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At least 991 records · Page 55Linked to original sources
PubMed1989

The frog palate mucosa as a model for studying bacterial adhesion to mucus-coated respiratory epithelium.

Most of the methods proposed to quantify bacterial adherence to respiratory mucosa differ mainly from in vivo conditions in the absence of the mucus blanket and in the exposure of the sub-mucosal connective tissue (SMCT) to the micro-organisms. We propose the frog palate as a model to study bacterial adhesion to the respiratory mucosa, with a system which allows the mucus to be preserved and the bacterial adhesion to be quantified in a standardized mucosal area, where mucociliary transport is still active. In order to evaluate the role of respiratory mucus in bacteria-mucosa interaction, we compared the adhesion of radiolabelled pneumococci to 12 mucus-coated and 10 non-mucus-coated frog palate mucosae. The presence or absence of mucus was controlled by scanning electron microscopy (SEM). After a 10 min incubation period, the bacterial adhesion to mucus-coated palate mucosa was five times greater (P less than 0.01) than that to uncoated mucosa. By SEM, bacteria were never seen attached to ciliated cells but could be detected on small areas where mucus was not totally eliminated. Even after a 120 min contact of bacteria to uncoated mucosa, bacterial adhesion remained only half that to mucus-coated epithelium. In order to ascertain whether the exposure of the SMCT represented a means of attraction to bacteria, we incubated the frog palate mucosa face-down with radiolabelled Pseudomonas aeruginosa. As much as 44 per cent of added bacteria adhered to exposed SMCT and, by SEM, numerous micro-organisms were seen attached to connective tissue. In contrast, only a few bacteria were observed adhering to the mucosa, mainly to granules of mucus.

Animals↗
PubMed1983

Inhibition by Ba of background current and of its modifications by carbachol in frog atrium.

In previous work on frog atrium [11], we have shown that the carbachol-induced K current (iCCh) and the inward rectifying K channel (iK1) are both inhibited by cesium ions. A more detailed study [1, 2] indicates that the dose-response and the voltage dependence of the inhibition by Cs of iK1 and iCCh are similar. These results are in favor of a modulation by acetylcholine of the iK1 channels. Such a conclusion has been put forward by [3] and by [9]. However, Cs ions can also block the pacemaker currents iK2 [8] and if [5]. An 'if like' component seems to be present in frog atrium (Bonvallet and Ojeda, unpublished results). For these reasons, we have studied the action of barium which can be considered as a more specific inhibitor of the inward rectifying K channels in skeletal muscle [13], [14] and in heart muscle [4]. We report here results obtained on two types of preparations: one in which carbachol increases the background conductance (typical effect) and another one (four fibres from the same frog heart) where carbachol decreases the background conductance (atypical effect) as observed by Carmeliet and Ramon (1980) in sheep Purkinje fibres. In both cases, the results show that, in presence of 5 mM barium, carbachol has no effect on the background current.

Animals↗
PubMed1983

Distinct molecular forms of opiate binding in the frog brain.

In frog brain membranes, equilibrium saturation binding of the opiate agonist: 3H-etorphine and of the opiate antagonist: 3H-diprenorphine is biphasic. In the presence of sodium ions (120 mM), "kinetic conversions" (unchanged Bmax) are observed: high affinity binding of the 3H-agonist is decreased while high affinity binding of the antagonist is increased. Frog brain membranes were labelled either with 3H-etorphine or with 3H-diprenorphine and solubilized with digitonin. The soluble extracts were centrifuged in sucrose gradients: two distinct components were labelled which sedimented respectively faster (approximately 12 S) and slower (approximately 10 S) than did catalase, used as marker. Pre-incubation of membrane and of 3H-ligand in the presence of 120 mM NaCl resulted in 1) considerably reduced recovery of the 12 S component in labelled form and 2) substantially enhanced labelling of the 10 S component with the 3H-antagonist. Gpp(NH)p (guanyl-5'-yl imidodiphosphate) exerted similar effects as did sodium ions. Taken together, these data suggest that the two components in question represent physically distinct agonist and antagonist forms of frog brain opiate receptors.

Animals↗
PubMed1986

Neuropeptide Y in the intermediate lobe of the frog pituitary acts as an alpha-MSH-release inhibiting factor.

The presence of neuropeptide tyrosine (NPY) in the intermediate lobe of the frog pituitary was demonstrated using indirect immunofluorescence, the immunogold technique and a specific radioimmunoassay combined with high pressure liquid chromatography (HPLC). A high density of NPY-containing fibers, was found among the parenchymal cells of the intermediate lobe. These fibers originated from the ventral infundibular nucleus, travelled via the median eminence to the pars intermedia. At the electron microscopic level, NPY-like material was found exclusively in nerve fibers where the product of the immunoreaction was associated to dense-core vesicles. High concentrations of NPY-like peptide were found in neurointermediate lobe extracts. After Sephadex G-50 gel filtration the major peak of immunoreactive material appeared to co-elute with synthetic porcine NPY. Conversely, HPLC analysis revealed that the NPY-like peptide of the frog pituitary had a retention time shorter than the porcine NPY. The localization of NPY-like material in the pars intermedia suggested a possible role of NPY in the regulation of melanotropic cell secretion. In fact, graded concentrations of synthetic NPY induced a dose-dependent inhibition of alpha-melanotropin (alpha-MSH) release in vitro. The lack of effect of a dopaminergic antagonist on NPY-induced alpha-MSH release inhibition demonstrated that the local dopaminergic system could not account for the NPY action. These results indicate that NPY located in the hypothalamo-hypophyseal system of the frog may act as a melanotropin-release inhibiting factor.

Animals↗
PubMed1985

The effect of substance P on the mechanical and electrical responses of frog, chick and rat skeletal muscle.

The effect of substance P (SP) on the electrical and contractile responses of skeletal muscles of frog, chick and rat were studied using electrophysiological techniques. In low concentrations, SP increased the amplitude of twitch and tetanic contractions in response to motor nerve stimulation of frog, chick and rat preparations, increased the amplitude and duration of frog sciatic nerve compound action potential and reduced the contracture responses produced by acetylcholine (ACh) or tetraethylammonium (TEA) in the chick skeletal muscle. In all these actions, the effect of SP was calcium-dependent. The results provide evidence that SP had a dual action; a prejunctional facilitatory effect by causing a further release of ACh and/or Ca2+ entry or release, and postjunctional effect by reducing the sensitivity of the postjunctional membrane to depolarizing drugs.

Acetylcholine↗
PubMed1985

Assessment of neuromuscular blockade produced by atracurium in frog sartorius muscle.

The neuromuscular effects of atracurium in frog sartorius muscle were studied and the results were compared with those obtained by tubocurarine in the same preparation. Single twitch (at 1 per 5 s) and tetanic stimulation (at 1-100 per s) of the motor nerve, stimulated with 5-10 V (maximum) and 0.2 ms pulse duration, were used to assess the neuromuscular blockade produced by atracurium and tubocurarine in the frog sartorius muscle. The results showed that atracurium was twice as potent as tubocurarine in reducing the amplitude of the indirectly-elicited twitch contractions in the frog sartorius muscle. The mean IC50 values (concentration to produce 50% inhibition of twitch tension) of atracurium and tubocurarine-induced depression of the indirectly-elicited twitch tension were 0.64 +/- 0.1 microM and 1.2 +/- 0.2 microM respectively (means +/- s.e., n = 6, P less than 0.001). Furthermore, atracurium had a shorter time of onset, time to 50% block and time to 95% recovery than tubocurarine.

Animals↗
PubMed1978

Respiratory control and CO2 conductance: temperature effects in a turtle and a frog.

The respiratory control systems of the predominantly lung-breathing turtle. Pseudemys scripta, and the bimodal breathing frog, Rana catesbeiana, are compared. At constant temperature, control is effected in both species primarily by pulmonary ventilation, and appears to be similar in basic organization to the mammalian system. The skin CO2 exchange of the frog is largely passive and apparently under little adaptive control. CO2 exchange at different temperature is analyzed by means of the conductance equations: convective conductance [MCO2 = (VA/RT).pACO2] for lung exchange, and diffusive conductance (MCO2 = GCO2.transcutaneous deltaPCO2) for skin exchange. Predictions of conductance values, based on data for PaCO2 and MO2, agree well with measured values of both the turtle's ventilation and the frog's skin CO2 conductance at different temperatures. In each case the conductances increase only moderately, if at all, with temperature, a result that can be attributed to the similar Q10 values of PaCO2 and MO2. Because the conductances exhibit this blunted temperature dependence, both lung and skin breathers are provided with the respiratory effector mechanisms necessary to regulate PaCO2 and pHa at their characteristic values over the ectothermic temperature range.

Animals↗
PubMed1986

Regulation of cutaneous gas exchange by environmental O2 and CO2 in the frog.

The effects of environmental PO2 and PCO2 on cutaneous blood flow and gas exchange were investigated in the frog, Rana pipiens. Halothane (Ha) anesthetized frogs were equilibrated with 9.5% Freon-22 (Fr), 1.1% Ha and air while placed in a box. A gas mixture, initially free of Ha and Fr, was drawn through a small test chamber placed on the abdomen. The excretion of Fr, Ha and CO2 into the sample chamber was analyzed by a mass spectrometer. Under these conditions, changes in Fr or Ha excretion into the sample chamber reflected local changes in skin perfusion. Raising sample chamber [O2] produced concentration-dependent increases in the excretion of all gases measured. Lowering chamber [O2] reduced gas excretion. Increasing chamber [CO2] to 5% decreased the excretion of Fr and Ha. Increasing box [O2] to 86.5% while keeping sample chamber [O2] constant at 21% decreased gas excretion into the chamber. Selectively raising box [CO2] to 4.3% increased gas excretion into the chamber. The results indicate that regional cutaneous blood flow and gas exchange is a direct function of the [O2] directly above that portion of skin, and inversely related to the [O2] over adjacent skin. This regional perfusion-O2 matching may act to optimize total cutaneous gas exchange in the frog. In addition, CO2 may be an important regulator of cutaneous blood flow distribution.

Animals↗
PubMed1979

Morphology of the granular secretory glands in skin of poison-dart frogs (Dendrobatidae).

The granular glands of nine species of dendrobatid frogs were examined using light and electron microscopy. The glands are surrounded by a discontinuous layer of smooth muscle cells. Within the glands proper the secretory cells form a true syncytium. Multiple flattened nuclei lie at the periphery of the gland. The peripheral cytoplasm also contains mitochondria, rough surfaced endoplasmic reticulum, the Golgi apparatus, and an abundance of smooth endoplasmic reticulum. Centrally, most of the gland is filled with membrane-bound granules surrounded by amorphous cytoplasm. Few other organelles are found in this region. Early in the secretory cycle, the central part of the gland is filled with flocculent material which appears to be progressively partitioned off by membranes to form the droplet anlage. As granules form, the structure of the contents becomes progressively more vesicular. Dense vesicles, which bud off from the Golgi apparatus, fuse with the granular membrane during the development of granules, and might contain enzymes involved in toxin synthesis. The granules at this point resemble multivesicular bodies. Their structure is similar in all species of dendrobatid frogs even though the different frogs secrete substances of different chemical structure and toxicity.

Animals↗
PubMed1987

Nuclear changes and morphology of the epidermis in the hibernating frog.

Cytochemical changes of chromatin and DNA in frog epidermal cells were correlated with some morphological features to investigate the skin physiology during hibernation in comparison with the active period. The epidermal cells of hibernating frogs showed less condensed chromatin in all the layers; a greater loss of DNA was found during the transition from the middle to the superficial layer. In the germinative layer, a lesser frequency of hyperdiploid cells and a remarkably low amount of mitoses were detected; this is accompanied by the increase of epidermal thickness and the presence of two layers of cornified cells. The slowing of tissue differentiation and cell renewal kinetics during hibernation can be related to lowered activity of the frog skin. Further, the smaller intercellular spaces as well as the scarcity of puffed ER and vacuoles may be indicative of a lower ion transport in epidermal cells during hibernation.

Animals↗
PubMed1992

Role of the dermal tracts in the pigment pattern of the frog.

The pigment pattern of the ventral skin of the frog Rana esculenta is compared in skin fragments grown for 24 hr with or without antiserum directed to fibronectin (anti-FN). Melanocyte-stimulating hormone (MSH) was added to the medium during the last hour in culture in order to enhance visibility of melanophores in the ventral region of the frog skin. Comparison of these two treatments provides information regarding the precise localization of melanophores in the dermal tracts and their involvement in the pigment pattern of the ventral frog skin. In this regard, the whitish pigment pattern of skin fragments is compared to the tiny black spots found on anti-FN treated skin fragments and the abundant blotchy spots found on skin cultured alone. The distribution of melanophores in the dermal tracts observed in vertical semithin sections is found to be related to the three different levels of the dermal tracts. This report demonstrates the importance of fibronectin as a substrate for the melanophore migration, the importance of the tract level for the melanophore localization both involved in the pigment pattern of the ventral skin.

Animals↗
PubMed1993

Structural study of the frog Rana temporaria larval stomach.

The gastric wall of Rana temporaria tadpoles consists of a well-developed mucosa and thin muscular and serosa layers. Three cellular types--mucous, ciliated and endocrine cells--make up the lining epithelium. Different types of endocrine cells exist. Argyrophylic endocrine cells can be recognized in semithin sections of plastic-embedded material while non-argyrophylic endocrine cells can only be identified under the electron microscope. Glands are composed mainly of well-differentiated oxyntic cells and, occasionally, scarce endocrine cells. Oxyntic cells show abundant mitochondria and smooth endoplasmic reticulum, but do not contain zymogen granules as do those present in adults. Secretory canaliculi with microvilli are also well-developed. The lamina propria contains numerous vascular sinuses and nerve bundles which innervate the endothelium and some endocrine cells. The neuroendocrine regulation of frog gastric functions seems therefore to have developed in young tadpoles. Nerve fibers also innervate the muscular propria, which is composed of a single layer of smooth muscle cells. Underlying the muscle, connective fibers and a flattened layer of mesothelial cells make up the serosa. In summary, the structure of the frog larval stomach shows a well-differentiated histological pattern, especially referring to surface epithelium and glands. Some of the histological traits will also be present in adult frogs while others are characteristic of the tadpole's stage.

Animals↗
PubMed1983

Effects of a cercarial toxin derived from venom of the scorpion Leiurus quinquestriatus on frog skeletal muscle.

Cercarial toxin, a protein purified from Leiurus quinquestriatus venom and toxic to Schistosoma mansoni cercariae, was examined for its effects on frog twitch muscle fibres. In concentrations of 3.4-12 microM the toxin, after a delay of several minutes, produced a slowly developing depolarization of the resting membrane and high frequency miniature endplate potentials associated with spontaneous firing of muscle fibre action potentials and twitching. The action potential duration increased from about 3 to more than 100 msec. In advanced stages of poisoning the amplitude of action potentials decreased while oscillations on the plateau level occurred. Short electrical pulses were followed by repetitive firing of prolonged action potentials, while long stimuli elicited long-lasting action potentials with oscillations on the plateau level. Addition of d-tubocurarine blocked spontaneous sub- and suprathreshold activity. Increasing the Ca concentration of the medium markedly shortened the action potentials and stopped repetitive firing. It is concluded that cercarial toxin interferes with the ionic permeabilities of frog twitch fibres in a way similar to that reported for crude venom or one of its highly toxic fractions in frog nerve.

Action Potentials↗
PubMed1982

Cone lamellae and red and green rod outer segment disks contain a large intrinsic membrane protein on their margins: an ultrastructural immunocytochemical study of frog retinas.

In addition to rhodopsin, the disk membranes of rod outer segments (ROS) contain a large integral membrane protein (mol. wt 290,000). This protein was previously localized by immunocytochemistry to the margins and incisures of disks in frog red ROS by specific antibody applied to thin sections of bovine serum albumin embedded retinas (Papermaster et al., 1978b, J. Cell Biol. 78, 415-425). Upon further study of the reactions of this antibody with outer segments of other photoreceptor classes in frog retina, labeling of the short incisures and margins of green ROS and margins of cone outer segment lamellae is also observed. Thus the large protein participates in the structure of the edges of disks and lamellae of all photoreceptors in the frog. In addition, labeling of the inter-incisure surface of all photoreceptor classes was observed at high antibody concentration. In order to interpret this labeling, the effect of dilution on labeling density was determined and double reciprocal plots (Markham and Benton, 1931, J. Am. Chem. Soc. 53, 497) were employed to evaluate the relative affinity and heterogeneity. There was considerable deviation from linearity in the plots of labeling disk interiors compared to the relatively linear plots of disk incisure labeling which suggests that the interior sites contain a weakly cross-reacting antigen or that the serum contains a lower concentration of antibody weakly reactive with another antigen.

Animals↗
PubMed1985

The specific inhibition of 11-cis-retinyl palmitate formation in the frog eye by diaminophenoxypentane, an inhibitor of rhodopsin regeneration.

The antischistosomal drug 1,5-di-(p-aminophenoxy) pentane (DAPP), an inhibitor of rhodopsin regeneration in the vertebrate retina, is shown to completely block the production of 11-cis-retinyl palmitate in the frog eye. An untreated frog generates a large amount of 11-cis-retinyl palmitate during 1-2 days in the dark after a strong bleach. Also, it is demonstrated that DAPP can deplete the stores of 11-cis-retinyl palmitate in the dark-adapted frog eye. The specificity of DAPP's inhibition of dark-adaptation is explored, and the usefulness of employing retinotoxic drugs to investigate the physiology and biochemistry of rhodopsin regeneration is discussed.

Aniline Compounds↗
PubMed1992

Directional asymmetry of the frog monocular optokinetic nystagmus: cholinergic modulation.

The frog monocular optokinetic gaze nystagmus (OKN) was studied by coil recordings after intravitreal administration of cholinergic drugs into the closed eye. Before injection, the frog displayed OKN for stimulations in the temporo-nasal (T-N) direction only. The injection of muscarinic agonists, as well as that of nicotinic antagonists, provoked the appearance of a naso-temporal (N-T) component, the slow phase velocity gain then being strongly and significantly increased. The abolition of the OKN directional asymmetry indicates that acetylcholine seems to act in opposite ways through muscarinic and nicotinic binding sites. The GABAergic and cholinergic systems may interact to generate and modulate OKN in the frog.

Acetylcholine↗
PubMed1986

Involvement of prostaglandins in the response of frog adrenocortical cells to muscarinic receptor activation.

The role of prostaglandins (PGs) in the mechanism of action of acetylcholine (ACh) on frog adrenocortical cells has been examined. Administration of a single dose of ACh (5 X 10(-5) M) to perifused frog interrenal fragments, for 20 min, stimulated the production of corticosterone, aldosterone, PGE2 and 6-keto-PGF1 alpha. In contrast ACh did not significantly alter TXB2 production. The effect of ACh could be mimicked by muscarine (10(-5) M). Conversely, nicotine (10(-6) to 10(-4) M) was totally inactive. The increase in PG biosynthesis preceded the peak of corticosteroid release. Repeated 20-min pulses of ACh (5 X 10(-5) M) or muscarine (10(-5) M) given at 130-min intervals induced a desensitization phenomenon. In presence of indomethacin (5 X 10(-6) M), the effect of ACh on PG and steroid secretion was totally abolished. In calcium-free medium, the effect of ACh on PG and corticosteroid production was completely blocked. These results indicate that, in the frog, ACh stimulates corticosteroid secretion through a PG-dependent mechanism.

6-Ketoprostaglandin F1 alpha↗
PubMed1994

[3H]dynorphin1-8 binding sites in frog (Rana esculenta) brain membranes.

Opioid binding sites specific for [3H]dynorphin1-8 were characterized in the particulate membrane fraction of frog (Rana esculenta) brain. The degradation of the radioligand during the assay was prevented by the use of a broad spectrum of peptidase inhibitors. The binding of [3H]dynorphin1-8 to frog brain membranes was stereoselective, reversible, saturable, and displaceable by a series of opioid ligands including dynorphin1-13, bremazocine, levorphanol and naloxone. The specific binding of [3H]dynorphin1-8 can be significantly inhibited by Na+ ions and/or guanine nucleotides confirming the agonist property of the ligand in vitro. A single set of high affinity opioid binding sites with a Kd approximately 7.5 nM is present in the membranes. The maximum density of binding sites (Bmax approximately 1.1 pmol [3H]dynorphin1-8 per mg protein) was considerably higher than such sites in guinea-pig brain. In addition, comparison with binding of tritiated opioid peptides selective for the mu- and delta-types of opioid receptor showed that in the frog brain most of the sites labelled by [3H]dynorphin1-8 are kappa-sites and that this is a rich source of such sites.

Amino Acid Sequence↗