Threshold For Induction Research Articles

The relationship between tetanus intensity and the magnitude of hippocampal long-term potentiation in vivo

In this study, we assessed the effects of varying tetanus and test-pulse intensity on the magnitude of long-term potentiation (LTP) in the perforant path–dentate gyrus projection of urethane-anaesthetized rats. We developed a novel within-subjects procedure in which test-pulse-stimulation intensity (60–1000μA) was varied quasi-randomly under computer control throughout the recording period. After a baseline period, we applied a high-frequency tetanus, the intensity of which was varied over the same range as test-pulse intensity, but between subjects. The time-course of LTP was thus monitored continuously across a range of test-pulse intensities in each rat. Intense high-frequency tetanization at 1000μA resulted in a paradoxical depression of the dentate field excitatory post-synaptic potential (fEPSP) slope at the lowest test intensity used (60μA), but caused a potentiation at higher test intensities in the same animal. Moreover, intense tetanization induced less LTP than a moderate tetanus over most of the test-intensity range. Explanations for this pattern of data include a potentiation of feed-forward inhibition in conjunction with LTP of excitatory neurotransmission, or local tissue damage at the stimulation site. To address this issue, we conducted an additional experiment in which a second stimulating electrode was placed in the perforant path at a site closer to the dentate, in order to activate a common population of afferents at a location ‘downstream’ of the original stimulation site. After 1000-μA tetanization of the original (‘upstream’) site, fEPSPs were again depressed in response to test stimulation of the upstream site, but only potentiation was observed in response to stimulation of the downstream site. This is consistent with the idea that the depression induced by intense tetanization results from local changes at the stimulation site. In conclusion, while tetanus intensity must exceed the LTP induction threshold, intensities above 500μA should be avoided; in the present study, tetanization at 250–500μA yielded maximal levels of LTP.

Prevalence of Poor Cardiac Anatomy in Carcinoma of the Breast Treated With Whole-breast Radiotherapy

: The purpose of the study was to identify patient characteristics that predict for increased cardiac exposure through dosimetric analysis of the anatomy of a cohort of women treated with left-sided tangential breast radiation. Statistical analyses estimations for the appropriate sample sizes required for detection of significant differences in cardiac mortality at 15 years were conducted, assuming a threshold V25 for radiation-induced coronary artery disease (CAD) beyond which women are at risk for radiation-induced coronary artery disease. : Detailed heart dosimetry was recorded. Clinical factors (age, history of CAD, diabetes, receipt of cardiotoxic agents, weight/body mass index) and anatomic factors (heart volume, breast volume, cardiac contact distance) were recorded for each patient. : The average heart V25 was 3.57%. The median percentage of the heart included in the tangential beam was 4.02%. There were no clinical or anatomic factors that predict suboptimal heart anatomy (ie, V25 of ≥6%) on multivariate analysis. The sample size calculations using thresholds for induction of CAD of V25 ≥1%, 6%, and 10% yielded sample sizes of 1314, 9504, and 61,342, respectively; considering node-positive breast cancer mortality and 15% loss to follow-up, these change to 2237, 16,166, and 104,334, respectively. : Current studies with modern radiotherapy techniques would be underpowered to detect a difference in cardiac mortality where only some women are at risk. The heart, chest wall, and breast have a complex relationship to tangential breast radiation, and their interplay prevented this anatomic metric's success.

Ultrasensitivity of the Bacillus subtilis sporulation decision

Starving Bacillus subtilis cells execute a gene expression program resulting in the formation of stress-resistant spores. Sporulation master regulator, Spo0A, is activated by a phosphorelay and controls the expression of a multitude of genes, including the forespore-specific sigma factor σ(F) and the mother cell-specific sigma factor σ(E). Identification of the system-level mechanism of the sporulation decision is hindered by a lack of direct control over Spo0A activity. This limitation can be overcome by using a synthetic system in which Spo0A activation is controlled by inducing expression of phosphorelay kinase KinA. This induction results in a switch-like increase in the number of sporulating cells at a threshold of KinA. Using a combination of mathematical modeling and single-cell microscopy, we investigate the origin and physiological significance of this ultrasensitive threshold. The results indicate that the phosphorelay is unable to achieve a sufficiently fast and ultrasensitive response via its positive feedback architecture, suggesting that the sporulation decision is made downstream. In contrast, activation of σ(F) in the forespore and of σ(E) in the mother cell compartments occurs via a cascade of coherent feed-forward loops, and thereby can produce fast and ultrasensitive responses as a result of KinA induction. Unlike σ(F) activation, σ(E) activation in the mother cell compartment only occurs above the KinA threshold, resulting in completion of sporulation. Thus, ultrasensitive σ(E) activation explains the KinA threshold for sporulation induction. We therefore infer that under uncertain conditions, cells initiate sporulation but postpone making the sporulation decision to average stochastic fluctuations and to achieve a robust population response.

A Preclinical Canine Model of in Utero Hematopoietic Cell Transplantation–Induced Graft Vs. Host Disease.

AbstractAbstract 3002 Introduction:In utero hematopoietic cell transplantation (IUHCT) offers the potential to achieve allo-engraftment and associated donor-specific tolerance (DST) without toxic conditioning. To evaluate IUHCT in a clinically relevant large animal model, we have developed the haploidentical canine model of IUHCT. Recent optimization of the model using a CD3 depleted graft has achieved consistent and stable levels of mixed hematopoietic chimerism (average > 10%) without graft versus host disease (GVHD). However, since GVHD represents the greatest theoretical risk of clinical IUHCT, it is important to identify the phenotype and requirements for IUHCT-induced GVHD in the canine model prior to clinical application. In the current study, we attempted to establish a threshold dose of CD3+ cells required for IUHCT-induced GVHD in the haploidentical canine model by increasing the absolute percentage of CD3+ cells in the donor inoculum and we characterized the GVHD phenotype observed. Methods:43 fetuses of 9 pregnant bitches underwent ultrasound-guided intracardiac injection of maternal BM cells at 37.5–43 days gestational age (GA). In our large animal model, bone marrow yields, cellularity and litter size differ between dams. Due to these factors and because the targeted gestational age range coincides with an exponential growth phase for the dog fetus, standardization of cell dose per weight was not possible. Following MACS CD3 depletion, graft composition was standardized by adding back the CD3+ fraction to achieve donor CD3 content of 1%, 3%, 7.5%, and 16% (whole bone marrow [WBM] positive control) (Table 1). Live born puppies were monitored daily for signs of GVHD, including skin lesions, diarrhea, hematochezia, jaundice, weight loss and lethargy. Chimerism was measured by a PCR-based VNTR assay using commercially available primers. Results:Though prenatal survival of 75% was not significantly different than baseline (76%) and pups were not runted at birth, acute GVHD was observed postnatally in all ten live born recipients of either 7.5% CD3 cells or WBM, with onset ranging from 1–14 days of age. Recipients of grafts containing 1% and 3% CD3 cells showed no clinical evidence of GVHD.Weight loss was the earliest and most consistent clinical feature of IUHCT-induced GVHD in our model. Various affected animals manifested additional symptoms in all GVHD target organs, including increased respiratory rate/effort, hepatic dysfunction, bloody diarrhea and skin lesions. The phenotype was severe and all ten ultimately required euthanasia between 2 and 21 days of age.Necropsies performed during acute GVHD revealed significant erythematous and/or ulcerated skin change, hepatosplenomegaly, and punctate hemorrhage throughout the gastrointestinal tract and lung. Histology (H&E) demonstrated lymphocytic infiltrates and focal necrosis in target tissues as well as effacement of the dermal-epidermal junction and villous surfaces. Canalicular bile stasis was the most uniform and characteristic microscopic finding irrespective of hepatic functional status.Chimerism levels in pups who survived to birth were compared based upon CD3 content of the donor graft (Table 1). Increasing CD3 percentage trended toward an increase in chimerism, though only the WBM group reached statistical significance (p=.043). Conclusions:In the preclinical haploidentical canine model of IUHCT the threshold for induction of GVHD appears to be between 3% and 7.5% graft CD3+cell content. Interestingly, the absolute dose of CD3+ cells/kg fetal weight does not entirely correlate with the occurrence of GVHD, suggesting that the composition of the graft rather than the absolute T-cell content may determine the likelihood of GVHD. Given the complete absence of GVHD at a CD3 dose of 1% and the excellent engraftment achieved, it appears that there is a safe therapeutic index for achievement of chimerism without GVHD. When IUHCT-induced GVHD occurs, it is severe and clinically similar to postnatal GVHD. Notably, clinical GVHD only occurred after birth, suggesting suppressive mechanisms in utero. Additional studies are needed to further optimize the graft for support of engraftment without GVHD.Table 1DosenGA at IUHCTCD3 cells/kgCD34 cells/kgMean ChimerismGVHD1%2039–41.37–2.72 × 10 (9)5.8–58.2 × 10 (8)12.1%N3%4381.26 × 10 (9)9.8 × 10 (8)7.3%N7.5%341.52.26 × 10 (9)7.0 × 10 (8)17.7%Y16% (WBM)7432.0 × 10 (9)5.1 × 10 (8)20.3%Y Disclosures:No relevant conflicts of interest to declare.

Endocannabinoid-Mediated Long-Term Depression of Afferent Excitatory Synapses in Hippocampal Pyramidal Cells and GABAergic Interneurons

Although endocannabinoids have emerged as essential retrograde messengers in several forms of synaptic plasticity, it remains controversial whether they mediate long-term depression (LTD) of glutamatergic synapses onto excitatory and inhibitory neurons in the hippocampus. Here, we show that parvalbumin- and somatostatin/metabotropic glutamate receptor 1(a) (mGlu(1a))-positive GABAergic interneurons express diacylglycerol lipase-α (DGL-α), a synthesizing enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG), albeit at lower levels than principal cells. Moreover, this lipase accumulates postsynaptically around afferent excitatory synapses in all three cell types. To address the role of retrograde 2-AG signaling in LTD, we investigated two forms: (1) produced by postsynaptic spiking paired with subsequent presynaptic stimulation or (2) induced by group I mGlu activation by (S)-3,5-dihydroxyphenylglycine (DHPG). Neither form of LTD was evoked in the presence of the mGlu(5) antagonist MPEP [2-methyl-6-(phenylethynyl)-pyridine], the DGL inhibitor THL [N-formyl-l-leucine (1S)-1-[[(2S,3S)-3-hexyl-4-oxo-2-oxetanyl]methyl]dodecyl ester], or the intracellularly applied Ca(2+) chelator BAPTA in CA1 pyramidal cells, fast-spiking interneurons (representing parvalbumin-containing cells) and interneurons projecting to stratum lacunosum-moleculare (representing somatostatin/mGlu(1a)-expressing interneurons). Both forms of LTD were completely absent in CB(1) cannabinoid receptor knock-out mice, whereas pharmacological blockade of CB(1) led to inconsistent results. Notably, in accordance with their lower DGL-α level, a higher stimulation frequency or higher DHPG concentration was required for LTD induction in interneurons compared with pyramidal cells. These findings demonstrate that hippocampal principal cells and interneurons produce endocannabinoids to mediate LTD in a qualitatively similar, but quantitatively different manner. The shifted induction threshold implies that endocannabinoid-LTD contributes to cortical information processing during distinct network activity patterns in a cell type-specific manner.

Effects of extremely low frequency electromagnetic field (50 Hz) on pentylenetetrazol-induced seizures in mice

The electromagnetic fields (EMF) have various behavioral and biological effects on human body. There are growing concerns about the consequences of exposure to EMF. However, some studies have shown beneficial effects of these waves on human. In this paper, we study the effect of acute, sub acute and long-term exposure to 50Hz, 0.1mT magnetic fields (MF) on the seizure induction threshold in mice. 64 mice are used and divided into four groups. Eight mice in any group were selected to be exposed to MF for specific duration and the others were used as a control group. The duration of the applied exposures was as follows: (1) 1day (acute), (2) 3days (sub acute), (3) 2weeks (sub acute), (4) 1month (long term). The mice were exposed 2h for a day. After exposure, the pentylentetrazol (PTZ) is injected to the mice to induce seizure and the needed dose for the seizure induction threshold is measured. In the acute exposure, the threshold to induce seizure in the exposed and sham-exposed groups was 44.25 and 46.5mg, respectively, while the difference was not significant (p value=0.5). In the sub acute exposure (3days), the mean amount of drug to induce seizure was 47.38mg in the exposed and 43.88mg in the sham-exposed groups, however, the difference was not significant (p value=0.3). The results were 52.38 and 46.75mg after 2weeks of exposure which were not significantly different either (p value=0.2). After 1month of exposure to MF, the threshold for the induction of seizure was significantly increased (p value<0.05). The mean dosage to induce seizure in the exposed and control group was 54.3 and 45.75mg, respectively. However, considering the p value, the difference in the seizure induction threshold between the exposed and sham-exposed groups after acute and sub acute exposure was not significant, analyzing the effects of acute, sub acute and long-term exposures totally indicates that increasing the exposure time increases the seizure induction threshold.

Unraveling the Time Domains of Corticosteroid Hormone Influences on Brain Activity: Rapid, Slow, and Chronic Modes

Brain cells are continuously exposed to corticosteroid hormones, although the levels vary (e.g., after stress). Corticosteroids alter neural activity via two receptor types, mineralocorticoid (MR) and glucocorticoid receptors (GR). These receptors regulate gene transcription but also, as we now know, act nongenomically. Via nongenomic pathways, MRs enhance and GRs suppress neural activity. In the hypothalamus, inhibitory GR effects contribute to negative feedback regulation of the stress axis. Nongenomic MR actions are also important extrahypothalamically and help organisms to immediately select an appropriate response strategy. Via genomic mechanisms, corticosteroid actions in the basolateral amygdala and ventral-most part of the cornu ammonis 1 hippocampal area are generally excitatory, providing an extended window for encoding of emotional aspects of a stressful event. GRs in hippocampal and prefrontal pyramidal cells increase surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and strengthen glutamatergic signaling through pathways partly overlapping with those involved in long-term potentiation. This raises the threshold for subsequent induction of synaptic potentiation and promotes long-term depression. Synapses activated during stress are thus presumably strengthened but protected against excitatory inputs reaching the cells later. This restores higher cognitive control and promotes, for example, consolidation of stress-related contextual information. When an organism experiences stress early in life or repeatedly in adulthood, the ability to induce synaptic potentiation is strongly reduced and the likelihood to induce depression enhanced, even under rest. Treatment with antiglucocorticoids can ameliorate cellular effects after chronic stress and thus provide an interesting lead for treatment of stress-related disorders.

Direct in situ determination of the mechanisms controlling nanoparticle nucleation and growth.

Although nanocrystal morphology is controllable using conventional colloidal synthesis, multiple characterization techniques are typically needed to determine key properties like the nucleation rate, induction time, growth rate, and the resulting morphology. Recently, researchers have demonstrated growth of nanocrystals by in situ electron beam reduction, offering direct observations of single nanocrystals and eliminating the need for multiple characterization techniques; however, they found nanocrystal morphologies consistent with two different growth mechanisms for the same electron beam parameters. Here we show that the electron beam current plays a role analogous to the concentration of reducing agent in conventional synthesis, by controlling the growth mechanism and final morphology of silver nanocrystals grown via in situ electron beam reduction. We demonstrate that low beam currents encourage reaction limited growth that yield nanocrystals with faceted structures, while higher beam currents encourage diffusion limited growth that yield spherical nanocrystals. By isolating these two growth regimes, we demonstrate a new level of control over nanocrystal morphology, regulated by the fundamental growth mechanism. We find that the induction threshold dose for nucleation is independent of the beam current, pixel dwell time, and magnification being used. Our results indicate that in situ electron microscopy data can be interpreted by classical models and that systematic dose experiments should be performed for all future in situ liquid studies to confirm the exact mechanisms underlying observations of nucleation and growth.

An experimental investigation of the role of perceived justice in acute pain

Emerging research suggests that perceiving injustice can compound the suffering of chronic pain, while perceiving justice serves as a positive psychological resource in this context. However, little more is currently known about the function of justice beliefs, particularly in the context of acute pain. The present study undertook this investigation, using cold pressor methodology to investigate whether trusting in the fairness of the world would help someone to cope with short-term pain. Sixty-five men and 65 women completed measures of personal and general just world beliefs and state anxiety before pain induction and measures of the intensity and quality of pain, in addition to state anxiety following pain induction. The personal and general beliefs in a just world were negatively correlated with pre-task anxiety but not with measures of pain induction (threshold, tolerance and sensitivity) or measures of post-task pain. Gender had a moderating role, whereby men with a stronger general just world belief reported lower post-task state anxiety and men who had a stronger personal just world belief reported lower pain intensity. However, unexpectedly, women with a stronger personal just world belief reported higher pain intensity. The observed gender differences may be attributed to gender variations in cognitive appraisals of the task. Overall, while perceived injustice may be undesirable and a potential target for intervention, perceived justice is not necessarily a desired cognition in pain. Research is needed to replicate and extend this emerging research.

5 Properties of real phototherapy laser and LED devices

Much of our understanding of dendritic and synaptic physiology comes from in vitro experimentation, where the afforded mechanical stability and convenience of applying drugs allowed patch-clamping based recording techniques to investigate ion channel distributions, their gating kinetics, and to uncover dendritic integrative and synaptic plasticity rules. However, with current efforts to study these questions in vivo, there is a great need to translate existing knowledge between in vitro and in vivo experimental conditions. In this review, we identify discrepancies between in vitro and in vivo ionic composition of extracellular media and discuss how changes in ionic composition alter dendritic excitability and plasticity induction. Here, we argue that under physiological in vivo ionic conditions, dendrites are expected to be more excitable and the threshold for synaptic plasticity induction to be lowered. Consequently, the plasticity rules described in vitro vary significantly from those implemented in vivo.

Neurogranin targets calmodulin and lowers the threshold for the induction of long-term potentiation.

Calcium entry and the subsequent activation of CaMKII trigger synaptic plasticity in many brain regions. The induction of long-term potentiation (LTP) in the CA1 region of the hippocampus requires a relatively high amount of calcium-calmodulin. This requirement is usually explained, based on in vitro and theoretical studies, by the low affinity of CaMKII for calmodulin. An untested hypothesis, however, is that calmodulin is not randomly distributed within the spine and its targeting within the spine regulates LTP. We have previously shown that overexpression of neurogranin enhances synaptic strength in a calmodulin-dependent manner. Here, using post-embedding immunogold labeling, we show that calmodulin is not randomly distributed, but spatially organized in the spine. Moreover, neurogranin regulates calmodulin distribution such that its overexpression concentrates calmodulin closer to the plasma membrane, where a high level of CaMKII immunogold labeling is also found. Interestingly, the targeting of calmodulin by neurogranin results in lowering the threshold for LTP induction. These findings highlight the significance of calmodulin targeting within the spine in synaptic plasticity.

Increased mechanically-induced ectopy in the hypertrophied heart

IntroductionLeft ventricular hypertrophy (LVH) predisposes patients to arrhythmias, but the mechanism of these arrhythmias is unclear. Here we show that hearts from spontaneously hypertensive rats (SHR) have a lower threshold for induction mechanically induced arrhythmias compared to age matched Wistar-Kyoto (WKY). MethodsRecordings were made from isolated hearts from nine month old SHR (n = 18) and WKY (n = 17) rats. A water filled balloon in the left ventricle had its volume controlled by a servo-driven syringe. LVEDP was abruptly increased in increments until an ectopic beat was detected by an epicardial MAP electrode. Alternatively, LVEDP was abruptly reduced back to 5 mm Hg from an elevated pressure. ResultsSHR hearts had a lower threshold for stretch induced ectopics (29.87 ± 2.79 mm Hg vs. 42.23 ± 2.33 mm Hg, p < 0.01) and for release induced ectopics (24.09 ± 1.40 vs. 37.23 ± 3.22, p < 0.01). Perfusion with 100 μM streptomycin increased threshold for stretch induced ectopics in both strains (from 49.4 ± 4.7 to 69.5 ± 6.9 mm Hg in WKY; p < 0.05 and from 21.2 ± 3.5 to 39.7 ± 9.0 mm Hg in SHR; p = 0.07). 100 μM streptomycin also increased threshold for release induced ectopics in SHR (from 23.5 ± 3.6 to 32.6 ± 4.9 mm Hg; p < 0.05) but not in WKY. Perfusion with 0.01 μM isoprenaline decreased the threshold for stretch induced ectopics in both strains (from 40.6 ± 5.0 to 22.6 ± 2.5 mm Hg in WKY; not significant at p < 0.05; p = 0.07 and from 31.0 ± 5.5 to 14.3 ± 2.5 mm Hg in SHR; p < 0.05). ConclusionsHearts from SHR are more susceptible to both stretch-induced and release-induced arrhythmia.

VEGF Receptor-2 (Flk-1) Overexpression in Mice Counteracts Focal Epileptic Seizures

Vascular endothelial growth factor (VEGF) was first described as an angiogenic agent, but has recently also been shown to exert various neurotrophic and neuroprotective effects in the nervous system. These effects of VEGF are mainly mediated by its receptor, VEGFR-2, which is also referred to as the fetal liver kinase receptor 1 (Flk-1). VEGF is up-regulated in neurons and glial cells after epileptic seizures and counteracts seizure-induced neurodegeneration. In vitro, VEGF administration suppresses ictal and interictal epileptiform activity caused by AP4 and 0 Mg2+ via Flk-1 receptor. We therefore explored whether increased VEGF signaling through Flk-1 overexpression may regulate epileptogenesis and ictogenesis in vivo. To this extent, we used transgenic mice overexpressing Flk-1 postnatally in neurons. Intriguingly, Flk-1 overexpressing mice were characterized by an elevated threshold for seizure induction and a decreased duration of focal afterdischarges, indicating anti-ictal action. On the other hand, the kindling progression in these mice was similar to wild-type controls. No significant effects on blood vessels or glia cells, as assessed by Glut1 and GFAP immunohistochemistry, were detected. These results suggest that increased VEGF signaling via overexpression of Flk-1 receptors may directly affect seizure activity even without altering angiogenesis. Thus, Flk-1 could be considered as a novel target for developing future gene therapy strategies against ictal epileptic activity.

Prediction of skin sensitization potency of chemicals by human Cell Line Activation Test (h-CLAT) and an attempt at classifying skin sensitization potency

The human Cell Line Activation Test (h-CLAT), an in vitro skin sensitization test, is based on the augmentation of CD86 and CD54 expression in THP-1 cells following exposure to chemicals. The h-CLAT was found to be capable of determining the hazard of skin sensitization. In contrast, the local lymph node assay (LLNA), widely used as a stand-alone method in Europe and US, identifies the same hazard, but also classifies the potency by using the estimated concentration of SI=3 (EC3). In this study, several values calculated from the h-CLAT data were evaluated for its correlation to the LLNA EC3 determination. A statistically significant correlation was observed between h-CLAT concentration providing a cell viability of 75% (CV75), h-CLAT estimated concentration of RFI=150 for CD86 (EC150), and for CD54 (EC200) with LLNA’s EC3. From EC150 and EC200, a minimum induction threshold (MIT) was determined as the smaller of either EC150 or EC200. MIT showed a correlation with EC3 (R=0.638). Also, MIT had an approximate 80% accuracy for sub-categories of the globally harmonized system (GHS) when a tentative threshold of 13μg/mL was used. From these data, the h-CLAT values may be one of the useful tools to predict the allergic potency of chemicals.

Quantitative Analysis of the Bidirectional Viral G-Protein-Coupled Receptor and Lytic Latency-Associated Nuclear Antigen Promoter of Kaposi's Sarcoma-Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) establishes sustained latent persistence in susceptible cells. This is dependent on the latency-associated nuclear antigen (LANA). Understanding how LANA transcription is regulated thus aids our fundamental understanding of KSHV biology. Two hundred ninety-four base pairs are sufficient to regulate LANA transcription in response to the viral RTA protein and RBPjκ. The same region controls K14/viral G-protein-coupled receptor (vGPCR) transcription in the opposite direction. We used a quantitative analysis in conjunction with specific nucleotide substitutions and defined gain-of-function and loss-of-function RTA mutants to dissect this region. We used a bidirectional reporter driving red and green luciferase to study the LANApi and K14p promoters simultaneously. This established that LANApi/K14p functions as a canonical bidirectional promoter. Both were TATA dependent. K14p was favored by ∼50-fold in this context. Eliminating the distal LANApi TATA box increased maximal output and lowered the induction threshold (T) of K14p even further. Two RBPjκ binding sites were independently required; however, at high concentrations of RTA, direct interactions with an RTA-responsive element (RRE) could complement the loss of one RBPjκ binding site. Intracellular Notch (ICN) was no longer able to activate RBPjκ in the viral context. This suggests a model whereby KSHV alters ICN-RBPjκ gene regulation. When the architecture of this pair of head-to-head RBPjκ binding sites is changed, the sites now respond exclusively to the viral transactivator RTA and no longer to the host mediator ICN.

Russell body inducing threshold depends on the variable domain sequences of individual human IgG clones and the cellular protein homeostasis

Russell bodies are intracellular aggregates of immunoglobulins. Although the mechanism of Russell body biogenesis has been extensively studied by using truncated mutant heavy chains, the importance of the variable domain sequences in this process and in immunoglobulin biosynthesis remains largely unknown. Using a panel of structurally and functionally normal human immunoglobulin Gs, we show that individual immunoglobulin G clones possess distinctive Russell body inducing propensities that can surface differently under normal and abnormal cellular conditions. Russell body inducing predisposition unique to each immunoglobulin G clone was corroborated by the intrinsic physicochemical properties encoded in the heavy chain variable domain/light chain variable domain sequence combinations that define each immunoglobulin G clone. While the sequence based intrinsic factors predispose certain immunoglobulin G clones to be more prone to induce Russell bodies, extrinsic factors such as stressful cell culture conditions also play roles in unmasking Russell body propensity from immunoglobulin G clones that are normally refractory to developing Russell bodies. By taking advantage of heterologous expression systems, we dissected the roles of individual subunit chains in Russell body formation and examined the effect of non-cognate subunit chain pair co-expression on Russell body forming propensity. The results suggest that the properties embedded in the variable domain of individual light chain clones and their compatibility with the partnering heavy chain variable domain sequences underscore the efficiency of immunoglobulin G biosynthesis, the threshold for Russell body induction, and the level of immunoglobulin G secretion. We propose that an interplay between the unique properties encoded in variable domain sequences and the state of protein homeostasis determines whether an immunoglobulin G expressing cell will develop the Russell body phenotype in a dynamic cellular setting.

Calcium-Dependent But Action Potential-Independent BCM-Like Metaplasticity in the Hippocampus

The Bienenstock, Cooper and Munro (BCM) computational model, which incorporates a metaplastic sliding threshold for LTP induction, accounts well for experience-dependent changes in synaptic plasticity in the visual cortex. BCM-like metaplasticity over a shorter timescale has also been observed in the hippocampus, thus providing a tractable experimental preparation for testing specific predictions of the model. Here, using extracellular and intracellular electrophysiological recordings from acute rat hippocampal slices, we tested the critical BCM predictions (1) that high levels of synaptic activation will induce a metaplastic state that spreads across dendritic compartments, and (2) that postsynaptic cell-firing is the critical trigger for inducing that state. In support of the first premise, high-frequency priming stimulation inhibited subsequent long-term potentiation and facilitated subsequent long-term depression at synapses quiescent during priming, including those located in a dendritic compartment different to that of the primed pathway. These effects were not dependent on changes in synaptic inhibition or NMDA/metabotropic glutamate receptor function. However, in contrast to the BCM prediction, somatic action potentials during priming were neither necessary nor sufficient to induce the metaplasticity effect. Instead, in broad agreement with derivatives of the BCM model, calcium as released from intracellular stores and triggered by M1 muscarinic acetylcholine receptor activation was critical for altering subsequent synaptic plasticity. These results indicate that synaptic plasticity in stratum radiatum of CA1 can be homeostatically regulated by the cell-wide history of synaptic activity through a calcium-dependent but action potential-independent mechanism.

A quantitative approach to assess the potency of skin sensitizers in the elicitation phase

The concept that thresholds exist for the induction of allergic contact dermatitis by chemicals with skin sensitizing properties has been used for a quantitative risk assessment approach. In this approach the potency of skin sensitizers as determined in the Local Lymph Node Assay is used to calculate the threshold for induction of sensitization. These are then used to estimate safe exposure levels for consumers. Whether these exposure levels will protect subjects that are already sensitized is unknown. The elicitation of allergic contact dermatitis supposedly occurs above a certain threshold as well and this threshold is most likely lower than that for the induction. It is unclear if induction thresholds can be extrapolated to elicitation thresholds. The aim of this study was to assess the potency of sensitizers with different sensitizing potencies in the elicitation phase in a mouse model for elicitation. Mice were sensitized by topical application on days 0 and 7 using equipotent concentrations of oxazolone, 2,4-dinitrochlorobenzene (DNCB) and eugenol to ensure that the sensitization strength would not influence the elicitation potency. Mice were challenged on day 21 by topical application on the ears in a dose-dependent manner and dose–response data were used to calculate the elicitation potency. Unexpectedly, sensitizers with different sensitizing potencies induced not the same dose–response curves in sensitized mice. The most potent sensitizer in the elicitation phase was oxazolone, followed by DNCB and eugenol. Similar to the induction phase, under equipotent sensitization conditions strong sensitizers such as oxazolone and DNCB elicit allergic reactions at lower concentrations than weak sensitizers such as eugenol. Our results indicate that elicitation thresholds cannot be readily deduced from sensitization thresholds.

Role of AMPA receptor regulation in stress-induced prolongation of incisional pain

Chronic pain after surgery is a serious issue in clinical practice that has received increased interest in recent years. Previous studies have shown that psychosocial and socio-environmental factors are involved in the development of chronic postsurgical pain. However, it is unclear how the transition from acute to chronic postsurgical pain occurs. In our studies, we found that forced swim stress markedly enhanced plantar incision-induced α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor phosphorylation in the spinal cord and greatly prolonged plantar incision-induced pain, but forced swim stress alone did not produce pain behaviors. We also found that targeted mutation of AMPA receptor GluA1 phosphorylation site Ser831 significantly inhibited stress-induced prolongation of incisional pain. It has been demonstrated that the stress hormone norepinephrine enhances AMPA receptor phosphorylation and in turn facilitates the synaptic delivery of GluA1-containing AMPA receptors, thereby lowering the threshold for long-term potentiation induction and increasing the probability of synaptic plasticity. Therefore, AMPA receptor regulation may play an important role in spinal neuronal plasticity by which chronic postsurgical pain develops after surgery. Chronic pain after surgery is a serious issue in clinical practice that has received increased interest in recent years. Previous studies have shown that psychosocial and socio-environmental factors are involved in the development of chronic postsurgical pain. However, it is unclear how the transition from acute to chronic postsurgical pain occurs. In our studies, we found that forced swim stress markedly enhanced plantar incision-induced α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor phosphorylation in the spinal cord and greatly prolonged plantar incision-induced pain, but forced swim stress alone did not produce pain behaviors. We also found that targeted mutation of AMPA receptor GluA1 phosphorylation site Ser831 significantly inhibited stress-induced prolongation of incisional pain. It has been demonstrated that the stress hormone norepinephrine enhances AMPA receptor phosphorylation and in turn facilitates the synaptic delivery of GluA1-containing AMPA receptors, thereby lowering the threshold for long-term potentiation induction and increasing the probability of synaptic plasticity. Therefore, AMPA receptor regulation may play an important role in spinal neuronal plasticity by which chronic postsurgical pain develops after surgery.

Origin of excitation underlying locomotion in the spinal circuit of zebrafish

Neural circuits in the spinal cord transform instructive signals from the brain into well-coordinated locomotor movements by virtue of rhythm-generating components. Although evidence suggests that excitatory interneurons are the essence of locomotor rhythm generation, their molecular identity and the assessment of their necessity have remained unclear. Here we show, using larval zebrafish, that V2a interneurons represent an intrinsic source of excitation necessary for the normal expression of the locomotor rhythm. Acute and selective ablation of these interneurons increases the threshold of induction of swimming activity, decreases the burst frequency, and alters the coordination of the rostro-caudal propagation of activity. Thus, our results argue that V2a interneurons represent a source of excitation that endows the spinal circuit with the capacity to generate locomotion.