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PubMed1992

Immunocytochemical localization of a galanin-like peptidergic system in the brain of two urodele and two anuran species (Amphibia).

Galanin-like immunoreactivity was localized in the brain of Urodela (Ambystoma, Pleurodeles) and Anura (Bufo, Xenopus) by immunocytochemistry with anti-porcine galanin antiserum. In the four species, immunoreactive perikarya were observed in the telencephalon (striatum, amygdala), diencephalon preoptic area mainly along the anterodorsal wall of the preoptic recessus, suprachiasmatic nucleus, lateral hypothalamus, ventral and dorsal infundibular nuclei, paraventricular organ, and rhombencephalon (nucleus of the solitary tract). Galaninergic fibres extended in similar regions and in the medial septum, ventral telencephalon, ventral hypothalamus, median eminence, and various mesencephalic and rhombencephalic regions. Contacts with the cerebrospinal fluid cavity occurred along the preoptic recessus (Ambystoma) and the ventral infundibular wall (all species). Fibres were scarce in the neurohypophysis. The distal and intermediate lobes of the pituitary were virtually devoid of immunoreactivity. The galaninergic system appeared more developed in adult amphibia than in young animals, suggesting the stimulating influence of sex steroids on the expression of galanin as previously described in Anguilla. The extensive distribution of the galanin-like immunoreactive neurons in amphibian brains suggests that this peptide may act as a neuromodulatur and/or neurotransmitter.

Ambystoma↗
PubMed1986

The structural organization of the kidney of Typhlonectes compressicaudus (Amphibia, Gymnophiona).

The structural organization of the kidney of Typhlonectes compressicaudus (Amphibia, Gymnophiona) was studied by light microscopic (LM) examination of serial paraffin and semithin Epon sections. The kidney is slender and quite long and has a mesonephric segmental construction; the excretory duct (Wolffian duct), running along the lateral side of the kidney, segmentally receives the terminal trunks of the collecting duct system. The nephron has the following parts: renal corpuscle, neck segment, proximal tubule, intermediate segment, distal tubule and connecting tubule. The distal tubule is located in a ventromedial (central) zone of the kidney; all other tubular segments lie in a dorsolateral (peripheral) zone. The renal corpuscles are found at the border between these two zones. The renal corpuscle is very large; its urinary pole faces the peripheral zone. A small proportion of neck segments receive either a nephrostomal duct or a blind branch. The proximal tubule is a thick, highly convoluted tubule. The intermediate segment is ciliated and makes a few coils. The distal tubule is composed of three portions: a highly convoluted part in the central zone, subsequently an attachment site with the renal corpuscle and a short postattachment-part. The connecting tubule and the collecting duct have a heterogeneous epithelium consisting of light and dark cells. The collecting duct is distinguished by dilated intercellular spaces. The Wolffian duct has a pseudostratified epithelium. The present study correlates the course and segmentation of the renal tubule of Typhlonectes. The tubule has three major convolutions. The first occurs in the proximal tubule in the peripheral zone; the second is established by the distal tubule and occurs in the central zone; the third is formed by the connecting tubule and is found in the peripheral zone.

Amphibians↗
PubMed1979

Comparative metabolism of histamine in two Amphibia anura.

The metabolism of histamine has been compared in Rana ridibunda and Discoglossus pictus, both Amphibia anura. An intralymphatic injection of 14C-histamine (5 microCi) was administered to the animals and the total radioactivity excreted in the urine was measured 24, 48, and 72 hours later. The metabolites excreted in the urine at 24 hours were analyzed by thin-layer chromatography and subsequent autoradiography. In both species approximately 60--70% of the injected dose was found in the urine by 72 hours. In Rana ridibunda two histamine metabolites were found: imidazoleacetic and methylimidazoleacetic acid. The present results suggest that the catabolism of histamine differs in the two species.

Amphibians↗
PubMed1986

A comparative study of the innervation of the choroid plexus in amphibia.

The aminergic and cholinergic innervation of choroid plexuses in three species of amphibia was investigated. Plexuses of the Japanese toad and the bullfrog had poor innervation by adrenergic nerves of sympathetic origin, but in the clawed toad, these plexuses were heavily innervated by adrenergic axons from ganglion cells located in the plexus stroma. Nerve fibers positive for acetylcholinesterase were not found in the plexuses, except for a few fibers with very weak enzyme activity in the clawed toad.

Acetylcholine↗
PubMed1985

3,5,3'-Triiodothyronine receptors and thyroxine 5'-monodeiodinating activity in thyroid hormone-insensitive amphibia.

Adult anuran Amphibia and neotenous urodeles, such as Necturus maculosus, rarely respond to thyroid hormone (TH). In this study, the possibility was examined that this lack of response is due either to an inability to convert thyroxine (T4) to 3,5,3'-triiodothyronine (T3) or to the absence of nuclear TH receptors. Following injection of [125I]T4, significant amounts of [125I]T3, analyzed by chromatography, were detected in the serum and liver of Necturus and Rana catesbeiana frog indicating that both possesses a T4 5'-monodeiodinating system. Nuclear binding of T3 was studied in suspensions of purified hepatic nuclei and intact red blood cells (RBC). Analysis of binding data revealed that frog liver nuclei contained two sets of saturable T3 binding sets with affinities comparable to those of the two sets of sites previously demonstrated in tadpole liver nuclei (Galton and Schaafsma, 1983). However, the number of sites per nuclei was small compared to tadpole; expressed as pmol/mg DNA, the maximum binding capacity of the high affinity set of sites (MBC1) was 2.2 +/- 0.31 versus 12.9 +/- 1.80 and MBC2 was 24.9 +/- 4.5 versus 42.2 +/- 54. Receptor number in RBC nuclei was also smaller in frog than tadpole: 90 +/- 26 versus 882 +/- 56 sites/nucleus (Kd less than 10(-11) M in both groups). No comparable high affinity binding sites were detected in Necturus liver, but some sites were found in Necturus RBC. These cells contained 2111 +/- 120 sites/nucleus, more than twice the number found in tadpole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Molecular organization of ribosomal RNA genes clustered at variable chromosomal sites in Triturus vulgaris meridionalis (Amphibia, Urodela).

The ribosomal RNA genes of Triturus vulgaris meridionalis (Amphibia, Urodela) show the peculiar feature of being clustered not only at the nucleolar organizer, present in the species at a definite chromosome location, but also at "additional ribosomal sites" which are highly variable in number and chromosomal distribution among individuals. The additional ribosomal sites are most often found at specific chromosome regions, such as telomeres, C-bands and centromeres, in virtually all the chromosomes. With increasing numbers of additional clusters, the genomic dosages of ribosomal RNA genes are found to increase over a tenfold range, though not linearly. At a molecular level, the ribosomal DNA repeats differ in size because of discrete variations in the length of the non-transcribed spacers. However, the resulting length heterogeneity of the gene family is rather limited within a single genome as well as within the species. Many of the ribosomal loci appear to be internally homogeneous with respect to the repeat length. Moreover, separate clusters from distant genomic regions can share the same size class of ribosomal repeats even in the same specimen. The nucleolar organizer is mostly endowed with "shorter" ribosomal repeating units, ranging in size from 13.7 X 10(3) to 15.2 X 10(3) base-pairs. The additional ribosomal sites are characterized by the occurrence of "longer" repeats, ranging in size from 16.2 X 10(3) to 19.7 X 10(3) base-pairs. The "shorter" class of ribosomal repeats is always detected in the amplified ribosomal DNA, suggesting that the nucleolar organizer locus is involved in the amplification process in most oocytes. "Longer" ribosomal repeats are also detectable in the amplified ribosomal DNA of a few females.

Animals↗
PubMed1987

Further classification of skin alkaloids from neotropical poison frogs (Dendrobatidae), with a general survey of toxic/noxious substances in the amphibia.

Cutaneous granular glands are a shared character of adult amphibians, including caecilians, and are thought to be the source of most biologically active compounds in amphibian skin. Data are available from one or more species in over 100 of nearly 400 genera comprising the three living orders of Amphibia. Many species contain unidentified substances judged to be noxious based on predator aversion or human taste. Additionally, there is a great diversity of known compounds, some highly toxic as well as noxious, which can be tabulated under four broad categories: biogenic amines, peptides, bufodienolides (bufogenins) and alkaloids. The last category includes alkaloids derived from biogenic amines, water-soluble alkaloids (tetrodotoxins) and lipophilic alkaloids. Most compounds are known only from skin of adult amphibians, but the toxic and noxious properties of eggs and larvae of certain salamanders and toads can be attributed to tetrodotoxins and bufodienolides, which occur also in adult tissues other than skin. Predator aversion and various antipredator behaviors and aposematic colorations clearly prove the defensive value of these diverse metabolites, whether or not they are elaborated primarily (e.g. alkaloids) or secondarily (e.g. some peptides and biogenic amines) for this function. Lipophilic alkaloids include the samandarine alkaloids, known definitely only from an Old World genus of salamanders, and the more than 200 dendrobatid alkaloids. Nearly all the latter are unique to neotropical poison frogs of the genera Dendrobates and Phyllobates (Dendrobatidae), except for seemingly homoplastic occurrences of a few such alkaloids in small brightly colored anurans of several other families. Owing to recent discoveries and new structural information, the dendrobatid alkaloids are here partitioned among the following major and minor classes: batrachotoxins, histrionicotoxins, indolizidines, pumiliotoxin-A class and its allopumiliotoxin and homopumiliotoxin subclasses, decahydroquinolines, gephyrotoxins, 2,6-disubstituted piperidines, 2,5-disubstituted pyrrolidines, pyridyl-piperidines, indole alkaloids, azatricyclododecenes and amidine alkaloids. Except for the steroidal batrachotoxins, and the minor classes of pyrrolidine alkaloids, indole alkaloids and amidine alkaloids, all the above contain a piperidine ring. A large number of piperidine-based alkaloids occur mainly as trace compounds in Dendrobates and remain unclassified; the only water-soluble toxin so far discovered in a dendrobatid (Colostethus) is structurally unknown, but conceivably an alkaloid.

Alkaloids↗
PubMed1991

Carnosine in the brain and olfactory system of amphibia and reptilia: a comparative study using immunocytochemical and biochemical methods.

The pattern of distribution of carnosine-like immunoreactivity and its relation to glial fibrillary acidic protein immunoreactivity have been studied in two lizards (Gallotia galloti and Tarentola delalandii) and in two anuran amphibians (Rana esculenta and Xenopus laevis) using immunocytochemical techniques. Biochemical data obtained by paper electrophoresis show that the dipeptides carnosine and homocarnosine are both present in the brain of all the species examined. In the central nervous system of both anurans and reptilians, carnosine immunoreactivity is localized in glial cells. An important species difference is, however, seen in the olfactory system since primary olfactory neurons and their processes extending to the olfactory bulb are carnosine positive in reptiles, whereas they are not immunostained in anurans. Thus, the cellular distribution of carnosine immunoreactivity in reptilians is very similar to that observed in birds and mammals and is distinct from that seen in amphibia.

Animals↗
PubMed1989

The Florey lecture, 1988. From egg to embryo: the initiation of cell differentiation in Amphibia.

Some of the principles by which different cell types first arise at the beginning of animal development are illustrated by muscle cell formation in Amphibia. If the nucleus of a differentiated muscle cell is transplanted to an enucleated egg, some of the resulting embryos develop into tadpoles with a wide range of normally differentiated cells. These experiments show that genes undergo major changes in activity as a response to components of egg cytoplasm. Two fundamental mechanisms account for the regional activation of genes in early embryos. One involves the effect of localized 'determinants' in egg cytoplasm, and the other concerns cell interactions or embryonic induction. Both these mechanisms seem to be responsible for muscle cell formation in amphibian development. The old problem of embryonic induction has recently become accessible to analysis at the molecular level, especially in the case of the mesoderm or muscle-forming induction. This has been greatly facilitated by using a sensitive and quantitative assay to detect the first transcripts of muscle genes a few hours after the start of induction. The role of early events and of interactions among like cells during response to induction is discussed. In analysing specific gene activation following induction, DNA injection into fertilized eggs has shown that a very small part of the cardiac actin gene promoter is sufficient to enable it to respond to induction. Although the experimental work summarized here has been done on amphibian embryos, which are more suitable than other embryos for embryological manipulation, the conclusions reached are believed to be generally applicable to the development of other organisms.

Amphibians↗
PubMed1988

Spontaneous neoplasms in amphibia.

Cases of spontaneous neoplasms in amphibia are updated and the rarity of spontaneous neoplasia is considered as a result of either inadequate research or the regenerative capacity of these animals.

Amphibians↗
PubMed1978

Plasma thyroxine and triiodothyronine levels in spontaneously metamorphosing Rana catesbeiana tadpoles and in adult anuran amphibia.

We have developed sensitive and reliable radioimmunoassays for T4 and T3 in amphibian plasma and have used these procedures to measure plasma T4 and T3 levels in spontaneously developing Rana catesbeiana tadpoles at various stages of metamorphosis. During premetamorphosis circulating levels of both T4 and T3 were below the limits of detection of the RIA procedures (T4 less than 50 ng/100 ml, T3 less than 5 ng/100 ml). A gradual rise in plasma T3 and T4 became apparent during prometamorphosis, and at the onset of metamorphic climax the levels of both T4 and T3 increased sharply. Peak levels for both hormones were observed in the middle of metamorphic climax (stage XXIII). The circulating T3 level reached a mean peak of 78 ng/100 mg, at least 15 times greater than the level during premetamorphosis. The peak T4 level was 0.5 microgram/100 ml, about a 10-fold increase over the premetamorphosis level. The surge in thyroid hormone secretion lasted only for several days, and during the latter half of metamorphic climax there was a fairly rapid decrease in plasma T4 and T3. By 2 days post-climax the levels had declined to about 20% of their peak values. Free T4 and T3 levels in plasma followed the same general pattern as the total hormone levels during the various stages of tadpole development. In adult R. catesbeiana, plasma T4 and T3 levels were surprisingly low. Similarly low values were observed in Bufo marinus and in Rana pipiens. The very low levels of circulating T4 and T3 both in premetamorphosis tadpoles and in adults suggest that thyroid hormones in anuran Amphibia may be of importance only during the period of metamorphosis.

Animals↗
PubMed1990

[Cranial morphology of an American siphonopid, Microcaecilia unicolor (Amphibia, Gymnophiona) and its functional interpretation].

The skull of Microcaecilia unicolor, american Siphonopidae (Amphibia, Gymnophiona), shows 3 notable morphological characteristics: The mandibular shortening, the verticalization of the retroarticular process, and the verticalization of the quadrate. They define a peculiar morphofunctional pattern, which seems to exist in dwarf forms moving in the complex root system of trees. These morphological characters, associated with modifications of the muscle depressor mandibulae, give functional advantages: A wider gaping of the mouth and the ability of the ingestion of preys which have a great cross-section. In keeping its macrophageous habits, Microcaecilia unicolor does not compete with other dwarf vertebrates living in the same environment and feeding on microinvertebrates.

Amphibians↗
PubMed1989

[Asymmetry of the habenular nuclei during ontogenesis in Pleurodeles waltl (Amphibia, Urodela)].

Qualitative and quantitative studies of the habenular nuclei in Pleurodeles waltl (Amphibia, Urodela) were done. Histological and cytological differences are shown between left and right habenula, the latter being smaller and located more caudal than the former. The right habenula is not as differentiated as the left one whose dorsal part can be subdivided in two parts: medialis and lateralis. A quantitative study of each habenula was undertaken using an automatic analyser system. The result shows that the differentiation into dorsal and ventral populations, appears later in the right habenula (stage 48) than in the left one (stage 36).

Animals↗
PubMed1977

[Ultrastructural features of ureter-mesenchyme interaction, during nephrogenic induction in Amphibia].

Transmission electron microscopy was used to study the interface between the ureter and the mesonephric blastema. When the blastema is induced in a functional organ, numerous pseudopodial protrusions of the ureter and of the mesonephric cells lead to a close appostion between the two structures. The presence of squamous material, perhaps of a mucopolysaccharidic nature, with a network of collagen fibres is always found on this interface. These particular processes seem to play a role as a morphological basis for the phenomenon of induction. The importance of the extracellular matrix is discussed. Neither the occurrence of zones of close contact, reported by several authors, in other species, nor the fusion of membranes has ever been observed in Amphibia.

Animals↗
PubMed1979

[Enzyme histochemical study of the brain of Chthonerpeton indistinctum (Gymnophiona, Amphibia)].

In the brain of the Caecilian species Chthonerpeton indistinctum the following enzymes have been demonstrated by means of histochemical techniques: acid phosphatase, alpha-naphthylacetate esterase, acetylcholin esterase. Acid phosphatase occurs in the cytoplasm of the neurons in 4 different types of localization. Its activity in the ventral parts of the brain is markedly higher than in the dorsal ones. Of particularly high activity are: the motor neurons in the tegmentum, the nucleus mesencephali trigemini, individual large neurons in the marginal zone of the grey matter of the telencephalon, which seems to be a special character of the Caecilians among the Amphibia. The ependyma exhibits local differences in respect of acid phosphatase activity. alpha-Naphthylacetate esterase marks in particular the secretory neurons of the hypothalamus, the large perikarya of the nucleus mesencephali trigemini and the motor neurons of the tegmentum. In the telencephalon the alpha-naphthylacetate esterase activity corresponds to that of acid phosphatase. Acetylcholin esterase marks--with certain restrictions--cholinergic neurons. These predominate in Chthonerpeton in the caudal parts of the brain. In the telencephalon amygdala, septal area striatum and the mitral cells are of comparatively high activity. The neurosecretory neurons of the hypothalamus are particularly rich in this enzyme. As an anurans the cholinergic fasciculus retroflexus as asymmetric. The tectum opticum is of secondary simplicity and does not exhibit a clearly recognizable stratification.

Acetylcholinesterase↗
PubMed1980

[Cytologic and ultrastructural organization of the kidney tubules of certain amphibia].

As the investigation performed demonstrated, there is no principle differences in cytological organization in kidneys of five species of Amphibia whose mode of life to a certain extent is connected with water environment. Nevertheless, in different species epithelium of proximal parts of nephrons demonstrates various intensity of apocrinic secretion. Granules situating in the supranuclear zone of the epithelial cells of these parts are, in fact, autophagic lysosomes, their function is evidently connected with both lysis of the absorbed proteins and with autolysis of the apical cellular part in the process of secretion. The epithelial cytoplasm in the distal part of the nephron is characterized by a high succinate dehydrogenase activity; it is connected with its main function--osmoregulation. There are dark and light cells, resembling those in higher vertebrates, in the connecting part and in the collecting tubes. Ultrastructural organization of the brown frog nephron cells has much in common with that of epithelium of the secondary kidney urinary canaliculi.

Animals↗
PubMedDate not supplied

Effects of carcinogens on regenerating and non-regenerating limbs in amphibia (review).

The effects of chemical carcinogens on regenerating and non-regenerating limbs in amphibia are reviewed. The regeneration-competent tissues show a remarkable resistance to chemical carcinogenesis. However, chemical carcinogens can induce teratogenesis when they are administered to the regeneration blastema, while normal differentiation occurs in limited cases when they are administered to the intact limbs. The regenerative capacity may be considered as the deterrent to neoplasia in these tissues.

Abnormalities, Drug-Induced↗
PubMed1983

[Experimental anatomic study of the topography of the retinofugal projections in Discoglossus pictus (Amphibia, Anura). I. The thalamus: re-examination of the contralateral retinotopy and the origin of the uncrossed optic fibers].

The topography of retinofugal projections on the thalamus of an Anuran Amphibia was studied by Fink-Heimer technique. After small lesions in retina, degeneration was found in all contralateral neuropils and in one or several ipsilateral neuropils according to retinal location: A lesion in temporal retina is followed by large axonal degeneration in neuropil of Bellonci; a dorsal lesion invaded whole geniculate neuropil while within it, contralateral ventral and nasal projections are scarce. Ipsilaterally, excepted for the nasal retina, all territories project to anterior neuropils; but, only temporal fibres ended in ipsilateral pretectal neuropil. The incinate neuropil receives bilateral projections from the whole retina. This study shows that, rather than a strict segregation, an overlap of quadratic projections into the same neuropil and a divisional repartition of these projections between the two anterior neuropils seem to be the rule.

Animals↗