Fig. 6.

Sagittal and transverse sections of the tongue in E19 wild-type (wt) and E19 BDNF-transgenic mice (tg), visualizing DiI-labeled gustatory fibers of the chorda tympani nerve (gustatory branch of the seventh cranial nerve).A, In wild-type mice, gustatory fibers enter the tongue, pass through muscle tissue (I), and reach the lingual epithelium and innervate fungiform taste buds (arrows). A, inset, shows a higher magnification of the fungiform papilla located on the left side. B, Chorda tympani fibers generally do not reach the lingual epithelium in BDNF-transgenic mice. In these mice, labeled gustatory nerves enter the tongue (C,arrow), and several branches are found in more anterior locations (D, arrows) than the place of entrance. E, In the midportion part of the tongue, a few labeled chorda tympani fibers are found projecting toward the lingual epithelium (arrow). F–H, Occasional labeled fine chorda tympani fiber tangles are observed in the core part of the tongue, among the muscle tissue. I, In wild-type littermates, labeled gustatory fibers traverse through the muscle tissue toward the lingual epithelium (arrows), and fiber tangles are not observed. Scale bars:A–E, I, 200 μm;F–H, 50 μm.