Cortical neuronal loss after chronic prenatal hypoxia: a comparative laboratory study

Hypoxia of Rats Subjected to Carotid Artery Ligation Results in Impaired Neurogenesis and Reduced Number of Cortical Neurons

BACKGROUND/AIM

Cerebral ischemia is a major cause of abnormal brain development. In a cerebral ischemia model, periventricular leukomalacia (PVL), white matter lesion and a decrease in the number of subcortical neurons were observed. The aim of this study was to investigate the effect of hypoxia on neurogenesis and cell survival.

MATERIALS AND METHODS

In seven-day postnatal rats, the right carotid artery was ligated. The rats were incubated either in a regular normoxic chamber (control group) or in a hypoxic chamber (PVL group, 8% 02 and 92% N2 at 37°C) for 2 h. Nestin- and NeuN-positive neurons were detected by immunohistochemistry.

RESULTS

The densities of nestin-immunoreactivity (IR) cells in the cerebral parietal cortex and subventricular zone were increased with hypoxia. NeuN-IR cells in the cerebral cortex were significantly decreased in the PVL group.

CONCLUSION

Perinatal white matter injury induced neurogenesis, while the survival of neurons was decreased in the cerebral cortex.

Role of Prenatal Hypoxia in Brain Development, Cognitive Functions, and Neurodegeneration

This review focuses on the role of prenatal hypoxia in the development of brain functions in the postnatal period and subsequent increased risk of neurodegenerative disorders in later life. Accumulating evidence suggests that prenatal hypoxia in critical periods of brain formation results in significant changes in development of cognitive functions at various stages of postnatal life which correlate with morphological changes in brain structures involved in learning and memory. Prenatal hypoxia also leads to a decrease in brain adaptive potential and plasticity due to the disturbance in the process of formation of new contacts between cells and propagation of neuronal stimuli, especially in the cortex and hippocampus. On the other hand, prenatal hypoxia has a significant impact on expression and processing of a variety of genes involved in normal brain function and their epigenetic regulation. This results in changes in the patterns of mRNA and protein expression and their post-translational modifications, including protein misfolding and clearance. Among proteins affected by prenatal hypoxia are a key enzyme of the cholinergic system-acetylcholinesterase, and the amyloid precursor protein (APP), both of which have important roles in brain function. Disruption of their expression and metabolism caused by prenatal hypoxia can also result, apart from early cognitive dysfunctions, in development of neurodegeneration in later life. Another group of enzymes affected by prenatal hypoxia are peptidases involved in catabolism of neuropeptides, including amyloid-β peptide (Aβ). The decrease in the activity of neprilysin and other amyloid-degrading enzymes observed after prenatal hypoxia could result over the years in an Aβ clearance deficit and accumulation of its toxic species which cause neuronal cell death and development of neurodegeneration. Applying various approaches to restore expression of neuronal genes disrupted by prenatal hypoxia during postnatal development opens an avenue for therapeutic compensation of cognitive dysfunctions and prevention of Aβ accumulation in the aging brain and the model of prenatal hypoxia in rodents can be used as a reliable tool for assessment of their efficacy.

Prenatal hypoxia–ischemia decreases spatial memory and increases aggression during adolescence

Prenatal hypoxia–ischemia (HI) is a major cause of mortality and chronic neurological diseases in newborns. HI contributes to the emergence of several neurological disorders such as cognitive and behavioral deficits due to the atypical brain development. This study aimed at assessing the effects of prenatal HI on the spatial memory and aggression of rats during adolescence. Pregnant rats were divided into treatment and control groups. The rats of the treatment groups underwent unilateral ligation of the uterine artery on pregnancy day 7, 12, or 17. The offspring of these rats were tested for spatial memory and aggression when they reached 33 days of age. It has been found that the percentages of alternations in the Y-maze and the number of crossings in the Morris water maze tests of the HI groups were lower than those of the control groups. The total offense and defense aggression scores of the HI groups were higher than those of the control groups. In conclusion, the longer the duration of HI, the more deficits it causes in the spatial memory and aggression of rats during adolescence.

Regional Immunoreactivity of Pax6 in the Neurogenic Zone After Chronic Prenatal Hypoxia

BACKGROUND/AIM

Neurogenesis is a complex process to generate new neurons from neural progenitor cells. Neural progenitor cells are observed in two principal neurogenic regions of the forebrain, the subventricular zone and the subgranular zone of the hippocampal dentate gyrus. The cerebral cortex also plays a role as the neurogenic zone under hypoxic conditions. Hypoxia has many effects on neurogenesis, but the effect of chronic prenatal hypoxia on paired box 6 (Pax6), a protein that plays an important role in neurogenesis, has not been studied in vivo. In the present study, we used a rat model to evaluate the effect of hypoxia on Pax6 immunoreactivity.

MATERIALS AND METHODS

Hypoxia status was induced by unilateral uterine-artery ligation in pregnant rats. The fetuses were obtained from the uterine horn on the twenty-first day of pregnancy and immunohistochemistry of the fetal brain was examined regarding anti-hypoxia-induced factor 1α and Pax6 antibody.

RESULTS

The density of HIF1α-IR cells in the hypoxia group was greater than the density of HIF1α-IR cells in the control group in the subventricular zone, subgranular zone, and cerebral cortex. The density of Pax6-IR cells in the hypoxic group was higher in both the subventricular zone and the subgranular zone than in the control group. However, the density of Pax6-IR cells in the cerebral cortex was lower in fetuses that experienced hypoxia than in control fetuses.

CONCLUSION

These results suggest that Pax6 immunoreactivity showed diverse patterns in the neurogenic zone after prenatal hypoxia and Pax6 has important effects on neurogenesis.