Intermolar Eminence Research Articles

Comparative observations on the squamous- -columnar junction of Von Ebner's glandular duct at the bottom of vallate papillae in dogs, rats, mice and human.

This paper aims to comparatively observe similarities of squamous- columnar junction (SCJ) at the opening of Von Ebner's glandular ducts at the vallate papillae in dogs, mice, rats and humans, lay a foundation for the selection of the model in future study of the carcinogenesis in SCJ at vallate papillae. The localization of the vallate papillae in three laboratory animals and humans was comparatively observed. The differences of SCJ at vallate papillae were comparatively observed by alcian blue, immunohistochemistry and H&E staining. Anatomically, the canine vallate papillae were most similar to those of humans in location, whereas mice and rats only had a single, Ω-shaped, vallate papilla lying directly anterior to the posterior border of the intermolar eminence. In histology, the SCJ of dogs lacked a transition zone similar to that of the human SCJ, and there was glandular epithelium secreting acidic mucus at the opening of the rats' Von Ebner's glandular ducts. All of this suggested that the histological structure of SCJ in rats and dogs is more distinct from that of humans, whereas the histological structure of SCJ at vallate papilla in mice was more similar. The structure of SCJ at vallate papilla in mice is most similar to that of humans, so we conclude that mouse is the most suitable model for studying tumourigenesis in SCJ at vallate papillae in these three common laboratory animals.

Developmental plasticity of epithelial stem cells in tooth and taste bud renewal

In Lake Malawi cichlids, each tooth is replaced in one-for-one fashion every ∼20 to 50 d, and taste buds (TBs) are continuously renewed as in mammals. These structures are colocalized in the fish mouth and throat, from the point of initiation through adulthood. Here, we found that replacement teeth (RT) share a continuous band of epithelium with adjacent TBs and that both organs coexpress stem cell factors in subsets of label-retaining cells. We used RNA-seq to characterize transcriptomes of RT germs and TB-bearing oral epithelium. Analysis revealed differential usage of developmental pathways in RT compared to TB oral epithelia, as well as a repertoire of genome paralogues expressed complimentarily in each organ. Notably, BMP ligands were expressed in RT but excluded from TBs. Morphant fishes bathed in a BMP chemical antagonist exhibited RT with abrogated shh expression in the inner dental epithelium (IDE) and ectopic expression of calb2 (a TB marker) in these very cells. In the mouse, teeth are located on the jaw margin while TBs and other oral papillae are located on the tongue. Previous study reported that tongue intermolar eminence (IE) oral papillae of Follistatin (a BMP antagonist) mouse mutants exhibited dysmorphic invagination. We used these mutants to demonstrate altered transcriptomes and ectopic expression of dental markers in tongue IE. Our results suggest that vertebrate oral epithelium retains inherent plasticity to form tooth and taste-like cell types, mediated by BMP specification of progenitor cells. These findings indicate underappreciated epithelial cell populations with promising potential in bioengineering and dental therapeutics.

Nigella Sativa: Protecting the Oral Cavity During X-Irradiation in a Mouse Model

Despite advances in radiation delivery, mucositis and xerostomia continue to be debilitating problems for patients undergoing treatment for head and neck cancers. Nigella sativa oil (NSO) is produced from an annual flowering plant that has shown biochemically reproducible and significant cytoprotective properties through anti-inflammatory and anti-oxidant mechanisms when given orally. The goal of this study is to determine whether topical NSO demonstrates radioprotection in oral cavity tissues in mice. Eight-week old, female C3H mice (n=78) are randomly assigned to five groups. They either receive 15 Gy or 18 Gy to the head according to previously established radiation-induced xerostomia and mucositis models. Topical medication, or sham NSO (saline), is administered according to the following schedule: 1mL applied evenly to oral cavity once daily 3 days prior to radiation, 15 minutes prior to radiation on the day of radiation, and then daily for 14 days following radiation. One control group receives topical NSO (without radiation). Endpoints are histopathological changes and weight loss. Weight will be monitored throughout as a measure of food intake, and the mucosal reactions scored daily for signs of inflammation, swelling, ulceration and loss of surface integrity. Subgroups of mice will be sacrificed in intervals starting at day 10 post-irradiation and checked for normal tissue responses including ulceration, reduction in intermolar eminence and salivary gland hypofunction. Histological analyses will be performed on tongue, floor of mouth, buccal mucosa, submandibular gland, and parotid tissues by a single pathologist who will grade radiation tissue damage according to previously described scale. T-tests will be performed to detect significant differences between groups and a P-value <.05 regarded as statistically significant. NSO promises to significantly improve the quality of life of head and neck cancer patients undergoing radiation treatment with and without chemotherapy by alleviating debilitating normal tissue toxicity. Additional studies confirming the therapeutic gain (absence of tumor protection) as well as on optimal timing and dosing are warranted if this trial is successful.

Single-Dose Radiation-Induced Oral Mucositis Mouse Model.

The generation of a self-resolved radiation-induced oral mucositis (RIOM) mouse model using the highest possibly tolerable single ionizing radiation (RT) dose was needed in order to study RIOM management solutions. We used 10-week-old male BALB/c mice with average weight of 23 g for model production. Mice were treated with an orthovoltage X-ray irradiator to induce the RIOM ulceration at the intermolar eminence of the animal tongue. General anesthesia was injected intraperitoneally for proper animal immobilization during the procedure. Ten days after irradiation, a single RT dose of 10, 15, 18, 20, and 25 Gy generated a RIOM ulcer at the intermolar eminence (posterior upper tongue surface) with mean ulcer floor (posterior epithelium) heights of 190, 150, 25, 10, and 10 μm, respectively, compared to 200 μm in non-irradiated animals. The mean RIOM ulcer size % of the total epithelialized upper surface of the animal tongue was RT dose dependent. At day 10, the ulcer size % was 2, 5, 27, and 31% for 15, 18, 20, and 25 Gy RT, respectively. The mean relative surface area of the total epithelialized upper surface of the tongue was RT dose dependent, since it was significantly decreased to 97, 95, 88, and 38% with 15, 18, 20, and 25 Gy doses, respectively, at day 10 after RT. Subcutaneous injection of 1 mL of 0.9% saline/6 h for 24 h yielded a 100% survival only with 18 Gy self-resolved RIOM, which had 5.6 ± 0.3 days ulcer duration. In conclusion, we have generated a 100% survival self-resolved single-dose RIOM male mouse model with long enough duration for application in RIOM management research. Oral mucositis ulceration was radiation dose dependent. Sufficient hydration of animals after radiation exposure significantly improved their survival.

Cell-Autonomous and Non-Cell-Autonomous Roles for Irf6 during Development of the Tongue

Interferon regulatory factor 6 (IRF6) encodes a highly conserved helix-turn-helix DNA binding protein and is a member of the interferon regulatory family of DNA transcription factors. Mutations in IRF6 lead to isolated and syndromic forms of cleft lip and palate, most notably Van der Woude syndrome (VWS) and Popliteal Ptyerigium Syndrome (PPS). Mice lacking both copies of Irf6 have severe limb, skin, palatal and esophageal abnormalities, due to significantly altered and delayed epithelial development. However, a recent report showed that MCS9.7, an enhancer near Irf6, is active in the tongue, suggesting that Irf6 may also be expressed in the tongue. Indeed, we detected Irf6 staining in the mesoderm-derived muscle during development of the tongue. Dual labeling experiments demonstrated that Irf6 was expressed only in the Myf5+ cell lineage, which originates from the segmental paraxial mesoderm and gives rise to the muscles of the tongue. Fate mapping of the segmental paraxial mesoderm cells revealed a cell-autonomous Irf6 function with reduced and poorly organized Myf5+ cell lineage in the tongue. Molecular analyses showed that the Irf6−/− embryos had aberrant cytoskeletal formation of the segmental paraxial mesoderm in the tongue. Fate mapping of the cranial neural crest cells revealed non-cell-autonomous Irf6 function with the loss of the inter-molar eminence. Loss of Irf6 function altered Bmp2, Bmp4, Shh, and Fgf10 signaling suggesting that these genes are involved in Irf6 signaling. Based on these data, Irf6 plays important cell-autonomous and non-cell-autonomous roles in muscular differentiation and cytoskeletal formation in the tongue.

Bmp signalling in filiform tongue papillae development

ObjectiveTongue papillae are critical organs in mastication. There are four different types of tongue papillae; fungiform, circumvallate, foliate, and filiform papillae. Unlike the other three taste papillae, non-gustatory papillae, filiform papillae cover the entire dorsal surface of the tongue and are important structures for the mechanical stress of sucking. Filiform papillae are further classified into two subtypes with different morphologies, depending on their location on the dorsum of the tongue. The filiform papillae at the intermolar eminence have pointed tips, whereas filiform papillae with rounded tips are found in other regions (anterior tongue). It remains unknown how the shape of each type of filiform papillae are determined during their development. Bmp signalling pathway has been known to regulate mechanisms that determine the shapes of many ectodermal organs. The aim of this study was to investigate the role of Bmp signalling in filiform papillae development. DesignComparative in situ hybridization analysis of six Bmps (Bmp2–Bmp7) and two Bmpr genes (Bmpr1a and Bmpr1b) were carried out in filiform papillae development. We further examined tongue papillae in mice over-expressing Noggin under the keratin14 promoter (K14-Noggin). ResultsWe identified a dynamic temporo-spatial expression of Bmps in filiform papillae development. The K14-Noggin mice showed pointed filiform papillae in regions of the tongue normally occupied by the rounded type. ConclusionsBmp signalling thus regulates the shape of filiform papillae.

Morphology of the Filiform Lingual Papillae in Porcupine (Hystrix cristata)

The light and scanning electron microscopic structure of the filiform lingual papillae was studied in five adult porcupine (three males and two females). The tongue was characterised by a round tip, a rostral median sulcus and a deep lingual fossa which was situated just rostral to a prominent inter-molar eminence corresponding to a torus linguae. The filiform papillae were curved, enclosed a large connective tissue core and were separated by wide inter-papillary zones covered by a thick epithelium. Most filiform papillae had a cylindrical shape, but the rostral and central parts of the tongue contained a number of flat, comb-shaped papillae with rounded tips.

Sonic hedgehog exerts distinct, stage-specific effects on tongue and taste papilla development

Taste papillae are ectodermal specializations that serve to house and distribute the taste buds and their renewing cell populations in specific locations on the tongue. We previously showed that Sonic hedgehog (Shh) has a major role in regulating the number and spatial pattern of fungiform taste papillae on embryonic rat tongue, during a specific period of papilla formation from the prepapilla placode. Now we have immunolocalized the Shh protein and the Patched receptor protein (Ptc), and have tested potential roles for Shh in formation of the tongue, emergence of papilla placodes, development of papilla number and size, and maintenance of papillae after morphogenesis is advanced. Cultures of entire embryonic mandible or tongues from gestational days 12 to 18 [gestational or embryonic days (E)12–E18] were used, in which tongues and papillae develop with native spatial, temporal, and molecular characteristics. The Shh signaling pathway was disrupted with addition of cyclopamine, jervine, or the 5E1 blocking antibody. Shh and Ptc proteins are diffuse in prelingual tissue and early tongue swellings, and are progressively restricted to papilla placodes and then to regions of developing papillae. Ptc encircles the dense Shh immunoproduct in papillae at various stages. When the Shh signal is disrupted in cultures of E12 mandible, tongue formation is completely prevented. At later stages of tongue culture initiation, Shh signal disruption alters development of tongue shape (E13) and results in a repatterned fungiform papilla distribution that does not respect normally papilla-free tongue regions (E13–E14). Only a few hours of Shh signal disruption can irreversibly alter number and location of fungiform papillae on anterior tongue and elicit papilla formation on the intermolar eminence. However, once papillae are well formed (E16–E18), Shh apparently does not have a clear role in papilla maintenance, nor does the tongue retain competency to add fungiform papillae in atypical locations. Our data not only provide evidence for inductive and morphogenetic roles for Shh in tongue and fungiform papilla formation, but also suggest that Shh functions to maintain the interpapilla space and papilla-free lingual regions. We propose a model for Shh function at high concentration to form and maintain papillae and, at low concentration, to activate between-papilla genes that maintain a papilla-free epithelium.

Functional and positional difference and classification of the fungiform papillae on the rabbit tongue seen in microvascular cast specimens by means of scanning electron microscope

The relationships between the functional and morphological characteristics, the positional difference and classification seen in microvascular cast specimens (MVCS) of the fungiform papillae (FuP) on the anterodorsal surface and both sides of the intermolar eminence (IME) of the rabbit tongue were examined and compared by means of scanning electron microscopy (SEM). The small fungiform papillae (S-FuP), scattered sporadically among the numerous small filiform papillae (SfP), were found to be distributed irregularly over the anterodorsal surface. The large fungiform papillae (L-FuP), distributed in a length-wise line in the anterior to the posterior direction among the SfP, were found to be distributed on both peripheral sides of the IME. FuPs consisted of the ascending and descending capillary loops, forming the central hole on the top of the FuP, resembling a carnation, the petals of which numbered eight to twelve, and were wider and more complex in shape and size than SfPs were morphologically different. S-FuPs can be classified into three types: type I (consisting of eight petals), type II (ten petals) and type III (twelve petals) according to the shape of the FuP and the number of petals, L-FuPs, were larger and wider than S-FuPs and of a more complex shape, classified into two types: type I (consisting of ten petals) and type II (twelve petals) according to the shape of the FuP and the number of petals in the MVCS of FuPs as seen in SEM. These results suggest that the petals in the ascending and descending capillary loops of the FuP expand into flower-like figures, increase on the surface and play an effective role in receiving the taste sense from foods and liquids on the antero-dorsal surface and both peripheral sides of the IME.

Angioarchitectural structure and functional distributive pattern of the filiform papillae on the meso-dorsal surface of the rabbit tongue

The angioarchitectural classification and distributive patterns were investigated in the filiform papillae (FiP) on the meso-dorsal surface of the rabbit tongue by using microvascular cast specimens (MVCS) and the scanning electron microscope (SEM). The author examined the microvascular network structures, which consisted of ascending and descending branches entering the FiP. They inclined in a posterior (pharynx) direction, and densely and geometrically covered the meso-dorsal surface, directing the spoon-like concave face in an anterior direction. FiPs could be classified into three types: a small filiform papilla (SfP) covering on the meso-dorsal surface except for the marginal part of the intermolar eminence (MIME) and the intermolar eminence itself (IME): a spoon-like concave structure facing in an anterior (apex) direction with an arrowhead-like top: a middle filiform papilla (MfP) on the MIME, made up of a long triangle-like concave structure with a sharp arrowhead-like top and inclined at right angles to the IME. A large filiform papilla (LfP) on the whole swelling dorsal area of the IME was formed by a long triangle-like concave structure with a sharper arrowhead-like top. LfPs are longer and larger than MfPs and inclined towards the pharynx.

Angioarchitectural structure of the fungiform papillae on the anterodorsal surface of the rat tongue

To ascertain whether the microvascular morphological differences of fungiform papillae (FuP) on the anterodorsal surface of the rat tongue are locationally and functionally related, this study aimed at examining and comparing, in greater detail, the comparative morphological characteristics of FuP. FuP were sporadically and consistently scattered among numerous filiform papillae (FiP) in three parts: the apical, central and in front of the intermolar eminence on the anterodorsal surface. We studied these by means of the microvascular cast specimen (MVCS) of FuP using scanning electron microscopy (SEM). The results obtained in this study showed that in all three parts on the anterodorsal region, the capillary bed of FuP presented as a netbasket-like and cylindrical figure with a central hole consisting of 4-5 horizontal rings of several ascending and descending roots. FuP in the central part on the anterodorsal region were relatively larger in size and more cylindrical in shape than those of both the other parts, and they play the leading part as sensory organs for the taste sense and were regarded as taste receptive organs.

Responses of parabrachial nucleus neurons to chemical stimulation of posterior tongue in chorda tympani-sectioned rats

Responses of parabrachial nucleus (PBN) neurons ( n=43) to chemical stimulation of the posterior tongue were recorded in chorda tympani (CT)-sectioned rats and compared with those ( n=45) in CT-intact. The chemical stimuli used were 0.5 M sucrose, 0.5 M sodium chloride (NaCl), 0.03 M hydrochloric acid (HCl), 0.01 M quinine hydrochloride, and distilled water. These stimuli were applied to an area posterior to the intermolar eminence of the tongue. Neurons of CT-sectioned rats responsive to the chemical stimuli were located in more caudal areas of the PBN compared with those of CT-intact. Numbers of responses to the five stimuli and breadth of responsiveness to the four basics were not different between both groups of rats. However, average response magnitudes of the neurons in CT-sectioned rats were lower than those in CT-intact. In both groups of rats, the response magnitudes to NaCl and HCl were larger than those to the other three stimuli, and responses to NaCl and those to HCl were highly correlated. It is suggested that glossopharyngeal fibers responding strongly to acids and salts are likely to be the main source of PBN responses from the posterior tongue.

Study by scanning electron microscopy of the morphogenesis of three types of lingual papilla in the rat.

Many mammals have four different types of lingual papilla, namely filiform, fungiform, circumvallate, and foliate papillae, on the dorsal or lateral surface of the tongue. However, details of the morphogenesis of these lingual papillae have not been reported. We have investigated the changes in the three-dimensional ultrastructure that occur during the morphogenesis of filiform, fungiform, and circumvallate papillae in rats during fetal and postnatal development. Tongues were removed from rat fetuses on days 12 (E12) and 16 (E16) of gestation from newborns (P0) and from juveniles on days 7 (P7) and 14 (P14), and 21 (P21) after birth. Scanning electron microscopy was used for all observations. In fetuses at E12, the rudiments of fungiform papillae could be observed as two rows of bulges that extended bilaterally and parallel to the median sulcus on the anterior half of the dorsal surface of the tongue. In fetuses at E16, the arrangement of the rudiments of fungiform papillae was relatively regular, with a latticelike pattern. At this stage, the outline of the rudiment of the circumvallate papilla could be recognized on the median line between the lingual body and the lingual radix. No rudiments of filiform papillae were visible. At P0, rudiments of filiform papillae were compactly distributed over the dorsal surface in the same way as in the adult. The width of these rudiments was about one-fourth that of fungiform papillae, and their tips were round as compared with those of filiform papillae in the adult. The fungiform and circumvallate papillae were large, and their outlines were somewhat irregular, as in the adult. In juveniles at P7, filiform papillae were long and slender. On the intermolar eminence, filiform papillar structures were quite large. A taste pore was clearly visible at the center of each fungiform papilla at this stage. The shape of the circumvallate papilla was similar to that in the adult. In juveniles at P14 and P21, the shapes of all three types of papilla were almost same as those in the adult. The rudiments of each of the three different kinds of lingual papilla appeared at a different respective stage of development in rats. The rudiments of the fungiform and circumvallate papillae, which are related to the sense of taste, were visible earlier than those of the filiform papillae, which are not involved in this sense.

Study by scanning electron microscopy of the morphogenesis of three types of lingual papilla in the mouse.

Tongues were removed from fetuses of mice on the 15th day of gestation (E15), from newborns (P0), from juveniles on the 7th day (P7) and on the 14th day (P14) after birth for examination by scanning electron microscopy. In the fetuses at E15, rudiments of fungiform papillae with a relatively regular, lattice-like pattern were visible on the anterior half of the dorsal surface of the tongue. The outline of the rudiment of a circumvallate papilla could be recognized on the median line between the lingual body and the lingual radix. No rudiments of filiform papillae could be seen. At P0, rudiments of filiform papillae were compactly distributed over the dorsal surface, as are the filiform papillae in the adult, their width was approximately one-third of that of fungiform papillae, and their tips were rounded than those of the filiform papillae in the adult. The fungiform papillae then increased in size and became somewhat irregular in shape. In juveniles at P7, the filiform papillae were long and slender, being relatively large on the intermolar eminence. A taste pore was visible in the center of each fungiform papilla at this stage. The shape of the circumvallate papilla was similar to that in the adult. In juveniles at P14, the shapes of all three types of papilla were almost the same as those in the adult. The rudiments of each of the three kinds of lingual papilla appeared at a different stage of development of mice; rudiments of the fungiform and circumvallate papillae, which are related to the sense of taste, were formed earlier than those of the filiform papillae, which are not involved in taste.

Videofluorographic analysis of tongue movement in the rabbit (Oryctolagus cuniculus)

The movement of the entire tongue and intermolar eminence during mastication is described in the domestic rabbit (Oryctolagus cuniculus). Tongue movement and jaw position were analyzed videofluorographically from separate lateral and dorso-ventral views in six rabbits. Metallic markers were inserted into the tongue so that its movement was visible on the fluorographic image. Frame-by-frame analysis of the videofluorographic tape recordings demonstrates that tongue movement in all animals was identical in direction during each part of the chewing cycle. In the lateral view the forepart of the tongue moves down and forward during the opening stroke, whereas the intermolar eminence moves up and forward to appose the palate. During the closing stroke, as the tip of the tongue moves up and back, the intermolar eminence lowers from the palate and retracts. During the power stroke the forepart of the tongue is at its most elevated and retruded position, while the intermolar eminence is its lowest and most retruded. The dorso-ventral view showed that lateral movement of the tongue and mandible are highly synchronous. The intermolar eminence decreases in width during the power stroke, possibly twisting to place or keep food on the teeth. An anterior to posterior undulating movement of the entire tongue occurs throughout the chewing cycle. As the intermolar eminence elevates to appose the palate during the opening stroke, it may replace the bolus on the teeth on the chewing side. The intermolar eminence also appears to be twisting during the closing and power strokes to place or maintain food on the teeth.

Separation of opioid from nonopioid mediation of affect in neonatal rats: Nonopioid mechanisms mediate maternal contact influences.

A causal distinction is established in infant Norway rats between opioid- and nonopioid-mediated determinants of behavior. Contact influences are shown to be mediated by nonopioid pathways, whereas gustatory influences are shown to be opioid mediated. Specifically, naltrexone (0.5 and 1.0 mg/kg) did not at all diminish quieting exerted by contact with an anesthetized dam but completely reversed the quieting effects of morphine in isolated rats. Naloxone (5 mg/kg) did not affect the latencies with which nondeprived or 8-hr deprived rats 9, 12, 15, and 18 days of age attached to the nipples of anesthetized dams, nor did naloxone (5 and 10 mg/kg) cause any systematic change in nipple attachment in 10- and 18-day-old rats that had been deprived of their dam for either 0, 8, or 24 hr. In a 3rd experiment, naloxone (5 mg/kg) did not significantly reduce milk intake by 9-, 12-, 15-, or 18-day-old rats from the nipple when milk letdown was induced by oxytocin. Moreover, naloxone (5 and 10 mg/kg) did not reduce milk intake in Day-10 rats that, while suckling, received milk via a cannula placed in the posterior portion of the tongue at the level of the intermolar eminence or in rats that obtained milk directly from their awake mother. In contrast, milk intake was significantly reduced by naltrexone (0.25-1.0 mg/kg) in Day-10 rats that obtained milk (a) by licking it off a saturated substrate or (b) through an indwelling cannula located in the anterior portion of the lower jaw. (Milk delivered at this placement is thought to engage feeding systems by its taste and texture.) In a final set of experiments in Day-10 rats, intake of milk delivered via anterior jaw cannulae was reduced by naloxone (5 and 10 mg/kg) in rats that were either isolated, in contact with an anesthetized dam, or attached to her nipples. On the basis of resistance to naloxone and naltrexone administration, these experiments demonstrate that behavioral influences of the tactile (and possibly olfactory) qualities of the mother are not mediated by opioid systems. Implications for understanding the means through which mothers can influence their young and the infantile mediators of these maternal influences are discussed.

Receptive field properties of the parabrachio-thalamic taste and mechanoreceptive neurons in rats.

Receptive fields (RFs) of 36 taste (the 22 parabrachio-thalamic relay (P-T) and 14 non-P-T) and 23 mechanoreceptive neurons (7 P-T and 16 non-P-T) were located in the oral cavity of rats. All of the taste and most of the mechanoreceptive units examined had an RF on the ipsilateral side of the tongue or palate, but some mechanoreceptive P-T and non-P-T units had RFs bilaterally. When the RFs of taste neurons were examined with the most effective of the four basic taste (the best stimulus) and non-best stimuli, no difference was noticed in the location of RFs between the P-T and non-P-T neurons. Though most of the P-T neurons (7/11) and all of the non-P-T neurons (6/6) had an RF for non-best stimuli at a region similar to that for the best stimulus, some P-T neurons (4/11) had an RFs for non-best stimulus outside the RF for the best stimulus and/or on the region separate from the RF for the best stimulus. The P-T neurons, responding vigorously to non-optimal stimuli as well as to the best stimulus, had an RF outside the RF for the best stimulus. RFs for mechanical stimulation were also examined in some taste and mechanoreceptive neurons. The mechanoreceptive P-T units rarely had an RF exclusively on the palate. Some mechanoreceptive units had an RF on the region where no taste RF has been found, e.g. the intermolar eminence and the folium of the hard palate.

Quantitative anatomical study of taste buds in fungiform papillae of young and old Fischer rats.

To determine if differences in neural taste responses relate to taste bud loss in old age, taste buds were counted in fungiform papillae of Fischer 344 rats aged 4 to 6 months, 20 to 24 months, and 30 to 37 months. Papillae anterior to the intermolar eminence on one half of the tongue were examined in serial sections. Presence or absence of a taste bud was noted and taste bud diameter was measured. Average percentages of papillae that contained a taste bud in the three groups were 99.6, 99.3, and 94.7%. This is a significant age-related difference but actual number of taste buds lost in the oldest rats was small. Taste bud diameter did not differ with age and general anatomical characteristics of buds were similar in all groups. Thus, anatomical observations on taste bud maintenance in rats over a wide age range, coupled with neurophysiological data, demonstrate that the integrity of the peripheral gustatory system is not altered greatly in old age.

Conditioned aversions and their memories in 5-day-old rats during suckling.

Association learning during suckling was investigated. Five-day-old rats equipped with tongue cannulae placed either 2 mm rostral or 4-6 mm caudal to the intermolar eminence received sweet or salty solutions while suckling. This ingestion was followed by lithium chloride toxicosis. Pups with anterior cannulae took in considerably less fluid than control pups when tested 5 or 16 days later. A series of control groups demonstrated that this acquired aversion was associative in nature. Pups with posterior cannulae did not form the association. The failure of 5-day-old rats with posterior cannulae to form associations while suckling is not due to the prevention of conditioning by the act of suckling per se. Rather, the failure rests in the fluid's not reaching anterior taste receptors when injected into the posterior oropharynx, where the nipple normally empties its contents. These findings are discussed in terms of the transfer of information obtained during suckling prior to weaning, to feeding and drinking during and after weaning.

Gustatory determinants of suckling in albino rats 5-20 days of age.

Taste reactivity in suckling rat pups was assessed. Five-day-old rats in Experiment I were equipped with tongue cannulae seated 2 mm rostral, 0-3 mm caudal, or 4-6 mm caudal to the intermolar eminence. Either water, 1.4 X 10(-3) QHC1, .50M NH4Cl, or .43M NaCl was delivered in one of three fashions during suckling: (1) continuous: fluid was continuously available from a reservoir connected to the cannula, and could be obtained by exerting suction; (2) discrete: same procedure as above, save that fluid was available for only 30 sec every 3 min of the 30-min test; (3) pulsatile: here, .05 ml fluid was delivered by infusion pump 8-10 sec every 3 min, provided the pups were attached to a nipple. Based on intake, time and behavioral measures, we conclude behavioral reactivity exists especially to NH4Cl and NaCl. As to quinine, Day 5 pups were responsive only when QHCl was delivered in the continuous mode. In Experiment II, rats 10, 15, and 20 days of age received the above solutions by infusions with the cannulae located in one of the three positions. Quinine reactivity developed sequentially in an anterior to posterior direction. NH4Cl disrupted behavior in 5-, 10-, and especially 20-day-old rats. Remarkably, Day 15 rats were not behaviorally reactive to NH4Cl. Sodium chloride, especially in the anterior and middle positions, was treated as an aversive solution during suckling throughout development. Based on existing electrophysiological data, the last finding was unexpected.