The development of nerve-muscle junctions in Rana catesbeiana tadpoles

The physiological properties of developing nerve-muscle junctions in Rana catesbeiana tadpoles are described. Developing neurons at different stages of ontogeny formed functional synaptic connections with a section of tail muscle implanted in place of the hind limb bud. Transmission is quantal in nature, sensitive in normal ways to calcium and magnesium concentrations, and conforms to a Poisson distribution. The quantal content is initially low and increases with development. Mepp's occur randomly and have low frequencies which increase slightly with development. The size of a single quantum of transmitter does not change during development. The muscle fibers are multiply innervated, resulting in Epp's with distinct peaks and complex skewed mepp amplitude histograms. No significant increases were observed in the level of differentiation of the developing motor neurons as a result of their having innervated a portion of mature tail muscle. The numbers of developing motor neurons increased in the experimental lateral motor column, and a lag in their maturity was observed relative to motor neurons in the control lateral motor column.     

Inhibition of thyroxine-induced metamorphosis by prolactin in tadpoles, Rana catesbeiana.

Thyroxine (T4)-prolactin interactions on hepatic arginase and ornithine transcarbamylase (OTC) as well as hind legs, tail, digestive tract and median eminence were investigated in tadpoles, Rana catesbeiana. Prolactin completely blocked T4-induced tail resorption, but failed to suppress hind-leg growth, shortening of digestive tract and promotion by T4 of the median eminence development. Prolactin blocked T4-induced increase in hepatic arginase activity but not in hepatic OTC activity. A possibility that T4 and prolactin are regulating the hepatic arginase indirectly is discussed.     

Effect of phenylhydrazine on the multiple hemoglobins of Rana catesbeiana tadpoles

Tadpoles of Rana catesbeiana immersed in or injected with phenylhydrazine show a preferential loss from the circulation of the electrophoretically fastest hemoglobin (Hb) and retention of the electrophoretically slower Hb's on polyacrylamide disk-gels.The electrophoretically slowest Hb has previously been found to be synthesized in the kidney while the other Hb's are synthesized in the liver. We postulate that the differential response of the tadpole hemoglobins to the action of phenylhydrazine results from the different Hb's being found in different red blood cell lines that originate in different erythropoietic tissues.     

Sequence of ossification in the skeleton of growing and metamorphosing tadpoles of Rana pipiens

The order of ossification of bones in the skeleton of Rana pipiens during larval growth and metamorphosis has been determined from observations on specimens fixed in 70% alcohol and stained with alizarin red S. The axial skeleton ossifies in a generally cephalo-caudal sequence, beginning with the parasphenoid bone at Taylor-Kollros stages IV-IX, followed by vertebrae (V-IX) and then the urostyle (IX-XIV). Exoccipitals (VII-IX), frontoparietals (XI-XII) and prootics (XIII-XVII) are additional cranial bones which successively ossify before metamorphosis. With the onset of metamorphosis at stage XVIII jawbones and rostral bones of the skull ossify in the following succession: premaxilla, maxilla, septomaxilla, nasal, dentary, angular, squamosal, pterygoid, prevomer, mentomeckelian, quadratojugal, palatine, columella, posteromedial process of “hyoid.” The sphenethmoid does not ossify until after metamorphosis. Ossification of limbbones begins with the femur or humerus at stages X-XII and progresses proximo-distally to the phalanges by stages XIII-XV. Carpals, however, do not ossify until stage XXV or after metamorphosis. The ilium of the pelvic girdle begins to ossify at stages X-XII, but the ischium is delayed until stages XX-XXIII. Scapula and coracoid of the pectoral girdle undergo initial ossification at stages XII-XIV, suprascapula and clavicle at stages XIII-XV. The sternum does not begin to ossify until stage XXIV. The possible role of thyroid hormones in stimulating osteogenesis is discussed.     

Determination of hemoglobin expression patterns in erythroid cells of Rana catesbeiana tadpoles

1. Rana catesbeiana (bullfrog) tadpoles are heterogeneous in the relative amounts of four major tadpole hemoglobins (Hbs), as well as in the relative amounts of two tadpole red blood cell types in the peripheral blood. 2. Previous work has shown that this heterogeneity is present at all stages of larval development and growth. 3. Although some tadpoles lack one of the Hbs in their peripheral blood (i.e. the electrophoretically slowest form, Td-4), the missing Hb can be found in the erythropoietic organ from which it emanates (the kidneys), indicating that the heterogeneity results from quantitative differences in gene expression. 4. We wished to know whether this in vivo regulation is subject to external environmental perturbation and report that tadpoles of known Hb phenotypes regenerate precisely the pre-anemia Hb profile during early as well as late stages of recovery from phenylhydrazine-induced anemia. 5. These and other results indicate that the in vivo mechanism for regulating the pattern of Hb expression has become firmly determined in the erythropoietic system by the earliest larval stage of development.     

Bile pigments and bilirubin UDP-glucuronyl transferase during the metamorphosis of Rana catesbeiana tadpoles

1. Cold-acclimated (1 degree C) goldfish (Carassius auratus) branchial Na/K-ATPase activity was elevated 100% while renal Na/K-ATPase activity was not significantly affected compared with warm-acclimated (20 degrees C) goldfish. 2. Cold-acclimated goldfish branchial and renal Mg-ATPase activity was reduced 18 and 30% on a per mg protein basis, respectively. 3. Renal Na/K-ATPase activity was 4.6- and 1.6-fold greater than gill in cold- and warm-acclimated fish, respectively. 4. The elevated branchial Na/K-ATPase activity and the unchanged renal Na/K-ATPase activity are consistent with the maintenance of the reduced blood ion level in cold-acclimated goldfish.     

Autolysis in the tail muscles of metamorphosing tadpoles

Degradation of muscle homogenate from the metamorphosing tadpole tail of bullfrog, Rana catesbeiana, was examined at acid and neutral pHs. More rapid and complete degradation was observed at acid pH. Proteinases working at acid pH were not inhibited by pepstatin but were inhibited by leupeptin. However, the inhibition by leupeptin was enhanced by pepstatin. These results show that lysosomal proteinases, a thiol proteinase(s) rather than cathepsin D, are involved in the degradation of tail muscle proteins.     

Adrenergic receptors and the regulation of vascular resistance in bullfrog tadpoles (Rana catesbeiana)

Summary Vascular adrenergic sensitivity to exogenous catecholamines was examined in tadpoles of the American bullfrog (Rana catesbeiana), ranging from stage III to XIV. Central arterial blood pressure was measured in decerebrate bullfrog tadpoles to determine a reasonable initial infusion pressure. Solutions of epinephrine and phenylephrine were infused into the vasculature of pithed tadpoles, and the resulting changes in vascular resistance (R _v) were used to construct log dose-response relationships. Epinephrine infusion produced a dose-dependent increase in R _v (EC₅₀=5.3·10^-7 M), which could be reversed by sodium nitroprusside (a smooth muscle relaxant) and blocked by phenoxybenzamine (an -adrenergic antagonist). Larval R _v also increased with infusion of the -agonist phenylephrine (EC₅₀=7.4·10⁸ M). Infusion of 10^-6 M isoproterenol (a -agonist) largely reversed the phenylephrine-induced increase in R _v. These results indicate that the capacity exists for both -mediated vasoconstriction and -mediated vasodilation early in bullfrog ontogeny. Neither initial R _v nor the responses to infused epinephrine or phenylephrine were significantly correlated to development over the range of larval stages used in this study.Abbreviations ECG electrocardiogram - EPI epinephrine - ISO isoproterenol - PHE phenylephrine - POB phenoxybenzamine - R _v vascular resistance - SNP sodium nitroprusside     

Interrelationships among epidermal Na-K ATPase, developmental stage and length of Rana catesbeiana tadpoles

Sodium and potassium activated adenosine triphosphatase (Na-K ATPase) was extracted from the skin of Rana catesbeiana tadpoles and adults. Using carefully staged tadpoles, it was noted that the enzyme level increases two or three stages before there is a perceptible potential difference generated across the skin. The level of non-ouabain-inhibitable ATPase remains constant throughout the life cycle. It was also concluded that Rana catesbeiana tadpoles cannot be reliably staged using length as a key trait.     

Chromatin condensation and nucleolar segregation induced in nuclei of parenchymal cells of Rana catesbeiana tadpoles

The effect of increased levels of cAMP upon the differentiation of primary cultures of chick myo blasts has been investigated. 0.1 mM But₂ cAMP or 1 mM 3-isobutyl-1-methylxanthine was added to the cultures 24 h after plating and maintained throughout the 70 h period of culture examined. Both reagents were found to markedly delay the time of fusion of the myoblasts but had no observable effect upon the increase in activity of creatine phosphokinase. Morphological examination of the cells revealed no difference in the relative numbers of myoblasts and fibroblasts between the control, But₂ cAMP and 3-isobutyl-1-methylxanthine cultures, but the latter reagent appeared to cause some inhibition of cell proliferation.     

Effects of nitrate on the interactions of the tadpoles of two ranids (Rana clamitans and R. catesbeiana)

Nitrogen pollution as a result of agricultural runoff and atmospheric deposition is a major challenge to aquatic ecosystems, and is likely to increase in the future. Nitrogenous pollutants are potential stressors of amphibian larvae through their toxicological impacts on individuals; however, they may also increase primary productivity. We examined how such an anthropogenic stressor could influence the interactions between two potentially competing species of tadpoles (Rana clamitans and R. catesbeiana). In a 42 d mesocosm experiment, R. catesbeiana survival, but not final mass, was reduced by nitrate addition. Rana catesbeiana survival was lower when in competition with R. clamitans than when only experiencing intraspecific competition. For R. clamitans, survival was not affected by nitrate addition or competition type. Rana clamitans in nitrate addition mesocosms were heavier than tadpoles from no nitrate mesocosms, and were heavier in intraspecific than in interspecific mesocosms. Our results suggest that nitrate can influence the performance of amphibian larvae, and that its effects could have complex effects on aquatic ecosystems.     

Different sensitivity to amiloride of body and tail skins of Rana catesbeiana tadpoles during metamorphosis

Regional differences in potential difference and short-circuit current between the body (dorsal) and the tail skin during metamorphosis of Rana catesbeiana tadpoles were investigated. In body skin, the potential difference and the short-circuit current across the skin develop in two successive steps. At stage XX, the potential difference and the short-circuit current across the body skins were amiloride-insensitive (1st step). At stage XXII, however, amiloride-sensitive potential difference and the short circuit current appeared (2nd step). By contrast, in tail skin the potential difference and the short-circuit current remained amiloride-insensitive (1st step) even at stage XXIII. Since the tail regresses after stage XXIII, the appearance of the second step could not be followed in vivo. To determine whether or not the second step can be induced in the tail, tail skin was cultured under conditions where the skin survives for a much longer period than it does in normally developing tadpoles. Such cultured tail skin generated the amiloride-sensitive potential difference and the short-circuit current and cultured body skin also generated them. Therefore, development of the 2nd step in the tail skin may be delayed in vivo. To characterize the differences between body and tail skin, skins were mutally grafted between body and tail at stage XIII–XV. The body skin grafted on the tail underwent both the 1st and 2nd steps by stage XXII, whereas the tail skin grafted on the body only showed the 1st step by the same stage. These results suggest that the regional specificity of the skin is already established before the prometamorphic stage.Abbreviations CMFS Ca²⁺- and Mg²⁺-free saline - CTS charcoal-treated serum - EDTA ethylene diamine tetra-acetate - I current - PD potential difference - R skin resistance - SCC short-circuit current