A major challenge in neuroscience is to understand how the brain transforms sensory information into appropriate behavioural outputs.
To try and understand this question we are using the optic tectum of larval zebrafish. In this system retinal ganglion cell axons navigate from the retina to the tectum where they establish synaptic connections with tectal cell dendrites.
These connections are topographically organised- that is their arrangement reflects the spatial relationships of retinal ganglion cell bodies in the eye. Such topographic wiring generates a map of visual space in the brain which the tectum then uses to control complex motor behaviours such as prey capture and predator avoidance. The tectum of larval zebrafish is highly accessible to optical imaging and genetic labelling methods. Thus, the optic tectum provides a readily assessable system for studying the formation of retinotopic maps and the mechanisms of visual processing. Our lab uses transgenic zebrafish, time-lapse and functional imaging in vivo, optogenetic tools and patterned visual stimulation to address three broad questions that are each outlined next.
Development of the retinotectal projection
What are the cellular, molecular and activity-dependent mechanisms that generate retinotopically organised connections in the visual system?
The elaboration of appropriately shaped and accurately positioned axonal and dendritic arbours is crucial to the generation of retinotopy.
To understand the process of arbour morphogenesis we use molecular genetic methods to perturb gene function or neural activity in vivo. We then use time-lapse imaging of single cells in vivo to ask how these manipulations alter the development of axonal and dendritic arbours, the formation of synapses and hence the generation of retinotopic maps.
Emergence of visual system function
When and how does visual system function emerge during development? What are the functional properties of neurons at various stages in the visual pathway from retinal ganglion cells to their downstream targets in the tectum? Answering these questions will helps us understand the mechanisms of circuit assembly and also how sensory information is processed within the brain.
We are addressing these questions using transgenic zebrafish expressing genetically encoded reporters of neural activity. We then use patterned visual stimulation to probe the functional properties of identified neurons within the visual system.
Characterisation of tectal cell types
The optic tectum converts visual sensory information into behaviours such as prey capture and predator avoidance. How this transformation takes place is not known. A morphological, molecular and functional description of each of the tectal cell types is an essential prerequisite to understanding the role that each cell type plays in visual processing and the generation of behaviours. We are combining imaging of neuronal structure with functional imaging and in so doing characterise the various cell types within the tectum.