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PubMed1976

Renewal of normal and degenerating photoreceptor outer segments in the Ozark cave salamander.

To determine whether photoreceptor degeneration in the Ozark cave salamander is associated with cessation or changes in the kinetics of outer segment (OS) renewal, an autoradiographic study of 3H-leucine incorporation in photoreceptors was carried out. Six days after isotope injection rods and cones showed labeling in both inner and outer segments. Cone OS were diffusely labeled whereas rods contained a band of radioactivity at the base of the OS. At 13 and 21 days the radioactive band in rods was located progressively nearer the distal tip of the OS. The rate of rod OS renewal ranged from 0.30 to 0.38 mu of OS length per day at 18 degrees C. L-thyroxin induced metamorphosis and light increased the renewal rate compared to larvae in darkness, and adults with photoreceptors in an early stage of degeneration had a slightly higher renewal rate than larvae. Light and electron microscope autoradiographs of degenerate photoreceptors revealed that even in the final stages of degeneration when OS are reduced to small, irregular whorls of membrane, 3H-leucine labeling was present in inner segments and OS membranes. These observations demonstrate that OS renewal occurs in both larvae and adults, and suggest that photoreceptor degeneration may be due to disruption of some aspect of the OS disposal process.

Animals↗
PubMed1977

Tail regeneration in the plethodontid salamander, Plethodon cinereus: induced autotomy versus surgical amputation.

Regeneration of the tail in the plethodontid salamander, Plethodon cinereus, occurs following either surgical amputation or induced autotomy. Autotomy may occur along any one of the caudal myosepta which form natural cleavage planes. The distally attached myofibers break away from the myoseptum which then becomes part of the stump surface remaining intact during subsequent regeneration of the distal segments. Under these conditions, therefore, muscle fibers do not normally participate in tail regeneration. If, however, the myofibers of a caudal myotome are interrupted as in mid-segment amputation, the damaged fibers undergo hyaline degeneration and are largely replaced by connective tissue often as far proximally as the next myoseptum. Other tissues at the amputation surface are concurrently engaged in the epimorphic regeneration of the tail, including myogenesis, though at a slower initial rate than that following autotomy. Muscle cells, therefore, appear not to participate in epimorphic tail regeneration in Plethodon cinereus following either surgical amputation or induced autotomy.

Amputation, Surgical↗
PubMed1984

Stump currents in regenerating salamanders and newts.

We report here that a variety of salamanders and newts from differing habitats all drive a steady ionic electric current out of the forelimb stump tip after forelimb amputation. Several hours after amputation the density of this stump current ranges from about 10 to 100 microA/cm2 in most species, and declines with time. In most cases, the magnitude of the stump current is dependent on the concentration of Na+ in the external medium (an artificial pondwater), suggesting that the well-known Na+ -dependent transcutaneous voltage described in amphibia (particularly frogs) is the EMF for this stump current. These measurements add to those previously reported for the North American red spotted newt (Notophthalmus viridescens), and suggest that electrical changes following amputation of urodele limbs are widespread among members of this group.

Amputation, Surgical↗
PubMed1987

Adenohypophysial-thyroid activity of the tiger salamander, Ambystoma tigrinum, as a function of metamorphosis and captivity.

The aim of this study was to determine the timing of adenohypophysial activation during metamorphosis of the tiger salamander, Ambystoma tigrinum. It consisted of two parts: 1) determination of plasma thyroid hormone concentrations and analysis of thyroid gland histology as a function of metamorphic stage and 2) analysis of the time-course of uptake of 125I by the thyroids during metamorphosis as an indicator of endogenous thyrotropin (TSH) levels. Significant increases in both triiodothyronine (T3) and thyroxine (T4) first were evident at the onset of metamorphic climax (stage II). Maximum levels of both hormones were not observed, however, until the completion of gill resorption (stage VII). No changes in thyroid histology were observed that could be unambiguously related to metamorphic transformation. The thyroids accumulated 125I in a slow but linear fashion in premetamorphic larvae (stage I). However, uptake exhibited a rapid peak during early climax (stage II), before maximum concentrations of thyroid hormones were observed. In addition, uptake was maintained above premetamorphic levels at stage VII, in conjunction with maximum levels of T4 and T3. Captivity alone produced a small but significant increase in plasma concentrations of T3. It produced no significant effect on either thyroid histology or uptake of 125I. These results indicate that adenohypophysial activation occurs rapidly and is maximal at the onset of metamorphic climax.

Ambystoma↗
PubMed1993

Effects of prolactin, growth hormone, and triiodothyronine on prolactin receptors in larval and adult tiger salamanders (Ambystoma tigrinum).

The effects of porcine growth hormone (pGH) or ovine prolactin (oPRL) alone and in combination with triiodothyronine (T3) on renal PRL receptors were determined in both pre- and post-metamorphic tiger salamanders (Ambystoma tigrinum). The protein hormones were given at a dose of 1.0 micrograms/gm body weight/day and the T3 was given at 10.0 ng/gm body weight/day. The duration of treatment was 7 days. Effects on growth, and plasma thyroid hormone levels were also determined. Ovine PRL increased growth in both larvae and adults and reversed metamorphic changes. Administration of T3 increased the plasma T3 concentration, as measured by radioimmunoassay, and when given alone caused weight loss at both stages. The GH decreased plasma T4 and increased plasma T3 concentrations, indicating that it caused an increase in T4 deiodination. In adults the renal PRL receptor affinity of 2.9 +/- 0.7 x 10(10) L/mol and capacity of 160 +/- 22 fmol/mg protein were higher than the corresponding values of 1.8 +/- 0.3 x 10(10) L/mol and 29.2 +/- 3.8 fmol/mg in larvae. In adults only, there is an additional low-affinity, high capacity PRL binding site. The oPRL treatment decreased the binding capacity of 33.2 +/- 1.2 and 5.9 +/- 4.9 fmol/mg in adults and larvae, respectively. By contrast, pGH increased the capacities to 249 +/- 18 and 62.1 +/- 6.8 fmol/mg in adults and larvae, respectively. Treatment with T3 alone doubled the oPRL binding capacity to 58.3 +/- 4.7 fmol/mg in larvae, but there was no effect in adults. In both developmental stages the effects of oPRL and pGH on the receptors were not changed by the simultaneous T3 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambystoma↗
PubMed2003

Morphology and escape performance of tiger salamander larvae (Ambystoma tigrinum mavortium).

The ability of an individual to escape predators is an important component of fitness. Several adaptive explanations of body shape variation in amphibians hypothesize relationships between swimming performance and morphology, but these ideas have rarely been tested. Here we investigate bivariate and multivariate relationships between natural variation in morphology and performance. We used high-speed video to examine fast-starts associated with escape responses in small tiger salamander larvae (Ambystoma tigrinum). Our results indicate that performance is influenced by interactions among aspects of morphology, physiology, and behavior. Relationships between morphometric variables and velocity could be detected with multivariate, but not bivariate statistical analyses. In particular, relationships between morphology and velocity depend on tail beat frequency (potentially a measure of effort or vigor). Relationships between morphology and acceleration were detected with bivariate analyses, but multivariate analysis suggests that acceleration performance, too, depends on interactions between morphology and tail beat frequency. We found a positive relationship between tail area and propulsive performance, which supports adaptive interpretations of variation in larval tail shape within and between amphibian species.

Adaptation, Physiological↗
PubMed2004

Ultrastructure of the annual cycle of female sperm storage in spermathecae of the torrent salamander, Rhyacotriton variegatus (Amphibia: Rhyacotritonidae).

This study is the first report on the ultrastructure of the sperm storage glands (spermathecae) in the salamander Rhyacotriton variegatus. The population studied is associated with cold-water, rocky streams of the redwood (Sequoia) zone in northern California. Males possess sperm in their vasa deferentia and undergo spermiation throughout the year, but mating is seasonal. Most females with large, vitellogenic follicles (2.0-3.9 mm mean dia.) collected from February-June contain sperm in their spermathecae, although some females with large follicles lack sperm. Other mature-size females collected during this period have small ovarian follicles (0.9-1.2 mm mean dia.) and lack stored sperm. All females collected from September-November have small follicles (0.6-1.6 mm mean dia.) and lack sperm, except in one instance in which a female collected in November had a small amount of degraded sperm, apparently retained from the previous breeding season. The spermathecae consist of simple tubulo-alveolar glands in which the neck tubules produce a mucoid secretory product, and the distal bulbs, where sperm are stored, contain secretory vacuoles of uniform density that stain positively for glycosaminoglycans. In specimens containing sperm, some bulbs have abundant sperm and others lack sperm, but the ultrastructure is similar in both conditions. The acini contain columnar epithelial cells with wide intercellular canaliculi, and a merocrine process releases the secretion. Spermiophagy occurs. In specimens from spring and summer with small ovarian follicles, the neck tubules are similar to those of breeding females, but the distal bulbs are reduced to cords of cells lacking a discernible lumen. Secretory activity in the distal bulbs is initiated in the fall. Spermathecae of R. variegatus are most similar to those of a stream-dwelling plethodontid, Eurycea cirrigera.

Animals↗
PubMed2004

Histology and ultrastructure of the gut epithelium of the neotenic cave salamander, Proteus anguinus (Amphibia, Caudata).

Histological, histochemical, and ultrastructural features of the gut of the European endemic cave salamander Proteus anguinus were studied. The gut is a relatively undifferentiated muscular tube lined with a simple columnar epithelium containing numerous goblet cells. The mucosa and underlying lamina propria/submucosa are elevated into a number of high longitudinal folds projecting into the lumen. The enterocytes are covered apically with uniform microvilli. Irregularity in the arrangement of microvilli was observed. Occasionally, irregular protrusions of the cytoplasm appear between groups of microvilli. Pinocytotic activity occurs at the bases of the intermicrovillous space. Mitochondria are numerous in the apical cytoplasm and basally beneath the nuclei. The supranuclear cytoplasm contains most of the cell organelles. The lateral plasma membranes of adjacent cells interdigitate and are joined by junctional complexes. The periodic acid-Schiff (PAS) reaction, indicating neutral mucosubstances, is positive only in the apical brush border of enterocytes and in goblet cells. The goblet cells also stained with Alcian blue (AB), at pH 2.5, thus revealing the presence of carboxylated glycosaminoglycans. Compact aggregations of AB- and PAS-negative cells are situated directly below the epithelium. Mitotic figures are present in individual clusters of cells. The fine structure of cells in these clusters indicated that these cells could be responsible for renewal of intestinal epithelium. Numerous endocrine-like cells could also be seen. The closely packed smooth muscle cells and amorphous extracellular material with collagen fibrils constitute a net-like structure under the basal lamina that is very closely associated with the epithelium. There are numerous acidophilic granular cells between epithelial cells, in the lamina propria/submucosa, and between cells aggregations. They seem to be associated with nematode infections and possibly constitute a humoral defense mechanism.

Animals↗
PubMed1978

The relationship of a monoamine fiber system to a somatosensory tectal projection in the salamander Ambystoma tigrinum.

After hemisection of the spinal cord and medulla oblongata, a projection has been traced to the inner half of the tectal white of the tiger salamander, using Fink-Heimer degeneration staining. By microelectrode recording it was found that the tectal projection forms a topographic somatosensory map of the contralateral half of the body. This map is in register with the overlying retino-tectal visual projection. Using the Falck-Hillarp technique, it was found that the somatosensory tectal input is associated with yellow-fluorescing 5-hydroxytryptamine fibers.

Animals↗
PubMed1979

Ultrastructural and histochemical features of the thymus glands of the adult lungless salamander, Plethodon glutinosus (Caudata: Plethodontidae).

The thymus glands of adult slimy salamanders (Plethodon glutinosus) were examined by light and electron microscopy with the objective of describing the populations of epithelial cells believed to be secretory. The results of various histochemical procedures designed to demonstrate nucleic acids, proteins, lipids, and mucosubstances were evaluated by light microscopy. Each thymus is incompletely subdivided into a variable number of interconnected lobules by trabeculae extending inward from a thin capsule composed of connective tissues. The thymic parenchyma lacks distinct cortical and medullary regions, although developing lymphocytes and plasma cells tend to accumulate in larger numbers in the outermost portions of the glands. Basophils are found regularly in the capsule and trabeculae, but only very rarely within the thymic parenchyma. The epithelial cells of the thymus can be classified into five categories: epithelial reticular cells; three varieties of granulated cells (types I, II, and III), and myoid cells. Epithelial reticular cells form a three-dimensional network which extends throughout all portions of the thymus. Type I and type II granulated cells can be distinguished from one another by various morphological criteria at the ultrastructural level, but only small differences in the composition of their inclusions can be demonstrated histochemically. Both types of granules are composed principally of a proteinaceous material containing an abundance of primary amino and guanidyl groups. In addition, most type I inclusions possess a lipid component that cannot be demonstrated in type II granules. Type III granulated cells possess very small cytoplasmic inclusions resembling those of gastroenteric endocrine cells. Myoid cells contain concentrically arranged myofibrils composed of sarcomeres. In favorably oriented material, small cysts can be identified whose walls are composed of mixtures of type I cells, type II cells, and epithelial reticular cells. Groups of degenerating epithelial cells form lamellated structures corresponding to Hassall's (thymic) corpuscles.

Animals↗
PubMed1985

Aquatic prey capture in ambystomatid salamanders: patterns of variation in muscle activity.

Functional morphologists commonly study feeding behavior in vertebrates by recording electrical activity from head muscles during unrestrained prey capture. Rarely are experiments designed to permit a partitioning variation in muscle electrical activity patterns. Analysis of muscle activity during aquatic prey capture in two morphologically distinct species of salamanders, Ambystoma dumerilii and A. mexicanum, is conducted to assess variation at four levels: between species, among individuals within species, among experiments conducted on different days, and among feedings. The results show that 1) mean correlations among the 11 electromyographic variables measured for each feeding are low and vary considerably among individuals, 2) many of the variables show significant differences among experimental days, 3) only one variable, the difference in timing between the depressor mandibulae and sternohyoideus muscles, showed significant variation between species, and 4) seven of the 11 variables showed significant variation among individuals within species. Overall, the variation between feedings (trials) was high, and there was some variation between days on which the experiments were conducted. Neither electrode position within the muscle nor satiation contributed to the high trial variance. The results suggest that functional analyses of feeding behavior should include an assessment of variation due to individuals, days, and trials, because the amount of variation at these levels may render differences between species nonsignificant.

Activity Cycles↗
PubMed1986

Morphological and fine structural features of the basilar papilla in ambystomatid salamanders (Amphibia; Caudata).

The morphology and fine structure of the basilar recess and basilar papilla were investigated in four species of salamanders from the family Ambystomatidae. The otic relationships of the recess and papilla to the proximal part of the lagena and saccule are described, and new terminology is suggested for the periotic relationships of the basilar recess to a diverticulum of an intracapsular periotic sac. The basilar papilla consists of supporting cells united laterally by gap junctions, capped by microvilli uniformly arranged around a short, central cilium, and hair cells that typically show several synapses with a single afferent nerve fiber, each marked by a rounded synaptic body surrounded by vesicles. In contrast to anuran basilar papillae, efferent nerve terminals were observed in synapse with hair cells and, rarely, upon afferent fibers. The distal half of the ambystomatid papilla contained hair cells capped by tall ciliary bundles, with kinocilia that show swellings near their tips with delicate attachments to adjacent tall stereocilia. A tectorial body covers only this region of the papilla. Hair cells with shorter stereocilia, situated in the proximal half and at the papillar margins, are related only to filamentous extensions of the tectorial body. The ambystomatid basilar recess and papilla are compared to auditory end-organs in other vertebrates, and it is suggested that a basic distinction can be made between aural neuroepithelia in amniotes versus that in nonamniotic vertebrate ears.

Ambystomatidae↗
PubMed1986

Comparative features of the surface morphology of the basilar papilla in five families of salamanders (Amphibia; Caudata).

The surface morphology of the basilar recess and papilla was examined in 14 species of newts and salamanders selected from the five families of urodeles (Ambystomatidae, Salamandridae, Hynobiidae, Cryptobranchidae, and Amphiumidae) known to have this end-organ. In this sampling, the general organization of basilar structures is essentially similar across species investigated. The recess forms a tubular diverticulum of the proximal part of the lagena. One wall of the recess is associated with a diverticulum of the intracapsular periotic sac, and an adjacent wall is occupied by the basilar papilla. The papilla contained from as few as five hair cells in specimens of Taricha torosa to over 200 hair cells in Cryptobranchus allegheniensis. In most species, the papilla showed a morphological continuum between tall centrally or distally placed ciliary bundles and short ciliary bundles near the papillar margins. In certain species examined, tall bundles had kinocilia with swellings near their tips. Most forms showed a tendency to have groups of ciliary bundles morphologically polarized either toward or away from the saccule. In Cryptobranchus and Dicamptodon, many bundles had a random orientation. The gross and fine structural features of the basilar complex are compared in urodeles and anurans, and "generalized" features for the amphibian basilar complex are suggested. The basilar complex of Cryptobranchus is interpreted as being most generalized, representing a structural form from which most features of the basilar complex in other urodeles and anurans can be derived.

Ambystomatidae↗
PubMed1986

Adrenergic innervation of the gills, pulmonary arterial plexus, and dorsal aorta in the neotenic salamander, Ambystoma tigrinum.

The presence of adrenergic innervation was investigated in four different vascular segments of the neotenic tiger salamander, Ambystoma tigrinum, by histofluorescent staining for catecholamines. The segments were the respiratory section of the gill, the branchial shunt vessels, a vascular plexus in the pulmonary artery, and the dorsal aorta. No adrenergic fibers were detected in the respiratory section of the gill or the pulmonary arterial plexus. In contrast, the branchial shunt vessels contained both adrenergic varicosities and catecholamine-containing cell bodies. These cells resemble Type I cells of the mammalian carotid body and amphibian carotid labyrinth. Adrenergic innervation of the dorsal aorta was sparse and restricted to the adventitia. The results suggest that adrenergic nerves may directly regulate blood flow in the gill, and thus gas exchange, by controlling vascular resistance of the branchial shunts. The contractile state of the dorsal aorta may also be under adrenergic control. In addition, it is suggested that the adrenergic cells of the branchial shunts may serve a receptor function in being sensitive to arterial blood gases.

Adrenergic Fibers↗
PubMed1986

Native variant limb skeletal patterns in the red-backed salamander, Plethodon cinereus, are not regenerated.

Species of the salamander genus Plethodon have a characteristically uniform morphology. Morphological conservation at the level of interspecific comparisons, however, is not always reflected within species. Perhaps the most extreme example of intraspecific variation is the recent description of extensive variability in limb-skeletal patterning both within and between populations of the widespread species P. cinereus. We utilized limb regeneration following experimental amputation as a tool to examine whether naturally occurring variant skeletal patterns result from limb loss and regeneration in nature, and to assay the intrinsic (i.e., genetic) component of between-individual variation in mesopodial patterning. We observed the following. First, regenerate patterns are strikingly different from native patterns: interelement fusions in regenerates are typically between proximodistally adjacent cartilages, whereas interelement fusions in native variant limbs occur exclusively between laterally adjacent cartilages. Fusions also are over ten times more frequent in regenerates than in native limbs. Second, there is no strong correlation between native limb pattern (typical vs. variant) and the regenerate pattern. We conclude that variability in field-collected P. cinereus reflects extensive intrapopulation variation in limb-skeletal patterning during original limb development, rather than regeneration in nature, and that limb regeneration analysis provides no evidence of a strong genetic component to between-individual variation. Finally, unusual mesopodial patterns produced during limb regeneration may be related to the mechanical factors impinging on the regenerating limb in this terrestrial species.

Animals↗
PubMed1991

Collagen type conservation during metamorphic repatterning of the dermal fibers in salamanders.

The orientation of the fibers in the dermis of the tiger salamander, Ambystoma tigrinum, undergoes a dramatic repatterning at metamorphosis. The pre-metamorphic, larval dermis is a tight layer composed of crossed fibers that wind helically around the trunk. This condition is retained by neotenic adults which do not undergo metamorphosis. In contrast, the neotenic adults which do not undergo metamorphosis. In contrast, the metamorphosed adult dermis consists of a superficial, loose network of fibers invested with large multicellular glands--the stratum spongiosum--and a deeper tight layer of fibers--the stratum densum. However, unlike the crossed fibers of the pre-metamorphic dermis, there is no preferred orientation to the fibers in either layer of the post-metamorphic dermis. In order to evaluate whether these two distinctly different fiber patterns are constructed from biochemically similar fibers, the collagen types present in the pre- and post-metamorphic dermis were determined using SDS-polyacrylamide gel electrophoresis. Type I collagen is the predominant collagen of the dermis and the same major collagen types are present for all individuals, whether pre- or post-metamorphic. Thus, the major types of collagen that compose the dermal fibers do not change during metamorphic repatterning of the dermis.

Animals↗
PubMed2002

Video-microscopic analysis of dye coupling in the salamander olfactory bulb.

Cells in the mitral cell (MCL) and granule cell (GCL) layers of the olfactory bulb shape the representation of odor information in the brain. After intracellular Lucifer Yellow (LY) injections into lightly fixed olfactory bulb slices, clusters of dye coupled cells were previously observed in the MCL and GCL, but the relative extent of coupling in the two layers was unknown in adults. In the present study, the time course of LY coupling in the adult salamander olfactory bulb was quantified using video-microscopic methods. Analysis of fluorescent cell body counts showed that the incidence and the extent of LY coupling are greater in the GCL than in the MCL. With optimal low-current injection procedures, 97% of the injections into the GCL exhibited at least one coupled cell, and on average groups of six to eight cells were counted. Fewer injections into the MCL exhibited only one to three coupled cells. Some of these coupled cells were clearly mitral cells. No staining of cells was observed after extracellular LY injections, and intracellular injections of dextran dyes stained single cells, providing evidence that the LY coupled cells were stained through an intercellular route, presumably gap junctions. In live intact preparations, rapid LY staining of cell clusters was also observed using patch pipettes. Together, these results provide evidence that robust coupling occurs among olfactory bulb neurons in adults, which could have functional significance.

Animals↗
PubMed1997

Courtship behaviour in male red-backed salamanders: the ESS dating game

Social interactions in red-backed salamanders, Plethodon cinereusare complex and often depend upon the sex and reproductive status of individuals. In the population at Mountain Lake Biological Station, Virginia, adult males outnumber sexually active (gravid) females by approximately 2:1, because males court annually while females accept mates only biennially. Field observations of male P. cinereus suggest that males maintain feeding territories and allow non-gravid (not sexually active) females access to their territories for foraging, whereas they defend their territories against intrusion by males. We used a game-theoretic analysis of models of male fitness to examine conditions that would favour the evolution of this 'permissive' behaviour. Under a series of increasingly realistic behavioural assumptions, we found that the critical factor in the evolution of male permissive behaviour is female preference for permissive males. If non-gravid females are more likely to return to mate with a male that allows access to his territory, then permissive behaviour is likely to evolve. Furthermore, the evolution of permissive behaviour is facilitated when energetic losses due to territorial defence exceed those due to allowing females to forage.1997The Association for the Study of Animal Behaviour

Journal Article↗