AMPA receptor-elicited excitotoxicity is manifested as both a type of programmed cell death termed dark cell degeneration and edematous
necrosis, both of which are linked to increased intracellular Ca2+ concentration. The appearance of marked cytoskeletal changes in response to abusive
AMPA receptor activation, coupled with increased intracellular Ca2+ concentration suggests activation of various destructive
enzymes such as calpains, a family of Ca2+-dependent
cysteine proteases. Since calpains and
AMPA have been linked to both necrotic cell death and programmed cell death, we sought to determine the role of calpains in mediating both types of
AMPA-mediated toxicity in Purkinje neurons of the cerebellum. These studies employed immunohistochemistry for cytoskeletal breakdown products of
calpain activity coupled with confocal microscopy and pharmacological interventions with
calpain and
AMPA receptor antagonists. The present study identifies an early involvement of calpains in mediating
AMPA-induced dark cell degeneration, but not edematous
necrosis, based upon the effectiveness of
AMPA to generate
calpain-derived
alpha-spectrin cleavage products in cerebellar Purkinje neurons that express dark cell degeneration, and the effectiveness of
calpain antagonists,
PD150606 and
MDL28170, to attenuate
AMPA-induced dark cell degeneration. Moreover, the
AMPA receptor antagonist
CNQX, a proven inhibitor of
AMPA-elicited dark cell degeneration, also blocked
AMPA-induced increases in
alpha-spectrin, further suggesting interplay between abusive
AMPA receptor activation,
calpain activation and dark cell degeneration. Since
AMPA-induced dark cell degeneration possesses morphological changes that resemble those that occur following
brain ischemia in vivo,
hypoglycemia, or extended seizure episodes, the involvement of calpains as mediators of cell death is potentially far reaching and has widespread therapeutic implications in numerous CNS disorders.