GLUTAMATE-RECEPTOR ANTAGONISTS INHIBIT CALPAIN-MEDIATED CYTOSKELETAL PROTEOLYSIS IN FOCAL CEREBRAL-ISCHEMIA

Excitatory amino acids may promote microtubular proteolysis observed i n ischemic neuronal degeneration by calcium-mediated activation of cal pain, a neutral protease. We tested this hypothesis in an animal model of focal cerebral ischemia without reperfusion. Spontaneously hyperte nsive rats were treated with dihydroxy-6-nitro-7-sulfamoyl-benzo-(F)qu inoxaline (NBQX), a competitive antagonist of the neuronal receptor fo r lpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or c is-4-[phosphono-methyl]-2-piperidine carboxylic acid (CGS 19755), a co mpetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. Afte r treatment, all animals were subjected to permanent occlusion of the middle cerebral artery for 6 or 24 h. Infarct volumes measured in anim als pretreated with CGS 19755 after 24 h of ischemia were significantl y smaller than those quantified in ischemic controls. Rats pretreated with NBQX showed partial amelioration of cytoskeletal injury with pres erved immunolabeling of microtubule-associated protein 2 (MAP 2) at 6 and 24 h and reduced accumulation of calpain-cleaved spectrin byproduc ts only at 6 h. Prevention of cytoskeletal damage was more effective a fter pretreatment with CGS 19755, as shown by retention of MAP 2 immun olabeling and significant restriction of calpain activity at both 6 an d 24 h. Preserved immunolabeling of tau protein was observed at 6 and 24 h only in animals pretreated with CGS 19755. Western analysis perfo rmed on ischemic cortex taken from controls or rats pretreated with ei ther NBQX or CGS 19755 suggested that loss of tan protein immunoreacti vity was caused by dephosphorylation, rather than proteolysis. These r esults demonstrate a crucial link between excitotoxic neurotransmissio n, microtubular proteolysis, and neuronal degeneration in focal cerebr al ischemia. (C) 1998 Elsevier Science B.V. All rights reserved.