QUANTITATIVE-ANALYSIS OF MICROGLIAL REACTION TO A CORTICAL EXCITOTOXIC LESION IN THE EARLY POSTNATAL BRAIN

This study was designed to quantify the microglial response following an injection of N-methyl-D-aspartate (NMDA) into the sensorimotor cort ex of 6-day-old rats, After survival times ranging from 10 h to 28 day s, cryostat sections were processed for the demonstration of microglia l cells by means of tomato lectin histochemistry. The injection of NMD A caused an extensive primary lesion involving the neocortex, the rost ral hippocampus, and rostral thalamus. In addition, secondary retrogra de/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, Quan titative analysis was performed an digitized images using NIH image so ftware and a Macintosh computer, The method is based on densitometric ratios, referred to as the ''reactivity grade,'' between the ipsilater al lesion side and the contralateral control side. Measurements were m ade to determine a possible increase in the number of microglial cells as well as an increase in lectin binding, The analysis showed that mi croglial 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 n eocortex, showing the highest reactivity grade, as well as in other ar eas of primary degeneration, returned to control levels by Day 7. Micr oglial 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) . (C) 1997 Academic Press.