire of lactating CD-1 mouse dams when tested in an environment associated with cocaine in the pre-mating period. Virgin females were randomly assigned for conditioning (8-day long schedule with four cocaine or saline injections administered every other day) to three experimental groups: i) Coc-Test females received one injection of cocaine (5 or 20 mg/kg IP) in the testing chamber and saline 24 h later in the home cage, ii) Coc-Home females received one injection of the same doses of cocaine in the home cage and saline 24 h later in the testing chamber, and iii) Sal-Sal control females received one saline injection in both environments. All females underwent a 25-day long wash out period during which they were mated. Their behavior was subsequently scored in the testing chamber on postpartum day 2 (drug-free state) in the presence of 3 pups from their own litter (single 15-min session). As a whole, Coc-Test dams appeared to be more involved in pup-directed activities such as pup-nosing and nest-building when compared with the Coc-Home group. In addition, non-pup directed behaviors, such as crossing, self-grooming, and rearing were higher in Coc-Test group than in other groups. The opposite was true for stereotyped gnawing activity. A measure of females' body weight gain revealed that Coc-Test 20 group was significantly higher than other groups particularly during the postpartum phase. On postpartum day 6, lactating dams were injected with the low cocaine dose (5mg/kg) and their response to a male intruder was assessed in the testing chamber (single 5-min session). A higher number of Coc-Test 5 dams showed the on nest and the upright offensive postures compared to the corresponding Coc-Home 5 group, whereas a significant higher number of Sal-Sal females showed the on top posture with respect to the Coc-Test 20 group. Oxytocin levels measured after the behavioral test showed a tendency, even if not significant, to be higher in the hypothalamus of Coc-Test dams. As a whole, the present results suggest that the alterations in maternal behavior here observed as well as the trend underlined by oxytocin values, cannot be ascribed to carry-over effects of cocaine administration in the pre-mating phase per se; rather, they seem to represent a conditioned response to the distinct environment previously associated with the drug experience.

Evidence for embryonic prostaglandin H synthase-catalyzed bioactivation and reactive oxygen species-mediated oxidation of cellular macromolecules in phenytoin and benzo[a]pyrene teratogenesis

A mouse embryo culture model was used to determine whether embryonic prostaglandin H synthase (PHS)-catalyzed bioactivation and resultant oxidative damage to embryonic protein and DNA may constitute a molecular mechanism mediating phenytoin and benzo[a]pyrene teratogenesis. Embryos were explanted from CD-1 mouse dams on gestational day 9.5 (vaginal plug = day 1) and incubated for either 4 h (biochemistry) or 24 h (embryotoxicity) at 37°C in medium containing either phenytoin (20 μg/ml, 80 μM), benzo[a]pyrene (10 μM), or their respective vehicles. As previously observed with phenytoin (Mol. Pharmacol.48:112–120, 1995), embryos incubated with benzo[a]pyrene showed decreases in anterior neuropore closure, turning, yolk sac diameter, and somite development (p < .05). Addition of the antioxidative enzyme superoxide dismutase (SOD) substantially enhanced embryonic SOD activity (p < .05) and completely inhibited benzo[a]pyrene embryotoxicity (p < .05). Substantial PHS was detected in day 9.5 embryos using SDS/PAGE, anti-PHS antibody, and alkaline phosphatase-conjugated donkey anti-goat IgG. Embryonic protein oxidation was detected by the reaction of 0.5 mM 2,4-dinitrophenylhydrazine with protein carbonyl groups. This method was first validated by using a known hydroxyl radical-generating system consisting of vanadyl sulfate and H2O2, with bovine serum albumin or embryonic protein as the target. Embryonic proteins were characterized by SDS/PAGE, anti-dinitrophenyl antisera, and peroxidase-labeled goat anti-donkey IgG. Using enhanced chemiluminescence, the number and content of oxidized protein bands detected between 25 and 200 kDa were substantially increased by both phenytoin and benzo[a]pyrene. Addition of the reducing agent dithiothreitol, or SOD or catalase, decreased protein oxidation in phenytoin-exposed embryos. Both phenytoin (Mol. Pharmacol.48:112–120, 1995) and benzo[a]pyrene enhanced embryonic DNA oxidation, determined by the formation of 8-hydroxy-2′-deoxyguanosine, as measured by high-performance liquid chromatography (HPLC) (p < .05). Phenytoin also enhanced the oxidation of embryonic glutathione (GSH) to its GSSG disulfide, as measured by HPLC (p < .05). These results provide direct evidence that, in the absence of maternal or placental processes, embryonic PHS-catalyzed bioactivation and reactive oxygen species-mediated oxidation of embryonic protein, thiols, and DNA may constitute a molecular mechanism mediating phenytoin and benzo[a]pyrene teratogenesis.Copyright © 1997 Elsevier Science Inc.

Limited changes of mouse maternal care after prenatal oxazepam: dissociation from pup-related stimulus perception

There is evidence that activity at the GABA/benzodiazepine receptor complex in specific brain areas might be enhanced during rodent motherhood. We tested the hypothesis that the manipulation of this neurochemical system by prenatal benzodiazepine exposure affects typical behavioral responses of lactating mouse dams. Outbred CD-1 mouse fetuses were administered either oxazepam (OX, 15 mg/kg) or vehicle twice a day on embryonic days 12-16 and fostered at birth to untreated dams. Female offspring were subsequently mated at the young adult stage. In a first experiment, the behavioural repertoire of the two groups of lactating females was scored (single 10-min session) from postpartum days 3 to 18. When compared with VEH dams, OX females showed a shorter duration of pup-sniffing at 7-10 days and enhanced crouching behaviour when pups had reached the age of 14-18 days. In addition, OX-treated dams used more cotton for nest construction than the controls. The two female groups were differentiated only in the presence of their offspring. In a second experiment aimed at investigating possible OX-induced changes in pup-stimulus perception, the same lactating females were challenged in sequence on postpartum day 8 with three different patterns of pup-related cues consisting of: three 8-day-old live male pups (LP), three same-age dead pups DP, or three dead pups accompanied by pre-recorded ultrasounds (DPU). In the absence of carry-over effects of prenatal dam treatment, LP stimuli elicited a higher frequency of sniffing and digging than the others, whereas the level of licking, and grooming was reduced. In conclusion, the present results indicate that the slight alteration in maternal care resulting from prenatal OX treatment can be dissociated from changes in pup-related stimulus perception.

Prenatal oxazepam affects maternal care of CD-1 mouse dams without altering the response to pup-related stimuli

Laboratorio di Fisiopatologia di Organo e di Sistema, Istituto Superiors di Sanitá, V. le Regina Elena 299, 00161 Rome, Italy.

Evaluation of the Developmental Toxicity of Ethylene Glycol Aerosol in the CD Rat and CD-1 Mouse by Whole-Body Exposure

Evaluation of the Developmental Toxicity of Ethylene Glycol Aerosol in the CD Rat and CD-1 Mouse by Whole-Body Exposure. Tyl, R. W., Ballantyne, B., Fisher, L. C., Fait, D. L., Savine, T. A., Dodd, D. E., Klonne, D. R., and Pritts, I. M. (1995). Fundam. Appl. Toxicol.24, 57-75.Ethylene glycol (EG) is a major industrial chemical, shown to be teratogenic at high doses by gavage in rodents. Since one route of industrial exposure is to the aerosol at high concentrations, timed-pregnant CD rats and CD-1 mice were exposed, whole-body, to a respirable aerosol of EG (mass median aerodynamic diameter, 2.3 μm) on Gestational Days (GD) 6 through 15 for 6 hr per day at target exposure concentrations of 0, 150, 1000, or 2500 mg/m3 (analytical concentrations of 0, 119 ± 13, 888 ± 149, and 2090 ± 244 mg/m3, respectively), with 25 plug-positive animals per species per group. Clinical observations and maternal body weights were documented throughout gestation for both species. Maternal food and water consumption was measured in rats only throughout gestation. At scheduled necropsy (GD 21 for rats, GD 18 for mice), maternal animals were evaluated for body weight, liver weight, kidney weight, gravid uterine weight, number of ovarian corpora lutea, and status of implantation sites, i.e., resorptions, dead fetuses, live fetuses. Fetuses were dissected from the uterus, counted, weighed, sexed, and examined for external, visceral, and skeletal malformations and variations. All rat dams survived to scheduled termination. Minimal maternal toxicity was indicated by a significant increase in absolute and relative liver weight at 2500 mg/m3. Food and water consumption, maternal body weights and weight gain, and maternal organ weights (other than liver) were unaffected by exposure. Gestational parameters were unaffected by exposure, including pre- and post-implantation loss, live fetuses/litter, sex ratio, and fetal body weight/litter. There was no treatment-related increase in the incidence of any individual malformation, in the incidence of pooled external, visceral, or skeletal malformations, or in the incidence of total malformations by fetus or by litter. There were no increases in the incidence of external or visceral variations. Evidence of fetotoxicity, expressed as reduced ossification in the humerus, the zygomatic arch, and the metatarsals and proximal phalanges of the hind-limb, was observed at 1000 and 2500 mg/m3. All mouse dams survived to scheduled termination. One dam at 2500 mg/m3 was carrying a totally resorbed litter at termination. Maternal toxicity was observed at 1000 and 2500 mg/m3, expressed as reduced body weight and weight gain during and after the exposure period, and reduced gravid uterine weight. (Maternal effects may have been due, in part or in whole, to effects on the conceptuses; see below.) Embryo/fetal toxicity was also observed at 1000 and 2500 mg/m3, expressed as an increase in nonviable implantations/litter, a reduction in viable implantations/litter, and reduced fetal body weights (male, female, and total)/litter. The incidences of individual and pooled external, visceral, and skeletal malformations were increased at 1000 and 2500 mg/m3, as was the incidence of total malformations. Malformations were found in the head (exencephaly), face (cleft palate, foreshortened and abnormal face, and abnormal facial bones), and skeleton (vertebral fusions, and fused, forked, and missing ribs). The incidences of many fetal variations were also increased at 1000 and 2500 mg/m3 (and only a few at 150 mg/m3). The no observable adverse effect level (NOAEL) for maternal toxicity in rats was 1000 mg/m3 (analytical concentration 888 mg/m3) and in mice was 150 mg/m3 (analytical concentration 119 mg/m3). The NOAEL for development toxicity in rats was 150 mg/m3 and in mice was at or below 150 mg/m3, under the conditions of this study. Analysis of EG on the fur of rats and mice during and after the exposure period at 2500 mg/m3 indicated that much of the EG "dose" (∼65-95%) was potentially derived from ingestion after grooming and/or percutaneous absorption. This contribution of the ingested and/or absorbed chemical could have been sufficient, per se, to produce the teratogenic effects observed in mice. The definitive evaluation of the possible role of inhaled EG aerosol alone in teratogenesis requires an exposure regimen which limits or precludes exposure by any other route.

Dietary α-linolenate/linoleate balance influences learning and memory in the senescence-accelerated mouse (SAM)

The senescence-accelerated mouse (SAMP8) is a model of age-related deterioration of memory and learning ability. A semipurified diet supplemented either with safflower oil (rich in linoleate) or with perilla oil (rich in α-linolenate) was fed to SAMP8 mouse dams and their pups. The offspring (males from several mothers) at 28 weeks of age were used for behavioral tests. The proportions of n-3 and n-6 highly unsaturated fatty acids in brain phospholipids reflected the n-3/n-6 balance of the diets. The learning and memory abilities of the two dietary groups were tested with the Sidman active avoidance task and the light and dark discrimination learning test. The group given perilla oil showed much greater improvement in learning in the Sidman active avoidance task than did the group fed safflower oil. In the light and dark discrimination learning test, the total number of responses to positive and negative stimuli was lower in those fed perilla oil, and their responses to positive stimuli were higher than to negative stimuli after the 10th session. Consequently, the correct response ratios of discrimination were higher in the perilla oil group than in the safflower oil group. In the open field test, the total amount of locomotor activity during 5 min was lower in the perilla oil group at 7 months of age than in the group fed safflower oil. Observations of the circadian rhythm of spontaneous motor activity (SMA) indicated that the mice in the safflower oil group tended to be more active than those in the perilla oil group in both light and dark periods, and SMA counts in the safflower group were significantly higher in the second half of the light period than in the first half. These results indicate that in the SAMP8 mouse, the dietary α-linolenate/linoleate balance affects the n-3/n-6 ratio of brain phospholipid acyl chains and this may influence learning, memory and behavior.

The developmental toxicity of boric acid in mice, rats, and rabbits.

Boric acid (BA) is a naturally occurring agent used in manufacturing processes and numerous consumer products. Because of the potential for both industrial and consumer exposure to boron-containing compounds, and the lack of developmental toxicity data, the National Toxicology Program evaluated the potential for boric acid to cause developmental toxicity in pregnant Swiss (CD-1) mice, Sprague-Dawley rats (n = 26-28/group), and New Zealand rabbits (n = 18-23/group). BA was provided in the feed to mice and rats at 0, 0.1, 0.2, or 0.4% throughout gestation to attain steady-state exposure as early as possible during development. Average doses (mg/kg/day) were 248, 452, or 1003 for mice, and 78, 163, or 330 in rats. A separate group of rats received 0.8% BA in the feed, or 539 mg/kg/day only on gestation days (gd) 6 to 15. Rabbits were given BA (0, 62.5, 125, or 250 mg/kg) by gavage administration on gd 6 to 19. Maternal body weight, food and/or water consumption and signs of toxicity were monitored at regular intervals. At termination, gd 17 (mice), 20 (rats), or 30 (rabbits), the uterus was examined to determine the number of resorptions, dead, or live fetuses. Fetuses were weighed and live fetuses were examined for external, visceral, and skeletal defects. Mouse dams exhibited mild renal lesions (> or = 248 mg/kg/day BA), increased water intake and relative kidney weight (1003 mg/kg/day BA), and decreased weight gain during treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Open-field thigmotaxis during various phases of the reproductive cycle.

Three experiments were conducted on female Swiss albino mice in order to determine whether open-field (OF) ambulation and thigmotaxis (wall-seeking) alter both as functions of reproductive phases such as estrus, mating, gestation, partus, lactation, weaning, as well as of presence, absence and OF location of a newborn pup. The results revealed increased thigmotaxis as an effect of estrus (p < 0.001). From mating to one month postpartum a growing tendency towards maternal occupation of centre OF partitions was observed. Maternal ambulation reached its peak two days before partus but dropped to its lowest level during the lactation period at which time the mice were the least wall-seeking. Ambulation was enhanced (p < 0.001) in the presence of a pup regardless of OF starting point and the pup's placement. However, when the mouse dam was initially placed together with the pup by the OF wall, she hardly penetrated centre units at all.

Consummatory behaviors and weight regulation in pregnant, lactating, and pregnant-lactating mice.

Pregnant Rockland-Swiss (R-S) albino mice consumed significantly more food and water and gained significantly more weight between gestation days 8-17 compared to virgin R-S females maintained in isolation for a comparable period. Postpartum (days 1-10) patterns of ingestion and weight change among thelectomized (nipple-deprived) mouse dams provided with young did not differ significantly from those of virgin animals without young. Sham- and nonoperated dams received suckling stimulation from young and consumed about 100% more food than thelectomized or virgin females (Experiment 1). Pregnancy concurrent with lactation does not increase further the hyperphagic response of female mice. Nipple presence is the principle regulator of postpartum hyperphagia in lactating and simultaneously pregnant-lactating mouse dams (Experiment 2).

Selective changes in mouse behavioral development after prenatal benzodiazepine exposure: A progress report

1. Animal studies of the effects of early exposure to CNS agents devoid of a major teratogenic potential must assess possible deviations from normal behavioral development in both a stage-specific and a behavior-specific fashion; several experiments on prenatal benzodiazepine (BDZ) exposure are reviewed, illustrating such an assessment strategy and discussing caveats on experimental designs and statistical analysis. 2. The offspring of mouse dams treated in late pregnancy with oxazepam (15 mg/kg p.o. twice daily on days 12–16) show a mild and reversible impairment in somatic and neurobehavioral development which is unlikely to be responsible for a series of other more specific changes. 3. The treatment produces a selective reduction of locomotor activity and amphetamine hyperactivity at the end of the second postnatal week, as well as a selective impairment of active avoidance at the young adult stage, in the absence of similar changes in scopolamine hyperactivity and passive avoidance. 4. The treatment also prevents the appearance at 28 days of morphine hyperactivity and of rebound hyperactivity after muscimol depression, without modifying the developmental profile of pain reactivity and of morphine and muscimol analgesia. 5. Young adult females previously exposed to oxazepam in utero show a marked enhancement of maternal aggression towards male intruders; mother-pup interactions are also modified, leading either to reduced or to exaggerated maternal care as a function of fostering procedures. 6. Overall, several effects of prenatal BDZ exposure appear to be amenable to modifications in monoaminergic system functions and/or to an accelerated development of GABAergic mechanisms; some of the changes in social and parental interactions, however, point to subtle modifications in the balance between different components of the fear-defensive repertoire, possibly due to an altered stimulus reactivity by mechanisms which are still poorly understood.

Developmental toxicity of boric acid in mice and rats

Boric acid (BORA), an ingredient of many cosmetics, pharmaceuticals, and pesticides, was tested for developmental toxicity in timed-pregnant Swiss mice and Sprague-Dawley rats ( n = 26–28/group). BORA (0, 0.1, 0.2, or 0.4% in feed) was provided throughout gestation to attain steady-state exposure as early as possible during prenatal development. Average doses (mg/kg/day) were 248, 452, or 1003 in mice, and 78, 163, or 330 in rats. To limit prenatal mortality, BORA (0.8% or 539 mg/kg/day) was provided to an additional group of rats on Gestational Days (GD) 6 to 15 only. On GD 17 (mice) or 20 (rats), fetuses were weighed and examined for malformations (external, visceral, skeletal). Mouse dams exhibited mild renal lesions (≥0.1%), increased water intake and relative kidney weight (0.4%), and decreased weight gain (0.4%) during treatment. There was a reduction of fetal body weight (≥0.2%) and an increased incidence of resorptions and malformed fetuses per litter (0.4%). Morphological changes included an increased incidence of short rib XIII (a malformation) and a decreased incidence of rudimentary or full rib(s) at lumbar I (an anatomical variation). Maternal rats exhibited increased liver and kidney weights at ≥0.2%, altered water and/or food intake at >0.2%, and decreased weight gain at >0.4%. Average fetal body weight/litter was reduced at all doses. Prenatal mortality was increased only at 0.8%. The incidence of fetal malformations was significantly increased at ≥0.2%. The most frequently observed malformations were enlarged lateral ventricles of the brain and agenesis or shortening of rib XIII. In rats, the no-observable-adverse-effect level (NOAEL) for maternal toxicity was 78 mg/kg (0.1%), while in mice the low dose of 248 mg/kg (0.1%) approached the maternal NOAEL with mild renal lesions in only 2 of 10 females. Embryo/fetal toxicity occurred in all groups of rats at ≥78 mg/kg (≥0.1%) while the NOAEL for developmental toxicity in mice was 248 mg/kg (0.1%). Thus developmental toxicity occurred below maternally toxic levels in rats as well as in the presence of maternal toxicity in mice and rats.

Passage of methoxychlor in milk and reproductive organs of nursing female mice; 1. Light and scanning electron microscopic observations

To determine whether the pesticide methoxychlor can be excreted in milk, lactating mouse dams received 14 daily intraperitoneal injections of either sesame oil, or 10.0 μg of 17- β estradiol, or 1.0, 2.0, or 5.0 mg of technical grade methoxychlor. At 15 days, suckling female pups were sacrificed and the effects of the chemicals in milk on the morphology of the immature reproductive tract were examined. The stimulatory changes in both the vagina and uterine horns indicate that the estradiol or methoxychlor doses were excreted in milk and remained biologically active in the suckling mice. Although the stimulatory changes from estradiol or methoxychlor were similar, the higher methoxychlor doses produced some cellular atypia in uterine horns. The possible consequences of early stimulatory influence of methoxychlor on adult reproductive organs are discussed in the text.

Interacting effects of oxazepam in late pregnancy and fostering procedure on mouse maternal behavior

The present study was designed to assess the proactive effects of late pregnancy benzodiazepine (BDZ) treatment on maternal behavior in the postpartum period, using cross-fostering procedures to control for the role of changes produced prenatally in the offspring. Outbred CD-1 mouse dams were treated with either oxazepam (OX, 15 mg/kg PO twice/day on pregnancy days 12-16) or vehicle (VEH). After parturition, entire litters were exchanged either within treatments (in-fostered groups, IF) or between treatments (cross-fostered groups, CF), while additional litters were left undisturbed (un-fostered groups, UF). The behavior of lactating dams was observed in their home cages at 4, 8, and 12 days postpartum. Maternal responses, particularly nursing, were reduced in the OX-UF and OX-CF conditions and either normal or enhanced in the OX-IF condition. Correspondingly, locomotor/exploratory activity was markedly enhanced in the former conditions and close to the control level in the latter condition. In sum, the fostering variable appeared to determine whether pups raised by dams treated previously with BDZ receive either insufficient or exaggerated maternal care. This points to the need for a better understanding of mother/pup interactions in studies aimed at characterizing drug and toxicant effects on offspring development.

Cadmium-induced bone loss: Increased susceptibility in females

An overview is presented of studies on effects of Cd on (1) female mice during pregnancy and lactation and after ovariectomy and (2) bone organ/cell culture systems. The gastrointestinal absorption of Cd increased two- to threefold in mouse dams during pregnancy and lactation, with both the kidneys and duodenum of the dam showing striking increases in Cd deposition. Dietary Cd at 5 or 50 μg g−1 caused a dose-dependent decrease in femur Ca content in multiparous mouse dams but not in nonpregnant controls. In addition, dietary Cd at 50 μg g−1 significantly increased the loss of bone mineral that occurs normally in mice after removal of the ovaries. In cultures of fetal rat limb bones prelabeled with 45Ca, Cd at 10 nM (1 ng g−1) caused a release of 70% of the 45Ca, similar to the release caused by 10 nM parathyroid hormone. This level of Cd also caused a fivefold increase in the number of multinucleated osteoclast-like cells formed during invitro incubation of progenitor-enriched mononuclear bone marrow cells. These results support the view that Cd exposure contributed to the pathogenesis of Itai-Itai disease among multiparous, postmenopausal women in Japan and provide evidence that Cd may act directly on bone.

Onset of puberty in CD-1 mouse pups exposed prenatally through weaning to endophyte-infected tall fescue seed

This study was undertaken to investigate the effects of feeding endophyte - infected ( Acremonium coenophialum ) tall fescue seed to CD-1 mouse dams (P 1) during gestation and lactation, and on the subsequent growth and sexual maturity (onset of puberty) of their male and female offspring (F 1). Forty-eight 21 d old pups (24 male and 24 female F 1 mice) were weaned from dams fed one of two diets containing 50% rodent chow (w/w) and 50% KY-31 tall fescue ( Festuca arundinacea ) seed. The seed in Diet 1 was noninfected, while the seed in Diet 2 was 80% endophyte-infected. At weaning (21 d), the F 1 pups were fed rodent chow, ad libitum throughout the remaining experimental period. At 24 d, they were paired with sexually mature non-treated virgin CD-1 mice (fed 100% rodent chow) for one parturition cycle. Male F 1 mice were sacrificed at 84 d to determine testicular development. The age at the birth of the first litter for Diet 2 F 1 male (76.8 ± 2.2 d) and female (58.4 ± 2.1 d) was significantly greater (P<0.05) than the age at parturition for Diet 1 male and female F 1 test mice (64.1 ± 1.8 and 51.9 ± 1.2 d, respectively). At parturition, the female F 1 mice showed no significant differences (P>0.05) in either mean parturition weight or number of F 2 pups born per litter. However, total F 2 litter wight (11.38 ± 1.14 g) and mean weight per F 2 pup (1.40 ± 0.04 g) for Diet 2 female F 1 mice litters were lower (P<0.05) when compared with Diet 1 females (14.53 ± 0.57 g and 1.66 ± 0.02 g, respectively). No significant differences were observed between the two male F 1 treatment groups, for total F 2 litter weight or the number of pups born per F 2 litter. Although Diet 2 F 1 males weighed significantly less (P<0.05) at weaning and at pairing, final body weights at sacrifice (84 d) were not different (P>0.05) from the Diet 1 males.

Litter Gender Composition, Food Availability, and Maternal Defence of the Young in House Mice (Mus Domesticus)

AbstractLitter gender composition (LGC) of 33 litters of outbred Swiss albino mice was manipulated at birth to obtain 100%-male litters (MM), 50%-male litters (MF) and 100%-female litters (FF). Litter size was 10 in all cases. Litter defence by their respective dams (5-min exposure to an unfamiliar adult male) was scored on postpartum day 7. The influence of litter gender composition on the female's litter defence was tested, with identical procedure, under conditions of restricted feeding. In this case, dams were fed from postpartum days 1-7 with 80% of their normal daily requirement. Under both ad lib. and restricted feeding body weight of mothers and their litters was assessed daily. Under ad lib. feeding, dams rearing MM litters showed higher scores of Total Attacking Time than both MF and FF dams and higher frequency of Attacks and Tail Rattling episodes than MF dams. Food-restricted females showed a sharp decline in body weight and their litters a slower gain in weight than control animals. LGC did not affect mother and litter weight changes in both conditions but MM females tended to cannibalize more pups on days 6-7 than MF and FF females. Food-restricted MM and MF dams showed, respectively, lower Total Attacking Time and higher number of Attacks and Tail Rattling episodes than their own Control groups. These results show that, under ad lib. feeding, LGC affects significantly female mouse litter defence. Some possible underlying mechanisms are discussed. These results support only partly the TRIVERS-WILLARD'S hypothesis (1973) about sex-biased investment in the offspring since, even though mouse dams under ad lib. feeding defended more vigorously all-male litters, as predicted by the model, among food-restricted animals no clear shift toward a prevalent defence of female-skewed litters appeared.