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PubMed1999

Leap-frog is a robust algorithm for training neural networks.

Optimization of perceptron neural network classifiers requires an optimization algorithm that is robust. In general, the best network is selected after a number of optimization trials. An effective optimization algorithm generates good weight-vector solutions in a few optimization trial runs owing to its inherent ability to escape local minima, where a less effective algorithm requires a larger number of trial runs. Repetitive training and testing is a tedious process, so that an effective algorithm is desirable to reduce training time and increase the quality of the set of available weight-vector solutions. We present leap-frog as a robust optimization algorithm for training neural networks. In this paper the dynamic principles of leap-frog are described together with experiments to show the ability of leap-frog to generate reliable weight-vector solutions. Performance histograms are used to compare leap-frog with a variable-metric method, a conjugate-gradient method with modified restarts, and a constrained-momentum-based algorithm. Results indicate that leap-frog performs better in terms of classification error than the remaining three algorithms on two distinctly different test problems.

Algorithms↗
PubMed2000

Modifications of the isolated frog heart preparation in Carl Ludwig's Leipzig Physiological Institute: relevance for cardiovascular research.

Carl Ludwig was the first physiologist to systematically study isolated organs (heart, muscle, kidney, liver, lung). In his Leipzig Physiological Institute, the isolated perfused frog heart preparation was established in 1866 by Elias Cyon. This preparation was subsequently subjected to various modifications, and many important observations were made by scientists such as Joseph Coats, Henry Pickering Bowditch, Luigi Luciani, Michael Joseph Rossbach, Hugo Kronecker and Otto Frank. The influence of filling pressure on contraction amplitude, the all-or-none law of the heart, the absolute refractory period, postextrasystolic potentiation, the staircase ('Treppe') phenomenon and the dependence of heart function on oxidative metabolism were discovered. The negative chronotropic and inotropic effects of vagus nerve stimulation were also first documented, and a model to induce arrhythmias was established. The isolated frog heart preparation became a widely used standard model for teaching and for basic cardiovascular research. Sidney Ringer discovered the essential role of calcium ions for heart function. Otto Loewi discovered the chemical transduction mechanism of the vagus with acetylcholine as transmitter. In more recent times, the cyclical changes in cAMP and cGMP that occur during the cardiac cycle were first described in the frog heart by Wollenberger and associates. Thus, the isolated perfused frog heart established and modified in Carl Ludwig's Leipzig Physiological Institute led not only to the discovery of basic phenomena, but also to observations that became the basis for concepts to be developed and elaborated later. Furthermore, the isolated perfused frog heart was the starting point for the development of the isolated mammalian heart in the retrogradely perfused, nonworking mode in the heart-lung modification and in the working heart preparation.

Cardiology↗
PubMed1976

Effects of ethanol on the permeability of frog skin.

Ethanol (3%) decreases the potential difference and short-circuit current across the isolated frog skin in chloride Ringer's solution. Unidirectional fluxes of Na and Cl indicate that the drop in short-circuit current is due to an inhibition of the sodium influx. However, ethanol had no effect on the electrical parameters or sodium fluxes, when the frog skin was bathed in chloride-free solutions on both sides or the outside alone. The ethanol response is anion-dependent. In addition, chloride-free media in the inside bathing solution reduced the short-circuit current, indicating a sodium transport pathway which is dependent on chloride and confirming previous data in the literature. Other anions such as sulfate and nitrate could not substitute for chloride. The vasopressin-induced natriferic response and the ethanol effect were found to work independently of each other and different pathways of action are suggested for these agents. The intracellular sodium content of the isolated frog skin epithelium increased and potassium decreased in the presence of the Na-K adenosine triphosphatase inhibitor, ouabain, whereas ethanol or amiloride had no effect. The oxygen consumption of the isolated frog skin was unaffected by up to 10% ethanol. A general metabolic action is probably thus not mediating the response. Urea, in iso-osmotic concentrations to the ethanol, did not mimic its effect. Tritiated water fluxes (in the absence of an osmotic gradient) were reduced by 30% in the presence of 3% ethanol. It is suggested that ethanol may impede the flow of water across frog skin by a physicochemical interaction with membrane pores and the water molecules. The permeability coefficient (Ktrans) for ethanol was found to be 10 times smaller than the Ktrans for water.

Animals↗
PubMed2000

Isoflurane anesthesia in the African clawed frog (Xenopus laevis).

Isoflurane is one of the safest and most accepted anesthetic agents for reptiles, birds, and mammals. It has also been used in terrestrial amphibians. The use of inhalation agents in an entirely aquatic frog presents a new dilemma for delivery in contrast to terrestrial species. The African Clawed Frog respires by using both transcutaneous gas exchange and air breathing. These frogs remain submerged for long periods of time, thus making standard inhalation techniques impractical. We tested five methods for delivering isoflurane: 1) bubbling isoflurane and oxygen in the water, 2) intracoelomic injection, 3) subcutaneous injection, 4) intramuscular injection, and 5) topical application. For the topical application, we developed a simple technique by using an absorptive pad with a vapor-barrier backing, saturating the pad with the liquid isoflurane, and placing the pad on the back of the frog while it was confined in a plastic bowl. Although two of the three injectable routes induced anesthesia, only the topical route produced rapid induction with consistent, safe recovery. Bubbling isoflurane with oxygen into water was unsuccessful. Topical application of isoflurane was most successful and appears to be a safe and practical method that can be used as an alternative to tricaine methylsulphonate, hypothermia, or other methods for anesthetizing African Clawed Frogs.

Administration, Topical↗
PubMed2003

Immunosuppression in the northern leopard frog (Rana pipiens) induced by pesticide exposure.

An injection study and a field study were used to investigate the hypothesis that environmental xenobiotics have the potential to alter the immune function of northern leopard frogs (Rana pipiens). Three assays, IgM-specific antibody response to keyhole limpet hemocyanin linked to dinitrophenyl (KLH-DNP), zymozan induced chemiluminescence (CL) of whole blood and the delayed-type hypersensitivity (DTH), were used to assay humoral, innate and cell-mediated immune endpoints. Sublethal doses of DDT (923 ng/g wet wt), malathion (990 ng/g wet wt), and dieldrin (50 ng/g wet wt) were used in the injection study. In all pesticide-injected groups, antibody response was dramatically suppressed, DTH reactions were enhanced, and respiratory burst was lower. When the order of administration of pesticides and antigens was reversed, no differences in immune function between the control and dosed groups were apparent, indicating that frogs exposed to pathogens prior to pesticide exposure can still respond. A field study found significant differences in immune function between frog populations in pesticide-exposed and pesticide-free locations. The antibody response and CL were suppressed and the DTH enhanced in frogs from Essex County (ON, Canada). Overall, the results suggest that exposure to these pesticides can cause both stimulatory and suppressive immune changes in adult frogs and is doing so in wild populations.

Animals↗
PubMed1999

[Regulating effects of VEGF and ANG II on the frog's pericardial mesothelium, stomata, and angiogenesis].

OBJECTIVE: To observe the regulating effects of vascular endothelial growth factor (VEGF) and angiotensin II (ANG II) on the frog's pericardium, lymphatic stomata, and angionesis so as to understand their influences on the mesothelial permeability, lymphatic stoma regulation, and myocardial hypertrophy. METHODS: VEGF and ANG II were injected into the frog's peritoneal cavity. The results were obtained by using LM, SEM, and computerized imaging analysis. RESULTS: Scattered distributed pericardial stomata were found on the parietal pericardium of the frog with a few sinusoid mesothelial cells. Since there were no blood vessels in the frog's myocardium, its blood supply was directly from the cardiac chambers flowing into the trabecular spaces of the myocardium. The average diameters of the pericardial stomata in VEGF and ANG II groups were 1.50 and 1.79 microns respectively, which were much larger than those in the control group (0.72 micron, P < 0.01). The average distribution density of the stomata was 8.25/0.1 mm2 and 12.80/0.1 mm2 in VEGF and ANG II groups, which was also much higher than that in the control group (3.57/0.1 mm2, P < 0.01). The sinusoid areas in VEGF and ANG II groups were 2443.95 microns 2/0.1 mm2 and 2121.79 microns 2/0.1 mm2, which was larger than that in the control group (995.08 microns 2/0.1 mm2, P < 0.01). No angionesis were found in the frogs of the experimental groups. CONCLUSIONS: VEGF and ANG II strongly regulate the pericardial stomata by increasing their numbers and openings with larger diameters and higher distribution density. They can also increase the sinusoid areas with the result of the higher permeability of the pericardium, which clealy indicated that VEGF and ANG II can speed up the material transfer of the pericardial cavity and play an important role in preventing myocardial interstitial edema. Yet there is no strong evidence showing angionesis in the myocardium.

Angiotensin II↗
PubMed1975

Thalamocortical relations in the brain of the frog, Their role in the genesis of epileptic electrographic phenomena.

The existence of a thalamocortical reverberating circuit between the dorsal thalamic and primordial hippocampal structures could be proved in the brain of the frog (Rana temporarial) by evoking recruiting potentials. Unlike the turtle, this circuit does not take part in the genesis of electrographic phenomena in the corticogram of the frog under normal resting conditions. Spindle activity could not be observed in the EEG of curarized frogs. On the other hand, thalamic structures can influence paroxysmal susceptibility of the frog forebrain. The generation of the penicillin focus could be accelerated and paroxysmal electrographic activities elicited by iontophoretic application of penicillin into dorsal thalamic structures and/or rhythmic electric stimulation of this region. The features of thalamocortical cooperation in the frog and in the turtle have been compared.

Animals↗
PubMed2003

The 35 kDa acid metallophosphatase of the frog Rana esculenta liver: studies on its cellular localization and protein phosphatase activity.

The cellular localization of the 35 kDa, low molecular mass acid metallophosphatase (LMW AcPase) from the frog (Rana esculenta) liver and its activity towards P-Ser and P-Tyr phosphorylated peptides were studied. This enzyme was localized to the cytoplasm of hepatocytes but did not appear in other cells of liver tissue (endothelium, macrophages, blood cells). This LMW AcPase does not display activity towards (32)P-phosphorylase a under conditions standard for the enzymes of PPP family. Proteins containing P-Ser: rabbit (32)P-phosphorylasea and phosvitin are hydrolysed only at acidic pH and are poor substrates for this enzyme. The frog AcPase is not inhibited by okadaic acid and F(-) ions, the Ser/Thr protein phosphatase inhibitors. Moreover, the frog enzyme does not cross-react with specific antisera directed against N-terminal fragment of human PP2A and C-terminal conserved fragment of the eukaryotic PP2A catalytic subunits. These results exclude LMW AcPase from belonging to Ser/Thr protein phosphatases: PP1c or PP2Ac. In addition to P-Tyr, this enzyme hydrolyses efficiently at acidic pH P-Tyr phosphorylated peptides (hirudin and gastrin fragments). K(m) value for the hirudin fragment (7.55 +/- 1.59 x 10(-6) M) is 2-3 orders of magnitude lower in comparison with other substrates tested. The enzyme is inhibited competitively by typical inhibitors of protein tyrosine phosphatases (PTPases): sodium orthovanadate, molybdate and tungstate. These results may suggest that the LMW AcPase of frog liver can act as PTPase in vivo. A different cellular localization and different response to inhibition by tetrahedral oxyanions (molybdate, vanadate and tungstate) provide further evidence that LMW AcPase of frog liver is distinct from the mammalian tartrate-resistant acid phosphatases.

Acid Phosphatase↗
PubMed2001

Regulating effects of vascular endothelial growth factor and ANG II on frog's pericardial stomata, mesothelium and angiogenesis.

OBJECTIVE: To observe the regulating effects of vascular endothelial growth factor (VEGF) and angiotensin II (ANG II) on the frog's pericardium, lymphatic stomata and angiogenesis so as to reveal their effects and mechanism on the mesothelial permeability, lymphatic stoma regulation and myocardial hypertrophy. METHODS: VEGF and ANG II were injected into the frog's peritoneal cavity so as to examine the changes of the pericardial stromata by using transmission electron microscopy, scanning electron microscopy and computerized imaging analysis. RESULTS: Scattered distributed pericardial stomata were found on the parietal pericardium of the frog with a few sinusoid mesothelial cells, whose blood supply was directly from the cardiac chambers flowing into the trabecular spaces of the myocardium (because there are no blood vessels in the myocardium of the frog). The average diameters of the pericardial stomata in VEGF and ANG II groups were 1. 50 microm and 1.79 microm respectively, which were much larger than those in the control group (0.72 microm, P < 0.01); the average distribution densities of the stomata were 8. 25/0.1 mm2 and 12.80/0.1 mm2 in VEGF and ANG II groups, which were also much higher than those in the control group (3.57/0.1 mm2, P < 0.01); the sinusoid areas in VEGF and ANG II groups were 2442.95 microm2/0.1 mm2 and 2121.79 microm2/0.1 mm2, which were larger than that in the control group (995.08 microm2/0.1 mm2 , P < 0.01); no angiogenesis was found in the frogs of the experimental groups. CONCLUSIONS: VEGF and ANG II could strongly regulate the pericardial stomata by increasing their numbers and openings with larger diameters and higher distribution density. They could also increase the sinusoid areas with the result of the higher permeability of the pericardium, which clearly indicated that VEGF and ANG II could speed up the material transfer of the pericardial cavity and play an important role in preventing myocardial interstitial edema. Yet there was no strong evidence to show the angiogenesis in the myocardium.

Angiotensin II↗
PubMed1992

Interaction of the frog brain kainate receptor expressed in Chinese hamster ovary cells with a GTP-binding protein.

A protein that binds kainate with high affinity has been purified and cloned from frog brain (Rana pipiens) and has approximately 35% sequence homology with mammalian non-N-methyl-D-aspartate glutamate receptors, some of which have been shown to be ligand-gated ion channels. Frog brain membranes and membranes from Chinese hamster ovary (CHO) cells transfected with the cDNA coding for the frog kainate-binding protein (CHO-4 cells) bound kainate with essentially identical affinity (KD values of 1.9 and 2.1 nM, respectively). In both tissues, the affinity for kainate decreased 9-fold in the presence of 100 microM GTP gamma S (guanosine 5'-O-(3-thio)triphosphate). No specific kainate binding to nontransfected CHO cell membranes was observed. GTP gamma S and GDP were effective inhibitors of kainate binding, while cGMP and adenosine 5'-O-(3-thio)triphosphate had no effect in either frog brain membranes or CHO-4 membranes. Pretreatment of CHO-4 cell membranes with pertussis toxin led to a 34% decrease in kainate binding. Kainate increased the binding of [3H]5'-guanylyl imidodiphosphate by 61%, and the rate of GTP hydrolysis by up to 5-fold. These results indicate that the kainate receptor cloned from frog brain can interact functionally with a G protein present in CHO-4 cell membranes.

Adenosine Triphosphate↗
PubMed1992

Efficacy of ivermectin as an anthelmintic in leopard frogs.

Ivermectin administered cutaneously at dosages of 2 mg/kg of body weight eliminated nematode infections in leopard frogs. Three clinical trials were conducted. In the first trial, 5 groups of 11 frogs were given ivermectin IM at dosages of 0, 0.2, 0.4, 2, or 20 mg/kg. All frogs given ivermectin IM at dosages of 2.0 mg/kg or greater died. In trial 2, 44 frogs, allotted to 5 groups, were given ivermectin cutaneously at 0, 0.2, 2, or 20 mg/kg. Cutaneously administered ivermectin was not toxic at dosages up to 20 mg/kg. In trial 3, nematode infections were eliminated in all 10 frogs treated cutaneously with ivermectin at 2.0 mg/kg.

Administration, Cutaneous↗
PubMedDate not supplied

Tricaine (MS-222) is a safe anesthetic compound compared to benzocaine and pentobarbital to induce anesthesia in leopard frogs (Rana pipiens).

Tricaine (MS-222) is used commonly for sedation, immobilization, and anesthesia of poikilothermic animals. The anesthetic efficacy of different concentrations of MS-222 was compared to benzocaine and pentobarbital on the physiological changes, heart rate and ECG (electrocardiogram) parameters in the leopard frog, Rana pipiens. Loss of righting reflex (RR), loss of pain response (NR = nociceptor response) and recovery time were measured. Heart rate and ECG parameters were also tested before and during anesthesia. The time to loss of RR and NR decreased while recovery time markedly increased with the increasing concentration of MS-222. Benzocaine at 200 mg/l induced a rapid anesthesia, but all frogs needed resuscitation. Pentobarbital at 300 mg/l induced a slow anesthesia, however, all of the frogs also needed resuscitation. All anesthetics at the mentioned concentrations decreased heart rate significantly as well as altered the ECG parameters. All anesthetics prolonged the Q-T interval, and MS-222 at 800 mg/l and benzocaine at 200 mg/l were the most effective anesthetic concentrations in increasing the Q-T interval. Frogs anesthetized by benzocaine and pentobarbital and high concentrations of MS-222 required resuscitation due to hypoxia. Pentobarbital and benzocaine seem to be very effective compounds, but their safety margins are narrow because of ventilatory failure. Therefore, MS-222 at a concentration of 200 mg/l or less is highly recommended for leopard frogs because prolonged recovery, high mortality rate and significant ECG changes are observed with higher concentrations of MS-222.

Aminobenzoates↗
PubMed2006

Agmatine facilitates sympathetic neurotransmission in frog myocardium via an action on alfa 2-adrenergic receptors.

OBJECTIVE: In this study, the effect of agmatine was studied on sympathetic neurotransmission in the frog isolated ventricular strips. METHODS: Ventricular strips were prepared from the heart of the pitched frog. Each strip was mounted vertically in an organ bath. Muscle contractions were recorded isometrically by a force displacement transducer and displayed on a polygraph. RESULTS: Concentration-response relationships to noradrenaline were obtained on contractility of frog ventricular strips evoked by electrical stimulation. The responses of noradrenaline were re-obtained in presence of agmatine (3X10(-4) M). Agmatine was found to be ineffective on contractile responses of noradrenaline in electrically driven ventricular strips of frog heart. Transient additional stimulations (TAS) induced contractions. The contractions induced by TAS were re-obtained in presence of agmatine, idazoxan + agmatine and yohimbine + agmatine. Agmatine significantly increased the positive inotropic responses of TAS. The effect of agmatine on contractile responses of TAS was not changed by idazoxan, indicating that imidazoline receptors have not functions in this response. The effect of agmatine on the contractile responses to TAS was reversed by yohimbine, indicating involvement of alpha2 adrenoceptors in this response. Agmatine did not change the contractile responses of ventricular strips to exogenous noradrenaline, indicating that agmatine does not affect postjunctional adrenoceptors. CONCLUSION: These results suggest that agmatine facilitates sympathetic neurotransmission in frog myocardium via an action on prejunctional alpha2 adrenergic receptors located on sympathetic nerve terminals.

Adrenergic Fibers↗
PubMed1991

The vomeronasal organ in the frog, Rana esculenta. An electron microscopy study.

The ultrastructure of the vomeronasal organ (Jacobson's VNO) of the frog, Rana esculenta, was studied under the transmission and scanning electron microscope. Four cell types were identified: ciliated, bipolar, glial-like, and basal. Ciliated cells are unique to the frog VNO and show morphological evidence of secretion; bipolar (neuronal) cells are arranged in columns and reach the free surface of the epithelium with knobs bearing microvilli. The latter are in contact with amorphous material not described previously. Glial-like cells wrap bipolar cells in the epithelium and poorly differentiated basal cells are found just over the basal lamina. The vascular pump described in mammal VNO is not present at all in the frog VNO. We conclude that in the frog the VNO is closer to the reptilian than the mammalian VNO, although the frog VNO shows some unique morphological characteristics.

Animals↗
PubMed1990

[Changes in body fluids of the frog Leptodactylus fuscus during estivation (Anura, Leptodactylidae)].

The frog, L. fuscus, becomes dormant during the dry season in southeastern Brazil. Plasma and urine were obtained and analyzed for K+, Na+, and osmotic concentrations in active and estivating frogs. Soil water potential from the estivation sites was compared with the osmotic concentrations of the frog. Plasma and urine osmotic concentrations (286.2 +/- 13.8 and 242.3 +/- 17.2 mOsm1(-1), respectively) were higher in the estivating than in active frogs (240.3 +/- 12.8 and 112.7 +/- 15.6 mOsm1(-1); plasma and urine), and the same holds true for plasma K+ content. The Na+ concentration was the same for active and estivating frogs. Soil water potential corresponded to osmotic pressure of 110 mOsm1(-1), showing that L. fuscus may uptake water from the soil during the estivation.

Animals↗
PubMed1990

Role of temperature in regulation of ovarian cycle in bull frog Rana tigerina.

Effect of temperature on the ovarian cycle was studied in R. tigerina by exposing them to (1) constant low (22 degrees C) temperature during preparatory (active vitellogenic growth) phase (March-May) when the mean ambient temperature ranged from 26 degrees-28 degrees C and (2) to constant high (30 degrees +/- 1 degrees C) temperature during postbreeding regression phase (August-November) when the mean ambient temperature ranged from 22 degrees-26 degrees C. The ovaries of initial controls (biopsy samples taken prior to the commencement of the experiment) in March contained only first growth phase (FGP) oocytes with a maximum size range of 361-480 microns in diameter. In the frogs exposed to constant low temperature for 2 months, only 7% of FGP oocytes were recruited to second growth phase (SGP) with a mean largest diameter of 631 microns compared to 31% large SGP oocytes with a mean diameter of 1114 microns in the frogs collected from natural fields. The number of atretic follicles (AF) was lower and fat body weights were significantly higher in low temperature exposed frogs. The exposure of the frogs to constant high temperature during postbreeding months caused an increase in the mean diameter and number of large FGP oocytes, numerical increase in AF and decrease in fat body weights over corresponding controls maintained at room temperature. The pituitary gonadotrophs of these frogs showed stimulatory changes such as increase in cell size and appearance of secretory granules in the cytoplasm. The results suggest that in R. tigerina high temperature stimulates oocyte growth while low temperature retards it.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Temporal distributions of red cell supply rate to individual capillaries of resting skeletal muscle, in frog and rat.

Microvascular red cell (RBC) supply in resting skeletal muscle fluctuates with time and varies from capillary to capillary. Our aim was to quantitate this heterogeneity in two species (frog, rat) with very different oxygen requirements. Video recordings were made of RBC flow in capillaries associated with superficial fibers of frog sartorius and rat gracilis muscles, for periods of 2-10 min. RBC supply rate (cell/s) to individual capillaries was computed as the product of RBC 'content' (measured as lineal density, cells/mm, by a video-densitometric method) and RBC velocity (mm/s, measured by a spatial correlation technique). The videotapes were analyzed at rates of 6 to 15 samples per second. Regression analysis of the mean data showed little or no correlation between RBC content and RBC velocity (r2: frog 0.095, rat 0.002), both parameters contributing equally to variations in RBC supply rate. Temporal distributions of the three supply parameters demonstrate (1) the wide range of values present within each capillary, and (2) the symmetry of the distributions at high mean values versus a pronounced skewness as mean values approached zero. The wide range of mean values of each parameter, found in both species, suggests considerable 'spatial' heterogeneity of RBC supply among capillaries in resting muscle. Temporal heterogeneity of RBC supply rate to individual capillaries increased markedly as either velocity or content (or both) approached zero (overall mean coefficient of variation: frog, 62%; rat, 100%). Both species show remarkably similar rates of convective transport of RBCs per capillary in resting muscle (e.g. mean supply rates 3.2 and 6.2 RBCs/s in frog and rat, respectively).

Animals↗
PubMed1990

Leptospires in the whistling frog (Eleutherodactylus johnstonei) on Barbados.

Two groups of whistling frogs (Eleutherodactylus johnstonei) comprising 99 and 117 animals were examined for leptospiral infection. Group I animals were caught in 14 areas of Barbados, and Group II animals in seven areas of suburban Bridgetown. Leptospires were isolated from the kidneys or body fluid of six frogs in Group I and the kidneys of 3 frogs in Group II. Two of the Group I isolates died out; the others were identified as bajan (a new serovar in the Australis serogroup) (6) and bim (Autumnalis) (1). The macerated body tissues and fluid of Group I frogs were put into phosphate buffered saline and examined by the microscopic agglutination test using 22 antigens. The results were all negative. For the Group II frogs the methodology was altered; blood was collected onto filter paper discs and allowed to dry out before being agitated in PBS and examined by the MAT. 15/117 (12.8%) animals were positive at greater than or equal to 1:100 and 19 (16.2%) at greater than or equal to 1:50. The geometric mean titre was 179. Seventeen of the sera reacted predominantly to antigens in the Australis serogroup, and two to Pyrogenes on its own. The serological results reflected the identity of the isolates. Serovars of Australis are not known to cause illness on Barbados, but bim is the commonest cause of severe leptospirosis on the island.

Animals↗