Transgenic mice (4 mo. old) were i.v. injected with PBS (A), or GDNF-transfected (B), or sham-transfected (C) macrophages (2x106 cells/100 μL/mouse) weekly 3x times. Wild type mice were systemically injected with PBS (D). Animals were sacrificed at mo 16, and brain slides were stained with TH, a marker for dopaminergic neurons. The obtained confocal images and quantification of TH+ neurons (E) indicate significant increases in neuronal survival in Parkin Q311(X)A mice upon GDNF-BMM treatment (B) compared to PD mice treated with saline (A). The administration of PD/sham BMM (C) also increased number of dopaminergic neurons in PD mice although at lesser extent than GDNF-transfected macrophages. The bar: 1 mm. Values are means ± SEM (N = 6), and *p < 0.05.