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Biomedical subjects

K Donner

Publications and source records attributed to K Donner.

At least 55 records · Page 3Linked to original sources
PubMed1988

Temperature-dependence of rod photoresponses from the aspartate-treated retina of the frog (Rana temporaria).

The effects of temperature changes on rod photoresponses were studied by recording the aspartate-isolated mass receptor potential in the dark-adapted retina of the frog Rana temporaria. The amplitude of saturating responses, indicating the magnitude of the dark current, increased linearly with temperature in the measured range 6-26 degrees C, extrapolating to zero dark current at 0 degrees C. Sensitivity was maximal around 18 degrees C but the decrease towards lower temperatures was shallow. The results show that rod phototransduction in the frog Rana temporaria is adapted to lower temperatures than in the tropical toad Bufo marinus. Responses to dim flashes were, approximately up to peak, well fitted by the same 'independent activation' model with four delay stages as have been found to best describe current responses from single toad rods. The kinetics (reciprocal time-to-peak) showed Arrhenius-type temperature-dependence with apparent activation energy 12.4 kcal mol-1 and Q10 = 2.1.

Adaptation, Physiological↗
PubMed1987

Surround control of center adaptation in the receptive fields of frog retinal ganglion cells.

The sensitivity and intensity-response [R(log I)] functions of the receptive field center were determined by extracellular recording from frog retinal ganglion cells. The object was to study the steady-state adapting effects of peripheral background patterns: steady annuli and spinning "windmills" of light. Steady annular backgrounds could not be shown to directly effect any change of center responsiveness, only an enhancement of late response components attributable to depression of surround sensitivity. Movement of a windmill pattern shifted R(log I) functions to higher log intensities and decreased the maximal number of spikes in the response, but did not depress the saturation level of the impulse frequency. Its action thus resembled direct light-adaptation of the center.

Action Potentials↗
PubMed1987

Transient sensitivity reduction and biphasic photoresponses observed when frog retinal rods are oxidized.

1. Rod photoresponses and the effects of oxidation have been studied by recording either the transretinal voltage in aspartate-treated retinas or the outer segment current of single rods. 2. Oxidizing conditions transiently decreased, reducing conditions increased sensitivity. 3. Biphasic photoresponses were seen when the level of oxidation was rising and also in some other sensitivity-depressing conditions. 4. A model is proposed which explains the biphasic responses in terms of sensitivity differences between the tip and the base of the rod outer segment.

Animals↗
PubMed1987

Adaptation-related changes in the spatial and temporal summation of frog retinal ganglion cells.

The spatial and temporal summation of light by the receptive field centre of frog retinal ganglion cells were studied by extracellular recording in the eyecup preparation. The purpose was to quantify how summation changes with the state of light and dark adaptation and to clarify whether changes are due to the transition between rod and cone vision. Spatial summation was found to decrease by 30-50% as the cell was light-adapted to a threshold some 4 log units above the dark-adapted one. Temporal summation for threshold responses fell as the power -0.17 of the intensity of an adapting steady background. Neither change was bound to the rod-cone transition but occurred in the ranges of both receptor types; at equal sensitivities the summation of both receptor systems was matched.

Adaptation, Ocular↗
PubMed1987

Ganglion cell performance at absolute threshold in toad retina: effects of dark events in rods.

1. The performance of ganglion cells in detecting flashes of light near the absolute threshold was studied in an isolated eye-cup preparation of toad retina. Retinal ganglion cells, through which all visual information from the rods must flow to the brain, are in a key position for evaluating the still unproven hypothesis that the absolute light sensitivity is limited by rod noise (Barlow, 1956). 2. The dark-adapted threshold intensity for these cells, which were selected on the basis of their high sensitivity, averaged 0.029 Rh* flash-1 (range 0.008-0.062), where Rh* signifies one photoisomerization per rod. On average, 46 photoisomerizations were needed per receptive field per flash to evoke a threshold response (range 16-84). 3. In the threshold region, frequency of responses versus mean flash intensity was determined. Threshold performance could be described by theoretical frequency of response curves, allowing intrinsic noise to be estimated in terms of an equivalent rate of photoisomerization-like (dark) events. In two completely characterized cells the rate of dark events corresponded to 0.03 and 0.06 Rh*DS-1, where Rh*D signifies one dark event per rod. 4. Threshold elevations produced by dim backgrounds were studied. The results of these experiments are consistent with a dark event rate equivalent to 0.046 Rh*DS-1, or 0.037 Rh*DS-1 after correcting for a probable decrease in summation time. 5. The rate of actual dark events (0.028 Rh*DS-1, 20 degrees C) measured in Bufo rods (Baylor, Lamb & Yau, 1980) is close to the equivalent rates determined here. Thus, for the ganglion cells signalling the dimmest lights, the dark events in rods appear to be the most significant intrinsic retinal noise source limiting detection.

Action Potentials↗
PubMed1987

Retinal noise, the performance of retinal ganglion cells, and visual sensitivity in the dark-adapted frog.

By extracellular recording of action potentials from single ganglion cells in the dark-adapted eyecup of the frog, we show that four different characteristics of a cell, the frequency-of-response function, the variability in responses to low suprathreshold stimulation, the maintained discharge, and the susceptibility to desensitization by weak background lights, all seem to reflect the same intrinsic noise. In a small fraction of reliable cells this noise is close to that expected from dark isomerizationlike events in rods, but it differs by orders of magnitude between cells. We have also determined a threshold intensity for the phototactic jumping behavior of frogs in darkness. This intensity, while below the human threshold, is still above the threshold for an appreciable fraction of frog retinal ganglion cells, and the sensitivity of this visually guided behavior at 16 degrees C is not strictly limited by dark events in rods.

Animals↗
PubMed1986

Impromptu micturitional flow parameters in normal boys.

Nonintrusive measurement of the hydrodynamic properties of the urinary stream (uroflowmetry) has been included in many adult urological evaluations as an objective diagnostic tool. Measurement and behavioral problems interfere with practical applications in children. We describe a standard procedure for obtaining "impromptu" micturitional flow parameters in clinical pediatric practice. Statistical correlations of these flow parameters in an unselected group of 142 normal boys between 2 and 12 years old are presented. Useful linear regression equations were derived from the sample to assist the clinician in predicting deviations from normal values. Limitations of the methodology are noted.

Child↗
PubMed1985

Rhodopsin phosphorylation inhibited by adenosine in frog rods: lack of effects on excitation.

The rod photocurrent was studied by recording the transretinal voltage from the aspartate-treated isolated frog retina before and after perfusion with 2 mM adenosine, which inhibited 60-80% of the light-induced rhodopsin phosphorylation. Adenosine did not affect the time courses of the flash photoresponses or the OFF responses after a steady light. The introduction of adenosine while the retina was illuminated by a steady background did not enhance the effect of light. Instead, the opposite change, due to PDE inhibition, was observed. The results indicate that rhodopsin phosphorylation does not determine the time course of the decay of excitation.

1-Methyl-3-isobutylxanthine↗
PubMed1985

Intraoperative profilometry.

Intraoperative profilometry measurements were done on 28 patients during various types of urethropexy to determine whether useful information could be provided to the operating surgeon. Successful Burch, Marshall-Marchetti and Stamey-Pereyra procedures resulted in a 50 per cent increase in urethral length. Closure pressure increases were noted only with the Stamey-Pereyra procedure (plus 49 per cent). Intraoperative profilometry measurements were considered to be informative and useful, particularly during the Stamey-Pereyra urethropexy in which case suture ties could be regulated to provide desired urethral elongation and closure pressure changes.

Female↗
PubMed1984

Center and surround excitation in the receptive fields of frog retinal ganglion cells.

We have reexamined the receptive fields of frog retinal ganglion cells focussing on their surround properties. Carefully excluding artifacts due to stimulation of the (Gaussian) RF center, we found that spiking responses can be elicited by step stimulation of any receptor type in the surrounds of all the classes 1-4 Maturana et al. (1960) (J. gen. Physiol. 43, 129-175). The surround responses are antagonized by the responsive center and suppressed by the inhibitory surround, but are seen because of their slower dynamics. The responsive surround differs spectrally from the center: in the latter, cones and green rods compete, in the former, their signals sum.

Action Potentials↗
PubMed1982

[Surgical treatment of the elbow joint in chronic polyarthritis].

Compared to the frequency of manifestation of rheumatoid arthritis in the elbow joint the quota of surgical intervention in this area is low. In most cases pain and disability are only moderate, especially if the reduced range of motion is compensated by maintained function of the equilateral shoulder and wrist joint. Surgical treatment is indicated if instability increases, the independency of the patients in daily life is endangered and inflammation increases acutely. A persistent compression of n. ulnaris has to be operated as soon as possible. Often the preferred early synovectomy is impossible because of priority of other joints. By late synovectomy, however, good results can be expected regarding stability, function and extent of pain. In our cases the joint was opened from radial and ulnar in combination with ventralization of the ulnaris nerve. The replacement of the head of radius by a silastic-spacer seems to reduce the secondary irritation in the radial part of the joint and to increase stability. The own method for resection-arthroplasty in modification of the method of Hass with interposition of the middle part of triceps tendon is described and discussed. Because of imminent loosening prostheses are implanted very rarely.

Arthritis, Rheumatoid↗
PubMed1981

Urodynamics in children. Part I. Methodology.

We evaluated 237 children for various disorders in the urodynamic laboratory. A total of 334 studies was done, using a 6-channel recorder combined with a portable fluoroscopic unit. Simultaneous recordings of intravesical pressure, intra-abdominal pressure, urine flow rate, external urethral electromyography and cystourethrography were obtained during bladder filling and voiding. These objective tests have provided us with an insight into the nature of a variety of voiding dysfunctions in children. Details of the methods used for urodynamic testing in these children are outlined and compared to other methods that have been proposed.

Adolescent↗
PubMed1981

Urodynamics in children. Part II. The pseudoneurogenic bladder.

We evaluated 83 children for recurrent urinary infections, day and night urinary incontinence or both for more than 1 year in the urodynamic laboratory. Bladder instability and/or bladder sphincter dyssynergia was encountered in 74 children. Pharmacologic manipulation of detrusor and sphincter function and biofeedback therapy were highly successful. Routine and random urethral dilation, urethrotomy and fulguration, and/or resection of ill-defined urethral obstructions is unwarranted. Rational treatment requires individualization based upon an objective evaluation by thorough and careful urodynamic testing.

Adolescent↗
PubMed1981

Receptive fields of frog retinal ganglion cells: response formation and light-dark-adaptation.

1. The excitatory and inhibitory receptive field mechanisms of retinal ganglion cells were studied by extracellular recording from the eyecup of Rana temporaria in order to elucidate the nature of adaptational changes in the functioning of the receptive field. 2. The responses to large stimuli were always strongly depressed relative to responses evoked by smaller spots. This was true even in the fully dark-adapted state and at the very lowest stimuli intensities. 3. Threshold measurements confirmed earlier findings, usually revealing the surround only in light-adapted states. However, in more than 10% of fully dark-adapted cells thresholds to large stimuli were significantly elevated. 4. The central summation area of the receptive field was found to shrink with light-adaptation. There was a gradual decrease in diameters, amounting to some 20-30%, from the dark-adapted, rod-determined receptive fields to the cone-determined ones. 5. Adaptation by bleaching and adaptation by backgrounds changed the effects of the surround in different ways. After a rhodopsin bleach the transition from a light-adapted to a dark-adapted situation was seen as an abrupt drop of large-stimulus thresholds at some time during adaptation. Steady backgrounds produced no such dramatic changes, but the increment threshold lines were somewhat steeper with test spots stimulated the surround than with smaller spots. 6. Although the discharge patterns generally show the strength of the surround influence, they underwent no qualitative change at the time of the drop of large-stimulus thresholds after a bleach. 7. It is suggested that the drop does not reflect a sudden reorganization of the receptive field, but is the consequence of the different ways the response to large stimuli are formed in different ranges of stimulus intensity (pre-inhibitory at high intensities, post-inhibitory at low intensities), and of gradual changes in signal dynamics.

Action Potentials↗