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Microglial response to N-methyl-D-aspartate-mediated excitotoxicity in the immature rat brain
L Acarin1, B González, B Castellano
1Department of Cell Biology, Neurobiology and Anatomy, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153, USA.
Abstract:
The intracerebral injection of N-methyl-D-aspartate (NMDA) has been proposed as a model for hypoxic-ischemic insult in the immature brain. In this light, the aim of this study was to describe the time course of the microglial reaction in the areas undergoing primary degeneration at the site of intracortical NMDA injection as well as in areas undergoing secondary anterograde and/or retrograde degeneration. Fifty nanomoles of NMDA were injected in the sensorimotor cortex of 6-day-old rats. After survival times ranging from 10 hours to 28 days, cryostat sections were stained for routine histology and for the demonstration of microglial cells by means of tomato lectin histochemistry. The areas affected by primary degeneration caused by the intracortical injection of NMDA were the neocortex, the hippocampus, and the rostral thalamus. Secondary degeneration (retrograde and anterograde) was observed in the ventrobasal complex of the thalamus. The cortical lesion also caused Wallerian degeneration of the cortical descending efferents as observed in the basilar pons. Microglial reactivity in all these areas was present at 10 hours postinjection and was restricted to the areas undergoing neuronal or axonal degeneration. Reactive microglial cells were stained intensely and showed a round or pseudopodic morphology. At 3 days, an apparent increase in the number of tomato lectin-positive cells was observed in the areas undergoing neuronal death. By 7 days after the injection, the lesion became nonprogressive, and by 14 and 28 days, microglial cells showed moderate lectin binding and a more ramified morphology.
Insights
This study modeled hypoxic-ischemic brain injury in immature rats using N-methyl-D-aspartate (NMDA) injections. It tracked microglial cell responses in degenerating brain areas, revealing their early activation and changing morphology over 28 days.
Area of Science:
- Neuroscience
- Neuroinflammation
- Developmental Neuroscience
Background:
- N-methyl-D-aspartate (NMDA) intracerebral injection serves as a model for hypoxic-ischemic brain injury in immature brains.
- Understanding microglial responses is crucial for characterizing neuroinflammatory processes following brain injury.
Purpose of the Study:
- To investigate the temporal dynamics of microglial reactions in primary and secondary degeneration zones after NMDA-induced cortical injury in young rats.
- To correlate microglial morphology and reactivity with neuronal and axonal degeneration.
Main Methods:
- Intracortical injection of 50 nanomoles of NMDA into the sensorimotor cortex of 6-day-old rats.
- Histological analysis of cryostat sections at various survival times (10 hours to 28 days).
- Tomato lectin histochemistry to identify and characterize microglial cells.
Main Results:
- NMDA injection induced primary degeneration in the neocortex, hippocampus, and rostral thalamus, with secondary degeneration in the thalamus and basilar pons.
- Microglial reactivity, marked by intense staining and round/pseudopodic morphology, was evident at 10 hours post-injection in degenerating areas.
- An increase in microglial numbers was observed by day 3, with a shift towards a more ramified morphology by days 14-28 as the lesion stabilized.
Conclusions:
- Microglial activation is an early and localized response to NMDA-induced neurodegeneration in the immature brain.
- The observed microglial morphological changes reflect distinct phases of neuroinflammation and tissue response following injury.
- This model provides insights into the spatiotemporal patterns of microglial involvement in hypoxic-ischemic insult-like conditions.