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The microglia/macrophage response in the neonatal rat facial nucleus following axotomy
M B Graeber1, F López-Redondo, E Ikoma
1Department of Neuromorphology, Max-Planck-Institute for Psychiatry, Martinsried 82152, Germany.
Abstract:
Microglia represent a population of brain macrophage precursor cells which are intrinsic to the CNS parenchyma. Transection of the facial nerve in the newborn rat causes death of the affected motor neurons which is accompanied by massive activation of local microglia. Many of these cells develop into macrophages as can be shown by immunocytochemistry for OX-42 and ED1. Using the new polyclonal microglial marker ionized calcium binding adapter molecule 1, iba1, in combination with immunocytochemical double-labeling for the proliferating cell nuclear antigen (PCNA), or [3H]thymidine autoradiography, and confocal microscopy, qualitative as well as quantitative differences can be demonstrated between the newborn and the adult axotomized rat facial nucleus. While microglial cells are the only cell population which responds to axotomy by cell division in the adult facial nucleus, GFAP positive reactive astrocytes can be shown to undergo mitosis following axotomy in the newborn rat. Furthermore, ED1 immunoreactivity, early expression of MHC class II molecules and morphological transformation of microglia into macrophages can only be observed under conditions of neuronal degeneration, i.e., in the neonatal rat facial nucleus. Thus, the combination of cellular markers described here should be useful for studies employing the neonatal rat facial nucleus as an in vivo assay system to test the efficacy of neurotrophic factors.
Insights
Microglia in the neonatal rat brain transform into macrophages after nerve injury, unlike in adults. This study identifies key markers for studying neurotrophic factors in neonatal brain injury.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are intrinsic brain macrophage precursor cells within the CNS parenchyma.
- Facial nerve transection in newborn rats leads to motor neuron death and significant microglial activation.
- Some activated microglia differentiate into macrophages, identifiable by OX-42 and ED1 markers.
Purpose of the Study:
- To investigate qualitative and quantitative differences in microglial responses to axotomy between newborn and adult rats.
- To characterize microglial and astrocyte proliferation and differentiation following neuronal injury.
- To establish the neonatal rat facial nucleus as an in vivo model for testing neurotrophic factors.
Main Methods:
- Utilized ionized calcium binding adapter molecule 1 (Iba1) as a microglial marker.
- Employed immunocytochemical double-labeling with proliferating cell nuclear antigen (PCNA) and [3H]thymidine autoradiography for cell division.
- Applied confocal microscopy for detailed cellular analysis.
- Assessed ED1 immunoreactivity and MHC class II expression for macrophage differentiation.
Main Results:
- Microglial cells are the sole dividing cell population in response to axotomy in the adult rat facial nucleus.
- GFAP-positive reactive astrocytes undergo mitosis after axotomy in the newborn rat.
- ED1 immunoreactivity, early MHC class II expression, and microglial transformation into macrophages are observed only in the neonatal rat facial nucleus during neuronal degeneration.
Conclusions:
- Significant differences exist in cellular responses to neuronal injury between neonatal and adult rats.
- The neonatal rat facial nucleus serves as a valuable in vivo system for evaluating neurotrophic factor efficacy.
- Specific cellular markers (Iba1, PCNA, ED1, MHC class II) are crucial for distinguishing microglial responses and macrophage differentiation in neurodegenerative contexts.