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Biomedical subjects

C W Schneider

Publications and source records attributed to C W Schneider.

At least 19 recordsLinked to original sources
PubMed2006

Tunable quasi-two-dimensional electron gases in oxide heterostructures.

We report on a large electric-field response of quasi-two-dimensional electron gases generated at interfaces in epitaxial heterostructures grown from insulating oxides. These device structures are characterized by doping layers that are spatially separated from high-mobility quasi-two-dimensional electron gases and therefore present an oxide analog to semiconducting high-electron mobility transistors. By applying a gate voltage, the conductivity of the electron gases can be modulated through a quantum phase transition from an insulating to a metallic state.

Journal Article↗
PubMed2004

Electron transport through YBa2Cu3O7-delta grain boundary interfaces between 4.2 and 300 K.

The current-induced dissipation in YBa(2)Cu(3)O(7-delta) grain boundary tunnel junctions has been measured between 4.2 and 300 K. It is found that the resistance of 45 degrees (100)/(110) junctions decreases linearly by a factor of 4 when their temperature is increased from 100 to 300 K. At the superconducting transition temperature T(c) the grain boundary resistance of the normal state and of the superconducting state extrapolates to the same value.

Journal Article↗
PubMed2002

d-wave induced zero-field resonances in dc pi-superconducting quantum interference devices.

A dc pi SQUID consists of a superconducting ring interrupted by two Josephson junctions, one of which carries in equilibrium a pi phase difference, caused, for example, by the d-wave pairing symmetry of the high- T(c) cuprates. If this phase shift is maintained in the voltage state, anomalous resonance currents are expected in the SQUIDs transport characteristics. Here we report the observation of such resonances for high- T(c) dc pi SQUIDs, providing evidence for the influence of the d-wave symmetry on the voltage state of a Josephson junction for frequencies of several tens of GHz.

Journal Article↗
PubMed2001

Evidence of doping-dependent pairing symmetry in cuprate superconductors.

Scanning tunneling spectroscopy studies reveal long-range spatial homogeneity and predominantly d(x(2)-y(2))-pairing spectral characteristics in under- and optimally doped YBa2Cu 3O (7-delta) superconductors, whereas STS on YBa2(Cu 0.9934Zn 0.0026Mg (0.004))3O (6.9) exhibits microscopic spatial modulations and strong scattering near the Zn or Mg impurity sites, together with global suppression of the pairing potential. In contrast, in overdoped (Y 0.7Ca (0.3))Ba 2Cu 3O (7-delta), (d(x(2)-y(2))+s)-pairing symmetry is found, suggesting significant changes in the superconducting ground state at a critical doping value.

Journal Article↗
PubMed1993

Phototaxic behavior and the retinotectal transport of horseradish peroxidase (HRP) in surgically created cyclopean salamander larvae (Ambystoma).

UNLABELLED: Negative phototaxis (NP) was used to evaluate the recovery of vision in albino axolotl larvae with one eye discarded and the other transplanted either to the orbit (orthoclops) or to the top of the head (cyclops). NP was assessed at approximately 1, 2 and 3 months postoperatively, using an automated, infrared monitor. Some 88% of the orthoclopes and 64% of the cyclopes recovered NP. However, among the cyclopes that did recover, the quantitative aspects of NP were virtually the same as those of the orthoclopes. That the cyclopean eye can regenerate retinotectal pathways was established by anterograde tracing of horseradish peroxidase (HRP). But where previously uninjured animals transported HRP to the contralateral tectum, both the cyclopes and the orthoclopes distributed the enzyme to the left and right tectal halves. Heavy deposits of HRP were found in the tecta of some animals that lacked NP. To find out if an optic tectum is actually required for NP, a series of ablation experiments were performed, using Ambystoma punctatum larvae. Tectectomy had the same effect on NP as bilaterally extirpating the eyes or intracranially severing both optic nerves, i.e. removing the tectum abolished NP. THE RESULTS: (1) confirm the efficacy of the ectopic eye in the cyclops preparation; (2) show that the ectopic eye can regenerate retinotectal pathways; (3) indicate that retinotectal contact is a necessary but insufficient condition for NP.

Ambystoma↗
PubMed1991

Tectectomy in the cyclopean salamander.

In an Ambystoma larva with both natural eyes removed and one eye grafted atop the head (Cyclops preparation), vision-dependent behavior usually recovers from the enucleation inherent in the operation, but the optically activated skin blanching reaction reappears in a very small number of instances. In the present studies, while the latter trend continued for the conventional Cyclops preparation, tectectomy concurrent with the ectopic eye transplantation resulted in a several-fold increase in the recovery of blanching competency. Some 60 percent of the tectectomized Cyclops animals exhibited the same Hogben-Slome pigmentation indices as larvae with one natural eye intact (controls). As measured planimetrically with an image analyzer, the pigment spots (melanosome containing portions of dermal melanocytes) contracted to the same extent in the blanch-competent Cyclops animals as in controls with a single natural eye.

Ambystoma↗
PubMed1991

Measures of phototaxis and movement detection in the larval salamander.

In this investigation, we describe two precise tests of visual function that integrate quasinatural situations with time-lapse video recording and infrared computerized monitoring of activity to assess movement detection and phototaxic tendencies, respectively. Four groups of larvae from A. punctatum, A. tigrinum, A. mexicanum, and a mutant albino axolotl were tested in an alley containing light and dark halves and lined with infrared sensors to monitor their phototaxic response. A. punctatum showed no phototaxic tendency, while the other three groups displayed a strong negative phototaxic response. Enucleation of the eyes in mutant albinos eliminated the negative phototaxis. Visual detection of motion was tested by videorecording the behavior of A. punctatum, A. mexicanum, and the mutant albino axolotl larvae while they explored a large bowl with 6 small vials on the perimeter, one of which contained white worms. A. punctatum rapidly approached the worm vial and engaged in intense predatory behavior. A. mexicanum responded to the presence of worms very slowly and rapidly lost interest. Albino axolotls displayed no visual recognition of the worms. The results indicate that visual function can be precisely determined in larval salamanders utilizing behavioral measures consistent with the animal's natural tendencies.

Ambystoma↗
PubMed1991

A longitudinal investigation of the effects of experience on the behavior of aging mice.

The effects of differential experience over most of the adult lifespan of mice were examined utilizing longitudinal designs. Repeated experience with nest building was contrasted with one-time only experience at various age levels from 4 to 24 months of age. The results suggest that the presence or absence of repeated exposure to nest building opportunities affects stability of nest building, while open field activity remains stable regardless of experience and vitality declines regardless of experience. Because nest building at maturation is not influenced by prior experience, the effect of differential experience during the course of aging is not interpreted as a reflection of differential initial acquisition of the behavior. Rather, performance differences are interpreted as providing evidence for the differential maintenance of neural integrity of the underlying mediator for the behavior. The discrepancy among the patterns of change for nest building, open field activity, and performance on the tightrope test is interpreted as reflecting differences in the relative importance of deterioration of the underlying neural mediators in comparison with decreases in muscular strength and flexibility. Implications for design issues in animal research in aging are discussed.

Aging↗
PubMed1990

Two-eyed versus one-eyed salamanders: does binocularity enhance the optically evoked skin blanching reactions of Ambystoma larvae?

A wide variety of visual functions show increases attributable to binocularity, and the question pursued here was whether a second eye enhances the visually stimulated skin blanching reaction of the larval salamander. Dermal melanin spots (produced by the aggregations of melanosomes within dermal melanophores and which contract or expand to lighten or darken the skin) were measured in eyeless (controls), one-eyed and two-eyed Ambystoma punctatum larvae after chronic adaptation of the subjects to a white background (i.e., stimulus conditions for maximum blanching). The eyeless subjects showed no blanching (thus remained dark) in white cups, and they exhibited melanin spots 7 or 8 times the size of those of the other two groups. All one-eyed or two-eyed subjects exhibited blanching reactions; planometric comparison revealed a significantly larger melanin spot area for one-eyed than for two-eyed animals; i.e., the binocular condition permitted greater contraction of the pigment spots than did the monocular condition. Analytical data compared favorably with independently ascertained pigmentation indices. The results indicate that a second eye quantitatively elevates the blanching maximum of a larval salamander.

Ambystoma↗
PubMed1990

Anterior decerebration blocks visual habituation in the larval salamander (Ambystoma punctatum).

Amputation of the rostral half of the cerebrum induces a compulsion-like reaction in larval Ambystoma punctatum towards Enchytraeus protected within glass vials. Normal and craniotomized larvae are visually attracted to worm-containing vials, as revealed by time-lapse video taping but, after several unsuccessful attempts to get the prey, habituate and depart. The video tapes revealed that anteriorly decerebrated animals spent as much as 100 of 120 minutes at the worm-containing vial, repeatedly but futilely attacking the glass. The data indicate that the telencephalon plays an active negative role in the salamander larva's visually guided behavior.

Ambystoma↗
PubMed1986

The ethanol sensitivity of calcium taken up by a depolarization-dependent process in mouse strains DBA and C57BL.

In vitro effects of ethanol on calcium taken up by synaptosomes were examined in two strains of mice, C57BL and DBA, that exhibit marked differences in alcohol sensitivity and preference. There were no significant strain differences in basal or depolarization-dependent synaptosomal calcium levels. Ethanol did not reduce the basal calcium level but instead reduced depolarization-dependent calcium levels with the same potency in both strains. These results do not support a role for changes of calcium levels as the basis for differences in ethanol sensitivity in these mouse strains.

Animals↗
PubMed1985

Vision and the skin camouflage reactions of Ambystoma larvae: the effects of eye transplants and brain lesions.

Salamander larvae typically adapt their dermal melanophores to achieve camouflage, and it has been known for some time that removal of the eyes abolishes the response. Here we survey the contribution of the optic system to the bright and dark camouflage reactions and report that: the stimulus depends on an interaction between the direct and reflected light; an eye mounted atop the head and oriented vertically tended not to support camouflage, even though the animal responded to visual cues and learned a vision-dependent task; deviating the transplanted eye off the vertical axis enhanced the recovery of camouflage reactions; amputating or reorienting the telencephalon, epithalamus, pretectum or tectum did not abolish either camouflage reaction whereas lesions of the ventral optic pathway blocked brightening; transection near the midbrain-hindbrain junction--well posterior to known optic terminals--retarded the dark reaction; when the latter lesion was combined with disconnection of the telencephalon and epithalamus, contrary to predictions from the lesions executed separately, the animals lost the bright reaction; the hypophysis is necessary for darkening, but the organ supported this reaction even though detached, displaced or reoriented; and the pineal body was not essential for the grosser aspects of camouflage in Ambystoma larvae but may play an adjunctive role in fine tuning.

Ambystoma↗
PubMed1984

Age differences in the oxidation of and neural response to ethanol in mice.

Male mice (C57BL/6J) from three age groups, 4, 14, and 26 months, were tested to determine their oxidation rate of intragastrically infused ethanol and the response of the centrally mediated jaw-jerk reflex to ethanol challenge. There were no age-related differences in the rate of oxidation of ethanol. However, age differences in ethanol-induced decrement of the jaw-jerk amplitude were significant. The 26 month animals were the most affected, followed by the 4 month group. The middle aged mice (14 month) showed the greatest resistance to the depression induced by ethanol. The results were evaluated with regard to the current hypotheses.

Age Factors↗
PubMed1981

Oxidation of alcohol in free-moving mice from high and low preference strains.

Free-moving mice from the high-alcohol preference C57BL/6J strain and low-preference DBA/2J strain were slowly fed [2-14C]ethanol intragastrically until anesthesia was achieved. Behavior was monitored in a Plexiglas metabolic chamber while 14CO2 was simultaneously trapped to determine the rate of ethanol metabolism. Average time to the loss of the righting reflex in the DBA/2J was 21.9 min and 27.9 min for the C57BL/6J strain (p less than 0.005). Elimination of 14CO2 was slightly higher (n.s.) in the DBA/2J strain for the entire monitoring period. Infusion of ethanol via the tail vein yielded identical results indicating that the slower elimination rate in the C57BL/6J strain could not be the result of slower absorption across the gut wall. Infusion via the tail vein with radioactive sodium bicarbonate indicated that the DBA/2J strain has a higher rate of CO2 expiration (n.s.). Consequently, the higher rate of 14CO2 expiration from ethanol oxidation may not reflect a higher rate of metabolism. These results are discussed in terms of the apparent differences between these strains in neural sensitivity to ethanol.

Alcohol Drinking↗
PubMed1980

A quantitative analysis of ethanol and acetaldehyde expired by inbred mouse strains.

Expired ethanol and acetaldehyde were measured after an oral injection of ethanol in C57BL/6J and DBA/2J mouse strains by a combination of several techniques in a sequence involving a method for trapping expired radioactive compounds, separation of compounds by gas chromatography, isolation of radioactive ethanol and acetaldehyde, and their quantitative analysis by liquid scintillation spectrophotometry. With the specific activities used in evaluation of the technique (0.1 Ci/mole, acetaldehyde; 1.1 Ci/mol, ethanol) the lower limit of sensitivity using 500 microliters from a 10 ml trap is 955 pmoles for acetaldehyde and 101 pmoles for ethanol. However, in the animal experiments, injected ethanol has a specific activity of 1.1 Ci/mol which would make the specific activity of expired metabolically formed acetaldehyde the same. This results in a lower limit of sensitivity for acetaldehyde of 80 pmoles. The two strains were monitored for 80 min following an oral injection of 3.8 g/Kg of (2-14C) ethanol. Comparing the two strains on the expiration of each compound the curves were identical.

Acetaldehyde↗
PubMed1976

Butanediols: selection, open field activity, and NAD reduction by liver extracts in inbred mouse strains.

Mice from the high-ethanol preferring C57BL strain and low-ethanol preferring DBA strain were tested for their preference for butanediols. The C57BL strain showed a significantly higher preference for a 10% (v/v) solution of 1,3-butanediol than the DBA strain. The C57BL strain also showed a significantly greater consumption of 1,2- and 2,3-butanediol, but the separation between strains was much smaller than with 1,3-butanediol. Both strains uniformly avoided 1,4-butanediol. Tolerance for 1,3-butanediol was tested in an open-field monitor at 3 doses. At the lowest dose the DBA strain was hyperactive and the C57BL were unaffected. At the highest dose both strains were equally depressed. The specific activity of NAD reduction on incubation of liver extracts with 1,3-butanediol and ethanol as substrates was higher with both compounds in extracts from the C57BL strain.

Alcohol Drinking↗