Fig. 4. Pten-null neurons are highly resistant to apoptosis. Cerebellar neurons (Tuj1 positive) grown for 7 days were switched to a serum-free medium containing either 30 mM KCl or 5 mM KCl for 24 hours. (A) Neuronal viability was estimated by DAPI staining of the apoptotic nuclei. Fewer apoptotic neurons could be identified in mutants when compared with littermate controls (lower panel). Mutant neurons were also significantly larger than littermate control granule neurons (upper panel). (B) Histogram (quantitation of apoptotic nuclei) indicates Pten-null neurons are highly resistant to low K⁺-induced cell death under the serum deprivation condition (P<0.001).