Death in the taste bud: engulfment of dying taste receptor cells by glial-like Type I cells.

Taste buds comprise 50-100 epithelial derived cells, including glial-like cells (Type I) and two types of receptor cells (Types II and III). All of these taste cells are renewed throughout the life of an organism from a pool of uncommitted basal cells. Immature cells enter the bud at its base, maturing into one of the three mature cell types.

Taste Bud Connectome: Implications for Taste Information Processing.

Taste buds contain multiple cell types, two of which mediate transduction of specific taste qualities: Type III cells transduce sour while Type II cells transduce either sweet, or bitter or umami. In order to discern the degree of interaction between different cell types and specificity of connectivity with the afferent nerve fibers (NFs), we employed serial blockface scanning electron microscopy (sbfSEM) through five circumvallate mouse taste buds. Points of contact between Type II and Type III cells are rare and lack morphologically identifiable synapses, suggesting that interaction between these cell types does not occur via synapses.

Three-dimensional reconstructions of mouse circumvallate taste buds using serial blockface scanning electron microscopy: I. Cell types and the apical region of the taste bud.

Taste buds comprise four types of taste cells: three mature, elongate types, Types I-III; and basally situated, immature postmitotic type, Type IV cells. We employed serial blockface scanning electron microscopy to delineate the characteristics and interrelationships of the taste cells in the circumvallate papillae of adult mice. Type I cells have an indented, elongate nucleus with invaginations, folded plasma membrane, and multiple apical microvilli in the taste pore.

Chemical synapses without synaptic vesicles: Purinergic neurotransmission through a CALHM1 channel-mitochondrial signaling complex.

Conventional chemical synapses in the nervous system involve a presynaptic accumulation of neurotransmitter-containing vesicles, which fuse with the plasma membrane to release neurotransmitters that activate postsynaptic receptors. In taste buds, type II receptor cells do not have conventional synaptic features but nonetheless show regulated release of their afferent neurotransmitter, ATP, through a large-pore, voltage-gated channel, CALHM1. Immunohistochemistry revealed that CALHM1 was localized to points of contact between the receptor cells and sensory nerve fibers.

Microwave processing of gustatory tissues for immunohistochemistry.

We use immunohistochemistry to study taste cell structure and function as a means to elucidate how taste receptor cells communicate with nerve fibers and adjacent taste cells. This conventional method, however, is time consuming. In the present study we used taste buds from rat circumvallate papillae to compare conventional immunohistochemical tissue processing with microwave processing for the colocalization of several biochemical pathway markers (PLCβ2, syntaxin-1, IP3R3, α-gustducin) and the nuclear stain, Sytox.

Immunocytochemical analysis of P2X2 in rat circumvallate taste buds.

Background: Our laboratory has shown that classical synapses and synaptic proteins are associated with Type III cells. Yet it is generally accepted that Type II cells transduce bitter, sweet and umami stimuli. No classical synapses, however, have been found associated with Type II cells.

Knocking out P2X receptors reduces transmitter secretion in taste buds.

In response to gustatory stimulation, taste bud cells release a transmitter, ATP, that activates P2X2 and P2X3 receptors on gustatory afferent fibers. Taste behavior and gustatory neural responses are largely abolished in mice lacking P2X2 and P2X3 receptors [P2X2 and P2X3 double knock-out (DKO) mice]. The assumption has been that eliminating P2X2 and P2X3 receptors only removes postsynaptic targets but that transmitter secretion in mice is normal.

The candidate sour taste receptor, PKD2L1, is expressed by type III taste cells in the mouse.

The transient receptor potential channel, PKD2L1, is reported to be a candidate receptor for sour taste based on molecular biological and functional studies. Here, we investigated the expression pattern of PKD2L1-immunoreactivity (IR) in taste buds of the mouse. PKD2L1-IR is present in a few elongate cells in each taste bud as reported previously.

Immunocytochemical analysis of syntaxin-1 in rat circumvallate taste buds.

Mammalian buds contain a variety of morphological taste cell types, but the type III taste cell is the only cell type that has synapses onto nerve processes. We hypothesize that taste cell synapses utilize the SNARE protein machinery syntaxin, SNAP-25, and synaptobrevin, as is used by synapses in the central nervous system (CNS) for Ca2+-dependent exocytosis. Previous studies have shown that taste cells with synapses display SNAP-25- and synaptobrevin-2-like immunoreactivity (LIR) (Yang et al.

Qualitative and quantitative differences between taste buds of the rat and mouse.

Background: Numerous electrophysiological, ultrastructural, and immunocytochemical studies on rodent taste buds have been carried out on rat taste buds. In recent years, however, the mouse has become the species of choice for molecular and other studies on sensory transduction in taste buds. Do rat and mouse taste buds have the same cell types, sensory transduction markers and synaptic proteins? In the present study we have used antisera directed against PLCbeta2, alpha-gustducin, serotonin (5-HT), PGP 9.

Synaptobrevin-2-like immunoreactivity is associated with vesicles at synapses in rat circumvallate taste buds.

Synaptobrevin is a vesicle-associated membrane protein (VAMP) that is believed to play a critical role with presynaptic membrane proteins (SNAP-25 and syntaxin) during regulated synaptic vesicle docking and exocytosis of neurotransmitter at the central nervous system. Synaptic contacts between taste cells and nerve processes have been found to exist, but little is known about synaptic vesicle docking and neurotransmitter release at taste cell synapses. Previously we demonstrated that immunoreactivity to SNAP-25 is present in taste cells with synapses.

Morphologic characterization of rat taste receptor cells that express components of the phospholipase C signaling pathway.

Rat taste buds contain three morphologically distinct cell types that are candidates for taste transduction. The physiologic roles of these cells are, however, not clear. Inositol 1,4,5-triphosphate (IP(3)) has been implicated as an important second messenger in bitter, sweet, and umami taste transductions.

"Type III" cells of rat taste buds: immunohistochemical and ultrastructural studies of neuron-specific enolase, protein gene product 9.5, and serotonin.

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.

Ultrastructural localization of gustducin immunoreactivity in microvilli of type II taste cells in the rat.

Gustducin is a transducin-like G protein (guanine nucleotide-binding protein) that is expressed in taste bud cells. Gustducin is believed to be involved in bitter and possibly sweet taste transduction. In the present study, we demonstrate that a subset of type II cells displays immunoreactivity to antisera directed against gustducin in taste buds of rat circumvallate papilla.

Taste cells with synapses in rat circumvallate papillae display SNAP-25-like immunoreactivity.

SNAP-25 is a 25 kDa protein believed to be involved in the processes of membrane fusion and exocytosis associated with neurotransmitter release. In the present study we present evidence that SNAP-25-like immunoreactivity can be used as a marker for taste cells with synapses in rat circumvallate papillae. SNAP-25 immunoreactivity is present in most intragemmal nerve processes and a small subset of taste cells.

High-voltage electron microscopy and 3-D reconstruction of solitary chemosensory cells in the anterior dorsal fin of the Gadid fish Ciliata mustela (Teleostei).

Solitary chemosensory cells (SCCs) are secondary sensory cells present in the epidermis of most primary aquatic vertebrates. In rocklings, the epidermis of the anterior dorsal fin (ADF) contains approximately 5 million SCCs. High-voltage electron microscopy and three-dimensional reconstructions from serial sections were used to examine the ultrastructure, arrangement, and synaptic contacts of the SCCs in the rockling ADF.

Identified taste bud cell proliferation in the perihatching chick.

Developing taste buds in the anterior mandibular floor of perihatching chicks were studied by high voltage electron microscopic autoradiography in order to identify proliferating gemmal cell types. Montaged profiles of 29 taste buds in five cases euthanized between embryonic day 21 and posthatching day 2 were analyzed after a single [3H]thymidine injection administered on embryonic day 16, 17 or 18. Results showed that dark cells comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568 cells) gemmal cells as compared with light, intermediate, basal or perigemmal bud cells.

Comparison of high-pressure freezing/freeze substitution and chemical fixation of catfish barbel taste buds.

The barbel taste buds of catfish are widely used as a model system for investigating the structure and function of vertebrate taste buds. We have examined the ultrastructure of the taste buds of the channel catfish, Ictalurus punctatus, as part of a comparative study of the morphology of taste buds in various mammalian and non-mammalian vertebrates. Since conventional chemical fixation methods have limited usefulness for certain kinds of ultrastructural studies (i.

Taste bud cell generation in the perihatching chick.

Chick taste bud primordia initially appear in late gestation on embryonic day 17 (E17), 4 days before hatching. To track DNA synthesis and subsequent taste bud cell proliferation between E17 and the second day post-hatching (H2), single 25 muCi injections of tritiated thymidine (specific activity = 72.5 Ci/mmol) were administered in ovo during E15, E16, E17 or E18.

Application of serial sectioning and three-dimensional reconstruction to the study of taste bud ultrastructure and organization.

The lingual taste buds of mammals are complex organs containing dozens of cells of varying morphology and numerous nerve fibers that are intermingled among the cellular processes. Some of the taste bud cells form synaptic contacts with these nerve fibers. Important questions remain to be answered regarding the structure and function of the cells of various types within taste buds and the means by which responses to gustatory stimuli are transmitted to the nerve fibers that communicate with the brain.

Electrophysiological and morphological properties of light and dark cells isolated from mudpuppy taste buds.

Isolated Necturus taste receptor cells were studied by giga-seal whole-cell recording and electron microscopy to correlate electrophysiological properties with taste cell structural features. Dark (type I) cells were identified by the presence of dense granular packets in the supranuclear and apical regions of the cytoplasm. In response to a series of depolarizing voltage commands from a holding potential of -80 mV, these cells exhibited a transient, TTX-sensitive inward Na+ current, a sustained outward K+ current, and a slowly inactivating inward Ca++ current.

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

Taste bud cell turnover rate was examined in oral epithelium of the precocial chick, which at hatching contains the adult complement of taste buds. Forty newly hatched chicks received single or double pulse injections of tritiated thymidine (specific activity was 6.7 Curies/millimole; dosage was 0.

HVEM ultrastructural analysis of mouse fungiform taste buds, cell types, and associated synapses.

We have used high voltage electron microscopy and computer-generated three-dimensional reconstructions from serial sections to elucidate the structure of taste bud cells and their associated synapses in fungiform taste buds of the mouse. Five fungiform taste buds (two of which were serially sectioned) were examined with the high-voltage electron microscope (HVEM). We identified the synaptic connections from taste cells onto sensory nerve fibers and classified the presynaptic taste cells based on previously established ultrastructural criteria.

Aspects of vertebrate gustatory phylogeny: morphology and turnover of chick taste bud cells.

The taste bud is a receptor form observed across vertebrates. The present report compares chick taste buds to those of other vertebrates using light and electron microscopy. Unlike mammals, but common to many modern avians, the dorsal surface of chick anterior tongue lacks taste papillae and taste buds.