Acute in vitro neurotoxicity of some pyrethroids using microelectrode arrays

Pyrethroid-mediated changes on microelectrode array (MEA) parameters, such as mean firing rate (MFR), mean burst rate (MBR), and number of active channels (nAC) were investigated by exposing neuronal networks to cumulative concentrations (0.01, 0.1, 1, 10, and 100μM) of pyrethroids (Type-1, bifenthrin and permethrin; Type-2, beta-cyfluthrin, cypermethrin, deltamethrin, and lambda-cyhalothrin). The average MFR, MBR, and nAC increased for all pyrethroids (except nAC for deltamethrin) at lower concentrations and decreased at higher concentrations. The increase in the average MFR, MBR, and nAC was not statistically significant in most of the cases. Increase in MFR, MBR, and nAC was observed in 19/19, 18/19, and 12/19 individual experiments, respectively, at lower concentrations. The IC₅₀s calculated on MEA parameters were more or less similar. The relative potencies calculated on the IC₅₀s of MEA parameters had a strong positive correlation. These observations indicate that the MEA parameters MFR, MBR, and nAC follow the same trend for pyrethroid-mediated changes, and provide a similar outcome. The rank orders of relative potencies on the IC₅₀s of the MEA parameters distinguish type-1 pyrethroids from type-2 pyrethroids, with type-2 being more potent. As increase in MFR at the lower concentrations of pyrethroids was observed in all the individual experiments (19/19), it may be considered as the characteristic effect of pyrethroids on neuronal excitability.