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Biomedical subjects

H Karst

Publications and source records attributed to H Karst.

At least 37 records · Page 2Linked to original sources
PubMed1993

Bicuculline increases the intracellular calcium response of CA1 hippocampal neurons to synaptic stimulation.

Intracellular calcium levels were measured by ratio imaging of Fura-2-injected CA1 pyramidal neurons during repetitive electrical stimulation of the Schaffer collaterals in rat hippocampal slices. Baseline intracellular calcium levels of 102 nM increased to 190 nM during a 3-s stimulus train of 5 Hz. Bicuculline (20 microM) significantly enhanced this stimulus-dependent rise in intracellular calcium, while the baseline calcium levels remained unchanged. Concomitantly performed extra- and intracellular electrophysiological recordings indicate that the increased calcium response in the presence of bicuculline is linked to a prolongation of the excitatory postsynaptic potential and the induction of multiple action potentials. The bicuculline-induced increased calcium response could have long-term implications for cell function and eventually lead to cell degeneration.

Action Potentials↗
PubMed1993

Long-term control by corticosteroids of the inward rectifier in rat CA1 pyramidal neurons, in vitro.

In this study we examined long-lasting effects mediated by intracellular mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) on two voltage dependent potassium conductances in CA1 pyramidal neurons, i.e. the transient current IA and the delayed rectifier, and on the inward rectifier IQ, a mixed sodium/potassium current. All experiments were carried out in hippocampal slices with the in situ patch clamp technique, in the whole cell mode. Neurons recorded 30 min to 3 h after a brief application of 30 nM corticosterone to slices from adrenalectomized rats, thus saturating MRs and occupying most of the GRs, displayed a large IQ-conductance similar to neurons in slices from the sham-operated controls. By contrast, if only MRs or only GRs were activated, the IQ-conductance was significantly smaller than for the corticosterone-treated group of cells, indicating that simultaneous activation of both MRs and GRs is necessary to achieve a large IQ-conductance. If corticosterone was applied in the presence of a protein synthesis inhibitor, the IQ conductance was significantly smaller than in the absence of the inhibitor. Properties of the IA and the delayed rectifier were not affected by the various corticosteroid treatments. In conclusion, the data indicate that in particular the IQ-conductance is under a gene-mediated control of corticosteroid hormones. The IQ-conductance is relatively low when only MRs are activated, as occurs for the rat in the morning under rest, and high when both MRs and GRs are occupied, as occurs at the peak of the circadian cycle and after stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗
PubMed1993

Intra- and inter-individual variations in energy expenditure of 14-15-year-old schoolgirls as determined by indirect calorimetry.

Eleven 14-15-year-old schoolgirls were investigated four times within 1 year to determine variations in energy expenditure between individuals (inter-individual variability) and within subjects (intra-individual variability). Indirect calorimetry was used to determine metabolic rates in the fasting and resting state (RMR), and during physical activities which were grouped into standardized and non-standardized activities. Analyses of variance supplied information about intra- and inter-individual variabilities of rates of energy expenditure. The mean resting metabolic rate in adolescent girls was 4.41 (SD 0.40) kJ/min. The overall coefficient of variation (9.1%) was approximately twice as high as the mean coefficient within subjects (4.3%). The reproducibility of the RMR of the girls was high (significant F value of variance analysis), even over a prolonged investigation of 1 year. This seemed to depend primarily on the constant body weight during the period of investigation. A workload of 30 W on a bicycle ergometer and walking at an individually chosen speed did not reveal significant differences between inter- and intra-individual variabilities of energy metabolic rates. However, in most non-standardized activities, e.g. relaxation at home, washing dishes and vacuum cleaning, inter-individual variability was significantly higher than intra-individual variability. There are true differences in energy expenditure rates between subjects which may be demonstrated by duplicated measurements. Conclusions on future experimental design were drawn, where differences between groups rather than between individuals are to be studied.

Adolescent↗
PubMed1991

The induction of corticosteroid actions on membrane properties of hippocampal CA1 neurons requires protein synthesis.

Corticosterone can affect electrical properties of CA1 pyramidal neurons via binding to two corticoid receptor types, the mineralocorticoid (MR) and glucocorticoid receptor (GR). Previously we have shown that MR-activation leads to attenuation of serotonin (5-HT)-induced membrane hyperpolarization, while GR-activation induces an increase in the amplitude of the afterhyperpolarization (AHP) following a short current pulse. In this study we show that the MR- and GR-mediated changes of the membrane properties are prevented in the presence of the protein synthesis inhibitor cycloheximide, thus suggesting a genomic action of the steroids.

Adrenalectomy↗
PubMed1991

Structure-activity relationship of philanthotoxins--I. Pre- and postsynaptic inhibition of the locust neuromuscular transmission.

1. Like the natural toxin, synthetic delta-philanthotoxin, now called PTX-4.3.3 acts as a reversible postsynaptic open ion-channel blocker of the glutamatergic neuromuscular system of the locust. 2. It also inhibits the high-affinity re-uptake of glutamate in the nerve endings and glial cells. 3. To study the structure-activity relationship, three parts of the PTX-4.3.3 molecule were changed. 4. One of these PTX-analogues, trifluoromethyl-PTX-4.3.3, proved to be a more potent postsynaptic blocker. 5. Moreover, compared with PTX-4.3.3 a delayed recovery period is seen with trifluoromethyl-PTX-4.3.3. 6. A number of PTX-analogues were equipotent to PTX-4.3.3 regarding the inhibition of iontophoretically evoked, postsynaptic glutamate potentials. 7. However, complete inactivation was achieved by reducing the length of the polyamine chain, moreover dideaza-PTX-12 was nearly completely inactive and a reduced activity was seen with dephenol-PTX-4.3.3. 8. A decrease of the decay time constant of glutamate potentials, normally seen by open ion-channel blockers in Con A pretreated preparations, was unaffected during application of the latter two analogues. 9. Possibly these two toxins act as weak receptor antagonists. 10. The presynaptic inhibition of the glutamate re-uptake, seemed to be a very specific property of PTX-4.3.3. Only one of the tested analogues (dehydroxy-PTX-4.3.3) exhibited this capacity.

Animals↗
PubMed1991

Structure-activity relationship of philanthotoxins--II. Effects on the glutamate gated ion channels of the locust muscle fibre membrane.

1. PTX-4.3.3, the synthetic product of the wasp toxin, delta-philanthotoxin, blocks the open, glutamate gated, ion channels of the locust muscle. 2. This block is accompanied by the appearance of double exponential distribution of the closed times frequency, and a decrease of the inverse relationship between the open and closed states. 3. The analogues with the shortened polyamine chain, PTX-4.3 and PTX-3.3, are less potent, trifluoromethyl-PTX-4.3.3 is a more potent analogue. 4. Yet, they still behave like PTX-4.3.3 as open ion-channel blockers. 5. Another analogue, without the aromatic nucleus, dephenol-PTX-4.3.3, proved to act in a different way. 6. This less potent analogue, doesn't block the open ion channels. 7. Most likely, the not-activation induced, non-competitive antagonism, caused by dephenol-PTX-4.3.3, has a modulatory effect on glutamate receptors. 8. Methyl-PTX-4.3.3 is also an open ion-channel blocker. However, at relatively low concentrations it has an agonistic-like effect, probably of a modulatory origin as well. 9. A long-term inhibition of PTX-4.3.3 applied at low concentrations also indicates that beside an open ion-channel block, also other inhibitory processes are involved.

Animals↗
PubMed1991

Poneratoxin, a novel peptide neurotoxin from the venom of the ant, Paraponera clavata.

1. At concentrations varying from 10(-8) to 10(-6) M synthetic poneratoxin (PoTX) is a strong, but very slowly acting agonist for smooth muscles and its blocks synaptic transmission in the insect CNS in a concentration-dependent manner and depolarizes giant interneurons. 2. However, in isolated dorsal unpaired median cells 10(-6) M PoTX causes only a reversible hyperpolarization of about 5 mV. 3. At concentrations from 10(-8) to 10(-6) M PoTX affects the electrical activity of isolated cockroach axons, as well as isolated frog and rat skeletal muscle fibres. 4. PoTX prolongs action potentials and induces slow automatic activity, due to a slow Na(+)-current activation at very negative values of potential and due to slow deactivation.

Action Potentials↗
PubMed1989

Presynaptic effects of spider toxins: increase of high affinity uptake in the arthropod peripheral glutamatergic system.

In contrast to the reported effects of polyamines on the high affinity neurotransmitter uptake, two polyamine-like spider toxins significantly increase the high affinity uptake of glutamate as demonstrated with high resolution autoradiography. The effects of both spider toxins were compared to those of a polyamine toxin from the wasp Philanthus triangulum, which is known to inhibit the high affinity glutamate uptake.

Animals↗
PubMed1987

Diet-induced thermogenesis in man: thermic effects of single protein and carbohydrate test meals in lean and obese subjects.

Postprandial thermogenesis of 8 healthy males of normal body weight and 17 healthy obese subjects with a body weight gain of more than 10 kg per year was measured continuously by means of a respiratory chamber over 10 h after test meals of 1 and 2 MJ protein (casein) and 2 MJ carbohydrate (hydrolized starch). The total thermic response to all test meals was reduced by about 50% in the obese subjects. The thermic response was related to body weight, energy intake, resting metabolic rate and weight loss during restricted energy intake. The necessity for a careful characterization of the obese subjects in studies of thermogenesis and of efficiency of energy utilization in obesity is pointed out. It is suggested that thermic response to food can be considered as a suitable indicator for the distinction between people of different metabolic efficiency.

Body Weight↗
PubMed1985

The course of paraventricular hypothalamic efferents to autonomic structures in medulla and spinal cord.

By application of the anterograde transport technique of Phaseolus vulgaris leuco-agglutinin the descending autonomic projection of the paraventricular hypothalamic nucleus was investigated. The Phaseolus lectin technique allowed the detection of the cells of origin in the paraventricular PVN, the precise position of two distinct descending axon pathways and the detailed morphology of terminal structures in midbrain, medulla oblongata and spinal cord.

Animals↗
PubMed1984

Phaseolus vulgaris leuco-agglutinin immunohistochemistry. A comparison between autoradiographic and lectin tracing of neuronal efferents.

The autoradiographic pattern of anterograde labeling as a result from injections with tritiated amino acids is compared to the labeling of efferents with Phaseolus vulgaris leuco-agglutinin after lectin injections in the same nucleus visualized by immunohistochemical methods. This comparison is made for efferents from the ventromedial hypothalamic nucleus to the amygdaloid body.

Amygdala↗
PubMed1984

Diet-induced thermogenesis in man: thermic effects of single proteins, carbohydrates and fats depending on their energy amount.

The diet-induced thermogenesis of 12 healthy males of normal body weight was measured by means of indirect calorimetry over 6 h after test meals of 1, 2 or 4 MJ protein (white egg, gelatin, casein), carbohydrate (starch, hydrolyzed starch) or fat (sunflower oil, butter). The totals of the thermic responses proved to be dependent on the type of nutrient supplied as much as on its quantity. The effect of 1 MJ protein was at least three times as large as that of an isocaloric carbohydrate supply. The investigated dietary fats produced no evident thermic response. The doubling of the energy intake of either casein or hydrolyzed starch led to the approximate doubling of the thermic effect.

Adult↗
PubMed1979

[Dietary interview. I. Comparison between dietary history versus repeated daily recalls].

In the course of 12 months, 43 men and 53 women aged 30-40 years were subjected to 14 24-hours recalls and one dietary history concerned with their individual dietary habits. The mean values yielded by the first and the second method for energy, 4 nutrient groups and 8 food groups were statistically evaluated and compared with each other, from which the following conclusions can be drawn as to the reliability and the precision of the dietary history: 1. The dietary history permits the quantitative estimate of the energy and nutrient intake in groups of about 50 subjects with an error of less than 10%. Underestimation of the actual food intake is more likely than overestimation. 2. The same holds true for the quantitative estimate of the consumption of foods from great food groups. The method is considerably less precise in case of single food or irregularly consumed foods. The differences between the results from the two methods ranged from 0 to 25%. 3. The precision of the individual results obtained for energy and nutrient intake from the dietary history was +/- 20% with a probability of 80-90%. In 75% of the cases, the differences in the consumption of food groups as determined by the two methods were smaller than 20%. As to single foods, however, individual misestimations ranging from 30 to 50% are to be expected.

Adult↗
PubMed1979

[Dietary interview. 2. Comparison of the results obtained with different numbers of daily recalls].

From energy, nutrient and food intake data obtained with 14 24-hours recalls from 43 male and 53 female employees, aged from 30 to 40 years, the authors calculated and compared the single and group means for 1, 3, 5, 7, 10 and 14 days, respectively. It is tried to deduce from them the lowest number of interviews necessary for reliable statements. As the intra-individual variances were greater than the variances within the groups, the diet of such a group cannot be characterized on the basis of a single interview. Statements regarding the mean intakes of energy, nutrients and high-aggregated food groups could be made for groups of subjects on the basis of 3-5 interviews, with a tolerance of +/- 5%. The stable estimation of the consumption of single foods (with a tolerance of +/- 10%) required at least 7 interviews. 10 interviews were necessary for estimating (with a tolerance of +/- 10%) the mean intakes of energy, nutrients and great food groups of single persons. These results will hold true only when the workdays and weekends are in due proportion.

Adult↗