FIG. 9.

Repeated Aβ treatment abrogates the neuroprotective effect of astrocytes. Primary murine cortical neurons were treated (a, b) or untreated (c) with Aβ (50 μM) for ∼14 h in the presence of either fresh or conditioned medium from astrocytes that were either untreated or treated with either 25–35 (a, b) or 1–42 (c) Aβ (acute or repeated) for 12–14 h. Bar graphs represent the mean±SD of apoptotic neuronal cells measured by TUNEL labeling as a percentage of total cells (labeled by Hoechst). (a) Representative micrographs of apoptotic neurons are presented. (b,c) Quantitative analysis of microscopic data from 2 independent experiments. For statistical analysis, at least 1000–2000 cells were counted from each experiment and are shown as mean±SD. *p≤0.05, **p≤0.01, ***p≤0.001, ns, not significant.