Chronic perinatal hypoxia causes a significant loss of total brain volume, brain weight and cortical neuron number. These measures are completely reversed following recovery in normoxic conditions. Yet the cellular and molecular mechanisms underlying this plasticity are not well understood. Here, we show that hypoxia from postnatal days 3 (P3) to 10-11 causes a 30 percent decrease in cortical neurons and a 24 percent decrease in cortical volume. Excitatory neuron numbers were completely recovered 1 month after the insult, but the mice showed a residual deficit in GABAergic interneurons. In...