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PubMed1989

Effects of gonadectomy and steroids on pituitary gonadotropin secretion in a frog, Rana pipiens.

Secretory dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured at various times following gonadectomy in adult male grass frogs, Rana pipiens. Plasma levels and in vitro initial secretory rates of both LH and FSH increased significantly within 1 wk and remained elevated for 3-4 wk of castration. Pituitary FSH and LH content were unchanged. However, dissociation between the two gonadotropins (Gth) occurred thereafter: Secretion of FSH remained elevated for 70 days, but those of LH declined to control levels after 30 days. In vitro secretion of Gth from gonadectomized (gonadx) frogs declined progressively over time reaching control levels after 24 h incubation. The results indicate that elevated pituitary secretion contributes to the observed circulating LH and FSH levels in gonadx frogs, and that FSH and LH may be controlled independently. Replacement therapy with 17 beta-estradiol (E2) suppressed post-gonadectomy increases in plasma Gth and in vitro responses to GnRH, whereas 5 alpha-dihydrotestosterone (DHT) had little effect in vivo and augmented GnRH responses in long-term castrates. In vitro, E2 also inhibited, while 48 h of DHT treatment had no effect on GnRH responsiveness of pituitaries from gonadx frogs. The actions of these steroids were opposite to those typically observed in mammals (and birds), and support the hypothesis that E2 may contribute to seasonal testicular regression in ranid frogs.

Androgens↗
PubMed2006

Mosquito repellents in frog skin.

The search for novel insect repellents has been driven by health concerns over established synthetic compounds such as diethyl-m-toluamide (DEET). Given the diversity of compounds known from frog skin and records of mosquito bite and ectoparasite infestation, the presence of mosquito repellents in frogs seemed plausible. We investigated frog skin secretions to confirm the existence of mosquito repellent properties. Litoria caerulea secretions were assessed for mosquito repellency by topical application on mice. The secretions provided protection against host-seeking Culex annulirostris mosquitoes. Olfactometer tests using aqueous washes of skin secretions from L. caerulea and four other frog species were conducted to determine whether volatile components were responsible for repellency. Volatiles from Litoria rubella and Uperoleia mjobergi secretions were repellent to C. annulirostris, albeit not as repellent as a DEET control. The demonstration of endogenous insect repellents in amphibians is novel, and demonstrates that many aspects of frog chemical ecology remain unexplored.

Animals↗
PubMed2004

Habitat fragmentation causes bottlenecks and inbreeding in the European tree frog (Hyla arborea).

A genetic study of the European tree frog, Hyla arborea, in Denmark was undertaken to examine the population structure on mainland Jutland and the island of Lolland after a period of reduction in suitable habitat and population sizes. The two regions have experienced the same rate of habitat loss but fragmentation has been more severe on Lolland. Genetic variation based on 12 polymorphic DNA microsatellites was analysed in 494 tree frogs sampled from two ponds in Jutland and 10 ponds on Lolland. A significant overall deviation from Hardy-Weinberg expectations could be attributed to three ponds, all on Lolland. This was most probably caused by an inbreeding effect reducing fitness, which was supported by the observed significant negative correlation between larva survival and mean F(IS) value and mean individual inbreeding coefficient. A significant reduction in genetic variation (bottleneck) was detected in most of the ponds on Lolland. Population-structure analysis suggested the existence of at least 11 genetically different populations, corresponding to most of the sampled population units. The results indicated that the populations were unique genetic units and could be used to illustrate the migration pattern between newly established ponds arisen either by natural colonization of tree frogs or by artificial introduction. A high degree of pond fidelity in the tree frogs was suggested. A severe fragmentation process reducing population size and fitness within some of the populations probably caused the significant reduction in genetic variation of tree frog populations on Lolland.

Animal Migration↗
PubMed1984

Active transepithelial potassium transport in frog skin via specific potassium channels in the apical membrane.

In frog skin bathed in Cl--Ringer's solution the short circuit current (SCC) is equal to the net Na+ flux. In the present study Na+ and K+ transport across frog skin have been investigated in skins bathed in a solution where all Cl- has been substituted by the impermeable anion gluconate. In this solution the net Na+ flux (9.22 +/- 0.72 nmole/cm2/min) was significantly higher than the SCC (7.61 +/- 0.63) nmole/cm2/min). Measurement of the transepithelial K+ influx and K+ efflux showed that the discrepancy between the net Na+ flux and the SCC was caused by an active outwards going transepithelial K+ transport. The K+ but not the Na+ transport could be blocked by adding the K+ channel blocking agent Ba++ to the apical solution. Thus, the K+ transport occurs via a K+ specific pathway in the apical membrane. Ouabain blocked both the Na+ and the K+ transport, whereas the presence of the Na+ channel blocking agent amiloride in the apical solution blocked the Na+ transport and reduced the K+ transport. In the presence of amiloride in the apical solution the SCC and the transepithelial potential difference (PD) reversed so that the outside (the apical side) of the frog skin became positive with respect to the basolateral side. The inverted SCC was carried by an active transepithelial K+ transport, this K+ transport required the presence of Na+ in the basolateral solution. The experiments show that frog skin can insert or activate K+ channels in the apical membrane, indicating that the frog may regulate its K+ content by varying the K+ permeability of the apical membrane.

Amiloride↗
PubMed1968

The release of adenosine triphosphate from frog skeletal muscle in vitro.

1. Active frog sartorius muscle in vitro liberates a substance into the bathing solution which has a pronounced stimulatory action on the frog heart.2. The stimulatory effect is not due to an increase in the K(+) concentration of the bathing solution, nor is it due to the liberation of catecholamines.3. In a molecular sieve chromatography procedure the stimulatory substance can be eluted in a single fraction which shows a maximum absorption of U.V. light at a wave-length of 265 nm, indicative of the presence of substances containing a purine ring.4. Low concentrations (10(-7)-10(-8) g/ml.) of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and uridine triphosphate (UTP) have a marked stimulatory action on the frog heart. The action of ATP and ADP on the heart is qualitatively very similar to that of the muscle bathing solution, while the action of UTP is distinctly different. The triphosphates of inosine, cytidine and guanosine stimulate the heart when in high concentration only. Adenosine and adenosine monophosphate do not stimulate the heart.5. Incubation of the muscle bathing solution and of solutions of ATP with the enzyme apyrase for the same time produces a similar marked reduction in the stimulatory action of both on the heart. Apyrase catalyses the break-down of nucleotide triphosphates to monophosphates.6. The elution behaviour of the stimulatory substance determined by molecular sieve chromatography is the same as that for ATP.7. The muscle bathing solution causes light to be emitted from firefly lantern extract, the pattern of light emission being similar to that produced by nucleotide triphosphates.8. The concentrations of ATP having the same quantitative action on the frog heart and on firefly extract as a given muscle bathing solution are almost identical, whereas the matching concentrations of ADP and UTP in the two methods of assay are widely different.9. It is concluded that ATP is released from active frog skeletal muscle in vitro. This release may play an important part in the reactive hyperaemia of muscular exercise since ATP has a powerful vasodilator action.

Adenosine Triphosphate↗
PubMed1976

Osmotic reflextion coefficients of capillary walls to low molecular weight hydrophilic solutes measured in single perfused capillaries of the frog mesentery.

1. Individual capillaries of the transilluminated frog mesentery have been perfused with suspensions of human red cells in frog Ringer solution containing 1-0 g albumin 100 ml.-1. The outer surface of the mesentery has been washed with normal frog Ringer solution and with frog Ringer solutions made hypertonic by addition of one of the following solutes: sodium chloride (100 m-mole. 1.-1); urea (100 m-mole.1.-1); sucrose (20-50 m-mole. 1.-1); cyanocobalamin (8-5 m-mole. 1.-1). The temperature of the mesentery was between 14 and 16 degrees C in all experiments. 2. Wtih the mesentery superfused with normal Ringer, the filtration coefficient was determined from measurements of the rate of fluid filtration across the capillary wall, at a series of known capillary pressures (Michel, Mason, Curry & Tooke, 1974). Filtration coefficient varied from 0-69 X 10(-3) to 4-45 X 10(-3) mum. sec-1 .cm H2O-1 with an average value of 1-87 X 10(-3) mum. sec-1. cm H2O-1. 3. When the superfusate was made hypertonic by the addition of a test solute, the osmotic reflextion coefficient (sigma) of the capillary wall to test solute was calculated from the additional rate of filtration, the concentration of test solute in the superfusate and the filtration coefficient. Average values for sigma were: sodium chloride, 0-068 +/- 0-03 (three capillaries); urea, 0-071 +/- 0.015 (four capillaries); sucrose, 0-115 +/- 0-023 (seven capillaries); cyanocobalamin, 0-100 +/- 0-03 (three capillaries). 4. In further experiments, the osmotic reflextion coefficients to sodium chloride, urea and sucrose were determined in the same capillary. Five technically acceptable experiments were carried out. Although there were differences in the value of sigma between different capillaries, in any one capillary values of sigma were of the same magnitude and there appeared to be no significant trend with the molecular size of the test solute. 5. Our findings are inconsistent with the hypothesis that there is a single pathway for water and small hydrophilic molecules across the capillary wall. 6. Our results may be interpreted in terms of an exclusive channel for water in parallel with a channel shared by both water and small hydrophilic molecules. It is suggested that the exclusive water channel may be the membranes and cytoplasm of the endothelial cells and the shared channel may be located in the intercellular junctions. 7. Our data suggest the exclusive water channel represents about 10% of the total filtration coefficient in frog mesenteric capillaries. The shared channel shows relatively little restriction to the molecules investigated. Estimates of the volume flow throught the two channels are made for conditions where hydrostatic pressure differences and osmotic pressure differences are the driving forces.

Animals↗
PubMed1976

The passive permeability of the skin of anuran amphibia: a comparison of frogs (Rana pipiens) and toads (Bufo marinus).

1. Efflux of Na across dorsal skin, in vitro (bathed on both sides with Ringer solution), of frogs and toads were similar, but it was greater in ventral skin from the latter. 2. The efflux of Na declined, in both species, when the external surface of ventral, but not dorsal, skin was exposed to hyposmotic solutions with a low Na concentration. This change in Na permeability was influenced by the low osmotic concentration as well as the low Na concentration. 3. Efflux of Cl was similar in both the dorsal and ventral skin preparations (Ringer on both sides) from frogs and toads. 4. Chloride efflux declined in all skin preparations exposed on the external surface to dilute Ringer solution. Solute replacement with sucrose or choline or Na2SO4 showed that the decreased Cl efflux was principally due to the low Cl concentration, though Na may also contribute. This observation suggests the presence of Cl-/Cl- exchange diffusion mechanism. 5. Cutaneous urea permeability was less in toads than frogs and the dorsal and ventral skin was similar with respect to this solute in each species. 6. The presence of external hyposmotic solutions reduced the efflux, but not the influx, of urea across frog, but not toad, skin and it appeared that solvent 'drag' may contribute to this change. 7. Diffusion permeability to water was greater in frogs than toads and in the latter the ventral skin was more permeable than the dorsal. 8. The passive permeability of amphibian skin shows considerable interspecific and regional differences to various molecules which do not necessarily parallel each other. The control of passive cutaneous permeability appears to involve a variety of specific mechanisms, the distribution of which may have evolved during their adaptation to different environments.

Animals↗
PubMed1977

A role for endogneous prostaglandins in the short-circuit current responses to osmolal changes in isolated frog skin.

1. Reduction in osmolality of the Ringer solution bathing the morphological inside of frog skin (by lowering the NaCl concentration) caused a significant increase in sodium transport as measured by the short-circuit current. Pretreatment of the skin with acetylsalicylic acid (2.5 x 10(-4)M) abolished the short-circuit current and open-circuit potential responses to osmolal change.2. The output of prostaglandin-like material from isolated frog skin was increased by incubating the skin in hypotonic Ringer solution.3. The cyclic AMP levels of isolated frog skin were also increased by a reduction in the osmolality of the Ringer fluid bathing the skin.4. Prostaglandin-like material was released both by the separated epithelial and dermal layers of frog skin and the output from both layers, on a unit wet weight basis, did not differ.5. The output of prostaglandin-like material from the separated layers of the skin was substantially greater than from whole skin. Indomethacin (6 x 10(-6)M) reduced the output of this material by more than 90% from both layers.6. The release of prostaglandin-like material from the separated layers of the skin was not altered by a reduction in osmolality of the bathing medium.7. It is concluded that a reduction in the osmolality of the solution bathing frog skin stimulates prostaglandin production and that the increased level of prostaglandins stimulates transepithelial sodium transport by stimulating cyclic AMP accumulation. It is also concluded that the response to osmolal change can only occur in intact skin since separation of the epithelial and dermal layers abolished the increase in the release of prostaglandin-like material to osmolal change. The site of the increased prostaglandin production and the exact nature of the stimulus remain to be determined.

Animals↗
PubMed1981

A comparative study of charge movement in rat and frog skeletal muscle fibres.

1. The middle of the fibre voltage--clamp technique (Adrian & Marshall, 1977), modified where necessary for electrically short muscle fibres, has been used to measure non-linear charge movements in mammalian fast twitch (rat extensor digitorum longus), mammalian slow twitch (rat soleus) and frog (sartorius) muscles. 2. The maximum amount of charge moved in mammalian fast twitch muscle at 2 degrees C in hypertonic solution, was 3--5 times greater than in slow twitch muscle. The voltage distribution of fast twitch charge was 10--15 mV more positive when compared to slow twitch. 3. In both mammalian muscle types hypertonic Ringer solution negatively shifted the voltage distribution of charge some 6 mV. The steepness of charge moved around mechanical threshold was unaffected by hypertonicity. 4. The amount of charge in frog sartorius fibres at 2 degrees C in hypertonic solution was about half of that in rat fast twitch muscle; the voltage distribution of the frog charge was similar to rat soleus muscle. 5. Warming between 2 and 15 degrees C had no effect on either the amount of steady-state distribution of charge in mammalian or frog muscles. 6. At 2 degrees C, the kinetics of charge movement in fast and slow twitch mammalian muscles were similar and 2--3 times faster than frog muscle at the same temperature. In fast and slow mammalian fibres at 2 degrees C similar times were taken to shift the same fractions of the total amount of charge. The Q10 of charge movement kinetics was between 1.2 and 2.0 in the three muscles studied.

Animals↗
PubMed1977

Comparison of methods for the isolation of Salmonella from imported frog legs.

Four methods of sample preparation were compared for their relative efficiency in recovering Salmonella from imported frog legs. No significant difference (P greater than 0.10) was observed in the efficiency of submersion, blending, and stomaching methods, but rinsing recovered significantly fewer (P less than 0.01) Salmonella-positive frog legs than the other three methods. No significant difference (P less than 0.25) was observed in the number of positive frog legs recovered by selenite cystine or tetrathionate broth. Salmonella-Shigella agar, when streaked from either of these broths, gave significantly fewer (P less than 0.01) Salmonella-positive frog legs than brilliant green, bismuth sulfite, xylose lysine deoxycholate, and Hektoen-enteric agars. Use selective agars, resulted in detection of an additional 11 and 6 Salmonella-positive frog legs, respectively. A variety of serotypes, mostly uncommon, was recovered. One Salmonella serotype (6,14,24:r,i:e,n,z15), possessing a heretofore unreported antigenic formula, was isolated.

Bacteriological Techniques↗
PubMed1969

Biophysical properties of frog virus and its deoxyribonucleic acid: fate of radioactive virus in the early stage of infection.

Frog virus (FV-3) was banded by isopycnic centrifugation in cesium chloride, sucrose, or potassium tartrate. Two bands of infectivity were regularly found at positions in cesium chloride corresponding to densities of 1.26 and 1.30 g/cm(3), respectively. Deoxyribonucleic acid from either band had the following characteristics: double-stranded; a T(m) of 76.3 C in 0.1 SSC (0.015 m NaCl plus 0.015 m sodium citrate) and a buoyant density of 1.720 g/cm(3) in cesium chloride, corresponding to a guanine plus cytosine content of 56 to 58% and a molecular weight of 130 x 10(6) daltons, determined by velocity sedimentation. These data, together with electron micrographs of sections of cells infected with material from either band suggest that two types of infectious frog virus particles exists, rather than a second virus in the frog virus stocks. The composition of frog virus was determined. It was found that highly purified preparations of frog virus were composed of 55.8% protein, 30.1% deoxyribonucleic acid, and 14.2% lipid. The kinetics of adsorption and uncoating of FV-3 was studied with radioactive virus. Uncoating is comparatively rapid and in contrast to poxvirus is unaffected by inhibitors of protein synthesis.

Adsorption↗
PubMed1992

Cyclic nucleotide phosphodiesterases from frog atrial fibers: isolation and drug sensitivities.

The cyclic nucleotide phosphodiesterase (PDE) forms present in frog atrial fibers were isolated and characterized by their drug sensitivities. DEAE-sephacel chromatography of cytosolic PDE activity resolved three major PDE forms: peak A hydrolyzed both adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) and was activated by calcium-calmodulin (PDE I); peak B also hydrolyzed both cAMP and cGMP but was activated by 5 microM cGMP (PDE II); peak C specifically hydrolyzed cAMP (PDE IV). Rolipram specifically inhibited PDE IV (Ki = 1.1 microM), whereas dipyridamole potently inhibited both PDE II (Ki = 4.6 microM) and PDE IV (Ki = 0.8 microM). Atrial fiber PDE I was preferentially inhibited by zaprinast (Ki = 10 microM). 3-Isobutyl-1-methyl xanthine (IBMX) and theophylline inhibited nonspecifically all three different enzymes. The positive inotropic drug CI 930 only inhibited the different isolated atrial PDE forms at concentrations greater than 200 microM. However, under assay conditions for which PDE IV was specifically inhibited (presence of 100 microM rolipram), an IC50 of 17 microM for CI 930 was observed on the remaining 26% cAMP hydrolytic activity of peak C (which could represent a cGMP-inhibited PDE form: PDE III). The same PDE forms were also found in frog ventricle. The major difference between frog atrial fiber (and ventricular tissue) PDEs and mammalian cardiac PDEs is that the main cytosolic cAMP-specific hydrolytic activity in frog heart is due to PDE IV rather than PDE III. Rolipram, dipyridamole, and zaprinast might be useful tools to investigate the participation of cAMP in frog atrial contraction (unpublished observations).

1-Methyl-3-isobutylxanthine↗
PubMed1991

Resumption of physiological functions in the wood frog (Rana sylvatica) after freezing.

We monitored the resumption of physiological functions in frogs that were frozen at -2 to -3 degrees C for 24 h and thawed rapidly (at 23-25 degrees C) or slowly (at 6-8 degrees C). Bodily functions were restored sooner during fast thawing, but this did not enhance the survival of frogs. The first physiological parameter to return was cardiac function, but during the early stages of thawing heart rates were lower than heart rates of unfrozen frogs at comparable body temperatures. Heart rates increased thereafter in conjunction with the rise in frog body temperatures. Spontaneous breathing and hindleg reflexes resumed after cardiac function, but neither response was exhibited by all frogs after the conclusion of the observation periods (3-4 h). Finally, isolated gastrocnemius muscles that had undergone in vitro freezing showed no significant (P greater than 0.05) impairment of twitch and tetanic tensions even as soon as 1 h after the onset of thawing. Body systems thus vary in their rates of recovery after nonlethal freezing episodes. Furthermore, recovery of specific body systems corresponds to essential needs that must be met immediately after thawing, such as reperfusion of body tissues.

Animals↗
PubMed1993

Dehydration tolerance in wood frogs: a new perspective on development of amphibian freeze tolerance.

Wood frogs, Rana sylvatica, tolerate the loss of 50-60% of total body water during experimental dehydration. The rate of water loss for unprotected frogs is the same whether animals are frozen (at -2 degrees C) or unfrozen (at 1 degrees C) but is greatly reduced when frogs are frozen under a protective layer of moss. Dehydrational death could occur in as little as 7-9 days for unprotected animals; this indicates the importance for winter survival of selecting well-protected and damp hibernation sites. Prior dehydration affected the cooling and freezing properties of frogs, reducing supercooling point and the amount of ice formed after 24 h at -2 degrees C and acting synergistically with freezing exposure in stimulating cryoprotectant synthesis. Analysis of the effects of controlled dehydration at 5 degrees C showed that changes in body water content alone (without freezing) stimulated liver glycogenolysis and the export of high concentrations of glucose into blood and other organs. Autumn-collected frogs dehydrated to 50% of total body water lost showed glucose levels of 165-1,409 nmol/mg protein in different organs, increases of 9- to 313-fold compared with control values and reaching final levels very similar to those induced by freezing exposure. The data support the proposal that various adaptations for natural freeze tolerance may have been derived from preexisting mechanisms for dealing with water stress in amphibians and that cell volume change may be one of the signals involved in triggering and sustaining molecular adaptations (e.g., cryoprotectant output) that support freezing survival.

Adaptation, Physiological↗
PubMed1997

Freezing-induced genes in wood frog (Rana sylvatica): fibrinogen upregulation by freezing and dehydration.

Differential screening of a cDNA library produced from liver of the freeze-tolerant wood frog, Rana sylvatica, was used to search for freezing-induced genes. Five freezing-responsive cDNA clones representing different genes were isolated when approximately 80,000 plaques of a cDNA library, prepared from liver of frozen frogs (24 h at -2.5 degrees C), were screened with 32P-labeled total cDNA probes from control (5 degrees C) versus freezing-exposed frogs. Two clones, pBfFR45 and pBfFR04, are reported here in detail and were found to be homologous with the genes for the alpha- and gamma-subunits of fibrinogen, respectively. The clone pBfFR45 carried a 2,305-hp cDNA sequence that was of bipartite structure, containing two open reading frames (ORFs). The first ORF potentially encoded a 332-residue polypeptide, covering a partial sequence of the NH2-terminal region of the alpha-chain. The second ORF encoded a 247-amino acid sequence, covering the whole COOH-terminal region of the alpha-chain; this was highly homologous to the FASORF (fibrinogen-alpha second ORF) of chicken alpha-fibrinogen and the extended alpha-chain of the human protein. Under control (5 degrees C) conditions, moderate levels of fibrinogen alpha- and gamma-transcripts were exclusively found in liver. When frogs were given survivable freezing exposures, levels of these transcripts in liver were highly induced. Transcription of these genes was also elevated in gut and lung during freezing, but mRNA levels in these tissues were lower than in liver. A time course assay confirmed that the transcript levels of both alpha- and gamma-subunit genes were dramatically elevated within the early hours of freezing and reached a maximum threefold increase over control levels after 8 h of freezing exposure. Two other physiological stresses, whole body dehydration and anoxia exposure, mimic individual elements of freezing stress in wood frogs. Northern blot hybridization analysis showed that the expression of both the alpha- and gamma-genes was also upregulated in response to dehydration in vivo (20% of total body water lost), but both were completely inhibited by anoxia exposure.

Amino Acid Sequence↗
PubMed1985

cAMP- and beta-adrenergic-stimulated chloride-dependent Ca2+ secretion in frog skin.

This study examined the possible existence and nature of Ca2+ transport in frog skin using 45Ca fluxes and short-circuiting technique. Following the addition to full-thickness frog skin (FTFS) of 8-[p-chlorophenylthio]cAMP (8-CPT-cAMP), forskolin, or 1-methyl-3-isobutylxanthine, the secretory Ca2+ flux increased severalfold, inducing net Ca2+ secretion. The absorptive flux was unchanged. Isoproterenol (10(-6)M) reproduced the effects of cAMP on Ca2+ secretion (-3.76 +/- 0.80 nmol X cm-2 X h-1 vs. +0.04 +/- 0.05 in control) while vasopressin and parathyroid hormone did not alter Ca2+ fluxes. Because FTFS contains subepidermal glands capable of Cl- secretion in response to beta-adrenergic stimulation, split-thickness frog skin (STFS) consisting of the gland-free Na-absorbing surface epithelium was used to localize the anatomic site of Ca2+ secretion. In STFS, addition of 8-CPT-cAMP or isoproterenol failed to induce Ca2+ secretion, suggesting that this transport in FTFS is localized in skin glands. Additional studies explored the relationship between Ca2+ and Cl- transport in FTFS. Furosemide prevented the stimulation of both Ca2+ and Cl- secretion. Removal of Cl- from the bathing medium abolished Ca2+ secretion. Thus, FTFS exhibits a beta-adrenergic, cAMP-stimulated net Ca2+ secretion that is Cl- dependent. As this effect is not observed in STFS, the pathway of Ca2+ secretion in frog skin is probably localized in the subepidermal glandular epithelium in association with Cl- secretion. Frog skin glands may represent a useful model for the study of Ca2+ transport in Cl--transporting epithelia.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Mucus-depleted frog palate as a model for the study of mucociliary clearance.

To better understand the frog palate model of mucociliary transport, we measured the transport rate of mucus (MTR) from the leopard frog, Rana pipiens, and from the bullfrog, R. catesbeiana, recorded the stability of the MTR over a period of hours and days and over the course of 1 yr, and measured the viscoelasticity, percent solid composition, and spinnability (filance) of mucus from both species. Bullfrog mucus was less rigid than leopard frog mucus (log G* at 1 rad/s 2.09 vs. 2.61; P less than 0.01) and had a higher viscosity-to-elasticity ratio (tan delta at 1 rad/s 0.36 vs. 0.26; P less than 0.05). It also had a lower solids content (8.71 vs. 13.72%; P = 0.02), and there was a trend to lower spinnability for bullfrog mucus (filance 26.7 vs. 33.5 mm). These data suggest that bullfrog mucus has viscoelastic properties similar to normal mammalian respiratory mucus and leopard frog mucus has viscoelasticity similar to sputum samples. MTR was significantly slower in the winter than in the summer months (17 vs. 30 mm/min; P less than 0.0001). Although the leopard frog palate could be used for at least 7 consecutive days without exhaustion, bullfrog palates could be used for only 5 days. Palates of either species could generally be tested for 6 h/day without a significant decrease in MTR. These data clarify some of the sources of variability in the use of this system and suggest methods of standardization.

Animals↗
PubMed1991

Kinematics and control of frog hindlimb movements.

1. The determinants of the motion path of the hindlimb were explored in both intact and spinal frogs. In the spinal preparations the kinematic properties of withdrawal and crossed-extension reflexes were studied. In the intact frog the kinematics of withdrawal and swimming movements were examined. Frog hindlimb paths were described in joint angle (intrinsic) coordinates rather than limb endpoint (extrinsic) coordinates. 2. To study withdrawal and crossed-extension reflexes, the initial angles at the hip, knee, and ankle were varied. Withdrawal and crossed extension were recorded in three dimension (3-D) with the use of an infra-red spatial imaging system. Swimming movements against currents of different speeds were obtained with high-speed film. 3. Three strategies were considered related to the form of the hypothesized equilibrium paths specified by the nervous system: all trajectories lie on a single line in angular coordinates; all trajectories are directed toward a common final position; and all trajectories have the same direction independent of initial joint configuration. 4. Joint space paths in withdrawal were found to be straight and parallel independent of the initial joint configuration. The hip and knee were found to start simultaneously and in 75% of the conditions tested to reach maximum velocity simultaneously. Hip-knee maximum velocity ratios were similar in magnitude over differences in initial joint angles. This is consistent with the observation of parallel paths and supports the view that the nervous system specifies a single direction for equilibrium trajectories. 5. Straight line paths with slopes similar to those observed in withdrawal in the spinal preparation were found in swimming movements in the intact frog. Straight line paths in joint space are consistent with the idea that swimming and withdrawal are organized and controlled in a joint-level coordinate system. The similarities observed between spinal and intact preparations suggest that a common set of constructive elements underlies these behaviors. 6. Path curvature was introduced when joint limits were approached toward the end of the movement. Depending on the initial joint angles, the joint movements ended at different times. When initial joint angles were unequal, joints moving from smaller initial angles reached their functional limits earlier and stopped first. 7. In withdrawal and crossed extension in the spinal frog, velocity profiles at a given joint were similar over the initial portion of the curve for movements of different amplitude. This is consistent with the idea that withdrawal and crossed-extension movements of different amplitude are produced by a constant rate of shift of the equilibrium position.

Animals↗