Positive modulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors elicits neuroprotection after trimethyltin exposure in hippocampus.

The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamatergic receptors have been linked to survival signaling, especially when the receptors are allosterically modulated by members of the Ampakine family. While increased glutamatergic communication through AMPA receptors has been shown to protect against toxic conditions that target hippocampal subfield CA1, protection in other subfields has not been shown. Accordingly, positive modulation of AMPA receptors by Ampakine compounds CX727 and CX516 was tested for effects on trimethyltin (TMT) neurotoxicity in rat hippocampal slice cultures. TMT was applied for 4 h followed by a rapid washout and antagonistic quenching of AMPA and N-methyl-D-aspartate (NMDA) receptors. After a 24-h period, the TMT-exposed slices exhibited increased levels of calpain-mediated spectrin breakdown as well as synaptic deterioration. TMT selectively targeted CA3 pyramidal neurons and dentate gyrus (DG) granule cells as evidenced by degeneration and neuronal loss. The cytoskeletal and synaptic damage was reduced when Ampakine modulation was initiated during the postinsult period. Furthermore, the extent of protection was comparable to that produced by the NMDA receptor antagonist AP5. The above results were substantiated by histological experiments, revealing that Ampakine treatment prevented TMT-induced cell loss in CA3 and DG. These results indicate that AMPA receptor signals are part of cellular repair responses following exposure to an environmental toxin.