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Biomedical subjects

A Hamberger

Publications and source records attributed to A Hamberger.

At least 145 records · Page 8Linked to original sources
PubMed1978

The influence of early protein-calorie malnutrition on neuronal and glial protein synthesis. An experimental study on rats.

The effect of pre- and postnatal undernutrition, produced according to the method of Chow and Lee (3), on the rate of protein synthesis in the brains of rats 11, 21, 34 and 90 days of age was studied by measuring the incorporation of L-[14C]valine in vivo and L-[3H]lysine in vitro. Both in vivo and in vitro experiments were performed with high concentration of the precursor to decrease the effects of pool variations and protein degradation. Particular interest was given to the effects of this form of early protein-calorie malnutrition (PCM) on neuronal and glial cells which were isolated from the brains by gradient centrifugation. Brain protein synthesis measured in vivo which showed a peak at 21 days in both animal series, was depressed by PCM at 11 days but stimulated at 34 days of animal age. Small effect was observed in the 90-day-old animals. A similar response as in whole brain was seen for neuronal cells, while glial cells showed a different reaction. Studies of in vitro protein synthesis did not reveal appreciable effects of undernutrition in whole brain. Both neuronal and glial cells showed a moderate but not statistically significant elevation of protein synthesis in animals subjected to early PCM.

Animals↗
PubMed1978

Effect of calcium on brain metabolism in vitro.

In attempts to distinguish between direct and indirect effects of Ca on brain cell metabolism, respiration, glycolysis, ATP, phosphocreatine, incorporation of [14C] leucine into protein, and accumulation of 45Ca was determined in brain slices. Incubation was carried out in normal salt-balanced medium, in high-potassium-or ouabain-containing medium under aerobic and anaerobic conditions. Calcium ions inhibited slightly glycolysis and respiration in normal medium and activated amino acid incorporation into proteins. Levels of ATP and phosphocreatine remained normal. The effects were interpreted as due to a stabilization of plasma membranes by Ca ions to prevent their spontaneous depolarization. Incubation of slices in high-potassium and ouabain media in aerobic conditions in the presence of Ca resulted in activation of respiration and glycolysis, decrease of ATP and phosphocreatine levels, and inhibition of amino acid incorporation into proteins. The disturbances in energy metabolism, caused by the respiration-linked Ca uptake in brain mitochondria and concomitant inhibition of oxidative phosphorylation, may lead to the inhibition of amino acid incorporation into proteins. An increase in Ca levels in the cytoplasm may only be expected in anaerobic conditions during the incubation in high-potassium and ouabain media. This is manifested by a direct inhibition of glycolysis by Ca ions and a drastic decrease of ATP and phosphocreatine in slices. The results suggest that stimulation of aerobic glycolysis and inhibition of anaerobic glycolysis by Ca may explain the unknown mechanism of the so-called "reversed Pasteur effect" of brain slices incubated in high-potassium media.

Aerobiosis↗
PubMed1978

Attachment of herpes simplex virus to neurons and glial cells.

Cells of brain tissue of rabbits, rats and mice were dissociated and glial cells, neuronal perikarya and synaptosomes were separated by centrifugation on discontinuous Ficol gradients. HSV was shown to attach well to rat and rabbit glial cells and synaptosomes but not to neuronal perikarya. Of intracerebrally infected mice the fractions with glial cells contained the infective virus. The interactions between HSV and neuronal cells and the implication of the observations on the HSV infection of the nervous system are discussed.

Adsorption↗
PubMed1977

Glial cell characteristics in bulk-prepared cell fractions from human brain tumours.

The heterogeneity of brain tumours, especially in the glioblastoma group, makes biochemical characterization of pieces of the tumours hazardous even with extensive histological controls. This study employs a technique by which separate cell populations are subsequently isolated from the tumours by means of density gradient centrifugation. Cells isolated from glial brain tumours with low density sedimentation rates show the highest levels of glial cell characteristics, i.e. S-100 content and active uptake of the neurotransmitter GABA.

Astrocytoma↗
PubMed1977

Potassium-stimulated gamma-aminobutyric acid release from neurons and glia.

Potassium-stimulated [3H]GABA release has been studied with fractions of glial cells, neuronal perikarya and synaptosomes using a superfusion technique. A monotonic increase in the [3H]GABA release was observed when external K+ concentration was raised from 5 to 15 mM. However, there was no further increase in the [3H]GABA release when K+ was raised above 15 mM. The KCl-stimulated release was saturable at the level of 60-100% stimulation. Potassium-stimulated [3H]GABA release from glial cells was unchanged in the absence of calcium while release from synaptosomes and neuronal perikarya demonstrated Ca2+-dependence. The potassium-stimulated [3H]GABA release was enhanced when superfusion was performed in the presence of 10(-5) M ouabain.

Aminobutyrates↗
PubMed1977

Effects of portacaval anastomosis on liver and brain protein synthesis in rats.

In vivo and in vitro protein synthesis was measured in livers from rats 3 weeks after a portacaval shunt (PCS) operation. A marked reduction in protein synthesis was observed, amounting to a 66 and 47% of inhibition, respectively. Above-saturation levels of amino acids were used in both conditions. The level of free exogenous amino acid was elevated consistently in the PCS animals 1 hour after isotope injection. In support of the data on liver protein synthesis, the incorporated radioactivity in serum proteins was reduced markedly. Heart muscle protein synthesis was unchanged while brain protein synthesis was inhibited when assayed in vivo. Neuronal cells showed a more marked inhibition of protein synthesis than did glial cells.

Amino Acids↗
PubMed1976

Immunoelectrophoretic determination of brain-specific antigens in bulk-prepared neuronal and glial cells.

The relative amounts of brain-specific antigens, S-100, glial fibrillary acidic protein (GFA), 14.3.2, synaptin C1, D1, D2 and D3 were determined by crossed immunoelectrophoresis in bulk-prepared neuronal, glial and synaptosomal fractions from 35-day-old rat brains. Little enrichment was ontained for any antigen in the neuronal perikaryal fraction. The glial fraction showed a 3.5-fold enrichment in GFA but had levels similar to whole brain with respect to S-100. Synaptosomes were somewhat enriched in the synaptin C1 protein, but did not differ markedly from whole brain with respect to the most antigens. The extent of cross-contamination in the various fractions could be judged only tentatively, partly due to differences in extractability of the proteins.

Animals↗
PubMed1976

Cellular and subcellular distribution of the S-100 protein in rabbit and rat central nervous system.

The cellular and subcellular distribution of the S-100 protein in rabbit and rat central nervous system was studied both quantitatively and qualitatively. Microcomplement fixation estimations on bulk-prepared neuronal and glial cells showed at least five to six times higher amounts of water-soluble S-100 in glial cell-enriched fractions as compared to fractions enriched in neuronal perikarya. Nerve cell fractions contained a higher percent of tissue-bound S-100 protein. High levels of S-100 protein were found in mitochondria and soluble protein fractions. Immunoelectron microscope investigations demonstrated S-100 protein in neuronal structures, such as the postsynaptic membrane and part of the plasma membrane. Among glial cells the astrocytic filaments contained high levels of S-100 protein. S-100 was also found in most subcellular membranes of astrocytes and oligodendrocytes.

Animals↗
PubMed1976

Biosynthesis of DNA and RNA in neuronal and glial cells from various regions of developing rat brain.

Slices of cerebral hemispheres, brain stem, and cerebellum from rats 5-30 days old were used for in vitro incorporation of [methyl-3H]thymidine and [6-14C]orotic acid into DNA and RNA, respectively. The rates of DNA and RNA synthesis decreased markedly during development, with the most marked decrease observed for DNA. The different brain regions showed specific patterns of decline of DNA and RNA synthesis. Following incubation of slices, the tissues were fractionated to obtain fractions enriched in neuronal cells and in glial cells. In cerebellum, the granule neurons were separated from the Purkinje neurons. The glial:neuronal ratio of DNA specific activity was different in the three regions examined: in cortex it decreased from 6 at 10 days to 3 at 20-30 days; in brain stem it was 3 throughout 10-30 days; in the cerebellum (glia:granule neuron ratio) it was also 3 at 30 days but only 0.3 at 10 days. Concerning the RNA incorporation, small differences were found between neuronal and glial cells.

Age Factors↗
PubMed1976

Amino acid transport in isolated neurons and glia.

Our efforts have been directed towards characterizing amino acid uptake, metabolism and release in bulk-isolated glia and neuronal perikarya studied in parallel with nerve-endings, especially as it concerns the transmitter amino acids and the participation of glia in the clearing of the synpatic space during impulse conduction. A possible neuromodulator role for the glia at the synapse is also suggested by K+-stimulated release. Our most definitive conclusions have been based so far on studies with GABA, although we are also beginning to accumulate data for glutamate related to glutamate-glutamine compartmentation. Glia preferentially accumulate potassium and amino acids compared to neuronal perikarya, have higher Na+/K+-ATPase activity, possess high-affinity, sodium-dependent uptake systems for GABA and glutamate similar to the ones in synaptosomes, and release amino acid in response to a potassium pulse by a calcium-independent process. Low neuronal uptake could be due to loss of dendrites. Unidirectional GABA-flux from the synaptosomal to glial compartment is supported by high GAD in nerve endings compared to high GABA-T in glia. Glutamine may be a transmitter glutamate-precursor in nerve-endings since glutaminase activity is high in nerve-endings, but low in glia where glutamine is presumably made. Glutamine uptake in both glia and synaptosomes obeys low-affinity kinetics in contrast to glutamate, consistent with the inability of glutamine to excite the neuronal membrane. The studies with GABA, which are considerably more extensive, are supported by related work using glia in tissue-culture and autoradiography. There appears to be a suggested difference in the behavior of amines which were poorly taken up by the glial system. Glia, synaptosomes and neuronal perikarya, in general behaved similarly with respect to requirements for uptake and release, except in the case of Ca++, which exerted opposite effects on glial and synaptosomal uptake of GABA. We believe that work along these lines tends to firmly establish a direct role for glial cells as modulators of neuronal excitability and represents a convergence between transmitter amino acid neuropharmacology and cellular biochemistry. This not only deepens and enlarges the vocabulary of synaptic biochemistry but also undoubtedly will have major clinical applications in the fields of epilepsy and behavior.

Adenosine Triphosphatases↗
PubMed1976

Gamma-aminobutyric acid release from neurons and glia.

Release of 3H-GABA into the medium from bulk-isolated glial cells, neuronal perikarya and synaptosomes has been studied, using a continuous perfusion system. The fractions were incubated with 3H-GABA and spontaneous efflux of label in the presence and absence of aminooxyacetic acid (AOAA) was recorded. Unlabelled GABA at micromolar concentrations markedly stimulated 3H-GABA efflux from glia, synaptosomes and neurons. 3H-GABA from all fractions was also markedly sensitive to stimulation by ouabain. Glutamate was effective in stimulating the spontaneous efflux in the presence of AOAA, while superfusion with a calcium-deprived medium only slightly stimulated the 3H-GABA efflux from neurons and glia.

Aminobutyrates↗
PubMed1975

Amino acid incorporation into neurons and glia of guinea pigs with experimental allergic encephalomyelitis.

After in vitro incubation of brain slices from guinea pigs in the intermediate (10 days postinduction) stage of experimental allergic encephalomyelitis (EAE), incorporation of [14C]leucine into protein was increased in a glial-enriched fraction. By the late (17-18 days postinduction) stage of the disease, when EAE symptoms were manifest, both the neuronal- and glial-enriched fractions showed increased specific activity of their total protein. SDS polyacrylamide gel electrophoresis showed that the increased leucine incorporation occurred in those proteins which labeled in a control material. After intraperitoneal injection of [3H]leucine the incorporated radioactivity was slightly increased in unfractionated brains from EAE animals. The neuronal-glial ratios for protein-bound radioactivity indicated that the increased incorporation resided mainly in the glial population.

Animals↗
PubMed1975

Evidence for differential function of neuronal and glial cells in protein metabolism and amino acid transport.

Amino acid incorporation in neuronal and glial cells has been investigated in several laboratories employing bulk-separation techniques to obtain cell-enriched fractions. The relative rates of incorporation into the proteins of both cell types vary substantially with the method of isotope administration. Through the use of single-pulse perfusions with a duration of 30-40 sec the early time course of labeling has been studied. The difference between neuronal and glial cells with respect to indicating cell interactions will be discussed. The in vitro amino acid incorporation has been measured in neurons and glia after slice incubation. In material from animals developing experimental allergic encephalitis the rate of 3H-leucine incorporation more than doubles in the unfractionated brain. Glial cells increased their rate of incorporation by approximately 400% under the same conditions. The involvement of specific proteins in the cells and organelles has been studied by gel electrophoresis. The high uptake capacity of glial cells for certain amino acids with possible transmitter function has been further characterized. The release of these substances is measured in a superfusion system where beds of cells, preloaded with the labeled substance, are used. High potassium pulses stimulate release of, for example, GABA in both neuronal and glial cells.

Amino Acids↗