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Over the past three decades in cellular neuroscience there has been a shift towards the view of the 'tripartite synapse', where, astrocytes -- as well as the pre-synapse and post-synapse -- are involved in synaptic signalling. The migration of astrocytes to form branched networks in the brain is, therefore, of great interest in understanding brain development and neuronal function. Migration is a complex interplay between cytoskeletal reorganisation and cell mechanical stiffness. In order to improve understanding of this process, correlative measurements of cytoskeletal organisation and mechanical stiffness are required. To investigate astrocyte migration a technique combining atomic force microscopy (AFM) with stimulated emission depletion (STED) microscopy was developed. First a custom STED microscope was developed. To facilitate the design of this system the theoretical performance of a range of STED techniques (cw-STED, time-gated STED, pulsed STED and RESOLFT) were compared, identifying that pulsed STED theoretically has the highest photon efficiency. A pulsed STED microscope, which uses adaptive optics, was then designed, developed and characterised. The microscope was found to achieve resolutions below 50 nm. The STED microscope was combined with a commercial AFM to study live cells. Using the recently developed SiR-actin and SiR-tubulin dyes and AFM probes optimised for live cell mechanical property studies, images of the actin and tubulin cytoskeleton were correlated with AFM topography and mechanical stiffness measurements. It was found that, in astrocytes, actin contributes significantly both to astrocyte stiffness and topography. Investigations of migrating cells showed differences in actin organisation and mechanical stiffness between the basis and leading edge of migration. A further study was performed, investigating the effects of the gap-junction protein connexin30, which is expressed during the early stages of brain development, on migration. This protein was found to inhibit the actin reorganisation and mechanical stiffness changes observed in basal conditions. Overall the combination of mechanosensitive AFM measurements with advanced microscopy, such as super-resolution, on live cells is a promising approach which will enable a range of investigations, for instance when studying cell structural remodeling during brain development or tumorigenesis.

The purpose of this descriptive study was be to determine if there were differences in the implementation of professional learning communities components between elementary and secondary teachers and administrators. This study examined the relationship between demographic characteristics and teacher implementation of professional learning communities components. The study also examined the impact of teachers' perceptions of efficacy based on their involvement in professional learning communities and determined if this involvement impacted their self-efficacy in a positive or negative manner. The implementation of professional learning communities components by principals and assistant principals were also examined. This study focused on a SA public school district in north Texas that implemented professional learning communities components for six years. Random selection was used to create a sample of 200 elementary teachers and 200 secondary teachers from the selected school district. The participants were asked to take the professional learning communities Survey and Teachers' Sense of Efficacy Scale. The 41 campus-level principals and assistant principals were asked to take the Professional Learning Communities Survey in order to make comparisons with the teachers' responses. This study used a series of multivariate analyses of variance and a multiple regression to address the research questions and to look for significant differences. The results of the study showed that differences did exist between elementary and secondary teachers in the implementation of professional learning communities components and perceptions of self-efficacy. The multiple regression showed that the participant's score on the Professional Learning Communities Survey was a good predictor for the participant's score on the Teachers Sense of Efficacy Scale. Differences also existed between teachers and administrators in the implementation of professional learning communities components. The conclusions stated that differences between elementary and secondary teachers could be explained by structural differences, and when professional learning communities are operated effectively, the differences are minimized. The significance of this study was to help teachers and administrators understand the professional learning communities components that exist within elementary and secondary schools. This study would add to the existing body of research on professional learning communities and help educators create better learning environments for all students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]