Do microglial cells have a neuroprotective function?

To explore the possible neuroprotective role of microglia after a peripheral nerve lesion, the present study used athymic mice shown to have a lower number of microglia to highlight some functions of microglia not normally obvious in animals with a normal number of such cells. Observation of semithin sections showed that unoperated 5-day-old athymic mice had a significant lower number of microglial cells around sciatic motoneurons, compared to their BALB/c littermates. After right sciatic nerve cut at mid-thigh level, motoneuron loss occurred faster at 5 and 10 days after operation in neonatal athymic mice than BALB/c mice. The motoneuron loss by 15 days after nerve cut was, however, the same in both strains of mice. Microglial reaction after sciatic neurectomy, as revealed by Mac-1 immunohistochemistry, was obviously less in intensity and number in athymic mice than in BALB/c mice. The results indicated a neuroprotective function of microglia, which, when not present in adequate numbers, could result in a faster motoneuron death. The study also showed that while microglia were reduced in number in athymic mice, there was no significant difference in the number of astrocytes and oligodendrocytes in the spinal cord of the athymic mice, compared to that in BALB/c mice. This indicates that the development of astrocytes and oligodendrocytes in the spinal cord may not be affected by a reduced number of microglia.