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PubMed1994

Dynamics of retinotectal synaptogenesis in normal and 3-eyed frogs: evidence for the postsynaptic regulation of synapse number.

Quantitative stereological methods were used to determine if the number, density, and types of synaptic connections formed during development are regulated by presynaptic input or by postsynaptic target cells in the optic tectum of normal and 3-eyed Rana pipiens tadpoles and frogs. Our analysis indicates that the number and size of synapses is approximately the same in both tecta of 3-eyed tadpoles and frogs, even though one tectal lobe is receiving input from twice the normal complement of retinal ganglion cells. Moreover, the number and size of synapses in the tectal lobes of 3-eyed animals did not differ significantly from values determined for normal tadpoles and frogs of the same developmental stage. These data suggest strongly that developing tectal cells regulate the number of synaptic contacts they will form. Differences in several morphological features between singly and doubly innervated tecta, however, including synapse density, distribution and complexity, amount of extracellular space, and number of myelin figures, suggest that the presence of supernumerary input retards tectal maturation. We propose that the noncorrelated activity of retinal ganglion cell terminals in the doubly innervated tectum results in fewer stabilized synapses per unit volume of neuropil and in the delayed maturation of the tectal neuropil. Taken together, our data suggest a complex dynamic interaction between retina and tectum during development.

Animals↗
PubMed1978

Antibody diversity in amphibians: inheritance of isoelectric focusing antibody patterns in isogenic frogs.

Anti-sheep red cell, anti-dinitrophenyl, anti-phosphorylcholine antibody responses have been followed in isogenic frogs of the genus Xenopus. Isoelectric focusing antibody patterns show a high degree of overlap for all antigens studied, and a heterogeneity that is lower than in mammals for the same antigens. Inheritance of antibody isoelectric focusing spectrotypes was demonstrated for sheep red cells and dinitrophenyl in two clones of isogenic animals. Outbred frogs show a higher frequency of spectrotype sharing than outbred mammals. It is therefore suggested that antibody diversity is lower in frogs than in mammals.

Animals↗
PubMed1994

Characteristics of Na+ current in Schwann cells cultured from frog sciatic nerve.

Characteristics of voltage-dependent currents in cultured frog Schwann cells were investigated by the whole-cell clamp technique. An inward current was detectable at a membrane potential level more positive than -50 mV and reached a maximum value at about -10 mV, while no rectifying channel was present. The inward current was carried by Na+ ions, because the extrapolated reversal potential of the current agreed with the calculated ENa, and the current was sensitive to tetrodotoxin. The membrane potential for half-maximal inactivation was -82 mV. The inactivation curve indicated that more than 90% of the Na+ channels were inactivated at the resting membrane potential, suggesting that the cultured frog Schwann cells could not generate an action potential under physiological conditions. The time constant for the inactivation at a maximum current was 5.3 ms (-10 mV, 13 degrees C). The electrophysiological characteristics of the Na+ current in the cultured frog Schwann cells were compared with those in other tissues. This Na+ current was quantitatively different from that observed in the amphibian node of Ranvier but was similar to that in the mammalian Schwann or glial cells, especially in the more hyperpolarized half-maximal inactivation potential and in the slower inactivation time course.

Animals↗
PubMedDate not supplied

Exposure of Rana ridibunda to lead II. Impact of lead on various parameters of liver metabolism of the frog Rana ridibunda.

There are no data at present on the impact of lead (Pb) on amphibian metabolism, although declines of amphibian populations due to man-made changes in the environment have been recorded in recent years. We studied the impact of Pb on the liver metabolism of the frog Rana ridibunda by measuring the hepatic levels of glycogen, lactate, total fat, protein and glucose. Liver is one of the primary target organs of Pb bioaccumulation. Frogs were exposed for 4, 10 and 30 days to 14 mg l(-1) of Pb (in the form of Pb(NO(3))(2) dissolved in water) and compared with matched controls. The level of glycogen in the liver increased until day 30. The increase of the metabolite was time-dependent because there was a positive correlation (r = 0.994, P = 0.006) between glycogen concentration and the days of Pb exposure. Lactate concentration declined continuously up to day 30. Liver fat content decreased from day 10 to day 30. Protein concentration declined continuously until day 30. Glucose concentration increased up to day 30. Glycogen concentration was correlated negatively with liver fat content (r = -0.474, P = 0.005), liver protein content (r = -0.562, P = 0.0004) and lactate concentration (r = -0.472, P = 0.005), whereas it was correlated positively with the Pb burden of the liver (r = 0.578, P = 0.0005). The frog appeared to face a metabolic stress over the 30 days of Pb exposure, without being able to control it. We concluded that the increase of liver glycogen concentration was due to gluconeogenesis via lactate and lipolysis. Further experimentation on key gluconeogenic and lipolytic enzymes over the 30 days of Pb exposure would elucidate the mechanisms that may lead to such phenomena.

Animals↗
PubMed2005

A serotonin receptor antagonist induces oocyte maturation in both frogs and mice: evidence that the same G protein-coupled receptor is responsible for maintaining meiosis arrest in both species.

Accumulating evidence has indicated that vertebrate oocytes are arrested at late prophase (G2 arrest) by a G protein coupled receptor (GpCR) that activates adenylyl cyclases. However, the identity of this GpCR or its regulation in G2 oocytes is unknown. We demonstrated that ritanserin (RIT), a potent antagonist of serotonin receptors 5-HT2R and 5-HT7R, released G2 arrest in denuded frog oocytes, as well as in follicle-enclosed mouse oocytes. In contrast to RIT, several other serotonin receptor antagonists (mesulergine, methiothepine, and risperidone) had no effect on oocyte maturation. The unique ability of RIT, among serotonergic antagonists, to induce GVBD did not match the antagonist profile of any known serotonin receptors including Xenopus 5-HT7R, the only known G(s)-coupled serotonin receptor cloned so far in this species. Unexpectedly, injection of x5-HT7R mRNA in frog oocytes resulted in hormone-independent frog oocyte maturation. The addition of exogenous serotonin abolished x5-HT7R-induced oocyte maturation. Furthermore, the combination of x5-HT7R and exogenous serotonin potently inhibited progesterone-induced oocyte maturation. These results provide the first evidence that a G-protein coupled receptor related to 5-HT7R may play a pivotal role in maintaining G2 arrest in vertebrate oocytes.

Animals↗
PubMed2002

Identification of alpha1-adrenergic receptors and their involvement in phosphoinositide hydrolysis in the frog heart.

The aim of this study was to characterize alpha(1)-adrenergic receptors in frog heart and to examine their related signal transduction pathway. alpha(1)-Adrenergic binding sites were studied in purified heart membranes using the specific alpha(1)-adrenergic antagonist [(3)H]prazosin. Analysis of the binding data indicated one class of binding sites displaying a K(d) of 4.19 +/- 0.56 nM and a B(max) of 14.66 +/- 1.61 fmol/mg original wet weight. Adrenaline, noradrenaline, or phenylephrine, in the presence of propranolol, competed with [(3)H]prazosin binding with a similar potency and a K(i) value of about 10 microM. The kinetics of adrenaline binding was closely related to its biological effect. Adrenaline concentration dependently increased the production of inositol phosphates in the heart in the presence or absence of propranolol. Maximal stimulation was about 8.5-fold, and the half-maximum effective concentration was 30 and 21 microM in the absence and presence of propranolol, respectively. These data clearly show that alpha(1)-adrenergic receptors are coupled to the phosphoinositide hydrolysis in frog heart. To our knowledge, this is the first direct evidence supporting the presence of functional alpha(1)-adrenergic receptors in the frog heart.

Animals↗
PubMed1988

Electrophysiological study of the effects of cardiodilatin 1-16 on the frog spinal cord in vitro.

Using the isolated spinal cord of the frog, hemisected and further divided into two distinct quadrants, we studied electrophysiological changes produced by peptides present in the atrial natriuretic factor (ANF) preprohormone. ANF and related peptides (atriopeptin I and atriopeptin III) did not affect the frog spinal cord. The 1-16 fragment from cardiodilatin (10(-5) M) induced slow depolarization in ventral and dorsal nerve stumps. The depolarization was associated with an increase of the evoked dorsal root potentials and depression of the fast component of the reflex responses. When depolarization approached its maximum value, spontaneous slow potentials appeared progressively similar to the evoked potentials, and became rhythmic until they reached a frequency of one potential every 15-20 seconds. The effects of cardiodilatin 1-16 are localized at dorsal horn level. It is suggested that this substance exerts a modulatory effect on frog cord physiology.

Animals↗
PubMed1992

Intrinsic pigment cell stimulating activity in the skin of the leopard frog, Rana pipiens.

Consistent with the concept that specific pigment patterns of amphibians might result from the highly localized distribution of stimulators and inhibitors of pigment cell expression in the skin, the spot pattern of the leopard frog, Rana pipiens, was examined through the use of the Xenopus neural tube explant assay system (Fukuzawa and Ide, 1988). Media conditioned with pieces of skin from dorsal black spotted areas promoted melanization of neural crest cells at a significantly higher level than did media conditioned with dorsal interspot skin in the absence of extra tyrosine. All conditioned media contained exceedingly low concentrations of tyrosine. With the addition of supplemental tyrosine, the melanization capacity of conditioned media from the interspot areas was elevated to that of the spotted skin. Control media conditioned with ventral frog skin inhibited melanization, as usual, because of the presumed presence of melanization inhibiting factor (MIF). It is considered that dorsal skin contains a melanization stimulating factor (MSF) which is present in significantly higher levels in spotted skin than in interspot areas and that expression of the particular pigmentary pattern of this leopard frog is regulated by the relative distribution of MIF, MSF, and possibly other intrinsic substances present in the skin.

Animals↗
PubMed2004

Sexually dimorphic basal water absorption at the isolated pelvic patch of Japanese tree frog, Hyla japonica.

Frogs ingest little water orally, but absorb the majority of the water needed for normal physiological performance through a specific region of the ventral skin, the pelvic patch. We observed non-stimulated (basal water absorption, BWA) water flux through the isolated pelvic patch in vitro in Japanese tree frog (Hyla japonica). We found that water flux through non-stimulated skin from the pelvic patch was greater in males than females. This water flux was confirmed as BWA by observing no effect following the in vitro administration of propranolol and [adamantaneacetyl(1), O-Et-D-Tyr(2), Val(1), aminobutyryl(6), Arg(8, 9)] vasopressin, which are a beta-adrenergic receptor antagonist and a vasopressin V2 receptor antagonist, respectively. We further examined this phenomenon following gonadectomy, treatment with sex hormones (E2, 17beta-estradiol; TP, testosterone propionate), estrogenic chemicals (BPA, bisphenol A; MTX, methoxychlor) or prolactin (PRL, a hormone regulated by sex hormones that has osmoregulatory activity). Ovariectomy increased BWA in females. Injection (in vivo treatment) of E2 or PRL reduced BWA in males, whereas TP injection increased BWA in females. However, the in vitro addition of E2, TP, or PRL to the Ringer's solution on the serosal side of the ventral skin patch did not alter BWA. Subsequently, we injected (in vivo treatment) BPA or MTX, environmental chemical contaminants with known hormonal actions in mammals. Injection of BPA or MTX reduced BWA in males as observed following treatment with E2. These results provide the first evidence of sexual dimorphism in BWA through the isolated pelvic patch. The gonad appears essential for observed sexual dimorphism in BWA, and we hypothesize that sex hormones regulate the release of PRL, that in turn influences BWA indirectly. E2 is known to exert a specific stimulatory effect on PRL secretion. In addition, we have observed that some endocrine disrupting contaminants also eliminate the sexual dimorphism in BWA observed in the Japanese tree frog.

Adrenergic beta-Agonists↗
PubMed2006

The tactile-stimulated startle response of tadpoles: acceleration performance and its relationship to the anatomy of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles.

I described the tactile-stimulated startle response (TSR) of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles. One purpose was to rank species in terms of maximum acceleration performance. Also, I tested whether anatomical indicators of performance potential were predictive of realized performance. TSRs were elicited in a laboratory setting, filmed at 250 Hz, and digitally analyzed. TSRs began with two, initial body curls during which tadpoles showed a broad spectrum of movement patterns. TSR performance was quantified by maximum linear acceleration and maximum rotational acceleration of the head/body, both of which tended to occur immediately upon initiation of motion (< 0.012 sec into the response). Bullfrog tadpoles had higher maximum acceleration than the other species, but other interspecific differences were not significant. The species' rank order for the anatomical indicator of linear acceleration potential was bullfrog > wood frog > American toad. The species' rank order for the anatomical indicator of rotational acceleration potential was bullfrog > wood frog = American toad. Thus, the anatomical indicators roughly predicted the rank order of interspecific average performance. However, the anatomical indicators did not correlate with individual tadpole performance. Variability in behavioral patterns may obscure the connection between anatomy and performance. This is seen in the current lack of intraspecific correlation between a morphological indicator of acceleration capacity and acceleration performance.

Animals↗
PubMed2004

The crab-eating frog, Rana cancrivora, up-regulates hepatic carbamoyl phosphate synthetase I activity and tissue osmolyte levels in response to increased salinity.

The crab-eating frog Rana cancrivora is one of only a handful of amphibians worldwide that tolerate saline waters. They typically inhabit brackish water of mangrove forests of Southeast Asia, but live happily in freshwater and can be acclimated to 75% seawater (25 ppt) or higher. We report here that after transfer of juvenile R. cancrivora from freshwater (1 ppt) to brackish water (10 -->20 or 20 -->25 ppt; 4-8 d) there was a significant increase in the specific activity of the key hepatic ornithine urea cycle enzyme (OUC), carbamoyl phosphate synthetase I (CPSase I). At 20 ppt, plasma, liver and muscle urea levels increased by 22-, 21-, and 11-fold, respectively. As well, muscle total amino acid levels were significantly elevated by 6-fold, with the largest changes occurring in glycine and beta-alanine levels. In liver, taurine levels were 5-fold higher in frogs acclimated to 20 ppt. There were no significant changes in urea or ammonia excretion rates to the environment. As well, the rate of urea influx (J(in) (urea)) and efflux (J(out) (urea)) across the ventral pelvic skin did not differ between frogs acclimated to 1 versus 20 ppt. Taken together, these findings suggest that acclimation to saline water involves the up-regulation of hepatic urea synthesis, which in turn contributes to the dramatic rise in tissue urea levels. The lack of change in urea excretion rates, despite the large increase in tissue-to-water gradients further indicates that mechanisms must be in place to prevent excessive loss of urea in saline waters, but these mechanisms do not include cutaneous urea uptake. Also, amino acid accumulation may contribute to an overall rise in the osmolarity of the muscle tissue, but relative to urea, the contribution is small.

Amino Acids↗
PubMed2004

Muscles of the pes of hylid frogs.

Complete or partial dissection of the foot musculature of 404 hylid frogs representing 247 species and 33 genera, along with representatives of eight other families, revealed a number of apomorphic characters that distinguish the hyloid frogs (Hylidae plus Allophryne and Centrolenidae) from other bufonoid frogs. Additional characters were found to define some of the hylid subfamilies. Addition of characters from the foot musculature to Duellman's phylogenetic tree of the hyloids produced a tree in which Allophryne and Centrolenidae are nested within Hylidae. Support was found for the monophyly of the 30-chromosome group within Hyla, and for a large number of the groups that comprise "Boana," viz., the Hyla albomarginata, H. albopunctata, H. boans (except H. vasta), H. geographica, and H. pulchella groups, but foot muscle characters provide no information relating to relationships of the West Indies hylines.

Animals↗
PubMed1979

The chemoarchitectonics of the diencephalon of frog (Rana tigrina).

The study deals with the distribution of acid and alkaline phosphatases, ATPase, 5-nucleotidase, nonspecific esterase, specific cholinesterase, and beta-galactosidase in the diencephalon of the frog. The highlights of the present study are the following: i) Acid phosphatase is present in all the neurons, whereas the tracts and commissures are completely negative. ii) Most of the tracts and commissures are positive for 5-nucleotidase. This confirms the author's previous findings that the tracts and commissures of all the areas of frog brain are intensely positive for 5-nucleotidase. iii) beta-galactosidase activity in the nuclei of the diencephalon is either mild or completely absent, whereas the commissures and tracts show positive activity. iv) Habenulothalamic connections are intensely positive for specific cholinesterase and non-specific esterase, moderately positive for beta-galactosidase and completely negative for other enzymes. v) The epiphysis (pineal organ) shows intense reaction for adenosine triphosphatase, acid phosphatase, and 5-nucleotidase and moderate reaction for alkaline phosphatase and non-specific esterase. In contrast to the above enzymes, the specific cholinesterase and beta-galactosidase are completely missing. vi) Lateral forebrain bundles are completely negative for all the enzymes except alkaline phosphatase and beta-galactosidase. The distribution of these enzymes has been correlated with the functional aspects of various nuclei, tracts, and commissures of the diencephalon of the frog.

Acid Phosphatase↗
PubMed2002

Electrophysiologic effect of gallium arsenide laser on frog gastrocnemius muscle.

BACKGROUND AND OBJECTIVE: In this study, the effect of low energy Gallium arsenide (GaAs) laser irradiation on the compound action potential of frog gastrocnemius muscle were investigated. STUDY DESIGN/MATERIALS AND METHODS: Sixty frogs were divided into different six dose groups: laser 1 (1 Hz), laser 2 ( 4 Hz), laser 3 (16 Hz), laser 4 (64 Hz), laser 5 (128 Hz), and laser 6 (1,000 Hz, DC, continue) (in each group n=10). Low energy GaAs laser (wavelenght: 904 nm, pulsed duration: 220 nanoseconds, peak power per pulse: 27 W, total applied energy density: 0.001-25.7 J/cm2) was used for the experiment. Compound muscle action potentials were recorded before laser irradiation and these data were accepted as control group. After recording the control data, each muscle was irradiated by the laser. Action potentials were recorded at 1, 5, 10, 15, and 20 minutes of irradiation time in each group by using standartized needle electromyography and nerve conduction study techniques. Distal motor latency, peak to peak amplitude, area, and total duration of action potential were measured. Repeated measures analysis of variance were used for the statistical evaluation. RESULTS: No significant differences were detected between control and laser dose groups in muscle action potential parameters. CONCLUSIONS: This study revealed that at the different repetition rate and exposure time, low energy GaAs laser does not have any significant effect on frog gastrocnemius action potential.

Animals↗
PubMed1990

Metamorphosis alters the response to spinal cord transection in Xenopus laevis frogs.

A series of studies has examined the response of the spinal cord to lesions made at various stages prior to and after metamorphic climax in the clawed frog Xenopus laevis. Complete transections made between Nieuwkoop and Faber (1956) stages 50 and 62 were followed by gradual recovery of righting and coordinated swimming as animals metamorphosed into juveniles (stage 66). Examination of descending axonal projections using horseradish peroxidase (HRP) showed fibers crossing the lesion site and distributing to the caudal lumbar spinal cord. These fibers could be traced from more rostral spinal segments as well as from brainstem injections of HRP. No evidence for rostrally projecting fibers crossing the lesion was obtained. Juvenile frogs of varying ages failed to demonstrate recovery of coordinated swimming or reconstitution of spinal descending pathways. In an additional series of animals, spinal transections were made within 1 or 2 days of tail resorption to assess whether regenerative capacities extended at all into post-metamorphic stages. No evidence for regeneration was found. Studies of metamorphosing frogs after spinal transections showed that fibers crossed the lesion within 5-12 days of transection, well prior to the end of metamorphic climax; however, in some cases in which metamorphosis seemed arrested, little regeneration was observed. Immunocytochemical studies showed that fibers containing serotonin (5-HT) were included in the population of axons that rapidly crossed the lesion after transection at metamorphic stages. These results are compared to those for lesions of the dorsal columns and other systems in developing and juvenile Xenopus. It is suggested that both metamorphosis-related hormonal changes, and axon substrate pathways, may affect the regenerative response in the Xenopus central nervous system (CNS).

Animals↗
PubMed1991

Elevated levels of polyneuronal innervation persist for as long as two years in reinnervated frog neuromuscular junctions.

When the nerve to an adult frog sartorius muscle is crushed, and axons are allowed to regenerate, the level of polyneuronal innervation at reinnervated neuromuscular junctions is higher than normal. With time, much of this polyneuronal innervation is reduced by the process of synapse elimination (Werle and Herrera, 1988). Using intracellular recording, we estimated the level of polyneuronal innervation in adult frog (Rana pipiens) sartorius muscles 2 years (range: 1.7-2.4 years) after crushing the sartorius nerve. We found that 27% (S.E. = 1.4%) of the junctions in muscles 2 years after reinnervation were polyneuronally innervated, whereas only 10% (S.E. = 1.2%) of the junctions in normal frog muscles were polyneuronally innervated. Thus, the synapse elimination that occurs following reinnervation does not restore the normal level of polyneuronal innervation. Histological comparisons of junctional structure between muscles 2 years after reinnervation and normal muscles revealed substantial differences. Reinnervated junctions had a greater length of synaptic gutter apposed by nerve terminal processes, more axonal inputs, more empty synaptic gutter, more instances of single synaptic gutters innervated by more than one axon, and longer lengths of nerve terminal processes that connect synaptic gutters within a junction. On the basis of this physiological and anatomical evidence, we conclude that nerve injury causes persistent changes in the pattern of muscle innervation.

Animals↗
PubMed1994

Neural organization of the ventilatory activity in the frog, Rana catesbeiana. I.

In order to elucidate the neural basis for lung ventilation in the frog, we have investigated the efferent neural activity to oropharyngeal muscles in the decerebrate, paralyzed, unanesthetized bullfrog, Rana catesbeiana. Efferent motor output was recorded from the mandibular branch of the trigeminal (Vmd), the laryngeal branch of the vagus (Xl), and the main and sternohyoid branches of the hypoglossal nerve (Hm and Hsh, respectively). Two types of rhythmic bursting outputs were observed: (1) a high-frequency, low-amplitude, reciprocal oscillation between Vmd, a buccal levator nerve, and Hsh, a buccal depressor nerve; and (2) a low-frequency, high-amplitude, synchronous bursting of Vmd, Hm, Hsh, and Xl. The first type is inferred to represent fictive oropharyngeal ventilation. The second type of burst was divided into four intervals: (a) augmenting activity of Hsh; (b) activation of Xl with continued activation of Hsh; (c) activation of Vmd and Hm (a buccal levator nerve), continued activation of Xl, and termination of Hsh activity; and (d) warning activity in Vmd and Hm associated with a prominent second wave in Xl. This coordinated activity is inferred to represent fictive pulmonary ventilation because the neurograms in these four intervals correspond closely to EMGs and neurograms recorded in the intact frog during the four phases of pulmonary ventilation, namely, buccal depression, pulmonary expiration, pulmonary inspiration, and glottal closure. Hypercapnia, vagotomy, and cutaneous pinching enhanced the high-amplitude, low-frequency rhythm, but not the low-amplitude, high-frequency oscillation. Lung inflation generally inhibited the former and not the latter, but in some cases lung inflation stimulated pulmonary ventilation. We conclude that oropharyngeal and pulmonary ventilation of the frog are produced by one or, possibly, two intrinsically active generators.

Animals↗
PubMed1999

Temporal call changes and prior experience affect graded signalling in the cricket frog.

We investigated how male cricket frogs Acris crepitans, alter their advertisement calls in response to broadcasts of synthetic calls that were either 'attractive' or 'aggressive'. The stimulus calls differed in temporal but not spectral characteristics. Male cricket frogs produced a more aggressive call when presented with the aggressive stimulus, indicating that they perceived the temporal differences between the two call categories. The direction and degree of temporal and spectral changes depended on the relative dominant frequency of the resident and opponent. If the resident's dominant frequency was initially higher than the stimulus frequency, the pattern of change in dominant frequency mirrored that seen for the temporal call characters. In contrast, if the resident's initial dominant frequency was below that of the stimulus, then the temporal and spectral changes were in opposite directions. Furthermore, stimulus order influenced whether males responded differently to playbacks of aggressive and attractive calls; males that received the aggressive call first produced more aggressive calls during the aggressive stimulus, while males that received the attractive call first produced similar calls in response to the two stimuli. This suggests that experience with different types of signals influences the subsequent calling behaviour of male cricket frogs. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗