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PubMed1988

Biosynthesis and function of melanins in hepatic pigmentary system.

In this report we show the most important results obtained from our study of the pigment liver cells of Amphibia and Reptilia. Contrary to the cutaneous pigment cells that derive from the neural crest, the liver pigment cells, instead, derive from the Kupffer cells: this can be seen from the results obtained from labelled precursor incorporation experiments, not only in vivo but also in vitro, using surviving liver slices or isolated melanosomes. Chemical analysis of both liver and cutaneous melanosomes reveal a great difference in their chemical composition, and this is in agreement with the different origins of these cells. We therefore propose that: liver pigment cells of Amphibia and Reptilia should be classified as "Extra Cutaneous Pigment Cells from Histocytic Origin". As regards the function of melanins, we show that O2 is trapped by these substances. Moreover, in my laboratory we have shown in several animal species, that the superoxide dismutase activity is inversely proportional to the quantity of melanin present; thus, we think that melanin could mime SOD activity.

Animals↗
PubMed2004

Micropuncture: unlocking the secrets of renal function.

This essay looks at the historical significance of five APS classic papers that are freely available online: Wearn JT and Richards AN. Observations on the composition of glomerular urine, with particular reference to the problem of reabsorption in the renal tubules. Am J Physiol 71: 209-227, 1924 (http://ajplegacy.physiology.org/cgi/reprint/71/1/209). Richards AN and Walker AM. Methods of collecting fluid from known regions of the renal tubules of Amphibia and of perfusing the lumen of a single tubule. Am J Physiol 118: 111-120, 1936 (http://ajplegacy.physiology.org/cgi/reprint/118/1/111). Walker AM and Hudson CL. The reabsorption of glucose from the renal tubule in Amphibia and the action of phlorhizin upon it. Am J Physiol 118: 130-143, 1936 (http://ajplegacy.physiology.org/cgi/reprint/118/1/130). Walker AM and Oliver J. Methods for the collection of fluid from single glomeruli and tubules of the mammalian kidney. Am J Physiol 134: 562-579, 1941 (http://ajplegacy.physiology.org/cgi/reprint/134/3/562). Walker AM, Bott PA, Oliver J, and MacDowell MC. The collection and analysis of fluid from single nephrons of the mammalian kidney. Am J Physiol 134: 580-595, 1941 (http://ajplegacy.physiology.org/cgi/reprint/134/3/580).

Absorption↗
PubMed1993

Two molecular forms of gonadotropin-releasing hormone from the brain of the frog, Rana ribibunda: purification, characterization, and distribution.

The molecular forms of GnRH in amphibia have not been characterized structurally. An antiserum to mammalian GnRH that shows appreciable cross-reactivity with chicken GnRH-I ([Gln8]GnRH), chicken GnRH-II ([His5,Trp7,Tyr8]GnRH), and salmon GnRH ([Trp7, Leu8]GnRH) was used in a RIA to detect GnRH-related peptides in an extract of the brain of the European green frog, Rana ridibunda. Two peptides were purified to apparent homogeneity, and determination of their primary structures showed that they are identical to mammalian GnRH and chicken GnRH-II. Salmon GnRH and lamprey GnRH-I ([Tyr3,Leu5,Glu6,Trp7,Lys8]GnRH) were not identified in this species of frog. Immunocytochemical analysis using specific antisera has identified regions of the frog diencephalon and telencephalon in which chicken GnRH-II and mammalian GnRH are localized to different populations of neurons. This differential distribution suggests distinct physiological roles for the two forms of GnRH in amphibia.

Animals↗
PubMed1992

Characterization of the genomic corticotropin-releasing factor (CRF) gene from Xenopus laevis: two members of the CRF family exist in amphibians.

In mammals, the release of pituitary ACTH is stimulated by CRF. Two related peptides exist in nonmammalian vertebrates, sauvagine from frog skin and urotensin-I from the urophysis of teleost fish. Their related structures (approximately 50%) and capacity to stimulate the release of ACTH from mammalian and fish pituitaries has led to the proposal that sauvagine and urotensin-I are homologs of mammalian CRF. However, sauvagine does not appear to stimulate ACTH release in amphibians, although mammalian CRF (ovine) induces a potent response from amphibian pituitaries. This could indicate that the main function of sauvagine does not involve ACTH regulation and suggests that an additional CRF-like peptide exists in Amphibia. We report here the isolation of two highly homologous CRF-like genes from the frog, Xenopus laevis. Analysis of the expression pattern of these CRF-like genes revealed mRNA in splenic tissue and in the preoptic nucleus and paraventricular organ of the brain. The amino acid sequence of the mature peptide regions (1-41) of both X. laevis genes is strikingly conserved, sharing more than 93% homology with mammalian CRFs, yet only 50% homology with sauvagine. In view of the fact that these new amphibian CRF-like genes share far greater homology with mammalian CRF than that exhibited by sauvagine, we propose that the new Xenopus CRF-like genes are the amphibian counterparts to mammalian CRF. Thus, two members of the CRF family have now been identified in the Amphibia, namely CRF and sauvagine.

Amino Acid Sequence↗
PubMed1988

Somitomeres: mesodermal segments of vertebrate embryos.

Well before the somites form, the paraxial mesoderm of vertebrate embryos is segmented into somitomeres. When newly formed, somitomeres are patterned arrays of mesenchymal cells, arranged into squat, bilaminar discs. The dorsal and ventral faces of these discs are composed of concentric rings of cells. Somitomeres are formed along the length of the embryo during gastrulation, and in the segmental plate and tail bud at later stages. They form in strict cranial to caudal order. They appear in bilateral pairs, just lateral to Hensen's node in the chick embryo. When the nervous system begins to form, the brain parts and neuromeres are in a consistent relationship to the somitomeres. Somitomeres first appear in the head, and the cranial somitomeres do not become somites, but disperse to contribute to the head the same cell types contributed by somites in the trunk region. In the trunk and tail, somitomeres gradually condense and epithelialize to become somites. Models of vertebrate segmentation must now take into account the early presence of these new morphological units, the somitomeres. Somitomeres were discovered in the head of the chick embryo (Meier, 1979), with the use of stereo scanning electron microscopy. The old question of whether the heads of the craniates are segmented is now settled, at least for the paraxial mesoderm. Somitomeres have now been identified in the embryos of a chick, quail, mouse, snapping turtle, newt, anuran (Xenopus) and a teleost (the medaka). In all forms studied, the first pair of somitomeres abut the prosencephalon, but caudal to that, for each tandem pair of somitomeres in the amniote and teleost, there is but one somitomere in the amphibia. The mesodermal segments of the shark embryo are arranged like those of the amphibia.

Animals↗
PubMed1999

Effects of endocrine-disrupting contaminants on amphibian oogenesis: methoxychlor inhibits progesterone-induced maturation of Xenopus laevis oocytes in vitro.

There is currently little evidence of pollution-induced endocrine dysfunction in amphibia, in spite of widespread concern over global declines in this ecologically diverse group. Data regarding the potential effects of endocrine-disrupting contaminants (EDCs) on reproductive function in amphibia are particularly lacking. We hypothesized that estrogenic EDCs may disrupt progesterone-induced oocyte maturation in the adult amphibian ovary, and tested this with an in vitro germinal vesicle breakdown assay using defolliculated oocytes from the African clawed frog, Xenopus laevis. While a variety of natural and synthetic estrogens and xenoestrogens were inactive in this system, the proestrogenic pesticide methoxychlor was a surprisingly potent inhibitor of progesterone-induced oocyte maturation (median inhibitive concentration, 72 nM). This inhibitory activity was specific to methoxychlor, rather than to its estrogenic contaminants or metabolites, and was not antagonized by the estrogen receptor antagonist ICI 182,780, suggesting that this activity is not estrogenic per se. The inhibitory activity of methoxychlor was dose dependent, reversible, and early acting. However, washout was unable to reverse the effect of short methoxychlor exposure, and methoxychlor did not competitively displace [3H]progesterone from a specific binding site in the oocyte plasma membrane. Therefore, methoxychlor may exert its action not directly at the site of progesterone action, but downstream on early events in maturational signaling, although the precise mechanism of action is unclear. The activity of methoxychlor in this system indicates that xenobiotics may exert endocrine-disrupting effects through interference with progestin-regulated processes and through mechanisms other than receptor antagonism.

Animals↗
PubMed1992

[Sparganosis in some Brazilian vertebrates. Difficulties in the identification of Luheella (Spirometra) species].

Some species of Amphibia and Reptilia are listed as new hosts of spargana, from material deposited in the Helminthological Collection of Oswaldo Cruz Institute. It is discussed the difficulties in identifying the larvae (Sparganum) and also the identification of adults of Luheella species from South America. The histopathology induced by spargana in the liver of a species of Amphibia is briefly described.

Amphibians↗
PubMed2002

Lymph heart scintigraphy in the toad.

To our knowledge, there are no reports on the use of radionuclide labeled agents to image the lymphatic system of anuran amphibia. Lymphoscintigraphy was performed in 18 toads Bufo marinus L, after the injection of Tc-99m-serum albumin within the ventral lymph sac. Images were obtained with a rectilinear scanner immediately after tracer administration. Scintigrams were digitalized and densitometric profiles were obtained. One or more lymph hearts were demonstrated on all 18 scans. Scintigrams showed the four lymph hearts functioning simultaneously in only 17% of the toads. Lymphoscintigraphy with Tc-99m serum albumin is useful to study the movement of lymph from the lymph sacs or to study the function of lymph hearts in amphibia.

Animals↗
PubMed1976

[Comparison of the histochemical bases of epidermis differentiation in vertebrates].

It was been shown that in the line of forms of amphibia, reptiles, mammals, including man, the histochemical differentiation of the epidermis is related with changes in protective and transitory zones. For instance, in amphibia the accomodation to the terranian medium is accompanied by establishment of the vertical histochemical gradient in the epidermis which is manifested by accumulation of a protein rich in cationic and sulfhydril groups in the protective zone. The epidermis of reptiles is characterized by presence of high concentrations of a protein rich in cystine in the protective zone. The transient zone is formed on the border of the protective and germinative zones. The epidermis of mammals retains in general features the histochemical type of differentiation of the protective zone which had appeared in reptiles. However, the transient zone of the mammalian epidermis has a high concentration of proteins rich in histidine and arginin. The histochemical differentiation of the human epidermis is related with the distribution of the hairy integument.

Amphibians↗
PubMed1991

The transcription of DNA in chicken mitochondria initiates from one major bidirectional promoter.

Transcription start sites of chicken mitochondrial DNA have been mapped in the control region by direct sequencing of in vitro capped mitochondrial RNA species, by primer extension and by S1 nuclease protection analysis. Transcription of the heavy strand initiates predominantly at a site 156 nucleotides upstream of the tRNA(Phe) gene, i.e. about 135 nucleotides further upstream than the corresponding sites in amphibia and mammals. On the opposite strand, transcription starts predominantly one nucleotide removed from the site in the heavy strand. The L-strand position start site is similar to that found in other vertebrates. The chicken mitochondrial DNA control region thus contains one major transcriptional promoter, whose bidirectional capacity is similar to the situation in amphibia but which contrasts to the mainly unidirectional capacity of mammalian promoters. In chicken mitochondria, the sequence comprising the start sites is A + T rich and contains an almost perfect inverted repeat which can be folded into a cruciform structure. The heavy and light strand initiation sites are flanked on their respective 3' ends by an octanucleotide sequence matching those surrounding the start sites in Xenopus laevis (5'-ACPuTTATA-3'). This motif is found associated with the H-strand start sites in mouse but is not present in human nor bovine mitochondrial DNA promoters.

Animals↗
PubMed1990

[Organization of the osseous framework of the nasal septum and its homologues. IV-A. The vomero-transversalis and axial palatine systems (during fetal life of various ++pair-hoofed animals)].

The aim of this investigation was the differentiation and systematization of the vomer elements in ontogenesis and the comparison with axial palatal system in fishes and reptiles. The collection of pig heads (18 fetal, 10 young, 4 adults) and of cow heads (15 fetal, 6 young, 3 adults) was examined. The methodology was described elsewhere. It has been proved that vomer in ++pair-hoofed mammals as well as parasphenoid in fishes and amphibia, is not a single and uniform element of the skull ++ out a biochemically integrated system (systema vomero-transversale). It has been also proved that in examined ++ mammals as well as in fishes there exists a palato-axiale system. All these monominals elements in mammals, amphibia and +fishes are homologues.

Animals↗
PubMed1984

[Structural and functional characteristics of arteries and veins in the common frog].

Histochemical, electron-microscopic, pharmacological and physiological studies of structural and functional features of the frog blood vessels revealed a difference in the peripheral neural apparata of different vessels as expressed by different grades of the contractile responses to exogenous substances and electrical stimulation: the better innervated a vessel the better response is mediated by the alpha-adrenoreceptors. The beta-adrenoreceptors have only been found in innervated vessels. The data obtained suggest that vessels of amphibia are in general similar to vessels of vertebrates but the species specifics associated with behaviour and environment of animals determine a number of specific features in structural-functional organization of vessels. The diversity of structure and functioning of blood vessels found in amphibia attests a differentiation of mechanisms of vessel regulation in different areas of the vascular bed.

Acetylcholine↗
PubMed1983

[Precipitation reactions between secretory products in amphibian oviducts].

The existence of precipitin reactions between some molecules in egg jellies (oviduct secretions) of tailed amphibians (Amphibia caudata) has been demonstrated by double diffusion on agarose plates. These reactions do not exist in frogs and toads (Amphibia salientia). One precipitin reaction was related to compounds with a common molecular site of interaction for all A. caudata: all cross-species reactions were possible; a common antigenic rate has been shown. Another precipitin reaction, positively demonstrated in Pleurodeles waltl, probably exists in other A. caudata. The putative influence of these reactions on egg jelly-spermatozoon interactions has been discussed. An homology between these intra-egg jelly reactions and cortical granule content-egg jelly reactions in A. salientia has been suggested.

Amphibians↗
PubMed1983

[Effect of metavanadate on papillary water uptake].

It has been examined the influence of vanadium on the papillary osmotic water-salts uptake in order to differentiate it from water flow of other biological substrates as amphibia epithelia. Between the different vanadium compounds only the metavanadate is active and only after administration in the abdominal vein. The general influence of metavanadate is a facilitating one and concerns: electrical receptor afferent discharge, osmotic water uptake and ciliary motility. At the papillary level therefore vanadium is not at all an inhibitory agent as observed in many biological substrates. This observation rule out any analogy in the processes of water inflow operating respectively at the fungiform papillae and amphibia epithelia.

Animals↗
PubMedDate not supplied

[Brain proteolipids in representatives of different vertebrate classes].

The Folch-Lees proteolipid complexes of different purity (crude proteolipids and relative pure proteolipids) were isolated from vertebrate brain: mammalia (Macaca irus, Macaca rhesus and white rat), birds (Columbia livia), reptilia (Testudo horsfieldi), amphibia (Rana temporaria) and fishes (Salmo irideus). The proteolipid complexes were isolated by emulsion-centrifugation method. The content of proteolipid protein (mg/g w. w.) correlates with the level of phylogenetic development of the animals studied. It is the highest in monkey brain (10.5 and 8.6 mg/g) and the lowest in fish brain (2.2 mg/g). The yield of proteolipids from the brains of animals studied shows the same pattern. Crude proteolipids of mammalia, birds and reptiles contain 40-50% of protein and 60-50% of lipids. The content of phospholipids is about 40%. Proteolipids of amphibia and fish brain contain less protein--about 30%. In the conditions of mild purification, the protein content in mammalia, birds and reptilia makes up about 70% and lipid content--about 30-35%. The crude and purified proteolipids in all the animals studied (as compared with the original lipid extracts from which they were isolated) are enriched in acid phospholipids: phosphatidyl serine, phosphatidyl inositol and diphosphatidyl glycerol. Acid phospholipids in total lipid extract make up 10-20% of total phospholipids, in crude proteolipids 16-32 and in purified proteolipids--56-75%. There are no marked differences between fatty acid composition of phospholipids in proteolipids and in the same phospholipids isolated from total lipid extract.

Animals↗
PubMed1984

Different modes of pronephric duct origin among vertebrates.

It is possible to distinguish differences in pronephric duct morphogenesis by using scanning electron microscopy to observe the results of blocking, marking and grafting experiments as well as the normal course of development. Here we compare the mode of pronephric duct development in embryos representing three orders of vertebrates: birds (class, Aves; order, Gallus); frogs (class, Amphibia; order, Anura); and salamanders (class, Amphibia; order, Urodela). The axolotl (a urodele) pronephric duct is formed by the caudal extension of a solid stream of cells segregated below somites 2 through 7. During its migration, cells are rearranged so that a short, wide rudiment is extended to form a long, thin one of similar volume. The pronephric duct rudiment of Xenopus laevis (an anuran) shows no evidence of caudal migration. Rather, pronephric duct cells are segregated out in situ by the formation of a fissure which separates them from the lateral plate mesoderm over ten somite widths. The chick pronephric duct forms a part of the intermediate mesoblast that extends by a caudal migration which does not, however, involve extensive cell rearrangements. Instead, cells near the tip of the duct rudiment in the chick proliferate, extending the duct by true growth as well as by active cell locomotion.

Ambystoma↗
PubMed1978

[Comparative histochemical characteristics of the secretion of superficial gastric epitheliocytes].

Comparative histological investigation of the gastric pavement epitheliocytes in a number of species (amphibia, reptile, birds, mammals, man including) has demonstrated that in amphibia, protective function of the stomach is connected with the presence of a certain neutral carbohydrate component in its secrete. In reptiles, the barrier function is performed by the neutral carbohydrate component and sialosaccharides, in birds, besides the carbohydrates mentioned, sulphosaccharides, as well. Histochemical properties of the mammal stomach as a barrier are determined by phylogenetically dependent peculiarities of food specialization.

Animals↗
PubMed1978

[Ultrastructure of the oocyte nucleus and cytoplasm in the mollusk, Littorina saxatilis. I. The structure of the meiotic chromosomes and of the products of their activity in the period of great oocyte growth].

At the beginning of the early diplotene, the chromosomes are getting despiralized and are seen to be made of a mass of fibrous material and chromocentres. During previtellogenesis the chromosomes are made of fibrilles 4--20 nm in diameter. At the beginning of vitellogenesis nucleolus-like bodies are seen to appear on bivalents made of granules (25--30 nm) and fine fibrilles. At the same time, in association with chromosomes a structure of irregular form was observed made of granules 25--30 nm in diameter and a string 20 nm in diameter. This structure is analogous to granular loops of the lampbrush chromosomes of the amphibia. During the large growth of the oocyte perichromatin and interchromatin granules are seen in the nuclei. By the end of the large growth numerous protein spheres, formed by fibrilles 12--13 nm in diameter are seen on the chromosomes. It is concluded that chromosomes of the L. saxatilis oocytes function as the lampbrush chromosomes of the amphibia and other animals having the solitary type oogenesis.

Animals↗