A possible contribution by glial cells to neuronal energy production enzyme-histochemical studies in the developing rat cerebellum

Summary Recent reports have revealed that certain neurons do not survive in vitro in the presence of glucose, which is the primary substrate and exclusive source of energy in the brain. But these neurons can survive in the presence of low-molecular-weight agents such as pyruvate, which are supplied by glial cells (Selak et al. 1984). To test whether this result also holds true in vivo, we investigated the distribution of hexokinase, lipoic dehydrogenase, -hydroxybutyrate dehydrogenase, and glucose-6-phosphate dehydrogenase activities in the developing rat cerebellum. Hexokinase activity was relatively higher in glial cells than in neurons. After postnatal day 8, the activity of hexokinase could hardly be detected in Purkinje cells, whereas it was highest in Bergmann glial cells. Purkinje cells were the only type of neuron with high levels of lipoic dehydrogenase at all ages tested. -Hydroxybutylate dehydrogenase activity was also high in Purkinje cells, especially in those from young rats. Relatively high glucose-6-phosphate dehydrogenase activity was demonstrated in basket and stellate cells from adult brain. Thus, it appears that, in vivo, certain neurons utilize relatively little glucose, and it is indeed possible that glial cells may supply some substance(s) other than glucose, for example pyruvate, as the primary source of energy.     

Regional brain GABA metabolism and release during hepatic coma produced in rats chronically treated with carbon tetrachloride

Hepatic coma was induced in rats chronically treated with CCl₄, by means of a single injection of ammonium acetate. The activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), as well as the synaptosomal uptake and release of [³H]GABA, were measured in the following brain areas of the comatose rats: cortex, striatum, hypothalamus, hippocampus, midbrain and cerebellum. Hepatic coma was associated with a general decrease of GAD activity, whereas GABA-T activity was diminished only in the hypothalamus, striatum and midbrain. During hepatic coma, the K⁺-stimulated [³H]GABA release was notably diminished in the striatum and cerebellum, whereas a significant increase was observed in the hippocampus. [³H]GABA uptake increased in most regions after CCl₄ treatment, independently of the presence of coma. The results indicate that GABAergic transmission seems to be decreased in most cerebral regions during hepatic coma.     

Energy metabolism in glutamatergic neurons,GABAergic neurons and astrocytes in primary cultures

Several aspects of energy metabolism (glucose utilization, lactate production,¹⁴CO₂ production from labeled glucose, glutamate or pyruvate, oxygen consumption and contents of ATP and phosphocreatine) were measured in cerebellar granule cells (glutamatergic) in primary cultures and compared with corresponding data for cerebral cortical neurons (mainly GABA-ergic) and astrocytes. Cerebellar granule cells and astrocytes were metabolically more active than cerebral cortical neurons. Glutamate which is utilized as a major metabolic fuel as astrocytes and, to a lesser extent, in cerebral cortical neurons, was virtually not oxidized in cerebellar granule cells.Special Issue dedicated to Prof. Holger Hydén.     

Changes of mitochondrial membrane proteins in rat cerebellum during aging

Qualitative and quantitative changes of mitochondrial membrane proteind during aging were investigated. Free (non-synaptic) mitochondria were purified from rat cerebellum at different ages (4, 8, 12, 16, 20, and 24 months). Mitochondrial outer membrane (OM), inner membrane (IM) and matrix (MX) were separated and the proteins were extracted and analyzed by gel-electrophoresis.After staining, the gels were scanned densitometrically to quantify the proteins. No significant changes in the quantity of OM or MX protein subunits were observed, while serveral statistically significant quantitative changes in IM proteins with age were found. These age-dependent modifications of inner membrane mitochondrial proteins may play an important role in energy transduction, transport systems and regulatory enzymatic activities in mitochondria.     

Isolation of a cAMP-requiring mutant in Escherichia coli K-12: evidence of growth regulation via N-acetylglucosamine metabolism controlled by cAMP

Abstract An adenylate cyclase gene ( cya ) mutant was mutagenized and an adenosine 3,5-cyclic monophosphate (cAMP)-requiring mutant (KM8161) was obtained on Davis minimal medium containing glucose in the presence or absence of cAMP. KM8161 also required N -acetylglucosamine for its growth instead of cAMP. Furthermore, the mutant could use neither glucosamine nor N -acetylglucosamine as the carbon source. These results indicate that the cAMP-requiring property is due to multiple mutations of a few genes involved in amino sugar metabolism in addition to cya . By genetic analysis of KM8161, one gene, which was tentatively termed cidA and located near 2 min on the chromosomal map, proved to be defective. Reversion of cidA mutation in KM8161 resulted in recovery of not only the cAMP-requiring phenotype but also non-utilization of amino sugars. When both cAMP and N -acetylglucosamine or glucosamine were added to the culture medium for KM8161, only N -acetylglucosamine could be utilized as the carbon source. These studies s strongly suggest that the cidA or cya mutation in KM8161 causes deficiency in different stages of amino sugar metabolism and the regulatory circuit of growth by cAMP is mediated via control of N -acetylglucosamine metabolism.     

The effects of cultural conditions on growth and secondary metabolism in Streptomyces thermoviolaceus

Abstract Granaticin, an isochromate quinone antibiotic is synthesized as a secondary metabolite by Streptomyces thermoviolaceus . Antibiotic productivity was investigated under a variety of cultural conditions, including complex and defined media, mesophilic and thermophilic temperatures and a variety of sole carbon sources. In a defined medium growth was supported, to varying extents, by different carbon sources and in most cases granaticin production was observed. Highest biomass and granaticin yields were obtained when cultures were grown in the presence of xylan, fructose, glutamate or proline as carbon source. Changes in pH during growth affected both the timing and extent of granaticin production.     

Transfer of the CMS trait in Daucus carota L. by donor-recipient protoplast fusion

Summary X-irradiated protoplasts of Daucus carota L., 28A1, carrying cytoplasmic male sterile (CMS) cytoplasm and iodoacetamide-treated protoplasts of a fertile carrot cultivar, K5, were fused with polyethylene glycol (PEG), and 73 plants were regenerated. Twenty-six randomly chosen regenerated plants had non-parental mitochondrial DNA (mtDNA) as revealed by XbaI restriction fragment patterns, and all of the plants investigated had diploid chromosome numbers. Of the 11 cybrid plants that showed mtDNA fragment patterns clearly different from those of the parents, 10 plants showed male sterility with brown or red anthers, and one plant possessed partially sterile yellow anthers. The mtDNA fragment patterns of the ten cybrid plants with male sterile flowers resembled that of a CMS parent, 28A1; and four fragments were identified that were common between the sterile cybrid plants and 28A1, but absent from the partially sterile cybrid plants and a fertile cultivar, K5. The results indicated that the CMS trait of the donor was efficiently transferred into the cybrid plants by donor-recipient protoplast fusion.     

Carbon balance during CAM: an assessment of respiratory CO2 recycling in the epiphytic bromeliads Aechmea nudicaulis and Aechmea fendleri

Abstract The regulation of crassulacean acid metabolism (CAM) under controlled environmental conditions has been investigated for two tropical epiphytes, relating plant water and carbon balance to growth form and habitat preference under natural conditions. Aechmea fendleri is restricted to wet, upper montane regions of Trinidad, while A. nudicaulis has a wider distribution extending into more arid regions of the island. Morphological characteristics of these plants are related to habitat preference in terms of leaf succulence (0.44 and 0.94 kg m^?2 for the two species respectively) and a distinct layer of water storage parenchyma in A. nudicaulis In contrast, the thinner leaves of A. fendleri contain little water-storage parenchyma and less chlorenchyma per unit area, but the plants have a more open leaf rosette. The two species differ in expression of CAM, since the proportion of respiratory CO₂ recycled as part of CAM had been found to be much lower in A. fendleri This study compared the efficiency of water use and role of respiratory CO₂ recycling under two PAR regimes (300 and 120 μnol m^?2 s^?1) and three night temperatures (12, 18 and 25 °C). Dark CO₂ uptake rates for both species were comparable to plants in the field (maximum of 2.3 ± 0.2 μmol m^?2s^?1± SD, n= 3). Total net CO₂ uptake at night increased on leaf area basis with temperature for both species under higher PAR, although under the low PAR regime CO₂ uptake was maximal at 18 °C. Water-use efficiency (WUE) increased at 18 °C and 25 °C during dark CO₂ uptake (Phase I) and also during late afternoon photosynthesis (Phase IV) in both species. For A. fendleri, dawn to dusk changes in titrable acidity (ΔH ⁺) were similar under high and low PAR, although ΔH⁺ was correlated to night temperature and PAR in A. nudicaulis. The proportion of ΔH⁺ derived from respiratory CO₂ also varied with experimental conditions. Thus percentage recycling was lower in A. fendleri under high PAR (0–10%), but was only reduced at 18 °C under low PAR. Recycling by A. nudicaulis ranged from 32–42% under high PAR, but was also reduced to 6% under low PAR at 18 °C; at 12 °C and 25 °C, recycling was 37% and 52% respectively. Previous studies have suggested a relationship between the proportion of recycling and degree of water stress. This study indicated that CAM as a CO₂ concentrating mechanism regulates both water-use efficiency and plant carbon balance in these epiphytes, in response to PAR and night temperature. However, the precise relationship between respiratory processes and the balance between external and internal sources of CO₂ is as yet unresolved.     

Complexity and tissue specificity of the mitochondrial respiratory chain

There is a renewed interest in the structure and functioning of the mitochondrial respiratory chain with the realization that a number of genetic disorders result from defects in mitochondrial electron transfer. These so-called mitochondrial myopathies include diseases of muscle, heart, and brain. The respiratory chain can be fractionated into four large multipeptide complexes, an NADH ubiquinone reductase (complex I), succinate ubiquinone reductase (complex II), ubiquinol oxidoreductase (complex III), and cytochromec oxidase (complex IV). Mitochondrial myopathies involving each of these complexes have been described. This review summarizes compositional and structural data on the respiratory chain proteins and describes the arrangement of these complexes in the mitochondrial inner membrane. This biochemical information is provided as a framework for the diagnosis and molecular characterization of mitochondrial diseases.     

Trace elements in human parotid saliva

Although various proteins and some electrolytes have been measured in human saliva, little systematic data about the major and minor elemental components of this body fluid have been obtained. In order to obtain such data, concentrations of C, Na, P, Cl, K, Ca, Sc, Cr, Fe, Co, Zn, Se, Br, Rb, Sb, I, and Cs in human parotid saliva were measured by instrumental nuclear methods. The data obtained confirmed the relative lack of Zn in saliva of patients with hypogeusia (decreased taste acuity) and suggested that concentrations of Na, Cl, Br, and Ca followed the order: normals > hypogeusia > hyposmia (decreased smell acuity). To compare concentrations of elements in saliva with those in blood and urine, absolute concentrations were normalized to that of Na through the use of a concept called an enrichment factor. On this basis, parotid saliva is relatively depleted in Se, Zn, and Fe and enriched for most other elements relative to blood plasma indicating that the fluid is not simply a transudate of blood plasma. Using this same technique, saliva composition was found more similar to urine than blood plasma, being relatively depleted in Se, Cs, and Co, being enriched in I, Br, and Cr and having about the same relative concentrations of P, Cl, Zn, Fe, Ca, K, and Rb. As the total body concentrations of many of the enriched elements in saliva are extremely small, their enrichment in saliva suggests special roles for these elements in the oral cavity. Because of its accessibility, ease of collection, and interaction with some body constituents, saliva represents a useful, albeit neglected, tool in the diagnosis of some physiological and pathological changes in body function and in understanding important aspects of trace metal metabolism.