New and Exciting in PLoS Medicine and PLoS Biology

Circadian Remodeling of Neuronal Circuits Involved in Rhythmic Behavior:

Circadian systems evolved as a mechanism that allows organisms to adapt to the environmental changes in light and dark which occur as a consequence of the rotation of Earth. Because of its unique repertoire of genetic tools, Drosophila is a well established model for the study of the circadian clock. Although the biochemical components underlying the molecular oscillations have been characterized in detail, the mechanisms used by the clock neurons to convey information to the downstream pathways remain elusive. In the fruit fly, the small ventral lateral neurons (LNv) are capable of synchronizing other clock cells relying on a neuropeptide named pigment dispersing factor. In this work we introduce a novel mechanism as a possible candidate for contributing to the transmission of information downstream of the small LNvs, involving clock-controlled remodeling of their axonal morphology. By labeling the entire neuronal membrane and analyzing the complexity of the axonal arbor at different times we showed that there is a circadian variation in the complexity of the axonal arbor. This phenomenon was not observed in flies carrying null mutations in two canonical clock genes, underscoring the dependence of the circadian clock for the structural plasticity of its pacemaker neurons.

It's the Network, Stupid: Why Everything in Medicine Is Connected:

Once the domain of social scientists--who have used social network analysis to study such diverse phenomena as kinship ties, organizational behavior, rumor spreading, and global air traffic--network theory has now entered the purview of health scientists. Network theory is concerned with mapping the links between entities, and social network analysis is the application of that theory to the social sciences. Searching for more social and environmental explanations for the obesity epidemic in America, for example, Christakis and Fowler [1] showed that obesity can spread from person to person, and that this spread depends on the nature of social ties: a person's chance of becoming obese increased by 171% if he or she had a mutual friend who had become obese (even if they lived far away). Their risk increased by 40% if it was their sibling or spouse who became obese. Christakis and Fowler concluded that the social network is a crucial component--perhaps more so than genetics--in explaining obesity, a problem normally thought of as solely biological and behavioral.

Social Contacts and Mixing Patterns Relevant to the Spread of Infectious Diseases:

Mathematical modelling of infectious diseases transmitted by the respiratory or close-contact route (e.g., pandemic influenza) is increasingly being used to determine the impact of possible interventions. Although mixing patterns are known to be crucial determinants for model outcome, researchers often rely on a priori contact assumptions with little or no empirical basis. We conducted a population-based prospective survey of mixing patterns in eight European countries using a common paper-diary methodology. 7,290 participants recorded characteristics of 97,904 contacts with different individuals during one day, including age, sex, location, duration, frequency, and occurrence of physical contact. We found that mixing patterns and contact characteristics were remarkably similar across different European countries. Contact patterns were highly assortative with age: schoolchildren and young adults in particular tended to mix with people of the same age. Contacts lasting at least one hour or occurring on a daily basis mostly involved physical contact, while short duration and infrequent contacts tended to be nonphysical. Contacts at home, school, or leisure were more likely to be physical than contacts at the workplace or while travelling. Preliminary modelling indicates that 5- to 19-year-olds are expected to suffer the highest incidence during the initial epidemic phase of an emerging infection transmitted through social contacts measured here when the population is completely susceptible. To our knowledge, our study provides the first large-scale quantitative approach to contact patterns relevant for infections transmitted by the respiratory or close-contact route, and the results should lead to improved parameterisation of mathematical models used to design control strategies.