Differential Control of Axonal and Somatic Resting Potential by Voltage-Dependent Conductances in Cortical Layer 5 Pyramidal Neurons

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Kinetic Theory Model for Ion Movement through Biological Membranes: I. Field-Dependent Conductances in the Presence of Solution Symmetry

A model for ion movement through specialized sites in the plasma membrane is presented and analyzed using techniques from nonequilibrium kinetic theory. It is assumed that ions traversing these specialized regions interact with membrane molecules through central conservative forces. The membrane molecules are approximated as massive spherical scattering centers so that ionic fractional energy losses per collision are much less than one. Equations for steady-state membrane ionic currents and conductances as functions of externally applied electric field strength are derived and numerically analyzed, under the restriction of identical solutions on each size of the membrane and constant electric fields within the membrane. The analysis is carried through for a number of idealized ion-membrane molecule central force interactions. For any interaction leading to a velocity-dependent ion-membrane molecule collision frequency, the membrane chord conductance is a function of the externally applied electric field. Interactions leading to a collision frequency that is an increasing (decreasing) function of ionic velocity are characterized by chord conductances that are decreasing (increasing) functions of field strength. For ion-neutral molecule interactions, the conductance is such a rapidly decreasing function of field strength that the slope conductance becomes negative for all field strengths above a certain value.     

Robust Modeling of Differential Gene Expression Data Using Normal/Independent Distributions: A Bayesian Approach

In this paper, the problem of identifying differentially expressed genes under different conditions using gene expression microarray data, in the presence of outliers, is discussed. For this purpose, the robust modeling of gene expression data using some powerful distributions known as normal/independent distributions is considered. These distributions include the Student’s t and normal distributions which have been used previously, but also include extensions such as the slash, the contaminated normal and the Laplace distributions. The purpose of this paper is to identify differentially expressed genes by considering these distributional assumptions instead of the normal distribution. A Bayesian approach using the Markov Chain Monte Carlo method is adopted for parameter estimation. Two publicly available gene expression data sets are analyzed using the proposed approach. The use of the robust models for detecting differentially expressed genes is investigated. This investigation shows that the choice of model for differentiating gene expression data is very important. This is due to the small number of replicates for each gene and the existence of outlying data. Comparison of the performance of these models is made using different statistical criteria and the ROC curve. The method is illustrated using some simulation studies. We demonstrate the flexibility of these robust models in identifying differentially expressed genes.     

Remote Modulation of Current Transfer from Dendritic Glutamatergic Synapses by GABA-ergic Synapses of the Somatic Zone of Motoneurons: a Simulation Study

Until now, information concerning spatial interaction of postsynaptic excitation and inhibition in neuronal dendrites remains rather limited. In model experiments, we studied spatial effects of tonic co-activation of GABA-ergic synapses situated on the soma and axon hillock of a motoneuron and dendritic glutamatergic synapses with receptors sensitive or insensitive to N-methyl-D-aspartate. We analyzed distribution maps of the transmembrane potentials and excitatory currents transferred toward the soma over the reconstructed dendritic arborization of a rat abducens motoneuron (three-dimensional reconstruction). In the motoneuron, isolated tonic excitation of glutamatergic synapses induced two stable states of low (downstate) or high (upstate) spatially heterogeneous dendritic depolarization, which decayed with unequal rates along different dendritic paths. In this case, the local steady-state current-voltage relation of the dendritic membrane became N-shaped due to a limb of the negative slope within a certain voltage range. The upstate corresponding to plateau potentials associated with stereotyped motor activity patterns was analyzed in detail. In this state, most proximal dendritic sites were the main sources of the excitatory current reaching the soma, while the contribution from distal sites was negligible. Co-activation of GABA-synapses located at the soma and axon hillock reduced this depolarization and shifted the main excitatory current source from a perisomatic location to the middle, structurally more complex, region of the dendritic arborization. The more remote dendritic region having a greater membrane area and receiving a greater number of synaptic contacts became directly involved in the supply of the trigger zone by the excitatory current. We suggest that a special, not described earlier, operational mechanism of postsynaptic inhibition is manifested in the above spatial effects of activation of strategically located inhibitory synapses, and that the list of known crucial inhibitory mechanisms (namely hyperpolarization and shunting of the postsynaptic membrane) must be expanded.     

Biased belief priors versus biased belief updating: Differential correlates of depression and anxiety

Individuals prone to anxiety and depression often report beliefs and make judgements about themselves that are more negative than those reported by others. We use computational modeling of a richly naturalistic task to disentangle the role of negative priors versus negatively biased belief updating and to investigate their association with different dimensions of Internalizing psychopathology. Undergraduate participants first provided profiles for a hypothetical tech internship. They then viewed pairs of other profiles and selected the individual they would prefer to work alongside out of each pair. In a subsequent phase of the experiment, participants made judgments about their relative popularity as hypothetical internship partners both before any feedback and after each of 20 items of feedback revealing whether or not they had been selected as the preferred teammate from a given pairing. Scores on latent factors of general negative affect, anxiety-specific affect and depression-specific affect were estimated using participants’ self-report scores on standardized measures of anxiety and depression together with factor loadings from a bifactor analysis conducted previously. Higher scores on the depression-specific factor were linked to more negative prior beliefs but were not associated with differences in belief updating. In contrast, higher scores on the anxiety-specific factor were associated with a negative bias in belief updating but no difference in prior beliefs. These findings indicate that, to at least some extent, distinct processes may impact the formation of belief priors and in-the-moment belief updating and that these processes may be differentially disrupted in depression and anxiety. Future directions for enquiry include examination of the possibility that prior beliefs biases in depression might reflect generalization from prior experiences or global schema whereas belief updating biases in anxiety might be more situationally specific.     

Active site identification through geometry-based and sequence profile-based calculations: burial of catalytic clefts

Electrostatics calculations with proteins that are uniformly charged over volume can aid enzyme/non-enzyme discrimination. For known enzymes, such methods locate active sites to within 5% on the enzyme surface, in 77% of a test set. We now report that removing the dielectric boundary improves active site location to 80%, with optimal discrimination between enzymes and non-enzymes of around 80% specificity and 80% sensitivity. This calculation quantifies burial of solvent-accessible regions. Many of the true enzymes incorrectly assigned as non-enzymes have active sites at subunit boundaries. These are missed in monomer-based calculations. Catalytic and non-catalytic antibodies are studied in this context of active/binding site burial. Whilst catalytic antibodies, on average, have marginally higher active site burial than non-catalytic antibodies, these values are generally smaller than for non-antibody enzymes, possibly contributing to their relatively low turnover. Prediction of active site location improves further when sequence profile-based weights replace the uniform charge distribution, so that a combination of burial and amino acid conservation is assessed. Accuracy rises to 93% of active sites to within 5%, in the test set, for the optimal profile weights scheme. The equivalent value in a separate validation set is 89% to within 5%. Enzyme/non-enzyme and enzyme functional site predictions are made for structural genomics proteins, suggesting that a substantial majority of these are non-enzymes.     

High-Field Open versus Short-Bore Magnetic Resonance Imaging of the Spine: A Randomized Controlled Comparison of Image Quality

Background

The purpose of the present study was to compare the image quality of spinal magnetic resonance (MR) imaging performed on a high-field horizontal open versus a short-bore MR scanner in a randomized controlled study setup.

Methods

Altogether, 93 (80% women, mean age 53) consecutive patients underwent spine imaging after random assignement to a 1-T horizontal open MR scanner with a vertical magnetic field or a 1.5-T short-bore MR scanner. This patient subset was part of a larger cohort. Image quality was assessed by determining qualitative parameters, signal-to-noise (SNR) and contrast-to-noise ratios (CNR), and quantitative contour sharpness.

Results

The image quality parameters were higher for short-bore MR imaging. Regarding all sequences, the relative differences were 39% for the mean overall qualitative image quality, 53% for the mean SNR values, and 34–37% for the quantitative contour sharpness (P<0.0001). The CNR values were also higher for images obtained with the short-bore MR scanner. No sequence was of very poor (nondiagnostic) image quality. Scanning times were significantly longer for examinations performed on the open MR scanner (mean: 32±22 min versus 20±9 min; P<0.0001).

Conclusions

In this randomized controlled comparison of spinal MR imaging with an open versus a short-bore scanner, short-bore MR imaging revealed considerably higher image quality with shorter scanning times.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00715806","term_id":"NCT00715806"}}NCT00715806     

Differential activity of soluble versus cellular Fas ligand: regulation by an accessory molecule.

Fas ligand induces apoptosis by binding to its receptor Fas. This process has been shown to be important for activation-induced cell death of T lymphocytes, homeostasis of T cell numbers, cytotoxicity, and the maintenance of immunological privilege. Fas ligand is a type II membrane protein that is cleaved by a metalloproteinase to produce an active, soluble molecule. It has been found that a variety of target cells are differentially sensitive to soluble and membrane-associated forms of Fas ligand. However, the explanation for this differential activity has not been determined. One proposed explanation for this differential activity is that membrane-associated Fas ligand is more efficiently aggregated than soluble Fas ligand. Another possibility that we have investigated is that accessory molecules may act to enhance the activity of cellular Fas ligand. We have transfected cells to express membrane-associated Fas ligand and have characterized clones of these transfected cells in terms of Fas ligand and ICAM-1 surface expression. Enhanced activity was associated with enhanced levels of both Fas ligand and ICAM-1. Moreover, inhibition of ICAM-1 modulated the activity of membrane-associated Fas ligand so that its cellular specificity was similar to that of soluble Fas ligand. Thus, ICAM-1 plays a significant role in regulating Fas ligand activity, and this role explains, at least in part, the different functional attributes of the soluble versus the cell-associated molecule.     

Differential effects of apoptotic versus lysed cells on macrophage production of cytokines: role of proteases

Granulocytes undergoing apoptosis are recognized and removed by phagocytes before their lysis. The release of their formidable arsenal of proteases and other toxic intracellular contents into tissues can create significant damage, prolonging the inflammatory response. Binding and/or uptake of apoptotic cells by macrophages inhibits release of proinflammatory cytokines by mechanisms that involve anti-inflammatory mediators, including TGF-beta. To model the direct effects of necrotic cells on macrophage cytokine production, we added lysed or apoptotic neutrophils and lymphocytes to mouse and human macrophages in the absence of serum to avoid complement activation. The results confirmed the ability of lysed neutrophils, but not lymphocytes, to significantly stimulate production of macrophage-inflammatory protein 2 or IL-8, TNF-alpha, and IL-10. Concomitantly, induction of TGF-beta1 by lysed neutrophils was significantly lower than that observed for apoptotic cells. The addition of selected serine protease inhibitors and anti-human elastase Ab markedly reduced the proinflammatory effects, the lysed neutrophils then behaving as an anti-inflammatory stimulus similar to intact apoptotic cells. Separation of lysed neutrophils into membrane and soluble fractions showed that the neutrophil membranes behaved like apoptotic cells. Thus, the cytokine response seen when macrophages were exposed to lysed neutrophils was largely due to liberated proteases. Therefore, we suggest that anti-inflammatory signals can be given by PtdSer-containing cell membranes, whether from early apoptotic, late apoptotic, or lysed cells, but can be overcome by proteases liberated during lysis. Therefore, the outcome of an inflammatory reaction and the potential immunogenicity of Ags within the damaged cell will be determined by which signals predominate.     

Cutting Edge: 4-1BB Controls Regulatory Activity in Dendritic Cells through Promoting Optimal Expression of Retinal Dehydrogenase

Dendritic cells (DC) in the gut promote immune tolerance by expressing retinal dehydrogenase (RALDH), an enzyme that promotes retinoic acid, which aids differentiation of Foxp3(+) inducible regulatory T cells (iTreg) in the intestinal mucosa. How RALDH expression is regulated is unclear. We found that 4-1BB (CD137), a member of the TNFR family, together with CD103, marked mesenteric lymph node DC with the highest level of RALDH activity, and ligation of 4-1BB maintained RALDH expression in these gut DC. Moreover, 4-1BB signals synergized with those through TLR2 or GM-CSFR to promote RALDH activity in undifferentiated DC. Correspondingly, 4-1BB-deficient mice were impaired in their ability to generate iTreg in the GALT when exposed to oral Ag, and 4-1BB-deficient mesenteric lymph node DC displayed weak RALDH activity and were poor at promoting iTreg development. Thus, our data demonstrate a novel activity of 4-1BB in controlling RALDH expression and the regulatory activity of DC.     

Differential regulation of dihydroceramide desaturase by palmitate versus monounsaturated fatty acids: implications for insulin resistance

Much data implicate saturated fatty acids in deleterious processes associated with obesity, diabetes, and the metabolic syndrome. Many of these changes may be due to aberrant generation of bioactive lipids when saturated fatty acid availability to tissues is increased. On the other hand, studies are emerging that implicate the monounsaturated fatty acid oleate in protection from saturated fat mediated toxicity; however, the mechanisms are not well understood. Our data demonstrate a novel role for palmitate in increasing mRNA encoding DES1, which is the enzyme responsible for generating ceramide from its precursor dihydroceramide and thus controls synthesis of the bioactive lipid ceramide. Moreover, co-treatment with oleate prevented the increase in ceramide, and this occurred through attenuation of the increase in message and activity of DES1. Knockdown of DES1 also protected from palmitate-induced insulin resistance, and overexpression of this enzyme ameliorated the protective effect of oleate. Together, these findings provide insight into the mechanisms of oleate-mediated protection against metabolic disease and provide novel evidence for fatty acid-mediated regulation of a key enzyme of ceramide biosynthesis.     

Immature versus mature dura mater: II. Differential expression of genes important to calvarial reossification

The ability of immature animals and newborns to orchestrate successful calvarial reossification is well described. This capacity is markedly attenuated in mature animals and in humans greater than 2 years of age. Previous studies have implicated the dura mater as critical to successful calvarial reossification. The authors have previously reported that immature, but not mature, dural tissues are capable of elaborating a high expression of osteogenic growth factors and extracellular matrix molecules. These findings led to the hypothesis that a differential expression of osteogenic growth factors and extracellular matrix molecules by immature and mature dural tissues may be responsible for the clinically observed phenotypes (i.e., immature animals reossify calvarial defects; mature animals do not). This study continues to explore the hypothesis through an analysis of transforming growth factor (TGF)-beta3, collagen type III, and alkaline phosphatase mRNA expression. Northern blot analysis of total RNA isolated from freshly harvested immature (n = 60) and mature (n = 10) dural tissues demonstrated a greater than three-fold, 18-fold, and nine-fold increase in TGF-beta3, collagen type III, and alkaline phosphatase mRNA expression, respectively, in immature dural tissues as compared with mature dural tissues. Additionally, dural cell cultures derived from immature (n = 60) and mature dura mater (n = 10) were stained for alkaline phosphatase activity to identify the presence of osteoblast-like cells. Alkaline phosphatase staining of immature dural cells revealed a significant increase in the number of alkaline phosphatase-positive cells as compared with mature dural tissues (p < 0.001). In addition to providing osteogenic humoral factors (i.e., growth factors and extracellular matrix molecules), this finding suggests that immature, but not mature, dura mater may provide cellular elements (i.e., osteoblasts) that augment successful calvarial reossification. These studies support the hypothesis that elaboration of osteogenic growth factors (i.e., TGF-beta33) and extracellular matrix molecules (i.e., collagen type III and alkaline phosphatase) by immature, but not mature, dural tissues may be critical for successful calvarial reossification. In addition, these studies suggest for the first time that immature dural tissues may provide cellular elements (i.e., osteoblasts) to augment this process.     

Differential passive and active biaxial mechanical behaviors of muscular and elastic arteries: basilar versus common carotid

Cerebrovascular disease continues to be responsible for significant morbidity and mortality. There is, therefore, a pressing need to understand better the biomechanics of both intracranial arteries and the extracranial arteries that feed these vessels. We used a validated four-fiber family constitutive relation to model passive biaxial stress-stretch behaviors of basilar and common carotid arteries and we developed a new relation to model their active biaxial responses. These data and constitutive relations allow the first full comparison of circumferential and axial biomechanical behaviors between a muscular (basilar) and an elastic (carotid) artery from the same species. Our active model describes the responses by both types of vessels to four doses of the vasoconstrictor endothelin-1 (10(-10)M, 10(-9)M, 10(-8)M, and 10(-7)M) and predicts levels of smooth muscle cell activation associated with basal tone under specific in vitro testing conditions. These results advance our understanding of the biomechanics of intracranial and extracranial arteries, which is needed to understand better their differential responses to similar perturbations in hemodynamic loading.     

Differential regulation of gonadotropin-releasing hormone secretion and gene expression by androgen: membrane versus nuclear receptor activation

Steroid hormones induce rapid membrane receptor-mediated effects that appear to be separate from long-term genomic events. The membrane receptor-mediated effects of androgens on GT1-7 GnRH-secreting neurons were examined. We observed androgen binding activity with a cell-impermeable BSA-conjugated testosterone [testosterone 3-(O-carboxymethyl)oxime (T-3-BSA)] and were able to detect a 110-kDa protein recognized by the androgen receptor (AR) monoclonal MA1-150 antibody in the plasma membrane fraction of the GT1-7 cells by Western analysis. Further, a transfected green fluorescent protein-tagged AR translocates and colocalizes to the plasma membrane of the GT1-7 neuron. Treatment with 10 nM 5alpha-dihydrotestosterone (DHT) inhibits forskolin-stimulated accumulation of cAMP, through a pertussis toxin-sensitive G protein, but has no effect on basal cAMP levels. The inhibition of forskolin-stimulated cAMP accumulation by DHT was blocked by hydroxyflutamide, a specific inhibitor of the nuclear AR. DHT, testosterone (T), and T-3-BSA, all caused significant elevations in intracellular calcium concentrations ([Ca(2+)](i)). T-3-BSA stimulates GnRH secretion 2-fold in the GT1-7 neuron, as did DHT or T. Interestingly GnRH mRNA levels were down-regulated by DHT and T as has been reported, but not by treatment with T-3-BSA or testosterone 17beta-hemisuccinate BSA. These studies indicate that androgen can differentially regulate GnRH secretion and gene expression through specific membrane-mediated or nuclear mechanisms.     

Differential regulation of cAMP by endogenous versus transfected formylpeptide chemoattractant receptors: implications for Gi-coupled receptor signaling.

Endogenous neutrophil formylpeptide receptors do not inhibit adenylylcyclase activation. The ability of a cloned and transfected human formylpeptide receptor to mediate the inhibition of adenylylcyclase was assessed in the human embryonic kidney 293 TSA cell line. Inclusion of 1 microM fMetLeuPhe resulted in a ca. 50% inhibition of isoproterenol-stimulated cAMP in transfected cells. Activation of adenylylcyclase by isoproterenol was inhibited ca. 30% by fMetLeuPhe in membranes prepared from transfected cells but not in membranes prepared from neutrophils. Prior treatment of transfected cells with pertussis toxin abrogated the inhibitory effect of fMetLeuPhe. These data indicate that factors in addition to the primary structure of the formylpeptide receptor govern its transductional activities.     

Isolation versus grouped housing in rats: Differential effects of low doses of heroin in the place preference paradigm

Male Long Evans rats were reared from weaning (21–23 days) either in isolation or in groups of four for 40 days. Animals were then individually introduced to a testing apparatus consisting of two distinct chambers. A modified place preference paradigm was used consisting of 3 phases: (1) An habituation phase (4 days) during which rats were allowed free access to the entire test apparatus for 15 min. periods daily; (2) A conditioning phase (4 days) during which rats were confined to their non-preferred side for 15 minutes each day immediately following subcutaneous injection of 0, 20, 40 and 80 μg/kg of heroin HCl; (3) A test phase (1 day) during which rats were again allowed free access to the testing chamber following injection of vehicle. The difference in time spent on the conditioned side during habituation and test periods was determined. The group-reared rats showed similar effects for all doses of heroin whereas the same magnitude of drug effect was attained only at the highest dose used in the isolated rats. This differential sensitivity to heroin in the place preference paradigm is discussed in terms of the modification of behavioral effects of opiates by environmental influences.