Histologic peripheral nerve changes in rats induced by deltamethrin

Synthetic pyrethroid insecticides have been used in the last two decades largely because of their high activity as an insecticide and low mammalian toxicity. Some studies have demonstrated that these products, especially compounds with an alpha-cyano group, are toxic to the mammalian central nervous system (CNS) in acute intoxications. However, morphological studies are scarce. In the present work the histopathologic changes of the sciatic and tibial nerves of rats submitted to acute intoxication with the cyanopyrethroid deltamethrin were studied. For 3 consecutive days male Wistar rats received by oral gavage deltamethrin at a dose of 45 mg/kg body wt. On the 4th day fragments of sciatic and tibial nerves were studied by transmission electron microscopy (TEM) and teasing of individual nerve fibers. In addition, another group of rats were allowed to recover until the 10th day. Teasing of nerves of animals sacrificed on the 4th day revealed myelin ovoids, which are indicative of axonal damage. TEM demonstrated rare degenerated axons completely filled with organelles, in particular mitochondria, and with electron-dense lamellar bodies that resemble myelin figures. In addition, great cytoplasmic vacuolization caused by proliferation and dilation of the rough and smooth endoplasmic reticulum and Golgi apparatus was observed in some Schwann cells. No lesion was found 7 days after discontinuation of the treatment (group2). Since these histologic changes are transitory and scarce, the question arises: Are they related to the changes in NA(+), K(+)-ATPase activity or Na(+) channels caused by pyrethroid compounds?