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W Tetzlaff

Publications and source records attributed to W Tetzlaff.

68 records · Page 4Linked to original sources
PubMed1987

Synaptic and extrasynaptic localization of adenosine binding sites in the rat hippocampus.

In vitro binding sites for [125I]iodohydroxyphenylisopropyladenosine, an A1 adenosine agonist, were visualized in the CA1 area of the rat hippocampus by electron microscopical autoradiography. By fixing hippocampal slices after incubation in paraformaldehyde and osmium tetroxide, the specifically bound radioactive ligands were preferentially retained and cross-linked to the tissue. Autoradiographic silver grains were localized by a statistical evaluation according to the '50% probability circle analysis' and by measuring the distance of the grains from neighbouring membrane structures. A significant association of silver grains, indicating the presence of A1 adenosine receptors, was found at synaptic complexes and in addition at extrasynaptic sites on dendritic membranes. This suggests that modulation of nerve cell activity by adenosine involves synaptic as well as non-synaptic mechanisms.

Adenosine↗
PubMed1986

Rapid down regulation of hippocampal adenosine receptors following brief anoxia.

Adenosine A1 receptors, as demonstrated by [3H]cyclohexyladenosine (CHA) binding to cryostat sections of the brain, were studied utilizing quantitative autoradiographic techniques. A brief period of global CNS anoxia resulted in the rapid and persistent down regulation of [3H]CHA binding sites in the hippocampus but not in the neocortex or striatum. The density of adenosine A1 receptors in a given brain region has previously been shown to be a critical factor in determining the strength of the inhibitory action of adenosine. Since the down regulation of these sites is correlated temporally with the onset of hyperactivity following transient anoxia, it is suggested that a reduction in the strength of the neuromodulatory action of adenosine contributes to the postanoxic hyperactivity of CA1 pyramidal cells and perhaps to their selective vulnerability.

Adenosine↗
PubMed1986

A technique for the electron microscopic autoradiography of Al adenosine receptors in brain tissue. Ligand-receptor fixation by osmium tetroxide.

A procedure for the electron microscopic autoradiography of Al adenosine receptors is described. Fresh tissue slices from rat hippocampus were incubated with the radioactive adenosine analogs: Cyclohexyl[3H]adenosine, 5'-N-ethylcarboxamido[3H]adenosine or or [125I]-iodohydroxyphenylisopropyladenosine. Various fixation agents were tested with respect to the retention of these ligands by the tissue. While most of the ligands were lost in aldehyde fixation they were retained by osmium tetroxide probably via a crosslinking reaction. The final method of choice was an aldehyde prefixation (in the case of [125I]-iodohydroxyphenylisopropyladenosine with 4% buffered paraformaldehyde) during which more than 90% of the nonspecifically bound ligands were washed out while 40% of the specifically bound ligands remained. Subsequent fixation with osmium tetroxide (1%) allowed a standard protocoll for dehydration and embedding to be used with only minimal (less than 5%) further loss of the ligands. Electron microscopic autoradiography provided evidence for a specific distribution of the binding sites for [125I]-iodohydroxyphenylisopropyladenosine.

Animals↗
PubMed1985

Ornithine decarboxylase in motoneurons during regeneration.

The activity of ornithine decarboxylase, the rate-limiting enzyme in polyamine synthesis, was assayed in the isolated facial nucleus of the rat at various times after axotomy of the facial nerve. In addition, it was measured 24 h after the second of a series of two lesions (conditioning lesion design) with various times between the first and second operations. Ornithine decarboxylase activity was found to increase 8 h after nerve transection and was maximum after 24 h (300% of control). Thereafter the activity declined to subnormal levels where it remained for several weeks. Ornithine decarboxylase activity did not increase again when a second axotomy was made 2 weeks after the first lesion. However, ornithine decarboxylase did respond to the second axotomy if it was carried out 3 weeks after the first lesion. Histochemical localization of ornithine decarboxylase demonstrated that the increase in enzyme activity was mainly confined to the perikarya of the motoneurons. These data suggest that this enzyme is somehow involved in triggering the "regeneration program" and clearly indicate that at least some aspects of the neuronal response to axotomy are not further stimulated by a conditioning lesion.

Animals↗
PubMed1984

Enzyme changes in the rat facial nucleus following a conditioning lesion.

The enzymatic changes in the facial nucleus of the rat occurring after single nerve transection were compared with those after double lesion. In a first operation the left facial nerve was transected and 2 weeks later, both the left and the right facial nerves were axotomized. The double or "conditioning" lesion produced a complex pattern of changes that differed from those after a single lesion. Three enzymes were investigated both biochemically and histochemically. Acetylcholinesterase is representative of the group of transmitter-related enzymes which in general showed a decrease after a single lesion. The hexose monophosphate shunt enzymes, represented here by glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, are known to increase in the perikaryon. 5'-Nucleotidase is a marker enzyme for the perineuronal satellite glia which also increase in number during chromatolysis. The following results were obtained: (i) In comparison with the single-lesion side the conditioning-lesion side exhibited less activity of the pentose phosphate shunt enzymes on days 7 and 12 after the second operation. On the conditioning-lesion side the amount of enzyme per perikaryon was higher on days 1 and 3, approximately the same on day 7, and less on day 12 compared with the single-lesion side. (ii) The conditioning-lesion side displayed a more pronounced decrease of acetylcholinesterase. (iii) 5'-Nucleotidase increased again after a second axotomy and reached the same level of activity as after a single lesion. These data suggest that a conditioning lesion does not simply amplify the ongoing axonal reaction of the cells in a linear fashion, but that it leads to a complex response. The data are in favor of a shorter initial delay prior to the axonal outgrowth which occurs after a conditioning lesion. However, our data could not explain an enhancement of axonal outgrowth velocity after the second operation.

Acetylcholinesterase↗
PubMed1982

Tight junction contact events and temporary gap junctions in the sciatic nerve fibres of the chicken during Wallerian degeneration and subsequent regeneration.

Tight and gap junctions are described on the basis of freeze-fractures in normal chicken sciatic nerves as well as during Wallerian degeneration and subsequent regeneration. 1. Small calibre nerve fibres display a fairly continuous tight junction contact zone in the membranes of the mesaxons, paranodal loops and Schmidt-Lanterman incisures. Large fibres with more than 40 lamellae have only focal tight junction contacts in the mesaxonal membranes. 2. With the onset of Wallerian degeneration (days 2-4 post-crush, distal stump) myelinic tight junctions become arranged as maculae composed of one circular or several polygonally oriented strands that are criss-crossed by other tight junctional strands. These maculae are subsequently found in the membranes of cytoplasmic vacuoles of the Schwann cells, indicating an endocytotic mode of uptake. Tight junctions are not found between the 5th and 6th day after crush. 3. During the proliferation phase of the Schwann cells and the arrangement of these cells into Büngner cell bands (2 to 8 days post-crush) gap junctions appear between the Schwann cells of the bands. These junctions then disappear with the onset of remyelination (8 days post-crush). 4. With the onset of remyelination (from the 8th day onwards) short focal tight junctions appear in the membranes of the outer mesaxons. Shortly thereafter, when the sheaths possess 4 to 8 lamellae, tight junctions also appear in the membranes of the inner mesaxons, the paranodal loops and the cytoplasmic inclusions. The characteristic differences of tight junction elaboration in small versus large nerve fibres are re-established after three months of regeneration. The elaborated tight junctions in small and early remyelinating fibres point to a specific function; in small fibres (versus large fibres) the tight junctions might effect a separation of the intramyelinic extracellular space as a single compartment. The tight junction contacts in early remyelinating fibres support the hypothesis that myelin growth occurs within the myelin spiral and not by a free rotation and elongation of the Schwann cell tongues. It is assumed that the gap junctions between the Schwann cells contribute to the co-ordination of the Schwann cell band formation, which is involved in the guidance of sprouting axons.

Animals↗
PubMed1982

Distribution of REM latencies after sleep interruption in depressive patients and control subjects.

The REM sleep latency of 16 endogenous depressives and 10 normal controls was obtained over a series of nights, once at evening onset of sleep and once after a deliberate sleep interruption at 2:30 AM. Twelve of the patients were studied again during a follow-up some months later, when they were free of depressive symptoms. The patients were classified into Group A (n = 9) if they displayed sleep onset REM episodes (SOREMs) at evening sleep onset, or Group B if they did not have SOREMs at evening sleep onset. Group A patients had significantly more SOREMs after the deliberate sleep interruption than Group B patients, during depression as well as in the symptom-free interval. REM latency appears to depend on several different factors: (a) the predisposition of the person, (b) the time of day, and (c) REM pressure, which seems to increase within a REM-REM interval.

Adult↗
PubMed1978

The development of a zonula occludens in peripheral myelin of the chick embryo. A freeze-fracture study.

Sciatic nerves of chick embryos, 12 to 18 days incubation, were examined in freeze-fracture replicas with special emphasis placed on the development of tight junctional contacts in the myelin sheaths. In stages of beginning myelination short isolated particulate chains (focal tight junctions) appear in fracture faces of the adjacent membranes in the outer myelin lamellae, i.e., the outer mesaxon. In stages of progressing myelination these tight junctional elements elongate and become more numerous. They can also be found in the membranes of the inner mesaxons, the paranodal loops and the intramyelinic cytoplasmic inclusions. In fibers of advanced myelinogenesis a fusion of these isolated tight junctions--either end-to-end or at an angle--gives rise to continuous zonulae occludentes. This contact zone extends in the mesaxonal membranes along the direction of the fiber, whereas in paranodal myelin it acquires a helical course joining the membranes of the paranodal loops. It is proposed that this zonula occludens, which seals the cytoplasmic border of the Schwann cell, separates an intramyelinic from an extramyelinic, extracellular space already during the developmental stages of myelinogenesis.

Animals↗
PubMed1977

In vivo and in vitro formation of the junctional complex in choroid epithelium. A freeze-etching study.

The junctional complex of choroid epithelial cells was studied during in vivo formation, disaggregation after trypsin treatment, and in vitro reaggregation. The in vivo formation begins with the occurrence of amorphous patches of particles followed by the formation of small particulate rows and polygonal-ordered particle assemblies. Further arrangement of the zonula occludens continues with the confluence of particles and smooth contoured ridges. At the 9th day stage a fully developed zonula occludens has developed. In a subsequent step nexus become integrated within the tight junction formation. Disaggregation after trypsination results in fragmentation of the zonulae occludentes. Parts of the disassembling aggregates become incorporated in vacuoles indicating an endocytotic mode of "digestion". The in vitro reconstruction of the zonula occludens proceeds from remnants of the former zonula occludens. On the 3rd to 4th day of cultivation mature tight junctions are visible. In vitro integrations of nexus were observed during a later phase. On the 7th day, cultivated choroid epithelial cells reveal well differentiated junctional complexes consisting of continuous zonulae occludentes and integrated gap junctions.

Animals↗
PubMed1977

The development of membrane specializations in the receptor-bipolar-horizontal cell synapse of the chick embryo retina. A freeze-fracture study.

Retinae of chick embryos and chicks one to six weeks after hatching were examined in ultrathin sections and in freeze-etch specimens. The development of the synaptic contacts between receptor cells and bipolar cells starts at the end of the second week of incubation with the enclosure of the dendritic prolongations, invaginating receptor terminals accompanied by the appearance of electron dense material at the synaptic contact sites. Subsequently receptor terminals become filled with synaptic vesicles which surround the synaptic lamellae that appear on the 16th day of incubation. The application of the freeze-fracture technique demonstrates that the differentiation of the synaptic membranes continues into the first week post hatching. E-fracture faces of the presynaptic membranes are characterized by crater-like structures, called synaptopores. Their number is rather small during incubation and increases after hatching. In the P-fracture faces of the dendrites, which are enclosed by the receptor terminals, small particle aggregations appear on the 16th day of incubation. These small particle clusters increase by the apposition of further particles which become arranged in lines and bring out a lattice-like aspect. This arrangement of particles in the inner part of the cell membrane is the morphological expression of the maturation process. The significance of these aggregations as a postsynaptic receptor for neurotransmitters in excitatory cells is discussed.

Animals↗
PubMed1976

Scanning electron microscopic studies on the development of the chick retina.

Fixed retinae of chick embryos and chicks of the first week after hatching were fractured and examined with the scanning electron microscope. The matrix cells of the retina proliferate up to the beginning of the second week. The migrating cells are oriented in cell cords. This columnar organizaion prevails up to the development of the plexiform layers formed as a consequence of the outgrowth of the dendritic and axonal cell processes. Special attention was paid to the differentiation of the ganglion, bipolar and receptor cells, and the radial fibers (Müller cells). Two main morphological patterns are significant for the organization of the retina during neurogenesis: a)the cell to cell contacts of migrating cells and b)the spatial arrangement of Müller cells which could provide guidelines for migration of neuronal elements.

Animals↗
PubMed1975

Neuronal migration during the early development of the cerebral cortex: a scanning electron microscopic study.

Fixed cerebral vesicles of mouse foetuses were fractured and examined with the scanning electron microscope. This method provides a study of the three dimensional developmental features of the pseudostratified columnar epithelium up to the formation of the early cortex plate. Matrix cells are a cell population of homogeneous shape, however, mitotic cells are easily identified by their spherical form. The external surface of the brain is formed by the closely packed end feet of these cells covered by a basal membrane. The formation of the cortical plate is the result of a continuous cell migration in columnar arrangement towards the pia. Glioependymal cells extend along the whole brain wall and most likely provide guidance for the migrating cell cords. The formation of the so-called migratory zone is a consequence of the growth of the basal and the horizontal prolongations of emigrating cells. The significance of the cell to cell contacts for the neuronal migration processes is discussed.

Animals↗
PubMedDate not supplied

Changes in cytoskeletal protein synthesis following axon injury and during axon regeneration.

Injury to the axons of facial motoneurons stimulates increases in the synthesis of actin, tubulins, and GAP-43, and decreases in the synthesis of neurofilament proteins: mRNA levels change correspondingly. In contrast to this robust response of peripheral neurons to axotomy, injured central nervous system neurons show either an attenuated response that is subsequently aborted (rubrospinal neurons) or overall decreases in cytoskeletal protein mRNA expression (corticospinal and retinal ganglion neurons). There is evidence that these changes in synthesis are regulated by a variety of factors, including loss of endoneurially or target-derived trophic factors, positive signals arising from the site of injury, changes in the intraaxonal turnover of proteins, and substitution of target-derived trophic support by factors produced by glial cells. It is concluded that there is, as yet, no coherent explanation for the upregulation or downregulation of any of the cytoskeletal proteins following axotomy or during regeneration. In considering the relevance of these changes in cytoskeletal protein synthesis to regeneration, it is emphasized that they are unlikely to be involved in the initial outgrowth of the injured axons, both because transit times between cell body and injury site are too long, and because sprouting can occur in isolated axons. Injury-induced acceleration of the axonal transport of tubulin and actin in the proximal axon is likely to be more important in providing the cytoskeletal protein required for initial axonal outgrowth. Subsequently, the increased synthesis and transport velocity for actin and tubulin increase the delivery of these proteins to support the increased volume of the maturing regenerating axons. Reduction in neurofilament synthesis and changes in neurofilament phosphorylation may permit the increased transport velocity of the other cytoskeletal proteins. There is little direct evidence that alterations in cytoskeletal protein synthesis are necessary for successful regeneration, nor are they sufficient in the absence of a supportive environment. Nevertheless, the correlation that exists between a robust cell body response and successful regeneration suggests that an understanding of the regulation of cytoskeletal protein synthesis following axon injury must be a part of any successful strategy to improve the regenerative capacity of the central nervous system.

Actins↗