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PubMed1992

Prey-catching and predator-avoidance in frog and toad: defining the schemas.

The present model postulates the construction of motor actions through the interaction of different motor schemas via a process of competition and co-operation wherein there is no need for a unique schema to win the competition (although that might well be the result) since two or more schemas may simultaneously be active and co-operate to yield a more complicated motor pattern. Based on lesion data, our model is structured on the principles of segregation of co-ordinate systems and participation of maps intermediate between sensory and motor schemas. The motor schemas are driven by specific internal maps which between them constitute a distributed internal representation of the world. These maps collectively provide the transition from topographically-coded sensory information to frequency-coded inputs to the diverse motor schemas that drive muscle activity. We stimulate data on approach and avoidance behavior of the frog or toad under normal conditions and under lesion of different brain centers. For example, the model generates different motor zones for prey-catching behavior which match those observed experimentally in normal conditions and in the medullary hemifield deficit, and offers predictions for new experiments on both approach and avoidance behaviors.

Animals↗
PubMed1995

Rhythmic electrical and mechanical activity in stomach of toad and frog.

Rhythmic slow spikes and contractions at 2-5/min occur in frog/toad stomach when longitudinal muscle is present, not in the circular layer after removal of the longitudinal layer. Interstitial cells of Cajal occur in frog stomach in the longitudinal layer and in toad stomach mainly in the longitudinal layer, with some between layers. They were identified by staining with methylene blue, the fluorescent dye rhodamine 123, toluidine blue, and by electron microscopy. Interstitial cells resemble in ultrastructure those observed in mammalian intestine by small cell diameter, long processes forming a network, large nuclei, mitochondria, caveolae, endoplasmic reticulum, and absence of fibrillae. Rhythmic activity in stomachs stained with methylene blue is abolished by bright illumination. Rhythmic slow spikes and contractions are reduced and frequency is lowered when Ca2+ concentration in the medium is significantly decreased; in high Ca2+ these functions are increased. Threshold concentration of Ca2+ for maintaining slow spikes was between 10(-7) and 10(-6) M Ca2+. Ba2+ and 2.5 mM increases slow spike frequency and amplitude; Ba2+ increases contractions proportionately more than spikes. Slow spikes are reduced or blocked by verapamil, nifedipine, and Cd2+ and are enhanced by BAY K 8644. Quaternary ammonium compounds tetraethylammonium and tetrapentyl-ammonium bromide prolong slow spikes and enhance contractions. Replacement of NaCl by LiCl, methyl glutamine, or treatment with amiloride reduces slow spike amplitude and to a lesser extent frequency. This indicates efflux of Ca2+ by Na+/Ca2+ exchange. Contractions, but not spikes, are reduced by the calmodulin blocker trifluoroperazine. Contractions are enhanced, but slow spikes are not altered by ouabain. This suggests retention of Ca2+ when a tonic Na+/K+ pump is blocked. A model for rhythmicity includes influx of Ca2+ via L-channels, repolarization by IKCa2+, efflux of Ca2+ by Na+/Ca2+ exchange, and efflux of Na+ by a Na+/K+ pump. Frequency is determined by rate constants for both influx and efflux of Ca2+.

Animals↗
PubMed2005

Acanthocephalans from some frogs and toads (Anura) and chameleons (Squamata) from Tanzania with the description of a new species.

The following Acanthocephala, all Echinorhynchidae, were found on examination of 229 amphibians and 191 reptiles collected in the Eastern Arc Range, Tanzania: Acanthocephalus bufonis from the frogs Arthroleptis stenodactylus and Arthroleptides martiensseni, the toad Nectophnyroides viviparous, and the chameleon Rhampholeon brevicaudatus; Pseudoacanthocephalus betsileo from the frogs Probreviceps macrodactylus and Ptychadero anchietae; and Pseudoacanthocephalus rhampholeontos n. sp. from the chameleons Rhampholeon sp. and Rhampholeon uluguruensis. Pseudoacanthocephalus rhampholeontos differs from the only other acanthocephalan occurring in chameleons, Pseudoacanthocephalus bigueti, in being a larger worm with fewer, smaller hooks in the proboscis armature. The status of the Acanthocephalus and Pseudoacanthocephalus is still problematic and requires further attention and study.

Acanthocephala↗
PubMed1998

Noxious toads and frogs of South Africa.

The major defence mechanism in frogs in via the secretion of toxins from their skin. In humans, intoxication may occur when part of the amphibian integument is ingested, as in the form of herbal medicines. Two groups of South African frogs have skin secretions that are potentially lethal to humans and animals. Toads (Bufo and Schismaderma species), the amphibians with which man and his pets most frequently have contact, secrete potent toxins with cardiac glycoside activity. Topical and systemic intoxication, while seen in humans, remains predominantly a veterinary problem. Intoxication by the red-banded rubber frog, which secretes an unidentified cardiotoxin, is far less common. The probable mechanisms of intoxication and management of a poisoned patient are discussed.

Animals↗
PubMed2000

Amphibian respiratory diseases.

This article describes the diseases that commonly affect the lungs, gills, and nasal passages of frogs, toads, and salamanders. Although these organs often are affected by systemic infections, only diseases that are limited to the respiratory system are discussed. Gills of aquatic amphibians commonly are affected by poor water quality, infestations by protozoa or trematodes, or infections by water molds. Nematodes in the genus Rhabias are significant pulmonary pathogens in frogs and toads. The nasal passages of frogs, toads, and salamanders may be parasitized by Bufolucilia fly larvae.

Amphibians↗
PubMed1997

Response of frog and toad skin to norepinephrine.

Maintenance of a hydrated integument is essential to the normal function of amphibian skin, and amphibians have developed mechanisms to minimize cutaneous dessication. The present work was conducted on skins of amphibians exhibiting a clear preference for either of two such mechanisms to study the influence of such mechanisms on the characteristics of epithelial transport. The response to norepinephrine (NE) was studied in isolated skins of a semiaquatic frog (Leptodactylus chaquensis), known to maintain indispensable skin moisture by secreting a superficial film of mucus via sympathetic stimulation of skin glands, and a terrestrial toad (Bufo arenarum), which replenishes a superficial film of fluid by drawing soil water upward by capillarity. In L. chaquensis skin, NE 5.0 x 10(-7) M, induced slow onset, sustained increases in short-circuit current (SCC) and transepithelial conductance, which were abolished by amiloride, a specific sodium transport inhibitor. At 1.2 x 10(-5) M, the response to NE exhibited a faster onset and a shorter time course. The SCC response also became insensitive to amiloride and could thus be induced by exposing the skin to NE in the presence of the inhibitor. The response was also greatly reduced in the absence of chloride, strongly suggesting a greater dependence on the glandular secretory response. In B. arenarum skin, the response to NE was far more sensitive to amiloride, regardless of the concentration of NE used. Induction of a response in the amiloride-blocked skin required a 10-fold higher concentration of NE, and the resulting effect was still considerably smaller than that observed in the skin of L. chaquensis after the same treatment. The number of mucous glands per unit area in B. arenarum skin was found to be around one-fifth of that observed in L. chaquensis, thus in part explaining the difference in the magnitude of the responses. The response of the skin of L. chaquensis to NE in the presence of sulfate was found to be consistent with the postulated involvement of frog skin glands in sulfate excretion. In contrast, this function was not evident in the skin of B. arenarum. The pattern of response of B. arenarum skin to all concentrations of NE tested closely resembles that seen after exposure to agents known to activate a cyclic AMP-dependent, high-permeability Cl pathway previously described by us in the skin of the toad. Our observations underscore the physiological differences existing in skins from different species, particularly regarding the relative importance of the glandular component of transport.

Adrenergic Agonists↗
PubMed1980

Widespread occurrence in frogs and toads of skin compounds interacting with the ouabain site of Na+, K+-ATPase.

Amphibians of the family Bufonidae contain high levels of skin compounds that both inhibit Na+- and K+-dependent adenosinetriphosphatase and antagonize the binding of ouabain to the enzyme. In species of Bufo and Atelopus, these compounds are relatively nonpolar bufodienolides, whereas Dendrophryniscus and Melanophryniscus contain more polar compounds of unknown structure. Skin extracts from 30 of 48 species of frogs representing an additional eight families contained relatively low levels of compounds that inhibit binding of ouabain to Na+,K+-adenosinetriphosphatase. The widespread occurrence of low levels of inhibitory compounds is consonant with the role for these compounds as physiological regulators of Na+,K+-adenosinetriphosphatase in amphibian skin; high levels in the Bufonidae probably also serve as a defense against some predators.

Animals↗
PubMed1998

Rhodopsins from three frog and toad species: sequences and functional comparisons.

The frequency of thermal 'dark events' in the membrane current of rhodopsin rods of the bullfrog, Rana catesbeiana, is considerably lower than observed in rods of two toad species, even though all three rhodopsins have approximately the same absorbance characteristics. In order to map amino acid substitutions possibly associated with thermal stability in the genus Rana, the cDNA's coding for the rhodopsins of Bufo bufo, B. marinus and R. temporaria were sequenced and the conceptually translated protein sequences aligned to the previously sequenced rhodopsins of R. catesbeiana, R. pipiens and Xenopus laevis. Across the six anuran species studied, there are sixteen non-conserved substitutions and six changes that include gain or loss of a hydroxyl group. Serine or threonine at position 220 is unique to the three Rana species, phenylalanine at position 270 is unique to all three Ranas and to X. laevis, and phenylalanine at position 274 is unique to both species of the genus Bufo. This investigation produces a list of substitutions that are candidates for future studies of thermal stability. In addition, a number of amino acids are identified that apparently do not influence absorbance characteristics, at least not cumulatively.

Amino Acid Sequence↗
PubMed1987

In vivo generation of 5-lipoxygenase products in frogs and toads.

Eicosanoid production by inflammatory cells which resulted from infection of the peritoneal cavity of Rana catesbeiana and Bufo americanus was studied after addition of exogenous arachidonic acid and for metabolites generated in vivo. From exogenous substrate, the cells of Rana catesbeiana produced substantial amounts of 5-hydroxyeicosatetraenoic acid, leukotriene B4, the non-enzymatic isomers of leukotriene B4 and leukotriene C4. From endogenous substrate, 5-hydroxyeicosatetraenoic acid and leukotriene B4 were produced. Cells from Bufo americanus produced leukotriene B4 and 5-hydroxyeicosatetraenoic acid, from both exogenous and endogenous substrate. These observations of in vivo eicosanoid production confirm the participation of 5-lipoxygenase activity in the inflammatory response to infection.

Animals↗
PubMed2002

Frogs and toads in front of a mirror: lateralisation of response to social stimuli in tadpoles of five anuran species.

Tadpoles of five anuran species were tested for preferences in the use of the eyes during inspection of their own visual image in a mirror. When tested in a tank with several small mirrors, tadpoles of five different species (Bufo bufo, Bufo viridis, Rana temporaria, Rana esculenta, Bombina variegata) preferentially approached and positioned themselves with the mirror located on their left side, thus looking at the image with the monocular field of their left eye. Similar results were obtained with tadpoles of R. temporaria tested in a simple task in which they had to choose approaching one or other of two large mirrors located on their left and right side. Control experiment showed that the behavioural asymmetry was not due to motor preferences and that it was independent of morphological asymmetries in the positions of the spiracles. This is the first demonstration of a functional visual lateralisation among juvenile amphibia before metamorphosis.

Animals↗