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PubMed1987

Barium reverses the transretinal potassium gradient of the amphibian retina.

Barium chloride (Ba2+) was added to the bathing medium of the perfused retina-eyecup preparation of the tiger salamander. The electroretinogram (ERG) and intraretinal extracellular potassium activity ([K+]o) were analyzed using a double-barrel electrode, one of which was ion-selective for K+. The action of Ba2+ on the ERG was to attenuate the c-wave/slow PIII complex. In addition, Ba2+ dramatically decreased the [K+]o in the outer retina, enough to reverse the transretinal potassium gradient. These findings, together with the known properties of Müller cell K+ channels, form the basis of an explanation of why Ba2+ blocks slow PIII and not the b-wave of the ERG.

Animals↗
PubMed1987

The development of the amphibian trochlear nucleus. An HRP study.

The quantitative and qualitative development of the trochlear nucleus of salamanders and frogs was studied using horseradish peroxidase (HRP) as a retrograde marker. A higher number of labelled motoneurons significantly declined in later larval stages, presumably by cell death, as in birds and mammals. In agreement with this assumption, HRP-filled apoptotic cells were found in larvae. Many more labelled trochlear motoneurons were found in adult than in larval amphibians, and [3H]thymidine labelling showed postlarval cell production in the area of the trochlear nucleus. Data are discussed in the context of cell death and ongoing cell proliferation.

Ambystoma↗
PubMed1988

Tools for tachykinin and neuropeptide research: a conference report.

A symposium entitled 'Tools for Tachykinin and Neuropeptide Research' was held on 29th and 30th August 1987, at Salamander Bay, N.S.W., Australia, as a Satellite Meeting of the Xth International Congress of Pharmacology. The major emphasis of the symposium was on methods and technical approaches which may be used for the study of tachykinins and other neuropeptides.

Animals↗
PubMed1990

Time-dependent reduction of glutamate current in retinal bipolar cells.

Glutamate hyperpolarizes retinal depolarizing bipolar cells (DBCs) by decreasing a non-specific cation conductance. We have investigated this action of glutamate using whole-cell voltage clamp of DBCs in larval tiger salamander retinal slices and here report two observations: a wash-out of the glutamate response and a concomitant decrease in resting membrane conductance. The wash-out may be due to the loss of a second messenger-mediated mechanism linking the receptor to the response. The decrease in resting membrane conductance suggests that this second messenger may be required to maintain DBC glutamate channels in an open state in the absence of the receptor ligand.

Animals↗
PubMed1991

The glossopharyngeal nerve of the axolotl labeled with carbocyanine dye (diI).

Fluorescent carbocyanine dye (diI) was used to label the glossopharyngeal (IX) nerve in the fixed preparation of the Mexican salamander, axolotl. When the cell bodies were viewed with a confocal laser scanning microscope and Nomarski optics, the cytoplasm was brightly fluorescent, but not the cell nucleus. The cell bodies which send peripheral axons in the two branches of the IX nerve were mainly distributed in the rostral part of the combined glossopharyngeal-vagus ganglion, but a few cells were also distributed in the middle and caudal parts. This may indicate a relatively undifferentiated organization of the IX nerve in the ganglion.

Ambystoma↗
PubMed1994

Proton modulation of M-like potassium current (IKx) in rod photoreceptors.

The effect of extracellular pH (pHe 6.9-8.1) and intracellular pH (pHi 6.4-8.1) on the non-inactivating voltage-sensitive M-like potassium current (IKx) was studied in patch-clamped salamander rod photoreceptors. The midpoint of the IKx activation curve shifted by 6.6 mV per pHe unit, with acidification producing positive shifts and alkalinization producing negative shifts. The time constant of IKx activation shifted with pHe in a manner consistent with the shifts in the activation curve. Maximum conductance and gating charge were unaffected by changes in pHe. IKx did not depend on pHi. Given the importance of IKx in rod function, these results suggest that pHe could affect the signal transmitted from rods by changing IKx activation parameters.

Ambystoma↗
PubMed1996

Immunocytochemical localization of the high-affinity glutamate transporter, EAAC1, in the retina of representative vertebrate species.

The glutamate transporter, EAAC1, was localized immunocytochemically in goldfish, salamander, turtle, chicken, and rat retinas, using affinity-purified oligopeptide antibodies. Immunoreactive (IR) EAAC1 was present in the inner plexiform layer of all species, and in cell bodies of bipolar, amacrine, and ganglion cells of most species, but absent from photoreceptors and Müller's glial cells. Western blots revealed an IR-EAAC1 band at 70 kDa. Staining was abolished by preabsorption with EAAC1 peptide.

ATP-Binding Cassette Transporters↗
PubMed1979

Phylogenetic distribution of glutathione peroxidase.

1. The enzyme glutathione peroxidase (E.C.1.11.1.9), known to be a selenoprotein from mammalian sources, was detected in the following vertebrates: fish, frog, salamander, and turtle. 2. Among invertebrates, the enzyme was detected in crayfish and snail but not in insects or earthworm. 3. No plant tissues or microorganisms showed any evidence of the enzyme activity. 4. The presence of the enzyme activity in so many animal groups implies the widespread occurrence of genetic information for the specific assimilation of the selenium atom.

Animals↗
PubMed1984

The distribution of monosaccharides and hexosamines in the oviduct of Salamandra salamandra (L.) (Amphibia, Urodela).

Biochemical analysis of the different segments of the oviduct in the ovoviviparous salamander, Salamandra salamandra, reveals the monosaccharides glucose, galactose, fucose, mannose, ribose and the hexosamines glucosamine and mannosamine. In segment 1 (pars recta) ribose and mannose are absent, and in segments 2 (p. convoluta I) and 5 (p. convoluta IV, uterus) mannose is not detectable; fucose is absent in the uterus. Segments 3 (p. convoluta II) and 4 (p. convoluta II) contain all sugars identified. The main hexoses present in the glandular segments are galactose, fucose and glucose.

Animals↗
PubMed1993

Expression of a P0-like glycoprotein in central nervous system myelin of amphibians (Ambystoma mexicanus, Xenopus laevis and Rana catesbeiana).

1. The myelin protein profiles in the CNS and PNS of three species of amphibians were analyzed by biochemical and immunohistochemical methods. 2. The CNS myelin of the African clawed frog (Xenopus) and the Mexican salamander (axolotl) contained, in addition to proteolipid protein, a unique protein zero (P0)-like protein, whereas the adult bullfrog did not. 3. A strong expression of the P0-like protein in the bullfrog CNS myelin was found transiently at ontogenetically early phases including at the time of metamorphosis. 4. The CNS P0-like protein and the PNS P0 protein showed a difference in reactivity with lectins and anti-L2/HNK-1 antibodies, suggesting that the two proteins differ in some aspects of their carbohydrate structures.

Ambystoma↗
PubMed1989

A theoretical and experimental study of the effects of non-uniform membrane resistance on the shape of single-cell charging curves.

The isolated Muller glial cell of the neotenous tiger salamander retina is used as an experimental model for studying the effects of non-uniform membrane conductance on the shape of charging curves in response to step current inputs. A simple cable model of the Muller cell is formulated and used to interpret the experimental data. The Muller cell model is completely described by three parameters: (a) electrotonic length L; (b) the membrane time constant tau m; and (c) the percentage of the total membrane conductance accounted for by the endfoot S. Model analysis indicates that increasing S produces monotonic decreases in the rise time of charging curves. This effect is greatest when L is small. In such cases charging curve rise time can be substantially faster than that of a semi-infinite cable. When S greater than 0, the first time constant obtained by fitting the late exponential tail of the charging curve is not the membrane time constant (as is the case when S = 0), but is instead an equalizing time constant equal to the membrane time constant times a scale factor in the range of 0 to 1. This scaling factor becomes quite small as S approaches 100%. We describe a convergent numerical procedure for generating unique estimates of all three model parameters from charging curves. Application of the algorithm to experimentally measured Muller cell charging curves confirms Newman's finding that a large fraction of membrane conductance in these cells is accounted for by the endfoot (greater than 90%). The model prediction that charging curve rise time may be substantially faster than that of the semi-infinite cable when S greater than 0 is also confirmed. The error that results from misinterpreting the first equalizing time constant tau l as the membrane time constant tau m can have a significant effect on estimates of specific membrane resistance and capacitance. The algorithm described in this paper provides a means for obtaining direct estimates of the membrane time constant and will make possible more accurate estimates of specific membrane resistance and capacitance in Muller glial cells. The fact that the estimation procedure is based on a simple electrophysiological measurement suggests that it may be useful for studying asymmetry of membrane conductance in glial and neural elements of the intact nervous system.

Animals↗
PubMed1992

Species differences in amphibian olfactory neuron reactivity to a monoclonal antibody.

A monoclonal antibody immunostained a subpopulation of olfactory sensory neurons in cryostat sections of the olfactory mucosa of the grass frog, Rana pipiens, and the bullfrog, Rana catesbeiana. However, in the olfactory tissues of the African clawed frog, Xenopus laevis, only mucus and mucus-secreting components were stained, and no cell-specific immunoreactivity was seen in the tiger salamander, Ambystoma tigrinum. This antibody is a useful marker of olfactory neuronal subpopulations in some amphibians and illustrates the difficulties in cross-species immunocytochemistry.

Ambystoma↗
PubMed1996

Cloning and characterization of extended hammerheads from a diverse set of caudate amphibians.

Satellite 2 (sat2) elements from six species representing four caudate amphibian families were cloned and analyzed. Despite differences in the abundance of this element, the tandemly repeated genomic organization found for sat2 in earlier investigations was conserved in the newly investigated species. The ability of sat2 transcripts to catalyze their own site-specific self-cleavage using an extended hammerhead (HH) motif had also been conserved. This motif is similar to the HH found in a number of infectious plant RNAs, but has an abbreviated stem III region and an internally looped stem I extension that distinguish it from the prototypical HH. The extended HH analyzed in this survey can be further organized into two groups on the basis of shared sequences and structural details in the peripheral stem-loop structures. HH derived from the family Salamandridae constitute one group, whereas HH from all other salamanders that have been investigated belong to the other group. Although many of the natural variants did not cleave efficiently in vitro, examples of relatively active variants for each design were found. This survey has therefore identified two designs that are suitable starting models for the structural and functional analysis of the extended HH.

Amphibians↗
PubMed1985

Response of amphibian (Ambystoma tigrinum) oviduct to arginine vasotocin and acetylcholine in vitro: influence of steroid hormone pretreatment in vivo.

Oviducts of the salamander Ambystoma tigrinum contract in vitro in response to stimulation by arginine vasotocin (AVT) and acetylcholine (ACh). Steroid hormone pretreatment significantly affects the responsiveness of the oviductal tissue to AVT and ACh. Oviducts initially pretreated with estradiol, testosterone and saline or a combination of estradiol and testosterone exhibit no response to AVT and only saline or estradiol/testosterone treated oviducts respond to ACh. Secondary pretreatment with progesterone stimulated a significant increase in responsiveness to AVT and ACH in all groups.

Acetylcholine↗
PubMed1989

Characterization of a voltage-gated K+ channel that accelerates the rod response to dim light.

In this study a K+ current, IKx, in isolated salamander rod photoreceptors was characterized and its role in shaping small photovoltages was examined. IKx is a standing outward current of about 40 pA at -30 mV that deactivates slowly when the cell is hyperpolarized (tau max = 0.25 s). The voltage and time dependence of IKx are similar to that of M-current, but IKx can be distinguished from M-current because it is not suppressed by acetylcholine and is "blocked" by external Ba2+ in a surprising manner: the activation range of IKx is shifted strongly in the positive direction. Using current-clamp recordings and a computer simulation of the photo-response, we show that IKx figures prominently in setting the dark resting potential and accelerates the voltage response to small photocurrents.

Animals↗
PubMed1990

Synapsins in the vertebrate retina: absence from ribbon synapses and heterogeneous distribution among conventional synapses.

The vertebrate retina contains two ultrastructurally distinct types of vesicle-containing synapses: conventional synapses, made predominantly by amacrine cells, and ribbon synapses, formed by photoreceptor and bipolar cells. To identify molecular differences between these synapse types, we have compared the distribution of the synapsins, a family of nerve terminal phosphoproteins, with that of synaptophysin (p38) and SV2, two intrinsic membrane proteins of synaptic vesicles. We report an absence of synapsin I and II immunoreactivity from all ribbon-containing nerve terminals. These include terminals of rod cells in developing and adult rat retina, rod and cone cells in monkey and salamander retinas, and rat bipolar cells. Furthermore, we show that synapsins I and II are differentially distributed among conventional synapses of amacrine cells. The absence of the synapsins from ribbon synapses suggests that vesicle clustering and mobilization in these terminals differ from that in conventional synapses.

Aging↗
PubMed1991

cGMP-gated conductance in retinal bipolar cells is suppressed by the photoreceptor transmitter.

Transmitter release from photoreceptors is decreased by light, resulting in a conductance increase in depolarizing bipolar cells. Addition of exogenous cGMP through a patch pipette to depolarizing bipolar cells from slices of dark-adapted tiger salamander retina resulted in an enhancement of the light response. This enhancement was blocked by GTP-gamma-S and dipyridamole, an inhibitor of phosphodiesterase. GTP-gamma-S and dipyridamole also blocked responses to exogenously applied 2-amino-4-phosphonobutyrate (APB), the glutamate agonist selective for this receptor. These data support the hypothesis that the postsynaptic receptor is linked via a G protein to a phosphodiesterase. The binding of glutamate or APB to the receptor suppresses a cGMP-activated current by increasing the rate of cyclic nucleotide hydrolysis.

Alkaloids↗
PubMed1993

Noncovalent occupancy of the retinal-binding pocket of opsin diminishes bleaching adaptation of retinal cones.

Bright light bleaches visual pigment and leads to a persistent desensitization of isolated rod and cone photoreceptors called bleaching adaptation. Bleaching adaptation results from the combined effects of pigment depletion and adaptational modulation of certain cellular reactions in the visual transduction cascade. Here, we present evidence that in solitary cone photoreceptors isolated from the salamander retina, the latter effect is due to the presence of free opsin in the outer segment. Also, we demonstrate that this "opsin adaptation" can be reversed by treating the cells with synthetic retinoids similar to 11-cis retinal but having polyene chains too short to form protonated Schiff base attachments to opsin.

Adaptation, Physiological↗