Ultrastructure of palatal taste buds in the perihatching chick

Abstract

Palatal taste buds of perihatching chicks were examined by electron microscopy. Four intragemmal cell types were characterized. 1) Light: with voluminous, electron-lucent cytoplasm containing scattered free ribosomes, rough and smooth endoplasmic reticulum, plump mitochondria, sparse perinuclear filaments, occasional Golgi bodies, and numerous clear and dense-cored vesicles. Clear vesicles sometimes aggregate in a presynaptic-like configuration apposed to an axonal profile. These cells contained large, spherical, uniformly granular nuclei with one nucleolus. 2) Dark: with dense cytoplasm containing filamentous bundles surrounding the nucleus, occasional clear vesicles, centrioles, rough endoplasmic reticulum, and compact mitochrondria. The apical cytoplasm noticeably lacks dense secretory granules. Irregular to lobulated nuclei are densely granular, and contain scattered clumps of chromatin, adhering especially to the inner leaflet of the nuclear membrane, and at least one nucleolus. Cytoplasmic extensions of dark cells envelop other intragemmal cell types and nerve fibers. Light and dark cells project microvilli into the taste pore. 3) Intermediate: contain gradations of features of light and dark cells. 4) Basal: darker than the other intragemmal cell types and confined to the ventral bud region. Putative afferent synapses in relation to light cells, and axo-axonal contacts are described. While the appearance of axo-axonal contacts may be a transient developmental event, other bud features are consonant with observations in adult chickens and suggest that the peripheral gustatory apparatus is mature at hatching in this precocial avian species.

Fingerprinting taste buds: intermediate filaments and their implication for taste bud formation

“…The especially dense distribution of intermediate ¢laments in electron-dense taste bud cells in ¢shes (Reutter & Witt 1993) may indicate the presence of vimentin, although immunohistochemical evidence is lacking. The taste disc of Xenopus is of particular interest, since the ¢lament distribution in electron-dense taste cells (¢gure 3) resembles that seen in ¢shes and chick (Ganchrow et al 1991;Reutter & Witt 1993). Intermediate ¢laments occurring in Merkel-like basal cells of amphibian taste discs are most probably CKs, since epidermal Merkel cells also are known to possess CK20, suggesting an ectodermal origin (Moll 1993 The di¡erences in the extent and location of vimentin expression in early developing taste buds of humans and chicks, however, suggest that mechanisms of di¡erentiation of the same receptor organ vary among vertebrate forms.…”

Distribution of α-Gustducin and Vimentin in premature and mature taste buds in chickens

“…The α-Gustducin + , Vimentin + , α-Gustducin + Vimentin + , and α-Gustducin − Vimentin − taste bud cells may represent different taste cell types or taste cells at different phases of development. Four different cell types (dark, light, intermediate and basal cells) have been identified in chickens [21, 22]. So far there are no molecular markers available that can be used to identify the specific cell types.…”

Ontogenesis and taste bud cell turnover in the chicken. I. Gemmal cell renewal in the hatchling

“…Conversely, round-clear cells often were found in lateral as well as central positions in sections cut through the gemmal center. Ultrastructural studies of hatchling buds indicate a range of cell types [dark, intermediate, light, basal and peripheral (perigemmal)] (Ganchrow and Ganchrow, 1989;Ganchrow et al, 1991). Compared with measurements of bud cell nuclear diameter obtained ultrastructurally, roundclear nuclei correspond most closely with nuclei of "light" cells, and gracile-dense nuclei with nuclei of "perigemmal" and "basal" cells.…”

“…Ultrastructural studies of palatal taste buds indicate that bud cell morphology and receptoneural profiles are very similar in perihatching and adult chickens (Kurosawa et al, 1983;Ganchrow and Ganchrow, 1989;Ganchrow et al, 1991Ganchrow et al, , 1993. Taste pores begin to appear already on embryonic day 19, thereby facilitating bud communication with oral tastants and discriminative taste reactivity at perihatching (Vince, 1977;Ganchrow and Ganchrow, 1987;Ganchrow et al, 1990).…”

“…In contrast to gemmal development in altricial rodents, buds in the anterior floor of the lower beak (innervated by the chorda tympani branch of the facial nerve) of the precocial chick develop during the last four days in ovo, and the adult complement of buds is achieved by hatching (gestation is 21 days in rat and chick; Saito, 1966;Gentle and Hunter, 1983;Berkhoudt, 1985;Ganchrow et al, 1986;Ganchrow, 1987, 1989). Ultrastructural studies of palatal taste buds indicate that bud cell morphology and receptoneural profiles are very similar in perihatching and adult chickens (Kurosawa et al, 1983;Ganchrow and Ganchrow, 1989;Ganchrow et al, 1991Ganchrow et al, , 1993. Taste pores begin to appear already on embryonic day 19, thereby facilitating bud communication with oral tastants and discriminative taste reactivity at perihatching (Vince, 1977;Ganchrow and Ganchrow, 1987;Ganchrow et al, 1990).…”