GTTR uptake in tongue and vibrissae. (A) In the tongue, GTTR fluorescence is present in filiform (sh=rtrif) and fungiform (f) papillae (the latter has a ring of labeled gustatory neurons; r in inset) within 3 h of GT/GTTR injection. (B) Within 24 h, GTTR fluorescence is diminished, particularly in fungiform papillae. By 3 days post-injection, linguinal tissues only weakly retain GTTR fluorescence (C) above background, non-specific fluorescence levels (D). (E) The tissues surrounding the vibrissae on the muzzle are rapidly infiltrated with GTTR fluorescence within 3 h, but this had largely cleared 3 days later (F). (G) Vibrissa displaying weak, non-specific fluorescence 3 h after injection of hydrolyzed TR only. Scale bar in D applies to A–C. Scale bar in G applies to E and F.