Fig. 4. Excitotoxic challenge to primary cortical neuron cultures. 2The bars represent the ratio between pycnotic nuclei (see fig. 3) and the total number of nuclei in the same fields ± SD. The proportion of dead neurons after NMDA application alone was defined as 100% excitotoxicity; proportions after NMDA and α2-adrenoceptor agonists were compared with this maximum excitotoxicity. Treatment conditions: (A ) dexmedetomidine (0.1–100 μm) and (B ) clonidine (0.1–100 μm). Experiments were performed at least twice. At least 200 cells per plate were counted (three plates per condition for each experiment). Yohimbine = 10 μm. Statistically significant differences between control and treatment conditions are shown:**P < 0.01 versus NMDA alone by analysis of variance followed by Dunnett multiple comparison of means test.