AMPA receptor desensitization predicts the selective vulnerability of cerebellar Purkinje cells to excitotoxicity

Cerebellar Purkinje cells are selectively vulnerable to ischemia, although the reasons for this are unknown. In cultured embryonic rat cerebellar neurons, the steady state responses to the desensitizing agonist AMPA relative to responses to the nondesensitizing agonist kainate were greater in Purkinje cells compared to other cells, as measured by whole cell voltage clamp studies. Fluorimetric [Ca²⁺](i) imaging experiments similarly found greater responses to AMPA relative to kainate in Purkinje cells than in other cerebellar neurons. In toxicity experiments measuring cell survival 24 hr following agonist exposure, AMPA and glutamate produced Ca²⁺-dependent toxicity which was selective for the Purkinje cell fraction of the neurons, whereas kainate produced nonselective toxicity, and NMDA selectively spared the mature Purkinje cells. Cyclothiazide, which inhibits AMPA receptor desensitization enhanced steady state current responses to AMPA and increased the toxicity of AMPA. We conclude that the vulnerability of cerebellar neurons in culture to glutamate agonist-induced toxicity parallels the magnitude of the steady state currents produced, and that Purkinje cells may be selectively vulnerable because they express AMPA receptors which undergo less complete desensitization.