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PubMed1994

The brain tryptophan hydroxylase activity in the sleep-like states in frog.

The activity of the rate-limiting enzyme of serotonin biosynthesis, tryptophan hydroxylase, was determined in the brain stem in active awake frogs, and frogs in three sleep-like states: with plastic muscle tone (SLS-1), with rigid muscle tone (SLS-2), and with relaxed muscle tone (SLS-3). Significant decrease in the enzyme activity has been found in frogs in SLS-1 and SLS-2 compared to awake animals. The development in frogs a cataleptic-like immobility after treating the animals with rhythmic lighting was accompanied with a decrease in the brain tryptophan hydroxylase activity. These results provide strong evidence for the involvement of the brain serotonin in frogs in the control of evolutionary ancient sleep-like states, probably by the regulation of muscle tone.

Animals↗
PubMed1994

Isolation and characterization of peptides derived from the cleavage of the cytoplasmic domain of synaptophysin in frog brain.

Three overlapping peptides have been isolated from the whole brain of the European green frog, Rana ridibunda and identified as fragments of the cytoplasmic domain of the synaptic vesicle membrane protein, synaptophysin. The primary structures of the peptides define the amino acid sequence of the 58 residues at the COOH-terminus of the protein and indicate that fragments arose from proteolytic cleavages at the COOH-terminal side of aspartyl residues. The overall conservation of structure of the cytoplasmic domain between the mammalian and amphibian proteins is relatively poor (58% sequence identity between frog and rat synaptophysin). However, the pattern of repeating tyrosine residues that is present in mammalian and Torpedo synaptophysins is also found in the frog protein suggesting that this structural motif is necessary for the, as yet unknown, function of the protein. The cytoplasmic region of frog synaptophysin is also rich in glutamine and glycine residues, but the putative consensus repeating sequence Tyr-Gly-Pro/Gln-Gln-Gly in mammalian synaptophysins does not occur in the frog protein. The data raise the possibility that synaptophysin, like the chromogranins and secretogranin II, may function as the precursor of biologically active peptides.

Amino Acid Sequence↗
PubMed1990

Evolution of the MHC: antigenicity and unusual tissue distribution of Xenopus (frog) class II molecules.

Antibodies that recognize Xenopus class II molecules have been developed. Mouse monoclonal antibodies were prepared by immunizing BALB/c mice with frog MHC antigens that had been partially purified with alloantisera, and by immunizing mouse spleen cells in vitro with activated Xenopus T lymphocytes. In addition, five mouse monoclonal antibodies specific for human class II antigens were found to cross-react with Xenopus class II antigens. A.TH mice, which do not express E class II molecules, always produce immunoprecipitating antibodies reactive with frog class II molecules after immunization with frog lymphocytes; other mouse strains rarely produce such antibodies. Two of the monoclonal antibodies raised against frog class II molecules recognize the denatured class II beta chain on Western blots, and the other three appear to recognize only the class II heterodimeric complex. The antibodies display differential reactivity with the allelic class II products of Xenopus. The monoclonal antibodies react with all adult lymphocytes in the spleen and peripheral blood, T cells and B cells having equivalent levels of class II antigens per cell. Class II molecules are "differentiation antigens" on adult thymocytes as the expression is greatest on the mature medullary population. The number of class II molecules/lymphocyte increases after culturing in medium containing fetal bovine serum. Sequential immunoprecipitation and isoelectric focusing experiments have shown that cell surface class II molecules immunoprecipitated with the monoclonal antibodies are the same as those immunoprecipitated with the cross-reactive antiserum specific for DR antigens which was previously used to identify frog class II molecules.

Animals↗
PubMed1988

Lack of effect of rat atrial natriuretic factor (rANF) on the renal function in frogs.

1. The aim of the present experiments was to examine the question whether the rat atrial natriuretic factor (rANF 1-28) could alter the fractional excretion of sodium (FENa) and other solutes in the frog (Rana esculenta). 2. Although experiments were performed throughout the year possible seasonal changes in the animals were considered in particular. 3. In all frogs, a hypotonic diuresis was induced. 4. Under these conditions in winter frogs, the control FENa was 8.8 +/- 5.8% (15) [means +/- SD (n)], and during rANF administration 7.7 +/- 6.6% (13) (NS). 5. In summer frogs, the control and experimental FENa was 5.2 +/- 2.8% (5) and 6.0 +/- 2.5% (5), respectively (NS). 6. These results show that there was no significant effect of this polypeptide on the fractional excretion of sodium in the frog.

Animals↗
PubMed1980

Use of cell fusion techniques to probe the mechanism of catecholamine-induced desensitization of adenylate cyclase in frog erythrocytes.

The catecholamine-sensitive adenylate cyclase system appears to be comprised of at least three components; the beta-adrenergic receptor (R component), the catalytic unit of adenylate cyclase (C component) and a nucleotide regulatory protein (N component), responsible for mediating the effects of guanine nucleotides on the system. Cell fusion techniques were used to investigate the role of these three components in the process of homologous desensitization in the frog erythrocyte. Dicyclohexylcarbodiimide (DCCD) was used to inhibit beta-receptor function in one population of frog erythrocytes, whilst phenyl glyoxal was employed to inactivate the N and C components in a second population of frog erythrocytes. Using Sendai virus to fuse the two types of modified cell, heterologous beta-adrenergic receptor-adenylate cyclase systems were constructed which contained components from each cell type. When beta receptors from cells previously desensitized to catecholamines were coupled to N-C components derived from fresh erythrocytes, the resulting hybrid exhibited a densitized response to isoproterenol. By contrast, when beta-adrenergic receptors from fresh cells were coupled to N-C components derived from desensitized erythrocytes, no decreased responsiveness to isoproterenol was apparent in the hybrid. That this resensitization was the result of the addition of fresh beta-adrenergic receptors was demonstrated in a control experiment. Frog erythrocytes were desensitized simultaneously to catecholamines and prostaglandin E1 and modified with DCCD which inactivates the beta-adrenergic receptor but not the prostaglandin receptor. When fresh beta-adrenergic receptors were supplied by cell fusion to these doubly desensitized erythrocytes, only the beta-adrenergic response was restored to control levels. The response to prostaglandin remained desensitized in the hybrids, indicating that the observed resensitization of catecholamine-stimulated adenylate cyclase activity was specific and was due to the addition of fresh beta-adrenergic receptors. These data suggest that in the frog erythrocyte, homologous desensitization is primarily the result of receptor-related alterations.

Adenylyl Cyclases↗
PubMed1982

Hepatic cytochrome P-450-dependent monooxygenase systems of the trout, frog and snake--I. Components.

1. Components of the hepatic monooxygenase systems (cytochrome P-450, cytochrome b5, NADPH cytochrome P-450- or c-reductase) of the brown trout (Salmo trutta), leopard frog (Rana pipiens) and garter snake (Thamnophis) were considerably lower than those found in the rat. 2. Reactivity of snake NADPH-cytochrome P-450-reductase with cytochrome P-450 was about twice that of the rat reductase; reactivities of trout and frog reductases were similar, but lower than that of the rat. The optimal temperature for the rat, frog and snake reductase activity was 37 degrees C, but 26 C for the trout reductase, regardless of whether cytochrome P-450 or cytochrome c was the electron acceptor for the reaction. 3. A type I substrate (benzphetamine) and a type II substrate (aniline) were less reactive with P-450 cytochrome from the trout, frog and snake than with P-450 cytochrome from the rat. 4. Qualitative differences were seen in the ethylisocyanide spectrum of microsomes from the rat, trout, frog and snake; these differences reflect qualitative differences in the populations of P-450 cytochromes among each of the four species.

Animals↗
PubMed1982

Hepatic cytochrome P-450-dependent monooxygenase systems of the trout, frog and snake--II. Monooxygenase activities.

1. Activities of hepatic monooxygenase systems (aminopyrine N-demethylase, benzo[a]pyrene hydroxylase and p-nitrophenetole O-deethylase) of the brown trout (Salmo trutta), leopard frog (Rana pipiens) and garter snake (Thamnophis) were observed to be considerably lower than those of the rat. The specific activities of their P-450 cytochromes relative to rates of product formation were also much lower than those of the rat, except benzo[a]pyrene hydroxylation by frog microsomes, in which case, the value was about the same as that for the rat. 2. The monooxygenase systems of the trout, frog and snake were identified as cytochrome P-450 systems by the inhibitory effects of carbon monoxide, SKF 535-A, alpha-naphthoflavone and by the requirement for NADPH. 3. NADH synergism of NADPH-supported monooxygenase activities of hepatic microsomes of the trout, frog and snake suggest the participation of cytochrome b5 in these reactions. For the trout, p-nitrophenetole metabolism was supported almost as well by NADH as by NADPH, which suggests that in this species, cytochrome b5 may play an important role in certain monooxygenase reactions. 4. Qualitative differences in the P-450 cytochromes of the trout, frog, snake and rat were indicated by differences in the inhibitory effects of SKF 525-A and alpha-naphthoflavone on monooxygenase activities.

Aminopyrine N-Demethylase↗
PubMed1995

Effects of gonadectomy and temperature on the N-acetyltransferase activity in the harderian gland of the green frog Rana esculenta.

Since, in the Harderian gland (HG) of the hamster, the N-acetyltransferase (NAT), the specific enzyme involved in the biosynthesis of melatonin, exhibits a sexual dimorphism, in the present study, we investigated whether such a dimorphism is present also in the HG of the green frog Rana esculenta. In intact frogs, no significant differences emerged between males and females in the HG NAT activity under both cold (10 degrees C) and warm (22 degrees C) temperature conditions. In female frogs, the HG NAT activity was significantly decreased by both gonadectomy (P < 0.001) and warm temperature (P < 0.001), the two effects being not additive. In male animals, neither gonadectomy nor temperature alone significantly affected the activity of the NAT enzyme in the HG. However, gonadectomized male frogs exposed to warm temperature exhibited a significant drop in the HG NAT activity (P < 0.005). These data show that, in Rana esculenta, although no sexual dimorphism exists in the HG NAT activity, a sex difference is evident in the modulation of the enzyme activity by gonads and temperature, the female frogs being more sensitive to the impairing effects of both gonadectomy and higher temperature.

Animals↗
PubMed1984

The cyclo-oxygenase pathway in the avascular heart of the frog, Rana esculenta L.

A modification of Vane's cascade is reported, allowing the superfusion bioassay of prostaglandin-like substances (PLS) in the outflow of isolated and perfused heart of the frog Rana esculenta L. Using both this technique and radioimmunoassay determination, the cyclo-oxygenase pathway in perfused frog heart has been investigated. Arachidonate (AA) (2-20 micrograms) injected into the perfusing fluid, was transformed by the heart into PLS, as shown by the response of the bioassay tissues (rat stomach strip, chick rectum, rat colon). A compound capable of relaxing rabbit mesenteric artery and a rabbit aorta contracting substance were also generated. The release was inhibited by indomethacin (1.0 X 10(-5)M). Radioimmunoassay determination of PGE2, TXB2 and 6-keto-PGF1 alpha in frog heart effluent, before and after AA injection (20 micrograms), gave the following yields (ng/ml of effluent). Basal: PGE2 = 0.45 +/- 0.15; TXB2 = 0.46 +/- 0.13; 6-keto-PGF1 alpha = 2.21 +/- 0.3. Following AA: PGE2 = 1.55 +/- 0.35; 6-keto-PGF1 alpha = 3.4 +/- 0.4; TXB2 = 1.00 +/- 0.06. Our results suggest that prostacyclin is a major product of the cyclo-oxygenase pathway in frog perfused heart. The biological significance of this finding is discussed in relation to both the absence of a coronary circulation in amphibians and to the spongy nature of frog myocardium.

Animals↗
PubMed1988

Localization of synapsin I at the frog neuromuscular junction.

We report here the results of immunocytochemical and biochemical studies on the localization of synapsin I, a nerve terminal--specific phosphoprotein, at the frog neuromuscular junction. Our results show that in this in situ synapse synapsin I is concentrated in the presynaptic compartment, where it appears to be associated with the synaptic vesicle membrane. Double immunoprecipitated synapsin I from homogenates of frog cutaneous pectoris muscles could be phosphorylated by the catalytic subunit of cyclic adenosine 5'-monophosphate-dependent protein kinase after gel electrophoresis and blotting onto nitrocellulose and could be subsequently identified by an immunoperoxidase technique. Experiments carried out in frog brain preparations indicate that frog synapsin I, like the mammalian protein, can be phosphorylated at different sites by exogenously added catalytic subunit of cyclic adenosine 5'-monophosphate-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II prepared from mammalian sources. The phosphorylation sites of frog synapsin I, as judged by phosphopeptide mapping, are somewhat different from those of mammalian synapsin I. The study of synapsin I and of the regulation of its state of phosphorylation at the neuromuscular junction may provide important information on its role in synaptic function, since at the present time this is one of the few systems in which a correlation among biochemical, immunocytochemical and electrophysiological results is possible.

Animals↗
PubMed1993

Expression of GAP-43 in normal and regenerating nerves in the frog.

A polyclonal antiserum to chicken, growth-associated protein-43 (GAP-43), raised in rabbit, was shown to recognize a molecule with similar properties to GAP-43 in frogs. Using this antiserum, GAP-43 immunoreactivity was shown to be present throughout the brain and white matter of the spinal cord of larval frogs, but became restricted to specific regions in the adult frog central nervous system. In the peripheral nervous system, GAP-43 was present in normal tadpole and adult axons. After cutting the adult sciatic nerve, GAP-43 slowly disappeared from axons in the distal stump, but appeared in Schwann cells and other (uncharacterized) cells. The constitutive expression of GAP-43 in the adult frog sciatic nerve may be related to the phenomenon of remodelling of motor end-plates, which is known to occur throughout life in frogs.

Animals↗
PubMed1993

Acetylcholine receptor bars and transmitter release in frog neuromuscular junctions.

After labelling with rhodaminated alpha-bungarotoxin, acetylcholine receptors in cutaneous pectoris muscles of normal adult frogs (Rana temporaria) appear as brightly fluorescent straight bars, usually extending over the whole gutter. Here we investigated first whether receptor bars can undergo changes and secondly whether they would provide a structural correlate for the strength of a junction. Bars of low fluorescence intensity, as well as short or discontinuous receptor bars consisting of two or three segments, suggest plasticity at the receptor/active zone level. In order to elucidate this notion, receptor bars were studied at different seasons which have previously been shown to be associated with structural changes. In two groups of frogs kept under laboratory conditions simulating wintertime and summertime, respectively, the length and number of receptor bars and the amount of discontinuous bars were investigated. Synaptic contact length, which is the summed length of labelled synaptic branches, and the number and total length of receptor bars did not differ significantly. A clear difference between Group I ("winter" frogs) and Group II ("summer" frogs) was found in the number of discontinuous bars, which was almost twice as high in Group I compared with Group II (6.4 +/- 3.3% S.D. vs 3.4 +/- 1.3% S.D., n = 8 and 7 muscles, respectively, P < 0.05). In addition, the average length of individual bars was slightly longer in Group I frogs (2.16 +/- 0.7 micron S.D. vs 2.07 +/- 0.12 microns S.D., 0.1 < P < 0.05). Transmitter release has been shown to be different in these two groups--as determined from endplate potential measurements in tubocurarine-containing bathing solutions--although it was equal when measured in low Ca2+/high Mg2+ [Dorlöchter M. et al. (1991) Pflügers Arch. 418, Suppl. 1, R31]. We also investigated whether receptor bars would be a reasonable structural correlate of synaptic function by comparing different measures of transmitters release with different structural parameters in 19 identified junctions. The mean quantal content (m) of a junction was positively correlated with the number and total length of receptor bars, but not with synaptic contact area or length. Amplitudes of the first, maximum, and plateau endplate potentials (corrected for a common resting potential and apparent input resistance) at tetanic nerve stimulation (40 Hz for 2 s) in tubocurarine block were strongly correlated with both synaptic contact length and total receptor bar length (r = 0.90 for maximum endplate potential); correlations between m and any structural measure were significantly worse.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗
PubMed1981

Peripheral basis of sound localization in anurans. Acoustic properties of the frog's ear.

Directional responses of single auditory fibers in the eighth nerve of northern leopard frogs (Rana pipiens) were studied in order to gain some insights into the acoustical properties of the frog's ear. In addition to the actual directional response of a fiber, a theoretical directional-response curve to the intensity-rate function of the unit. The difference in the two responses provided a measure of the directional characteristics of the frog's ear at the stimulating frequency which can be plotted in a polar diagram to show the directivity pattern of the frog's acoustic receiver. Directivity patterns were obtained from three groups of experimental animals under the following conditions: (I) mouth filled with moistened cotton; (II) contralateral ear coated with silicone rubber cement; (III) open mouth. Changes in the directivity patterns were observed with experimental manipulations and these were compared to those obtained from normal animals (Feng, A.S. (1980) J. Acoust. Soc. AM. 68, 1107-1114). The results suggest that the frog's ear behaves as a combination pressure-pressure gradient receiver.

Animals↗
PubMed2006

Plasma steroid hormone concentrations, aromatase activities and GSI in ranid frogs collected from agricultural and non-agricultural sites in Michigan (USA).

The triazine herbicide atrazine has been hypothesized to disrupt sexual development in frogs by up-regulating aromatase activity, resulting in greater estradiol (E2) concentrations and causing feminization in males. The goal of this study was to collect native ranid frogs from atrazine-exposed ponds and determine whether relationships exist between measured atrazine concentrations and the gonadosomatic index (GSI), plasma concentrations of testosterone (T), E2 or 11-ketotestosterone (KT), or with aromatase activity. In the summer of 2002 and 2003, adult and juvenile green frogs (Rana clamitans), bullfrogs (R. catesbeiana) and Northern leopard frogs (R. pipiens) were collected from areas with extensive corn cultivation and areas where there was little agricultural activity in south-central Michigan. Atrazine concentrations were below the limit of quantification at non-agricultural sites. Atrazine concentrations did not exceed 2 microg/L at most agricultural sites, but a concentration of 250 microg atrazine/L was measured in one sample from one site in 2002. Plasma steroid concentrations varied among locations. Aromatase activity was measurable in less than 11% of testes in adult males, and in less than 4% of testes in juvenile males. Median aromatase activities in ovaries of adult females ranged from 3 to 245 pmol/h/mg protein, and maximum activities were 2.5-fold greater in juveniles than in adults. Atrazine concentrations were not significantly correlated with any of the parameters measured in this study. These results indicate that atrazine does not up-regulate aromatase in green frogs in the wild, and does not appear to affect plasma steroid hormone concentrations.

Animals↗
PubMed2004

The epithalamus of the developing and adult frog: calretinin expression and habenular asymmetry in Rana esculenta.

Expression of the calcium binding protein (CaBP) calretinin (CR) was studied with immunohistochemistry in the pineal complex and habenular nuclei (HN) of the developing and adult frog Rana esculenta. The frog pineal complex is a medial structure formed by two interconnected components, the frontal organ and the pineal organ or epiphysis; the habenular nuclei are bilateral and are asymmetric due to subdivision of the left dorsal nucleus into medial and lateral components. In the pineal complex, calretinin immunostaining of cells and fibers was consistently observed in developing and adult frogs. In the habenulae, calretinin immunoreactivity exhibited instead marked variations during development, and was expressed only in cells of the medial subnucleus of the left dorsal habenula. In particular, calretinin was detected at larval stages, peaked during metamorphosis, was markedly downregulated at the end of metamorphosis, and was evident again in adulthood. This sequence of calretinin expression was confirmed by quantitative analysis of immunoreactive cells in the left habenula. In tadpoles, calretinin-positive cells exhibited a dorsoventral gradient of density, while in adulthood, they were distributed throughout the dorsoventral extent of the medial subnucleus. The study demonstrates a peculiar developmental pattern, with transient downregulation, of asymmetric calretinin expression in the frog epithalamus. The findings indicate that calcium and calcium buffering systems may play critical roles in neurogenetic and neuronal migration processes implicated in the formation of the asymmetric habenular portion in amphibians. In addition, the reappearance of calretinin expression in the adult frog supports a distinct functional role of the asymmetric habenular component in amphibians.

Animals↗
PubMed2006

Membrane excitability of wing and rod cells in frog taste discs following denervation.

The frog tongue has a disc-shaped taste organ (taste disc) on the top of fungiform papillae. The taste disc contains two types of cells, wing cells with a sheet-like apical process and rod cells with a rod-like apical process. Both wing and rod cells can produce action potentials. Unlike the taste buds of mammals, frog taste discs do not degenerate over a long period after denervation. Here we report that the shapes of wing and rod cells isolated from taste discs in the bullfrog (Rana catesbeiana) remained unchanged 1 month after cutting bilateral glossopharyngeal nerves. By applying the whole cell patch-clamp technique to isolated wing and rod cells, we found voltage-dependent inward currents and outward currents and action potentials in denervated frogs as seen in normal frogs. These results suggest that the maintenance of morphological integrity and electrical excitability of taste cells does not require a nerve supply in frogs.

Action Potentials↗
PubMed2006

Stress-induced activation of the AMP-activated protein kinase in the freeze-tolerant frog Rana sylvatica.

Survival in the frozen state depends on biochemical adaptations that deal with multiple stresses on cells including long-term ischaemia and tissue dehydration. We investigated whether the AMP-activated protein kinase (AMPK) could play a regulatory role in the metabolic re-sculpting that occurs during freezing. AMPK activity and the phosphorylation state of translation factors were measured in liver and skeletal muscle of wood frogs (Rana sylvatica) subjected to anoxia, dehydration, freezing, and thawing after freezing. AMPK activity was increased 2-fold in livers of frozen frogs compared with the controls whereas in skeletal muscle, AMPK activity increased 2.5-, 4.5- and 3-fold in dehydrated, frozen and frozen/thawed animals, respectively. Immunoblotting with phospho-specific antibodies revealed an increase in the phosphorylation state of eukaryotic elongation factor-2 at the inactivating Thr56 site in livers from frozen frogs and in skeletal muscles of anoxic frogs. No change in phosphorylation state of eukaryotic initiation factor-2alpha at the inactivating Ser51 site was seen in the tissues under any of the stress conditions. Surprisingly, ribosomal protein S6 phosphorylation was increased 2-fold in livers from frozen frogs and 10-fold in skeletal muscle from frozen/thawed animals. However, no change in translation capacity was detected in cell-free translation assays with skeletal muscle extracts under any of the experimental conditions. The changes in phosphorylation state of translation factors are discussed in relation to the control of protein synthesis and stress-induced AMPK activation.

AMP-Activated Protein Kinases↗
PubMed2005

Evidence from peptidomic analysis of skin secretions that the red-legged frogs, Rana aurora draytonii and Rana aurora aurora, are distinct species.

The northern red-legged frog Rana aurora aurora and the California red-legged frog Rana aurora draytonii are traditionally classified together in the same species group. Ten peptides with antimicrobial activity were isolated from norepinephrine-stimulated skin secretions of R. aurora draytonii and purified to near homogeneity. The peptides were identified as belonging to the ranatuerin-2 family (two peptides), brevinin-1 family (four peptides), temporin family (three peptides), and a novel peptide, RV-23 (RIGVLLARLPKLFSLFKLMGKKV) that has limited structural similarity to the bee venom peptide, melittin. This distribution of peptides contrasts with that found previously in skin secretions from R. aurora aurora collected under the same conditions and at the same time of year (one ranatuerin-2 peptide, two brevinin-1 peptides, and one temporin peptide). The variation in amino acid sequences between corresponding R. aurora draytonii and R. aurora aurora peptides is comparable with the variation in sequences of orthologs from other members of the Amerana group of New World ranid frogs (Rana boylii, Rana muscosa, and Rana luteiventris). It is proposed, therefore, that the red-legged frogs should be regarded as separate species (R. aurora and R. draytonii) within the Amerana group rather than conspecific subspecies. The data emphasize that amino acid sequences of antimicrobial peptides in skin secretions may be used to infer taxonomic and phylogenetic relationships between species of ranid frogs.

Amino Acid Sequence↗