Fig. 4.

Greater ratios of isolated VTA, but not SN, astrocytes protect both SN and VTA DA neurons from MPP⁺ toxicity in the presence of microglia, but increased numbers of microglia counter this protection. Regionally homo- and heterotypic cultures were established with SN and VTA neurons/astrocytes. Greater ratios of SN astrocytes fail to increase SN (solid blue bars) or VTA (solid red bars) DA neuron survival in the presence of microglia. Conversely, VTA astrocytes robustly protect both SN (blue hatched bars) and VTA (red hatched bars) DA neurons from exacerbation of MPP⁺ toxicity when microglia are present. The protective effect of VTA astrocytes on SN (blue vertical striped bar) and VTA (red vertical striped bar) neurons is diminished when the ratio of microglia to neurons is increased from 1:1 to 2:1. Data are presented as mean ± SEM; one-way ANOVA with Tukey’s post hoc multiple comparison test; F (9, 28) = 270.8, ****p < 0.0001