Chronic postnatal hypoxia increases the numbers of cortical neurons.

Premature infants have been shown to undergo prolonged periods of sublethal hypoxia. There is considerable evidence to link these hypoxic events with neurodevelopmental disorders. As an animal model for this clinical problem, rats were raised from the third day of life in a chamber where the O2 level was 9.5%. After 30 days of hypoxia the rats were sacrificed and their brains processed for determination of the number of cortical neurons. This work was performed to test the hypothesis that chronic hypoxia would result in increased cortical cell death. The hypoxic rats had lower body and brain weights as well as decreased cortical volumes. However, hypoxic rats had increased neuronal density and significantly more cortical neurons than controls (P < 0.05). The results of this study suggest that chronic sublethal hypoxia may lead to reduction in the amount of programmed cell death in the developing neocortex.