Neurodevelopmental toxicity in mammals
Principal investigator: Per Eriksson
Developmental toxicology is a relatively new science, but its roots are firmly embedded in teratology. In the field of developmental neurotoxicology it is essential to identify critical stages when chemical agents can be harmful. Much of our present knowledge concerning the adverse effects of chemicals on mammalian development and human brain development relates to events during the early stages of development, during the embryonic part of gestation. The gestation period is divided into two major periods, the embryonic period and the foetal period. In humans the embryonic period constitutes 20% of the whole gestation period and the foetal period 80%. In animals used in research, such as mouse and rat, the opposite is seen where the embryonic period constitutes 80% of the gestation period and the foetal period 20%. It is known that exposure during the foetal period can cause functional anomalies of CNS that results in behavioural, cognitive and motor defects.
The results of our research to date have demonstrated that low-dose exposure to environmental agents during the rapid development of the neonatal mouse brain ('brain growth spurt') can lead to irreversible changes in the adult brain function. The induction of these disturbances occurs at doses that apparently have no permanent effects when administered to the adult animal. Our studies have also shown that there is a short defined critical period in the neonatal development of the mouse brain when these persistent effects are induced. In recent research we have indicated that environmental toxicants can interact to enhance developmental neurotoxic effects. Furthermore, we have reported on increased susceptibility to toxic agents at adult age in animals exposed during neonatal life, indicating that neonatal exposure to toxic agents can potentiate and/or modify the reaction to adult exposure to xenobiotics. Therefore differences in adult susceptibility to environmental pollutants may not necessarily be an inherited condition. Rather, they might well be acquired by low dose exposure to environmental agents during perinatal life when the maturational processes of the developing brain and CNS are at a stage of critical vulnerability.
Examples of compounds that have been investigated in this neonatal
Flame-retardants [polybrominated flame retardants such as PBDEs (polybrominated diphenylethers), HBCDD, TBBPA and organophosphorous compounds used as flame-retardants (tris(2-chlorethyl)phosphate, triphenylphosphate], perfluorinated chemicals (PFOS, PFOA, PFDA), PCBs, DDT, pyrethroids, organophosphorous compounds (paraoxon, DFP), paraquat, nicotine, ethanol, MPTP, methyl mercury, iron, acryl amide, anaesthetics.
Staff presently involved: Assistant professor Henrik Viberg and associate professor Anders Fredriksson.
Recent doctoral theses: Niclas Johansson 2009, Celia Fischer 2008, Henrik Viberg 2004, Emma Ankarberg 2003, Ulrika Talts 1996 and Jonas Ahlbom 1995.
Developmental toxicity in birds
Principal investigator: Björn Brunström
To study the effects of xenobiotics during embryonic development in birds, we expose embryos to various compounds via egg-injection. Chicken and Japanese quail are the species predominantly used in these studies. The compounds studied include various endocrine modulators, e.g. compounds interacting with the estrogen system.
Among the effects investigated are interactions with differentiation of the reproductive organs and the brain, resulting in structural changes of the reproductive organs and altered reproductive behaviour of the adult birds.
Treatment of bird embryos with exogenous estrogen induces transformation of the left testicle into an ovotestis in males (only the left gonad develops in females). Furthermore, exogenous estrogen may cause persisting Müllerian ducts (embryonic oviducts) in males and anomalies of the ducts in females.
In a project carried out in cooperation with the Swedish Agricultural University (Professor Yvonne Ridderstråle, Dr Lena Holm, and PhD student Alexandra Hermansson) we study effects of estrogen exposure during embryo development on shell quality of the eggs produced at adulthood. Effects on the reproductive system of the adult roosters are also studied. Dr Cecilia Berg at our department is assistant supervisor to Alexandra Hermansson in this project.
Differentiation of sexual behaviour in birds mainly consists of the demasculinisation of females by embryonic ovarian estrogens, which results in loss of ability of females to show male copulatory behaviour even after testosterone treatment. Experimental treatment of male quail embryos with synthetic estrogens early in development results in complete demasculinisation of the reproductive behaviour.
The molecular changes in the male embryonic brain that are induced by exogenous estrogen are largely unknown. In cooperation with Professor Lennart Dencker's group at the Department of Pharmaceutical Biosciences, Uppsala University, we use cDNA microarray techniques and proteomics to reveal sex differences in gene expression in the brain of bird embryos and to elucidate changes in gene expression following exposure to hormone modulators.
Using in situ hybridisation and RT-PCR, we study the expression of estrogen receptor alpha and beta at different stages of embryonic development in Japanese quail. To investigate the respective roles of estrogen receptor alpha and beta in avian embryo development we study the effects of selective agonists/antagonists to the two receptor subtypes. We also develop reporter cell systems to determine the interaction of various compounds with the two receptor forms.
We also collaborate with Dr Krister Halldin at IMM, Karolinska Institutet.
The projects are/have been financially supported by the ReproSafe programme (the Swedish Environmental Protection Agency), the EU project Compare, and the Research Council Formas.
Recent theses: Anna Mattsson (PhD 2008) Jeanette Axelsson (PhD 2008), Krister Halldin (PhD 2002), Cecilia Berg (PhD 2000).
Developmental toxicity in amphibians
Principal investigator: Cecilia Berg
The main objective of the project is to develop methods and use them to study developmental effects of environmental pollutants on the reproductive system in amphibians. The project also aims at the development of amphibian biomarkers for exposure and effect of various classes of environmental pollutants.
The effects on sex differentiation following exposure to environmental contaminants are investigated using a hierarchy of endpoints ranging from molecular to behavioural.
We have shown that low environmentally relevant concentrations of the pharmaceutical ethynylestradiol cause male-to-female sex-reversal in the common frog (Rana temporaria) and the African clawed frog (Xenopus tropicalis).
We have also shown that exposure to estrogenic environmental pollutants during the larval period causes malformations of the oviducts that persist in adult frogs, making them sterile.
Staff presently involved: Graduate student Moa Kvarnryd.
Economic support is given by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS), Oscar and Lilli Lamm's foundation and Carl Tryggers foundation.
Recent theses: Irina Gyllenhammar (PhD 2008)
Mechanistic studies of developmental effects caused by perfluorinated chemicalsUlrika Bergström
Perfluorinated chemicals such as PFOS and PFOA have been used as surfactants in a wide range of applications. Both PFOS and PFOA are persistent in the environment and can now be found world-wide, including in humans, birds and fish. Other researchers have shown that exposure of rodents to PFOS during late foetal development induced pulmonary insufficiency and immaturity of the lungs. Because of negative effects of PFOS and PFOA, new perfluorinated compounds are now coming into use.The hypothesis of this project is that some perfluorinated chemicals can inhibit specific processes of lung development and thereby inhibit the capacity for ventilation. The project aims to in detail elucidate these mechanistic effects of PFOS on cell differentiation. Identified molecular targets will be used in vitro to identify potentially hazardous fluorinated compounds among the new perfluorinated compounds.
Project collaboration: Graduate student Daniel Borg, Dr Krister Halldin and professor Helen Håkansson at IMM, Karolinska Institutet. The project is financially supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS).
Studies of protein biomarkers of neurotoxicity in the newborn
Principal investigator: Henrik VibergThe objectives of this project are to establish methods in the developing mouse brain and in primary neuronal cultures from mouse to determine whether neurochemical markers related to processes of maturation of axonal and dendritic outgrowth and establishment of neural connections of neuronal differentiation and growth can be used to predict developmental neurotoxicity.
In recent studies by the research group of Per Eriksson it has been shown that neonatal exposure to several environmental pollutants and other compounds, though having markedly different physical and chemical characteristics, can nevertheless cause the same functional disorders. These disorders are manifested as persistent, irreversible disturbances in adult behaviour and learning and memory, as well as disturbances in the adult cholinergic system. This project is focused on finding out how these disturbances are induced and the mechanisms behind these functional disorders.Depending on the toxicant and dose, developmental neurotoxicity may not only manifest itself as gross anatomic malformations, but also as subtle defects in brain cytoarchitecture and cognitive function. This may occur right after the toxicant exposure or later in life and may be difficult and time consuming to detect. Therefore neurochemical methods may prove to be more descriptive, efficient and more suitable for high-throughput screening, and may also provide information regarding the mechanism and/or site of action of a neurotoxicant. At present much of the work is focused on analysis of proteins important during a critical window of brain susceptibility, such as cytoskeletal proteins associated with neurite growth and synaptogenesis.
Staff presently involved: Professor Per Eriksson and associate professor Anders Fredriksson.
We collaborate with Dr William Mundy at NHEERL, Neurotoxicology Division, USEPA. The project is financially supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS).