This application describes a series of experiments with zebrafish (Danio rerio) to explore the potential relationship among PCB-induced hyperactivity, the neurochemicals serotonin and dopamine, and attention deficit/hyperactivity disorder (ADHD). PCBs are ubiquitous environmental contaminants that pose a risk to human health, especially the unborn child. A multilevel set of assays will be used to investigate a specific neurodevelopmental effect, hyperactivity, of embryonic exposure to environmentally relevant concentrations of Aroclor 1254, a mixture of coplanar and non-coplanar PCBs. Our working hypothesis is that early embryonic exposure to PCBs induces behavioral hyperactivity, a defining symptom of ADHD, by altering the balance of the brain neurochemicals serotonin and dopamine. Behavioral studies will characterize the developmental onset, persistence over time, and windows of susceptibility of the PCB-induced hyperactivity that we have identified in zebrafish larvae. Additional behavioral experiments using an avoidance behavior assay will characterize the influence of salient stimulation on this hyperactivity response and attempt to disentangle the contribution of PCB-induced deficits in attention, learning, timing, fine-motor control, and general performance. PCB exposure is known to cause alterations in neurotransmitter levels. A shift in the normal balance between the neurotransmitters serotonin and dopamine is thought to mediate ADHD. Changes in serotonin and dopamine levels will be investigated by HPLC and immunocytochemistry. Levels of neurotransmitter metabolites will be quantified in order to determine the mechanism of neurotransmitter level changes. These results will be correlated with the hyperactivity observed in the behavioral studies for individual fish. Rescue studies will supplement the HPLC studies as appropriate. Preliminary data from this application will be used for a more extensive R01 application to develop the zebrafish as a model system for studying the link between ADHD and PCB-exposure. Methods used in this application include behavior, HPLC, immunocytochemistry, and recreation of 3D images in an automated virtual environment (CAVE). These studies provide a unique and interdisciplinary approach where the neurodevelopmental effects of PCB exposure can be investigated at levels of analysis ranging from molecular mechanisms, to brain wiring, to gross developmental effects and finally to behavior. Understanding the mechanism of PCB-induced hyperactivity will facilitate development of preventative measures, will aid in the creation of treatments for exposed individuals, and will advance our knowledge of the neural basis of ADHD.
This project examines the hyperactivity induced by chronic, low level exposure to PCBs during embryonic development in the zebrafish. Results of behavioral studies will be correlated with results of studies of the neurotransmitters serotonin and dopamine to examine the idea that hyperactivity is mediated by a disruption in the balance of serotonin and dopamine.
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