Plested, A. J. | bioRxiv Science

bioRxiv2025

The polyamine naphthyl-acetyl spermine trihydrochloride (NASPM) lacks specificity for Ca2+-permeable AMPA receptors and suppresses seizure like activity in human brain tissue by inhibition of NMDA receptors.

For decades, naphthyl-acetyl spermine trihydrochloride (NASPM) has been used as a selective inhibitor of calcium-permeable AMPA receptors (CP-AMPAR). In rodents, NASPM is known to suppress seizures in vivo and seizure-like events (SLE) in vitro, suggesting possible involvement of CP-AMPAR in ictogenesis and epileptogenesis. To address whether these findings can be translated to human brain, we investigated the involvement of glutamatergic receptor subclasses in SLE in human cortex ex vivo, demonstrating that glutamatergic receptor antagonists can block (NASPM and APV) or reduce (UBP302, GYKI52466, GYKI53655) SLE. Using a multimethodological approach we were able to demonstrate that both NASPM and APV inhibit human SLE by inhibition of NMDA receptors. Our results further show that the inhibitory effect of NASPM on NMDA receptors is sufficient to explain its inhibition of seizure like activity, rather than its action on CP-AMPA receptors. Thus, our findings challenge previous knowledge on the use of NASPM as a specific CP-AMPAR inhibitor. Some phenomena previously attributed to CP-AMPAR, may need to be re-examined more closely. Overall, our study raises awareness about potential pitfalls in the use of existing pharmacological agents and sets a new paradigm for the use of NASPM in neuroscience research while questioning its therapeutic potential in a clinical context.

neuroscience↗

bioRxiv2021

The action of Con-ikot-ikot toxin on single AMPA-type glutamate receptors

Conotoxins are a large group of naturally occurring toxic peptides produced by the predatory sea snails of the genus Conus. Many of these toxins target ion channels, often with high specificity and affinity. As such, they have proven to be invaluable for basic research as well as acting as leads for therapeutic strategies. Con-ikot-ikot is the only conotoxin so far identified that targets AMPA-type glutamate receptors, the main mediators of excitatory neurotransmission in the vertebrate brain. Here, we describe how the toxin modifies the activity of AMPA receptors at the single-channel level. The toxin binds to the AMPA receptor with high affinity (EC50 = 5 nM) and once bound, takes minutes to wash out. As shown previously, it effectively blocks desensitization of AMPA receptors, however, compared to other desensitisation blockers, it is a poor stabiliser of the open channel because toxin-bound AMPA receptors undergo frequent, brief closures. We propose this is a direct consequence of the toxins unique binding mode to the ligand binding domains. Unlike other blockers of desensitization, which stabilise individual dimers within an AMPA receptor tetramer, the toxin immobilizes all four ligand binding domains of the tetramer. This result further emphasises that quaternary reorganization of independent LBD dimers is essential for the full activity of AMPA receptors.

neuroscience↗