Long-term stability of adipose tissue generated from a vascularized pedicled fat flap inside a chamber

Background Numerous studies demonstrate the generation and short-term survival of adipose tissue; however, long-term persistence remains elusive. This study evaluates long-term survival and transferability of de novo adipose constructs based on a ligated vascular pedicle and tissue engineering chamber combination. Methods Defined adipose tissue flaps were implanted into rats in either intact or perforated domed chambers. In half of the groups, the chambers were removed after 10 weeks and the constructs transferred on their vascular pedicle to a new site, where they were observed for a further 10 weeks. In the remaining groups, the tissue construct was observed for 20 weeks inside the chamber. Tissue volume was assessed using magnetic resonance imaging and histologic measures, and constructs were assessed for stability and necrosis. Sections were assessed histologically and for proliferation using Ki-67. Results At 20 weeks, volume analysis revealed an increase in adipose volume from 0.04 ± 0.001 ml at the time of insertion into the chambers to 0.27 ± 0.004 ml in the closed and 0.44 ± 0.014 ml in the perforated chambers. There was an additional increase of approximately 10 to 15 percent in tissue volume in flaps that remained in chambers for 20 weeks, whereas the volume of the transferred tissue not in chambers remained unaltered. Histomorphometric assessment of the tissues documented no signs of hypertrophy, fat necrosis, or atypical changes of the newly generated tissue. Conclusion This study presents a promising new method of generating significant amounts of mature, vascularized, stable, and transferable adipose tissue for permanent autologous soft-tissue replacement.

Power buffer with model predictive control for stability of vehicular power systems with constant power loads

Electrification of vehicular systems has gained increased momentum in recent years with particular attention to constant power loads (CPLs). Since a CPL potentially threatens system stability, stability analysis of hybrid electric vehicle with CPLs becomes necessary. A new power buffer configuration with battery is introduced to mitigate the effect of instability caused by CPLs. Model predictive control (MPC) is applied to regulate the power buffer to decouple source and load dynamics. Moreover, MPC provides an optimal tradeoff between modification of load impedance, variation of dc-link voltage and battery current ripples. This is particularly important during transients or starting of system faults, since battery response is not very fast. Optimal tradeoff becomes even more significant when considering low-cost power buffer without battery. This paper analyzes system models for both voltage swell and voltage dip faults. Furthermore, a dual mode MPC algorithm is implemented in real time offering improved stability. A comprehensive set of experimental results is included to verify the efficacy of the proposed power buffer.

Morphometric stability of the corneal subbasal nerve plexus in healthy individuals a 3-year longitudinal study using corneal confocal microscopy

Purpose We examined the age-dependent alterations and longitudinal course of subbasal nerve plexus (SNP) morphology in healthy individuals. Methods Laser-scanning corneal confocal microscopy, ocular screening, and health and metabolic assessment were performed on 64 healthy participants at baseline and at 12-month intervals for 3 years. At each annual visit, eight central corneal images of the SNP were selected and analyzed using a fully-automated analysis system to quantify corneal nerve fiber length (CNFL). Two linear mixed model approaches were fitted to examine the relationship between age and CNFL, and the longitudinal changes of CNFL over three years. Results At baseline, mean age was 51.9 ± 14.7 years. The cohort was sex balanced (χ2 = 0.56, P = 0.45). Age (t = 1.6, P = 0.12) and CNFL (t = -0.50, P = 0.62) did not differ between sexes. A total of 52 participants completed the 36-month visit and 49 participants completed all visits. Age had a significant effect on CNFL (F1,33 = 5.67, P = 0.02) with a linear decrease of 0.05 mm/mm2 in CNFL per one year increase in age. No significant change in CNFL was observed over the 36-month period (F1,55 = 0.69, P = 0.41). Conclusions The CNFL showed a stable course over a 36-month period in healthy individuals, although there was a slight linear reduction in CNFL with age. The findings of this study have implications for understanding the time-course of the effect of pathology and surgical or therapeutic interventions on the morphology of the SNP, and serves to confirm the suitability of CNFL as a screening/monitoring marker for peripheral neuropathies.

Propagating excitatory potentials within the fear conditioning circuit of the lateral amygdala

In the Hebbian postulate, transiently reverberating cellular ensembles can sustain activity to facilitate temporal coincidence detection. Auditory fear conditioning is believed to be formed in the lateral amygdala (LA), by way of plasticity at auditory input synapses on principal neurons. To evaluate the contribution of LA cellular ensembles in the formation of conditioned fear memories, we investigated the LA micro-circuitry by electrophysiological and anatomical approaches. Polysynaptic field potentials evoked in the LA by stimulation of auditory thalamus(MGm/PIN) or auditory cortical (TE3) afferents were analyzed in vitro and in vivo. In vivo, two potentials were identified following stimulation of either pathway. In vitro, these multiple potentials were revealed by adding 75uM Picrotoxin or 30uM Bicuculine, with the first potential peaking at 15-20 ms, followed by two additional potentials at 20 – 25 and 30 – 35 ms, respectively. These data show single stimulation events can result in multiple synchronized excitatory events within the lateral amygdala. In order to determine underlying mechanisms of auditory signal propagation, LA principal neuron axon collateral trajectory patterns and morphology were analyzed. Neurons were found to have local axon collaterals that are topographically organized. Each axon collateral within the LA totaled 14.1 ± 2.73mm, had 29.8 ± 9.1 branch points and 1870.8 ± 1035 boutons (n=9). Electrophysiological and anatomical data show that a network of extensive axon collaterals within the LA may facilitate preservation of auditory afferent signals.

Quantification of the total neuronal structure of the fear conditioning circuit of the lateral amygdala of the rat

During Pavlovian auditory fear conditioning a previously neutral auditory stimulus (CS) gains emotional significance through pairing with a noxious unconditioned stimulus (US). These associations are believed to be formed by way of plasticity at auditory input synapses on principal neurons in the lateral nucleus of the amygdala (LA). In order to begin to understand how fear memories are stored and processed by synaptic changes in the LA, we have quantified both the entire neural number and the sub-cellular structure of LA principal neurons.We first used stereological cell counting methods on Gimsa or GABA immunostained rat brain. We identified 60,322+/-1408 neurons in the LA unilaterally (n=7). Of these 16,917+/-471 were GABA positive. The intercalated nuclei were excluded from the counts and thus GABA cells are believed to represent GABAergic interneurons. The sub-nuclei of the LA were also independently counted. We then quantified the morphometric properties of in vitro electrophysiologically identified principal neurons of the LA, corrected for shrinkage in xyz planes. The total dendritic length was 9.97+/-2.57mm, with 21+/-4 nodes (n=6). Dendritic spine density was 0.19+/-0.03 spines/um (n=6). Intra-LA axon collaterals had a bouton density of 0.1+/-0.02 boutons/um (n=5). These data begin to reveal the finite cellular and sub-cellular processing capacity of the lateral amygdala, and should facilitate efforts to understand mechanisms of plasticity in LA.

Influence of the structural characteristic of pyrolysis products on thermal stability of styrene-butadiene rubber composites reinforced by different particle sized kaolinites

A series of rubber composites were prepared by blending styrene-butadiene rubber (SBR) latex and the different particle sized kaolinites. The thermal stabilities of the rubber composites were characterized using thermogravimetry, digital photography, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Kaolinite SBR composites showed much greater thermal stability when compared with that of the pure SBR. With the increase of kaolinite particle size, the pyrolysis products became much looser; the char layer and crystalline carbon content gradually decreased in the pyrolysis residues. The pyrolysis residues of the SBR composites filled with the different particle sized kaolinites showed some remarkable changes in structural characteristics. The increase of kaolinite particle size was not beneficial to form the compact and stable crystalline carbon in the pyrolysis process, and resulted in a negative influence in improving the thermal stability of kaolinite/SBR composites.

GABAergic inhibition in the fear conditioning circuit of the lateral amygdala is potentiated by dopamine D1 agonists

Auditory fear conditioning is dependent on auditory signaling from the medial geniculate (MGm) and the auditory cortex (TE3) to principal neurons of the lateral amygdala (LA). Local circuit GABAergic interneurons are known to inhibit LA principal neurons via fast and slow IPSP's. Stimulation of MGm and TE3 produces excitatory post-synaptic potentials in both LA principal and interneurons, followed by inhibitory post-synaptic potentials. Manipulations of D1 receptors in the lateral and basal amygdala modulate the retrieval of learned association between an auditory CS and foot shock. Here we examined the effects of D1 agonists on GABAergic IPSP's evoked by stimulation of MGm and TE3 afferents in vitro. Whole cell patch recordings were made from principal neurons of the LA, at room temperature, in coronal brain slices using standard methods. Stimulating electrodes were placed on the fiber tracts medial to the LA and at the external capsule/layer VI border dorsal to the LA to activate (0.1-0.2mA) MGm and TE3 afferents respectively. Neurons were held at -55.0 mV by positive current injection to measure the amplitude of the fast IPSP. Changes in input resistance and membrane potential were measured in the absence of current injection. Stimulation of MGm or TE3 afferents produced EPSP's in the majority of principal neurons and in some an EPSP/IPSP sequence. Stimulation of MGm afferents produced IPSP's with amplitudes of -2.30 ± 0.53 mV and stimulation of TE3 afferents produced IPSP's with amplitudes of -1.98 ± 1.26 mV. Bath application of 20μM SKF38393 increased IPSP amplitudes to -5.94 ± 1.62 mV (MGm, n=3) and-5.46 ± 0.31 mV (TE3, n=3). Maximal effect occurred <10mins. A small increase in resting membrane potential and decrease in input resistance were observed. These data suggest that DA modulates both the auditory thalamic and auditory cortical inputs to the LA fear conditioning circuit via local GABAergic circuits. Supported by NIMH Grants 00956, 46516, and 58911.

Automated 3D mapping & shape analysis of the lateral ventricles via fluid registration of multiple surface-based atlases

We developed and validated a new method to create automated 3D parametric surface models of the lateral ventricles, designed for monitoring degenerative disease effects in clinical neuroscience studies and drug trials. First we used a set of parameterized surfaces to represent the ventricles in a manually labeled set of 9 subjects' MRIs (atlases). We fluidly registered each of these atlases and mesh models to a set of MRIs from 12 Alzheimer's disease (AD) patients and 14 matched healthy elderly subjects, and we averaged the resulting meshes for each of these images. Validation experiments on expert segmentations showed that (1) the Hausdorff labeling error rapidly decreased, and (2) the power to detect disease-related alterations monotonically improved as the number of atlases, N, was increased from 1 to 9. We then combined the segmentations with a radial mapping approach to localize ventricular shape differences in patients. In surface-based statistical maps, we detected more widespread and intense anatomical deficits as we increased the number of atlases, and we formulated a statistical stopping criterion to determine the optimal value of N. Anterior horn anomalies in Alzheimer's patients were only detected with the multi-atlas segmentation, which clearly outperformed the standard single-atlas approach.

The effect of pH on the unfolding pathway and stability of ribosome-inactivating protein abrin-II

The effect of pH on the unfolding pathway acid the stability of the toxic protein abrin-II have been studied by increasing denaturant concentrations of guanidine hydrochloride and by monitoring the change in 8,1-anilino naphthalene sulfonic acid (ANS) fluorescence upon binding to the hydrophobic sites of the protein. Intrinsic protein fluorescence, far and near UV-circular dichroism (CD) spectroscopy and ANS binding studies reveal that the unfolding of abrin-II occurs through two intermediates at pH 7.2 and one intermediate at pH 4.5. At pH 7.2, the two subunits A and B of abrin-II unfold sequentially. The native protein is more stable at pH 4.5 than at pH 7.2. However, the stability of the abrin-II A-subunit is not affected by a change in pH. These observations may assist in an understanding of the physiologically relevant transmembrane translocation of the toxin.

Thermodynamic characterization of the conformational stability of the homodimeric protein, pea lectin

The conformational stability of the homodimeric pea lectin was determined by both isothermal urea-induced and thermal denaturation in the absence and presence of urea. The denaturation profiles were analyzed to obtain the thermodynamic parameters associated with the unfolding of the protein. The data not only conform to the simple A(2) double left right arrow 2U model of unfolding but also are well described by the linear extrapolation model for the nature of denaturant-protein interactions. In addition, both the conformational stability (Delta G(s)) and the Delta C-p for the protein unfolding is quite high, at about 18.79 kcal/ mol and 5.32 kcal/(mol K), respectively, which may be a reflection of the relatively larger size of the dimeric molecule (M-r 49 000) and, perhaps, a consequent larger buried hydrophobic core in the folded protein. The simple two-state (A(2) double left right arrow 2U) nature of the unfolding process, with the absence of any monomeric intermediate, suggests that the quaternary interactions alone may contribute significantly to the conformational stability of the oligomer-a point that may be general to many oligomeric proteins.

Stability of a Random Diffusion with Linear Drift

We consider a Linear system with Markovian switching which is perturbed by Gaussian type noise, If the linear system is mean square stable then we show that under certain conditions the perturbed system is also stable, We also shaw that under certain conditions the linear system with Markovian switching can be stabilized by such noisy perturbation.

Stability of Dimeric Interface in Banana Lectin: Insight from Molecular Dynamics Simulations

Banana lectin (Banlec) is a homodimeric non-glycosylated protein. It exhibits the b-prism I structure. High-temperature molecular dynamics simulations have been utilized to monitor and understand early stages of thermally induced unfolding of Banlec. The present study elucidates the behavior of the dimeric protein at four different temperatures and compares the structural and conformational changes to that of the minimized crystal structure. The process of unfolding was monitored by following the radius of gyration, the rms deviation of each residue, change in relative solvent accessibility and the pattern of inter- and intra-subunit interactions. The overall study demonstrates that the Banlec dimer is a highly stable structure, and the stability is mostly contributed by interfacial interactions. It maintains its overall conformation during high-temperature (400–500 K) simulations, with only the unstructured loop regions acquiring greater momentum under such condition. Nevertheless, at still higher temperatures (600 K) the tertiary structure is gradually lost which later extends to loss of secondary structural elements. The pattern of hydrogen bonding within the subunit and at the interface across different stages has been analyzed and has provided rationale for its intrinsic high stability.