Nitric oxide-mediated cGMP signal transduction in the central nervous system

Nitric oxide (NO) functions as a signalling molecule throughout the brain where, via the intracellular generation of cGMP, it participates in many functions, such as in synaptic plasticity. The initial experiments were based on the finding that, in optic nerve, NO released from blood vessels tonically depolarises axons. The aim was to test the hypothesis that the tonic NO production is maintained by phosphorylation of endothelial NO synthase (eNOS). The results from extracellular recordings of changes in the axonal membrane potential suggested that PI3 kinase-mediated eNOS phosphorylation is partially responsible. The subsequent aim was to determine if blood vessel-neuron communication may be more widespread, by investigating if this mechanism accounts for basal NO production in the developing rat hippocampus. For this purpose, measurements of cGMP were chosen as a sensitive index of the local NO concentration. Contrary to expectations, no clear evidence for a dominant role of either eNOS or the neuronal NO synthase emerged, although the data suggested that NO formation was calcium-dependent. The next step was to characterise the target cells of endogenous and exogenous NO in the hippocampus, particularly in the light of findings that, with a better tool for inhibiting the dominant phosphodiesterase activity (phosphodiesterase-2), much higher cGMP levels could be evoked than previously. Accordingly, instead of a predominant location in astrocytes, cGMP immunocytochemistry showed widespread staining of neuronal elements (somata, dendrites, neuropil) throughout the tissue. The final objective was to begin to analyse NO transduction in cells in real-time, using a newly developed fluorescent cGMP sensor. Cell lines expressing various levels of guanylyl cyclase and phosphodiesterase were selected for study. Cellular responsiveness to extremely low NO concentrations (down to 3 pM) could be detected. Moreover, the findings illustrated how the interplay between guanylyl cyclase and phosphodiesterase activities serves to generate distinct cellular cGMP profiles

Multicolour photometry of the M0V+M5V eclipsing binary V405 And

We present multicolour photometry and modelling of the active eclipsing binary star V405 And. The components of 0.2 and 0.5 solar masses are just below and above the theoretical limit of the full convection, that is thought to be around 0.3 solar mass. The light curves are compositions of constant and variable features: the distorted shape of the components (about 25%), a small eclipse, and mainly of spots (about 75%) and flares.Comment: 4 pages, 2 figures, 1 table, proceedings of Cool Stars 15, St Andrews, July 2008, to be published in the Conference Proceedings Series of the AIP; typo in Table 1. (value of rotation period) correcte

Signaling from blood vessels to CNS axons through nitric oxide

Brain function is usually perceived as being performed by neurons with the support of glial cells, the network of blood vessels situated nearby serving simply to provide nutrient and to dispose of metabolic waste. Revising this view, we find from experiments on a rodent central white matter tract (the optic nerve) in vitro that microvascular endothelial cells signal persistently to axons using nitric oxide (NO) derived from the endothelial NO synthase (eNOS). The endogenous NO acts to stimulate guanylyl cyclase-coupled NO receptors in the axons, leading to a raised cGMP level which then causes membrane depolarization, apparently by directly engaging hyperpolarization-activated cyclic nucleotide-gated ion channels. The tonic depolarization and associated endogenous NO-dependent cGMP generation was absent in optic nerves from mice lacking eNOS, although such nerves responded to exogenous NO, with raised cGMP generation in the axons and associated depolarization. In addition to the tonic activity, exposure of optic nerves to bradykinin, a classical stimulator of eNOS in endothelial cells, elicited reversible NO- and cGMP-dependent depolarization through activation of bradykinin B-2 receptors, to which eNOS is physically complexed. No contribution of other NO synthase isoforms to either the action of bradykinin or the continuous ambient NO level could be detected. The results suggest that microvascular endothelial cells participate in signal processing in the brain and can do so by generating both tonic and phasic NO signals

On the selectivity of neuronal NOS inhibitors.

Isoform-selective inhibitors of NOS enzymes are desirable as research tools and for potential therapeutic purposes. Vinyl-l-N-5-(1-imino-3-butenyl)-l-ornithine (l-VNIO) and N(ω) -propyl-l-arginine (NPA) purportedly have good selectivity for neuronal over endothelial NOS under cell-free conditions, as does N-[(3-aminomethyl)benzyl]acetamidine (1400W), which is primarily an inducible NOS inhibitor. Although used in numerous investigations in vitro and in vivo, there have been surprisingly few tests of the potency and selectivity of these compounds in cells. This study addresses this deficiency and evaluates the activity of new and potentially better pyrrolidine-based compounds

Cellular targets of nitric oxide in the hippocampus.

In the hippocampus, as in many other CNS areas, nitric oxide (NO) participates in synaptic plasticity, manifested as changes in pre- and/or postsynaptic function. While it is known that these changes are brought about by cGMP following activation of guanylyl cyclase-coupled NO receptors attempts to locate cGMP by immunocytochemistry in hippocampal slices in response to NO have failed to detect the cGMP elevation where expected, i.e. in the pyramidal neurones. Instead, astrocytes, unidentified varicose fibres and GABA-ergic nerve terminals are reported to be the prominent NO targets, raising the possibility that NO acts indirectly via other cells. We have re-investigated the distribution of cGMP generated in response to endogenous and exogenous NO in hippocampal slices using immunohistochemistry and new conditions designed to optimise cGMP accumulation and, hence, its detectability. The conditions included use of tissue from the developing rat hippocampus, a potent inhibitor of phosphodiesterase-2, and an allosteric enhancer of the NO-receptive guanylyl cyclase. Under these conditions, cGMP was formed in response to endogenous NO and was found in a population of pyramidal cell somata in area CA3 and subiculum as well as in structures described previously. The additional presence of exogenous NO resulted in hippocampal cGMP reaching the highest level recorded for brain tissue (1700 pmol/mg protein) and in cGMP immunolabelling throughout the pyramidal cell layer. Populations of axons and interneurones were also stained. According with these results, immunohistochemistry for the common NO receptor β1-subunit indicated widespread expression. A similar staining pattern for the α1-subunit with an antibody used previously in the hippocampus and elsewhere, however, proved to be artefactual. The results indicate that the targets of NO in the hippocampus are more varied and extensive than previous evidence had suggested and, in particular, that the pyramidal neurones participating in NO-dependent synaptic plasticity are direct NO targets

Doppler maps and surface differential rotation of EI Eri from the MUSICOS 1998 observations

We present time-series Doppler images of the rapidly-rotating active binary star EI Eri from spectroscopic observations collected during the MUSICOS multi-site campaign in 1998, since the critical rotation period of 1.947 days makes it impossible to obtain time-resolved images from a single site. From the surface reconstructions a weak solar-type differential rotation, as well as a tiny poleward meridional flow are measured.Comment: 4 pages, 3 figures, 1 table, proceedings of Cool Stars 15, St Andrews, July 2008, to be published in the Conference Proceedings Series of the AI

Morphometrical features of left atrial appendage in the AF patients subjected to left atrial appendage closure

Background: This study aimed to evaluate the morphometrical features of left atrial appendage (LAA) in patients with atrial fibrillation, subjected to left atrial appendage percutaneous closure (LARIAT) for stroke prevention. Materials and methods: Computed tomography (CT) scans of 51 patients with atrial fibrillation subjected to LARIAT procedure were comparatively evaluated with 50 patients with sinus rhythm (control group). Three-dimensional (3D) reconstructions were created using volume-rendering for evaluation. Results: No differences were found in LAA types of distribution (cauliflower: 25.5 vs. 34.0%, chicken wing: 45.1 vs. 46.0%, windsock: 29.4 vs. 20.0%, all p>0.05) between groups. However, the study group was characterized by LAAs with a lower number of lobes. The LAA orifice anteroposterior and transverse diameters (19.3±4.12 vs. 17.2±4.0mm, p=0.01 and 25.1±5.1 vs. 20.5±4.4mm, p=0.001), orifice area (387.2±133.9 vs. 327.1±128.3mm2, p=0.02) and orifice perimeter (70.2±12.5 vs. 61.2±11.6mm, p=0.04) was significantly larger in atrial fibrillation patients. More oval LAA orifices was found in atrial fibrillation group (94.0 vs. 70.4%, p=0.001). No statistically significant differences were found in LAA body length (47.4±15.4 vs. 43.7±10.9mm, p=0.17), body width (24.7±5.6 vs. 24.4±5.8mm, p=0.81), and chamber depth (17.7±3.5 vs. 16.5±3.8mm, p=0.11). Calculated LAA ejection fraction was significantly lower in study group compared to healthy patients (16.4±14.9 vs. 48.2±12.9%, p=0.001). Conclusions: Important morphometrical differences in LAA orifice have been found, which was significantly larger and more oval in patients with atrial fibrillation compared to healthy controls. Although no difference in LAA body type and size was observed; the LAA ejection fraction was significantly lower in atrial fibrillation rhythm patients

Binary-induced magnetic activity? Time-series echelle spectroscopy and photometry of HD123351 = CZ CVn

We present a first and detailed study of the bright and active K0IV-III star HD 123351. The star is found to be a single-lined spectroscopic binary with a period of 147.8919+-0.0003 days and a large eccentricity of e=0.8086+-0.0001. The rms of the orbital solution is just 47 m/s, making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32+-0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. Four years of Halpha, CaII H&K and HeI D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542+-72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70+-0.05. The star's position in the H-R diagram indicates a mass of 1.2+-0.1 Msun and an age of 6-7 Gyr. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component

Antisolar differential rotation of the K1-giant sigma Geminorum revisited

Context. Surface differential rotation and other global surface flows on magnetically active stars are among the observable manifes- tations of the stellar dynamo working underneath. Therefore, such observations are important for stellar dynamo theory and useful constraints for solar dynamo studies as well. Aims. The active K1-giant component of the long-period RS CVn-type binary system σ Gem and its global surface flow pattern is revisited. Methods. We refine the differential rotation law from recovering the spot migration pattern. We apply a detailed cross-correlation technique to a unique set of 34 time-series Doppler images recovered using data from 1996/97. By increasing the number of the avail- able cross-correlation function maps from the formerly used 4 to 17 we expect a more robust determination of the differential surface rotation law. In addition, we present a new time-series Doppler imaging study of σ Gem using our advanced surface reconstruction code iMap for a dataset collected in 2006/07. Results. Results from the reprocessed cross-correlation study confirm that the star performs antisolar-type differential rotation with a surface shear α of −0.04 ± 0.01, i.e., almost a factor of two stronger compared to the previously claimed value. We also confirm the evidence of a global poleward spot migration with an average velocity of 0.21 ± 0.03 km s−1, in accordance with theoretical predictions. From the new observations we obtain three subsequent Doppler images. The time evolution of these images confirms the antisolar-type differential rotation of the same amount