Showing papers on "Toad published in 1990"
TL;DR: Steady-state analysis of the acid extracts of the intermediate pituitary of the toad, Bufo marinus, revealed the presence of multiple forms of beta-endorphin and alpha-MSH, indicating that the N-acetylation ofbeta-endomorphin andalpha- MSH occurs at distinct subcellular sites in intermediate pituitsary cells of anuran amphibians.
20 citations
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18 citations
TL;DR: IGF-I was produced for at least 72 hr when toad liver explants were cultured in serum-free medium, indicating that the liver is a source of IGF-I in anurans.
13 citations
Journal Article•
TL;DR: The toad direct-current electroretinogram recorded from a neural retina-RPE-choroid preparation differed from other amphibians and was more similar to responses recorded in reptiles, birds, and mammals.
Abstract: Electrophysiologic responses were recorded in vitro from the retina of the toad, Bufo marinus. In the isolated retinal pigment epithelium (RPE)-choroid preparation, a decrease in the K + concentration outside the apical membrane evoked a sequence of trans-epithelial (TEP) and membrane potential changes. A hyperpolarization originating at the RPE apical membrane that increased the TEP was followed by a delayed hyperpolarization originating at the basal membrane that decreased the TEP. This response sequence differed from the well-studied bullfrog RPE in exhibiting potentials generated at the basal membrane; it more closely resembleed responses from the reptilian and avian RPE. The toad direct-current electroretinogram recorded from a neural retina-RPE-choroid preparation also differed from other amphibians and was more similar to responses recorded in reptiles, birds, and mammals. In this initial study, the electrophysiologic characteristics of the RPE's Na + /K + pump were examined. Contrary to a previous report, ouabain, a specific inhibitor of the pump, depolarized the apical membrane and decreased the TEP. Ba 2+ was used to block apical K + conductance and unmasked a modulation of the Na + /K + pump by subretinal K + . Decreasing the K + concentration in the presence of Ba 2+ depolarized the apical membrane and decreased the TEP. These responses were blocked by ouabain, indicating that the K + concentration decrease slowed the Na + /K + pump. Invest Ophthalmol Vis Sci 31:2353-2360, 1990 The retinal pigment epithelium (RPE) consists of a single layer of cells whose apical membrane faces the neural retina and whose basal membrane faces the choroid. This report describes responses from the toad, Bufo marinus, and establishes the toad retina as a novel amphibian model. Two different RPE response patterns have been evoked by light stimulation of the vertebrate neural retina and recorded in the direct-current electroretinogram (DC-ERG), depending on the species. In fish and amphibians that have been studied previously (carp, eel, frog, and newt), the DC-ERG is relatively simple; after the aand b-waves of the ERG, the c-wave rises to a peak and then slowly decays toward the dark-adapted baseline. 1 ' 2 In reptiles, birds, and mammals, after the peak of the c-wave, there is a trough, the fast-oscillation trough, and then a slow rise to the light peak. 13 " 5 Intracellular RPE recordings in the cat, chick, and gecko show that the fast-oscillation trough and the light peak are generated by potentials that originate primarily at the RPE basal membrane. 3 ' 5 However, the study of basal membrane mechanisms has been
12 citations
TL;DR: Interestingly, absorptive cells of the duodenum were totally devoid of calbindin D28k while the colon contained high amounts of the calcium‐binding protein, which should correspond to a different scheme of calcium absorption regulation between amphibians and higher vertebrates.
11 citations
TL;DR: It is suggested that, in intact toads at low temperatures, cardiac output decreases and the consequent accumulation of acetylcholine leads to increased vagal effectiveness.
Abstract: The effect of temperature on the action of the vagus nerve on the heart was studied in the toad Bufo marinus. Experiments were performed on two groups of toads, in one the heart was perfused at a constant rate with oxygenated Ringer's solution and in the other the circulation was left intact. In all toads there was a linear relationship between pulse interval (PI) and the frequency of vagal stimulation (fv) at any one temperature. The slope of this relationship changed with temperature, the effectiveness of the vagus (delta PI/delta fv) increasing with decreasing temperature. At low temperatures the vagus nerves of intact toads were more effective than in those with perfused hearts. It is suggested that, in intact toads at low temperatures, cardiac output decreases and the consequent accumulation of acetylcholine leads to increased vagal effectiveness.
9 citations
TL;DR: Incubation of aldoslerone with confluent layers of A6 (toad kidney) cells leads to its hydroxylation at the 6β-position, which is the major metabolite when the incubation is carried out at pH 6.8.
7 citations
TL;DR: Results suggest that the angiotensin converting enzyme present in the vascular wall from Bufo arenarum toad may be involved in the metabolism of ANP.
6 citations
01 Jan 1990
5 citations
TL;DR: Mucosal intra-epithelial nerve terminals have been found in the colon of the toad, Bufo marinus, and co-localized in the fibres are calcitonin gene-related peptide-like immunoreactivity and substance P (SP)-LI.
5 citations
TL;DR: In order to fully characterize the forces driving Na+ movement across the series apical and basolateral membranes, it is necessary to measure intracellular potential and ionic composition.
Abstract: Sodium ion transport across tight epithelia has been investigated particularly extensively by studying two model systems: the urinary bladder of the toad and the frog skin. The greatest advantage presented by these models is the capability of monitoring net transepithelial Na+ flux simply, precisely, and instantaneously by measurement of the short circuit current (ISC). Many of the caveats involved in the measurement are discussed in detail. In order to fully characterize the forces driving Na+ movement across the series apical and basolateral membranes, it is necessary to measure intracellular potential and ionic composition. Such measurements are far more easily conducted with frog skin than with toad bladder, using the major biophysical techniques currently available. Regulation of transepithelial Na+ movement across tight epithelia is largely conducted at the apical membranes. This regulation can be clarified by study of the isolated Na+ channels in membrane vesicles. Such vesicles are far more easily prepared from toad urinary bladder than from frog skin. The strengths and potential misappropriations of this technique are considered in detail.
TL;DR: The data indicate that forskolin acts on at least two sites: stratum granulosum cells (the main pathway for sodium transport, and an alternate site, responsible for the increase in permeability to chloride), and at high concentration of the agent, glandular secretion is also stimulated.
Abstract: Forskolin stimulated short-circuit current (SCC) and transepitelial electrical conductance (G) in the isolated skin of the toad Bufo arenarum in a concentration-dependent manner, between 1.0 x 10(-6) and 2.4 x 10(-5) M. At the latter concentration, glandular secretion appeared to be stimulated also. The increase in G was considerably greater in skins bathed in Ringer solution than in solutions containing no chloride. The increased SCC was abolished by amiloride, a specific blocker of sodium transport in amphibian membranes, irrespective of the anion present in the solution bathing the skin. G was also decreased by amiloride to control values in skins bathed in solutions without chloride, but remained elevated in the presence of Cl-. The increase in SCC following exposure to forskolin, 4.4 x 10(-6) M, was not altered when furosemide, a specific blocker of chloride transport, was present in the Ringer solution bathing the dermal side of the skin. The response to forskolin, 2.4 x 10(-5) M, however, was significantly decreased by dermal furosemide; the inhibitor was ineffective in the absence of chloride. The data indicate that forskolin acts on at least two sites: stratum granulosum cells (the main pathway for sodium transport, and an alternate site, responsible for the increase in permeability to chloride. In addition, at high concentration of the agent, glandular secretion is also stimulated. The data suggest that the adenylate cyclase-cyclic AMP system is involved in the regulation of the permeability of the toad skin to sodium and chloride, probably by separate cell types.
Journal Article•
TL;DR: Weight, number of follicles and corpora lutea of Bidder's organ increased significantly after castration of adult toad in breeding season and Administration of luteinizing hormone (LH) in castrated and hypophysectomized toad showed more or less similar result as that of control indicating that LH has an effect on the histology of Bidster's organ in the toad.
Abstract: Weight, number of follicles and corpora lutea of Bidder's organ increased significantly after castration of adult toad in breeding season. Removal of pituitary along with testes decreased both weight and number of follicles and corpora lutea. Administration of luteinizing hormone (LH) in castrated and hypophysectomized toad showed more or less similar result as that of control indicating that LH has an effect on the histology of Bidder's organ in the toad.
TL;DR: This study shows that d-hydrin can serve as a foundation molecule to which reporter groups, such as fluorescent residues, can be attached with better preservation of hydrosmotic activity than is possible with similar modifications of vasotocin.
Abstract: Hydrin 1 is the biosynthetic precursor of vasotocin in Xenopus laevis. We have synthesized deamino and fluorescein analogues of hydrin 1 and characterized their physiological action in the urinary bladder of the toad, Bufo marinus. 1-Deamino-hydrin 1 (d-hydrin) was more potent than vasotocin in stimulating osmotic water flow across intact bladders and more potent than vasotocin in displacing tritium-labeled vasopressin [( 3H]AVP) from cell membranes. 1-Deamino-[11-lysine (fluorescein)]-hydrin 1 (flu-hydrin) was found to be the most potent fluorescent vasotocin receptor probe synthesized to date. Flu-hydrin increased osmotic water flow across bladders with a half-maximal effective dose (ED50) value of 6 x 10(-10) M and displaced [3H]AVP from membranes with a half-maximal concentration (IC50) value of 3 x 10(-9) M. The hydrosmotic response to flu-hydrin was blocked by 1-deamino-[4-lysine (p-azido-benzoyl)]arginine vasotocin [d4Lys(N3)-AVT]. Epifluorescence light microscopic studies showed vesicular uptake of flu-hydrin at the basolateral membrane of toad bladder epithelial cells, and this uptake was blocked by d4Lys(N3)AVT. This study shows that d-hydrin can serve as a foundation molecule to which reporter groups, such as fluorescent residues, can be attached with better preservation of hydrosmotic activity than is possible with similar modifications of vasotocin.
TL;DR: The time course of the heat produced by the toad sartorius muscle in response to nerve stimulation was determined by using a new type of heat-sensor with a high time resolution to show the existence of a brief burst of large heat production prior to the onset of the muscle heat associated with contraction.
Abstract: The time course of the heat produced by the toad sartorius muscle in response to nerve stimulation was determined by using a new type of heat-sensor with a high time resolution. The records obtained showed the existence of a brief burst of large heat production prior to the onset of the muscle heat associated with contraction. This initial heat-burst was shown to be produced at the motor endplates. The implications of these findings are discussed.
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TL;DR: It is suggested that one or several AFB1 metabolites may be responsible for suppression of spermatogenesis in the given toads, through inhibition of testicular androgenic activity.
Abstract: Aflatoxin-B1 was injected in a dose of 0.01 mg/50 g body weight into the dorsal lymph sac of male toads (Bufo regularis) to evaluate its effect on the testes. After three and six weeks' treatment the diameters of the seminiferous tubules were significantly reduced. Furthermore, spermatogenic cells were almost completely absent. The histological evidence also showed complete suppression of spermatogenesis. It is suggested that one or several AFB1 metabolites may be responsible for suppression of spermatogenesis in the given toads, through inhibition of testicular androgenic activity.
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TL;DR: Based on evaluation of animal reactivity and on EEG analysis performed by presentation of the power of EEG signals via the frequency spectrum, it is possible to obtain a reliable identification of functional condition of amphibians.
Abstract: Studies have been made on the spectral EEG parameters in the forebrain and midbrain of the toad and frog during active and passive forms of natural behaviour within a diurnal cycle. Basing on evaluation of animal reactivity and on EEG analysis performed by presentation of the power of EEG signals via the frequency spectrum, it is possible to obtain a reliable identification of functional condition of amphibians. Behavioural and EEG patterns of 3 forms of wakefulness and 2 forms of rest are presented for frogs and toads.
Journal Article•
TL;DR: Progesterone had a higher effect on the sodium potential than on any other parameter of an equivalent electrical circuit of toad skin and measurement of oxygen consumption indicated that progesterone can act as a blocking agent of the respiratory chain of the sodium transporting cells of toads.
Abstract: To understand the mechanism of progesterone inhibition of the sodium influx in the toad skin, the effects of the hormone on the active sodium transport and oxidative metabolism of the transporting cells were examined. A direct relationship was observed between the initial value of the short circuit current and the sensitivity of a given skin toad preparation to progesterone. Progesterone had a higher effect on the sodium potential than on any other parameter of an equivalent electrical circuit of toad skin. Direct measurement of oxygen consumption indicated that progesterone can act as a blocking agent of the respiratory chain of the sodium transporting cells of toad skin.
Dissertation•
01 Jan 1990
TL;DR: The results suggest that NEM induces a specific increase in transepithelial water flow by activating, via one or more sulphydryl reactions, the cellular apparatus stimulated by VP.
Abstract: This thesis sets out a characterisation of the effects of the sulphydryl agent N-ethylmaleimide (NEM) on water flow across the urinary bladder of the toad, Bufo marinus . and compares the effects of NEM with those of vasopressin (VP). This has been done using functional, biochemical, and ultrastructural studies of bladders treated with NEM or VP. The introduction reviews the action of VP in the toad bladder, and summarises the previous experiments with NEM in this tissue. The results show that NEM causes a specific, irreversible, increase in transepithelial osmotic water flow, but inhibits sodium transport. The increase in water flow does not appear to be mediated by cAMP, or changes of pH or calcium ion concentration, but can be inhibited by low pH, raised calcium, or disruption of the cytoskeleton or cellular metabolism. NEM-induced water flow is additive with that induced by a sub-maximal, but not a maximal, VP dose. NEM treatment leaves the overall epithelial structure intact, while causing changes consistent with increased water flow through the granular cells. Membrane fusion profiles, similar to those seen after VP stimulation, are visible at the apical plasma membrane, and particle aggregates morphologically identical to those believed to mediate the hydrosmotic response to VP can be visualised by freeze-fracture electron microscopy. These results suggest that NEM induces a specific increase in transepithelial water flow by activating, via one or more sulphydryl reactions, the cellular apparatus stimulated by VP. This activation must occur distal to cAMP production, but proximal to cytoskeletal involvement. NEM may prove valuable in understanding the action of vasopressin, by providing an agonist that acts later in the pathway than others currently available. The implications of the experiments reported here, and suggestions for further work, are discussed.
TL;DR: Results obtained suggest that the chymotrypsin-like activity can be assigned to the multicatalytic proteinase, which is found both in unfertilized eggs and in embryos of Bufo bufo.
Abstract: 1. 1. A chymotrypsin-like proteolytic activity was found both in unfertilized eggs and in embryos of Bufo bufo . 2. 2. A dramatical change of activity can be observed in the course of embryonic development. The activity rapidly increases after fertilization up to the stage 9 followed by a fall to a level close to unfertilized eggs. 3. 3. Gel chromatography analysis reveals, in all stages of development, the presence of a single peak of proteinase activity characterized by a very high molecular mass. 4. 4. Proteinase activity, found change during the development of Bufo bufo , was characterized by substrate specificity, protease inhibitor and pH effect. All results obtained suggest that the chymotrypsin-like activity can be assigned to the multicatalytic proteinase.