Fig. 3. Consequences of unilateral rhombic lip ablations. (A,B) Explant in which the left rhombic lip was extirpated at the time of explantation (indicated by dots on the right side of the panels). (B) Higher magnification of the area outlined in (A). Some TAG-1- and BrdU-labeled cells have crossed the floor plate. (C,D) Ablation of the left rhombic lip (dots on the right side of the panels) in E11.5 bulbar explants prevents the formation of the ipsilateral inferior olive, indicating that these neurons were located in the dorsal neural plate at the onset of the culture. (D) Vibratome section through the explant illustrated in (C). The olivary neurons cross beneath the floor plate but stop at its contralateral limit. ION, inferior olive; arrowheads, floor plate.