Differential susceptibility of brain areas to cyanide involves different modes of cell death

We have demonstrated that cyanide (KCN) induces selective degeneration of dopaminergic neurons in mice and apoptotic cell death in cultured neurons. In the present study the mode of cyanide-induced cell death was determined in the susceptible brain areas. Mice were treated with KCN (6 mg/kg ip) or vehicle (saline) twice daily for 1 to 12 days. After 3 days of KCN treatment, two separate lesions were observed in coronal brain sections. Widespread DNA fragmentation in parietal and suprarhinal regions of the motor cortex was observed by the in situ terminal deoxynucleotide transferase nick-end labeling (TUNEL) technique. Pyknosis and chromatin condensation, morphological hallmarks of apoptotic cells, were observed in TUNEL-positive regions. On the other hand, in the substantia nigra (SN), KCN produced a progressive, bilateral necrotic lesion that was evident by 3 days of treatment. The SN lesion was circumscribed by a prominent ring of glial infiltration, as determined by glial-acidic fibrillary protein (GFAP) immunostaining. The extent of the SN lesion steadily increased with treatment duration, and DNA fragmentation was not observed over the 1- to 12-day period. On the other hand, cortical apoptosis was not associated with necrotic cell loss or astrogliosis. Pretreatment of animals with the antioxidant alpha-phenyl-tert-butyl nitrone (PBN) for 7 days prior to and during 3 days of KCN administration markedly reduced cortical DNA fragmentation whereas the PBN treatment did not influence the SN necrosis or astrocytic gliosis. Except for moderate GFAP immunostaining in corpus callosum, other brain areas were not affected by cyanide. It is concluded that KCN-induced neuronal loss involves selective activation of necrosis or apoptosis in different neuronal populations, and involves divergent mechanisms and sensitivity to antioxidants.