Microglial activation can lead to microglial apoptosis, which may serve to remove highly reactive and possibly neurotoxic microglia. However the loss of microglia may have consequences for future recovery, protection and repair. P53, a nuclear phosphoprotein transcription factor, is critical for activating the expression of genes involved in cell-cycle arrest and stress-induced apoptosis. In neurodegenerative diseases the expression of p53 is significantly increased in glial cells, and microglial numbers fall. Following activation with chromogranin A (100 nM), or beta-amyloid(25-35), (10 microM), microglia became apoptotic. Furthermore, p53 expression was enhanced, peaking at 4-6 h after exposure to activators. The p53 transcription inhibitor, pifithrin-alpha, (10 microM) significantly reduced the expression of p53 in microglia and significantly modulated the levels of microglial apoptosis induced by activation. Lithium chloride (5 mM), which can modulate p53-mediated pathways, also reduced p53 expression and reduced microglial apoptosis suggesting glycogen synthase kinase-3 plays a role. Regulating p53 pathways modulated microglial inducible nitric oxide synthase expression and tumour necrosis factor alpha secretion. Inhibiting p53 mediated microglial apoptosis prevented microglial neurotoxicity suggesting targeting of p53-mediated pathways in microglia may have therapeutic benefit in Alzheimer's disease.