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PubMed2006

Toxicological responses of red-backed salamanders (Plethodon cinereus) to subchronic soil exposures of 2,4-dinitrotoluene.

Dinitrotoluenes are used as propellants and in explosives by the military and as such have been found at relatively high concentrations in the soil. To determine whether concentrations of 2,4-dinitrotoluene (2,4-DNT) in soil are toxic to amphibians, 100 red-backed salamanders (Plethodon cinereus) were exposed to either 1500, 800, 200, 75 or 0mg 2,4-DNT/kg soil for 28 days and evaluated for indicators of toxicity. Concentrations of 2,4-DNT were less than targets and varied with time. Most salamanders exposed to concentrations exceeding 1050 mg/kg died or were moribund within the first week. Salamanders exposed to soil concentrations exceeding 345 mg/kg lost >6% of their body mass though no mortality occurred. Overt effects included a reduction in feed consumption and an increase in bucco-pharyngeal oscillations in salamanders. These results suggest that only high soil concentrations of 2,4-DNT have the potential to cause overtly toxic effects in terrestrial salamanders.

Animals↗
PubMed2005

Transcriptional and phylogenetic analysis of five complete ambystomatid salamander mitochondrial genomes.

We report on a study that extended mitochondrial transcript information from a recent EST project to obtain complete mitochondrial genome sequence for 5 tiger salamander complex species (Ambystoma mexicanum, A. t. tigrinum, A. andersoni, A. californiense, and A. dumerilii). We describe, for the first time, aspects of mitochondrial transcription in a representative amphibian, and then use complete mitochondrial sequence data to examine salamander phylogeny at both deep and shallow levels of evolutionary divergence. The available mitochondrial ESTs for A. mexicanum (N=2481) and A. t. tigrinum (N=1205) provided 92% and 87% coverage of the mitochondrial genome, respectively. Complete mitochondrial sequences for all species were rapidly obtained by using long distance PCR and DNA sequencing. A number of genome structural characteristics (base pair length, base composition, gene number, gene boundaries, codon usage) were highly similar among all species and to other distantly related salamanders. Overall, mitochondrial transcription in Ambystoma approximated the pattern observed in other vertebrates. We inferred from the mapping of ESTs onto mtDNA that transcription occurs from both heavy and light strand promoters and continues around the entire length of the mtDNA, followed by post-transcriptional processing. However, the observation of many short transcripts corresponding to rRNA genes indicates that transcription may often terminate prematurely to bias transcription of rRNA genes; indeed an rRNA transcription termination signal sequence was observed immediately following the 16S rRNA gene. Phylogenetic analyses of salamander family relationships consistently grouped Ambystomatidae in a clade containing Cryptobranchidae and Hynobiidae, to the exclusion of Salamandridae. This robust result suggests a novel alternative hypothesis because previous studies have consistently identified Ambystomatidae and Salamandridae as closely related taxa. Phylogenetic analyses of tiger salamander complex species also produced robustly supported trees. The D-loop, used in previous molecular phylogenetic studies of the complex, was found to contain a relatively low level of variation and we identified mitochondrial regions with higher rates of molecular evolution that are more useful in resolving relationships among species. Our results show the benefit of using complete genome mitochondrial information in studies of recently and rapidly diverged taxa.

Ambystomatidae↗
PubMedDate not supplied

Salamander rods and cones contain distinct transducin alpha subunits.

The mammalian retina is known to contain two distinct transducins that interact with their respective rod and cone pigments. However, there are no reports of a nonmammalian species having two distinct transducins. In the present study, we report the cloning and cellular localization of two transducin a subunits (G alpha t) from the tiger salamander. Through degenerate polymerase chain reaction (PCR) and subsequent screening of a salamander retina cDNA library, we have identified two forms of G alpha t. When compared to existing sequences in GenBank, the cloned subunits showed high similarity to rod and cone transducins. The salamander G alpha t-1 has 91.2-93.7% amino acid sequence identity to mammalian rod G alpha t subunits and 79.7-80.9% to mammalian cone Gats. The salamander G alpha t-2 has 86.2-87.9% sequence identity to mammalian cone G alpha ts and 78.9-80.9% to mammalian rod G alpha ts at the amino acid level. The G alpha t-1 cDNA encodes 350 amino acids while the G alpha t-2 cDNA encodes 354 residues, which is typical for rod and cone G alpha ts, respectively, and we thus identified the G alpha t- 1 as rod and G alpha t-2 as cone G alpha t. Sequences identified as effector binding sites and GTPase activity regions are highly conserved between the two subunits. Genomic Southern blot analysis showed that rod and cone G alpha t subunits are both encoded by single-copy genes. Northern blot analysis identified retina-specific transcripts of 3.0 kb for rod G alpha t and 2.6 kb for cone G alpha t. Immunohistochemistry in the flat-mounted salamander retina demonstrated that rod G alpha t is localized to rods, predominantly in the outer segments; similarly, cone G alpha t is localized to cone outer segments. The results confirm that the two sequences encode rod and cone transducins and demonstrate that this lower vertebrate contains two distinct transducins that are localized specifically to rod and cone photoreceptors.

Amino Acid Sequence↗
PubMed2003

Earliest known crown-group salamanders.

Salamanders are a model system for studying the rates and patterns of the evolution of new anatomical structures. Recent discoveries of abundant Late Jurassic and Early Cretaceous salamanders are helping to address these issues. Here we report the discovery of well-preserved Middle Jurassic salamanders from China, which constitutes the earliest known record of crown-group urodeles (living salamanders and their closest relatives). The new specimens are from the volcanic deposits of the Jiulongshan Formation (Bathonian), Inner Mongolia, China, and represent basal members of the Cryptobranchidae, a family that includes the endangered Asian giant salamander (Andrias) and the North American hellbender (Cryptobranchus). These fossils document a Mesozoic record of the Cryptobranchidae, predating the previous record of the group by some 100 million years. This discovery provides evidence to support the hypothesis that the divergence of the Cryptobranchidae from the Hynobiidae had taken place in Asia before the Middle Jurassic period.

Animals↗
PubMed2005

Discovery of the first Asian plethodontid salamander.

Nearly 70% of the 535 species of salamanders in the world are members of a single family, the Plethodontidae, or lungless salamanders. The centre of diversity for this clade is North and Middle America, where the vast majority (99%) of species are found. We report the discovery of the first Asian plethodontid salamander, from montane woodlands in southwestern Korea. The new species superficially resembles members of North American genera, in particular the morphologically conservative genus Plethodon. However, phylogenetic analysis of the nuclear encoded gene Rag-1 shows the new taxon to be widely divergent from Plethodon. The new salamander differs osteologically from putative relatives, especially with respect to the tongue (attached protrusible) and the derived tarsus. We place the species in a new genus on the basis of the morphological and molecular data. The distribution of the new salamander adds to the enigma of Old World plethodontids, which are otherwise restricted to the western Mediterranean region, suggesting a more extensive past distribution of the family.

Animals↗
PubMed1997

Taste disks are induced in the lingual epithelium of salamanders during metamorphosis.

Morphological changes of oral cavity during metamorphosis with special reference to the taste organ were examined in Ezo salamanders (Hynobius retardatus) and axolotis (Ambystoma mexicanum), and compared with those in bullfrogs (Rana catesbeiana). The non-distensible tongue of salamanders changed the structure progressively during metamorphosis: a small area of the rostrum protruded and developed caudally with recession of the flat area of the tongue. The protrusion that developed on the tongue had numerous papillae, as seen in the frog tongue. The apical region of the papillae occasionally had a cell mass similar to the taste disk of frogs (termed a taste disk-like cell mass). On the flat area of the tongue, the barrel-shaped taste buds of larval salamanders were transformed into taste buds with a wider receptor area. The barrel-shaped taste buds decreased progressively during metamorphosis, while taste disk-like cell masses increased. Neuronal labeling with an antibody to neuron-specific enolase and fluorescent carbocyanine dye showed that the taste disk-like cell masses in metamorphosed salamanders were innervated by the glossopharyngeal nerve (nerve IX). Nerve IX responded to taste stimulation as well as mechanical stimulation applied to the rostral tongue. During metamorphosis the salamanders undergo transformation and rearrangement of taste organs on the tongue possibly as an adaptation to the terrestrial environment.

Animals↗
PubMed1984

A comparative study of potassium-induced relaxation in vascular smooth muscle of tiger salamanders and rats.

This study compares potassium-induced relaxation in vascular tissue of an amphibian (Ambystoma tigrinum) and a mammal (rat). Aortas (salamanders) and tail arteries (rats) were cut into helical strips for isometric force recording. After norepinephrine-induced contraction in potassium-free solution, arteries relaxed in response to added potassium (1-20 mmol/l). Potassium-induced relaxation was greater in rat tail arteries than in salamander aortas. Half-maximal relaxation occurred at a potassium concentration of approximately 3 mmol/l in both species. Ouabain inhibited potassium-induced relaxation; salamanders were more sensitive to the glycoside than rats. Potassium-induced relaxation decreased as the temperature of the bathing medium was lowered; half-maximal inhibition occurred at 19 and 29 degrees C for salamander aortas and rat tail arteries, respectively. Potassium-induced relaxation also varied with the interval in potassium-free solution, the hydrogen ion concentration (rats only), and the magnitude of norepinephrine-induced contraction. It appears that the cellular mechanism causing potassium-induced relaxation is similar in blood vessels of salamanders and rats. The observations are consistent with the hypothesis that stimulated electrogenic sodium transport produced membrane hyperpolarization and relaxation in vascular smooth muscle.

Animals↗
PubMed1992

Axial motor organization in postmetamorphic tiger salamanders (Ambystoma tigrinum): a segregation of epaxial and hypaxial motor pools is not necessarily associated with terrestrial locomotion.

The axial motor column has undergone a major reorganization during the evolution of vertebrates. In aquatic anamniotes including lampreys, goldfish, and mudpuppies, epaxial and hypaxial motoneurons are intermingled in the column. In contrast, epaxial and hypaxial motoneurons are spatially segregated in water snakes, rats, and monkeys, apparently as a consequence of an isomorphic mapping of motoneuron location onto the position of innervated muscle in the embryonic myotome. The presence of these two very different arrangements of motoneurons requires a major restructuring of the motor column during vertebrate evolution. The time of this reorganization is unknown. All amniotes studied to date have an epaxial/hypaxial segregation, and all anamniotes do not, suggesting that the map arose with the origin of amniotes. All the anamniotes examined previously were permanently aquatic, however, and the map might therefore be associated with terrestrial locomotion. If so, we would expect terrestrial anamniotes to have an arrangement of motoneurons like that in amniotes. We studied the organization of motoneurons innervating the trunk muscles of postmetamorphic, terrestrial tiger salamanders and asked whether their motor columns are more like those of amniotes or those of aquatic anamniotes. The motor column in tiger salamanders is similar to that seen in aquatic anamniotes and very like that in mudpuppies--permanently aquatic salamanders. There are several classes of motoneurons with morphological similarities to the primary and secondary motoneurons characteristic of aquatic anamniotes. Epaxial and hypaxial motoneurons show no obvious morphological differences and occupy extensively overlapping positions in the motor column. The only epaxial/hypaxial distinction is the presence of a few, small, relatively undifferentiated motoneurons located subadjacent to the ependymal layer. These motoneurons are filled only by horseradish peroxidase (HRP) applied to hypaxial nerves. They are probably newly born motoneurons, and their presence suggests continued addition of motoneurons, even in adult salamanders. We conclude that the epaxial/hypaxial segregation seen in amniotes is not necessarily associated with terrestrial locomotion. The segregation and the topographic map it reflects may have arisen in conjunction with the origin of amniotes. If they instead arose prior to the origin of extant amphibians, they must have been secondarily lost in those salamanders studied to date. An examination of the motor column of other amphibians should help to resolve this issue.

Ambystoma↗
PubMed2002

Cardiac effects of hypoxia in the neotenous tiger salamander Ambystoma tigrinum.

The aquatic form of the tiger salamander Ambystoma tigrinum lives in high-altitude ponds and is exposed to a hypoxic environment that may be either chronic or intermittent. In many animal species, exposure to hypoxia stimulates cardiac output and is followed by an increase in cardiac mass. The working hypothesis of the present study was that the hearts of these aquatic salamanders exposed to 10-14 days of 5 % oxygen in a laboratory setting would become larger and would differentially express proteins that would help confer tolerance to hypoxia. During exposure to hypoxia, cardiac output increased, as did hematocrit. Cardiac mass also increased, but mitotic figures were not detected in the cardiac myocytes of colchicine-injected animals. The mass increase was probably due to hypertrophy, although a very slow rate of hyperplasia cannot be ruled out. Representational difference analysis indicated that at least 14 mRNAs were expressed in hearts from the hypoxic animals that were not expressed in hearts from normoxic animals. The differentially expressed genes were cloned and sequenced and confirmed as coming from the ventricles of the hypoxic salamanders. Genes differentially expressed include mitochondrial genes and genes for elongation factor 2, a protein synthesis gene. The mechanical performance of buffer-perfused hearts isolated from normoxic and hypoxic animals did not differ. Acute responses to hypoxia were also measured. The rate of oxygen consumption of unanesthetized salamanders in metabolism chambers decreased when chamber oxygen concentration was reduced below 12 % oxygen. At a chamber oxygen concentration of 4-6 %, the rate of oxygen consumption of the salamanders was reduced to approximately one-third of the normoxic rate.

Altitude↗
PubMed1985

Ultrastructural changes in development and aging of the interrenal cell of the salamander, Hynobius nebulosus.

The fine structure of interrenal cells in the salamander, Hynobius nebulosus, from prometamorphic larvae to its adult stage, was observed with electron and light microscopes. In all the animals examined the interrenal cell clusters were located at the medial edge of the ventral surface along the total length of each kidney, suggestive of a primitive nature. In larval salamanders, the interrenal cells contained small to moderate numbers of lipid droplets, and their cytoplasm was filled with a tubular network of smooth endoplasmic reticulum (SER) and numerous mitochondria with tubulo-vesicular cristae. In the adult and young adult salamanders, however, most interrenal cells were filled with lipid droplets, so that both tubular SER and mitochondria were decreased in amount in inverse proportion to the increased lipid droplets. These mitochondria frequently contained a crystalloid structure composed of closely packed tubules which were continuous with the cristae. These findings suggest that the interrenal cells in the larvae are more active than those in the adult or young adult salamanders. In addition, the interrenal cells at the end of metamorphosis contained a greater number of enlarged mitochondria with loosely distributed tubular cristae and with a less dense matrix and more numerous membrane-bounded dense bodies, 0.1-0.3 micron in diameter, than those at the prometamorphic stage. These findings suggest that the cells are their most active at this stage. In the prometamorphic larvae, bundles of filaments frequently occurred in the cytoplasm, especially around the nucleus. These filaments gradually decreased in number with the advance of age, and in young adult salamanders they appeared only occasionally.

Adrenal Glands↗
PubMed1998

Molecular cloning of the salamander red and blue cone visual pigments.

PURPOSE: Salamander retinas are known to contain at least three cone pigments and two rod pigments. The purpose of this study was to clone and characterize the visual pigments from salamander cones. METHODS: cDNA fragments of cone pigments were amplified from a salamander retina cDNA library by PCR using a pair of primers with consensus for visual pigments. These fragments were cloned and used as probes for library-screening. The full-length cDNAs were isolated from the retinal library using the cloned PCR products as probes. DNA sequences were determined by the dideoxynucleotide chain termination method. RESULTS: Two pigment cDNAs were cloned and sequenced from the salamander library. The global GenBank search showed that they do not match any existing sequences but have significant sequence similarity to visual pigments. One of the pigment cDNAs showed a high sequence homology with red cone pigments from other species and thus, was designated as a red cone opsin. The other pigment was designated as a blue cone opsin as it is most homologous to the chicken and goldfish blue cone pigments. Both cDNAs contain a full-length coding region encoding 365 amino acids in the red and 363 amino acids in the blue cone pigment. Hydropathy analysis predicted that both pigments could form seven hydrophobic transmembrane helices. Both pigments retain the key amino acid residues critical for maintaining the structure and function of opsins and have similar G-protein interaction sequences which differ from that of rod opsin. Phylogenetic analysis indicates that the red opsin belongs to the L group and the blue opsin belongs to the M1 group of visual pigments. CONCLUSIONS: The salamander red and blue cone pigments share high sequence homology with the cone pigments of other species.

Amino Acid Sequence↗
PubMed1999

Morphological variation of hypaxial musculature in salamanders (Lissamphibia: caudata).

Despite the acknowledged importance of the locomotory and respiratory functions associated with hypaxial musculature in salamanders, variation in gross morphology of this musculature has not been documented or evaluated within a phylogenetic or ecological context. In this study, we characterize and quantify the morphological variation of lateral hypaxial muscles using phylogenetically and ecologically diverse salamander species from eight families: Ambystomatidae (Ambystoma tigrinum), Amphiumidae (Amphiuma tridactylum), Cryptobranchidae (Cryptobranchus alleganiensis), Dicamptodontidae (Dicamptodon sp.), Plethodontidae (Gyrinophilus porphyriticus), Proteidae (Necturus maculosus), Salamandridae (Pachytriton sp.), and Sirenidae (Siren lacertina). For the lateral hypaxial musculature, we document 1) the presence or absence of muscle layers, 2) the muscle fiber angles of layers at mid-trunk, and 3) the relative dorsoventral positions and cross-sectional areas of muscle layers. Combinations of two, three, or four layers are observed. However, all species retain at least two layers with opposing fiber angles. The number of layers and the presence or absence of layers vary within species (Necturus maculosus and Siren lacertina), within genera (e.g., Triturus), and within families. No phylogenetic pattern in the number of layers can be detected with a family-level phylogeny. Fiber angle variation of hypaxial muscles is considerable: fiber angles of the M. obliquus externus range from 20-80 degrees; M. obliquus internus, 14-34 degrees; M. transversus abdominis, 58-80 degrees (acute angles measured relative to the horizontal septum). Hypaxial musculature comprises 17-37% of total trunk cross-sectional area. Aquatic salamanders show relatively larger total cross-sectional hypaxial area than salamanders that are primarily terrestrial.

Anatomy, Cross-Sectional↗
PubMed1984

Histological and histochemical studies of the secretory components of the salamander olfactory mucosa: effects of isoproterenol and olfactory nerve section.

Secretory components of the salamander olfactory mucosa, sustentacular cells (SC), and Bowman's glands (BG), were examined histologically and histochemically. In the aquatic larval salamander, SC in sensory grooves contained secretory granules; the submucosa contained a single layer of homogeneous, ductless glands. In the land-dwelling adult salamander, SC spanning a flat epithelial sheet contained vesicles. Subjacent to the epithelium in both dorsal and ventral mucosae lay BG whose ducts opened at the surface of the epithelium. In the ventral mucosa, two additional layers of olfactory glands (OG) lying below the BG were identified; ducts were not observed in association with the OG. The beta-adrenergic agonist isoproterenol caused depletion of secretory granules from BG and OG of larval, young, and adult salamanders but had no discernible effect on SC. Histochemical techniques (Alcian blue at pH 2.5 and pH 1.0, high-iron diamine, and the periodic acid-Schiff reaction) demonstrated that SC contained neutral, acidic, and small amounts of sulfated mucopolysaccharides (MPS), BG and OG contained only neutral MPS. In contrast, glands under adjacent respiratory epithelium contained both acidic and sulfated MPS. Unilateral olfactory nerve section ( ONX ) caused changes in the histochemical reactivity of acidic and sulfated MPS in SC on the ipsilateral and later on the contralateral side. Neutral MPS staining became enhanced first in the OG that lay under the BG, then in BG cells, and later in the deepest OG layer. Ipsilateral changes preceded contralateral ones. At 24 days post- ONX , some acinar cells in the deep OG contained acidic but not sulfated MPS.

Animals↗
PubMed1995

Ultrastructural changes of secretory cells of salamander lingual salivary glands under varying conditions.

BACKGROUND: In general the ultrastructure of secretory cells can be modified under secretory stimulated and non-stimulated conditions. The ultrastructure of the lingual salivary glands of hibernating salamanders in the natural environment was examined and compared to those of fasted and fed animals kept in the laboratory. METHODS: Hibernating salamanders of the species Hynobius tokyoensis were collected from the natural environment during the winter breeding season and sacrificed for this study. One group was sacrificed immediately, another group was kept under fasted condition, and another group was regularly fed; both of the latter groups were kept at room temperature for 1 month and then sacrificed. The tongue was fixed for electron microscopy and processed by conventional method, and semithin sections were histochemically examined for glycoconjugates. RESULTS: The lingual salivary glands of this salamander species were composed of simple or often branched tubular glands opening onto the dorsal surface of the tongue. The secretory cells which composed their terminal portions were all columnar in morphology and histochemically mucous in nature. Under hibernation or prolonged fasting at room temperature, the mucous granules of these columnar secretory cells were decreased in number and the Golgi apparatus appeared inactive. A conspicuous structural peculiarity was multiple fingerprint-like structures of the rough-surfaced endoplasmic reticulum (RER). Most of these membranes were composed of stacks of tightly packed cisternae. Under regular feeding, the mucous granules were closely packed in the cytoplasm of the secretory cells and the basal nucleus was slightly enlarged. The Golgi apparatus showed progressive activation with distended saccules. The unique membranous arrangement of the RER which was observed in the fasting animals was completely absent, and the cisternae were irregular in width with considerable variation of the intercisternal spaces. CONCLUSIONS: The tongue of the salamander H. tokyoensis has numerous tubular salivary glands which are mucous in nature. The architecture of the organelles in the secretory cells is subject to modification in response to the cellular metabolism.

Animals↗
PubMed2002

Morphology and projection pattern of medial and dorsal pallial neurons in the frog Discoglossus pictus and the salamander Plethodon jordani.

In the frog Discoglossus pictus and the salamander Plethodon jordani, the morphology and axonal projection pattern of neurons in the medial and dorsal pallium were determined by intracellular biocytin labeling. A total of 77 pallial neurons were labeled in the frog and 58 pallial neurons in the salamander. Within the medial pallium (MP) of the frog, four types of neurons were identified on the basis of differences in their axonal projection pattern. Type I neurons have bilateral projections into telencephalic and diencephalic areas; type II neurons have bilateral projections to telencephalic areas and ipsilaterally descending projections to diencephalic regions; type III neurons have only intratelencephalic connections, and a single type IV neuron has ipsilaterally descending projections. The somata of the four types occupy four nonoverlapping zones. Neurons of the dorsal pallium (DP) project exclusively to the ipsilateral MP and to the dorsal edge of the lateral pallium. In the ventral MP of the salamander, neurons have mostly intratelencephalic projections. Neurons in the dorsal MP project bilaterally to diencephalic and telencephalic regions. Neurons in the medial DP project ipsilaterally to the MP, lateral septum, nucleus accumbens, medial amygdala, and the internal granule layer of the olfactory bulb. In five cases, fibers were found in the commissura hippocampi, but in only two cases could these fibers be followed toward the contralateral MP and septum. Neurons in the lateral DP had no contralateral projections; they projected to the ipsilateral MP and in eight cases to the ipsilateral septum as well. Based on similarities of cytoarchitecture and projection pattern in neurons of the MP and DP, it is proposed that both frogs and salamanders have an MP subdivided into a ventral and dorsal portion, and a DP subdivided into a medial and a lateral portion.

Animals↗
PubMed2004

Expression of calcium transporters in the retina of the tiger salamander (Ambystoma tigrinum).

Changes in intracellular calcium concentration, [Ca2+]i, modulate the flow of visual signals across all stages of processing in the retina, yet the identities of Ca2+ transporters responsible for these changes are still largely unknown. In the current study, the distribution of plasma membrane and intracellular Ca2+ transporters in the retina of tiger salamander, a model system for physiological studies of retinal function, was determined. Plasma membrane calcium ATPases (PMCAs), responsible for high-affinity Ca2+ extrusion, were highly expressed in the salamander retina. PMCA isoforms 1, 2, and 4 were localized to photoreceptors, whereas the inner retina expressed all four isoforms. PMCA3 was expressed in a sparse population of amacrine and ganglion neurons, whereas PMCA2 was expressed in most amacrine and ganglion cells. Na+/Ca2+ exchangers, a high-capacity Ca2+ extrusion system, were expressed in the outer plexiform layer and in a subset of inner nuclear and ganglion layer cells. Intracellular Ca2+ store transporters were also represented prominently. SERCA2a, a splice variant of the sarcoplasmic-endoplasmic Ca2+ ATPase, was found mostly in photoreceptors, whereas SERCA2b was found in the majority of retinal neurons and in glial cells. The predominant endoplasmic reticulum (ER) Ca2+ channels in the salamander retina are represented by the isoform 2 of the IP3 receptor family and the isoform 2 of the ryanodine receptor family. These results indicate that Ca2+ transporters in the salamander retina are expressed in a cell type-specific manner.

Ambystoma↗
PubMed1982

Prolactin induces increase in the specific gravity of salamander, Hynobius retardatus, that raises adaptability to water.

The migration of the salamander, Hynobius retardatus, from land to water, which normally occurs in the breeding season, was induced by the injection of prolactin. The migration was accompanied by certain morphological changes (wider tail or swollen body); the observed morphological changes resembled those of salamanders collected from ponds during the breeding season. The prolactin-treated salamanders sank to the bottom of the water. In contrast, the control salamanders that did not receive prolactin floated near the water surface. The specific gravity of the whole body of the prolactin-treated animals was greater than unity. Prolactin injection induced a remarkable enlargement of the tissue between the skin and muscle, in which a considerable amount of mucopolysaccharide-rich substance accumulated. Because of the hydrophilic nature of the mucopolysaccharides, and increased mucopolysaccharide may absorb more water, which, in turn, may result in an increase of the osmotic pressure of the serum. This may eventually cause the animals to migrate from land to water to quench the "thirst." The absorption of water may make the specific gravity greater, and this allows the animals to sink in water.

Acclimatization↗
PubMed1998

Age-related changes in the tiger salamander retina.

Tiger salamanders have been used in visual science because of the large size of their cells and the ease of preparation and maintenance of in vitro retinal preparations. We have found that salamanders over 27 cm in length show a variety of visual abnormalities. Compared to smaller animals (15-23 cm), large animals exhibited a decrease in visual responses determined by tests of the optomotor reflex. Small animals responded correctly an average of 84.5% of the time in visual testing at three light levels compared to an average of 68.4% for the large animals with the poorest visual performance at the lowest level of illumination. In addition, large animals contained (i) histological degeneration of the outer retina, in particular, loss and disruption of outer segments and abnormalities of the retinal pigmented epithelium, (ii) loss of cells, including photoreceptors, by apoptosis as evaluated with the TUNEL technique, and (iii) an increase in the number of macrophages and lymphocytes within the retina as determined by morphological examination. These histological changes were present in all large animals and all quadrants of their retinas. In contrast, small animals showed virtually no retinal degeneration, no TUNEL-positive cells, and few immune-like cells in the retina. Since large animals are also older animals. the visual changes are age-related. Loss of visual function and histological degeneration in the outer retina also typify aged human eyes. Thus, we propose that large salamanders serve as an animal model for age-related retinal degeneration. In addition to providing a source of aging retina that is readily accessible to experimental manipulation, the salamander provides a pigmented retina with a mixed (2:1, rod:cone) population of photoreceptors, similar to the degeneration-prone parafoveal region of the human eye.

Aging↗