In another experiment, Aizenman and Spawn, who was an undergraduate at the time and has since graduated, exposed the tadpoles to another chemical known to induce seizures. The tadpoles who were not exposed to MIT and those exposed to the lower concentration each had the same ability to hold off seizures, but the ones who had been exposed to the 7.6 ppm concentration succumbed to the seizures significantly more readily.
In these experiments, seizure susceptibility had nothing to do with epilepsy, Aizenman said, but was instead a measure of more general neural development.
After observing the two significant behavioral effects in the tadpoles, Aizenman and Spawn then sought the underlying physiological difference between exposed and unexposed tadpoles that might cause them. They performed an electrophysiological analysis of each tadpole's optic tectum, a part of the brain responsible for processing visual information. They found evidence that the chemical seems to have stunted the process by which tadpoles prune and refine neural connections, a key developmental step.
"The neural circuits act like the neural circuits of a much more immature tadpole," Aizenman said. "This is consistent with the previous findings in cell cultures."
Aizenman said consumers should know about the study's results and pay attention to the ingredients in the products they use, but should not become worried based on the basic science study.
Aizenman said one area where further studies may be warranted is in cases of repeated exposure in industrial or occupational settings, but the study's broader message may be that chemical manufacturers and independent labs should test more for neurodevelopmental effects of even low concentrations of products. In the specific case of MIT in tadpoles, he noted, "It's resulting
|Contact: David Orenstein|