Evidence for a frontal-organ homologue in the pineal complex of the salamander,Hynobius dunni

The pineal complex of larval and adult salamanders, Hynobius dunni, was examined by light and scanning electron microscopy. This pineal complex displays an anterior and a posterior portion, both of which possess a lumen. The anterior lumen is small and closed, whereas the posterior lumen is in open communication with the third ventricle. Cell processes of the photoreceptor cells and microvilli of the supportive cells are visible in both lumina. The anterior part of the complex is formed by an independent, second evagination from the common pineal anlage; this process takes place immediately after hatching. The anterior body of the pineal complex of H. dunni appears to be homologous to the frontal organ of anurans.     

Immunocytochemical identification of growth hormote (GH) cells in the pituitary of three anuran species using an antiserum against purified bullforg GH

An antiserum was prepared against the recently purified bullfrog (bf) growth hormone (GH); it was applied to sections of brain and pituitary of three urodele (Ambystoma, Pleurodeles and Cynops) and three anuran (Xenopus, Bufo vulgaris and B. japonicus) species. No immunostaining was obtained in the urodele pituitary, being consistent with the results of immunoblot analysis of the pituitary homogenate. In the three anuran species, strong immunoreactivity was observed in GH cells that were concentrated in the posterodorsal region of the pars distalis. No GH-like immunoreactivity was detectable in the brain of any of the species. A comparison using adjacent sections stained with anti-bf prolactin (PRL) confirmed the anteroventral localization of PRL cells. Colocalization of GH and PRL was not apparent. These data suggest that the molecular structure of amphibian GHs is considerably different between anurans and urodeles. The antiserum used in the present work shows a high species specificity, recognizing only anuran GHs. In contrast anti-bfPRLlabeled PRL cells in all the amphibian species studied in the present work, suggesting that PRLs possess common amino acid sequences recognized by the anti-bfPRL.     

Comparative ultrastructural investigations of the uterine epithelium in the viviparous Salamandra atra Laur. and the ovoviviparous Salamandra salamandra (L.) (Amphibia,Urodela)

The uterine epithelium of the viviparous Salamandra atra and the ovoviviparous Salamandra salamandra was studied in non pregnant and ovulating females and in females during different stages of pregnancy. The epithelium of both species is organized in a monolayer. The epithelial cells are characterized by a moderate secretory activity, a variable amount of apical granules which include PAS-positive material and by some apical and basal exo- or endocytotic vesicles. Adjacent cells are joined by junctional complexes. The lateral surfaces form a tortuous boundary with adjoining cells which suggest that the epithelium is involved in transport. Sporadic light cells possess highly variable cytoplasmic inclusions and are not joined with neighbouring cells. Possibly they represent migratory cells. The entire epithelium, except for a small cranial portion of the uterus in S. atra, undergoes no remarkable morphological changes during the different physiological stages examined except that flattened cells seem to be more numerous in pregnant females. The results are discussed with regard to the possible supply of the developing young by the mother.     

Geographic nestedness of Lyciasalamandra billae (Amphibia: Salamandridae) populations within L. antalyana and description of a new subspecies

A new subspecies of the Bille’s Lycian Salamander Lyciasalamandra billae is described from four localities in the vicinity of Geyikbay?r? nearby Antalya, Turkey. It is distinguished from the nominotypical subspecies by colouration and surface pattern. The distribution area of the new subspecies is nested within the range of Lyciasalamandra antalyana, with L. a. gocmeni bordering in the north and the range of L. a. antalyana bordering in the south. New localities of both L. antalyana subspecies are reported.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:8F541E98-61F3-4EDD-A432614B0A250711     

Enameloid/enamel transition through successive tooth replacements in <Emphasis Type="Italic">Pleurodeles waltl</Emphasis> (Lissamphibia,Caudata)

Study of the evolutionary enameloid/enamel transition suffers from discontinuous data in the fossil record, although a developmental enameloid/enamel transition exists in living caudates, salamanders and newts. The timing and manner in which the enameloid/enamel transition is achieved during caudate ontogeny is of great interest, because the caudate situation could reflect events that have occurred during evolution. Using light and transmission electron microscopy, we have monitored the formation of the upper tooth region in six successive teeth of a tooth family (position I) in Pleurodeles waltl from late embryos to young adult. Enameloid has only been identified in embryonic tooth I₁ and in larval teeth I₂ and I₃. A thin layer of enamel is deposited later by ameloblasts on the enameloid surface of these teeth. From post-metamorphic juvenile onwards, teeth are covered with enamel only. The collagen-rich enameloid matrix is deposited by odontoblasts, which subsequently form dentin. Enameloid, like enamel, mineralizes and then matures but ameloblast participation in enameloid matrix deposition has not been established. From tooth I₁ to tooth I₃, the enameloid matrix becomes ever more dense and increasingly comes to resemble the dentin matrix, although it is still subjected to maturation. Our data suggest the absence of an enameloid/enamel transition and, instead, the occurrence of an enameloid/dentin transition, which seems to result from a progressive slowing down of odontoblast activity. As a consequence, the ameloblasts in post-metamorphic teeth appear to synthesize the enamel matrix earlier than in larval teeth.     

Cellular localization of a putative Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> exchanger 3 during ontogeny in the pronephros and mesonephros of the Japanese black salamander (<Emphasis Type="Italic">Hynobius nigrescens</Emphasis> Stejneger)

The cloning of cDNA and an examination of the tissue distribution of Na⁺/H⁺ exchanger 3 (NHE3) were carried out in the Japanese black salamander, Hynobius nigrescens. The cellular localization of Hynobius NHE3 was examined by in situ hybridization and immunohistochemistry during ontogeny in the nephron of the pronephros and mesonephros of the salamander. The partial amino acid sequence of Hynobius NHE3 was 81% and 72% identical to rat NHE3 and stingray NHE3, respectively. Hynobius NHE3 mRNA and protein were exclusively expressed along the late portion of the distal tubule to the anterior part of the pronephric duct of premetamorphic larvae (IY stages 43–50). NHE3 mRNA was expressed in the pronephros but not in the external gills in the larvae at the digit differentiation stage (IY stage 50). In the adult, mRNA was strongly expressed in the mesonephros but not in the ventral and dorsal skin. In juvenile and adult specimens, NHE3 immunoreactivity was observed at the apical membrane of the initial parts of the distal tubules of the mesonephric kidney. Immunohistochemical and in situ hybridization studies suggested that Na⁺ absorption coupled with H⁺ secretion via NHE3 occurred in the distal nephron of the pronephros and mesonephros. This is the first study to indicate NHE3 expression during ontogeny in amphibians. This work was supported in part by a research grant (a priority project in Science Faculty) from the University of Toyama to M.U.     

Surface glycoconjugates in the olfactory system of Ambystoma mexicanum

Lectin binding histochemistry was performed on the olfactory system of neotenic and metamorphosed Ambystoma mexicanum to investigate the distribution and density of defined carbohydrate residues on the cell surface glycoproteins of the olfactory and vomeronasal receptor cells and their terminals in the olfactory bulbs. The lectin binding patterns indicate that the main olfactory system possesses a high density of N-acetyl-galactosamine and N-acetyl-glucosamine residues, while the vomeronasal system contains a high density of N-acetyl-galactosamine and galactose moieties and a moderate density of N-acetyl-glucosamine. The presence of specific glycoproteins, whose terminal sugars are detected by lectin binding, might be related to the chemoreception and transduction of the odorous message into a nervous signal or to the histogenesis and development of the olfactory system. In fact, the olfactory and vomeronasal receptor cells are neurons that undergo a continuous cycle of proliferation not only during development but also in mature animals.     

Localization of prolactin receptor in the newt brain

In the male newt Cynops pyrrhogaster, prolactin (PRL) acts directly on the central nervous system and induces courtship behavior. As a step to elucidate the localization of neurons on which PRL acts, we developed a polyclonal antibody against an oligopeptide having a sequence completely identical with a part of the sequence of PRL receptors (PRLRs) of two species of newts, C. pyrrhogaster and C. ensicauda, and performed an immunohistochemical study with this antibody. PRLR-immunoreactive cells were observed in the medial amygdala, anterior preoptic area, magnocellular preoptic nucleus, suprachiasmatic nucleus, nucleus of the periventricular organ, ventral hypothalamic nucleus, and choroid plexus. We also performed in situ hybridization with a ³⁵S-labeled newt PRLR antisense RNA probe and detected signals in the preoptic area and choroid plexus. Colocalization of both PRLR-like immunoreactivity and arginine vasotocin-like or mesotocin-like immunoreactivity was demonstrated in the magnocellular preoptic nucleus. This is the first report of PRLR localization in the amphibian brain.This study was supported by a research grant from Waseda University to S.K. and by a grant-in-aid from the Ministry of Education, Science, and Culture of Japan to I.H., F.T., and S.K.     

Locomotion pattern and trunk musculoskeletal architecture among Urodela

We comparatively examined the trunk musculature and prezygapophyseal angle of mid‐trunk vertebra in eight urodele species with different locomotive modes (aquatic Siren intermedia, Amphiuma tridactylum, Necturus maculosus and Andrias japonicus; semi‐aquatic Cynops pyrrhogaster, Cynops ensicauda; and terrestrial Hynobius nigrescens, Hynobius lichenatus and Ambystoma tigrinum). We found that the more terrestrial species were characterized by larger dorsal and abdominal muscle weight ratios compared with those of the more aquatic species, whereas muscle ratios of the lateral hypaxial musculature were larger in the more aquatic species. The lateral hypaxial muscles were thicker in the more aquatic species, whereas the M. rectus abdominis was more differentiated in the more terrestrial species. Our results suggest that larger lateral hypaxial muscles function for lateral bending during underwater locomotion in aquatic species. Larger dorsalis and abdominal muscles facilitate resistance against sagittal extension of the trunk, stabilization and support of the ventral contour line against gravity in terrestrial species. The more aquatic species possessed a more horizontal prezygapophyseal angle for more flexible lateral locomotion. In contrast, the more terrestrial species have an increasingly vertical prezygapophyseal angle to provide stronger column support against gravity. Thus, we conclude trunk structure in urodeles differs clearly according to their locomotive modes.