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Biomedical subjects

W Singer

Publications and source records attributed to W Singer.

At least 289 records · Page 16Linked to original sources
PubMed1973

Fine structure and morphogenesis of spironolactone bodies in the zona glomerulosa of the human adrenal cortex.

Numerous spironolactone bodies have been detected in the zona glomerulosa cells of the adrenal cortex of a 36-year-old spironolactone-treated woman whose non-tumorous right adrenal gland was removed surgically because of primary hyperaldosteronism. Electron microscopy revealed spherical laminated whorls which consisted of a central core composed of an amorphous electron-dense material surrounded by numerous smooth-walled concentric membranes. Continuous with and deriving from the endoplasmic reticulum, they were present in viable cells and were not associated with ultrastructural features indicating cellular injury. Cytoplasmic inclusions similar to spironolactone bodies can be detected in other organs after the administration of various compounds. Thus, they can be regarded as neither specific to spironolactone treatment nor exclusively inducible in the zona glomerulosa of the adrenal cortex.

Adrenal Glands↗
PubMedDate not supplied

Eye alignment and cortical binocularity in strabismic kittens: a comparison between tenotomy and recession.

Interocular alignment was assessed by corneal light reflex photography in 15 normal and 26 strabismic kittens. Strabismus was induced at 3-4 weeks of age by severing one extraocular muscle (tenotomy), by cutting and reinserting the muscle at another position on the ocular globe (recession), or by combining recession of the medial rectus muscle with resection of the lateral rectus muscle of the same eye. Nineteen strabismic and five normal kittens were followed longitudinally from 12 days to about 6 months of age. Three out of six longitudinally followed tenotomized cats and six out of the 13 recessed cats conserved their postoperative ocular deviation throughout the testing period ("large-angle strabismics"). Three tenotomized and seven recessed cats showed a transient deviation for 1-2 weeks after surgery, after which the interocular deviation diminished to values found in normal cats ("microstrabismic" cats). Both recessed-resected cats showed a transient interocular deviation. In spite of their different developmental histories, all cats showed a clear breakdown of binocularity in area 17. Large-angle strabismics showed a dominance of the non-operated eye, while in microstrabismic cats, both eyes were equally effective in driving cortical cells. It thus appears that a transient strabismus is sufficient to produce a reduction of binocularity in area 17.

Animals↗
PubMedDate not supplied

Synchronization of neuronal responses in the optic tectum of awake pigeons.

Multiunit activity was recorded in the optic tectum of awake pigeons with two electrodes at sites varying in depth and separated by 0.3 to 3.0 mm. Autocorrelation and cross-correlation functions were computed from the recorded spike trains to determine temporal relationships in the neuronal firing patterns. Cross-correlation analysis revealed that spatially separate groups of cells in the tectum show synchronous responses to a visual stimulus. Strong synchronization occurred in both superficial and deep layers of the tectum, in general with zero-phase shift. The response synchronization in the avian optic tectum resembles that observed in the mammalian cortex, suggesting that it may subserve common functions in visual processing.

Action Potentials↗
PubMedDate not supplied

Modulation of visual cortical plasticity by acetylcholine and noradrenaline.

During a critical period of postnatal development, the temporary closure of one eye in kittens will permanently shift the ocular dominance (OD) of neurones in the striate cortex to the eye that remains open. The OD plasticity can be substantially reduced if the cortex is infused continuously with the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) during the period of monocular deprivation, an effect that has been attributed to selective depletion of cortical noradrenaline. However, several other methods causing noradrenaline (NA) depletion leave the plasticity intact. Here we present a possible explanation for the conflicting results. Combined destruction of the cortical noradrenergic and cholinergic innervations reduces the physiological response to monocular deprivation although lesions of either system alone are ineffective. We also find that 6-OHDA can interfere directly with the action of acetylcholine (ACh) on cortical neurones. Taken together, our results suggest that intracortical 6-OHDA disrupts plasticity by interfering with both cholinergic and noradrenergic transmission and raise the possibility that ACh and NA facilitate synaptic modifications in the striate cortex by a common molecular mechanism.

Acetylcholine↗
PubMedDate not supplied

Long-term potentiation and NMDA receptors in rat visual cortex.

In the hippocampus, which is phylogenetically older than the cerebral neocortex, high frequency stimulation of afferent pathways leads to long-term potentiation (LTP) of synaptic transmission. This use-dependent malleability is of considerable interest because it may serve as a substrate for memory processes. However, in the neocortex, whose involvement in learning is undisputed, attempts to demonstrate LTP have remained inconclusive. Here we use intracellular recording techniques to show that LTP can be induced by high frequency stimulation of the optic radiation in slices of the visual cortex of adult rats. We identify as a necessary prerequisite for the induction of LTP the activation of the membrane channel that is associated with the NMDA (N-methyl-D-aspartate) receptor. Selective blockade of this receptor system with DL-2-amino-5-phosphonovalerate consistently prevents LTP as in most hippocampal pathways. In most cortical neurons the activation of the NMDA mechanism and hence the induction of LTP in these experiments requires a concomitant reduction of GABAergic inhibition by low doses of the GABAA antagonist bicuculline. This indicates that in the neocortex the activation threshold of the NMDA-mechanism and consequently the susceptibility to LTP, are strongly influenced by inhibitory processes.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Laminar and columnar organization of immunoreactivity for calcineurin, a calcium- and calmodulin-regulated protein phosphatase, in monkey striate cortex.

Protein phosphorylation and dephosphorylation play an important role in neuronal signal transduction. In this study the distribution of calcineurin, a calcium/calmodulin-dependent protein phosphatase, was investigated in the striate cortex of two Old World monkeys, Macaca fascicularis and Papio anubis, using a well-characterized, affinity-purified polyclonal antibody to calcineurin. In order to relate the calcineurin distributions to established cytochemical markers, adjacent sections were processed for the visualization of cytochrome oxidase. The staining patterns obtained from the two species were remarkably similar. The results indicate that (1) monkey striate cortex exhibits strong calcineurin-like immunoreactivity that is present both in the neuropil and in neurons, most of which have characteristics of pyramidal cells; (2) the distribution of calcineurin is laminar specific; and (3) it is complementary to that of cytochrome oxidase activity with respect to both its laminar and its tangential pattern. In sections perpendicular to the cortical lamination calcineurin immunoreactivity is high in layers II and III, reduced in layer IVA, nearly as dense as in supragranular layers in layer IVB, minimal in layer IVC, and again enhanced, but not as much as in supragranular layers, in layers V and VI. In addition to these lamina-specific variations, the density of calcineurin-like immunoreactivity exhibits a periodic modulation along trajectories parallel to the pial surface that is most marked in layer III but also discernable in infragranular layers. Accordingly, in tangential sections through supragranular layers the calcineurin distribution is mosaic-like with patches of high density corresponding to cytochrome-poor regions (interblob regions) and zones of low density corresponding to areas of high cytochrome oxidase activity (blobs).

Animals↗