Developmental changes in the sensitivity of the neonatal rat brain to hypoxic/ischemic injury

Developmental changes in the response of the neonatal rat brain to hypoxic/ischemic injury were examined. Hypoxic/ischemic injury was produced by unilateral carotid ligation followed by exposure to hypoxia in 1- (D1), 3- (D3), 5- (D5) and 7-day-old (D7) rats. Injury was produced in most D7 animals exposed to > or = 120 min of 7.6 or 8% oxygen after carotid ligation. The extent of neuronal injury was variable, ranging from focal neuronal death to massive infarction. In D5 and D3 animals, there was a progressive decline in the extent of neuronal injury in response to hypoxia/ischemia. In the younger animals, bilateral injury was occasionally seen. Sham-operated animals exposed to hypoxia alone had numbers of karyorrhectic neurons similar to normal control animals in all age groups. The underlying developmental changes which account for these differences are not yet known but are likely to be multiple.