Primary cortical neurons of the indicated genotypes were infected with a lentivirus expressing Cre at the time of plating and analysed for the presence of the caspase‐cleaved fragment of the caspase‐3 substrate CAS5 days later. Alternatively (E), the neurons were analysed for cytochrome c release by immunofluorescence. Data are expressed as percent of positive cells for at least three embryos per genotype±s.d. 