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Biomedical subjects

M Kessler

Publications and source records attributed to M Kessler.

At least 271 records · Page 15Linked to original sources
PubMed1990

The nature and causes of hippocampal long-term potentiation.

One of the most fascinating features of the hippocampus is its capacity for plasticity. Long-term potentiation (LTP), a stable facilitation of synaptic potentials after high-frequency synaptic activity, is very prominent in hippocampus and is a leading candidate memory storage mechanism. Here, we discuss the nature and causes of LTP and relate them to endogenous rhythmic neuronal activity patterns and their potential roles in memory. Anatomical studies indicate that LTP is accompanied by postsynaptic structural modifications while pharmacological studies strongly suggest that LTP is not due to an increase in presynaptic transmitter release. In field CA1, LTP induction appears to be triggered by a postsynaptic influx of calcium through NMDA receptor-linked channels. Possible roles of several calcium-sensitive enzyme systems in LTP are discussed and it is argued that activation of a calcium-dependent protease (calpain) could produce the structural changes linked to LTP. Rhythmic bursting activity is highly effective in inducing LTP and it is argued that the endogenous hippocampal theta rhythm plays a role in LTP induction in vivo. Finally, studies indicate that LTP and certain types of memory share a common pharmacology and the use of electrical brain stimulation as a sensory cue suggests that LTP develops when the significance of that cue is learned.

Action Potentials↗
PubMed1990

Random number generation, absorption, and hypnotizability: a brief communication.

Graham and Evans (1977) found that a measure of random number generation (RNG) was related to hypnotizability. In 2 studies, the relationship between hypnotizability and Graham and Evans' RNG (1977) index was examined. In Study 1 Evans' (1981) measures of controlled and automatic absorption were also evaluated. In Study 1 no relationship was found between the measures of absorption or RNG and hypnotizability. Since Study 1 was carried out primarily to evaluate methods for modifying hypnotizability, Study 2 was designed to evaluate RNG measure directly. Study 2 found no consistent relationship between RNG and hypnotizability, or between RNG and measures of the experience of hypnotic depth and nonvolition.

Adolescent↗
PubMed1990

Regulation of capillary blood flow and oxygen supply in skeletal muscle in dogs during hypoxaemia.

1. Multiwire surface electrodes were used to measure local hydrogen clearance curves and tissue PO2 in vivo. Evaluation of the initial slopes of the hydrogen clearance curves enabled the measurement of capillary blood flow and its distribution. 2. Capillary blood flow and tissue PO2 frequency distribution histograms were measured in the m. sartorius of anaesthetized, relaxed mongrel dogs under conditions of normoxic (Fi, O2 = 0.3) and hypoxic (Fi, O2 = 0.15 and 0.1) artificial ventilation. 3. Stepwise hypoxaemia (hypoxic hypoxia) induced an increasing discrepancy between capillary blood flow and arterial blood flow. The former decreased by 6% whereas the latter increased by 86%. 4. PO2 histograms provided no evidence of cellular anoxia even at Fi,O2 = 0.1. Capillary blood flow histograms suggested a redistribution of the local pattern of flow. 5. A 34.7% reduction of O2 consumption was observed as the result of severe hypoxaemia. 6. The concept of heterogeneity of capillary blood flow as a functional O2 reserve is presented, together with evidence for oxygen-dependent regulation of capillary blood flow and oxygen consumption.

Animals↗
PubMed1990

Local oxygen supply and blood flow regulation in contracting muscle in dogs and rabbits.

1. Multiwire surface electrodes were used to measure local hydrogen clearance curves and tissues PO2 in the sartorius muscle in dogs under resting conditions and during stimulation of the muscle at 1, 2, 4, 8 and 20 Hz via the femoral nerve. Tissue oxygen supply was assessed by means of PO2 histograms; evaluation of the initial slopes of the hydrogen clearance curves enabled the measurement of capillary blood flow. 2. In a further model, the analysis of hydrogen clearance curves measured in the femoral vein using intravascular needle electrodes in rabbits enabled the distribution of blood flow to be evaluated both under resting conditions and during direct 2 Hz stimulation of the vastus medialis muscle. 3. Increased oxygen consumption, induced by stimulation, caused increases in capillary flow which were not necessarily accompanied by augmentation of femoral artery flow. 4. PO2 histograms provided no evidence of cellular anoxia even at the maximum level of oxygen consumption. 5. A two-compartment distribution of flow was measured under resting conditions, whereas only one compartment could be resolved during 2 Hz stimulation of the vastus medialis muscle in the rabbit experiments. A clear redistribution of flow was observed in the absence of any increase in total flow. 6. A model for oxygen-dependent regulation of capillary blood flow involving high-flow and normal-flow compartments is proposed.

Anesthesia, Intravenous↗
PubMed1990

Sternoclavicular joint infection in hemodialysis patients.

Infection of the sternoclavicular joint due to Staphylococcus aureus occurred in 2 hemodialysis patients. Good results were achieved in both cases by applying appropriate antibiotic therapy. Sternoclavicular joint sepsis is rare. However, it is often associated with underlying conditions, and hemodialysis must be recalled as one of the possible predisposing factors.

Arthritis, Infectious↗
PubMed1990

Listeria monocytogenes endophthalmitis in a renal-transplant patient receiving ciclosporin.

Endophthalmitis due to Listeria monocytogenes developed suddenly in a 52-year-old man receiving immunosuppressive therapy for a renal transplantation carried out 2 months previously. The treatment combined low doses of ciclosporin and prednisone. The initial clinical picture was of acute hypertensive uveitis with hypopyon. Despite prompt paracentesis and appropriate antibiotic therapy, the long-term course was unfavorable, and enucleation became necessary. The occurrence of listeriosis is classic in renal-transplant recipients, but no ocular form has been reported hitherto.

Aqueous Humor↗
PubMed1990

[Allergic risks of hemodialysis. Results of an allergologic investigation in 138 patients].

One hundred and thirty eight unselected hemodialysis patients were screened for allergic symptoms, atopy, total IgE, eosinophil count, specific IgE against ethylene oxyde (ETO), formaldehyde (FA) and isocyanates (Iso) and delayed hypersensitivity to formaldehyde. Six patients demonstrated hypersensitivity to formaldehyde. Six patients demonstrated hypersensitivity reactions at the beginning of hemodialysis; one had recurrent urticaria and one aggravated a preexistent asthma. There were no predicting factors but 6 out of these 8 patients (62%) had positive RAST against ETO, FA or Iso. Eczematous lesions occurred in 40 patients (20%) mainly located around the fistula. Eczema is significantly more frequent in men, atopic patients, and patients using a type of machine where we measured high residual FA concentrations (greater than 50 mg/l). A positive FA patch test was observed in 22% of the patients with an eczema compared to 1.3% in the asymptomatic patients (p less than 0.01).

Adult↗
PubMed1990

[Osteo-articular manifestations in dialysis of patients over 70 years].

A clinical, biological and radiological prospective study was carried out in 21 patients over 70 years of age and treated by hemodialysis or chronic ambulatory peritoneal dialysis (CAPD) to evaluate the frequency and specificity of rheumatic diseases observed in aged chronic renal failure patients. Some are caused or favored by old age and are not in any way related to renal failure and its replacement therapy. Such was the case with arthrosis which was present in 85% of patients, ankylosing vertebral hyperostosis (14%), Paget's disease (5%) and gouty arthritis (10%). Elsewhere there is an implication between abnormalities due to aging and those linked to renal failure and/or dialysis, some of which can worsen or accelerate others. Secondary hyperparathyroidism seems less frequent in the elderly than in the young patients. Common vitamin dependent osteomalacia should not be neglected because it can be either prevented or efficiently treated. Osteoporosis is another important factor in osteopenia. Extra-skeletal calcifications are frequent: periarticular calcifications (38%), chondrocalcinosis (14%) and disc calcifications (24%). Dialysis arthropathy comprising: carpal tunnel syndrome, erosive lesions of large and intermediate limb joint articulations and destructive spondylarthropathy is observed in 43% of patients after an average dialysis period of 44 months. The advent of this complication seems to be quite early in the elderly, as compared to the young population, which confirms the role played by age as a favoring factor.

Aged↗
PubMed1990

N-Methyl-D-aspartate and quisqualate/DL-alpha-amino-3-hydroxy-5- methylisoxazole-4-propionic acid receptors: differential regulation by phospholipase C treatment.

The effect of phospholipase C (PLC) treatment of rat brain membranes on the binding properties of excitatory amino acid receptors was investigated using both a phosphsphatidylcholine-hydrolyzing PLC from Clostridium perfringens and a phosphatidylinositol-specific PLC from Bacillus thuringiensis. PLC from C. perfringens produced an increased affinity of the quisqualate/DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor for its ligand, whereas kainate receptor binding was not affected. Both kinetic analysis and equilibrium saturation experiments indicated that PLC treatment produced a decrease in affinity for [3H]N-(1-[thienyl]cyclohexyl)-piperidine [( 3H]TCP), a ligand for the N-methyl-D-aspartate (NMDA) receptor-associated ionic channel, when the channel was fully activated by high concentrations of glutamate and glycine but increased its binding under conditions in which the channel was presumably closed. This latter component of the binding was not due to an interaction of [3H]TCP with non-glutamate receptor sites, such as sigma opioid and histamine H3 receptors. Binding of [3H]glutamate and [3H] glycine to the NMDA receptors was not modified by PLC treatment, but there was a large decrease in the binding of the NMDA antagonist [3H]3-[(+/-)-2-carboxypiperazine-4-yl)propyl-1-phosphonic acid. Stimulation by glycine of [3H]glutamate binding was also abolished following PLC treatment. In contrast to PLC from C. perfringens, phosphatidylinositol-specific PLC treatment did not detectably modify the binding properties of the quisqualate/AMPA receptor or the NMDA receptor channel. These data indicate that alterations in the lipid microenvironment of the glutamate receptors modulate both the conformation and the function of the receptors and suggest a possible role for phospholipases in the regulation of synaptic transmission at excitatory synapses.

Animals↗
PubMed1990

[Value of arterioscopy in the prevention of renal artery stenosis after transplantation].

Renal artery stenosis is frequent after transplantation. The systematic pre-operative search for arterial injuries by angioscopy allows a reduction in their incidence. The authors report a series of 60 transplantations with pre-operative angioscopy, which revealed benign injuries and two major injuries which were successfully treated surgically. This prevention allows a reduction in the incidence of stenosis from 12 to 6.6% according to a previous series of 210 transplantations without angioscopy.

Endoscopy↗
PubMed1990

[Error of dialysis concentrate: a cause of severe metabolic acidosis not detected by certain generators].

The authors report three cases of severe metabolic acidosis caused by errors of concentrate during hemodialysis "acide concentrate" instead of "acetate" bath. Symptoms began towards the second hour of the session with sickness and important vomits. Blood chemistries showed in all severe acidosis with hyperchloremia and hyperkaliemia while proper conductivity was obtained without alarm. Reconnection on dialysis with a correct bath was able to improve the above mentioned abnormalities. In vitro errors with different types of concentrates and machines have been simulated and the safeguards are discussed. The pH meter with alarm is proposed for all proportioning equipments, not only on "bicarbonate" generator but also on "acetate" delivery systems and especially in centers where these two types of concentrates are prescribed. Being vigilant remains nevertheless the best safeguard against human errors.

Acetates↗
PubMed1989

The block to transcription elongation at the SV40 attenuation site is decreased in vitro by oligomers complementary to segments of the attenuator RNA.

We have previously reported that a mechanism resembling attenuation in prokaryotes regulates simian virus 40 (SV40) late gene expression. We have suggested that modulation of the attenuator RNA secondary structure is an integral element regulating the elongation block at the attenuation site [Hay et al., Cell 29 (1982) 183-193]. In the present study, oligodeoxyribonucleotides (oligos), 13-19 nucleotides long, were used to probe the involvement of the attenuator RNA secondary structure in the control of elongation block at the SV40 attenuation site. These oligos are complementary to segments of the attenuator RNA suggested to play a role in the regulation of attenuation. The oligos were added to an in vitro transcription reaction containing SV40 transcription complexes, and their effect on transcription through the attenuation site was measured. As predicted, the three oligos caused specific decreases in the elongation block at the SV40 attenuation site. These results provide direct evidence for the involvement of RNA secondary structure in the attenuation mechanism in SV40.

Animals↗