Characterization of cyclothiazide-enhanced kainate excitotoxicity in rat hippocampal cultures

Abstract

Cyclothiazide has been shown to block desensitization of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-preferring receptors and to enhance quisqualate-, AMPA- and kainate-induced neurotoxicity. The pharmacology behind this cyclothiazide-enhanced kainate-induced excitotoxicity was characterized in embryonic rat hippocampal cell cultures. Treatment of cell cultures with a combination of cyclothiazide and kainate for 24 h resulted in excessive neuronal death as measured by the release of lactate dehydrogenase into the culture media. Cyclothiazide produced a leftward shift of the kainate dose-response curve and enhanced the maximum response of kainate excitotoxicity. AMPA-preferring receptor antagonists, 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX) and 1-(4-amino-phenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466) blocked cyclothiazide-enhanced kainate toxicity completely, and cyclothiazide increased the IC 50 S for NBQX and GYKI 52466 against kainate toxicity. The N-methyl- d-aspartate (NMDA) antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK801) also blocked cyclothiazide-enhanced kainate toxicity, but only partially. Cyclothiazide also increased the IC 50 for MK801 against kainate toxicity. These data suggest that cyclothiazide enhances both AMPA-preferring receptor- and NMDA receptor-mediated toxicity in kainate-induced toxicity in embryonic rat hippocampal cultures.