Cyclothiazide acts at a site on the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor complex that does not recognize competitive or noncompetitive AMPA receptor antagonists.

Activation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtype of ionotropic glutamate receptors by certain agonists, including AMPA and glutamate, has been shown to result in a rapid desensitization of the receptor. This desensitization is profoundly inhibited by the benzothiadiazide diuretic, cyclothiazide. We previously reported that cyclothiazide potentiates AMPA-induced [3H]norepinephrine ([3H]NE) release from rat hippocampal slices. We used this system to investigate the possible interaction of cyclothiazide with various AMPA receptor antagonists, including the competitive antagonist LY293558 and the 2,3-benzodiazepine noncompetitive antagonist GYKI 53655. Cyclothiazide significantly potentiated both AMPA- and KA-induced [3H]NE release from slices of the rat hippocampus. LY293558 and GYKI 53655 inhibited the potentiated and nonpotentiated AMPA- and KA-induced [3H]NE release in a concentration-dependent manner. The IC50 values for inhibition of AMPA- or KA-induced [3H]NE release by either antagonist were not affected by the presence of cyclothiazide. Thus, cyclothiazide seems to interact at a site on the AMPA receptor complex which differs from either the glutamate recognition site or the 2,3-benzodiazepine allosteric site.