Ambystoma: A genus of the Ambystomatidae family. The best known species are the axolotl AMBYSTOMA MEXICANUM and the closely related tiger salamander Ambystoma tigrinum. They may retain gills and remain aquatic without developing all of the adult characteristics. However, under proper changes in the environment they metamorphose.Ambystoma mexicanum: A salamander found in Mexican mountain lakes and accounting for about 30 percent of the urodeles used in research. The axolotl remains in larval form throughout its life, a phenomenon known as neoteny.Urodela: An order of the Amphibia class which includes salamanders and newts. They are characterized by usually having slim bodies and tails, four limbs of about equal size (except in Sirenidae), and a reduction in skull bones.Ranavirus: A genus of IRIDOVIRIDAE which infects fish, amphibians and reptiles. It is non-pathogenic for its natural host, Rana pipiens, but is lethal for other frogs, toads, turtles and salamanders. Frog virus 3 is the type species.Ambystomatidae: A family of the class Urodela which includes 4 living genera, about 33 species, and occurs only in North America. Adults are usually terrestrial, but the larval forms are aquatic.Amphibians: VERTEBRATES belonging to the class amphibia such as frogs, toads, newts and salamanders that live in a semiaquatic environment.Metamorphosis, Biological: Profound physical changes during maturation of living organisms from the immature forms to the adult forms, such as from TADPOLES to frogs; caterpillars to BUTTERFLIES.DNA Virus InfectionsLarva: Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals.Pleurodeles: A genus of aquatic newts belonging to the family Salamandridae and sometimes referred to as "spiny" tritons. There are two species P. waltlii and P. poireti. P. waltlii is commonly used in the laboratory. Since this genus adapts to aquarium living, it is easy to maintain in laboratories.Chromatophores: The large pigment cells of fish, amphibia, reptiles and many invertebrates which actively disperse and aggregate their pigment granules. These cells include MELANOPHORES, erythrophores, xanthophores, leucophores and iridiophores. (In algae, chromatophores refer to CHLOROPLASTS. In phototrophic bacteria chromatophores refer to membranous organelles (BACTERIAL CHROMATOPHORES).)Sugar Alcohols: Polyhydric alcohols having no more than one hydroxy group attached to each carbon atom. They are formed by the reduction of the carbonyl group of a sugar to a hydroxyl group.(From Dorland, 28th ed)Regeneration: The physiological renewal, repair, or replacement of tissue.Extremities: The farthest or outermost projections of the body, such as the HAND and FOOT.Parabiosis: The experimental joining of two individuals for the purpose of studying the effects of one on the other.Photoreceptor Cells: Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.TailKentuckyForelimb: A front limb of a quadruped. (The Random House College Dictionary, 1980)Contig Mapping: Overlapping of cloned or sequenced DNA to construct a continuous region of a gene, chromosome or genome.NebraskaTennesseeFirefighters: Professional or volunteer members of a fire department who are trained to suppress fire and respond to related emergency.Liquidambar: A plant genus of the family HAMAMELIDACEAE. The sap is a source of storax, which should not be confused with the similar named STYRAX genus.Acer: A plant genus of the family ACERACEAE, best known for trees with palmately lobed leaves.Magnolia: A plant genus of the family MAGNOLIACEAE. The germacranolide sesquiterpene lactones costunolide, parthenolide, and costunolide diepoxide have been isolated from the leaves. Bark contains honokiol and magnolol. Parts are an ingredient of Banxia Houpo Tang.Hypericum: Genus of perennial plants in the family CLUSIACEAE (sometimes classified as Hypericaceae). Herbal and homeopathic preparations are used for depression, neuralgias, and a variety of other conditions. Hypericum contains flavonoids; GLYCOSIDES; mucilage, TANNINS; volatile oils (OILS, ESSENTIAL), hypericin and hyperforin.Fraxinus: A plant genus of the family OLEACEAE. Members contain secoiridoid glucosides.Nyssa: A plant genus of the family NYSSACEAE (or Cornaceae by some).Styrax: A plant genus of the family STYRACACEAE. Sap of these Asian trees are a source of a balsam (BALSAMS). This styrax balsam is 3/4 coniferyl benzoate, 1/8 free BENZOIC ACID, along with benzyl cinnamate, vanillin, and TRITERPENES.Rodent Control: The reduction or regulation of the population of noxious, destructive, or dangerous rodents through chemical, biological, or other means.NevadaTigers: The species Panthera tigris, a large feline inhabiting Asia. Several subspecies exist including the Siberian tiger and Sumatran tiger.Halorubrum: A genus of HALOBACTERIACEAE which are chemoorganotrophic and strictly aerobic. They have been isolated from multiple hypersaline environments that vary widely in chemical and physical properties.Sciuridae: A family of the order Rodentia which contains 49 genera. Some of the more common genera are MARMOTA, which includes the marmot and woodchuck; Sciurus, the gray squirrel, S. carolinensis, and the fox squirrel, S. niger; Tamias, the eastern and western chipmunk; and Tamiasciurus, the red squirrel. The flying squirrels, except the scaly-tailed Anomaluridae, also belong to this family.Benzopyrenes: A class of chemicals that contain an anthracene ring with a naphthalene ring attached to it.Benz(a)Anthracenes: Four fused benzyl rings with three linear and one angular, that can be viewed as a benzyl-phenanthrenes. Compare with NAPHTHACENES which are four linear rings.Methylcholanthrene: A carcinogen that is often used in experimental cancer studies.Libraries, Digital: Libraries in which a major proportion of the resources are available in machine-readable format, rather than on paper or MICROFORM.Cities: A large or important municipality of a country, usually a major metropolitan center.Urbanization: The process whereby a society changes from a rural to an urban way of life. It refers also to the gradual increase in the proportion of people living in urban areas.Gilbert Disease: A benign familial disorder, transmitted as an autosomal dominant trait. It is characterized by low-grade chronic hyperbilirubinemia with considerable daily fluctuations of the bilirubin level.Carbon: A nonmetallic element with atomic symbol C, atomic number 6, and atomic weight [12.0096; 12.0116]. It may occur as several different allotropes including DIAMOND; CHARCOAL; and GRAPHITE; and as SOOT from incompletely burned fuel.Photosynthesis: The synthesis by organisms of organic chemical compounds, especially carbohydrates, from carbon dioxide using energy obtained from light rather than from the oxidation of chemical compounds. Photosynthesis comprises two separate processes: the light reactions and the dark reactions. In higher plants; GREEN ALGAE; and CYANOBACTERIA; NADPH and ATP formed by the light reactions drive the dark reactions which result in the fixation of carbon dioxide. (from Oxford Dictionary of Biochemistry and Molecular Biology, 2001)Regression Analysis: Procedures for finding the mathematical function which best describes the relationship between a dependent variable and one or more independent variables. In linear regression (see LINEAR MODELS) the relationship is constrained to be a straight line and LEAST-SQUARES ANALYSIS is used to determine the best fit. In logistic regression (see LOGISTIC MODELS) the dependent variable is qualitative rather than continuously variable and LIKELIHOOD FUNCTIONS are used to find the best relationship. In multiple regression, the dependent variable is considered to depend on more than a single independent variable.Triturus: A genus of aquatic newts in the Salamandridae family. During breeding season many Triturus males have a dorsal crest which also serves as an accessory respiratory organ. One of the common Triturus species is Triturus cristatus (crested newt).Indigo Carmine: Indolesulfonic acid used as a dye in renal function testing for the detection of nitrates and chlorates, and in the testing of milk.BooksRanunculus: A plant genus of the family RANUNCULACEAE that contains protoanemonin, anemonin, and ranunculin.Endoderm: The inner of the three germ layers of an embryo.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Homozygote: An individual in which both alleles at a given locus are identical.

Occupancy of the chromophore binding site of opsin activates visual transduction in rod photoreceptors. (1/599)

The retinal analogue beta-ionone was used to investigate possible physiological effects of the noncovalent interaction between rod opsin and its chromophore 11-cis retinal. Isolated salamander rod photoreceptors were exposed to bright light that bleached a significant fraction of their pigment, were allowed to recover to a steady state, and then were exposed to beta-ionone. Our experiments show that in bleach-adapted rods beta-ionone causes a decrease in light sensitivity and dark current and an acceleration of the dim flash photoresponse and the rate constants of guanylyl cyclase and cGMP phosphodiesterase. Together, these observations indicate that in bleach-adapted rods beta-ionone activates phototransduction in the dark. Control experiments showed no effect of beta-ionone in either fully dark-adapted or background light-adapted cells, indicating direct interaction of beta-ionone with the free opsin produced by bleaching. We speculate that beta-ionone binds specifically in the chromophore pocket of opsin to produce a complex that is more catalytically potent than free opsin alone. We hypothesize that a similar reaction may occur in the intact retina during pigment regeneration. We propose a model of rod pigment regeneration in which binding of 11-cis retinal to opsin leads to activation of the complex accompanied by a decrease in light sensitivity. The subsequent covalent attachment of retinal to opsin completely inactivates opsin and leads to the recovery of sensitivity. Our findings resolve the conflict between biochemical and physiological data concerning the effect of the occupancy of the chromophore binding site on the catalytic potency of opsin. We show that binding of beta-ionone to rod opsin produces effects opposite to its previously described effects on cone opsin. We propose that this distinction is due to a fundamental difference in the interaction of rod and cone opsins with retinal, which may have implications for the different physiology of the two types of photoreceptors.  (+info)

Modulation of glycine receptors in retinal ganglion cells by zinc. (2/599)

Effects of zinc, an endogenous neuromodulator in the central nervous system, on glycine receptors (GlyRs) in retinal ganglion cells were investigated by using the whole-cell voltage-clamp technique. Zn2+ at low concentration (<2 microM) potentiated the glycine-induced chloride current and at higher concentration (>10 microM) suppressed it. This biphasic regulatory action of zinc acted selectively on the fast component of the glycine-induced current mediated by the strychnine-sensitive GlyRs, but not on the slow component mediated by the 5,7-dichlorokynurenic acid-sensitive GlyRs. Dose-response studies showed that 1 microM Zn2+ increased the maximum glycine response (I approximately) and shifted the EC50 to the left, suggesting that Zn2+ at low concentrations acts as an allosteric activator of the strychnine-sensitive GlyRs. Zn2+ at a concentration of 100 microM did not alter I approximately and shifted the EC50 to the right, indicating that Zn2+ at high concentrations acts as a competitive inhibitor of the GlyRs. Physiological functions of zinc modulation of GlyRs in retinal ganglion cells are discussed.  (+info)

Blastemal kinetics and pattern formation during amphibian limb regeneration. (3/599)

To investigate whether the uniqueness of proximal and distal limb regenerates could be attributed simply to differing blastemal growth characteristics, their increase in volume, cell number and cell-cycle times were determined. With respect to these parameters proximal and distal blastemas were identical and, furthermore, no evidence could be found for the existance of separate growth zones such as an apical proliferation centre or a progress zone within the blastema. It was therefore concluded that level-specific properties of the blastemal cells play the major role in determining the structure of the regenerate, not their growth characteristics. The only discernible difference was in the cell number within the two types of blastema at the onset of cartilage redifferentiation - proximal regenerates had 60% more cells. Thus it seems that the larger the pattern to be regenerated (the more proximal the amputation plane), the larger the primordium within which that pattern first appears. These two conclusions are discussed in relation to current theories of pattern formation during limb regeneration and development and a few way of envisaging the regeneration of pattern is described.  (+info)

Impulse encoding across the dendritic morphologies of retinal ganglion cells. (4/599)

Nerve impulse entrainment and other excitation and passive phenomena are analyzed for a morphologically diverse and exhaustive data set (n = 57) of realistic (3-dimensional computer traced) soma-dendritic tree structures of ganglion cells in the tiger salamander (Ambystoma tigrinum) retina. The neurons, including axon and an anatomically specialized thin axonal segment that is observed in every ganglion cell, were supplied with five voltage- or ligand-gated ion channels (plus leakage), which were distributed in accordance with those found in a recent study that employed an equivalent dendritic cylinder. A wide variety of impulse-entrainment responses was observed, including regular low-frequency firing, impulse doublets, and more complex patterns involving impulse propagation failures (or aborted spikes) within the encoder region, all of which have been observed experimentally. The impulse-frequency response curves of the cells fell into three groups called FAST, MEDIUM, and SLOW in approximate proportion as seen experimentally. In addition to these, a new group was found among the traced cells that exhibited an impulse-frequency response twice that of the FAST category. The total amount of soma-dendritic surface area exhibited by a given cell is decisive in determining its electrophysiological classification. On the other hand, we found only a weak correlation between the electrophysiological group and the morphological classification of a given cell, which is based on the complexity of dendritic branching and the physical reach or "receptive field" area of the cell. Dendritic morphology determines discharge patterns to dendritic (synaptic) stimulation. Orthodromic impulses can be initiated on the axon hillock, the thin axonal segment, the soma, or even the proximal axon beyond the thin segment, depending on stimulus magnitude, soma-dendritic membrane area, channel distribution, and state within the repetitive impulse cycle. Although a sufficiently high dendritic Na-channel density can lead to dendritic impulse initiation, this does not occur with our "standard" channel densities and is not seen experimentally. Even so, impulses initiated elsewhere do invade all except very thin dendritic processes. Impulse-encoding irregularities increase when channel conductances are reduced in the encoder region, and the F/I properties of the cells are a strong function of the calcium- and Ca-activated K-channel densities. Use of equivalent dendritic cylinders requires more soma-dendritic surface area than real dendritic trees, and the source of the discrepancy is discussed.  (+info)

Metabotropic GABA receptors facilitate L-type and inhibit N-type calcium channels in single salamander retinal neurons. (5/599)

1. Whole-cell voltage clamp experiments were performed on isolated spiking retinal neurons from the salamander retina. Calcium channel currents were studied using barium as the charge carrier while potassium and sodium currents were suppressed with TEA and TTX, respectively. 2. Baclofen, a metabotropic GABA receptor agonist, both enhanced and suppressed high-voltage-activated calcium channel current. Baclofen facilitated an L-type channel current, and this effect was not voltage dependent. As reported previously, baclofen inhibited an N-type channel current and this action was voltage dependent. 3. While the suppressive effect was mediated by a fast-acting, direct G-protein action, the facilitatory effect was slower and was blocked by inhibitors of protein kinase C (PKC), either GF-109203x or the PKC (19-36) sequence fragment. 4. The pharmacology of the inhibitory and facilitatory responses differed. Commonly used antagonists of metabotropic GABA receptors, CGP35348 and CGP55845, were more potent antagonists of the inhibitory response. Similarly, a selective agonist at the metabotropic GABA receptor, APMPA, was also more effective in eliciting the inhibitory response. 5. These observations indicate that there may be two baclofen-sensitive metabotropic GABA receptors with opposing effects on calcium channel current. This is the first description of a facilitatory action of GABAB receptors and indicates that GABA may not function exclusively as an inhibitory transmitter.  (+info)

Divalent cation selectivity is a function of gating in native and recombinant cyclic nucleotide-gated ion channels from retinal photoreceptors. (6/599)

The selectivity of Ca2+ over Na+ is approximately 3.3-fold larger in cGMP-gated channels of cone photoreceptors than in those of rods when measured under saturating cGMP concentrations, where the probability of channel opening is 85-90%. Under physiological conditions, however, the probability of opening of the cGMP-gated channels ranges from its largest value in darkness of 1-5% to essentially zero under continuous, bright illumination. We investigated the ion selectivity of cGMP-gated channels as a function of cyclic nucleotide concentration in membrane patches detached from the outer segments of rod and cone photoreceptors and have found that ion selectivity is linked to gating. We determined ion selectivity relative to Na+ (PX/PNa) from the value of reversal potentials measured under ion concentration gradients. The selectivity for Ca2+ over Na+ increases continuously as the probability of channel opening rises. The dependence of PCa/PNa on cGMP concentration, in both rods and cones, is well described by the same Hill function that describes the cGMP dependence of current amplitude. At the cytoplasmic cGMP concentrations expected in dark-adapted intact photoreceptors, PCa/PNa in cone channels is approximately 7.4-fold greater than that in rods. The linkage between selectivity and gating is specific for divalent cations. The selectivity of Ca2+ and Sr2+ changes with cGMP concentration, but the selectivity of inorganic monovalent cations, Cs+ and NH4+, and organic cations, methylammonium+ and dimethylammonium+, is invariant with cGMP. Cyclic nucleotide-gated channels in rod photoreceptors are heteromeric assemblies of alpha and beta subunits. The maximal PCa/PNa of channels formed from alpha subunits of bovine rod channels is less than that of heteromeric channels formed from alpha and beta subunits. In addition, Ca2+ is a more effective blocker of channels formed by alpha subunits than of channels formed by alpha and beta subunits. The cGMP-dependent shift in divalent cation selectivity is a property of alphabeta channels and not of channels formed from alpha subunits alone.  (+info)

Sodium action potentials are not required for light-evoked release of GABA or glycine from retinal amacrine cells. (7/599)

Although most CNS neurons require sodium action potentials (Na-APs) for normal stimulus-evoked release of classical neurotransmitters, many types of retinal and other sensory neurons instead use only graded potentials for neurotransmitter release. The physiological properties and information processing capacity of Na-AP-producing neurons appear significantly different from those of graded potential neurons. To classify amacrine cells in this dichotomy, we investigated whether Na-APs, which are often observed in these cells, are required for functional light-evoked release of inhibitory neurotransmitters from these cells. We recorded light-evoked inhibitory postsynaptic currents (IPSCs) from retinal ganglion cells, neurons directly postsynaptic to amacrine cells, and applied TTX to block Na-APs. In control solution, TTX application always led to partial suppression of the light-evoked IPSC. To isolate release from glycinergic amacrine cells, we used either bicuculline, a GABAA receptor antagonist, or picrotoxin, a GABAA and GABAC receptor antagonist. TTX application only partially suppressed the glycinergic IPSC. To isolate release from GABAergic amacrine cells, we used the glycine receptor blocker strychnine. TTX application only partially suppressed the light-evoked GABAergic IPSC. Glycinergic and GABAergic amacrine cells did not obviously differ in the usage of Na-APs for release. These observations, in conjunction with previous studies of other retinal neurons, indicate that amacrine cells, taken as a class, are the only type of retinal neuron that uses both Na-AP-dependent and -independent modes for light-evoked release of neurotransmitters. These results also provide evidence for another parallel between the properties of retinal amacrine cells and olfactory bulb granule cells.  (+info)

Spatial heterogeneity and function of voltage- and ligand-gated ion channels in retinal amacrine neurons. (8/599)

The spatial distribution of ion channels within amacrine cells of the tiger salamander retina was studied using patch recording in the retinal slice preparation. By focally puffing kainate, GABA and glycine at amacrine cell processes in the inner plexiform layer, it was determined that the cell's glutamate receptors were located in a confined region of the processes near the soma, while glycine and GABA receptors were located throughout the processes. Likewise, similar techniques in conjunction with voltage steps demonstrated that voltage-gated sodium channels were located throughout the cell and were shown to generate sodium-dependent spikes, while only the processes contained voltage-gated calcium channels. These results suggest that this form of transient amacrine cell collects its excitatory synaptic inputs in a region confined to a central annular region near the soma, that the signal is actively propagated throughout its processes by voltage-gated sodium channels and that calcium-dependent neurotransmitter release of glycine from this neuron can occur throughout its processes. Thus, excitatory signals are collected in the processes near the soma, inhibitory signals throughout the processes and excitation is probably propagated throughout the processes of the amacrine cell.  (+info)

  • It is proposed that this cytological marker identifies these two chromosomes as being derived from A. laterale and lends further support to the hypothesis that A. tremblayi is 'two-thirds A. laterale and one-third A. jeffersonianum' as proposed by Uzzell inhis studies of the Ambystoma jeffersonianum complex. (
  • This study aimed at assessing the prevalence of genome exchange among unisexuals of the Ambystoma laterale -jeffersonianum complex from 10 sites in the northern part of their distribution. (
  • This study evaluates the loads on the limb bones of the tiger salamander ( Ambystoma tigrinum ) and the Argentine black and white tegu ( Tupinambus merianae ) during terrestrial locomotion using three-dimensional measurements of the ground reaction force (GRF) and hindlimb kinematics, anatomical measurements of the femur and hindlimb muscles, and in vivo measurements of bone strain (tegus only). (
  • Ambystoma tigrinum nebulosum (Arizona Tiger salamander) inhabits montane ecosystems throughout Colorado, Utah, Arizona, and New Mexico. (
  • We identified 14 large linkage groups (125.5-836.7 cM) that presumably correspond to the 14 haploid chromosomes in the Ambystoma genome. (
  • Presumably, the large physical genome size (∼30 Gbp) is a major determinant of map size in Ambystoma. (
  • This new collection of EST-based PCR markers will better enable the Ambystoma system by facilitating development of new molecular probes, and the linkage map will allow comparative studies of this important vertebrate group. (
  • Jancovich JK, Davidson EW, Seiler A, Jacobs BL, Collins JP (2001) Transmission of the Ambystoma tigrinum virus to alternative hosts. (
  • Recent and ancient evolutionary histories of unisexual Ambystoma were proposed by a few separate studies that constructed phylogenies using mitochondrial DNA markers (cytochrome b gene vs. non-coding region). (
  • Differences in optimal temperature for enzyme induction and activity were noted in organ culture of human and Ambystoma tissues, and ratios of benzpyrene metabolites differed between Ambystoma and Mus. (