Neurofilaments form flexible bundles during neuritogenesis in culture and in mature axons in situ

Neurofilaments (NFs) undergo cation-dependent phospho-mediated associations with each other and other cytoskeletal elements that support axonal outgrowth. Progressive NF-NF associations generate a resident, bundled population that undergoes exchange with transporting NFs. We examined the properties of bundled NFs. Bundles did not always display a fully linear profile but curved and twisted at various points along the neurite length. Bundles retracted faster than neurites and retracted bundles did not expand following extraction with Triton, indicating that they coiled passively rather than due to pressure from the cell. Bundles consisted of helically wound NFs, which may provide flexibility necessary for turning of growing axons during pathfinding. Interactions between NFs and other cytoskeletal elements may be disrupted en masse during neurite retraction or regionally during remodeling. It is suggested that bundles within long axons that cannot be fully retracted into the soma could provide maintain proximal support yet still allow more distal flexibility for remodeling and changing direction during pathfinding

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Behaviour, preferences and cities: urban theory and urban resurgence

The resurgence of big, old cities and their regions is real, but it is merely a part of a broader pattern of urban change in the developed countries, whose broadest tendency is urban emergence, including suburbanisation, and movements of population to certain 'Sunbelt' regions. The problem is that it is difficult to accommodate explanation of both resurgence and emergence using the main explanations in the field today. These include: theories of the knowledge or creative economy, urban amenities, diversity and tolerance, and urban beauty. In most of their common specifications, they do well for either resurgent or emergent cities, but not for both at the same time. This suggests that these ideas, interesting as they are, require much greater specification and, in some cases, overhaul, in order to offer satisfactory responses to the diversity of patterns of urban growth. By examining some of these deficiencies, we conclude that urban theory needs a better understanding of urban choice behaviours and especially the effects of bundling, the limits to preference substitutions and the relationship between past and present preferences, in order to become fully effective in explaining urban resurgence and urban emergence. When these aspects of choice and preference are better integrated into urban theory, then the 'exogenous' causes of urbanisation can be made more endogenous and, in addition, they can be applied better to both emergence and resurgence. Urban research can, by so doing, also potentially become more policy-relevant