Fig. 4. Ketamine induces neuronal caspase-3 activation in vivo . Immunohistochemistry with antibody to cleaved caspase-3 (brown ) (arrows identify cleaved caspase-3 positive cells) on cortical sections from postnatal day 7 (P7) rat pups receiving either saline (A ) or 20 mg/kg every 90 min for 6 h ketamine (B ) (scale bar = 200 μm). (C ) Quantitation of cleaved caspase-3-immunoreactive cells in P7 cortex and thalamus demonstrated increased cleaved caspase-3 positive cells in the ketamine-treated animals. Data are presented as mean ± standard error compared with saline (n = 4, *P < 0.05). (D ) Double staining with antibodies to cleaved caspase-3 (red ) and NeuN antibodies, neuron-specific nuclear protein (green ) antibodies, demonstrated that most of the cleaved caspase-3 positive cells were neurons (scale bar = 20 μm).