There is consistent evidence that better access to relevant neighborhood destinations (e.g., local stores, services, transit stops) can be conducive to adults' utilitarian walking. Some evidence also suggests that availability of sidewalks and well-connected streets can facilitate utilitarian walking. To better inform initiatives to promote adults' walking in the planning and transport sectors, future studies need to examine how accessible such destinations should be, as well as the effect of the quality of recreational destinations.

© 2 0 0 2 L a n d e s B i o s c i e n c e . N o t f o r d i s t r i b u t i o n .[Cell ABSTRACTProgression through the cell cycle is temperature sensitive, but the relationship is not straightforward. In culture, many types of mammalian cells fail to undergo the G 2 /M transition after cooling from 37˚C to 16-20˚C (moderate hypothermia). However, progression through G 1 and S is not blocked at these temperatures, nor is progression through mitosis in cells cooled after they have become committed to the division process. Thus, at least one pathway is present during G 2 --but not during G 1 , S or mitosis-that is selectively disrupted at or below a critical temperature. As a result, a prolonged (24-48 hr) exposure to moderate hypothermia can be used to enrich cultures for G 2 cells. A brief (1 hr) exposure to severe hypothermia (4-10˚C) is also reported to induce a high degree of mitotic synchrony (up to 80%) in some mammalian cultures. Although the mechanism behind this synchronization remains vague, it may involve a cell cycle checkpoint, triggered in response to the cold shock, that transiently inhibits the G 1 /S transition.

When cell cultures in growth are treated with drugs that cause microtubules to disassemble, the mitotic index (MI) progressively increases as the cells accumulate in a C-mitosis. For many cell types, however, including rat kangaroo kidney PtK(1) cells, the MI does not increase during the first several hours of treatment [1-3] (Figure 1). This 'lag' implies either that cells are entering mitosis but rapidly escaping the block, or that they are delayed from entering division. To differentiate between these possibilities, we fixed PtK(1) cultures 0, 90 and 270 minutes after treatment with nocodazole, colcemid, lumi-colcemid, taxol or cytochalasin D. After 90 minutes, we found that the numbers of prophase cells in cultures treated with nocodazole or colcemid were reduced by approximately 80% relative to cultures treated with lumi-colcemid, cytochalasin D or taxol. Thus, destroying microtubules delays late G(2 )cells from entering prophase and, as the MI does not increase during this time, existing prophase cells do not enter prometaphase. When mid-prophase cells were treated with nocodazole, the majority (70%) decondensed their chromosomes and returned to G(2) before re-entering and completing prophase 3-10 hours later. Thus, a pathway exists in vertebrates that delays the G(2)-M transition when microtubules are disassembled during the terminal stages of G(2). As this pathway induces mid-prophase cells to transiently decondense their chromosomes, it is likely that it downregulates the cyclin A-cyclin-dependent kinase 2 (CDK2) complex, which is required in vertebrates for the early stages of prophase [4].

The relationships of Walk Score, a publicly-accessible walkability assessment tool, with walking for transport to and from home were examined among a large representative sample of Australian adults aged 18-64 years (N=16,944). Residents in highly and somewhat walkable areas were twice and 1.4 times more likely to accumulate 30 min of walking per day compared to those in very car-dependent neighborhoods, respectively. Mean duration of walking was also longer for participants living in highly and somewhat walkable areas compared to those in very car-dependent areas. Walk Score has potential as a widely-applicable tool for identifying the walkability of local neighborhoods.