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Prenatal hypoxia impairs memory function but does not result in overt structural alterations in the postnatal chick
Emily J Camm1, Marie E Gibbs, Richard Harding
1Fetal and Neonatal Research Group, Department of Physiology, Monash University, Victoria 3800, Australia.
Insights
Prenatal hypoxia in ovo impairs chick memory but does not cause overt brain structural changes. This study found no differences in neuron number, synaptic density, or astrocyte markers despite cognitive deficits.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Models
Background:
- Prenatal hypoxia is known to impair memory consolidation in newly hatched chicks.
- The morphological consequences of prenatal hypoxia on the developing avian brain remain largely uncharacterized.
Purpose of the Study:
- To investigate whether prenatal hypoxia induces morphological alterations in the chick brain.
- To examine the effects of prenatal hypoxia on neuronal number, astrocyte development, and synaptic structures.
Main Methods:
- Hypoxia was induced in ovo by partially wrapping eggs during critical incubation periods (days 10-18 or 14-18).
- Blood gas analysis confirmed reduced pO2 and increased pCO2.
- Brain tissue was analyzed for neuronal counts, glutamine synthetase, synaptophysin immunoreactivity, and astrocyte-to-neuron ratios.
Main Results:
- Prenatal hypoxia impaired cognitive processing in post-hatch chicks.
- No significant differences were observed in neuronal number, synaptic density, or astrocyte markers in the multimodal integration area.
- Astrocyte presence was confirmed from embryonic day 12 onwards.
Conclusions:
- The tested regimen of prenatal hypoxia did not induce detectable structural brain changes in chicks.
- Cognitive deficits observed post-hatch are not explained by the measured morphological parameters.
- Potential cellular or molecular changes, or alterations in specific neurotransmitter systems, warrant further investigation.
Abstract:
We showed previously that hypoxia in ovo impairs memory consolidation in the chick tested 2 days after hatching. Our present aim was to investigate whether we could detect any morphological effects of the same prenatal hypoxia. Hypoxia was induced by half-wrapping the egg with an impermeable membrane from either days 10-18 (W10-18 chicks) or days 14-18 (W14-18 chicks) of incubation (hatching approximately 21 days). Measurement of blood gases showed that reducing the surface area of the egg for gas exchange resulted in reduced pO2 and increased pCO2 2 days after wrapping. Although this hypoxia was sufficient to impair cognitive processing in the postnatal chick, our data suggest that it did not produce overt structural alterations or changes in the number of neurons, glutamine synthetase-immunoreactive cells or immunoreactivity to synaptophysin in the presynaptic vesicles in the multimodal integration (cortical) area compared to controls. Hence, we found no differences in the astrocyte to neuron ratio, synaptic density and/or vesicle number. Analysis of the ontogeny of astrocytes during the prenatal period of hypoxia showed them to be present at embryonic day 12, but not at the earlier ages examined. Although we found cognitive deficits in chicks from embryos made hypoxic during incubation, our regimen of prenatal hypoxia did not alter any of the parameters measured in the brains. This does not preclude the possibility that changes have occurred at the cellular or molecular levels or in specific neurotransmitter systems.
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