• Dr. M.B. Rook, Medical Physiology, Utrecht University.
• Dr. G.M.J. Ramakers, Rudolf Magnus Institute of Neuroscience, Utrecht University.
• Dr. R.J. van den Berg, Dept Molecular Cell Biology, Leiden University Medical Center, Leiden.
• Dr. W. Scheenen, Dept Cellular Animal Physiology, Radboud University Nijmegen.
• Dr. A.G. Ewing, Department of Chemistry, Gothenburg University, Gothenburg, Sweden.
• Dr. G. Alvarez de Toledo, Medical physiology and Biophysics, University of Sevilla, Spain.
• Dr. E. Fritsche, Molecular Toxicology, Institut für Umweltmedizinische Forschung, Düsseldorf, Germany.

This project aims at revealing (in neural and immune cells) the adverse effects of environmental toxicants, drugs and endogenous substances on membrane signaling through membrane receptors and ion channels, and on cellular communication through exocytosis. Additionally, intracellular signaling cascades and neurodevelopment will be studied for further hazard characterization of these various classes of environmental toxicants. Projects focus mainly on pesticides and xenoestrogens, though heavy metals, solvents, PCBs and flame retardants are included as well.

Cell lines, primary cultured mast cells, neuroendocrine chromaffin cells, dopaminergic neurons and brain slices. Measurements of exocytosis using amperometry, (cell-attached) capacitance measurements and patch-amperometry. Measurements of the intracellular Ca2+ concentration using fluorescent dyes. Patch clamp techniques for studying voltage-gated and ligand-gated ion channels.

Dopaminergic neurotransmission, which is critical for normal motor-, motivational- and reward-related functions, is generally initiated by the vesicular release (exocytosis) of dopamine into the extracellular space. Consequently, the frequency of exocytosis and the amount of dopamine released per vesicle are important parameters for dopaminergic neurotransmission. These parameters are regulated by the vesicle cycle, which includes dopamine uptake, synthesis and breakdown, and vesicle filling, translocation, fusion and endocytosis.

Previously, it was shown that heavy metals, solvents and polychlorinated biphenyls can interfere with the processes underlying the vesicle cycle, and consequently with dopaminergic neurotransmission. Evidence that pesticides and xenoestrogens affect these processes as well, e.g., by affecting the synthesis of dopamine or the efficiency of vesicle filling, is fragmentary. Nonetheless, even subtle changes can exert profound effects during the development of the dopaminergic system, e.g., by causing a sustained elevation of the intracellular dopamine concentration, eventually resulting in oxidative damage and cell death. These subtle changes are also expected to interfere with dopaminergic neurotransmission directly.

As pesticides are still widely being used and persist in the environment, exposure to pesticides is a current societal concern (pesticide residues on food); the same applies to xenoestrogens. It is therefore surprising that only little is known about the neurotoxic modulation of dopaminergic neurotransmission by these substances. Therefore, the effects of selected pesticides and xenoestrogens on the individual processes contributing to the vesicle cycle in relation to dopamine exocytosis will be investigated using an array of electrophysiological, biochemical and imaging techniques.

Recent publications (for reprint requests mail to r.westerink@uu.nl):

Westerink, R.H.S. (2004). Exocytosis: Using amperometry to study presynaptic mechanisms of neurotoxicity. Neurotoxicology 25, 461-470.

Westerink, R.H.S. (2006). Dopaminergic neurotransmission - Editorial. CNS & Neurological Disorders - Drug Targets 5, 1.

Westerink, R.H.S. (2006). Targeting exocytosis: Ins and outs of the modulation of quantal dopamine release. CNS & Neurological Disorders - Drug Targets 5, 57-77.

Westerink, R.H.S., Rook, M.B., Beekwilder, J.P., & Wadman, W.J. (2006). Dual role of Calbindin-D28K in vesicular catecholamine release from mouse chromaffin cells. Journal of Neurochemistry 99, 628-640.

Dingemans, M.M.L., Ramakers, G.M.J., Gardoni, F., van Kleef, R.G.D.M., Bergman, Å., Di Luca, M., van den Berg, M., Westerink, R.H.S., & Vijverberg, H.P.M. (2007) Neonatal exposure to brominated flame retardant BDE-47 reduces long-term potentiation and postsynaptic protein levels in mouse hippocampus. Environmental Health Perspectives, 115, 865-870.

Westerink, R.H.S. & Ewing, A.G. (2008). The PC12 cell as a model for neurosecretion. Acta Physiologica, 192, 273-285.

Dingemans, M.M.L., de Groot, A., van Kleef, R.G.D.M., Bergman, Å, van den Berg, M., Vijverberg, H.P.M. & Westerink, R.H.S. (2008). Hydroxylation increases the neurotoxic potential of BDE47 to affect exocytosis and Ca2+ homeostasis in PC12 cells. Environmental Health Perspectives, 116, 637-643.

Bal-Price, A.K., Suñol, C., Weiss, D.G., van Vliet, E., Westerink, R.H.S. & Costa, L.G. (2008). Application of in vitro neurotoxicity testing for regulatory purposes: Symposium III Summary and Research Needs. Neurotoxicology, 29, 520-531.

Van Kleef, R.G.D.M., Vijverberg, H.P.M. & Westerink, R.H.S. (2008). Selective inhibition of human heteromeric ?9?10 nicotinic acetylcholine receptors at a low agonist concentration by low concentrations of ototoxic organic solvents. Toxicology In Vitro 22, 1568-1572.

Dingemans, M.M.L., Heusinkveld, H.J., de Groot, A., Bergman, A., van den Berg, M., & Westerink, R.H.S. (2009) Hexabromocyclododecane inhibits depolarization-induced increase in intracellular calcium levels and neurotransmitter release in PC12 cells. Toxicological Sciences, 107, 490-497.