No abstract

Zebrafish has been in the forefront of developmental biology and genetics, but only recently has interest in their behavior increased. Zebrafish are small and prolific, which lends this species to high throughput screening applications. A typical feature of zebrafish is its propensity to aggregate in groups, a behavior known as shoaling. Thus, zebrafish has been proposed as a possible model organism appropriate for the analysis of the genetics of vertebrate social behavior. However, shoaling behavior is not well characterized in zebrafish. Here, using a recently developed software application, we first investigate how zebrafish respond to conspecific and heterospecific fish species that differ in coloration and/or shoaling tendencies. We found that zebrafish shoaled with their own species but not with two heterospecific species, one of which was a shoaling the other a non-shoaling species. In addition, we have started the analysis of visual stimuli that zebrafish may utilize to determine whether to shoal with a fish or not. We systematically modified the color, the location, the pattern, and the body shape of computer animated zebrafish images and presented them to experimental zebrafish. The subjects responded differentially to some of these stimuli showing preference for yellow and avoidance of elongated zebrafish images. Our results suggest that computerized stimulus presentation and automated behavioral quantification of zebrafish responses are feasible, which in turn implies that high throughput forward genetic mutation or drug screening will be possible in the analysis of social behavior with this model organism.

Recent work suggests that the default mode network (DMN) includes two core regions, the ventromedial prefrontal cortex and posterior cingulate cortex (PCC), and several unique subsystems that are functionally distinct. These include a medial temporal lobe (MTL) subsystem, active during remembering and future projection, and a dorsomedial prefrontal cortex (dmPFC) subsystem, active during self-reference. The PCC has been further subdivided into ventral (vPCC) and dorsal (dPCC) regions that are more strongly connected with the DMN and cognitive control networks, respectively. The goal of this study was to examine age differences in resting state functional connectivity within these subsystems. After applying a rigorous procedure to reduce the effects of head motion, we used a multivariate technique to identify both common and unique patterns of functional connectivity in the MTL vs. the dmPFC, and in vPCC vs. dPCC. All four areas had robust functional connectivity with other DMN regions, and each also showed distinct connectivity patterns in both age groups. Young and older adults had equivalent functional connectivity in the MTL subsystem. Older adults showed weaker connectivity in the vPCC and dmPFC subsystems, particularly with other DMN areas, but stronger connectivity than younger adults in the dPCC subsystem, which included areas involved in cognitive control. Our data provide evidence for distinct subsystems involving DMN nodes, which are maintained with age. Nevertheless, there are age differences in the strength of functional connectivity within these subsystems, supporting prior evidence that DMN connectivity is particularly vulnerable to age, whereas connectivity involving cognitive control regions is relatively maintained. These results suggest an age difference in the integrated activity among brain networks that can have implications for cognition in older adults.

Traumatic brain injury (TBI) is one of the leading causes of death and disability in North America and as such requires ongoing surveillance 1,2 . Tracking health resource utilization over time, by age, and by gender provides valuable information regarding the burden of TBI on health care services, including post acute care. Furthermore, accurately identifying the rates of TBI is critical to the planning and evaluation of prevention efforts.Recent reports based on hospital admission data in Canada and the United States have documented a decrease in the number of in-patient admissions over the last two decades 3,4 , particularly for children and for incidents of "mild" TBI (mTBI). Studies that focus on in-patient admissions, however, may be misleading in that the decrease in numbers could reflect a shift towards treating children and mTBI sufferers at emergency departments (EDs). To date, there are no recent peer reviewed studies documenting TBI-related ED visits at a population based level, in a publicly ABSTRACT: Objective: The aim of this study was to determine the number of annual hospitalizations and overall episodes of care that involve a traumatic brain injury (TBI) by age and gender in the province of Ontario. To provide a more accurate assessment of the prevalence of TBI, episodes of care included visits to the emergency department (ED), as well as admissions to hospital. Mechanisms of injury for overall episodes were also investigated. Methods: Traumatic brain injury cases from fiscal years 2002/03-2006/07 were identified by means of ICD-10 codes. Data were collected from the National Ambulatory Care Reporting System and the Discharge Abstract Database. Results: The rate of hospitalization was highest for elderly persons over 75 years-of-age. Males generally had higher rates for both hospitalizations and episodes of care than did females. The inclusion of ED visits to hospitalizations had the greatest impact on the rates of TBI in the youngest age groups. Episodes of care for TBI were greatest in youth under the age of 14 and elderly over the age of 85. Falls (41.6%) and being struck by or against an object (31.1%) were the most frequent causes for a TBI. Conclusions:The study provides estimates for TBI from the only Canadian province that has systematically captured ED visits in a national registry. It shows the importance of tracking ED visits, in addition to hospitalizations, to capture the burden of TBI on the health care system. Prevention strategies should include information on ED visits, particularly for those at younger ages. Cette étude fournit des estimés de LCT dans la seule province canadienne qui inscrit a systématiquement les visites à l'urgence dans un registre nationale. Elle montre l'importance de faire le suivi des visites à l'urgence en plus des hospitalisations pour apprécier le fardeau que constitue la LCT sur le système de santé. Les stratégies de prévention devraient mentionner l'information sur les visites à l'urgence, particulièrement chez les jeunes.