Light and dark cells of rat vallate taste buds are morphologically distinct cell types

Cells of mammalian taste buds have been classified into morphological types based on ultrastructural criteria, but investigators have disagreed as to whether these are distinct cell types or the extremes of a continuum. To address this issue, we examined taste buds from rat vallate papillae that had been sectioned transversely, rather than longitudinally, to their longest axis. In these transverse sections, dark (Type I) and light (Type II) cells were easily distinguished by their relative electron density, shape and topological relationships. Cells with electron-lucent cytoplasm (light cells) were circular or oval in outline, while those with electron-dense cytoplasm (dark cells) had an irregular outline with sheetlike cytoplasmic projections that separated adjacent light cells. A hierarchical cluster analysis of 314 cells across five morphological parameters (cell shape and area, and nuclear ellipticity, electron density and invagination) revealed two distinct groups of cells, which largely corresponded to the dark and light cells identified visually. These cells were not continuously distributed within a principal components factor solution. Differences in the means for dark and light cells were highly significant for each morphological parameter, but within either cell type, changes in one parameter correlated little with changes in any other. These analyses all failed to reveal cells with a consistent set of intermediate characteristics, suggesting that dark and light cells of rat vallate taste buds are distinct cell types rather than extremes of a continuum. Sections of taste buds were stained with antibodies to several carbohydrates, then observed by indirect immunofluorescence. Optical sections taken with a confocal laser-scanning microscope showed that the Lewis antigen was present only on spindle-shaped cells with circular or oval outlines and lacking transverse projections; these characteristic shapes matched those of light cells seen by electron microscopy. The H blood group antigen and the 2B8 epitope appeared at most cell-cell interfaces in the bud and are present on dark cells and possibly on some light cells. These findings relate molecular markers to morphological phenotypes and should facilitate future studies of taste cell turnover, development and regeneration.     

Comparative ultrastructure of vallate, foliate and fungiform taste buds of golden Syrian hamster

A fine-structure study of the hamster fungiform, foliate and vallate taste buds was undertaken for comparative purposes. All three taste bud types shared in common composition of the dark cells, light cells, basal cells, nerve fibers and nerve endings and undifferentiated peripheral cells, but morphological difference existed among them. The foliate and vallate taste buds were quite similar in their ultrastructural morphology. Their dark cells displayed long apical necks, long apical microvilli, apical osmiophilic secretory granules and an abundant rough endoplasmic reticulum. The dark cells of the fungiform taste buds, however, showed no neck formation and lacked apical osmiophilic granules. They had short apical microvilli and relatively scant rough endoplasmic reticulum. There was no difference in the fine structure features of the light cells, basal cells and neural elements of different types of taste buds. Both light and dark cells were much more readily distinguishable in foliate and vallate buds than in fungiform buds at both light-and electron-microscopic levels. Foliate and vallate buds demonstrated homogeneous dense substance within the taste pores while fungiform pores were frequently empty. It is speculated that the differences in taste bud morphology may be due to their different lingual locations and/or may be a reflection of the differences in the inductive influences from different nerves. Furthermore, structural differences may be responsible for varying thresholds to different taste modalities.     

BDNF-dependent enhancement of exocytosis in cultured cortical neurons requires translation but not transcription

PURPOSE: The surgical management of chronic atherosclerotic renal artery occlusion (RA-OCC) was studied. METHODS: From January 1987 through December 1996, 397 consecutive patients were treated for atherosclerotic renal artery disease. Ninety-five hypertensive patients (mean blood pressure, 204 +/- 31/106 +/- 20 mm Hg; mean medications, 3.0 +/- 1.1 drugs) were treated for 100 RA-OCCs. Eighty-four (88%) patients had renal dysfunction, defined by serum creatinine levels >/=1.3 mg/dL (mean serum creatinine level, 2.8 +/- 2.0 mg/dL). Demographic characteristics, operative morbidity and mortality, blood pressure/renal function response, and postoperative decline in renal function were examined and compared with that of 302 patients treated for renal artery stenosis (RAS). RESULTS: After operation, there were 5 perioperative deaths (5.2%), 2 (2.8%) after revascularization and 3 (12%) after nephrectomy (P =.11), compared with 12 (4.0%) perioperative deaths in the RAS group (P =.59). After controlling for important covariates, estimated survival and blood pressure benefits did not differ between RA-OCC patients treated by nephrectomy or revascularization (P =.13; 87% vs 92%, P =.54). Excretory renal function was considered improved in 49% of 79 RA-OCC patients with renal dysfunction, including 9 patients removed from dialysis-dependence. Among patients treated for unilateral disease, revascularization for RA-OCC was associated with significant improvement in renal function (P <.01); however, nephrectomy alone did not increase renal function significantly. Improved renal function after operation was associated with a significant and independent increase in survival (P <.01) and dialysis-free survival (P <.01) among patients treated for RA-OCC. In addition, blood pressure benefit, renal function response, and estimated survival did not differ significantly after reconstruction for RA-OCC or RAS. CONCLUSION: Among hypertensive patients treated for RA-OCC, equivalent beneficial blood pressure response was observed after both revascularization and nephrectomy. In patients who underwent bilateral renal artery revascularization, the change in excretory renal function attributable to repair of RA-OCC cannot be defined. In patients treated for unilateral disease, however, improvement in function was observed only after revascularization. Moreover, improved renal function demonstrated a significant and independent association with improved survival. This experience supports renal revascularization in preference to nephrectomy for RA-OCC in select hypertensive patients when a normal distal artery is demonstrated at operation.     

Biology of taste buds and the clinical problem of taste loss

Taste buds are the anatomical structures that mediate the sense of taste. They comprise taste cells and nerve fibers within specialized epithelial structures. Taste cells are traditionally described by histologic methods as basal, dark, intermediate, and light cells, with the nerve fibers surrounding and infiltrating the taste buds. By means of immunohistochemical methods, taste cells and gustatory nerve fibers can be classified in functional groups based on the expression of various cell adhesion molecules and other proteins. When taste buds become damaged, the loss of the ability to taste results. This loss is not uncommon and can impact health and quality of life. Patients who receive radiation therapy for head and neck cancer often experience taste loss, which leads to compromised nutritional intake and a worse outcome than patients who do not experience taste loss. The mode of radiation damage to taste cells and nerve fibers has been investigated using cell adhesion molecules, synaptic vesicle proteins, and other cell markers. The light and intermediate cells are preferentially affected by ionizing radiation, whereas the nerve fibers remain structurally intact. Experimental studies of radiation-induced taste loss are performed via a unique animal/human model.     

Mice with a targeted disruption of the neurotrophin receptor trkB lose their gustatory ganglion cells early but do develop taste buds

The alleged ability of taste afferents to induce taste buds in developing animals is investigated using a mouse model with a targeted deletion of the tyrosine kinase receptor trkB for the neurotrophin BDNF. This neurotrophin was recently shown to be expressed in developing taste buds and the receptor trkB has been shown to be expressed in the developing ganglion cells that innervate the taste buds. Our data show a reduction of geniculate ganglion cells to about 5% of control animals in neonates. Degeneration of ganglion cells starts when processes reach the central target (solitary tract) but before they reach the peripheral target (taste buds). Degeneration of ganglion cells is almost completed in trkB knockout mice before taste afferents reach in control animals the developing fungiform papillae. Four days later the first taste buds can be identified in fungiform papillae of both control and trkB knockout mice in about equal number and density. Many taste buds undergo a normal maturation compared to control animals. However, the more lateral and caudal fungiform papillae grow less in size and become less conspicuous in older trkB knockout mice. No intragemmal innervation can be found in trkB knockout taste buds but a few extragemmal fibers enter the apex and end between taste had cells without forming specialized synapses. Taste buds of trkB knockout mice appear less well organized than those of control mice, but some cells show similar vesicle accumulations as control taste bud cells in their base but no synaptic contact to an afferent. These data strongly suggest that the initial-development of many fungiform papillae and taste buds is independent of the specific taste innervation. It remains to be shown why others appear to be more dependent on proper innervation.     

Innervation of developing human taste buds. An immunohistochemical study

1. Vinorelbine produced a dominant metabolite (M1) after incubation with rat liver microsomes. 2. Several major metabolites other than M1 were identified by HPLC in bile and faeces of rat after intravenous administration. 3. The structures of the major metabolites were identified as 15,16-epoxyvinorelbine (M1), 11'-hydroxyvinorelbine (M2), 19'-hydroxyvinorelbine (M3a), 15,16-epoxy-10'-hydroxyvinorelbine (M3b) and 10'-hydroxyvinorelbine (M4) by comparison of HPLC retention times and by extensive analyses of two-dimensional NMR and hybrid MS/MS spectra.     

Reinnervation of cross-regenerated gustatory nerve fibers into amiloride-sensitive and amiloride-insensitive taste receptor cells

Single nerve fiber responses to NaCl and their inhibition by amiloride were compared among the chorda tympani (CT) and glossopharyngeal (IXth), and their cross-regenerated nerves in the C57BL/KsJ mice. The CT nerve innervating the anterior part of the tongue contained approximately equal numbers of two types of NaCl-responsive neurons; one type showed strong suppression of NaCl responses by amiloride [amiloride-sensitive (AS) type], and the other type showed only weak or no suppression of NaCl responses by amiloride [amiloride-insensitive (AI) type]. In contrast, the IXth nerve innervating the posterior part of the tongue has almost exclusively the AI type. This relative abundance of the AS and AI types of fibers was not altered by cross-regeneration of the two gustatory nerves into the reverse tongue regions. This suggests that regenerated taste axons selectively recouple with the appropriate type of receptor cell whether they innervate the front or the back of the tongue. Such selective synapse reformation may help explain the stability of response profiles of taste neurons during continual receptor cell turnover.     

Thalamocortical relations in taste aversion learning: I. Involvement of gustatory thalamocortical projections in taste aversion learning.

Examined the involvement of presumed gustatory thalamocortical projections in conditioned taste aversion (CTA) learning, using 108 male Long-Evans rats in 4 experiments. Neuroanatomical and neurobehavioral manipulations in the ventrolateral neostriatum were used. Findings demonstrate that projections from posterior ventromedial thalamic nuclei, parvicellular division (VPMpc), and thalamus to the anterior insular gustatory neocortex (AIGN) were essential for normal CTA learning. Because both VPMpc thalamus and the AIGN each have been implicated as functional substrates of CTA learning, the present results suggest that the gustatory thalamocortical relay per se is necessary for normal taste-illness learning. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modification of unit responses to gustatory stimuli by conditioned taste aversion in rats

Secretion of trypsin, chymotrypsin, lipase and amylase was measured in male rats under urethane anaesthesia using a method of continuous perfusion of the duodenum. Prolonged infusion of cholecystokinin-pancreozymin (CCK-PZ) over a period lasting 200-360 min was administered either alone or together with a submaximal dose of secretin (1 unit/100 g - 10 min). Infusion of CCK-PZ was carried out using maximal doses (1--1.5 unit/100 g - 10 min) with and without secretin. Supramaximal doses of CCK-PZ (2 and 4 units/100 g - 10 min) were used only in combination with secretin. In all experiments secretion of enzymes showed a triphasic pattern including an initial peak followed by a plateau secretion after 10--20 min (phase 1), a decreasing second phase and finally base-line secretion (phase 3), thus demonstrating exhaustion of enzyme output from the gland with time. With increasing and supramaximal dose of CCK-PZ the cumulative output of enzymes from start to baseline secretion decreased progressively. Under the same conditions the levels of peak and plateau secretion were lower, the duration of plateau secretion was longer and the decreasing phase of secretion was shortened. These features indicate inhibition of secretion with increasing supramaximal doses of CCK-PZ infusion. Whereas the proteolytic enzymes and lipase reacted in a parallel way always amylase secretion was sustained on a higher level, implicating an alternative pathway for secretion.     

NMDA and non-NMDA receptors mediate taste afferent inputs to cortical taste neurons in rats

Two main subclasses of ionotropic receptors for excitatory amino acids (EAAs), N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors, are involved in neurotransmission in the cortex of mammals. To examine whether EAAs are transmitters at the cortical taste area (CTA) in rats and to elucidate which types of the two ionotropic receptors operate at these synapses, we studied the effects of microiontophoretic administration of EAA antagonists on the responses of 64 taste cortical neurons to four basic taste stimuli in urethane-anesthetized rats. Both D-2-amino-5-phosphonovalerate (APV), a selective antagonist for NMDA receptors, and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a selective antagonist for non-NMDA receptors, suppressed most of the taste responses. The percentage of neurons suppressed by APV (70.3%) was almost the same as that suppressed by CNQX (64.1%). These suppressive effects were independent of the effects of background discharges during the prestimulus, water-rinsing period. The percentage of neurons suppressed by the antagonists did not differ between any pairs of taste stimuli. The number of neurons possessing both receptors was larger in the granular insular area (area GI), one of the two CTAs, than in the dysgranular insular area (area DI). In addition, taste responses were suppressed by CNQX or by both APV and CNQX in area GI in a significantly larger number of layer V neurons than in area DI. The present results indicate that normal excitatory transmission of taste afferents in the CTA in rats was mediated by both NMDA and non-NMDA receptors. The finding that a large fraction of neurons in the CTA in rats mediated taste information through NMDA receptors in normal transmission might be related to the higher potency of the plasticity observed in the CTA.     

Effects of lesions of the gustatory neocortex on taste aversion learning in the rat.

In 5 experiments, 110 normal male Long-Evans hooded rats and 125 Ss with lesions of the gustatory neocortex (GN) were compared for their ability to learn aversions to taste cues paired with toxicosis. When the taste presentation was followed immediately by toxicosis, normal Ss and 8 Ss with lesions of the posterior (visual) neocortex learned aversions to sucrose, sodium chloride, quinine hydrochloride, and hydrochloric acid solutions. Ss with GN lesions learned aversions to all solutions except sucrose. In preference tests, all solutions were shown to be discriminable from water by both normal and GN-lesioned Ss. Under conditions in which a 6-hr delay separated taste presentation and toxicosis, normals again learned specific aversions to all 4 solutions, but Ss with GN lesions failed to learn specific aversions to sucrose, sodium chloride, and hydrochloric acid solutions. It was shown that the ability of Ss with GN lesions to learn aversions to sucrose and quinine depended on stimulus concentration. It is proposed that the data can be accounted for by postulating a change in the threshold for taste illness associations following GN lesions. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste agnosia following gustatory neocortex ablation: Dissociation from odor and generality across taste qualities.

In Exp I, 18 male Long-Evans hooded rats trained to avoid drinking in the presence of a compound odor (benzyl acetate) and taste (sucrose) CS lost the taste habit but retained the odor habit following gustatory neocortex (GN) ablation. Conversely, olfactory bulb ablation resulted in loss of the odor habit but retention of the taste habit. In Exp II, with 60 Ss, Ss lacking GN did not retain preoperatively instated learned aversions to a suprathreshold quinine hydrochloride (bitter) taste solution that had been employed as a CS. However, Ss with GN lesions that were virtually identical to those of the bitter-trained group retained a preoperatively learned aversion to a hydrochloric acid (sour) CS. Exp III, with 60 Ss, demonstrated that reliable agnosia for an acid CS could be produced by lesions that extended more deeply into perirhinal areas near the claustrum at the level of the GN. It is concluded that the agnosia following GN ablation is relatively specific to gustation and that agnosia for preoperatively acquired tasted aversion habits occurs for all 4 basic gustatory stimuli following anterolateral cortex ablations centered on the GN. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal ablations of the gustatory neocortex in the rat: Taste aversion learning and taste reactivity.

Sprague-Dawley rats sustaining ablations of gustatory neocortex (GN) at 2, 10, 20, or 60 days of age were compared with control-lesion and anesthetized controls (N?=?151) in the acquisition and extinction of a learned taste aversion. Ss were also tested for taste preference across 5 concentrations of NaCl solution (.04, .08, .15, .3, and .6 M). Results indicate that GN ablation disrupted aversion acquisition and extinction regardless of age at surgery. Taste-response functions for solutions shown by all GN Ss mirrored those of controls: preference (relative to water baseline) for middle concentrations and rejection of the strongest concentration. It is suggested that the 20- and 60-day-old GN Ss were hyperresponsive to the suprathreshold concentrations of NaCl (excepting the .6-M concentration). The increased response to NaCl in 20- and 60-day-old GN Ss may have been related to the significant decreases in water consumption relative to that of controls. Water consumption of controls and GN Ss in 2- and 10-day-olds was essentially equal. It is concluded that infant ablation of the GN does not spare normal taste aversion learning and that rats with GN ablations, regardless of age at surgery, respond in a normal manner to the hedonic aspects of NaCl solutions. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of differential associative responses to novel and familiar taste stimuli in rats lacking gustatory neocortex.

24 Long-Evans hooded rats lacking gustatory neocortex and 24 normal rats were familiarized to either hydrochloric acid or quinine hydrochloride solutions during free-drinking trials. Ss were subsequently trained to avoid either the familiar or the novel taste stimulus, using a balanced design, by pairing the to-be-associated taste with ip injections of apomorphine hydrochloride. Balanced, nonpaired presentations of the other taste solution and water were also presented. Normal Ss learned to avoid the novel taste more efficiently than the familiar taste. Ss with gustatory neocortex lesions did not differentiate novel from familiar tastes. They learned aversions to both in a manner highly similar to the aversion learning of familiar tastes by the normal group. Therefore, results demonstrate that Ss lacking gustatory neocortex displayed an associative deficiency only when they were trained on novel stimuli. This suggests that gustatory neocortex lesions disrupt the conditionability of taste stimuli by reducing or eliminating responses to taste novelty. This interpretation is supported by the absence of a "neophobic" response in the lesioned rats to the first presentation of a taste stimulus. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

GABAergic neurotransmission in rat taste buds: immunocytochemical study for GABA and GABA transporter subtypes

Gamma-aminobutyric acid (GABA) is known to be a candidate for the neurotransmitter involved in the sense of taste. We hereby studied GABA and its termination system, GABA transporters, in rat taste buds by immunocytochemical approaches. Immunoblot analysis of three GABA transporter subtypes (GAT1, GAT2 and GAT3) revealed that the immunoreactive bands of GAT2 and GAT3, but not GAT1, were detected in the tongue. GAT3-immunoreactive band was recognized only in the circumvallate papilla containing a large number of taste buds while GAT2-immunoreactive bands were seen in all areas of the tongue. GAT2 immunoreactivity appeared to be specifically in the nerve fibers beneath the lingual epithelium. Both GAT3 and GABA immunoreactivities were detected only in taste buds. A few GAT3-immunoreactive cells were found in a cross-section of each taste bud but most GAT3-immunoreactive cells were localized in the margin of the taste bud. GAT3 was predominantly concentrated in the distal portion of the GAT3-immunoreactive cells. In contrast, GABA-immunoreactive cells were seen more frequently within each taste bud and the immunoreactivity was distributed throughout the perikarya of the cells. These results suggest that the GABA-uptake system is present in the taste buds and the GABAergic neurotransmission involved in the sensation of taste is terminated by the uptake of GABA into certain taste cells via GAT3.     

Odorant responses in taste neurons of the rat NTS

In the experiment reported in this paper, 22 of 35 neurons in the gustatory NTS were found to respond to odorant as well as taste stimuli. This odorant response was apparently mediated by the ethmoid nerve and at least one other odorant-responsive system, possibly other nasal trigeminal afferents. These gustatory neurons responded to odorants, as they did to taste stimuli, in a manner consistent with an encoding of stimulus quality information. Thus at least some of the neurons of the gustatory NTS carry information concerning several of the senses involved in ingestion.     

The relative effects of transection of the gustatory branches of the seventh and ninth cranial nerves on NaCl taste detection in rats.

Chorda tympani nerve (CT) transection in rats severely impairs NaCl taste detection. These rats can detect higher concentrations of NaCl, however, suggesting that remaining oral nerves maintain some salt sensibility. Rats were tested in a gustometer with a 2-response operant taste-detection task before and after sham surgery (n = 5), combined transection of the CT and the greater superficial petrosal nerves (GSP; 7x, n = 6), or transection of the glossopharyngeal nerve (GL; 9x, n = 4). Thresholds did not significantly change after sham surgery. Although the GL responds to NaCl and innervates nearly 60% of total taste buds, 9x surgery had no effect. However, 7x surgery increased NaCl detection threshold by ～2.5 log?? units, greater than that reported for CT transection alone. These results suggest that the GSP contributes to NaCl sensitivity in rats and also demonstrate that the GL and perhaps the superior laryngeal and lingual nerve proper can maintain some NaCl detectability at high concentrations. These findings confirm the primacy of the 7th nerve relative to the 9th nerve in sensibility of NaCl in the rat model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish

The second gustatory nucleus of teleost fishes receives ascending fibers from the primary gustatory center in the medulla and sends efferent fibers to several nuclei in the inferior lobe of the diencephalon. Similar to the corresponding parabrachial nucleus in birds and mammals, the secondary gustatory nucleus of catfish consists of several cytoarchitectonically distinct subnuclei which receive input from different portions of the primary gustatory nuclei. However, it is unclear how the subnuclear organization relates to the processing of gustatory information in the hindbrain and the subsequent transmission of that information to the forebrain. To determine whether cells within different subnuclei of the secondary gustatory nucleus of channel catfish project to different diencephalic targets, single cells were intracellularly labeled with biocytin. Three subnuclei have been identified in the secondary gustatory nucleus: a medial subnucleus spanning most of the rostrocaudal extent of the nucleus, a central subnucleus and a dorsal subnucleus, the latter two located in the rostrolateral portion of the complex. Cells throughout the secondary gustatory nucleus typically possessed similar collateral projections to several nuclei in the inferior lobe, although four of the six cells filled in the medial subnucleus projected only to nucleus centralis. The only apparent subnucleus-specific projection pattern involved cells at the rostral edge of the secondary gustatory nucleus and in the secondary visceral nucleus. Axons of these cells terminated only in restricted portions of nucleus lobobulbaris. These results suggest that efferents from different subnuclei of the secondary gustatory nucleus of catfish, like those of the parabrachial nucleus of birds and mammals, do not possess simple, topographical projections to target nuclei in the diencephalon.     

Medial cell mixing during axial morphogenesis of the amphibian embryo requires cadherin function

A truncated form of Xenopus E-cadherin (deltaE-cad) comprising the cytoplasmic and transmembrane domains was overexpressed generating a dominant negative mutation in the urodelan amphibian embryo Pleurodeles waltl. deltaE-cad mRNA and rhodamine-lysinated-dextran (RLDx) cell lineage tracer were microinjected into 32-cell stage blastomeres which contribute principally to the notochord and central nervous system. deltaE-cad expression causes defects in forebrain and hindbrain formation coupled with the development of supernumerary vesicles. Duplication of the notochord also occurs due to the retardation of medial cell intercalation with correlated duplications of spinal cord and somites. These results emphasize the role of cadherins in mediating cell-cell adhesion in early amphibian embryogenesis. They extend to Pleurodeles the observations made in Xenopus, illustrating that despite differences in morphogenetic processes, the molecular mechanisms are conserved in these two species.