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The distribution of taste buds of layer‐type chickens, from day 1 (H1) to day 140 (H140) post‐hatching, were investigated histologically and with a scanning electron microscope. Two types of openings were observed on the oral epithelium: large openings that were greater than 10 μm in width, and had an ellipsoid or spindle shape; and small openings that were less than 7 μm in width, and had a circular or polygon shape. It was defined that the former represent the openings of the salivary glands, and the latter are those of the taste buds. The number of taste buds remained constant from H1 to H140. Therefore, no significant change was observed between these two time points. To investigate the distribution of the taste buds in the whole oral cavity, a distribution map was created.

The relationship between taste sensitivity and the number of taste buds using a bitter tastant, quinine hydrochloride, was investigated in White Leghorn, Rhode Island Red, and broiler chickens. The White Leghorn and Rhode Island Red strains were able to perceive 2.0 mmol/L quinine hydrochloride, but the taste sensitivity of Rhode Island Red chickens was higher than that of White Leghorn chickens. Broiler chickens perceived 0.5 mmol/L quinine hydrochloride. The number of taste buds in the White Leghorn strain was the lowest, then the Rhode Island Red strain, with the number of taste buds highest in the broiler chickens. The number of taste buds was well correlated with bitter taste sensitivity. Therefore, we suggest that the number of taste buds is a vital factor in the perception of bitter taste and may be useful in selecting appropriate feeds for chickens.

We investigated the expression of gustducin in chicken taste buds using molecular biological, biochemical and immunohistochemical techniques. Expression of a gustducin-like sequence was detected by RT-PCR in the tissues containing taste buds, and corresponded to the predicted gustducin gene in the chicken. Expression of this sequence was not detected in the brain, heart, liver, pancreas, intestine, kidney and testis of the chicken. The expressed sequence had a high specificity for oral tissues that contained taste buds. These results suggest that the detected sequence was the chicken gustducin gene. Next, we generated a polyclonal antiserum against the chicken gustducin protein to observe its localization in the oral tissues. The results revealed that the chicken gustducin was specifically expressed in the taste buds. It is suggested that the chicken has a gustatory system mediated by gustducin, and chicken gustducin is a reliable marker for taste buds or taste cells. This is the first molecular biological, biochemical and immunohistochemical demonstration of the presence of gustducin in the chicken.

We isolated chicken taste buds and used a real-time Ca2+ imaging technique to investigate the functions of the taste cells. With RT-PCR, we found that isolated chicken taste bud-like cell subsets express chicken gustducin messenger RNA. Immunocytochemical techniques revealed that the cell subsets were also immunopositive for chicken gustducin. These results provided strong evidence that the isolated cell subsets contain chicken taste buds. The isolated cell subsets were spindle-shaped and approximately 61-75 μm wide and 88-98 μm long, and these characteristics are similar to those of sectional chicken taste buds. Using Ca2+ imaging, we observed the buds' response to 2 mmol/L quinine hydrochloride (a bitter substance) and their response to a mixture of 25 mmol/L L-glutamic acid monopotassium salt monohydrate and 1 mmol/L inosine 5'-monophosphate disodium salt, umami substances. The present study is the first morphological demonstration of isolated chicken taste buds, and our results indicate that the isolated taste buds were intact and functional approaches for examining the taste senses of the chicken using Ca2+ imaging can be informative.

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ABSTRACT. The taste buds of bovine fungiform papillae were studied by light and electron microscopy using both histological and immunohistochemical methods. The taste buds existed in the epithelium of the apical region of the papillae. By electron microscopy, two types of taste cells, namely type I and type II cells, could be classified according to the presence of dense-cored vesicles, the cytoplasmic density and the cell shape. Type I cells were thin, had an electron-dense cytoplasm containing dense-cored vesicles, and possessed long thick apical processes in the taste pore. Type II cells were thick, had an electron-lucent cytoplasm containing many electron-lucent vesicles, rather than dense-cored vesicles, and possessed microvilli in the taste pore. Immunohistochemical staining with an antiserum against gustducin was investigated by both light and electron microscopy using the avidin-biotin complex (ABC) method. Some, but not all, of the type II cells exhibited gustducin immunoreactivity, whereas none of the type I cells showed any immunoreactivity. KEY WORDS: bovine, fungiform papilla, gustducin, structure, taste bud.J. Vet. Med. Sci. 68(9): 953-957, 2006 Gustducin, a G-protein specific for taste cells [7], has been reported to be involved in not only bitter but also sweet taste transduction [5-7, 9, 14]. Our previous study of bovine circumvallate papillae demonstrated that type II taste cells exhibit immunoreactivity for a gustducin antiserum [12]. In the bovine tongue, two types of papillae, namely the circumvallate and fungiform papillae, contain taste buds. The present study investigated the structures of the taste cells in bovine fungiform papillae and their immunoreactivities for the gustducin antiserum. MATERIALS AND METHODSAfter collecting bovine tongues from a local slaughterhouse, the fungiform papillae were removed and fixed with 2% glutaraldehyde and 2% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) for the histological study or 0.1% glutaraldehyde and 4% paraformaldehyde for the immunocytological study. For the histological study, the fungiform papillae were placed into the above-mentioned fixatives for 4 hr on ice. The specimens were then washed in the phosphate buffer overnight, and post-fixed in 1% OsO 4 in the same phosphate buffer for 1 hr on ice. After dehydration in an ascending series of ethanol and absolute acetone, the specimens were embedded in epoxy resin. Semi-thin sections were cut with glass knives, stained with toluidine blue and observed with a Nikon Eclipse E 800 microscope. Ultra-thin sections were cut with a diamond knife, mounted on formvar-supported one-slot grids, stained with lead citrate and uranyl acetate and observed with a Hitachi H-600 transmission electron microscope.The avidin-biotin complex (ABC) visualization method was carried out as described previously [11,12]. Briefly, the fungiform papillae were fixed in a phosphate buffer containing 0.1% glutaraldehyde and 4% paraformaldehyde for 4 hr on ice, and then cut into 50 µm sections with a microslicer (Dosa...