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Quantitative analysis of microglial reaction to a cortical excitotoxic lesion in the early postnatal brain
L Acarin1, B González, B Castellano
1Department of Cell Biology, Neurobiology and Anatomy, Stritch School of Medicine, Loyola University at Chicago, Maywood, Illinois 60153, USA.
Abstract:
This study was designed to quantify the microglial response following an injection of N-methyl-D-aspartate (NMDA) into the sensorimotor cortex of 6-day-old rats. After survival times ranging from 10 h to 28 days, cryostat sections were processed for the demonstration of microglial cells by means of tomato lectin histochemistry. The injection of NMDA caused an extensive primary lesion involving the neocortex, the rostral hippocampus, and rostral thalamus. In addition, secondary retrograde/anterograde degeneration was also observed in the ventrobasal (VB) complex of the thalamus. Microglial reactivity was already present at 10 h postlesion and restricted to areas of neuronal degeneration. Quantitative analysis was performed on digitized images using NIH Image software and a Macintosh computer. The method is based on densitometric ratios, referred to as the "reactivity grade," between the ipsilateral lesion side and the contralateral control side. Measurements were made to determine a possible increase in the number of microglial cells as well as an increase in lectin binding. The analysis showed that microglial reactivity in areas of primary degeneration peaked at 3 days postlesion, when it was significantly (P < 0.01) higher in comparison to saline-injected litter mates. Microglial response in the cerebral neocortex, showing the highest reactivity grade, as well as in other areas of primary degeneration, returned to control levels by Day 7. Microglial response in the VB complex also peaked at Day 3 (P < 0.05) but maintained this level of reactivity until 7 days postlesion (P < 0.01).
Insights
Microglial cells showed significant reactivity to N-methyl-D-aspartate (NMDA) induced brain lesions in young rats, peaking at 3 days post-injury. This microglial response returned to normal levels within 7 days in most affected brain areas.
Area of Science:
- Neuroscience
- Neuroinflammation
- Developmental Neuroscience
Background:
- Microglia are the primary immune cells in the central nervous system.
- Understanding microglial responses to injury is crucial for developing therapeutic strategies.
- N-methyl-D-aspartate (NMDA) is an excitotoxin that can induce neuronal damage.
Purpose of the Study:
- To quantify the temporal and spatial microglial response to NMDA-induced lesions in the developing rat brain.
- To assess microglial reactivity in areas of primary and secondary neuronal degeneration.
Main Methods:
- Intracortical injection of NMDA in 6-day-old rats.
- Tomato lectin histochemistry to label microglial cells.
- Quantitative analysis of microglial reactivity using densitometric ratios (reactivity grade).
- Survival times ranged from 10 hours to 28 days post-lesion.
Main Results:
- NMDA injection caused widespread primary lesions and secondary degeneration.
- Microglial reactivity was evident within 10 hours and peaked at 3 days post-lesion.
- Reactivity returned to baseline by Day 7 in the neocortex but persisted longer in the ventrobasal complex of the thalamus.
Conclusions:
- The study quantifies the dynamic microglial response to excitotoxic brain injury in early development.
- Microglial activation is a rapid and significant event following NMDA-induced neurodegeneration.
- The temporal profile of microglial response varies between different brain regions affected by the lesion.