A stress-activated protein kinase pathway comprising mitogen-activated protein kinase kinases (MKKs), c-Jun N-terminal kinase (JNK) and the transcription factor c-Jun is implicated in neuronal apoptosis. Using an immune-complex kinase assay, we measured the activation of MKK4 and MKK7 in low potassium (LK)-induced apoptosis of rat cerebellar granule neurons (CGN). MKK7, but not MKK4, was activated within the first 4-6 h in four independent sets of 14-h CGN apoptosis time-courses. CEP-1347 (500 nM), an mixed-lineage kinase 3 inhibitor, prevented MKK7 activation and cell death following exposure of CGN cultures to LK-induced apoptosis. Western blot analysis revealed that levels of phosphorylated c-Jun were elevated between 30 min and 10 h of CGN apoptosis, temporally consistent with MKK7 activation. These data suggest that MKK7 is responsible for activating the JNK pathway during LK-induced CGN apoptosis.