Differentiation of the lingual and palatal gustatory epithelium of the ratas revealed by immunohistochemistry of alpha-gustducin

We used alpha -gustducin, a taste-cell-specific G protein to investigate th e onset of taste transduction and its relation to the development of the pa latal and lingual taste buds. Frozen cryostat and paraffin sections were pr epared from the palatal and lingual gustatory epithelium of the rat from bi rth till postnatal ay (PN 21d). At PN 1-7d, alpha -gustducin-immunoreactive solitary ovoid or bipolar cells were scattered among the oral epithelium e ither horizontally along the oral surface or vertically oriented between th e basal lamina and oral surface. In the circumvallate and foliate papillae, these cells became wrapped in alpha -gustducin-immuno-negative cells surro unded by an extracellular space forming a bud-like structure. Simultaneousl y, different stages of typical taste buds were recognized, but alpha -gustd ucin was only expressed in some neonatally developed pored buds. At PN 1d, alpha -gustducin was expressed in pored taste buds with a relatively higher frequency recorded in the soft palate as compared with the nasoin-cisor, c ircumvallate, and foliate papillae. The immunoreactive cells were spindle s haped with elongated processes extending from the base to the pore of the t aste buds. During the second week, the solitary cells could no longer be re cognized while the total counts of immunoreactive cells within the taste bu ds gradually increased. We argue that taste transduction is essentially req uired from the time of birth and can be fulfilled by both of the solitary c hemosensory cells, which are immunoreactive for alpha -gustducin and scatte red in the oral epithelium, and the taste cells within the mature taste bud s. Moreover, the onset of taste transduction accomplished by the palatal ta ste buds developed earlier than that achieved by taste buds in the circumva llate and foliate papillae.