Abstract
Background: Lasting motor and cognitive impairments can be a consequence of hypoxic-ischemic (HI) injury to the immature brain. Functional deficits could be due to neuronal loss or altered synaptogenesis. Little is known about the effect of neonatal HI brain injury on synaptic indices, either in injured or unaffected brain tissue. Quantitation of dendritic morphology, e.g. dendritic spine density, branching and length in Golgi-stained tissue, is frequently used to evaluate the effects of brain injury on synaptic organization. We hypothesized that unilateral neonatal cerebral HI elicits distinct ipsilateral and contralateral dendritic abnormalities.
Methods: We evaluated hippocampal dendritic trees in seven-day-old (P7) Long-Evans male rats (n=12) that underwent either unilateral cerebral HI (n=6, right carotid ligation followed by 1.5h in 8% O2) or a sham procedure (neck incision followed by 1.5h in 8% O2). These conditions elicit mild to moderate neuronal loss in ipsilateral striatum, cortex and hippocampus, with no visible contralateral abnormalities. Rats were weaned at P21 and were housed in standard cages until P60. Brains were perfused with saline followed by 1% paraformaldehyde, placed in Golgi-Cox solution for 2 wk, then sectioned at 200 μm. Neurons (10 CA1 pyramidal neurons/side/rat ) were considered suitable for analysis if they were well impregnated and not obscured by blood vessels, astrocytes, or dendrites of other neurons, and their branching was intact within the section. Cells were drawn via camera lucida. Total dendritic length/neuron was estimated by counting dendritic intersections with a series of concentric spheres at 20 μm intervals centered on the soma. Spine density was calculated by tracing a length of third order terminal basilar dendrite (≥70 μm long) at 2000X. The exact length of the dendritic segment was calculated, and the number of spines along the entire length counted and expressed as spines/10 μm.
Results: Bilateral hippocampal reductions in dendritic length, branch number and spine density were associated with HI. CA1 pyramidal spine density was reduced both ipsilaterally (Spines/10μm, mean±SD: Sham 10.6±0.6 vs. HI 8.4±0.3, p<0.001, t-test) and contralaterally (Sham 10.7±0.4 vs. HI 9.1±0.7, p<0.001, t-test).
Conclusion: These findings indicate that abnormalities of synaptic organization persist into adulthood after neonatal HI brain injury, and these abnormalities affect regions of the brain distant from the site of HI neuronal injury.
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Barks, J., Liu, Y. & Kolb, B. 17 Bilateral Alterations in Dendritic Morphology after Unilateral Neonatal Cerebral Hypoxia-Ischemia. Pediatr Res 56, 467 (2004). https://doi.org/10.1203/00006450-200409000-00040
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DOI: https://doi.org/10.1203/00006450-200409000-00040