Abstract
1. The present study examined whether primary cultured rat A2B5+ cerebrocortical oligodendrocyte progenitor cells (OPC) were susceptible to Zn2+- and excitotoxin-induced cell death. 2. Initial pharmacological studies demonstrated the selective ionotropic glutamate receptor agonists' kainate and (S)-5-Iodowillardiine induced OPC death after 24-hour exposure. (S)-AMPA and L-glutamate only induced cell death in the presence of 100muM cyclothiazide (a selective AMPA receptor desensitisation blocker). The selective AMPA- receptor antagonists, GYKI 52466 and Evans' Blue, attenuated 300muM kainate-induced toxicity and therefore suggested OPC excitotoxic insult was via AMPA receptor activation. 3. Metabotropic glutamate receptor (mGluR) involvement was also established as (S)-DBPG (100muM), a selective group I mGluR agonist, afforded significant (p<0.05) protection against 300muM kainate-induced toxicity. The selective mGIuR antagonist (S)-MCPG reversed the effects of (S)-DHPG protection. 4. OPC death was partially prevented by the broad-spectrum caspase inhibitor Z-VAD-fmk (100muM) at 6-hour and 24-hour paradigms. Hoechst 33342 staining revealed the presence of pyknotic nuclei following 6-hour kainate (300muM) exposure and Western Blotting using anti-caspase-3 antibody and anti-a-fodrin antibody indicated potential activation of the apoptotic executioner caspase-3. 300muM Kainate-induced OPC death did not appear to result in the activation of reactive oxygen species (ROS). 5. Zn2+ exposure over 24-hours resulted in OPC death (pECso 4.1+0.1). 100muM Zn2+- induced OPC death was not potentiated by 300muM kainate and Evans Blue afforded no protection. Nicardipine also failed to influence OPC viability. The lack of effect of kainate and nicardipine was confirmed by 65Zn2+ uptake studies. 6. 100muM and 300muM Zn2+-induced OPC death did not appear to result in activation of ROS. Hoechst 33342 staining revealed the presence of chromatin condensation with 300muM Zn2 (6-hour exposure). 100|muM and 300muM Zn2+ (24-hour exposure) was not influenced by Z-VAD-fmk or PD 150606. 7. Zn2+-induced OPC toxicity resulted in significant ATP depletion 6-hours following 300muM Zn2+ exposure (p<0.05) and was attenuated in the presence of 5mM pyruvate. These data therefore suggest the mechanisms of Zn2+ toxicity may involve disruption of the glycolytic cascade.