Co-localization and functional interaction between adenosine A(2A) and metabotropic group 5 receptors in glutamatergic nerve terminals of the rat striatum

The anti-Parkinsonian effect of glutamate metabotropic group 5 (mGluR5) and adenosine A(2A) receptor antagonists is believed to result from their ability to postsynaptically control the responsiveness of the indirect pathway that is hyperfunctioning in Parkinson's disease. mGluR5 and A(2A) antagonists are also neuroprotective in brain injury models involving glutamate excitotoxicity. Thus, we hypothesized that the anti-Parkinsonian and neuroprotective effects of A(2A) and mGluR5 receptors might be related to their control of striatal glutamate release that actually triggers the indirect pathway. The A(2A) agonist, CGS21680 (1-30 nM) facilitated glutamate release from striatal nerve terminals up to 57%, an effect prevented by the A(2A) antagonist, SCH58261 (50 nM). The mGluR5 agonist, CHPG (300-600 mum) also facilitated glutamate release up to 29%, an effect prevented by the mGluR5 antagonist, MPEP (10 microm). Both mGluR5 and A(2A) receptors were located in the active zone and 57 +/- 6% of striatal glutamatergic nerve terminals possessed both A(2A) and mGluR5 receptors, suggesting a presynaptic functional interaction. Indeed, submaximal concentrations of CGS21680 (1 nM) and CHPG (100 microm) synergistically facilitated glutamate release and the facilitation of glutamate release by 10 nM CGS21680 was prevented by 10 microm MPEP, whereas facilitation by 300 microm CHPG was prevented by 10 nM SCH58261. These results provide the first direct evidence that A(2A) and mGluR5 receptors are co-located in more than half of the striatal glutamatergic terminals where they facilitate glutamate release in a synergistic manner. This emphasizes the role of the modulation of glutamate release as a likely mechanism of action of these receptors both in striatal neuroprotection and in Parkinson's disease.     

Use of infrared thermography for monitoring stomatal closure in the field: application to grapevine

This paper reviews and discusses strategies for the use of thermal imaging for studies of stomatal conductance in the field and compares techniques for image collection and analysis. Measurements were taken under a range of environmental conditions and on sunlit and shaded canopies to illustrate the variability of temperatures and derived stress indices. A simple procedure is presented for correcting for calibration drift within the images from the low-cost thermal imager used (SnapShot 225, Infrared Solutions, Inc.). The use of wet and dry reference surfaces as thresholds to eliminate the inclusion of non-leaf material in the analysis of canopy temperature is discussed. An index that is proportional to stomatal conductance was compared with stomatal measurements with a porometer. The advantages and disadvantages of a possible new approach to the use of thermal imagery for the detection of stomatal closure in grapevine canopies, based on an analysis of the temperature of shaded leaves, rather than sunlit leaves, are discussed. Evidence is presented that the temperature of reference surfaces exposed within the canopy can be affected by the canopy water status.     

Direct organogenesis from hypocotyl-derived explants of annatto (Bixa orellana)

The relative importance of explant, cytokinin type, carbon source and gelling agent for annatto organogenesis was studied. The best organogenic response, including adventitious shoot number and elongation, was obtained when hypocotyl segments and rooted hypocotyls were cultured onto MS medium supplemented with 4.56 M zeatin, 87.6 mM sucrose, and 2.8 g l^–1 Phytagel®. Adventitious shoots derived from hypocotyl segments were less frequent and more difficult to elongate than those derived from rooted hypocotyls. Thidiazuron (TDZ) promoted a higher organogenic response in rooted hypocotyls, resembling a rosette-like structure, but impaired shoot elongation. Histological investigation showed that zeatin-induced meristemoids originated mainly from wounding tissues, and that TDZ induced a high level of mitotic division resulting in several proliferation zones nearby the epidermis and outer cortical tissues. Rhizogenesis efficiency (rooting frequency and root number) was greater at the highest indole-3-butyric acid (IBA) concentration (5.0 M) employed, although calli occurred at the basal end of shoots. Eighty percent of rooted plantlets survived after acclimatization. This optimized regeneration protocol may enable further development of an efficient genetic transformation protocol for this species.     

Sources of glucose production in cirrhosis by 2H2O ingestion and 2H NMR analysis of plasma glucose

Plasma glucose 2H enrichment was quantified by 2H NMR in patients with cirrhosis (n=6) and healthy subjects (n=5) fasted for 16 h and given 2H(2)O to approximately 0.5% body water. The percent contribution of glycogenolysis and gluconeogenesis to glucose production (GP) was estimated from the relative enrichments of hydrogen 5 and hydrogen 2 of plasma glucose. Fasting plasma glucose levels were normal in both groups (87+/-7 and 87+/-24 mg/dl for healthy and cirrhotic subjects, respectively). The percent contribution of glycogen to GP was smaller in cirrhotics than controls (22+/-7% versus 46+/-4%, P<0.001), while the contribution from gluconeogenesis was larger (78+/-7% versus 54+/-4%, P<0.001). In all subjects, glucose 6R and 6S hydrogens had similar enrichments, consistent with extensive exchange of 2H between body water and the hydrogens of gluconeogenic oxaloacetate (OAA). The difference in 2H-enrichment between hydrogen 5 and hydrogen 6S was significantly larger in cirrhotics, suggesting that the fractional contribution of glycerol to the glyceraldehyde-3-phosphate (G3P)-moiety of plasma glucose was higher compared to controls (19+/-6% versus 7+/-6%, P<0.01). In all subjects, hydrogens 4 and 5 of glucose had identical enrichments while hydrogen 3 enrichments were systematically lower. This reflects incomplete exchange between the hydrogen of water and that of 1-R-dihydroxyacetone phosphate (DHAP) or incomplete exchange of DHAP and G3P pools via triose phosphate isomerase.     

The interaction of flavonoids with mitochondria: effects on energetic processes

The study addressed aspects of energetics of isolated rat liver mitochondria exposed to the flavonoids quercetin, taxifolin, catechin and galangin, taking into account influences of the 2,3 double bond/3-OH group and 4-oxo function on the C-ring, and o-di-OH on the B-ring of their structures, as well as mitochondrial mechanisms potentially involved in cell necrosis and apoptosis. The major findings/hypothesis, were: The 2,3 double bond/3-OH group in conjugation with the 4-oxo function on the C-ring in the flavonoid structure seems favour the interaction of these compounds with the mitochondrial membrane, decreasing its fluidity either inhibiting the respiratory chain of mitochondria or causing uncoupling; while the o-di-OH on the B-ring seems favour the respiratory chain inhibition, the absence of this structure seems favour the uncoupling activity. The flavonoids not affecting the respiration of mitochondria, induced MPT. The ability of flavonoids to induce the release of mitochondria-accumulated Ca(2+) correlated well with their ability to affect mitochondrial respiration on the one hand, and their inability to induce MPT, on the other. The flavonoids causing substantial respiratory chain inhibition or mitochondrial uncoupling, quercetin and galangin, respectively, also decreased the mitochondrial ATP levels, thus suggesting an apparent higher potential for necrosis induction in relation to the flavonoids inducing MPT, taxifolin and cathechin, which did not decrease significantly the ATP levels, rather suggesting an apparent higher potential for apoptosis induction.     

A Rieske ferredoxin typifying a subtype within Rieske proteins: spectroscopic, biochemical and stability studies

A new subtype of archaeal Rieske ferredoxin (RFd) has been identified in the genome of the thermoacidophilic archaeon Acidianus ambivalens. The gene is inserted in an atypical genomic context in a gene cluster encoding a NiFe hydrogenase. Sequence and phyletic analysis showed that the protein is related to bacterial RFd but not to any of the known archaeal Rieske proteins. The recombinant 14 kDa protein isolated from Escherichia coli behaved as a dimer in solution. It contained approximately 2 Fe/mol and all visible and EPR spectroscopic features typical of Rieske centre-containing proteins. However, its redox potential (+170 mV) was significantly higher than those of canonical RFd. This difference is rationalized in terms of the protein structure environment, as discrete amino acid substitutions in key positions around the metal centre account for the higher potential.     

Mitochondrial D-Loop instability in thyroid tumours is not a marker of malignancy

Despite the numerous studies describing a high frequency of mitochondrial DNA (mtDNA) somatic mutations in many types of human primary tumors the mechanisms that generate such mutations and the role of mtDNA mutations in tumor development remain unclear. We present the results obtained in the study of mtDNA displacement-loop (D-Loop) region in a series of 66 thyroid tumors, and respective adjacent parenchyma, including benign (adenomas, n=30) and malignant tumors (follicular carcinomas, n=17 and papillary carcinomas, n=19). Three repetitive regions were analyzed [two mononucleotide repetitive (D310 and D568) and one dinucleotide repetitive (D514)]. Thirty-two (48.5%) of the 66 tumors [15/30 (50.0%) adenomas, 8/17 (47.1%) follicular carcinomas and 9/19 (47.4%) papillary carcinomas] harbored somatic insertions in D-Loop repetitive regions. Twenty (30.3%) of the 66 tumors [12/30 (40%) adenomas, 3/17 (17.6%) follicular carcinomas and 5/19 (26.3%) papillary carcinomas] harbored somatic insertions at the D310 mononucleotide repeat. Three (4.6%) of the 66 tumors [1/30 (3.3%) adenomas and 2/17 (11.8%) follicular carcinomas] harbored somatic insertions at the D568 mononucleotide repeat. Fifteen (22.7%) of the 66 tumors [3/30 (10.0%) adenomas, 5/17 (29.4%) follicular carcinomas and 7/19 (36.8%) papillary carcinomas] harbored somatic insertions at the D514 dinucleotide repeat. Five (7.6%) of the 66 tumors [1/30 (3.3%) adenomas, 1/17 (5.9%) follicular carcinomas and 2/19 (10.5%) papillary carcinomas] harbored somatic insertions in more than one region, and in one of them (a carcinoma) alterations were detected in the three regions. We conclude that mutations in the mtDNA D-Loop region are frequent in benign and malignant thyroid tumors and cannot be considered a marker of malignancy. Our study shows, furthermore, two repetitive regions (D310 and D514) that appear to be susceptible to mutation in thyroid tumors.     

Harvesting in a resource dependent age structured Leslie type population model

We analyse the effect of harvesting in a resource dependent age structured population model, deriving the conditions for the existence of a stable steady state as a function of fertility coefficients, harvesting mortality and carrying capacity of the resources. Under the effect of proportional harvest, we give a sufficient condition for a population to extinguish, and we show that the magnitude of proportional harvest depends on the resources available to the population. We show that the harvesting yield can be periodic, quasi-periodic or chaotic, depending on the dynamics of the harvested population. For populations with large fertility numbers, small harvesting mortality leads to abrupt extinction, but larger harvesting mortality leads to controlled population numbers by avoiding over consumption of resources. Harvesting can be a strategy in order to stabilise periodic or quasi-periodic oscillations in the number of individuals of a population.