Peptide-containing nerve fibers in the circumvallate papillae

Taste Buds and Neuronal Markers in Patients with Chronic Renal Failure

Objective

To study the number of taste buds and, with the use of specific markers for peripheral nervous tissue, to study the neuronal pattern in taste buds from 36 patients with chronic renal failure (CRF), 19 renal transplant recipients, and 40 healthy subjects. Of the patients with CRF, 17 patients had not started dialysis, 12 patients were on peritoneal dialysis, and 7 patients were on hemodialysis.

Design

From all subjects, two or three fungiform papillae were collected from the anterior part of the tongue. Cryostat sections were cut and inspected under light microscopy to determine the presence of taste buds. The sections were subsequently incubated with primary rabbit antibodies against protein gene product 9.5, substance P, and nerve growth factor receptor.

Results

Using these antibodies, no differences between the groups were observed. However, patients with CRF had fewer taste buds than control subjects.

Conclusion

No immunohistochemical differences were observed between patients with CRF and healthy controls. However, patients with CRF had significantly fewer fungiform taste buds, suggesting an important factor contributing to the well-known impairment of taste acuity in this patient group.

[Changes in the innervation of the taste buds in diabetic rats]

INTRODUCTION

Abnormal sensations such as pain and impairment of taste are symptoms of approximately 10% of patients having diabetes mellitus.

AIM

The aim of the study was to investigate and quantify the different neuropeptide containing nerve fibres in the vallate papilla of the diabetic rat.

METHODS

Immunohistochemical methods were used to study the changes of the number of different neuropeptide containing nerve terminals located in the vallate papillae in diabetic rats. Diabetes was induced in the rats with streptozotocin.

RESULTS

Two weeks after streptozotocin treatment the number of the substance P, galanin, vasoactive intestinal polypeptide and neuropeptide Y immunoreactive nerve terminals was significantly increased (p<0.05) in the tunica mucosa of the tongue. The number of the lymphocytes and mast cells was also increased significantly. Some of the immunoreactive nerve terminals were located in the lingual epithelium both intragemmally and extragemmally and were seen to comprise dense bundles in the lamina propria just beneath the epithelium. No taste cells were immunoreactive for any of the investigated peptides. Vasoactive intestinal polypeptide and neuropeptide Y immunoreactive nerve fibres were not detected in the taste buds. For weeks after streptozotocin administration the number of the substance P, calcitonin gene related peptide and galanin immunoreactive nerve terminals was decreased both intragemmally and intergemmally. In case of immediate insulin treatment, the number of the immunoreactive nerve terminals was similar to that of the controls, however, insulin treatment given 1 week later to diabetic rats produced a decreased number of nerve fibers. Morphometry revealed no significant difference in papilla size between the control and diabetic groups, but there were fewer taste buds (per papilla).

CONCLUSIONS

Increased number of immunoreactive nerve terminals and mast cells 2 weeks after the development of diabetes was the consequence of neurogenic inflammation which might cause vasoconstriction and lesions of the oral mucosa. Taste impairment, which developed 4 weeks after streptozotocin treatment could be caused by neuropathic defects and degeneration or morphological changes in the taste buds and nerve fibres.

Extending the enteric nervous system

The work reviews the evidence suggesting that lingual components of the autonomic system may be considered the most rostral portion of the enteric nervous system (ENS) defining the concept of lingual ENS (LENS). The LENS is not dissimilar from the more distally located portions of the ENS, however, it is characterized by a massive sensory input generated by collaterals of gustatory and trigeminal fibers. The different neuronal subpopulations that compose the LENS operate reflexes involved in regulation of secretion and vasomotility. Systemic reflexes on the digestive and respiratory apparatus are operated by means of neural connections through the pharynx or larynx. The LENS can modulate the activity of distally located organs by means of the annexed glands.The LENS seems therefore to be a "chemical eye" located at the beginning of the digestive apparatus which analyses the foods before their ingestion and diffuses this information distally. The definition of the LENS supports the concept of an elevated degree of autonomy in the ENS and puts in a new light the role of the gustatory system in modulation of the digestive functions. For its characteristics, the LENS appears to be an ideal model to study the elementary connectivity of the ENS.

Morphological evidence of sensory neurons in the root of the rat tongue

In our previous studies, a large number of substance P (SP)-immunoreactive (IR) nerve fibers were detected in the rat tongue and their number increased after inflammation, suggesting that these fibers might be involved in the axon reflex. Therefore, in this study, we have examined the different neuropeptide-containing nerve elements by light, electron, and confocal laser microscopy. SP, vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) IR varicose fibers were numerous compared with other ones. Small groups of ganglia with perikarya IR for SP, VIP, NPY, galanin, and somatostatin were observed. The SP-IR nerve cell bodies were mainly located in the tunica propria just below the epithelial lining. Double-labeling immunohistochemistry showed that the intrinsic SP-IR neurons did not colocalize VIP. The SP containing nerve terminals were observed in and below the epithelium as well as in very close contact to or making real synapses with other neurons in the intralingual ganglion. Our data confirmed the possibility of intrinsic sensory neurons, which might be the afferent branch of the intralingual reflex arch, while the VIP- and NPY-IR neurons located in the salivary glands, around the blood vessels, and in the muscle layer might constitute the efferent site of this reflex.

Co-expression patterns of the neuropeptides vasoactive intestinal peptide and cholecystokinin with the transduction molecules α-gustducin and T1R2 in rat taste receptor cells

Taste receptor cells are primary sensory receptors utilized by the nervous system to detect the presence of gustatory stimuli in the oral cavity. These cells are particularly heterogeneous and may be divided into various subtypes based on morphological, histochemical, or physiological criteria. One example is the heterogeneous expression of neuropeptides, such as cholecystokinin and vasoactive intestinal polypeptide. These peptides are hypothesized to participate in the transduction processes. To pursue examination of this hypothesis, this study explored the relationship of peptide expression with two important and mostly non-overlapping transductive elements--the taste-specific G protein gustducin, involved in bitter and sweet transduction cascades, and the seven transmembrane taste receptor T1R2, hypothesized to respond to sweet compounds. Double labeling experiments were performed on taste buds of the posterior rat tongue combining immunocytochemistry for peptide expression and in situ hybridization experiments for either gustducin or T1R2 expression. Additionally, vasoactive intestinal peptide (VIP)-expression in posterior taste receptor cells was confirmed using the technique of RT-PCR. More than half (56%) of the CCK-expressing taste receptor cells co-expressed alpha-gustducin mRNA whereas far fewer (15%) co-expressed T1R2 mRNA. A majority of VIP-expressing taste receptor cells co-expressed alpha-gustducin mRNA (60%) whereas only 19% of these cells co-expressed T1R2 mRNA. More remarkable was the observation that these two peptides displayed almost identical expression patterns with these signal transduction molecules, suggesting that peptides are not randomly expressed with relation to signal transduction molecules. This observation supports the hypothesis that peptides may play roles in transduction. Further physiological exploration will be required to elucidate the nature of these roles.

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.

Peptide-containing Neurons Projecting to the Tongue of the Rat: Retrograde Tracing and Immunocytochemistry

The origin and neuropeptide content of nerve fibres in the rat circumvallate papilla was studied by retrograde tracing in combination with immunocytochemistry. An injection of the retrograde tracer True Blue into the circumvallate papilla resulted in the appearance of labelled nerve cell bodies in the superior cervical, the stellate, the thyroid, the nodose, the jugular, the petrosal, the otic, the trigeminal and the dorsal root ganglia at level C2. Most of the True Blue-labelled nerve cells in the superior cervical ganglia contained neuropeptide Y. The majority of labelled cell bodies in the thyroid ganglia contained vasoactive intestinal peptide. In the jugular and trigeminal ganglia, the majority of the labelled nerve cell bodies stored calcitonin gene-related peptide. A small number of neurons in the medial reticular formation of the central nervous system was labelled. Tracer injections deep into the tongue tissue beneath the circumvallate papilla gave rise to True Blue-labelled neurons in the hypoglossal nucleus.

Ganglion cells and topographically related nerves in the vallate papilla/von Ebner gland complex

Ganglion cells and topographically related nerves in the vallate papilla/von Ebner gland complex were investigated in rat tongue by cytochemical, immunocytochemical, and ultrastructural methods to evaluate the possible presence of different neuronal subpopulations. Immunostaining for neurofilaments and protein gene product 9.5 revealed ganglionic cell bodies and nerve fibers. A large part of the neurons were positive at immunostaining for neuronal nitric oxide synthase (NOS), vesicular acetylcholine transporter (VAChT), or vasoactive intestinal peptide (VIP). A small subset of nerve fibers revealed immunoreactivity for cholecystokinin. Axons traveling under the lingual epithelium were evidenced by their content of calcitonin gene-related peptide (CGRP) or substance P (SP). Cell bodies positive for SP or CGRP were not detected. Using methods of co-localization, three different neuronal classes were detected. The main population was composed of AChE/NADPH-diaphorase (NADPHd)-positive cells. Small groups of acetylcholine esterase (AChE)-positive/NADPHd-negative cells were visible. Isolated neurons were AChE-negative/NADPHd-positive. The results of co-localization experiments for VAChT/NOS were consistent with those obtained by cytochemical co-localization of AChE and NADPHd. Experiments of co-localization for peptidergic and nitrergic structures revealed CGRP- and SP-immunoreactive fibers in the vallate papilla/von Ebner gland ganglion. In conclusion, the results demonstrated in the VP/VEG complex peptidergic, cholinergic, and nitrergic neurons. The presence of different neuronal subclasses suggests that a certain degree of functional specialization may exist.

Taste cell function. Structural and biochemical implications

Maintenance of constant relations between receptor cell types and branching from a single gustatory nerve fiber during normal cell turnover and regeneration requires cell-cell recognition likely mediated by timed expression of molecules at surfaces of taste bud cells, nerve endings, and in extracellular matrix. These processes assure stability of gustatory quality representation during intragemmal remodeling. Coincidentally, features of gemmal cell lifespan, including elongation, differentiation, and migration prior to apoptosis, must also be orchestrated by molecular signals. This article reviews the potential roles played by a variety of molecular markers for some relevant classes of proteins, peptides, and enzymes, which were presumed to be important for carrying out these gustatory cellular functions.

NADPH-diaphorase and NOS-1 positive ganglion cells are found in the rat vallate papilla/von Ebner gland complex

The nervous system of the vallata papilla and von Ebner glands was investigated in the rat tongue. Cells involved in the production of nitric oxide were identified by immunohistochemical detection of neuronal nitric oxide synthase type-1 and by cytochemical detection of NADPH-diaphorase. The analysis of serial sections showed that a ganglion composed of about 180-190 neuronal cells was present between the vallata papilla and von Ebner glands. These cells were positive for nitric oxide synthase type-1 and NADPH-diaphorase. From the ganglion, we observed nitrergic fibres running: (a) in the lamina propria of the receptor-free mucosa; (b) just below the gustatory epithelium; (c) in the von Ebner glands; and (d) around the vascular system of the vallata papilla. Our study suggests that the nitrergic ganglion cells may mediate interactions between chemoreceptorial systems in the vallata papilla and secretory cells in the von Ebner glands and that nitric oxide could be involved in the regulation of the blood supply to the vallata papilla and in the regulation of the von Ebner glands.

Immunohistochemical localisation of regulatory neuropeptides in human circumvallate papillae

The occurrence and distribution of neuropeptide-containing nerve fibres in the human circumvallate papillae were examined by the peroxidase-antiperoxidase immunolocalisation method using surgical specimens that had not been subjected to radiotherapy, and the abundance of neuropeptide-containing fibres was expressed as the percentage of total nerve fibres demonstrated by protein gene product (PGP) 9.5 immunoreactivity for a quantitative representation of these peptidergic fibres. Substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive (IR) nerve fibres were densely distributed in the connective tissue core of the circumvallate papillae, and some SP and CGRP-IR fibres were associated with the taste buds. A moderate number of vasoactive intestinal polypeptide (VIP)-IR fibres and a few galanin (GAL)-IR fibres were also seen in the connective tissue core and subepithelial layer. There were, however, no VIP-IR or GAL-IR fibres associated with the taste buds. Neuropeptide Y (NPY)-IR fibres were few and were associated with the blood vessels. Within the epithelium of the circumvallate papillae, no peptidergic fibres were found, although a number of PGP 9.5-IR fibres were detected. The abundance of SP, CGRP, VIP, and GAL-IR fibres expressed as the percentage of total PGP 9.5 IR fibres was 25.35+/-3.45%, 22.18+/-3.26%, 10.23+/-1.18%, and 4.12+/-1.05%, respectively. The percentage of NPY-IR fibres was below 3%. In a deeper layer of the papillae, a few VIP, GAL, and NPY-IR ganglion cells were found, and VIP immunoreactivity was detected in a few cells of the taste buds. There was no somatostatin, leucine enkephalin, or methionine enkephalin immunoreactivity in the circumvallate papillae. These results suggest that the dense SP and CGRP-IR fibres within the connective tissue core of the human circumvallate papillae may be involved in the deep sensation of the tongue.

Morphological study of the intrapharyngeal ganglia and ganglionic neurons in cats

The distribution, number and nature of intrapharyngeal ganglia and their neurons in cats were examined by means of serial sections, histochemical and immunohistochemical methods. Six to eight large ganglia around the palatine tonsils and five to eight small ganglia in the laterodorsal wall of pharyngeal mucous membrane were observed. The intrapharyngeal ganglionic neuron (25-30 microns in diameter) totalled 600-800 and more than 80% of them were located around the palatine tonsils. The ganglionic neurons were acetylcholinesterase reaction positive. On immunohistochemistry, many choline acetyltransferase-immunoreactive and vasoactive intestinal polypeptide-immunoreactive neurons and a few tyrosine hydroxylase-immunoreactive nerve cells were found, but no calcitonin gene-related peptide-immunoreactive or substance P-immunoreactive neurons were recognized in the ganglion. The present findings indicate that intrapharyngeal ganglionic neurons are mainly parasympathetic and partially sympathetic in nature.

Innervation of taste buds in the canine larynx as revealed by immunohistochemistry for the various neurochemical markers

The distribution and innervation of the canine laryngeal taste buds were observed using immunohistochemistry with antibodies against protein gene product 9.5 (PGP 9.5) and neurofilament protein (NFP). We also observed the immunohistochemical distribution of serotonin, tyrosine hydroxylase (TH) and various neuropeptides including calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), galanin, methionine enkephalin (ENK) and neuropeptide Y (NPY). The taste buds in the canine larynx were densely distributed in the mucosa at the basal portion of the epiglottis and cuneiform process of the arytenoid cartilage. The taste cells were immunoreactive for PGP 9.5 and serotonin. The nerve fibers with immunoreactivity for PGP 9.5 in the taste buds were observed in the perigemmal region and intra- and subgemmal plexuses, and these were classified into two types based on their diameter. The thick nerve fibers corresponded to the fibers immunoreactive for NFP, while the thin nerve fibers corresponded to the fibers immunoreactive for TH and various neuropeptides. Numerous nerve fibers immunoreactive for SP and CGRP were observed in the perigemmal region, and intra- and subgemmal plexuses. A few galanin- and ENK-immunoreactive nerve fibers were also observed in the taste buds, whereas NPY-immunoreactive nerve fibers were noted beneath them. All peptide-containing fibers except for VIP-immunoreactive nerves were situated in the subgemmal regions. In conclusion, the multiple innervation to the laryngeal taste buds were documented. Thick nerve fibers are likely to be irritant receptors, while thin varicose nerve fibers seem to regulate taste buds themselves. The laryngeal taste buds may be among the important structures which are sensitive to exogeneous chemical and/or mechanical stimuli, for the protection of the airway and the regulation of the respiratory function.

Peptidergic innervation in human von Ebner's glands: an immunohistochemical study

The occurrence and distribution of several neuropeptides were studied in human von Ebner's glands. Immunoreactivity for substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), galanin, and somatostatin was found in the nerve fibers around the acini, ducts, and blood vessels. VIP-immunoreactive varicose fibers were numerous compared with the other five neuropeptides. Most NPY fibers were associated with the vasculature in the gland. These findings suggest that the neuropeptides may regulate the secretion and vascular tone in human von Ebner's glands.

An immunohistochemical screening of neurochemical markers in fungiform papillae and taste buds of the anterior rat tongue

The occurrence and distribution of several neurochemical markers were investigated. Numerous nerve fibres were shown, using antibodies to protein gene product (PGP) 9.5, neurone-specific enolase, calcitonin gene-related peptide (CGRP), substance P. neurokinin A or protein S-100. The presence of vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), neuropeptide tyrosine, dopamine-beta-hydroxylase (DBH), cholecystokinin/gastrin, glutamate and galanin was more scarce. Nerve fibres containing these above-mentioned markers were found at several locations, i.e. in the epithelium, connective tissue, and around blood vessels. In the taste buds, numerous PGP 9.5, neurone-specific enolase-, CGRP-, substance P-, neurokinin A- and protein S-100-containing structures were found, but few VIP and galanin ones. No immunoreactivity was found with antibodies against somatostatin, bombesin, enkephalin or dynorphin. These findings extend knowledge about the general as well as the neurochemical messenger-based innervation of rat fungiform papillae, forming a firm basis for future functional investigations of normal, experimental and also clinical materials.

Protein gene-product 9.5 in developing mouse circumvallate papilla: comparison with neuron-specific enolase and calcitonin gene-related peptide

The present study was made to investigate the ontogeny of protein gene-product 9.5 (PGP 9.5)-like immunoreactivity (-LI) in the developing mouse circumvallate papilla (CVP), and its distribution was compared to that of neuron-specific enolase (NSE) and calcitonin gene-related peptide (CGRP). In adult CVP, PGP 9.5-LI was observed in the subgemmal nerve plexus; some thin PGP 9.5-like immunoreactive (-IR) nerve fibers penetrated taste buds and apical epithelium. PGP 9.5-LI was also observed in the spindle-shaped cells in taste buds, and a small number of round- or oval-shaped ganglionic cells in the lamina propria. The distribution of NSE-LI was comparable to that of PGP 9.5-LI. CGRP-LI was observed in the nerve fibers only; distribution of CGRP-IR nerve fibers was similar to that of PGP 9.5-IR nerve fibers, although the number of CGRP-IR nerve fibers was smaller than that of PGP 9.5-IR nerve fibers. At least six developmental stages were defined with regard to the developmental changes in the distribution of PGP 9.5-LI from embryonic day (E) 12 to adulthood: Stage I (E12-13)-a dense nerve plexus of PGP 9.5-IR nerve fibers was detected in the lamina propria beneath the core of newly-formed papilla. Stage II (E14-16) - thin PGP 9.5-IR nerve fibers penetrated the apical epithelium, and a few round-shaped cells in the apical epithelium also displayed PGP 9.5-LI. Stage III (E17-18) - thin PGP 9.5-IR nerve fibers penetrated the inner lateral epithelium of the trench. Stage IV [Postnatal day (P) 0-3] - many PGP 9.5-IR nerve fibers penetrated the outer lateral epithelium of the trench; later in this stage, taste buds appeared. Stage V (P5-10) - a small number of PGP 9.5-IR cells in the taste buds appeared, and their number increased gradually. Stage VI (P14-adult) - the number of PGP 9.5-IR taste cells increased and reached the adult level, while the number of PGP 9.5-IR nerve fibers decreased. The development of NSE-LI was similar to that of PGP 9.5-LI. CGRP-IR nerve fibers were detected at E12 in the lamina propria, and the development of the intraepithelial CGRP-IR nerve fibers was similar to that of PGP 9.5-IR nerve fibers. The present results indicate that invasion by nerve fibers of the epithelium of lingual papillae occurs in a complex manner, and that these nerve fibers may participate in the formation of the taste buds.

Protein gene product 9.5-immunoreactive nerves and cells in human oral mucosa

BACKGROUND

Current conflicting information on the innervation of the human oral cavity indicates technical problems such as different detectability of the neural structures according to the various staining methods used and difficulties in reproducibility. The possibility of intraoral regional differences has not been properly considered.

METHODS

Human biopsies of mucosa from different intraoral regions were prepared for immunohistochemistry using protein gene product 9.5 (PGP 9.5; a marker for neuronal structures).

RESULTS

Nerves were found consistently in all the biopsies. The neural pattern showed clear regional differences. Intraepithelial nerve fibers were found in the gingiva, labia, palate, within certain fungiform papillae, and in some salivary excretory ducts. Organized nerve endings were found in varying frequencies in all but one (sublingual) region, appearing as lamellar (Meissner-like), coiled or glomerular neural structures. Merkel cell-neurite complexes were observed in the buccal, gingival, and palatal epithelia. Immunoreactive cells with many similarities to Merkel cells but without a neural connection were also encountered.

CONCLUSIONS

Conflicting results from earlier innervation studies of the oral cavity could be attributed to regional innervation differences. The distribution of the nerves also casts doubt on some of the present theories concerning the function(s) of intraoral nerves, such as the free nerve endings and the Merkel cell-neurite complexes.

Distribution of peptidergic nerve fibres in bullfrog lingual papillae demonstrated by a combination of double immunofluorescence labelling and a multiple dye filter

Immunoreactivity of substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, and galanin is localized in nerve fibres distributed in the fungiform and filiform papillae of the tongue of the bullfrog, Rana catesbeiana. A combination of indirect double immunofluorescence labelling and a multiple dye filter system clearly demonstrated that all substance P fibres in the connective tissue core of the fungiform and filiform papillae, and within the rim of ciliated cells located on the top of the fungiform papillae showed coexistence with calcitonin gene-related peptide. A few fibres in the epithelial discs, which are located in the centre of the top of the fungiform papillae, showed the immunoreactivity of calcitonin gene-related peptide alone. There were no substance P fibres which showed coexistence with vasoactive intestinal polypeptide, galanin, and neuropeptide Y. In high magnification images, substance P and vasoactive intestinal polypeptide, and substance P and galanin fibres were recognized as two intertwined fibres within the same thin nerve bundle. No immunoreactivity of leucine- and methionine-enkephalins can be detected. These findings suggest that the chemoreceptor function of the bullfrog gustatory organ may be under the control of complicated peptidergic innervation.

An age-dependent novel hyperinnervation of circumvallate papillae by tyrosine hydroxylase-containing nerve fibers in NGF-overexpressing transgenic mice

The density of protein gene product 9.5- and tyrosine hydroxylase-immunoreactive nerve fibers innervating circumvallate papillae of the tongue was substantially increased in transgenic mice that overexpressed nerve growth factor (NGF) when compared with age-matched controls. The fiber density was age-dependent. Only transgenic mice contained NGF-immunoreactive basal cells in the vicinity of taste buds, indicating that target-derived NGF induced novel hyperinnervation of the circumvallate papillae.

Neurochemical markers of human fungiform papillae and taste buds

The presence of distribution of several neurochemical markers in human fungiform papillae and taste buds were investigated by the immunohistochemical technique. The gustatory cells of the taste buds are in synaptic contact with sensory nerve endings, and considering the taste buds strictly as specialized sensory organs, the amounts and distribution of some of the neurochemical markers were different to what we expected. For example, few structures showed immunoreactivity to the tachykinins substance P (SP), calcitonin gene-related peptide (CGRP), and neurokinin A (NKA) also for the peptides vasoactive intestinal polypeptide (VIP), neuropeptide tyrosine (NPY) and galanin, low amounts of immunoreactivity occurred. On the other hand, using antibodies to protein gene product 9.5 (PGP 9.5), protein S-100, and glutamate, numerous nerve fibres and/or immunoreactive cells were found in the fungiform papillae, in the epithelium, in the connective tissue and around blood vessels, as well as in or near taste buds. Incubation with the antibodies against somatostatin, enkephalin, bombesin, peptide histidine isoleucine amide (PHI), cholecystokinin (CCK)/gastrin and dopamine-beta-hydroxylase (DBH) was negative for the fungiform papillae. In conclusion, the present study has shown several immunoreactive structures using antibodies against certain neurochemical markers. Further investigations will hopefully correlate these morphological findings with functional taste perception data. Future studies of patients with taste disorders or other pathological changes correlated with taste and tongue will also be of utmost importance.

Innervation in human taste buds and its decrease in Alzheimer's disease patients

The innervation in human taste buds of the foliate and circumvallate papillae was studied immunohistochemically using several neuronal markers in patients with Alzheimer's disease (AD) and their control (ADC) patients. Antisera to protein gene product 9.5 (PGP 9.5), neuron-specific enolase (NSE), tyrosine hydroxylase (TH), dopamine-beta hydroxylase (DbetaH) and calcitonin gene-related peptide (CGRP) were used in immunofluorescence and streptavidin-biotin-peroxidase complex studies. The antiserum to PGP 9.5 stained a greater number of intragemmal nerve fibers in taste buds than that of other antisera. PGP 9.5 immunoreactivity was strictly localized in the nerve fibers, whereas NSE immunoreactivity was observed not only in the nerve fibers, but also in taste bud cells. Intragemmal TH- and DbetaH-immunoreactive nerve fibers were not identified in taste buds. Only a few intragemmal nerve fibers immunoreactive for anti-CGRP antiserum were observe in a small number of taste buds. Furthermore, quantitive analysis in AD and ADC patients demonstrated that the mean number of PGP 9.5-immunoreactive intragemmal nerve fibers in taste buds of the foliate and circumvallate papillae decreased significantly in AD patients. These results indicated that PGP 9.5 is a most suitable molecular marker for the demonstration of the extrinsic innervation in human taste buds, and that the decreased innervation may account partially for the decrement in chemosensory capacity in AD patients.

Comparison of the effects of hydrophobicity, amphiphilicity, and alpha-helicity on the activities of antimicrobial peptides

Multiple linear regression was used to quantify the dependence of the antimicrobial activity of 13 peptides upon three calculated or experimentally determined parameters: mean hydrophobicity, mean hydrophobic moment, and alpha-helix content. Mean hydrophobic moment is a measure of the amphiphilicity of peptides in an alpha-helical conformation. Antimicrobial activity was quantified as the reciprocal of the measured minimal inhibitory concentration (MIC) against Escherichia coli. One of the peptides was magainin 2, and the remainder were novel peptides designed for this study. The multiple linear regression results revealed that the amphiphilicity of the peptides was the most important factor governing antimicrobial activity compared to mean hydrophobicity or alpha-helix content. A better regression of the data was obtained using ln(1/MIC+constant) as the dependent variable than with either 1/MIC or ln(1/MIC). These results should be useful in designing peptides with higher antimicrobial activity.

Immunohistochemical studies of neurochemical markers in normal human buccal mucosa

The content of various substances, such as regulatory peptides, hormones and structural proteins, was investigated in normal buccal mucosa using indirect immunofluorescence. Thin nerve fibres, which from a morphological point of view were most probably sensory, showed immunoreactivity for substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide K (NPK) and neurokinin A (NKA). Also galanin (GAL), gamma-melanocyte stimulating hormone (gamma-MSH) and somatostatin (SOM) stained thin fibres were found in the propria, which were, however, few in number and the gamma-MSH staining was weak. CGRP, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI) and neuropeptide Y (NPY) immunoreactive nerve fibres were observed in close connection to blood vessels. SOM positive cells with processes were found, mostly scattered, in the connective tissue. A population of cells within the epithelium also showed somatostatin immunoreactivity. Protein S-100 (S-100) stained distinct populations of cells at two separate locations. In the propria, cells with one or two slender processes were seen, being mostly single but sometimes forming groups. In the epithelium, dendritic cells with many processes with or without 'spines' were observed, mainly located to the basal layer of the lamina epithelialis. Single nerve fibres and nerve bundles were also stained. Neurofilament (NF) positive fibres, singly and in bundles, as well as endorgan-like structures were seen. Neuron-specific enolase (NSE) and protein gene product 9.5 (PGP 9.5) both stained the same structures, namely single fibres, nerve bundles, nerves surrounding vessels and innervating muscles and glands (if present in the section), as well as Merkel cells. Also with these two markers endorgan-like structures were seen. No clear innervation of the epithelium could be observed with the markers used. No methionine-enkephalin (ENK) or synaptophysin (SYN) immunoreactive material was found.

The effect of neonatal capsaicin treatment on gustatory behavior in the albino rat

Small-diameter fibers present in gustatory peripheral nerves have historically been suspected of relaying information about the bitter quality of a taste stimulus. Neonatally injected capsaicin irreversibly destroys a proportion of unmyelinated C- and some A delta-fibers. Consummatory responses to increasing concentrations of quinine and other chemical solutions following neonatal capsaicin injection were compared to those of untreated and vehicle-injected control Sabra albino rats. Capsaicin-treated rats significantly increased their withdrawal thresholds to noxious, CO2 laser-generated heat pulses verifying treatment effectiveness. Furthermore, neonatal capsaicin treatment diminished sensitivity to pungent capsaicin solutions in mature rats. However, there were no group differences in quinine intake, suggesting that the full array of unmyelinated fibers associated with taste buds is not essential for the transmission of bitter taste. Capsaicin-treated animals showed a significant reduction in intake of normally highly preferred sodium chloride and sucrose concentrations. These results were probably not due to loss of peripheral unmyelinated afferent fibers per se, but rather to secondary central changes.

Immunocytochemical survey of putative neurotransmitters in taste buds from Necturus maculosus

To investigate synaptic mechanisms in taste buds and collect information about synaptic transmission in these sensory organs, we have examined taste buds of the mudpuppy, Necturus maculosus for the presence of neurotransmitters and neuromodulators. Immunocytochemical staining at the light microscopic level revealed the presence of serotonin-like and cholecystokinin-like (CCK) immunoreactivity in basal cells in the taste bud. Nerve fibers innervating taste buds were immunoreactive for vasoactive intestinal peptide-like (VIP), substance P-like, and calcitonin gene-related peptide-like (CGRP) or compounds closely related to these substances. Immunoreactivity for tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) in the taste cells and nerve fibers was absent. These data suggest that serotonin, CCK, VIP, substance P, and CGRP are involved in synaptic transmission or neuromodulation in the peripheral organs of taste. No evidence was found for cholinergic or adrenergic mechanisms on the basis of the absence of immunocytochemical staining for key enzymes involved in these two transmitter systems.

Presence of gastrin-releasing peptide in neurons of the geniculate ganglion in rat and man

Gastrin-releasing peptide (GRP) was demonstrated by immunohistochemistry and high-performance liquid chromatography to be present in the great majority of neurons in the geniculate ganglion of rat and man. This was in contrast to findings in the sphenopalatine ganglion of rat, where only little GRP was found, and in the otic, trigeminal, glossopharyngeal-vagal and internal carotid ganglia, where no GRP-containing cells could be demonstrated. The peptide was not detected by immunohistochemistry in nerve fibers within structures innervated from the ganglion (tongue, soft palate, retroauricular skin and facial musculature). The retrograde axonal tracer True blue accumulated in these neurons of rat after application not only in the tongue and soft palate but also in the retroauricular skin.

Immunohistochemical localization of neuron-specific enolase and calcitonin gene-related peptide in pig taste papillae

Immunoreactivity to neuron-specific enolase (NSE), a specific neuronal marker, and calcitonin gene-related peptide (CGRP) was localized in lingual taste papillae in the pigs. Sequential staining for NSE and CGRP by an elution technique allowed the identification of neuronal subpopulations. NSE-staining revealed a large neuronal network within the subepithelial layer of all taste papillae. NSE-positive fibers then penetrated the epithelium as isolated fibers, primarily in the foliate and circumvallate papillae, or as brush-shaped units formed by a multitude of fibers, especially in the fungiform papillae and in the apical epithelium of the circumvallate papilla. Taste buds of any type of taste papillae were found to express a dense subgemmal/intragemmal NSE-positive neuronal network. CGRP-positive nerve fibers were numerous in the subepithelial layer of all three types of taste papillae. In the foliate and circumvallate papillae, these fibers penetrated the epithelium to form extragemmal and intragemmal fibers, while in the fungiforms, they concentrated almost exclusively in the taste buds as intragemmal nerve fibers. Intragemmal NSE- and CGRP-positive fiber populations were not readily distinguishable by typical neural swellings as previously observed in the rat. The NSE-positive neuronal extragemmal brushes never expressed any CGRP-like immunoreactivity. Even more surprising, fungiform taste buds, whether richly innervated by or devoid of NSE-positive intragemmal fibers, always harboured numerous intragemmal CGRP-positive fibers. Consequently, NSE is not a general neuronal marker in porcine taste papillae. Our observations also suggest that subgemmal/intragemmal NSE-positive fibers are actively involved in synaptogenesis within taste buds. NSE-positive taste bud cells were found in all three types of taste papillae. CGRP-positive taste bud cells were never observed.

Immunohistochemical localization of neuron-specific enolase and calcitonin gene-related peptide in rat taste papillae

Calcitonin gene-related peptide-like and neuron-specific enolase-like immunoreactivity (CGRP-IR and NSE-IR) were surveyed immunohistochemically in the fungi-form, foliate and circumvallate papillae in rats. A dense CGRP-IR network (subgemmal and extragemmal) in the taste papillae is linked to the presence of taste buds, even though CGRP-IR fibers are rarely present in the taste buds. Three typical fiber populations were detected with these two markers. (a) A population of coarse NSE-IR intragemmal fibers characterized by thick neural swellings, never expressing CGRP-immunoreactivity. (b) A population of thin varicose intragemmal NSE/CGRP-IR fibers. (c) A population of subgemmal and extragemmal NSE-/CGRP-IR fibers that partly penetrated the epithelium. The common distribution of CGRP-IR and NSE-IR fibers at the base of taste buds, their differential distribution and morphology within taste buds, added to their restricted nature (gustatory or somatosensory) suggest that a population of CGRP-IR fibers undergoes a target-induced inhibition of its CGRP phenotype while entering the taste buds. The combined use of NSE and CGRP allowed a better characterization of nerve fibers within and between all three types of taste papillae. NSE was also a very good marker for a subtype of taste bud cells in the foliate and in the circumvallate papillae, but no such cells could be observed in the fungiform papillae.

Peptide-containing nerve fibers in the fungiform papillae of pigs and rats

The occurrence and distribution of an array of neuropeptides and dopamine-beta-hydroxylase in the fungiform papillae of pigs and rats were studied by immunocytochemistry. Structural differences between the fungiform papillae of the two species were correlated to differences in the occurrence and distribution of neuropeptides. Calcitonin gene-related peptide-, substance P- and neurokinin A-containing fibers were numerous in the fungiform papillae of both species, although their distribution within the papilla differed. In the pig, the majority of these fibers ended within the taste buds, while in the rat numerous fibers also penetrated the adjacent epithelium. Galanin- and bombesin-immunoreactive nerve fibers could not be detected in the rat fungiform papillae, while in the pig many, but not all, of the fungiform papillae contained bombesin- and galanin-positive nerve fibers. Vasoactive intestinal peptide- and peptide histidine isoleucine-immunoreactive fibers occurred in the fungiform papillae of both species. A few neuropeptide Y-containing fibers and dopamine-beta-hydroxylase-positive (presumably adrenergic) fibers could be observed in the porcine papillae only.