Differences in reactivity between asphyxial and normal Rhesus monkeys

Perinatal hypoxic-ischemic brain injury in large animal models: Relevance to human neonatal encephalopathy

Perinatal hypoxia-ischemia resulting in death or lifelong disabilities remains a major clinical disorder. Neonatal models of hypoxia-ischemia in rodents have enhanced our understanding of cellular mechanisms of neural injury in developing brain, but have limitations in simulating the range, accuracy, and physiology of clinical hypoxia-ischemia and the relevant systems neuropathology that contribute to the human brain injury pattern. Large animal models of perinatal hypoxia-ischemia, such as partial or complete asphyxia at the time of delivery of fetal monkeys, umbilical cord occlusion and cerebral hypoperfusion at different stages of gestation in fetal sheep, and severe hypoxia and hypoperfusion in newborn piglets, have largely overcome these limitations. In monkey, complete asphyxia produces preferential injury to cerebellum and primary sensory nuclei in brainstem and thalamus, whereas partial asphyxia produces preferential injury to somatosensory and motor cortex, basal ganglia, and thalamus. Mid-gestational fetal sheep provide a valuable model for studying vulnerability of progenitor oligodendrocytes. Hypoxia followed by asphyxia in newborn piglets replicates the systems injury seen in term newborns. Efficacy of post-insult hypothermia in animal models led to the success of clinical trials in term human neonates. Large animal models are now being used to explore adjunct therapy to augment hypothermic neuroprotection.

The behavioral effects of prenatal hypoxia in the rat

Pregnant rats were exposed to an oxygen depleted atmosphere (13% oxygen in nitrogen) at normal pressure in 2-hr daily sessions extending over approximately the last 14 days of pregnancy. Their progeny were compared with control progeny in terms of age of eye-opening, open-field behavior, and Hebb-Williams maze problem solving ability. The groups were not distinguishable by their performance in the open-field, but the experimental animals opened their eyes significantly earlier and made significantly more errors on Hebb-Williams maze problems.

Neuropathology of Certain Forms of Mental Retardation: Experiments on monkeys illustrate probable mechanisms of brain damage in human infants

In presenting the neuropathology of asphyxia neonatorum and some related conditions, as illustrated in experiments with monkeys (12), I have tried to make six principal points. (i) Newborn monkeys need not be asphyxiated to the point of terminal apnea to suffer structural brain damage. Mental retardation has not been proved, but neither has it been excluded, in these monkeys. (ii) Asphyxia neonatorum requiring resuscitation of the offspring, which otherwise would die, is associated with a remarkably constant syndrome of bilaterally symmetrical, nonhemorrhagic lesions in thalamic and brain-stem nuclei, mainly those of afferent systems. The individuals in this category clearly are retarded. (iii) Asphyxia neonatorum of this second degree may be associated with postpartum complications leading to neocortical atrophy, often of considerable magnitude. The individuals are markedly retarded, often palsied, epileptic, and in a few instances even comatose. (iv) Increased intrauterine pressure in the monkey during prolonged labor leads to fetal and postpartum depression, in connection with which cerebral cortical injury occurs in the absence of typical asphyxial lesions. (v) The relationship of cerebral hemorrhages to mental retardation is not clear, but their presence at autopsy probably signifies trauma during birth, or is an agonal artifact associated with death after postpartum depression. (vi) Finally, kernicterus, a condition in which bile pigment escapes into the brain tissues from the blood when the bilirubin level is high and when there is, in combination with it, some depressing factor such as asphyxia, has been produced in the newborn monkey. It, too, is associated with mental retardation.