Ulex Europaeus Agglutinin-1 Is a Reliable Taste Bud Marker for In Situ Hybridization Analyses

SARS-CoV-2 recombinant proteins-induced degeneration of taste buds in rat circumvallate papillae

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections cause loss or alteration of taste and smell as early symptoms and sequelae, but the detailed mechanism remains unclear. This study investigated whether coronavirus disease 2019-induced taste disorders are caused by direct effects on taste bud cells. SARS-CoV-2 recombinant spike and nucleocapsid proteins were applied to circumvallate papillae of male Sprague–Dawley rats. Immunohistochemistry and image analysis were used to compare the number of taste buds, and taste bud cells and area, together with confirmation of angiotensin-converting enzyme 2 (ACE2) expression. Immunohistochemical analysis revealed ACE2 expression in the taste buds of rat circumvallate papillae. Decreases in the number of taste buds, taste bud cells, and their area were observed at 12 days after application of SARS-CoV-2 recombinant spike and nucleocapsid proteins. These data suggest that SARS-CoV-2 proteins induce degeneration of taste buds.

A large increase of sour taste receptor cells in Skn-1-deficient mice does not alter the number of their sour taste signal-transmitting gustatory neurons

The connections between taste receptor cells (TRCs) and innervating gustatory neurons are formed in a mutually dependent manner during development. To investigate whether a change in the ratio of cell types that compose taste buds influences the number of innervating gustatory neurons, we analyzed the proportion of gustatory neurons that transmit sour taste signals in adult Skn-1a^-/- mice in which the number of sour TRCs is greatly increased. We generated polycystic kidney disease 1 like 3-wheat germ agglutinin (pkd1l3-WGA)/Skn-1a^+/+ and pkd1l3-WGA/Skn-1a^-/- mice by crossing Skn-1a^-/- mice and pkd1l3-WGA transgenic mice, in which neural pathways of sour taste signals can be visualized. The number of WGA-positive cells in the circumvallate papillae is 3-fold higher in taste buds of pkd1l3-WGA/Skn-1a^-/- mice relative to pkd1l3-WGA/Skn-1a^+/+ mice. Intriguingly, the ratio of WGA-positive neurons to P2X₂-expressing gustatory neurons in nodose/petrosal ganglia was similar between pkd1l3-WGA/Skn-1a^+/+ and pkd1l3-WGA/Skn-1a^-/- mice. In conclusion, an alteration in the ratio of cell types that compose taste buds does not influence the number of gustatory neurons that transmit sour taste signals.