Fig. 6.

Innervation defects at embryonic day (E) 18.5. A: Injection of lipophilic tracers into the brain reliably labels fibers to all six sensory epithelia of the ear (insert). A,D: In the wild-type, there is innervation to the anterior and horizontal cristae and utricle (A) and the cochlea (D). B,C: In contrast, in Foxg1 null mutants, there are no labeled fibers to the remaining two canal cristae, the anterior (B,C) and posterior crista (insert in C). In contrast, the utricle, saccule, and cochlea are well innervated after carbocyanine dye injection into the brainstem (B,C). D: The wild-type cochlea shows three rows of outer and one row of inner hair cells densely innervated, with no fibers projecting beyond the organ of Corti. F: In contrast, innervation of the apical tip of the cochlea in Foxg1 null mutants shows the multiple rows of hair cells, outlined by numerous fibers extending beyond the multiple rows of hair cells, forming loops in the outer spiral sulcus. E: Innervation of the middle turn of the Foxg1 mutant is more clearly organized and shows prominent labeling of inner hair cells but poorly organized innervation to outer hair cells and is not organized into discrete rows of fibers (compare D and E). AC, anterior crista; HC, horizontal crista; PC, posterior crista; S, saccule; SpGl, spiral ganglion; IHCs, inner hair cells; OHCs, outer hair cells; OC, organ of Corti. Scale bars = 100 μm.