K. Meller

Elektronenmikroskopische Befunde zur Differenzierung der Rezeptorzellen und Bipolarzellen der Retina und ihrer synaptischen Verbindungen

SummaryThe differentiation of the birds retina is described, paying special attention to the development of synapses and bipolar cells. The structural differentiation of receptor cells and bipolars, the topography and the time sequence of synaptic development has been studied in embryonic material ranging from 6 to 21 days of incubation.Due to the intimate interdigitation of opposing cell membranes in contact with each other, the formation of specialized contacts (synapses) occurs at selected places and shows special features. Their differentiation is characterized by a) accumulation of electrondense material close to the pre- and postsynaptic membrane, b) the presence of large numbers of synaptic vesicles initially perinuclear and moving later in the cytoplasmatic presynaptic processes, c) a special type of synaptic lamella surrounded by vesicles.

Synaptic organization of the molecular and the outer granular layer in the motor cortex in the white mouse during postnatal development. A Golgi- and electronmicroscopical study

SummaryThe motor cortex of white mice has been studied from the first postnatal day up to an age of three weeks electronmicroscopically and with the Golgi method. Special attention has been paid to the dendritic organization in the molecular and outer granular layers. The following observations were made:1.Branching of the apical dendrites of neurons of the second layer occur already from the third day, whereas the basal dendrites start branching only at the end of the first week.2.The deeper laying cells of the second layer mature at an earlier stage than the more superficial cells.3.Immediately after birth, the first axodendritic synapses are found on the large stem dendrites. Their spines develop by the end of the first postnatal week. The spines of the apical dendrites develop before those of the basal ones.4.Axosomatic synapses are found on the cell bodies of the external granular layer in the second postnatal week.5.The development of the apical dendrites from the deeper layers (III–V) is an important factor in the maturation of the external layers. These dendrites have acquired their final number of spines by the end of the second week.6.During their development the dendrites of the third to fifth layer show intimate contact by mutual indentation. The cells of the second layer complete their maturation by the end of the third week.ZusammenfassungDer motorische Cortex von weißen Mäusen wurde vom ersten Tag nach der Geburt bis zum Alter von 3 Wochen mit Hilfe der Golgi-Methode und elektronen-mikroskopisch untersucht. Besonderes Interesse galt seiner dendritischen Organisation in Molekularis und äußerer Körnerschicht.Die apikalen Dendriten der Nervenzellen der II. Schicht verzweigen sich nach dem 3. Tag, die basalen Dendriten am Ende der 1. Woche.Die tiefgelegenen Zellen der zweiten Schicht reifen früher als die mehr oberflächlich liegenden Zellen. Die ersten axodendritischen Synapsen findet man unmittelbar nach der Geburt an den großen Stammdendriten. Ihre Dornen entwickeln sich am Ende der ersten postnatalen Woche. Die synaptischen Dornen der apikalen Dendriten entwickeln sich früher als jene der basalen.Die axosomatischen Synapsen finden sich an den Zellen der äußeren Körnerschicht im Laufe der 2. Woche. Einen wichtigen Faktor in der Ausreifung der beiden oberen Schichten stellt die Entwicklung der apikalen Dendriten der unteren Schichten (III–V) dar. Diese Dendriten entwickeln ihren endgültigen Dornenbesatz am Ende der 2. Woche.Die Dendriten der Schichten III–IV verzahnen sich im Laufe der Entwicklung eng miteinander. Ihre Ausreifung entspricht am Ende der 3. Woche den Verhältnissen bei der erwachsenen Maus.

Terminal degeneration in the lateral geniculate body of the monkey; An electron-microscope study

Summary1.The degeneration of optic terminals in the lateral geniculate body (LGB) has been studied in 16 monkeys after enucleation of one eye. In contrast to the results of our previous studies with the ligth-microscope, electronmicroscopical studies of normal and degenerated LGB now reveal complex synaptic structures, many of them arranged in synaptic islands.2.The presence of bulbous enlargement of synapses, the functional portion of terminals, occuring during the process of degeneration, previously reported, is confirmed. They are considered to be due to a marked fibrillisation of the cytoplasm.3.Other clear signs of synaptic degeneration besides the enlargement are the disappearance of synaptic vesicles and an irregular disintegration of the intersynaptic connecting (“cementing”) substance.4.Reactive neuroglia produce a complex of enveloped synaptic and myelin débris, penetrating normal neighbouring layers. Great care must be taken in interpreting late stages of degeneration.

The differentiation of endoplasmatic reticulum in developing neurons of the chick spinal cord

Summary1.We have failed in the early stages of development to separate neuroblasts from glioblasts with the means of electronmicroscopy. All cells forming the wall of the neural groove or tube have the same cytological structure seen in other primitive somatic cells.2.Some identification is possible around the 7th day of incubation when synaptic differentiation permits the recognition of neuroblasts.3.Neurons are characterised by a continuous and prolonged formation of granular ER which eventually becomes organized in parallel cisterns around the 14th–16th days when typical Nissl bodies can be recognized.

Early cytological differentiation in the cerebral hemisphere of mice

Summary1. The parietal region of the telencephalic vesicle of mice embryos and newborn mice has been studied electronmicroscopically. Special attention has been paid to developing glia cells. 2. In early stages it is impossible to differentiate neuroblasts from glioblasts. 3. Late pre-natal stages allow a recognition of glioblasts on account of their ultrastructure, as the overall structure of the nucleus and the cytoplasm of a glioblast has a greater electron-density than that of a neuroblast. 4. Glioblasts have a lobulated nucleus at this stage (20th day i.u.) while neuroblasts possess an ovoid nucleus. The quantity of endoplasmic reticulum and of the number of ribosomes is relatively greater in neuroblasts than in glioblasts.

The cytology of the developing molecular layer of mouse motor cortex

SummaryThe cytological differentiation of the first and uppermost cortical layer of the mouse motor cortex has been studied, having used the Golgi-Cox technique and electronmicroscopy.The present investigation concentrates on the following topics: the differentiation of 1 neuroglia and 2. neurons in this layer and 3. the ultrastructure of the developing neuropil. Whenever possible the lightmicroscopy of the Golgi section has been compared with relevant features in electronmicroscopy.1.Two types of neuroglial cells have been found. One specialised type which is responsible for sealing on the neuroectoderm from the pia and delivers the membrana limitans gliae. The other type has the structure of an ordinary astrocyte.2.The horizontal cell changes from a primitive bipolar cell into a multipolar cell around the 6thday of postnatal life. It takes about 3 weeks before the general shape and the ultrastructure has reached maturity.3.The development of the neuropil has been studied paying special attention to synaptic organisation. Axo-dendritic synapses of horizontal cells can be detected one day after birth, while axo-somatic synapses are established from the 9th day onwards. Increasing complexity of synaptic organisation occurs with progressing maturation.ZusammenfassungDie Cytodifferenzierung der Schicht I des motorischen Cortex der weißen Maus wird mit Hilfe der Golgi-Methode und elektronenmikroskopisch untersucht.Die Gliadifferenzierung wird unter besonderer Berücksichtigung der Feinstruktur der „membrana limitans gliae“ verfolgt. Die Gliazellen der Molekularis lassen sich im Laufe der Entwicklung in zwei Typen unterteilen. Es bleibt fraglich, ob es sich um zwei unterschiedliche Modifikationen von Astrocyten handelt.Die Peinstruktur des sich entwickelnden Neuropils wird beschrieben. Axodendritische Synapsen finden sich in der Molekularis bereits am 1. Tag der postnatalen Entwicklung. Axosomatische Synapsen der Horizontalzellen fanden sich ab dem 9. Tag nach der Geburt.Die Horizontalzellen beginnen um den 6. Tag nach der Geburt ihre anfängliche, embryonale, bipolare Gestalt zu ändern und Fortsätze auszusenden. Nach etwa drei Wochen haben sie ihre endgültige, morphologische Reife erreicht.

Die Feinstruktur und Differenzierung des inneren Segmentes und des Paraboloids der Photorezeptoren in der Retina von Hhnerembryonen

SummaryThe development of the inner segment of the chick photoreceptors has been studied from the 6th to 21st day of incubation.The inner segment is essentially an elongation of the apical cytoplasm of the growing receptor, distally from the outer limiting membrane. An emigration of mitochondria follows, forming the ellipsoid.The paraboloid is a portion of the agranular endoplasmic reticulum and occupies a sharply localised non variable position within the receptor.Possible interrelatations between paraboloid, endoplasmic reticulum and Golgi apparatus are discussed. The presence of glycogen in the paraboloid seems to indicate that this specialised portion of e.r. may be either involved in glycolysis or a store for glycogen.The development of the inner segment of the chick photoreceptors has been studied from the 6th to 21st day of incubation.

Ontogeny of the mouse motor cortex. The polymorph layer or layer VI. A Golgi and electronmicroscopical study

SummaryThe development of neurons and their synapses of the mouse motor cortex has been studied from the first postnatal day up to an age of three weeks both electronmicroscopically and with the Golgi method. Special attention has been paid to the maturation of the different cell types in the sixth cortical layer and their dendritic organization within this layer.The polymorph layer is subdivided into two zones: an internal (VIb) and an external one (VIa). In these zones six different cell types can be identified both electronmicroscopically and with the Golgi method: large, small and inverted pyramidal cells in VIa; horizontal cells, star cells and small pyramidal cells in VIb.Spines of apical dendrites of large pyramidal cells in sublayer VIa can be detected as early as the 6th postnatal day. About the ninth day the basal dendrites as well show emerging spines. Somatic spines are found only on the large pyramidal cells and disappear slowly towards the end of the 3rd postnatal week.The small pyramidal cells show developing spines on their apical dendrite in the first half of the second postnatal week. The final density and distribution of spines is reached by the stem dendrites towards the end of the second week, by the basal dendrites during the third week. The maturation process of the “improperly orientated” neurons occurs in time in between the large and the small pyramidal cells.The axo-somatic synapses appear in general at a later date than the axo-dendritic ones. In the horizontal cells axo-somatic synapses are visible already at the seventh postnatal day.At the end of the first week especially in layer VIb many immature neurons with an ovoid or round nucleus are present having little if any endoplasmic reticulum organised as ergastoplasm.Towards the end of the second week however most neurons in the polymorph layer have a well developed endoplasmic reticulum.Electronmicroscopical pictures reveal in outgrowing dendrites many enlargements filled with vesicles, these correspond to the varicosities seen in Golgi pictures. At nine days postnatally the first myelinated fibres appear.

Vergleichende elektronenmikroskopische Untersuchungen des Plexus chorioideus der Maus in vivo und in vitro

Summary1.Choroid plexus of 1 to 15 day-old mice has been cultured and then examined electronmicroscopically. At the same time and in vivo a comparative electronmicroscopical study of the mouse choroid plexus, from the prenatal to the adult stage was made.2.Some days after explantation foci of glycogen concentration are found in the plexus cells. These foci disappear gradually after the second week of incubation.3.Simultaneously to the disappearance of the intracellular glycogen, the agranular endoplasmic reticulum undergoes a pronounced increase in size. At this stage the ultrastructure of the cells is similar to that of the adult plexus cells in vivo. This process can be accelerated by removal of glucose from the nutritive medium.Zusammenfassung1.Die Plexus chorioides von 1–15 Tage alten Mäusen wurden nach verschiedenen Inkubationszeiten in Gewebekulturen elektronenmikroskopisch untersucht. Außerdem wurden zum Vergleich elektronenmikroskopische Untersuchungen des Plexus chorioideus pränataler bis erwachsener Stadien der Maus durchgeführt.2.Einige Tage nach der Explantation finden sich in den Plexuszellen Glykogenansammlungen, die nach der 2. Inkubationswoche allmählich zurückgehen.3.Parallel zu dem Abbau des intrazellulären Glykogens entwickelt sich das agranuläre endoplasmatische Reticulum stark. Die Feinstruktur der Zellen ist dann der erwachsener, in vivo befindlicher Plexuszellen vergleichbar. Dieser Prozeß kann durch Entfernen der Glukose aus dem Nährmedium beschleunigt werden.

The behavior of trypsinized choroid plexus cells in tissue cultures. An electron microscopic study

SummaryPlexus cells of 10 days old chicken embryos were trypsinized. After various periods of culturing the material was studied both light- and electronmicroscopically. Directly after dissociation most of the plexus cells are found to be separated from each other in the liquid medium. However after 12 hours of culturing the individual cells reaggregate themselves in small rosettes which enlarge until the stages of 36 hours. Simultaneously the aggregational process of previously dissociated cells is combined with an ultrastructural differentiation and desmosomes, basal labyrinth, basement membrane and ergastoplasm are formed.Both the isolated cells and the rosettes exhibit quick rotational movements due to their ciliar action.ZusammenfassungDie Plexus chorioidei der Seitenventrikel 10 Tage alter Hühnerembryonen wurden trypsiniert, kultiviert und anschließend licht- und elektronenmikroskopisch untersucht. Unmittelbar nach der Trypsinierung sind die Plexuszellen bei der Kultivation in flüßigen Medium als Einzelzellen anzutreffen. Nach 12stündiger Kulturzeit sieht man kleine Rosetten, deren Größe bis zum Alter von 36 Std noch zunimmt. Die isolierten Zellen und die Zellen der Rosetten weisen eine rege Zilientätigkeit auf, durch die sie in lebhafter Bewegung gehalten werden.Mit der Zusammenlagerung der isolierten Zellen zu Gewebsverbänden geht gleichzeitig eine feinstrukturelle Differenzierung einher. Es treten Desmosomen, ein basales Labyrinth, eine Basalmembran und oft ein Ergastoplasma auf.