Increase In Respiratory Activity Research Articles

Imbalance in Glucose Metabolism Regulates the Transition of Microglia from Homeostasis to Disease-Associated Microglia Stage 1.

Microglia undergo two-stage activation in neurodegenerative diseases, known as disease-associated microglia (DAM). TREM2 mediates the DAM2 stage transition, but what regulates the first DAM1 stage transition is unknown. We report that glucose dyshomeostasis inhibits DAM1 activation and PKM2 plays a role. As in tumors, PKM2 was aberrantly elevated in both male and female human AD brains, but unlike in tumors, it is expressed as active tetramers, as well as among TREM2+ microglia surrounding plaques in 5XFAD male and female mice. snRNAseq analyses of microglia without Pkm2 in 5XFAD mice revealed significant increases in DAM1 markers in a distinct metabolic cluster, which is enriched in genes for glucose metabolism, DAM1, and AD risk. 5XFAD mice incidentally exhibited a significant reduction in amyloid pathology without microglial Pkm2 Surprisingly, microglia in 5XFAD without Pkm2 exhibited increases in glycolysis and spare respiratory capacity, which correlated with restoration of mitochondrial cristae alterations. In addition, in situ spatial metabolomics of plaque-bearing microglia revealed an increase in respiratory activity. These results together suggest that it is not only glycolytic but also respiratory inputs that are critical to the development of DAM signatures in 5XFAD mice.

Impact of some mineral fertilizers on the pulmonary and direct surface respiration of the allospecies of Planorbarius corneus superspecies (Gastropoda: Pulmonata: Planorbidae) from the Ukrainian water bodies

The vicariant genetic allospecies of the superspecies complex of the great ramshorn snail Planorbarius corneus s. lato, “western” and “eastern” – in Right Bank and Left Bank Ukraine, respectively, – are among the widespread and numerous gastropods in the Ukrainian river network. They possess two modes of respiration: pulmonary and surface (diffusive). The gas exchange in these snails is connected to the presence of the respiratory pigment hemoglobin in their internal liquid medium (hemolymph), which transports oxygen in their tissues and organs, and carbon dioxide to the lungs. We studied the features of impact of three mineral fertilizers widespread in Ukraine (nitrate, potassium and phosphate) used in concentrations measured in MPC 0.01 mg/L (0.5, 1, 2, 3) on the indexes of pulmonary and surface diffusive respiration in both P. corneus s. lato allospecies. Exposure of experimental individuals to 0.5 MPC-solutions of mentioned fertilizers does not affect them. The increase of toxicant concentration up to 2 MPC, however, is followed by an increase in respiratory activity (p≤0.05–0.001), but beyond that up to 3 MPC induces a significant decline (p≤0.001). Considered individually, the examined mineral fertilizers presented the following order by their impact on great ramshorns: nitrate > potassium > phosphate. The “eastern” allospecies appeared to be more sensitive and less durable for all aforementioned pollutants by both lung and direct diffusive respiration, compared to the “western” allospecies (p≤0.05–0.001).

Potential of Serratia plymuthica IV-11-34 strain for biodegradation of polylactide and poly(ethylene terephthalate)

Serratia plymuthica strain IV-11-34 belongs to the plant growth promoting bacteria (PGPR). In the sequenced genome of S. plymuthica IV-11-34, we have identified the genes involved in biodegradation and metabolisms of xenobiotics. The potential of S. plymuthica IV-11-34 for the degradation of biodegradable aliphatic polyester polylactide (PLA) and resistant to biodegradation – poly(ethylene terephthalate) (PET) was assessed by biochemical oxygen consumption (BOD) and carbon dioxide methods. After seven days of growth, the bacteria strain showed more than 80% and 60% increase in respiratory activity in the presence of PLA and PET, respectively. We assume that during biodegradation, S. plymuthica IV-11-34 colonise the surface of PLA and PET, since the formation of a biofilm on the surface of polymers was shown by the LIVE/DEAD method. We have demonstrated for the relA gene, which is an alarmone synthetase, a 1.2-fold increase in expression in the presence of PLA, and a 4-fold decrease in expression in the presence of PET for the spoT gene, which is a hydrolase of alarmones. Research has shown that the bacterium has the ability to biodegrade PLA and PET, and the first stage of this process involves bacterial stringent response genes responsible for survival under extreme conditions.

On the use of inhalations of carbon dioxide in surgery according to Dzialoszunskiy (Zentr. f. Chir., 1926, No. 23)

According to Dzialoszunsky (Zentr. F. Chir., 1926, No. 23), carbon dioxide during inhalation causes strong irritation of the respiratory center and deep and frequent breathing. Due to a noticeable increase in respiratory activity, the inhaled drug is released from the body faster, the lungs are ventilated down to the smallest bronchi, and a secret is released that fills the respiratory tract.

Germinative metabolism and seedling growth of cowpea (Vigna unguiculata) under salt and osmotic stress

Cowpea (Vigna unguiculata) plays a strategic role in arid and semi-arid regions being used in both human food and animal supplementation. Although it is described as moderately tolerant plant to soil salinity, little is known about the salinity tolerance amongst different cultivars and phenological phases. In this study, we investigated the response of seed germination and seedling establishment of V. unguiculata cv. BRS Imponente under conditions of both salt (NaCl) and osmotic stress (Polyethylene glycol 6000; PEG). Although such conditions lead to an accumulation of hydrogen peroxide (H2O2), oxidative damage was observed only in seeds exposed to PEG. The maintenance of H2O2 concentrations in seeds exposed to NaCl, as well as the increase in respiratory activity, were the main mechanisms of tolerance identified in seeds exposed to NaCl. However, although germination was not affected, NaCl concentrations ≥75 mM were phytotoxic, reducing seedling growth. The osmotic component of salinity (PEG) reduced germination (Ѱo < -0.123 MPa) and seedling establishment (all osmotic potentials) showing the cultivar sensitive to osmotic stress in the early stages of development. After germination, the BRS Imponente cultivar presented reduced tolerance to salt stress, which limits its performance in soils with high salinity (≥ 75 mM of NaCl).

Post-harvest physiology of pitaya at different ripening stages

Red-fleshed pitaya is an attractive fruit not due only to the color of its flesh and skin, but also the scaly shape of its skin. In addition to being a source of vitamins and minerals, it has high commercial value and represents an alternative for cultivation in semiarid regions. Information about the post-harvest physiology of pitaya, which interferes with its ripening, allows the adoption of preservation and quality-maintenance practices. This study examines the respiratory activity and post harvest alterations of pitaya picked in the commercially immature stage of ripeness, by comparing them with fruits picked fully ripe. Physical and chemical aspects of the fruits were evaluated in two harvests, in 2019 and 2020. Six days after harvest, there was an increase in respiratory activity and a change in color in both ripe and commercially immature fruits. Therefore, pitayas picked commercially immature in both harvests had an increase in respiratory activity post-harvest, with a change in skin color during storage; and six days after harvest, in the 2019 harvest, the fruits resembled those that ripened on the plant, without having their quality compromised. However, in the 2020 harvest, six days after harvest, the fruits picked fully ripe showed soluble solids/titratable acidity ratio, betacyanins and ascorbic acid contents similar to those measured in the commercially immature fruits.

Effects of Propranolol on Growth, Lipids and Energy Metabolism and Oxidative Stress Response of Phaeodactylum tricornutum.

Simple SummaryIn the past two decades, increasing attention has been directed to investigate the incidence and consequences of pharmaceuticals in the aquatic environment. Propranolol is a non-selective β-adrenoceptor blocker used in large quantities worldwide to treat cardiovascular conditions. Diatoms (model organism) exposed to this compound showed evident signs of oxidative stress, a significant reduction of the autotrophic O2 production and an increase in the heterotrophic mitochondrial respiration. Additionally, diatoms exposed to propranolol showed a consumption of its storage lipids. In ecological terms this will have cascading impacts in the marine trophic webs, where these organisms are key elements, through a reduction of the water column oxygenation and essential fatty acid availability to the heterotrophic organisms that depend on these primary producers. In ecotoxicological terms, diatoms photochemical and fatty acid traits showed to be potential good biomarkers for toxicity assessment of diatoms exposed to this widespread pharmaceutical compound.Present demographic trends suggest a rise in the contributions of human pharmaceuticals into coastal ecosystems, underpinning an increasing demand to evaluate the ecotoxicological effects and implications of drug residues in marine risk assessments. Propranolol, a non-selective β-adrenoceptor blocker, is used worldwide to treat high blood pressure conditions and other related cardiovascular conditions. Although diatoms lack β-adrenoceptors, this microalgal group presents receptor-like kinases and proteins with a functional analogy to the animal receptors and that can be targeted by propranolol. In the present work, the authors evaluated the effect of this non-selective β-adrenoceptor blocker in diatom cells using P. tricornutum as a model organism, to evaluate the potential effect of this compound in cell physiology (growth, lipids and energy metabolism and oxidative stress) and its potential relevance for marine ecosystems. Propranolol exposure leads to a significant reduction in diatom cell growth, more evident in the highest concentrations tested. This is likely due to the observed impairment of the main primary photochemistry processes and the enhancement of the mitochondrial respiratory activity. More specifically, propranolol decreased the energy transduction from photosystem II (PSII) to the electron transport chain, leading to an increase in oxidative stress levels. Cells exposed to propranolol also exhibited high-dissipated energy flux, indicating that this excessive energy is efficiently diverted, to some extent, from the photosystems, acting to prevent irreversible photoinhibition. As energy production is impaired at the PSII donor side, preventing energy production through the electron transport chain, diatoms appear to be consuming storage lipids as an energy backup system, to maintain essential cellular functions. This consumption will be attained by an increase in respiratory activity. Considering the primary oxygen production and consumption pathways, propranolol showed a significant reduction of the autotrophic O2 production and an increase in the heterotrophic mitochondrial respiration. Both mechanisms can have negative effects on marine trophic webs, due to a decrease in the energetic input from marine primary producers and a simultaneous oxygen production decrease for heterotrophic species. In ecotoxicological terms, bio-optical and fatty acid data appear as highly efficient tools for ecotoxicity assessment, with an overall high degree of classification when these traits are used to build a toxicological profile, instead of individually assessed.

Syncytialization and prolonged exposure to palmitate impacts BeWo respiration.

Placental villous trophoblast mitochondrial respiratory function is critical for a successful pregnancy and environmental influences such as maternal obesity have been associated with respiratory impairment at term. More recently, a gestational high fat diet independent of maternal body composition, has been highlighted as a potential independent regulator of placental mitochondrial metabolism. The current study aimed to characterize the direct impact of a prolonged and isolated exposure to the dietary fatty acids Palmitate (PA) and Oleate (OA) upon placental cell mitochondrial respiratory function. BeWo cytotrophoblast (CT) and syncytiotrophoblast (SCT) cells were treated for 72 h with 100 µM PA, OA or PA+OA (P/O). Live-cell metabolic function was analyzed via the Seahorse XF Mito and Glycolysis Stress tests. Immunoblots and spectrophotometric activity assays were utilized to examine the protein expression and function of electron transport chain (ETC) complexes and key mitochondrial regulatory enzymes. Syncytialization of BeWo cells resulted reduced respiratory activity in conjunction with altered complex I and II activity and decreased pyruvate dehydrogenase (PDH) protein expression and activity. PA and P/O treatments were associated with increased basal and maximal respiratory activities in BeWo CT cells without alterations in protein expression or activity of individual ETC complexes and mitochondrial substrate regulators. The metabolic suppression in BeWo SCTs was consistent with that previously observed in primary human trophoblast cell cultures, while the observed increases in respiratory activity in PA-treated BeWo CTs may be indicative of an early timepoint of specific dietary saturated fat-mediated placental cell mitochondrial dysfunction.

Effect of a cold quarantine treatment on physiological disorders and quality of cactus pear fruit

Despite Italy is second only to Mexico for fresh production of cactus pears worldwide, postharvest handling and treatments are quite simply, being fruit immediately marketed after harvest. However, as the demand for fresh fruit beyond the harvesting period is constantly growing, in the next future the cactus pear industry likely will have to adopt postharvest treatments and technologies that can widen the marketable window. Yet, the potential exploitation of new markets in countries where the introduction of pests like Mediterranean fruit fly are considered risky, can be achieved only if fruit are subjected to approved quarantine protocols. Of the three main cultivated varieties (‘Bianca’, ‘Gialla’ and ‘Rossa’) limited studies concerning cold storage have been done mainly on fruit of cv ’Gialla’, while knowledge on response to cold quarantine treatments lacks for all cultivars. Thus this study was undertaken to get knowledge on postharvest behavior of the three main Italian cultivated cactus pears varieties, i.e. ‘Bianca’, ‘Gialla’ and ‘Rossa’ subjected to a cold quarantine treatment followed by either a week of simulated marketing conditions at 20 °C or by two additional weeks of storage at 8 °C before transfer to simulated marketing conditions at 20 °C for three days. These storage conditions so far are not practiced by packing houses as fruit are directly marketed after harvest, but could be a typical protocol in case fruit should be sold in countries that require approved cold quarantine treatments. Results showed an abnormal increase in respiratory activity and ethylene production rates following transfer from cold storage to 20 °C, especially after the two additional weeks of storage at 8 °C. Peel disorders and decay incidence were slight at the end of storage at 2 °C or 8 °C, but severe peel disorders developed when fruit were moved to 20 °C. Peel injury, decay incidence, the loss of overall appearance upon transfer to 20 °C were more severe in fruit stored for two additional weeks at 8 °C. Among the three cultivars, susceptibility to chilling injury and decay was higher in cv ‘Bianca’. Nevertheless, cold storage seems not to affect the chemical and sensory quality of fruit, whose changes were similar in all cultivars.

ATP and astrocytes play a prominent role in the control of the respiratory pattern generator in the lamprey.

The paratrigeminal respiratory group (pTRG) is responsible for the respiratory pattern generation in the lamprey. The role of ATP and astrocytes, known to control respiratory activity in mammals, was investigated in the lamprey respiratory network. ATP microinjected into the pTRG induces a biphasic response consisting of marked increases in respiratory frequency mediated by P2X receptors followed by a decrease in the respiratory motor output due to the ATP metabolite adenosine. We provide evidence that astrocytes are involved in the genesis of the normal respiratory pattern, ATP-induced responses and acidification-induced increases of the respiratory activity. The function of astrocytes in rhythmic networks appears to be phylogenetically conserved. The role of ATP and astrocytes in respiratory rhythm modulation has been recently investigated in neonatal rodents. However, no information on the role of ATP and astrocytes within the respiratory network of the lamprey is available, particularly within the paratrigeminal respiratory group (pTRG), the proposed respiratory central pattern generator. To address these issues, the present study was carried out on isolated brainstems of the adult lamprey. Bath application of ATP caused marked increases in respiratory frequency followed by decreases in the respiratory motor output, mediated by the ATP metabolite adenosine at the level of the pTRG. Bath applications and microinjections of agonists and antagonists of purinergic receptors showed that ATP increased respiratory activity through an action on pTRG P2X receptors. To disclose the respiratory role of astrocytes, we used bath application of the gliotoxin aminoadipic acid, which dramatically depressed the respiratory motor output that, however, promptly recovered following glutamine application. Furthermore, the excitatory responses to ATP-γ-S (a non-hydrolysable ATP analogue), but not to substance P, microinjected into the pTRG, were abolished. Finally, we also demonstrated that acidification-induced increases in respiratory activity were ATP-independent, but mediated by the astrocytes' glutamate-glutamine cycle. The results show for the first time that ATP and especially astrocytes strongly contribute to the modulation of the lamprey respiratory pattern. Their role in the modulation or maintenance of rhythmic neuronal activities appears to be phylogenetically conserved.

Effects of ocean acidification and warming on the mitochondrial physiology of Atlantic cod

The Atlantic cod (Gadus morhua) is an economically important marine fish species exploited by both fishery and aquaculture, especially in the North Atlantic and Arctic oceans. Ongoing climate changes are happening faster in the high latitude oceans with a higher increase of temperature and a steeper decrease in water pH due to anthropogenic CO2 than in the temperate regions threatening the existence of the Atlantic cod in the areas of its maximum exploitation. In this study, we investigated the mitochondrial physiology of two life-stages of cod under the sea water temperatures and pCO2 conditions forecasted for the year 2100 in the North Atlantic (+ 5 °C, 1000 μatm CO2). In embryos, the metabolism during development showed to be sensitive to rising temperatures with a general increase in respiratory activity until 9 °C (5 °C over the natural range) and a drop in activity at 12 °C mainly caused by a dramatic decrease in Complex I activity, which was not compensated by Complex II. In the adults, already well known for their metabolic plasticity, mitochondria from liver and heart are not affected by either increasing temperature or pCO2. However, in heart mitochondria of animals that were reared under warm hypercapnia (10 °C + 1000 μatm CO2), we found OXPHOS to exploit already 100% of the ETS capacity. This suggests that a further increase in temperature or pCO2 might lead to a mismatch in the ATP demand/production and consequently decrease heart performances. The different mitochondrial plasticities of the two life-stages reflect the sensitivity range at population level and thus can provide a more realistic reading frame of the potential survival of the North Atlantic cod population under climate change.

Extension of Chronological Lifespan byScEcl1 Depends on Mitochondria inSaccharomyces cerevisiae

Ecl1, a product of the YGR146C gene in Saccharomyces cerevisiae, was identified as a factor involved in chronological lifespan. In this study we found evidence that the function of Ecl1 in the extension of chronological lifespan is dependent on mitochondrial function. The respiratory activity of cells increased when Ecl1 was overexpressed or cells were grown under calorie restriction, but there was no additive effect of calorie restriction and Ecl1 overexpression on increases in respiratory activity or on the extension of chronological lifespan. Based on these results, we propose that overexpression of Ecl1 has same effect as caloric restriction and that its function also depends on mitochondria, just like caloric restriction.

Influence of Phosphorus and Carbon on Soil Microbial Activity in a Savannah Agroecosystem of Brazil

The microbial activity of soil plays an important role in the regulation of the transformation of carbon (C) and phosphorus (P). However, the activity of soil microbes is strongly related to the type of land-use system. The present work aimed to compare the microbial activity and metabolic responses of three different land-use systems to P (0 to 600 mg kg−1 of dry soil) and C additions in an Oxisol of the Brazilian savannah. The land-use systems studied were savannah vegetation (SV), 32-year-old pine plantation (PP), and 11-year-old no-tillage system (NT). The following analyses were carried out: amount of C carbon dioxide (CO2) evolved, total organic carbon (TOC), total glucose (TG), microbial biomass carbon (MBC), and metabolic yields (Y) from P and C additions to the soil. The different land-use systems affected the respiratory activity of microbiota, indicating an increase in SV and a decrease in PP when compared to the SV system under incubation for 17 days. The addition of P resulted in an increase of respiratory activity. The responses were adjusted by the Michaelis–Menten equation for all three land-use systems. The greatest TOC and lowest MBC were observed in NT and PP, respectively, when compared to SV. However, a lower content of TG was observed in NT in comparison to SV. Under bioassay conditions, the results confirm the greater microbial demand for P in PP and SV than in NT. The NT system showed greater metabolic yields when glucose was applied to the soil, suggesting that the response of microbiota in this system depends on easily available forms of C, as shown by the sugar content. The results showed expressive metabolic differences among the systems, suggesting that different soil uses change the dynamic of the responses of soil microorganisms.

Microinjection of methysergide into the raphe nucleus attenuated phrenic long-term facilitation in rats

Exposure to acute intermittent hypoxia (AIH) evokes persistent increase in respiratory activity that lasts up to 60 min after hypoxic episodes have ceased. This persistent increase in phrenic nerve activity (PNA) is known as phrenic long-term facilitation (LTF). AIH-induced phrenic LTF in anesthetized rats is serotonin dependant. The present study was performed to determine whether microinjection of methysergide (4 mM, 20 +/- 5 nl), a broad spectrum 5-HT receptor antagonist, into the caudal raphe nuclei influences phrenic LTF. Peak integrated PNA and respiratory frequency were recorded at 15, 30, and 60 min after five 3-min episodes of normocapnic hypoxia in urethane-anesthetized, vagotomized, paralyzed and ventilated male Sprague-Dawley rats. In control animals, phrenic nerve amplitude was elevated 66.7 +/- 8.6% from baseline 1 h after episodic hypoxia, indicating phrenic LTF. Experimental microinjections of methysergide prior to AIH exposure attenuated phrenic LTF (amplitude increase 2.62 +/- 2.9% over baseline). We conclude that methysergide microinjections into the caudal raphe region attenuated phrenic LTF induced by AIH, indicating involvement of 5-HT receptor activation at a supraspinal level.

Microbial biomass dynamics after addition of EDTA into heavy metal contaminated soils

An incubation experiment with addition of EDTA and alfalfa into soils contaminated with heavy metal over 200 years was carried out in order to evaluate the EDTA effects on microbial properties. Alfalfa was added to soils together with EDTA to examine its abilities to improve microbial activities affected by EDTA. The obtained results showed that the addition of EDTA led to a significant decrease of microbial biomass C during the first 24 days of incubation. At the end of the experiment the microbial biomass C significantly increased quite close to the original level. The EDTA amendment caused, probably due to the toxic effects, a significant increase in respiratory activities and of the metabolic quotient &lt;i&gt;q&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt;. An addition of alfalfa significantly improved the microbial biomass C contents in arable soils treated together with EDTA. Both, respiratory activities and &lt;i&gt;q&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; significantly increased after the soil treatment with EDTA together with alfalfa. EDTA alone decreased the microbial biomass, alfalfa alone as organic substrate was mineralised and utilised by soil microorganisms for their metabolism.

Intermittent hypoxia and respiratory plasticity in humans and other animals: does exposure to intermittent hypoxia promote or mitigate sleep apnoea?

This review focuses on two phenomena that are initiated during and after exposure to intermittent hypoxia. The two phenomena are referred to as long-term facilitation and progressive augmentation of respiratory motor output. Both phenomena are forms of respiratory plasticity. Long-term facilitation is characterized by a sustained elevation in respiratory activity after exposure to intermittent hypoxia. Progressive augmentation is characterized by a gradual increase in respiratory activity from the initial to the final hypoxic exposure. There is much speculation that long-term facilitation may have a significant role in individuals with sleep apnoea because this disorder is characterized by periods of upper airway collapse accompanied by intermittent hypoxia, one stimulus known to induce long-term facilitation. It has been suggested that activation of long-term facilitation may serve to mitigate apnoea by facilitating ventilation and, more importantly, upper airway muscle activity. We examine the less discussed but equally plausible situation that exposure to intermittent hypoxia might ultimately lead to the promotion of apnoea. There are at least two scenarios in which apnoea might be promoted following exposure to intermittent hypoxia. In both scenarios, long-term facilitation of upper airway muscle activity is initiated but ultimately rendered ineffective because of other physiological conditions. Thus, one of the primary goals of this review is to discuss, with support from basic and clinical studies, whether various forms of respiratory motor neuronal plasticity have a beneficial and/or a detrimental impact on breathing stability in individuals with sleep apnoea.

Effect of plastic permeability and exposure to light during storage on the quality of minimally processed broccoli and cauliflower

The impact of lighting on minimally processed broccoli and cauliflower packaged in four different film types (PVC and three P-Plus) has been measured and compared. The effect on the sensory quality of storage at 4 °C in darkness and under lighting was evaluated. The gas concentration in the packages, pH, mesophilic counts and weight loss was also determined. Neither the type of film used for packaging nor the storage conditions led to changes in the evolution of pH or the microorganism count in broccoli and cauliflower. However, exposure to light stimulated stomatic opening facilitate the exchange of gases between the plant tissue and the atmosphere within the packaging. Thus, a considerable loss of water vapor was observed in the packages of both vegetables stored in the presence of illumination. Moreover, exposure to light stimulated respiratory activity so that for the cauliflower, the composition of the atmosphere within the packages varied depending on the permeability of the packaging film used and the storage conditions. However, in the case of the broccoli, the increase in respiratory activity due to the lighting was compensated by the photosynthetic activity which took place in these conditions, in such a way that the composition of the atmosphere inside the packs solely depended on the permeability of the film. This difference in the physiological response conditioned the most suitable kind of packaging film in each case. For cauliflower, in conditions of darkness, P-Plus 120 film proved the most suitable for preserving its sensory qualities, while under conditions of lighting, this film did not prove suitable due to its low permeability. However, in broccoli the different packaging films tested behaved in a very similar way whether stored under lighting or in the dark.

Difference in metabolite levels between photoautotrophic and photomixotrophic cultures of Synechocystis sp. PCC 6803 examined by capillary electrophoresis electrospray ionization mass spectrometry

Capillary electrophoresis mass spectrometry (CE/MS) was applied for the comprehensive survey of changes in the amounts of metabolites upon the shift from photoautotrophic to photomixotrophic conditions in Synechocystis sp. PCC 6803. When glucose was added to the photoautotrophically grown culture, the increase in the metabolites for the oxidative pentose phosphate (OPP) pathway and glycolysis, together with the decrease in those for the Calvin cycle, was observed. Concomitantly, the increase in respiratory activity and the decrease in photosynthetic activity took place in the wild-type cells. In the pmgA-disrupted mutant that shows growth inhibition under photomixotrophic conditions, lower enzymatic activities of the OPP pathway and higher photosynthetic activity were observed, irrespective of trophic conditions. These defects brought about metabolic disorders such as a decrease in ATP and NADPH contents, a failure in the activation of respiratory activity, and the aberrant accumulation of isocitrate under photomixotrophic but not under photoautotrophic conditions. A delicate balancing of the carbon flow between the Calvin cycle and the OPP pathway seems indispensable for growth specifically under photomixotrophic conditions and PmgA is likely to be involved in the regulation.

Effects of disinhibition of neurons in the dorsomedial hypothalamus on central respiratory drive

Neurons within the dorsomedial hypothalamus (DMH) play a critical role in subserving the cardiovascular and neuroendocrine response to psychological stress. An increase in respiratory activity is also a characteristic feature of the physiological response to psychological stress, but there have been few studies of the role of DMH neurons in regulating respiratory activity. In this study we determined the effects of activation of DMH neurons on respiratory activity (assessed by measuring phrenic nerve activity, PNA) and the relationship between evoked changes in respiratory activity and changes in sympathetic vasomotor activity in spontaneously breathing urethane-anesthetized rats. Microinjections of bicuculline (4-40 pmol in 20 nl) into the DMH evoked dose-dependent increases in PNA burst frequency and amplitude. These were accompanied by dose-dependent decreases in mean tracheal CO(2) levels, indicative of hyperventilation. In control experiments, microinjections of bicuculline into sites adjacent to the DMH evoked much smaller or no changes in PNA. In experiments where renal sympathetic nerve activity (RSNA) was also measured, cycle-triggered averaging revealed that RSNA under resting conditions was partly correlated with the PNA, but in response to DMH disinhibition there was no consistent change in the amplitude of the respiratory-related variations in RSNA. The results indicate that DMH neurons can exert a powerful stimulatory effect on respiratory activity, causing hyperventilation. This is not associated with an increase in the degree of coupling between PNA and RSNA, indicating that the DMH-evoked increase in RSNA is not a consequence of increased central respiratory drive.

Adenosine stimulates anabolic metabolism in developing castor bean (Ricinus communis L.) cotyledons

In previous experiments it was shown that Castor-bean (Ricinus communis) endosperm releases carbohydrates, amino acids and nucleoside derivatives, which are subsequently imported into the developing cotyledons (Kombrink and Beevers in Plant Physiol 73:370-376, 1983). To investigate the importance of the most prominent nucleoside adenosine for the metabolism of growing Ricinus seedlings, we supplied adenosine to cotyledons of 5-days-old seedlings after removal of the endosperm. This treatment led to a 16% increase in freshweight of intact seedlings within 16 h, compared to controls. Using detached cotyledons, we followed uptake of radiolabelled adenosine and identified 40% of label in solubles (mostly ATP and ADP), 46% incorporation in RNA and 2.5% in DNA, indicating a highly active salvage pathway. About 7% of freshly imported adenosine entered the phloem, which indicates a major function of adenosine for cotyledon metabolism. Import and conversion of adenosine improved the energy content of cotyledons as revealed by a substantially increased ATP/ADP ratio. This effect was accompanied by slight increases in respiratory activity, decreased levels of hexose phosphates and increased levels of fructose-1,6-bisphosphate and triose phosphates. These alterations indicate a stimulation of glycolytic flux by activation of phosphofructokinase, and accordingly we determined a higher activity of this enzyme. Furthermore the rate of [(14)C]-sucrose driven starch biosynthesis in developing castor-bean is significantly increased by feeding of adenosine. In conclusion, our data indicate that adenosine imported from mobilizing endosperm into developing castor-bean cotyledons fulfils an important function as it promotes anabolic reactions in this rapidly developing tissue.