P2X7 receptors (Rs) mediate apoptosis/necrosis in neuronal and non-neuronal systems. Patch-clamp recordings from dentate gyrus (DG) granule cells in acutely prepared hippocampal slices of mice showed that incubation with 4-aminopyridine (4-AP) causes an excitability increase. This led to an enhanced sensitivity of P2X7Rs of the underlying subgranular zone neural progenitor cells (NPCs) towards dibenzoyl-ATP (Bz-ATP). The glutamatergic agonists NMDA and AMPA, as well as the purinergic agonist ATP also increased the Bz-ATP-induced current amplitudes (IBzATP). Tetrodotoxin as well as the standard antiepileptic drugs phenytoin, valproic acid and gabapentin counteracted the effect of 4-AP, most likely by decreasing the firing rate and/or action potential duration of DG granule cells and in consequence the release of ATP/glutamate onto NPCs. Experiments with organotypic hippocampal slice cultures confirmed these results also under conditions when 4-AP was applied for longer time periods and at much lower concentrations than used in acute slices. It was concluded that pathological firing modelled by 4-AP might trigger a sensitivity increase of P2X7Rs leading to necrosis/apoptosis of NPCs with the subsequent decrease of NPC, and in consequence, granule cell number. Hence, supersensitive P2X7Rs may exert a beneficial counter-regulatory effect by reducing the chances for the evolution of chronic temporal lobe epilepsy by ectopically located granule cells.
Keywords: 4-aminopyridine; Hippocampal slice culture; Necrosis/apoptosis; Neural progenitor cells; P2X7 receptors; Temporal lobe epilepsy.
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