FIGURE 6.

TH-negative/tdTomato-positive and TH-positive/tdTomato-positive innervation was present in circumvallate papilla (a–c, z-stack, 70 μm). Single optical sections show that TH-negative/tdTomato-positive (arrowhead) and TH-positive/tdTomato-positive (arrow) fibers in circumvallate papillae appeared to run together, making it difficult to distinguish whether there was also a population of TH-positive, tdTomato-negative nerve fibers (d–f). Only TH-negative/tdTomato-positive innervation was observed within circumvallate taste buds (a–f). Fungiform papillae demonstrated a similar pattern of innervation in whole-mount preparations. The tdTomato-labeled (red, g), TH-labeled (green, h), and merged innervation is shown on the z axis of a whole mount fungiform taste bud (keratin 8, blue, i). Both TH-negative/tdTomato-positive (arrowhead) and TH-positive/tdTomato-positive (arrow) fibers were present in some fungiform papillae and ran closely alongside each other. Interestingly, TH-negative/tdTomato-positive fibers penetrated the epithelium, whereas double-labeled fibers tended not to extend above taste buds (g–i). We used the keratin 8 border to mask the label within the taste bud and remove the label outside the taste bud. This illustrates that tdTomato-positive innervation (red) is present within the taste bud (j), whereas TH-positive innervation (green) was not (k). This can also be seen in a single optical section through the same taste bud, where green innervation is only outside the keratin 8 border (i). Scale bar in (f) =20 μm and applies to (a–f), scale bar in (k) =15 μm and applies to (g–k), scale bar in (l) =10 μm