Monocytes facilitate astrocyte migration. Astrocytes and monocytes were co-cultured in the each compartment of PDMS devices (A) as described in “Materials and Methods”. (B) At 7 d after co-culture, astrocytes were visualized with calcein AM. Convective flow was generated by the difference in media volumes (250 vs. 300 μl) in the compartments in PDMS. The volume difference was maintained to day 7. Astrocytes migrated toward monocytes through the groove only when the convective flow was from monocytes to astrocytes (white arrows in B, left panel). The lower panels in (B) represent higher magnification of the indicated areas in the upper panels. Bars 200 μm (B upper panel); 50 μm (B lower panel).