Chronic and cyclical neuronal loss in hippocampal slice cultures followingtransient inhibition of the type 1 isoform of superoxide dismutase

Increased oxidative stress contributes to chronic neurodegenerative disease s, yet the underlying mechanisms are poorly understood. Hippocampal slice c ultures prepared from 20-30-day-old mice or rats were used to model chronic neuronal loss following oxidative stress. Neuronal loss was initiated by i nhibition of the antioxidant enzyme, superoxide dismutase type I (SOD1), us ing the copper chelator diethyldithiocarbamate (DDC). Continuous DDC treatm ent of slice cultures induced delayed neuronal loss beginning at 9 days of treatment that lasted for over 4 weeks. Neuronal loss was not uniform, rath er it was cyclic: peaking at days 9-13 and at days 19-21 after DDC exposure . Neuronal loss was significantly attenuated in slice cultures that overexp ress SOD1, suggesting that SOD1 inhibition was responsible. Inhibitors of n itric oxide synthase also attenuated DDC-induced neuronal loss. Chronic neu ronal loss, however, did not require continuous SOD1 inhibition. Applicatio n of DDC for 13 days resulted in loss of SOD1 activity. Removal of DDC rest ored SOD1 activity, yet the cycles of cell loss continued until no neurons remained. Astrocyte activation was observed following the second peak of ne uronal loss. Media conditioned by cultures following DDC removal induced ne uronal loss and microglial activation in recipient cultures. These data sug gest that slice cultures released soluble neurotoxic factor(s) following DD C removal. These data also suggest that a transient reduction of SOD1 activ ity leads to chronic loss of hippocampal neurons. This neuronal loss may be mediated by soluble neurotoxic factor(s) and microglial activation. Cyclic al neuronal loss may also underlie chronic neurodegeneration in vivo. (C) 2 001 Elsevier Science B.V. All rights reserved.