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PubMed2000

Hind limb malformations in free-living northern leopard frogs (Rana pipiens) from Maine, Minnesota, and Vermont suggest multiple etiologies.

BACKGROUND: Reports of malformed frogs have increased throughout the North American continent in recent years. Most of the observed malformations have involved the hind limbs. The goal of this study was to accurately characterize the hind limb malformations in wild frogs as an important step toward understanding the possible etiologies. METHODS: During 1997 and 1998, 182 recently metamorphosed northern leopard frogs (Rana pipiens) were collected from Minnesota, Vermont, and Maine. Malformed hind limbs were present in 157 (86%) of these frogs, which underwent necropsy and radiographic evaluation at the National Wildlife Health Center. These malformations are described in detail and classified into four major categories: (1) no limb (amelia); (2) multiple limbs or limb elements (polymelia, polydactyly, polyphalangy); (3) reduced limb segments or elements (phocomelia, ectromelia, ectrodactyly, and brachydactyly; and (4) distally complete but malformed limb (bone rotations, bridging, skin webbing, and micromelia). RESULTS: Amelia and reduced segments and/or elements were the most common finding. Frogs with bilateral hind limb malformations were not common, and in only eight of these 22 frogs were the malformations symmetrical. Malformations of a given type tended to occur in frogs collected from the same site, but the types of malformations varied widely among all three states, and between study sites within Minnesota. CONCLUSIONS: Clustering of malformation type suggests that developmental events may produce a variety of phenotypes depending on the timing, sequence, and severity of the environmental insult. Hind limb malformations in free-living frogs transcend current mechanistic explanations of tetrapod limb development.

Animals↗
PubMed2004

Seasonal effects of dehydration on glucose mobilization in freeze-tolerant chorus frogs (Pseudacris triseriata) and freeze-intolerant toads (Bufo woodhousii and B. cognatus).

It has been hypothesized that freeze-tolerance in anurans evolved from a predisposition for dehydration tolerance. To test this hypothesis, we dehydrated summer/fall-collected and winter acclimated freeze-tolerant chorus frogs and dehydration-tolerant, but freeze-intolerant, Woodhouse's and Great Plains toads to 25% and 50% body water loss (BWL). Following treatments, we measured glucose, glycogen, and glycogen phosphorylase and glycogen synthetase (summer/fall only) activities in liver and leg muscle. Hepatic glucose levels were not significantly altered by dehydration in either summer/fall-collected frogs or toads. Conversely, winter acclimated frogs did show an increment (2.9-fold) in hepatic glucose with dehydration, accompanied by a reduction in hepatic glycogen levels. Winter acclimated toads did not mobilize hepatic glucose in response to dehydration. Further, hepatic glycogen and phosphorylase activities did not vary in any consistent manner with dehydration in winter toads. Mean leg muscle glucose values were elevated at 50% BWL relative to other treatments, significantly so compared to 25% BWL for summer/fall-collected frogs. The pattern of hepatic glucose mobilization with dehydration in winter frogs is consistent with that in other freeze-tolerant frog species, and provides additional support for the hypothesis that freezing tolerance evolved from a capacity for dehydration tolerance. However, the lack of hepatic glucose mobilization in response to dehydration in fall frogs suggests that a seasonal component to dehydration-induced regulation of glucose metabolism exists in chorus frogs. Furthermore, the absence of a dehydration-induced mobilization of hepatic glucose at both seasons in toads suggests that this dehydration response is not universal for terrestrial anurans.

Acclimatization↗
PubMed1993

Observations on the development of unusual melanization of leopard frog ventral skin.

The ontogeny of ventral pigmentation of two species of leopard frog, Rana pipiens and R. chiricahuensis, was examined by light microscopy and transmission electron microscopy to reveal how the unusual melanistic ventral pigmentation of R. chiricahuensis is achieved at the cellular level. Ventral skin of R. pipiens is always white. Ventral skin of adult R. chiricahuensis is white when frogs are background-adapted to a white substrate, but ventral skin becomes nearly as dark colored as the dorsal skin when frogs darken in response to a black background. Skin samples from tadpoles of both species, newly metamorphosed frogs, and adult frogs were analyzed for chromatophore composition and distribution. Ventral skin of R. pipiens larvae, newly metamorphosed frogs, and adults and of R. chiricahuensis larvae was white due to abundant iridophores and no melanophores. Melanophore density in the ventral integument of R. chiricahuensis was 9.1 +/- 2.8/mm2 in newly metamorphosed frogs and 87.0 +/- 4.8/mm2 in adult frogs. Pigment within ventral melanophores migrated during physiological color change during background adaptation.

Animals↗
PubMed1986

Differential effects of manganese and magnesium on two types of slowly adapting cutaneous mechanoreceptor afferent units in frogs.

While perfusing a frog leg with various solutions, the mechanical responsiveness of slowly adapting (SA) cutaneous mechanoreceptor afferent units innervating the plantar surface of the hindfoot was examined. Perfusion with normal Ringer solutions enhanced the mechanical responsiveness of two types of the SA units, irregularly discharging Frog type I units and regularly discharging Frog type II units, in comparison with that by normal blood supply. On the other hand, when the perfusion was made with Ringer solutions containing Ca blockers, i.e., Mn and Mg, the response magnitudes of both units were reversibly and dose-dependently decreased. Ringer solutions containing 3 mM Mn or 20 mM Mg almost abolished the maintained responses of the Frog type I units to ramp stimulation of the skin, while Ringer solutions of 10 mM Mn significantly decreased those of the Frog type II units. It is suggested that Ca in the medium is a prerequisite to mechanoelectric transduction and the spike generation process at the terminal regions of these slowly adapting cutaneous mechanoreceptor afferent units. Findings that the Frog type I units were quantitatively more sensitive to these Ca blockers than the Frog type II units suggest that an additional process of higher Ca-sensitivity, e.g., chemical synaptic transmission, may be involved on the way from mechanoelectric transduction to the spike generation of the Frog type I units.

Afferent Pathways↗
PubMed1983

Unusual features of the Ca2+-ATPase activity of myosin from fast skeletal muscle of the frog: effect of actin and SH1 thiol group modification.

The K+-ATPase and actin-activated Mg2+-ATPase activity of myosin from fast skeletal muscle of the frog, Rana esculenta or Rana temporaria, are comparable to the respective activities of rabbit fast skeletal muscle. On the other hand, the Ca2+-ATPase activity of the same preparations of frog myosin is 6-7-fold lower than that of myosin from rabbit muscle. Various control experiments indicate that the small extent of Ca2+ stimulation is an intrinsic property of frog muscle myosin. Unlike myosin from rabbit muscle, the Ca2+-ATPase activity of frog myosin is strongly activated by actin; at high actin concentrations it approaches the level of the Ca2+-ATPase activity of rabbit myosin. The levels of Ca2+-ATPase activity of frog and rabbit myosins also become comparable upon modification of myosin SH1 thiol groups; this means that the modification of the SH1 groups results in a much higher activation of the Ca2+-ATPase of frog myosin than that of rabbit myosin. The results suggest a difference in the active site conformation in frog and rabbit muscle myosins. The effects of actin and SH1 group modification are discussed in terms of allosteric changes which diminish the difference in the active site conformation of the two myosins. We have also observed a difference in the reactivity of thiol groups which are not essential for the enzymatic activity in frog and rabbit myosin, indicating structural differences in regions other than the active site.

Actins↗
PubMed2006

Whole animal measurements of shear and adhesive forces in adult tree frogs: insights into underlying mechanisms of adhesion obtained from studying the effects of size and scale.

This allometric study of adhesion in 15 Trinidadian tree frog species investigates how relationships between length, area and mass limit the ability of adult frog species of different sizes to adhere to inclined and overhanging surfaces. Our experiments show that hylid frogs possess an area-based wet adhesive system in which larger species are lighter than expected from isometry and adhere better than expected from their toe pad area. However, in spite of these adaptations, larger species adhere less well than smaller species. In addition to these adhesive forces, tree frogs also generate significant shear forces that scale with mass, suggesting that they are frictional forces. Toe pads detach by peeling and frogs have strategies to prevent peeling from taking place while they are adhering to surfaces, including orienting themselves head-up on slopes. The scaling of tree frog adhesion is also used to distinguish between different models for adhesion, including classic formulae for capillarity and Stefan adhesion. These classic equations grossly overestimate the adhesive forces that tree frogs produce. More promising are peeling models, designed to predict the pull-off forces of adhesive tape. However, more work is required before we can qualitatively and quantitatively describe the adhesive mechanism of tree frogs.

Adaptation, Physiological↗
PubMed1999

Electrophysiological and ultrastructural correlates of cryoinjury in sciatic nerve of the freeze-tolerant wood frog, Rana sylvatica.

We investigated function and ultrastructure of sciatic nerves isolated from wood frogs (Rana sylvatica) endemic to the Northwest Territories, Canada, following freezing at -2.5 degrees C, -5.0 degrees C, or -7.5 degrees C. All frogs frozen at -2.5 degrees C, and most frogs (71%) frozen at -5.0 degrees C, recovered within 14 h after thawing began; however, frogs did not survive exposure to -7.5 degrees C. Sciatic nerves isolated from frogs frozen at -7.5 degrees C were refractory to electrical stimulation, whereas those obtained from frogs surviving exposure to -2.5 degrees C or -5.0 degrees C generally exhibited normal characteristics of compound action potentials. Frogs responded to freezing by mobilizing hepatic glycogen reserves to synthesize the cryoprotectant glucose, which increased 20-fold in the liver and 40-fold in the blood. Ultrastructural analyses of nerves harvested from frogs in each treatment group revealed that freezing at -2.5 degrees C or -5.0 degrees C had little or no effect on tissue and cellular organization, but that (lethal) exposure to -7.5 degrees C resulted in marked shrinkage of the axon, degeneration of mitochondria within the axoplasm, and extensive delamination of myelin sheaths of the surrounding Schwann cells.

Action Potentials↗
PubMed1986

Differential immunogold-dextran labeling of bovine and frog rod and cone cells using monoclonal antibodies against bovine rhodopsin.

Eleven monoclonal antibodies against different segments of bovine rhodopsin were used with immunogold-dextran markers to label Lowicryl thin sections of bovine and frog retinal photoreceptor cells for visualization by transmission electron microscopy. Antibodies against the C-terminus, F1-F2 loop and N-terminus of rhodopsin were all observed to label bovine rod outer segments (ROS) densely, but to label rod inner segments (RIS) only sparsely. Most antibodies bound 200-600 gold particles per micron2 in the ROS, 10-60 gold particles per micron2 in the RIS and 5-20 particles per micron2 on the Lowicryl resin. One antibody against the N-terminus and one antibody against the C-terminus resulted in the binding of over 1000 particles per micron2 in bovine ROS. Cone outer segments (COS) were labeled with only one antibody, rho 3D6, having a specificity for the 1'-4' C-terminus of bovine rhodopsin. Ninety per cent of the COS were observed to be labeled with this antibody. Immunogold-dextran labeling was also used to study the cross-reactivity of these antibodies to rhodopsin in red and green frog ROS and COS. Monoclonal antibodies directed against sites along the F1-F2 loop, and the N-terminus labeled red frog ROS densely, but did not label either green ROS or COS. Three C-terminal specific antibodies against binding sites along the 1'-8' segment labeled both green and red ROS, but a higher extent of labeling was observed on the green ROS. Antibody rho 3D6, which bound to bovine COS, also labeled frog COS. These results indicate that the F1-F2 loop and segments along to the N-terminus and the C-terminus of bovine rhodopsin show a high degree of homology with corresponding regions of frog rhodopsin from red ROS; the C-terminal 1'-8' segment of bovine rhodopsin is closely related to the corresponding segment of frog rhodopsin from green ROS; and the 1'-4' C-terminus of bovine rhodopsin is highly homologous to segments of opsin from most bovine and frog COS. The labeling of frog red ROS in relation to multiple forms of rhodopsin observed by SDS-gel electrophoresis is discussed.

Animals↗
PubMed1985

Comparative effects of homoplastic pituitary pars distalis homogenate (PDH), pregnant mare serum gonadotrophin (PMSG), human chorionic gonadotrophin (HCG), growth hormone (GH), PMSG + GH, and HCG + GH on oocyte recruitment and development in the long-term hypophysectomized frog, Rana cyanophlyctis (Schn).

Follicular development and oocyte recruitment were studied in the ovaries of long-term (2 months) hypophysectomized frogs Rana cyanophlyctis during the postbreeding season (October/November). The effects of homoplastic pituitary pars distalis homogenate (PDH) (1 pituitary per frog), 40 IU pregnant mare serum gonadotrophin (PMSG), 40 IU human chorionic gonadotrophin (HCG), 10 micrograms growth hormone (GH), 40 IU PMSG + 10 micrograms GH, and 40 IU HCG + 10 micrograms GH in 0.2 ml saline on oocyte growth and recruitment were also studied in these frogs. Injections (ip) were given on alternate days for 30 days, with autopsy on the 31st day. The frogs were fed with minced thigh muscles of other frogs and injected twice a week with 0.02 IU adrenocorticotrophic hormone (ACTH) in 0.2 ml saline to maintain their health. One month after hypophysectomy there was a significant reduction in the weight of the ovaries and oviducts, mean diameter of the largest oocytes, and the total number of oocytes in the ovaries. Oogonial mitosis was not impaired. In 2-month hypophysectomized saline-treated frogs, oocyte growth occurred and as a result there was an increase in the mean size. Also, the total number of oocytes in the ovaries increased compared to 1-month hypophysectomized controls. HCG induced maximum recruitment of oocytes from first growth phase (FGP) to second growth phase (SGP) but the number of oocytes in the ovary remained unchanged. In contrast, PMSG induced the recruitment of FGP oocytes and to a lesser extent SGP oocytes. Thus, PMSG, unlike HCG, caused a significant increase in the total number of oocytes in the ovary. Bovine GH alone had no effect on the recruitment of FGP or SGP oocytes but it enhanced the gonadotrophic action of PMSG and HCG when given in combination. The PDH caused a greater stimulation of the ovary by inducing the recruitment of both FGP and SGP oocytes in the long-term hypophysectomized frogs. The percentage of oocytes undergoing atresia was considerably reduced following PDH, PMSG, HCG, and even GH treatment. The decrease in the weight of the oviduct caused by hypophysectomy was not overcome by any of the hormone treatments. The present findings suggest that in R. cyanophlyctis oogonial proliferation may be independent of hypophysial hormones and show that recruitment of FGP and SGP oocytes can be induced in long-term hypophysectomized frogs using PDH, PMSG, and HCG.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Expression and localization of cytochrome P450(11beta,aldo) mRNA in the frog brain.

The present study is focused on biosynthesis of adrenal steroids in the frog brain. Employing RT-PCR method using total RNA from the adult Rana nigromaculata brain, we isolated a 419-bp fragment of cDNA encoding cytochrome P450(11beta,aldo), which catalyzes the final step of biosynthesis of the frog adrenal steroids, corticosterone and aldosterone. The deduced amino acid sequence of R. nigromaculata brain cytochrome P450(11beta,aldo) shared a high homology (88.8%) with that of R. catesbeiana adrenal cytochrome P450(11beta,aldo). Southern blot analysis of the RT-PCR product confirmed the P450(11beta,aldo) transcription in the frog brain without a clear-cut sex difference. Then, we analyzed the P450(11beta,aldo) mRNA expression in different brain regions of the adult frog by RT-PCR method. The P450(11beta,aldo) gene was transcribed in the telencephalon, diencephalon, midbrain, and cerebellum. The transcript level of the frog beta-actin gene was relatively constant in all the frog samples examined. In situ hybridization analysis showed that the P450(11beta,aldo) gene was transcribed abundantly in the cells throughout the frog brain, such as the pallium mediale in the telencephalon, the nucleus preopticus in the diencephalon, the stratum griseum superficiale tecti in the midbrain, and Purkinje cells in the cerebellum. These results taken together suggest that the frog brain synthesizes adrenal steroids, such as corticosterone and aldosterone.

Amino Acid Sequence↗
PubMed1997

Impaired vision for binocular tasks after unilateral optic nerve regeneration in the frog Litoria moorei.

Behavioural responses to objects in the binocular field were examined in frogs with one regenerate and one intact optic nerve. Data were compared to those for normal controls and for frogs with vision via one intact optic nerve. During prey acquisition, frogs with regenerated optic nerves underestimated the distance to the prey on their first strike; as a consequence, the regenerate series made several attempts to achieve a successful prey capture. By contrast, normal frogs and those using only one eye struck accurately at the prey and usually captured it on the first attempt. However, frogs using only one eye struck from a closer distance than either the regenerate or normal series. Frogs with regenerated optic nerves also made more errors than either of the other series when leaping through a set of closely spaced horizontally aligned rods. Our results show that prey capture and the negotiation of horizontally aligned rods is impaired in animals using one regenerated and one intact optic nerve as compared to both normal frogs and those using only one eye. We suggest that the poor visual performance for frogs with one regenerated and one intact optic nerve for tasks presented in the binocular field is related to the integration of a degraded and a normal image within the visual centres.

Animals↗
PubMed2006

Insular shifts in body size of rice frogs in the Zhoushan Archipelago, China.

1. Differences in body size between mainland and island populations have been reported for reptiles, birds and mammals. Despite widespread recognition of insular shifts in body size in these taxa, there have been no reports of such body size shifts in amphibians. 2. We provide the first evidence of an insular shift in body size for an amphibian species, the rice frog Rana limnocharis. We found significant increases in body size of rice frogs on most sampled islands in the Zhoushan archipelago when compared with neighbouring mainland China. 3. Large body size in rice frogs on islands was significantly related to increased population density, in both breeding and non-breeding seasons. Increases in rice frog density were significantly related to higher resource availability on islands. Increased resource availability on islands has led to higher carrying capacities, which has subsequently facilitated higher densities and individual growth rates, resulting in larger body size in rice frogs. We also suggest that large body size has evolved on islands, as larger individuals are competitively superior under conditions of harsh intraspecific competition at high densities. 4. Increases in body size in rice frogs were not related to several factors that have been implicated previously in insular shifts in body size in other taxa. We found no significant relationships between body size of rice frogs and prey size, number of larger or smaller frog species, island area or distance of islands from the mainland. 5. Our findings contribute to the formation of a broad, repeatable ecological generality for insular shifts in body size across a range of terrestrial vertebrate taxa, and provide support for recent theoretical work concerning the importance of resource availability for insular shifts in body size.

Animals↗
PubMed1991

Electrophysiological effects of calcitonin gene-related peptide in bull-frog and guinea-pig atrial myocytes.

1. Electrophysiological effects of calcitonin gene-related peptide (CGRP) on action potentials and corresponding transmembrane currents in single myocytes from bull-frog and guinea-pig atria were studied using a whole-cell voltage-clamp method. 2. CGRP at relatively low concentrations increased the height of the action potential plateau in a dose-dependent manner in both bull-frog and guinea-pig myocytes. In addition, in bull-frog cells CGRP accelerated the early phase of repolarization, thus shortening the overall duration of the action potential. In contrast, in guinea-pig myocytes CGRP prolonged the action potential duration at all concentrations that were studied. 3. Voltage-clamp measurements demonstrated that CGRP increased transmembrane calcium current (ICa) in guinea-pig myocytes without a significant change in its voltage dependence. The ED50 value for this effect on ICa was 1.28 +/- 0.55 X 10(-8) M (n = 4). The time course of the inactivation of ICa was not affected by CGRP. 4. CGRP increased the delayed rectifier K+ current (IK) at relatively low concentrations in bull-frog atria, whereas relatively high concentrations were needed to increase IK in guinea-pig myocytes. This effect was observed even after complete inhibition of ICa. 5. CGRP had no significant effect on the inwardly rectifying background K+ current, IK1, even at very high concentrations. 6. Comparison of the time course of ICa augmentation in bull-frog and guinea-pig myocytes revealed an important difference in the effect of CGRP in these two types of cells. CGRP at maximal concentrations increased ICa transiently in bull-frog myocytes, whereas this response was sustained in guinea-pig myocytes. Isoprenaline (Iso) induced sustained increase in ICa in both species. When ICa was fully activated by Iso, CGRP at high concentrations strongly inhibited ICa in the bull-frog, whereas it had little effect on ICa in guinea-pig myocytes. 7. Intracellular application of GTP gamma S (guanosine 5'-O-(3-thiotriphosphate) 10(-4) M) greatly potentiated the CGRP effect on ICa; in contrast, GDP beta S (guanosine 5'-O-(2-thiodiphosphate), 2 x 10(-3) M) partially inhibited the CGRP-induced augmentation of ICa. Taken together, these results indicate that the stimulation of ICa by CGRP is mediated by a GTP-binding protein. 8. The observed dose-dependent changes in ICa and IK in bull-frog and guinea-pig myocytes can explain the different patterns of CGRP-induced changes in action potential shape in these two myocyte preparations.

Action Potentials↗
PubMed1980

M-line protein preparations from frog skeletal muscle: isolation and localization of an M-line protein and a 105 000 dalton polypeptide contaminant.

A 165 000 dalton polypeptide was purified and characterized from high salt extracted crude M-line protein preparations of frog skeletal muscle. It has an isoelectric point of 5.8-6.2 and an amino acid composition similar to that reported for the putative M-line protein in chicken muscle (termed component I) and rabbit muscle. Antibodies prepared against the 165 000 dalton polypeptide not not react with purified frog debranching enzyme, and indirect immunofluorescent studies localize this polypeptide wholly in the middle of the A band (presumably the M line) of frog skeletal muscle. We conclude that this 165 000 dalton polypeptide is a basic constituent of the M line in frog skeletal muscle. Crude M-line protein preparations from frog muscle invariably contained a 105 000 dalton polypeptide contaminant. In crude M-line protein preparation from chicken muscle, a polypeptide with a similar molecular mass was identified as phosphorylase b. Characterization of the 105 000 dalton polypeptide isolated from crude M-line protein preparations establishes that in frog muscle extracts this component has an amino acid composition which is different from phosphorylase b, but similar to frog alpha-actinin. Since it also exhibits immunochemical cross-reactivity with alpha-actinin and not with purified phosphorylase b, and is localized wholly at the Z line, we conclude that the 105 000 dalton polypeptide contaminant in crude M-line protein preparations from frog muscle is alpha-actinin.

Amino Acids↗
PubMed1992

Metabolic fate of lactate after vigorous activity in the leopard frog, Rana pipiens.

Although the ability of isolated frog muscle to synthesize glycogen from lactate has long been known, it has never been demonstrated that this metabolic activity occurs in the intact frog. Our results clearly indicate that lactate glycogenesis in frog muscle occurs to a significant extent in vivo. During recovery from strenuous exercise, most of the lactate accumulated by frogs seems to be recycled into muscle glycogen because the lactate that disappears during recovery could account nearly stoichiometrically for the glycogen that accumulates in muscle. Furthermore, the decrease in body lactate and the increase in muscle glycogen follow corresponding time courses, suggesting a precursor-product relationship between lactate and glycogen. During recovery from intense exercise, hepatectomized and normal frogs have nearly identical extents of lactate elimination and glycogen synthesis. This suggests that muscle is the main tissue responsible for the recycling of lactate into muscle glycogen and that liver plays a negligible role in lactate disposal. The negligible hepatic contribution to lactate recycling results in part from the liver's incapacity to produce glucose from lactate. In support of this proposition, we show that frog liver perfused in vitro is unable to incorporate any detectable labeled lactate into glucose despite its excellent physiological integrity. Changes in dietary status, training state, season at which the experiments were done, exercise status, and composition of the perfusion media (pH, hormonal composition, physiological saline vs. culture medium) did not give rise to lactate gluconeogenesis. Because frog liver contains all the regulatory enzymes of the gluconeogenic pathway, its inability to synthesize glucose from lactate is not due to an absence of pyruvate carboxylase. A limited ability for lactate uptake may explain why frog liver cannot produce glucose from lactate.

Animals↗
PubMed1995

Frog vasoactive intestinal polypeptide and galanin: primary structures and effects on pituitary adenylate cyclase.

Vasoactive intestinal polypeptide (VIP) and galanin were isolated in pure form from the stomach of the European green frog, Rana ridibunda. Frog VIP is identical to the previously characterized VIP from chicken and alligator. The primary structure of frog galanin contains only two amino acid substitutions (asparagine for histidine at position 23 and histidine for tyrosine at position 26) compared with porcine galanin. The data indicate that evolutionary pressure to conserve the amino acid sequence of both peptides during the evolution of amphibia to mammals has been strong. Synthetic frog VIP produced a dose-dependent increase in cAMP concentration in frog anterior pituitary fragments. The potency of the peptide (ED50 = 1.2 x 10(-6) M; mean +/- SE; n = 8) was comparable to that of porcine VIP (EC50 = 1.3 x 10(-6) M), but was approximately 10-fold less than that of frog pituitary adenylate cyclase-activating polypeptide [PACAP-(1-38); ED50 = 1.1 x 10(-7) M] in the same system. The increases in cAMP concentrations produced by maximal doses of PACAP (10(-5) M) and VIP (10(-5) M) were not additive. The data suggest that the effects of both peptides are mediated through a common PACAP-preferring receptor that is pharmacologically different from the mammalian PACAP type I receptor. Synthetic frog galanin also produced a dose-dependent increase in the concentration of cAMP in isolated frog anterior pituitary fragments (ED50 = 9.3 x 10(-8) M) consistent with a possible role for the peptide as a hypophysiotropic factor in amphibians.

Adenylyl Cyclases↗
PubMed1999

Does behavioural hypothermia promote post-exercise recovery in cold-submerged frogs?

At the low temperatures of the overwintering environment of the frog Rana temporaria, small changes in ambient temperature have large effects on metabolism and behaviour, especially since Q10 values are often greatly elevated in the cold. How the overwintering aquatic frog copes with variable thermal environments in terms of its overall activity metabolism and recovery from pursuit by predators is poorly understood, as is the role of behavioural thermoregulation in furthering recovery from intense activity. Exhaustive exercise was chosen as the method of evaluating activity capacity (defined by time to exhaustion, total distance swum and number of leg contractions before exhaustion) and was determined at 1.5 and 7 degreesC. Other cohorts of frogs were examined at both temperatures to determine the metabolic (acid-base, lactate, glucose, ATP and creatine phosphate) and respiratory responses to exercise in cold-submerged frogs. Finally, temperature preference before and after exercise was determined in a thermal gradient to define the importance of behavioural thermoregulation on the recovery rates of relevant metabolic and respiratory processes. Activity capacity was significantly reduced in frogs exercised at 1.5 versus 7 degreesC, although similar levels of tissue acid-base metabolites and lactate were reached. Blood pH, plasma PCO2 and lactate levels recovered more rapidly at 1.5 degreesC than at 7 degreesC; however, intracellular pH and the recovery of tissue metabolite levels were independent of temperature. Resting aerobic metabolic rates were strongly affected by temperature (Q10=3.82); however, rates determined immediately after exercise showed a reduced temperature sensitivity (Q10=1.67) and, therefore, a reduced factorial aerobic scope. Excess oxygen consumption recovered to resting values after 5-6.25 h, and 67 % recovery times tended to be slightly faster at the lower temperatures. Exercise in the cold, therefore, provided an immediately higher factorial scope, which could be involved in the faster rate of recovery of blood lactate levels in the colder frogs. In addition, exercise significantly lowered the preferred temperature of the frogs from 6.7 to 3.6 degreesC for nearly 7 h, after which they returned to their normal, unstressed preferred temperatures. Thus, a transient behavioural hypothermia in the skin-breathing, overwintering frog may be an important strategy for minimising post-exercise stress and maintaining aerobic metabolism during recovery from intense activity.

Journal Article↗
PubMed2004

Modular premotor drives and unit bursts as primitives for frog motor behaviors.

Spinal cord modularity impacts on our understanding of reflexes, development, descending systems in normal motor control, and recovery from injury. We used independent component analysis and best-basis or matching pursuit wavepacket analysis to extract the composition and temporal structure of bursts in hindlimb muscles of frogs. These techniques make minimal a priori assumptions about drive and motor pattern structure. We compared premotor drive and burst structures in spinal frogs with less reduced frogs with a fuller repertoire of locomotory, kicking, and scratching behaviors. Six multimuscle drives explain most of the variance of motor patterns (approximately 80%). Each extracted drive was activated with pulses at a single time scale or common duration (approximately 275 msec) burst structure. The data show that complex behaviors in brainstem frogs arise as a result of focusing drives to smaller core groups of muscles. Brainstem drives were subsets of the muscle groups from spinal frogs. The 275 msec burst duration was preserved across all behaviors and was most precise in brainstem frogs. These data support a modular decomposition of frog behaviors into a small collection of unit burst generators and associated muscle drives in spinal cord. Our data also show that the modular organization of drives seen in isolated spinal cord is fine-tuned by descending controls to enable a fuller movement repertoire. The unit burst generators and their associated muscle synergies extracted here link the biomechanical "primitives," described earlier in the frog, rat, and cat, and to the elements of pattern generation examined in fictive preparations.

Animals↗