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Results for “Taste Receptors, Type 2”

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At least 145 records · Page 8Linked to original sources

PubMed2002

Triterpenoid saponins stimulate the sugar taste receptor cell through a G protein-mediated mechanism in the blowfly, Phormia regina.

The blowfly has taste chemosensilla on the labellum. The sensory receptor cells in the chemosensillum are highly specialized for the tastes of sugar, salt and water, respectively. Previously we introduced chromosaponin I (CSI) and glycyrrhizin (GL), as sweet substances for the blowfly, Phormia regina. Application of these triterpenoid saponins induced feeding responses as well as impulses of the sugar taste receptor cell in the LL-type sensillum at a much lower concentration than that of sucrose. In the present paper, we show the involvement of G protein-mediated cascade in the CSI- and GL-responses as well as in sugar responses. CSI activates the sugar signal transduction cascade after penetrating through the membrane. On the other hand, GL exerts dual effects to stimulate the sugar signal transduction possibly by activating it inside the cell and also by interacting with the pyranose sugar receptor site. A non hydrolyzable G protein inhibitor guanosine 5'-O-(2-thiodiphosphate), GDPbetaS, markedly decreased the responses of the sugar receptor cell to the two triterpenoid saponins as well as the response to sucrose and fructose. These results suggest that CSI and GL are direct activators of G protein.

Journal Article↗

PubMed2000

Transduction ion channels directly gated by sugars on the insect taste cell.

Insects detect sugars and amino acids by a specialized taste cell, the sugar receptor cell, in the taste hairs located on their labela and tarsi. We patch-clamped sensory processes of taste cells regenerated from the cut end of the taste hairs on the labelum of the flashfly isolated from the pupa approximately 20 h before emergence. We recorded both single channel and ensemble currents of novel ion channels located on the distal membrane of the sensory process of the sugar receptor cell. In the stable outside-out patch membrane excised from the sensory processes, we could repeatedly record sucrose-induced currents for tens of minutes without appreciable decrease. An inhibitor of G-protein activation, GDP-beta-S, did not significantly decrease the sucrose response. These results strongly suggested that the channel is an ionotropic receptor (a receptor/channel complex), activated directly by sucrose without mediation by second messengers or G protein. The channel was shown to be a nonselective cation channel. Analyses of single channel currents showed that the sucrose-gated channel has a single channel conductance of approximately 30 pS and has a very short mean open time of approximately 0.23 ms. It is inhibited by external Ca(2+) and the dose-current amplitude relation could be described by a Michaelis-Menten curve with an apparent dissociation constant of approximately 270 mM. We also report transduction ion channels of the receptor/channel complex type directly gated by fructose and those gated by L-valine located on the sensory process.

Algorithms↗

PubMed2006

Characterization and long-term maintenance of rat taste cells in culture.

Taste cells have a limited life span and are replaced from a basal cell population, although the specific factors involved in this process are not well known. Short- and long-term cultures of other sensory cells have facilitated efforts to understand the signals involved in proliferation, differentiation, and senescence, yet few studies have reported successful primary culture protocols for taste cells. Furthermore, no studies have demonstrated both proliferation and differentiation in vitro. In this study, we have developed an in vitro culture system to maintain and utilize rat primary taste cells for more than 2 months without losing key molecular and biochemical features. Gustducin, phospholipase C-beta2 (PLC-beta2), T1R3, and T2R5 mRNA were detected in the cultured cells by reverse transcriptase-polymerase chain reaction. Western blot analysis demonstrated gustducin and PLC-beta2 expression in the same samples, which was confirmed by immunocytochemistry. Labeling with bromo-2-deoxyuridine (BrdU) demonstrated proliferation, and a subset of BrdU-labeled cells were also immunoreactive for either gustducin or PLC-beta2, indicating differentiation of newly generated cells in vitro. Cultured cells also exhibited increases in intracellular calcium in response to several taste stimuli. These results indicate that taste cells from adult rats can be generated and maintained under the described conditions for at least 2 months. This system will enable further studies of the processes involved in proliferation, differentiation, and function of mammalian taste receptor cells in an in vitro preparation.

Animals↗

PubMed2005

Expression of synaptotagmin 1 in the taste buds of rat gustatory papillae.

Synapses between taste receptor cells and primary sensory afferent fibers transmit the output signal from taste buds to the central nervous system. The synaptic vesicle cycle at the synapses involves vesicle docking, priming, fusion, endocytosis, and recycling. Many kinds of synaptic vesicle proteins participate in synaptic vesicle cycles. One of these, synaptotagmin 1, binds Ca(2+) phospholipids with high affinity and plays a role in Ca(2+) regulated neurotransmitter release in the central and peripheral nervous systems. However, the expression patterns of synaptotagmin 1 in rat taste tissues have not been determined. We therefore examined the expression patterns of synaptotagmin 1 and several cell specific markers of type II and III cells in rat taste buds. RT-PCR assay showed that synaptotagmin 1 mRNA was expressed in circumvallate papillae. In fungiform, foliate, and circumvallate papillae, the antibody against synaptotagmin 1 yielded the labeling of a subset of taste bud cells and intra- and subgemmal nerve processes. Double labeled experiments showed that synaptotagmin 1 positive cells co-expressed type III cell markers, PGP 9.5, and NCAM. Intragemmal nerve processes positive for synaptotagmin 1 co-expressed PGP 9.5. Conversely, all synaptotagmin 1 expressing cells did not co-expressed type II cell markers, PLCbeta2, or gustducin. These results show that synaptotagmin 1 may play some regulatory roles in vesicle membrane fusion events with the plasma membrane at the synapses of type III cells in rat taste buds.

Animals↗

PubMed1989

Evidence for a novel mechanism of binding and release of stimuli in the primate taste bud.

In previous work, we showed that thaumatin, an intensely sweet protein, binds to certain formed elements in taste pores of Rhesus monkey foliate papillae, namely, microvilli and small vesicles shed from microvilli, in addition to amorphous secretions (Farbman et al., 1987). We suggested that the taste bud responds to a thaumatin stimulus by shedding the small vesicles containing fragments of microvillar membrane bearing the stimulus-binding site complex. To examine this hypothesis further, we used electron microscopy to examine taste pores of both vallate and foliate papillae from Rhesus monkeys before or after stimulation with thaumatin or sucrose. We also recorded the neural activity from the glossopharyngeal nerve during stimulation with thaumatin, sucrose, citric acid, and NaCl. The results indicate (1) with no stimulation, vesicles are found in pores of foliate papilla taste buds much more frequently than in pores of vallate papilla buds, (2) in both types of papillae, stimulation with sucrose has no apparent effect on the number of pores containing vesicles, (3) stimulation with thaumatin elicits release of vesicles into pores of both foliate and vallate buds, (4) repeated stimulation of taste buds with thaumatin results in a declining neural response, not seen after repeated stimulation with sucrose, citric acid, or NaCl, and (5) stimulation with thaumatin suppresses the neural response to sucrose, but the reverse does not occur. The combined morphological and physiological data support our original hypothesis that, in response to thaumatin stimulation, binding sites on taste microvillar membranes may be shed as a stimulus-receptor complex into the pore. Alternatively, the binding sites may in some way be altered by the shedding of part of the membrane. The data suggest further that the binding site for sucrose may be close to that for thaumatin because it too is lost or altered after thaumatin stimulation. The reduced neural response after repeated thaumatin stimulation indicates that cells may have suffered a net loss of functional receptors or at least a loss in functional capacity of the receptors. The data indicate that the cellular mechanism for handling the protein sweetener, thaumatin, is strikingly different from the adsorption-desorption response to saccharide sweeteners.

Adaptation, Physiological↗

PubMed1989

Taste thresholds in man are differentially influenced by hydrocortisone and dexamethasone.

The present study focused on sensory processing (taste threshold) in healthy young men given different cortisol doses within the normal physiological range. It aimed to differentiate the effects of dexamethasone, a synthetic pure glucocorticoid, compared to hydrocortisone, which has both glucocorticoid and mineralocorticoid properties. In a double-blind, cross-over design, 18 male subjects participated in three sessions. Subjects were pretreated orally with hydrocortisone (50 mg), dexamethasone (2 mg) or placebo. Taste detection was tested by a forced-choice three stimulus drop technique to determine detection acuity and a signal detection procedure to determine the ability to detect differences in NaCl concentration. Cortisol concentrations were determined in blood and saliva. Hydrocortisone and dexamethasone had opposite effects on taste detection acuity. With the highest cortisol levels after intake of hydrocortisone, subjects made more errors in detection trials with respect to stimuli close to the absolute taste detection threshold than after intake of dexamethasone. Detection of differences was impaired by both glucocorticoids. This type of behavioral study in man may help clarify the roles of heterogeneous corticosteroid receptor systems within the human brain.

Adolescent↗

PubMed2006

GABA(B(1)) receptor isoforms differentially mediate the acquisition and extinction of aversive taste memories.

Conditioned taste aversion (CTA) is a form of aversive memory in which an association is made between a consumed substance and a subsequent malaise. CTA is a critical mechanism for the successful survival, and hence evolution, of most animal species. The role of excitatory neurotransmitters in the neurochemical mechanisms of CTA is well recognized; however, less is known about the involvement of inhibitory receptor systems. In particular, the potential functions of metabotropic GABA(B) receptors in CTA have not yet been fully explored. GABA(B) receptors are metabotropic GABA receptors that are comprised of two subunits, GABA(B(1)) and GABA(B(2)), which form heterodimers. The Gabbr1 gene is transcribed into two predominant isoforms, GABA(B(1a)) and GABA(B(1b)), which differ in sequence primarily by the inclusion of a pair of sushi domains (also known as short consensus repeats) in the GABA(B(1a)) N terminus. The behavioral function of mammalian GABA(B(1)) receptor isoforms is currently unknown. Here, using a point mutation strategy in mice, we demonstrate that these two GABA(B(1)) receptor isoforms are differentially involved in critical components of CTA. In contrast to GABA(B(1b))-/- and wild-type mice, GABA(B(1a))-/- mice failed to acquire CTA. In contrast, GABA(B(1b))-/- mice robustly acquired CTA but failed to show any extinction of this aversion. The data demonstrate that GABA(B) receptors are involved in both the acquisition and extinction of CTA; however, receptors containing the GABA(B(1a)) or the GABA(B(1b)) isoform differentially contribute to the mechanisms used to learn and remember the salience of aversive stimuli.

Animals↗

PubMed2004

5-HT(3A) receptor subunit is required for 5-HT3 antagonist-induced reductions in alcohol drinking.

The ionotropic serotonin subtype-3 (5-HT3) receptor has emerged as a potential therapeutic target in the treatment of alcohol abuse and alcoholism because selective pharmacological antagonists reduce alcohol consumption in preclinical and clinical models. 5-HT binds to the extracellular N-terminus of the 5-HT(3A) receptor subunit but receptor activation is also enhanced by distinct allosteric sites, which indicates the presence of other receptor subunits. It is not known if specific molecular subunits of the 5-HT3 receptor modulate alcohol drinking. To address this issue, we characterized acute locomotor response to alcohol and alcohol consumption in a two-bottle home-cage procedure by congenic C57BL/6J mice with a targeted deletion of the 5-HT(3A) receptor subunit gene. 5-HT(3A)-null mice did not differ from wild-type littermate controls on measures of spontaneous locomotor activity, habituation to a novel environment, or locomotor response to ethanol (0, 0.5, 1, or 2 g/kg). Moreover, null mice did not differ from controls on measures of ethanol (2-10%) intake and preference during or after a two-bottle home-cage sucrose fading procedure. Systemic administration of the 5-HT3 antagonist LY-278,584 (0-10 mg/kg) decreased intake of both sweetened (2% sucrose+10% ethanol) and unsweetened (10% ethanol) ethanol in wild-type mice only. These findings indicate that reduction of alcohol drinking produced by 5-HT3 antagonism is dependent on the presence of 5-HT(3A)-containing receptors.

Alcohol Drinking↗

PubMed1988

Ultrastructure of taste cells and synapses in the mudpuppy Necturus maculosus.

Taste buds in the mudpuppy Necturus maculosus were examined with electron microscopy. Three cell types (dark, light, and basal) were identified and reconstructed from serial thick sections. Dark and light cells extend from the basal lamina to the surface of the tongue. The apical process of the dark cells was usually quite lamellar when viewed in cross section, in contrast to light cells, whose apical process appeared more cylindrical. Basal cells are situated at the base of the bud and do not extend processes to the surface of the tongue. The cytoplasm of basal cells contains numerous clear and dense-cored vesicles. Small, spinelike processes (2-3 microns in length) project outward from the basal cells into the cytoplasm of the surrounding tast receptor cells. Morphologically, basal cells in mudpuppy taste buds resemble Merkel cells. Unmyelinated afferent nerve fibers enter the taste bud at the base and course through the lower portion of the bud. Synapses were found between taste receptor cells and nerve fibers, between basal cells and nerve fibers, and between basal cells and taste receptor cells. Over 65% of the synapses observed in the mudpuppy taste bud involved the basal cell. These findings suggest that basal cells play some role in chemosensory signal processing or integration of the taste response.

Animals↗

PubMed2004

Ca2+/calmodulin-dependent protein kinase II in the rat cranial sensory ganglia.

Immunohistochemistry for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) was performed on the rat cranial sensory ganglia. More than one half of neurons was immunoreactive for the enzyme in the trigeminal (60%), jugular (70%), petrosal (55%) and nodose ganglia (63%). These neurons were mainly small to medium-sized. The co-expression study demonstrated that one half of CaMKII-immunoreactive (ir) neurons was also immunoreactive for calcitonin gene-related peptide (CGRP) or the vanilloid receptor subtype 1 (VR1) in the trigeminal, jugular and petrosal ganglia. In the nodose ganglion, CaMKII-ir neurons were mostly devoid of CGRP-immunoreactivity (ir) (8.2%) whereas the co-expression with VR1-ir was common among such neurons (72%). In the facial skin, nasal mucosa and palate, the epithelium and taste bud were innervated by CaMKII-ir nerve fibers. In addition, the retrograde tracing study demonstrated that 39.6% and 44.8% of trigeminal neurons which were retrogradely traced with fluorogold from the facial skin and nasal mucosa exhibited CaMKII-ir. Forty-six percent of petrosal neurons which innervated the soft palate were immunoreactive for the enzyme.

Animals↗

PubMed2005

Specific recognition, detoxification and metabolism of pyrrolizidine alkaloids by the polyphagous arctiid Estigmene acrea.

Evidence is presented that the polyphagous arctiid Estigmene acrea is well adapted to sequester and specifically handle pyrrolizidine alkaloids of almost all known structural types representative of the major plant families with pyrrolizidine alkaloid-containing species, i.e. Asteraceae with the tribes Senecioneae and Eupatorieae, Boraginaceae, Fabaceae, Apocynaceae and Orchidaceae. The adaptation of E. acrea to pyrrolizidine alkaloids includes a number of specialized characters: (i) highly sensitive recognition of alkaloid sources by pyrrolizidine alkaloid-specific taste receptors; (ii) detoxification of pyrrolizidine alkaloids by N-oxidation catalyzed by a specific flavin-dependent monooxygenase; (iii) transfer and maintenance of all types of pyrrolizidine N-oxides through all developmental stages; (iv) conversion of the various structures into the male courtship pheromone hydroxydanaidal most probably through retronecine and insect specific retronecine esters (creatonotines) as common intermediates; (v) specific integration into mating behavior and defense strategies. Toxic otonecine derivatives, e.g. the senecionine analogue senkirkine, which often accompany the common retronecine derivatives and which cannot be detoxified by N-oxidation do not affect the development of E. acrea larvae. Senkirkine is not sequestered at all. Non-toxic 1,2-saturated platynecine derivatives that frequently occur together with toxic retronecine esters are sequestered and metabolized to hydroxydanaidal, indicating the ability of E. acrea to aromatize saturated pyrrolizidines. Although pyrrolizidine alkaloids, even if they are offered continuously at a high level (2%) in the larval diet, are non-toxic, E. acrea larvae are not able to develop exclusively on a pyrrolizidine alkaloid-containing plant like Crotalaria. Therefore, E. acrea appears to be specifically adapted to exploit pyrrolizidine alkaloid-containing plants as "drug source" but not as a food source.

Animals↗

PubMedDate not supplied

Issues of gustatory neural coding: where they stand today.

The basic issues of gustatory neural coding are revisited. Questions addressed and conclusions drawn are: (1) what is the physical dimension across which gustatory neurons are sensitive, and upon which taste perceptions are based? The dimension that unites the various taste qualities is not physical, but physiological: a dimension of well-being, bounded by toxins at one extreme and nutrients at the other. (2) How broadly tuned are taste cells across the dimension? There are instances of specificity, but most mammalian taste cells respond to a range of qualities. (3) Are there basic taste qualities? Sweet, salty, sour, and bitter are widely accepted as basic tastes. Umami and starch tastes are considered basic by some. (4) Is taste topographically organized? There is some degree of physical separation among neurons most responsive to different taste qualities, but this does not appear to be sufficient precision to act as a meaningful coding mechanism. (5) Are there gustatory neuron types? Neurons, separated into categories according to their response profiles, respond as members of their category to the challenges of conditioned aversions and preferences, sodium deprivation, hyperglycemia, and receptor blockade, while cells from other categories react differently. This indicates the existence of functionally distinct types of taste cells. (6) Is the quality signal coded within the activity of the single most appropriate category of neurons, or is it carried by the pattern of response across neuronal categories? Both the breadth of responsiveness and the logical ambiguity of the signal in any one category of neurons argue that the taste message is carried by a pattern of activity across gustatory neuron types.

Animals↗

PubMedDate not supplied

Sex-specific non-pheromonal taste receptors in Drosophila.

Taste receptors have recently been reported in Drosophila [1,2], but little is known of the relation between receptor and response. Morphological studies of the distribution of chemosensory sensilla indicate that the fruit fly has two major sites of gustation: the proboscis and the legs [3]. The taste sensilla on both these sites are similar in structure and each sensillum generally houses four gustatory neurons [4]. Early anatomical observations have demonstrated a sexual dimorphism in the number of tarsal sensilla [5] and in their central projections [6]. We measured the electrophysiological responses of the prothoracic taste sensilla to non-pheromonal substances--salts, sugars and water--and found a clear sexual dimorphism. From the response profile of individual sensilla, we were able to distinguish three types of tarsal sensilla in females as against only two types in males. The female-specific type, which responded specifically to sugar, was absent in males except when male gustatory neurons were genetically feminised. The fact that tarsal gustatory hairs exhibit a sexual dimorphism that affects the perception of non-pheromonal compounds suggests that sexual identity is more complex than has previously been thought [7,8].

Animals↗

PubMed1991

[The correlation of consciousness level and the concentration of CSF ammonia in a patient with adult-type citrullinemia].

A 29-year-old man who had a taste for peanuts frequently showed abnormal behaviors. Physical examination revealed consciousness disturbance associated with flapping tremor, hypotonus in the extremities, and hypoactive deep tendon reflexes. Laboratory examination showed hyperammonemia with mild liver injury. A level of serum citrulline was 14 times higher than the upper limit of normal. A diagnosis of type 2 citrullinemia (Seheki et al) was established by the decreased argininosuccinate synthetase (ASS) in liver with low amount of ASS protein and normal kinetic properties. Diurnal fluctuation of consciousness level in this patient was not correlated with the concentration of ammonia in serum, but with that in cerebrospinal fluid. Main metabolic pathway of ammonia in brain is considered to be localized in astrocytes which have receptors for glucocorticoids. Glucocorticoids induce additional glutamine synthetase activity. Circadian rhythm of cortisol level might play a role in diurnal fluctuation of consciousness level in patients with citrullinemia.

Adult↗

PubMed1999

IP(3)-Independent release of Ca(2+) from intracellular stores: A novel mechanism for transduction of bitter stimuli.

A variety of substances with different chemical structures elicits a bitter taste. Several different transduction mechanisms underlie detection of bitter tastants; however, these have been described in detail for only a few compounds. In addition, most studies have focused on mammalian taste cells, of which only a small subset is responsive to any particular bitter compound. In contrast, approximately 80% of the taste cells in the mudpuppy, Necturus maculosus, are bitter-responsive. In this study, we used Ca(2+) imaging and giga-seal whole cell recording to compare the transduction of dextromethorphan (DEX), a bitter antitussive, with transduction of the well-studied bitter compound denatonium. Bath perfusion of DEX (2.5 mM) increased the intracellular Ca(2+) level in most taste cells. The DEX-induced Ca(2+) increase was inhibited by thapsigargin, an inhibitor of Ca(2+) transport into intracellular stores, but not by U73122, an inhibitor of phospholipase C, or by ryanodine, an inhibitor of ryanodine-sensitive Ca(2+) stores. Increasing intracellular cAMP levels with a cell-permeant cAMP analogue and a phosphodiesterase inhibitor enhanced the DEX-induced Ca(2+) increase, which was inhibited partially by H89, a protein kinase A inhibitor. Electrophysiological measurements showed that DEX depolarized the membrane potential and inhibited voltage-gated Na(+) and K(+) currents in the presence of GDP-beta-S, a blocker of G-protein activation. DEX also inhibited voltage-gated Ca(2+) channels. We suggest that DEX, like quinine, depolarizes taste cells by block of voltage-gated K channels, which are localized to the apical membrane in mudpuppy. In addition, DEX causes release of Ca(2+) from intracellular stores by a phospholipase C-independent mechanism. We speculate that the membrane-permeant DEX may enter taste cells and interact directly with Ca(2+) stores. Comparing transduction of DEX with that of denatonium, both compounds release Ca(2+) from intracellular stores. However, denatonium requires activation of phospholipase C, and the mechanism results in a hyperpolarization rather than a depolarization of the membrane potential. These data support the hypothesis that single taste receptor cells can use multiple mechanisms for transducing the same bitter compound.

1-Methyl-3-isobutylxanthine↗

PubMed1990

Lipid metabolic interrelationships and phospholipase activity in gustatory epithelium of Ictalurus punctatus in vitro.

The catfish, Ictalurus punctatus, is an important model for studying the biochemical mechanisms of taste at the peripheral level. The type, amount and metabolic activity of the lipids within this tissue play important roles in taste transduction by forming the matrix in which the receptors for taste stimuli are imbedded and by acting as precursors to second messengers. The metabolic interconversions that occur among the lipids on the taste organ (barbels) of this animal are reported here. When sodium [32P]phosphate was incubated with minced pieces of epithelium from the taste organ of I. punctatus, phospholipids became labeled. Maximal incorporation occurred near 20 min for lysophosphatidylcholines (LPC), phosphatidylcholines (PC) and phosphatidylinositols (PI). The phosphatidylethanolamines (PE) and phosphatidylserines (PS) became labeled more slowly. The label in LPC and PC declined from 20 min to 120 min, while that of the other fractions increased or was stable over the 20-120 min time period. Upon addition of 1,2-di-[1'-14C]palmitoyl-sn-glycero-3-phosphocholine to the medium, 14C was found within minutes in all of the phospholipids assayed. The amount of label incorporated increased with time, with maximum labeling for all phospholipids occurring at 15 min. However, 14C appeared predominantly first (by 5 min) in a neutral lipid fraction (fraction AG, consisting of free fatty acids, mono- and diglycerides, triglycerides and methyl esters), then declined rapidly as the phospholipids gradually incorporated more label. Within minutes of addition of 1-[1'-14C]palmitoyl-sn-glycero-3-phosphocholine (lysophosphatidylcholine) the 14C-label was detected in the neutral lipid fraction AG, then in the PC fraction, and later in the other phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Immunoelectron microscopic studies on protein gene product 9.5 and calcitonin gene-related peptide in vallate taste cells and related nerves in the guinea pig.

On the basis of our previous report that protein gene product 9.5 (PGP 9.5)-immunoreactive nerve fibers and taste cells and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers are found in guinea pig vallate papillae [Huang and Lu (1996b) Arch. Histol. Cytol. 59:433-441]. We speculated that PGP 9.5 might be a marker for taste receptor cells and that CGRP might play an important role in taste transmission. We, therefore, performed an immunohistochemical and ultrastructural analysis of taste cells and related nerves in guinea pig vallate papillae. In the connective tissue of the vallate papilla, the ultrastructural data revealed that the PGP 9.5-immunoreactive nerve fibers were both myelinated and unmyelinated. The CGRP-immunoreactive nerve fibers were unmyelinated and surrounded by the cytoplasm of Schwann cells as were the non-immunoreactive fibers. In the vallate taste buds, only type III cells, which make synaptic contacts with intragemmal nerves, were PGP 9.5-immunoreactive, while the nerve terminals making synaptic contact with the underlying type III cells were CGRP-immunoreactive. From these observations, we conclude that: (1) PGP 9.5 might be a useful specific marker for type III cells in guinea pig vallate taste buds; and (2) CGRP-containing nerve fibers might be primarily involved in the neural transmission of taste stimuli.

Animals↗

PubMed1993

Quantitative autoradiographic demonstration of changes in binding to delta opioid, but not mu or kappa receptors, in chick forebrain 30 minutes after passive avoidance training.

Day-old domestic chicks (Gallus domesticus) were trained on a one-trial passive avoidance task in which the aversive stimulus was a bitter tasting substance, methylanthranilate. Thirty minutes later, localization of binding of highly specific ligands (([D-Ala2, Gly-ol]-enkephalin ([3H]DAGO) for mu (mu) receptor sites, [D-Pen2,D-Pen5]-enkephalin ([3H]-DPDPE) for delta (delta) sites, and [3H]-U- 69593 for kappa (kappa 1) sites) to opioid receptors in various regions of the forebrain of methyl-anthranilate trained (M-) and control (water trained (W-)) chicks was determined using quantitative receptor autoradiography. Significant differences in binding to delta ([3H]-DPDPE), but not mu or kappa receptors, were found in several regions of the forebrain, of trained compared to control chicks. There were decreases in binding in the hyperstriatum dorsale of the left hemisphere (14%) and a decrease in binding in the lateral hyperstriatum ventrale of the right hemisphere (14%). However, significant increases were observed in delta binding in the paleostriatum augmentatum of the right hemisphere (16%) and the lobus parolfactorius of both hemispheres (left, 20%; right, 21%). In a control experiment designed to determine whether the taste of methylanthranilate contributed to the increase in 3H-DPDPE binding, there was no significant difference in the level of binding between blindfolded birds in which methylanthranilate was placed in the beak, and blindfolded birds in which water was placed on the bead and inserted into the beak. These findings demonstrate that changes occur in an opioid receptor sub-type in specific regions of forebrain of the chick following passive avoidance training which may be related to events concerned with the process of memory formation.

Animals↗