Mean Burst Research Articles

Understanding the quality of protein loaded PLGA nanoparticles variability by Plackett–Burman design

The aim of this investigation was to screen and understand the product variability due to important factors affecting the characteristics CyA-PLGA nanoparticles prepared by O/W emulsification-solvent evaporation method. Independent variables studied were cyclosporine A (CyA) ( X 1), PLGA ( X 2), and emulsifier concentration namely SLS ( X 3), stirring rate ( X 4), type of organic solvent employed (chloroform or dichloromethane, X 5) and organic to aqueous phase ratio ( X 6). The nanoparticles properties considered were encapsulation efficiency ( Y 1), mean particle size ( Y 2), zeta potential ( Y 3), burst effect ( Y 4) and dissolution efficiency ( Y 5). The statistical analysis of the results allowed determining the most influent factors. The nanoparticles were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The factors combination showed variability of entrapment efficiency ( Y 1), mean particle size ( Y 2) and zeta potential ( Y 3) from 10.17% to 93.01%, 41.60 to 372.80 nm and 29.60 to 34.90 mV, respectively. Initially, nanoparticles showed burst effect followed by sustained release during the 7-day in vitro release study period. The dissolution efficiency ( Y 5) varied from 52.67% to 84.11%. The nanoparticles revealed Higuchi release pattern and release occurred by coupling of diffusion and erosion. In conclusion, this study revealed the potential of QbD in understanding the effect of formulation and process variables on the characteristics on CyA-PLGA nanoparticles.

Effect of the Stimulation of Sensory Inputs on the Firing of Neurons of the Trigeminal Main Sensory Nucleus in the Rat

Mastication can be triggered by repetitive stimulation of the cortex or of sensory inputs, but is patterned by a brain stem central pattern generator (CPG). This CPG may include the dorsal part of the principal trigeminal sensory nucleus (NVsnpr), where neurons burst repetitively when the extracellular concentration of Ca(2+) ([Ca(2+)](e)) drops. We examined the effects of repetitive stimulation of sensory afferents of the trigeminal tract on activity of NVsnpr neurons recorded extracellularly in vitro under physiologic [Ca(2+)](e) (1.6 mM). Spontaneously active cells had either a tonic (n = 145) or a bursting (n = 46) firing pattern. Afferent stimulation altered burst duration and/or burst frequency in bursting cells and firing frequency in most tonic cells. In 28% of the latter, the firing pattern switched to rhythmic bursting. This effect could be mimicked by local application of N-methyl-d-aspartate and blocked by APV but not DNQX. Detailed analysis showed that rhythm indices (RIs) of 35 tonic neurons that were negative (nonrhythmic) before stimulation became significantly rhythmic (RI > or = 0.01) after stimulation. Mean and median bursting frequency of these units were 8.32 +/- 0.72 (SE) Hz and 6.25 Hz (range, 2.5-17.5 Hz). In seven instances, two units were recorded simultaneously, and cross-correlation analysis showed that firing of six pairs was rhythmic and synchronized after stimulation. Optimal stimulation parameters for eliciting rhythmic bursting consisted in 500-ms trains of pulses delivered at 40-60 Hz. Together, our results show that repetitive stimulation of sensory afferents in vitro can elicit masticatory-like rhythmic bursting in NVsnpr neurons at physiological [Ca(2+)](e).

Endoscopic closure of duodenal perforations by using an over-the-scope clip: a randomized, controlled porcine study

Duodenal perforations during diagnostic upper endoscopy are rare; however, when therapeutic techniques are performed, the reported incidence is as great as 2.8%. Surgical repair is usually mandated, but it is associated with significant morbidity and mortality. To compare closure of duodenal perforations by using an over-the-scope clip (OTSC) with a surgical closure. Randomized, controlled animal study. Animal facility laboratory. Domestic pigs (24 females). Large (10-mm) duodenal perforations were created by using an endoscopic needle-knife. The animals were randomly assigned to either open surgical repair (n=12) or endoscopic closure by using the OTSC system (n=12). Pressurized leak tests were performed during necropsy. One major bleed occurred because of a liver injury during creation of the duodenotomy. Mean time for endoscopic closure was 5 minutes (range, 3-8 min; SD +/- 2). No complications occurred during any of the closure procedures. At necropsy, all OTSC and surgical closures demonstrated complete sealing of duodenotomy sites. Pressurized leak tests demonstrated a mean burst pressure of 166 mm Hg (range, 80-260; SD +/- 65) for OTSC closures and 143 mm Hg (range, 30-300, SD +/- 83) for surgical sutures. Ex vivo intact duodenal specimens exhibited a mean burst pressure of 247 mm Hg (range, 200-300; SD +/- 35), which was significantly higher compared with in vivo OTSC and surgical closures (P < .01). There were no significant differences between burst pressures of OTSC and surgical closures (P = .461). Nonsurvival setting. Endoscopic closure of duodenal perforations by using the OTSC system is comparable with surgical closure in a nonsurvival porcine model. This technique is easy to perform and seems suitable for repairing duodenal perforations.

Encircling the Tendon Repair Site with Collagen-GAG Reduces the Formation of Postoperative Tendon Adhesions in a Chicken Flexor Tendon Model

Tendon healing is a complex and coordinated event involving the activation of extrinsic mechanisms as in classic reparative skin wound healing as well as intrinsic mechanisms characteristic of regenerative wound healing. Despite improvements in surgical and rehabilitative techniques, tendon adhesions remain the most frequent cause of disability following tendon surgery. In this animal model, we evaluated the use of a clinically available, biocompatible collagen- glycosaminoglycan (GAG) material as an adjunct to surgical tendon repair. Thirty-two white leghorn chickens underwent surgical tendon repair of their left second and fourth digits. Digits were randomized to study and control groups. In both groups, the long flexor tendon was divided and repaired using a modified Kessler's repair. In the study group, collagen-GAG membrane was wrapped around the repair site. Animals were immobilized with a plaster cast and sacrificed at 3 wk. Sixteen animals had their tendon repair sites histologically assessed and graded for healing and adhesion formation. Eight animals had their tendon repairs assessed for quantification of the work associated with flexion, employing a specifically designed biomechanical apparatus. Eight animals had their repair sites tested for bursting strength. Control (untreated) tendons showed fibrous tissue surrounding the repair sites with approximately 50% of the circumference of the repair site adherent to surrounding tissue elements. The mean histologic grades for control and study group were 3.1+/-0.2 and 1.9+/-0.2, respectively. The difference between mean grades for control and study group samples was statistically significant (paired t-test: P<0.01). The work of flexion (WOF) for flexion cycles 1, 2, 3, and 4 for the control group was 0.58, 0.55, 0.46, and 0.44N/mm, respectively. The study (collagen-GAG wrapped) group had WOF values 0.16, 0.14, 0.10, 0.09N/mm, and the difference between the groups was statistically significant (paired t-test, P<0.01). The mean bursting strength of repaired tendons for control and study groups were 14.3+/-1.87N and 11.5+/-1.85N, respectively. There was no significant difference in bursting strength between the groups (paired t-test, P=0.71). Collagen-GAG reduces formation of early postoperative tendon adhesions in this chicken flexor tendon repair model. Collagen-GAG wrapped tendons healed with minimal peritendinous adhesion formation and required less effort for flexion. The investing collagen-GAG membrane did not appear to interfere with either the quality or strength of healing.

Loop-anchor purse-string versus endoscopic clips for gastric closure: a natural orifice transluminal endoscopic surgery comparison study using burst pressures

The success of natural orifice surgery depends on a reliable, secure closure of the opening in the gut. Few tests of the integrity of these closures have been published. To determine whether a gastrotomy can be closed safely and effectively from within the stomach by using looped T-anchors-a novel, endoscopically placed device. Head-to-head comparison trial of 2 closure methods in 9 explanted porcine stomachs. Animal laboratory. Paired gastrotomies were made in porcine explants. One was closed by using endoscopic clips, and the other was closed by using modified T-anchors in a purse-string fashion. Gastric transmural pressure gradients at bursting of these closures were measured while the explanted stomachs were inflated with a high-pressure insufflator. The mean burst pressure of the looped T-anchors was 27.3 mm Hg, whereas that of the clip closures was 14 mm Hg. By using 10 mm Hg as a threshold for a "secure" closure, 7 of 9 clip closures failed to meet the threshold value, whereas all 9 of the T-anchor closures met or exceeded the threshold value (P = .0023, 2-tailed Fisher exact test). Nonsurvival study. Looped T-anchors provide a secure gastric closure for natural orifice surgery and are superior to endoscopic clips for this purpose.

Self-organized dendritic sidebranching in directional solidification: Sidebranch coherence within uncorrelated bursts

We experimentally study the level of organization of dendritic sidebranching in directional solidification. For this, we extract successive interface positions at a fixed distance from the dendrite tips and we perform various correlation analyses. The sidebranching signals appear composed of randomly distributed bursts in which sidebranching coherence is surprisingly large and robust. This is attested by the large autocorrelation found in single bursts and the large cross-correlation found in any couple of bursts, even belonging to different sides of a dendrite or to different dendrites. However, the phase coherence of sidebranching breaks down at the transition between bursts. This restricts the coherence of extended sidebranching signals to a mean burst length and prevents the occurrence of large scale cross-correlation between them. This balanced view on sidebranching coherence stresses the capability of self-organization of dendrites in material science and sheds light on the nature of sidebranching on curved growing forms.

Natural orifice transluminal endoscopic surgery gastrotomy closure with an over-the-endoscope clip: a randomized, controlled porcine study (with videos)

Secure endoscopic closure of transgastric natural orifice transluminal endoscopic surgery (NOTES) access is of paramount importance. The over-the-scope clip (OTSC) system has previously been shown to be effective for NOTES gastrotomy closure. To compare OTSC gastrotomy closure with surgical closure. Randomized, controlled animal study. Animal facility laboratory. Thirty-six female domestic pigs. Gastrotomies were created by using a needle-knife and an 18-mm balloon. The animals were subsequently randomized to either open surgical repair with interrupted sutures or endoscopic repair with 12-mm OTSCs. In addition, pressurized leak tests were performed in ex vivo specimens of 18-mm scalpel incisions closed with suture (n = 14) and of intact stomachs (n = 10). The mean time for endoscopic closure was 9.8 minutes (range 3-22, SD 5.5). No complications occurred during either type of gastrotomy closure. At necropsy, examination of all OTSC and surgical closures demonstrated complete sealing of gastrotomy sites without evidence of injury to adjacent organs. Pressurized leak tests showed a mean burst pressure of 83 mm Hg (range 30-140, SD 27) for OTSC closures and 67 mm Hg (range 30-130, SD 27.7) for surgical sutures. Ex vivo hand-sewn sutures of 18-mm gastrotomies (n = 14) exhibited a mean burst pressure of 65 mm Hg (range 20-140, SD 31) and intact ex vivo stomachs (n = 10) had a mean burst pressure of 126 mm Hg (range 90-170, SD 28). The burst pressure of ex vivo intact stomachs was significantly higher compared with OTSC closures (P < .01), in vivo surgical closures (P < .01), and ex vivo hand-sewn closures (P < .01). There was a trend toward higher burst pressures in the OTSC closures compared with surgical closures (P = .063) and ex vivo hand-sewn closures (P = .094). In vivo surgical closures demonstrated similar burst pressures compared with ex vivo hand-sewn closures (P = .848). Nonsurvival setting. Endoscopic closure by using the OTSC system is comparable to surgical closure in a nonsurvival porcine model. This technique is easy to perform and is suitable for NOTES gastrotomy closure.

Distinct actions of etomidate and propofol at β3-containing γ-aminobutyric acid type A receptors

Etomidate and propofol have clearly distinguishable effects on the central nervous system. However, studies in knock-in mice provided evidence that these agents produce anesthesia via largely overlapping molecular targets, namely GABA A receptors containing β3 subunits. Here the authors address the question as to whether etomidate and propofol are targeting different subpopulations of β3 subunit containing GABA A receptors. The effects of etomidate and propofol (0.5 μM and 1.0 μM) on spontaneous activity of neocortical neurons were investigated in organotypic slice cultures from wild-type and β3(N265M) knock-in mice. Firing patterns were characterized by mean burst length and number of action potentials per burst. Additionally, etomidate and propofol actions on GABA A receptor-mediated currents were investigated by whole-cell voltage clamp recordings. On the network level, the duration of spontaneously occurring bursts of action potentials was decreased by etomidate but increased by propofol in the wild-type. The effects of etomidate were abolished in β3(N265M) mutant slices while those of propofol were qualitatively inverted. On the receptor level, GABA A receptor-mediated inhibition of cortical neurons was modulated by etomidate and propofol in different ways. Again, drug-specific actions of etomidate and propofol were largely attenuated by the β3(N265M) mutation. Etomidate and propofol alter the firing patterns and GABA A receptor-mediated inhibition of neocortical neurons in different ways. This suggests that etomidate and propofol act via non-uniform molecular targets. Because the major effects induced by these anesthetics were attenuated by the β3(N265M) mutation, different subpopulations of β3-containing GABA A receptors are likely to be involved.

RAPID PULSATIONS IN SUB-THz SOLAR BURSTS

A new solar burst emission spectral component has been found showing sub-THz fluxes increasing with frequency, spectrally separated from the well known microwave component. Rapid pulsations are found present in all events observed at the two frequencies of the solar submillimeter-wave telescope: 212 and 405 GHz. They were studied in greater detail for three solar bursts exhibiting the new THz spectral component. The pulse amplitudes are of about 5%–8% of the mean flux throughout the bursts durations, being comparable for both frequencies. Pulsations range from one pulse every few seconds to 8–10 per second. The pulse repetition rates (R) are linearly proportional to the mean burst fluxes (S), following the simple relationship S = kR, suggesting that the pulsations might be the response to discrete flare particle accelerator injections quantized in energy. Although this result is consistent with qualitative trends previously found in the GHz range, the pulse amplitude relative to the mean fluxes at the sub-THz frequencies appear to be nearly ten times smaller than expected from the extrapolation of the trends found in the GHz range. However there are difficulties to reconcile the nearly simultaneous GHz and THz burst emission spectrally separated components, exhibiting rapid pulsations with considerably larger relative intensities in the GHz range.

Optimization of a Phage Amplification Assay To Permit Accurate Enumeration of Viable Mycobacterium avium subsp. paratuberculosis Cells

A commercially available phage amplification assay, FASTPlaqueTB (Biotec Laboratories, Ipswich, United Kingdom), when used according to the manufacturer's instructions, does not permit accurate enumeration of Mycobacterium avium subsp. paratuberculosis. The aim of this study was to optimize the phage amplification assay conditions to permit accurate quantification of viable M. avium subsp. paratuberculosis cells. The burst time for M. avium subsp. paratuberculosis was initially determined to inform decisions about optimal incubation time before plating, and then other test parameters were altered to evaluate how the correlation between plaque and colony counts was affected. The D29 mycobacteriophage replicates more slowly in M. avium subsp. paratuberculosis than in Mycobacterium smegmatis (used to optimize the commercial test originally), and the mean burst time for four M. avium subsp. paratuberulosis strains was 210 +/- 36.8 min at 37 degrees C compared to 63 +/- 17.5 min for M. smegmatis mc(2) 155. To achieve 100% correlation between plaque and colony counts, the optimized phage assay includes the following: (i) resuspension of the samples to be tested in Middlebrook 7H9 broth containing 10% oleic acid-albumin-dextrose-catalase and 2 mM calcium chloride, followed by overnight incubation at 37 degrees C before performance of the phage assay; (ii) a 2-h incubation of the sample with D29 mycobacteriophage before viricide treatment; and (iii) a further 90-min incubation after viricide treatment and neutralization up to the burst time (total incubation time, 210 min) before plating with M. smegmatis mc(2) 155 in 7H9 agar. The optimized phage amplification assay was able to detect 1 to 10 CFU/ml of M. avium subsp. paratuberculosis in spiked milk or broth within 48 h, as demonstrated by the results of several blind trials.

New electrophysiological mapping combined with MRI in parkinsonian’s subthalamic region

The subthalamic nucleus (STN) is the main target for deep brain stimulation in Parkinson's disease. We analysed the relationships between magnetic resonance imaging (MRI) anatomy and spontaneous neuronal activity to confirm the potential of microelectrode recordings to assist in determining the optimal surgical target. Ten bilateral surgeries were performed after 1.5-T (T2-weighted) anatomical MRI identification of the STN, zona incerta (ZI), Forel's field H2 (H2) and substantia nigra (SN). Spontaneous neuronal activity was recorded simultaneously along the distal 10 mm on a central track (optimally covering the STN) and a 2-mm anterior track. We calculated off-line mean firing rate and burst frequency on 248 neurons clustered according to anatomical structure. Subjective visual analysis of signal was also realized on-line, during surgery, to classify patterns of activity. Mean firing rate and burst frequency increased from H2-ZI to SN. The mean firing rate was higher in SN only using paired comparison (SN vs. its neighbours). The burst frequency was lower in H2 than in SN; using comparison with neighbours, it was lower in H2 and ZI. An irregular high activity (type 2C) was more often detected in STN and SN than in H2 and ZI. Anatomical boundaries and unitary recordings appear to be linked, supporting the ability of MRI to provide a detailed anatomy. Electrophysiological mapping combined with MRI is a useful tool for precise targeting in the subthalamic region.

Endoscopic Closure of Esophageal Perforations By Means of a Retractable Covered Nitinol Stent: A Randomized Controlled Animal Study

Background and Aims: Esophageal perforations during upper endoscopy are rare. However, since endoscopic techniques like EMR and ESD are increasingly used, so may the incidence of esophageal perforations. In addition, Spontanous esophageal perforations can occur due to barotrauma or ingestion of foreign material. Intentional opening of the esophageal wall has been used to perform NOTES mediastinoscopy. Material and Methods: In 12 domestic pigs 15mm oesophageal perforations were created using needle knife incision and a 15mm dilatation balloon with the animals under general anaesthesia. After randomisation pigs were assigned to either surgical repair (n=6) or endoscopic closure (n=6). A self-expandable nitinol stent covered by a plastic membrane preloaded in an emergency delivery system (SX-ELLA stent, ELLA-CS, diameter 25mm, length 135mm) was used for perforation closure. Surgical repair was achieved by open thoracoscopy. Pressurized leak tests of the perforation closures were performed following necropsy. Additionally pressurized leak test were performed in an ex vivo evaluation of hand-sewn closures of 15mm large esophageal scalpel incisions (n=15) and of healthy esophageal tissue (n=20). Tissue for ex vivo evaluation was obtained from freshly killed pigs. Results: Mean time for endoscopic stenting was 7 min. (Range 4-12 min., SD 2.8). No complication occurred during any of the closure procedures. At necropsy and macroscopic examination all perforation sites were completely covered by the stent membrane. Pressurized leak test showed a mean burst pressure of 138 mmHg (Range 100-270, SD 66) for stent closures and a mean burst pressure of 180 mmHg (Range 60-300, SD 103) for surgical sutures. Ex vivo hand-sewn sutures of 15mm scalpel incisions exhibited a mean burst pressure of 174 mmHg (Range 50-300, SD 89) and ex vivo esophageal tissue exhibited a burst pressure of >300 mmHg in 17/20 cases and a burst pressure of 300 mmHg in 3/20 cases. Ex vivo esophageal tissue burst pressure was significantly higher compared to stent closure (p<0.01), in vivo surgical closures (p<0.01), and ex vivo hand-sewn closures (p<0.01). Stent closures were comparable to surgical closures (p=0.428) and to ex vivo hand-sewn closures (p=0.378). In vivo surgical closures were comparable to ex vivo hand-sewn closures (p=0.912). Conclusions: Endoscopic closure of 15mm esophageal perforations by means of the retractable, covered nitionol stent is feasible. Further research in survival studies has to be conducted to evaluate wound healing of the esophageal perforations sites.

Sealing of the Cystic Duct During Transgastric NOTES® Cholecystectomy Is Reliable Using BELA, a New Flexible Bipolar Forceps

Introduction: To perform a safe NOTES cholecystectomy there is a need for a reliable tool to seal the cystic duct. Current endoscopic clips have been tried but shown not to be sufficient for sealing of the cystic duct during NOTES cholecystectomy. A new flexible device for bipolar coagulation from Ethicon Endosurgery, BELA, has been tested for sealing of the cystic duct in a porcine non-survival and survival model. Methods: Initially three gallbladders including the cystic duct were used for testing in vitro on the bench. Each cystic duct was sealed using the BELA-device. Five seals were tested. The burst-pressure of the seals were measured injecting saline into the gallbladder through a two-channel nasogastric tube connected to a pressure transducer. Secondly, the cystic duct was sealed and divided in vivo during cholecystectomy in four non-survival animals. The hepatic duct was ligated above the confluence of the cystic duct. A two-channel nasogastric tube was inserted through the papilla into the common bile duct. The seal was tested using saline injection through the tube into the common bile duct. Finally, cholecystectomy was performed in four survival animals using the BELA to seal the cystic duct. At post mortem two weeks later the common bile-duct was dissected and the hepatic duct was ligated above the confluence of the cystic duct ad a two-channel tube was inserted through the papilla. The seals were tested injecting saline into the common bile duct. Results: The burst pressure of the cystic duct seal ex vivo was 285-320 mmHg. Measuring the base line bile-duct pressure in vivo the pressure was 49.5 mmHg and the mean burst pressure of the cyctic duct seal was 160 mmHg (152-165). All survival pigs lived throughout the experiment without complications. At post mortem there was no sign of post operative leakage from the seals. The mean burst pressure was 427 mmHg (273-727). Conclusion: The BELA seals hold a pressure ex vivo more than three times the bile-duct base-line pressure and in the survival NOTES cholecystectomy model they hold more than eight times the base-line pressure after two weeks. Therefore, sealing of the cystic duct with the new bipolar device, BELA, seems sufficient.

Endoscopic Closure of Duodenal Perforations By Means of An Over the Scope Clip (OTSC): A Randomized Controlled Porcine Study

Background and study aims: Duodenal perforations during upper endoscopy are rare. However, since invasive endoscopic techniques like EMR, ESD, and EUS are increasingly used, so may the incidence of duodenal perforations. Surgical repair is still the mainstay of therapy but associated with significant morbidity and mortality. Endoscopic closure of such perforations would represent a minimal invasive alternative and was therefore evaluated in a randomized controlled animal study. Material and Methods: In 24 domestic pigs a 1cm large duodenal perforation was endoscopically created using needle knife incision with the animals under general anaesthesia. After randomisation pigs were assigned to either surgical repair (n=12) or endoscopic closure (n=12). Endoscopic repair was performed using a 2T160 double channel upper endoscope (Olympus, Hamburg, Germany), a Twin Grasper and 12mm traumatic Over The Scope Clips (OTSC, Ovesco, Germany). Surgical repair was achieved by open laparotomy. Pressurized leak tests of the perforation closures were performed following necropsy. Additionally pressurized leak test were performed in an ex vivo evaluation of hand-sewn closures of 1cm large scalpel incisions (n=18) and of healthy duodenal tissue (n=18). Tissue for ex vivo evaluation was obtained from freshly killed pigs. Results: Mean time for endoscopic closure was 5 min. (Range 3-8 min., SD 2). No complication occurred during any of the closure procedures. At necropsy and macroscopic examination all OTSC and surgical closures showed complete incorporation and closure of the duodenal needle-knife incisions. Pressurized leak test showed a mean burst pressure of 166 mmHg (Range 80-260, SD 65) for OTSC closures and a mean burst pressure of 143 mmHg (Range 30-300, SD 83) for surgical sutures. Ex vivo hand-sewn sutures of 1cm scalpel incisions exhibited a mean burst pressure of 81 mmHg (Range 43-140, SD 31) and ex vivo duodenal tissue exhibited a burst pressure of 247 mmHg (Range 200-300, SD 35). Ex vivo duodenal tissue burst pressure was significantly higher compared to OTSC closure (p<0.01), in vivo surgical closures (p<0.01), and ex vivo hand-sewn closures (p<0.01). OTSC closures were comparable to surgical closures (p=0.461) and superior to ex vivo hand-sewn closures (p<0.01). In vivo surgical closures were superior to ex vivo hand-sewn closures (p<0.01). Conclusions: Endoscopic closure by means of the OTSC system exhibits comparable results to in vivo surgical sutures and seems suitable to attempt closure of 1cm large duodenal perforations.

Neonatal percutaneous central venous lines: fit to burst

Objective:To examine pressure changes in neonatal percutaneous central venous catheters under varying laboratory conditions and to quantify the risks of rupture in clinical practice.Design:We tested 27-gauge polyurethane Premicath and 24-gauge...

Functional Characteristics of alpha3beta3gamma2 and alpha1beta2gamma2 GABA-A receptors

The GABAA receptor is a member of the cys-loop family of ligand gated ion channels and the major mediator of neuronal inhibition. Each receptor is a pentameric protein complex composed of homologous subunits, the combination of which gives rise to numerous GABAA receptor subtypes. Within the thalamus, two synaptic GABAA receptor isoforms predominate; the α1β2γ2 channels, which are found at the synapses of relay neurons, and the α3β3γ2 channels that are located at synapses in the reticular nucleus. We endeavoured to characterize the kinetic properties to these two GABAA receptors. Our preliminary data suggest that both receptors open to a single channel conductance level of 26 pS, irrespective of the GABA concentration used to elicit activity. α3β3γ2 GABAA receptors, however, exhibit longer active periods (bursts) at saturating (5 mM) and low (2 μM) concentrations of GABA compared to α1β2γ2 GABAA receptors. The mean burst length and intra-burst open probability (Po) for the α3β3γ2 channels was 136.7 ± 16.8 ms and 0.84 ± 0.05 (n = 4), respectively and for the α1β2γ2 channels was 87.4 ± 12.0 ms and 0.82 ± 0.02 (n = 3), respectively, when exposed to 5 mM GABA. At 2 μM GABA, the mean burst length and Po for α3β3γ2 channels was 25.8 ± 4.7 ms and 0.78 ± 0.03 (n = 3), respectively and for α1β2γ2 channels was 8.4 ± 1.9 ms and 0.73 ± 0.02 (n = 3), respectively. These measurements are consistent with the reported slower deactivation phase of ensemble, α3β3γ2 mediated synaptic currents and suggest that GABA has a longer occupancy at α3β3γ2 channels than at α1β2γ2 channels.

A Triad of Residues F1296-N1303-R1358 in NBD2 of CFTR is Involved in ATP-driven Gating

Despite the general agreement that dimerization of CFTR's two Nucleotide Binding Domains (NBDs) drives channel opening, little is known about how nucleotide binding to individual NBDs promotes dimer formation. We investigated the allosteric interaction between three NBD2 residues, F1296, N1303 and R1358, because statistical coupling analysis reveals coevolution of these positions. Considering frequently occurring pairs in the multiple sequence alignment, we chose mutations F1296S and N1303Q for building a mutant cycle. The mutations had no significant effect on the apparent ATP affinity measured in inside-out macropatches. However, we observed elevated ATP-independent activity (Po,bas) in F1296S/N1303Q. Po,bas was 0.0048±0.0024, 0.0034±0.0007, 0.013±0.0027, and 0.115±0.028 for WT, F1296S, N1303Q, and F1296S/N1303Q, respectively. A thermodynamic mutant cycle built on these values implies a change in coupling (ΔΔG= -5.74±1.45 kJ/mol) between positions 1296 and 1303 upon channel opening in the absence of ATP. To study the coupling between these two positions in the presence of ATP, but under equilibrium conditions, we introduced the same mutations into a non-hydrolytic background (K1250R). The high ATP-independent basal activity caused by the F1296S/N1303Q double-mutation was preserved in non-hydrolytic background. In addition, the mean burst duration of F1296S/N1303Q/K1250R in saturating ATP - estimated from the monoexponential macroscopic current decay time course following ATP removal - was more than 3-fold longer (31.34±4.99 s) than that of K1250R (8.25±0.58 s), F1296S/K1250R (7.77±0.48 s), or N1303Q/K1250R (9.09±0.95 s), predicting a change in coupling (ΔΔG=-2.95±0.48 kJ/mol) between positions 1296 and 1303 as the channel closes from the ATP-bound open conformation. Thus, the interaction between F1296 and N1303 is important to stabilize the open state but is not an important determinant of ATP affinity. The N1303-R1358 interaction is under current investigation.

Thermonuclear (Type I) X‐Ray Bursts Observed by theRossi X‐Ray Timing Explorer

We have assembled a sample of 1187 thermonuclear (type I) X-ray bursts from observations of 48 accreting neutron stars by the Rossi X-ray Timing Explorer, spanning more than 10 years. The sample contains examples of two of the three theoretical ignition regimes (confirmed via comparisons with numerical models) and likely examples of the third. We present a detailed analysis of the variation of the burst profiles, energetics, recurrence times, presence of photospheric radius expansion, and presence of burst oscillations, as a function of accretion rate. We estimated the distance for 35 sources exhibiting radius-expansion bursts, and found that the peak flux of such bursts varies typically by 13%. We classified sources into two main groups based on the burst properties: (1) both long and short bursts (indicating mixed H/He accretion), and (2) consistently short bursts (primarily He accretion), and we calculated the mean burst rate as a function of accretion rate for the two groups. The decrease in burst rate observed at > 0.06dot MEdd (~2 × 10^37 ergs s^−1) is associated with a transition in the persistent spectral state and (as has been suggested previously) may be related to the increasing role of steady He burning. We found many examples of bursts with recurrence times <30 minutes, including burst triplets and even quadruplets. We describe the oscillation amplitudes for 13 of the 16 burst oscillation sources, as well as the stages and properties of the bursts in which the oscillations are detected. The burst properties are correlated with the burst oscillation frequency; sources spinning at <400 Hz generally have consistently short bursts, while the more rapidly spinning systems have both long and short bursts. This correlation suggests either that shear-mediated mixing dominates the burst properties, or alternatively that the nature of the mass donor (and hence the evolutionary history) has an influence on the long-term spin evolution.

Comparative Study of In Vivo Lymphatic Sealing Capability of the Porcine Thoracic Duct Using Laparoscopic Dissection Devices

Sealing the lymphatic vessels during abdominal and pelvic surgery is important to prevent the leakage of lymphatic fluid and its resultant sequelae. To our knowledge we compared for the first time the quality of lymphatic sealing by each of 4 commonly used laparoscopic dissection devices. A total of 12 domestic pigs were used to test dissecting devices, including monopolar scissors (Ethicon Endo-Surgery, Cincinnati, Ohio), Harmonic ACE Scalpel, LigaSure V, EnSeal and Trissector. A midline incision was made from mid sternum to umbilicus, the diaphragm was divided and the porcine thoracic duct was isolated. In all animals each device was used to seal an area of the duct and each seal was placed at least 2 cm from the prior seal. In group 1 the thoracic duct of 6 pigs was cannulated with a 5Fr catheter and the seal was subjected to burst pressure testing using a burst pressure measuring device (Cole-Parmer, Vernon Hills, Illinois). In the 6 pigs in group 2 each seal was immediately sent for histopathological evaluation. Specimens were given a score for the extent of cautery damage, including 0-none, 1-minimal, 2-moderate, 3-severe and 4-extreme. A total of 64 seals were created, of which 35 were subjected to burst pressure testing. Mean size of the thoracic duct was 2.6 mm. No acute seal failures were observed with any bipolar device or the harmonic shears. However, 2 immediate failures (33%) were seen with monopolar scissors. Mean burst pressure for monopolar scissors, Harmonic ACE Scalpel, LigaSure V, EnSeal and Trissector was 46 (range 0 to 165), 540 (range 175 to 795), 258 (range 75 to 435), 453 (range 255 to 825) and 379 mm Hg (range 175 to 605), respectively (p <0.05). Trissector, Harmonic ACE Scalpel and EnSeal generated seals with significantly higher burst pressure than that of monopolar scissors (p <0.05). Histopathological evaluation revealed that LigaSure caused less thermal damage than Trissector and EnSeal (p <0.05). Each device tested except monopolar scissors consistently produced a supraphysiological seal and should be suitable for sealing lymphatic vessels during laparoscopic surgery.

Abstract 2470: Augmented Tonic Activation Of Chemoreceptors May Contribute To Sympathetic Overactivity In Patients With Essential Hypertension

Rationale : Peripheral chemoreflex contributes to regulation of arterial blood pressure and chemoreceptors respond not only to hypoxia but they are also continuously activated by normal ambient oxygen concentration. Stimulation of chemoreceptors activates sympathetic traffic and this response may be altered in subjects with essential hypertension.. Objective: The aim of our study was to investigate the effect of deactivation of carotid body chemoreceptors on sympathetic activity directly measured as MSNA (muscle sympathetic nerve activity) in young subjects with mild to moderate untreated hypertension. Methods: Twelve patients with essential hypertension (36±9 years, all men, BMI 29±4 kg/m 2 ,) and 8 controls (37±7, men BMI 27±5kg/m 2 ) participated in the study. None of the patients or controls received any medications. MSNA (burst/minute and mean burst amplitude - au), systolic blood pressure (SBP) and diastolic blood pressure (DBP), heart rate (HR), ECG, hemoglobin saturation with oxygen (Sat%), end tidal CO 2 and respiratory movements were monitored and measured after 10 minute of respiration by non-rebreathing mask with 100% 0 2 or 21% O 2 applied in blinded fashion. Results: Hypertensives had higher resting MSNA (38.6 ±8.6 burst/min vs. 30.3±.7 burst/min, p&lt;0.05), SBP (149.1± 9.9 vs. 124.1 ±11.6, p &lt; 0.05) and DBP (92.1 ±8.6 vs. 78.1 ± 8.9, p&lt; 0.05) than controls. Breathing with 100% oxygen caused significant decrease in MSNA in hypertensives (from 38.6 ± 8.6 burst/min to 26.3 burst/min ± 6.8 and from 100 ± 0 au to 86 ± 18 au, p&lt; 0.05) and no change in MSNA in controls (30.3 ± 5.7 burst/min initially and 27.3 burst/min ± 6.2 after 100% 0 2 , 100 ± 0 au vs. 98 ± 11 au). Blood pressure, end tidal CO 2 , respiration frequency did not change significantly after hyperoxia while HR decreased (from 69.6 ± 9 to 64.1 ± 7 in hypertensives p&lt;0.05 and from 67± 8 to 62.5 ± 7 in controls, p&lt; 0.05). Sat% increased significantly in both groups to 99%. Conclusions: Increased sympathetic activity in young, untreated hypertensives may be caused by the elevated tonic chemoreflex activation.