Pheochromocytoma PC-12 Cell Line: The Herbicide Picloram Enhances Neurite Growth Induced by Nerve Growth Factor

When cultured rat pheochromocytoma PC12 cell line, of peripheral nervous system origin, were exposed to 0.5 to 3 mM Picloram (4-amino-3,5,6- trichloropicolinic acid), a pyridine derivative herbicide, analogous to the naturally occurring picolinic acid), cell proliferation ceases in a dose- and time-dependent manner. The PC12 cells were growth arrested and remained in a quiescent state and viable for 96 h. 3 mM Picloram induced in most PC12 cells very dense nucleoli, in comparison to control, untreated cells. 3 mM Picloram alone also induced short neurite extensions around the PC12 cell bodies. When PC12 cells were simultaneously treated with 3 mM Picloram and Nerve Growth Factor (NGF, 10 ng/mL or 50 ng/mL; NGF subunit 7S), neurite length was enhanced in a time- and dose-dependent manner. NGF (10 ng/mL) in the presence of 3 mM Picloram, showed enhanced neurite length, in comparison to 10 ng/mL NGF alone (control). The neurite length, induced by 50 ng/mL NGF plus 3 mM Picloram, was greatly enhanced in comparison to 50 ng/mL NGF alone (control). These studies indicate that it is possible to potentiate PC12 neurite growth, in the form of both increase neurite number and length by the combination of Picloram and NGF. Additional experiments with non-neurogenic, virally transformed cells showed that 3 mM Picloram can induced neurite outgrowth in this type of cells. These findings may be useful to understand the neurotoxic effects of Picloram in the peripheral nervous system of animals and humans.