The structure of the nasal chemosensory system in squamate reptiles. 1. The olfactory organ,with special reference to olfaction in geckos

The luminal surface of the chemosensory epithelia of the main olfactory organ of terrestrial vertebrates is covered by a layer of fluid. The source of this fluid layer varies among vertebrates. Little is known regarding the relative development of the sources of fluid (sustentacular cells and Bowman's glands) in reptiles, especially in gekkotan lizards (despite recent assertions of olfactory speciality). This study examined the extent and morphology of the main olfactory organ in several Australian squamate reptiles, including three species of gekkotans, two species of skinks and one snake species. The olfactory mucosa of two gekkotan species (Christinus marmoratus and Strophurus intermedius) is spread over a large area of the nasal cavity. Additionally, the sustentacular cells of all three gekkotan species contained a comparatively reduced number of secretory granules, in relation to the skinks or snake examined. These observations imply that the gekkotan olfactory system may function differently from that of either skinks or snakes. Similar variation in secretory granule abundance was previously noted between mammalian and non-mammalian olfactory sustentacular cells. The observations in gekkotans suggests that the secretory capacity of the non-mammalian olfactory sustentacular cells show far more variation than initially thought.     

Comparative morphology of the dermal palate in squamate reptiles, with comments on phylogenetic implications

The differentiation of the dermal palate and of the septomaxilla in extant squamate reptiles is reviewed in terms of Lakjer's distinctions of a palaeochoanate, incomplete neochoanate, and neochoanate condition. The differentiation of the bones surrounding the mushroom body, Jacobson's organ, and the internal naris (choana) supports a number of clades including Squamata, Scleroglossa, and Autarchoglossa, with Serpentes nested within Autarchoglossa. Dermal palate morphology and the differentiation of the septomaxilla in squamates reflect the evolution of the chemosensory system in general, and the vomeronasal system in particular, and strongly contradict a recent hypothesis of squamate phylogeny based on molecular data.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 131–152.     

Fine structure of the vomeronasal organ in the grass lizard, Takydromus tachydromoides

The squamates are composed of many taxa, among which there is morphological variation in the vomeronasal organ (VNO). To elucidate the evolution of chemoreception in squamate reptiles, morphological data from the VNO from a variety of squamate species is required. In this study, the morphology of the VNO of the grass lizard Takydromus tachydromoides was examined using light and electron microscopy. The VNO consists of a pair of dome-shaped structures, which communicate with the oral cavity. There are no associated glandular structures. Microvilli are present on the apical surfaces of receptor cells in its sensory epithelium, as well as on supporting cells, and there are centrioles and ciliary precursor bodies on the dendrites. In addition to ciliated cells and basal cells in the non-sensory epithelium, there is a novel type of non-ciliated cell in T. tachydromoides. They have constricted apical cytoplasm and microvilli instead of cilia, and are sparsely distributed in the epithelium. Based on these results, the variation in the morphology of the VNO in scincomorpha, a representative squamate taxon, is discussed.     

4种两栖爬行动物嗅器和犁鼻器的显微结构比较

用光镜观察了4种两栖爬行动物嗅器和犁鼻器的组织结构.结果显示,北方山溪鲵(Batrachuperus tibetanus)鼻囊内开始分化出犁鼻器,犁鼻器位于嗅器的腹外侧,但犁鼻器还不发达;隆肛蛙(Feirana quadranus)犁鼻器与嗅器虽然共同位于鼻囊内,但犁鼻器较为发达且其周围有发达的犁鼻腺,犁鼻器通过一细小管道与嗅器相通;秦岭蝮(Gloydius qinlingensis)和菜花烙铁头(Trimeresurus jerdonii)犁鼻腔与鼻腔已经完全分离形成两个独立的囊,而且鼻腔又进一步分化为嗅部与呼吸部.说明犁鼻器从有尾两栖动物开始出现,至无尾两栖类开始分化,到蛇类高度发达且成为一个独立器官.犁鼻器的形成是脊椎动物适应陆地生活的直接结果,是四足动物的特征之一.     

Morphology of the Harderian gland of some Australian geckos

This study of the morphology, histology, histochemistry, and ultrastructure of the Harderian gland in Geckos (Squamata, Gekkota) revealed previously unreported variation. The gecko Harderian gland is unlike that of other squamates in that each cell of the secretory epithelium has both lipid and protein secretory granules. Lipid secretion has not been reported previously for the squamate Harderian gland. The structure of the protein granules resembles that described for a scincomorph lizard (Podarcis, Lacertidae). Differences between representatives of the subfamilies Gekkoninae and Diplodactylinae suggest possible phylogenetic constraints in the structure or function of Harderian glands within gekkotan lineages. The structural relationship between the Harderian gland and the lacrimal duct supports previous suggestions of a possible functional link between the Harderian gland and the vomeronasal organ. J Morphol 231:253–259, 1997. © 1997 Wiley-Liss, Inc.     

Enhanced extrinsic innervation of nasal and oral chemosensory mucosae in keratin 14-NGF transgenic mice

The role of nerve growth factor (NGF) in neurotrophic support for the extrinsic innervation of the nasal and oral mucosae was investigated in keratin 14 (K14)-NGF transgenic mice in which NGF was over-expressed in K14-synthesizing cells. K14 immunoreactivity was localized in the epithelial basal cells of the whisker pad skin, the hard palate, the floor of the ventral meatus, and the anterior tongue that are stratified squamous epithelia, and also in basal cells of the vomeronasal, olfactory, and respiratory epithelia that are non-stratified epithelia. In transgenic mice, NGF expression was identified and confined primarily to the basal cells of stratified epithelia. The nasal mucosae including the vomeronasal, olfactory, and respiratory mucosae, and the glands associated with the vomeronasal organ received a greater innervation of protein gene product 9.5-immunoreactive extrinsic fibers in transgenic animals than nontransgenic controls. An increased density of calcitonin gene-related peptide-immunoreactive extrinsic fibers was observed in the nonsensory epithelia of the vomeronasal organ, the olfactory sensory and respiratory epithelia in transgenic animals. Our results indicated that the hyperinnervation of the nasal and oral mucosae by extrinsic neurons is due at least partially to target-derived NGF synthesis and release by K14-expressing basal cells.This work was supported by NIH grants NIDCD-00159 (T.V.G.), NIDCO-01715 (M.L.G.), and NINDS-31826 (K.M.A.).     

Olfactory and vomeronasal systems of caecilians (Amphibia: Gymnophiona)

The morphology of both the main nasal cavity and the vomeronasal organ differs among species representing six families of caecilians. The main nasal cavity is either divided or undivided. The vomeronasal organ differs in position (mediolateral, lateral), size (large vomeronasal organ in the aquatic species), and shape (mediolateral extension, vomeronasal organ with a lateral rostral projection). The great amount of respiratory epithelium of the main nasal cavity, the large vomeronasal organ, and its extensive innervation in typhlonectids may reflect both phylogeny and habitat adaptation, for these taxa are secondarily aquatic or semiaquatic and have several concomitant morphological and physiological modifications. The vomeronasal organ is associated with the caecilian tentacle as the tentacular ducts open into it. This association is further evidence for the involvement of the caecilian tentacle in vomeronasal chemoperception and may represent the mechanism by which these animals smell though the main nasal cavity is closed during burrowing or swimming. Labelings of primary olfactory and vomeronasal projections by means of horseradish peroxidase reaction reveal that the pattern of vomeronasal projections is similar in Ichthyophis kohtaoensis, Dermophis mexicanus, and Typhlonectes natans, even though T. natans possess stronger vomeronasal projections relative to olfactory projections than I. kohtaoensis and D. mexicanus. However, there are differences with respect to the patterns of olfactory projections. The olfactory projection of I. kohtaoensis is characterized by many displaced glomeruli. T. natans has the smallest olfactory projection. The nervus terminalis is associated with the olfactory system as shown by selective labelings of olfactory projections. Six characters potentially useful for phylogenetic analysis emerge from this study of comparative morphology. The characters were subjected to analysis using PAUP to see (1) if any resolution occurred and (2) if any groups were distinguished, whether they corresponded to phylogenetic arrangements based on other morphological characters. The characters are too few to produce nested dichotomous sets for all cases, but they do support the two typhlonectid genera examined and Dermophis and Gymnopis as sister taxa discrete from other groups, and they show that species within genera cluster together.     

The mechanism of chemical delivery to the vomeronasal organs in squamate reptiles: a comparative morphological approach

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.     

On the vomer in Acrochordidae (Reptilia: Serpentes), and its cladistic significance

It is reported that in certain features the form of the vomer is significantly different in Caenophidia than in Henophidia (except acrochordids). In Henophidia the vomer typically has one or a few apertures for the exit of the vomeronasal nerve from the bony surround of the vomeronasal organ, well- or moderately-developed vertical and horizontal (palatal) posterior laminae, and only a partially-developed cup-like enclosure for the vomeronasal organ. In Caenophidia the vomer typically has very many tiny foramina for the passage of the vomeronasal nerve, the horizontal posterior lamina in particular is much reduced or absent, and the vomer forms a globular enclosure for the vomeronasal organ. A comparison with the vomer in lizards suggests that the henophidian type of vomer is primitive within snakes and the caenophidian type is derived. Scolecophidia are not discussed. The vomer in acrochordids closely resembles that of Caenophidia, and this form of vomerine morphology is proposed as a synapomorphy indicating the strict monophyly of the group acrochordids-Caenophidia. The acrochordids have been treated very differently by various snake taxonomists and their phyletic position has always been highly problematical. The synapomorphy proposed herein contributes to a solution of this problem.     

Vomeroglandin/CRP-Ductin is strongly expressed in the glands associated with the mouse vomeronasal organ: identification and characterization of mouse vomeroglandin

Vomeroglandin, a subform of mouse CRP-ductin, is a protein strongly expressed in the glands of mouse vomeronasal system. Both the proteins contain several of scavenger receptor cysteine-rich and CUB domains and one ZP domain. This domain arrangement is similar to those of rat Ebnerin, human DMBT1, and rabbit hensin. In situ hybridization analysis shows strong expression of vomeroglandin mRNA in the glands of vomeronasal system. Immunological analyses detect both membrane-bound and secreted forms of vomeroglandin. The secreted protein seems to be localized in the lumen of the vomeronasal organ, playing a certain role in the pheromone perception.     

Thermoregulation during gravidity in the children's python (Antaresia childreni): a test of the preadaptation hypothesis for maternal thermophily in snakes

Pregnant squamate reptiles (i.e. lizards and snakes) often maintain higher and more stable body temperatures than their nonpregnant conspecifics, and this maternal thermophily enhances developmental rate and can lead to increased offspring quality. However, it is unclear when this behaviour evolved relative to the evolution of viviparity. A preadaptation hypothesis suggests that maternal thermophily was a preadaptation to viviparity. Oviparous squamates are unique among oviparous reptiles for generally retaining their eggs until the embryos achieve one fourth of their development. As a result, maternal thermophily by gravid squamates may provide the same thermoregulatory benefits, at least during early development, that have been associated with viviparity. Thus, the evolution of viviparity in squamates may reflect an expanded duration of a pre-existing maternal thermoregulatory behaviour. Despite its evolutionary relevance, thermoregulation during gravidity in oviparous squamates has not yet been explored in depth. In the present study, we examined whether gravidity was associated with thermoregulatory changes in the oviparous children's python, Antaresia childreni . First, we discovered that, compared to most snakes, A. childreni is at an advanced stage of embryonic development at oviposition. Second, using surgically implanted temperature loggers, we detected a significant influence of reproductive status on thermoregulation. Reproductive females maintained higher and less variable body temperatures than nonreproductive females and this difference was most pronounced during the last 3 weeks of gravidity. Overall, these results highlight the continuum between oviparity and viviparity in squamate reptiles and emphasize the importance of thermal control of early embryonic development independent of reproductive mode.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 499–508.     

Evolution of the Nasal Structure in the Lower Tetrapods

The gross structure of the nasal cavities and the distributionof the various types of epithelium lining them are describedbriefly; each living order of amphibians and reptiles possessesa characteristic and distinctive pattern. In most groups thereare two sensory areas, one lined by olfactory epithelium withnerve libers leading to the main olfactory bulb and the otherby vomeronasal epithelium with fibers to the accessory bulb.All amniotes except turtles have the vomeronasal epitheliumin a ventromedial outpocketing of the nose, the Jacobson's organ,and have one or more conchae projecting into the nasal cavityfrom the lateral wall. Although urodeles and turtles possessthe simplest nasal structure, it is not possible to show thatthey are primitive or to define a basic pattern for either amphibiansor reptiles; all the living orders are specialized and the nasalanatomy of extinct orders is unknown. Thus it is impossible,at present, to give a convincing picture of the course of nasalevolution in the lower tetrapods.     

Possible pheromone-carrier function of two lipocalin proteins in the vomeronasal organ.

We report the molecular cloning and characterization of two secretory proteins specifically expressed in vomeronasal and posterior glands of the nasal septum, the ducts of which open into the lumen of the vomeronasal organ. These two proteins are members of the lipocalin superfamily, consisting of hydrophobic ligand carriers. We immunohistochemically localized one of the proteins in the mucus covering the vomeronasal sensory epithelium, where the primary reception of pheromone takes place. The immunoreactivity on the vomeronasal sensory epithelium was evident in the neonatal and post-pubertal periods, when the close contact between animals plays critical roles in suckling and sexual behaviors, respectively. These results suggest that small lipophilic molecules stimulate the accessory olfactory system to regulate the reproductive behavior of mice.     

Morphological diversity of anatomical strepsirrhinism and the evolution of the lemuriform toothcomb

The hypothesis that the vomeronasal organ has an important functional relationship with, and led to the evolution of, the prosimian toothcomb has not been well tested. This paper examines the diversity of anatomical strepsirrhinism across several mammalian taxa to determine if fossil and living strepsirrhine primates exhibit any derived characters that may highlight the functional link between the vomeronasal organ and the toothcomb, and to examine the potential importance of anatomical strepsirrhinism to toothcomb origins. Results indicate that extant gregarious lemuriforms are derived in having a relatively wide interincisal gap, providing an unobstructed line of communication between the vomeronasal organ and anterior rostral structures such as the toothcomb. This finding is consistent with the proposal that anatomical strepsirrhinism is functionally related to use of the toothcomb in grooming. However, the importance of the vomeronasal organ to toothcomb origins is less clear. If the morphology of adapiforms and non-gregarious lemuriforms is representative of the morphology of basal lemuriforms, then it can be inferred that early lemuriforms did not possess the wide-gap autapomorphy; hence, anatomical evidence discussed here cannot be used to rule out non-social hypotheses of toothcomb origins. Am J Phys Anthropol 105:355–367, 1998. © 1998 Wiley-Liss, Inc.     

Social behavior and pheromonal communication in reptiles

The role of pheromones in orchestrating social behaviors in reptiles is reviewed. Although all reptile orders are examined, the vast majority of the literature has dealt only with squamates, primarily snakes and lizards. The literature is surprisingly large, but most studies have explored relatively few behaviors. The evolution of chemical signaling in reptiles is discussed along with behaviors governed by pheromones including conspecific trailing, male-male agonistic interactions, sex recognition and sex pheromones, and reptilian predator recognition. Nonreptilian prey recognition by chemical cues was not reviewed. The recent literature has focused on two model systems where extensive chemical ecology studies have been conducted: the reproductive ecology of garter snakes and the behavioral ecology of Iberian lacertid lizards. In these two systems, enough is known about the chemical constituents that mediate behaviors to explore the evolution of chemical signaling mechanisms that affect life history patterns. In addition, these models illuminate natural and sexual selection processes which have lead to complex chemical signals whose different components and concentrations provide essential information about individuals to conspecifics. Reptiles provide excellent candidates for further studies in this regard not only in squamates, but also in the orders where little experimental work has been conducted to date.     

Données histologiques sur les fosses nasales et leurs annexes chezCrocodylus niloticus Laurenti etCaiman crocodilus (Linnaeus) (Reptilia,Crocodylidae)

Summary The vestibulum is very short and lined by stratified squamous epithelium which contains many alveolar cells. The cavum nasi proprium is exceedingly complex, with three conchal formations and a series of six recesses and sinuses. Olfactory epithelium lines the whole dorsal or dorso-medial half of the cavum, but not the deep sinuses. Non sensory respiratory epithelium lines the ventral or ventro-lateral half of the cavum, all the caviconchal recess, the posterolateral recess, the postturbinal sinus, the postconchal cavity, and the nasopharyngeal duct. In olfactory epithelium the proportion of sensory cells is about 61 % inCrocodylus and 59 % inCaiman; the ratio of sensory cells to supporting cells is about 2.6/1 in the former and 1.8/1 in the latter. Bowman's glands are sero-mucous and normally developed. As in other reptiles, the respiratory epithelium is composed with mucous and ciliated cells; but, in ventrolateral part of the cavum, there are also sero-mucous cells forming small multicellular glands. The hypertrophied lachrymal duct constitutes a very large naso-lachrymal not previously described gland. The lumen is lined by mucous and ciliated cells, the collet of each branched tubular gland by mucous cells and the glandular tubes by sero-mucous cells. Adult crocodilians lack a Jacobson's organ and there are no vomeronasal sensory epithelium in the cavum.In reptiles, aquatic way of life generally involves regression in olfactory epithelium, while Jacobson's organ (or, in Testudines, vomeronasal epithelium) persists and occasionally increases. In crocodilians, things are exactly reverse. After comparing with other Tetrapods, it seems likely that Jacobson's organ has been lost by terrestrial ancestor of crocodilians and birds. Now, only crocodilians posses olfactory epithelium, and naso-lachrymal gland gives them a supplementary protection, necessary in semiaquatic environment.     

Non-involvement of the accessory olfactory system in the LH response of anoestrous ewes to male odour

In anoestrous ewes, male chemosignals elicit rapid increases in luteinizing hormone (LH) secretion that can ultimately lead to ovulation. To assess the possible involvement of the accessory (vomeronasal) olfactory system in the mediation of those chemical cues, we destroyed this pathway by vomeronasal organ electrocauterization (Exp. I) and vomeronasal nerve section (Exp. II). Neither of these lesions inhibited the LH response of ewes to the odour of the male. These results suggest that the vomeronasal system is not necessary to mediate the neuroendocrine response of the ewe to the male odour. As both surgical methods spared the main olfactory system but destroyed the vomeronasal system, it is likely that the main olfactory system is involved in the LH response to chemical stimulation in sexually experienced ewes.     

Postembryonic development of the olfactory and vomeronasal organs in the frog Rana chensinensis

We studied by light microscopy the histological development of the olfactory and vomeronasal organ in tadpoles of the Chinese forest frog, Rana chensinensis, from postembryonic periods to the end of metamorphosis. Unlike Bufo americanus, the olfactory epithelium in larval R. chensinensis is not divided into dorsal and ventral branches in the rostral and mid-nasal regions. The olfactory epithelium in the dorsal portion of the buccal cavity in larval R. chensinensis may correspond to the ventral olfactory epithelium of Bufo, which has been argued to provide a chemosensory function in the tadpoles analogous to the role of taste buds in adults. Bowman's glands were present in the olfactory epithelium of R. chensinensis only after the appearance of the forelimbs during metamorphosis. The appearance of Bowman's glands in the olfactory epithelium at this time suggests that the nose first begins to detect odorants in the air, and this is thus also a metamorphic event. The vomeronasal epithelium appeared a little earlier than the vomeronasal gland in R. chensinensis, unlike in toads (bufonids). This study supports Eisthen's hypothesis that the most recent common ancestor to the tetrapods was aquatic and once had a vomeronasal organ, and that this has been lost in various evolutionary lineages.     

Timing of neuronal intermediate filament proteins expression in the mouse vomeronasal organ during pre- and postnatal development. An immunohistochemical study

Several types of intermediate filament proteins are expressed in developing and mature neurons; they cooperate with other cytoskeletal components to sustain neuronal function from early neurogenesis onward. In this work the timing of expression of nestin, peripherin, internexin, and the neuronal intermediate filament triplet [polypeptide subunits of low (NF-L), medium (NF-M), and high (NF-H) molecular weight] was investigated in the developing fetal and postnatal mouse vomeronasal organ (VNO) by means of immunohistochemistry. The results show that the sequence of expression of intermediate filament proteins is internexin, nestin, and NF-M in the developing vomeronasal sensory epithelium; internexin, peripherin, and NF-M in the developing vomeronasal nerve; and nestin, internexin and peripherin, NF-L, and NF-M in the nerve supply to accessory structures of the VNO. At sexual maturity (2 months) NF-M is only expressed in vomeronasal neurons and NF-M, NF-L and peripherin are expressed in extrinsic nerves supplying VNO structures. The differential distribution of intermediate filament proteins in the vomeronasal sensory epithelium and nerve is discussed in terms of the cell types present therein. It is concluded that several intermediate filament proteins are sequentially expressed during intrauterine development of the VNO neural structures in a different pattern according to the different components of the VNO.     

Morphology of the nasal fossae and associated structures of the hamster (Mesocricetus auratus)

The hamster nasal cavity consists of vestibular, non-olfactory and olfactory portions. Much of the non-olfactory nasal cavity surface is lined by cuboidal, stratified cuboidal, and low columnar epithelia, devoid of cilia. Goblet cells and ciliated respiratory epithelium are present over only a small portion of the nasal cavity surface. The largest glandular masses in the hamster nose are the maxillary recess glands, the vomeronasal glands and the lateral nasal gland 1; these three glands contain neutral mucopolysaccharides (PAS-positive). Other nasal glands contain both acidic and neutral mucopolysaccharides; the staining reaction for acidic mucopolysaccharide is stronger in goblet cells and olfactory glands than in the other nasal glands. The ducts which open into the nasal vestibule are the excretory ducts of compound tubuloacinar serous glands. The one major PAS-positive gland whose duct opens into the nasal vestibule is the lateral nasal gland 1. The ducts of the compound tubuloacinar vomeronasal glands open into the lumen of the vomeronasal organ, which is connected to the ventral nasal meatus by means of the vomeronasal duct. The ducts of the branched tubuloacinar maxillary recess glands open into the maxillary recess. Few ducts open into the caudal half of the nasal cavity.