Article

The tongue of Leopard Gecko ( Eublepharis macularius ): LM, SEM and confocal laser study

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Abstract

The leopard gecko is a crepuscular and insectivorous reptile. The role of the tongue in this reptile is fundamental for the prey capture and ingestion and is not related with eyes cleaning as usual in other geckos. The elongated tongue can be divided into a foretongue with a slightly bifurcated apex and a hindtongue. Scanning electron microscopy demonstrated that several different papillae are present on the dorsal surface, foliate and dome‐shaped in the foretongue, becoming thicker and stouter with reduced interpapillary spaces in the lateral parts. The hindtongue is characterised by wide foliate papillae with indented margins and deep fissures of the mucosa. Light microscopy showed the presence of a stratified slightly keratinized squamous epithelium in the apex of the foretongue, a stratified non‐keratinized squamous epithelium in the fore and in the hindtongue. In the foretongue, numerous muciparous caliciform cells were observed. Moreover, the presence of taste buds on the tongue ventral surface was demonstrated for the first time in this species and the confocal laser study revealed a strong immunoreactivity for the S‐100 protein in the sensory cells. Therefore, the results obtained could give a contribution to the knowledge of the tongue anatomy and are a basis for eventual further studies regarding the feeding habits in a reptile become a popular pet.

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... An important role by different hormones in feeding, related to the morphological characteristics, has been recently demonstrated in the digestive system in teleosts (Audira et al., 2018;Carnovali, Luzi, Terruzzi, Banfi, & Mariotti, 2018;Mania et al., 2017;Montalbano et al., 2016Montalbano et al., , 2018. The most of the functional processes inside the oral cavity are carried out by the tongue, whose presence and description have been showed in different species of fish, demonstrating the variation in the presence of anatomical structures like taste buds, mucous cells and teeth in teleosts, also of commercial interest (Abbate et al., 2006(Abbate et al., ,2020a(Abbate et al., ,2020bAbbate, Guerrera, Montalbano, De Carlos, et al., 2012;Alsafy, Bassuoni, & Hanafy, 2018;Amato et al., 2012;Dos Santos, Arantes, Santiago, & Dos Santos, 2015;El Bakary, 2014;Elgendy, Alsafy, & Tanekhy, 2016;Germanà et al., 2009;Guerrera et al., 2015;Ikpegbu, Ibe, & Nlebedum, 2019;Kasumyan, 2019;Kettratad, Senarat, Boonyoung, & Jiraungkoorsku, 2017;Levanti et al., 2017;Mahmoud, Essa, & Sayed, 2016;Sadeghinezhad, Rahmatiholasoo, Fayyaz, & Zargar, 2015;Sayed, Mahmoud, & Essa, 2019;Yu et al., 2019). Several significant papers, important as comparative data, are present in the literature in upper vertebrates like birds, reptiles and mammals (Abbate et al., 2008(Abbate et al., , 2010(Abbate et al., , 2020b Abumandour & Kandyel, 2020; Barbosa et al., 2020;Bels et al., 2020; Cizek, Hamouzova, Goździewska-Harłajczuk, Klećkowska-Nawrot, & Kvapil, 2020;Cizek, Hamouzova, Kvapil, & Kyllar, 2019;Emura, 2016aEmura, ,2016bEmura, ,2016cEmura, ,2017Emura, ,2018aEmura, ,2018bEmura, ,2018cEmura, ,2018dEmura, ,2019Erdoğan & Alan, 2012;Erdoğan & Iwasaki, 2014;Erdoğan Lima & Pérez, 2016;Erdoğan Villar Arias & Pérez, 2016;Erdoğan, Villar Arias, et al., 2016;Erdoğan et al., 2018a;Erdoğan and Sağsöz, 2018b;Freire et al., 2019;Gonçalves et al., 2020;Gunawan et al., 2020;Haddad et al., 2019;Herrel, Redding, Meyers, & Nishikawa, 2014;Iwasaki, Yoshimura, Shindo, & Kageyama, 2019;Massoud & Abumandour, 2020;Nabil & Tawfiek, 2020;Sadeghinezhad et al., 2015;Sadeghinezhad, Sheibani, Memarian, & Chiocchetti, 2017;Sadeghinezhad, Tootian, & Javadi, 2018;Saragih et al., 2020;Skieresz-Szewczyk Cornillie & Jackowiak, 2018;Skieresz-Szewczyk & Jackowiak, 2016,2017Skieresz-Szewczyk Jackowiak, & Ratajczak, 2018. ...
... The most of the functional processes inside the oral cavity are carried out by the tongue, whose presence and description have been showed in different species of fish, demonstrating the variation in the presence of anatomical structures like taste buds, mucous cells and teeth in teleosts, also of commercial interest (Abbate et al., 2006(Abbate et al., ,2020a(Abbate et al., ,2020bAbbate, Guerrera, Montalbano, De Carlos, et al., 2012;Alsafy, Bassuoni, & Hanafy, 2018;Amato et al., 2012;Dos Santos, Arantes, Santiago, & Dos Santos, 2015;El Bakary, 2014;Elgendy, Alsafy, & Tanekhy, 2016;Germanà et al., 2009;Guerrera et al., 2015;Ikpegbu, Ibe, & Nlebedum, 2019;Kasumyan, 2019;Kettratad, Senarat, Boonyoung, & Jiraungkoorsku, 2017;Levanti et al., 2017;Mahmoud, Essa, & Sayed, 2016;Sadeghinezhad, Rahmatiholasoo, Fayyaz, & Zargar, 2015;Sayed, Mahmoud, & Essa, 2019;Yu et al., 2019). Several significant papers, important as comparative data, are present in the literature in upper vertebrates like birds, reptiles and mammals (Abbate et al., 2008(Abbate et al., , 2010(Abbate et al., , 2020b Abumandour & Kandyel, 2020; Barbosa et al., 2020;Bels et al., 2020; Cizek, Hamouzova, Goździewska-Harłajczuk, Klećkowska-Nawrot, & Kvapil, 2020;Cizek, Hamouzova, Kvapil, & Kyllar, 2019;Emura, 2016aEmura, ,2016bEmura, ,2016cEmura, ,2017Emura, ,2018aEmura, ,2018bEmura, ,2018cEmura, ,2018dEmura, ,2019Erdoğan & Alan, 2012;Erdoğan & Iwasaki, 2014;Erdoğan Lima & Pérez, 2016;Erdoğan Villar Arias & Pérez, 2016;Erdoğan, Villar Arias, et al., 2016;Erdoğan et al., 2018a;Erdoğan and Sağsöz, 2018b;Freire et al., 2019;Gonçalves et al., 2020;Gunawan et al., 2020;Haddad et al., 2019;Herrel, Redding, Meyers, & Nishikawa, 2014;Iwasaki, Yoshimura, Shindo, & Kageyama, 2019;Massoud & Abumandour, 2020;Nabil & Tawfiek, 2020;Sadeghinezhad et al., 2015;Sadeghinezhad, Sheibani, Memarian, & Chiocchetti, 2017;Sadeghinezhad, Tootian, & Javadi, 2018;Saragih et al., 2020;Skieresz-Szewczyk Cornillie & Jackowiak, 2018;Skieresz-Szewczyk & Jackowiak, 2016,2017Skieresz-Szewczyk Jackowiak, & Ratajczak, 2018. Considering that no data are available in the literature about the morphology of the rainbow trout tongue and in order to give a contribution to the anatomical knowledge of this well-known farmed species of fish, the aim of this study was to investigate by light, scanning electron and confocal laser microscopy, the morphological characteristics of the tongue. ...
... Until the last decade, the fish tongue was mainly described as a simple thickening of the oral cavity pavement mucosa (Buddington & Kuz'mina, 2000). Several studies demonstrated in different teleosts the presence of a true tongue (Abbate et al., 2006(Abbate et al., ,2020a(Abbate et al., ,2020bAbbate, Guerrera, Montalbano, De Carlos, et al., 2012;Guerrera et al., 2015;Levanti et al., 2017;Yu et al., 2019). The morphological characteristics of the tongue in the rainbow trout match with that of other described teleost species; therefore, also in this fish of commercial interest an apex, a body and a root can be clearly showed, and these three distin- Abbate, Guerrera, Montalbano, De Carlos, et al., 2012;Guerrera et al., 2015), and in swordfish and Atlantic salmon, there was no evidence of them (Abbate et al., ,2020a. ...
Article
The rainbow trout (Oncorhynchus mykiss Walbaum, 1792) is a fish commercially farmed all over the world. These fish are usually fed, in aquaculture, with pellets rich in proteins and fat. It is well known that there are close relationships among the adaptation of vertebrates to their environment, the capacity and the modality of feeding and the oral cavity morphology, especially the tongue one. No data are so far available about the morphology of the rainbow trout tongue, and therefore, the aim of this study was to investigate by light, scanning electron and confocal laser microscopy, the morphological characteristics of the tongue. An apex, a body and a root can be distinguished in the tongue, and the presence of teeth, taste buds and fungiform‐like papillae was demonstrated. Light microscopy shows the presence of an adipose tissue pad in the deeper layer of the apex and in the most superficial layer of the root. In the deeper layer of the body, a triangular‐shaped pad consisting of fusiform cells immersed in abundant extracellular matrix of the mesenchymal tissue was observed. The confocal laser microscopy shows the presence of cells with a fibroblast‐like morphology positive for vimentin. In the deepest layer of the tongue root, a large area of osteo‐cartilaginous tissue was observed. The results, besides the description of the morphological characteristics of the tongue, related to studies regarding the feeding, could be considered for the eventual applications of the use of mesenchymal cells, observed in adult fish, in cell therapies in different pathologies.
... Lizards are known to employ the tongue in a variety of behaviours, including chemosensory detection, drinking, food procurement and/or capture, food transport, swallowing, and grooming (Russell & Rosenberg, 1981;Bels, Chardon & Kardong, 1994;Schwenk & Rubega, 2005;Bels et al., 2007;Baeckens, Van Damme & Cooper Jr, 2017bb;Bels et al., 2019a,b). Several authors offer functional explanations for the morphological diversity seen in the tongue epithelia of lizards Herrel et al., 2005;Meyers & Herrel, 2005;Abbate et al., 2009Abbate et al., , 2010Abbate et al., , 2019Zghikh et al., 2014;Iwasaki, Erdogan, & Asami, 2019). The phylogenetic implications of morphological, functional and behavioural lingual features have been extensively discussed in relation to the previously advocated dichotomous division of squamates into the Iguania and Scleroglossa, reflective of a perceived fundamental evolutionary dichotomy between the primary deployment of the tongue for prey capture vs. vomerolfaction (Estes & Pregill, 1988;Schwenk & Throckmorton, 1989;Schwenk, 2000;Wagner & Schwenk, 2000;Vitt et al., 2003). ...
... Like all geckos, the leopard gecko uses its tongue for drinking but not for food prehension or chemosensation (Bels, Brillet & Delheusy, 1995;Delheusy & Bels, 1999), so its movements can be regarded as being largely dedicated to this purpose. Detailed anatomical studies of its tongue revealed regions likely to be involved in water collection and transport (Jamniczky et al., 2009;Abbate et al., 2019). Tongue movements, deformation and contact patterns with the water are all involved with these processes. ...
Chapter
Living lizards exploit almost all terrestrial ecosystems where they play the roles of both predator and prey in complex food webs. Bels et al. (Biomechanics of feeding in Vertebrates, 197–240, 1994) and Schwenk (Feeding: form, function and evolution in Tetrapod Vertebrates, 459–485, 2000) provided first detailed overviews about the anatomical and functional traits of the feeding stages and phases of the feeding cycle in these tetrapods. Here, we synthesize recent literature in order to provide discussion of the evolution of their feeding behavior from capture to swallowing.
... In central-western Africa, the African bony-tongue represents an important food resource and, consequently, a source of income. However, although some studies on the digestive system of African bony-tongue have been conducted [32], literature is still scarce. We would like to enrich the currently available scientific knowledge with more precise details correlating gross and microscopic anatomy. ...
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... It has been shown that the capacity and modality of feeding are strictly related to the morphofunctional adaptations of fish to the environment, thus explaining the several differences observed in the presence, morphology, abundance and distribution of taste buds, papillae with mechanic or sensitive properties and teeth of different shapes in several species of fish (Abbate et al., 2006(Abbate et al., , 2020b(Abbate et al., , 2020a(Abbate et al., , 2012b(Abbate et al., , 2012aGermanà et al., 2009;Amato et al., 2012;Dos Santos et al., 2015;Sadeghinezhad et al., 2015;Guerrera et al., 2015 ;Mahmoud et al., 2016;Kettratad et al., 2017;Levanti et al., 2017;Ik pegbu et al., 2019;Kasumyan, 2019). Also, a strict comparative correlations with numerous studies carried out in other vertebrates like birds and reptiles are significative (Abbate et al., 2020c(Abbate et al., , 2010(Abbate et al., , 2008Erdoğan and Alan, 2012;Erdoğan and Iwasaki, 2014;Herrel et al., 2014;Cizek et al., 2019;Bels et al., 2020). In addition, recent data demonstrate that the role of some hormones is strictly related to the anatomical aspects of the digestive system and particularly of the teleosts oral cavity (Montalbano et al., 2016(Montalbano et al., , 2018aMania et al., 2017;Audira et al., 2018;Carnovali et al., 2018). ...
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Summary In this paper we document the activity of key muscles of the tongue, hyobranchial apparatus and head during prey capture in the lizard Chanzaeleo jacksonii Boulcnger and use these data to test current hypothescs of chameleon tongue function. Electromyographic recordings were made during 27 feedings from nine individuals and synchronized with high-speed video recordings (200fields sl), permitting an assessment of the activity of muscles relative to the onset of tongue projection, contact between tongue and prey, and tongue retraction. Four major results were obtained. (1) The hyoglossi muscles exhibit a single burst of activity that begins between 10 ms before and 20 ms after the onset of tongue projection and continues throughout the period of tongue retraction. (2) The accelerator muscle exhibits a biphasic activity pattern, with the first burst lasting about 185ms and ending an average of 10.6ms prior to the onset of projection. (3) The accelerator muscle shows regional variation in morphology that corresponds with variation in motor pattern. The anterior region of the muscle, unlike the posterior portion, exhibits only a single burst of activity that begins 2.5ms after the onset of tongue projection and is thus not involved in launching the tongue. (4) The geniohyoidei, sternohyoidei, sternothyroidei, depressor mandibulae, adductor mandibulae and pterygoideus all exhibit activity patterns consistent with previously reported kinematic patterns and their pro- posed roles. The major implications of these results for models of the chameleon feeding mechanism are (1) that the hyoglossi do not act to hold the tongue on the entoglossal process during a loading period prior to tongue projection, and (2) that the presence of 185 ms of intense activity in the accelerator muscle prior to tongue projection suggests the presence of a preloading mechanism, the nature of which is the subject of the companion paper.
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In tetrapods, the ability to ingest food on land is based on certain morphological features of the oropharynx in general and the feeding apparatus in particular. Recent paleoecological studies imply that terrestrial feeding has evolved secondarily in turtles, so they had to meet the morphological oropharyngeal requirements independently to other amniotes. This study is designed to improve our limited knowledge about the oropharyngeal morphology of tortoises by analyzing in detail the oropharynx in Manouria emys emys. Special emphasis is placed on the form and function of the tongue. Even if Manouria is considered a basal member of the only terrestrial turtle clade and was hypothesized to have retained some features reflecting an aquatic ancestry, Manouria shows oropharyngeal characteristics found in more derived testudinids. Accordingly, the oropharyngeal cavity in Manouria is richly structured and the glands are large and complexly organized. The tongue is large and fleshy and bears numerous slender papillae lacking lingual muscles. The hyolingual skeleton is mainly cartilaginous, and the enlarged anterior elements support the tongue and provide insertion sides for the well-developed lingual muscles, which show striking differences to other reptiles. We conclude that the oropharyngeal design in Manouria differs clearly from semiaquatic and aquatic turtles, as well as from other reptilian sauropsids.
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The nutcracker Nucifraga caryocatactes belongs to a group of bird species that use their beak and tongue as tools for obtaining food, such as seeds from hard-to-reach cones or nuts from shells. The aim of the present study, carried out with a scanning electron microscope, was to define the morphological features of the tongue of the nutcracker, which seems to be adapted to its environment through specific methods of obtaining food. One of the characteristic features of the nutcracker's tongue is the unique structure of the anterior part of the tongue, which has two long and highly keratinized processes - a product of the renewable keratinized layer of the epithelium covering the ventral surface of the tongue. These dagger-like processes, which are a modified "lingual nail," take a major role in levering up and shelling seeds, which are transported over the short sulcus-shaped body of the tongue. A unique feature of the nutcracker's tongue is the groove separating the body from the root. Two rows of highly keratinized, mechanical, conical papillae are located at the junction of the body and the root. These papillae are mechanically protective elements for passing food particles in the form of seeds. Among lingual glands, only the posterior lingual glands on the root of the tongue have been observed. Their secretion agglutinates dry food before it is swallowed. Results of the present study indicate that the nutcracker's tongue is an efficient tool resembling a lever that is helpful in shelling seeds.
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Extremely specialized and long tongues used for prey capture have evolved independently in plethodontid salamanders and chameleons. In both systems, the demands on tongue projection are probably similar: to maximize projection velocity and distance. Consequently, many of the design features of the projection system in these two groups have converged to an astonishing degree. Both involve the use of power amplification systems based on helically wound muscle fibers that load internal connective tissue sheets as illustrated in previous studies. Demands imposed on tongue retraction, however, are different to some degree. Although in both groups there is a clear demand for retraction capacity (given the long projection distances), in chameleons there is an added demand for force because they eat large and heavy prey. As indicated by our data, plethodontid salamanders have extremely long tongue retractors with normal striated muscle. Chameleons, on the other hand, evolved long retractors of the supercontracting type. Interestingly, our data show that at least in chameleons, the extreme design of the tongue in function of prey capture appears to have consequences on prey transport, resulting in an increased dependence on the hyoid. In turn, this has lead to an increase in transport-cycle duration and an increase in the number of cycles needed to transport prey in comparison with closely related agamid lizards. Clearly, extreme morphological specializations are tuned to functional and ecological demands and may induce a reduced performance in other functions performed by the same set of integrated structures.
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Vomeronasal chemoreception, an important chemical sense in squamate reptiles (lizards and snakes), is mediated by paired vomeronasal organs (VNOs), which are only accessible via ducts opening through the palate anteriorly. We comparatively examined the morphology of the oral cavity in lizards with unforked tongues to elucidate the mechanism of stage I delivery (transport of chemical-laden fluid from the tongue tips to the VNO fenestrae) and to test the generality of the Gillingham and Clark (1981. Can J Zool 59:1651-1657) hypothesis (based on derived snakes), which suggests that the sublingual plicae act as the direct conveyors of chemicals to the VNOs. At rest, the foretongue lies within a chamber formed by the sublingual plicae ventrally and the palate dorsally, with little or no space around the anterior foretongue when the mouth is closed. There is a remarkable conformity between the shape of this chamber and the shape of the foretongue. We propose a hydraulic mechanism for stage I chemical transport in squamates: during mouth closure, the compliant tongue is compressed within this cavity and the floor of the mouth is elevated, expressing fluid from the sublingual glands within the plicae. Chemical-laden fluid covering the tongue tips is forced dorsally and posteriorly toward the VNO fenestrae. In effect, the tongue acts as a piston, pressurizing the fluid surrounding the foretongue so that chemical transport to the VNO ducts is effected almost instantaneously. Our findings falsify the Gillingham and Clark (1981. Can J Zool 59:1651-1657) hypothesis for lizards lacking forked, retractile tongues.
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The histology and the ultrastructure of the dorsal lingual epithelium of the Japanese lizard, Takydromus tachydromoides, were investigated by light and transmission electron microscopy. The epithelium of the anterior and middle portions of the tongue showed "orthokeratinization," being composed of a thick layer of keratinized cells. The epithelium of the posterior portion of the tongue showed "parakeratinization" and "nonkeratinization." Most of the nonkeratinized cells contained large numbers of secretory granules.
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Three different types of lingual papilla were observed by scanning electron microscopy on the dorsal lingual epithelium of the lizard Gekko japonicus. Dome-shaped lingual papillae were located at the apex. Flat, fan-shaped lingual papillae were seen in the widest area of the lingual body. Long, scale-like lingual papillae were arranged on the latero-posterior dorsal surface. At higher magnification, microvilli and microridges were seen to be widely distributed over the surface of the papillae. By light microscopy, the epithelium of the dome-shaped papillae was composed of single, columnar epithelial cells filled with secretory granules. The tip of the epithelium of the fan-shaped and scale-like papillae was composed of stratified squamous epithelial cells without granules. The major part of the epithelium of these two types of papilla, except the tip area, was also composed of single, columnar epithelial cells with secretory granules. By transmission electron microscopy, a nucleus without a defined shape was seen to be located in the basal part of each of the single, columnar epithelial cells. Rough-surfaced endoplasmic reticulum and Golgi apparatus were well developed around the nucleus. The other, major part of the cytoplasm was filled with the spherical secretory granules, a large number of which had very electron-dense cores and moderately electron-dense peripheral regions. In the stratified squamous epithelium, a nucleus, which tended to be condensed on the free-surface side, was located in the center of each cell. Mitochondria, endoplasmic reticulum, and vesicles were observed in the cytoplasm.
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An incipient form of tongue projection occurs in Phrynocephalus helioscopus, a generalized agamid lizard. We argue that this condition represents a functional intermediate between typical lingual prehension and chamaeleontid tongue projection, and that tongue projection evolved in chameleons by augmentation of ancestral mechanisms still operating in related, generalized lizards.
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The goal of this study was to investigate the function of the hyolingual muscles used during tongue protraction in iguanian lizards. High-speed videography and nerve-transection techniques were used to study prey capture in the iguanid Sceloporus undulatus, the agamid Pseudoptrapelus sinaitus and the chameleonid Chamaeleo jacksonii. Denervation of the mandibulohyoideus muscle slips had an effect only on P. sinaitus and C. jacksonii, in which tongue protrusion or projection distance was reduced. In C. jacksonii, denervation of the M. mandibulohyoideus completely prevented little hyoid protraction. Denervation of the M. verticalis had no effect on S. undulatus, but reduced tongue protrusion distance in P. sinaitus. Denervation of the accelerator muscle in C. jacksonii inhibited tongue projection completely. The function of the M. mandibulohyoideus and M. verticalis has become increasingly specialized in P. sinaitus and especially in C. jacksonii to allow greater tongue protrusion. The combined results of these treatments suggest that these three groups represent transitional forms, both morphologically and functionally, in the development of a projectile tongue.
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The ultrastructure of the dorsal lingual epithelium of the semi-aquatic West African mud turtle, Pelusios castaneus, is described. Our goal is to give additional information to previous studies of this species such as feeding pattern analysis and gross morphology. Tissue specimens were fixed in modified Karnovsky solution followed by osmium tetroxide, embedded in epoxy resin and observed using light and transmission electron microscopy. The dorsal tongue surface is covered with moderate papillae, which are coated by a stratified epithelium overlying a connective tissue core. Two epithelial regions can be differentiated, although differences are not very obvious: the apical area, where granular cells are more abundant than mucus cells, and the lateral area, where cell distribution is opposite. Within the epithelium, different layers are discernable on the basis of the cells' organelles, corresponding with a process of cell maturation and formation of different granules. These results together with data of previous studies of this species show that the ultrastructure of the lingual epithelium is similar to other turtles adapted to semi-aquatic environments; functional and morphological data indicate a generalist, being well but not highly adapted to feeding in an aquatic environment.
Chapter
The hyolingual system of Squamata is a highly versatile system used in different feeding, drinking, chemoreception, and social behaviors. In each of these activities, either the entire hyolingual system or one of its elements is used. For instance, in the majority of lizards, the tongue acts as the main element for liquid uptake, intraoral food and liquid transport, and in chemoreception, whereas the hyoid apparatus plays a major role during social interactions by acting on the ventral floor of the throat. In varanids, the hyoid apparatus is involved in both deglutition of foods and liquids, and during social displays.
Article
Agamid lizards use tongue prehension for capturing all types of prey. The purpose of this study was to investigate the functional relationship between tongue structure, both surface and musculature, and function during prey capture in Pogona vitticeps. The lack of a detailed description of the distribution of fibre-types in the tongue muscles in some iguanian lizards has hindered the understanding of the functional morphology of the lizard tongue. Three methodological approaches were used to fill this gap. First, morphological analyses were performed (i) on the tongue surface through scanning electron microscopy, and (ii) on the lingual muscle by histological coloration and histochemistry to identify fibre-typing. Secondly, kinematics of prey capture was quantified by using high-speed video recordings to determine the movement capabilities of the tongue. Finally, electromyography (EMG) was used to identify the motor pattern tongue muscles during prey capture. Morphological and functional data were combined to discuss the functional morphology of the tongue in agamid lizards, in relation to their diet. During tongue protraction, M. genioglossus contracts 420 ± 96 ms before tongue-prey contact. Subsequently, Mm. verticalis and hyoglossus contract throughout tongue protraction and retraction. Significant differences are found between the timing of activity of the protractor muscles between omnivorous agamids (Pogona sp., this study) and insectivorous species (Agama sp.), despite similar tongue and jaw kinematics. The data confirm that specialisation toward a diet which includes more vegetal materials is associated with significant changes in tongue morphology and function. Histoenzymology demonstrates that protractor and retractor muscles differ in fibre composition. The proportion of fast glycolytic fibres is significantly higher in the M. hyoglossus (retractor muscle) than in the M. genioglossus (protractor muscle), and this difference is proposed to be associated with differences in the velocity of tongue protrusion and retraction (5 ± 5 and 40 ± 13 cm s(-1) , respectively), similar to Chamaeleonidae. This study provides a way to compare fibre-types and composition in all iguanian and scleroglossan lizards that use tongue prehension to catch prey.
Article
The location and distribution of mucosal sensory structures of the crocodilian oral cavity are poorly understood. Although there are several descriptions of these structures in adults, nothing is known about their development. The purpose of this study was to document location, morphology, and relative abundance of these mucosal sensory structures in both hatchling and subadult alligators. Numerous mucosal sensory structures and pale staining dome-shaped papillae were observed only in the upper palate and tongue. In hatchlings, these papillae, which house either mechanoreceptive or chemosensory (taste buds) structures, were larger and more prevalent on the tongue than the upper palate. In the subadult, however, these papillae housed primarily mechanoreceptive structures and possibly degenerate taste buds. Although the presence of the mechanoreceptive structures in the palates of the suabadult alligator are to be expected, the loss of most taste buds is hitherto undocumented. Thus, there is morphological support for an ontogenetic shift in the role of the sensory palate, from a prey detection gustatory sensory system in hatchlings to a prey-manipulative mechanoreceptive system in subadults. J. Morphol., 2014. © 2014 Wiley Periodicals, Inc.
Article
In the present study, the tongue dorsal surface of the white sea bream Diplodus sargus sargus (Linnaeus, 1758) (teleosts, Sparidae) was studied, to give a support to the knowledge of the anatomical characteristics of the oral cavity of a species with a future potential use in aquaculture. The feeding habits in captivity are one of the critical steps in the species of commercial interest, strictly related to the morphological characteristics of the oropharyngeal cavity. This study was undertaken, using light and scanning electron microscopy, to analyse the morphology of the dorsal tongue surface to show whether relationships are present between the anatomy and the nutritional habits and choices of this farmed species. Three zones, an apex, a body and a root, can be clearly distinguished, with a pouch partially covering the apex. In the pouch, cylindroid and mucosal ridges were observed. Along the whole tongue surface, from the apex to the root, on the medial and lateral parts, many papillae are present, with a fungiform, cylindroid and cone-like aspect. Taste buds are showed on the dorsal surface of some papillae.
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To elucidate the functional significance of the three distinct types of generation glands that have been identified among cordylid lizards, we mapped gland type to the terminal taxa in the most recent phylogenetic tree for the Cordylidae. We used the phylogenetic programme Mesquite and applied the principle of parsimony to infer character states for the ancestral nodes in the tree. For those species where information on gland type was not available from the literature, we conducted a histological investigation of generation gland morphology, using standard histological techniques. We included two species of the sister family Gerrhosauridae in the analysis to serve as outgroups. In both Gerrhosaurus typicus and G. flavigularis, scales immediately anterior to the femoral pores displayed glandular activity, but differed from generation glands of cordylids in the absence of mature glandular generations. Among the cordylids investigated, we identified a fourth type of generation gland in Pseudocordylus subviridis, P. spinosus, and in the two Hemicordylus species, one where the glands consistently comprise of two mature glandular generations. In H. capensis, both single- and two-layer type glands are present. Our reconstruction of ancestral character states suggests a minimum of six transformations from one gland type to another during the evolutionary history of the family. The reconstruction furthermore suggests that the single-layer type gland reappeared at least once (in Hemicordylus) in the Cordylinae after having been lost. The reconstruction also unequivocally shows that the pit-like multiple-layer type gland evolved directly from the single-layer type and not from the protruding multiple-layer type. The two-layer type gland appears to be an intermediary condition between the multiple-layer and single-layer types. The evolutionary transformation of generation gland type appears to be linked to changes in lifestyle and associated changes in degree of territoriality and the need for chemical communication. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.
Article
Prey capture in Agama stellio was recorded by high-speed video in combination with the electrical activity of both jaw and hyolingual muscles. Quantification of kinematics and muscle activity patterns facilitated their correlation during kinematic phases. Changes in angular velocity of the gape let the strike be subdivided into four kinematic phases: slow open (SOI and SOII), fast open (FO), fast close (FC), and slow close-power stroke (SC/PS). The SOI phase is marked by initial activity in the tongue protractor, the hyoid protractor, and the ring muscle. These muscles project the tongue beyond the anterior margin of the jaw. During the SOII phase, a low level of activity in the jaw closers correlates with a decline of the jaw-opening velocity. Next, bilateral activity in the jaw openers defines the start of the FO phase. This activity ends at maximal gape. Simultaneously, the hyoid retractor and the hyoglossus become active, causing tongue retraction during the FO phase. At maximal gape, the jaw closers contract simultaneously, initiating the FC phase. After a short pause, they contract again and the prey is crushed during the SC/PS phase. Our results support the hypothesis of tongue projection in agamids by Smith ([1988] J. Morphol. 196:157–171), and show some striking similarities with muscle activity patterns during the strike in chameleons (Wainwright and Bennett [1992a] J. Exp. Biol. 168:1–21). Differences are in the activation pattern of the hyoglossus. The agamid tongue projection mechanism appears to be an ideal mechanical precursor for the ballistic tongue projection mechanism of chameleonids; the key derived feature in the chameleon tongue projection mechanism most likely lies in the changed motor pattern controlling the hyoglossus muscle.
Article
Summary The kinematics of prey capture by the chamaeleonid lizard Chamaeleo oustaleti were studied using high-speed cinematography. Three feeding sequences from each of two individuals were analyzed for strike distances of 20 and 35 cm, at 30°C. Ten distances and angles were measured from sequential frames beginning approximately 0.5 s prior to tongue projection and continuing for about 1.0 s. Sixteen additional variables, documenting maximum excursions and the timing of events, were calculated from the kinematic profiles. Quantified descriptions of head, hyoid and tongue movements are presented. Previously unrecognized rapid protraction of the hyobranchial skeleton simultaneously with the onset of tongue projection was documented and it is proposed that this assists the accelerator muscle in powering tongue projection. Acceleration of the tongue occurred in about 20ms, reaching a maximum acceleration of 486 m s~2 and maximum velocity of 5.8m s" 1 in 35 cm strikes. Deceleration of the tongue usually began within 5 ms before prey contract and the direction of tongue movement was reversed within 10 ms of prey contact. Retraction of the tongue, caused by shortening of the retractor muscles, reached a maximum velocity of 2.99 ms" 1 and was complete 330 ms after prey contact. Projection distance influences many aspects of prey capture kinematics, particularly projection time, tongue retraction time and the extent of gape and head movements during tongue retraction, all of which are smaller in shorter feedings. Though several features of the chameleon strike have apparently been retained from lizards not capable of ballistic tongue projection, key differences are documented. Unlike members of a related family, the Agamidae, C. oustaleti uses no body lunge during prey capture, exhibits gape reduction during tongue projection and strongly depresses the head and jaws during tongue retraction.
Article
Visual and acoustic mechanisms of communication are compared. Their properties are found to be similar except that acoustic systems function more efficiently when light levels are low. The ability of geckos to receive and produce visual and acoustic messages is discussed. Geckos are found to have excellent vision and good hearing. They also possess the visual attributes and sound producing mechanisms necessary for complex displays. The display behavior of geckos is reviewed. Display types are categorized according to the display mechanism used. Visual displays are found to utilize color, pattern, posture, and movement. These displays are used in predator threat as well as in intraspecific social contexts such as aggression and courtship. Combined visual-acoustic displays involve color, pattern, postures, movement, and sound. Combined displays are used in predator threat and in intraspecific aggressive encounters. Acoustic displays have little or no visual component and involve sounds that may be single chirps or temporally patterned multiple chirps. The single chirps are associated with distress while the multiple chirp calls are heard in intraspecific social contexts. The displays of diurnal and nocturnal geckos are compared and it is found that differences are correlated with differences in their diel activity cycles. In conclusion, it is pointed out that many areas remain to be studied before gecko display behavior is well understood.
Article
The gilthead seabream is a food fish, one of the most frequently used in aquaculture. In the species of commercial interest, feeding in captivity is very important and this process is strictly related to the morphological characteristics of the oral cavity. The aim of this study is, using the standard procedures for light and scanning electron microscopy, to analyze the morphology of the tongue dorsal surface to show if relationships are present between the tongue morphology and the nutritional habits and choices of this farmed species. The main characteristic of the gilthead seabream oral cavity floor is the presence of an apical pouch, with, probably, a protective role mainly for the apical, free part of the tongue. Three zones, like in other teleosts, an apex, a body and a root, can be clearly distinguished. In the pouch foliate-like papillae were observed, while the whole tongue is characterized by the presence of two types of papillae, respectively with a fungiform and cylindroid aspect, both randomly distributed throughout the whole dorsal surface of the tongue. Scattered and numerous taste buds, with the typical pear-onion shape, together with small and numerous taste pores are also present, distributed throughout the tongue surface. Our results demonstrate that in the gilthead seabream important mechanic and sensory roles are carried out by specific anatomical structures. Our anatomical data could give, together with further biochemical and physiological data, an important support with the aim of improving the nutrition of aquaculture species. Microsc. Res. Tech. © 2012 Wiley Periodicals, Inc.
Article
High speed video recordings (200 fields per second) of prey capture and food processing in Agama agama permit the identification of strikes, chews and transport movements. Ten variables from strike movements and seven variables from chewing sequences are digitized; transport movements are inspected only. Univariate and multivariate statistical analyses disclose significant interindividual differences for three variables (maximum gape distance, maximum head angle, and maximum throat distance); but neither these nor principal components analysis show differences between strikes and chews for any of the gape change and hyoid depression variables. However, strikes and chews obviously differ in tongue protrusion and body movements. Chewing may be divided into four stages, comparable to those of transport cycles of other lizards and the generalized tetrapod model. Transport differs from chewing by having a shorter power stroke and relatively more cranial and less jaw movement. The kinematics of feeding in Agama agama are compared with those of other lizards studied previously.
Article
Background: The ability to detect chemical cues is highly developed in Scleroglossa, and particularly in anguid lizards. This ability was predicted because anguids possess a well-developed vomeronasal organ (VNO) (or Jacobson's organ) and rely largely on chemical cues in various behaviours as other active foragers. In this work, we have investigated the possible functional association between tongue flicking and the VNO in the lizard Anguis fragilis. Methods: The morphology of the tongue and the buccal cavity was investigated by light and scanning electron microscopy. The kinematics of tongue and jaw movements was studied by high speed cinematography. Results: The epithelial cells of the ventral aspect of the tongue tips show microstructures (microridges, microfacets, micropores) which are not present on other areas of the mouth. Beneath the tongue, the floor of the buccal cavity shows two concave-like elevations suggesting a structural analogy with the anterior processes described in snakes. The apex and the internal margin of these processes bear parallel oblique ridges. Taste buds occur anteriorly on the buccal floor and on the palate and are abundant on the internal side and on the edge on the anterior processes. The tongue showed three modes of tongue flicking: simple downward extension, single oscillation, and multiple oscillations. At each tongue flick, the ventral surface of the tips was observed contacting the substratum. Immediately after the tongue retraction, the buccal floor moved slightly upward. The observation of tongue flicking with the mouth open showed that the anterior processes moved upward when the tongue was retracted. Conclusions: These observations suggest that following: 1) during tongue flicking the ventral surface of the tongue tips invariably makes contact with the substratum; 2) the microstructures of the tongue tips and the ridges of the anterior processes might be helpful for collecting and receiving, respectively, chemicals during tongue flicking; 3) the anterior processes may be apposed on the roof of the mouth next to the ducts of VNOs when the buccal floor is fully elevated; 4) due to their localization, the taste buds could be equally stimulated by the molecules transferred during tongue flicking.
Article
The kinematic profiles of jaw movements are described for Anolis carolinensis and Lacerta viridis feeding on the same prey item (maggot). A. carolinensis is an iguanian (typified by lingual prey capture) and L. viridis is a scleroglossan (typified by prey capture using jaws alone). A. carolinensis, however, catches maggots by using only the jaws. In so doing, it exhibits the four stages of gape profile considered typical for lizards (slow open, fast open, fast close, slow close). Gape cycle in L. viridis shows a hyperbolic curve (no slow open). Two hypotheses concerning the relationship between the two gape cycles are discussed.
Article
Detailed descriptions of tongue morphology of members of Squamata that refer to functional implications other than food processing are rare. Herein we focus on the morphology of the dorsal epithelium and internal structure of the tongue of the Leopard Gecko, Eublepharis macularius, emphasizing the foretongue and its relation to fluid uptake. We employ both scanning electron microscopy and serial histology to examine the morphology of the entire tongue, its component regions, and its situation in the oral chamber. We recognize five distinct morphological regions of the dorsal tongue surface, each of which is distinctive both morphologically and histologically. The foretongue bears papillae quite different in structure and spacing from those of all other tongue regions, and these non-glandular structures are involved in gathering and transporting fluid from the environment. Fluid unloaded from the foretongue in the region of the vomeronasal sinus is channeled through the network of cuboidal papillae and directed towards a pair of compartments lateral to the tongue in which fluid pools during a drinking bout. This allows the dorsal surface of the mid- and hind-tongue, which are involved in food processing and manipulation, to be largely segregated from the pathway of fluid flow. We relate our findings to descriptions of the tongue of other taxa, and propose functional hypotheses for the observed morphology. This study provides new anatomical information upon which future studies of the functional morphology of the buccal apparatus in the Gekkota can be based.
Article
The European sea bass, a member of the Moronidae family, is a food fish, considered one of the first models for the intensive breeding in salt water. It has nowadays an important and increasing presence in the international fishing markets. Sea basses are carnivorous, feeding on little fishes and invertebrates. Considering the important role of the tongue during the intraoral transport and the swallowing of food, scarce data are present in literature about its morphology. The aim of this study was to analyze the morphology of the tongue by means of scanning electron and light microscopy. Adult sea basses were obtained from the aquarium of the Sicilian Center of Experimental Ichthyiopathology of the University of Messina. The fishes were anaesthetized with MS 222 and the heads were then quickly removed and processed for the paraffin embedding and SEM processing. Three different tongue regions could be distinguished: an apex, a body, and a root. Scanning electron and light microscopy showed the presence of numerous canine-like teeth, surrounded by taste buds and numerous fungiform and conical papillae. The teeth were curved and their tips were posteriorly oriented. The results confirm, in teleosts too, the fundamental role of the tongue in the mechanics of food ingestion. Moreover, the presence of taste buds demonstrates the interaction of food processing and taste. These data could be a potential source to identify new and better methods of nutrition in the breeding of this fish.
Article
Using LM and SEM methods, the study describes microstructures in particular areas of the tongue of the goose. A thick multilayered keratinized epithelium forms the "lingual nail" and covers small and giant conical papillae, whereby the first functions as an exoskeleton of the tongue apex, and the latter are arranged along the lingual and well-developed connective tissue cores, and together with the bill lamellae are involved in cutting. The row of conical papillae on the lingual prominence prevents regurgitation of transported food. In the area of the "lingual nail" and in the anterior part of the lingual prominence, Herbst corpuscles are accumulated, which allow to recognize food position. Filiform papillae, as widely distributed between the conical papillae of the body, are responsible for filtering. They can be explained as long keratinized processes of the epithelium and are devoid of connective tissue cores. During food transport, the flattened areas of the lingual body and the lingual prominence are protected by a parakeratinized epithelium, but the root is covered by a nonkeratinized epithelium. The presence of adipose tissue in the tongue probably reduces pressure during food passage, but also promotes mucus evacuation from the lingual glands, thus facilitating food transport. An entoglossal bone with a continuation as cartilage is the stable structural basis of the tongue system. Anat Rec, 2011. © 2011 Wiley-Liss, Inc.
Article
With 4 figures The Italian lizard (Podarcis sicula) is the most diffused reptile in Italy, but it is also present in other European countries. This lizard belongs to the Lacertidae family, lives near walls, slants and along the borders of the paths; its diet includes bugs and aracnids. No data are so far available in literature about the three-dimensional morphology of the tongue of Podarcis sicula, therefore the aim of the present paper was to study by scanning electron and light microscopy the three-dimensional characteristics of the dorsal lingual surface and moreover the presence of chemosensory receptors like the taste buds in the oral cavity. Our results demonstrate that the Podarcis sicula tongue is a triangular muscular membranous organ, dorsoventrally flattened and that three different areas can be observed: a bifid apex, a body and a root. No papillae were observed in the apex, characterized by a flattened mucosa and by two deep median pouches. In the body cylindrical papillae with a flat surface are present, aborally gradually substituted by imbricated papillae. Foliate-like papillae were observed in the lateral parts of the tongue body. No sensory structures were showed on the lingual dorsal surface, while they were numerous in the oral cavity, particularly on the gingival epithelium. The light microscopy shows, on the dorsal surface, a stratified pavimentous not keratinized epithelium, conversely keratinized along the ventral surface. Many caliciform cells on the lateral parts of the papillae, deputed to the secretion of mucus, were also observed. Therefore, the results obtained in this paper could give a contribution to the knowledge of the tongue anatomy in a species widely diffused in different European countries and could be of help for clinical purposes in reptiles.
Article
The blue-tongue lizard (Tiliqua scincoides) is a variety of large skink common throughout Australia. There are seven species of Tiliqua and all of them have long bodies, short limbs and short and robust tails. T. scincoides occurs in a wide range of habitats; its diet is omnivorous. When threatened, it opens the mouth and protrudes its characteristic large fleshy cobalt blue tongue. It is currently found as a popular species and also as a pet animal in the European countries. No data are available in literature about the morphology of the tongue of T. scincoides; therefore, the aim of the present study was to investigate by means of scanning electron microscopy and light microscopy, the anatomy of the dorsal lingual surface. Our results demonstrate the presence of a tongue tip with a smooth surface without papillae. The foretongue was characterized by a stratified epithelium with foliate-like papillae and deep inter-papillar spaces in the middle part and cylindrical papillae with a flat surface in the lateral parts. All the posterior area of the tongue was characterized by more compacted papillae and the inter-papillar spaces were very narrow. Light microscopy showed the presence of melanin throughout the tongue. No taste buds were recognized on the lingual dorsal surface. Therefore, the papillae probably have a mechanical function showing an important role in the swallowing phase. The morphology of the tongue surface can be correlated to the diet and, different roles, as in other examined species, can be hypothesized for different areas.
Article
The histological characteristics and ultrastructure of the dorsal lingual epithelium of the rat snake, Elaphe quadrivirgata, were investigated by light microscopy and scanning and transmission electron microscopy. Most of the surface of the bifurcated part of the tongue was relatively smooth. Dome-shaped, hemispherical bulges were compactly arranged on the epithelial cell surface of the basal area of this region. Intercellular borders were clearly recognizable as striations. Microridges were densely distributed on the epithelial cell surface of the lingual body. Intercellular borders were thickened. A keratinized layer was clearly visible in the epithelium of the anterior bifurcated area, namely, at the apex of the tongue. Although keratohyalin granules were not found in any layer of the epithelium in this area, the cells of the surface layer were filled with keratin filaments. The dorsal lingual epithelium of the posterior area, namely, the lingual body, did not show any evidence of keratinization. Each cell on the surface side still had a large, oval nucleus and intact organelles, such as mitochondria, rough endoplasmic reticulum, ribosomes, tonofibrils, and tonofilaments. Cellular interdigitation was evident between adjacent cells and clear microridges or microvilli were observed on the cell membranes on the free-surface side of cells located in the surface layer. The phylogenetic relevance of these findings is discussed.
Article
Various species of turtles are adapted to different environments, such as freshwater, seawater, and terrestrial habitats. Comparisons of histological and ultrastructural features of the tongue of the juvenile Hawksbill turtle, Eretmochelys imbricata bissa, with those of freshwater turtles should reveal some aspects of the relationship between the structure of the lingual epithelium and the environment. The light microscope, scanning electron microscope and transmission electron microscope were used. Light microscopy revealed that the mucosal epithelium of the tongue was of the keratinized, stratified squamous type. Under the scanning electron microscope, no lingual papillae were visible on the dorsal surface of the tongue. Micropits and the thickening of cell margins were clearly seen on the surface of cells located on the outermost side. The transmission electron microscope revealed that the cells in the intermediate layer were gradually flattened from the basal side to the surface side, as were their nuclei. In the shallow intermediate layer, the cells were significantly flattened, and their nuclei were condensed or had disappeared. The cytoplasm contained keratohyalin granules, tonofibrils, free ribosomes, mitochondria, and rough endoplasmic reticulum. Numerous free ribosomes were attached to the surface of small keratohyalin granules. The cells of the keratinized layer were significantly flattened, and their nuclei had completely disappeared. Most of cytoplasm was filled with keratin fibers of high electron density. Keratin fibers of the shedding cells, which were located on the outermost side of the keratinized layer, appeared looser, and each fiber, which was somewhat thicker than the tonofibrils and tonofilaments, was clearly distinguishable. The lingual epithelium of the juvenile Hawksbill turtle differs significantly from that of the adult freshwater turtle, in spite of the similarity in gross morphology of the tongues of these species.
Article
Feeding mechanics of vertebrates depend on physical constraints of the surrounding media, water or air. Such functions are inseparably combined with form. The aim of this study is to show this linkage for the pleurodiran freshwater turtle Pelusios castaneus and, additionally, to point out the major functional and biomechanical distinctions between aquatic and terrestrial feeding turtles as well as several intermediate forms. Gross morphological investigations of skull, hyoid, tongue, and connected musculature, as well as scanning electron microscopy of the tongue surface, show typical features of an aquatic feeder, e.g., strongly developed hyoid apparatus vs. a small tongue with only moderate papillae, and massive jaw and hyoid musculature. Additionally, the special function of the esophagus during feeding is investigated to elucidate the problems of a bidirectional feeder. The esophagus is highly distensible in order to store the excess water sucked in during feeding until the prey is fixed by the jaws. The distension is probably achieved by a coincidence of active (branchial horn) as well as passive (water) components. P. castaneus is a feeding generalist, and is well adapted to the aquatic medium in terms of its functional as well as morphological features.
Article
The oral sensory papillae of the snake (Elaphe quadrivirgata), comprising a compound sensory system located along the tooth rows, were studied by light microscopy, immunohistochemistry for neuron specific enolase and S 100 protein, and scanning and transmission electron microscopy. Each sensory papilla exhibited a single taste bud and free nerve endings in the epithelium, and Meissner-like corpuscles, branched coiled terminals, and lamellated corpuscles in the connective tissue. The taste buds consisted of four types of cells; the type III cells, exclusively synapsing onto intragemmal nerves, were identified as gustatory in function. The gustatory cells included dense-cored and clear vesicles in the cytoplasm. These vesicles were accumulated both in the presynaptic and infranuclear regions, suggesting dual functions: the synaptocrine and paracrine/endocrine release of signal substances. The free nerve endings constantly contained mitochondria and frequent clear vesicles. The Meissner-like corpuscles were located in the uppermost zone of the connective tissue. These corpuscles consisted of nerve fibers and lamellar cells. The nerve fibers, rich in mitochondria, were folded and layered on each other. The branched coiled terminals were localized in the connective tissue along the side wall of the papillae. Nerve fibers, free from a Schwann-cell covering, swelled up to make terminals which accumulated mitochondria and glycogen particles. The lamellated corpuscles were associated with the nerve-fiber bundles in the connective tissue. Consisting of a central nerve axon and lamellar cells encircling it, these corpuscles resembled mammalian Vater-Pacini corpuscles, except that they lacked a capsule. These findings demonstrated that the snake sensory papilla represents one of the most specialized, compound sensory systems among vertebrates, which may play an important role in receiving chemical and mechanical information on prey.
Article
Taste buds are chemosensory endorgans consisting of modified epithelial cells. Fish and other vertebrates use their taste bud cells to sample potential food, either selecting or rejecting substances according to their edibility. The adult gustatory system in fish has been studied thoroughly, including regeneration experiments. Taste buds occur in the epithelia of the lips, the mouth cavity, the oropharyngeal cavity, and also in the skin of the barbels, the head, and sometimes even all over the body surface. Despite its importance for feeding, little is known about the ontogeny of the fish taste system. We examined the development of taste buds in the zebrafish on the light microscopical and the scanning and transmission electron microscopical levels. Taste buds develop later than the olfactory organ and the solitary chemosensory cells, two other chemosensory systems in aquatic vertebrates. The first few taste bud primordia are visible within the epithelia of lips and gill arches 3 to 4 days after fertilization, and the first few taste buds with open receptor areas appear on the lips and simultaneously on the gill arches 4-5 days after fertilization, which coincides with the onset of feeding. Taste buds in the mouth cavity, on the head, and on the barbels are formed later in development. As seen in other fish, zebrafish taste buds contain elongate dark and light cells, termed according to their electron density. Dark cells with a cell apex of many short microvilli appear first, followed by the light cells with one large microvillus. In addition, the zebrafish has a third fusiform cell type, which appears last. This cell type is low in electron density and has a brush-like apical ending with several small microvilli. This cell type has not been described previously. Furthermore, in zebrafish, the ontogenetic processes of taste bud formation differ from regenerative processes described in the literature.
Article
The distribution of S100 protein in the neuromast of the lateral line system (LLS) was investigated immunohistochemically in alevins of three species of teleosts (Salmo trutta, Salmo salar and Dicentrarchus labrax), using a polyclonal antibody. In both the neuromasts of the canals, as well as in the pit organs, the hair cells, regarded as the specific sensory cells, displayed cytoplasmic immunoreactivity for S100 protein. Conversely, the supporting cells, mantle cells and basal cells were devoid of immunoreaction. These results demonstrate for the first time the occurrence of S100 in the LLS of teleosts. Due to the cell specific localization, this protein might serve as a marker for sensory hair cells in neuromasts.
Article
Studies of the comparative morphology of the tongues of living vertebrates have revealed how variations in the morphology and function of the organ might be related to evolutional events. The tongue, which plays a very important role in food intake by vertebrates, exhibits significant morphological variations that appear to represent adaptation to the current environmental conditions of each respective habitat. This review examines the fundamental importance of morphology in the evolution of the vertebrate tongue, focusing on the origin of the tongue and on the relationship between morphology and environmental conditions. Tongues of various extant vertebrates, including those of amphibians, reptiles, birds and mammals, were analysed in terms of gross anatomy and microanatomy by light microscopy and by scanning and transmission electron microscopy. Comparisons of tongue morphology revealed a relationship between changes in the appearance of the tongue and changes in habitat, from a freshwater environment to a terrestrial environment, as well as a relationship between the extent of keratinization of the lingual epithelium and the transition from a moist or wet environment to a dry environment. The lingual epithelium of amphibians is devoid of keratinization while that of reptilians is keratinized to different extents. Reptiles live in a variety of habitats, from seawater to regions of high temperature and very high or very low humidity. Keratinization of the lingual epithelium is considered to have been acquired concomitantly with the evolution of amniotes. The variations in the extent of keratinization of the lingual epithelium, which is observed between various amniotes, appear to be secondary, reflecting the environmental conditions of different species.
Article
The neuromast of the lateral line system of zebrafish has become an ideal model for the study of both developmental genetics and the vertebrate auditory system. Interestingly, the hair cells of this system have been found to selectively display immunoreactivity for S100 protein in some teleosts. In order to provide a selective marker for the sensory cells of the lateral line system, we have analyzed immunohistochemically the expression of S100 protein in zebrafish from the larval to the adult stage. In larval and adult animals S100 protein immunoreactivity was detected restricted to the hair cells of both superficial and canal neuromasts. Apparently the expression of S100 protein by hair cells was independent of the age, but it was expressed heterogeneously in the hair cells of canal neuromasts. The results of this work provide a feasible method to easily identify sensory cells in the neuromasts, and may be of interest in studies regarding development, differentiation or turnover of hair cells.