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Biomedical subjects

L Hertz

Publications and source records attributed to L Hertz.

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

Glutamine transaminase K and omega-amidase activities in primary cultures of astrocytes and neurons and in embryonic chick forebrain: marked induction of brain glutamine transaminase K at time of hatching.

Glutamine transaminase K and omega-amidase activities are present in the chick brain and in the brains of adult mice, rats, and humans. However, the activity of glutamine transaminase K in adult mouse brain is relatively low. In the chick embryo, cerebral glutamine transaminase K activity is low between embryonic days 5 and 17, but by day 23 (day of hatching) activity rises dramatically (> 15-fold). Cerebral omega-amidase activity is relatively high at embryonic day 5 but lower between days 5 and 17; at embryonic day 23 the activity rises to a maximum. Both glutamine transaminase K and omega-amidase are present in cultured chick, rat, and mouse astrocytes and neurons. For each species, the activity of glutamine transaminase K is higher in the astrocytes than in the neurons. The activity of omega-amidase is about the same in the cultured chick astrocytes and neurons but significantly higher in rat astrocytes than in rat neurons. The data suggest that the rise in brain glutamine transaminase K activity in the chick embryo at hatching correlates with maturation of astrocytes. Glutamine transaminase K may be involved in glutamine cycling in astrocytes. Glutamine transaminase K appears to be a major cysteine S-conjugate beta-lyase of the brain and may play a role in the neurotoxicity associated with exposure to dichloroacetylene and perhaps to other toxins.

Amidohydrolases↗
PubMed1994

Signalling effect of elevated potassium concentrations and monoamines on brain energy metabolism at the cellular level.

The effects of elevated K+ concentrations and monoamine transmitters on different cell types in the CNS and on different subcellular structures in these cells are reviewed. Pronounced differences exist in the metabolic processes that are stimulated by excess K+ and by adrenergic agonists, e.g., noradrenaline. An elevation in the extracellular K+ concentration appears to enhance neuronal-astrocytic interaction by stimulating metabolic processes involved in (1) the promotion of supply of precursors for transmitter glutamate, and (2) reestablishment of resting ion distribution following neuronal excitation. The monoamine transmitters stimulate energy production and Na+,K(+)-ATPase activity in astrocytes in a complex manner and, in so doing, facilitate their role in ion regulation. However, in contrast to excess K+, they do not enhance the production of astrocytic precursors for neuronal glutamate production. Emphasis is placed on possible profound differences in metabolic effects on excitatory and inhibitory neurotransmission and on the importance of stimulation of glycolytic metabolism in astrocytes versus oxidative metabolism in neurons.

Animals↗
PubMed1993

Potassium-induced stimulation of oxidative metabolism of glucose in cultures of intact cerebellar granule cells but not in corresponding cells with dendritic degeneration.

Production of 14CO2 from uniformly labelled glucose was measured in conventional cultures of mouse cerebellar granule cells (a glutamatergic cell type) and in corresponding cultures which had been grown in such a manner that they showed massive degeneration of dendrites, but were otherwise morphologically normal. Both kind of cultures were studied during exposure to either a physiological potassium concentration (5 mM) or an elevated extracellular potassium concentration. During exposure to the normal extracellular potassium concentration, the rate of CO2 production in the two types of culture was identical. In the conventional granule cell cultures, the CO2 production showed a rectilinear increase as a function of the extracellular potassium concentration from 5-100 mM; this stimulation was abolished by ouabain, a specific inhibitor of Na+,K(+)-ATPase. In granule cells showing dendritic degeneration, CO2 production increased only slightly at extracellular potassium concentrations of 25-100 mM. These findings suggest that the metabolic stimulation in morphologically intact cells may be the result of a depolarization-induced sodium uptake, which has a mainly or exclusively dendritic localization, and secondarily leads to a stimulation of the Na+,K(+)-ATPase at its intracellular sodium-sensitive site.

Animals↗
PubMed1993

Stimulation of glycogenolysis in astrocytes by fluoxetine, an antidepressant acting like 5-HT.

Fluoxetine is a recently introduced, widely used antidepressant. It is known as a specific inhibitor of serotonin uptake into synaptosomes but has not previously been recognized as having any direct effect on brain cell serotonin receptors. The present study describes direct effects of fluoxetine on free cytosolic calcium concentration and on breakdown of glycogen in astrocytes (a glial cell type), which are known to express serotonin receptors. Evidence is presented, suggesting that these effects are evoked by an agonist action on the 5-HT1C receptor.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Glutamate uptake and glutamate content in primary cultures of mouse astrocytes during anoxia, substrate deprivation and simulated ischemia under normothermic and hypothermic conditions.

During brain ischemia in vivo the extracellular concentration of the excitotoxic amino acid, glutamate, increases. This increase could be caused either by an enhanced formation rate of glutamate (from glutamine) or by an impaired re-uptake (or both). This re-uptake occurs to a large extent in astrocytes. In the present study we have determined glutamate uptake and the ability of the cells to maintain their glutamate content during exposure to anoxia, substrate deprivation and combined substrate deprivation and anoxia ('simulated ischemia') for a duration of up to 4 h. Isolated anoxia had no significant effect, whereas both substrate deprivation alone and 'simulated ischemia' reduced glutamate uptake and glutamate content by one-half after 2 h. Under hypothermic conditions (incubation at 32 degrees C), which in in vivo experiments exerts some protection against ischemic cell death in neurons, ischemia of intermediate duration (2 h) decreased glutamate uptake and glutamate content to a less extent than at 37 degrees C. Hypothermia did not have a similar effect during exposure to isolated substrate deprivation.

Animals↗
PubMed1993

Uptake, release, and metabolism of alanine in neurons and astrocytes in primary cultures.

The uptake, release, and metabolism of alanine were studied in primary cultures of cerebral cortical neurons or astrocytes and cerebellar granule neurons. All three cell types exhibited a saturable, sodium-dependent uptake of alanine with Km values (microM) of 256 +/- 30, 463 +/- 39, and 292 +/- 39, respectively, and Vmax values (nmol/min/mg) of 15.9 +/- 0.7, 7.9 +/- 0.01, and 17.4 +/- 0.8, respectively. The corresponding values (nmol/min/mg) for the specific activity of alanine aminotransferase were 4.7 +/- 0.4, 17.1 +/- 2.5, and 4.5 +/- 0.9 (all values represent the mean +/- SEM). Release of alanine from the cells was rectilinear with time over a 10 hr period in case of astrocytes (40 nmol/hr/mg) and cerebellar granule neurons (21 nmol/hr/mg). In cortical neurons the release rate declined from an initial value of 19 nmol/hr/mg during the first 3 hr to a value of less than 3 nmol/hr/mg during the subsequent 7 hr of incubation. Metabolism of [14C]alanine to 14CO2 was found to have a lag period of 15 min and subsequently the rate of CO2 production was constant over a 45 min period with a value of 0.5 nmol/min/mg in granule neurons and about 0.3 nmol/min/mg in the other two cell types. Altogether the results show that alanine is preferentially produced in and released from astrocytes and accumulated into both GABAergic cortical neurons and glutamatergic cerebellar granule neurons.

Aging↗
PubMed1993

Ischemia-induced death of astrocytes and neurons in primary culture: pitfalls in quantifying neuronal cell death.

We have demonstrated that both astrocytes and cerebellar granule cell neurons die during an ischemic insult only when there is complete loss of mitochondrial membrane potential. This was determined by comparing the ability of mitochondria to sequester rhodamine 123 with the ability of cells to exclude propidium iodide. We have also demonstrated that in astrocyte cultures cellular LDH loss correlates directly with propidium iodide uptake, i.e. cell death, and inversely with rhodamine 123 uptake. Thus, both LDH loss and rhodamine 123 uptake can be used to quantitatively measure astrocyte cell death in culture; however, this is not the case with neuronal cultures. It was demonstrated that even in highly enriched cerebellar granule cell neuron cultures where astrocytes comprise less than 10% of the total culture protein, approximately 40% of total culture LDH was in the astrocytes. This was also the case with rhodamine 123 sequestration. Caution must therefore be used when using the LDH technique to determine the proportion of neurons that have died in such enriched neuronal cultures.

Animals↗
PubMed1993

Protective effect of hypothermia during ischemia in neural cell cultures.

Hypothermia offers protection from the effects of ischemia in small animals. We have recently shown that similar to small animals, hypothermia may also be protective in an astrocytic model of "simulated ischemia" in cell culture. This study was designed to look at the protective effects of hypothermia in cultures of cerebellar granular (glutamatergic) and cortical (GABAergic) neurons. We used LDH release into the medium as an indicator for neuron damage. Experiments were all done in sister cultures, in groups of six cultures at two temperatures (37 and 32 degrees Celsius). The duration of ischemia was three hours in cerebellar granular neuronal cell cultures and six hours in cortical neurons. LDH release was measured immediately after the insult. Hypothermia protected both granular and cortical neurons. In granular cells, LDH release was 62 +/- 18 at 32 degrees and 212 +/- 15 at 37 degrees (p = 0.02). Cortical neurons showed LDH release of 15 +/- 2 at 32 degrees and 32 +/- 2 at 37 degrees (p = 0.005). Our study suggests that similar to astrocytes, the protective effects of hypothermia are evident in neuronal cell cultures from the cerebellum and the cerebral cortex. Cell culture systems should prove useful techniques in understanding mechanisms of hypothermic protection during simulated ischemia in neurons from different sites.

Animals↗
PubMed1993

NMR spectroscopic studies of 13C acetate and 13C glucose metabolism in neocortical astrocytes: evidence for mitochondrial heterogeneity.

Neocortical astrocytes were incubated with 13C-labeled substrates to determine metabolic pathways. 13C NMR spectroscopy was used to analyze 13C incorporation into glutamine and citrate from the different precursors--[1-13C]glucose or [2-13C]acetate. When glucose was the labeling substrate, incorporation due to pyruvate carboxylation should be observed in the C-2 position in glutamine and the C-4 position in citrate. A large incorporation due to pyruvate carboxylation was observed in glutamine in the C-2 and C-3 positions, but not in citrate. When acetate was the precursor, the labeling ratios in the C-2/C-4 positions in glutamine and in the equivalent positions in citrate were 0.27 and 0.11, respectively. Moreover, acetate labeled lactate in the C-2 position much less than did glucose. Altogether, these observations led to the conclusion that glutamine precursors and citrate are either produced in different types of astrocytes or in different tricarboxylic acid cycles, situated in functionally different mitochondria in the same cell, and that in all likelihood pyruvate carboxylase is expressed differently in these mitochondria.

Acetates↗
PubMed1993

Glutamate and glutamine metabolism and compartmentation in astrocytes.

Metabolism of glutamate and glutamine in cultured mouse cerebral cortical astrocytes has been investigated using either radioactively labelled (14C) amino acids or 13C-labelled amino acids combined with NMR spectroscopy of cell extracts and lyophilyzed incubation media. Using [U-13C]glutamate it has been shown that in astrocytes exogenously supplied glutamate is primarily (70%) metabolized oxidatively through the tricarboxylic acid (TCA) cycle and to a lesser extent (30%) directly to glutamine. Glutamate metabolized in the TCA cycle is to a large extent recovered as lactate showing that the astrocyte-specific enzyme, malic enzyme is functionally active. Incubation with [U-14C]glutamine led to a higher specific radioactivity in glutamate than in glutamine. It could also be shown that glutamate and glutamine were metabolized differently to aspartate and alanine. These results taken together strongly suggest that glutamate/glutamine metabolism in astrocytes is compartmentalized and a model with multiple cytoplasmic and mitochondrial compartments of these amino acids is proposed.

Animals↗
PubMed1993

Utilization of glutamine and of TCA cycle constituents as precursors for transmitter glutamate and GABA.

In the present review evidence is presented that (1) glutamine synthesis in astrocytes is essential for synthesis of GABA in neurons; (2) alpha-ketoglutarate in the presence of alanine (as an amino group donor) can replace glutamine as a precursor for synthesis of transmitter glutamate, but maybe not as a precursor for transmitter GABA; (3) differences exist in the intraneuronal metabolic pathways for utilization of alpha-ketoglutarate plus alanine and of glutamine, and (4) alanine also functions as a substrate for oxidative metabolism in glutamatergic neurons. It should be emphasized that the supply of precursors for transmitter glutamate and GABA in glutamatergic and GABAergic neurons depends on metabolic processes in astrocytes regardless whether glutamine or alpha-ketoglutarate plus L-alanine function as the transmitter precursors. The key reason that an interaction with astrocytes is essential is that both pyruvate carboxylase, the major enzyme in the brain for net synthesis of tricarboxylic acid cycle intermediates, and glutamine synthetase, the enzyme forming glutamine from glutamate, are specifically located in astrocytes, but not in neurons.

Animals↗
PubMed1992

Hypothermia protects astrocytes during ischemia in cell culture.

A mild decrease in temperature (2-3 degrees) can result in marked attenuation of ischemic neuronal damage in living animals. We now report the protective effects of hypothermia in an astrocyte with simulated ischemia in cell culture system. Hypothermia when used during ischemia showed significant reduction of damage. Brief episodes of post-ischemic hypothermia were not protective whereas more prolonged post-ischemic hypothermia showed moderate protection. Cell culture systems may prove to be useful tools to study the mechanisms of hypothermic protection during ischemia.

Animals↗
PubMed1992

Long-lasting abolishment of noradrenaline induced stimulation of oxidative metabolism after chronic exposure of developing mouse astrocytes to cocaine.

Rate of 14CO2 production from [l-14C]glutamate was determined as a measurement of oxidative metabolism in developing primary cultures of astrocytes, obtained from the neonatal mouse brain and grown in the absence (control) or presence of cocaine. From the age of 3 days, the drug-exposed cultures were grown in a tissue culture medium containing either 1 or 3 microM cocaine. After 2 months of chronic exposure to cocaine the metabolic rate showed an increase of approximately 50%, but there was a long lag period (several weeks) before this response occurred. In contrast to a marked stimulation of CO2 production when noradrenaline was added to untreated cultures of the same age, there was no similar effect of noradrenaline on cultures treated with cocaine. After exposure to cocaine for 21 days (24-day-old cultures), both the enhanced CO2 production and the abolishment of the normal response to noradrenaline persisted during 'withdrawal' (cessation of drug exposure) throughout the total period investigated, i.e. to an age of 60 days (corresponding to a withdrawal period of 36 days). The correlation of these findings with in vivo data is discussed.

Animals↗
PubMed1992

Uptake and metabolism of malate in neurons and astrocytes in primary cultures.

Uptake and oxidative metabolism of [14C]malate as well as its incorporation into aspartate, glutamate, glutamine, and GABA were studied in cultured cerebral cortical neurons (GABAergic), cerebellar granule neurons (glutamatergic), and cerebral cortical astrocytes. All cell types exhibited high affinity uptake of malate (Km 10-85 microM) with slightly higher Vmax values in neurons (0.1-0.2 nmol x min-1 x mg-1) than in astrocytes (0.06 nmol x min-1 x mg-1). Malate was oxidatively metabolized in all three cell types with nominal rates of 14CO2 production of 2-15 pmol x min-1 x mg-1. The oxidation of malate was only slightly inhibited by 5 mM aminooxyacetic acid (AOAA). In granule cell preparations [14C]malate was incorporated into aspartate and glutamate and, to a much less extent, into glutamine. This incorporation was blocked by 5 mM AOAA. Astrocytes exhibited slightly higher incorporation rates into aspartate and glutamate, but in these cells glutamine was labelled to a considerable extent. AOAA (5 mM) inhibited the incorporation by 60-70%. In cultures of cerebral cortical neurons, very low levels of radioactivity derived from [14C]malate were found in aspartate and glutamate, and GABA was not labelled at all. Glutamine had the same specific activity as glutamate, indicating that the low rates of incorporation of radioactivity into amino acids in this preparation is likely to exclusively represent metabolism of malate in the small population of astrocytes (5% of total cell number), contaminating the neuronal cultures. The findings suggest that exogenous malate to a quantitatively limited extent may serve as a precursor for transmitter glutamate in glutamatergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Dexmedetomidine, a potent and highly specific alpha 2 agonist, evokes cytosolic calcium surge in astrocytes but not in neurons.

Dexmedetomidine is an extremely potent alpha 2 adrenoceptor agonist which can reduce anaesthetic requirements by up to 90%. However, the precise cellular mechanism of action of this agent is not known. Primary cultures of murine neurons and astrocytes were grown to test the hypothesis that changes in free intracellular calcium may trigger cellular responses to this drug. In astrocyte cultures, experiments revealed a pronounced increase in cytosolic calcium concentration when 100 nM dexmedetomidine was administered. However, in cultured cerebellar granule cell neurons there was no calcium response observed with similar or even higher concentrations of the drug. Results suggest dexmedetomidine may exert its primary effect on the central nervous system via astrocytes.

Adrenergic alpha-Agonists↗