Several research groups have applied elevated hydrostatic pressure to ONH astrocytes cultured on a rigid substrate as an in vitro model for glaucoma. These studies have shown significant biological effects and this hydrostatic pressure model is now becoming generally accepted in the ophthalmic community. However, since the applied pressures were modest the finding of significant biological effects due to pressure alone is surprising. We hypothesized that the application of hydrostatic pressure as described in these studies also altered gas tensions in the culture media. Our goal was to design equipment and carry out experiments to separate the biologic effects of pressure from those of hypoxia on cultured astrocytes. We designed equipment and carried out experiments to subject cultures of DITNC1 astrocytes to the four combinations of two levels of each parameter. We explored the morphology and migration rates of astrocytes, but observed no significant change in any of these properties.

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No abstract available. / Thesis (M.A.)-University of Durban-Westville, 2001.

No description available.

Rats learn to navigate to a specific location faster in a familiar environment (Keith and Mcvety 1988). It has been proposed that place learning does not require specific reward signals, but rather, that it occurs automatically. One of the strongest pieces of evidence for the automatic nature of place learning comes from the observation that place and head direction cells reference their receptive fields to prominent landmarks in an environment without needing a reward signal (O’Keefe and Conway 1978; Taube et al. 1990b). It has also been proposed that an allocentric representation of an environment would be bound to the landmarks with the greatest relative stability to guide its orientation (O’Keefe and Nadel 1978). The first two parts of this thesis explore whether place and head direction cells automatically use the most coherent landmarks for orientation. Head direction cells have been shown to orient their preferred firing directs coherently when being exposed to conflicting landmarks in an environment (Yoganarasimha et al. 2006). A model of head direction cells was thus used to explore the necessary mechanisms required to implement an allocentric system that selects landmarks based on their relative stability. We found that the simple addition of Hebbian projections combined with units representing the orientation of landmarks to the head direction cell system is sufficient for the system to exhibit such a capacity. We then recorded both entorhinal head direction cells and CA1 place cells and at the same time subjected the rats to repeated experiences of landmark conflicts. During the conflicts a subset of landmarks always maintained a fixed relative relationship with each other. We found that the visual landmarks retained their ability to control the place and head direction cells even after repeated experience of conflict and that the simultaneously recorded place cells exhibited coherent representations between conflicts. However, the ’stable landmarks’ did not show significantly greater control over the place and head direction cells when comparing to the unstable landmarks. This argues against the hypothesis that the relative stability between landmarks is encoded automatically. We did observe a trend that, with more conflict experience, the ’stable landmarks’ appeared to exert greater control over the cells. The last part of the thesis explores whether goal sensitive cells (Ainge et al. 2007a) discovered from CA1 of hippocampus are developed due to familiarity with the environment or from the demands for rats to perform a win-stay behaviour. We used the same win-stay task as in Ainge et al. and found that there were few or no goal sensitive cells on the first day of training. Subsequent development of goal sensitive activity correlated significantly with the rat’s performance during the learning phase of the task. The correlation provides support to the hypothesis that the development of goal sensitive cells is associated to the learning of the win-stay task though it does not rule out the possibility that these goal sensitive cells are developed due to the accumulated experience on the maze. In summary, this thesis explores what kind of spatial information is encoded by place and head direction cells and finds that relative stability between landmarks without a reward signal is not automatically encoded. On the other hand, when additional information is required to solve a task, CA1 place cells adapt their spatial code to provide the necessary information to guide successful navigation.

Anatomical changes can have significant clinical impact during head and neck radiotherapy. Adaptive radiotherapy (ART) may be applied to account for such changes. Implementation of ART to alter dose delivery requires deformable image registration (DIR) to assess 3D deformations. This study evaluates the performance and accuracy of a commercial DIR system for clinical applications. The investigations in this project were carried out using images of induced changes in two standard radiotherapy phantoms (RANDO® and CIRS®) and one in-house built phantom. CT image data before and after deformation of the phantoms were processed using Eclipse / SmartAdapt® v.10 system employing a Demons-based algorithm. A DIR protocol was designed, and algorithm performance was assessed quantitatively, using volume analysis and the Dice Similarity Index (DSI), and also evaluated qualitatively. In addition, algorithm performance was assessed for 5 head and neck cancer patients using clinical CT images. Each original planning CT image containing contours of 10 volumes of interest including treatment target volumes and organs at risk was deformed to match a second CT image acquired during the course of the treatment. The original structures were deformed, copied onto the target image and compared to reference contours drawn by 3 radiation oncologists. Phantom investigations gave varied results with average DSI scores ranging from 0.69 to 0.93, with an overall average of 0.86 ± 0.08. These quantitative results were reflected qualitatively, with generally accurate matching between reference and DIR-generated structures. Although air gaps in the phantoms compromised algorithm performance and gave rise to physically aberrant results. Clinical results were generally better with a DSI range of 0.75-0.99 and an overall average of 0.89 ± 0.05, suggesting high DIR accuracy. Qualitatively, some minor contour deformations were noted, as well as artefacts in the axial direction that were due to the CT slice resolution (3 mm) that was used to scan the patients. In addition, contour propagation between images using DIR reduced the time required by physicians to contour the images of head and neck cancer patients by ~47%. This study demonstrated that deformable image registration using a Modified Demons algorithm yields clinically acceptable results and time-saving benefits in contouring that improve clinical workflow. The study also showed that it is feasible to incorporate deformable image registration as part of an adaptive radiotherapy strategy for head and neck cancer, provided further studies are designed to carry out accurate and verifiable dose deformation.

No description available.

Clinical neuropsychologists who assess patients following mild closed head injury (CHI) are often asked to offer an opinion whether there is evidence of malingering. Factors that impact the ability of a person to intentionally portray impairment are quite important since mis-diagnosis of malingering can result in delayed treatment. In this study knowledge of the sequelae of mild CHI was provided to normal college students in an effort to change reporting of symptoms and influence the type of malingering strategy used when completing the Neuropsychological Symptom Inventory (NSI). Subjects were randomly assigned to either a prior knowledge malingering group (PK;N=57), no prior knowledge malingering group (NPK;N=58), or control group (CON;N=61). The results showed that PK subjects endorsed more general and attention/concentration symptoms than NPK or CON subjects. The results also showed PK subjects were as likely to be detected by the NSI lie scale as NPK subjects. Thus, the NSI lie scale demonstrated sensitivity to malingering despite subjects having brief instruction about mild CHI. Also, having prior knowledge did not result in significantly different strategies when completing the NSI. Instead, both malingering groups reportedly used exaggeration and attempted to be consistent as frequent strategies. / Department of Educational Psychology

Magnetic neural stimulation of straight neurons with bends (1) in a semi-infinite volume conductor with a planar interface and (2) in the model of the human head is analyzed. Two stimulating coils, namely the double-square and the double circular, producing the magnetic field for the neuron stimulation are considered. The results indicate that the stimulating coil characteristics (size, shape and location) and the neuron shape affect the magnitude and location of the stimulation. The activating function, defined as the electric field derivative along the neuron, has two components. One component depends on the derivative of the electric field along the straight section of the neuron, and the other on the field magnitude. For bent neurons in a semi-infinite volume conductor, an analytical expression of the activating function (the stimulus) of the neuron was derived. The maximal stimulation point is at the bend of the nerve and its position depends on the nerve shape and coil parameters. The analysis also shows a better performance (a stronger stimulus) for a double-circular (figure eight) coil than for a double-square coil of comparable size. Stimulating bent neurons in the human head is also analyzed. The head model consists of an outer sphere representing the skull and scalp and two inner spheres such that each represents one half of the brain. The 3D-impedance method was used to obtain the induced electric fields by the double-square and double-circular coils. Quasi-static conditions are assumed. The geometry of the neuron in this model approximates the normal configuration of motor neurons in the human head. The analysis shows that the stimulation occurs almost at the highest point on the nerve (the closest point to the coil) with the coil positioned in such a way that its center is directly over the highest point on the nerve. It is also shown that the double-square coil produces a stronger stimulus than the double-circular coil. This result is in contradiction with that for a bent neuron in a semi-infinite volume conductor, however, it agrees with the results obtained for a straight neuron [1]. The analysis of bent neurons represents a more realistic approximation of the actual anatomy. The results of this analyses confirms the conclusions and, therefore, usefulness of simplified analyses of straight neurons. The results are expected to be of some use in clinical applications where non-invasive neural stimulation is desired and location of stimulation needs to be known. / Graduate / 0544