Figure 6

Gray-scale montages representing DiI-tracked projections from the VN neurons. (A,B) E12.5_{(+1 DIV)}; (C,D) E13.5_{(+1 DIV)}; (E,F) E14.5_{(+1 DIV).} after the injection of PBS (control) (A,C,F) or Ch^ABC (test) (B,D,F). (A) At E12.5_{(+1 DIV)} in PBS, projections assumed fascicles as they advanced toward the midline. (B) At E12.5_{(+1 DIV)} in Ch^ABC, many projections were unfasciculated as they approached normal to the midline and a subpopulation crossed the midline. (C) At E13.5_{(+1 DIV)} in PBS, projections were fasciculated as they approached and crossed the midline. (D) At E13.5_{(+1 DIV)} in Ch^ABC, pioneer projections advanced normal to the midline as fascicles and beyond towards the contralateral VN. Later projections traversed the enzyme-treated matrix as unfasciculated fibers and deviated from the course of the pioneers (arrows). (E) At E14.5_{(+1 DIV)} in PBS, projections advanced as fascicles to the contralateral VN and then turned in the anterior direction. (F) At E14.5_{(+1 DIV)} in Ch^ABC, commissural projections were partly fasciculated and partly not but mostly unfasciculated as they made the anterior turn. Zoomed-in views of boxed areas are shown in Figure 7. Asterisks indicate the site of DiI injection, dotted lines the rhombomere boundaries, and dashed lines the midline. Abbreviations: r, rhombomere;. Scale bar: 100 μm.