Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “FROGS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources
PubMed1990

Repeated, in vivo observation of frog neuromuscular junctions: remodelling involves concurrent growth and retraction.

The fluorescent dye 4-(4-diethylaminostyryl)-N-methylpyridinium iodide was used as a vital stain to study remodelling of motor nerve terminals in sartorius muscles of living frogs (Rana pipiens). Identified terminals were observed twice in vivo at intervals of 87-192 days. After the second observation, muscles were fixed and stained with the nitroblue tetrazolium method for nerve terminals and with cholinesterase stain. Observations were made of 243 junctions in 26 frogs. Most nerve terminals grew during the observation interval, with an average increase in total terminal length of 29%. This growth involved substantial remodelling. Within single junctions, the change in size was the net result of differing degrees of growth or shrinkage in individual nerve terminal branches. At least one new terminal branch appeared in 25% of the junctions. Terminal retraction was also common, with branch shortening seen in 60% of junctions and the complete disappearance of a branch in 12%. In one case the original axonal input retracted completely and the junction was partially reinnervated by a terminal sprout from a junction on an adjacent fibre. Some discrepancies between histological and in vivo observations of remodelling were noted. These observations confirm that frog neuromuscular junctions are highly dynamic synapses, subject to profound structural remodelling throughout adult life.

Animals↗
PubMed1982

The effects of chronic stimulation on the morphology of the frog neuromuscular junction.

A quantitative study was made of the effects of 24 h continuous stimulation on the morphology of the frog neuromuscular junction. The synaptic vesicle concentration in the nerve endings of frog sartorius muscles stimulated in vitro for 24 h at 2 Hz was the same as that in controls stimulated for only 0.3 h at 2 Hz. The control preparations were either freshly dissected or maintained at rest in vitro for 23 h prior to stimulation. Chronically stimulated terminals differed from their controls only in having more cisternae and fewer dense cored vesicles. Varying the lengths of the nerves to both chronically stimulated an in vitro control muscles had little effect on the morphology of the nerve endings. Continuous recording of muscle twitch tension demonstrated that neurotransmission was effective throughout the 24 h period of stimulation. Additional evidence that nerve failure or degeneration was not a factor in the results came from a second set of control and chronically stimulated preparations that were tetanized at 30 Hz for 0.3 h before fixation. Changes attributable to rapid stimulation were evident in 87 to 100% of their nerve terminals. Although the distribution of membrane among various membrane organelles differed from one treatment group to another, the total amount of measurable membrane in the nerve terminals was the same in all of the treatment groups; that is, the total amount of membrane was not altered by maintenance in vitro, chronic stimulation at 2 Hz, rapid stimulation at 30 Hz, reduced nerve length, or any tested combination of these treatments. This conservation of total membrane suggests that membrane exchange between axon and nerve terminal occurs at a relatively slow rate which is unaffected by synaptic activity, and that the local mechanism for recycling synaptic vesicle membrane in frog neuromuscular junctions is more autonomous and durable than has been suspected.

Animals↗
PubMed1986

The volume of mitochondria-rich cells of frog skin epithelium.

The pathway for movement of chloride ions across frog skin is not well understood. Mitochondria-rich (MR) cells have been proposed as the route for chloride across the skin. To test this hypothesis we studied the MR cells of the skin of the frog, Rana pipiens, by quantitative light microscopic determination of cell volume. MR cell volume was influenced by changes in the chloride concentration or osmolality of the outside bathing solution. MR cells shrank about 23% when all chloride was removed from the outside (mucosal) bathing solution. MR cells were also shown to be responsive to changes in the osmolality of either the mucosal or serosal bath. Osmotically-induced swelling caused by dilution of the serosal bath resulted in volume regulatory decrease. These results are consistent with the hypothesis that MR cells constitute the pathway for chloride movement across frog skin.

Animals↗
PubMed1987

Diacylglycerols stimulate short-circuit current across frog skin by increasing apical Na+ permeability.

The phorbol ester TPA (12-O-tetradecanoylphorbol-13-acetate) stimulates baseline Na+ transport across frog skin epithelium and partially inhibits the natriferic response to vasopressin. The effects are produced largely or solely when TPA is added to the mucosal surface of the tissue. Although TPA activates protein kinase C, it has other effects, as well. Thus, the biochemical basis for the effects and the ionic events involved have been unclear. Furthermore, the physiologic implications have been obscure because of the sidedness of TPA's actions. We now report that two synthetic diacylglycerols (DAG) replicate the stimulatory and inhibitory effects of TPA on frog skin. DAG is the physiologic activator of PKC. In this tissue, it produces half-maximal stimulation at a concentration of less than or equal to 19 microM. In contrast to TPA, DAG is about equally effective from either tissue surface. In a series of eight experiments, DAG was found to depolarize the apical membrane. Diacylglycerol also increases the paracellular conductance of frog skins bathed with mucosal Cl- Ringer's solution. The latter effect can be minimized by replacing NO3- for Cl- in the mucosal solution. Under these conditions, combined intracellular and transepithelial measurements indicated that DAG increased both the apical Na+ permeability and intracellular Na+ concentration. These results are qualitatively similar to the effects of cyclic 3',5'-AMP on this tissue, suggesting that activation of PKC by DAG causes phosphorylation of the same or nearby gating sites phosphorylated by cAMP. We propose that apical Na+ entry is regulated in part by activation of PKC, and that insulin may be a physiologic trigger of this activation.

Animals↗
PubMed1987

Prostaglandin E2-stimulated glandular ion and water secretion in isolated frog skin (Rana esculenta).

Prostaglandins are known to stimulate the active sodium absorption in frog skin. In this paper it is shown that prostaglandin E2 (PGE2) stimulates an active secretion of Cl-, Na+, and K+ from the skin glands in Rana esculenta. The active Cl secretion is enhanced more than the Na and K secretion. Therefore, in skins where the Na absorption is inhibited by amiloride, the addition of PGE2 results in an increase in the short-circuit current (SCC). The PGE2-stimulated Cl secretion could be inhibited by the presence of ouabain or furosemide in the basolateral solution or diphenylamine-2-carboxylate in the apical solution. The PGE2-stimulated Cl secretion was enhanced by the phosphodiesterase inhibitor, theophylline, indicating that the effect of PGE2 was caused by an increase in the intracellular cAMP level in the gland cells. The calcium ionophore A23187, which increases the PGE2 synthesis in frog skin, stimulated the glandular Cl secretion. This secretion could be blocked by the prostaglandin synthesis inhibitor indomethacin, indicating that A23187 acts by increasing the prostaglandin synthesis and not by a direct action of Ca2+ ions per se. The net water flow (Jw) and the Cl secretion were measured simultaneously under the conditions outlined above. The stimulation, inhibition, and the time-course of the outward-directed Jw were similar to the change observed for the Cl secretion. These results show that PGE2 stimulates a glandular secretion of Cl and water in frog skin, probably by increasing the cAMP level in the gland cells.

Amiloride↗
PubMed1983

Microelectrode study of K+ accumulation by tight epithelia: I. Baseline values of split frog skin and toad urinary bladder.

Toad bladder and split frog skin were impaled with fine-tipped single- and double-barrelled K+-selective microelectrodes. In order to circumvent membrane damage induced by impaling toad bladder, a null point method was developed, involving elevations of mucosal potassium concentration. The results suggest that intracellular potassium activity of short-circuited toad bladder is approximately 82 mM, twice as large as earlier estimates. Far more stable and rigorously defined intracellular measurements were recorded from short-circuited split frog skins. The intracellular positions of the micropipette and microelectrode tips were verified by transient hyperpolarizations of the membrane potential with mucosal amiloride or by transient depolarizations with serosal barium or strophanthidin. Simultaneous impalement of distant cells with separate micropipettes demonstrated that both the baseline membrane potentials and the responses to depolarizing agents were similar, further documenting that frog skin is a functional syncytium. Measurements with double-barrelled microelectrodes and simultaneous single-barrelled microelectrodes and reference micropipettes suggest that the intracellular potassium activity is about 104 mM, lower than previously reported. Taken together with measurements of intracellular potassium concentration, this datum suggests that potassium is uniformly distributed within the epithelial cells.

Animals↗
PubMed1984

Apical sodium entry in split frog skin: current-voltage relationship.

Apical Na+ entry into frog skin epithelium is widely presumed to be electrodiffusive in nature, as for other tight epithelia. However, in contrast to rabbit descending colon and Necturus urinary bladder, the constant field equation has been reported to fit the apical sodium current (INa)-membrane potential (psi mc) relationship over only a narrow range of apical membrane potentials or to be inapplicable altogether. We have re-examined this issue by impaling split frog skins across the basolateral membrane and examining the current-voltage relationships at extremely early endpoints in time after initiating pulses of constant transepithelial voltage. In this study, the rapid transient responses in psi mc were completed within 0.5 to 3.5 msec. Using endpoints to 1 to 25 msec, the Goldman equation provided excellent fits of the data over large ranges in apical potential of 300 to 420 mV, from approximately -200 to about +145 mV (cell relative to mucosa). Split skins were also studied when superfused with high serosal K+ in order to determine whether the INapsi mc relationship could be generated purely by transepithelial measurements. Under these conditions, the basolateral membrane potential was found to be -10 +/- 3 mV (cell relative to serosa, mean +/- SE), the basolateral fractional resistance was greater than zero, and the transepithelial current was markedly and reversibly reduced. For these reasons, use of high serosal K+ is considered inadvisable for determining the INa-psi mc relationship, at least in those tissues (such as frog skin) where more direct measurements are technically feasible. Analysis of the INa-psi mc relationships under baseline conditions provided estimates of intracellular Na+ concentration and of apical Na+ permeability of 9 to 14 mM and of approximately 3 X 10(-7) cm X sec-1, respectively, in reasonable agreement with estimates obtained by different techniques.

Amiloride↗
PubMed1977

Influence of lithium upon the intracellular potential of frog skin epithelium.

The effect of Li upon the intracellular potential of frog skin (Rana esculenta) was investigated. In the range between 1 and 25 mM Li in the epithelial bathing solution, a semilogarithmic linear relationship between [Li] and intracellular potential under short circuit conditions was obtained. The intracellular potential at all [Li] is quantitatively sufficient to explain the previously reported accumulation of Li in the intracellular space of the frog skin epithelium (Leblanc, G. 1972. Pfluegers Arch. 337:1) on the basis of a passibe entrance step at the outer border. A reduction of the intracellular potential by Li is also observed in the presence of 6 mM Na in the epithelial bathing solution. Consequences regarding the mechanism of uptake of Na across the outer border of the frog skin are discussed.

Amiloride↗
PubMed1989

A gonadotropin releasing hormone analog induces spermiation in intact and hypophysectomized frogs, Rana esculenta.

The sperm-releasing activity of a gonadotropin releasing hormone (GnRH) agonist, Buserelin (GnRH) and hypophysis homogenate (PD) preparations was studied in intact and hypophysectomized (PDX) frogs, Rana esculenta. In addition, human chorion gonadotropin (hCG) was tested in PDX animals, and GnRH antagonist (GnRHA) treatments were carried out in intact and PDX animals, in combination with the hormonal injections. GnRH or PD treatments were able to elicit spermiation in intact and PDX animals. While GnRH, injected 24 h later, was again effective in inducing spermiation in intact animals, this was not the case in PDX frogs. GnRHA counteracted GnRH effects in intact frogs. Moreover, in PDX animals GnRHA injections counteracted the sperm-releasing activity induced by hCG or GnRH, but failed to inhibit sperm-releasing activity induced by PD homogenate.

Animals↗
PubMed1984

Inhibitory effect of ouabain on in vitro and in vivo gastric acid secretion in the frog and the rat.

The in vitro and in vivo effects of ouabain on gastric acid secretion in the frog and the rat, the 2 species known to have different sensitivity to ouabain, were studied. It was found that ouabain was a potent inhibitor of histamine-stimulated acid secretion in the isolated frog gastric mucosa. Ouabain administered i.v. at dose levels far below the lethal range also produced a marked and significant reduction of histamine-stimulated gastric acid secretion in the anesthetized frogs and rats. It is considered that the inhibitory effect of ouabain on acid secretion could be partly related to its specific antagonizing action on the Na+ -K+ -ATPase in the gastric mucosa.

Animals↗
PubMed1987

Evidence for Na+ dependent rheogenic HCO3- transport in fused cells of frog distal tubules.

The mechanism of HCO3- transport was studied applying microelectrodes in "giant" cells fused from single epithelial cells of the diluting segment of frog kidney. A sudden increase of extracellular HCO3- concentration from 10 to 20 mmol/l at constant pH hyperpolarized the cell membrane potential of the fused cell. This cell-voltage response was totally abolished by 10(-3) mol/l SITS and significantly reduced by 10(-4) mol/l acetazolamide or by omission of Na+ from the extracellular perfusate. Removal of Na+ from the perfusate caused a transient depolarization. Reapplication of Na+ induced a transient hyperpolarization. 10(-3) mol/l SITS abolished the cell-voltage response to removal and reapplication of Na+. In the intact diluting segment of the isolated perfused frog kidney peritubular perfusion of 10(-4) mol/l acetazolamide reduced the limiting transepithelial electrochemical gradient for H+ significantly from 30 +/- 4 mV to 14 +/- 3 mV. The results suggest: In the diluting segment of the frog kidney a Na+-dependent rheogenic HCO3- transport system exists across the peritubular cell membrane. This rheogenic peritubular Na+/HCO3- cotransporter cooperates with a Na+/H+ exchanger in the luminal membrane, thus driving HCO3- reabsorption. Reabsorption of HCO3- and secretion of H+ depend upon the presence of carbonic anhydrase.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1978

Properties of morphologically variant haploid frog cells formed by combined treatment with Mengo virus and the polyene antibiotic mediocidin.

Comparisons have been made of cell surface glycoproteins, concanavalin A agglutinability, and cloning efficiencies in liquid media of ICR 2A (haploid frog cells), ICR 2A M (three cloned populations of haploid frog cells resistant to 5 microgram per ml of the polyene antibiotic mediocidin), and ICR 2A M/MV cells (five cloned populations of morphologically variant haploid frog cells produced by exposure of the parental cells to the combined effects of mediocidin and an RNA mammalian virus, Mengo virus). Independently isolated ICR 2A M/MV clones exhibited altered cell surface glycoproteins, increased concanavalin A agglutinability, and enhanced cloning efficiency in liquid media when compared with ICR 2A parental cells. In contrast, ICR 2A M cells had properties similar to ICR 2A cells, with the exception of the former's increased resistance to mediocidin. The differences in properties between ICR 2A M/MV and ICR 2A cells suggest that alterations resembling transformation have occurred in ICR 2A M/MV cells as a consequence of combined treatment with mediocidin and Mengo virus.

Agglutination↗
PubMed1986

Regeneration of the frog optic nerve. Comparisons with development.

Developing and regenerating frog optic axons grow within optic pathways and form connections only with optic targets. However, unlike normal development, many regenerating optic axons in the adult frog are misrouted within optic pathways, including axons that grow into the opposite retina. Many of the axons misrouted during regeneration appear to be collaterals of axons that grow in normal directions. Ganglion cell loss of up to 60% occurs after optic nerve damage, beginning prior to reinnervation of optic targets. Massive axonal collateralization also takes place near the point of nerve damage, causing the normal order found within the nerve to be lost. Collaterals are eliminated as selective reinnervation is completed, and the smaller complement of optic cell axons remaining after regeneration form an expanded projection within optic targets. Evidence is reviewed that suggests that factors involved in axonal guidance and target recognition during development remain intact in the adult frog brain. Additional conditions resulting from nerve injury causes axonal guidance to be less successful during regeneration.

Animals↗
PubMed1997

Fluorescence replication banding of frog chromosomes.

To identify individual chromosomes of a frog karyotype by their fluorescence banding patterns, chromosomes were stained with actinomycin D and 4,6-diamidino-2-phenylindole (DAPI) after incorporation of BrdU during the late S-phase. The chromosomes of three Rana species which were selected for this study (R. ridibunda, R. lessonae and R. japonica) showed well-defined late replication bands. The fluorescence patterns obtained were the reverse of those produced by a 4Na-EDTA Giemsa-staining technique. Fluorescence patterns of the two water frog species (R. ridibunda and R. lessonae) were similar to each other, except for the different fluorescence of the centromeric heterochromatin, which gave extremely bright signals in R. ridibunda but no signal in R. lessonae. Experiments also showed differences between the fluorescence patterns of R. lessonae chromosome 13 in the Italian and Luxembourgian populations. These results show that the fluorescence replication banding using actinomycin D and DAPI is very effective in identifying individual frog chromosomes and detecting their structural changes.

Animals↗
PubMed1997

Segmental and propriospinal projection systems of frog lumbar interneurons.

Spinal interneuronal networks have been implicated in the coordination of reflex behaviors and limb postures in the spinal frog. As a first step in defining these networks, retrograde transport of horseradish peroxidase (HRP) was used to examine the anatomical organization of interneuronal circuitry in the lumbar spinal cord of the frog. Following neuronal degeneration induced by spinal transection and section of the dorsal and ventral roots, HRP was placed at different locations in the spinal cord and the positions of labeled neuronal cell bodies plotted using a Eutectics Neuron Tracing System. We describe four spinal interneuronal systems, three with cell bodies located in the lumbar cord and one with descending projections to the lumbar cord. Interneurons with cell bodies located in the lumbar cord include: (1) Lumbar neurons projecting rostrally. Those projecting to thoracic segments tended to be located in the lateral and ventrolateral gray and in the lower two-thirds of the dorsal horn, with projections that were predominantly uncrossed. Those projecting to the brachial plexus and beyond were located in the dorsal part of the dorsal horn (uncrossed) and in the lateral, ventrolateral, and ventromedial gray (crossed). (2) Lumbar neurons with segmental projections within the lumbar cord. These neurons, which were by far the most numerous, had both uncrossed and crossed projections and were distributed throughout the dorsal, lateral, ventrolateral, and ventromedial gray matter. (3) Lumbar neurons projecting to the sacral cord. This population, which arose mainly from the dorsal horn and lateral or ventrolateral gray, was much smaller than in the other systems. Neuronal density of some of these populations of lumbar interneurons appeared to vary with rostrocaudal level. Finally, a population of neurons with cell bodies in the brachial and thoracic segments that projects to the lumbar cord is described. The most rostral of these neurons were multipolar cells with uncrossed projections, while those with crossed projections were confined almost exclusively to the ventral half of the cord. The distribution of spinal interneurons reported here will provide guidance for future studies of the role of interneuronal networks in the control of movements using the spinal frog as a model system.

Animals↗
PubMed1998

Biochemistry of frog ribonucleases.

Frogs have unique pyrimidine base-specific RNases, with structures similar to those of turtle, iguana and chicken RNases. Among the four frog RNases discussed here, three from Rana pipiens, R. catesbeiana and R. japonica oocyte cells show antitumour activity, and the latter two show lectin activity towards sialic acid-rich glycoproteins. In this review, (i) we compare their unique primary structures with respect to the locations of their disulphide bridges, three-dimensional structure, base specificity and heat stability as compared with RNase A, and (ii) we summarize current knowledge about the mode of action of lectin and the antitumour activities of the three frog RNases.

Amino Acid Sequence↗
PubMed2006

Single retinal changing contrast (third) detector elicits NMDA receptor response and higher activity level of frog tectum neuron network.

The present study was designed to explore whether a discharge of a certain type of frog retinal ganglion cell [likely changing contrast (third) detector] can evoke NMDA response in frog tectum neurons and higher level of activity of tectal neuron network. Discharge of a single retinal ganglion cell was elicited by electrical stimulation of the retina. Evoked electrical activity of the tectum was recorded by the carbon-fiber microelectrode brought into the optic fiber layer F. We show that: (1) strong discharge of a frog individual retinal ganglion cell (third detector) has evoked NMDA response of tectal neurons and higher level of tectal neuron network activity characterized by prominent suprathreshold excitation of efferent neurons. Consequently, the firing of only one retinal ganglion cell (third detector) could lead to the activation of the tectobulbospinal tract and motor reaction. (2) The excitation of a retinotectal fiber of the first kind (axon of third detector) gave rise to the same effects as activation of a retinotectal fiber of the second kind (axon of fifth detector): the suprathreshold excitation of recurrent and efferent tectal neurons, the slow depolarizing potential (seen as the sNW), and the NMDA receptor activation were observed. However, stronger excitation (longer bursts of action potentials) was needed to evoke those effects in the considered case of the retinotectal input of the first kind. This difference could be attributed to the lower quantal size of neurotransmitter release in synapses of the retinotectal input of the first than second kind.

2-Amino-5-phosphonovalerate↗
PubMed2000

Convergence pattern of uncrossed excitatory and inhibitory semicircular canal-specific inputs onto second-order vestibular neurons of frogs. Organization of vestibular side loops.

Second-order vestibular neurons of frogs receive converging monosynaptic excitatory and disynaptic excitatory and inhibitory inputs following electrical pulse stimulation of an individual semicircular canal nerve on the ipsilateral side. Here we revealed, in the in vitro frog brain, disynaptic inhibitory postsynaptic potentials (IPSPs) by bath application of antagonists specific for glycine or gamma-aminobutyric acid-A (GABA(A)) receptors. Differences in the response parameters between disynaptic IPSPs and excitatory postsynaptic potentials (EPSPs) suggested that disynaptic IPSPs originated from a more homogeneous subpopulation of thicker vestibular nerve afferent fibers than mono- or disynaptic EPSPs. To investigate a possible size-related organization of these canal-specific, parallel pathways, we combined long-lasting anodal currents of variable intensities with strong cathodal test pulses, to block pulse-evoked responses reversibly in a graded manner according to the size-related sensitivity of vestibular nerve afferent fibers. The anodal current intensity required to block a particular response component was about 15 times lower than the strength of the cathodal test pulse that activated this response component. These large threshold differences were exploited for a selective anodal suppression of the responses from thick vestibular nerve afferent fibers. In fact, response components known to originate exclusively from thick-caliber afferent fibers such as the electrically transmitted monosynaptic EPSP component exhibited the lowest thresholds for cathodal test pulses and were the first to disappear in the presence of small anodal polarization steps. Thresholds for the activation/inactivation of responses and current intensities required for response saturation/blockade were used to assess the fiber spectrum that evoked the different response components. Mono- and disynaptic EPSPs appeared to originate from a broad spectrum of thick and thin vestibular nerve afferent fibers. The spectrum of afferent fibers that activated disynaptic IPSPs on the other hand was more homogeneous and consisted of thick and intermediate fibers. Such a canal-specific and fiber type-related organization of converging inputs of second-order vestibular neurons via feedforward projections was shown for the first time by this study in frogs, but might also prevail in mammals. Similar differences in these feedforward pathways have been proposed earlier in a vestibular side-loop model. Our results are consistent with the basic assumptions of this model and relate to the processing and tuning of dynamic vestibular signals.

Animals↗