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Biomedical subjects

M Kessler

Publications and source records attributed to M Kessler.

At least 37 records · Page 2Linked to original sources
PubMed1992

Intraperitoneal pressure, peritoneal permeability and volume of ultrafiltration in CAPD.

Peritoneal permeability (PP), hydrostatic intraperitoneal pressure (IPP) and the overall volume of ultrafiltration (UF) were measured in 23 patients treated by CAPD under stable conditions. PP, IPP and UF were measured during the same exchange with a 2-liter bag with 3.86% glucose, dwell time of 2 hours. PP was evaluated with 3 indices: glucose peritoneal desaturation at 2 hours, urea peritoneal saturation at 2 hours, and crossing time of glucose and urea peritoneal equilibration curves. IPP was evaluated at inspiration (IPPinsp) and at expiration (IPPexp)-giving IPPmean-by measuring the height of the dialysis fluid in the PD line under atmospheric pressure, with point zero located on the axillary line of the subject in strict supine position. Net UF volume was inversely correlated with IPPmean. The net UF volume was strongly affected by IPP since a 1 cmH2O increase in IPPmean caused a decrease of 74 ml in global UF in 2 hours, probably by modification of the lymphatic reabsorption and perhaps of the transcapillary UF.

Adult↗
PubMed1992

Surface EMG topography and pain distribution in pre-chronic back pain patients.

The relationship between surface EMG recordings from paraspinalis recording sites and subjective pain ratings were examined in a group of pre-chronic back pain patients. thirty-eight back pain patients without major orthopedic diagnosis and a pain duration between 2 to 6 months participated in a three week long subjective pain rating. Following the completion of their pain diary, the paraspinal sites were assessed under the "static" postural conditions of sitting and standing using an EMG scanning procedure. Results of the correlational analysis revealed significant and positive relationships between pain and muscle activity in the upper back (Trapezius, T1 paraspinalis sites) and significant but negative relationships between erector spinae activity (L3 paraspinalis site) and pain. When considering etiological factors of pre-chronic back pain, the results support both the organicity model for upper back, as well as the biomechanical model for the lower back.

Adult↗
PubMed1991

Tat transactivation of the human immunodeficiency virus type 1 promoter is influenced by basal promoter activity and the simian virus 40 origin of DNA replication.

We examined the activation of transcription from the human immunodeficiency virus type 1 (HIV-1) promoter by the viral Tat protein in a transient expression system. Plasmids contained a HIV-reporter gene cassette and a simian virus 40 origin of DNA replication. Run-on assays of transcription complex distribution and analysis of cytoplasmic RNA accumulation confirmed that Tat is able to activate transcription by two mechanisms: by increasing the rate of transcriptional initiation and the efficiency of transcriptional elongation. The degree to which Tat stimulated initiation is determined by the basal level of HIV-directed transcription, which is influenced by the presence [corrected] of the simian virus 40 replication origin. Tat functions primarily to increase the efficiency of elongation when the origin is present and the basal level of transcription is high [corrected]. On the other hand, Tat functions primarily to increase the rate of initiation when the origin is absent [corrected] and the basal level of transcription is 10-fold lower. These studies suggest that the site of integration of the virus into the cellular genome may significantly affect the level of expression from the HIV promoter and consequently the pathobiology of the virus.

Animals↗
PubMed1991

Failure to detect changes in AMPA receptor binding after long-term potentiation.

Recent experimental evidence suggests that changes in (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/quisqualate receptor mediated currents account for the increase in synaptic responses known as long-term potentiation (LTP). These changes could occur in several parameters including receptor density, binding affinity or in the kinetics and conductance properties of the receptor channel. In this study we tested if LTP modifies the affinity or overall number of binding sites. Hippocampal slices were stimulated electrically in at least 12 locations in the stratum radiatum of CA1 in order to induce potentiation in a maximal number of Schaffer-collateral axons. Sections were then prepared from the middle of the slices, incubated with [3H]AMPA or [3H]CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) and processed for autoradiography. To correct for variability among sections, binding in CA1 was expressed relative to that in the molecular layer of the dentate gyrus, which did not receive potentiation. No differences were observed in the absolute or relative amount of binding except for a small decrease of about 5% in [3H]AMPA binding that was not statistically significant. Although the percentage of synapses which were potentiated by our stimulation procedure cannot be determined with certainty, it is unlikely that an increase in the number or affinity of AMPA receptors could explain the 50% LTP effect typically observed in slices.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1991

A brief period of hypoxia causes proteolysis of cytoskeletal proteins in hippocampal slices.

Breakdown products (BDPs) resulting from the partial proteolysis of spectrin were examined in hippocampal slices after periods of hypoxia lasting for 5 or 10 min. The concentration of a approximately 155 kDa BDP increased nearly twofold after 5 min of hypoxia; further increases were not seen with 10 min episodes or 10 min of hypoxia followed by reoxygenation. The hypoxia-induced proteolysis was blocked by prior infusion of a newly introduced inhibitor of calpain (calpain inhibitor I, 200 microM). Together with previously published data showing improved recovery of hippocampal slices from hypoxia in the presence of calpain inhibitors, these data suggest that activation of calpain may contribute significantly to the pathophysiology of ischemia.

Animals↗
PubMed1991

A 21-base pair DNA fragment directs transcription attenuation within the simian virus 40 late leader.

Transcription through the late simian virus 40 (SV40) sequences have been examined in vivo and in vitro for identifying attenuation signals involved in regulating late RNA transcription. In addition to the previously identified and characterized attenuator 1 situated 93 nucleotides downstream from the major late transcription start site, a second attenuator, attenuator 2, situated 55 nucleotides downstream from it, has been identified. Attenuated transcripts mapping to this site have been observed in vivo as well as in several different in vitro transcription systems. The signal inducing transcription attenuation has been localized to a 21-base pair DNA fragment and has been found to function independently of the promoter directing transcription or its distance from the transcription start site. Furthermore, this attenuator, unlike that preceding it, does not include a region of dyad symmetry or A+T-rich sequences. Also, similar to the adenovirus 2 attenuator, but in contrast to SV40 attenuator 1, the block to elongation at the SV40 attenuator 2 appears to be modulated by the general transcription factors. It is concluded that in SV40 there are at least two types of attenuators: one that is dependent on RNA secondary structure and a second that is sequence specific and is modulated, at least in part, by the general transcription factors.

Animals↗
PubMed1991

Selective effects of aniracetam across receptor types and forms of synaptic facilitation in hippocampus.

Aniracetam reversibly increased synaptic responses mediated by the AMPA but not the NMDA subclass of glutamate receptors in hippocampus and was considerably more potent than structurally similar nootropics. The drug had greater effects on field excitatory postsynaptic potentials (EPSPs) in the dentate gyrus and CA1 region than it did in the CA3 region, suggesting that it differentiates between variants of the AMPA receptor. Ligand binding to glutamate receptors in synaptosomal membrane fractions was minimally changed by aniracetam. Finally, the percent facilitation produced by aniracetam in the CA1 region was not reduced by any of three treatments (4-aminopyridine, changes in extracellular calcium concentrations, paired-pulse stimulation) that affect release but, in accord with a previous report, was substantially decreased by long-term potentiation. These results support the conclusion that aniracetam selectively increases the conductance of a subgroup of synaptic AMPA receptors in hippocampus and suggest that receptor changes underlie the expression of long-term potentiation.

4-Aminopyridine↗
PubMed1991

Spectrometric measurements in the anterior eye vasculature of the albino rabbit--a study with the EMPHO I.

Intracapillary haemoglobin oxygenation (oxygen saturation) and haemoglobin concentration (corresponding with blood volume) were measured in different regions of the albino rabbit anterior eye segment using the Erlangen micro-lightguide spectrophotometer (EMPHO I). The tip of the microlightguide (active diameter 210 microns, cover diameter 0.5 mm) was placed in the vitreous by a goniometric mounting and controlled by a micromanipulator. After stepwise elevation of intraocular pressure (IOP) the haemoglobin oxygenation decreased slightly in the iris at an IOP-level of 60 mmHg, whereas in the three regions of the ciliary processes and in the peripheral choroid haemoglobin oxygenation did not decrease until values of 80 mmHg were applied. In contrast, haemoglobin concentration decreases when the IOP increases in all regions except in the pars plana where the haemoglobin concentration increased at 40 and 60 mmHg. The most pronounced reactive hyperaemia was found in the major ciliary processes. Quite passive changes of haemoglobin concentration were seen in the peripheral choroid. Effective regulatory mechanisms must exist which result in IOP-independent (20-60 mmHg) haemoglobin oxygenation, whereas pronounced changes in intracapillary haemoglobin concentration were observed. The decay of both parameters at IOP 80 mmHg is indicative of an exhaustion of their regulatory capacity. Epinephrine topically applied onto the conjunctival sac or injected into the common carotid artery led to a short-term decrease of haemoglobin concentration and, later, a hyperaemic response. A short-term haemoglobin deoxygenation was found especially in the major ciliary processes.

Animals↗
PubMed1991

Image correlation of MRI and CT in treatment planning for radiosurgery of intracranial vascular malformations.

Magnetic resonance imaging (MRI) has been incorporated with stereotactic cerebral angiography and computed tomography (CT) in the treatment planning process of heavy ion radiosurgery of intracranial arteriovenous malformations (AVM's). Correlation of the images of the AVM and normal tissue on each of these neuroradiological imaging modalities is achieved by means of fiducial markers. The computerized transfer of angiographic information to the CT images regarding the size, shape, and location of the abnormal vasculature has been described in an earlier report. A separate computer program calculates a fit between individual fiducial markers on the CT and MR images that enables the transfer of contours between the two imaging modalities. The MR images aid in the determination of the 3-dimensional shape of the AVM, adding to the information derived from the two angiographic projections. Currently, MRI cannot replace cerebral angiography in delineating the entire arterial phase of the AVM. Magnetic resonance imaging is invaluable in the treatment planning of angiographically-occult AVM's, determining the location, size, and shape of the volume to be treated. Correlation of the CT and MRI images allows for the transfer of CT-calculated isodose contours to the MRI images to aid in the determination of optimal treatment plans.

Adolescent↗
PubMed1991

Reoperation for secondary hyperparathyroidism in chronic renal failure.

From 1972 to 1987, 112 parathyroidectomy (PTX) operations were carried out in 105 haemodialysis or transplant patients by the same surgeon. Twelve had to be reoperated on (19 operations in all) for persistent (9 cases) or recurrent (3 cases) hyperparathyroidism. In six patients morphological tests (echography and technetium-thallium scintigraphy) contributed usefully by detecting parathyroid masses. Repeated surgery was finally effective in nine cases.

Adult↗
PubMed1991

Acquired renal cystic disease mimicking adult polycystic kidney disease in a patient undergoing long-term hemodialysis.

Acquired renal cystic disease (ARCD) is defined as the development of multiple cysts in the renal cortex and medulla in patients with chronic renal failure who are free from congenital polycystic kidney disease. ARCD develops generally in contracted kidneys. We report a case of grotesque enlargement of a single kidney in a patient who had been receiving hemodialysis for 18 years. Although the exact causes of ARCD are not known, 3 factors may contribute to the development of nephromegaly; the sex, the duration of hemodialysis and previous unilateral nephrectomy. As in polycystic disease, when the involved kidney reaches considerable size, ARCD may have a favorable effect on anemia caused by chronic renal failure.

Adult↗
PubMed1991

Constitutional delay of growth and puberty: do they really reach their target height?

We compared the final adult height (FH) of patients with classic constitutional delay of growth and puberty with their target height (TH) and with the height prediction by the Bayley-Pinneau method (BP). 20 patients and their parents were included in our study: 6 females (mean age 19.1 years) and 14 males (mean age 20.6 years). No significant difference could be detected between TH, FH and BP prognosis. This is in contrast to recent studies using height data partly obtained by self-estimation. We measured our patients and their parents ourselves and were accurately able to calculate their genetically determined TH. This proceeding could explain our results. Our study shows that adolescents with true constitutional delay do not need treatment and that height prediction seems to be accurate.

Adolescent↗