SELECTIVE N-TYPE CALCIUM-CHANNEL ANTAGONIST OMEGA-CONOTOXIN MVIIA IS NEUROPROTECTIVE AGAINST HYPOXIC NEURODEGENERATION IN ORGANOTYPIC HIPPOCAMPAL-SLICE CULTURES

Background and Purpose Neuroprotection by antagonists of both L-type a nd N-type calcium channels occurs in in vivo models of ischemia. The s ite of action of calcium channel antagonists is unclear, however, and it is likely that a combination of vascular and direct neuronal action s occurs. We have investigated the effects of blocking neuronal calciu m channels using an organotypic hippocampal-slice model of ischemia. M ethods Organotypic hippocampal-slice cultures prepared from 10-day-old rats were maintained in vitro for 14 days. Cultures were exposed to e ither 3 hours of oxygen deprivation (hypoxia) or 1 hour of combined ox ygen and glucose deprivation (ischemia). Neuronal damage was quantifie d after 24 hours by propidium iodide fluorescence. Results Three hours of anoxia produced damage exclusively in CA1 pyramidal cells. This da mage was prevented by preincubation with omega conotoxin MVIIA, a sele ctive N-type calcium channel blocker, and omega conotoxin MVIIC, which blocks N-type and other presynaptic neuronal calcium channels. The di hydropyridine nifedipine and the mixed calcium channel blocker SB20182 3-A were not protective. Furthermore, if addition of conotoxin MVIIA w as delayed until after the hypoxic episode, a dose-dependent neuroprot ective effect was observed, with an IC50 of 50 nmol/L. In contrast to hypoxia, none of the compounds was neuroprotective in the model of oxy gen-glucose deprivation, although it was determined that extracellular calcium was essential for the generation of ischemic damage.Conclusio ns These studies present clear evidence that neuroprotection by select ive N-type calcium channel antagonists is mediated directly through ne uronal calcium channels. In contrast, the neuroprotective effects of d ihydropyridines may be mediated through vascular calcium channels or i ndirectly through actions in other brain regions.