Figure 1.

The telencephalic spread of ventrally derived interneurons occurs in three streams. Calbindin- immunopositive cells (white) in the MZ at various embryonic ages are shown in lateral views of whole-mount hemisphere preparations. ob, Position of olfactory bulb at the rostral end of the telencephalic vesicle. Theses series of images were taken from the pial surface. The brightly stained cells are at the surface of the telencephalon and are at the same depth as Cajal–Retzius cells. Similar experiments were performed with both calbindin and CR-50 to localize the relative depth of the calbindin interneurons imaged (data not shown). The less brightly stained cells are farther below the pial surface. Two streams of migrating interneurons emerge as early as E11.5 A, Stream I moves from a caudal to rostral and lateral to medial direction (arrow). Stream II moves in a rostral to caudal direction (arrowheads) and is confined to ventral cortical areas such as the poc. On E12 (B) and E12.5 (D), stream I extends over the lateral and rostral surface of the dorsal telencephalon, whereas stream II extends caudally over the ventral telencephalon. The boxed region in B is shown at a higher magnification in C. Each stream has two components (C): an initial wave of interneurons oriented toward the leading edge of the stream (small arrows) and a subsequent front of cells with multiple orientations (below dashed line). The boxed region inDis shown at a higher magnification inE. Streams I and II in E remain segregated from each other by a cell-sparse gap (between red dashed lines). A third stream (III) emerges just dorsal to the olfactory bulb at E13 (F) and moves in a rostral to caudal direction (arrows). D, Dorsal; M, medial; C, caudal; R, rostral; V, ventral; L, lateral (n = 4 brains for each age).