Developmental Landmarks Research Articles

Developmental neurotoxicity study of styrene by inhalation in Crl‐CD rats

This study was conducted to assess potential adverse functional and/or morphological effects of styrene on the neurological system in the F2 offspring following F0 and F1 generation whole-body inhalation exposures. Four groups of male and female Crl:CD (SD)IGS BR rats (25/sex/group) were exposed to 0, 50, 150, and 500 ppm styrene for 6 hr daily for at least 70 consecutive days prior to mating for the F0 and F1 generations. Inhalation exposure continued for the F0 and F1 females throughout mating and through gestation day 20. On lactation days 1 through 4, the F0 and F1 females received styrene in virgin olive oil via oral gavage at dose levels of 66, 117, and 300 mg/kg/day (divided into three equal doses, approximately 2 hr apart). Inhalation exposure of the F0 and F1 females was re-initiated on lactation day 5 and continued through weaning of the F1 or F2 pups on postnatal day (PND) 21. Developmental landmarks were assessed in F1 and F2 offspring. The neurological development of randomly selected pups from the F2 generation was assessed by functional observational battery, locomotor activity, acoustic startle response, learning and memory evaluations, brain weights and dimension measurements, and brain morphometric and histologic evaluation. Styrene exposure did not affect survival or the clinical condition of the animals. As expected from previous studies, slight body weight and histopathologic effects on the nasal olfactory epithelium were found in F0 and F1 rats exposed to 500 ppm and, to a lesser extent, 150 ppm. There were no indications of adverse effects on reproductive performance in either the F0 or F1 generation. There were exposure-related reductions in mean body weights of the F1 and F2 offspring from the mid and high-exposure groups and an overall pattern of slightly delayed development evident in the F2 offspring only from the 500-ppm group. This developmental delay included reduced body weight (which continued through day 70) and slightly delayed acquisition of some physical landmarks of development. Styrene exposure of the F0 and F1 animals had no effect on survival, the clinical condition or necropsy findings of the F2 animals. Functional observational battery evaluations conducted for all F1 dams during the gestation and lactation periods and for the F2 offspring were unaffected by styrene exposure. Swimming ability as determined by straight channel escape times measured on PND 24 were increased, and reduced grip strength values were evident for both sexes on PND 45 and 60 in the 500-ppm group compared to controls. There were no other parental exposure-related findings in the F2 pre-weaning and post-weaning functional observational battery assessments, the PND 20 and PND 60 auditory startle habituation parameters, in endpoints of learning and memory performance (escape times and errors) in the Biel water maze task at either testing age, or in activity levels measured on PND 61 in the 500-ppm group. Taken together, the exposure-related developmental and neuromotor changes identified in F2 pups from dams exposed to 500 ppm occurred in endpoints known to be both age- and weight-sensitive parameters, and were observed in the absence of any other remarkable indicators of neurobehavioral toxicity. Based on the results of this study, an exposure level of 50 ppm was considered to be the NOAEL for growth of F2 offspring; an exposure level of 500 ppm was considered to be the NOAEL for F2 developmental neurotoxicity.

A comparative study of embryonic development of some bird species with different patterns of postnatal growth

Some studies show that birds with high postnatal growth rates (e.g. altricial species) are characterized by a rapid early development of “supply” organs, such as digestive organs. Birds with low postnatal growth rates (e.g. precocial species) exhibit a slower early development of these organs and a more rapid early development of other “demand” organs, such as brain, muscles, skeleton and feathers. To test whether these differences can be traced back to early embryonic development and whether they can be associated with changes in developmental timing, i.e. heterochrony, we compared embryos of the precocial quail and the altricial fieldfare, two bird species with low and high postnatal growth rates, respectively. We used classical staging techniques that use developmental landmarks to categorize embryonic maturity as well as morphological measurements. These techniques were combined with immune detection of muscle specific proteins in the somites. Our data showed that the anlagen of the head, brain and eyes develop earlier in the quail than in the fieldfare in contrast to the gut which develops earlier in the fieldfare than in the quail. Our data also showed that the quail and the fieldfare displayed different rates of myotome formation in the somites which contribute to muscle formation in the limbs and thorax. We believe these observations are connected with important differences in neonatal characteristics, such as the size of the brain, eyes, organs for locomotion and digestion. This leads us to the conclusion that selection for late ontogenetic characteristics can alter early embryonic development and that growth rate is of fundamental importance for the patterning of avian embryonic development. It also appears that this comparative system offers excellent opportunities to test hypotheses about heterochrony.

Preliminary evaluation of an in utero-lactation assay using 6-n-propyl-2-thiouracil

In this preliminary study, the potential of an in utero-lactation assay to detect thyroid effectors was evaluated by treating three dams/group with 6-n-propyl-2-thiouracil (PTU), a known thyroid antagonist, by oral gavage at doses of 0, 0.0032, 0.016, 0.08 and 0.4 mg/kg/day during fetal organogenesis and lactation. Hearing disturbances and an elevated relative thyroid weight were observed in offspring of both sexes in the 0.4 mg/kg/day group. The Biel-type water T-maze test showed an increase in the number of errors made by females in the 0.4 mg/kg/day group. Histopathologically, flattening of follicular epithelium, a decrease in resorptive colloid droplets, degeneration of follicular epithelium, and hyperplasia of follicular epithelium were observed in males belonging to the 0.4 mg/kg/day group. Histopathological abnormalities were also observed in some offspring belonging to the 0.08 mg/kg/day group. In the dams, hypertrophy of the follicular epithelium of the thyroid was observed in the 0.4 mg/kg/day group. Although we could not explain the mechanism for the difference in the effects seen in the offspring and the dams, the effect of PTU in utero through lactational exposure is apparently different from that resulting from exposure in homeostatically mature rats. Most reports studying PTU have involved administration in water or in food, and reports on the oral gavage of PTU during the fetal organogenesis and lactation period are very rare. This assumes that dosages >0.4 mg/kg/day would also produce clear anti-thyroid effects by oral gavage and, possibly, emphasizes that dosages <0.4 mg/kg/day did not have a noticeable effect. Based on the present results, a study to determine the reproducibility of the data in a much larger number of dams will be performed to confirm the findings in the present study, and to evaluate other endpoints, such as hormonal evaluation of dams and their offspring, sexual developmental landmarks, and fertility of the offspring.

Asymmetric Auxin Response Precedes Asymmetric Growth and Differentiation of asymmetric leaf1 and asymmetric leaf2 Arabidopsis Leaves

We have analyzed the development of leaf shape and vascular pattern in leaves mutant for ASYMMETRIC LEAVES1 (AS1) or AS2 and compared the timing of developmental landmarks to cellular response to auxin, as measured by expression of the DR5:beta-glucuronidase (GUS) transgene and to cell division, as measured by expression of the cycB1:GUS transgene. We found that the earliest visible defect in both as1 and as2 first leaves is the asymmetric placement of auxin response at the distal leaf tip. This precedes visible changes in leaf morphology, asymmetric placement of the distal margin gap, formation of margin gaps along the leaf border, asymmetric distribution of marginal auxin, and asymmetry in cell division patterns. Moreover, treatment of developing leaves with either exogenous auxin or an auxin transport inhibitor eliminates asymmetric auxin response and subsequent asymmetric leaf development. We propose that the initial asymmetric placement of auxin at the leaf tip gives rise to later asymmetries in the internal auxin sources, which subsequently result in asymmetrical cell differentiation and division patterns.

Short stature and functional impairment: a systematic review.

To review the available evidence on the association between primary short stature and intellectual and physical dysfunction among children. Systematic searches were performed through October 2001 of English-language studies of children with short stature and functional limitations. Included studies evaluated children with isolated short stature, constitutional growth delay, growth hormone deficiency, or multiple hormone deficiency. Evaluated outcomes included intelligence, academic achievement, visual-motor skills, psychomotor development, and behavior problems. Eleven studies evaluated academic achievement, and 22 evaluated intelligence. No substantial deviation from normal was seen among short children, but many studies found that children with short stature had significantly lower intelligence and academic achievement scores than controls. Three studies found significant visual-motor skill reduction among short children. One study of psychomotor development found a delay in meeting early developmental landmarks among children with Russell-Silver syndrome. Five studies evaluating teacher-rated behavior found that short children had no more behavior problems than controls. While, on average, children with short stature score lower than their peers on functional tests, few short children scored outside the normal range. Furthermore, there is no evidence to explain the cause of any deficits, and limited data suggest that treatment of short stature does not improve children's functional status. Nevertheless, treatment may be warranted in children with severe short stature to alleviate restrictions on activities of daily living. Further research focusing on physical limitations due to short stature is needed to address these issues.

CatSper1 required for evoked Ca2+ entry and control of flagellar function in sperm.

CatSper family proteins are putative ion channels expressed exclusively in membranes of the sperm flagellum and required for male fertility. Here, we show that mouse CatSper1 is essential for depolarization-evoked Ca2+ entry and for hyperactivated movement, a key flagellar function. CatSper1 is not needed for other developmental landmarks, including regional distributions of CaV1.2, CaV2.2, and CaV2.3 ion channel proteins, the cAMP-mediated activation of motility by HCO3-, and the protein phosphorylation cascade of sperm capacitation. We propose that CatSper1 functions as a voltage-gated Ca2+ channel that controls Ca2+ entry to mediate the hyperactivated motility needed late in the preparation of sperm for fertilization.

Peri- and postnatal developmental toxicity of the fluoroquinolone antibacterial DW-116 in rats

DW-116 is a fluoroquinolone antibacterial developed by Dong-Wha Pharmaceutical Industry Co. The aim of this study is to determine the potential adverse effects of this chemical on pregnancy, delivery and lactation of dams and on peri- and postnatal development of F1 offspring. The test chemical was orally administered to pregnant rats from day 16 of pregnancy, through parturition and throughout the period of lactation up to weaning (postnatal day 21) at dose levels of 0, 10, 50, or 250 mg/kg/day. The progeny were examined at birth and subsequently to weaning. Mortality, body weight change, physical signs of postnatal development (pinna detachment, incisor eruption, fur development, eye opening, testis descent and vaginal opening) and behavioral function (righting reflex, negative geotaxis, grip-strength, pupillary reflex, acoustic startle response, rotating rod test, open field test and water-filled T-maze test) were evaluated. When the exposed offspring reached maturity (11 weeks old) their reproductive capacity was assessed. Maternal toxicity was observed only in the highest dose group and was limited to decreased food consumption during the late stage of pregnancy. However, this change was not observed during the lactation period. There were no adverse effects on mortality, clinical signs, body weight, necropsy findings, organ weight of dams in any treatment group. No adverse effects on the offspring were seen with the low and middle doses tested, but the highest dose increased postnatal mortality. The number of stillborn was also increased at the highest dose but the difference was not statistically significant. Meanwhile, no treatment-related effects were observed in clinical sign, developmental and behavioral landmarks and necropsy findings at any dose levels tested. There were no treatment-related effects on the mating of the F1 generation and resulting F2 offspring. The results of this study indicate that the peri- and postnatal administration of DW-116 to female rats results in an increase in postnatal mortality at a minimally maternotoxic dose, i.e., 250 mg/kg/day. Under the experimental conditions, the no-observed-adverse-effect level for peri- and postnatal developmental toxicity was considered to be 50 mg/kg/day.

Meiotic cytology and chromosome behaviour in wild-type Arabidopsis thaliana.

This article reviews the historical development of cytology and cytogenetics in Arabidopsis, and summarizes recent developments in molecular cytogenetics, with special emphasis on meiotic studies. Despite the small genome and small chromosomes of Arabidopsis, considerable progress has been made in developing appropriate cytogenetical techniques for chromosome analysis. Fluorescence in situ hybridization (FISH) applied to extended meiotic pachytene chromosomes has resulted in a standardized karyotype (idiogram) for the species that has also been aligned with the genetical map. A better understanding of floral and meiotic development has been achieved by combining cytological studies, based on both sectioning and spreading techniques, with morphometric data and developmental landmarks. The meiotic interphase, preceding prophase I, has been investigated by marking the nuclei undergoing DNA replication with BrdU. This allowed the subclasses of meiotic interphase to be distinguished and also provided a means to time the duration of meiosis and its constituent phases. The FISH technique has been used to analyse in detail the meiotic organization of telomeres and centromeric regions. The results indicate that centromere regions do not play an active role in chromosome pairing and synapsis; however, telomeres pair homologously in advance of general chromosome synapsis. The FISH technique is currently being applied to analysing the pairing and synapsis of interstitial chromosome regions through interphase and prophase I. FISH probes also allow the five bivalents of Arabidopsis to be identified at metaphase I and this has permitted an analysis of chiasma frequencies in individual bivalents, both in wild-type Arabidopsis and in two meiotic mutants.

Estado psiconeurológico de los recién nacidos afectados de cardiopatía congénita antes de Su intervención

This study was conducted to evaluate, from a psychological and neurological point of view, the situation of newborn infants (NI) suffering from congenital heart disease before they are treated surgically. At the same time, we aimed to compare this group of patients with another group of children who were considered to be healthy. Patients psychological development was evaluated using developmental landmarks from the Observational Scale of Development (OSD), which provides a percentage of elements acquired in different areas. Behaviour was evaluated by the observational recording of particular patterns of behaviour. The neurological study was based on a detailed neonatal examination, performed by people from the Child Neurology Section at our hospital, and which took into account the different behaviours displayed by the NI: reactive, grasping, communicative and affective. Findings show significant differences both in the psychological and neurological variables studied. They show how, generally speaking, healthy infants score higher in the areas of development that were evaluated than children suffering from heart disease. Likewise, lower average scores were observed in heart disease patients who require an early intervention, as compared with those who will be submitted to surgery later on. From the neurological point of view, a number of significant differences were found in their muscular activity. This analysis, a groundbreaker in the study of infants suffering from heart disease before their surgical intervention, shows how newborn infants who have been submitted to surgery in the neonatal period present a significant degree of hypotonia, a certain frailness and retardation in their motor development.

Neurobehavioral development of two mouse lines commonly used in transgenic studies

The present study was aimed at establishing the differences in the neurodevelopmental profile between two F2 lines derived from two F1 hybrid mouse strains (129×C57BL/6 and C57BL/6×SJL). The choice of the given strains was based on the frequent use of these mice in transgenic research. For the neurodevelopment phenotyping, we employed a test battery consisting of 23 somatometric, sensorial and motor tests. Significant variations between the strains were established in different functional domains. Some specific delays in the appearance of developmental landmarks were observed in F2 mice derived from crosses of F1 C57BL/6×129, whereas they acquired early developmental functions, such as the righting reflex, sooner than C57BL/6×SJL-derived mice. C57BL/6×129 F2 offspring were spontaneously hypoactive, and their poorer motor performance was confirmed by low performance in the negative geotaxis test. However, there were no differences in the general psychomotor development as shown by the good performance in the homing test in both F2 lines. Both strains were susceptible to the handling procedures used, presenting a similar alteration in the response observed in the homing test as compared to nonhandled control mice. In conclusion, our work highlights the importance of the genetic background for transgenesis experiments and also the need for well-established testing protocols to obtain sufficient information at the first stage of behavioral screening of genetically modified mice.

Effects of prenatal exposure to manganese on postnatal development and behavior in mice:: Influence of maternal restraint

Manganese (Mn) is an essential trace element whose deficiency and excess have been reported to cause central nervous system (CNS) disturbances. On the other hand, during pregnancy, maternal stress has been shown to enhance the developmental toxicity of a number of metals. In this study, the maternal toxicity and developmental effects of a concurrent exposure to Mn and restraint stress were evaluated in mice. Pregnant animals were divided into three groups and received subcutaneous injections of manganese chloride tetrahydrate (MnCl 2·4H 2O) at 0, 1 and 2 mg/kg/day on Gestation Days 6–18. Each group was divided into two subgroups. Mice in one subgroup were subjected to restraint for 2 h/day on Days 6–18 of gestation. Pregnant mice were allowed to deliver, and pups were evaluated for physical and neuromotor maturation. Subsequently, adult mice were also evaluated for activity and learning. A significant increase in perinatal mortality was observed at 2 mg/kg/day Mn. A delay in some developmental landmarks (eye opening, testes descent) due to Mn exposure (2 mg/kg/day) was also seen in both restrained and unrestrained animals. No differences in motor resistance and coordination, or in learning at the passive avoidance test, were noted in adult mice. At the current Mn doses, combined exposure to Mn and stress during the prenatal period did not produce long-lasting effects on adult mice.

Endocrine active agents: implications of adverse and non-adverse changes.

The US Environmental Protection Agency (EPA) is currently in the process of developing screening and testing methodologies for the assessment of agents that may possess endocrine-like activity--the so-called endocrine disruptors. Moreover, the EPA has signaled its intention of placing information arising from such studies on the worldwide web. This has created significant interest in how such information may be used in risk assessment and by policymakers and the public in the potential regulation or deselection of specific chemical agents. The construction of lists of endocrine disruptors, although fulfilling the requirements of some parties, is really of little use when the nature of the response, the dose level employed, and the lifestage of the test species used are not given. Thus, we have already seen positive in vitro information available on the interaction with a receptor being used as a key indicator when the results of large, high quality in vivo studies showing no adverse changes have been ignored. Clearly a number of in vitro systems are available to ascertain chemical interaction with specific (mainly steroid) hormone receptors including a number of reporter gene assays. These assays only provide indicators of potential problems and should not be, in isolation, indicators of toxicity. Likewise, short-term in vivo screens such as the uterotrophic and Hershberger studies are frequently conducted in castrated animals and thus indicate the potential for a pharmacological response in vivo rather than an adverse effect. A number of new end points have been added to standard rodent testing protocols in the belief of providing more sensitivity to detect endocrine related changes. These include the measurement of anogenital distance (AGD), developmental landmarks [vaginal opening (VO), preputial separation (PPS)], and in some studies the counting of nipples and areolae on males. AGD, VO, and PPS are all affected by the size of the pup in which they are measured and should always be compared using bodyweight as a covariate. The historical control database for such changes is gradually growing, albeit that if pups are not individually identified it becomes problematic to associate any change with a specific malformation or to assess whether a delay or advance in, for example, developmental landmarks is biologically significant. Agents that significantly reduce AGD in males (it is an androgen-dependent variable) frequently have other more adverse changes associated with this end point (eg, reproductive tract malformations), but a 2 to 3% change in AGD although measurable is unlikely to be biologically of importance and in isolation would not necessarily be considered adverse. Retention of thoracic nipples in male rat pups is also an indicator of impaired androgen status. Recent studies have also shown that this retention for some endocrine active chemicals is permanent. Thus, the presence of a permanent structural change that is rarely found in adult control animals could be considered a malformation and therefore a developmental adverse effect on which risk assessment decisions could be made. The advent of multigeneration reproduction studies as the definitive studies for the assessment of the dose-response relationships and risk assessment for endocrine disruptors has shown that current testing protocols may be inadequate to reliably detect the adverse effects of concern as only 1 adult/sex/litter is examined. A number of the effects on reproductive development although, due to an in utero exposure, will not be manifest until after puberty or at adulthood. The use of only a limited number of animals to examine such changes, particularly for weaker acting materials indicates that some agents may have been examined in well-conducted, modern protocols but have insufficient power to detect low incidence phenomena (eg, a 5% incidence of malformations).

Brain maldevelopment and neurobehavioural deviations in adult rats treated neonatally with indomethacin

The risk of neurodevelopmental toxicity was studied in indomethacin (INDO), an inhibitor of prostaglandin synthesis, which is used in at-risk neonates to prevent the consequences of brain intraventricular haemorrhage or to accelerate the closure of patent ductus arteriosus. Model experiments were carried out in rats of the Wistar strain and Konárovice breed. The drug dose (2 mg/kg, s.c.) was applied to rat pups either once or twice in the following way: (1) on postnatal day 4 (PD:4) or postnatal days 4 and 5 (PD:4–5), i.e. model of brain ontogenic developmental stage in human fetus/preterm neonate of 7-month-gestational age; (2) on postnatal day 9 (PD:9) or postnatal days 9–10 (PD:9–10), i.e. model of brain ontogenic stage in full-term human newborn. The rats were followed up during development (body weight, maturation) until adulthood (age 3–9 months) using tests of behaviour (open field, social memory), nociception (tail flick, plantar test), reproduction and brain neurobiological analysis. The results were evaluated by comparison of litter-mates: treated vs control. No differences between INDO and controls were found in developmental landmarks, adult social memory or reproduction. The pattern of behavioural and neuroendocrine deviations in adult animals was dependent on the ontogenic stage exposed to drug insult. INDO rats of the groups PD:4 and PD:4–5 revealed depression of open field motor activity and emotional reactivity, and higher pituitary weight with lower TSH content. On the other hand, deviations in adult INDO groups PD:9 and PD:9–10 were characterized by pain hypersensitivity, lower pituitary weight with unchanged TSH content and deficit of monoamine transmission in the hypothalamus.

Developmental landmarks in offspring of rats exposed singly and in combination to Aroclor 1016 and levothyroxine.

Developmental landmarks in offspring of rats exposed singly and in combination to Aroclor 1016 and levothyroxine.

Developmental Landmarks in Offspring of Rats Exposed Singly and in Combination to Aroclor 1016 and Levothyroxine

Developmental Landmarks in Offspring of Rats Exposed Singly and in Combination to Aroclor 1016 and Levothyroxine

Growth and development in rats given recombinant human epidermal growth factor(1-48) as neonates.

To assess effects of supraphysiologic doses of human recombinant epidermal growth factor(1-48) (rhEGF(1-48)) on neonatal rats, 10 litters of Wistar rats/treatment group were given 0 (formulated vehicle), 10, 100, or 1000 microg/kg daily by subcutaneous injection on postnatal days (PND) 1 through 6. Clinical signs, body weight, acquisition of developmental landmarks and reflexes, and behavior were monitored during treatment and for 5 weeks thereafter (to PND 42). A subset of animals was euthanized weekly from PND 7-28 and necropsied. Selected tissues were examined microscopically. Body weight gain at 1000 microg/kg during treatment was significantly less than control. Precocious incisor eruption, eye opening, vaginal opening, and preputial separation occurred at 100 and/or 1000 microg/kg. Acquisition of reflexes (negative geotaxis, wire maneuver, acoustic startle reflex, and visual placing) was delayed at 1000 microg/kg. Acquisition of adult locomotion was also delayed at 1000 microg/kg. These effects were transient, as locomotor activity at PND 28 and 42 did not differ from control. Effects on acoustic-startle responding persisted in females to final assessment on PND 42. Habituation to repeated acoustic stimuli was impaired, as well as response inhibition following a prepulse acoustic stimulus. rhEGF(1-48) induced structural changes in the skin, retina, kidney, oral and nasal mucosa, lung, and liver. Many of these changes were consistent with the expected mitogenic activity of rhEGF(1-48) and were transient in nature, as severity and incidence diminished with time. An exception was changes observed in the retina at 1000 microg/kg (rosettes/folds and focal defects in the outer nuclear/photoreceptor layers) that were still present 3 weeks after termination of treatment. Acceleration of developmental landmarks; suppression of reflexes, behavior, and somatic growth; and mitogenic responses in epidermal tissues have been reported in rodents treated with epidermal growth factor (EGF) derived from various mammalian species. These results demonstrate that a 48-amino acid fragment of human EGF produced by recombinant technology also induces such effects.

Improved data processing for optical imaging of developing neuronal connectivity in the neonatal mouse barrel cortex

Optical recording methods using voltage-sensitive dyes have proven valuable for the analysis of neuronal networks both in vivo and in vitro. This technique detects membrane potential changes as changes in the absorption or fluorescence of voltage-sensitive dyes incorporated into the cellular plasma membranes. The reliability of the optical recording technique is dependent on the dye-related response being fast enough to follow the electrical activity and of the response being more or less proportional to the amplitude of the membrane potential change. A high spatial resolution can be achieved using an appropriate imaging system and a dye with a response of sufficiently high signal-to-noise ratio. Thus, it is now anticipated that this method will be able to shed more light on the spatio-temporal information processing of neocortical circuitry. While the FUJIX HR Deltaron 1700 optical imaging system offers a reasonably high time (0.6 ms) and space-resolution (7 μm at 10× magnification), one drawback of this system, however, is its relatively poor data processing capabilities. We have therefore developed a protocol to improve the signal-to-noise ratio by modifying the calculation algorithm of the optical data. Consequently, we characterized optical responses in thalamocortical slices to find developmental landmarks of thalamocortical and intracortical connectivity in the neonatal mouse barrel cortex. Successful application of this method has been published on the analysis of thalamocortical glutamatergic connectivity [8].

Two-Generation Reproduction Study and Immunotoxicity Screen in Rats Dosed with Phenol via the Drinking Water

This study evaluated the potential reproductive toxicity of phenol in a rat two-generation reproduction study, which included additional study endpoints, such as sperm count and motility, developmental landmarks, histological evaluation of suspect target organs (liver, kidneys, spleen, and thymus), weanling reproductive organ weights, and an immunotoxicity screening plaque assay. Phenol was administered to 30 Sprague-Dawley rats/sex/group in the drinking water at concentrations of 0, 200, 1000, or 5000 ppm. Parental (P1) animals were treated for 10 weeks prior to mating, during mating, gestation, lactation, and until sacrifice. The F1 generation (P1 offspring) was treated using a similar regimen, while the F2 generation was not treated. After mating, 10 P1 males/group were evaluated using standard clinical pathology parameters and an immunotoxicity screening plaque assay. Significant reductions in water and food consumption were observed in the 5000-ppm group in both generations; corollary reductions in body weight/body weight gain were also observed. Mating performance and fertility in both generations were similar to controls, and no adverse effects on vaginal cytology or male reproductive function were observed. Vaginal opening and preputial separation were delayed in the 5000-ppm group, and were considered to be secondary to the reduction in F1 body weight. Litter survival of both generations was reduced in the 5000-ppm group. Absolute uterus and prostate weights were decreased in the F1 generation at all dose levels; however, no underlying pathology was observed and there was no functional deficit in reproductive performance. Therefore, these findings were not considered to be adverse. No evidence of immunotoxicity was noted in the 5000-ppm group. The effects noted at the high concentration were presumed to be associated with flavor aversion to phenol in the drinking water. Based on a comprehensive examination of all parameters, the no-observable-adverse-effect level (NOAEL) for reproductive toxicity of phenol administered in drinking water to rats is 1000 ppm. The corresponding daily intake of phenol for an adult rat at the NOAEL of 1000 ppm is equivalent to about 70 mg/kg/day for males and 93 mg/kg/day for females.

Two-generation reproduction studies in Rats fed di-isodecyl phthalate

Di-isodecyl phthalate (DIDP) is a commercial plasticizer with low toxicity in many animal studies. The effects of dietary DIDP administration on fertility and developmental parameters were assessed in Sprague-Dawley rats utilizing two generation reproductive toxicity studies generally consistent with current regulatory guidelines. Dietary levels ranged from 0.02 to 0.8% (or approximately 15 to 600 mg/kg/day). In the reproductive studies, there were no effects on fertility, but there were decreases in adult body weight along with corresponding increases in liver and kidney weights and histopathologic changes indicative of peroxisomal proliferation. There were no effects on live birth index, but reduced offspring survival was observed at postnatal days 1 to 4. This reduced survival was more pronounced in the F 2 generation in which statistical significance was achieved at levels of 0.2% DIDP and greater. There were also transient decreases in offspring body weights prior to weaning, corresponding to rapid offspring growth, and high levels of food consumption. There were no notable alterations in developmental landmarks. Overall, these studies provided experimentally defined No-Observed-Adverse-Effect Levels (NOAELs) of 0.06% (approximately 50 mg/kg/day) for F 2 offspring survival and 0.8% (approximately 600 mg/kg/day) for fertility, other measures of reproductive function, and developmental landmarks. Statistical evaluation of the data from both studies identified 108 mg/kg/day with a 95% lower bound value of 86 mg/kg/day as a theoretical NOAEL for reduced F 2 offspring survival.

Effects of Prenatal Styrene Exposure on Postnatal Development and Brain Serotonin and Catecholamine Levels in Rats

Maternal reproductive effects in Wistar rats exposed to 0, 50, or 300 ppm styrene for 6 h/day during gestational days 6 to 20 were evaluated. Their offspring were observed postnatally for neurochemical changes, growth, and physical landmarks of development. Mothers exposed to styrene were compared with pair-fed and ad-lib-fed controls in order to adjust nutrient conditions. Prolongation of the gestational period, food intake, and the number of neonatal deaths or stillbirths in 300-ppm-exposed dams showed evidence of styrene-related effects. Other reproductive parameters, such as litter size, birth weight, and sex ratio, were found to exhibit no effects within the variation range studied. A neurochemical effect was observed in that the 5-HT and HVA concentrations in cerebrum were significantly decreased. Incisor eruption (mandible), eye opening, and the air-righting reflex were delayed in rat pups born to dams receiving 300 ppm styrene exposure compared with the pair-fed and ad lib control groups. Pups born to dams exposed to 50 ppm styrene also had a significantly delayed air-righting reflex compared with ad lib controls. These results suggest that the offspring were susceptible to the effects of styrene on a few developmental landmarks even when nutritional effects were controlled.