Relative cerebellar weight: a potential indicator of developmental neurotoxicity

A new assay system for evaluation of developmental immunotoxicity of chemical compounds using respiratory syncytial virus infection to offspring mice

We evaluated the effect of 6-propyl-2-thiouracil (PTU), an anti-thyroid agent, on developmental immunity using respiratory syncytial virus (RSV) infection to offspring mice as a new risk assessment for brominated flame retardants (BFRs), because some BFRs are suspected of affecting the thyroid system. Pregnant mice were exposed to PTU in drinking water from gestation day 10 to weaning on postnatal day 21. Their offspring mice were infected intranasally with RSV. Exposure of 100ppm PTU significantly increased virus titers in the lungs of RSV-infected offspring compared with the control, and the 10ppm also elevated levels of interferon-γ, a marker of pneumonia, in the bronchoalveolar lavage fluids of offspring. Histopathological analysis revealed that PTU-exposure exacerbated pneumonia in RSV-infected offspring. Thus, exacerbation of RSV infection suggested PTU-exposure of dams elicited developmental immune disorder in the offspring. The murine RSV infection model may be useful to evaluate the developmental immunotoxicity of BFRs.

Undertaking positive control studies as part of developmental neurotoxicity testing: a report from the ILSI Research Foundation/Risk Science Institute expert working group on neurodevelopmental endpoints

Developmental neurotoxicity testing involves functional and neurohistological assessments in offspring during and following maternal and/or neonatal exposure. Data from positive control studies are an integral component in developmental neurotoxicity risk assessments. Positive control data are crucial for evaluating a laboratory's capability to detect chemical-induced changes in measured endpoints. Positive control data are also valuable in a weight-of-evidence approach to help determine the biological significance of results and provide confidence in negative results from developmental neurotoxicity (DNT) studies. This review is a practical guide for the selection and use of positive control agents in developmental neurotoxicology. The advantages and disadvantages of various positive control agents are discussed for the endpoints in developmental neurotoxicity studies. Design issues specific to positive control studies in developmental neurotoxicity are considered and recommendations on how to interpret and report positive control data are made. Positive control studies should be conducted as an integral component of the incorporation and use of developmental neurotoxicity testing methods in laboratories that generate data used in risk decisions.

Refining the effects observed in a developmental neurobehavioral study of ammonium perchlorate administered orally in drinking water to rats. II. Behavioral and neurodevelopment effects

A developmental neurotoxicity study was conducted to generate additional data on the potential functional and morphological hazard to the central nervous system caused by ammonium perchlorate in offspring from in utero and lactation exposure. Female Sprague-Dawley rats (23 to 25/group) were given continuous access to 0 (carrier), 0.1, 1.0, 3.0, and 10.0 mg/kg-day perchlorate in the drinking water beginning 2 weeks prior to mating and continuing through day 10 of lactation for the behavioral function assessment or given continuous access to 0 (carrier), 0.1, 1.0, 3.0, and 30.0 mg/kg-day beginning on gestation day 0 and continuing through day 10 of lactation for neurodevelopment assessments. Motor activity was conducted on postpartum days 14, 18, and 22 and juvenile brain weights, neurohistopathological examinations, and regional brain morphometry were conducted on postpartum days 10 and 22. This research revealed a sexually dimorphic response, with some brain regions being larger in perchlorate-treated male rats than in comparable controls. Even so, there was no evidence of any obvious exposure-related effects on male rat brain weights or neuropathology. The most consistent exposure-related effect in the male pups was on the thickness of the corpus callosum, with both the right- and left-sided measures of the thickness of this white matter tract being significantly greater for the male pups in the 0.1 and 1.0 mg/kg-day exposure groups. The behavioral testing suggests prenatal exposure to ammonium perchlorate does not affect the development of gross motor movements in the pups.

An evaluation of neurobehavioral tests used to assess the neurodevelopmental effects of early ammonium perchlorate exposure

Perchlorate is an anion known to interfere with normal production of thyroid hormones that are integrally involved in the development of the central nervous system and neurobehavioral capacities. Given the identification of drinking water contamination with perchlorate, there are efforts to investigate the effects of exposure in developing fetuses and children in order to guide the establishment of regulatory standards. Systematic neurobehavioral investigations in animal models have been completed to evaluate neurodevelopmental consequences of exposures at different concentrations in drinking water. However, these investigations have not directly addressed the public concern for increased incidences of childhood attention deficit disorders, autism, and lowered IQs of children in areas with known contamination. Although epidemiological data suggest there is not a relationship between drinking-water perchlorate exposure and these childhood disorders, it may be prudent to use animal models to systematically assess the potential for such problems. Given the behavioral complexity of these problems, an appropriate evaluation will require the use of nontraditional neurobehavioral tests such as operant conditioning tasks of varying levels of complexity, and juvenile rat play. Such tests will provide a more direct evaluation of the potential for attention deficits, autism, and lowered IQ scores related to thyroid hormone disruption due to early perchlorate exposure.

Cell population depletion associated with fetal alcohol brain damage: mechanisms of BAC-dependent cell loss

Neuronal death is one of the most serious consequences of alcohol exposure during development. Studies described in this paper used a neonatal rat model to address factors affecting neuronal death following alcohol exposure during the period of rapid brain growth, and relate them to possible mechanisms of damage. The profile of blood alcohol concentrations (BACs) is an important variable influencing both brain growth deficits and neuronal death--a smaller daily dose of alcohol can be more damaging than a larger daily dose, if it is consumed in a binge-like pattern that produces relatively higher BACs. Alcohol exposure for a single day also can be damaging, producing both brain growth deficits and neuron loss, if high BACs are obtained. Various brain regions and different neuronal populations within a given brain area exhibit different degrees of vulnerability. Some neuronal loss clearly is a function of cell death due to direct effects of alcohol, while other deficits may be due to either primary or secondary effects of the alcohol insult. In the cerebellum, a maturational or metabolic factor also appears to be involved with alcohol-induced neuronal death. Immunocytochemical studies using a monoclonal antibody against microtubule-associated protein 2 (MAP2) indicated that cerebellar lobules containing Purkinje cells that are in the process of extending dendrites are ones that are more vulnerable to alcohol than lobules containing Purkinje cells that mature later. Alcohol exposure during brain development may be producing neuron attrition in multiple ways, including disruption of membrane integrity, inhibition of protein synthesis or other alterations such as lipid solubility, or by disruption of cytoskeletal elements.