Takayuki Marui

Distribution and Morphological Features of Taste Buds in the Zebrafish, Danio rerio

The distribution and morphological features of taste buds in zebrafish (Danio rerio) were investigated with scanning electron (SEM) and light microscopy (LM). The total number of taste buds in zebrafish is approximately 2,200. Taste buds are distributed in almost equal numbers on the external facial skin surface and within the oral cavity, including the gill regions, however, the highest density of taste buds occur along the barbels. Taste buds located on the outer facial skin and within the oral cavity differ in appearance. Those in the oral cavity protrude from the epithelia, whereas those on the external skin surface are sunken. This difference in appearance might be caused by the thickness of the epithelia. The height (30—80 μm) and width (20—50 μm) of taste buds in these two regions are similar, but are of smaller dimensions than those observed in other teleosts. The number (20—23) of cells within a taste bud is less than that reported for other teleost species. The small-sized taste buds and small number of cells may be attributable to the small body size of zebrafish.

Specific Amino Acid Binding to Membrane Fractions of Carp Taste Epithelium

The gustatory system of the carp, Cyprinus carpio, is highly sensitive to amino acid stimuli. The amino acid receptor mechanisms have been characterized in previous electrophysiological studies to have thresholds in the nM range. Self- and cross-adaptation experiments have indicated independent taste receptors for the L-isomers of alanine, glutamate, aspartate, proline, and cysteine, and for glycine betaine [1]. Receptor adaptation with each of these amino acids did not affect taste responses to the other amino acids. This study of Marui et al. [1] suggested the presence of six different types of high affinity amino acid receptors in the taste cell membranes of the carp.