Showing papers on "Toad published in 2000"

Toad envenoming in dogs: effects and treatment

Abstract: Toads (order: Anura; family: Bufonidae; genus: Bufo) are distributed throughout the world, but more species are found in areas of tropical and humid temperate climates. Although toads do not have a venom inoculation system, they are venomous animals because the glands covering the whole surface of their bodies secrete a milk-like venom of which composition is not yet completely known. Some of these glands are the bilateral glands located in post-orbital position. These glands, which are somewhat diamond-shaped and can be seen by the naked eye, are known as parotids. Toad envenoming in dogs may cause local and systemic alterations and may cause death by cardiac ventricular fibrillation. The electrocardiographic alterations observed consist of gradual deterioration of the normal standards with progressive appearance of negative ventricular deflections that can result in ventricular fibrillation and death if the envenomed dog is not promptly treated. Traditional therapy consists mainly of administration of atropine and propranolol; the latter used to prevent ventricular fibrillation.

Diversity of opsin immunoreactivities in the extraretinal tissues of four anuran amphibians.

Abstract: The pineal complex, deep brain, and skin have been known to function as extraretinal photoreceptors in non-mammalian vertebrates. To see the diversity of localization of extraretinal photoreceptors in lower vertebrates having different habitats, we analyzed the opsin-like immunoreactivities in anuran amphibians, Xenopus laevis, Rana catesbeiana, Rana nigromaculata, and Bufo japonicus. An antiserum (toad Rh-AS) was raised against rhodopsin purified from the retinas of Japanese toad, B. japonicus. In the retina of all the anurans examined, the outer segments of rods were immunopositive to toad Rh-AS. The outer segments of most pinealocytes were immunopositive in R. catesbeiana, R. nigromaculata, and B. japonicus. The outer segments of photoreceptor-like cells within the frontal organ of R. nigromaculata were immunostained. Interestingly, toad Rh-AS immunostained many secretory cells of mucous glands in the head skin of B. japonicus, implying the presence of a novel photoreceptive molecule. Within the hypothalamus, toad Rh-AS immunostained many cells in the magnocellular preoptic nucleus of R. catesbeiana and B. japonicus. Toad Rh-AS also labeled cerebrospinal fluid (CSF)-contacting cells in the anterior preoptic nucleus of R. nigromaculata and those adjacent to the lateral ventricle within the septum of R. catesbeiana. Thus the distribution patterns of the rhodopsin-like immunoreactivities among the anurans were highly diverged, and there was no relationship between the distribution patterns and their habitats. J. Exp. Zool. 286:136-142, 2000.

The importance of glucose for the freezing tolerance/intolerance of the anuran amphibians Rana catesbeiana and Bufo paracnemis.

Abstract: Several species of terrestrially hibernating frogs, turtles and insects have developed mechanisms, such as increased plasma glucose, anti-freeze proteins and antioxidant enzymes that resist to freezing, for survival at subzero temperatures. In the present study, we assessed the importance of glucose to cryoresistance of two anuran amphibians: the frog Rana catesbeiana and the toad Bufo paracnemis. Both animals were exposed to -2 degrees C for measurements of plasma glucose levels, liver and muscle glycogen content, haematocrit and red blood cell volume. Frogs survived cold exposure but toads did not. Blood glucose concentration increased from 40.35 +/- 7.25 to 131.87 +/- 20.72 mg/dl (P < 0.01) when the frogs were transferred from 20 to -2 degrees C. Glucose accumulation in response to cold exposition in the frogs was accompanied by a decrease (P < 0.05) in liver glycogen content from 3.94 +/- 0.42 to 1.33 +/- 0.36 mg/100 mg tissue, indicating that liver carbohydrate reserves were probably the primary carbon source of glucose synthesis whereas muscle carbohydrate seems unimportant. In the toads, the cold-induced hyperglycaemia was less (P < 0.05) pronounced (from 27.25 +/- 1.14 to 73.72 +/- 13.50 mg/dl) and no significant change could be measured in liver or muscle glycogen. Cold exposition had no effect on the haematocrit of the frogs but significantly reduced (P < 0.01) the haematocrit of toads from 20.0 +/- 2.1% to 5.8 +/- 1.7% due to a decreased red blood cell volume (from 1532 +/- 63 to 728 +/- 87 mm3). When toads were injected with glucose, blood glucose increased to levels similar to those of frogs and haematocrit did not change, but this failed to make them cryoresistent. In conclusion, the lack of cold-induced glucose catabolism may not be the only mechanism responsible for the freeze intolerance of Bufo paracnemis, a freeze-intolerant species.

Effects of resibufogenin from toad venom on isolated Purkinje fibers.

Abstract: Chan su (dried toad venom) is a traditional Chinese medicine obtained from the skin venom gland of the toad. Chan su has long been used as a therapeutic agent in China and other Asian countries. Recent reports indicate that Chan su toxicity carries a high mortality rate in the United States. This study focused upon the cardiac electrophysiological and electro-toxicity effects of resibufogenin (RBG), one of the major components in Chan su. Action potentials of isolated sheep and canine heart Purkinje fibers were studied using glass microelectrode recording techniques. The results indicate that RBG significantly affected all parameters of transmembrane action potential, induced delayed after depolarization, and triggered arrhythmias in sheep and canine Purkinje fibers.

Dynamics of the intensity of respiration in early embryogenesis of amphibians

Abstract: We studied growth and respiration rate during early ontogenesis of the axolotl Ambystoma mexicanum, Bosca's newt Triturus waltlii, the green toad Bufo viridis, and the smooth clawed frog Xenopus laevis. The respiration rate in these amphibian species increases during embryonal and larval development, peaks after transition to active feeding, and decreases at later stages of ontogenesis. The patterns of dynamics of this energy metabolism index in tailed and tailless amphibians have some differences related to their specific development. The changes in respiration rate in the embryos and larvae are correlated with the concentrations of mitochondria.

Bufokinin: actions and distribution in the toad cardiovascular system.

Abstract: 1. Bufokinin is a substance P-like neuropeptide and potent spasmogen isolated from the intestine of the cane toad Bufo marinus. In the present study, we investigated the effects of bufokinin on systemic blood pressure and heart rate in the anaesthetized toad and the distribution of bufokinin-like immunoreactivity in the toad vasculature. 2. Intravenous bufokinin caused a dose-dependent fall in systemic blood pressure (maximum fall 20 mmHg) with an ED50 of 2.9 pmol. At higher doses, the effect was prolonged and blood pressure did not return to baseline within 60 min. There was no significant change in heart rate associated with hypotension. 3. Bufokinin-like immunoreactivity was mapped in whole mounts of toad blood vessels and organs using a mouse polyclonal antibody BK3 (at 1:5000) and the avidin-biotin method. Bufokinin-immunoreactive fibres were associated with most blood vessels examined: a moderately dense perivascular network of varicose fibres was present around renal arteries, with sparser immunoreactive fibres in the ventral aorta, sciatic artery, anterior abdominal vein and hepatic portal vein. 4. Bufokinin-immunoreactive fibres, mainly following blood vessels, were seen in whole mounts of the urinary/bladder and tongue, but not in the air sac. In the heart ventricle, varicose fibres were found in the valve cusps, intracardiac ganglia, epicardium and myocardium close to the endocardium, but not in the rest of the myocardium. 5. The vasodepressor action of bufokinin and the presence of bufokinin-like immunoreactivity in varicose fibres in various vessels suggest a role for bufokinin in haemodynamic regulation and/or sensory nerve function in the toad. The lack of any reflex tachycardia in response to the falls in blood pressure was of note.

A study of the role of glycogen in skeletal muscle performance and of myosin heavy chain isoform expression in amphibian skeletal muscle using the toad Bufo marinus

Abstract: The overall aim of this study was to contribute knowledge to two areas of inquiry in muscle research: one concerned with the molecular mechanism(s) underlying the positive correlation between intracellular glycogen content and skeletal muscle performance and the other with the MHC isoform composition in amphibian skeletal muscle and single muscle fibres. The organism used throughout this study was the cane toad Bufo marinus.

Inhibition of basolateral cAMP permeability in the toad urinary bladder.

Abstract: 1 The effect of sulphonylurea drugs on hydrosmotic flow across toad urinary bladder epithelium was re‐evaluated in the present study. Glibenclamide, added to the basolateral medium, significantly enhanced the osmotic flow induced by low doses of antidiuretic hormone (ADH) or forskolin (FK), while it inhibited the effect of exogenous cyclic adenosine monophosphate (cAMP) or its non‐hydrolysable bromo derivative, 8‐Br‐cAMP, added to the basolateral medium. These opposite effects of glibenclamide on the transepithelial osmotic flow can be explained by a reduction of cAMP permeability across the basolateral membrane of the epithelium. The decrease in cAMP permeability leads, according to the direction of the cAMP gradient, to firstly an enhanced osmotic flow when cAMP is generated intracellularly by addition of ADH and FK, glibenclamide reducing cAMP exit from the cell, and secondly a decreased osmotic flow in response to cAMP (and 8‐Br‐cAMP) added to the basolateral medium, glibenclamide inhibiting, in this case, their entry into the cell 2 The demonstration that glibenclamide actually inhibits the basolateral cAMP permeability rests on the fact that firstly it decreases the release of cAMP into the basolateral medium by about 40 %, at each concentration of ADH or forskolin tested, secondly it increases the cAMP content of paired hemibladders incubated in the presence of ADH or FK, when intracellular degradation was prevented by phosphodiesterase inhibition, and thirdly it decreases also the uptake of basolateral 8‐Br‐[3H]cAMP into paired toad hemibladders. 3 Taken together, the present data demonstrate that glibenclamide inhibits the toad urinary bladder basolateral membrane permeability to cAMP, most probably by a direct interaction with a membrane protein not yet indentified but distinct from the sulphonylurea receptor.

Peculiarities of osmoregulation of circulating red blood cells in steno- and euryhaline marine fish species under hypoosmotic conditions

Abstract: The peculiarities of osmoregulation of circulating red blood cells of the stenohaline giant gobyGobius cobitis and the euryhaline toad gobyGobius batrachocephalus have been studied under experimental conditions. In the giant goby, volume of the red blood cells increased steadily by 10.6–18.1% (p < 0.05) after reduction of the medium salinity from 15–17 to 6.0–6.8‰ and this volume increase remained during the entire experimental period (40–45 days). Lysis of red blood cells was noticed in some cases, which was indicated by a decrease of the number of red blood cells and an increase of concentration of free hemoglobin in the blood plasma. No similar reactions were observed in the euryhaline toad goby; the mean cell volume did not change statistically significantly. The volume regulation resulted in K+ efflux from red blood cells. The blood red cells of the toad goby had a high resistance to osmotic stress. The Na+,K+-ATPase activity in the red blood cell membranes of the toad goby was higher by 18.8% (p < 0.001) than in the giant goby.