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W Paschen

Publications and source records attributed to W Paschen.

At least 73 records · Page 4Linked to original sources
PubMed1994

Protein synthesis and energy metabolism in hippocampal slices during extended (24 hours) recovery following different periods of ischemia.

Hippocampal slices were successfully maintained for 24 hours in vitro in a flow-through chamber by using a modified artificial CSF (amino acids included). Measurement of energy metabolism parameters (adenine nucleotides) and the slice response to KCl-induced depolarization (release of GABA and aspartate) indicated that hippocampal slices were metabolically stable for at least 24 hours. The preparation was used to study recovery of protein synthesis after different periods of in vitro ischemia (5, 10, or 15 min). Protein synthesis inhibition was only partly reversed after 15 min of ischemia, but fully reversible after 5- or 10-min ischemia at 24 hours of recovery. Furthermore, the model was used to study a possible role of glutamate in postischemic inhibition of protein synthesis. Glutamate receptor agonists (glutamate or quinolinic acid) or antagonist (kynurenic acid) were applied during ischemia. Neither treatment affected the late (24 hours) outcome of ischemia, arguing against the critical role of glutamate in ischemic cell damage. The present approach allows use of the hippocampal slice preparation in the study of delayed effects of ischemia of different duration.

Adenosine Triphosphate↗
PubMed1994

RNA editing of the glutamate receptor subunits GluR2 and GluR6 in human brain tissue.

Editing of mRNA in the coding region of the second transmembrane domain of glutamate receptor subunits GluR2, GluR5, and GluR6 involves a change of the base A in genomic DNA to the base G in mRNA as described in rat brain. To determine whether this reaction occurs in humans as well as rats, we studied RNA editing of GluR2 and GluR6 in human brain. We compared the extent of editing in controls and cases with Huntington's disease. To assay the extent of editing in brain RNA, first strand cDNA was amplified using the polymerase chain reaction yielding a product across the region of the second transmembrane spanning segment in which editing takes place in rats. The PCR product was incubated with the restriction enzyme BbvI, which recognizes the sequence GCAGC present in the nonedited sequence of the mRNA in subunits GluR2 and GluR6. Thus, BbvI cuts the nonedited version but leaves the edited version intact. As in the rat, the GluR2 subunit mRNA was completely edited in human brain. The GluR6 subunit was nearly completely edited in all gray matter structures investigated including cortex, striatum, thalamus, hippocampus, amygdala, and cerebellum with extent of editing ranging from 89% in the cerebellum to 95% in the cortex and striatum. No significant differences in the extent of RNA editing were apparent in control versus Huntington's disease brains. To compare the extent of editing in neurons and glia in the brain, editing in cerebral cortex (predominantly gray matter and thus neurons) was compared with editing in corpus callosum (white matter and thus nearly completely glial cells).(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1993

Polyamine metabolism in experimental brain tumors of rat.

Biosynthesis and accumulation of the polyamines putrescine, spermidine, and spermine are closely associated with cellular growth processes. We examined polyamine levels and the activity of their first rate-limiting enzyme, ornithine decarboxylase (ODC), in stereotactically induced experimental gliomas of the rat brain 1 and 2 weeks after implantation. Regional ODC activity and polyamine levels were determined in the tumor and in the ipsi- and contralateral striatum, white matter, and cerebral cortex. In the tumor, both ODC activity and polyamine levels markedly increased with progressive tumor growth, as compared to those in the white matter of the opposite hemisphere. In the peritumoral brain tissue, ODC activity did not change, but there was a marked increase of putrescine and, to a lesser degree, of spermidine and spermine almost throughout the whole ipsilateral hemisphere. ODC activity, therefore, seems to be a reliable marker of neoplastic growth in the brain, which may be of use for new clinical concepts of the diagnosis and therapy of brain tumors. The more diffuse distribution of polyamines, however, may be associated with the formation and spreading of edema, which would explain some of the biological effects of tumors on distant brain tissue.

Animals↗
PubMed1992

Changes in regional polyamine profiles in rat brains after transient cerebral ischemia (single versus repetitive ischemia): evidence for release of polyamines from injured neurons.

Reversible cerebral ischemia (of 5 min, 15 min, or 3-times 5 min) was produced in 14 Mongolian gerbils by occluding both common carotid arteries. After 72 h of recirculation, brains were frozen and processed for measuring regional levels of the polyamines putrescine, spermidine and spermine using HPLC and fluorescent detector. Ischemia induced a marked increase in putrescine levels throughout the brain, most pronounced after 3-times 5 min ischemia (P less than or equal to 0.05 - P less than or equal to 0.001). Spermine levels were significantly reduced, in the hippocampal CA1-subfield after 5 min of ischemia and, in addition, in the striatum and thalamus after 3-times 5 min ischemia. It is suggested that polyamines are released from necrotic neurons and cleared into the blood. Spermine, released from neurons into the extracellular compartment, may bind to the N-methyl-D-aspartate (NMDA) receptor of cells located in close vicinity and may thus render neurons vulnerable to otherwise subtoxic levels of excitotoxins.

Animals↗
PubMed1992

Polyamine metabolism in different pathological states of the brain.

Biosynthesis of the polyamines spermidine and spermine and their precursor putrescine is controlled by the activity of the two key enzymes ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). In the adult brain, polyamine synthesis is activated by a variety of physiological and pathological stimuli, resulting most prominently in an increase in ODC activity and putrescine levels. The sharp rise in putrescine levels observed following severe cellular stress is most probably the result of an increase in ODC activity and decrease in SAMDC activity or an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Spermidine and spermine levels are usually less affected by stress and are reduced in severely injured areas. Changes of polyamine synthesis and metabolism are most pronounced in those pathological conditions that induce cell injury, such as severe metabolic stress, exposure to neurotoxins or seizure. Putrescine levels correlate closely with the density of cell necrosis. Because of the close relationship between the extent of post-stress changes in polyamine metabolism and density of cellular injury, it has been suggested that polyamines play a role in the manifestation of structural defects. Four different mechanisms of polyamine-dependent cell injury are plausible: (1) an overactivation of calcium fluxes and neurotransmitter release in areas with an overshoot in putrescine formation; (2) disturbances of the calcium homeostasis resulting from an impairment of the calcium buffering capacity of mitochondria in regions in which spermine levels are reduced; (3) an overactivation of the NMDA receptor complex caused by a release of polyamines into the extracellular space during ischemia or after ischemia and prolonged recirculation in the tissue surrounding severely damaged areas; (4) an overproduction of hydrogen peroxide resulting from an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Insofar as a sharp activation of polyamine synthesis is a common response to a variety of physiological and pathological stimuli, studying stress-induced changes in polyamine synthesis and metabolism may help to elucidate the molecular mechanisms involved in the development of cell injury induced by severe stress.

Adenosylmethionine Decarboxylase↗
PubMed1992

Activity of ornithine decarboxylase and S-adenosylmethionine decarboxylase in transient cerebral ischemia: relationship to the duration of vascular occlusion.

Mongolian gerbils were anesthetized with halothane and forebrain ischemia was induced by occluding both common carotid arteries. After 2, 4, 6, 8, or 10 min of vascular occlusion clips were removed and animals allowed to recover for 8 or 24 h. At the end of the experiments animals were reanesthetized and their brains frozen in situ. Tissue samples were taken from the cerebral cortex, striatum, hippocampus, and thalamus for determination of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) activity by measurement of the release of 14CO2 from [14C]ornithine and S-[14C]adenosylmethionine, respectively. A transient increase in ODC activity was found after 8 h of recirculation following cerebral ischemia in all brain structures studied. ODC activity was significantly increased after 8 h of recirculation in the hippocampus of animals subjected to 4 min of ischemia, in the cortex and striatum after 6 min of ischemia, and in the thalamus after 8 min of vascular occlusion. ODC activity had already reached a plateau in the hippocampus after 4 min of vascular occlusion and in the cortex, striatum, and thalamus after 8 min, since there is no further increase in activity even after 10 min of ischemia. After cerebral ischemia and 24 h of recirculation ODC activity returned to control levels throughout the forebrain regardless of the duration of ischemia. SAMDC activity was significantly reduced after 8 h of recirculation following 4 to 10 min of ischemia in the cortex and 8 min of ischemia in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosylmethionine Decarboxylase↗
PubMed1992

Threshold relationship between cerebral blood flow, glucose utilization, and energy metabolites during development of stroke in gerbils.

Focal brain ischemia was produced in halothane-anesthetized Mongolian gerbils by occluding the right common and the left external carotid artery. Ninety minutes after vascular occlusion the following regional hemodynamic and metabolic parameters were evaluated in adjacent cryostat sections taken from seven different coronal planes of each brain: cerebral blood flow (CBF), glucose utilization (CMRG), and the tissue content of ATP and glucose. NADH fluorescence was recorded from the surface of the cryostat block. In addition, tissue slices were taken from each brain to determine the rate of phosphorylation of 2-deoxyglucose in ischemic and nonischemic regions. Depending on the density of ischemia, the following metabolic disturbances were observed. At CBF values below 35 ml x 100 g-1 x min-1 CMRG increased and at values below 25 ml x 100 g-1 x min-1 it declined sharply. Glucose content declined when CBF was below 35 ml x 100 g-1 x min-1 and ATP fell at CBF below 20 ml x 100 g-1 x min-1. At 10 ml x 100 g-1 x min-1 ATP was completely depleted. NADH fluorescence was found elevated at flow rates that caused an increase of glucose utilization and was maximal when CBF stopped. The ischemic thresholds for the initial increase in CMRG and the complete depletion of ATP content represent the metabolic equivalent of the penumbra zone and provide a basis for the evaluation of therapeutic procedures for the treatment of stroke.

Adenosine Triphosphate↗
PubMed1992

Transglutaminase activity in human brain tumors.

Transglutaminase (TG) activity was measured in tissue samples of 45 human brain tumors (pituitary adenomas, meningiomas and gliomas) obtained during neurosurgery. Biochemical analysis and histopathological classification were carried out in the same samples. Mean enzyme activity was highest in non-glial tumors, but due to a high variability of values no significant changes were found between the various histological groups. Thus, TG activity, although considered to play a role in neoplastic growth, does not represent a biochemical marker of malignancy in human brain tumors.

Adenoma↗
PubMed1992

Polyamine metabolism in reversible cerebral ischemia.

Synthesis of the polyamines putrescine, spermidine, and spermine is controlled by the activity of the key enzymes ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). Beside their function in cellular growth processes, polyamines and particularly putrescine play a role in calcium-related events at the cell membrane, coupling an extracellular stimulus to an intracellular response (second messenger-like reactions), modulate the calcium-buffering capacity of mitochondria (spermine), and, if present in the extracellular compartment, modulate the activity of the N-methyl-D-aspartate receptor (spermidine and spermine). Reversible cerebral ischemia triggers pathological disturbances in polyamine metabolism that are characterized by a sharp increase in ODC synthesis, even in the most vulnerable hippocampal CA1 subfield in which overall protein synthesis is severely depressed at the same time, and a marked suppression of SAMDC synthesis in parallel with the inhibition of overall protein synthesis. ODC immunohistochemistry has revealed that the observed changes are neuronal responses to reversible ischemia. These changes in enzyme activities result in an overshoot in the formation of putrescine, the product of ODC activity. Spermine levels are significantly reduced in vulnerable brain structures after prolonged recirculation. In addition, evidence is accumulating that polyamines may be released from the cell during ischemia and after prolonged recirculation at a time when cell necrosis is apparent. This review will summarize the major features of ischemia-induced disturbances in polyamine metabolism and the possible consequences for the cells involved, taking into account that the underlying changes may be indicative of either the activation of a recovery process of neurons from the metabolic stress produced by reversible ischemia or pathological disturbances resulting in the manifestation of neuronal necrosis. Elucidating the mechanisms responsible for the postischemic disturbances in polyamine metabolism may lead to a better understanding of the molecular mechanisms involved in the development of neuronal necrosis after different pathological stimuli.

Animals↗
PubMed1992

Activity of ornithine decarboxylase (ODC) and polyamine levels as biochemical markers of malignancy in human brain tumors.

The content of the polyamines putrescine, spermidine and spermine, and the activity of their metabolic key enzyme ornithine decarboxylase (ODC) were measured in tissue samples obtained during operation of 45 patients with primary or recurrent gliomas, meningiomas and pituitary adenomas. Biochemical analysis and histopathological classification were carried out in the same tumor samples. In benign tumors ODC activity was less than 10 nmol/g/h, whereas in malignant gliomas values up to 34 nmol/g/h were observed. In rapidly growing tumors pronounced heterogeneity was observed with high values in solid tumor parts and low values in necrotic areas. Thus, high ODC activity represents a reliable biochemical marker of malignancy in brain tumors, but low values do not prove benignity.

Adenoma↗
PubMed1991

Polyamine metabolism in transient focal ischemia of rat brain.

Polyamine metabolism was studied in rat brains subjected to 30 min transient cerebral ischemia by measuring the activity of the key enzyme ornithine decarboxylase (ODC) and levels of the polyamines putrescine, spermidine and spermine. A transient increase in ODC activity was apparent after 4 h of recirculation in the ipsilateral cortex and striatum (P less than 0.05). Putrescine levels were significantly increased in the ipsilateral striatum after 4 h of recirculation, and after 24 h of recirculation in both the ipsilateral cortex and striatum. During ischemia spermidine levels were significantly reduced in the ipsilateral hemisphere and spermine levels in the ipsilateral cortex. It is suggested that during ischemia polyamines are released from neurons into the extracellular compartment and cleared into the blood.

Animals↗
PubMed1991

Ornithine decarboxylase in reversible cerebral ischemia: an immunohistochemical study.

Anesthetized Mongolian gerbils were subjected to 5-min ischemia and 8 h of recirculation. Vibratom sections were taken for studying changes in ornithine decarboxylase (ODC) immunoreactivity using an antiserum to ODC, and tissue samples were taken for measuring ODC activity. After 5-min ischemia and 8-h recirculation ODC activity increased 11.5-, 5.9-, and 7.9-fold in the cerebral cortex, striatum and hippocampus, respectively (P less than or equal to 0.05 to 0.01). In the cortex, striatum and hippocampus of control animals immunoreactivity was low but clearly above the detection limit. The reaction was confined to neurons. After 5-min ischemia and 8-h recirculation a sharp increase in immunoreactivity was observed confined to neurons, indicating that the postischemic activation of polyamine metabolism is a neuronal response to ischemia. The immunoreactivity was markedly increased in the perinuclear cytoplasm and the dendrites. In the striatum the density of neurons exhibiting a sharp increase in immunoreactivity was more pronounced in the lateral than in the ventral part. In the hippocampus a strong reaction was present in all subfields but the CA1 subfield was particularly affected. The present study demonstrates for the first time that biosynthesis of a protein is markedly activated during the first 24 h of recirculation after 5-min cerebral ischemia of gerbils even in the vulnerable CA1 subfield, in which the overall protein synthesis is sharply reduced at the same time. Studying polyamine metabolism after ischemia may, thus, provide new information about the basic molecular mechanisms responsible for the altered gene expression after metabolic stress.

Animals↗
PubMed1991

Cerebral polyamine metabolism in reversible hypoglycemia of rat: relationship to energy metabolites and calcium.

Thirty minutes of insulin-induced reversible hypoglycemic coma (defined in terms of cessation of EEG activity) was produced in anesthetized rats. At the end of the hypoglycemic coma or after recovery for 3, 24, or 72 h induced by glucose infusion, the animals were reanesthetized and their brains frozen in situ. Two control groups were used: untreated controls without prior manipulations, and insulin controls, which received injections of insulin followed by glucose infusion to maintain blood glucose within the physiological range. The brains of these latter animals were frozen 3, 24, or 72 h after glucose infusion. Tissue samples from the cortex, striatum, hippocampus, and thalamus were taken to measure ornithine decarboxylase (ODC) activity, and putrescine and spermidine levels, as well as phosphocreatine (PCr), ATP, glucose, and lactate content. In addition, 20-microns thick coronal sections taken from the striatum and dorsal hippocampus were used for histological evaluation of cell damage and also stained for calcium. Insulin in the absence of hypoglycemia produced a significant increase in ODC activity and putrescine level but had no effect on the profiles of energy metabolites or spermidine. During hypoglycemic coma, brain PCr, ATP, glucose, and lactate levels were sharply reduced, as expected. Energy metabolites normalized after 3 h of recovery. In the striatum, significant secondary decreases in PCr and ATP contents and rises in glucose and lactate levels were observed after 24 h of recovery. ODC activity, and putrescine and spermidine levels were unchanged during hypoglycemic coma. After 3 h of recovery, ODC activity increased markedly throughout the brain, except in the striatum. After 24 h of recovery, ODC activity decreased and approached control values 2 days later. Putrescine levels increased significantly throughout the brain after reversible hypoglycemic coma, the highest values observed after 24 h of recovery (p less than or equal to 0.001, compared with controls). After 72 h of recovery, putrescine levels decreased, but still significantly exceeded control values. Reversible hypoglycemic coma did not produce significant changes in regional spermidine levels except in the striatum, where an approximately 30% increase was observed after 3 and 72 h of recovery (p less than or equal to 0.01 and p less than or equal to 0.05, respectively). Twenty-four hours after hypoglycemic coma, intense calcium staining was apparent in layer III of the cerebral cortex, the lateral striatum, and the crest of the dentate gyrus. After 72 h of recovery, the intense calcium staining included also cortical layer II, the septal nuclei, the subiculum, and the hippocampal CA1-subfield.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Transglutaminase activity in reversible cerebral ischemia in the rat.

Transglutaminase (TG, EC 2.3.2.13) activity and levels of putrescine (a natural acyl-acceptor in the transglutaminase reaction) were measured in rat brains after 30 min ischemia and 8 or 24 h recirculation. TG activity was significantly increased in the striatum and hippocampus already during cerebral ischemia and, more pronounced, after 8 and 24 h recirculation. In the cortex, in contrast, TG activity did not change during ischemia and 8 h recirculation but was significantly increased after 24 h recirculation. Putrescine levels were sharply increased after 8 h recirculation and even further after 24 h recirculation. It is suggested that in vivo during ischemia and early recirculation, when cells are overloaded with calcium ions, a pathological increase in the TG-catalyzed cross-linking of proteins may be apparent especially in the nerve endings of the hippocampus where the intrinsic concentration of the acyl-donor (protein-bound glutamyl-moiety) has been shown to be high.

Animals↗
PubMed1990

Relationship between of blood flow, glucose metabolism, protein synthesis, glucose and ATP content in experimentally-induced glioma (RG1 2.2) of rat brain.

In experimental RG1 2.2 glioma of rat brain, local blood flow, glucose utilization, protein synthesis, glucose and ATP content were measured by means of triple tracer autoradiography and bioluminescence technique, respectively, to determine hemodynamic and metabolic thresholds for local tumor energy failure. Perfusion thresholds were estimated at tumor blood flow values of 69.0 +/- 0.1 ml/100 g/min (estimate +/- standard error) and of 69 +/- 7.1 ml/100 g/min for the beginning of the decline in regional ATP and glucose content, respectively. Metabolic thresholds were derived at tumor glucose utilization values of 70.6 +/- 8.3 mumol/100 g/min for reduced protein synthesis, of 55.0 +/- 0.2 mumol/100 g/min for the decrease in glucose content, and 34.7 +/- 4.7 mumol/100 g/min for decline in ATP content. Our results suggest that blood flow limits glucose supply to tumor tissue at much higher flow rates than in normal brain which, in turn, is associated with a decrease in tumor glucose utilization. A reduction and not an increase in tumor glucose availability could be a more appropriate strategy for the induction of energy failure in tumors.

Adenosine Triphosphate↗
PubMed1990

Putrescine content and structural defects in isolated fractions of rat brain after reversible cerebral ischemia.

Reversible cerebral ischemia was produced in rats by occluding both vertebral and both carotid arteries. Following 30 min of ischemia, brains were recirculated for 24 h. The hippocampus, the striatum, and the cortex were sampled, homogenized, and fractionated on a discontinuous sucrose gradient. The fractions were evaluated morphologically by electron microscopy and biochemically by measuring the activity of marker enzymes. Putrescine was extracted from the isolated fractions and measured quantitatively using HPLC and a fluorescence detector. In the total tissue homogenate of control animals putrescine content amounted to 72.0 +/- 3.1, 70.2 +/- 7.6, and 72.7 +/- 2.1 pmol/mg protein in samples prepared from the cortex, the hippocampus, and the striatum, respectively. In the mitochondrial fraction the content was lower, while in the synaptosomal fraction and in myelin it was higher than that in total tissue homogenate. Following cerebral ischemia there was a 6- to 10-fold increase in putrescine in tissue homogenate: In the cortex it increased to 429 +/- 24 pmol/mg protein, in the hippocampus to 585 +/- 70 pmol/mg protein, and in the striatum to 718 +/- 98 pmol/mg protein. Among the isolated fractions the highest levels of putrescine were found in synaptosomes from the striatum (663 +/- 196 pmol/mg protein), followed by the hippocampus (500 +/- 125 pmol/mg protein) and the cerebral cortex (349 +/- 45 pmol/mg protein). This order correlated to the degree of morphological injury which was most pronounced in the striatum and the hippocampus and less in the cerebral cortex. The results of the present study provide further evidence of a relationship between postischemic putrescine levels and the extent of ischemia-induced neuronal injury.

Animals↗