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At least 19 recordsLinked to original sources

PubMed2001

Neuroendocrine-immune system interactions in amphibians: implications for understanding global amphibian declines.

Amphibians are ancient creatures valued by biologists and naturalists around the world. They share with all other vertebrates a complex neuroendocrine system that enables them to flourish in a variety of aquatic and semiaquatic environments. Studies from a number of laboratories have demonstrated that the immune system of amphibian species is nearly as complex as that of mammals. Yet for reasons that are not well understood, amphibian species are facing greater survival challenges than in the recent past. This article will review our current understanding of the neuroendocrine immune system interactions in amphibians and address the question of whether environmental stressors may contribute to immunosuppression and amphibian declines.

Amphibians↗

PubMed1995

Possible interrelations among environmental toxicants, amphibian development, and decline of amphibian populations.

Many amphibian populations are declining in a number of geographical locations throughout the world. In most cases, the cause or causes are unknown, but are assumed to result from man-made alterations in the environment. We review existing evidence concerning how environmental xenobiotics could contribute to declines of amphibian populations by impacting growth and development of the young. This paper examines the potential roles of toxicants in: a) affecting the susceptibility of young to disease; b) retarding growth and development of amphibian young; c) affecting the ability of larvae to avoid predation; d) affecting the development of physiological, morphological, or behavioral processes in a manner that subsequently impairs the ability of the young for future reproduction; and e) directly causing mortality of young. These issues are not well studied, and more studies are needed before the roles of environmental xenobiotics in amphibian declines are fully understood.

Ambystoma↗

PubMed1982

Amphibian organ culture in experimental toxicology: the effects of paracetamol and phenacetin on cultured tissues from urodele and anuran amphibians.

Organ cultures of various tissues from urodele amphibians deacetylate paracetamol to p-aminophenol, which polymerises to form a brown precipitate. Paracetamol addition results in a loss of glycogen and lactate dehydrogenase (LDH) from urodele liver cultures and an increase in glucose release, and in LDH loss from kidney cultures. Organ cultures from anuran amphibians are unable to metabolise paracetamol and are not affected by its presence in the culture medium. The addition of unpolymerised p-aminophenol resulted in a loss of LDH from urodele and anuran organ cultures, whilst the addition of polymerised p-aminophenol had no such effects. This suggests that the toxic effects which follow the addition of paracetamol to urodele organ cultures are caused by unpolymerised p-aminophenol, a known toxicant in mammals. Cultures from both urodele and anuran amphibians are able to deacetylate phenacetin to p-phenetidine, but p-phenetidine was found to be much less toxic to amphibian tissues than p-aminophenol, causing LDH loss from kidney cultures only at very high dose levels.

Acetaminophen↗

PubMed2002

Assessment of the risk of solar ultraviolet radiation to amphibians. II. In situ characterzation of exposure in amphibian habitats.

Ultraviolet B (UVB) radiation has been hypothesized as a potential cause of amphibian population declines and increased incidence of malformations. Realistic studies documenting UV irradiance or dose have rarely been conducted in wetlands used by amphibians. Our data indicates that 99% of UVB is attenuated in the top 5-20 cm of wetlands in our study region (northern Minnesota and Wisconsin). Furthermore, vegetation and other habitat features have substantial impacts on local UVB irradiance levels and dose. UVB attenuation in the water columns of our wetlands is controlled by the specific absorption of dissolved organic carbon (DOC), and consequently, UVB attenuation is best predicted by simple laboratory absorbance measurements such as bulk water color (absorbance at 440 nm) or wavelength-specific absorbance coefficients. Seasonal data indicate thatthe UVB absorption by early and mid-season DOC is higher than that of late summer and fall DOC, suggesting increased protection from UVB during the potentially sensitive stages of amphibian development. In addition to dissolved components, our model indicates that suspended solids play a small role in UVB attenuation in our wetlands but apparently only at high concentrations. Models predicting UV attenuation in wetlands should be used cautiously and should consider temporal variability, given the volatility and dynamic nature of water column characteristics in wetlands. Organism behavior is a critical but poorly understood phenomenon that must be addressed for development of an accurate UV exposure risk model for amphibians.

Absorption↗

PubMed2005

Analyzing the radiation of the melanocortins in amphibians: cloning of POMC cDNAs from the pituitary of the urodele amphibians, Amphiuma means and Necturus maculosus.

Proopiomelanocortin (POMC) cDNAs were cloned and sequenced from brain extracts of two species of urodele amphibians: Amphiuma means and Necturus maculosus. Although the two species of urodele amphibians belong to separate families, and do not share a direct common ancestor, the level of primary sequence identity for the open reading of the POMC cDNAs was 90% at the amino acid level and 79% at the nucleotide level. It appears that the POMC gene in these urodele amphibians has been accumulating mutations at the amino acid level at a slower rate than the POMC gene in other sarcopterygian orders.

Amino Acid Sequence↗

PubMed2000

Organization of proenkephalin in amphibians: cloning of a proenkephalin cDNA from the brain of the anuran amphibian, Spea multiplicatus.

Cloning of a proenkephalin cDNA from the pelobatid anuran amphibian, Spea multiplicatus, provides additional evidence that Leu-enkephalin, although present in the brain of anuran amphibians, is not encoded by the proenkephalin gene. The S. multiplicatus proenkephalin cDNA is 1375 nucleotides in length, and the open reading frame contains the sequences of seven opioid sequences. There are five copies of the Met-enkephalin sequence, as well as an octapeptide opioid sequence (YGGFMRNY) and a heptapeptide opioid sequence (YGGFMRF). In the proenkephalin sequence of S. multiplicatus the penultimate opioid is a Met-enkephalin sequence rather than the Leu-enkephalin present in mammalian sequences. The same order of opioid sequences also is observed for the proenkephalin sequence of the pipid anuran amphibian, Xenopus laevis. Hence, from a phylogenetic standpoint the organization of tetrapod proenkephalin has been remarkably conserved. What remains to be resolved is whether the Leu-enkephalin sequence found in mammalian proenkephalin is an ancestral trait or a derived trait for the tetrapods. Unlike the proenkephalin precursor of X. laevis, all of the opioid sequences in the S. multiplicatus proenkephalin cDNA are flanked by paired-basic amino acid proteolytic cleavage sites. In this regard the proenkephalin sequence for S. multiplicatus is more similar to mammalian proenkephalins than the proenkephalin sequence of X. laevis. However, a comparison of the proenkephalin sequences in human, X. laevis, and S. multiplicatus revealed several conserved features in the evolution of the tetrapod proenkephalin gene. By contrast, a comparison of tetrapod proenkephalin sequences with the partial sequence of a sturgeon proenkephalin cDNA indicates that the position occupied by the penultimate opioid sequence in vertebrate proenkephalins may be a highly variable locus in this gene.

Amino Acid Sequence↗

PubMed2005

Comparative study of the comet assay and the micronucleus test in amphibian larvae (Xenopus laevis) using benzo(a)pyrene, ethyl methanesulfonate, and methyl methanesulfonate: establishment of a positive control in the amphibian comet assay.

The present investigation explored the potential use of the comet assay (CA) as a genotoxicity test in the amphibian Xenopus laevis and compared it with the French standard micronucleus test (MNT). Benzo[a]pyrene (B[a]P), methyl methanesulfonate (MMS), and ethyl methanesulfonate (EMS) were used as model compounds for assessing DNA damage. Damage levels were measured as DNA strand breaks after alkaline electrophoresis of nuclei isolated from larval amphibian erythrocytes using the CA in order to establish a positive control for further ecotoxicological investigations. The results led to the selection of MMS as a positive control on the basis of the higher sensitivity of Xenopus laevis to this compound. The CA and MNT were compared for their ability to detect DNA damage with the doses of chemical agents and exposure times applied. EMS and MMS were shown to increase micronucleus and DNA strand break formation in larval erythrocytes concurrently. However, B[a]P increased micronucleus formation but not that of DNA strand breaks. Time-dose experiments over 12 days of exposure suggest that the CA provides an earlier significant response to genotoxicants than does the MNT. In Xenopus the CA appears to be a sensitive and suitable method for detecting genotoxicity like that caused by EMS and MMS. It can be considered a genotoxicity-screening tool. The results for B[a]P show that both tests should be used in a complementary manner on Xenopus.

Animals↗

PubMed1992

Gastrin-releasing peptide (GRP) is not mammalian bombesin. Identification and molecular cloning of a true amphibian GRP distinct from amphibian bombesin in Bombina orientalis.

On the basis of structural homology and similar biological activity, gastrin-releasing peptide (GRP) has been considered the mammalian equivalent of amphibian bombesin. In this paper we now show this to be incorrect. Chromatography of frog (Bombina orientalis) gut extracts demonstrated two peaks of bombesin-like immunoreactivity (BLI), one similar in size to GRP and one similar in size to amphibian bombesin. These peaks were purified by high pressure liquid chromatography then subjected to mass spectrometric analyses to determine molecular weights and amino acid sequence. Based on the amino acid sequence of the lower molecular weight BLI species, a mixed oligonucleotide probe was prepared and used to screen a B. orientalis stomach cDNA library. Sequence analysis showed that all hybridizing clones encoded a 155-amino acid protein homologous to the mammalian GRP precursor. The mass spectra of the high and low molecular weight peaks of frog gut BLI were consistent with their origin from the processing of the frog GRP (fGRP) precursor into GRP-29 and GRP-10, just like the processing of the rat GRP precursor. Sequence homology showed that the fGRP precursor is more homology showed that the fGRP precursor is more closely related to the mammalian GRP precursors than to either the frog bombesin or frog ranatensin precursors. Northern blot analysis showed that fGRP is encoded by a mRNA of 980 bases, clearly different from the 750-base mRNA which encodes frog bombesin. Northern blot analysis and in situ hybridization showed fGRP mRNA in frog brain and stomach and bombesin mRNA in frog skin, brain, and stomach. That frogs have independent genes for both GRP and bombesin raises the possibility that mammals have an as yet uncharacterized gene encoding a true mammalian bombesin.

Amino Acid Sequence↗

PubMed1985

Active peptides from amphibian skin are also amphibian neuropeptides.

Immunohistochemical data on several newt brain areas showed a heterogeneous system of neuronal elements, immunopositive for antisera specifically directed to different antigenic determinants of tachykinin molecules. Acid extracts of newt brain areas were immunopositive for substance P with an antibody specific for the COOH-terminal (tachykinin determinant) and exhibits an elution profile by gel filtration characteristic to substance P. Bombesin-like immunoreactivity was demonstrable both by immunohistochemistry (fibers and cell bodies in forebrain and hypothalamic areas) and by radioimmunoassay, using an antiserum specific for the mid-region of the molecule. This immunoreactivity was separated into two peaks by gel filtration chromatography. Sauvagine-like material was detected by immunohistochemistry in newt hypothalamus as a loose preoptic cell system and as a thin fiber layer in the outer zone of the median eminence. Double staining procedures demonstrate that sauvagine and CRF are spatially closely related but separable in both the preoptic area and in the median eminence. This data on the presence of several amphibian skin peptides in the CNS of the newt suggests their possible role as neuropeptide.

Amphibian Proteins↗

PubMed1985

Amphibian lymphokines: 2. Migration inhibition factor produced by antigenic and mitogenic stimulation of amphibian leucocytes.

Migration of Rana temporaria peritoneal exudate cells (PEC) was examined in vitro using both direct and indirect assay systems. After sensitization in vivo followed by in vitro challenge 7-21 days later with the appropriate sensitizing antigen, spleen cell culture supernatants were obtained which inhibited the normal in vitro migration of PEC from non-sensitized animals. Cultures of spleen cells with mitogen also gave rise to supernatants with migration inhibitory properties. Sephadex separation of supernatants showed that maximum inhibitory activity was present in the 27-50,000 MW range and, furthermore, that this inhibition was blocked by alpha-L-fucose, but not by beta-D-galactose. The inhibition did not appear to be species specific. The results indicate that following appropriate stimulation amphibian leucocytes produce a soluble, migration inhibition factor (MIF) with characteristics similar to those described for the mammalian lymphokine MIF.

Animals↗

PubMed1990

Additional records of nematode parasites from Papua New Guinea amphibians with a list of recorded endohelminths by amphibian hosts.

An examination of a small sample of four species of frogs (Cophixalus riparius, Phrynomantis humicola, Ph. stictogaster, Ph. wilhelmana) from Papua New Guinea yielded altogether 5 species of nematodes, 2 of them being new to science. These include: Cosmocercella phrynomantisi sp. n. (type host Ph. humicola), Spinicaudinae gen. sp., Parathelandros andersoni sp. n. (type host C. riparius), Oswaldocruzia bakeri, and Paracapillaria spratti. C. phrynomantisi sp. n. differs from congeneric species mainly in the length of spicules (0.180 mm) and the character, arrangement and number of caudal papillae in the male, while P. andersoni sp. n. is characterized mainly by the presence of four well developed spines on the male tail. Pseudocapillaria spratti is redescribed in detail and it is transferred to Paracapillaria as P. spratti (Moravec et Sey, 1986) comb. n. Capillaria combesi Chabaud et Knoepffler, 1985 is transferred to Amphibiocapillaria Moravec, 1982 and Capillaria petiti Justine et Bain, 1987 to Pseudocapillaria Freitas, 1959. A survey of the endohelminths (excluding Hirudinea) hitherto reported from New Guinea amphibians is presented.

Animals↗

PubMed1972