“Type III” cells of rat taste buds: Immunohistochemical and ultrastructural studies of neuron‐specific enolase, protein gene product 9.5, and serotonin

Abstract

Taste buds contain a variety of morphological and histochemical types of elongate cells. Serotonin, neuron-specific enolase (NSE), ubiquitin carboxyl terminal hydrolase (PGP 9.5), and neural cell adhesion molecule (N-CAM) all have been described as being present in the morphologically defined Type III taste cells in rats. In order to determine whether these substances coexist in a single cell, we undertook immunohistochemical and ultrastructural analysis of taste buds in rats. Double-label studies show that PGP 9.5 and NSE always colocalize. In contrast, PGP 9.5 and serotonin seldom colocalize. Further, whereas the serotonin-immunoreactive cells are always slender and elongate, the PGP 9.5/NSE population comprise two morphological types--one slender, the other broader and pyriform. Although gustducin-immunoreactive taste cells appear similar in overall shape to the pyriform PGP 9.5/NSE population, gustducin never colocalizes with PGP 9.5 or NSE. The serotonin-immunoreactive taste cells have an invaginated nucleus, synaptic contacts with nerve fibers, and taper apically to a single, large microvillus. These are all characteristics of Type III taste cells described previously in rabbits (Murray [1973] Ultrastructure of Sensory Organs I. Amsterdam: North Holland. p 1-81). PGP 9.5-immunoreactive taste cells exhibit two morphological varieties. One type is similar to the serotonin-immunoreactive population, containing an invaginated nucleus, synapses with nerve fibers, and a single large microvillus. The other type of PGP 9.5-immunoreactive taste cell has a large round nucleus and the apical end of the cell tapers to a tuft of short microvilli, which are characteristics of Type II taste cells. Thus, in rats, some Type III cells accumulate serotonin but do not express PGP 9.5, whereas others express PGP 9.5 but do not accumulate amines. Similarly, Type II taste cells come in at least two varieties: those immunoreactive for gustducin and those immunoreactive for PGP 9.5.

Differential expression of a BMP4 reporter allele in anterior fungiform versus posterior circumvallate taste buds of mice

“…NCAM and serotonin antisera were used to assess BMP4-ß-gal expression in type III cells (Figure 3E,E',F,F'), and 8% of serotonin-IR cells and 12.5% of NCAM-IR cells were ß-gal-immunopositive (Figure 3G). Finally, PGP9.5 antiserum recognizes a subset of both type II and III cells, which are not immunoreactive for gustducin or serotonin, respectively [17]. Double immunolabeling for ß-gal and PGP9.5 revealed that 11.7% of PGP9.5-IR expressing cells also were ß-gal-IR (Figure 3D,D',G).…”

Espins and the actin cytoskeleton of hair cell stereocilia and sensory cell microvilli

“…They extend microvilli from their tapered apical surface into the taste pit and pore, which reflect a small, recessed opening in the surrounding epithelium. On the basis of microscopic features and specific markers, the sensory cells of taste buds are presently categorized as type II or type III cells, whereas the supporting cells are referred to as type I cells [40][41][42]. A majority of the sensory cells in taste buds are type II cells, which are believed to detect bitter, sweet and umami stimuli [42,43].…”

“…2D, arrowheads). Type III cells appear to represent a relatively minor population of taste bud cells and are believed to display a single blunt apical microvillus that projects far up into the taste pore [41,44,45] (fig. 2D, arrow).…”

FXYD6, a Na,K-ATPase Regulator, Is Expressed in Type II Taste Cells

“…1,[5][6][7] To determine which types of cells express Fxyd6 in CV taste buds, we carried out double-labeled in situ hybridization. Trpm5 and Pkd2l1 were used as cell markers in this analysis.…”

“…[4][5][6] Type III cells have synaptic vesicles including synaptic molecules and express the channels for sour taste. 1,5,7,8) Type II and III taste cells are known to be electrically excitable, 9) but the sodium ion (Na þ ) channel isoforms expressed by the 2 cell types differ. 10) Type II cells express Na þ channels (SCNs) SCN2A, SCN3A, and SCN9A, whereas type III cells express only SCN2A.…”