In vitro acrylamide exposure alters growth cone morphology

Acrylamide intoxication leads to degeneration of the longest axons of the central and peripheral nervous systems in humans and laboratory animals. Axonal derangements resulting from in vivo acrylamide exposure are first noted within synapses of the longest axons before involving more proximally located axonal segments or shorter axons, thus illustrating the specificity of acrylamide for the terminal axonal regions. As a possible model system for investigating the mechanism of toxicity of acrylamide on the distal axon, we exposed neurite-extending chick dorsal root ganglion (DRG) cells to acrylamide in vitro and then examined growth cones for alterations in morphology and function. Exposing DRG explants to media containing from 0.125 to 1.0 mM acrylamide for 16 hr leads to specific and dose-responsive alterations of growth cone morphology including: a nearly total loss of filopodial elements, the preservation of highly active but two-dimensional lamellar structures, an inappropriate extension of the axonal cytoskeleton into the forward region of most growth cones, and a frequent breakdown of the central and peripheral growth cone domains. The sulfhydryl alkylating agents ethacrynic acid, iodoacetamide, and iodoacetic acid were tested and none produced acrylamide-like morphological alterations at any dose. DRG cultures were also exposed to the neurotoxic acrylamide analogs glycidamide, N-hydroxymethacrylamide (HM-ACR), and methacrylamide (M-ACR). At concentrations of 0.25 to 1.0 mM, glycidamide exposure resulted in acrylamide-like growth cone alterations. HM-ACR exposure also resulted in growth cones that were acrylamide-like but only at concentrations > 1.5 mM. M-ACR did not produce acrylamide-like cones at doses of up to 16.6 mM. Thus, in vitro exposure of DRG explants to acrylamide and two neurotoxic acrylamide analogs leads to reproducible and specific morphological alterations that are dose-dependent and separable from the effects of sulfhydryl alkylation.