Christian Baumann

Die absolute Schwelle der isolierten Froschnetzhaut

Abstract1. The absolute treshold of the perfused isolated retina of Rana esculenta was measured by recording the electroretinogram and single units within the retina. The whole excised retina was stimulated with light of wavelength 507 mμ and of 1.5 sec duration.2. The retinal irradiance at the mean threshold of the most sensitive unit was equal to 13.8×10−14 watt/cm2 corresponding to 3.5×105 quanta/sec × cm2 (retina), or to one quantum absorbed per 11 rods per second. On the average of 8 single units the threshold energy density at the retina was at 62.9×10−14 watt/cm2.3. The retinal irradiance at threshold of the electroretinogram (b-wave height of about 8 μV) in two preparations out of ten was at 5.68×10−14 watt/cm2 (retina) which is roughly 12 times the minimum retinal illumination necessary for vision in man. The average threshold irradiance of ten preparations was at 14.72×10−14 watt/cm2 (retina).

Receptorpotentiale der Wirbeltiernetzhaut

Abstract1. The isolated retina of Rana esculenta was folded with the receptoral surface outermost in the fold, and mounted within a small perfusion chamber upon a microscope slide. At the edge of the fold placement of glass capillary microelectrodes on single rod outer segments could be done under visual control with the aid of a microscope. No signs of electrical activity following light stimulation could be recorded with electrodes making contact with surface of rod outer limbs.2. After insertion of the micro-pipet into the retina from its receptoral surface, graded slow potentials arose during illumination within a depth corresponding to the inner segments of the receptors.3. The potentials were negative in polarity when recorded extracellularly. Their shape was nearly monophasic at low light intensities but showed an initial overshoot and a very slow decay at high light intensities.4. The latency of the potentials (at 20°C) decreased from 350 to 40 msec when the light intensity was increased in logarithmic steps from 0.2 to 250 lm/m2. The amplitudes of the potentials varied within a range from 0.15 to 1.4mV yielding steep S-shaped curves when plotted against the logarithm of light intensity. As long as weak light stimuli were used the potential height was linearly related to light intensity.5. The potentials are held to be generated by the inner segments of the frogs photoreceptors.Zusammenfassung1. Die isolierte Retina von Rana esculenta wurde so zusammengefaltet, daß die Receptorseite nach außen zu liegen kam, und in einer Perfusionskammer auf einem Objektträger gehaltert. Unter mikroskopischer Kontrolle wurden Capillar-Mikroelektroden an der Kante der Präparation den freien Enden der Stäbchenaußenglieder angenähert. Bei Berührung der Außenglieder war auf Lichtreizung keine elektrische Aktivität abzuleiten.2. Wurde die Mikroelektrode zwischen den Stäbchenaußengliedern in Richtung auf die Membrana limitans externa vorgeschoben, so ließen sich in Höhe der Receptoreninnenglieder abgestufte Belichtungspotentiale extracellulär ableiten.3. Die Form der negativen Potentiale war bei schwachen Lichtintensitäten nahezu monophasisch, zeigte aber bei hohen Intensitäten initiales Überschießen und lange Abfallzeiten.4. Im untersuchten Intensitätsbereich (0,2–250 lx) traten (bei 20° C) Latenzen von 350–40 msec und Potentialhöhen von 0,15–1,4 mV auf. Bei schwachen Lichtreizen bestand eine lineare Beziehung zwischen Reizstärke und Potentialhöhe.5. Es wird angenommen, daß die registrierten Potentiale in den Innengliedern der Photoreceptoren entstehen.

Effect of luminance and contrast on stereoscopic acuity

The threshold of binocular depth perception was measured in 11 healthy volunteers. A three-rod arrangement was employed in which both the luminance of the rods and that of the adapting field could be adjusted independently. This allowed fixing the contrast when the effect of luminance was studied or fixing the luminance when the effect of contrast was investigated. The observation distance was 400 mm. Thresholds were expressed as angular disparities and were based on 75% correct responses. Points of subjective equality were also determined. Lowest thresholds (2.85 ± 0.67 s of arc) were found for a moderate contrast of 0.5 whereas low (0.05) and high (0.95) contrast both produced significantly higher thresholds (luminance 250 cd/m2). Altering the field luminance (50, 250, 1600 cd/m2) under constant contrast conditions (0.95) did not measurably influence stereoscopic acuity.

Effect of guanine nucleotides on the dark voltage of single frog rods

Single frog rods consisting of the outer segment and the ellipsoid were investigated by the whole-cell patch-clamp technique. When the recording pipette was filled with a simple intracellular medium containing potassium as the principal cation, a slow increase in dark voltage (hyperpolarization) associated with a decay of the photoresponses was observed. The hyperpolarization started at a dark voltage of -27 +/- 8 mV, followed an exponential course, and leveled out at -52 +/- 6 mV. The time constant was proportional to the access resistance of the preparations. With a pipette medium containing a 0.5 or 1.0 microM cGMP, the initial dark voltage was shifted to more positive values and the tendency of hyperpolarization was clearly attenuated. Similar results were obtained with 1 mM GTP. The effects of GDP and of ATP were less significant. In experiments with 1 mM GTP plus 1 mM ATP, the dark voltage behaved as in experiments with only GTP. The stabilizing action of GTP was amplified by EGTA so that with 1 mM GTP plus 1 mM free EGTA the dark voltage was stable at a level of -15 mV. It is concluded that the preparations lose intracellular components such as cGMP and GTP by diffusion into the recording pipette and that the losses are prevented or reduced when the pipette medium contains these nucleotides in nearly physiological concentrations. For the internal transmitter cGMP, the results suggest that its free concentration does not exceed 1 microM.

Effect of intracellularly applied sodium ions on the dark voltage of isolated retinal rods.

Isolated retinal rods of the frog consisting of the outer segment and the ellipsoid were patch-clamped and recorded in the whole-cell mode. The recording pipettes were filled with solutions of different composition in order to alter the cytoplasmic content of sodium, phosphate, and calcium ions, and guanine nucleotides. When a simple medium with potassium as the principal cation was used, the dark voltage slowly approached more negative values. This tendency of spontaneous hyperpolarization was reduced significantly when cGMP or GTP were present in the pipette medium. Sodium ions, on the other hand, clearly increased the speed of hyperpolarization. In the presence of sodium (20 mM), the stabilizing effect of GTP did not occur and that of cGMP was clearly diminished. Phosphate (20 mM) neutralized the sodium effect. High calcium levels (100 microM) did not measurably influence the time course of hyperpolarization. We conclude that the normal cytoplasmic sodium level in rods does not exceed 10 mM and that higher internal sodium concentrations interfere with the sodium-calcium exchange mechanism.

Psychic Blindness or Visual Agnosia: Early Descriptions of a Nervous Disorder

This article briefly reports on three early contributions to the understanding of visual agnosia as a syndrome sui generis. The authors of the respective papers worked in different fields such as physiology, ophthalmology, and neurology, and, although they were not in direct contact with each other, their results converged upon a consistent view of a nervous disorder that they called psychic blindness.

Henry Head in Ewald Hering’s Laboratory in Prague 1884–1886: An Early Study on the Nervous Control of Breathing

Henry Head, the English neurologist, received the main parts of his academic education in Cambridge and in London. In addition, he spent two years in Prague where he worked in the physiology department of the German university under the guidance of Ewald Hering. He was interested in the nervous control of breathing and worked out a new method of recording the tension and the contractions of the diaphragm in anaesthetised animals. His results substantiated the experimental basis of the Hering-Breuer reflexes and included the discovery of a new reflex now named Head’s paradoxical reflex. Head not only wrote an extensive paper about his scientific work, the recollections of his time in Prague also formed a considerable part of his autobiographical notes. These were written some forty years later and still expressed a deep affection for his teacher and mentor.

Kältezittern bei zentraler und peripherer Kühlung

SummaryShivering was induced in lightly anaesthetized dogs by either peripheral cooling, or internal cooling by means of a thermode placed into the oesophagus, or by localized cooling in the vertebral canal. Shivering was recorded electromyographically and mechanically by means of a strain gauge technique.No differences were observed by either recording means in the shivering elicited by the different methods of cooling.ZusammenfassungBei Hunden in leichter Pernoctonnarkose wurde Kältezittern durch periphere Kühlung, Oesophaguskühlung und isolierte Kühlung im Vertebralkanal ausgelöst und mittels Elektromyographie und Mechanographie registriert.Das durch die verschiedenen Kühlmethoden hervorgerufene Kältezittern ließ elektromyographisch und mechanographisch keine Unterschiede erkennen.

Neurognostics question: Wilbrand's knee.

The eponym Wilbrand’s knee refers to a bundle of nerve fibers that make a characteristic loop along their pathway in the central nervous system. If involved in a pathological process, the “knee” can give rise to a typical disorder the details of which will be given in the Neurognostics Answer. Hermann Wilbrand (1851–1935) who put forward this idea was born in Giessen, a small university town in the center of Germany, where his father Julius Wilbrand (1811–1894) was professor of “Staatsarzneikunde,” a topic mainly dealing with forensic medicine. The grandfather (Johann Bernhard Wilbrand, 1779–1846) had been a professor of anatomy, physiology, and natural history. As an exponent of Naturphilosophie, a German form of the philosophy of nature chiefly identified with the philosopher Friedrich Schelling (1775–1854), he had taught the idea of life as a metaphysical concept not accessible to experimental studies as practiced in modern life sciences. Bernhard Wilbrand’s influence vanished after the chemist Justus Liebig (1803–1873) had come to Giessen and opened the modern scientific era there. Hermann Wilbrand studied medicine in his native town until he received his MD degree in 1875. After that he went to Strasbourg and became assistant to Ludwig Laqueur (1837–1909), professor of ophthalmology at the then German university. The main part of his education in ophthalmology he received from Richard Foerster (1825–1902) in Breslau (now the Polish Wroclaw). Foerster was one of the leading German ophthalmologists at the time, and among his fields of interest was perimetry, i.e., a method for assessing the visual fields. In 1869, he presented a perimeter for clinical use and worked out a standard of the coordinates in terms of which the visual field was to be mapped (Foerster, 1869). The instrument was a modification of the arc perimeter invented by the physiologist Hermann Aubert (1826–1892) (Aubert, 1865, Fig. 19). Wilbrand soon became an expert in perimetry and concentrated his studies on visual field defects and their neurological implications. In 1879 he settled in Hamburg and stayed there until his death. He worked as ophthalmologist in his own practice and was a consultant in several Hamburg hospitals until 1919, when he was appointed professor of ophthalmology at the medical faculty of the then newly founded University of Hamburg. Wilbrand retired in 1923 and died in 1935 at the age of 84. Wilbrand’s first extensive publication was a clinical monograph on homonymous hemianopia (i.e., loss of one half of the field of vision in both eyes and on the same side) based on a collection of data from some 150 patients (Wilbrand, 1881). By linking clinical and pathological findings, he demonstrated that this type of visual field defect was due not

Neurognostics answer: Wilbrand's knee.

The answer is in Volume 3, Part 1 of Wilbrand and Saenger’s handbook (1904). Its title reads Anatomie und Physiologie der optischen Bahnen und Centren (Anatomy and Physiology of the Optical Pathways and Centers). In the chapter on the optic chiasm, Wilbrand extensively reviews the older and the then recent literature with special emphasis on the problem of decussation. Some of the authors Wilbrand mentioned still retained the view that all retinal fibers cross over to the contralateral side while others preferred the concept of partial decussation (which eventually proved to be correct). Wilbrand’s object was to contribute to this controversy with the help of studies on cases with a previous enucleation. Therefore, his illustrations always show an intact and an atrophic nerve, and all fibers stained with myelin come from the healthy nerve. Wilbrand’s illustrations show that, within the chiasm, those of the crossing fibers that are more anteriorly placed loop forward into the termination of the opposite (atrophic!) nerve before turning back to reach the optic tract and continuing their way to the visual centers. In the literature, this detour of a fiber bundle is named Wilbrand’s knee; a term introduced by Wilbrand himself. The fibers of Wilbrand’s knee carry information from the inferonasal retina or, in terms of the visual field, from the upper temporal quadrant. Therefore, a lesion that affects these fibers would lead to a visual field defect of that quadrant. Selective destruction of these fibers is hardly conceivable. However, within the framework of a circumscribed pathological process that destroys one optical nerve near its junction with the chiasm, the “knee fibers” also might be affected, because this is the site where they loop forward into the (opposite) nerve. Clinically, the result would be complete blindness at the side of the affected nerve accompanied by a contralateral superior temporal field defect. Such was Wilbrand’s postulate (cf. Fig. 11 in Wilbrand & Saenger, 1915) that, in modern clinical terms, is named anterior chiasmal syndrome. The concept of Wilbrand’s knee was generally accepted until Horton (1997) demonstrated that it is an artifact of monocular enucleation. The knee neither exists in normal chiasmata of primates (Rhesus and squirrels monkeys) nor can it be seen after a short-term enucleation (i.e., in a patient who died 5 months after the loss of one eye). It seems to form gradually over years due to shrinkage of the optic chiasm. As regards the clinical cases with tumors compressing the optical nerve, there are in fact perimetry results that correspond to Wilbrand’s postulate just quoted. But modern neuroimaging techniques show “that