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2003 Progress Report: Environmental Factors in the Etiology of Autism; Animal Models of Autism
EPA Grant Number: R829388C005Subproject: this is subproject number 005 , established and managed by the Center Director under grant R829388
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: CECEHDPR - University of California at Davis Center for the Study of Environmental Factors in the Etiology of Autism
Center Director: Pessah, Isaac N.
Title: Environmental Factors in the Etiology of Autism; Animal Models of Autism
Investigators: Amaral, David G. , Berman, Robert F. , Capitanio, John , Matsumura, Fumio
Current Investigators: Amaral, David G. , Berman, Robert F.
Institution: University of California - Davis
EPA Project Officer: Saint, Chris
Project Period: September 30, 2001 through September 29, 2002
Project Period Covered by this Report: September 30, 2002 through September 29, 2003
RFA: Centers for Children's Environmental Health and Disease Prevention Research (2001)
Research Category: Children's Health , Health Effects
Description:
Objective:The goals of this project are to establish in vivo exposure models in mice and primates with which to study how relevant xenobiotics of concern to childhood autism influence the development of social behavior. The specific aims of the mouse studies were to: (1) develop a battery of behavioral probes to assess social behavior in developing and mature mice, (2) to evaluate the effects of prenatal and early postnatal exposure to thimerosal, methyl mercury and congeners of PCB on the emergence and quality of social behavior in mice, (3) to determine whether the expected toxicity of exposure to xenobiotics is altered in mice whose immune systems have been activated early in postnatal development by administration of bacterial endotoxin lipopolysaccaride (LPS), and (4) to examine selected brain regions (e.g., amygdala) in xenobiotic treated mice for morphological alterations that may be similar to those observed in neuropathological studies of autism.
The aim of the monkey studies were to use a battery of social testing to evaluate potential alterations of conspecific social behavior following early postnatal exposure of realistic levels of thimerosal, methyl mercury and congeners of PCB.
Progress Summary:Aim I. Establishing models of human social behavior in mice and non-human primates
Mouse models: We have established a comprehensive battery of behavioral tests for mice that enable us to assess social communication and social interactions, motor performance, sensory systems (e.g., visual, auditory somatosensory), attention, and memory and learning. Each of these behavioral dimensions provides critical information on the development of brain systems following early toxin exposure. Infant communication is assessed in neonates (e.g., between postnatal days (PND) 8 and 16) by measuring ultrasonic vocalizations emitted when pups are briefly isolated from their mothers. More complex social interactions are assessed using a Noldus-based computerized system for scoring social dyadic interactions in young adult mice, as well as examining social transfer of food preference. Motor performance is tested on a variety of tasks, including beam walk, wire hanging, grip strength, balance, and basic motor reflexes. Attentional mechanisms are indexed using the acoustic startle and prepulse inhibition; memory and learning in the Morris water maze; and arousal levels in a sequence of tasks that measure responsiveness to sensory input, general locomotor activity, and novel object exploration. We will continue to develop the test battery to refine our ability to assess complex behaviors (e.g., social communication) in mice.
Primate model: Over the last 1.5 years we have established a comprehensive ethogram for testing many aspects of social behavior in the rhesus monkey at the CA Regional Primate Center. These measures provide the closest detail of modeling how early maternal viral challenges influences influence subtle aspect of social behavior and if the exposure influences susceptibility to postnatal thimerosal.
Aim II. Environmental and genetic influences on social behavior
Mouse Models: We are currently finishing behavioral testing of the first cohort of mice exposed to neonatal thimerosal. The exposure regimen closely mimics the exposure of children receiving all thimerosal preserved vaccines during the first two years of life. Two additional dose groups at 10X and 100X have been treated and examine for behavioral changes as a consequence of impaired brain development. These initial studies should be completed by the end of year two of the project. Tissue samples from sacrificed animals in each cohort are being extracted and analyzed for mercury levels by inductively coupled mass spectroscopy (ICP-MS). These measurements are being made by P. Green who has joined the Center (Core I), a recognized expert in analytical measurement of metals (e.g., mercury, lead, etc) and greatly strengthens this aspect of Project II. The mouse tissue bank containing brain, liver, muscle, blood and fur samples from mice exposed to neonatal thimerosal will permit us to correlate tissue levels, and brain levels in particular, of mercury with the behavioral results of mercury exposed mice in order to firmly establish any possible relationships between abnormal development of complex behaviors with early mercury exposure. These initial studies should be completed by the end of year two of the project.
We have also used our behavioral testing battery to characterize transgenic animals that lack expression of the Homer 1 gene since it is likely to provide a useful model for deficits in social interactions and anxiety. Homer 1 is an immediately early gene that is associated with the establishment of cell signaling pathways and synaptic conections in the developing brain. These studies are carried out in collaboration with I. N. Pessah, UC Davis (Project III) and P. Worley, Johns Hopkins University. Dr. Pessah is carrying out electrophysiological studies on hippocampal and amygdala circuitry of Homer 1 knockout mice, as well as carry out an analysis of calcium signaling mechanisms that we hypothesize are disrupted by this specific gene deletion. Dr. Worley both provides the Homer 1 animals and carries out the genotyping to ensure genetic fidelity of the animals. This line of research has both validated our test batteries and demonstrated that deletion of the Homer 1 gene dramatically alters the development and expression of complex behavioral, including social interactions, memory and learning and attention. The hyperactivity and impaired social behaviors documented in this transgenic mouse make it a novel and potentially important rodent model for the study of the development of brain and behavior. An abstract of this research will be presented at the 2003 Society for Neursocience Meeting in New Orleans.
We have added a new researcher to the Project II. Dr. Peggy Jourdes, a developmental neurobiologist with an interest in genetic regulation of behavior, is now working full-time on the project with a major responsibility for the assessment of potential abnormal brain development after neonatal toxin exposure and in transgenic animals of interest (e.g., Homer 1 knockout). She has set up the histological procedures for tissue sectioning, standard and immunohistological staining, and stereological cell counts in limbic system structure thought to be abnormal in autism and other neurodevelopmental disorders (e.g., amygdala, hippocampus).
Finally, we have begun collaboration with Dr. Phillip Schwartzkroin, UC Davis in order to study a recently developed rodent model of autism. Briefly, hyperserotonemia has been suggested to underlie disturbances in sleep patterns, sensory perceptual problems, attentional deficits, compulsive behaviors and seizures in some autistic children. This condition can be modeled by chronically exposing neonatal rodents to a serotonergic agonist (5-methoxytriptamine). Dr. Schwartzkroin will study seizure susceptibility in these animals, while we will explore behavioral manifestations of altered serotonergic tone in the brain during development and any possible relevance to autistic behaviors.
Future Activities:Animals have been reserved for fall 2003 to begin a study on the influence of early maternal exposure to flu virus on development of social behavior and anxiety. An important component of this study is that two groups of animals will be subjected to postnatal thimerosal using a dose protocol that mimics that received by children to test for changes in susceptibility to its toxic effects. Dr. P. Patterson, an eminent neurodevelopmental researcher at Cal Tech has agreed to collaborate on this project. Dr. Patterson recently reported that in rats, maternal exposure to flu virus causes not only significant behavioral deficits in the offspring but alters responses to CNS-active drugs. These ground breaking results are extremely relevant to our study in the primate.
Journal Articles:No journal articles submitted with this report: View all 3 publications for this subproject
Supplemental Keywords:Autism, thimerosal, amygdala, hippocampus, neurodevelopmental toxicity, animal models,
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ENVIRONMENTAL MANAGEMENT, Scientific Discipline, Health, RFA, PHYSICAL ASPECTS, Susceptibility/Sensitive Population/Genetic Susceptibility, Toxicology, Risk Assessment, Biology, Risk Assessments, Disease & Cumulative Effects, genetic susceptability, Health Risk Assessment, Physical Processes, Chemistry, Children's Health, biomarkers, exposure assessment, xenobiotics, neurological development, autism, synergistic interactions, mechanisms, human health risk, susceptibility, halogenated aromatics, etiology, gene-environment interaction, neurotoxic, biological markers, children, neurobehavioral, pesticides, chemical exposure, exposure, biomarker, neurobehavioral effects, neurodevelopmental, neurotoxicity
Progress and Final Reports:
2002 Progress Report
Original Abstract
2005 Progress Report
Main Center Abstract and Reports:
R829388 CECEHDPR - University of California at Davis Center for the Study of Environmental Factors in the Etiology of Autism
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R829388C001 Environmental Factors in the Etiology of Autism; Analytic Biomakers (xenobiotic) Core
R829388C002 Environmental Factors in the Etiology of Autism; Cell Activation/Signaling Core
R829388C003 Environmental Factors in the Etiology of Autism; Molecular Biomakers Core
R829388C004 Environmental Factors in the Etiology of Autism; Childhood Autism Risks from Genetics and the Environment (The CHARGE Study)
R829388C005 Environmental Factors in the Etiology of Autism; Animal Models of Autism
R829388C006 Environmental Factors in the Etiology of Autism; Molecular and Cellular Mechanisms of Autism