Biomedical subjects

Daniel Grucker

Publications and source records attributed to Daniel Grucker.

10 recordsLinked to original sources

PubMed2006

Texture analysis of brain MRI evidences the amygdala activation by nociceptive stimuli under deep anesthesia in the propofol-formalin rat model.

Magnetic resonance images of rat brain were analyzed by texture analysis in order to study the effects of a nociceptive stimulation (formalin test) under propofol deep anesthesia. Changes of the texture in different cerebral brain areas acquired before and after stimulation were checked. Our statistical analysis of texture shows that these changes were present only in the amygdala, in agreement with the facts already known about the unconscious memorization of nociceptive stimuli.

Amygdala↗

PubMed2006

Magnetic resonance imaging of acoustic streaming: absorption coefficient and acoustic field shape estimation.

In this study, magnetic resonance imaging (MRI) is used to visualize acoustic streaming in liquids. A single-shot spin echo sequence (HASTE) with a saturation band perpendicular to the acoustic beam permits the acquisition of an instantaneous image of the flow due to the application of ultrasound. An average acoustic streaming velocity can be estimated from the MR images, from which the ultrasonic absorption coefficient and the bulk viscosity of different glycerol-water mixtures can be deduced. In the same way, this MRI method could be used to assess the acoustic field and time-average power of ultrasonic transducers in water (or other liquids with known physical properties), after calibration of a geometrical parameter that is dependent on the experimental setup.

Absorption↗

PubMed2006

Brain dysmyelination and recovery assessment by noninvasive in vivo diffusion tensor magnetic resonance imaging.

Diffusion tensor magnetic resonance imaging (DT-MRI) was applied for in vivo quantification of myelin loss and regeneration. A transgenic mouse line (Oligo-TTK) expressing a truncated form of the herpes simplex virus 1 thymidine kinase gene (hsv1-tk) in oligodendrocytes was studied along with two induced phenotypes of myelin pathology. Myelin loss and axonal abnormalities differentially affect values of DT-MRI parameters in the brain of transgenic mice. Changes in the anisotropy of the white matter were assessed by calculating and mapping the radial (D perpendicular) and axial (D parallel) water diffusion to axonal tracts and fractional anisotropy (FA). A significant increase in D perpendicular attributed to the lack of myelin was observed in all selected brain white matter tracts in dysmyelinated mice. Lower D parallel values were consistent with the histological observation of axonal modifications, including reduced axonal caliber and overexpression of neurofilaments and III beta-tubulin. We show clearly that myelination and axonal changes play a role in the degree of diffusion anisotropy, because FA was significantly decreased in dysmyelinated brain. Importantly, myelin reparation during brain postnatal development induced a decrease in the magnitude of D( perpendicular) and an increase in FA compared with the same brain before recovery. The progressive increase in D parallel values was attributed to the gain in normal axonal morphology. This regeneration was confirmed by the detection of enlarged oligodendrocyte population, newly formed myelin sheaths around additional axons, and a gradual increase in axonal caliber.

Animals↗

PubMed2006

Use of insulin immunoassays in clinical studies involving rapid-acting insulin analogues: Bi-insulin IRMA preliminary assessment.

BACKGROUND: In clinical studies involving rapid-acting analogues (RAAs), insulin immunoreactivity is frequently measured, including endogenous, regular insulin (RI) and RAA immunoreactivities. Such a procedure implies equivalent cross-reactivities of all insulins present in serum. Commercially available human insulin immunoassays have been widely used, but their limitations (including hemolysis and anti-insulin antibodies) were not fully investigated. The aims of our study were to compare cross-reactivities of RI and RAAs in buffer and in serum and to investigate insulin immunoassay pitfalls. METHODS: Cross-reactivities were assessed using Bi-insulin IRMA (Schering Cis-Bio International) in phosphate-buffered saline (PBS)-1% bovine serum albumin (BSA) and in pools of sera spiked with RI and RAAs (lispro and aspart). To investigate the influence of hemolysis, a pool of sera spiked with RAA was mixed with a concentrated hemolysate (final hemoglobin concentration 10 g/L) and incubated for 3 h at room temperature. To determine interference by anti-insulin antibodies, insulin was removed using charcoal from 18 sera with anti-insulin antibodies and from 17 sera without detectable anti-insulin antibodies. These insulin-free samples were then spiked with RI and RAAs and the immunoreactivity was determined. RESULTS: Compared with buffer, cross-reactivity in serum for RI, lispro and aspart was lower (35%, 29% and 26% lower, respectively). Hemolysis degraded almost all RI and RAAs contained in the serum (>or=95%). Anti-insulin antibody interference was significant for RI and RAAs (p<or=0.004) and correlated with anti-insulin antibody level in the serum (p<or=0.001). CONCLUSIONS: In serum, RI and RAA cross-reactivities are slightly lower than in buffer. For RAA assessment, hemolysed samples should be discarded and anti-insulin antibodies should be removed from samples before immunoreactivity measurements.

Antibodies↗

PubMed2005

Recovery of myelin after induction of oligodendrocyte cell death in postnatal brain.

A transgenic mouse line (Oligo-TTK) was established to monitor oligodendrocyte cell death and myelin formation in the CNS. The expression of a conditionally toxic gene, the herpes simplex virus-1 thymidine kinase (HSV1-TK), was made under control of the MBP (myelin basic protein) gene promoter. A truncated form of the HSV1-TK (TTK) gene was used to avoid both bystander effect resulting from leaking in thymidine kinase activity and sterility in transgenic males observed in previous transgenic mice. The transgene was expressed in the CNS with a restricted localization in oligodendrocytes. Oligodendrocyte proliferation and myelin formation are therefore tightly controlled experimentally by administration of ganciclovir (GCV) via the induction of oligodendrocyte cell death. The most severe and irreversible hypomyelination was obtained when GCV was given daily from postnatal day 1 (P1) to P30. Oligodendrocyte plasticity and myelin recovery were analyzed in another phenotype generated by GCV treatment from P1 to P15. In this model, after dysmyelination, an apparent normal behavior was restored with no visible pathological symptoms by P30. Proliferating cells, which may be implicated in myelin repair in this model, are detected primarily in myelin tracts expressing the oligodendrocyte phenotype. Therefore, the endogenous potential of oligodendrocytes to remyelinate was clearly demonstrated in the mice of this study.

Age Factors↗

PubMed2004

Remyelination assessment by MRI texture analysis in a cuprizone mouse model.

The purpose of this study was to perform serial texture analysis of brain MRI of cuprizone-treated mice for the assessment of regional demyelination and remyelination. Cuprizone-fed mice undergo a brain demyelination process. This process was followed over 56 days by MRI in the olfactory bulbs, cerebellum, putamen and brain stem. The texture of T2-weighted images has been analyzed at two levels: (1) with the average intensity as first order parameter and (2) with several higher order parameters for the best differentiation between myelinated (controls) and demyelinated brains. The most pertinent of these parameters, called horizontal gray level nonuniformity (HGLNU), has been selected by stepwise discriminant analysis. The time evolution of the average value of HGLNU not only confirmed the overall demyelination tendency followed by the average intensity, but also more precisely characterized a transitory remyelination on day 41 in the olfactory bulbs and cerebellum, in agreement with already published immunohistochemical destructive studies.

Animals↗

PubMed2004

New insights on neuronal alterations in jimpy mutant brain.

In spite of abundant data on oligodendrocyte abnormalities in dysmyelinated jimpy brain, little is known about the axonal damage and the expression of neuronal genes. Recent findings indicate that Nogo-A, oligodendrocyte-myelin glycoprotein (OMgp), and myelin-associated glycoprotein (MAG) inhibit axonal growth by binding a common receptor, the Nogo-A receptor (NgR)-p75 complex. In order to evaluate neuronal modifications in the absence of myelin and in the presence of abnormal oligodendrocytes at different developmental stages, the expression of these inhibitory proteins and their receptors was investigated in jimpy mutant brain. Despite the decrease in oligodendrocyte number at P15 and P25 in jimpy, Nogo-A and OMgp mRNA levels are not significantly different compared with control, suggesting an overexpression of neuronal Nogo-A and OMgp in mutant. Double immunolabeling for Nogo-A and neurofilaments shows strong axonal staining of Nogo-A in jimpy and its down-regulation in oligodendrocytes. The current data raise questions about functions of Nogo-A other than neurite growth inhibition in the CNS. No significant changes in NgR mRNA levels were observed in jimpy, where the increase in p75 level can be correlated with the cell death of oligodendrocytes. In the paranodal region, the cell adhesion molecule neurofascin glial isoform NFN155 mRNA level is reduced by 40% whereas neuronal form NFN186 is up-regulated. These results may explain the failure of paranodal region organization, even with normal level of CASPR (paranodin) mRNA detected in jimpy brain.

Animals↗

PubMed2003

Fast measurement of relaxation times by steady-state free precession of 129Xe in carrier agents for hyperpolarized noble gases.

Hyperpolarized gases ((129)Xe and (3)He) are being used increasingly in both MRI and NMR spectroscopy studies. However, it has been shown that carrier agents are required to preserve the long relaxation times of gases in biological fluids. Optimized gas transport can be achieved through controlled T(1) and T(2) measurements of (129)Xe gas at equilibrium, using the steady-state free precession method (SSFP). The accuracy of the method was proven with the use of CuSO(4)-doped water samples and xenon dissolved in chloroform. The following T(1) and T(2) values were measured for xenon dissolved in a 30% intralipid emulsion: T(1) = 29 +/- 3 s; T(2) = 1.0 +/- 0.1 s. The values obtained in the intralipid emulsion contrast significantly with those obtained in conventional gas NMR experiments, in which it is commonly assumed that T(1) = T(2). This highlights the importance of obtaining accurate relaxation time measurements for medical applications of hyperpolarized gases.

Drug Carriers↗

PubMed2003

Flow effects in long-range dipolar field MRI.

Incoherent spin motion, such as diffusion, can lead to significant signal loss in multiple spin echoes (MSE) experiments, sometimes to its complete extinction. Coherent spin motion, such as laminar flow, can also modify the magnetization in MSE imaging and yield additional contrast. Our experimental results indicate that MSE is flow-sensitive. Our theoretical analysis and experimental results show how the effect of the distant dipolar field can be annihilated by flow. This effect can be quantified by directly solving the nonlinear Bloch equation, taking into account the deformation of the dipolar field by motion. Unexpected results have been observed, such as a recovery of the dipolar interaction due to flow in the "magic angle" condition.

Journal Article↗

PubMed2002

Free prolactin determinations in hyperprolactinemic men with suspicion of macroprolactinemia.

BACKGROUND: The Elecsys prolactin (PRL) assay reacts more strongly with macroprolactin than the Centaur PRL assay. We evaluated Elecsys direct and free PRL measurements vs. Centaur direct PRL measurements, in sera with and without macroprolactin. METHODS: PRL was measured using Elecsys and Centaur direct assays and the Elecsys assay in the supernatant obtained after PEG precipitation (free PRL) in 34 sera from 34 hyperprolactinemic male subjects (Elecsys direct PRL>434 mIU/l) classified, according to the PRL recovery after PEG precipitation, as: negative, i.e. without predominant macroprolactin (recovery %>50, n=12), positive (recovery %<40, n=18) or indeterminate (n=4). RESULTS: The positive bias between Elecsys direct and Centaur PRL results was clearly influenced by the presence of macroprolactin and the mean bias between Elecsys free and Centaur prolactin values was near zero in the negative and positive groups. Among 14 patients from the positive group presenting clinical conditions possibly ascribable to hyperprolactinemia, Elecsys free and Centaur PRL levels were normal in seven and increased in five. In the negative and positive groups considered together, Elecsys free PRL agreed well with Centaur prolactin (28/30). The poor concordance observed for the indeterminate samples underlined the heterogeneity of macroprolactin. CONCLUSION: Elecsys free PRL determination can be used to reduce the marked influence of macroprolactin in this assay.

Adolescent↗