[Astrocyte activation and Bcl-2 protein expression induced by lipopolysaccharide in mouse brain]

To investigate the changes of anti-apoptotic protein Bcl-2 expression in neurons and activation of brain astroglial cells, and the relationship between astrocytes and neurons in mice after a single intracerebroventricular (ICV) stereotaxic injection of lipopolysaccharide (LPS).

C57BL/6J mice of different ages were divided into a control group and an experiment group. Immunohistochemistry to Bcl-2 and that to GFAP were conducted to observe the expression of Bcl-2 protein in neurons and GFAP in astrocytes in the brain at different time-points after the LPS injection. The glial cell type expressing Bcl-2 was characterized with immunofluorescence double labeling.

GFAP-immunoreactive cells in the control mice were observed mainly within hippocampal formation, piriform, entorhinal cortex, septum, striatum, amygdaloid nucleus, subcortical white matter, as well as in the main fiber tracts. At 24 h after the LPS treatment there was no obvious difference in GFAP immunoreactivity compared with the controls. Astrocytes were markedly activated in periventricular brain regions such as hippocampus, the hypothalamic parenchyma surrounding the third ventricle, with larger cell body and hypertrophic processes 2 days after the endotoxin treatment. After the LPS injection, Bcl-2 positive cells were distributed widely in the brain, such as in the cortex (primary and secondary motor cortex, somatosensory cortex), hypothalamic parenchyma surrounding the third ventricle, diagonal band, hippocampus, septum and the red nucleus of the midbrain. At these sites, Bcl-2 induction increased significantly 2 days after the ICV LPS injection, with some subregional differences, peaking on 4th day. No immunofluorescent double labeling cells for GFAP and Bcl-2 were observed in the brain of the mice after the LPS administration, but merging GFAP positive astrocytes and Bcl-2 positive neurons were seen. Double staining for Bcl-2 and GFAP also showed that the projections of activated astrocytes were found in the sheath of Bcl-2 positive neurons 4 days after the ICV LPS administration.

LPS can activate astroglial cells and upregulate of Bcl-2 expression in the neurons in the mouse brain, which may participate in the administration of central nervous system to central-immunity stimulated regulation and the protective response to the inflammatory stimulus. The projections of activated astrocytes are found in the sheath of Bcl-2 positive neurons, indicating that there is close relationship between astrocytes and neurons.