THE MICROGLIA MACROPHAGE RESPONSE IN THE NEONATAL RAT FACIAL NUCLEUS FOLLOWING AXOTOMY/

Microglia represent a population of brain macrophage precursor cells w hich are intrinsic to the CNS parenchyma. Transection of the facial ne rve in the newborn rat causes death of the affected motor neurons whic h is accompanied by massive activation of local microglia. Many of the se cells develop into macrophages as can be shown by immunocytochemist ry for OX-42 and EDI. Using the new polyclonal microglial marker ioniz ed calcium binding adapter molecule. 1, iba1, in combination with immu nocytochemical double-labeling for the proliferating cell nuclear anti gen (PCNA), or [H-3]thymidine autoradiography, and confocal microscopy , qualitative as well as quantitative differences can be demonstrated between the newborn and the adult axotomized: rat facial nucleus. Whil e microglial cells are the only cell population which responds to axot omy by cell division in the adult facial nucleus, GFAP positive reacti ve astrocytes can be shown to undergo mitosis following axotomy in the newborn rat. Furthermore, EDI immunoreactivity, early expression of M HC class II molecules and morphological transformation of microglia in to macrophages can only be observed under conditions of neuronal degen eration, i.e., in the neonatal rat facial nucleus. Thus, the combinati on of cellular markers described here should be useful for studies emp loying the neonatal rat facial nucleus as an in vivo assay system to t est the efficacy of neurotrophic factors. (C) 1998 Elsevier Science B. V. All rights reserved.