Neuronal spatial learning

Neurons are electrically active structures determined by the evolution of ion-specific pumps and channels that allow the transfer of charges under the influence of electric fields and concentration gradients. Extensive studies of spike timing of neurons and the relationship to learning exist. However, the properties of spatial activations during action potential in the context of learning have to our knowledge not been consistently studied. We examined spatial propagation of electrical signal for many consecutive spikes using recorded information from tetrodes in freely behaving rats before and during rewarded T-maze learning tasks. Analyzing spatial spike propagation in expert medium spiny neurons with the charge movement model we show that electrical flow has directionality which becomes organized with behavioral learning. This implies that neurons within a network may behave as “weak learners” attending to preferred spatial directions in the probably approximately correct sense. Importantly, the organization of spatial electrical activity within the neuronal network could be interpreted as representing a change in spatial activation of neuronal ensemble termed “strong learning.” Together, the subtle yet critical modulations of electrical flow directivity during weak and strong learning represent the dynamics of what happens in the neuronal network during acquisition of a behavioral task.     

Development of soluble glasses for biomedical use Part II: The biological response of human osteoblast cell lines to phosphate-based soluble glasses

Soluble glasses are considered to be of potential clinical value in orthopaedic and dental surgery. However, the biological response to these materials is not well understood. To determine the effects of these glasses, two human osteoblast cell lines, MG63 and HOS (TE85), were incubated in vitro in the presence of increasing concentrations of extracts of the glasses. The effects of the extracts on cell growth was measured using the MTT assay and an ELISA assay was used to measure the expression of bone sialoprotein (BSP), osteonectin (ON) and fibronectin (FN), antigens which play a fundamental part in the integrity and function of hard connective tissue. The results showed that the proliferation of the cells was adversely affected only by the more soluble glasses, which also down-regulated the expression of the bone-associated proteins. In contrast, the extract of the glass with the lowest dissolution rate, which contains relatively elevated levels of Ca²⁺, was found to enhance bone cell growth and antigen expression. These findings suggest that the compositions of these glasses at least partly determine the response of cells and thus, that the glasses could be modified to elicit a more optimal biological response and clinical efficacy.     

The non-operative management of collateral ligament injuries of the knee joint

Severe knee ligament injuries are frequently underestimated, and this results in later problems of chronic instability. A history of an appropriate mechanism coupled with immediate reduction in function should arouse suspicion of a major disruption. Examination with the patient under anesthesia may be required to assess the extent of the injury. If the lesion is an isolated collateral tear, the intact cruciate ligaments prevent wide displacement. Such an injury can be managed non-operatively. A long leg plaster at 90 degrees for 2 weeks followed by 4 weeks in a cast brace with motion from 45 degrees to 100 degrees is recommended. The knee is then protected in a brace during athletic activities for approximately 6 months. Thirty collateral ligament tears have been managed in this fashion. Only one has significant residual complaints. It is emphasized that an isolated collateral ligament tear is a positive diagnosis, and associated cruciate lesions must be ruled out. The recovery is faster in those patients managed non-operatively than in those who have surgical repair. There has not been a problem with late instability.     

Polarimetric assay for the medium-throughput determination of alpha-amino acid racemase activity

A polarimetric assay has been developed for the identification of alpha-amino acid racemase activity. The setup consists of a microcuvette polarimeter (40 microL volume) connected to a pipetting robot for microtiter plates, a pump, and data processing. It could be demonstrated for a glutamate racemase from Lactobacillus fermentii, expressed in Escherichia coli, serving as model enzyme, that its activity can be determined from the time-dependent change of the optical rotation using l-glutamate as substrate. Thus, the specific activity was determined to 111.4 mdeg/min which corresponds to 45.7 micromol/min per mg purified enzyme. Moreover, a protocol was developed that allows the measurement of racemase activity from 96-well microtiter plates using purified enzymes. Thus, the method described can be used to determine racemase activity in an automatic manner. It should be also applicable for the screening of enzyme libraries created by directed evolution.     

Fabrication and characterization of narrow-band Bragg-reflectionfilters in silicon-on-insulator ridge waveguides

We describe the design, fabrication and measurement of an integrated-optical Bragg grating filter, operating at a freespace wavelength of 1543 nm, based upon a silicon-on-insulator (SOI) ridge waveguide. The measured spectral response for a 4-mm long grating has a bandwidth of 15 GHz (0.12 nm), and shows good agreement with theoretical predictions     

Size distribution and waiting times for the avalanches of the Cell Network Model of Fracture

The Cell Network Model is a fracture model recently introduced that resembles the microscopical structure and drying process of the parenchymatous tissue of the Bamboo Guadua angustifolia. The model exhibits a power-law distribution of avalanche sizes, with exponent −3.0 when the breaking thresholds are randomly distributed with uniform probability density. Hereby we show that the same exponent also holds when the breaking thresholds obey a broad set of Weibull distributions, and that the humidity decrements between successive avalanches (the equivalent to waiting times for this model) follow in all cases an exponential distribution. Moreover, the fraction of remaining junctures shows an exponential decay in time. In addition, introducing partial breakings and cumulative damages induces a crossover behavior between two power-laws in the histogram of avalanche sizes. This results support the idea that the Cell Network Model may be in the same universality class as the Random Fuse Model.