PURPOSE:To examine the influence of cardiac activity-related head movements and varying blood pulse frequencies on the shape of electroencephalography (EEG) recordings in a high magnetic field, and to implement a post-processing technique to eliminate cardiac activity-related artifacts.MATERIAL AND METHODS:Respiratory thoracic movements, changes of blood pulse frequency and passive head movements of 20 healthy subjects were examined outside and inside an MR magnet at rest in a simultaneously recorded 21-channel surface EEG. An electrocardiogram (ECG) was recorded simultaneously. On the basis of the correlation of the left ventricular ejection time (LVET) with the heart-rate, a post-processing heart-rate dependent subtraction of the cardiac activity-related artifacts of the EEG was developed. The quality of the post-processed EEG was tested by detecting alpha-activity in the pre- and post-processed EEGs.RESULTS:Inside the magnet, passive head motion but not respiratory thoracic movements resulted in EEG artifacts that correlated strongly with cardiac activity-related artifacts of the EEG. The blood pulse frequency influenced the appearance of the cardiac activity-related artifacts of the EEG. The removal of the cardiac activity-related artifacts of the EEG by the implemented post-processing algorithm resulted in an EEG of diagnostic quality with detected alpha-activity.CONCLUSION:When recording an EEG in MR environment, heart rate-dependent subtraction of EEG artifacts caused by ballistocardiogram contamination is essential to obtain EEG recordings of diagnostic quality and reliability.

Vascular gap junctions (GJ) are built by four different connexins (Cx37, Cx40, Cx43 and Cx45) in variable combination. GJ enable the exchange of currents and small signalling molecules between endothelial or smooth muscle cells, as well as between both cell types. Although the mechanisms are not yet fully understood it is obvious that the transfer of these signals via GJs is regulated. In experiments using Cx-transfected HeLa cells, which do not express Cx in their wild type form, we found that the autacoid NO had selective effects on different Cx. The transfer of a GJ-permeable dye was increased via Cx40-containing GJ and decreased via Cx37-containing GJ. The effect on Cx40 was mediated via cGMP leading to an increased insertion of Cx40 in the cell membrane, whereas the effect of NO on Cx37 was independent of cGMP and did not alter the expression of this Cx. Thus, the same compound can have contrasting effects on cellular coupling depending on the prevalence of certain connexins.

Gap junctions--clusters of intercellular channels built by connexins (Cx)--are thought to be important for vascular cell functions such as differentiation, control of tone, or growth. In the vascular system, gap junctions can be formed by four different connexins (Cx37, Cx40, Cx43 and Cx45). The permeability of these connexin-formed gap junctions determines the amount of intercellular coupling and can be modulated by several vasoactive substances such as prostacyclin or nitric oxide (NO). We demonstrate here that NO has specific effects on certain connexins. Using two different techniques--injection of a fluorescent dye in single cells as well as detection of the de novo formation of gap junctions by a flow cytometry based technique--we found that NO decreases the functional coupling in Cx37 containing gap junctions whereas it increases the de novo formation of gap junctions containing Cx40. We conclude that NO, in addition to its known vasomotor effects, has a novel role in controlling intercellular coupling resulting in opposing effects depending on the specific connexin expressed in the cells.

Objective: Gap junctions (formed by connexins, Cx) are important for functional coordination of cells in the vascular wall. However, little is known about their physiological regulation in this tissue. We examined the effects of nitric oxide (NO), an important mediator of vasomotion, wound healing and angiogenesis, on the formation of gap junctions in endothelial cells (human umbilical vein endothelial cells, HUVEC). Methods: Flow cytometry was used to determine dye transfer through newly formed gap junctions between acutely coincubated HUVECs. Parallel experiments in wild-type HeLa cells (no connexins) and transfected HeLa cells exclusively expressing Cx43, Cx40 or Cx37 were performed to determine the specific role of Cx subtypes. The intracellular distribution of Cx40 was examined after fractionation with triton by Western blotting. Intracellular levels of cGMP and cAMP were measured by radioimmunoassay. Results: The NO donor SNAP (1 muM) enhanced gap-junctional coupling in HUVECs by about 40%. This was associated with an enhanced incorporation of Cx40 into the membrane. Both effects were restricted to Cx40 as analyzed in experiments with Cx-selective HeLa cells. The NO-induced increase in cell coupling was elicited by a corresponding rise of cGMP, which secondarily increased intracellular cAMP levels. The latter was an integral part of the signal cascade, since the protein kinase A (PKA) inhibitor H89 blocked the SNAP-induced incorporation of Cx40 into the plasma membrane. Conclusions: We conclude that NO is a potent modulator of gap-junctional coupling in endothelial cells. It enhances de novo formation of endothelial gap junctions by increasing incorporation of Cx40 into the plasma membrane due to PKA activation. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.

Communication between leukocytes and endothelial cells is crucial for inflammatory reactions. Paracrine cross-talk and outside-in signaling (via adhesion molecules) have been characterized as communication pathways to date. As leukocytes and endothelial cells express connexins, we considered intercellular communication via gap junctions an intriguing additional concept. We found that gap-junctional coupling between neutrophils and endothelium occurred in a time-dependent, bidirectional manner and was facilitated by adhesion. After blockade of connexins, transmigration of neutrophils through the endothelial layer was enhanced, and the barrier function of cell monolayers was reduced during transmigration. Tumor necrosis factor alpha decreased coupling. In the presence of connexins, transmigration of neutrophils did not alter permeability. Thus, neutrophils couple to endothelium via gap junctions, functionally modulating transmigration and leakiness. Gap-junctional coupling may be a novel way of leukocyte-endothelial communication.

The purpose of this study was to develop a spike-related functional magnetic resonance (MR) imaging method to detect epileptic brain activity. Correlations between simultaneous spike-related functional MR imaging and electroencephalographic (EEG) recordings were performed in 10 patients with focal epilepsy. Postprocessing techniques were implemented to eliminate contamination of the EEG recording from ballistocardiography and the echo-planar MR imaging sequence. A diagnostic EEG recording was achieved during functional MR imaging. Spike location correlated with the site of blood oxygen level-dependent signal increase. Spike-related functional MR imaging is a promising technique for detecting focal epileptic brain activity.

Several papers report a hypoxia-induced upregulation of the endothelial nitric oxide synthase (eNOS) mRNA expression. Since there is no known hypoxia-sensitive element binding site in the eNOS promoter, we reasoned that the effect of hypoxia could be simulated by a metabolically elicited alteration of the redox state. Therefore, cultured porcine aortic endothelial cells (PAEC) were exposed to hypoxia (1-10% O(2)) or inhibitors of cellular energy metabolism including rotenone, 2, 4 dinitrophenol (DNP) and 2-deoxyglucose for 6 to 24 h. Additionally, cells were treated with lactate and nicotinic acid to alter the cellular NAD(P)H/NAD(P) ratio without changes of energy supply. The cellular NAD(P)H/NAD(P) ratio was used as an index of the cellular redox state and determined using the MTT-assay. Hypoxia increased eNOS mRNA transcription and MTT-reduction in a manner inversely proportional to pO(2). Exposure to rotenone, DNP, and lactate increased the NAD(P)H/NAD(P) ratio, MTT-reduction, and eNOS mRNA also in parallel. In contrast, 2-deoxyglucose and nicotinic acid attenuated both MTT-reduction and eNOS mRNA expression. In order to study a potential role of the redox regulated transcription factor complex AP-1 in hypoxia-induced eNOS mRNA transcription, c-jun expression was determined and decoy experiments were performed. c-jun expression paralleled changes of eNOS mRNA expression and MTT-reduction. Furthermore, in the presence of oligodeoxynucleotides corresponding to the AP-1 binding sites of the eNOS promoter, the hypoxia and chemically induced eNOS mRNA expression was completely abolished. We propose that hypoxia, by altering cellular metabolism, leads to an increase in the cellular NAD(P)H/NAD(P) ratio which favors enhanced eNOS expression by redox-sensitive AP-1 mediated transcriptional control.

EEG has been used to trigger functional MRI of patients with focal epilepsy, but EEG can be obscured by artifacts during MR data acquisition, and no continuous correlation of EEG and MRI has been possible without limiting the image time. Artifacts caused by an MRI sequence were investigated in five healthy subjects, and an EEG of five patients with epileptic discharges was recorded during echo-planar imaging. All interfering frequencies in the EEG were discrete and defined by loop structures in the MRI sequence. In post-processing of the EEG interfering frequencies were automatically detected by comparing the frequency spectra of the EEG recorded before and during imaging. After elimination of interfering frequencies by filters in the time domain or by Fourier transform, reliable spike detection in the EEG recorded during MR data acquisition became feasible, without loss of EEG quality.

Prior studies on the evaluation of stimulation by MRI were based on the subjective feeling of the volunteers. A wide variety of stimulation thresholds between the subjects was observed. In order to exclude subjective perception levels as a cause of this variation, we developed a method to investigate the activation of peripheral nerves after gradient switching by electromyography (EMG) within the MR‐imager. Five healthy volunteers were positioned in the MR‐scanner with the bridge of the nose at isocenter. The amplitude of sinusoidal pulse trains of the anterior–posterior gradient (rise‐times: 200 or 300 μs, various numbers of oscillations) was increased stepwise. Four surface electrodes were placed on the region where a muscle‐twitch was reported. Electric activity of the muscle during stimulation experiments was recorded with an MR‐compatible electro‐physiologic amplifier. Stimulation thresholds were defined by the appearance of an EMG‐signal. Thresholds were sharp and consistent with the report of the subjects. Magn Reson Med 43:534–539, 2000. © 2000 Wiley‐Liss, Inc.