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W Singer

Publications and source records attributed to W Singer.

At least 145 records · Page 8Linked to original sources
PubMed1991

Synchronization of oscillatory neuronal responses between striate and extrastriate visual cortical areas of the cat.

Recent studies have shown that neurons in area 17 of cat visual cortex display oscillatory responses which can synchronize across spatially separate orientation columns. Here, we demonstrate that unit responses recorded from the posteromedial lateral suprasylvian area, a visual association area specialized for the analysis of motion, also exhibit an oscillatory temporal structure. Cross-correlation analysis of unit responses reveals that cells in area 17 and the posteromedial lateral suprasylvian area can oscillate synchronously. Moreover, we find that the interareal synchronization is sensitive to features of the visual stimuli, such as spatial continuity and coherence of motion. These results support the hypothesis that synchronous neuronal oscillations may serve to establish relationships between features processed in different areas of visual cortex.

Animals↗
PubMed1991

Interhemispheric synchronization of oscillatory neuronal responses in cat visual cortex.

Neurons in area 17 of cat visual cortex display oscillatory responses that can synchronize across spatially separate columns in a stimulus-specific way. Response synchronization has now been shown to occur also between neurons in area 17 of the right and left cerebral hemispheres. This synchronization was abolished by section of the corpus callosum. Thus, the response synchronization is mediated by corticocortical connections. These data are compatible with the hypothesis that temporal synchrony of neuronal discharges serves to bind features within and between the visual hemifields.

Animals↗
PubMed1991

Developmental changes in the susceptibility to long-term potentiation of neurones in rat visual cortex slices.

We investigated with intracellular recordings from rat visual cortex slices whether the susceptibility to undergo long-term potentiation (LTP) is age-dependent and whether it is correlated with the expression of synaptic responses mediated by N-methyl-D-aspartate (NMDA) receptors. Test and tetanic stimuli were applied to the white matter and post-tetanic modifications of the amplitude of postsynaptic potentials (PSPs) were assessed in regular spiking cells of supragranular layers. At 2 weeks of age, the amplitudes of early (8-10 ms post-stimulus) and late (20 ms post-stimulus) PSP-components increased after tetanic stimulation to 137.1 +/- 13.4% and 141.3 +/- 12.1% of the pretetanic controls, respectively. At 3 weeks, potentiation of both PSP-components was less pronounced but still significant, the late component being on average more potentiated than the early one. At 4 weeks, PSPs were no longer potentiated. Bath application of 25 microM DL-2-amino-5-phosphonovalerate (APV), an NMDA receptor antagonist, blocked LTP induction both at 2 and at 3 weeks. We also studied developmental changes of two synaptic responses known to influence the susceptibility of cortical neurones to LTP, the NMDA receptor-mediated excitatory PSP (EPSP) and the initial inhibitory PSP (iIPSP). The amplitude of the APV-sensitive EPSP decreased with age and reached adult values in 4-week-old animals. The iIPSPs were pronounced already at 2 weeks and showed no marked change during further development. The results suggest a close correlation between the susceptibility to undergo LTP and the extent to which NMDA receptor-gated conductances contribute to the synaptic response.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1991

Developmental changes of calcium currents in the visual cortex of the cat.

During a critical period of postnatal development the visual cortex of kittens is susceptible to experience-dependent modifications of neuronal response properties. Evidence is accumulating that these modifications are triggered by a transient neuronal calcium (Ca) influx. To further investigate this issue we measured extracellular Ca concentrations with ion-sensitive microelectrodes and compared the magnitude and the distribution of stimulus-evoked Ca fluxes in slices of the visual cortex of 4- to 5-week-old kittens and of 6-month-old adult cats. Stimulation of the white matter at 15 Hz for 8 s caused transient decreases of the extracellular Ca concentration (delta Cao) in slices of both age groups and in all cortical layers. However, there were developmental changes in the laminar distribution of the delta Cao: in kittens, they were maximal in layer IV whereas in adult cats they were most pronounced in the supragranular layers. The ratios between the amplitudes of delta Cao in layer IV and the supragranular layers were 1.65 +/- 0.26 in kittens and 0.43 +/- 0.2 in adult cats. These changes in laminar distribution resemble the laminar specific decay of neuronal malleability and parallel the developmental redistribution of 1,4-Dihydropyridine-sensitive Ca channels. Because of these correlations we interpret our findings as support for the hypothesis that experience-dependent modifications are triggered by Ca influx.

Aging↗
PubMed1991

The effect of short periods of monocular deprivation on excitatory transmission in the striate cortex of kittens: a current source density analysis.

The goal of this study was to assess changes in synaptic activity in the visual cortex of kittens following brief periods of monocular deprivation. Field potentials evoked by electrical stimulation of both optic nerves were registered in vertical penetrations through areas 17 and 18 of 4-5 week-old kittens which had been monocularly deprived for 2-7 days. In order to assess the laminar distribution of synaptic currents these field potentials were subjected to a current source density analysis. Current source density profiles elicited from the deprived eye differed from those induced from the normal eye in several respects: 1) The amplitudes of the responses showed considerable variation at different recording sites across the tangential dimension of cortex. 2) On the average, sinks and sources were markedly reduced, and this reduction was relatively more pronounced in non-granular than in granular layers. 3) However, in 30% of the tracks the layer IV sink showed no attenuation. It was reduced in 48% of the tracks and completely suppressed in 22% of the tracks. These results indicate that a substantial fraction of the deprived thalamocortical synapses remained functional, but that many of these synaptic events remained subthreshold. The significance of these findings is discussed in the context of recovery processes following reverse suture.

Animals↗
PubMed1991

Neuroscience in the former GDR.

Until 1945, when Germany was subdivided into four occupied territories, scientific traditions and science policy were the same throughout Germany. Then came 45 years of increasing separation and diverging development. Now, the East and West are again formally united and their inhabitants are experiencing, with an intensity that was not anticipated, just how different their countries have become.

Academies and Institutes↗
PubMed1991

Hyperthyroxinemia in major affective disorders.

Ninety-nine patients fulfilling DSM-III criteria for primary major affective disorder, either bipolar or unipolar, were studied. A 12% prevalence of elevated thyroxine levels was found. Three of the 12 hyperthyroxinemia patients also had elevated free thyroxine index. No statistically significant difference in response to antidepressant treatment was observed between the hyperthyroxinemia group and the normal serum thyroxine group.

Adult↗
PubMed1991

Human fetal adenohypophysis: morphologic and functional analysis in vitro.

Pituitaries from 24 human fetuses at 7-20 weeks of gestation were studied in culture to assess hormone release, response to adenohypophysiotropic hormones and cytodifferentiation by electron microscopy in cultures lasting 4-8 days and in some cases up to 28 days. At 7 weeks of gestation, ACTH was released by cultured cells which included recognizable corticotrophs. GH was released by cells cultured from 8- to 9-week fetuses and densely granulated somatotrophs were present in the cultures. alpha-Subunit of glycoprotein hormones was present in cultures from 10-week fetuses and TSH and LH were released from 12-week fetuses. FSH was found in cultures of a 13-week female fetus but not before 14 weeks in cultures from males. The levels of FSH and LH were higher in media from cultures of females than from those of males at all ages from detection to 20 weeks, whereas alpha-subunit was slightly higher in media from males. While cells with features of the glycoprotein hormone cell line were found in cultures from 10-week fetuses, no characteristic thyrotrophs or gonadotrophs were recognized. PRL was not measured in basal incubations before 14 weeks. The amounts of all hormones released were proportional to fetal age and decreased with duration of culture. Cortisol suppressed ACTH release in cultures from 7- to 8-week fetuses. Responsiveness of GH release to GRH/SRIH, of ACTH to CRH, and of FSH to GnRH, was found at 12 weeks; LH stimulation by GnRH and TSH response to TRH were documented at 14 weeks. Increments of gonadotropin release during incubation with GnRH were greater in cultures from females than in those from males. PRL release responded to GRH stimulation and to SRIH inhibition in parallel with GH; this behavior is consistent with production of both hormones by mammosomatotrophs. The onset of hormone release by cultured human fetal pituitaries correlates with the detection of hormones biochemically and immunohistochemically. Responsiveness of fetal adenohypophysial cells to hormonal influences indicates functional maturity early in gestation.

Adrenocorticotropic Hormone↗
PubMed1990

Tangential intracortical pathways and the development of iso-orientation bands in cat striate cortex.

Evidence is accumulating that tangential connections are a prominent feature of cortical organization. In the mammalian visual cortex, these connections appear to be related to columnar systems and theoretical considerations have suggested that they contribute to the development of regularly spaced orientation columns. We tested this assumption and examined whether early cortical lesions affected the formation and layout of the pattern of iso-orientation bands. In the striate cortex of 2-week-old kittens, tangential fiber paths were disrupted unilaterally along the representation of the horizontal meridian either by cuts, or by suction or by implanting pieces of Teflon. At this age, tangential fibers are still growing, orientation selectivity is only poorly developed and 2-deoxyglucose mapping does not yet reveal orientation columns. When the kittens were 7-10 weeks old, the organization of orientation bands was studied with the 2-deoxyglucose technique in flat-mounts of both visual cortices. In addition, kittens from the same litters as the experimental animals, having received the same lesions at the same postnatal day were subjected to neuroanatomical experiments to assess the effect of the lesion on the tangential fibers. These investigations revealed that a small fraction of tangential fibers had grown across the lesion when no mechanical barrier was implanted while disruption of tangential connections was complete in cases who had received Teflon implants. Apart from minor irregularities that were confined to the vicinity of the lesion, the 2-deoxyglucose experiments showed no differences in the pattern of orientation bands between the lesioned and intact hemispheres. In both, the bands extended throughout all cortical layers and their main trajectories were orthogonal to the representation of the vertical meridian. We conclude that at least from two weeks of age onwards, intracortical tangential connections are not necessary for the development of the regular pattern of iso-orientation bands in the striate cortex of cats.

Amidines↗
PubMed1990

Different voltage-dependent thresholds for inducing long-term depression and long-term potentiation in slices of rat visual cortex.

In the hippocampus and neocortex, high-frequency (tetanic) stimulation of an afferent pathway leads to long-term potentiation (LTP) of synaptic transmission. In the hippocampus it has recently been shown that long-term depression (LTD) of excitatory transmission can also be induced by certain combinations of synaptic activation. In most hippocampal and all neocortical pathways studied so far, the induction of LTP requires the activation of N-methyl-D-aspartate (NMDA) receptor-gated conductances. Here we report that LTD can occur in neurons of slices of the rat visual cortex and that the same tetanic stimulation can induce either LTP or LTD depending on the level of depolarization of the postsynaptic neuron. By applying intracellular current injections or pharmacological disinhibition to modify the depolarizing response of the postsynaptic neuron to tetanic stimulation, we show that the mechanisms of induction of LTD and LTP are both postsynaptic. LTD is obtained if postsynaptic depolarization exceeds a critical level but remains below a threshold related to NMDA receptor-gated conductances, whereas LTP is induced if this second threshold is reached.

2-Amino-5-phosphonovalerate↗
PubMed1990

Ocular dominance plasticity and developmental changes of 5'-nucleotidase distributions in the kitten visual cortex.

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the visual cortex of normally reared and monocularly deprived kittens and cats. In normally reared kittens aged between 11 to 44 days, 5'-nucleotidase activity formed a band of intense neuropil staining throughout cortical layer IV of areas 17 and 18. The other layers were almost devoid of reaction product. Between the 4th and 6th week, this band had a patchy appearance in area 17, the center-to-center spacing of 5'-nucleotidase patches being approximately 1 mm. Monocular enucleation accentuated these patches of enhanced 5'-nucleotidase activity or made them reappear at developmental stages at which they had normally faded. Simultaneous visualization of ocular dominance columns by transneuronal transport of intraocularly injected 3H-proline showed that the patches of enhanced 5'-nucleotidase activity coincided with the territories of afferents from the intact eye. With increasing age and normal visual development, the patches disappeared and 5'-nucleotidase activity spread to the supra- and infragranular layers. The adult pattern was characterized by dense staining of all cortical laminae in both areas 17 and 18 and was established at about 8 weeks of age. At approximately 7 weeks of age, when the patches in layer IV had disappeared in the course of normal development, monocular enucleation caused a reappearance of the discontinuous pattern of 5'-nucleotidase activity in layer IV. These results reveal a close relation between the distribution of 5'-nucleotidase and the time course of the developmental phase during which the visual cortex is susceptible to experience-dependent alterations. As suggested by the correlation between sites of enzyme activity and eye dominance columns, the expression of 5'-nucleotidase patches in layer IV appears to be associated with the remodelling of ocular dominance territories that occurs both in normal development and after manipulation of afferent retinal input. Thus, 5'-nucleotidase is likely to serve a function in activity-dependent modifications of cortical circuitry. Moreover, 5'-nucleotidase activity is the only endogenous marker known to date that exhibits a columnar pattern in cat visual cortex.

5'-Nucleotidase↗
PubMed1990

The laminar distribution and postnatal development of serotonin-immunoreactive axons in the cat primary visual cortex.

The laminar distribution and postnatal development of profiles immunoreactive to antibodies directed against serotonin (5-hydroxytryptamine, 5-HT) have been investigated in the primary visual cortex (striate cortex, area 17) of cats. In the adult cat, profiles with serotonin-like immunoreactivity consist exclusively of fibers which exhibit laminar differences in density and predominant orientation. Immunoreactive fibers are dense in layers I-III, less dense in layer V, and sparse in layers IV and VI. In layers I and VI the trajectories of these fibers are mainly tangential to the pial surface; in layers II-V they are predominantly radial and more irregular. The vast majority of immunoreactive fibers consists of fine axons with frequent small varicosities. In addition, there are a few thick axons. In 2-week-old cats, immunoreactive fibers are sparsely distributed through layers II-V. By 4 weeks, fiber density has decreased still further in layer IV and increased in layers I-III. By 6 weeks, the laminar pattern resembles that of adult cats except that fiber density is still lower than in adults. At three months of age, the mature pattern is established.

Aging↗
PubMed1990

Ultrastructure of PkC(II/III)-immunopositive structures in rat primary visual cortex.

In the primary visual cortex of adult rats the cellular and subcellular distribution of protein kinase C isozymes II and III (PkCII/III) was examined by immunohistochemical methods with a monoclonal antibody against PkCII/III. Strong PkC(II/III)-immunoreactivity was found in neurons and astrocytes. Immunopositive neurons exhibited morphological features characteristic for both pyramidal and non-pyramidal cells. They were distributed in layers II through VI but were concentrated in layers II/III. At the electron microscopic level immunoprecipitate was found predominantly in distinct regions of the somata, except the nuclei, and only a few labeled dendrites and axons were seen. Two different patterns of cytoplasmic immunoreactivity could be distinguished. In most neurons, PkC(II/III)-staining was confined to cytoplasmic spots associated with the Golgi complex, while a few neurons exhibited additional labeling in the vicinity of the cell membrane. Moreover, PkC(II/III)-immunoreactivity was present in numerous astroglial processes and in the perikaryal cytoplasm of a subpopulation of astrocytes. The present data provide morphological indications for specific functions of PkC isozymes II and III in neurons as well as in astrocytes.

Animals↗
PubMed1990

A comparison of triiodothyronine and thyroxine in the potentiation of tricyclic antidepressants.

Several studies suggest that small amounts of triiodothyronine (T3) will convert tricyclic antidepressant nonresponders into responders within a few days to a few weeks. As thyroxine (T4) is converted to T3 to have its physiological effect, it has been assumed that T4 would have a similar antidepressant effect to that of T3. We carried out a randomized, double-blind evaluation of the antidepressant-potentiating effect of T3 as compared with T4. Significantly more patients responded to 3 weeks of T3 as compared with T4 potentiation. Small but significant differential effects of the two thyroid hormones were noted on the Hamilton Rating Scale for Depression.

Adult↗
PubMed1990

Excitatory amino acid receptors and synaptic plasticity.

Excitatory amino acid receptors are the mediators of synaptic transmission at many synapses that can undergo use-dependent modifications of synaptic efficiency. They also play an essential role in the induction of these plastic changes. Graham Collingridge and Wolf Singer describe how NMDA receptors can endow synapses with hebbian-like properties and discuss how these may be used by vertebrates for associative learning and experience-dependent modifications of synaptic connections during development. The role of AMPA receptors in the maintenance of long-term potentiation is also discussed.

Humans↗
PubMed1990

The effect of tricyclic antidepressants on basal thyroid hormone levels in depressed patients.

The effect of tricyclic antidepressant treatment on basal thyroid hormone levels was evaluated in 28 subjects with primary major depression. In the total group, tricyclic antidepressant treatment was associated with significant reductions in measures of thyroxine. Furthermore, responders to antidepressant treatment had significantly greater decrements in thyroxine and the free thyroxine index as compared with nonresponders. This finding appears consistent with the effects of a wide range of antidepressant treatments on thyroid function tests.

Adult↗