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Hypobaric-ischemic conditions produce glutamate-like cytopathology in infant rat brain
C Ikonomidou1, M T Price, J L Mosinger
1Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110.
Insights
This study introduces a new rat model for perinatal hypoxic-ischemic brain damage, finding it similar to excitotoxic damage caused by glutamate. MK-801, an N-methyl-D-aspartate receptor antagonist, protected against this brain injury.
Area of Science:
- Neuroscience
- Pathology
- Animal Models
Background:
- Perinatal hypoxic-ischemic brain damage is a significant concern.
- Excitotoxic brain damage, mediated by glutamate (Glu), is a known mechanism.
- Existing models may not fully capture the complexity of perinatal brain injury.
Purpose of the Study:
- To develop and characterize a novel animal model of perinatal hypoxic-ischemic brain damage in infant rats.
- To compare the neuropathological features of this model with excitotoxic brain damage induced by exogenous glutamate.
- To investigate the potential neuroprotective role of N-methyl-D-aspartate receptor antagonists in this model.
Main Methods:
- A unilateral carotid artery occlusion model was established in 10-day-old rats.
- Animals were subjected to hypobaric conditions for 75 minutes to induce hypoxia-ischemia.
- Brain tissue was examined using light and electron microscopy at 0-4 hours post-insult.
Main Results:
- The model demonstrated a low mortality rate (12%) and high incidence (94%) of brain damage ipsilateral to the occlusion.
- Affected brain regions included the medial habenula, dentate gyrus, caudate nucleus, neocortices, and thalamus.
- Rapid cytopathological changes, including neuronal degeneration and necrosis, were observed, mirroring excitotoxic damage.
Conclusions:
- The neurodegenerative process in this hypoxic-ischemic model is indistinguishable from excitotoxic damage.
- Endogenous glutamate or related excitotoxins likely mediate hypoxic-ischemic brain injury.
- N-methyl-D-aspartate receptor antagonists show promise for neuroprotection in perinatal brain injury.
Abstract:
We present a new animal model of perinatal hypoxic/ischemic brain damage and compare this type of brain damage with the excitotoxic type of damage previously described in the brains of infant rats and monkeys treated systemically with glutamate (Glu). Ten-d-old rats with unilateral occlusion of the common carotid artery were subjected to hypobaric conditions for 75 min and sacrificed 0-4 hr later for light and electron microscopic brain examination. The mortality rate was relatively low (12%), and brain damage was evident ipsilateral to the ligated carotid in 94% of surviving animals 4 hr after termination of the hypobaric event. Regions most frequently affected were the medial habenulum, dentate gyrus, caudate nucleus, frontoparietal neocortices, olfactory tubercle, and several thalamic nuclei. The acute cytopathological changes, primarily edematous degeneration of neuronal dendrites and cell bodies, evolved very rapidly, with some neurons manifesting end-stage necrosis at 0 hr (immediately after hypobaric exposure) and others developing such changes over a 1-4-hr period. We conclude that the neurodegenerative reaction induced in infant rat brain by hypoxia/ischemia is indistinguishable from the excitotoxic type of damage exogenous Glu is known to cause. Moreover, in a companion study (Olney et al., 1989) we show that MK-801, a powerful antagonist of the N-methyl-D-aspartate receptor complex (subtype of Glu receptor), protects against neuronal degeneration in this hypobaric/ischemic model. Our results reinforce other recent evidence suggesting that hypoxic/ischemic brain damage is mediated by endogenous Glu or related excitotoxins.