The diazoxide derivative 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4- benzothiadiazine-S,S-dioxide augments AMPA- and GABA-mediated synaptic responses in cultured hippocampal neurons

The diazoxide derivative 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4- benzothiadiazine-S,S-dioxide (IDRA21) enhances memory and learning in rodents, most likely by potentiating AMPAergic synaptic activity. We examined IDRA21's effect upon AMPAergic synaptic currents and whole-cell glutamate currents in cultured rat hippocampal neurons to determine whether IDRA21 was a partial modulator of AMPA receptor desensitization and deactivation. Comparable to cyclothiazide, IDRA21 prolonged AMPAergic autaptic currents (5.6 times control, EC₅₀ 150 μM) and slowed the rate of AMPA deactivation (3 times control) following 1-ms applications of 1 mM glutamate to excised, outside-out membrane patches. IDRA21 also augmented autaptic GABA currents by 27 ± 8.1%, although it had two opposing effects, reducing the peak amplitude versus prolonging autaptic GABA currents. IDRA21 (200 μM) inhibited whole- cell GABA currents elicited by exogenously applied 1 mM GABA by 41 ± 11%. At sufficient concentrations, IDRA21 reduced AMPA receptor desensitization and slowed the rate of deactivation, most consistent with full agonist activity with lower potency compared to cyclothiazide. IDRA21 slightly augments GABAergic synaptic currents.