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The effect of hypoxia on the functional and structural development of the chick brain
Candice L Rodricks1, Marie E Gibbs, Margie Castillo-Melendez
1Department of Physiology, Monash University, Victoria 3800, Australia.
Insights
Prenatal hypoxia exposure during critical developmental windows can impair brain development and lead to lasting memory deficits. Early embryonic day 10 hypoxia significantly impacts neuronal and astrocyte development, affecting memory formation.
Area of Science:
- Neuroscience
- Developmental Biology
- Cognitive Science
Background:
- Prenatal hypoxia, or decreased oxygen availability during gestation, is a known risk factor for altered brain development and cognitive impairments.
- Hypoxia can cause various neuropathologies, from gross brain lesions to subtle neuronal loss, white matter injury, and gliosis.
Purpose of the Study:
- To investigate the effects of 24-hour hypoxia at different embryonic ages (E10, E12, E14) on neuronal cell number and astrocyte density in chick brain regions crucial for learning and memory.
- To assess the impact of prehatch hypoxia on memory formation and consolidation in newly hatched chicks.
Main Methods:
- The study utilized developing chick embryos, exposing them to 24 hours of hypoxia (14% oxygen) at embryonic days 10, 12, or 14.
- Post-hypoxia, brain tissue was analyzed for the density of GFAP-positive astrocytes and NeuN-positive neuronal nuclei in specific brain areas (medial striatum, intermediate medial mesopallium, hippocampus).
- Memory function was evaluated using a bead discrimination learning task shortly after hatching.
Main Results:
- Hypoxia at embryonic day 10 (E10) increased astrocyte density in the medial striatum and reduced neuronal nuclei in the intermediate medial mesopallium, significantly impairing short-term memory and all subsequent memory stages.
- Hypoxia at embryonic day 14 (E14) increased astrocyte immunoreactivity in the hippocampus and decreased neuronal nuclei in the intermediate medial mesopallium, impairing long-term memory consolidation but not short-term memory.
- Hypoxia at embryonic day 12 (E12) did not result in significant changes in neuronal or astrocyte markers or memory deficits.
Conclusions:
- The timing of prenatal hypoxia exposure is critical in determining its impact on brain development and cognitive function.
- Alterations in neuronal number or astrocyte development due to hypoxia during sensitive developmental periods significantly disrupt memory formation and consolidation.
- These findings highlight the vulnerability of specific brain regions and developmental stages to hypoxic injury, with implications for understanding cognitive deficits.
Abstract:
Decreased oxygen availability during gestation is linked with altered structural development of the brain and cognitive deficits after birth. Prehatch hypoxia can induce gross neuropathology such as brain lesions or more subtle injury including selective neuronal cell loss, white matter injury and gliosis. In the current study we used the developing chick embryo to determine whether 24h of hypoxia at different prehatch ages, embryonic day 10, 12 or 14 (E10, E12 or E14), resulted in an alteration in neuronal cell number or astrocyte density in brain areas associated with learning and memory. Twenty-four hours of hypoxia (14% oxygen) commencing at E10 resulted in an increase in the density of GFAP-positive astrocytes in the medial striatum (MSt) (P<0.05) and a significant reduction in the number of NeuN-positive neuronal nuclei in the intermediate medial mesopallium (IMM) (P<0.02). Hypoxia at E14 resulted in an increase in GFAP immunoreactivity in the hippocampus (P < or = 0.02) and a significant decrease in the number of NeuN-positive cells in the IMM (P<0.04). Memory was tested soon after hatch using a bead discrimination learning task and results showed that E10 hypoxia significantly reduced short-term memory, which subsequently affected all stages of memory formation (P<0.001), whereas 24h of hypoxia at E14 did not alter short-term memory, but impaired consolidation into long-term memory (P<0.02). Interestingly, 24h of hypoxia at E12 did not alter GFAP immunoreactivity or NeuN-positive cells, nor did it result in memory deficits. We find that an alteration in the number or a disruption in the normal development of astrocytes and neurons significantly affects memory formation and consolidation in the young chick.
