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Biomedical subjects

W Wesemann

Publications and source records attributed to W Wesemann.

At least 73 records · Page 4Linked to original sources
PubMed1987

Automatic infrared refractors--a comparative study.

In order to determine the performance of seven automatic infrared (IR) eye refractors, measurements have been conducted on a model eye as well as on normal subjects and patients under standardized conditions. Concerning the model eye, a range of measurement slightly smaller than specified and linearity errors have been detected on several instruments. Using a group of 55 normal ametropic subjects, the results of the automatic refraction were compared to the results of a conventional subjective examination. The spherical equivalent differed by less than 0.51 D in more than 80% of all cases on all instruments. The error of the cylinder power was smaller than 0.51 D in more than 90% of all cases. Larger errors were found on patients with intra ocular lenses, aphakic eyes, or scattering eye media. In each of these groups the automatic refraction was at times either impossible or yielded a wrong result.

Aphakia↗
PubMed1987

Incoherent image formation in the presence of scattering eye media.

Incoherent image formation in human eyes that have scattering eye media is investigated as a function of the particle size and the optical density of the scattering medium and for test targets that differ in form and size. For single scattering by large particles (much greater than lambda), a point-spread function and the associated modulation-transfer function of the scattered light are derived from diffraction theory. It is shown that object structures with low spatial frequencies are also imaged by the scattered light. Following single scattering by small particles and/or multiple scattering, the scattered light forms an approximately uniform background. Consequently, the retinal contrast is reduced regardless of spatial frequency. The image quality is, contrary to what is found in normal image formation, extremely sensitive to the form and size of the test target. It is shown that the optimal readability of white-on-black letters is obtained at intermediate spatial frequencies. For an extended layer of arbitrary optical density and particle size, the influence of multiple scattering is approximated by using Hartel's scattering theory. It is shown that wavelength has only a small influence on retinal contrast for scattering by particles greater than lambda.

Humans↗
PubMed1986

Modern instruments for subjective refraction. A comparative study.

In a comparative study, subjective refractions were carried out on 115 normal subjects and 118 patients with four instruments (Humphrey Vision Analyzer, Möller/CooperVision Visutron, Reichert SR-IV, Rodenstock/Coburn Phoromat). The accuracy of the prescriptions obtained, the visual acuity results and the measurement time required were analyzed. The highest accuracy was obtained with the remote-controlled phoropters Phoromat and Visutron. The fastest instrument was the SR-IV.

Cataract↗
PubMed1986

[Changes in the concentration of pilocarpine eyedrops in normal storage].

The accommodative myopia induced by pilocarpine eye drops served as an indicator for the pharmacological activity. In a case of pigment glaucoma a reproducible 50% decay of the accomodative myopia was measured in the course of two weeks after opening an original bottle. Correlated to the reduction in accommodative myopia, a rise in intraocular pressure was observed. This may be due to an active principle decay caused by moderate temperatures.

Accommodation, Ocular↗
PubMed1986

Circadian rhythm of serotonin binding in rat brain--I. Effect of the light-dark cycle.

High affinity serotonin binding to rat brain membranes showed a circadian rhythm with minimal binding at 1000 and a maximal binding at 0000. Brain serotonin levels were almost inverse to the rhythm of serotonin binding. Under reverse light-dark conditions, lights on from 1900 to 0700, a significant phase shift in serotonin binding and concentration of about 8-10 hr was found. The adaptation of the rats to the inverse light-dark cycle was ascertained by plasma ACTH and corticosterone assay.

Adaptation, Physiological↗
PubMed1986

Circadian rhythm of serotonin binding in rat brain--II. Influence of sleep deprivation and imipramine.

Sleep deprivation (SD) modified the circadian rhythm of specific high affinity serotonin (5-HT) binding to rat brain membranes. In control rats a 24-hr rhythm was evident with a trough at 1000-1200 and a nadir at 0000. During the last 26 hr of a 49 hr SD period, trough and peak values were delayed by 4-6 hr. The 24-hr mean binding was significantly (P less than 0.001) different from that of controls. If sleep deprivation was followed by recovery sleep (RS), the normal rhythm of 5-HT binding was obtained already within 1 hr after SD. The effects of SD and RS were ascertained by plasma ACTH and corticosterone assay. No significant change in the hormone rhythms were observed through the mean plasma level of ACTH and corticosterone were enhanced to about 180 and 150%, respectively. Chronic treatment with the antidepressant imipramine resulted in a decrease of the 24-hr mean 5-HT binding by about 50% and a 2-hr delay of peak and trough values. Imipramine treatment decreased the peak value of 5-HT concentration at 1000 to about 65% and appears to abolish the rhythm of 5-HT concentration.

Adrenocorticotropic Hormone↗
PubMed1985

Solubilized ketanserin binding sites from pig platelet membranes.

Plasma membranes of pig platelets were isolated and subjected to solubilization with digitonin. Binding of [3H]ketanserin to the solubilized membrane fraction, optimal at pH 7.5, was time and protein dependent and was greatly reduced by increasing ionic strength of the incubation buffer. Saturation analysis and inhibition of binding with various 5-HT2 antagonists showed the presence of two binding sites with high and low affinity, respectively. High affinity binding to solubilized membrane proteins correlated well with that found in native membranes with regard to the dissociation constant KD (1.6 and 1.2 nM, respectively) and the displacement by 5-HT2 antagonists. Binding to this site was not inhibited by the dopamine antagonist haloperidol which, however, displaced [3H]ketanserin bound to the low affinity site. At present the nature of the low affinity binding site (KD = 71 nM) is not well understood. Centrifugation on sucrose gradients revealed only one peak of [3H]ketanserin binding corresponding to the molecular weight of catalase (232,000 Da), thus probably reflecting a close association of the two binding sites.

Animals↗
PubMed1985

Characterization of 5-hydroxytryptamine binding sites in the plasma membrane of pig blood platelets.

Plasma membranes were isolated from pig platelets after glycerol facilitated lysis by sucrose density gradient centrifugation. The purity of the membrane fraction was followed by electron microscopy, gel electrophoresis and analysis of acid phosphatase (EC 3.1.3.2) and phosphodiesterases (EC 3.1.4.1). (3H)5-Hydroxytryptamine ([3H]5-HT) was bound to two saturable binding sites of the membranes. The KD value for the high affinity sites was 0.85 nM and for the low affinity sites 0.48 microM. With the exception of tryptamines little or no (3H)5-HT was displaced by serotonin antagonists and uptake inhibitors suggesting another type of binding than that of 5-HT1. Apparently, enhancement of binding in the presence of Na+ was due to stimulation of an uptake process. Binding of (3H)ketanserin and (3H)LSD to pig platelet membranes showed the characteristics of 5-HT2 binding sites previously identified in rat brain. Since ketanserin inhibited 5-HT induced aggregation of pig platelets (IC50 = 14.2 nM), the ketanserin binding sites can be classified as 5-HT2 receptors. The functional properties of these binding sites and their density in pig platelets as compared with brain membranes may motivate studies on 5-HT2 receptors in pig platelets as models for those in nerve endings.

Animals↗
PubMed1985

A new laser interferometer for the stimulation of pattern-reversal visual evoked potentials.

A laser interferometer for visual-evoked-potential (VEP) stimulation that allows a rapid pattern reversal in less than 0.5 ms and a continuous variation of the spatial frequency of the pattern is described. The interferometer is applied for the assessment of objective visual acuity. The Fourier transform of the VEP response to the rapid pattern reversal shows an extremely small bandwidth.

Evoked Potentials, Visual↗
PubMed1985

Daytime noise stress and subsequent night sleep: interference with sleep patterns, endocrine and neurocrine functions.

The effects of strong daytime noise stress on subsequent undisturbed night sleep were studied in six male volunteers. They slept for seven consecutive nights in the laboratory, two nights being preceded by an 8 h exposure to 83 dB (A) pink noise. Continuously during all nights EEG, EOG, EMG, ECG and respiration were recorded. Additionally, during five nights, blood samples were taken every 30 min by an indwelling venous catheter for the determination of ACTH, hGH, PRL, TRP, 5-HT and 5-HIAA. After daytime noise load, increased sleep stage 4 stability, partly elevated hGH and PRL levels and decreased levels of the metabolites of the serotonergic system were found. This result may be explained by the assumption that high daytime noise stress is an additional load for the CNS which demands an intensification of recovery processes during the sleep of the subsequent night.

Adrenocorticotropic Hormone↗
PubMed1985

Isolation of mouse megakaryocytes. I. Separation of two fractions enriched in different maturational stages.

Megakaryocytes (MK) were isolated from mouse bone marrow by centrifugation on discontinuous gradients of isotonic albumin or Percoll and characterized by acetylcholinesterase (AChE) staining. The apparent density distributions of MK varied greatly depending upon the nature of the gradient medium and the composition of the cell suspension buffer while the density range of the other bone marrow cells remained largely unchanged. The present findings also indicate that the unusual morphological and functional characteristics of MK may underlie the observed shift in their density profile. Thrombocytopoietic stimulatory factor (TSF) was administered to mice 18 h before killing to elevate the normally low numbers of earlier MK in the bone marrow and to improve the yield of immature MK during the subsequent isolation procedure. Cells belonging to earlier stages in maturation were separated from the more mature ones on discontinuous Percoll density gradients, providing a basis for further investigation of MK development.

Acetylcholinesterase↗
PubMed1985

Isolation of mouse megakaryocytes. II. Functional and metabolic aspects of two different maturational stages.

Functional and metabolic parameters were compared in immature and mature megakaryocytes (MK) isolated from bone marrow of the mouse by Percoll density gradient centrifugation. Comparison of metabolic parameters revealed that the ability to take up serotonin was equal in both megakaryocytic fractions. The uptake of radioactively labeled adenine was increased in immature MK as compared with mature MK. Total adenosine triphosphate (ATP) content was enhanced during the differentiation from MK to platelets: immature MK: 5, mature MK: 29, platelets: 63 nmol ATP/mg protein. Since MK, like platelets, released ATP upon stimulation, thrombin-induced release was used as functional parameter to differentiate between secretable and non-secretable ATP compartments. Upon thrombin stimulation both MK fractions released about 25% of their total ATP as compared with about 40% secreted by platelets. Although the actual size of the non-secretable ATP pool was different in mature MK and platelets, they demonstrated similar percentages of retained ATP (20-25%) in contrast to a much higher retention (62%) by immature MK. The present findings suggest that the bulk of ATP is acquired by immature MK as they gain maturity, although some ATP is still obtained during even later stages of differentiation. This growing ATP pool could be attributed mainly to the enlargement of the secretable compartment during the transition of immature MK to mature MK.

Adenine↗
PubMed1983

Effects of endotoxin treatment on the differentiation of guinea pig megakaryocytes to blood platelets.

The effect of endotoxin treatment (30 micrograms/kg body weight) on megakaryocyte development and platelet production in guinea pigs was investigated. A moderate thrombocytopenia was noted at 24 h after endotoxin administration. Recovery was observed at 48 h when the platelet count had almost reached the normal level. A significant increase in platelet production was obtained at 48 h, indicated by an enhancement in incorporation of labelled sulphate into platelets and also by an increase in the number of circulating heavier platelets. Megakaryocytes were classified into different developmental stages - megakaryoblast, promegakaryocyte, megakaryocyte - using standard morphological criteria (size, shape of nucleus, nucleus/cytoplasm ratio). The number of mature megakaryocytes increased at 24 and 48 h after endotoxin treatment. It was possible to distinguish between two different types of mature megakaryocytes - early mature and mature megakaryocytes - by the presence of a methanol-sensitive acid phosphatase. This enzyme is found mainly in mature, presumably platelet-forming, megakaryocytes and in platelets. The increased number of mature megakaryocytes at 24 h was due to an enhancement in the number of early mature megakaryocytes, whereas the change at 48 h was due largely to an increased number of mature, platelet-forming megakaryocytes. Megakaryocytes were isolated from bone marrow of guinea pigs by Percoll density-gradient centrifugation and incubated with radioactively labelled leucine. Compared with the untreated controls megakaryocytes isolated 24 h after endotoxin treatment took up and incorporated higher amounts of leucine into protein, indicating a higher metabolic capacity of the early mature megakaryocytes. No alteration in the ploidy distribution of megakaryocytes was noted after endotoxin treatment.

Acid Phosphatase↗
PubMed1983

Serotonin binding in rat brain: circadian rhythm and effect of sleep deprivation.

Crude membrane fractions isolated from rat brain were used to measure specific serotonin (5-HT) binding. In untreated animals a 24 hours rhythm in 5-HT binding was evident. Sleep deprivation (SD) was applied to enhance sleep pressure. After 12, 24, and 72 hours SD the high affinity 5-HT binding, KD1 = 1-3 nM, remained unchanged, the apparent dissociation constant of the low affinity 5-HT binding, KD2 = 20-30 nM, was found to be enhanced almost by factor 2. The number of binding sites were only moderately affected by SD. If SD was followed by 1 or 4 hours recovery sleep, the dissociation constant KD2 was decreased towards control values. The brain levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) were not significantly changed immediately after 72 hours SD. A statistically significant increase was found only for 5-HIAA 4 hours after 72 hours SD. The results are consistent with the hypothesis that changes in the sensitivity of 5-HT binding may be involved in the regulation of the sleep-waking cycle.

Animals↗
PubMed1983

[Pharmacodynamics and pharmacokinetics of memantine].

The adamantane derivative memantine (1-amino-3,5-dimethylaminoadamantane, D-145, Akatinol) is clinically used as well in the therapy of neurogenic motor diseases (e.g. spasticity) as in the treatment of cerebral disorders like coma, cerebrovascular and geronto-psychiatric disturbances. The aim of the paper is to summarize experimental evidences that may help to explain the clinical observations. Biochemical, pharmacological, and electrophysiological studies show that memantine interferes with the metabolism of the transmitters dopamine, noradrenaline (norepinephrine), and serotonin and modulates synaptic transMission. In order to explain the antispastic activity of memantine, a spinal action must be assumed in addition to the supraspinal effect on transmitter systems. Since memantine reduces the membrane resistance as well as the membrane conductance of sodium, potassium, and chloride ions, it is very likely that memantine Is directly involved in the generation of action potentials.

Amantadine↗