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At least 541 records · Page 30Linked to original sources
PubMed1991

Somatic sodium channels of frog olfactory receptor neurones are inactivated at rest.

Membrane excitability of acutely isolated olfactory receptor neurones (ORNs) of the grass frog (R. pipiens) was studied with the use of the whole-cell "tight-seal" patch recording technique. ORNs of the frog had a mean resting membrane potential of -52 mV, a mean input resistance of 1-2 G omega, and a mean capacitance of 4.5 pF. In the majority of cells examined (over 70%), short duration (several milliseconds) action potentials were elicited at the end of a hyperpolarising pulse (off-spike) or following hyperpolarization of the membrane potential by injection of current. Under voltage-clamp conditions, a fast inward current followed by an outward current could be evoked upon depolarisation of the membrane. The fast inward current decayed with a time constant of 1-2 ms, with an e-fold decrease per 52 mV increase in voltage, and was blocked by the selective voltage-dependent sodium channel blocker tetrodotoxin (0.5-1 microM). Steady-state inactivation studies revealed that the mean voltage for half-inactivation (V1/2) was -82 mV (range -72 to -98 mV), which indicates that the voltage-dependent Na+ channels in the cell body or soma of frog ORNs are not available for conducting currents at the resting membrane potential. This finding raises the possibility that voltage-dependent Na+ channels may not play a significant role in sensory transduction at the soma. Our results indicate that ORNs of the frog are very efficient in transducing signals towards the brain since currents generated at the cilia will be directed towards depolarising the axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1975

Effect on Mn2+ on permeability properties of frog skin.

Mn2+ added to the inner bathing solution of frog skin caused a transient increase in potential difference (PD) and a decrease in total skin conductance and mannitol influx. Net Na flux and short-circuit current (Is. c.) were also reduced, the isotopic net flux being reduced more than Is. c. This observed discrepancy appears to be the result of Cl- retention in the outer medium since it was not observed when the skin was bathed in a sulfate-substituted chloride-free solution. The effect of Mn2+ on the inner side of the frog skin appears to be due to a reduced permeation of Na+ and Cl- through the outer barrier of the skin. Addition of Mn2+ to the outer solution bathing the frog skin caused an increase in PD and a smaller increase in Is. c. These changes were not associated with alterations in the fluxes of Na+ or mannitol and were observed only when chloride was present in the bathing solutions. The effect of Mn2+ on this side of the frog skin may therefore be due to a net retention of Cl- in the outer solution.

Animals↗
PubMed1988

Alteration of calcium sensitivity of skinned frog skeletal muscle fibres by inositol triphosphate and calmodulin antagonists.

We investigated the influence of inositol triphosphate (IP3), trifluoperazine (TFP), and perhexiline on the calcium sensitivity of freeze-dried frog semitendinosus muscle fibres. Further, the effect of IP3 on calcium release from the sarcoplasmic reticulum (SR) of frog semitendinosus fibres skinned by saponin was studied. IP3 decreased the calcium sensitivity of freeze-dried frog skeletal muscle fibres and failed to induce a calcium release from SR of saponin-skinned fibres. Freeze-dried frog skeletal muscle fibres were strongly sensitized for calcium by TFP and perhexiline.

Animals↗
PubMed1988

Frogs use retinal elevation as a cue to distance.

We have investigated the role that retinal elevation plays in a frog's (Rana pipiens) estimate of prey distance. We dissociated retinal elevation from other depth cues by artificially increasing the height of the frogs' eyes above the ground. Frogs then snapped short of their prey in their ventral visual field as if their estimate of distance were determined primarily by the retinal elevation of the image of the prey. The data suggest that the frog assumes its eyes to be about 3 cm above the ground. Other cues modify depth judgements when targets are close to this assumed ground-plane.

Animals↗
PubMed1983

Presynaptic action of trifluoperazine at the frog neuromuscular junction.

Treatment of frog neuromuscular preparations bathed in basic frog saline (1.8 mM Ca2+) with trifluoperazine (25 microM) caused an increase in MEPP frequency in 6 out of 10 preparations tested. The mean normalised MEPP frequency after 15 min of treatment was approximately 1.5. 10 microM trifluoperazine had a similar effect. In salines containing low concentrations of Ca2+ (50 microM Ca2+, 2 mM Mg2+ or 0 Ca2+, 1 mM EGTA) the stimulatory action of trifluoperazine was more marked and occurred in a higher proportion of the preparations tested (11 out of 14). When evoked release of transmitter was reduced to very low levels by Mg2+-containing salines treatment with trifluoperazine (2.5-25 microM) caused an increase in quantal content of 20-60%. Depolarisation of preparations bathed in standard frog saline by increasing [K+]o to 10 mM resulted in a 10-fold increase in MEPP frequency. This response was inhibited by about 25% in 10 microM trifluoperazine and by about 45% in 25 microM trifluoperazine. Pre-treatment of preparations with trifluoperazine (25 microM) caused a marked reduction in the response of MEPP frequency to tetanic stimulation (50 Hz) both in the presence of an inward electrochemical gradient for Ca2+ (50 microM Ca2+, 2 mM Mg2+) and in a Ca2+-free saline (0 Ca2+, 1 mM EGTA). The effects of trifluoperazine on tetanic enhancement of MEPP frequency are compared to those of other agents and it is shown that the results are inconsistent with an effect of the drug on Ca2+-fluxes at the plasma membrane. It is concluded that trifluoperazine has both stimulatory and inhibitory effects on transmitter release at the frog neuromuscular junction and that the inhibitory effect is probably due to inhibition of excitation-secretion coupling at a point subsequent to Ca2+ mobilization.

Animals↗
PubMed1983

The intracellular localization of amiloride in frog skin.

The diuretic compound amiloride is often used as a specific inhibitor of the passive Na+ entry step in the transepithelial transport of Na+ across frog skin. We have utilized the fluorescence properties of amiloride to study the distribution of this transport inhibitor in the ventral skin of Rana pipiens. After a 30 s exposure of 1-100 microM amiloride to the external surface of frog skin, amiloride fluorescence was evident in the cytoplasm of all cell layers of the epidermis and alveolar gland epithelium. Changes in the conditions of incubation which alter the pharmacological activity of amiloride did not affect the intracellular distribution of amiloride or the washout profile of [14C]amiloride. The presence of amiloride fluorescence in the cytoplasm prevented our examination of changes in the amiloride fluorescence at the cell surface with various conditions of incubation. Four derivatives of amiloride that differed in their ability to inhibit short-circuit current were also localized intracellularly but varied in their relative distribution among the cell layers of the epidermis. Our results indicate that when incubated at concentrations from 1 to 100 microM, a large fraction of the amiloride taken up by frog skin is not directly involved with the inhibition of passive Na+ transport at the apical surface of the stratum granulosum. The mechanism of intracellular uptake of amiloride is not clear. However, the cytoplasmic localization of amiloride could explain the action of the drug on intracellular enzymes and may account for the large proportion of non-displaceable [14C]amiloride that has been observed in frog skin.

Amiloride↗
PubMed1988

A morphometric study of the retinal ganglion cell response to optic nerve severance in the frog Rana pipiens.

This study examines the cell body response to axotomy of retinal ganglion cells in the frog Rana pipiens. Cell soma sizes were measured in carefully matched regions of Nissl-stained wholemounted retinae after either nerve crush, nerve cut with stump separation, nerve crush with intraocular nerve growth factor (NGF) or nerve cut with NGF applied to the proximal stump. The state of axonal regeneration was also assessed in each case by anterograde transport of HRP. Following nerve crush axons crossed the lesion by 7 days, reached the chiasma by 14 days and entered the tectum around 20-30 days. The normally evenly stained ganglion cells exhibited granular Nissl staining at 7 and 10 days but very little change in soma size. From 10 to 28 days the mean retinal ganglion cell area increased by 102% and maintained this size until at least 75 days. By 102 days soma size had nearly returned to normal. A population of displaced amacrine cells retained a normal appearance and soma size throughout regeneration. Following nerve cut and stump separation the retinal ganglion cells were slightly more reactive in appearance at 7 days after crush but otherwise the soma reaction developed in a similar manner. Axon tracing revealed no extension beyond the lesion site in these animals and therefore the state of axonal growth did not affect the early soma response. NGF applied at the time of the lesion had no detectable effect on the soma reaction. Although many retinal ganglion cells re-establish contact with visual centres after axotomy in the frog, a considerable proportion die. This contrasts with both the goldfish, where all cells regenerate successfully, and various mammals, where none do so and all retinal ganglion cells die. All retinal ganglion cells in the frog undergo reactive changes similar to those of goldfish and there is no sign of the cell shrinkage seen in mammals. Therefore the cell death in frog would appear to be different from that in mammalian retina but similar to that of mammalian peripheral nerve in which chromatolysis generally preceeds death.

Animals↗
PubMed1990

Neovascularization occurs in response to crush lesions of adult frog optic nerves.

The capacity of the adult frog optic nerve to regenerate following a crush lesion is well established and is in contrast to the lack of regeneration of mammalian optic nerves after similar lesions. One factor which may contribute to the enhanced regenerative capacity of amphibian optic nerves is the rapid removal of cellular debris from the nerve after injury. In this study the morphology of normal and crushed frog optic nerves has been compared. Although the intraorbital region of the normal adult frog optic nerve is avascular, new intraparenchymal blood vessels appear central to the crush site 24 h after the nerve lesion. The appearance of these blood vessels is coincident with the appearance of granulocytes and macrophages in the nerve. Successful regeneration of the adult frog optic nerve may depend on this neovascularization to facilitate the rapid removal of cellular debris and to supply regenerating axons with trophic substances.

Animals↗
PubMed1976

The structure of the rhombencephalic roof in the frog.

The structure of the rhombencephalic roof has been studied by serial section histology in 12 adult frogs, 3 recently metamorphosed frogs and 8 tadpoles of the species Rana temporaria. The roof of the rhombencephalon caudal to the choroid plexus consists of a delicate layer of ependyma which appears to be intact from the time of its development in the tadpole until the stage of metamorphosis. In the adult frog it is an attenuated structure displaying variable deficiencies with an apparent communication between the rhombencephalic ventricle and the surrounding subarachnoid space. The significance of this acquired communication between internal and external cerebrospinal fluid compartments in the adult frog is discussed in relationship to the classical concepts of bulk flow of the CSF in humans. Some of the limitations of these classical concepts are also discussed, and the approach to these problems by studying the comparative morphology of the CSF system in vertebrate animals is justified.

Animals↗
PubMed1990

Changes induced by progesterone treatment in the sulphatides of the frog oviduct.

Sulphatides have been studied by histochemical and biochemical procedures in the oviduct of the frog in different experimental conditions. In ovariectomized or hypophysectomized animals, compared to sham-operated, an increase in sulphatides was observed. The progesterone treatment did not significantly modify this lipid fraction in ovariectomized frogs, while in hypophysectomized frogs it induced a further increase. Densitographic profiles of the sulphatides, obtained by thin-layer chromatography (TLC) and also recorded by Tesak equipment, were similar in ovariectomized or hypophysectomized frogs following hormone treatment because they showed three distinct fractions in both experimental groups of animals. The appearance of a third fraction never previously observed was probably induced by the progesterone treatment. Moreover, under the effects of this hormone, the phospholipid fractions (phosphatidylcholine and phosphatidylethanolamine) also showed different densitographic profiles.

Animals↗
PubMed1989

Cholesterol metabolism in frog (Rana esculenta) liver: seasonal and sex-related variations.

Many aspects of lipid metabolism have been studied in amphibians, but seasonal lipid modulation in male and female frogs has not been investigated. We describe here the yearlong patterns of hepatic lipid content and enzyme activities related to cholesterol homeostasis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and acyl coenzyme A:cholesterol acyltransferase (ACAT) activity in liver of the male and female frog, Rana esculenta. Lipid storage follows distinct seasonal patterns, with an increase in June that is more pronounced in the female than in the male frog. Cholesterol content and cholesterol storage as cholesteryl ester in male liver are consistent with the activity of HMG-CoA reductase and of ACAT enzymes. HMG-CoA reductase activity of the female frog shows an extra peak in fall unrelated to cholesterol storage and probably related to the production of essential compound for oogenesis.

Animals↗
PubMed2004

Suprathreshold excitation of frog tectal neurons by short spike trains of single retinal ganglion cell.

It has been established that coincident inputs from multiple presynaptic axons are required to achieve a suprathreshold level of excitation for the most of central neurons. The present study, however, was designed to determine whether a train of spikes of an individual retinal ganglion cell (that is, input from a single presynaptic axon) targeting a frog tectum layer F could evoke suprathreshold excitation of tectal neurons. The lungs of immobilized frog were artificially ventilated during experiments. An individual ganglion cell was electrically stimulated in the retina through a multi-channel electrode. Responses evoked in the tectum by the stimulation were recorded extracellularly from a terminal arborization of the retinotectal fiber using the carbon-fiber microelectrode. Negative and negative-positive spikes (referred to as first type population responses) and polyphasic spikes followed by excitatory synaptic potentials (referred to as second type population responses) were observed in the recordings of retinotectal activity. Usually, the population responses have ensued after the frequency facilitated first and/or second testing individual retinotectal synaptic potential and disappeared in a threshold manner with a reduction of retinotectal transmission by an application of kynurenic acid. These observations have suggested that the population responses were a consequence of a suprathreshold excitation of tectal neurons and, therefore, could serve as the sign for such an excitation. Recordings have also demonstrated that sources of the first type population responses (likely, the hillocks of axons or somas of postsynaptic neurons) lie deeper than the optic fiber layer F of the tectum, whereas sources of the second type population responses (likely, axon terminal arborizations of these postsynaptic neurons) are scattered throughout the optic fiber layers. The findings have suggested: 1) a short train of action potentials of an individual retinal ganglion cell (likely darkness, also known as 5th, detector) can excite tectal neurons to suprathreshold level; 2) tectal and perhaps, nucleus isthmi neurons that make up recurrent connection circuits to the optic fiber layers of the tectum are also activated; 3) a suprathreshold level for an individual retinotectal input is achieved primarily due to the frequency facilitation of synaptic potentials; and 4) an artificial ventilation of the lungs of immobilized frog favors the eliciting of a suprathreshold excitation of tectal neurons, demonstrating that the ventilation certainly improves the physiological condition of a frog.

Action Potentials↗
PubMed1997

The H+ pump in frog skin (Rana esculenta): identification and localization of a V-ATPase.

We here report on studies on the frog skin epithelium to identify the nature of its excretory H+ pump by comparing transport studies, using inhibitors highly specific for V-ATPases, with results from immunocytochemistry using V-ATPase-directed antibodies. Bafilomycin A1 (10 microM) blocked H+ excretion (69 +/- 8% inhibition) and therefore Na+ absorption (61 +/- 17% inhibition after 60 min application, n = 6) in open-circuited skins bathed on their apical side with a 1 mm Na2SO4 solution, "low-Na+ conditions" under which H+ and Na+ fluxes are coupled 1:1. The electrogenic outward H+ current measured in absence of Na+ transport (in the presence of 50 microM amiloride) was also blocked by 10 microM bafilomycin A1 or 5 microM concanamycin A. In contrast, no effects were found on the large and dominant Na+ transport (short-circuit current), which develops with apical solutions containing 115 mm Na+ ("high-Na+ conditions"), demonstrating a specific action on H+ transport. In immunocytochemistry, V-ATPase-like immunoreactivity to the monoclonal antibody E11 directed to the 31-kDa subunit E of the bovine renal V-ATPase was localized only in mitochondria-rich cells (i) in their apical region which corresponds to apical plasma membrane infoldings, and (ii) intracellularly in their neck region and apically around the nucleus. In membrane extracts of the isolated frog skin epithelium, the selectivity of the antibody binding was tested with immunoblots. The antibody labeled exclusively a band of about 31 kDa, very likely the corresponding subunit E of the frog V-ATPase. Our investigations now deliver conclusive evidence that H+ excretion is mediated by a V-ATPase being the electrogenic H+ pump in frog skin.

Animals↗
PubMed2005

Auditory brainstem responses to airborne sounds in the aquatic frog Xenopus laevis: correlation with middle ear characteristics.

In this study we recorded auditory brainstem responses to airborne sounds to determine the hearing sensitivity of Xenopus laevis frogs and correlated their hearing profiles with middle ear characteristics. In newly metamorphosed frogs (body mass 0.5-0.76 gm, snout-vent length 17-20 mm) best hearing sensitivities were measured in the 2.4-2.8 kHz range, whereas optimal hearing sensitivity of older adults (body mass 18-90 gm; snout-vent length 57-100 mm) ranged from 1.0 to 1.2 kHz. Middle ear volumes reconstructed from serial sections showed approximate volume of 0.002 cc and 0.04-0.07 cc in newly metamorphosed and older frogs, respectively. This inverse frequency-volume relationship is consistent with the properties of an acoustic resonator indicating that differences in best hearing sensitivity are at least in part correlated to variation in middle ear volumes for airborne sounds. These results are consistent with peak frequency vibrational velocity profiles of Xenopus tympanic disk that have been shown to be dependent on underlying middle ear volumes and corroborate the occurrence of peak amplitudes of otoacoustic emissions in the 1.0-1.2 kHz region in adult Xenopus frogs.

Aging↗
PubMed2006

Auditory response characteristics of the piebald odorous frog and their implications.

The piebald odorous frog (Odorrana schmackeri), the large odorous frog (Odorrana livida) and the concave-eared torrent frog (Amolops tormotus) are sympatric species living near the same torrent streams in the vicinity of Mt. Huangshan, China. A recent study demonstrated that A. tormotus can use sound signals involving ultrasonic components for communication in a noisy environment, and another sympatric species, O. livida, can also perceive ultrasonic sound. Here we report data on the hearing range of O. schmackeri by studying auditory evoked potentials and single-unit data from the torus semicircularis. This frog exhibits its two most sensitive peaks at 2 kHz and 3.5-4.0 kHz with thresholds <42 dB SPL, with an upper frequency limit of hearing at 8.5 kHz with threshold of 87 dB SPL. The upper limit is much lower than those of O. livida and A. tormotus, at 22 and 34 kHz, respectively. It suggests that sympatric species may respond differently to similar environmental selection pressures sculpting auditory communication systems.

Acoustic Stimulation↗
PubMed2003

Activation of Na+/H+ exchange by protein phosphatase inhibitors in red blood cells of the frog Rana ridibunda.

The present study was designed to evaluate the role of protein phosphatases in regulation of sodium transport in the marsh frog erythrocytes using 22Na as a tracer. For this purpose the cells were treated with several known inhibitors of protein phosphatases. In standard isotonic medium, exposure of the cells to 10 mmol l(-1) NaF, 20 nmol l(-1) calyculin A or 0.1 mmol l(-1) cantharidin resulted in a significant (1.7-fold) increase in unidirectional ouabain-insensitive Na+ influx. The Na+ influx in frog red cells was progressively activated as the medium osmolality was increased by addition of 100, 200 or 300 mmol l(-1) sucrose to standard isotonic medium. The stimulatory effect of protein phosphatase blockers on Na+ influx was much higher in hypertonic medium containing 100 or 200 mmol l(-1) sucrose than that in isotonic medium. Stimulation of Na+ transport enhanced with increasing concentrations of calyculin A, and half-maximal activation (EC50) was obtained at 16 nmol l(-1). However, Na+ influx induced by strong hypertonic treatment (+300 mmol l(-1) sucrose) was not altered further in the presence of protein phosphatase inhibitors. The changes in Na+ influx evoked by protein phosphatase inhibitors and hypertonic treatment were associated with a rise in the intracellular Na+, but not K+, content. Enhancement in Na+ influx after addition of protein phosphatase blockers to cell suspension in isotonic or hypertonic media was almost completely inhibited by Na+/H+ exchange inhibitors, amiloride and ethyl-isopropyl-amiloride. The basal Na+ influx in frog erythrocytes in isotonic medium was relatively low (1.7 mmol/l cells/h) and not affected by 1 mmol l(-1) amiloride. Thus, the data obtained clearly indicate that Na+/H+ exchanger in the marsh frog red blood cells is under tight regulatory control, in all likelihood via protein phosphatases of types PP-1 and PP-2A.

Animals↗
PubMed1999

Effects of phorbol esters on excitation-contraction coupling and protein kinase C activity of frog twitch muscle fibers.

By recording the calcium transients evoked by voltage-clamp depolarizing pulse with arsenazo III as a calcium indicator, it has been shown that 1 micromol/l phorbol 12,13-dibutyrate (PDBu), a protein kinase C (PKC) agonist, causes a transient potentiation and then a depression of the calcium transients of twitch muscle fibers in frogs. PDBu also produces an initial translocation and activation of PKC, which is followed by a down-regulation. To find out whether the effect of PDBu on the calcium transients depends on PKC, a correlated study of the effect of phorbol esters on calcium transients and PKC activity was performed. The calcium transients and PKC activity were similarly affected by PDBu in ordinary and cold-accommodated frogs, but the effects occurred more quickly in the latter. However, they still changed in parallel as in ordinary frogs. 1 or 10 micromol/l, 4-alpha-phorbol, a PKC-inactive analogue of phorbol ester, caused a partial depression of the calcium transients in cold-accommodated frogs, while PKC activity was not affected. Moreover, the transient potentiation of the calcium transients induced by 1 micromol/l PDBu could be antagonized by the PKC inhibitors 10 micromol/l chelerythrine chloride or 10 micromol/l polymyxin B (PMB). All these results suggest that: (1) the transient potentiation of calcium transients induced by PDBu is caused by activation of PKC; (2) phorbol ester can depress the calcium transients by a mechanism that is independent of PKC.

Alkaloids↗
PubMed2002

Parallel microtubules and other conserved elements of dorsal axial specification in the direct developing frog, Eleutherodactylus coqui.

Specification of the dorsal axis in commonly studied frogs, such as Xenopus laevis and Rana pipiens, depends on a microtubule-mediated movement of cytoplasm in the fertilized egg. The Puerto Rican tree frog, Eleutherodactylus coqui, has an egg that is twenty times the volume of that of X. laevis, raising the question as to whether the mechanism of dorsal axial specification is conserved in these large eggs. Fertilized eggs of E. coqui develop a transient array of parallel microtubules, similar to other frogs, but proportionately larger. The array persists after first cleavage, longer than in other frogs, and is gone by the third cleavage. Correlated with the longer life of the parallel microtubules, both 2- and 8-cell E. coqui embryos remain sensitive to gravity-mediated axial specification, a sensitivity lost in X. laevis before the 2-cell stage. Activation of the Wnt/beta-catenin pathway by injected Xwnt8 RNA causes axial formation as in X. laevis. The results indicate that elements of dorsal axial specification are conserved in E. coqui, but they occur later compared to in X. laevis.

Animals↗