Brain damage due to cerebral hypoxia/ischemia in the neonate: pathology and pharmacological modification

Brain damage due to an episode of cerebral hypoxia/ischemia remains a major problem in the human infant, providing impetus for the testing of potential neuroprotective agents in animal models. Although these animal models do not mirror the human pathology exactly (e.g., with respect to regions vulnerable to damage), they usually have the histological characteristics of gray matter hypoxic/ischemic injury in the human. An important factor in comparing models directly is the stage of development of the brain at birth, which varies widely between species. Approaches to prevent or treat cerebral hypoxic/ischemic damage in neonates have paralleled those in adults. However, most of these results should be interpreted cautiously, since neonatal rat models with little concurrent physiological monitoring are often used. As in adults, moderate hypothermia during the insult or a preconditioning stress prior to the insult has prevented hypoxic/ ischemic brain damage. Different from adults is the demonstration that pretreatment with moderate doses of glucocorticoids or hyperglycemia during the hypoxic/ ischemic insult protects the brain against infarction. Partial protection, primarily in neonatal rats, has also been produced by pretreatment with voltage-sensitive calcium channel antagonists, free radical scavengers, growth factors, gangliosides, anticonvulsants, antiinflammatory agents, and nitric oxide synthase inhibitors. Posttreatment has been effective with a few agents. The most consistent has been the protective effect observed with glutamate receptor antagonists administered before but also up to 4 h after the insult. The effects of most of these therapies on blood glucose, body temperature, and/or the systemic circulation should be measured and the protective effects confirmed in larger species prior to considering clinical applications.