Showing papers by "Max Planck Society published in 1968"

Displacement of synaptic terminals from regenerating motoneurons by microglial cells.

Abstract: Axonal reaction of motoneurons has been shown to be usually accompanied by an early and brisk proliferation of perineuronal microgliacytes. In order to clarify the real nature of such newly formed microglial satellites and their fine structural relationships to the regenerating nerve cells, facial nuclei from bilateral preparations were examined by light and electron microscopy 4 days after cutting the right facial nerve in rats. On the transected side, microgliacytes could often be observed closely adjoining motoneuron perikarya and main dendrites over long distances, and thereby removing morphologically intact synaptic terminals from the neuronal surface membranes. This displacement of boutons by microglial cells is probably preceded by a loosening of the synaptic contacts due to some unknown membrane changes in the regenerating motoneurons. The functional significance of this considerable deafferentation process could not be entirely elucidated.

Relative and Absolute Terrestrial Abundances of the Rare Earths

Abstract: Results of analyses on composite samples of igneous and sedimentary rocks and chondritic meteorites, obtained by an improved analytical procedure, are reported. The relative rare-earth abundances in composite samples of shales, metamorphosed shales, basalts, rhyolites, and granites are remarkably similar to each other, but small differences are apparent, even among the heavier rare earths. Eu and Ce show “anomalous” abundances in several of the samples. A new value for the average Gd content of chondritic meteorites leads to the conclusion that common crustal rocks are deficient in Eu, relative to the other rare earths. Straight lines can be drawn on comparison diagrams between the elements Pr and Tb in most samples, and between La and Tb (Eu excepted) in some. Equally good lines can be drawn whether rare-earth atomic number, ionic radius, or reciprocal ionic radius is used as the abscissa.

Electron Impact Ionization Cross-Sections and Ionization Rate Coefficients for Atoms and Ions from Hydrogen to Calcium

Abstract: Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for all ionization stages from hydrogen to calcium (Z=20). Ionization rate coefficients are given for these species on the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.

Flight control in Drosophila by visual perception of motion

Abstract: Apparent motion was simulated in the visual system of the tethered fruitfly Drosophila melanogaster by projecting moving stripe patterns onto stationary screens positioned in front of the lateral eye regions. The reactions of the animal were recorded under conditions of stationary flight in still air. It was found that visual stimulation modifies, independently, torque and thrust of the flight system. The responses appear suitable to counteract involuntary changes of direction and altitude in free flight.

Isotropic Solutions of the Einstein‐Liouville Equations

Abstract: The gravitational fieldgenerated by a gas whose one‐particle distribution function obeys the Liouville equation is examined under the following assumptions: First, the distribution is locally isotropic in momentum space with respect to some world‐velocity field; second, if the particles have rest‐mass zero, the gas is irrotational. It is shown that the model is then either stationary or a Robertson‐Walker model. The time dependence of the radius in the Robertson‐Walker models is given in terms of integrals containing the distribution function.

Steady fluid flow in a precessing spheroidal shell

Abstract: The linear boundary-layer analysis by Stewartson & Roberts (1963) and by Roberts & Stewartson (1965) for the motion of a viscous fluid inside the spheroidal cavity of a precessing rigid body is extended to include effects due to the nonlinear terms in the boundary-layer equation. The most significant consequence is a differential rotation super-imposed on the constant vorticity flow given by the linear theory. In addition it is shown that a tidal bulge of the cavity forces a fluid motion similar to that caused by the precessional torque. The relevance of both effects for the liquid core of the earth is briefly discussed.

[Transplacental induction of malignant tumors of the nervous system. I. Ethyl-nitroso-urea (ENU) in BD IX rats].

Abstract: Eine einmalige Gabe von ANH an trachtige BD IX-Ratten am 15. Tage der Schwangerschaft injiziert, fuhrte bei praktisch allen Nachkommen zu malignent Tumoren im Gehirn, an Gehirnnerven, im Ruckenmark und peripheren Nervensystem. Selbst nach 5 mg/kg (2% der LD 50) wurde noch eine Tumor-Ausbeute von 63 Prozent beobachtet. Bei erwachsenen Ratten waren dagegen 200 mg/kg fur die gleiche Wirkung erforderlich. Die Empfindlichkeit des Nervensystems wahrend der pranatalen Entwicklung ist daher etwa 50 fach groser.

Functional synaptic organization of primary visual cortex neurones in the cat.

Abstract: The spontaneous and light evoked post-synaptic activity of cells of the primary visual cortex was investigated with intracellular and quasi-intracellular records. The resting membrane potential fluctuated mostly between 3–10 mV below the firing threshold owing to spontaneous EPSP- and IPSP-activity. Discharge activity was therefore low. Forms and amplitudes of the visible EPSP's showed a large variability, the frequency was 150–300/sec. Discrete IPSP's were between 0.5–3 mV and were less frequent than EPSP's (about 1∶10). Their duration was only slightly longer than that of EPSP's. EPSP's and IPSP's could be elicited at on or off by appropriately positioned small light stimuli. During the initial reaction following a stimulus, single PSP's could be distinguished. Geniculate on-center- as well as off-center-afferents could lead to excitation or inhibition in different neurones. The receptive fields of cortical cells to monocular stimulation were analysed with averaged records. In each neurone 2–4 overlapping areas of on- or off-activation or -inhibition could be distinguished. Each of these activation or inhibition zones had the functional properties of a single geniculo-cortical onor off-center fibre with their receptive field centers separated by 1–3°. The variety of functional organizations of the cortical neurones to monocular stimulation was explained by variable combinations of 2–4 converging geniculate on- or off-center fibres with either excitatory or inhibitory action and variable overlap of their receptive fields. This was tested in a simple computer model. — Most neurones with pronounced reactions to movement or with direction specific movement sensitivity (about half of the neurones investigated) had an excitatory contact with an off-center fibre, which seemed to be mainly responsible for the movement reaction.- The findings suggest that from each eye less than 5 geniculo-cortical afferent converging fibres have a major effect on the activity of one cortical cell. Inhibitory afferents may be indirect and relayed through another cortical pyramidal cell.

Genetic activities of the Y chromosome in Drosophila during spermatogenesis.

Abstract: Publisher Summary This chapter focuses on genetic activities of the Y chromosome in Drosophila during spermatogenesis. The Y chromosome of Drosophila contains a number of fertility factors which are all essential for the formation of normally functioning sperm. These factors are cell autonomous and act even during the diploid phase, so that X-bearing spermatids that do not possess a Y chromosome are able in normal males to differentiate into normal spermatozoa. In spermatocyte nuclei of Drosophila species, special structures occur, which are not found in the nuclei of other tissues. They are restricted to the growth phase of primary spermatocytes. The functional nature of the Y-chromosomal loops has been demonstrated in two independent ways: (1) in autoradiographs the loops appear labeled after incubation with tritiated uridine, (2) if the DNA-dependent synthesis of RNA is blocked by actinomycin, the loops disintegrate within a few hours. Irreversible damage such as inhibition of loop regeneration and breaks within loops are induced by X-rays. Histochemical studies reveal the presence of proteins, RNA, and DNA in the loops. The chapter presents the morphogenetic effects of Y deficiencies on spermiogenesis. If a segment of the Y chromosome containing any of the loop-forming sites is lacking, males are invariably sterile.

Factors involved in the expression of gene activity in polytene chromosomes.

Abstract: In order to separate some of the factors involved in the formation of puffs the antibiotic actinomycin D was applied at different stages of puff activity. Puffs were induced by temperature shocks or eodysone. Inhibition of RNA synthesis with actinomycin D before application of a puff inducing stimulus prevents neither the appearance of the stimulus specific puffs nor the accumulation of acidic proteins in the puff regions. The puffs attained under these conditions approximately 1/3 of the size normally produced by the stimulus. Indications were obtained that during puff formation acidic protein accumulation precedes the onset of RNA synthesis. Synthesis and storage of newly synthesized RNA within the puff region was studied on the basis of grain distribution in uridine-H3 autoradiographs after various incubation periods. RNA synthesis appears to be restricted to a particular area of the puff region. After a 3 min temperature shock following injection of uridine-H3 silver grains are located only over a particular area of the newly formed puff. The same area becomes labeled during a 1 min pulse of uridine-H3 applied at a stage of maximum puff development. Longer periods of incubation result in a random distribution of the grains over the whole puff region. Grain counts on different areas of experimentally induced puffs and on the same areas at a stage of puff regression indicate that the newly synthesized RNA becomes transferred from the area where it was synthesized and is stored for a certain period within the puff region. Complete release of newly synthesized RNA from puffs in which RNA synthesis was inhibited by actinomycin D at a stage of maximal activity is accomplished within 30 to 35 min.

Interpretation of Self‐Diffusion and Vacancy Properties in Copper

Abstract: Recent tracer measurements of the self-diffusion coefficient by Rothman and Peterson are analysed in conjunction with the determination of equilibrium concentrations of vacant lattice sites by Simmons and Balluffi and the isotope effect on self-diffusion. The following values for monovacancy and divacancy properties are obtained (in the usual notation): E = 1.03 eV, E = 1.06 eV, S ≈ 0.3 k, E − E 0.54 eV, divacancy association entropy ΔS2 V ≈ 2 k, temperature coefficient of monovacancy self-diffusion energy 2 α = d (E + E)/d(kT) ≈ 0.5, frequency factors for mono- and divacancy migration v exp (S) = 1.4 × 1014 s−1, v exp (S/k) = 1.6 × 1014s−1. The monovacancy jump frequencies near room temperature are in excellent agreement with the values obtained from dislocation pinning experiments of Thompson and Pare. Neue Messungen des Selbstdiffusionskoeffizienten mit radioaktiven Tracern von Rothman und Peterson werden in Verbindung mit der Bestimmung der Gleichgewichtskonzentration leerer Gitterplatze von Simmons und Balluffi und mit Messungen des Isotopen-effektes bei der Selbstdiffusion ausgewertet. Man erhalt folgende Werte fur die Eigenschaften von Einfach- und Doppelleerstellen (in der ublichen Bezeichnungsweise): E = 1,03 eV, E = 1,06 eV, S ≈ 0,3 k, E − E 0,54 eV, Assoziationsentropie der Doppelleerstelle ΔS2 V ≈ 2 k, Temperaturkoeffizient der Selbstdiffusionsenergie fur Einfachleerstellen 2 α = d (E + E)/d(kT) ≈ 0,5, Frequenzfaktoren fur Einfach- und Doppelleerstellenwanderung v exp (S) = 1,4 × 1014 s−1, v exp (S/k) = 1,6 × 1014s−1. Die Sprung-frequenzen der Einfachleerstellen in der Nahe der Raumtemperatur sind in ausgezeichneter Ubereinstimmung mit Werten, die man aus Experimenten von Thompson und Pare uber Versetzungsverankerung erhalt.

Optische Eigenschaften der Ommatidien im Komplexauge von Musca

Abstract: Optical characteristics of the dioptric system in the ommatidia of Musca have been analysed by use of “antidromic illumination” of the eye. The results indicate that the distal endings of the rhabdomers terminate near the focal plane of the dioptrics and that the quality of the lens is high enough to resolve some details of their shape. — Using optical methods it has been possible to confirm directly that the optical axes of 7 individual rhabdomers from 7 different ommatidia all converge to a common point in the distant surroundings. This is a characteristic for compound eyes of the “neural superposition” type. — The results are discussed on the basis of the hypothesis that the Musca eye is composed of two functionally different subsystems: One system (D) with high absolute sensitivity and low spatial resolution consisting of the sense cells no. 1 to 6, and a second system (H) with high spatial resolution and low absolute sensitivity composed of cells no. 7 and 8.

Protein-Kristallstrukturanalyse mit Elektronenstrahlen

Abstract: Nach den Erfolgen der R6ntgenstrukturanalyse von Proteinkristallen liegt es nahe zu fragen, ob auch mit Elektronenstrahlen eine Protein-Kristallstrukturanalyse m6glich ist. Zwei grundsfitzliche Vorteile sind unmittelbar einzusehen : 1. Die Wechselwirkung der Etektronenstrahlen ist um Gr6Benordnungen st~trker als die Wechselwirkung der R6ntgenstrahlen. Man kann daher bei kurzen Belichtungszeiten mit kleinen, im Extremfall mit mikroskopisch kleinen Kristallen arbeiten. 2. Elektronenstrahlen k6nnen im Gegensatz zu R6ntgenstrahlen nach Belieben gebrochen und reflektiert werden. Es scheint damit mSglich, das Phasenproblem 1 durch geeignete Interferenzexperimente zu 16sen. Diesen Vorteilen stehen zwei Nachteile gegentiber: t. Proteinkristalle sind (nach unseren heutigen Kenntnissen) nur in wasserigen oder zumindestens wasserhaltigen Medien hochgeordnet. Im Elektronenstrahl kSnnen abet nut trockene Priiparate untersucht wetden. Deren Ordnungsgrad ist viel geringer. 2. Die starke Wechselwirkung der Elektronen bewirkt auch eine StrahlscMdigung der Pr~parate, deren Mechanismus allerdings noch nicht gekl~irt ist. Es hat nicht an Versuchen gefehlt, Proteinkristalle mit Elektronen zu untersuchen, durchweg im Elektronenmikroskop. Ein elektronenmikroskopisches Bild registriert Amplituden und Phasen der yore Objekt abgestreuten Wellen. Man ntitzt also damit bereits die M6glichkeit aus, mit Elektronenstrahlen Phasen zu messen. Schon frtihzeitig hat man Abdrticke von Kristallflgchen [t3 untersucht. Sehr sch6ne elektronenmikroskopische Aufnahmen wurden yon FerritinKristallen hergestellt [2]; der im Ferritin-Molektil enthaltene Eisenkern ist ftir den hohen Kontrast solcher Aufnahmen verantwortlich. An einigen nur Leichtatome enthaltenden Proteinen wurden Streifensysteme mit Hilfe des Elektronenmikroskopes registriert [3], welche analog den Menterschen Untersuchungen [4] als Interferenzen niederer Beugungsordnungen angesehen werden k6nnen. An Proteinen wurden, mit Ausnahme yon [2], ausschlieBlich mit Sehweratomsalzen beladene Pr~iparate (Aufl6sung ca. 25--50 A) untersucht, um gentigend Kontrast in den mikroskopischen Aufnahmen zu erhalten. ~ a n studierte damit eigentlich die eine Art ,, Glas\" bildende Schweratomhiille (vgl. z.B. [5]). Damit dtirfte auch die Strahlensch~digung (soweit sie die organische Substanz betrifft) unwichtig sein.

Agonistic and Sexual Display in Aquatic and Semi-Terrestrial Brachyuran Grabs

Abstract: Behavioral patterns of inter-crab communications as shown in agonistic and sexual interactions are investigated in 26 genera within 9 aquatic and semi-terrestrial families of brachyurans. The investigation includes a review of literature and the author's observations. Species of the aquatic families, Dromiidae, Leucosiidae, Majidae, Parthenopidae, Cancridae, Portunidae, and Xanthidae, display agonistic activities mostly with more or less extended chelipeds. An encounter leads often to physical interactions, such as striking blows or grasping with chelae. Many of the semi-terrestrial ocypodids and grapsids, however, display with flexed chelipeds, showing the opponent the outer side of the chelae in a shield-like manner. Encounters usually follow a formalized set of patterns and only occasionally do they lead into a “wild fight”. Concerning sexual activities in many aquatic forms, a male catches and holds or cages a female between its legs for several days during the mating period. In many semi-terrestrial grapsids and ocypodids, patterns of up-down display of chelipeds have been observed during agonistic encounters, as well as during initial stages of mating. In other forms a special display of chelipeds occurs in courtship. In agonistic and sexual activities of aquatic forms intern-crab communication seems to depend mainly on tactile and possibly chemical stimuli. In the semi-terrestrial forms that have been investigated, mechanisms of communication are based predominantly on optical information.

Circannuale Periodik als Grundlage des jahreszeitlichen Funktionswandels bei Zugvögeln. Untersuchungen am Fitis (Phylloscopus trochilus) und am Waldlaubsänger (P. sibilatrix)

Abstract: 1. In der vorliegenden Arbeit wird nachgewiesen, das zwei in Aquatornahe uberwinternde palaearktische Zugvogelarten uber einen endogenen und angeborenen Mechanismus verfugen, der ihnen die zeitliche Orientierung im Jahresablauf ermoglicht. Junge Fitis- und Waldlaubsanger (Phylloscopus trochilus undP. sibilatrix), die von Mitte September ihres ersten Lebensjahres an bis mindestens zum Juni des darauffolgenden Jahres in einer temperaturkonstanten Kammer im kunstlichen 12 : 12 Stunden-Tag lebten, mauserten ungefahr zur selben Zeit wie die Kontrollen im naturlichen Licht-Dunkel-Wechsel ihres Brut- bzw. Uberwinterungsgebietes. Sie entwickelten im Fruhjahr ungefahr zur selben Zeit wie diese „Zugunruhe“ und auch ihre Gewichtskurven zeigten einen ahnlichen Verlauf. Bei zwei lange genug in diesen Bedingungen gehaltenen Vogeln konnte auch noch die Sommermauser beobachtet werden (Abb. 3, 4, 6). Ein Versuch mit zwei anderen Fitislaubsangern, die 27 Monate lang im 12 : 12 Stunden-Tag gehalten wurden, brachte den Beweis dafur, das Mauser und Zugunruhe nicht nur wahrend des Winterhalbjahres ungefahr zeitgerecht spontan auftreten, sondern auch spater in der erwarteten Folge periodisch wiederkehren (Abb. 7). Bei einem der Vogel wich die Periodenlange deutlich von 12 Monaten ab. Damit ist die mogliche Wirkung unkontrollierter Umweltfaktoren als Ursache dieser Periodik ausgeschlossen. — Da keiner der Vogel vor Versuchsbeginn mehr als 8 Monate lang unter naturlichen Lichtbedingungen gelebt hatte, ist zugleich gezeigt, das diese endogene Periodik angeboren ist. Die Phasenlage der endogenen Jahresperiodik hing bei den jungen Fitislaubsangern des ersten Versuchs vom Geburtstermin ab. Spater im Jahr geschlupfte Vogel beendeten auch spater ihre Jugendmauser, wurden spater im Herbst zugunruhig, begannen spater mit der Wintermauser und wurden spater im Fruhjahr zugunruhig (Abb. 8). 2. Auf dem Hohepunkt ihrer Zugunruhe im Herbst nach Afrika verfrachtete und dort teilweise unter freiem Himmel gehaltene Vogel blieben genau so lang zugunruhig wie Vogel, die nicht den Umweltreizen ihres Winterquartiers ausgesetzt waren (Abb. 5). Die im Uberwinterungsgebiet herrschenden Bedingungen ubten demnach keinen hemmenden Einflus auf die Zugunruhe der Vogel aus. Dieses Ergebnis steht im Widerspruch zu Befunden anderer Autoren. Es wird eine Hypothese diskutiert, nach welcher die Dauer und der zeitliche Ablauf des Herbstzuges junger Fitise vorwiegend von einem endogenen Zeitprogramm bestimmt wird, welches so organisiert ist, das der ziehende Vogel bei vorgegebenem Wanderweg das Winterquartier erreicht hat, wenn dieses Zeitprogramm abgelaufen ist.