Figure 2.

The protective effect of mGluRIII agonists against rotenone toxicity is dependent on the MAP kinase pathway. A–C, Midbrain neuronal cultures were treated with rotenone (Rot; 100 nm), l-AP-4 (100 μm), and the MEK inhibitor PD98059 (PD; 20 μm) (A), rotenone, l-AP-4, and cpt-cAMP (50 μm) (B), or PD98059 alone (C). Costaining for TH (green), TUNEL (red), and NeuN (blue) showed that the protective effect of l-AP-4 against rotenone toxicity on TH⁺ neurons was reversed by the MEK inhibitor. D, E, Midbrain neuronal cultures transfected with HA-tagged wild-type MEK (D) or dominant-negative MEK (E) were treated with rotenone (100 nm) plus l-AP-4 (100 μm). Costaining for TH (green), HA (red), and TUNEL (blue) showed that the protective effect of l-AP-4 against rotenone was not obviously affected by wild-type MEK1, but was abrogated by dominant-negative MEK1. Scale bar: (in E) A–E, 10 μm. F, A bar plot showing that the protective effect of l-AP-4 against rotenone was significantly blocked by the MEK inhibitor PD98059 or U0126 (both at 20 μm), or overexpression of dn-MEK, but was not significantly affected by overexpression of wt-MEK, the PI-3 kinase inhibitor wortmannin (0.5 μm), the phospholipase C inhibitor U73122 (1 μm), the PKA activator cpt-cAMP (50 μm), or myr-PKI (1 μm). By itself, PD98059 (20 μm), U0126 (20 μm), or overexpression of dn-MEK had no significant toxicity on TH⁺ neurons. *p < 0.001; n = 5 versus Rot plus l-AP-4. Error bars indicate SE.