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Biomedical subjects

D Geller

Publications and source records attributed to D Geller.

At least 37 records · Page 2Linked to original sources
PubMed1990

Reversal of the behavioral and electrophysiological abnormalities of an animal model of hepatic encephalopathy by benzodiazepine receptor ligands.

Behavioral and electrophysiological evidence implicating the GABA-benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy was obtained using an improved rat model of hepatic encephalopathy caused by thioacetamide-induced fulminant hepatic failure. After the administration of thioacetamide together with supportive therapy, acute hepatocellular failure developed in rats as a result of massive hepatocellular necrosis without evidence of renal failure or hypoglycemia. The evolution of hepatic encephalopathy in this model was sufficiently slow to readily permit the staging of the syndrome. Prominent features of the encephalopathy include a marked reduction in open field activity and an abnormal visual evoked response. Both the deficits in spontaneous motor function and visual evoked response abnormalities of rats in stages III to IV hepatic encephalopathy were significantly improved after the administration of the benzodiazepine receptor ligands flumazenil or Ro 15-4513. Doses of flumazenil or Ro 15-4513 that produced these effects in rats with hepatic encephalopathy had no detectable action on either the behavior or the visual evoked responses of normal rats. The ability of benzodiazepine receptor ligands to ameliorate both the behavioral depression and the visual evoked response abnormalities associated with hepatic encephalopathy in the thioacetamide-induced rat model suggest an involvement of the GABA/benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy. In addition, the similarity of these observations to those in rabbits with hepatic encephalopathy caused by galactosamine-induced fulminant hepatic failure is compatible with the hypothesis that the mechanisms of hepatic encephalopathy in these two distinct models share a common final pathway, the allosteric enhancement of GABAergic tone through the benzodiazepine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Identification of the cardiac and circulating form of atriopeptin in rabbit.

Analysis of peptides purified from high and low molecular weight fractions of rabbit atrial extracts indicates that the sequence of the first 30 residues of rabbit atriopeptigen exhibits 80% homology with the rat peptide, and that the low molecular weight rabbit peptide (28 residues) is identical to rat atriopeptin 28 (AP 28). The effects of infused 1-deaminoarginine8-vasopressin (dAVP) and phenylephrine, volume expansion, and water immersion on AP release into the circulation of the rabbit was studied. Neither dAVP, nor water immersion elevated right atrial pressure (RAP) or plasma AP levels in the anesthetized rabbits. Phenylephrine induced a sustained increase in systemic blood pressure and right atrial pressure which was accompanied by elevated plasma AP immunoreactivity which appeared to be identical to rat AP-28 on HPLC. There is obviously a preferential conservation of the AP sequence, since the C-terminal peptide is exactly the same in rabbit, rat and mouse and differs from human, dog, cow and pig only by the single substitution of an isoleucine for a methionine residue.

Amino Acid Sequence↗
PubMed1984

Magnitude estimation of loudness. I: Application to hearing aid selection.

Three experiments were conducted to explore the utility of magnitude estimation of loudness for hearing aid selection. In Experiment 1 the loudness discomfort level (LDL), most comfortable loudness (MCL), and magnitude estimations (MEs) of loudness were obtained from normal-hearing subjects. MCLs fell within a range of loudness that was relatively low on the loudness function. The LDLs were lower than previously published values. Experiment 2 was performed to identify the source of disparity between our LDL data and previously reported results. The effects of instructions are demonstrated and discussed. In Experiment 3 magnitude estimations of loudness were used to determine the loudness of tonal stimuli selected to represent 1/3 octave band levels of speech. Over the 500-4000 Hz range, the contributions of the various frequency regions to the loudness of speech appears to be nearly constant. Methods are proposed for (a) predicting the frequency-gain response of a hearing aid that restores normal loudness for speech for the hearing-impaired listener and (b) psychophysically evaluating the compression characteristic of a hearing aid.

Audiometry, Pure-Tone↗
PubMed1984

Mycotic aneurysm of the sinus of Valsalva due to Eikenella corrodens bacterial endocarditis.

A patient with a left sinus of Valsalva aneurysm secondary to bacterial endocarditis involving an unusual pathogen, Eikenella corrodens, is presented. This case and a review of previous reports on mycotic sinus of Valsalva aneurysm are analyzed. The distinctive M-mode and two-dimensional echocardiographic patterns of a sinus of Valsalva aneurysm as well as the usefulness and limitations of echocardiography in this condition are discussed. This rare complication of bacterial endocarditis can be diagnosed and clinically followed by serial echocardiographic studies, and its presence alone does not necessitate surgical intervention.

Adult↗
PubMed1981

Temperature mediated variation of DNA secondary structure in (A.T) clusters; evidence by use of the oligopeptide netropsin as a structural probe.

The titration viscometric investigation of the multi-mode interaction of netropsin (Nt) with (A.T) clusters of NaDNA12 and NH4DNA10 has been extended to different temperatures. The position of two boundaries on the r-scale (r= [Nt]bound/[DNA-P]) with increasing temperature steadily (rI/II) or more abruptly (rO/I) shifts to lower values. For the most (A.T) rich Nt-binding sites of modes (O), (I) and (II) this observation suggests the existence of an equilibrium between different DNA secondary structures with a different translation per base pair. The mode specific changes delta L1Nt of DNA contour length as induced by one Nt molecule proved to be almost independent of temperature. Concomitant stiffening effects increase with decreasing temperature, contrary to initial expectation. Conformational variability of (A.T) clusters may represent an essential feature in specific or selective DNA-protein interaction.

Chemical Phenomena↗
PubMed1980

The production and generalization of large-magnitude heart rate deceleration by contingently faded biofeedback.

Eight subjects were taught to decrease their heart rates via biofeedback training. Four of these received contingently faded, beat-by-beat analogue feedback and contingent reinforcement each time their performance met a specified and adjusting criterion. The other four received continuous, beat-by-beat analogue feedback, but not the contingent reinforcement. Subjects in the two groups were yoked to ensure equal densities of reinforcement. Subjects in the first group were asked to decrease heart rates 15% from baseline and were then trained using only 75%, 50% and 25% of beat-by-beat feedback. It was hypothesized that the immediate reinforcement of appropriate behavior and the contingent fading (following mastery) of feedback would aid in the generalization of the response. Following completion of all criterion steps or 10 training sessions, whichever came first, all subjects were tested with no feedback and no contingent reinforcement. The group receiving contingently faded feedback training showed a significantly greater heart rate decrease in the training sessions and also the test session. These results were interpreted as indicating that biofeedback can be conceptualized as an operant conditioning paradigm, and that the use of operant techniques may help subjects produce clinically significant changes.

Biofeedback, Psychology↗
PubMed1977

Fourier analysis on the Heisenberg group.

We obtain a usable characterization of the (group) Fourier transform of (H(n)) (Schwartz space on the Heisenberg group). The characterization involves writing elements of [Formula: see text] as asymptotic series in Planck's constant. In the process, we derive a new "discrete" version of spherical harmonics, and elucidate the theory of group contractions. We give an application to Hardy space theory.

Journal Article↗
PubMed1972

ATP formation.

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Adenosine Diphosphate↗