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Biomedical subjects

G Papageorgiou

Publications and source records attributed to G Papageorgiou.

At least 19 recordsLinked to original sources
PubMed2002

Microwave saturation of the Rydberg States of electrons on helium.

We present measurements of the resonant microwave excitation of Rydberg energy levels for surface-state electrons on superfluid helium. The temperature-dependent contribution to the linewidth gamma(T) agrees with theoretical predictions and is very small below 700 mK, in the ripplon scattering regime. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency Omega was determined as a function of microwave power. High values of the ratio Omega/gamma confirm this system as an excellent candidate for creating qubits.

Journal Article↗
PubMed2001

Photochemical and pharmacological evaluation of 7-nitroindolinyl-and 4-methoxy-7-nitroindolinyl-amino acids as novel, fast caged neurotransmitters.

Reagents capable of rapid and efficient release of neuroactive amino acids (L-glutamate, GABA and glycine) upon flash photolysis of thermally stable, inert precursors have been elusive. 7-Nitroindolinyl (NI)-caged and 4-methoxy-7-nitroindolinyl (MNI)-caged compounds that fulfil these criteria are evaluated here. These caged precursors are highly resistant to hydrolysis. Photolysis is fast (half time< or =0.26 ms) and the conversion achieved with a xenon flashlamp is about 15% for the NI-caged L-glutamate and about 35% for the MNI-caged L-glutamate. A procedure is described for calibration of photolysis in a microscope-based experimental apparatus. NI-caged L-glutamate itself showed no agonist or antagonist effects on AMPA and NMDA receptors in cultured neurones, and had no effect on climbing fibre activation of Purkinje neurones. A control compound with identical photochemistry that generated an inert phosphate upon photolysis was used to confirm that the intermediates and by-products of photolysis have no deleterious effects. MNI-caged L-glutamate is as stable and fast as NI-caged L-glutamate and similarly inert at glutamate receptors, but about 2.5 times more efficient. However, NI-caged GABA is an antagonist at GABA(A) receptors and NI-glycine an antagonist at glycine receptors. The results show the utility and limitations of these fast and stable caged neurotransmitters in the investigation of synaptic processes.

Animals↗
PubMed2001

Observation of dynamical ordering in a confined Wigner crystal.

We present measurements of the conduction of nondegenerate free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices. Above 1 K, the electrons form an ideal classical Drude conductor. Below 1 K, Coulomb interactions produce electronic spatial order, leading to strong non-Ohmic effects and negative differential conductivity. Evidence is presented for self-organized current filaments in the channel, created by a nonequilibrium phase transition. Periodic conductance oscillations suggest an anisotropic spatial order with lines of electrons along the channel edges.

Journal Article↗
PubMed2001

The conductance underlying the parallel fibre slow EPSP in rat cerebellar Purkinje neurones studied with photolytic release of L-glutamate.

1. Tetanic stimulation of parallel fibres (PFs) produces a slow EPSP (sEPSP) or slow EPSC (sEPSC) in Purkinje neurones (PNs), mediated by type 1 metabotropic glutamate receptors (mGluR1). The conductance change underlying the sEPSP was investigated with rapid photolytic release of L-glutamate from nitroindolinyl (NI)-caged glutamate with ionotropic glutamate receptors blocked, and showed a slow mGluR1-activated cation channel. 2. In cerebellar slices rapid photolytic release (t (1/2) < 0.7 ms) of 7--70 microM L-glutamate on PNs voltage clamped at -65 mV activated first a transient inward current, peaking in 8 ms, followed by a slow inward current with time course similar to the PF sEPSP, peaking at -1 nA in 700 ms. 3. The initial current was inhibited by 300 microM threo-hydroxyaspartate (THA) and did not reverse as the potential was made positive up to +50 mV, suggesting activation of electrogenic glutamate uptake. 4. The slow current was inhibited reversibly by 1 mM (R,S)-MCPG or the non-competitive mGluR1 antagonist CPCCOEt (20 microM), indicating activation of metabotropic type 1 glutamate receptors. The mGluR current was associated with increases of input conductance and membrane current noise, and reversed close to 0 mV, indicating activation of channels permeant to Na(+) and K(+). 5. The sEPSC was not blocked by Cd(2+), Co(2+), Mg(2+) or Gd(3+) ions, by the inhibitor of hyperpolarisation-activated current (I(H)) ZD7288, or by the purinoceptor inhibitor PPADS. Activation was not affected by inhibitors of phospholipase C (PLC) or protein kinase C (PKC), nor mimicked by photorelease of InsP(3) or Ca(2+). The results show that mGluR1 in PNs produces a slow activation of cation-permeable ion channels which is not mediated by PLC activation, Ca(2+) release from stores, or via the activation of PKC.

Animals↗
PubMed2001

Severe total hepatic ischemia and reperfusion: relationship between very high alpha-tocopherol uptake and lipid peroxidation.

Reperfusion injury of the liver occurs in liver transplantation and in major hepatectomies. It triggers a severe oxidative stress that leads to increased lipid peroxidation. In our study we examined the effect of parenteral supranutritional administration of alpha-tocopherol, a vitamin that plays a key role in the endogenous antioxidant system, to rats subjected to severe ischemia/reperfusion (I/R) injury of the liver. alpha-Tocopherol was administered to the animals at doses of 30 and 300 mg/kg bw, whereas total hepatic ischemia was induced for 60 min followed by 120 min reperfusion. Tissue and blood samples were collected for malonyldialdehyde (MDA) and serum alpha-tocopherol assay, respectively. In the sham operation group, mean MDA level in liver was 1.14 nmole/g wet tissue in the control subgroup, and 1.01 or 0.74 nmole/g wet tissue in the subgroups given 30 or 300 mg/kg alpha-tocopherol. In the I/R group, mean MDA level was 1.57 nmole/g wet tissue in the control subgroup, and 0.97 and 0.77 nmole/g wet tissue in the subgroups given 30 or 300 mg/kg alpha-tocopherol. Mean levels of alpha-tocopherol in serum (mumole/l) were 10.20 and 1.80 in the control subgroups, 25.28 and 11.25 in the subgroups treated with 30 and 300 mg/kg bw of alpha-tocopherol, and 31.00 and 13.02 in the subgroups treated with 30 and 300 mg/kg bw of alpha-tocopherol, within the sham-operation and I/R groups, respectively. A significant decrease of MDA accompanied by a significant increase of serum alpha-tocopherol was documented in the alpha-tocopherol-treated rats within both groups. Ischemia/reperfusion triggered a significant increase of the MDA level in the liver of the rats not treated with alpha-tocopherol as compares with the treated animals.

Animals↗
PubMed2001

Diplopia as a complication of local anesthesia: a case report.

Diplopia caused by local anesthesia at the superior posterior alveolar nerve for the removal of the maxillary third molar is a rare complication. The diplopia is due to facial palsy of the oculomotor muscles of the globe. This paper describes the case of a 22-year-old woman, in whom diplopia was observed after an overall uncomplicated removal of the semi-impacted third molar. Possible causes of the anesthetic effects are reported. The most accepted explanation is that the anesthetic diffuses on the abducent nerve in the cavernous sinus. The necessary actions that the dental surgeon must perform are reported.

Abducens Nerve↗
PubMed1999

Concurrent multivessel stenting in a patient with multifocal arterial disease.

PURPOSE: To report the concurrent endovascular treatment of multiple stenoses in different vascular territories. METHODS AND RESULTS: A 45-year-old male presented with an aortic arch syndrome, renovascular hypertension, and Leriche syndrome. Intra-arterial digital arteriography disclosed occlusion of the left subclavian artery and stenoses in the left common carotid artery (CCA), the right CCA at the bifurcation, the left renal artery, and both iliac arteries. In a single procedure, the patient received 5 stents in 2 carotid, 1 renal, and 2 iliac arteries. At 3-month follow-up, color flow duplex imaging confirmed continued patency of all stented arteries. CONCLUSIONS: This case illustrates the feasibility, safety, and cost effectiveness of treating multivessel stenoses using a single-session endovascular approach executed by experienced interventionists.

Angiography↗
PubMed1998

Lipid peroxidation of rat myocardial tissue following daunomycin administration.

Daunomycin-induced cardiotoxicity has been regarded to be the result of oxygen-mediated lipid peroxidation of cell membranes. The aim of the present work was to evaluate the extent of lipid peroxidation in rat heart after administration of this anticancer drug and, further, to examine possible activation of some endogenous antioxidant defense systems. Myocardial tissue from both control and drug-treated rats was tested for lipid peroxidation using a selective third-order derivative method that is based on the analysis of the free malondialdehyde produced. Determination of reduced/oxidized glutathione levels and measurement of the activity of DT-diaphorase, glutathione-S-transferase, glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-cytochrome P-450 reductase were also carried out using literature methods. Significant increase of malondialdehyde content, and DT-diaphorase and glutathione-S-transferase activities were found in myocardial tissue from daunomycin-treated rats. On the other hand, reduced and oxidized glutathione levels were significantly decreased while the activity of glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-cytochrome P-450 reductase remained unchanged after daunomycin administration. The results of the present study give further evidence that daunomycin can induce lipid peroxidation in heart. However, additional experimentation is needed in order to delineate the molecular details of this process as well as of the mechanisms evolved to limit it.

Animals↗
PubMed1997

Human leukocyte antigen system in clozapine-induced agranulocytosis.

Forty-three schizophrenic patients participating in this study were serotyped for human leukocyte antigens (HLA-A, -B, -C, -DR, -DQ antigens). Thirty-six of them were hospitalised in two state mental hospitals and 7 in our general hospital, psychiatric unit. The patients from our unit were typed for HLA before commencing clozapine treatment whereas the patients from state hospitals were typed after commencing treatment. Three out of 43 patients developed agranulocytosis. One had a combination of both 'high-risk' haplotypes (HLA-B16(38,39), DR4, DQ3 and HLA-DR2, DQ1), another had HLA-DR2, DQ1, whereas the last had a totally different haplotype. Between non-agranulocytic patients 1 was found to carry the HLA-B16(38,39), DR4, DQ3 haplotype and 14 (out of 40) had the HLA-DR2, DQ1. Taking into account other factors supposed to be involved (a noxious metabolite, and the presence of a humoral cytotoxic factor) we must admit that despite the finding of a high-risk haplotype in Jewish populations there are other aspects of this question awaiting clarification.

Adult↗
PubMed1996

Expression of apoptosis-related proteins in thyroid tumors and thyroid carcinoma cell lines.

Whereas in normal human thyroid tissue total cell mass is maintained by a balance between cell proliferation and apoptosis, the programmed cell death, in thyroid tumors this equilibrium is disrupted. In tumor cells, an augmented proliferation rate is no longer counterbalanced by an equally enhanced apoptosis resulting in an increased netto growth rate. To investigate regulation of apoptosis in thyroid tumors, we analyzed the expression of apoptosis-related proteins of the bcl-2 family in human thyroid tissues and in the human thyroid carcinoma cell lines FTC 133, HTC, HTC-TSHr and HTh74. In comparison to normal tissue, we detected an increased expression of the anti-apoptotic protein bcl-2 in adenomas, whereas follicular carcinomas showed various expression of bcl-2 with decreased levels in 32% of cases. BclxL expression was comparable in all tissues examined. The pro-apoptotic protein bax was expressed at lower levels in carcinomas than in adenomas, whereas bak and bclx were expressed in the same order of magnitude in all tissues examined. In contrast, thyroid carcinoma cell lines exhibited a relatively strong expression of bclxL, but a weak expression of bcl-2. In all four cell lines, the amounts of the pro-apoptotic proteins bax, bak and bclx were higher than in most tumor tissues. Our data show that in thyroid tumors expression of members of the bcl-2 protein family is not uniform. Rather, the expression pattern of pro- and anti-apoptotic proteins in thyroid tumors is heterogeneous. This may, at least in part, reflect the futile attempt of tumor cells to counterbalance the action of growth-promoting factors in thyroid tumor-igenesis.

Adenoma↗
PubMed1996

Lipid peroxidation and antioxidant defense mechanisms in rat renal tissue after daunorubicin administration.

Redox cycling compounds such as daunorubicin have been assumed to be toxic because they stimulate reactive oxygen-mediated lipid peroxidation. Furthermore, both DT-diaphorase and glutathione (GSH) have been regarded as protective cellular compounds against daunorubicin cardiotoxicity, but their role in daunorubicin nephrotoxicity remains unclear. To investigate this issue, 10 adult Wistar rats were twice injected with a single dose of 20 mg/kg body weight daunorubicin into the tail vein; the interval between injections was 48 h. A control group of 10 rats were injected with normal saline. One day after the second injection, all the animals were sacrificed and their kidneys were analyzed for malondialdehyde (MDA) as an index of lipid peroxidation, DT-diaphorase activity, and GSH and glutathione disulphide (GSSG) content. A significant increase of MDA concentration (2.41 vs. 1.64 p < 0.001) and DT-diaphorase activity (0.2 vs. 0.12, p < 0.001) was found in the renal tissue of daunorubicin injected rats. In contrast, GSH and GSSG levels were decreased in those animals (566 vs. 1282, p < 0.001 and 115 vs 187, p < 0.01, respectively). The results of this study give evidence that a high dosage of daunorubicin induces lipid peroxidation in renal tissue of rats stimulating the activation of DT-diaphorase and the detoxificative depletion of GSH.

Animals↗
PubMed1996

Lipid peroxidation after acute renal ischemia and reperfusion in rats: the effect of trimetazidine.

Lipid peroxidation is a critical pathway of reactive oxygen species inducing tissue injury in postischemic acute renal failure. In order to evaluate the effect of renal ischemia reperfusion on kidneys, renal tissue malondialdehyde (MDA, nmol/g wet weight) concentration was measured in 29 male Wistar rats subjected to a midline abdominal incision and 60 min occlusion of the left renal artery. A right nephrectomy was performed at the beginning of the ischemic period. The animals were separated in four groups. Groups 1 (n = 7) and 3 (n = 7) underwent 60 min of ischemia and 15 min of reperfusion, respectively. Groups 2 (n = 8) and 4 (n = 7) were subjected to the same procedure but, in addition, they received 2.5 mg/kg TMZ into the tail vein 2 h prior to the left renal artery occlusion. A significant elevation of MDA after 60 min of ischemia (1.43 vs. 2.1, p < 0.001), which was augmented after 15 min of reperfusion (1.4 vs. 3.72, p < 0.001) was observed. Furthermore, there was a significant reduction of renal tissue MDA in ischemic rats treated with TMZ (group 3) (2.1 vs. 1.52, p < 0.001). The maximum reduction of renal tissue MDA was observed in ischemic-reperfused rats (group 4) that had received TMZ (3.72 vs. 1.36, p < 0.001). It is suggested that lipid peroxidation is a critical event in postischemic acute renal failure, and TMZ is a useful protective agent of renal damage from oxygen free radicals.

Acute Kidney Injury↗
PubMed1994

A bleeding renal artery pseudo-aneurysm complicating renal biopsy. Treatment with transcatheter embolization.

We report the treatment of a bleeding renal artery pseudoaneurysm by transcatheter embolization. The patient, a 30 years old woman, developed macroscopic hematuria following renal biopsy. The presence of a leaking pseudoaneurysm of the lower pole segmental artery was confirmed by left selective renal angiogram; subsequently successful transcatheter embolization was performed using a 5.0 french Cobra catheter and 3 mm steel coils.

Adult↗
PubMed1988

Ovarian stimulation for in-vitro fertilization combining administration of gonadotrophins and blockade of the pituitary with D-Trp6-LHRH microcapsules: pilot studies with two protocols.

In women undergoing in-vitro fertilization and embryo transfer (IVF-ET), a total of 408 IVF cycles were stimulated using human menopausal gonadotrophin (HMG) or pure follicle stimulating hormone (FSH) plus HMG in combination with a single injection of D-Trp6-LHRH microcapsules in order to enhance the ovarian response to gonadotrophins and to avoid spontaneous LH surges. Sixty-seven pregnancies were achieved. Two protocols were employed. In protocol 1 ('blocking protocol', n = 268), the pituitary was first inhibited with a full dose (3.75 mg) of D-Trp6-LHRH in microcapsules and ovarian stimulation was started after the hypogonadotrophic hypogonadal state was ascertained (E2 less than 50 pg/ml). In protocol 2 ('flare-up protocol', n = 140), the treatment with D-Trp6-LHRH microcapsules (half-dose = 1.80 mg) and the ovarian stimulation with gonadotrophins were started at the same time. Higher doses of gonadotrophins were needed (39.5 +/- 11.2 ampoules FSH and/or HMG) in protocol 1, in which the pituitary was blocked prior to and during the stimulation, than in protocol 2 (20 +/- 9 ampoules) where the exogenous gonadotrophin stimulation appeared to be augmented by the initial agonistic effect of the injection of D-Trp6-LHRH microcapsules. In patients with purely tubal infertility, under 38 years old and no male factor, the results obtained with protocols 1 and 2 were similar in terms of pregnancy rate per cycle or per embryo transfer: 22.6 versus 20.5% and 28.3 versus 27.4%, respectively. However, considering the cost benefit, 'flare-up' protocols appeared to be a better choice and could be recommended.

Adult↗
PubMed1985

Hemipelvectomy for neoplasms not originating in the pelvis.

10 patients underwent hemipelvectomy, mainly for sarcomas originating high in the thigh, or melanomas and epidermoid carcinomas metastatic to the groin. 1 patient died postoperatively, 3 lived 5-12 years and 1 died of unrelated cause 2 years after the operation, all free of recurrence. Tumors treated successfully were large and with indolent locoregional growth, often despite repeated unsuccessful local treatment attempts. These tumor characteristics should be considered as favorable features, in selecting such patients for hemipelvectomy. Conversely 3 patients with melanoma had short history before and died soon after the operation, contraindicating hemipelvectomy in locally advanced melanoma.

Adult↗