Understanding brain-wide neuronal dynamics requires a detailed map of the underlying circuit architecture. We built an interactive cellular-resolution atlas of the zebrafish brain at 6 days post-fertilization (dpf) based on the reconstructions of over 2,000 individually GFP-labeled neurons. We clustered our dataset in "morphotypes,'' establishing a unique database of quantitatively described neuronal morphologies together with their spatial coordinates in vivo. Over 100 transgene expression patterns were imaged separately and co-registered with the single-neuron atlas. By annotating 72 non-overlapping brain regions, we generated from our dataset an inter-areal wiring diagram of the larval brain, which serves as ground truth for synapse-scale, electron microscopic reconstructions. Interrogating our atlas by "virtual tract tracing'' has already revealed previously unknown wiring principles in the tectum and the cerebellum. In conclusion, we present here an evolving computational resource and visualization tool, which will be essential to map function to structure in a vertebrate brain.

Animals use global image motion cues to actively stabilize their position by compensatory movements. Neurons in the zebrafish pretectum distinguish different optic flow patterns, e.g., rotation and translation, to drive appropriate behaviors. Combining functional imaging and morphological reconstruction of single cells, we revealed critical neuroanatomical features of this sensorimotor transformation. Terminals of direction-selective retinal ganglion cells (DS-RGCs) are located within the pretectal retinal arborization field 5 (AF5), where they meet dendrites of pretectal neurons with simple tuning to monocular optic flow. Translation-selective neurons, which respond selectively to optic flow in the same direction for both eyes, are intermingled with these simple cells but do not receive inputs from DS-RGCs. Mutually exclusive populations of pretectal projection neurons innervate either the reticular formation or the cerebellum, which in turn control motor responses. We posit that local computations in a defined pretectal circuit transform optic flow signals into neural commands driving optomotor behavior.

All-optical methods enable the control and monitoring of neuronal activity with minimal perturbation of the system. Although imaging and optogenetic manipulations can be performed at cellular resolution, the morphology of single cells in a dense neuronal population has often remained unresolvable. Here we describe in detail two recently established optogenetic protocols for systematic description of function and morphology of single neurons in zebrafish. First, the Optobow toolbox allows unbiased mapping of excitatory functional connectivity. Second, the FuGIMA technique enables selective labeling and anatomical tracing of neurons that are responsive to a given sensory stimulus or correlated with a specific behavior. Both strategies can be genetically targeted to a neuronal population of choice using the Gal4/UAS system. As these in vivo approaches are non-invasive, we envision useful applications for the study of neuronal structure, function and connectivity during development and behavior.

Fuelled by the province’s booming energy sector, Alberta’s two largest cities have experienced unprecedented levels of growth. As a result, they face a choice about how to best accommodate their expanding populations — whether to grow out or grow up. For decades, Calgary and Edmonton accommodated almost all growth through the former, suburban expansion. Indeed, the postwar period was marked by a focus on contiguous outward growth to ensure housing affordability and the efficient use of infrastructure, a policy that was widely supported by both the public and the development industry. In Calgary, at least, this has started to change. Beginning in the late 1990s, the city shifted its focus to livability and sustainability, a move that saw policies introduced to promote urban intensification and greater transit use. While this shift has proven popular in many quarters, it also has its fair share of detractors, including many in the development industry. In Edmonton, a city where growth has been relatively slower and authority over urban development dispersed among several local governments, this policy shift has not occurred. Although it is too early to see clear results from this policy shift, a spatial analysis shows that the density of Calgary’s built-up urban area increased in the first decade of the 21st century. Relatively high-density suburban growth led Calgary to consume less land compared with the previous decade (2 ha per 100 new residents in 2001–2011 versus 6.5 ha in 1991–2001). This growth was accompanied by modest intensification in core areas, although the dwelling unit density of the urban area increased by more than the population density (18 per cent versus 14 per cent). Edmonton’s development is roughly similar: denser suburban growth has led to the more efficient consumption of rural land (3 ha per 100 new residents in the 2001–11 period versus 7 ha in 1991–2001). The built-up area has also intensified slightly, especially in areas near transit stations. By way of comparison, Vancouver with its long-standing urban containment policies, including the expansion limits represented by the Agricultural Land Reserve, grew mostly through intensification between 1991 and 2011. In Toronto, the second comparator city examined and one in which local growth management policies have existed since the 1980s, growth is now almost equally divided between intensification and suburban expansion. The analysis suggests that it is difficult to alter a deep-seated policy regime that promotes outward growth. What is more, high levels of intensification may not be enough to offset the effects of a new demographic reality: smaller average household size because of such factors as longer lifespans, delayed family formation, family planning and divorce. So even with a greater number of housing units, the population of the built-up area may still fall. Finally, if the emerging polycentric structures of Calgary and Edmonton are to be successfully supported, major investments in infrastructure are going to be required.