Superfund Research Program
Zebrafish as a Detector and Discriminator of Organophosphate Exposure
Superfund experimentation conducted by Dr. Elwood Linney strongly suggests that very early embryonic exposure to chlorpyrifos (Dursban) results in an inhibition of acetylcholinesterase, and, in turn, this early inhibition, results in adult fish with learning deficiencies (this behavioral work was done in collaboration with the Levin Laboratory). Dr. Linney has followed the logic that if inhibition of acetylcholinesterase is the cause of the later effects in adult fish, then chlorpyrifos is acting as an indirect agonist of the acetylcholine receptors. In the past year, the research team has confirmed, with the aid of the Levin Laboratory, that early exposure to chemicals that activate the nicotinic and muscarinic acetylcholine receptors also result in adult learning/behavioral differences.
The researcher collaborators are taking a multi-faceted approach to this problem: 1) the previous attempt to generate a small, neurotransmitter pathway array was negated by the new opportunity to add genes to the Agilent 22k array. This was done with the help of Cogenics; the team has added 400 new genes to the Agilent array that will aid more thorough analysis of neurotransmitter pathway changes associated with organophosphate exposure; 2) Dr. Linney has determined concentrations of parathion and diazinon, two other organophosphates, that will inhibit embryonic acetylcholinesterase to the same extent as the chlorpyrifos exposures at 100 ng/ml; as a result, researchers can test whether inhibition of acetylcholinesterase is responsible for behavioral effects; and 3) they have collected Bac genomic clones for a number of different neurotransmitter marker genes so that indicator transgenic lines of zebrafish can be made. This will allow later researchers to identify live neurons producing specific neurotransmitters to be used in these exposure studies.
Additional collaborations with the Levin Lab point out that early chlorpyrifos exposure results in a lowering of the dopamine transmitter in larvae and adults. Dr. Linney is pursuing this as a clue to what might be happening in response to the organophophate exposures.
This work continues to point out the usefulness in using the zebrafish to screen the effects of Superfund chemicals on the developing nervous system. It also suggests that the very early fetal and embryonic nervous system may be extremely vulnerable to compounds that disturb or affect early neuronal activity.