Changes in extracellular action potential detect kainic acid and trimethyltin toxicity in hippocampal slice preparations earlier than do MAP2 density measurements

In vitro electrophysiological techniques for the assessment of neurotoxicity could have several advantages over other methods in current use, including the ability to detect damage at a very early stage, and could further assist in replacing animal experimentation in vivo. We investigated how an electrophysiological parameter, the extracellularly-recorded compound action potential ("population spike", PS) could be used as a marker of in vitro neurotoxicity in the case of two well-known toxic compounds, kainic acid (KA) and trimethyltin (TMT). We compared the use of this electrophysiological endpoint with changes in immunoreactivity for microtubule-associated protein 2 (MAP2), a standard histological test for neurotoxicity. We found that both toxic compounds reliably caused disappearance of the PS, and that such disappearance occurred after only 1 hour of exposure to the drug. By contrast, densitometric measurements of MAP2 immunoreactivity were unaffected by both KA and TMT after such a short exposure time. We conclude that, in the case of KA and TMT, the extracellular PS was abolished at a very early time-point, when MAP2 immunoreactivity levels were still comparable to those of the untreated controls. Electrophysiology could be a reliable and early indicator of neurotoxicity, which could improve our ability to test for neurotoxicity in vitro, thus further replacing the need for in vivo experimentation.