Large Positive Potential Research Articles

Salt-Dependence of DNA-Protein Binding: A Study of Four DNA-Binding Families

Long-range salt-mediated electrostatic interactions are crucial for DNA-protein complex formation and stability. The DNA backbone has a strong anionic character, while the DNA-binding proteins here studied display a large positive surface potential patch due to positively charged amino acids facing the DNA-binding site. A linear relationship between ln(Kobs) and ln[M+], where [M+] is the 1:1 salt concentration, is often interpreted as an indication of electrostatic effects and it is named SKobs. This parameter is usually equated to the number of ion pairs found in the complex. We determined the electrostatic binding free energy as a function of 1:1 salt concentration with the non-Linear Poisson-Boltzmann (NLPB) equation to predict SKobs. We investigated four families of DNA-binding proteins: (i) Homeodomains, (ii) High Mobility Group (HMG)-Box proteins, (iii) Interferon Regulatory Factors, and (iv) basic-region Leucine Zippers for which there is experimental binding data from the same laboratory. We correlated structural features to charge distribution, and determined surface accessibility of residues. We found a qualitative relationship between our NLPB predictions of SKobs and the experimental SKobs for homeodomains and for HMG proteins, but not for families in which protein and DNA suffer severe bend and conformational changes. This observation indicates SKobs is sensitive to conformational adaptability and thus this effects have to be accounted in order to improve NLPB predictions of SKobs. We did not find a relationship between SKobs and number of ion pairs, but we found that SKobs is better correlated with the Coulombic interaction energies between molecules of the complex.

Event-related brain potentials during the standard autonomic-based concealed information test

The concealed information test (CIT) has been used to detect information that examinees possess by means of their autonomic responses. However, the central activities related to these autonomic responses remain unclear. In this study, we simultaneously recorded 128-ch event-related potentials (ERPs) and various autonomic responses (heart rate, respiratory rate, respiratory amplitude, cutaneous blood flow, and skin conductance response) to a critical item (i.e., the item that participants memorized) and to non-critical items (i.e., items other than the critical item) using the standard protocol of the autonomic-based CIT. A topographic analysis of variance and a temporal–spatial principal component analysis revealed that the critical item elicited a larger negative potential (N2b, 205–298 ms) at central regions and a larger positive potential (positive slow wave, 502–744 ms) at parieto-occipital regions, compared to the non-critical items. Correlation analysis across 21 participants showed a significant correlation between N2b increase and heart rate deceleration in response to critical items compared to non-critical items, but there were no autonomic correlates of the positive slow wave. The results suggest that at least two brain processes are involved in the autonomic-based CIT: The first is an attentional-orienting process that facilitates the processing of critical items, to which heart rate deceleration was linked, and the second is an additional process after the identification of critical items.

Photophysical Characteristics and Reactivity of Bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I)

The recently synthesized sterically constrained copper(I) complex [Cu(dtbp)(2)](+) (1), where dtbp is 2,9-di-tert-butyl-1,10-phenanthroline, exhibits unique photophysical and reactivity properties. Complex 1 (lambda(abs), 425 nm; epsilon, 3100 L M(-1) cm(-1); lambda(emission), 599 nm) has the longest metal-to-ligand charge-transfer (MLCT) emission lifetime (tau, 3260 ns) and largest quantum yield (varphi, 5.6%) of all [Cu(R(2)phen)(2)](+) complexes. Complex 1 also exhibits a large positive reduction potential for the [Cu(2+)(dtbp)(2)]|[Cu(+)(dtbp)(2)] couple (E(1/2) = 0.70 V vs Fc(+/0)) and a large negative excited-state reduction potential for the [Cu(2+)(dtbp)(dtbp(-*))]|[Cu(2+)(dtbp)(2)] couple (E(1/2) = -1.66 V vs Fc(+/0)), indicating that this complex is a potent photoreductant in the excited state. The steric constraint imposed by the t-butyl substituents in 1 enables unusual ligand replacement reactivity. Either CH(3)CN or CO replaces one of the dtbp ligands, a reaction that is readily followed by loss of the unique emission signature of 1. Monodentate CH(3)CN binds to the copper(I) center with an affinity 2 orders of magnitude greater than that of the displaced dtbp, despite the fact that the displaced ligand is bidentate. CO-induced displacement of dtbp from 1 is reversible, but only in the presence of 1 equiv of unbound dtbp. The exceptionally strong donor ligand CH(3)NC displaces both dtbp ligands from 1. In contrast to the facile ligand displacement reactivity with good donor ligands, 1 does not react readily with O(2), by either a ligand displacement or an oxidative pathway. Rather, O(2) induces partial quenching of emission via an outer-sphere interaction with 1.

Functional and molecular characterizations of chloride channels in rat pleural mesothelial cells

The purposes of the present study were to clarify whether some Cl− channels exist in rat pleural mesothelial cells, and to investigate functional and molecular characteristics of these channels. Electrophysiological recordings were performed at room temperature using the whole-cell configuration of the patch-clamp technique. We could observe outwardly rectifying Cl− currents in rat pleural mesothelial cells under isotonic conditions. These currents exhibited time-dependent inactivation at potential over +60 mV and were inhibited by NPPB. It suggests the presence of voltage-dependent Cl− channels. Moreover, we observed the currents activated under hypotonic conditions. Their biophysical and pharmacological properties exhibited as follows; moderate outward rectification of whole-cell currents; time-dependent inactivation at large positive potential; anion selectivity with a type-I Eisenman's permeability sequence (I−>Br−>Cl−>F−>glutamate−); inhibited by NPPB. These properties are consistent with volume-regulated chloride channels (VRCCs), even though molecular identity of VRCCs could not have been determined, the molecular expressions of mRNA of the Cl− channels ClC-2, ClC-3, pICln, MDR1 were confirmed. The properties of VRCCs in the pleural mesothelial cells were consistent with those of ClC-3 channels, and different from those of ClC-2. Therefore, these results suggest that ClC-3 might contribute to the modulation of VRCCs in rat pleural mesothelial cells.

Platinum surface modification with cerium species and the effect against the methanol anodic reaction

Spontaneous deposition and electrochemical deposition by potential perturbation programs were used to place cerium-containing species on platinum surfaces in acid solution. Cyclic voltammetric profiles of cerium-modified platinum surfaces obtained after potentiostatic or potentiodynamic procedures (applied in the true hydrogen evolution region) differ from those recorded after spontaneous methods. However, the catalytic effects are nearly the same on these cerium-modified platinum surfaces for methanol electrooxidation, i.e. lower onset potential values for the anodic reaction. Besides, a different electrocatalytic effect was observed at large positive potentials on methanol oxidation due to the cerium oxide capability of oxygen storage. This effect is observed on platinum modified by a drastic potentiostatic procedure (by applying −2.0 V) in cerium(IV) acid solution.

Roles of two types of anion channels in glutamate release from mouse astrocytes under ischemic or osmotic stress

Astrocytes release glutamate upon hyperexcitation in the normal brain, and in response to pathologic insults such as ischemia and trauma. In our experiments, both hypotonic and ischemic stimuli caused the release of glutamate from cultured mouse astrocytes, which occurred with little or no contribution of gap junction hemichannels, vesicle-mediated exocytosis, or reversed operation of the Na-dependent glutamate transporter. Cell swelling and chemical ischemia activated, in cell-attached membrane patches, anionic channels with large unitary conductance (approximately 400 pS) and inactivation kinetics at potentials more positive than +20 mV or more negative than -20 mV. These properties are different from those of volume-sensitive outwardly rectifying (VSOR) Cl- channels, which were also expressed in these cells and exhibited intermediate unitary conductance (approximately 80 pS) and inactivation kinetics at large positive potentials of more than +40 mV. Both maxi-anion channels and VSOR Cl- channels were permeable to glutamate with permeability ratios of glutamate to chloride of 0.21 +/- 0.07 and 0.15 +/- 0.01, respectively. However, the release of glutamate was significantly more sensitive to Gd3+, a blocker of maxi-anion channels, than to phloretin, a blocker of VSOR Cl- channels. We conclude that these two channels jointly represent a major conductive pathway for the release of glutamate from swollen and ischemia-challenged astrocytes, with the contribution of maxi-anion channels being predominant.

Tyrosine kinase inhibitors and ATP modulate the conversion of smooth muscle L‐type Ca2+channels toward a second open state

Properties of smooth and cardiac L-type Ca2+ channels differ prominently in several physiological aspects, including sympathetic modulation. To assess the possible underlying mechanisms, we applied the whole cell patch-clamp technique to guinea pig detrusor smooth muscle cells, in which only L-type Ca2+ channel currents are observed in practice. During depolarization to large positive potentials, the conformation of the majority of L-type Ca2+ channels is converted from the normal (O1) to a second open state (O2), which undergoes little inactivation during depolarization. Extracellular application of genistein, a known tyrosine kinase inhibitor, significantly attenuated the voltage-dependent conversion of Ca2+ channels to O2, accompanied by reduction of availability, whereas genistin, an inactive analog, had little effect. In the absence of ATP in the patch pipette, intracellular application of either genistein or tyrphostin-47 suppressed the conversion to O2. Computer calculation revealed that the acceleration of the O1 to an inactivated state qualitatively reconstructs the unique effects of PTK inhibitors antagonized by ATP. We concluded that under normal conditions smooth muscle L-type Ca2+ channels are already modulated by tyrosine-kinase and ATP-related mechanism(s) and thereby easily achieve the second conversion, which yields voltage-dependent modulation of L-type Ca2+ current analogous to that in cardiac myocytes during beta-adrenoceptor stimulation.

Kinetic effects on relativistic solitons in plasmas

We present theoretical and numerical studies of nonlinear interactions between a short, intense laser-beam and a plasma containing hot electrons. Such plasmas are frequently observed in fast-ignition experiments where electrons are heated by intense laser beams. Due to the combined effects of relativistic electron mass increase and relativistic ponderomotive force of the intense laser fields, there appear localized laser pulses in association with large amplitude localized positive potentials. The latter can trap and accelerate electrons to ultra-relativistic energies. This is demonstrated by means of computer simulations of the time-dependent nonlinear electromagnetic wave equation, supplemented by the Vlasov and Poisson equations.

Acidic extracellular pH-activated outwardly rectifying chloride current in mammalian cardiac myocytes

Extracellular acidic pH was found to induce an outwardly rectifying Cl- current (I(Cl,acid)) in mouse ventricular cells, with a half-maximal activation at pH 5.9. The current showed the permeability sequence for anions to be SCN- > Br- > I- > Cl- > F- > aspartate, while it exhibited a time-dependent activation at large positive potentials. Similar currents were also observed in mouse atrial cells and in atrial and ventricular cells from guinea pig. Some Cl- channel blockers (DIDS, niflumic acid, and glibenclamide) inhibited ICl,acid, whereas tamoxifen had little effect on it. Unlike volume-regulated Cl- current (ICl,vol) and CFTR Cl- current (ICl,CFTR), ICl,acid was independent of the presence of intracellular ATP. Activation of ICl,acid appeared to be also independent of intracellular Ca2+ and G protein. ICl,acid and ICl,vol could develop in an additive fashion in acidic hypotonic solutions. Isoprenaline-induced ICl,CFTR was inhibited by acidification in a pH-dependent manner in guinea pig ventricular cells. Our results support the view that ICl,acid and ICl,vol stem from two distinct populations of anion channels and that the ICl,acid channels are present in cardiac cells. ICl,acid may play a role in the control of action potential duration or cell volume under pathological conditions, such as ischemia-related cardiac acidosis.

Effects of Stain Etchant Composition on the Photoluminescence and Morphology of Porous Silicon

Stain etching of silicon provides a spontaneous, self-limiting chemical method to produce nanocrystalline silicon films (porous Si). Whereas the existence of etchants capable of producing porous Si has been known for some time, little has been known concerning how solution composition influences the efficacy of porous Si production and the properties of the resulting films. We demonstrate that the fluoride species may be derived from either HF or acidified . A range of oxidants may be used as long as their counterions do not lead to precipitation. However, a large positive electrochemical potential is not a sufficient condition for efficient porous Si production. Bubble production, which is deleterious to film homogeneity and long thought to be inherent to the process, can be avoided by the use of transition metal-containing oxidants. Properties of the film, such as morphology, growth rate, porosity, and the wavelength of the photoluminescence maximum, respond to the etchant composition. We observe a blue shift in photoluminescence, which correlates with an increasingly positive electrochemical potential of the oxidant. It is argued that plays a role much like wavelength in photoelectrochemical etching and that smaller nanocrystals are produced with more positive values of .

Whole-cell Voltage Clamp Measurements of Anthrax Toxin Pore Current

Protective antigen (PA) of anthrax toxin binds cellular receptors and forms pores in target cell membranes, through which catalytic lethal factor (LF) and edema factor (EF) are believed to translocate to the cytoplasm. Using patch clamp electrophysiological techniques, we assayed pore formation by PA in real time on the surface of cultured cells. The membranes of CHO-K1 cells treated with activated PA had little to no electrical conductivity at neutral pH (7.3) but exhibited robust mixed ionic currents in response to voltage stimuli at pH 5.3. Pore formation depended on specific cellular receptors and exhibited voltage-dependent inactivation at large potentials (>60 mV). The pH requirement for pore formation was receptor-specific as membrane insertion occurs at significantly different pH values when measured in cells specifically expressing tumor endothelial marker 8 (TEM8) or capillary morphogenesis protein 2 (CMG2), the two known cellular receptors for anthrax toxin. Pores were inhibited by an N-terminal fragment of LF and by micromolar concentrations of tetrabutylammonium ions. These studies demonstrated basic biophysical properties of PA pores in cell membranes and served as a foundation for the study of LF and EF translocation in vivo.

Fast-activating channel controls cation fluxes across the native chloroplast envelope.

A prerequisite for photosynthetic CO(2) fixation is the maintenance of alkaline pH in the stroma. This is achieved by H(+) pumping from the stroma to the cytosol, electrically balanced by an influx of cations through some unidentified non-selective envelope channels. In this study, the patch-clamp technique was applied to isolated Pisum sativum L. (pea) chloroplasts, and a fast-activating chloroplast cation (FACC) channel was discovered in the native envelope. This channel opens within a few milliseconds upon voltage steps to large positive or negative potentials. Remarkably, the single-channel conductance increased fivefold, from approximately 40 pS to approximately 200 pS (symmetric 250 mM KCl), upon a potential change from zero to +/- 200 mV. The FACC channel conducts all physiologically essential inorganic cations (K(+), Na(+), Ca(2+), Mg(2+)) with little preference. An increase of stromal pH from 7.3 to 8.0, mimicking dark-light transition, caused about a 2-fold decrease of the FACC channel activity within a physiologically relevant potential range. The FACC channel was completely and irreversibly blocked by Gd(3+). Based on the estimated transport capacity of the whole chloroplast population of FACC channels together with the envelope H(+)-ATPases, these channels can mediate electroneutral K(+)/H(+) exchange across the envelope, enabling stroma alkalinization, thereby allowing an optimal photosynthetic performance.

Volume‐sensitive chloride channels in mouse cortical neurons: characterization and role in volume regulation

Because persistent swelling causes cell damage and often results in cell death, volume regulation is an important physiological function in both neuronal and non-neuronal cells. Brain cell swelling has been observed not only in various pathological conditions but also during physiological synaptic transmissions. Volume-sensitive anion channels have been reported to play an important role in the regulatory volume decrease occurring after osmotic swelling in many cell types. In this study, using a two-photon laser scanning microscope and patch-clamp techniques, we found that mouse cortical neurons in primary culture exhibit regulatory volume decrease after transient swelling and activation of Cl- currents during exposure to a hypotonic solution. The regulatory volume decrease was inhibited by Cl- channel blockers or K+ channel blockers. Swelling-activated Cl- currents exhibited outward rectification, time-dependent inactivation at large positive potentials, a low-field anion permeability sequence, an intermediate unitary conductance and sensitivity to known blockers of volume-sensitive Cl- channels. Thus, it is concluded that the activity of the volume-sensitive outwardly rectifying Cl- channel plays a role in the control of cell volume in cortical neurons.

Redox Equilibria in Hydroxylamine Oxidoreductase. Electrostatic Control of Electron Redistribution in Multielectron Oxidative Processes

We report results of continuum electrostatics calculations of the cofactor redox potentials, and of the titratable group pK(a) values, in hydroxylamine oxidoreductase (HAO). A picture of a sophisticated multicomponent control of electron flow in the protein emerged from the studies. First, we found that neighboring heme cofactors strongly interact electrostatically, with energies of 50-100 mV. Thus, cofactor redox potentials depend on the oxidation state of other cofactors, and cofactor redox potentials in the active (partially oxidized) enzyme differ substantially from the values obtained in electrochemical redox titration experiments. We found that, together, solvent-exposed heme 1 (having a large negative redox potential) and heme 2 (having a large positive redox potential) form a lock for electrons generated during the oxidation reaction The attachment of HAO's physiological electron transfer partner cytochrome c(554) results in a positive shift in the redox potential of heme 1, and "opens the electron gate". Electrons generated as a result of hydroxylamine oxidation travel to heme 3 and heme 8, which have redox potentials close to 0 mV versus NHE (this result is in partial disagreement with an existing experimental redox potential assignment). The closeness of hemes 3 and 8 from different enzyme subunits allows redistribution of the four electrons generated as a result of hydroxylamine oxidation, among the three enzyme subunits. For the multielectron oxidation process to be maximally efficient, the redox potentials of the electron-accepting cofactors should be roughly equal, and electrostatic interactions between extra electrons on these cofactors should be minimal. The redox potential assignments presented in the paper satisfy this general rule.

On the effect of near-equatorial thunderstorms on the global distribution of ionospheric potential

We develop our earlier attempts to perform an indirect quantitative examination of the hypothesis that electric currents flowing up from thunderstorms to the ionosphere (also known as Wilson currents) charge the ionosphere to a large positive potential with respect to the Earth. First, we take the electrostatic potential arising from the interaction of the solar wind with the Earth’s magnetosphere derived from an experimental data-based model of the high-latitude field-aligned currents. We then obtain the global distribution of ionospheric potential, utilizing a thin shell model, based on integration along field lines of the current continuity equation with a realistic model of ionospheric conductivity. Next, we include additional upward currents to simulate the effect of the three main thunderstorm regions over equatorial Asia/Oceania, Africa and the Americas. We compare the local time variation of the eastward electric field in the ionosphere produced by these three equatorial sources separately, and seek to understand the substantial differences between them. Finally, we examine the variation with local time of the eastward electric field in the ionosphere at low latitudes.

A role of reactive oxygen species in apoptotic activation of volume-sensitive Cl(-) channel.

Apoptotic volume decrease is a pivotal event triggering a cell to undergo apoptosis and is induced by ionic effluxes resulting mainly from increased K(+) and Cl(-) conductances. Here, we demonstrate that in human epithelia HeLa cells both mitochondrion- and death receptor-mediated apoptosis inducers [staurosporine and Fas ligand or tumor necrosis factor (TNF)-alpha] rapidly activate Cl(-) currents that show properties phenotypical of volume-sensitive outwardly rectifying Cl(-) channel currents, including outward rectification, voltage-dependent inactivation gating at large positive potentials, inhibition by osmotic shrinkage, sensitivity to classic Cl(-) channel blockers, and dependence on cytosolic ATP. Staurosporine, but not Fas ligand or TNF-alpha, rapidly (within 30 min) increased the intracellular level of reactive oxygen species (ROS). A ROS scavenger and an NAD(P)H oxidase inhibitor blocked the current activation by staurosporine but not by Fas ligand or TNF-alpha. A ROS scavenger also inhibited apoptotic volume decrease, caspase-3 activation, and apoptotic cell death induced by staurosporine. Thus, it is concluded that an apoptosis-triggering anion conductance is carried by the volume-sensitive outwardly rectifying Cl(-) channel and that the channel activation on apoptotic stimulation with staurosporine, but not with Fas ligand or TNF-alpha, is mediated by ROS.

Grid-controlled electron emission from a hollow-anode electron source

We describe the operation of a hollow-anode electron source with a biased output grid in a diode powered by a 200 kV 400 ns pulse. The hollow anode had a ferroelectric plasma source incorporated in it. Three electrical schemes for the hollow-anode output grid bias were tested and compared. It is shown that the use of an autobias grid allows electron-beam generation with a current amplitude up to 1.2 kA in a plasma emission-limited mode and with insignificant plasma prefilling of the accelerating gap. The use of an externally biased output grid (either with a positive or negative potential) showed the possibility to control the emission properties of the hollow-anode plasma without changing the amplitude of the discharge current. Electron beams with an amplitude up to 2 kA and insignificant plasma prefilling of the accelerating gap were obtained. It was found that the application of the accelerating pulse leads to a drastic increase in the potential of the plasma up to several kV. It is shown that, in spite of the large positive plasma potential, electron emission occurs due to the dynamics of ions inside the sheath near the hollow-anode grid.

Ca 2+-Dependent Excitation-Contraction Coupling Triggered by the Heterologous Cardiac/Brain DHPR β2a-Subunit in Skeletal Myotubes

Molecular determinants essential for skeletal-type excitation-contraction (EC) coupling have been described in the cytosolic loops of the dihydropyridine receptor (DHPR) α1S pore subunit and in the carboxyl terminus of the skeletal-specific DHPR β1a-subunit. It is unknown whether EC coupling domains present in the β-subunit influence those present in the pore subunit or if they act independent of each other. To address this question, we investigated the EC coupling signal that is generated when the endogenous DHPR pore subunit α1S is paired with the heterologous heart/brain DHPR β2a-subunit. Studies were conducted in primary cultured myotubes from β1 knockout (KO), ryanodine receptor type 1 (RyR1) KO, ryanodine receptor type 3 (RyR3) KO, and double RyR1/RyR3 KO mice under voltage clamp with simultaneous monitoring of confocal fluo-4 fluorescence. The β2a-mediated Ca 2+ current recovered in β1 KO myotubes lacking the endogenous DHPR β1a-subunit verified formation of the α1S/ β1a pair. In myotube genotypes which express no or low-density L-type Ca 2+ currents, namely β1 KO and RyR1 KO, β2a overexpression recovered a wild-type density of nifedipine-sensitive Ca 2+ currents with a slow activation kinetics typical of skeletal myotubes. Concurrent with Ca 2+ current recovery, there was a drastic reduction of voltage–dependent, skeletal-type EC coupling and emergence of Ca 2+ transients triggered by the Ca 2+ current. A comparison of β2a overexpression in RyR3 KO, RyR1 KO, and double RyR1/RyR3 KO myotubes concluded that both RyR1 and RyR3 isoforms participated in Ca 2+-dependent Ca 2+ release triggered by the β2a-subunit. In β1 KO and RyR1 KO myotubes, the Ca 2+-dependent EC coupling promoted by β2a overexpression had the following characteristics: 1), L-type Ca 2+ currents had a wild-type density; 2), Ca 2+ transients activated much slower than controls overexpressing β1a, and the rate of fluorescence increase was consistent with the activation kinetics of the Ca 2+ current; 3), the voltage dependence of the Ca 2+ transient was bell-shaped and the maximum was centered at ∼+30 mV, consistent with the voltage dependence of the Ca 2+ current; and 4), Ca 2+ currents and Ca 2+ transients were fully blocked by nifedipine. The loss in voltage-dependent EC coupling promoted by β2a was inferred by the drastic reduction in maximal Ca 2+ fluorescence at large positive potentials (Δ F/ F max) in double dysgenic/ β1 KO myotubes overexpressing the pore mutant α1S (E1014K) and β2a. The data indicate that β2a, upon interaction with the skeletal pore subunit α1S, overrides critical EC coupling determinants present in α1S. We propose that the α1S/ β pair, and not the α1S-subunit alone, controls the EC coupling signal in skeletal muscle.

Addendum to “Update on neutrino mixing in the early universe”

In the light of the recent WMAP results we update the constraints on a class of nonstandard big bang nucleosynthesis (BBN) models with a simultaneous combination of nonstandard neutrino distributions and an extra effective number of neutrinos in the expansion rate. These models can be described in terms of the two parameters $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\mathrm{tot}},$ constrained by the primordial helium abundance ${Y}_{p}$ measurement, and $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\ensuremath{\rho}},$ constrained by a combination of cosmic microwave background and primordial deuterium data. Small deviations from standard big bang nucleosynthesis are suggested. Different nonstandard scenarios can be distinguished by a measurement of the difference $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{{f}_{\ensuremath{\nu}}}=\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\mathrm{tot}}\ensuremath{-}\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\ensuremath{\rho}}.$ From the current data we estimate $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{{f}_{\ensuremath{\nu}}}\ensuremath{\simeq}\ensuremath{-}{1.4}_{\ensuremath{-}1.4}^{+0.9},$ mildly disfavoring solutions with a low expansion rate, characterized by $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{{f}_{\ensuremath{\nu}}}=0$ and negative $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\ensuremath{\rho}}.$ Active-sterile neutrino mixing could be a viable explanation only for high values of ${Y}_{p}\ensuremath{\gtrsim}0.24.$ The existence of large positive neutrino chemical potentials ${\ensuremath{\xi}}_{i}\ensuremath{\sim}0.05,$ implying $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}^{\ensuremath{\rho}}\ensuremath{\simeq}0,$ would be a possible explanation of the data within the analyzed class of nonstandard BBN models. Interestingly, it would also provide a way to evade the cosmological bounds for ``class A 3+1'' four neutrino mixing models. A scenario with a decaying sterile neutrino is also considered.

Identification and functional characterization of the trigeminal ventral cervical reflex pathway in the swine.

Trigeminal motor reflexes are clinically useful for diagnosing brain stem lesions. We identified and functionally characterized the neuronal circuit of a new variant of the trigemino-cervical reflex involving the ventral cervical muscles in the swine. The distribution and functional properties of the field potentials of the trigeminal reflex elicited by electrical stimulations of the snout were determined with electrodes in different regions of the brain. The generator of the reflex was determined from scanning evoked magnetic fields over the brainstem. The neuronal circuit was determined with electrodes placed along the trigeminal reflex pathway. The reflex produced a large positive potential in the brain (up to 200 microV in the primary somatosensory cortex) with a latency of about 14ms. Its amplitude declined rapidly with stimulation rate above 0.5Hz and was abolished by a muscle relaxant. The accompanying magnetic field was produced by a generator ventral to the pons. This generator was found to be the ventral cervical muscles that were activated by a circuit involving the brainstem trigeminal nuclei and cervical motor nuclei. It is not known whether this new variant of the trigeminal cervical reflex is species-specific or it also exists in humans. It should be possible to test this possibility in humans, since it produces strong characteristic electrical potentials and magnetic fields in the swine. If it exists in humans, then it may be useful as a clinical tool for testing the integrity of the brainstem and C1 and C2 since the circuit is now identified and characterized in the animal model.