Deltamethrin, a type II pyrethroid insecticide, has neurotrophic effects on neurons with continuous activation of the Bdnf promoter

Pyrethroids, widely used insecticides with low acute toxicity in mammals, affect sodium channels in neurons. In a primary culture of rat cortical neurons, deltamethrin (DM), a type II pyrethroid, markedly enhanced the expression of brain-derived neurotrophic factor (BDNF) exon IV-IX (Bdnf eIV-IX) mRNA. In this study, we found that DM has a neurotrophic effect on cultured neurons and investigated the mechanisms responsible for it. One μM DM increased cell survival, neurite complexity and length. Neurite complexity and length were reduced not only by a blockade of cellular excitation with GABA or Ca ²⁺ influx via L-type voltage-dependent calcium channels with nicardipine, but also by a blockade of TrkB, a specific receptor for BDNF, with TrkB/Fc. These data indicate DM has neurotrophic actions. DM-induced Bdnf eIV-IX mRNA expression through the calcineurin and ERK/MAPK pathways, the increase of which was reduced by GABA _A receptor activation. Using a promoter assay, we found that Ca ²⁺-responsive elements including a CRE are involved in the DM-induced activation of the Bdnf promoter IV (Bdnf-pIV). The intracellular concentration of Ca ²⁺ and activation of Bdnf-pIV remained elevated for, at least, 1 and 24 h, respectively. Moreover, GABA _A receptor activation or a blockade of Ca ²⁺ influx even after starting the incubation with DM reduced the elevated activity of Bdnf-pIV. These data demonstrated that the prolonged activation of Bdnf-pIV occurred because of this continuous increase in the intracellular Ca ²⁺ concentration. Thus, DM has neurotrophic effects on neurons, likely due to prolonged activation of Bdnf promoter in neurons.