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Why is it important?
Wiring of the neuronal network (the accurate connection each neuron makes to other neurons) both enables and restricts the functions the network can fulfill. Therefore structure and function of the neuronal circuits are inevitably linked. Soma location, dendrite and axon morphology and the synaptic contact points are key parameters of the structure of individual neurons forming the neural circuits. Here we developed a method to facilitate tracing the morphologic features of neurons. To this end we developed a novel anterograde variant of the recombinant glycoprotein-deleted rabies virus simplifying local infection of neurons sparsely or in bulk. We demonstrate the strength of the vector by computationally reconstructing all key morphological features of neurons: dendrites, spines, long-ranging axons throughout the brain and bouton terminals. More precise knowledge of the wiring of the mammalian brain would provide neuroscientists the possibility to test predictive hypotheses about brain organization/behavioral capability, compare variations between brains and find common denominators between species. Sparse reconstructions have been pivotal for revealing the canonical circuit organization of the neocortex, but single cell fillings and manual reconstructions throughout the whole brain are technically challenging and cumbersome. The new viral method permits sparse labeling exploiting the strengths of recombinant rabies virus, providing the intensity required for computational reconstructions. Single viral particles of the anterograde rabies virus strongly express fluorescent proteins, fully filling the entire neuronal processes including axons, which often project several mm through the mammalian brain. The described technique might facilitate current efforts of classifying neuron types based on their morphology. The vector is efficient in many cell types, brain areas and unlike many other viral tracers (eg. lenti or sindbis-virus) also in aged animals.
Perspectives
Sparse labeling and reconstruction of neurons has been the experimental gold standard method to reveal canonical circuits of the neocortex. This has been achieved using cumbersome methods of single cell filling and subsequent manual reconstruction of those neurons throughout the whole brain. The here newly developed method exploits the strengths of a viral tracer, which provides the required intense labeling for a subsequent computational automated reconstruct of the neuron morphology. We show that single viral particles of the anterograde rabies virus variant are sufficient to achieve the required high intensity fluorescence labeling.
Dr Matthias G Haberl
University of California San Diego
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This page is a summary of: An anterograde rabies virus vector for high-resolution large-scale reconstruction of 3D neuron morphology, Brain Structure and Function, April 2014, Springer Science + Business Media,
DOI: 10.1007/s00429-014-0730-z.
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